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verified gcc-4.6.4.tar.bz2.sig;
imported gcc-4.6.4 source tree from verified upstream tarball.

downloading a git-generated archive based on the 'upstream' tag
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1 files changed, 11241 insertions, 0 deletions

diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
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+@c Copyright (C) 1988,1989,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,
+@c 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
+@c Free Software Foundation, Inc.
+@c This is part of the GCC manual.
+@c For copying conditions, see the file gcc.texi.
+
+@node Target Macros
+@chapter Target Description Macros and Functions
+@cindex machine description macros
+@cindex target description macros
+@cindex macros, target description
+@cindex @file{tm.h} macros
+
+In addition to the file @file{@var{machine}.md}, a machine description
+includes a C header file conventionally given the name
+@file{@var{machine}.h} and a C source file named @file{@var{machine}.c}.
+The header file defines numerous macros that convey the information
+about the target machine that does not fit into the scheme of the
+@file{.md} file.  The file @file{tm.h} should be a link to
+@file{@var{machine}.h}.  The header file @file{config.h} includes
+@file{tm.h} and most compiler source files include @file{config.h}.  The
+source file defines a variable @code{targetm}, which is a structure
+containing pointers to functions and data relating to the target
+machine.  @file{@var{machine}.c} should also contain their definitions,
+if they are not defined elsewhere in GCC, and other functions called
+through the macros defined in the @file{.h} file.
+
+@menu
+* Target Structure::    The @code{targetm} variable.
+* Driver::              Controlling how the driver runs the compilation passes.
+* Run-time Target::     Defining @samp{-m} options like @option{-m68000} and @option{-m68020}.
+* Per-Function Data::   Defining data structures for per-function information.
+* Storage Layout::      Defining sizes and alignments of data.
+* Type Layout::         Defining sizes and properties of basic user data types.
+* Registers::           Naming and describing the hardware registers.
+* Register Classes::    Defining the classes of hardware registers.
+* Old Constraints::     The old way to define machine-specific constraints.
+* Stack and Calling::   Defining which way the stack grows and by how much.
+* Varargs::             Defining the varargs macros.
+* Trampolines::         Code set up at run time to enter a nested function.
+* Library Calls::       Controlling how library routines are implicitly called.
+* Addressing Modes::    Defining addressing modes valid for memory operands.
+* Anchored Addresses::  Defining how @option{-fsection-anchors} should work.
+* Condition Code::      Defining how insns update the condition code.
+* Costs::               Defining relative costs of different operations.
+* Scheduling::          Adjusting the behavior of the instruction scheduler.
+* Sections::            Dividing storage into text, data, and other sections.
+* PIC::                 Macros for position independent code.
+* Assembler Format::    Defining how to write insns and pseudo-ops to output.
+* Debugging Info::      Defining the format of debugging output.
+* Floating Point::      Handling floating point for cross-compilers.
+* Mode Switching::      Insertion of mode-switching instructions.
+* Target Attributes::   Defining target-specific uses of @code{__attribute__}.
+* Emulated TLS::        Emulated TLS support.
+* MIPS Coprocessors::   MIPS coprocessor support and how to customize it.
+* PCH Target::          Validity checking for precompiled headers.
+* C++ ABI::             Controlling C++ ABI changes.
+* Named Address Spaces:: Adding support for named address spaces
+* Misc::                Everything else.
+@end menu
+
+@node Target Structure
+@section The Global @code{targetm} Variable
+@cindex target hooks
+@cindex target functions
+
+@deftypevar {struct gcc_target} targetm
+The target @file{.c} file must define the global @code{targetm} variable
+which contains pointers to functions and data relating to the target
+machine.  The variable is declared in @file{target.h};
+@file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is
+used to initialize the variable, and macros for the default initializers
+for elements of the structure.  The @file{.c} file should override those
+macros for which the default definition is inappropriate.  For example:
+@smallexample
+#include "target.h"
+#include "target-def.h"
+
+/* @r{Initialize the GCC target structure.}  */
+
+#undef TARGET_COMP_TYPE_ATTRIBUTES
+#define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes
+
+struct gcc_target targetm = TARGET_INITIALIZER;
+@end smallexample
+@end deftypevar
+
+Where a macro should be defined in the @file{.c} file in this manner to
+form part of the @code{targetm} structure, it is documented below as a
+``Target Hook'' with a prototype.  Many macros will change in future
+from being defined in the @file{.h} file to being part of the
+@code{targetm} structure.
+
+@node Driver
+@section Controlling the Compilation Driver, @file{gcc}
+@cindex driver
+@cindex controlling the compilation driver
+
+@c prevent bad page break with this line
+You can control the compilation driver.
+
+@defmac DRIVER_SELF_SPECS
+A list of specs for the driver itself.  It should be a suitable
+initializer for an array of strings, with no surrounding braces.
+
+The driver applies these specs to its own command line between loading
+default @file{specs} files (but not command-line specified ones) and
+choosing the multilib directory or running any subcommands.  It
+applies them in the order given, so each spec can depend on the
+options added by earlier ones.  It is also possible to remove options
+using @samp{%<@var{option}} in the usual way.
+
+This macro can be useful when a port has several interdependent target
+options.  It provides a way of standardizing the command line so
+that the other specs are easier to write.
+
+Do not define this macro if it does not need to do anything.
+@end defmac
+
+@defmac OPTION_DEFAULT_SPECS
+A list of specs used to support configure-time default options (i.e.@:
+@option{--with} options) in the driver.  It should be a suitable initializer
+for an array of structures, each containing two strings, without the
+outermost pair of surrounding braces.
+
+The first item in the pair is the name of the default.  This must match
+the code in @file{config.gcc} for the target.  The second item is a spec
+to apply if a default with this name was specified.  The string
+@samp{%(VALUE)} in the spec will be replaced by the value of the default
+everywhere it occurs.
+
+The driver will apply these specs to its own command line between loading
+default @file{specs} files and processing @code{DRIVER_SELF_SPECS}, using
+the same mechanism as @code{DRIVER_SELF_SPECS}.
+
+Do not define this macro if it does not need to do anything.
+@end defmac
+
+@defmac CPP_SPEC
+A C string constant that tells the GCC driver program options to
+pass to CPP@.  It can also specify how to translate options you
+give to GCC into options for GCC to pass to the CPP@.
+
+Do not define this macro if it does not need to do anything.
+@end defmac
+
+@defmac CPLUSPLUS_CPP_SPEC
+This macro is just like @code{CPP_SPEC}, but is used for C++, rather
+than C@.  If you do not define this macro, then the value of
+@code{CPP_SPEC} (if any) will be used instead.
+@end defmac
+
+@defmac CC1_SPEC
+A C string constant that tells the GCC driver program options to
+pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language
+front ends.
+It can also specify how to translate options you give to GCC into options
+for GCC to pass to front ends.
+
+Do not define this macro if it does not need to do anything.
+@end defmac
+
+@defmac CC1PLUS_SPEC
+A C string constant that tells the GCC driver program options to
+pass to @code{cc1plus}.  It can also specify how to translate options you
+give to GCC into options for GCC to pass to the @code{cc1plus}.
+
+Do not define this macro if it does not need to do anything.
+Note that everything defined in CC1_SPEC is already passed to
+@code{cc1plus} so there is no need to duplicate the contents of
+CC1_SPEC in CC1PLUS_SPEC@.
+@end defmac
+
+@defmac ASM_SPEC
+A C string constant that tells the GCC driver program options to
+pass to the assembler.  It can also specify how to translate options
+you give to GCC into options for GCC to pass to the assembler.
+See the file @file{sun3.h} for an example of this.
+
+Do not define this macro if it does not need to do anything.
+@end defmac
+
+@defmac ASM_FINAL_SPEC
+A C string constant that tells the GCC driver program how to
+run any programs which cleanup after the normal assembler.
+Normally, this is not needed.  See the file @file{mips.h} for
+an example of this.
+
+Do not define this macro if it does not need to do anything.
+@end defmac
+
+@defmac AS_NEEDS_DASH_FOR_PIPED_INPUT
+Define this macro, with no value, if the driver should give the assembler
+an argument consisting of a single dash, @option{-}, to instruct it to
+read from its standard input (which will be a pipe connected to the
+output of the compiler proper).  This argument is given after any
+@option{-o} option specifying the name of the output file.
+
+If you do not define this macro, the assembler is assumed to read its
+standard input if given no non-option arguments.  If your assembler
+cannot read standard input at all, use a @samp{%@{pipe:%e@}} construct;
+see @file{mips.h} for instance.
+@end defmac
+
+@defmac LINK_SPEC
+A C string constant that tells the GCC driver program options to
+pass to the linker.  It can also specify how to translate options you
+give to GCC into options for GCC to pass to the linker.
+
+Do not define this macro if it does not need to do anything.
+@end defmac
+
+@defmac LIB_SPEC
+Another C string constant used much like @code{LINK_SPEC}.  The difference
+between the two is that @code{LIB_SPEC} is used at the end of the
+command given to the linker.
+
+If this macro is not defined, a default is provided that
+loads the standard C library from the usual place.  See @file{gcc.c}.
+@end defmac
+
+@defmac LIBGCC_SPEC
+Another C string constant that tells the GCC driver program
+how and when to place a reference to @file{libgcc.a} into the
+linker command line.  This constant is placed both before and after
+the value of @code{LIB_SPEC}.
+
+If this macro is not defined, the GCC driver provides a default that
+passes the string @option{-lgcc} to the linker.
+@end defmac
+
+@defmac REAL_LIBGCC_SPEC
+By default, if @code{ENABLE_SHARED_LIBGCC} is defined, the
+@code{LIBGCC_SPEC} is not directly used by the driver program but is
+instead modified to refer to different versions of @file{libgcc.a}
+depending on the values of the command line flags @option{-static},
+@option{-shared}, @option{-static-libgcc}, and @option{-shared-libgcc}.  On
+targets where these modifications are inappropriate, define
+@code{REAL_LIBGCC_SPEC} instead.  @code{REAL_LIBGCC_SPEC} tells the
+driver how to place a reference to @file{libgcc} on the link command
+line, but, unlike @code{LIBGCC_SPEC}, it is used unmodified.
+@end defmac
+
+@defmac USE_LD_AS_NEEDED
+A macro that controls the modifications to @code{LIBGCC_SPEC}
+mentioned in @code{REAL_LIBGCC_SPEC}.  If nonzero, a spec will be
+generated that uses --as-needed and the shared libgcc in place of the
+static exception handler library, when linking without any of
+@code{-static}, @code{-static-libgcc}, or @code{-shared-libgcc}.
+@end defmac
+
+@defmac LINK_EH_SPEC
+If defined, this C string constant is added to @code{LINK_SPEC}.
+When @code{USE_LD_AS_NEEDED} is zero or undefined, it also affects
+the modifications to @code{LIBGCC_SPEC} mentioned in
+@code{REAL_LIBGCC_SPEC}.
+@end defmac
+
+@defmac STARTFILE_SPEC
+Another C string constant used much like @code{LINK_SPEC}.  The
+difference between the two is that @code{STARTFILE_SPEC} is used at
+the very beginning of the command given to the linker.
+
+If this macro is not defined, a default is provided that loads the
+standard C startup file from the usual place.  See @file{gcc.c}.
+@end defmac
+
+@defmac ENDFILE_SPEC
+Another C string constant used much like @code{LINK_SPEC}.  The
+difference between the two is that @code{ENDFILE_SPEC} is used at
+the very end of the command given to the linker.
+
+Do not define this macro if it does not need to do anything.
+@end defmac
+
+@defmac THREAD_MODEL_SPEC
+GCC @code{-v} will print the thread model GCC was configured to use.
+However, this doesn't work on platforms that are multilibbed on thread
+models, such as AIX 4.3.  On such platforms, define
+@code{THREAD_MODEL_SPEC} such that it evaluates to a string without
+blanks that names one of the recognized thread models.  @code{%*}, the
+default value of this macro, will expand to the value of
+@code{thread_file} set in @file{config.gcc}.
+@end defmac
+
+@defmac SYSROOT_SUFFIX_SPEC
+Define this macro to add a suffix to the target sysroot when GCC is
+configured with a sysroot.  This will cause GCC to search for usr/lib,
+et al, within sysroot+suffix.
+@end defmac
+
+@defmac SYSROOT_HEADERS_SUFFIX_SPEC
+Define this macro to add a headers_suffix to the target sysroot when
+GCC is configured with a sysroot.  This will cause GCC to pass the
+updated sysroot+headers_suffix to CPP, causing it to search for
+usr/include, et al, within sysroot+headers_suffix.
+@end defmac
+
+@defmac EXTRA_SPECS
+Define this macro to provide additional specifications to put in the
+@file{specs} file that can be used in various specifications like
+@code{CC1_SPEC}.
+
+The definition should be an initializer for an array of structures,
+containing a string constant, that defines the specification name, and a
+string constant that provides the specification.
+
+Do not define this macro if it does not need to do anything.
+
+@code{EXTRA_SPECS} is useful when an architecture contains several
+related targets, which have various @code{@dots{}_SPECS} which are similar
+to each other, and the maintainer would like one central place to keep
+these definitions.
+
+For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to
+define either @code{_CALL_SYSV} when the System V calling sequence is
+used or @code{_CALL_AIX} when the older AIX-based calling sequence is
+used.
+
+The @file{config/rs6000/rs6000.h} target file defines:
+
+@smallexample
+#define EXTRA_SPECS \
+  @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @},
+
+#define CPP_SYS_DEFAULT ""
+@end smallexample
+
+The @file{config/rs6000/sysv.h} target file defines:
+@smallexample
+#undef CPP_SPEC
+#define CPP_SPEC \
+"%@{posix: -D_POSIX_SOURCE @} \
+%@{mcall-sysv: -D_CALL_SYSV @} \
+%@{!mcall-sysv: %(cpp_sysv_default) @} \
+%@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}"
+
+#undef CPP_SYSV_DEFAULT
+#define CPP_SYSV_DEFAULT "-D_CALL_SYSV"
+@end smallexample
+
+while the @file{config/rs6000/eabiaix.h} target file defines
+@code{CPP_SYSV_DEFAULT} as:
+
+@smallexample
+#undef CPP_SYSV_DEFAULT
+#define CPP_SYSV_DEFAULT "-D_CALL_AIX"
+@end smallexample
+@end defmac
+
+@defmac LINK_LIBGCC_SPECIAL_1
+Define this macro if the driver program should find the library
+@file{libgcc.a}.  If you do not define this macro, the driver program will pass
+the argument @option{-lgcc} to tell the linker to do the search.
+@end defmac
+
+@defmac LINK_GCC_C_SEQUENCE_SPEC
+The sequence in which libgcc and libc are specified to the linker.
+By default this is @code{%G %L %G}.
+@end defmac
+
+@defmac LINK_COMMAND_SPEC
+A C string constant giving the complete command line need to execute the
+linker.  When you do this, you will need to update your port each time a
+change is made to the link command line within @file{gcc.c}.  Therefore,
+define this macro only if you need to completely redefine the command
+line for invoking the linker and there is no other way to accomplish
+the effect you need.  Overriding this macro may be avoidable by overriding
+@code{LINK_GCC_C_SEQUENCE_SPEC} instead.
+@end defmac
+
+@defmac LINK_ELIMINATE_DUPLICATE_LDIRECTORIES
+A nonzero value causes @command{collect2} to remove duplicate @option{-L@var{directory}} search
+directories from linking commands.  Do not give it a nonzero value if
+removing duplicate search directories changes the linker's semantics.
+@end defmac
+
+@defmac MULTILIB_DEFAULTS
+Define this macro as a C expression for the initializer of an array of
+string to tell the driver program which options are defaults for this
+target and thus do not need to be handled specially when using
+@code{MULTILIB_OPTIONS}.
+
+Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in
+the target makefile fragment or if none of the options listed in
+@code{MULTILIB_OPTIONS} are set by default.
+@xref{Target Fragment}.
+@end defmac
+
+@defmac RELATIVE_PREFIX_NOT_LINKDIR
+Define this macro to tell @command{gcc} that it should only translate
+a @option{-B} prefix into a @option{-L} linker option if the prefix
+indicates an absolute file name.
+@end defmac
+
+@defmac MD_EXEC_PREFIX
+If defined, this macro is an additional prefix to try after
+@code{STANDARD_EXEC_PREFIX}.  @code{MD_EXEC_PREFIX} is not searched
+when the compiler is built as a cross
+compiler.  If you define @code{MD_EXEC_PREFIX}, then be sure to add it
+to the list of directories used to find the assembler in @file{configure.in}.
+@end defmac
+
+@defmac STANDARD_STARTFILE_PREFIX
+Define this macro as a C string constant if you wish to override the
+standard choice of @code{libdir} as the default prefix to
+try when searching for startup files such as @file{crt0.o}.
+@code{STANDARD_STARTFILE_PREFIX} is not searched when the compiler
+is built as a cross compiler.
+@end defmac
+
+@defmac STANDARD_STARTFILE_PREFIX_1
+Define this macro as a C string constant if you wish to override the
+standard choice of @code{/lib} as a prefix to try after the default prefix
+when searching for startup files such as @file{crt0.o}.
+@code{STANDARD_STARTFILE_PREFIX_1} is not searched when the compiler
+is built as a cross compiler.
+@end defmac
+
+@defmac STANDARD_STARTFILE_PREFIX_2
+Define this macro as a C string constant if you wish to override the
+standard choice of @code{/lib} as yet another prefix to try after the
+default prefix when searching for startup files such as @file{crt0.o}.
+@code{STANDARD_STARTFILE_PREFIX_2} is not searched when the compiler
+is built as a cross compiler.
+@end defmac
+
+@defmac MD_STARTFILE_PREFIX
+If defined, this macro supplies an additional prefix to try after the
+standard prefixes.  @code{MD_EXEC_PREFIX} is not searched when the
+compiler is built as a cross compiler.
+@end defmac
+
+@defmac MD_STARTFILE_PREFIX_1
+If defined, this macro supplies yet another prefix to try after the
+standard prefixes.  It is not searched when the compiler is built as a
+cross compiler.
+@end defmac
+
+@defmac INIT_ENVIRONMENT
+Define this macro as a C string constant if you wish to set environment
+variables for programs called by the driver, such as the assembler and
+loader.  The driver passes the value of this macro to @code{putenv} to
+initialize the necessary environment variables.
+@end defmac
+
+@defmac LOCAL_INCLUDE_DIR
+Define this macro as a C string constant if you wish to override the
+standard choice of @file{/usr/local/include} as the default prefix to
+try when searching for local header files.  @code{LOCAL_INCLUDE_DIR}
+comes before @code{SYSTEM_INCLUDE_DIR} in the search order.
+
+Cross compilers do not search either @file{/usr/local/include} or its
+replacement.
+@end defmac
+
+@defmac SYSTEM_INCLUDE_DIR
+Define this macro as a C string constant if you wish to specify a
+system-specific directory to search for header files before the standard
+directory.  @code{SYSTEM_INCLUDE_DIR} comes before
+@code{STANDARD_INCLUDE_DIR} in the search order.
+
+Cross compilers do not use this macro and do not search the directory
+specified.
+@end defmac
+
+@defmac STANDARD_INCLUDE_DIR
+Define this macro as a C string constant if you wish to override the
+standard choice of @file{/usr/include} as the default prefix to
+try when searching for header files.
+
+Cross compilers ignore this macro and do not search either
+@file{/usr/include} or its replacement.
+@end defmac
+
+@defmac STANDARD_INCLUDE_COMPONENT
+The ``component'' corresponding to @code{STANDARD_INCLUDE_DIR}.
+See @code{INCLUDE_DEFAULTS}, below, for the description of components.
+If you do not define this macro, no component is used.
+@end defmac
+
+@defmac INCLUDE_DEFAULTS
+Define this macro if you wish to override the entire default search path
+for include files.  For a native compiler, the default search path
+usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR},
+@code{SYSTEM_INCLUDE_DIR}, @code{GPLUSPLUS_INCLUDE_DIR}, and
+@code{STANDARD_INCLUDE_DIR}.  In addition, @code{GPLUSPLUS_INCLUDE_DIR}
+and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile},
+and specify private search areas for GCC@.  The directory
+@code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs.
+
+The definition should be an initializer for an array of structures.
+Each array element should have four elements: the directory name (a
+string constant), the component name (also a string constant), a flag
+for C++-only directories,
+and a flag showing that the includes in the directory don't need to be
+wrapped in @code{extern @samp{C}} when compiling C++.  Mark the end of
+the array with a null element.
+
+The component name denotes what GNU package the include file is part of,
+if any, in all uppercase letters.  For example, it might be @samp{GCC}
+or @samp{BINUTILS}.  If the package is part of a vendor-supplied
+operating system, code the component name as @samp{0}.
+
+For example, here is the definition used for VAX/VMS:
+
+@smallexample
+#define INCLUDE_DEFAULTS \
+@{                                       \
+  @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@},   \
+  @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@},    \
+  @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@},  \
+  @{ ".", 0, 0, 0@},                      \
+  @{ 0, 0, 0, 0@}                         \
+@}
+@end smallexample
+@end defmac
+
+Here is the order of prefixes tried for exec files:
+
+@enumerate
+@item
+Any prefixes specified by the user with @option{-B}.
+
+@item
+The environment variable @code{GCC_EXEC_PREFIX} or, if @code{GCC_EXEC_PREFIX}
+is not set and the compiler has not been installed in the configure-time 
+@var{prefix}, the location in which the compiler has actually been installed.
+
+@item
+The directories specified by the environment variable @code{COMPILER_PATH}.
+
+@item
+The macro @code{STANDARD_EXEC_PREFIX}, if the compiler has been installed
+in the configured-time @var{prefix}. 
+
+@item
+The location @file{/usr/libexec/gcc/}, but only if this is a native compiler. 
+
+@item
+The location @file{/usr/lib/gcc/}, but only if this is a native compiler. 
+
+@item
+The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native 
+compiler.
+@end enumerate
+
+Here is the order of prefixes tried for startfiles:
+
+@enumerate
+@item
+Any prefixes specified by the user with @option{-B}.
+
+@item
+The environment variable @code{GCC_EXEC_PREFIX} or its automatically determined
+value based on the installed toolchain location.
+
+@item
+The directories specified by the environment variable @code{LIBRARY_PATH}
+(or port-specific name; native only, cross compilers do not use this).
+
+@item
+The macro @code{STANDARD_EXEC_PREFIX}, but only if the toolchain is installed
+in the configured @var{prefix} or this is a native compiler. 
+
+@item
+The location @file{/usr/lib/gcc/}, but only if this is a native compiler.
+
+@item
+The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native 
+compiler.
+
+@item
+The macro @code{MD_STARTFILE_PREFIX}, if defined, but only if this is a 
+native compiler, or we have a target system root.
+
+@item
+The macro @code{MD_STARTFILE_PREFIX_1}, if defined, but only if this is a 
+native compiler, or we have a target system root.
+
+@item
+The macro @code{STANDARD_STARTFILE_PREFIX}, with any sysroot modifications.
+If this path is relative it will be prefixed by @code{GCC_EXEC_PREFIX} and
+the machine suffix or @code{STANDARD_EXEC_PREFIX} and the machine suffix.
+
+@item
+The macro @code{STANDARD_STARTFILE_PREFIX_1}, but only if this is a native
+compiler, or we have a target system root. The default for this macro is
+@file{/lib/}.
+
+@item
+The macro @code{STANDARD_STARTFILE_PREFIX_2}, but only if this is a native
+compiler, or we have a target system root. The default for this macro is
+@file{/usr/lib/}.
+@end enumerate
+
+@node Run-time Target
+@section Run-time Target Specification
+@cindex run-time target specification
+@cindex predefined macros
+@cindex target specifications
+
+@c prevent bad page break with this line
+Here are run-time target specifications.
+
+@defmac TARGET_CPU_CPP_BUILTINS ()
+This function-like macro expands to a block of code that defines
+built-in preprocessor macros and assertions for the target CPU, using
+the functions @code{builtin_define}, @code{builtin_define_std} and
+@code{builtin_assert}.  When the front end
+calls this macro it provides a trailing semicolon, and since it has
+finished command line option processing your code can use those
+results freely.
+
+@code{builtin_assert} takes a string in the form you pass to the
+command-line option @option{-A}, such as @code{cpu=mips}, and creates
+the assertion.  @code{builtin_define} takes a string in the form
+accepted by option @option{-D} and unconditionally defines the macro.
+
+@code{builtin_define_std} takes a string representing the name of an
+object-like macro.  If it doesn't lie in the user's namespace,
+@code{builtin_define_std} defines it unconditionally.  Otherwise, it
+defines a version with two leading underscores, and another version
+with two leading and trailing underscores, and defines the original
+only if an ISO standard was not requested on the command line.  For
+example, passing @code{unix} defines @code{__unix}, @code{__unix__}
+and possibly @code{unix}; passing @code{_mips} defines @code{__mips},
+@code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64}
+defines only @code{_ABI64}.
+
+You can also test for the C dialect being compiled.  The variable
+@code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus}
+or @code{clk_objective_c}.  Note that if we are preprocessing
+assembler, this variable will be @code{clk_c} but the function-like
+macro @code{preprocessing_asm_p()} will return true, so you might want
+to check for that first.  If you need to check for strict ANSI, the
+variable @code{flag_iso} can be used.  The function-like macro
+@code{preprocessing_trad_p()} can be used to check for traditional
+preprocessing.
+@end defmac
+
+@defmac TARGET_OS_CPP_BUILTINS ()
+Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
+and is used for the target operating system instead.
+@end defmac
+
+@defmac TARGET_OBJFMT_CPP_BUILTINS ()
+Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
+and is used for the target object format.  @file{elfos.h} uses this
+macro to define @code{__ELF__}, so you probably do not need to define
+it yourself.
+@end defmac
+
+@deftypevar {extern int} target_flags
+This variable is declared in @file{options.h}, which is included before
+any target-specific headers.
+@end deftypevar
+
+@hook TARGET_DEFAULT_TARGET_FLAGS
+This variable specifies the initial value of @code{target_flags}.
+Its default setting is 0.
+@end deftypevr
+
+@cindex optional hardware or system features
+@cindex features, optional, in system conventions
+
+@hook TARGET_HANDLE_OPTION
+This hook is called whenever the user specifies one of the
+target-specific options described by the @file{.opt} definition files
+(@pxref{Options}).  It has the opportunity to do some option-specific
+processing and should return true if the option is valid.  The default
+definition does nothing but return true.
+
+@var{code} specifies the @code{OPT_@var{name}} enumeration value
+associated with the selected option; @var{name} is just a rendering of
+the option name in which non-alphanumeric characters are replaced by
+underscores.  @var{arg} specifies the string argument and is null if
+no argument was given.  If the option is flagged as a @code{UInteger}
+(@pxref{Option properties}), @var{value} is the numeric value of the
+argument.  Otherwise @var{value} is 1 if the positive form of the
+option was used and 0 if the ``no-'' form was.
+@end deftypefn
+
+@hook TARGET_HANDLE_C_OPTION
+This target hook is called whenever the user specifies one of the
+target-specific C language family options described by the @file{.opt}
+definition files(@pxref{Options}).  It has the opportunity to do some
+option-specific processing and should return true if the option is
+valid.  The arguments are like for @code{TARGET_HANDLE_OPTION}.  The
+default definition does nothing but return false.
+
+In general, you should use @code{TARGET_HANDLE_OPTION} to handle
+options.  However, if processing an option requires routines that are
+only available in the C (and related language) front ends, then you
+should use @code{TARGET_HANDLE_C_OPTION} instead.
+@end deftypefn
+
+@hook TARGET_OBJC_CONSTRUCT_STRING_OBJECT
+
+@hook TARGET_STRING_OBJECT_REF_TYPE_P
+
+@hook TARGET_CHECK_STRING_OBJECT_FORMAT_ARG
+
+@defmac TARGET_VERSION
+This macro is a C statement to print on @code{stderr} a string
+describing the particular machine description choice.  Every machine
+description should define @code{TARGET_VERSION}.  For example:
+
+@smallexample
+#ifdef MOTOROLA
+#define TARGET_VERSION \
+  fprintf (stderr, " (68k, Motorola syntax)");
+#else
+#define TARGET_VERSION \
+  fprintf (stderr, " (68k, MIT syntax)");
+#endif
+@end smallexample
+@end defmac
+
+@hook TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE
+This target function is similar to the hook @code{TARGET_OPTION_OVERRIDE}
+but is called when the optimize level is changed via an attribute or
+pragma or when it is reset at the end of the code affected by the
+attribute or pragma.  It is not called at the beginning of compilation
+when @code{TARGET_OPTION_OVERRIDE} is called so if you want to perform these
+actions then, you should have @code{TARGET_OPTION_OVERRIDE} call
+@code{TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE}.
+@end deftypefn
+
+@defmac C_COMMON_OVERRIDE_OPTIONS
+This is similar to the @code{TARGET_OPTION_OVERRIDE} hook
+but is only used in the C
+language frontends (C, Objective-C, C++, Objective-C++) and so can be
+used to alter option flag variables which only exist in those
+frontends.
+@end defmac
+
+@hook TARGET_OPTION_OPTIMIZATION_TABLE
+Some machines may desire to change what optimizations are performed for
+various optimization levels.   This variable, if defined, describes
+options to enable at particular sets of optimization levels.  These
+options are processed once
+just after the optimization level is determined and before the remainder
+of the command options have been parsed, so may be overridden by other
+options passed explicitly.
+
+This processing is run once at program startup and when the optimization
+options are changed via @code{#pragma GCC optimize} or by using the
+@code{optimize} attribute.
+@end deftypevr
+
+@hook TARGET_OPTION_INIT_STRUCT
+
+@hook TARGET_OPTION_DEFAULT_PARAMS
+
+@hook TARGET_HELP
+This hook is called in response to the user invoking
+@option{--target-help} on the command line.  It gives the target a
+chance to display extra information on the target specific command
+line options found in its @file{.opt} file.
+@end deftypefn
+
+@defmac SWITCHABLE_TARGET
+Some targets need to switch between substantially different subtargets
+during compilation.  For example, the MIPS target has one subtarget for
+the traditional MIPS architecture and another for MIPS16.  Source code
+can switch between these two subarchitectures using the @code{mips16}
+and @code{nomips16} attributes.
+
+Such subtargets can differ in things like the set of available
+registers, the set of available instructions, the costs of various
+operations, and so on.  GCC caches a lot of this type of information
+in global variables, and recomputing them for each subtarget takes a
+significant amount of time.  The compiler therefore provides a facility
+for maintaining several versions of the global variables and quickly
+switching between them; see @file{target-globals.h} for details.
+
+Define this macro to 1 if your target needs this facility.  The default
+is 0.
+@end defmac
+
+@node Per-Function Data
+@section Defining data structures for per-function information.
+@cindex per-function data
+@cindex data structures
+
+If the target needs to store information on a per-function basis, GCC
+provides a macro and a couple of variables to allow this.  Note, just
+using statics to store the information is a bad idea, since GCC supports
+nested functions, so you can be halfway through encoding one function
+when another one comes along.
+
+GCC defines a data structure called @code{struct function} which
+contains all of the data specific to an individual function.  This
+structure contains a field called @code{machine} whose type is
+@code{struct machine_function *}, which can be used by targets to point
+to their own specific data.
+
+If a target needs per-function specific data it should define the type
+@code{struct machine_function} and also the macro @code{INIT_EXPANDERS}.
+This macro should be used to initialize the function pointer
+@code{init_machine_status}.  This pointer is explained below.
+
+One typical use of per-function, target specific data is to create an
+RTX to hold the register containing the function's return address.  This
+RTX can then be used to implement the @code{__builtin_return_address}
+function, for level 0.
+
+Note---earlier implementations of GCC used a single data area to hold
+all of the per-function information.  Thus when processing of a nested
+function began the old per-function data had to be pushed onto a
+stack, and when the processing was finished, it had to be popped off the
+stack.  GCC used to provide function pointers called
+@code{save_machine_status} and @code{restore_machine_status} to handle
+the saving and restoring of the target specific information.  Since the
+single data area approach is no longer used, these pointers are no
+longer supported.
+
+@defmac INIT_EXPANDERS
+Macro called to initialize any target specific information.  This macro
+is called once per function, before generation of any RTL has begun.
+The intention of this macro is to allow the initialization of the
+function pointer @code{init_machine_status}.
+@end defmac
+
+@deftypevar {void (*)(struct function *)} init_machine_status
+If this function pointer is non-@code{NULL} it will be called once per
+function, before function compilation starts, in order to allow the
+target to perform any target specific initialization of the
+@code{struct function} structure.  It is intended that this would be
+used to initialize the @code{machine} of that structure.
+
+@code{struct machine_function} structures are expected to be freed by GC@.
+Generally, any memory that they reference must be allocated by using
+GC allocation, including the structure itself.
+@end deftypevar
+
+@node Storage Layout
+@section Storage Layout
+@cindex storage layout
+
+Note that the definitions of the macros in this table which are sizes or
+alignments measured in bits do not need to be constant.  They can be C
+expressions that refer to static variables, such as the @code{target_flags}.
+@xref{Run-time Target}.
+
+@defmac BITS_BIG_ENDIAN
+Define this macro to have the value 1 if the most significant bit in a
+byte has the lowest number; otherwise define it to have the value zero.
+This means that bit-field instructions count from the most significant
+bit.  If the machine has no bit-field instructions, then this must still
+be defined, but it doesn't matter which value it is defined to.  This
+macro need not be a constant.
+
+This macro does not affect the way structure fields are packed into
+bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}.
+@end defmac
+
+@defmac BYTES_BIG_ENDIAN
+Define this macro to have the value 1 if the most significant byte in a
+word has the lowest number.  This macro need not be a constant.
+@end defmac
+
+@defmac WORDS_BIG_ENDIAN
+Define this macro to have the value 1 if, in a multiword object, the
+most significant word has the lowest number.  This applies to both
+memory locations and registers; GCC fundamentally assumes that the
+order of words in memory is the same as the order in registers.  This
+macro need not be a constant.
+@end defmac
+
+@defmac FLOAT_WORDS_BIG_ENDIAN
+Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or
+@code{TFmode} floating point numbers are stored in memory with the word
+containing the sign bit at the lowest address; otherwise define it to
+have the value 0.  This macro need not be a constant.
+
+You need not define this macro if the ordering is the same as for
+multi-word integers.
+@end defmac
+
+@defmac BITS_PER_UNIT
+Define this macro to be the number of bits in an addressable storage
+unit (byte).  If you do not define this macro the default is 8.
+@end defmac
+
+@defmac BITS_PER_WORD
+Number of bits in a word.  If you do not define this macro, the default
+is @code{BITS_PER_UNIT * UNITS_PER_WORD}.
+@end defmac
+
+@defmac MAX_BITS_PER_WORD
+Maximum number of bits in a word.  If this is undefined, the default is
+@code{BITS_PER_WORD}.  Otherwise, it is the constant value that is the
+largest value that @code{BITS_PER_WORD} can have at run-time.
+@end defmac
+
+@defmac UNITS_PER_WORD
+Number of storage units in a word; normally the size of a general-purpose
+register, a power of two from 1 or 8.
+@end defmac
+
+@defmac MIN_UNITS_PER_WORD
+Minimum number of units in a word.  If this is undefined, the default is
+@code{UNITS_PER_WORD}.  Otherwise, it is the constant value that is the
+smallest value that @code{UNITS_PER_WORD} can have at run-time.
+@end defmac
+
+@defmac POINTER_SIZE
+Width of a pointer, in bits.  You must specify a value no wider than the
+width of @code{Pmode}.  If it is not equal to the width of @code{Pmode},
+you must define @code{POINTERS_EXTEND_UNSIGNED}.  If you do not specify
+a value the default is @code{BITS_PER_WORD}.
+@end defmac
+
+@defmac POINTERS_EXTEND_UNSIGNED
+A C expression that determines how pointers should be extended from
+@code{ptr_mode} to either @code{Pmode} or @code{word_mode}.  It is
+greater than zero if pointers should be zero-extended, zero if they
+should be sign-extended, and negative if some other sort of conversion
+is needed.  In the last case, the extension is done by the target's
+@code{ptr_extend} instruction.
+
+You need not define this macro if the @code{ptr_mode}, @code{Pmode}
+and @code{word_mode} are all the same width.
+@end defmac
+
+@defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type})
+A macro to update @var{m} and @var{unsignedp} when an object whose type
+is @var{type} and which has the specified mode and signedness is to be
+stored in a register.  This macro is only called when @var{type} is a
+scalar type.
+
+On most RISC machines, which only have operations that operate on a full
+register, define this macro to set @var{m} to @code{word_mode} if
+@var{m} is an integer mode narrower than @code{BITS_PER_WORD}.  In most
+cases, only integer modes should be widened because wider-precision
+floating-point operations are usually more expensive than their narrower
+counterparts.
+
+For most machines, the macro definition does not change @var{unsignedp}.
+However, some machines, have instructions that preferentially handle
+either signed or unsigned quantities of certain modes.  For example, on
+the DEC Alpha, 32-bit loads from memory and 32-bit add instructions
+sign-extend the result to 64 bits.  On such machines, set
+@var{unsignedp} according to which kind of extension is more efficient.
+
+Do not define this macro if it would never modify @var{m}.
+@end defmac
+
+@hook TARGET_PROMOTE_FUNCTION_MODE
+Like @code{PROMOTE_MODE}, but it is applied to outgoing function arguments or
+function return values.  The target hook should return the new mode
+and possibly change @code{*@var{punsignedp}} if the promotion should
+change signedness.  This function is called only for scalar @emph{or
+pointer} types.
+
+@var{for_return} allows to distinguish the promotion of arguments and
+return values.  If it is @code{1}, a return value is being promoted and
+@code{TARGET_FUNCTION_VALUE} must perform the same promotions done here.
+If it is @code{2}, the returned mode should be that of the register in
+which an incoming parameter is copied, or the outgoing result is computed;
+then the hook should return the same mode as @code{promote_mode}, though
+the signedness may be different.
+
+The default is to not promote arguments and return values.  You can
+also define the hook to @code{default_promote_function_mode_always_promote}
+if you would like to apply the same rules given by @code{PROMOTE_MODE}.
+@end deftypefn
+
+@defmac PARM_BOUNDARY
+Normal alignment required for function parameters on the stack, in
+bits.  All stack parameters receive at least this much alignment
+regardless of data type.  On most machines, this is the same as the
+size of an integer.
+@end defmac
+
+@defmac STACK_BOUNDARY
+Define this macro to the minimum alignment enforced by hardware for the
+stack pointer on this machine.  The definition is a C expression for the
+desired alignment (measured in bits).  This value is used as a default
+if @code{PREFERRED_STACK_BOUNDARY} is not defined.  On most machines,
+this should be the same as @code{PARM_BOUNDARY}.
+@end defmac
+
+@defmac PREFERRED_STACK_BOUNDARY
+Define this macro if you wish to preserve a certain alignment for the
+stack pointer, greater than what the hardware enforces.  The definition
+is a C expression for the desired alignment (measured in bits).  This
+macro must evaluate to a value equal to or larger than
+@code{STACK_BOUNDARY}.
+@end defmac
+
+@defmac INCOMING_STACK_BOUNDARY
+Define this macro if the incoming stack boundary may be different
+from @code{PREFERRED_STACK_BOUNDARY}.  This macro must evaluate
+to a value equal to or larger than @code{STACK_BOUNDARY}.
+@end defmac
+
+@defmac FUNCTION_BOUNDARY
+Alignment required for a function entry point, in bits.
+@end defmac
+
+@defmac BIGGEST_ALIGNMENT
+Biggest alignment that any data type can require on this machine, in
+bits.  Note that this is not the biggest alignment that is supported,
+just the biggest alignment that, when violated, may cause a fault.
+@end defmac
+
+@defmac MALLOC_ABI_ALIGNMENT
+Alignment, in bits, a C conformant malloc implementation has to
+provide.  If not defined, the default value is @code{BITS_PER_WORD}.
+@end defmac
+
+@defmac ATTRIBUTE_ALIGNED_VALUE
+Alignment used by the @code{__attribute__ ((aligned))} construct.  If
+not defined, the default value is @code{BIGGEST_ALIGNMENT}.
+@end defmac
+
+@defmac MINIMUM_ATOMIC_ALIGNMENT
+If defined, the smallest alignment, in bits, that can be given to an
+object that can be referenced in one operation, without disturbing any
+nearby object.  Normally, this is @code{BITS_PER_UNIT}, but may be larger
+on machines that don't have byte or half-word store operations.
+@end defmac
+
+@defmac BIGGEST_FIELD_ALIGNMENT
+Biggest alignment that any structure or union field can require on this
+machine, in bits.  If defined, this overrides @code{BIGGEST_ALIGNMENT} for
+structure and union fields only, unless the field alignment has been set
+by the @code{__attribute__ ((aligned (@var{n})))} construct.
+@end defmac
+
+@defmac ADJUST_FIELD_ALIGN (@var{field}, @var{computed})
+An expression for the alignment of a structure field @var{field} if the
+alignment computed in the usual way (including applying of
+@code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the
+alignment) is @var{computed}.  It overrides alignment only if the
+field alignment has not been set by the
+@code{__attribute__ ((aligned (@var{n})))} construct.
+@end defmac
+
+@defmac MAX_STACK_ALIGNMENT
+Biggest stack alignment guaranteed by the backend.  Use this macro
+to specify the maximum alignment of a variable on stack.
+
+If not defined, the default value is @code{STACK_BOUNDARY}.
+
+@c FIXME: The default should be @code{PREFERRED_STACK_BOUNDARY}.
+@c But the fix for PR 32893 indicates that we can only guarantee
+@c maximum stack alignment on stack up to @code{STACK_BOUNDARY}, not
+@c @code{PREFERRED_STACK_BOUNDARY}, if stack alignment isn't supported.
+@end defmac
+
+@defmac MAX_OFILE_ALIGNMENT
+Biggest alignment supported by the object file format of this machine.
+Use this macro to limit the alignment which can be specified using the
+@code{__attribute__ ((aligned (@var{n})))} construct.  If not defined,
+the default value is @code{BIGGEST_ALIGNMENT}.
+
+On systems that use ELF, the default (in @file{config/elfos.h}) is
+the largest supported 32-bit ELF section alignment representable on
+a 32-bit host e.g. @samp{(((unsigned HOST_WIDEST_INT) 1 << 28) * 8)}.
+On 32-bit ELF the largest supported section alignment in bits is
+@samp{(0x80000000 * 8)}, but this is not representable on 32-bit hosts.
+@end defmac
+
+@defmac DATA_ALIGNMENT (@var{type}, @var{basic-align})
+If defined, a C expression to compute the alignment for a variable in
+the static store.  @var{type} is the data type, and @var{basic-align} is
+the alignment that the object would ordinarily have.  The value of this
+macro is used instead of that alignment to align the object.
+
+If this macro is not defined, then @var{basic-align} is used.
+
+@findex strcpy
+One use of this macro is to increase alignment of medium-size data to
+make it all fit in fewer cache lines.  Another is to cause character
+arrays to be word-aligned so that @code{strcpy} calls that copy
+constants to character arrays can be done inline.
+@end defmac
+
+@defmac CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align})
+If defined, a C expression to compute the alignment given to a constant
+that is being placed in memory.  @var{constant} is the constant and
+@var{basic-align} is the alignment that the object would ordinarily
+have.  The value of this macro is used instead of that alignment to
+align the object.
+
+If this macro is not defined, then @var{basic-align} is used.
+
+The typical use of this macro is to increase alignment for string
+constants to be word aligned so that @code{strcpy} calls that copy
+constants can be done inline.
+@end defmac
+
+@defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align})
+If defined, a C expression to compute the alignment for a variable in
+the local store.  @var{type} is the data type, and @var{basic-align} is
+the alignment that the object would ordinarily have.  The value of this
+macro is used instead of that alignment to align the object.
+
+If this macro is not defined, then @var{basic-align} is used.
+
+One use of this macro is to increase alignment of medium-size data to
+make it all fit in fewer cache lines.
+
+If the value of this macro has a type, it should be an unsigned type.
+@end defmac
+
+@hook TARGET_VECTOR_ALIGNMENT
+
+@defmac STACK_SLOT_ALIGNMENT (@var{type}, @var{mode}, @var{basic-align})
+If defined, a C expression to compute the alignment for stack slot.
+@var{type} is the data type, @var{mode} is the widest mode available,
+and @var{basic-align} is the alignment that the slot would ordinarily
+have.  The value of this macro is used instead of that alignment to
+align the slot.
+
+If this macro is not defined, then @var{basic-align} is used when
+@var{type} is @code{NULL}.  Otherwise, @code{LOCAL_ALIGNMENT} will
+be used.
+
+This macro is to set alignment of stack slot to the maximum alignment
+of all possible modes which the slot may have.
+
+If the value of this macro has a type, it should be an unsigned type.
+@end defmac
+
+@defmac LOCAL_DECL_ALIGNMENT (@var{decl})
+If defined, a C expression to compute the alignment for a local
+variable @var{decl}.
+
+If this macro is not defined, then
+@code{LOCAL_ALIGNMENT (TREE_TYPE (@var{decl}), DECL_ALIGN (@var{decl}))}
+is used.
+
+One use of this macro is to increase alignment of medium-size data to
+make it all fit in fewer cache lines.
+
+If the value of this macro has a type, it should be an unsigned type.
+@end defmac
+
+@defmac MINIMUM_ALIGNMENT (@var{exp}, @var{mode}, @var{align})
+If defined, a C expression to compute the minimum required alignment
+for dynamic stack realignment purposes for @var{exp} (a type or decl),
+@var{mode}, assuming normal alignment @var{align}.
+
+If this macro is not defined, then @var{align} will be used.
+@end defmac
+
+@defmac EMPTY_FIELD_BOUNDARY
+Alignment in bits to be given to a structure bit-field that follows an
+empty field such as @code{int : 0;}.
+
+If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro.
+@end defmac
+
+@defmac STRUCTURE_SIZE_BOUNDARY
+Number of bits which any structure or union's size must be a multiple of.
+Each structure or union's size is rounded up to a multiple of this.
+
+If you do not define this macro, the default is the same as
+@code{BITS_PER_UNIT}.
+@end defmac
+
+@defmac STRICT_ALIGNMENT
+Define this macro to be the value 1 if instructions will fail to work
+if given data not on the nominal alignment.  If instructions will merely
+go slower in that case, define this macro as 0.
+@end defmac
+
+@defmac PCC_BITFIELD_TYPE_MATTERS
+Define this if you wish to imitate the way many other C compilers handle
+alignment of bit-fields and the structures that contain them.
+
+The behavior is that the type written for a named bit-field (@code{int},
+@code{short}, or other integer type) imposes an alignment for the entire
+structure, as if the structure really did contain an ordinary field of
+that type.  In addition, the bit-field is placed within the structure so
+that it would fit within such a field, not crossing a boundary for it.
+
+Thus, on most machines, a named bit-field whose type is written as
+@code{int} would not cross a four-byte boundary, and would force
+four-byte alignment for the whole structure.  (The alignment used may
+not be four bytes; it is controlled by the other alignment parameters.)
+
+An unnamed bit-field will not affect the alignment of the containing
+structure.
+
+If the macro is defined, its definition should be a C expression;
+a nonzero value for the expression enables this behavior.
+
+Note that if this macro is not defined, or its value is zero, some
+bit-fields may cross more than one alignment boundary.  The compiler can
+support such references if there are @samp{insv}, @samp{extv}, and
+@samp{extzv} insns that can directly reference memory.
+
+The other known way of making bit-fields work is to define
+@code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}.
+Then every structure can be accessed with fullwords.
+
+Unless the machine has bit-field instructions or you define
+@code{STRUCTURE_SIZE_BOUNDARY} that way, you must define
+@code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value.
+
+If your aim is to make GCC use the same conventions for laying out
+bit-fields as are used by another compiler, here is how to investigate
+what the other compiler does.  Compile and run this program:
+
+@smallexample
+struct foo1
+@{
+  char x;
+  char :0;
+  char y;
+@};
+
+struct foo2
+@{
+  char x;
+  int :0;
+  char y;
+@};
+
+main ()
+@{
+  printf ("Size of foo1 is %d\n",
+          sizeof (struct foo1));
+  printf ("Size of foo2 is %d\n",
+          sizeof (struct foo2));
+  exit (0);
+@}
+@end smallexample
+
+If this prints 2 and 5, then the compiler's behavior is what you would
+get from @code{PCC_BITFIELD_TYPE_MATTERS}.
+@end defmac
+
+@defmac BITFIELD_NBYTES_LIMITED
+Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited
+to aligning a bit-field within the structure.
+@end defmac
+
+@hook TARGET_ALIGN_ANON_BITFIELD
+When @code{PCC_BITFIELD_TYPE_MATTERS} is true this hook will determine
+whether unnamed bitfields affect the alignment of the containing
+structure.  The hook should return true if the structure should inherit
+the alignment requirements of an unnamed bitfield's type.
+@end deftypefn
+
+@hook TARGET_NARROW_VOLATILE_BITFIELD
+This target hook should return @code{true} if accesses to volatile bitfields
+should use the narrowest mode possible.  It should return @code{false} if
+these accesses should use the bitfield container type.
+
+The default is @code{!TARGET_STRICT_ALIGN}.
+@end deftypefn
+
+@defmac MEMBER_TYPE_FORCES_BLK (@var{field}, @var{mode})
+Return 1 if a structure or array containing @var{field} should be accessed using
+@code{BLKMODE}.
+
+If @var{field} is the only field in the structure, @var{mode} is its
+mode, otherwise @var{mode} is VOIDmode.  @var{mode} is provided in the
+case where structures of one field would require the structure's mode to
+retain the field's mode.
+
+Normally, this is not needed.
+@end defmac
+
+@defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified})
+Define this macro as an expression for the alignment of a type (given
+by @var{type} as a tree node) if the alignment computed in the usual
+way is @var{computed} and the alignment explicitly specified was
+@var{specified}.
+
+The default is to use @var{specified} if it is larger; otherwise, use
+the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT}
+@end defmac
+
+@defmac MAX_FIXED_MODE_SIZE
+An integer expression for the size in bits of the largest integer
+machine mode that should actually be used.  All integer machine modes of
+this size or smaller can be used for structures and unions with the
+appropriate sizes.  If this macro is undefined, @code{GET_MODE_BITSIZE
+(DImode)} is assumed.
+@end defmac
+
+@defmac STACK_SAVEAREA_MODE (@var{save_level})
+If defined, an expression of type @code{enum machine_mode} that
+specifies the mode of the save area operand of a
+@code{save_stack_@var{level}} named pattern (@pxref{Standard Names}).
+@var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or
+@code{SAVE_NONLOCAL} and selects which of the three named patterns is
+having its mode specified.
+
+You need not define this macro if it always returns @code{Pmode}.  You
+would most commonly define this macro if the
+@code{save_stack_@var{level}} patterns need to support both a 32- and a
+64-bit mode.
+@end defmac
+
+@defmac STACK_SIZE_MODE
+If defined, an expression of type @code{enum machine_mode} that
+specifies the mode of the size increment operand of an
+@code{allocate_stack} named pattern (@pxref{Standard Names}).
+
+You need not define this macro if it always returns @code{word_mode}.
+You would most commonly define this macro if the @code{allocate_stack}
+pattern needs to support both a 32- and a 64-bit mode.
+@end defmac
+
+@hook TARGET_LIBGCC_CMP_RETURN_MODE
+This target hook should return the mode to be used for the return value
+of compare instructions expanded to libgcc calls.  If not defined
+@code{word_mode} is returned which is the right choice for a majority of
+targets.
+@end deftypefn
+
+@hook TARGET_LIBGCC_SHIFT_COUNT_MODE
+This target hook should return the mode to be used for the shift count operand
+of shift instructions expanded to libgcc calls.  If not defined
+@code{word_mode} is returned which is the right choice for a majority of
+targets.
+@end deftypefn
+
+@hook TARGET_UNWIND_WORD_MODE
+Return machine mode to be used for @code{_Unwind_Word} type.
+The default is to use @code{word_mode}.
+@end deftypefn
+
+@defmac ROUND_TOWARDS_ZERO
+If defined, this macro should be true if the prevailing rounding
+mode is towards zero.
+
+Defining this macro only affects the way @file{libgcc.a} emulates
+floating-point arithmetic.
+
+Not defining this macro is equivalent to returning zero.
+@end defmac
+
+@defmac LARGEST_EXPONENT_IS_NORMAL (@var{size})
+This macro should return true if floats with @var{size}
+bits do not have a NaN or infinity representation, but use the largest
+exponent for normal numbers instead.
+
+Defining this macro only affects the way @file{libgcc.a} emulates
+floating-point arithmetic.
+
+The default definition of this macro returns false for all sizes.
+@end defmac
+
+@hook TARGET_MS_BITFIELD_LAYOUT_P
+This target hook returns @code{true} if bit-fields in the given
+@var{record_type} are to be laid out following the rules of Microsoft
+Visual C/C++, namely: (i) a bit-field won't share the same storage
+unit with the previous bit-field if their underlying types have
+different sizes, and the bit-field will be aligned to the highest
+alignment of the underlying types of itself and of the previous
+bit-field; (ii) a zero-sized bit-field will affect the alignment of
+the whole enclosing structure, even if it is unnamed; except that
+(iii) a zero-sized bit-field will be disregarded unless it follows
+another bit-field of nonzero size.  If this hook returns @code{true},
+other macros that control bit-field layout are ignored.
+
+When a bit-field is inserted into a packed record, the whole size
+of the underlying type is used by one or more same-size adjacent
+bit-fields (that is, if its long:3, 32 bits is used in the record,
+and any additional adjacent long bit-fields are packed into the same
+chunk of 32 bits.  However, if the size changes, a new field of that
+size is allocated).  In an unpacked record, this is the same as using
+alignment, but not equivalent when packing.
+
+If both MS bit-fields and @samp{__attribute__((packed))} are used,
+the latter will take precedence.  If @samp{__attribute__((packed))} is
+used on a single field when MS bit-fields are in use, it will take
+precedence for that field, but the alignment of the rest of the structure
+may affect its placement.
+@end deftypefn
+
+@hook TARGET_DECIMAL_FLOAT_SUPPORTED_P
+Returns true if the target supports decimal floating point.
+@end deftypefn
+
+@hook TARGET_FIXED_POINT_SUPPORTED_P
+Returns true if the target supports fixed-point arithmetic.
+@end deftypefn
+
+@hook TARGET_EXPAND_TO_RTL_HOOK
+This hook is called just before expansion into rtl, allowing the target
+to perform additional initializations or analysis before the expansion.
+For example, the rs6000 port uses it to allocate a scratch stack slot
+for use in copying SDmode values between memory and floating point
+registers whenever the function being expanded has any SDmode
+usage.
+@end deftypefn
+
+@hook TARGET_INSTANTIATE_DECLS
+This hook allows the backend to perform additional instantiations on rtl
+that are not actually in any insns yet, but will be later.
+@end deftypefn
+
+@hook TARGET_MANGLE_TYPE
+If your target defines any fundamental types, or any types your target
+uses should be mangled differently from the default, define this hook
+to return the appropriate encoding for these types as part of a C++
+mangled name.  The @var{type} argument is the tree structure representing
+the type to be mangled.  The hook may be applied to trees which are
+not target-specific fundamental types; it should return @code{NULL}
+for all such types, as well as arguments it does not recognize.  If the
+return value is not @code{NULL}, it must point to a statically-allocated
+string constant.
+
+Target-specific fundamental types might be new fundamental types or
+qualified versions of ordinary fundamental types.  Encode new
+fundamental types as @samp{@w{u @var{n} @var{name}}}, where @var{name}
+is the name used for the type in source code, and @var{n} is the
+length of @var{name} in decimal.  Encode qualified versions of
+ordinary types as @samp{@w{U @var{n} @var{name} @var{code}}}, where
+@var{name} is the name used for the type qualifier in source code,
+@var{n} is the length of @var{name} as above, and @var{code} is the
+code used to represent the unqualified version of this type.  (See
+@code{write_builtin_type} in @file{cp/mangle.c} for the list of
+codes.)  In both cases the spaces are for clarity; do not include any
+spaces in your string.
+
+This hook is applied to types prior to typedef resolution.  If the mangled
+name for a particular type depends only on that type's main variant, you
+can perform typedef resolution yourself using @code{TYPE_MAIN_VARIANT}
+before mangling.
+
+The default version of this hook always returns @code{NULL}, which is
+appropriate for a target that does not define any new fundamental
+types.
+@end deftypefn
+
+@node Type Layout
+@section Layout of Source Language Data Types
+
+These macros define the sizes and other characteristics of the standard
+basic data types used in programs being compiled.  Unlike the macros in
+the previous section, these apply to specific features of C and related
+languages, rather than to fundamental aspects of storage layout.
+
+@defmac INT_TYPE_SIZE
+A C expression for the size in bits of the type @code{int} on the
+target machine.  If you don't define this, the default is one word.
+@end defmac
+
+@defmac SHORT_TYPE_SIZE
+A C expression for the size in bits of the type @code{short} on the
+target machine.  If you don't define this, the default is half a word.
+(If this would be less than one storage unit, it is rounded up to one
+unit.)
+@end defmac
+
+@defmac LONG_TYPE_SIZE
+A C expression for the size in bits of the type @code{long} on the
+target machine.  If you don't define this, the default is one word.
+@end defmac
+
+@defmac ADA_LONG_TYPE_SIZE
+On some machines, the size used for the Ada equivalent of the type
+@code{long} by a native Ada compiler differs from that used by C@.  In
+that situation, define this macro to be a C expression to be used for
+the size of that type.  If you don't define this, the default is the
+value of @code{LONG_TYPE_SIZE}.
+@end defmac
+
+@defmac LONG_LONG_TYPE_SIZE
+A C expression for the size in bits of the type @code{long long} on the
+target machine.  If you don't define this, the default is two
+words.  If you want to support GNU Ada on your machine, the value of this
+macro must be at least 64.
+@end defmac
+
+@defmac CHAR_TYPE_SIZE
+A C expression for the size in bits of the type @code{char} on the
+target machine.  If you don't define this, the default is
+@code{BITS_PER_UNIT}.
+@end defmac
+
+@defmac BOOL_TYPE_SIZE
+A C expression for the size in bits of the C++ type @code{bool} and
+C99 type @code{_Bool} on the target machine.  If you don't define
+this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}.
+@end defmac
+
+@defmac FLOAT_TYPE_SIZE
+A C expression for the size in bits of the type @code{float} on the
+target machine.  If you don't define this, the default is one word.
+@end defmac
+
+@defmac DOUBLE_TYPE_SIZE
+A C expression for the size in bits of the type @code{double} on the
+target machine.  If you don't define this, the default is two
+words.
+@end defmac
+
+@defmac LONG_DOUBLE_TYPE_SIZE
+A C expression for the size in bits of the type @code{long double} on
+the target machine.  If you don't define this, the default is two
+words.
+@end defmac
+
+@defmac SHORT_FRACT_TYPE_SIZE
+A C expression for the size in bits of the type @code{short _Fract} on
+the target machine.  If you don't define this, the default is
+@code{BITS_PER_UNIT}.
+@end defmac
+
+@defmac FRACT_TYPE_SIZE
+A C expression for the size in bits of the type @code{_Fract} on
+the target machine.  If you don't define this, the default is
+@code{BITS_PER_UNIT * 2}.
+@end defmac
+
+@defmac LONG_FRACT_TYPE_SIZE
+A C expression for the size in bits of the type @code{long _Fract} on
+the target machine.  If you don't define this, the default is
+@code{BITS_PER_UNIT * 4}.
+@end defmac
+
+@defmac LONG_LONG_FRACT_TYPE_SIZE
+A C expression for the size in bits of the type @code{long long _Fract} on
+the target machine.  If you don't define this, the default is
+@code{BITS_PER_UNIT * 8}.
+@end defmac
+
+@defmac SHORT_ACCUM_TYPE_SIZE
+A C expression for the size in bits of the type @code{short _Accum} on
+the target machine.  If you don't define this, the default is
+@code{BITS_PER_UNIT * 2}.
+@end defmac
+
+@defmac ACCUM_TYPE_SIZE
+A C expression for the size in bits of the type @code{_Accum} on
+the target machine.  If you don't define this, the default is
+@code{BITS_PER_UNIT * 4}.
+@end defmac
+
+@defmac LONG_ACCUM_TYPE_SIZE
+A C expression for the size in bits of the type @code{long _Accum} on
+the target machine.  If you don't define this, the default is
+@code{BITS_PER_UNIT * 8}.
+@end defmac
+
+@defmac LONG_LONG_ACCUM_TYPE_SIZE
+A C expression for the size in bits of the type @code{long long _Accum} on
+the target machine.  If you don't define this, the default is
+@code{BITS_PER_UNIT * 16}.
+@end defmac
+
+@defmac LIBGCC2_LONG_DOUBLE_TYPE_SIZE
+Define this macro if @code{LONG_DOUBLE_TYPE_SIZE} is not constant or
+if you want routines in @file{libgcc2.a} for a size other than
+@code{LONG_DOUBLE_TYPE_SIZE}.  If you don't define this, the
+default is @code{LONG_DOUBLE_TYPE_SIZE}.
+@end defmac
+
+@defmac LIBGCC2_HAS_DF_MODE
+Define this macro if neither @code{DOUBLE_TYPE_SIZE} nor
+@code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is
+@code{DFmode} but you want @code{DFmode} routines in @file{libgcc2.a}
+anyway.  If you don't define this and either @code{DOUBLE_TYPE_SIZE}
+or @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64 then the default is 1,
+otherwise it is 0.
+@end defmac
+
+@defmac LIBGCC2_HAS_XF_MODE
+Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not
+@code{XFmode} but you want @code{XFmode} routines in @file{libgcc2.a}
+anyway.  If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE}
+is 80 then the default is 1, otherwise it is 0.
+@end defmac
+
+@defmac LIBGCC2_HAS_TF_MODE
+Define this macro if @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is not
+@code{TFmode} but you want @code{TFmode} routines in @file{libgcc2.a}
+anyway.  If you don't define this and @code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE}
+is 128 then the default is 1, otherwise it is 0.
+@end defmac
+
+@defmac SF_SIZE
+@defmacx DF_SIZE
+@defmacx XF_SIZE
+@defmacx TF_SIZE
+Define these macros to be the size in bits of the mantissa of
+@code{SFmode}, @code{DFmode}, @code{XFmode} and @code{TFmode} values,
+if the defaults in @file{libgcc2.h} are inappropriate.  By default,
+@code{FLT_MANT_DIG} is used for @code{SF_SIZE}, @code{LDBL_MANT_DIG}
+for @code{XF_SIZE} and @code{TF_SIZE}, and @code{DBL_MANT_DIG} or
+@code{LDBL_MANT_DIG} for @code{DF_SIZE} according to whether
+@code{DOUBLE_TYPE_SIZE} or
+@code{LIBGCC2_LONG_DOUBLE_TYPE_SIZE} is 64.
+@end defmac
+
+@defmac TARGET_FLT_EVAL_METHOD
+A C expression for the value for @code{FLT_EVAL_METHOD} in @file{float.h},
+assuming, if applicable, that the floating-point control word is in its
+default state.  If you do not define this macro the value of
+@code{FLT_EVAL_METHOD} will be zero.
+@end defmac
+
+@defmac WIDEST_HARDWARE_FP_SIZE
+A C expression for the size in bits of the widest floating-point format
+supported by the hardware.  If you define this macro, you must specify a
+value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}.
+If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE}
+is the default.
+@end defmac
+
+@defmac DEFAULT_SIGNED_CHAR
+An expression whose value is 1 or 0, according to whether the type
+@code{char} should be signed or unsigned by default.  The user can
+always override this default with the options @option{-fsigned-char}
+and @option{-funsigned-char}.
+@end defmac
+
+@hook TARGET_DEFAULT_SHORT_ENUMS
+This target hook should return true if the compiler should give an
+@code{enum} type only as many bytes as it takes to represent the range
+of possible values of that type.  It should return false if all
+@code{enum} types should be allocated like @code{int}.
+
+The default is to return false.
+@end deftypefn
+
+@defmac SIZE_TYPE
+A C expression for a string describing the name of the data type to use
+for size values.  The typedef name @code{size_t} is defined using the
+contents of the string.
+
+The string can contain more than one keyword.  If so, separate them with
+spaces, and write first any length keyword, then @code{unsigned} if
+appropriate, and finally @code{int}.  The string must exactly match one
+of the data type names defined in the function
+@code{init_decl_processing} in the file @file{c-decl.c}.  You may not
+omit @code{int} or change the order---that would cause the compiler to
+crash on startup.
+
+If you don't define this macro, the default is @code{"long unsigned
+int"}.
+@end defmac
+
+@defmac PTRDIFF_TYPE
+A C expression for a string describing the name of the data type to use
+for the result of subtracting two pointers.  The typedef name
+@code{ptrdiff_t} is defined using the contents of the string.  See
+@code{SIZE_TYPE} above for more information.
+
+If you don't define this macro, the default is @code{"long int"}.
+@end defmac
+
+@defmac WCHAR_TYPE
+A C expression for a string describing the name of the data type to use
+for wide characters.  The typedef name @code{wchar_t} is defined using
+the contents of the string.  See @code{SIZE_TYPE} above for more
+information.
+
+If you don't define this macro, the default is @code{"int"}.
+@end defmac
+
+@defmac WCHAR_TYPE_SIZE
+A C expression for the size in bits of the data type for wide
+characters.  This is used in @code{cpp}, which cannot make use of
+@code{WCHAR_TYPE}.
+@end defmac
+
+@defmac WINT_TYPE
+A C expression for a string describing the name of the data type to
+use for wide characters passed to @code{printf} and returned from
+@code{getwc}.  The typedef name @code{wint_t} is defined using the
+contents of the string.  See @code{SIZE_TYPE} above for more
+information.
+
+If you don't define this macro, the default is @code{"unsigned int"}.
+@end defmac
+
+@defmac INTMAX_TYPE
+A C expression for a string describing the name of the data type that
+can represent any value of any standard or extended signed integer type.
+The typedef name @code{intmax_t} is defined using the contents of the
+string.  See @code{SIZE_TYPE} above for more information.
+
+If you don't define this macro, the default is the first of
+@code{"int"}, @code{"long int"}, or @code{"long long int"} that has as
+much precision as @code{long long int}.
+@end defmac
+
+@defmac UINTMAX_TYPE
+A C expression for a string describing the name of the data type that
+can represent any value of any standard or extended unsigned integer
+type.  The typedef name @code{uintmax_t} is defined using the contents
+of the string.  See @code{SIZE_TYPE} above for more information.
+
+If you don't define this macro, the default is the first of
+@code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long
+unsigned int"} that has as much precision as @code{long long unsigned
+int}.
+@end defmac
+
+@defmac SIG_ATOMIC_TYPE
+@defmacx INT8_TYPE
+@defmacx INT16_TYPE
+@defmacx INT32_TYPE
+@defmacx INT64_TYPE
+@defmacx UINT8_TYPE
+@defmacx UINT16_TYPE
+@defmacx UINT32_TYPE
+@defmacx UINT64_TYPE
+@defmacx INT_LEAST8_TYPE
+@defmacx INT_LEAST16_TYPE
+@defmacx INT_LEAST32_TYPE
+@defmacx INT_LEAST64_TYPE
+@defmacx UINT_LEAST8_TYPE
+@defmacx UINT_LEAST16_TYPE
+@defmacx UINT_LEAST32_TYPE
+@defmacx UINT_LEAST64_TYPE
+@defmacx INT_FAST8_TYPE
+@defmacx INT_FAST16_TYPE
+@defmacx INT_FAST32_TYPE
+@defmacx INT_FAST64_TYPE
+@defmacx UINT_FAST8_TYPE
+@defmacx UINT_FAST16_TYPE
+@defmacx UINT_FAST32_TYPE
+@defmacx UINT_FAST64_TYPE
+@defmacx INTPTR_TYPE
+@defmacx UINTPTR_TYPE
+C expressions for the standard types @code{sig_atomic_t},
+@code{int8_t}, @code{int16_t}, @code{int32_t}, @code{int64_t},
+@code{uint8_t}, @code{uint16_t}, @code{uint32_t}, @code{uint64_t},
+@code{int_least8_t}, @code{int_least16_t}, @code{int_least32_t},
+@code{int_least64_t}, @code{uint_least8_t}, @code{uint_least16_t},
+@code{uint_least32_t}, @code{uint_least64_t}, @code{int_fast8_t},
+@code{int_fast16_t}, @code{int_fast32_t}, @code{int_fast64_t},
+@code{uint_fast8_t}, @code{uint_fast16_t}, @code{uint_fast32_t},
+@code{uint_fast64_t}, @code{intptr_t}, and @code{uintptr_t}.  See
+@code{SIZE_TYPE} above for more information.
+
+If any of these macros evaluates to a null pointer, the corresponding
+type is not supported; if GCC is configured to provide
+@code{<stdint.h>} in such a case, the header provided may not conform
+to C99, depending on the type in question.  The defaults for all of
+these macros are null pointers.
+@end defmac
+
+@defmac TARGET_PTRMEMFUNC_VBIT_LOCATION
+The C++ compiler represents a pointer-to-member-function with a struct
+that looks like:
+
+@smallexample
+  struct @{
+    union @{
+      void (*fn)();
+      ptrdiff_t vtable_index;
+    @};
+    ptrdiff_t delta;
+  @};
+@end smallexample
+
+@noindent
+The C++ compiler must use one bit to indicate whether the function that
+will be called through a pointer-to-member-function is virtual.
+Normally, we assume that the low-order bit of a function pointer must
+always be zero.  Then, by ensuring that the vtable_index is odd, we can
+distinguish which variant of the union is in use.  But, on some
+platforms function pointers can be odd, and so this doesn't work.  In
+that case, we use the low-order bit of the @code{delta} field, and shift
+the remainder of the @code{delta} field to the left.
+
+GCC will automatically make the right selection about where to store
+this bit using the @code{FUNCTION_BOUNDARY} setting for your platform.
+However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY}
+set such that functions always start at even addresses, but the lowest
+bit of pointers to functions indicate whether the function at that
+address is in ARM or Thumb mode.  If this is the case of your
+architecture, you should define this macro to
+@code{ptrmemfunc_vbit_in_delta}.
+
+In general, you should not have to define this macro.  On architectures
+in which function addresses are always even, according to
+@code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to
+@code{ptrmemfunc_vbit_in_pfn}.
+@end defmac
+
+@defmac TARGET_VTABLE_USES_DESCRIPTORS
+Normally, the C++ compiler uses function pointers in vtables.  This
+macro allows the target to change to use ``function descriptors''
+instead.  Function descriptors are found on targets for whom a
+function pointer is actually a small data structure.  Normally the
+data structure consists of the actual code address plus a data
+pointer to which the function's data is relative.
+
+If vtables are used, the value of this macro should be the number
+of words that the function descriptor occupies.
+@end defmac
+
+@defmac TARGET_VTABLE_ENTRY_ALIGN
+By default, the vtable entries are void pointers, the so the alignment
+is the same as pointer alignment.  The value of this macro specifies
+the alignment of the vtable entry in bits.  It should be defined only
+when special alignment is necessary. */
+@end defmac
+
+@defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE
+There are a few non-descriptor entries in the vtable at offsets below
+zero.  If these entries must be padded (say, to preserve the alignment
+specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number
+of words in each data entry.
+@end defmac
+
+@node Registers
+@section Register Usage
+@cindex register usage
+
+This section explains how to describe what registers the target machine
+has, and how (in general) they can be used.
+
+The description of which registers a specific instruction can use is
+done with register classes; see @ref{Register Classes}.  For information
+on using registers to access a stack frame, see @ref{Frame Registers}.
+For passing values in registers, see @ref{Register Arguments}.
+For returning values in registers, see @ref{Scalar Return}.
+
+@menu
+* Register Basics::             Number and kinds of registers.
+* Allocation Order::            Order in which registers are allocated.
+* Values in Registers::         What kinds of values each reg can hold.
+* Leaf Functions::              Renumbering registers for leaf functions.
+* Stack Registers::             Handling a register stack such as 80387.
+@end menu
+
+@node Register Basics
+@subsection Basic Characteristics of Registers
+
+@c prevent bad page break with this line
+Registers have various characteristics.
+
+@defmac FIRST_PSEUDO_REGISTER
+Number of hardware registers known to the compiler.  They receive
+numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first
+pseudo register's number really is assigned the number
+@code{FIRST_PSEUDO_REGISTER}.
+@end defmac
+
+@defmac FIXED_REGISTERS
+@cindex fixed register
+An initializer that says which registers are used for fixed purposes
+all throughout the compiled code and are therefore not available for
+general allocation.  These would include the stack pointer, the frame
+pointer (except on machines where that can be used as a general
+register when no frame pointer is needed), the program counter on
+machines where that is considered one of the addressable registers,
+and any other numbered register with a standard use.
+
+This information is expressed as a sequence of numbers, separated by
+commas and surrounded by braces.  The @var{n}th number is 1 if
+register @var{n} is fixed, 0 otherwise.
+
+The table initialized from this macro, and the table initialized by
+the following one, may be overridden at run time either automatically,
+by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by
+the user with the command options @option{-ffixed-@var{reg}},
+@option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}.
+@end defmac
+
+@defmac CALL_USED_REGISTERS
+@cindex call-used register
+@cindex call-clobbered register
+@cindex call-saved register
+Like @code{FIXED_REGISTERS} but has 1 for each register that is
+clobbered (in general) by function calls as well as for fixed
+registers.  This macro therefore identifies the registers that are not
+available for general allocation of values that must live across
+function calls.
+
+If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler
+automatically saves it on function entry and restores it on function
+exit, if the register is used within the function.
+@end defmac
+
+@defmac CALL_REALLY_USED_REGISTERS
+@cindex call-used register
+@cindex call-clobbered register
+@cindex call-saved register
+Like @code{CALL_USED_REGISTERS} except this macro doesn't require
+that the entire set of @code{FIXED_REGISTERS} be included.
+(@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}).
+This macro is optional.  If not specified, it defaults to the value
+of @code{CALL_USED_REGISTERS}.
+@end defmac
+
+@defmac HARD_REGNO_CALL_PART_CLOBBERED (@var{regno}, @var{mode})
+@cindex call-used register
+@cindex call-clobbered register
+@cindex call-saved register
+A C expression that is nonzero if it is not permissible to store a
+value of mode @var{mode} in hard register number @var{regno} across a
+call without some part of it being clobbered.  For most machines this
+macro need not be defined.  It is only required for machines that do not
+preserve the entire contents of a register across a call.
+@end defmac
+
+@findex fixed_regs
+@findex call_used_regs
+@findex global_regs
+@findex reg_names
+@findex reg_class_contents
+@hook TARGET_CONDITIONAL_REGISTER_USAGE
+This hook may conditionally modify five variables
+@code{fixed_regs}, @code{call_used_regs}, @code{global_regs},
+@code{reg_names}, and @code{reg_class_contents}, to take into account
+any dependence of these register sets on target flags.  The first three
+of these are of type @code{char []} (interpreted as Boolean vectors).
+@code{global_regs} is a @code{const char *[]}, and
+@code{reg_class_contents} is a @code{HARD_REG_SET}.  Before the macro is
+called, @code{fixed_regs}, @code{call_used_regs},
+@code{reg_class_contents}, and @code{reg_names} have been initialized
+from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS},
+@code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively.
+@code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}},
+@option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}
+command options have been applied.
+
+@cindex disabling certain registers
+@cindex controlling register usage
+If the usage of an entire class of registers depends on the target
+flags, you may indicate this to GCC by using this macro to modify
+@code{fixed_regs} and @code{call_used_regs} to 1 for each of the
+registers in the classes which should not be used by GCC@.  Also define
+the macro @code{REG_CLASS_FROM_LETTER} / @code{REG_CLASS_FROM_CONSTRAINT}
+to return @code{NO_REGS} if it
+is called with a letter for a class that shouldn't be used.
+
+(However, if this class is not included in @code{GENERAL_REGS} and all
+of the insn patterns whose constraints permit this class are
+controlled by target switches, then GCC will automatically avoid using
+these registers when the target switches are opposed to them.)
+@end deftypefn
+
+@defmac INCOMING_REGNO (@var{out})
+Define this macro if the target machine has register windows.  This C
+expression returns the register number as seen by the called function
+corresponding to the register number @var{out} as seen by the calling
+function.  Return @var{out} if register number @var{out} is not an
+outbound register.
+@end defmac
+
+@defmac OUTGOING_REGNO (@var{in})
+Define this macro if the target machine has register windows.  This C
+expression returns the register number as seen by the calling function
+corresponding to the register number @var{in} as seen by the called
+function.  Return @var{in} if register number @var{in} is not an inbound
+register.
+@end defmac
+
+@defmac LOCAL_REGNO (@var{regno})
+Define this macro if the target machine has register windows.  This C
+expression returns true if the register is call-saved but is in the
+register window.  Unlike most call-saved registers, such registers
+need not be explicitly restored on function exit or during non-local
+gotos.
+@end defmac
+
+@defmac PC_REGNUM
+If the program counter has a register number, define this as that
+register number.  Otherwise, do not define it.
+@end defmac
+
+@node Allocation Order
+@subsection Order of Allocation of Registers
+@cindex order of register allocation
+@cindex register allocation order
+
+@c prevent bad page break with this line
+Registers are allocated in order.
+
+@defmac REG_ALLOC_ORDER
+If defined, an initializer for a vector of integers, containing the
+numbers of hard registers in the order in which GCC should prefer
+to use them (from most preferred to least).
+
+If this macro is not defined, registers are used lowest numbered first
+(all else being equal).
+
+One use of this macro is on machines where the highest numbered
+registers must always be saved and the save-multiple-registers
+instruction supports only sequences of consecutive registers.  On such
+machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists
+the highest numbered allocable register first.
+@end defmac
+
+@defmac ADJUST_REG_ALLOC_ORDER
+A C statement (sans semicolon) to choose the order in which to allocate
+hard registers for pseudo-registers local to a basic block.
+
+Store the desired register order in the array @code{reg_alloc_order}.
+Element 0 should be the register to allocate first; element 1, the next
+register; and so on.
+
+The macro body should not assume anything about the contents of
+@code{reg_alloc_order} before execution of the macro.
+
+On most machines, it is not necessary to define this macro.
+@end defmac
+
+@defmac HONOR_REG_ALLOC_ORDER
+Normally, IRA tries to estimate the costs for saving a register in the
+prologue and restoring it in the epilogue.  This discourages it from
+using call-saved registers.  If a machine wants to ensure that IRA
+allocates registers in the order given by REG_ALLOC_ORDER even if some
+call-saved registers appear earlier than call-used ones, this macro
+should be defined.
+@end defmac
+
+@defmac IRA_HARD_REGNO_ADD_COST_MULTIPLIER (@var{regno})
+In some case register allocation order is not enough for the
+Integrated Register Allocator (@acronym{IRA}) to generate a good code.
+If this macro is defined, it should return a floating point value
+based on @var{regno}.  The cost of using @var{regno} for a pseudo will
+be increased by approximately the pseudo's usage frequency times the
+value returned by this macro.  Not defining this macro is equivalent
+to having it always return @code{0.0}.
+
+On most machines, it is not necessary to define this macro.
+@end defmac
+
+@node Values in Registers
+@subsection How Values Fit in Registers
+
+This section discusses the macros that describe which kinds of values
+(specifically, which machine modes) each register can hold, and how many
+consecutive registers are needed for a given mode.
+
+@defmac HARD_REGNO_NREGS (@var{regno}, @var{mode})
+A C expression for the number of consecutive hard registers, starting
+at register number @var{regno}, required to hold a value of mode
+@var{mode}.  This macro must never return zero, even if a register
+cannot hold the requested mode - indicate that with HARD_REGNO_MODE_OK
+and/or CANNOT_CHANGE_MODE_CLASS instead.
+
+On a machine where all registers are exactly one word, a suitable
+definition of this macro is
+
+@smallexample
+#define HARD_REGNO_NREGS(REGNO, MODE)            \
+   ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1)  \
+    / UNITS_PER_WORD)
+@end smallexample
+@end defmac
+
+@defmac HARD_REGNO_NREGS_HAS_PADDING (@var{regno}, @var{mode})
+A C expression that is nonzero if a value of mode @var{mode}, stored
+in memory, ends with padding that causes it to take up more space than
+in registers starting at register number @var{regno} (as determined by
+multiplying GCC's notion of the size of the register when containing
+this mode by the number of registers returned by
+@code{HARD_REGNO_NREGS}).  By default this is zero.
+
+For example, if a floating-point value is stored in three 32-bit
+registers but takes up 128 bits in memory, then this would be
+nonzero.
+
+This macros only needs to be defined if there are cases where
+@code{subreg_get_info}
+would otherwise wrongly determine that a @code{subreg} can be
+represented by an offset to the register number, when in fact such a
+@code{subreg} would contain some of the padding not stored in
+registers and so not be representable.
+@end defmac
+
+@defmac HARD_REGNO_NREGS_WITH_PADDING (@var{regno}, @var{mode})
+For values of @var{regno} and @var{mode} for which
+@code{HARD_REGNO_NREGS_HAS_PADDING} returns nonzero, a C expression
+returning the greater number of registers required to hold the value
+including any padding.  In the example above, the value would be four.
+@end defmac
+
+@defmac REGMODE_NATURAL_SIZE (@var{mode})
+Define this macro if the natural size of registers that hold values
+of mode @var{mode} is not the word size.  It is a C expression that
+should give the natural size in bytes for the specified mode.  It is
+used by the register allocator to try to optimize its results.  This
+happens for example on SPARC 64-bit where the natural size of
+floating-point registers is still 32-bit.
+@end defmac
+
+@defmac HARD_REGNO_MODE_OK (@var{regno}, @var{mode})
+A C expression that is nonzero if it is permissible to store a value
+of mode @var{mode} in hard register number @var{regno} (or in several
+registers starting with that one).  For a machine where all registers
+are equivalent, a suitable definition is
+
+@smallexample
+#define HARD_REGNO_MODE_OK(REGNO, MODE) 1
+@end smallexample
+
+You need not include code to check for the numbers of fixed registers,
+because the allocation mechanism considers them to be always occupied.
+
+@cindex register pairs
+On some machines, double-precision values must be kept in even/odd
+register pairs.  You can implement that by defining this macro to reject
+odd register numbers for such modes.
+
+The minimum requirement for a mode to be OK in a register is that the
+@samp{mov@var{mode}} instruction pattern support moves between the
+register and other hard register in the same class and that moving a
+value into the register and back out not alter it.
+
+Since the same instruction used to move @code{word_mode} will work for
+all narrower integer modes, it is not necessary on any machine for
+@code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided
+you define patterns @samp{movhi}, etc., to take advantage of this.  This
+is useful because of the interaction between @code{HARD_REGNO_MODE_OK}
+and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes
+to be tieable.
+
+Many machines have special registers for floating point arithmetic.
+Often people assume that floating point machine modes are allowed only
+in floating point registers.  This is not true.  Any registers that
+can hold integers can safely @emph{hold} a floating point machine
+mode, whether or not floating arithmetic can be done on it in those
+registers.  Integer move instructions can be used to move the values.
+
+On some machines, though, the converse is true: fixed-point machine
+modes may not go in floating registers.  This is true if the floating
+registers normalize any value stored in them, because storing a
+non-floating value there would garble it.  In this case,
+@code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in
+floating registers.  But if the floating registers do not automatically
+normalize, if you can store any bit pattern in one and retrieve it
+unchanged without a trap, then any machine mode may go in a floating
+register, so you can define this macro to say so.
+
+The primary significance of special floating registers is rather that
+they are the registers acceptable in floating point arithmetic
+instructions.  However, this is of no concern to
+@code{HARD_REGNO_MODE_OK}.  You handle it by writing the proper
+constraints for those instructions.
+
+On some machines, the floating registers are especially slow to access,
+so that it is better to store a value in a stack frame than in such a
+register if floating point arithmetic is not being done.  As long as the
+floating registers are not in class @code{GENERAL_REGS}, they will not
+be used unless some pattern's constraint asks for one.
+@end defmac
+
+@defmac HARD_REGNO_RENAME_OK (@var{from}, @var{to})
+A C expression that is nonzero if it is OK to rename a hard register
+@var{from} to another hard register @var{to}.
+
+One common use of this macro is to prevent renaming of a register to
+another register that is not saved by a prologue in an interrupt
+handler.
+
+The default is always nonzero.
+@end defmac
+
+@defmac MODES_TIEABLE_P (@var{mode1}, @var{mode2})
+A C expression that is nonzero if a value of mode
+@var{mode1} is accessible in mode @var{mode2} without copying.
+
+If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and
+@code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for
+any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})}
+should be nonzero.  If they differ for any @var{r}, you should define
+this macro to return zero unless some other mechanism ensures the
+accessibility of the value in a narrower mode.
+
+You should define this macro to return nonzero in as many cases as
+possible since doing so will allow GCC to perform better register
+allocation.
+@end defmac
+
+@hook TARGET_HARD_REGNO_SCRATCH_OK
+This target hook should return @code{true} if it is OK to use a hard register
+@var{regno} as scratch reg in peephole2.
+
+One common use of this macro is to prevent using of a register that
+is not saved by a prologue in an interrupt handler.
+
+The default version of this hook always returns @code{true}.
+@end deftypefn
+
+@defmac AVOID_CCMODE_COPIES
+Define this macro if the compiler should avoid copies to/from @code{CCmode}
+registers.  You should only define this macro if support for copying to/from
+@code{CCmode} is incomplete.
+@end defmac
+
+@node Leaf Functions
+@subsection Handling Leaf Functions
+
+@cindex leaf functions
+@cindex functions, leaf
+On some machines, a leaf function (i.e., one which makes no calls) can run
+more efficiently if it does not make its own register window.  Often this
+means it is required to receive its arguments in the registers where they
+are passed by the caller, instead of the registers where they would
+normally arrive.
+
+The special treatment for leaf functions generally applies only when
+other conditions are met; for example, often they may use only those
+registers for its own variables and temporaries.  We use the term ``leaf
+function'' to mean a function that is suitable for this special
+handling, so that functions with no calls are not necessarily ``leaf
+functions''.
+
+GCC assigns register numbers before it knows whether the function is
+suitable for leaf function treatment.  So it needs to renumber the
+registers in order to output a leaf function.  The following macros
+accomplish this.
+
+@defmac LEAF_REGISTERS
+Name of a char vector, indexed by hard register number, which
+contains 1 for a register that is allowable in a candidate for leaf
+function treatment.
+
+If leaf function treatment involves renumbering the registers, then the
+registers marked here should be the ones before renumbering---those that
+GCC would ordinarily allocate.  The registers which will actually be
+used in the assembler code, after renumbering, should not be marked with 1
+in this vector.
+
+Define this macro only if the target machine offers a way to optimize
+the treatment of leaf functions.
+@end defmac
+
+@defmac LEAF_REG_REMAP (@var{regno})
+A C expression whose value is the register number to which @var{regno}
+should be renumbered, when a function is treated as a leaf function.
+
+If @var{regno} is a register number which should not appear in a leaf
+function before renumbering, then the expression should yield @minus{}1, which
+will cause the compiler to abort.
+
+Define this macro only if the target machine offers a way to optimize the
+treatment of leaf functions, and registers need to be renumbered to do
+this.
+@end defmac
+
+@findex current_function_is_leaf
+@findex current_function_uses_only_leaf_regs
+@code{TARGET_ASM_FUNCTION_PROLOGUE} and
+@code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions
+specially.  They can test the C variable @code{current_function_is_leaf}
+which is nonzero for leaf functions.  @code{current_function_is_leaf} is
+set prior to local register allocation and is valid for the remaining
+compiler passes.  They can also test the C variable
+@code{current_function_uses_only_leaf_regs} which is nonzero for leaf
+functions which only use leaf registers.
+@code{current_function_uses_only_leaf_regs} is valid after all passes
+that modify the instructions have been run and is only useful if
+@code{LEAF_REGISTERS} is defined.
+@c changed this to fix overfull.  ALSO:  why the "it" at the beginning
+@c of the next paragraph?!  --mew 2feb93
+
+@node Stack Registers
+@subsection Registers That Form a Stack
+
+There are special features to handle computers where some of the
+``registers'' form a stack.  Stack registers are normally written by
+pushing onto the stack, and are numbered relative to the top of the
+stack.
+
+Currently, GCC can only handle one group of stack-like registers, and
+they must be consecutively numbered.  Furthermore, the existing
+support for stack-like registers is specific to the 80387 floating
+point coprocessor.  If you have a new architecture that uses
+stack-like registers, you will need to do substantial work on
+@file{reg-stack.c} and write your machine description to cooperate
+with it, as well as defining these macros.
+
+@defmac STACK_REGS
+Define this if the machine has any stack-like registers.
+@end defmac
+
+@defmac STACK_REG_COVER_CLASS
+This is a cover class containing the stack registers.  Define this if
+the machine has any stack-like registers.
+@end defmac
+
+@defmac FIRST_STACK_REG
+The number of the first stack-like register.  This one is the top
+of the stack.
+@end defmac
+
+@defmac LAST_STACK_REG
+The number of the last stack-like register.  This one is the bottom of
+the stack.
+@end defmac
+
+@node Register Classes
+@section Register Classes
+@cindex register class definitions
+@cindex class definitions, register
+
+On many machines, the numbered registers are not all equivalent.
+For example, certain registers may not be allowed for indexed addressing;
+certain registers may not be allowed in some instructions.  These machine
+restrictions are described to the compiler using @dfn{register classes}.
+
+You define a number of register classes, giving each one a name and saying
+which of the registers belong to it.  Then you can specify register classes
+that are allowed as operands to particular instruction patterns.
+
+@findex ALL_REGS
+@findex NO_REGS
+In general, each register will belong to several classes.  In fact, one
+class must be named @code{ALL_REGS} and contain all the registers.  Another
+class must be named @code{NO_REGS} and contain no registers.  Often the
+union of two classes will be another class; however, this is not required.
+
+@findex GENERAL_REGS
+One of the classes must be named @code{GENERAL_REGS}.  There is nothing
+terribly special about the name, but the operand constraint letters
+@samp{r} and @samp{g} specify this class.  If @code{GENERAL_REGS} is
+the same as @code{ALL_REGS}, just define it as a macro which expands
+to @code{ALL_REGS}.
+
+Order the classes so that if class @var{x} is contained in class @var{y}
+then @var{x} has a lower class number than @var{y}.
+
+The way classes other than @code{GENERAL_REGS} are specified in operand
+constraints is through machine-dependent operand constraint letters.
+You can define such letters to correspond to various classes, then use
+them in operand constraints.
+
+You should define a class for the union of two classes whenever some
+instruction allows both classes.  For example, if an instruction allows
+either a floating point (coprocessor) register or a general register for a
+certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS}
+which includes both of them.  Otherwise you will get suboptimal code,
+or even internal compiler errors when reload cannot find a register in the
+the class computed via @code{reg_class_subunion}.
+
+You must also specify certain redundant information about the register
+classes: for each class, which classes contain it and which ones are
+contained in it; for each pair of classes, the largest class contained
+in their union.
+
+When a value occupying several consecutive registers is expected in a
+certain class, all the registers used must belong to that class.
+Therefore, register classes cannot be used to enforce a requirement for
+a register pair to start with an even-numbered register.  The way to
+specify this requirement is with @code{HARD_REGNO_MODE_OK}.
+
+Register classes used for input-operands of bitwise-and or shift
+instructions have a special requirement: each such class must have, for
+each fixed-point machine mode, a subclass whose registers can transfer that
+mode to or from memory.  For example, on some machines, the operations for
+single-byte values (@code{QImode}) are limited to certain registers.  When
+this is so, each register class that is used in a bitwise-and or shift
+instruction must have a subclass consisting of registers from which
+single-byte values can be loaded or stored.  This is so that
+@code{PREFERRED_RELOAD_CLASS} can always have a possible value to return.
+
+@deftp {Data type} {enum reg_class}
+An enumerated type that must be defined with all the register class names
+as enumerated values.  @code{NO_REGS} must be first.  @code{ALL_REGS}
+must be the last register class, followed by one more enumerated value,
+@code{LIM_REG_CLASSES}, which is not a register class but rather
+tells how many classes there are.
+
+Each register class has a number, which is the value of casting
+the class name to type @code{int}.  The number serves as an index
+in many of the tables described below.
+@end deftp
+
+@defmac N_REG_CLASSES
+The number of distinct register classes, defined as follows:
+
+@smallexample
+#define N_REG_CLASSES (int) LIM_REG_CLASSES
+@end smallexample
+@end defmac
+
+@defmac REG_CLASS_NAMES
+An initializer containing the names of the register classes as C string
+constants.  These names are used in writing some of the debugging dumps.
+@end defmac
+
+@defmac REG_CLASS_CONTENTS
+An initializer containing the contents of the register classes, as integers
+which are bit masks.  The @var{n}th integer specifies the contents of class
+@var{n}.  The way the integer @var{mask} is interpreted is that
+register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1.
+
+When the machine has more than 32 registers, an integer does not suffice.
+Then the integers are replaced by sub-initializers, braced groupings containing
+several integers.  Each sub-initializer must be suitable as an initializer
+for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}.
+In this situation, the first integer in each sub-initializer corresponds to
+registers 0 through 31, the second integer to registers 32 through 63, and
+so on.
+@end defmac
+
+@defmac REGNO_REG_CLASS (@var{regno})
+A C expression whose value is a register class containing hard register
+@var{regno}.  In general there is more than one such class; choose a class
+which is @dfn{minimal}, meaning that no smaller class also contains the
+register.
+@end defmac
+
+@defmac BASE_REG_CLASS
+A macro whose definition is the name of the class to which a valid
+base register must belong.  A base register is one used in an address
+which is the register value plus a displacement.
+@end defmac
+
+@defmac MODE_BASE_REG_CLASS (@var{mode})
+This is a variation of the @code{BASE_REG_CLASS} macro which allows
+the selection of a base register in a mode dependent manner.  If
+@var{mode} is VOIDmode then it should return the same value as
+@code{BASE_REG_CLASS}.
+@end defmac
+
+@defmac MODE_BASE_REG_REG_CLASS (@var{mode})
+A C expression whose value is the register class to which a valid
+base register must belong in order to be used in a base plus index
+register address.  You should define this macro if base plus index
+addresses have different requirements than other base register uses.
+@end defmac
+
+@defmac MODE_CODE_BASE_REG_CLASS (@var{mode}, @var{outer_code}, @var{index_code})
+A C expression whose value is the register class to which a valid
+base register must belong.  @var{outer_code} and @var{index_code} define the
+context in which the base register occurs.  @var{outer_code} is the code of
+the immediately enclosing expression (@code{MEM} for the top level of an
+address, @code{ADDRESS} for something that occurs in an
+@code{address_operand}).  @var{index_code} is the code of the corresponding
+index expression if @var{outer_code} is @code{PLUS}; @code{SCRATCH} otherwise.
+@end defmac
+
+@defmac INDEX_REG_CLASS
+A macro whose definition is the name of the class to which a valid
+index register must belong.  An index register is one used in an
+address where its value is either multiplied by a scale factor or
+added to another register (as well as added to a displacement).
+@end defmac
+
+@defmac REGNO_OK_FOR_BASE_P (@var{num})
+A C expression which is nonzero if register number @var{num} is
+suitable for use as a base register in operand addresses.
+@end defmac
+
+@defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode})
+A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that
+that expression may examine the mode of the memory reference in
+@var{mode}.  You should define this macro if the mode of the memory
+reference affects whether a register may be used as a base register.  If
+you define this macro, the compiler will use it instead of
+@code{REGNO_OK_FOR_BASE_P}.  The mode may be @code{VOIDmode} for
+addresses that appear outside a @code{MEM}, i.e., as an
+@code{address_operand}.
+@end defmac
+
+@defmac REGNO_MODE_OK_FOR_REG_BASE_P (@var{num}, @var{mode})
+A C expression which is nonzero if register number @var{num} is suitable for
+use as a base register in base plus index operand addresses, accessing
+memory in mode @var{mode}.  It may be either a suitable hard register or a
+pseudo register that has been allocated such a hard register.  You should
+define this macro if base plus index addresses have different requirements
+than other base register uses.
+
+Use of this macro is deprecated; please use the more general
+@code{REGNO_MODE_CODE_OK_FOR_BASE_P}.
+@end defmac
+
+@defmac REGNO_MODE_CODE_OK_FOR_BASE_P (@var{num}, @var{mode}, @var{outer_code}, @var{index_code})
+A C expression that is just like @code{REGNO_MODE_OK_FOR_BASE_P}, except
+that that expression may examine the context in which the register
+appears in the memory reference.  @var{outer_code} is the code of the
+immediately enclosing expression (@code{MEM} if at the top level of the
+address, @code{ADDRESS} for something that occurs in an
+@code{address_operand}).  @var{index_code} is the code of the
+corresponding index expression if @var{outer_code} is @code{PLUS};
+@code{SCRATCH} otherwise.  The mode may be @code{VOIDmode} for addresses
+that appear outside a @code{MEM}, i.e., as an @code{address_operand}.
+@end defmac
+
+@defmac REGNO_OK_FOR_INDEX_P (@var{num})
+A C expression which is nonzero if register number @var{num} is
+suitable for use as an index register in operand addresses.  It may be
+either a suitable hard register or a pseudo register that has been
+allocated such a hard register.
+
+The difference between an index register and a base register is that
+the index register may be scaled.  If an address involves the sum of
+two registers, neither one of them scaled, then either one may be
+labeled the ``base'' and the other the ``index''; but whichever
+labeling is used must fit the machine's constraints of which registers
+may serve in each capacity.  The compiler will try both labelings,
+looking for one that is valid, and will reload one or both registers
+only if neither labeling works.
+@end defmac
+
+@hook TARGET_PREFERRED_RENAME_CLASS
+
+@hook TARGET_PREFERRED_RELOAD_CLASS
+A target hook that places additional restrictions on the register class
+to use when it is necessary to copy value @var{x} into a register in class
+@var{rclass}.  The value is a register class; perhaps @var{rclass}, or perhaps
+another, smaller class.
+
+The default version of this hook always returns value of @code{rclass} argument.
+
+Sometimes returning a more restrictive class makes better code.  For
+example, on the 68000, when @var{x} is an integer constant that is in range
+for a @samp{moveq} instruction, the value of this macro is always
+@code{DATA_REGS} as long as @var{rclass} includes the data registers.
+Requiring a data register guarantees that a @samp{moveq} will be used.
+
+One case where @code{TARGET_PREFERRED_RELOAD_CLASS} must not return
+@var{rclass} is if @var{x} is a legitimate constant which cannot be
+loaded into some register class.  By returning @code{NO_REGS} you can
+force @var{x} into a memory location.  For example, rs6000 can load
+immediate values into general-purpose registers, but does not have an
+instruction for loading an immediate value into a floating-point
+register, so @code{TARGET_PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when
+@var{x} is a floating-point constant.  If the constant can't be loaded
+into any kind of register, code generation will be better if
+@code{LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead
+of using @code{TARGET_PREFERRED_RELOAD_CLASS}.
+
+If an insn has pseudos in it after register allocation, reload will go
+through the alternatives and call repeatedly @code{TARGET_PREFERRED_RELOAD_CLASS}
+to find the best one.  Returning @code{NO_REGS}, in this case, makes
+reload add a @code{!} in front of the constraint: the x86 back-end uses
+this feature to discourage usage of 387 registers when math is done in
+the SSE registers (and vice versa).
+@end deftypefn
+
+@defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class})
+A C expression that places additional restrictions on the register class
+to use when it is necessary to copy value @var{x} into a register in class
+@var{class}.  The value is a register class; perhaps @var{class}, or perhaps
+another, smaller class.  On many machines, the following definition is
+safe:
+
+@smallexample
+#define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS
+@end smallexample
+
+Sometimes returning a more restrictive class makes better code.  For
+example, on the 68000, when @var{x} is an integer constant that is in range
+for a @samp{moveq} instruction, the value of this macro is always
+@code{DATA_REGS} as long as @var{class} includes the data registers.
+Requiring a data register guarantees that a @samp{moveq} will be used.
+
+One case where @code{PREFERRED_RELOAD_CLASS} must not return
+@var{class} is if @var{x} is a legitimate constant which cannot be
+loaded into some register class.  By returning @code{NO_REGS} you can
+force @var{x} into a memory location.  For example, rs6000 can load
+immediate values into general-purpose registers, but does not have an
+instruction for loading an immediate value into a floating-point
+register, so @code{PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when
+@var{x} is a floating-point constant.  If the constant can't be loaded
+into any kind of register, code generation will be better if
+@code{LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead
+of using @code{PREFERRED_RELOAD_CLASS}.
+
+If an insn has pseudos in it after register allocation, reload will go
+through the alternatives and call repeatedly @code{PREFERRED_RELOAD_CLASS}
+to find the best one.  Returning @code{NO_REGS}, in this case, makes
+reload add a @code{!} in front of the constraint: the x86 back-end uses
+this feature to discourage usage of 387 registers when math is done in
+the SSE registers (and vice versa).
+@end defmac
+
+@defmac PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class})
+Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of
+input reloads.  If you don't define this macro, the default is to use
+@var{class}, unchanged.
+
+You can also use @code{PREFERRED_OUTPUT_RELOAD_CLASS} to discourage
+reload from using some alternatives, like @code{PREFERRED_RELOAD_CLASS}.
+@end defmac
+
+@hook TARGET_PREFERRED_OUTPUT_RELOAD_CLASS
+Like @code{TARGET_PREFERRED_RELOAD_CLASS}, but for output reloads instead of
+input reloads.
+
+The default version of this hook always returns value of @code{rclass}
+argument.
+
+You can also use @code{TARGET_PREFERRED_OUTPUT_RELOAD_CLASS} to discourage
+reload from using some alternatives, like @code{TARGET_PREFERRED_RELOAD_CLASS}.
+@end deftypefn
+
+@defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class})
+A C expression that places additional restrictions on the register class
+to use when it is necessary to be able to hold a value of mode
+@var{mode} in a reload register for which class @var{class} would
+ordinarily be used.
+
+Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when
+there are certain modes that simply can't go in certain reload classes.
+
+The value is a register class; perhaps @var{class}, or perhaps another,
+smaller class.
+
+Don't define this macro unless the target machine has limitations which
+require the macro to do something nontrivial.
+@end defmac
+
+@hook TARGET_SECONDARY_RELOAD
+Many machines have some registers that cannot be copied directly to or
+from memory or even from other types of registers.  An example is the
+@samp{MQ} register, which on most machines, can only be copied to or
+from general registers, but not memory.  Below, we shall be using the
+term 'intermediate register' when a move operation cannot be performed
+directly, but has to be done by copying the source into the intermediate
+register first, and then copying the intermediate register to the
+destination.  An intermediate register always has the same mode as
+source and destination.  Since it holds the actual value being copied,
+reload might apply optimizations to re-use an intermediate register
+and eliding the copy from the source when it can determine that the
+intermediate register still holds the required value.
+
+Another kind of secondary reload is required on some machines which
+allow copying all registers to and from memory, but require a scratch
+register for stores to some memory locations (e.g., those with symbolic
+address on the RT, and those with certain symbolic address on the SPARC
+when compiling PIC)@.  Scratch registers need not have the same mode
+as the value being copied, and usually hold a different value than
+that being copied.  Special patterns in the md file are needed to
+describe how the copy is performed with the help of the scratch register;
+these patterns also describe the number, register class(es) and mode(s)
+of the scratch register(s).
+
+In some cases, both an intermediate and a scratch register are required.
+
+For input reloads, this target hook is called with nonzero @var{in_p},
+and @var{x} is an rtx that needs to be copied to a register of class
+@var{reload_class} in @var{reload_mode}.  For output reloads, this target
+hook is called with zero @var{in_p}, and a register of class @var{reload_class}
+needs to be copied to rtx @var{x} in @var{reload_mode}.
+
+If copying a register of @var{reload_class} from/to @var{x} requires
+an intermediate register, the hook @code{secondary_reload} should
+return the register class required for this intermediate register.
+If no intermediate register is required, it should return NO_REGS.
+If more than one intermediate register is required, describe the one
+that is closest in the copy chain to the reload register.
+
+If scratch registers are needed, you also have to describe how to
+perform the copy from/to the reload register to/from this
+closest intermediate register.  Or if no intermediate register is
+required, but still a scratch register is needed, describe the
+copy  from/to the reload register to/from the reload operand @var{x}.
+
+You do this by setting @code{sri->icode} to the instruction code of a pattern
+in the md file which performs the move.  Operands 0 and 1 are the output
+and input of this copy, respectively.  Operands from operand 2 onward are
+for scratch operands.  These scratch operands must have a mode, and a
+single-register-class
+@c [later: or memory]
+output constraint.
+
+When an intermediate register is used, the @code{secondary_reload}
+hook will be called again to determine how to copy the intermediate
+register to/from the reload operand @var{x}, so your hook must also
+have code to handle the register class of the intermediate operand.
+
+@c [For later: maybe we'll allow multi-alternative reload patterns -
+@c   the port maintainer could name a mov<mode> pattern that has clobbers -
+@c   and match the constraints of input and output to determine the required
+@c   alternative.  A restriction would be that constraints used to match
+@c   against reloads registers would have to be written as register class
+@c   constraints, or we need a new target macro / hook that tells us if an
+@c   arbitrary constraint can match an unknown register of a given class.
+@c   Such a macro / hook would also be useful in other places.]
+
+
+@var{x} might be a pseudo-register or a @code{subreg} of a
+pseudo-register, which could either be in a hard register or in memory.
+Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
+in memory and the hard register number if it is in a register.
+
+Scratch operands in memory (constraint @code{"=m"} / @code{"=&m"}) are
+currently not supported.  For the time being, you will have to continue
+to use @code{SECONDARY_MEMORY_NEEDED} for that purpose.
+
+@code{copy_cost} also uses this target hook to find out how values are
+copied.  If you want it to include some extra cost for the need to allocate
+(a) scratch register(s), set @code{sri->extra_cost} to the additional cost.
+Or if two dependent moves are supposed to have a lower cost than the sum
+of the individual moves due to expected fortuitous scheduling and/or special
+forwarding logic, you can set @code{sri->extra_cost} to a negative amount.
+@end deftypefn
+
+@defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
+@defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
+@defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
+These macros are obsolete, new ports should use the target hook
+@code{TARGET_SECONDARY_RELOAD} instead.
+
+These are obsolete macros, replaced by the @code{TARGET_SECONDARY_RELOAD}
+target hook.  Older ports still define these macros to indicate to the
+reload phase that it may
+need to allocate at least one register for a reload in addition to the
+register to contain the data.  Specifically, if copying @var{x} to a
+register @var{class} in @var{mode} requires an intermediate register,
+you were supposed to define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the
+largest register class all of whose registers can be used as
+intermediate registers or scratch registers.
+
+If copying a register @var{class} in @var{mode} to @var{x} requires an
+intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS}
+was supposed to be defined be defined to return the largest register
+class required.  If the
+requirements for input and output reloads were the same, the macro
+@code{SECONDARY_RELOAD_CLASS} should have been used instead of defining both
+macros identically.
+
+The values returned by these macros are often @code{GENERAL_REGS}.
+Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x}
+can be directly copied to or from a register of @var{class} in
+@var{mode} without requiring a scratch register.  Do not define this
+macro if it would always return @code{NO_REGS}.
+
+If a scratch register is required (either with or without an
+intermediate register), you were supposed to define patterns for
+@samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required
+(@pxref{Standard Names}.  These patterns, which were normally
+implemented with a @code{define_expand}, should be similar to the
+@samp{mov@var{m}} patterns, except that operand 2 is the scratch
+register.
+
+These patterns need constraints for the reload register and scratch
+register that
+contain a single register class.  If the original reload register (whose
+class is @var{class}) can meet the constraint given in the pattern, the
+value returned by these macros is used for the class of the scratch
+register.  Otherwise, two additional reload registers are required.
+Their classes are obtained from the constraints in the insn pattern.
+
+@var{x} might be a pseudo-register or a @code{subreg} of a
+pseudo-register, which could either be in a hard register or in memory.
+Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
+in memory and the hard register number if it is in a register.
+
+These macros should not be used in the case where a particular class of
+registers can only be copied to memory and not to another class of
+registers.  In that case, secondary reload registers are not needed and
+would not be helpful.  Instead, a stack location must be used to perform
+the copy and the @code{mov@var{m}} pattern should use memory as an
+intermediate storage.  This case often occurs between floating-point and
+general registers.
+@end defmac
+
+@defmac SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m})
+Certain machines have the property that some registers cannot be copied
+to some other registers without using memory.  Define this macro on
+those machines to be a C expression that is nonzero if objects of mode
+@var{m} in registers of @var{class1} can only be copied to registers of
+class @var{class2} by storing a register of @var{class1} into memory
+and loading that memory location into a register of @var{class2}.
+
+Do not define this macro if its value would always be zero.
+@end defmac
+
+@defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode})
+Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler
+allocates a stack slot for a memory location needed for register copies.
+If this macro is defined, the compiler instead uses the memory location
+defined by this macro.
+
+Do not define this macro if you do not define
+@code{SECONDARY_MEMORY_NEEDED}.
+@end defmac
+
+@defmac SECONDARY_MEMORY_NEEDED_MODE (@var{mode})
+When the compiler needs a secondary memory location to copy between two
+registers of mode @var{mode}, it normally allocates sufficient memory to
+hold a quantity of @code{BITS_PER_WORD} bits and performs the store and
+load operations in a mode that many bits wide and whose class is the
+same as that of @var{mode}.
+
+This is right thing to do on most machines because it ensures that all
+bits of the register are copied and prevents accesses to the registers
+in a narrower mode, which some machines prohibit for floating-point
+registers.
+
+However, this default behavior is not correct on some machines, such as
+the DEC Alpha, that store short integers in floating-point registers
+differently than in integer registers.  On those machines, the default
+widening will not work correctly and you must define this macro to
+suppress that widening in some cases.  See the file @file{alpha.h} for
+details.
+
+Do not define this macro if you do not define
+@code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that
+is @code{BITS_PER_WORD} bits wide is correct for your machine.
+@end defmac
+
+@hook TARGET_CLASS_LIKELY_SPILLED_P
+A target hook which returns @code{true} if pseudos that have been assigned
+to registers of class @var{rclass} would likely be spilled because
+registers of @var{rclass} are needed for spill registers.
+
+The default version of this target hook returns @code{true} if @var{rclass}
+has exactly one register and @code{false} otherwise.  On most machines, this
+default should be used.  Only use this target hook to some other expression
+if pseudos allocated by @file{local-alloc.c} end up in memory because their
+hard registers were needed for spill registers.  If this target hook returns
+@code{false} for those classes, those pseudos will only be allocated by
+@file{global.c}, which knows how to reallocate the pseudo to another
+register.  If there would not be another register available for reallocation,
+you should not change the implementation of this target hook since
+the only effect of such implementation would be to slow down register
+allocation.
+@end deftypefn
+
+@defmac CLASS_MAX_NREGS (@var{class}, @var{mode})
+A C expression for the maximum number of consecutive registers
+of class @var{class} needed to hold a value of mode @var{mode}.
+
+This is closely related to the macro @code{HARD_REGNO_NREGS}.  In fact,
+the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})}
+should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno},
+@var{mode})} for all @var{regno} values in the class @var{class}.
+
+This macro helps control the handling of multiple-word values
+in the reload pass.
+@end defmac
+
+@defmac CANNOT_CHANGE_MODE_CLASS (@var{from}, @var{to}, @var{class})
+If defined, a C expression that returns nonzero for a @var{class} for which
+a change from mode @var{from} to mode @var{to} is invalid.
+
+For the example, loading 32-bit integer or floating-point objects into
+floating-point registers on the Alpha extends them to 64 bits.
+Therefore loading a 64-bit object and then storing it as a 32-bit object
+does not store the low-order 32 bits, as would be the case for a normal
+register.  Therefore, @file{alpha.h} defines @code{CANNOT_CHANGE_MODE_CLASS}
+as below:
+
+@smallexample
+#define CANNOT_CHANGE_MODE_CLASS(FROM, TO, CLASS) \
+  (GET_MODE_SIZE (FROM) != GET_MODE_SIZE (TO) \
+   ? reg_classes_intersect_p (FLOAT_REGS, (CLASS)) : 0)
+@end smallexample
+@end defmac
+
+@hook TARGET_IRA_COVER_CLASSES
+Return an array of cover classes for the Integrated Register Allocator
+(@acronym{IRA}).  Cover classes are a set of non-intersecting register
+classes covering all hard registers used for register allocation
+purposes.  If a move between two registers in the same cover class is
+possible, it should be cheaper than a load or store of the registers.
+The array is terminated by a @code{LIM_REG_CLASSES} element.
+
+The order of cover classes in the array is important.  If two classes
+have the same cost of usage for a pseudo, the class occurred first in
+the array is chosen for the pseudo.
+
+This hook is called once at compiler startup, after the command-line
+options have been processed. It is then re-examined by every call to
+@code{target_reinit}.
+
+The default implementation returns @code{IRA_COVER_CLASSES}, if defined,
+otherwise there is no default implementation.  You must define either this
+macro or @code{IRA_COVER_CLASSES} in order to use the integrated register
+allocator with Chaitin-Briggs coloring. If the macro is not defined,
+the only available coloring algorithm is Chow's priority coloring.
+
+This hook must not be modified from @code{NULL} to non-@code{NULL} or
+vice versa by command-line option processing.
+@end deftypefn
+
+@defmac IRA_COVER_CLASSES
+See the documentation for @code{TARGET_IRA_COVER_CLASSES}.
+@end defmac
+
+@node Old Constraints
+@section Obsolete Macros for Defining Constraints
+@cindex defining constraints, obsolete method
+@cindex constraints, defining, obsolete method
+
+Machine-specific constraints can be defined with these macros instead
+of the machine description constructs described in @ref{Define
+Constraints}.  This mechanism is obsolete.  New ports should not use
+it; old ports should convert to the new mechanism.
+
+@defmac CONSTRAINT_LEN (@var{char}, @var{str})
+For the constraint at the start of @var{str}, which starts with the letter
+@var{c}, return the length.  This allows you to have register class /
+constant / extra constraints that are longer than a single letter;
+you don't need to define this macro if you can do with single-letter
+constraints only.  The definition of this macro should use
+DEFAULT_CONSTRAINT_LEN for all the characters that you don't want
+to handle specially.
+There are some sanity checks in genoutput.c that check the constraint lengths
+for the md file, so you can also use this macro to help you while you are
+transitioning from a byzantine single-letter-constraint scheme: when you
+return a negative length for a constraint you want to re-use, genoutput
+will complain about every instance where it is used in the md file.
+@end defmac
+
+@defmac REG_CLASS_FROM_LETTER (@var{char})
+A C expression which defines the machine-dependent operand constraint
+letters for register classes.  If @var{char} is such a letter, the
+value should be the register class corresponding to it.  Otherwise,
+the value should be @code{NO_REGS}.  The register letter @samp{r},
+corresponding to class @code{GENERAL_REGS}, will not be passed
+to this macro; you do not need to handle it.
+@end defmac
+
+@defmac REG_CLASS_FROM_CONSTRAINT (@var{char}, @var{str})
+Like @code{REG_CLASS_FROM_LETTER}, but you also get the constraint string
+passed in @var{str}, so that you can use suffixes to distinguish between
+different variants.
+@end defmac
+
+@defmac CONST_OK_FOR_LETTER_P (@var{value}, @var{c})
+A C expression that defines the machine-dependent operand constraint
+letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify
+particular ranges of integer values.  If @var{c} is one of those
+letters, the expression should check that @var{value}, an integer, is in
+the appropriate range and return 1 if so, 0 otherwise.  If @var{c} is
+not one of those letters, the value should be 0 regardless of
+@var{value}.
+@end defmac
+
+@defmac CONST_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
+Like @code{CONST_OK_FOR_LETTER_P}, but you also get the constraint
+string passed in @var{str}, so that you can use suffixes to distinguish
+between different variants.
+@end defmac
+
+@defmac CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c})
+A C expression that defines the machine-dependent operand constraint
+letters that specify particular ranges of @code{const_double} values
+(@samp{G} or @samp{H}).
+
+If @var{c} is one of those letters, the expression should check that
+@var{value}, an RTX of code @code{const_double}, is in the appropriate
+range and return 1 if so, 0 otherwise.  If @var{c} is not one of those
+letters, the value should be 0 regardless of @var{value}.
+
+@code{const_double} is used for all floating-point constants and for
+@code{DImode} fixed-point constants.  A given letter can accept either
+or both kinds of values.  It can use @code{GET_MODE} to distinguish
+between these kinds.
+@end defmac
+
+@defmac CONST_DOUBLE_OK_FOR_CONSTRAINT_P (@var{value}, @var{c}, @var{str})
+Like @code{CONST_DOUBLE_OK_FOR_LETTER_P}, but you also get the constraint
+string passed in @var{str}, so that you can use suffixes to distinguish
+between different variants.
+@end defmac
+
+@defmac EXTRA_CONSTRAINT (@var{value}, @var{c})
+A C expression that defines the optional machine-dependent constraint
+letters that can be used to segregate specific types of operands, usually
+memory references, for the target machine.  Any letter that is not
+elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} /
+@code{REG_CLASS_FROM_CONSTRAINT}
+may be used.  Normally this macro will not be defined.
+
+If it is required for a particular target machine, it should return 1
+if @var{value} corresponds to the operand type represented by the
+constraint letter @var{c}.  If @var{c} is not defined as an extra
+constraint, the value returned should be 0 regardless of @var{value}.
+
+For example, on the ROMP, load instructions cannot have their output
+in r0 if the memory reference contains a symbolic address.  Constraint
+letter @samp{Q} is defined as representing a memory address that does
+@emph{not} contain a symbolic address.  An alternative is specified with
+a @samp{Q} constraint on the input and @samp{r} on the output.  The next
+alternative specifies @samp{m} on the input and a register class that
+does not include r0 on the output.
+@end defmac
+
+@defmac EXTRA_CONSTRAINT_STR (@var{value}, @var{c}, @var{str})
+Like @code{EXTRA_CONSTRAINT}, but you also get the constraint string passed
+in @var{str}, so that you can use suffixes to distinguish between different
+variants.
+@end defmac
+
+@defmac EXTRA_MEMORY_CONSTRAINT (@var{c}, @var{str})
+A C expression that defines the optional machine-dependent constraint
+letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should
+be treated like memory constraints by the reload pass.
+
+It should return 1 if the operand type represented by the constraint
+at the start of @var{str}, the first letter of which is the letter @var{c},
+comprises a subset of all memory references including
+all those whose address is simply a base register.  This allows the reload
+pass to reload an operand, if it does not directly correspond to the operand
+type of @var{c}, by copying its address into a base register.
+
+For example, on the S/390, some instructions do not accept arbitrary
+memory references, but only those that do not make use of an index
+register.  The constraint letter @samp{Q} is defined via
+@code{EXTRA_CONSTRAINT} as representing a memory address of this type.
+If the letter @samp{Q} is marked as @code{EXTRA_MEMORY_CONSTRAINT},
+a @samp{Q} constraint can handle any memory operand, because the
+reload pass knows it can be reloaded by copying the memory address
+into a base register if required.  This is analogous to the way
+an @samp{o} constraint can handle any memory operand.
+@end defmac
+
+@defmac EXTRA_ADDRESS_CONSTRAINT (@var{c}, @var{str})
+A C expression that defines the optional machine-dependent constraint
+letters, amongst those accepted by @code{EXTRA_CONSTRAINT} /
+@code{EXTRA_CONSTRAINT_STR}, that should
+be treated like address constraints by the reload pass.
+
+It should return 1 if the operand type represented by the constraint
+at the start of @var{str}, which starts with the letter @var{c}, comprises
+a subset of all memory addresses including
+all those that consist of just a base register.  This allows the reload
+pass to reload an operand, if it does not directly correspond to the operand
+type of @var{str}, by copying it into a base register.
+
+Any constraint marked as @code{EXTRA_ADDRESS_CONSTRAINT} can only
+be used with the @code{address_operand} predicate.  It is treated
+analogously to the @samp{p} constraint.
+@end defmac
+
+@node Stack and Calling
+@section Stack Layout and Calling Conventions
+@cindex calling conventions
+
+@c prevent bad page break with this line
+This describes the stack layout and calling conventions.
+
+@menu
+* Frame Layout::
+* Exception Handling::
+* Stack Checking::
+* Frame Registers::
+* Elimination::
+* Stack Arguments::
+* Register Arguments::
+* Scalar Return::
+* Aggregate Return::
+* Caller Saves::
+* Function Entry::
+* Profiling::
+* Tail Calls::
+* Stack Smashing Protection::
+@end menu
+
+@node Frame Layout
+@subsection Basic Stack Layout
+@cindex stack frame layout
+@cindex frame layout
+
+@c prevent bad page break with this line
+Here is the basic stack layout.
+
+@defmac STACK_GROWS_DOWNWARD
+Define this macro if pushing a word onto the stack moves the stack
+pointer to a smaller address.
+
+When we say, ``define this macro if @dots{}'', it means that the
+compiler checks this macro only with @code{#ifdef} so the precise
+definition used does not matter.
+@end defmac
+
+@defmac STACK_PUSH_CODE
+This macro defines the operation used when something is pushed
+on the stack.  In RTL, a push operation will be
+@code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})}
+
+The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC},
+and @code{POST_INC}.  Which of these is correct depends on
+the stack direction and on whether the stack pointer points
+to the last item on the stack or whether it points to the
+space for the next item on the stack.
+
+The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is
+defined, which is almost always right, and @code{PRE_INC} otherwise,
+which is often wrong.
+@end defmac
+
+@defmac FRAME_GROWS_DOWNWARD
+Define this macro to nonzero value if the addresses of local variable slots
+are at negative offsets from the frame pointer.
+@end defmac
+
+@defmac ARGS_GROW_DOWNWARD
+Define this macro if successive arguments to a function occupy decreasing
+addresses on the stack.
+@end defmac
+
+@defmac STARTING_FRAME_OFFSET
+Offset from the frame pointer to the first local variable slot to be allocated.
+
+If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by
+subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}.
+Otherwise, it is found by adding the length of the first slot to the
+value @code{STARTING_FRAME_OFFSET}.
+@c i'm not sure if the above is still correct.. had to change it to get
+@c rid of an overfull.  --mew 2feb93
+@end defmac
+
+@defmac STACK_ALIGNMENT_NEEDED
+Define to zero to disable final alignment of the stack during reload.
+The nonzero default for this macro is suitable for most ports.
+
+On ports where @code{STARTING_FRAME_OFFSET} is nonzero or where there
+is a register save block following the local block that doesn't require
+alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable
+stack alignment and do it in the backend.
+@end defmac
+
+@defmac STACK_POINTER_OFFSET
+Offset from the stack pointer register to the first location at which
+outgoing arguments are placed.  If not specified, the default value of
+zero is used.  This is the proper value for most machines.
+
+If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
+the first location at which outgoing arguments are placed.
+@end defmac
+
+@defmac FIRST_PARM_OFFSET (@var{fundecl})
+Offset from the argument pointer register to the first argument's
+address.  On some machines it may depend on the data type of the
+function.
+
+If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
+the first argument's address.
+@end defmac
+
+@defmac STACK_DYNAMIC_OFFSET (@var{fundecl})
+Offset from the stack pointer register to an item dynamically allocated
+on the stack, e.g., by @code{alloca}.
+
+The default value for this macro is @code{STACK_POINTER_OFFSET} plus the
+length of the outgoing arguments.  The default is correct for most
+machines.  See @file{function.c} for details.
+@end defmac
+
+@defmac INITIAL_FRAME_ADDRESS_RTX
+A C expression whose value is RTL representing the address of the initial
+stack frame. This address is passed to @code{RETURN_ADDR_RTX} and
+@code{DYNAMIC_CHAIN_ADDRESS}.  If you don't define this macro, a reasonable
+default value will be used.  Define this macro in order to make frame pointer
+elimination work in the presence of @code{__builtin_frame_address (count)} and
+@code{__builtin_return_address (count)} for @code{count} not equal to zero.
+@end defmac
+
+@defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr})
+A C expression whose value is RTL representing the address in a stack
+frame where the pointer to the caller's frame is stored.  Assume that
+@var{frameaddr} is an RTL expression for the address of the stack frame
+itself.
+
+If you don't define this macro, the default is to return the value
+of @var{frameaddr}---that is, the stack frame address is also the
+address of the stack word that points to the previous frame.
+@end defmac
+
+@defmac SETUP_FRAME_ADDRESSES
+If defined, a C expression that produces the machine-specific code to
+setup the stack so that arbitrary frames can be accessed.  For example,
+on the SPARC, we must flush all of the register windows to the stack
+before we can access arbitrary stack frames.  You will seldom need to
+define this macro.
+@end defmac
+
+@hook TARGET_BUILTIN_SETJMP_FRAME_VALUE
+This target hook should return an rtx that is used to store
+the address of the current frame into the built in @code{setjmp} buffer.
+The default value, @code{virtual_stack_vars_rtx}, is correct for most
+machines.  One reason you may need to define this target hook is if
+@code{hard_frame_pointer_rtx} is the appropriate value on your machine.
+@end deftypefn
+
+@defmac FRAME_ADDR_RTX (@var{frameaddr})
+A C expression whose value is RTL representing the value of the frame
+address for the current frame.  @var{frameaddr} is the frame pointer
+of the current frame.  This is used for __builtin_frame_address.
+You need only define this macro if the frame address is not the same
+as the frame pointer.  Most machines do not need to define it.
+@end defmac
+
+@defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr})
+A C expression whose value is RTL representing the value of the return
+address for the frame @var{count} steps up from the current frame, after
+the prologue.  @var{frameaddr} is the frame pointer of the @var{count}
+frame, or the frame pointer of the @var{count} @minus{} 1 frame if
+@code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined.
+
+The value of the expression must always be the correct address when
+@var{count} is zero, but may be @code{NULL_RTX} if there is no way to
+determine the return address of other frames.
+@end defmac
+
+@defmac RETURN_ADDR_IN_PREVIOUS_FRAME
+Define this if the return address of a particular stack frame is accessed
+from the frame pointer of the previous stack frame.
+@end defmac
+
+@defmac INCOMING_RETURN_ADDR_RTX
+A C expression whose value is RTL representing the location of the
+incoming return address at the beginning of any function, before the
+prologue.  This RTL is either a @code{REG}, indicating that the return
+value is saved in @samp{REG}, or a @code{MEM} representing a location in
+the stack.
+
+You only need to define this macro if you want to support call frame
+debugging information like that provided by DWARF 2.
+
+If this RTL is a @code{REG}, you should also define
+@code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}.
+@end defmac
+
+@defmac DWARF_ALT_FRAME_RETURN_COLUMN
+A C expression whose value is an integer giving a DWARF 2 column
+number that may be used as an alternative return column.  The column
+must not correspond to any gcc hard register (that is, it must not
+be in the range of @code{DWARF_FRAME_REGNUM}).
+
+This macro can be useful if @code{DWARF_FRAME_RETURN_COLUMN} is set to a
+general register, but an alternative column needs to be used for signal
+frames.  Some targets have also used different frame return columns
+over time.
+@end defmac
+
+@defmac DWARF_ZERO_REG
+A C expression whose value is an integer giving a DWARF 2 register
+number that is considered to always have the value zero.  This should
+only be defined if the target has an architected zero register, and
+someone decided it was a good idea to use that register number to
+terminate the stack backtrace.  New ports should avoid this.
+@end defmac
+
+@hook TARGET_DWARF_HANDLE_FRAME_UNSPEC
+This target hook allows the backend to emit frame-related insns that
+contain UNSPECs or UNSPEC_VOLATILEs.  The DWARF 2 call frame debugging
+info engine will invoke it on insns of the form
+@smallexample
+(set (reg) (unspec [@dots{}] UNSPEC_INDEX))
+@end smallexample
+and
+@smallexample
+(set (reg) (unspec_volatile [@dots{}] UNSPECV_INDEX)).
+@end smallexample
+to let the backend emit the call frame instructions.  @var{label} is
+the CFI label attached to the insn, @var{pattern} is the pattern of
+the insn and @var{index} is @code{UNSPEC_INDEX} or @code{UNSPECV_INDEX}.
+@end deftypefn
+
+@defmac INCOMING_FRAME_SP_OFFSET
+A C expression whose value is an integer giving the offset, in bytes,
+from the value of the stack pointer register to the top of the stack
+frame at the beginning of any function, before the prologue.  The top of
+the frame is defined to be the value of the stack pointer in the
+previous frame, just before the call instruction.
+
+You only need to define this macro if you want to support call frame
+debugging information like that provided by DWARF 2.
+@end defmac
+
+@defmac ARG_POINTER_CFA_OFFSET (@var{fundecl})
+A C expression whose value is an integer giving the offset, in bytes,
+from the argument pointer to the canonical frame address (cfa).  The
+final value should coincide with that calculated by
+@code{INCOMING_FRAME_SP_OFFSET}.  Which is unfortunately not usable
+during virtual register instantiation.
+
+The default value for this macro is
+@code{FIRST_PARM_OFFSET (fundecl) + crtl->args.pretend_args_size},
+which is correct for most machines; in general, the arguments are found
+immediately before the stack frame.  Note that this is not the case on
+some targets that save registers into the caller's frame, such as SPARC
+and rs6000, and so such targets need to define this macro.
+
+You only need to define this macro if the default is incorrect, and you
+want to support call frame debugging information like that provided by
+DWARF 2.
+@end defmac
+
+@defmac FRAME_POINTER_CFA_OFFSET (@var{fundecl})
+If defined, a C expression whose value is an integer giving the offset
+in bytes from the frame pointer to the canonical frame address (cfa).
+The final value should coincide with that calculated by
+@code{INCOMING_FRAME_SP_OFFSET}.
+
+Normally the CFA is calculated as an offset from the argument pointer,
+via @code{ARG_POINTER_CFA_OFFSET}, but if the argument pointer is
+variable due to the ABI, this may not be possible.  If this macro is
+defined, it implies that the virtual register instantiation should be
+based on the frame pointer instead of the argument pointer.  Only one
+of @code{FRAME_POINTER_CFA_OFFSET} and @code{ARG_POINTER_CFA_OFFSET}
+should be defined.
+@end defmac
+
+@defmac CFA_FRAME_BASE_OFFSET (@var{fundecl})
+If defined, a C expression whose value is an integer giving the offset
+in bytes from the canonical frame address (cfa) to the frame base used
+in DWARF 2 debug information.  The default is zero.  A different value
+may reduce the size of debug information on some ports.
+@end defmac
+
+@node Exception Handling
+@subsection Exception Handling Support
+@cindex exception handling
+
+@defmac EH_RETURN_DATA_REGNO (@var{N})
+A C expression whose value is the @var{N}th register number used for
+data by exception handlers, or @code{INVALID_REGNUM} if fewer than
+@var{N} registers are usable.
+
+The exception handling library routines communicate with the exception
+handlers via a set of agreed upon registers.  Ideally these registers
+should be call-clobbered; it is possible to use call-saved registers,
+but may negatively impact code size.  The target must support at least
+2 data registers, but should define 4 if there are enough free registers.
+
+You must define this macro if you want to support call frame exception
+handling like that provided by DWARF 2.
+@end defmac
+
+@defmac EH_RETURN_STACKADJ_RTX
+A C expression whose value is RTL representing a location in which
+to store a stack adjustment to be applied before function return.
+This is used to unwind the stack to an exception handler's call frame.
+It will be assigned zero on code paths that return normally.
+
+Typically this is a call-clobbered hard register that is otherwise
+untouched by the epilogue, but could also be a stack slot.
+
+Do not define this macro if the stack pointer is saved and restored
+by the regular prolog and epilog code in the call frame itself; in
+this case, the exception handling library routines will update the
+stack location to be restored in place.  Otherwise, you must define
+this macro if you want to support call frame exception handling like
+that provided by DWARF 2.
+@end defmac
+
+@defmac EH_RETURN_HANDLER_RTX
+A C expression whose value is RTL representing a location in which
+to store the address of an exception handler to which we should
+return.  It will not be assigned on code paths that return normally.
+
+Typically this is the location in the call frame at which the normal
+return address is stored.  For targets that return by popping an
+address off the stack, this might be a memory address just below
+the @emph{target} call frame rather than inside the current call
+frame.  If defined, @code{EH_RETURN_STACKADJ_RTX} will have already
+been assigned, so it may be used to calculate the location of the
+target call frame.
+
+Some targets have more complex requirements than storing to an
+address calculable during initial code generation.  In that case
+the @code{eh_return} instruction pattern should be used instead.
+
+If you want to support call frame exception handling, you must
+define either this macro or the @code{eh_return} instruction pattern.
+@end defmac
+
+@defmac RETURN_ADDR_OFFSET
+If defined, an integer-valued C expression for which rtl will be generated
+to add it to the exception handler address before it is searched in the
+exception handling tables, and to subtract it again from the address before
+using it to return to the exception handler.
+@end defmac
+
+@defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global})
+This macro chooses the encoding of pointers embedded in the exception
+handling sections.  If at all possible, this should be defined such
+that the exception handling section will not require dynamic relocations,
+and so may be read-only.
+
+@var{code} is 0 for data, 1 for code labels, 2 for function pointers.
+@var{global} is true if the symbol may be affected by dynamic relocations.
+The macro should return a combination of the @code{DW_EH_PE_*} defines
+as found in @file{dwarf2.h}.
+
+If this macro is not defined, pointers will not be encoded but
+represented directly.
+@end defmac
+
+@defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done})
+This macro allows the target to emit whatever special magic is required
+to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}.
+Generic code takes care of pc-relative and indirect encodings; this must
+be defined if the target uses text-relative or data-relative encodings.
+
+This is a C statement that branches to @var{done} if the format was
+handled.  @var{encoding} is the format chosen, @var{size} is the number
+of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF}
+to be emitted.
+@end defmac
+
+@defmac MD_UNWIND_SUPPORT
+A string specifying a file to be #include'd in unwind-dw2.c.  The file
+so included typically defines @code{MD_FALLBACK_FRAME_STATE_FOR}.
+@end defmac
+
+@defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs})
+This macro allows the target to add CPU and operating system specific
+code to the call-frame unwinder for use when there is no unwind data
+available.  The most common reason to implement this macro is to unwind
+through signal frames.
+
+This macro is called from @code{uw_frame_state_for} in
+@file{unwind-dw2.c}, @file{unwind-dw2-xtensa.c} and
+@file{unwind-ia64.c}.  @var{context} is an @code{_Unwind_Context};
+@var{fs} is an @code{_Unwind_FrameState}.  Examine @code{context->ra}
+for the address of the code being executed and @code{context->cfa} for
+the stack pointer value.  If the frame can be decoded, the register
+save addresses should be updated in @var{fs} and the macro should
+evaluate to @code{_URC_NO_REASON}.  If the frame cannot be decoded,
+the macro should evaluate to @code{_URC_END_OF_STACK}.
+
+For proper signal handling in Java this macro is accompanied by
+@code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers.
+@end defmac
+
+@defmac MD_HANDLE_UNWABI (@var{context}, @var{fs})
+This macro allows the target to add operating system specific code to the
+call-frame unwinder to handle the IA-64 @code{.unwabi} unwinding directive,
+usually used for signal or interrupt frames.
+
+This macro is called from @code{uw_update_context} in @file{unwind-ia64.c}.
+@var{context} is an @code{_Unwind_Context};
+@var{fs} is an @code{_Unwind_FrameState}.  Examine @code{fs->unwabi}
+for the abi and context in the @code{.unwabi} directive.  If the
+@code{.unwabi} directive can be handled, the register save addresses should
+be updated in @var{fs}.
+@end defmac
+
+@defmac TARGET_USES_WEAK_UNWIND_INFO
+A C expression that evaluates to true if the target requires unwind
+info to be given comdat linkage.  Define it to be @code{1} if comdat
+linkage is necessary.  The default is @code{0}.
+@end defmac
+
+@node Stack Checking
+@subsection Specifying How Stack Checking is Done
+
+GCC will check that stack references are within the boundaries of the
+stack, if the option @option{-fstack-check} is specified, in one of
+three ways:
+
+@enumerate
+@item
+If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC
+will assume that you have arranged for full stack checking to be done
+at appropriate places in the configuration files.  GCC will not do
+other special processing.
+
+@item
+If @code{STACK_CHECK_BUILTIN} is zero and the value of the
+@code{STACK_CHECK_STATIC_BUILTIN} macro is nonzero, GCC will assume
+that you have arranged for static stack checking (checking of the
+static stack frame of functions) to be done at appropriate places
+in the configuration files.  GCC will only emit code to do dynamic
+stack checking (checking on dynamic stack allocations) using the third
+approach below.
+
+@item
+If neither of the above are true, GCC will generate code to periodically
+``probe'' the stack pointer using the values of the macros defined below.
+@end enumerate
+
+If neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined,
+GCC will change its allocation strategy for large objects if the option
+@option{-fstack-check} is specified: they will always be allocated
+dynamically if their size exceeds @code{STACK_CHECK_MAX_VAR_SIZE} bytes.
+
+@defmac STACK_CHECK_BUILTIN
+A nonzero value if stack checking is done by the configuration files in a
+machine-dependent manner.  You should define this macro if stack checking
+is required by the ABI of your machine or if you would like to do stack
+checking in some more efficient way than the generic approach.  The default
+value of this macro is zero.
+@end defmac
+
+@defmac STACK_CHECK_STATIC_BUILTIN
+A nonzero value if static stack checking is done by the configuration files
+in a machine-dependent manner.  You should define this macro if you would
+like to do static stack checking in some more efficient way than the generic
+approach.  The default value of this macro is zero.
+@end defmac
+
+@defmac STACK_CHECK_PROBE_INTERVAL_EXP
+An integer specifying the interval at which GCC must generate stack probe
+instructions, defined as 2 raised to this integer.  You will normally
+define this macro so that the interval be no larger than the size of
+the ``guard pages'' at the end of a stack area.  The default value
+of 12 (4096-byte interval) is suitable for most systems.
+@end defmac
+
+@defmac STACK_CHECK_MOVING_SP
+An integer which is nonzero if GCC should move the stack pointer page by page
+when doing probes.  This can be necessary on systems where the stack pointer
+contains the bottom address of the memory area accessible to the executing
+thread at any point in time.  In this situation an alternate signal stack
+is required in order to be able to recover from a stack overflow.  The
+default value of this macro is zero.
+@end defmac
+
+@defmac STACK_CHECK_PROTECT
+The number of bytes of stack needed to recover from a stack overflow, for
+languages where such a recovery is supported.  The default value of 75 words
+with the @code{setjmp}/@code{longjmp}-based exception handling mechanism and
+8192 bytes with other exception handling mechanisms should be adequate for
+most machines.
+@end defmac
+
+The following macros are relevant only if neither STACK_CHECK_BUILTIN
+nor STACK_CHECK_STATIC_BUILTIN is defined; you can omit them altogether
+in the opposite case.
+
+@defmac STACK_CHECK_MAX_FRAME_SIZE
+The maximum size of a stack frame, in bytes.  GCC will generate probe
+instructions in non-leaf functions to ensure at least this many bytes of
+stack are available.  If a stack frame is larger than this size, stack
+checking will not be reliable and GCC will issue a warning.  The
+default is chosen so that GCC only generates one instruction on most
+systems.  You should normally not change the default value of this macro.
+@end defmac
+
+@defmac STACK_CHECK_FIXED_FRAME_SIZE
+GCC uses this value to generate the above warning message.  It
+represents the amount of fixed frame used by a function, not including
+space for any callee-saved registers, temporaries and user variables.
+You need only specify an upper bound for this amount and will normally
+use the default of four words.
+@end defmac
+
+@defmac STACK_CHECK_MAX_VAR_SIZE
+The maximum size, in bytes, of an object that GCC will place in the
+fixed area of the stack frame when the user specifies
+@option{-fstack-check}.
+GCC computed the default from the values of the above macros and you will
+normally not need to override that default.
+@end defmac
+
+@need 2000
+@node Frame Registers
+@subsection Registers That Address the Stack Frame
+
+@c prevent bad page break with this line
+This discusses registers that address the stack frame.
+
+@defmac STACK_POINTER_REGNUM
+The register number of the stack pointer register, which must also be a
+fixed register according to @code{FIXED_REGISTERS}.  On most machines,
+the hardware determines which register this is.
+@end defmac
+
+@defmac FRAME_POINTER_REGNUM
+The register number of the frame pointer register, which is used to
+access automatic variables in the stack frame.  On some machines, the
+hardware determines which register this is.  On other machines, you can
+choose any register you wish for this purpose.
+@end defmac
+
+@defmac HARD_FRAME_POINTER_REGNUM
+On some machines the offset between the frame pointer and starting
+offset of the automatic variables is not known until after register
+allocation has been done (for example, because the saved registers are
+between these two locations).  On those machines, define
+@code{FRAME_POINTER_REGNUM} the number of a special, fixed register to
+be used internally until the offset is known, and define
+@code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number
+used for the frame pointer.
+
+You should define this macro only in the very rare circumstances when it
+is not possible to calculate the offset between the frame pointer and
+the automatic variables until after register allocation has been
+completed.  When this macro is defined, you must also indicate in your
+definition of @code{ELIMINABLE_REGS} how to eliminate
+@code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM}
+or @code{STACK_POINTER_REGNUM}.
+
+Do not define this macro if it would be the same as
+@code{FRAME_POINTER_REGNUM}.
+@end defmac
+
+@defmac ARG_POINTER_REGNUM
+The register number of the arg pointer register, which is used to access
+the function's argument list.  On some machines, this is the same as the
+frame pointer register.  On some machines, the hardware determines which
+register this is.  On other machines, you can choose any register you
+wish for this purpose.  If this is not the same register as the frame
+pointer register, then you must mark it as a fixed register according to
+@code{FIXED_REGISTERS}, or arrange to be able to eliminate it
+(@pxref{Elimination}).
+@end defmac
+
+@defmac HARD_FRAME_POINTER_IS_FRAME_POINTER
+Define this to a preprocessor constant that is nonzero if
+@code{hard_frame_pointer_rtx} and @code{frame_pointer_rtx} should be
+the same.  The default definition is @samp{(HARD_FRAME_POINTER_REGNUM
+== FRAME_POINTER_REGNUM)}; you only need to define this macro if that
+definition is not suitable for use in preprocessor conditionals.
+@end defmac
+
+@defmac HARD_FRAME_POINTER_IS_ARG_POINTER
+Define this to a preprocessor constant that is nonzero if
+@code{hard_frame_pointer_rtx} and @code{arg_pointer_rtx} should be the
+same.  The default definition is @samp{(HARD_FRAME_POINTER_REGNUM ==
+ARG_POINTER_REGNUM)}; you only need to define this macro if that
+definition is not suitable for use in preprocessor conditionals.
+@end defmac
+
+@defmac RETURN_ADDRESS_POINTER_REGNUM
+The register number of the return address pointer register, which is used to
+access the current function's return address from the stack.  On some
+machines, the return address is not at a fixed offset from the frame
+pointer or stack pointer or argument pointer.  This register can be defined
+to point to the return address on the stack, and then be converted by
+@code{ELIMINABLE_REGS} into either the frame pointer or stack pointer.
+
+Do not define this macro unless there is no other way to get the return
+address from the stack.
+@end defmac
+
+@defmac STATIC_CHAIN_REGNUM
+@defmacx STATIC_CHAIN_INCOMING_REGNUM
+Register numbers used for passing a function's static chain pointer.  If
+register windows are used, the register number as seen by the called
+function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register
+number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}.  If
+these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need
+not be defined.
+
+The static chain register need not be a fixed register.
+
+If the static chain is passed in memory, these macros should not be
+defined; instead, the @code{TARGET_STATIC_CHAIN} hook should be used.
+@end defmac
+
+@hook TARGET_STATIC_CHAIN
+This hook replaces the use of @code{STATIC_CHAIN_REGNUM} et al for
+targets that may use different static chain locations for different
+nested functions.  This may be required if the target has function
+attributes that affect the calling conventions of the function and
+those calling conventions use different static chain locations.
+
+The default version of this hook uses @code{STATIC_CHAIN_REGNUM} et al.
+
+If the static chain is passed in memory, this hook should be used to
+provide rtx giving @code{mem} expressions that denote where they are stored.
+Often the @code{mem} expression as seen by the caller will be at an offset
+from the stack pointer and the @code{mem} expression as seen by the callee
+will be at an offset from the frame pointer.
+@findex stack_pointer_rtx
+@findex frame_pointer_rtx
+@findex arg_pointer_rtx
+The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and
+@code{arg_pointer_rtx} will have been initialized and should be used
+to refer to those items.
+@end deftypefn
+
+@defmac DWARF_FRAME_REGISTERS
+This macro specifies the maximum number of hard registers that can be
+saved in a call frame.  This is used to size data structures used in
+DWARF2 exception handling.
+
+Prior to GCC 3.0, this macro was needed in order to establish a stable
+exception handling ABI in the face of adding new hard registers for ISA
+extensions.  In GCC 3.0 and later, the EH ABI is insulated from changes
+in the number of hard registers.  Nevertheless, this macro can still be
+used to reduce the runtime memory requirements of the exception handling
+routines, which can be substantial if the ISA contains a lot of
+registers that are not call-saved.
+
+If this macro is not defined, it defaults to
+@code{FIRST_PSEUDO_REGISTER}.
+@end defmac
+
+@defmac PRE_GCC3_DWARF_FRAME_REGISTERS
+
+This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided
+for backward compatibility in pre GCC 3.0 compiled code.
+
+If this macro is not defined, it defaults to
+@code{DWARF_FRAME_REGISTERS}.
+@end defmac
+
+@defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno})
+
+Define this macro if the target's representation for dwarf registers
+is different than the internal representation for unwind column.
+Given a dwarf register, this macro should return the internal unwind
+column number to use instead.
+
+See the PowerPC's SPE target for an example.
+@end defmac
+
+@defmac DWARF_FRAME_REGNUM (@var{regno})
+
+Define this macro if the target's representation for dwarf registers
+used in .eh_frame or .debug_frame is different from that used in other
+debug info sections.  Given a GCC hard register number, this macro
+should return the .eh_frame register number.  The default is
+@code{DBX_REGISTER_NUMBER (@var{regno})}.
+
+@end defmac
+
+@defmac DWARF2_FRAME_REG_OUT (@var{regno}, @var{for_eh})
+
+Define this macro to map register numbers held in the call frame info
+that GCC has collected using @code{DWARF_FRAME_REGNUM} to those that
+should be output in .debug_frame (@code{@var{for_eh}} is zero) and
+.eh_frame (@code{@var{for_eh}} is nonzero).  The default is to
+return @code{@var{regno}}.
+
+@end defmac
+
+@node Elimination
+@subsection Eliminating Frame Pointer and Arg Pointer
+
+@c prevent bad page break with this line
+This is about eliminating the frame pointer and arg pointer.
+
+@hook TARGET_FRAME_POINTER_REQUIRED
+This target hook should return @code{true} if a function must have and use
+a frame pointer.  This target hook is called in the reload pass.  If its return
+value is @code{true} the function will have a frame pointer.
+
+This target hook can in principle examine the current function and decide
+according to the facts, but on most machines the constant @code{false} or the
+constant @code{true} suffices.  Use @code{false} when the machine allows code
+to be generated with no frame pointer, and doing so saves some time or space.
+Use @code{true} when there is no possible advantage to avoiding a frame
+pointer.
+
+In certain cases, the compiler does not know how to produce valid code
+without a frame pointer.  The compiler recognizes those cases and
+automatically gives the function a frame pointer regardless of what
+@code{TARGET_FRAME_POINTER_REQUIRED} returns.  You don't need to worry about
+them.
+
+In a function that does not require a frame pointer, the frame pointer
+register can be allocated for ordinary usage, unless you mark it as a
+fixed register.  See @code{FIXED_REGISTERS} for more information.
+
+Default return value is @code{false}.
+@end deftypefn
+
+@findex get_frame_size
+@defmac INITIAL_FRAME_POINTER_OFFSET (@var{depth-var})
+A C statement to store in the variable @var{depth-var} the difference
+between the frame pointer and the stack pointer values immediately after
+the function prologue.  The value would be computed from information
+such as the result of @code{get_frame_size ()} and the tables of
+registers @code{regs_ever_live} and @code{call_used_regs}.
+
+If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and
+need not be defined.  Otherwise, it must be defined even if
+@code{TARGET_FRAME_POINTER_REQUIRED} always returns true; in that
+case, you may set @var{depth-var} to anything.
+@end defmac
+
+@defmac ELIMINABLE_REGS
+If defined, this macro specifies a table of register pairs used to
+eliminate unneeded registers that point into the stack frame.  If it is not
+defined, the only elimination attempted by the compiler is to replace
+references to the frame pointer with references to the stack pointer.
+
+The definition of this macro is a list of structure initializations, each
+of which specifies an original and replacement register.
+
+On some machines, the position of the argument pointer is not known until
+the compilation is completed.  In such a case, a separate hard register
+must be used for the argument pointer.  This register can be eliminated by
+replacing it with either the frame pointer or the argument pointer,
+depending on whether or not the frame pointer has been eliminated.
+
+In this case, you might specify:
+@smallexample
+#define ELIMINABLE_REGS  \
+@{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \
+ @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \
+ @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@}
+@end smallexample
+
+Note that the elimination of the argument pointer with the stack pointer is
+specified first since that is the preferred elimination.
+@end defmac
+
+@hook TARGET_CAN_ELIMINATE
+This target hook should returns @code{true} if the compiler is allowed to
+try to replace register number @var{from_reg} with register number
+@var{to_reg}.  This target hook need only be defined if @code{ELIMINABLE_REGS}
+is defined, and will usually be @code{true}, since most of the cases
+preventing register elimination are things that the compiler already
+knows about.
+
+Default return value is @code{true}.
+@end deftypefn
+
+@defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var})
+This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}.  It
+specifies the initial difference between the specified pair of
+registers.  This macro must be defined if @code{ELIMINABLE_REGS} is
+defined.
+@end defmac
+
+@node Stack Arguments
+@subsection Passing Function Arguments on the Stack
+@cindex arguments on stack
+@cindex stack arguments
+
+The macros in this section control how arguments are passed
+on the stack.  See the following section for other macros that
+control passing certain arguments in registers.
+
+@hook TARGET_PROMOTE_PROTOTYPES
+This target hook returns @code{true} if an argument declared in a
+prototype as an integral type smaller than @code{int} should actually be
+passed as an @code{int}.  In addition to avoiding errors in certain
+cases of mismatch, it also makes for better code on certain machines.
+The default is to not promote prototypes.
+@end deftypefn
+
+@defmac PUSH_ARGS
+A C expression.  If nonzero, push insns will be used to pass
+outgoing arguments.
+If the target machine does not have a push instruction, set it to zero.
+That directs GCC to use an alternate strategy: to
+allocate the entire argument block and then store the arguments into
+it.  When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too.
+@end defmac
+
+@defmac PUSH_ARGS_REVERSED
+A C expression.  If nonzero, function arguments will be evaluated from
+last to first, rather than from first to last.  If this macro is not
+defined, it defaults to @code{PUSH_ARGS} on targets where the stack
+and args grow in opposite directions, and 0 otherwise.
+@end defmac
+
+@defmac PUSH_ROUNDING (@var{npushed})
+A C expression that is the number of bytes actually pushed onto the
+stack when an instruction attempts to push @var{npushed} bytes.
+
+On some machines, the definition
+
+@smallexample
+#define PUSH_ROUNDING(BYTES) (BYTES)
+@end smallexample
+
+@noindent
+will suffice.  But on other machines, instructions that appear
+to push one byte actually push two bytes in an attempt to maintain
+alignment.  Then the definition should be
+
+@smallexample
+#define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1)
+@end smallexample
+
+If the value of this macro has a type, it should be an unsigned type.
+@end defmac
+
+@findex current_function_outgoing_args_size
+@defmac ACCUMULATE_OUTGOING_ARGS
+A C expression.  If nonzero, the maximum amount of space required for outgoing arguments
+will be computed and placed into the variable
+@code{current_function_outgoing_args_size}.  No space will be pushed
+onto the stack for each call; instead, the function prologue should
+increase the stack frame size by this amount.
+
+Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS}
+is not proper.
+@end defmac
+
+@defmac REG_PARM_STACK_SPACE (@var{fndecl})
+Define this macro if functions should assume that stack space has been
+allocated for arguments even when their values are passed in
+registers.
+
+The value of this macro is the size, in bytes, of the area reserved for
+arguments passed in registers for the function represented by @var{fndecl},
+which can be zero if GCC is calling a library function.
+The argument @var{fndecl} can be the FUNCTION_DECL, or the type itself
+of the function.
+
+This space can be allocated by the caller, or be a part of the
+machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says
+which.
+@end defmac
+@c above is overfull.  not sure what to do.  --mew 5feb93  did
+@c something, not sure if it looks good.  --mew 10feb93
+
+@defmac OUTGOING_REG_PARM_STACK_SPACE (@var{fntype})
+Define this to a nonzero value if it is the responsibility of the
+caller to allocate the area reserved for arguments passed in registers
+when calling a function of @var{fntype}.  @var{fntype} may be NULL
+if the function called is a library function.
+
+If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls
+whether the space for these arguments counts in the value of
+@code{current_function_outgoing_args_size}.
+@end defmac
+
+@defmac STACK_PARMS_IN_REG_PARM_AREA
+Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the
+stack parameters don't skip the area specified by it.
+@c i changed this, makes more sens and it should have taken care of the
+@c overfull.. not as specific, tho.  --mew 5feb93
+
+Normally, when a parameter is not passed in registers, it is placed on the
+stack beyond the @code{REG_PARM_STACK_SPACE} area.  Defining this macro
+suppresses this behavior and causes the parameter to be passed on the
+stack in its natural location.
+@end defmac
+
+@hook TARGET_RETURN_POPS_ARGS
+This target hook returns the number of bytes of its own arguments that
+a function pops on returning, or 0 if the function pops no arguments
+and the caller must therefore pop them all after the function returns.
+
+@var{fundecl} is a C variable whose value is a tree node that describes
+the function in question.  Normally it is a node of type
+@code{FUNCTION_DECL} that describes the declaration of the function.
+From this you can obtain the @code{DECL_ATTRIBUTES} of the function.
+
+@var{funtype} is a C variable whose value is a tree node that
+describes the function in question.  Normally it is a node of type
+@code{FUNCTION_TYPE} that describes the data type of the function.
+From this it is possible to obtain the data types of the value and
+arguments (if known).
+
+When a call to a library function is being considered, @var{fundecl}
+will contain an identifier node for the library function.  Thus, if
+you need to distinguish among various library functions, you can do so
+by their names.  Note that ``library function'' in this context means
+a function used to perform arithmetic, whose name is known specially
+in the compiler and was not mentioned in the C code being compiled.
+
+@var{size} is the number of bytes of arguments passed on the
+stack.  If a variable number of bytes is passed, it is zero, and
+argument popping will always be the responsibility of the calling function.
+
+On the VAX, all functions always pop their arguments, so the definition
+of this macro is @var{size}.  On the 68000, using the standard
+calling convention, no functions pop their arguments, so the value of
+the macro is always 0 in this case.  But an alternative calling
+convention is available in which functions that take a fixed number of
+arguments pop them but other functions (such as @code{printf}) pop
+nothing (the caller pops all).  When this convention is in use,
+@var{funtype} is examined to determine whether a function takes a fixed
+number of arguments.
+@end deftypefn
+
+@defmac CALL_POPS_ARGS (@var{cum})
+A C expression that should indicate the number of bytes a call sequence
+pops off the stack.  It is added to the value of @code{RETURN_POPS_ARGS}
+when compiling a function call.
+
+@var{cum} is the variable in which all arguments to the called function
+have been accumulated.
+
+On certain architectures, such as the SH5, a call trampoline is used
+that pops certain registers off the stack, depending on the arguments
+that have been passed to the function.  Since this is a property of the
+call site, not of the called function, @code{RETURN_POPS_ARGS} is not
+appropriate.
+@end defmac
+
+@node Register Arguments
+@subsection Passing Arguments in Registers
+@cindex arguments in registers
+@cindex registers arguments
+
+This section describes the macros which let you control how various
+types of arguments are passed in registers or how they are arranged in
+the stack.
+
+@defmac FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
+A C expression that controls whether a function argument is passed
+in a register, and which register.
+
+The arguments are @var{cum}, which summarizes all the previous
+arguments; @var{mode}, the machine mode of the argument; @var{type},
+the data type of the argument as a tree node or 0 if that is not known
+(which happens for C support library functions); and @var{named},
+which is 1 for an ordinary argument and 0 for nameless arguments that
+correspond to @samp{@dots{}} in the called function's prototype.
+@var{type} can be an incomplete type if a syntax error has previously
+occurred.
+
+The value of the expression is usually either a @code{reg} RTX for the
+hard register in which to pass the argument, or zero to pass the
+argument on the stack.
+
+For machines like the VAX and 68000, where normally all arguments are
+pushed, zero suffices as a definition.
+
+The value of the expression can also be a @code{parallel} RTX@.  This is
+used when an argument is passed in multiple locations.  The mode of the
+@code{parallel} should be the mode of the entire argument.  The
+@code{parallel} holds any number of @code{expr_list} pairs; each one
+describes where part of the argument is passed.  In each
+@code{expr_list} the first operand must be a @code{reg} RTX for the hard
+register in which to pass this part of the argument, and the mode of the
+register RTX indicates how large this part of the argument is.  The
+second operand of the @code{expr_list} is a @code{const_int} which gives
+the offset in bytes into the entire argument of where this part starts.
+As a special exception the first @code{expr_list} in the @code{parallel}
+RTX may have a first operand of zero.  This indicates that the entire
+argument is also stored on the stack.
+
+The last time this macro is called, it is called with @code{MODE ==
+VOIDmode}, and its result is passed to the @code{call} or @code{call_value}
+pattern as operands 2 and 3 respectively.
+
+@cindex @file{stdarg.h} and register arguments
+The usual way to make the ISO library @file{stdarg.h} work on a machine
+where some arguments are usually passed in registers, is to cause
+nameless arguments to be passed on the stack instead.  This is done
+by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0.
+
+@cindex @code{TARGET_MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG}
+@cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG}
+You may use the hook @code{targetm.calls.must_pass_in_stack}
+in the definition of this macro to determine if this argument is of a
+type that must be passed in the stack.  If @code{REG_PARM_STACK_SPACE}
+is not defined and @code{FUNCTION_ARG} returns nonzero for such an
+argument, the compiler will abort.  If @code{REG_PARM_STACK_SPACE} is
+defined, the argument will be computed in the stack and then loaded into
+a register.
+@end defmac
+
+@hook TARGET_MUST_PASS_IN_STACK
+This target hook should return @code{true} if we should not pass @var{type}
+solely in registers.  The file @file{expr.h} defines a
+definition that is usually appropriate, refer to @file{expr.h} for additional
+documentation.
+@end deftypefn
+
+@defmac FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named})
+Define this macro if the target machine has ``register windows'', so
+that the register in which a function sees an arguments is not
+necessarily the same as the one in which the caller passed the
+argument.
+
+For such machines, @code{FUNCTION_ARG} computes the register in which
+the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should
+be defined in a similar fashion to tell the function being called
+where the arguments will arrive.
+
+If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG}
+serves both purposes.
+@end defmac
+
+@hook TARGET_ARG_PARTIAL_BYTES
+This target hook returns the number of bytes at the beginning of an
+argument that must be put in registers.  The value must be zero for
+arguments that are passed entirely in registers or that are entirely
+pushed on the stack.
+
+On some machines, certain arguments must be passed partially in
+registers and partially in memory.  On these machines, typically the
+first few words of arguments are passed in registers, and the rest
+on the stack.  If a multi-word argument (a @code{double} or a
+structure) crosses that boundary, its first few words must be passed
+in registers and the rest must be pushed.  This macro tells the
+compiler when this occurs, and how many bytes should go in registers.
+
+@code{FUNCTION_ARG} for these arguments should return the first
+register to be used by the caller for this argument; likewise
+@code{FUNCTION_INCOMING_ARG}, for the called function.
+@end deftypefn
+
+@hook TARGET_PASS_BY_REFERENCE
+This target hook should return @code{true} if an argument at the
+position indicated by @var{cum} should be passed by reference.  This
+predicate is queried after target independent reasons for being
+passed by reference, such as @code{TREE_ADDRESSABLE (type)}.
+
+If the hook returns true, a copy of that argument is made in memory and a
+pointer to the argument is passed instead of the argument itself.
+The pointer is passed in whatever way is appropriate for passing a pointer
+to that type.
+@end deftypefn
+
+@hook TARGET_CALLEE_COPIES
+The function argument described by the parameters to this hook is
+known to be passed by reference.  The hook should return true if the
+function argument should be copied by the callee instead of copied
+by the caller.
+
+For any argument for which the hook returns true, if it can be
+determined that the argument is not modified, then a copy need
+not be generated.
+
+The default version of this hook always returns false.
+@end deftypefn
+
+@defmac CUMULATIVE_ARGS
+A C type for declaring a variable that is used as the first argument of
+@code{FUNCTION_ARG} and other related values.  For some target machines,
+the type @code{int} suffices and can hold the number of bytes of
+argument so far.
+
+There is no need to record in @code{CUMULATIVE_ARGS} anything about the
+arguments that have been passed on the stack.  The compiler has other
+variables to keep track of that.  For target machines on which all
+arguments are passed on the stack, there is no need to store anything in
+@code{CUMULATIVE_ARGS}; however, the data structure must exist and
+should not be empty, so use @code{int}.
+@end defmac
+
+@defmac OVERRIDE_ABI_FORMAT (@var{fndecl})
+If defined, this macro is called before generating any code for a
+function, but after the @var{cfun} descriptor for the function has been
+created.  The back end may use this macro to update @var{cfun} to
+reflect an ABI other than that which would normally be used by default.
+If the compiler is generating code for a compiler-generated function,
+@var{fndecl} may be @code{NULL}.
+@end defmac
+
+@defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl}, @var{n_named_args})
+A C statement (sans semicolon) for initializing the variable
+@var{cum} for the state at the beginning of the argument list.  The
+variable has type @code{CUMULATIVE_ARGS}.  The value of @var{fntype}
+is the tree node for the data type of the function which will receive
+the args, or 0 if the args are to a compiler support library function.
+For direct calls that are not libcalls, @var{fndecl} contain the
+declaration node of the function.  @var{fndecl} is also set when
+@code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function
+being compiled.  @var{n_named_args} is set to the number of named
+arguments, including a structure return address if it is passed as a
+parameter, when making a call.  When processing incoming arguments,
+@var{n_named_args} is set to @minus{}1.
+
+When processing a call to a compiler support library function,
+@var{libname} identifies which one.  It is a @code{symbol_ref} rtx which
+contains the name of the function, as a string.  @var{libname} is 0 when
+an ordinary C function call is being processed.  Thus, each time this
+macro is called, either @var{libname} or @var{fntype} is nonzero, but
+never both of them at once.
+@end defmac
+
+@defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname})
+Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls,
+it gets a @code{MODE} argument instead of @var{fntype}, that would be
+@code{NULL}.  @var{indirect} would always be zero, too.  If this macro
+is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname,
+0)} is used instead.
+@end defmac
+
+@defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname})
+Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of
+finding the arguments for the function being compiled.  If this macro is
+undefined, @code{INIT_CUMULATIVE_ARGS} is used instead.
+
+The value passed for @var{libname} is always 0, since library routines
+with special calling conventions are never compiled with GCC@.  The
+argument @var{libname} exists for symmetry with
+@code{INIT_CUMULATIVE_ARGS}.
+@c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe.
+@c --mew 5feb93   i switched the order of the sentences.  --mew 10feb93
+@end defmac
+
+@defmac FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named})
+A C statement (sans semicolon) to update the summarizer variable
+@var{cum} to advance past an argument in the argument list.  The
+values @var{mode}, @var{type} and @var{named} describe that argument.
+Once this is done, the variable @var{cum} is suitable for analyzing
+the @emph{following} argument with @code{FUNCTION_ARG}, etc.
+
+This macro need not do anything if the argument in question was passed
+on the stack.  The compiler knows how to track the amount of stack space
+used for arguments without any special help.
+@end defmac
+
+@defmac FUNCTION_ARG_OFFSET (@var{mode}, @var{type})
+If defined, a C expression that is the number of bytes to add to the
+offset of the argument passed in memory.  This is needed for the SPU,
+which passes @code{char} and @code{short} arguments in the preferred
+slot that is in the middle of the quad word instead of starting at the
+top.
+@end defmac
+
+@defmac FUNCTION_ARG_PADDING (@var{mode}, @var{type})
+If defined, a C expression which determines whether, and in which direction,
+to pad out an argument with extra space.  The value should be of type
+@code{enum direction}: either @code{upward} to pad above the argument,
+@code{downward} to pad below, or @code{none} to inhibit padding.
+
+The @emph{amount} of padding is always just enough to reach the next
+multiple of @code{TARGET_FUNCTION_ARG_BOUNDARY}; this macro does not
+control it.
+
+This macro has a default definition which is right for most systems.
+For little-endian machines, the default is to pad upward.  For
+big-endian machines, the default is to pad downward for an argument of
+constant size shorter than an @code{int}, and upward otherwise.
+@end defmac
+
+@defmac PAD_VARARGS_DOWN
+If defined, a C expression which determines whether the default
+implementation of va_arg will attempt to pad down before reading the
+next argument, if that argument is smaller than its aligned space as
+controlled by @code{PARM_BOUNDARY}.  If this macro is not defined, all such
+arguments are padded down if @code{BYTES_BIG_ENDIAN} is true.
+@end defmac
+
+@defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first})
+Specify padding for the last element of a block move between registers and
+memory.  @var{first} is nonzero if this is the only element.  Defining this
+macro allows better control of register function parameters on big-endian
+machines, without using @code{PARALLEL} rtl.  In particular,
+@code{MUST_PASS_IN_STACK} need not test padding and mode of types in
+registers, as there is no longer a "wrong" part of a register;  For example,
+a three byte aggregate may be passed in the high part of a register if so
+required.
+@end defmac
+
+@hook TARGET_FUNCTION_ARG_BOUNDARY
+This hook returns the alignment boundary, in bits, of an argument
+with the specified mode and type.  The default hook returns
+@code{PARM_BOUNDARY} for all arguments.
+@end deftypefn
+
+@defmac FUNCTION_ARG_REGNO_P (@var{regno})
+A C expression that is nonzero if @var{regno} is the number of a hard
+register in which function arguments are sometimes passed.  This does
+@emph{not} include implicit arguments such as the static chain and
+the structure-value address.  On many machines, no registers can be
+used for this purpose since all function arguments are pushed on the
+stack.
+@end defmac
+
+@hook TARGET_SPLIT_COMPLEX_ARG
+This hook should return true if parameter of type @var{type} are passed
+as two scalar parameters.  By default, GCC will attempt to pack complex
+arguments into the target's word size.  Some ABIs require complex arguments
+to be split and treated as their individual components.  For example, on
+AIX64, complex floats should be passed in a pair of floating point
+registers, even though a complex float would fit in one 64-bit floating
+point register.
+
+The default value of this hook is @code{NULL}, which is treated as always
+false.
+@end deftypefn
+
+@hook TARGET_BUILD_BUILTIN_VA_LIST
+This hook returns a type node for @code{va_list} for the target.
+The default version of the hook returns @code{void*}.
+@end deftypefn
+
+@hook TARGET_ENUM_VA_LIST_P
+This target hook is used in function @code{c_common_nodes_and_builtins}
+to iterate through the target specific builtin types for va_list. The
+variable @var{idx} is used as iterator. @var{pname} has to be a pointer
+to a @code{const char *} and @var{ptree} a pointer to a @code{tree} typed
+variable.
+The arguments @var{pname} and @var{ptree} are used to store the result of
+this macro and are set to the name of the va_list builtin type and its
+internal type.
+If the return value of this macro is zero, then there is no more element.
+Otherwise the @var{IDX} should be increased for the next call of this
+macro to iterate through all types.
+@end deftypefn
+
+@hook TARGET_FN_ABI_VA_LIST
+This hook returns the va_list type of the calling convention specified by
+@var{fndecl}.
+The default version of this hook returns @code{va_list_type_node}.
+@end deftypefn
+
+@hook TARGET_CANONICAL_VA_LIST_TYPE
+This hook returns the va_list type of the calling convention specified by the
+type of @var{type}. If @var{type} is not a valid va_list type, it returns
+@code{NULL_TREE}.
+@end deftypefn
+
+@hook TARGET_GIMPLIFY_VA_ARG_EXPR
+This hook performs target-specific gimplification of
+@code{VA_ARG_EXPR}.  The first two parameters correspond to the
+arguments to @code{va_arg}; the latter two are as in
+@code{gimplify.c:gimplify_expr}.
+@end deftypefn
+
+@hook TARGET_VALID_POINTER_MODE
+Define this to return nonzero if the port can handle pointers
+with machine mode @var{mode}.  The default version of this
+hook returns true for both @code{ptr_mode} and @code{Pmode}.
+@end deftypefn
+
+@hook TARGET_REF_MAY_ALIAS_ERRNO
+
+@hook TARGET_SCALAR_MODE_SUPPORTED_P
+Define this to return nonzero if the port is prepared to handle
+insns involving scalar mode @var{mode}.  For a scalar mode to be
+considered supported, all the basic arithmetic and comparisons
+must work.
+
+The default version of this hook returns true for any mode
+required to handle the basic C types (as defined by the port).
+Included here are the double-word arithmetic supported by the
+code in @file{optabs.c}.
+@end deftypefn
+
+@hook TARGET_VECTOR_MODE_SUPPORTED_P
+Define this to return nonzero if the port is prepared to handle
+insns involving vector mode @var{mode}.  At the very least, it
+must have move patterns for this mode.
+@end deftypefn
+
+@hook TARGET_SMALL_REGISTER_CLASSES_FOR_MODE_P
+Define this to return nonzero for machine modes for which the port has
+small register classes.  If this target hook returns nonzero for a given
+@var{mode}, the compiler will try to minimize the lifetime of registers
+in @var{mode}.  The hook may be called with @code{VOIDmode} as argument.
+In this case, the hook is expected to return nonzero if it returns nonzero
+for any mode.
+
+On some machines, it is risky to let hard registers live across arbitrary
+insns.  Typically, these machines have instructions that require values
+to be in specific registers (like an accumulator), and reload will fail
+if the required hard register is used for another purpose across such an
+insn.
+
+Passes before reload do not know which hard registers will be used
+in an instruction, but the machine modes of the registers set or used in
+the instruction are already known.  And for some machines, register
+classes are small for, say, integer registers but not for floating point
+registers.  For example, the AMD x86-64 architecture requires specific
+registers for the legacy x86 integer instructions, but there are many
+SSE registers for floating point operations.  On such targets, a good
+strategy may be to return nonzero from this hook for @code{INTEGRAL_MODE_P}
+machine modes but zero for the SSE register classes.
+
+The default version of this hook returns false for any mode.  It is always
+safe to redefine this hook to return with a nonzero value.  But if you
+unnecessarily define it, you will reduce the amount of optimizations
+that can be performed in some cases.  If you do not define this hook
+to return a nonzero value when it is required, the compiler will run out
+of spill registers and print a fatal error message.
+@end deftypefn
+
+@hook TARGET_FLAGS_REGNUM
+
+@node Scalar Return
+@subsection How Scalar Function Values Are Returned
+@cindex return values in registers
+@cindex values, returned by functions
+@cindex scalars, returned as values
+
+This section discusses the macros that control returning scalars as
+values---values that can fit in registers.
+
+@hook TARGET_FUNCTION_VALUE
+
+Define this to return an RTX representing the place where a function
+returns or receives a value of data type @var{ret_type}, a tree node
+representing a data type.  @var{fn_decl_or_type} is a tree node
+representing @code{FUNCTION_DECL} or @code{FUNCTION_TYPE} of a
+function being called.  If @var{outgoing} is false, the hook should
+compute the register in which the caller will see the return value.
+Otherwise, the hook should return an RTX representing the place where
+a function returns a value.
+
+On many machines, only @code{TYPE_MODE (@var{ret_type})} is relevant.
+(Actually, on most machines, scalar values are returned in the same
+place regardless of mode.)  The value of the expression is usually a
+@code{reg} RTX for the hard register where the return value is stored.
+The value can also be a @code{parallel} RTX, if the return value is in
+multiple places.  See @code{FUNCTION_ARG} for an explanation of the
+@code{parallel} form.   Note that the callee will populate every
+location specified in the @code{parallel}, but if the first element of
+the @code{parallel} contains the whole return value, callers will use
+that element as the canonical location and ignore the others.  The m68k
+port uses this type of @code{parallel} to return pointers in both
+@samp{%a0} (the canonical location) and @samp{%d0}.
+
+If @code{TARGET_PROMOTE_FUNCTION_RETURN} returns true, you must apply
+the same promotion rules specified in @code{PROMOTE_MODE} if
+@var{valtype} is a scalar type.
+
+If the precise function being called is known, @var{func} is a tree
+node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null
+pointer.  This makes it possible to use a different value-returning
+convention for specific functions when all their calls are
+known.
+
+Some target machines have ``register windows'' so that the register in
+which a function returns its value is not the same as the one in which
+the caller sees the value.  For such machines, you should return
+different RTX depending on @var{outgoing}.
+
+@code{TARGET_FUNCTION_VALUE} is not used for return values with
+aggregate data types, because these are returned in another way.  See
+@code{TARGET_STRUCT_VALUE_RTX} and related macros, below.
+@end deftypefn
+
+@defmac FUNCTION_VALUE (@var{valtype}, @var{func})
+This macro has been deprecated.  Use @code{TARGET_FUNCTION_VALUE} for
+a new target instead.
+@end defmac
+
+@defmac LIBCALL_VALUE (@var{mode})
+A C expression to create an RTX representing the place where a library
+function returns a value of mode @var{mode}.
+
+Note that ``library function'' in this context means a compiler
+support routine, used to perform arithmetic, whose name is known
+specially by the compiler and was not mentioned in the C code being
+compiled.
+@end defmac
+
+@hook TARGET_LIBCALL_VALUE
+Define this hook if the back-end needs to know the name of the libcall
+function in order to determine where the result should be returned.  
+
+The mode of the result is given by @var{mode} and the name of the called
+library function is given by @var{fun}.  The hook should return an RTX 
+representing the place where the library function result will be returned.
+
+If this hook is not defined, then LIBCALL_VALUE will be used.
+@end deftypefn
+
+@defmac FUNCTION_VALUE_REGNO_P (@var{regno})
+A C expression that is nonzero if @var{regno} is the number of a hard
+register in which the values of called function may come back.
+
+A register whose use for returning values is limited to serving as the
+second of a pair (for a value of type @code{double}, say) need not be
+recognized by this macro.  So for most machines, this definition
+suffices:
+
+@smallexample
+#define FUNCTION_VALUE_REGNO_P(N) ((N) == 0)
+@end smallexample
+
+If the machine has register windows, so that the caller and the called
+function use different registers for the return value, this macro
+should recognize only the caller's register numbers.
+
+This macro has been deprecated.  Use @code{TARGET_FUNCTION_VALUE_REGNO_P}
+for a new target instead.
+@end defmac
+
+@hook TARGET_FUNCTION_VALUE_REGNO_P
+A target hook that return @code{true} if @var{regno} is the number of a hard
+register in which the values of called function may come back.
+
+A register whose use for returning values is limited to serving as the
+second of a pair (for a value of type @code{double}, say) need not be
+recognized by this target hook.
+
+If the machine has register windows, so that the caller and the called
+function use different registers for the return value, this target hook
+should recognize only the caller's register numbers.
+
+If this hook is not defined, then FUNCTION_VALUE_REGNO_P will be used.
+@end deftypefn
+
+@defmac APPLY_RESULT_SIZE
+Define this macro if @samp{untyped_call} and @samp{untyped_return}
+need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for
+saving and restoring an arbitrary return value.
+@end defmac
+
+@hook TARGET_RETURN_IN_MSB
+This hook should return true if values of type @var{type} are returned
+at the most significant end of a register (in other words, if they are
+padded at the least significant end).  You can assume that @var{type}
+is returned in a register; the caller is required to check this.
+
+Note that the register provided by @code{TARGET_FUNCTION_VALUE} must
+be able to hold the complete return value.  For example, if a 1-, 2-
+or 3-byte structure is returned at the most significant end of a
+4-byte register, @code{TARGET_FUNCTION_VALUE} should provide an
+@code{SImode} rtx.
+@end deftypefn
+
+@node Aggregate Return
+@subsection How Large Values Are Returned
+@cindex aggregates as return values
+@cindex large return values
+@cindex returning aggregate values
+@cindex structure value address
+
+When a function value's mode is @code{BLKmode} (and in some other
+cases), the value is not returned according to
+@code{TARGET_FUNCTION_VALUE} (@pxref{Scalar Return}).  Instead, the
+caller passes the address of a block of memory in which the value
+should be stored.  This address is called the @dfn{structure value
+address}.
+
+This section describes how to control returning structure values in
+memory.
+
+@hook TARGET_RETURN_IN_MEMORY
+This target hook should return a nonzero value to say to return the
+function value in memory, just as large structures are always returned.
+Here @var{type} will be the data type of the value, and @var{fntype}
+will be the type of the function doing the returning, or @code{NULL} for
+libcalls.
+
+Note that values of mode @code{BLKmode} must be explicitly handled
+by this function.  Also, the option @option{-fpcc-struct-return}
+takes effect regardless of this macro.  On most systems, it is
+possible to leave the hook undefined; this causes a default
+definition to be used, whose value is the constant 1 for @code{BLKmode}
+values, and 0 otherwise.
+
+Do not use this hook to indicate that structures and unions should always
+be returned in memory.  You should instead use @code{DEFAULT_PCC_STRUCT_RETURN}
+to indicate this.
+@end deftypefn
+
+@defmac DEFAULT_PCC_STRUCT_RETURN
+Define this macro to be 1 if all structure and union return values must be
+in memory.  Since this results in slower code, this should be defined
+only if needed for compatibility with other compilers or with an ABI@.
+If you define this macro to be 0, then the conventions used for structure
+and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY}
+target hook.
+
+If not defined, this defaults to the value 1.
+@end defmac
+
+@hook TARGET_STRUCT_VALUE_RTX
+This target hook should return the location of the structure value
+address (normally a @code{mem} or @code{reg}), or 0 if the address is
+passed as an ``invisible'' first argument.  Note that @var{fndecl} may
+be @code{NULL}, for libcalls.  You do not need to define this target
+hook if the address is always passed as an ``invisible'' first
+argument.
+
+On some architectures the place where the structure value address
+is found by the called function is not the same place that the
+caller put it.  This can be due to register windows, or it could
+be because the function prologue moves it to a different place.
+@var{incoming} is @code{1} or @code{2} when the location is needed in
+the context of the called function, and @code{0} in the context of
+the caller.
+
+If @var{incoming} is nonzero and the address is to be found on the
+stack, return a @code{mem} which refers to the frame pointer. If
+@var{incoming} is @code{2}, the result is being used to fetch the
+structure value address at the beginning of a function.  If you need
+to emit adjusting code, you should do it at this point.
+@end deftypefn
+
+@defmac PCC_STATIC_STRUCT_RETURN
+Define this macro if the usual system convention on the target machine
+for returning structures and unions is for the called function to return
+the address of a static variable containing the value.
+
+Do not define this if the usual system convention is for the caller to
+pass an address to the subroutine.
+
+This macro has effect in @option{-fpcc-struct-return} mode, but it does
+nothing when you use @option{-freg-struct-return} mode.
+@end defmac
+
+@hook TARGET_GET_RAW_RESULT_MODE
+
+@hook TARGET_GET_RAW_ARG_MODE
+
+@node Caller Saves
+@subsection Caller-Saves Register Allocation
+
+If you enable it, GCC can save registers around function calls.  This
+makes it possible to use call-clobbered registers to hold variables that
+must live across calls.
+
+@defmac CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls})
+A C expression to determine whether it is worthwhile to consider placing
+a pseudo-register in a call-clobbered hard register and saving and
+restoring it around each function call.  The expression should be 1 when
+this is worth doing, and 0 otherwise.
+
+If you don't define this macro, a default is used which is good on most
+machines: @code{4 * @var{calls} < @var{refs}}.
+@end defmac
+
+@defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs})
+A C expression specifying which mode is required for saving @var{nregs}
+of a pseudo-register in call-clobbered hard register @var{regno}.  If
+@var{regno} is unsuitable for caller save, @code{VOIDmode} should be
+returned.  For most machines this macro need not be defined since GCC
+will select the smallest suitable mode.
+@end defmac
+
+@node Function Entry
+@subsection Function Entry and Exit
+@cindex function entry and exit
+@cindex prologue
+@cindex epilogue
+
+This section describes the macros that output function entry
+(@dfn{prologue}) and exit (@dfn{epilogue}) code.
+
+@hook TARGET_ASM_FUNCTION_PROLOGUE
+If defined, a function that outputs the assembler code for entry to a
+function.  The prologue is responsible for setting up the stack frame,
+initializing the frame pointer register, saving registers that must be
+saved, and allocating @var{size} additional bytes of storage for the
+local variables.  @var{size} is an integer.  @var{file} is a stdio
+stream to which the assembler code should be output.
+
+The label for the beginning of the function need not be output by this
+macro.  That has already been done when the macro is run.
+
+@findex regs_ever_live
+To determine which registers to save, the macro can refer to the array
+@code{regs_ever_live}: element @var{r} is nonzero if hard register
+@var{r} is used anywhere within the function.  This implies the function
+prologue should save register @var{r}, provided it is not one of the
+call-used registers.  (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use
+@code{regs_ever_live}.)
+
+On machines that have ``register windows'', the function entry code does
+not save on the stack the registers that are in the windows, even if
+they are supposed to be preserved by function calls; instead it takes
+appropriate steps to ``push'' the register stack, if any non-call-used
+registers are used in the function.
+
+@findex frame_pointer_needed
+On machines where functions may or may not have frame-pointers, the
+function entry code must vary accordingly; it must set up the frame
+pointer if one is wanted, and not otherwise.  To determine whether a
+frame pointer is in wanted, the macro can refer to the variable
+@code{frame_pointer_needed}.  The variable's value will be 1 at run
+time in a function that needs a frame pointer.  @xref{Elimination}.
+
+The function entry code is responsible for allocating any stack space
+required for the function.  This stack space consists of the regions
+listed below.  In most cases, these regions are allocated in the
+order listed, with the last listed region closest to the top of the
+stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and
+the highest address if it is not defined).  You can use a different order
+for a machine if doing so is more convenient or required for
+compatibility reasons.  Except in cases where required by standard
+or by a debugger, there is no reason why the stack layout used by GCC
+need agree with that used by other compilers for a machine.
+@end deftypefn
+
+@hook TARGET_ASM_FUNCTION_END_PROLOGUE
+If defined, a function that outputs assembler code at the end of a
+prologue.  This should be used when the function prologue is being
+emitted as RTL, and you have some extra assembler that needs to be
+emitted.  @xref{prologue instruction pattern}.
+@end deftypefn
+
+@hook TARGET_ASM_FUNCTION_BEGIN_EPILOGUE
+If defined, a function that outputs assembler code at the start of an
+epilogue.  This should be used when the function epilogue is being
+emitted as RTL, and you have some extra assembler that needs to be
+emitted.  @xref{epilogue instruction pattern}.
+@end deftypefn
+
+@hook TARGET_ASM_FUNCTION_EPILOGUE
+If defined, a function that outputs the assembler code for exit from a
+function.  The epilogue is responsible for restoring the saved
+registers and stack pointer to their values when the function was
+called, and returning control to the caller.  This macro takes the
+same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the
+registers to restore are determined from @code{regs_ever_live} and
+@code{CALL_USED_REGISTERS} in the same way.
+
+On some machines, there is a single instruction that does all the work
+of returning from the function.  On these machines, give that
+instruction the name @samp{return} and do not define the macro
+@code{TARGET_ASM_FUNCTION_EPILOGUE} at all.
+
+Do not define a pattern named @samp{return} if you want the
+@code{TARGET_ASM_FUNCTION_EPILOGUE} to be used.  If you want the target
+switches to control whether return instructions or epilogues are used,
+define a @samp{return} pattern with a validity condition that tests the
+target switches appropriately.  If the @samp{return} pattern's validity
+condition is false, epilogues will be used.
+
+On machines where functions may or may not have frame-pointers, the
+function exit code must vary accordingly.  Sometimes the code for these
+two cases is completely different.  To determine whether a frame pointer
+is wanted, the macro can refer to the variable
+@code{frame_pointer_needed}.  The variable's value will be 1 when compiling
+a function that needs a frame pointer.
+
+Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and
+@code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially.
+The C variable @code{current_function_is_leaf} is nonzero for such a
+function.  @xref{Leaf Functions}.
+
+On some machines, some functions pop their arguments on exit while
+others leave that for the caller to do.  For example, the 68020 when
+given @option{-mrtd} pops arguments in functions that take a fixed
+number of arguments.
+
+@findex current_function_pops_args
+Your definition of the macro @code{RETURN_POPS_ARGS} decides which
+functions pop their own arguments.  @code{TARGET_ASM_FUNCTION_EPILOGUE}
+needs to know what was decided.  The number of bytes of the current
+function's arguments that this function should pop is available in
+@code{crtl->args.pops_args}.  @xref{Scalar Return}.
+@end deftypefn
+
+@itemize @bullet
+@item
+@findex current_function_pretend_args_size
+A region of @code{current_function_pretend_args_size} bytes of
+uninitialized space just underneath the first argument arriving on the
+stack.  (This may not be at the very start of the allocated stack region
+if the calling sequence has pushed anything else since pushing the stack
+arguments.  But usually, on such machines, nothing else has been pushed
+yet, because the function prologue itself does all the pushing.)  This
+region is used on machines where an argument may be passed partly in
+registers and partly in memory, and, in some cases to support the
+features in @code{<stdarg.h>}.
+
+@item
+An area of memory used to save certain registers used by the function.
+The size of this area, which may also include space for such things as
+the return address and pointers to previous stack frames, is
+machine-specific and usually depends on which registers have been used
+in the function.  Machines with register windows often do not require
+a save area.
+
+@item
+A region of at least @var{size} bytes, possibly rounded up to an allocation
+boundary, to contain the local variables of the function.  On some machines,
+this region and the save area may occur in the opposite order, with the
+save area closer to the top of the stack.
+
+@item
+@cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames
+Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of
+@code{current_function_outgoing_args_size} bytes to be used for outgoing
+argument lists of the function.  @xref{Stack Arguments}.
+@end itemize
+
+@defmac EXIT_IGNORE_STACK
+Define this macro as a C expression that is nonzero if the return
+instruction or the function epilogue ignores the value of the stack
+pointer; in other words, if it is safe to delete an instruction to
+adjust the stack pointer before a return from the function.  The
+default is 0.
+
+Note that this macro's value is relevant only for functions for which
+frame pointers are maintained.  It is never safe to delete a final
+stack adjustment in a function that has no frame pointer, and the
+compiler knows this regardless of @code{EXIT_IGNORE_STACK}.
+@end defmac
+
+@defmac EPILOGUE_USES (@var{regno})
+Define this macro as a C expression that is nonzero for registers that are
+used by the epilogue or the @samp{return} pattern.  The stack and frame
+pointer registers are already assumed to be used as needed.
+@end defmac
+
+@defmac EH_USES (@var{regno})
+Define this macro as a C expression that is nonzero for registers that are
+used by the exception handling mechanism, and so should be considered live
+on entry to an exception edge.
+@end defmac
+
+@defmac DELAY_SLOTS_FOR_EPILOGUE
+Define this macro if the function epilogue contains delay slots to which
+instructions from the rest of the function can be ``moved''.  The
+definition should be a C expression whose value is an integer
+representing the number of delay slots there.
+@end defmac
+
+@defmac ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n})
+A C expression that returns 1 if @var{insn} can be placed in delay
+slot number @var{n} of the epilogue.
+
+The argument @var{n} is an integer which identifies the delay slot now
+being considered (since different slots may have different rules of
+eligibility).  It is never negative and is always less than the number
+of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns).
+If you reject a particular insn for a given delay slot, in principle, it
+may be reconsidered for a subsequent delay slot.  Also, other insns may
+(at least in principle) be considered for the so far unfilled delay
+slot.
+
+@findex current_function_epilogue_delay_list
+@findex final_scan_insn
+The insns accepted to fill the epilogue delay slots are put in an RTL
+list made with @code{insn_list} objects, stored in the variable
+@code{current_function_epilogue_delay_list}.  The insn for the first
+delay slot comes first in the list.  Your definition of the macro
+@code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by
+outputting the insns in this list, usually by calling
+@code{final_scan_insn}.
+
+You need not define this macro if you did not define
+@code{DELAY_SLOTS_FOR_EPILOGUE}.
+@end defmac
+
+@hook TARGET_ASM_OUTPUT_MI_THUNK
+A function that outputs the assembler code for a thunk
+function, used to implement C++ virtual function calls with multiple
+inheritance.  The thunk acts as a wrapper around a virtual function,
+adjusting the implicit object parameter before handing control off to
+the real function.
+
+First, emit code to add the integer @var{delta} to the location that
+contains the incoming first argument.  Assume that this argument
+contains a pointer, and is the one used to pass the @code{this} pointer
+in C++.  This is the incoming argument @emph{before} the function prologue,
+e.g.@: @samp{%o0} on a sparc.  The addition must preserve the values of
+all other incoming arguments.
+
+Then, if @var{vcall_offset} is nonzero, an additional adjustment should be
+made after adding @code{delta}.  In particular, if @var{p} is the
+adjusted pointer, the following adjustment should be made:
+
+@smallexample
+p += (*((ptrdiff_t **)p))[vcall_offset/sizeof(ptrdiff_t)]
+@end smallexample
+
+After the additions, emit code to jump to @var{function}, which is a
+@code{FUNCTION_DECL}.  This is a direct pure jump, not a call, and does
+not touch the return address.  Hence returning from @var{FUNCTION} will
+return to whoever called the current @samp{thunk}.
+
+The effect must be as if @var{function} had been called directly with
+the adjusted first argument.  This macro is responsible for emitting all
+of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE}
+and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked.
+
+The @var{thunk_fndecl} is redundant.  (@var{delta} and @var{function}
+have already been extracted from it.)  It might possibly be useful on
+some targets, but probably not.
+
+If you do not define this macro, the target-independent code in the C++
+front end will generate a less efficient heavyweight thunk that calls
+@var{function} instead of jumping to it.  The generic approach does
+not support varargs.
+@end deftypefn
+
+@hook TARGET_ASM_CAN_OUTPUT_MI_THUNK
+A function that returns true if TARGET_ASM_OUTPUT_MI_THUNK would be able
+to output the assembler code for the thunk function specified by the
+arguments it is passed, and false otherwise.  In the latter case, the
+generic approach will be used by the C++ front end, with the limitations
+previously exposed.
+@end deftypefn
+
+@node Profiling
+@subsection Generating Code for Profiling
+@cindex profiling, code generation
+
+These macros will help you generate code for profiling.
+
+@defmac FUNCTION_PROFILER (@var{file}, @var{labelno})
+A C statement or compound statement to output to @var{file} some
+assembler code to call the profiling subroutine @code{mcount}.
+
+@findex mcount
+The details of how @code{mcount} expects to be called are determined by
+your operating system environment, not by GCC@.  To figure them out,
+compile a small program for profiling using the system's installed C
+compiler and look at the assembler code that results.
+
+Older implementations of @code{mcount} expect the address of a counter
+variable to be loaded into some register.  The name of this variable is
+@samp{LP} followed by the number @var{labelno}, so you would generate
+the name using @samp{LP%d} in a @code{fprintf}.
+@end defmac
+
+@defmac PROFILE_HOOK
+A C statement or compound statement to output to @var{file} some assembly
+code to call the profiling subroutine @code{mcount} even the target does
+not support profiling.
+@end defmac
+
+@defmac NO_PROFILE_COUNTERS
+Define this macro to be an expression with a nonzero value if the
+@code{mcount} subroutine on your system does not need a counter variable
+allocated for each function.  This is true for almost all modern
+implementations.  If you define this macro, you must not use the
+@var{labelno} argument to @code{FUNCTION_PROFILER}.
+@end defmac
+
+@defmac PROFILE_BEFORE_PROLOGUE
+Define this macro if the code for function profiling should come before
+the function prologue.  Normally, the profiling code comes after.
+@end defmac
+
+@node Tail Calls
+@subsection Permitting tail calls
+@cindex tail calls
+
+@hook TARGET_FUNCTION_OK_FOR_SIBCALL
+True if it is ok to do sibling call optimization for the specified
+call expression @var{exp}.  @var{decl} will be the called function,
+or @code{NULL} if this is an indirect call.
+
+It is not uncommon for limitations of calling conventions to prevent
+tail calls to functions outside the current unit of translation, or
+during PIC compilation.  The hook is used to enforce these restrictions,
+as the @code{sibcall} md pattern can not fail, or fall over to a
+``normal'' call.  The criteria for successful sibling call optimization
+may vary greatly between different architectures.
+@end deftypefn
+
+@hook TARGET_EXTRA_LIVE_ON_ENTRY
+Add any hard registers to @var{regs} that are live on entry to the
+function.  This hook only needs to be defined to provide registers that
+cannot be found by examination of FUNCTION_ARG_REGNO_P, the callee saved
+registers, STATIC_CHAIN_INCOMING_REGNUM, STATIC_CHAIN_REGNUM,
+TARGET_STRUCT_VALUE_RTX, FRAME_POINTER_REGNUM, EH_USES,
+FRAME_POINTER_REGNUM, ARG_POINTER_REGNUM, and the PIC_OFFSET_TABLE_REGNUM.
+@end deftypefn
+
+@node Stack Smashing Protection
+@subsection Stack smashing protection
+@cindex stack smashing protection
+
+@hook TARGET_STACK_PROTECT_GUARD
+This hook returns a @code{DECL} node for the external variable to use
+for the stack protection guard.  This variable is initialized by the
+runtime to some random value and is used to initialize the guard value
+that is placed at the top of the local stack frame.  The type of this
+variable must be @code{ptr_type_node}.
+
+The default version of this hook creates a variable called
+@samp{__stack_chk_guard}, which is normally defined in @file{libgcc2.c}.
+@end deftypefn
+
+@hook TARGET_STACK_PROTECT_FAIL
+This hook returns a tree expression that alerts the runtime that the
+stack protect guard variable has been modified.  This expression should
+involve a call to a @code{noreturn} function.
+
+The default version of this hook invokes a function called
+@samp{__stack_chk_fail}, taking no arguments.  This function is
+normally defined in @file{libgcc2.c}.
+@end deftypefn
+
+@hook TARGET_SUPPORTS_SPLIT_STACK
+
+@node Varargs
+@section Implementing the Varargs Macros
+@cindex varargs implementation
+
+GCC comes with an implementation of @code{<varargs.h>} and
+@code{<stdarg.h>} that work without change on machines that pass arguments
+on the stack.  Other machines require their own implementations of
+varargs, and the two machine independent header files must have
+conditionals to include it.
+
+ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in
+the calling convention for @code{va_start}.  The traditional
+implementation takes just one argument, which is the variable in which
+to store the argument pointer.  The ISO implementation of
+@code{va_start} takes an additional second argument.  The user is
+supposed to write the last named argument of the function here.
+
+However, @code{va_start} should not use this argument.  The way to find
+the end of the named arguments is with the built-in functions described
+below.
+
+@defmac __builtin_saveregs ()
+Use this built-in function to save the argument registers in memory so
+that the varargs mechanism can access them.  Both ISO and traditional
+versions of @code{va_start} must use @code{__builtin_saveregs}, unless
+you use @code{TARGET_SETUP_INCOMING_VARARGS} (see below) instead.
+
+On some machines, @code{__builtin_saveregs} is open-coded under the
+control of the target hook @code{TARGET_EXPAND_BUILTIN_SAVEREGS}.  On
+other machines, it calls a routine written in assembler language,
+found in @file{libgcc2.c}.
+
+Code generated for the call to @code{__builtin_saveregs} appears at the
+beginning of the function, as opposed to where the call to
+@code{__builtin_saveregs} is written, regardless of what the code is.
+This is because the registers must be saved before the function starts
+to use them for its own purposes.
+@c i rewrote the first sentence above to fix an overfull hbox. --mew
+@c 10feb93
+@end defmac
+
+@defmac __builtin_next_arg (@var{lastarg})
+This builtin returns the address of the first anonymous stack
+argument, as type @code{void *}.  If @code{ARGS_GROW_DOWNWARD}, it
+returns the address of the location above the first anonymous stack
+argument.  Use it in @code{va_start} to initialize the pointer for
+fetching arguments from the stack.  Also use it in @code{va_start} to
+verify that the second parameter @var{lastarg} is the last named argument
+of the current function.
+@end defmac
+
+@defmac __builtin_classify_type (@var{object})
+Since each machine has its own conventions for which data types are
+passed in which kind of register, your implementation of @code{va_arg}
+has to embody these conventions.  The easiest way to categorize the
+specified data type is to use @code{__builtin_classify_type} together
+with @code{sizeof} and @code{__alignof__}.
+
+@code{__builtin_classify_type} ignores the value of @var{object},
+considering only its data type.  It returns an integer describing what
+kind of type that is---integer, floating, pointer, structure, and so on.
+
+The file @file{typeclass.h} defines an enumeration that you can use to
+interpret the values of @code{__builtin_classify_type}.
+@end defmac
+
+These machine description macros help implement varargs:
+
+@hook TARGET_EXPAND_BUILTIN_SAVEREGS
+If defined, this hook produces the machine-specific code for a call to
+@code{__builtin_saveregs}.  This code will be moved to the very
+beginning of the function, before any parameter access are made.  The
+return value of this function should be an RTX that contains the value
+to use as the return of @code{__builtin_saveregs}.
+@end deftypefn
+
+@hook TARGET_SETUP_INCOMING_VARARGS
+This target hook offers an alternative to using
+@code{__builtin_saveregs} and defining the hook
+@code{TARGET_EXPAND_BUILTIN_SAVEREGS}.  Use it to store the anonymous
+register arguments into the stack so that all the arguments appear to
+have been passed consecutively on the stack.  Once this is done, you can
+use the standard implementation of varargs that works for machines that
+pass all their arguments on the stack.
+
+The argument @var{args_so_far} points to the @code{CUMULATIVE_ARGS} data
+structure, containing the values that are obtained after processing the
+named arguments.  The arguments @var{mode} and @var{type} describe the
+last named argument---its machine mode and its data type as a tree node.
+
+The target hook should do two things: first, push onto the stack all the
+argument registers @emph{not} used for the named arguments, and second,
+store the size of the data thus pushed into the @code{int}-valued
+variable pointed to by @var{pretend_args_size}.  The value that you
+store here will serve as additional offset for setting up the stack
+frame.
+
+Because you must generate code to push the anonymous arguments at
+compile time without knowing their data types,
+@code{TARGET_SETUP_INCOMING_VARARGS} is only useful on machines that
+have just a single category of argument register and use it uniformly
+for all data types.
+
+If the argument @var{second_time} is nonzero, it means that the
+arguments of the function are being analyzed for the second time.  This
+happens for an inline function, which is not actually compiled until the
+end of the source file.  The hook @code{TARGET_SETUP_INCOMING_VARARGS} should
+not generate any instructions in this case.
+@end deftypefn
+
+@hook TARGET_STRICT_ARGUMENT_NAMING
+Define this hook to return @code{true} if the location where a function
+argument is passed depends on whether or not it is a named argument.
+
+This hook controls how the @var{named} argument to @code{FUNCTION_ARG}
+is set for varargs and stdarg functions.  If this hook returns
+@code{true}, the @var{named} argument is always true for named
+arguments, and false for unnamed arguments.  If it returns @code{false},
+but @code{TARGET_PRETEND_OUTGOING_VARARGS_NAMED} returns @code{true},
+then all arguments are treated as named.  Otherwise, all named arguments
+except the last are treated as named.
+
+You need not define this hook if it always returns @code{false}.
+@end deftypefn
+
+@hook TARGET_PRETEND_OUTGOING_VARARGS_NAMED
+If you need to conditionally change ABIs so that one works with
+@code{TARGET_SETUP_INCOMING_VARARGS}, but the other works like neither
+@code{TARGET_SETUP_INCOMING_VARARGS} nor @code{TARGET_STRICT_ARGUMENT_NAMING} was
+defined, then define this hook to return @code{true} if
+@code{TARGET_SETUP_INCOMING_VARARGS} is used, @code{false} otherwise.
+Otherwise, you should not define this hook.
+@end deftypefn
+
+@node Trampolines
+@section Trampolines for Nested Functions
+@cindex trampolines for nested functions
+@cindex nested functions, trampolines for
+
+A @dfn{trampoline} is a small piece of code that is created at run time
+when the address of a nested function is taken.  It normally resides on
+the stack, in the stack frame of the containing function.  These macros
+tell GCC how to generate code to allocate and initialize a
+trampoline.
+
+The instructions in the trampoline must do two things: load a constant
+address into the static chain register, and jump to the real address of
+the nested function.  On CISC machines such as the m68k, this requires
+two instructions, a move immediate and a jump.  Then the two addresses
+exist in the trampoline as word-long immediate operands.  On RISC
+machines, it is often necessary to load each address into a register in
+two parts.  Then pieces of each address form separate immediate
+operands.
+
+The code generated to initialize the trampoline must store the variable
+parts---the static chain value and the function address---into the
+immediate operands of the instructions.  On a CISC machine, this is
+simply a matter of copying each address to a memory reference at the
+proper offset from the start of the trampoline.  On a RISC machine, it
+may be necessary to take out pieces of the address and store them
+separately.
+
+@hook TARGET_ASM_TRAMPOLINE_TEMPLATE
+This hook is called by @code{assemble_trampoline_template} to output,
+on the stream @var{f}, assembler code for a block of data that contains
+the constant parts of a trampoline.  This code should not include a
+label---the label is taken care of automatically.
+
+If you do not define this hook, it means no template is needed
+for the target.  Do not define this hook on systems where the block move
+code to copy the trampoline into place would be larger than the code
+to generate it on the spot.
+@end deftypefn
+
+@defmac TRAMPOLINE_SECTION
+Return the section into which the trampoline template is to be placed
+(@pxref{Sections}).  The default value is @code{readonly_data_section}.
+@end defmac
+
+@defmac TRAMPOLINE_SIZE
+A C expression for the size in bytes of the trampoline, as an integer.
+@end defmac
+
+@defmac TRAMPOLINE_ALIGNMENT
+Alignment required for trampolines, in bits.
+
+If you don't define this macro, the value of @code{FUNCTION_ALIGNMENT}
+is used for aligning trampolines.
+@end defmac
+
+@hook TARGET_TRAMPOLINE_INIT
+This hook is called to initialize a trampoline.
+@var{m_tramp} is an RTX for the memory block for the trampoline; @var{fndecl}
+is the @code{FUNCTION_DECL} for the nested function; @var{static_chain} is an
+RTX for the static chain value that should be passed to the function
+when it is called.
+
+If the target defines @code{TARGET_ASM_TRAMPOLINE_TEMPLATE}, then the
+first thing this hook should do is emit a block move into @var{m_tramp}
+from the memory block returned by @code{assemble_trampoline_template}.
+Note that the block move need only cover the constant parts of the 
+trampoline.  If the target isolates the variable parts of the trampoline
+to the end, not all @code{TRAMPOLINE_SIZE} bytes need be copied.
+
+If the target requires any other actions, such as flushing caches or
+enabling stack execution, these actions should be performed after 
+initializing the trampoline proper.
+@end deftypefn
+
+@hook TARGET_TRAMPOLINE_ADJUST_ADDRESS
+This hook should perform any machine-specific adjustment in
+the address of the trampoline.  Its argument contains the address of the
+memory block that was passed to @code{TARGET_TRAMPOLINE_INIT}.  In case
+the address to be used for a function call should be different from the
+address at which the template was stored, the different address should
+be returned; otherwise @var{addr} should be returned unchanged.
+If this hook is not defined, @var{addr} will be used for function calls.
+@end deftypefn
+
+Implementing trampolines is difficult on many machines because they have
+separate instruction and data caches.  Writing into a stack location
+fails to clear the memory in the instruction cache, so when the program
+jumps to that location, it executes the old contents.
+
+Here are two possible solutions.  One is to clear the relevant parts of
+the instruction cache whenever a trampoline is set up.  The other is to
+make all trampolines identical, by having them jump to a standard
+subroutine.  The former technique makes trampoline execution faster; the
+latter makes initialization faster.
+
+To clear the instruction cache when a trampoline is initialized, define
+the following macro.
+
+@defmac CLEAR_INSN_CACHE (@var{beg}, @var{end})
+If defined, expands to a C expression clearing the @emph{instruction
+cache} in the specified interval.  The definition of this macro would
+typically be a series of @code{asm} statements.  Both @var{beg} and
+@var{end} are both pointer expressions.
+@end defmac
+
+The operating system may also require the stack to be made executable
+before calling the trampoline.  To implement this requirement, define
+the following macro.
+
+@defmac ENABLE_EXECUTE_STACK
+Define this macro if certain operations must be performed before executing
+code located on the stack.  The macro should expand to a series of C
+file-scope constructs (e.g.@: functions) and provide a unique entry point
+named @code{__enable_execute_stack}.  The target is responsible for
+emitting calls to the entry point in the code, for example from the
+@code{TARGET_TRAMPOLINE_INIT} hook.
+@end defmac
+
+To use a standard subroutine, define the following macro.  In addition,
+you must make sure that the instructions in a trampoline fill an entire
+cache line with identical instructions, or else ensure that the
+beginning of the trampoline code is always aligned at the same point in
+its cache line.  Look in @file{m68k.h} as a guide.
+
+@defmac TRANSFER_FROM_TRAMPOLINE
+Define this macro if trampolines need a special subroutine to do their
+work.  The macro should expand to a series of @code{asm} statements
+which will be compiled with GCC@.  They go in a library function named
+@code{__transfer_from_trampoline}.
+
+If you need to avoid executing the ordinary prologue code of a compiled
+C function when you jump to the subroutine, you can do so by placing a
+special label of your own in the assembler code.  Use one @code{asm}
+statement to generate an assembler label, and another to make the label
+global.  Then trampolines can use that label to jump directly to your
+special assembler code.
+@end defmac
+
+@node Library Calls
+@section Implicit Calls to Library Routines
+@cindex library subroutine names
+@cindex @file{libgcc.a}
+
+@c prevent bad page break with this line
+Here is an explanation of implicit calls to library routines.
+
+@defmac DECLARE_LIBRARY_RENAMES
+This macro, if defined, should expand to a piece of C code that will get
+expanded when compiling functions for libgcc.a.  It can be used to
+provide alternate names for GCC's internal library functions if there
+are ABI-mandated names that the compiler should provide.
+@end defmac
+
+@findex set_optab_libfunc
+@findex init_one_libfunc
+@hook TARGET_INIT_LIBFUNCS
+This hook should declare additional library routines or rename
+existing ones, using the functions @code{set_optab_libfunc} and
+@code{init_one_libfunc} defined in @file{optabs.c}.
+@code{init_optabs} calls this macro after initializing all the normal
+library routines.
+
+The default is to do nothing.  Most ports don't need to define this hook.
+@end deftypefn
+
+@defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison})
+This macro should return @code{true} if the library routine that
+implements the floating point comparison operator @var{comparison} in
+mode @var{mode} will return a boolean, and @var{false} if it will
+return a tristate.
+
+GCC's own floating point libraries return tristates from the
+comparison operators, so the default returns false always.  Most ports
+don't need to define this macro.
+@end defmac
+
+@defmac TARGET_LIB_INT_CMP_BIASED
+This macro should evaluate to @code{true} if the integer comparison
+functions (like @code{__cmpdi2}) return 0 to indicate that the first
+operand is smaller than the second, 1 to indicate that they are equal,
+and 2 to indicate that the first operand is greater than the second.
+If this macro evaluates to @code{false} the comparison functions return
+@minus{}1, 0, and 1 instead of 0, 1, and 2.  If the target uses the routines
+in @file{libgcc.a}, you do not need to define this macro.
+@end defmac
+
+@cindex @code{EDOM}, implicit usage
+@findex matherr
+@defmac TARGET_EDOM
+The value of @code{EDOM} on the target machine, as a C integer constant
+expression.  If you don't define this macro, GCC does not attempt to
+deposit the value of @code{EDOM} into @code{errno} directly.  Look in
+@file{/usr/include/errno.h} to find the value of @code{EDOM} on your
+system.
+
+If you do not define @code{TARGET_EDOM}, then compiled code reports
+domain errors by calling the library function and letting it report the
+error.  If mathematical functions on your system use @code{matherr} when
+there is an error, then you should leave @code{TARGET_EDOM} undefined so
+that @code{matherr} is used normally.
+@end defmac
+
+@cindex @code{errno}, implicit usage
+@defmac GEN_ERRNO_RTX
+Define this macro as a C expression to create an rtl expression that
+refers to the global ``variable'' @code{errno}.  (On certain systems,
+@code{errno} may not actually be a variable.)  If you don't define this
+macro, a reasonable default is used.
+@end defmac
+
+@cindex C99 math functions, implicit usage
+@defmac TARGET_C99_FUNCTIONS
+When this macro is nonzero, GCC will implicitly optimize @code{sin} calls into
+@code{sinf} and similarly for other functions defined by C99 standard.  The
+default is zero because a number of existing systems lack support for these
+functions in their runtime so this macro needs to be redefined to one on
+systems that do support the C99 runtime.
+@end defmac
+
+@cindex sincos math function, implicit usage
+@defmac TARGET_HAS_SINCOS
+When this macro is nonzero, GCC will implicitly optimize calls to @code{sin}
+and @code{cos} with the same argument to a call to @code{sincos}.  The
+default is zero.  The target has to provide the following functions:
+@smallexample
+void sincos(double x, double *sin, double *cos);
+void sincosf(float x, float *sin, float *cos);
+void sincosl(long double x, long double *sin, long double *cos);
+@end smallexample
+@end defmac
+
+@defmac NEXT_OBJC_RUNTIME
+Define this macro to generate code for Objective-C message sending using
+the calling convention of the NeXT system.  This calling convention
+involves passing the object, the selector and the method arguments all
+at once to the method-lookup library function.
+
+The default calling convention passes just the object and the selector
+to the lookup function, which returns a pointer to the method.
+@end defmac
+
+@node Addressing Modes
+@section Addressing Modes
+@cindex addressing modes
+
+@c prevent bad page break with this line
+This is about addressing modes.
+
+@defmac HAVE_PRE_INCREMENT
+@defmacx HAVE_PRE_DECREMENT
+@defmacx HAVE_POST_INCREMENT
+@defmacx HAVE_POST_DECREMENT
+A C expression that is nonzero if the machine supports pre-increment,
+pre-decrement, post-increment, or post-decrement addressing respectively.
+@end defmac
+
+@defmac HAVE_PRE_MODIFY_DISP
+@defmacx HAVE_POST_MODIFY_DISP
+A C expression that is nonzero if the machine supports pre- or
+post-address side-effect generation involving constants other than
+the size of the memory operand.
+@end defmac
+
+@defmac HAVE_PRE_MODIFY_REG
+@defmacx HAVE_POST_MODIFY_REG
+A C expression that is nonzero if the machine supports pre- or
+post-address side-effect generation involving a register displacement.
+@end defmac
+
+@defmac CONSTANT_ADDRESS_P (@var{x})
+A C expression that is 1 if the RTX @var{x} is a constant which
+is a valid address.  On most machines the default definition of
+@code{(CONSTANT_P (@var{x}) && GET_CODE (@var{x}) != CONST_DOUBLE)}
+is acceptable, but a few machines are more restrictive as to which
+constant addresses are supported. 
+@end defmac
+
+@defmac CONSTANT_P (@var{x})
+@code{CONSTANT_P}, which is defined by target-independent code,
+accepts integer-values expressions whose values are not explicitly
+known, such as @code{symbol_ref}, @code{label_ref}, and @code{high}
+expressions and @code{const} arithmetic expressions, in addition to
+@code{const_int} and @code{const_double} expressions.
+@end defmac
+
+@defmac MAX_REGS_PER_ADDRESS
+A number, the maximum number of registers that can appear in a valid
+memory address.  Note that it is up to you to specify a value equal to
+the maximum number that @code{TARGET_LEGITIMATE_ADDRESS_P} would ever
+accept.
+@end defmac
+
+@hook TARGET_LEGITIMATE_ADDRESS_P
+A function that returns whether @var{x} (an RTX) is a legitimate memory
+address on the target machine for a memory operand of mode @var{mode}.
+
+Legitimate addresses are defined in two variants: a strict variant and a
+non-strict one.  The @var{strict} parameter chooses which variant is
+desired by the caller.
+
+The strict variant is used in the reload pass.  It must be defined so
+that any pseudo-register that has not been allocated a hard register is
+considered a memory reference.  This is because in contexts where some
+kind of register is required, a pseudo-register with no hard register
+must be rejected.  For non-hard registers, the strict variant should look
+up the @code{reg_renumber} array; it should then proceed using the hard
+register number in the array, or treat the pseudo as a memory reference
+if the array holds @code{-1}.
+
+The non-strict variant is used in other passes.  It must be defined to
+accept all pseudo-registers in every context where some kind of
+register is required.
+
+Normally, constant addresses which are the sum of a @code{symbol_ref}
+and an integer are stored inside a @code{const} RTX to mark them as
+constant.  Therefore, there is no need to recognize such sums
+specifically as legitimate addresses.  Normally you would simply
+recognize any @code{const} as legitimate.
+
+Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant
+sums that are not marked with  @code{const}.  It assumes that a naked
+@code{plus} indicates indexing.  If so, then you @emph{must} reject such
+naked constant sums as illegitimate addresses, so that none of them will
+be given to @code{PRINT_OPERAND_ADDRESS}.
+
+@cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation
+On some machines, whether a symbolic address is legitimate depends on
+the section that the address refers to.  On these machines, define the
+target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information
+into the @code{symbol_ref}, and then check for it here.  When you see a
+@code{const}, you will have to look inside it to find the
+@code{symbol_ref} in order to determine the section.  @xref{Assembler
+Format}.
+
+@cindex @code{GO_IF_LEGITIMATE_ADDRESS}
+Some ports are still using a deprecated legacy substitute for
+this hook, the @code{GO_IF_LEGITIMATE_ADDRESS} macro.  This macro
+has this syntax:
+
+@example
+#define GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label})
+@end example
+
+@noindent
+and should @code{goto @var{label}} if the address @var{x} is a valid
+address on the target machine for a memory operand of mode @var{mode}.
+
+@findex REG_OK_STRICT
+Compiler source files that want to use the strict variant of this
+macro define the macro @code{REG_OK_STRICT}.  You should use an
+@code{#ifdef REG_OK_STRICT} conditional to define the strict variant in
+that case and the non-strict variant otherwise.
+
+Using the hook is usually simpler because it limits the number of
+files that are recompiled when changes are made.
+@end deftypefn
+
+@defmac TARGET_MEM_CONSTRAINT
+A single character to be used instead of the default @code{'m'}
+character for general memory addresses.  This defines the constraint
+letter which matches the memory addresses accepted by
+@code{TARGET_LEGITIMATE_ADDRESS_P}.  Define this macro if you want to
+support new address formats in your back end without changing the
+semantics of the @code{'m'} constraint.  This is necessary in order to
+preserve functionality of inline assembly constructs using the
+@code{'m'} constraint.
+@end defmac
+
+@defmac FIND_BASE_TERM (@var{x})
+A C expression to determine the base term of address @var{x},
+or to provide a simplified version of @var{x} from which @file{alias.c}
+can easily find the base term.  This macro is used in only two places:
+@code{find_base_value} and @code{find_base_term} in @file{alias.c}.
+
+It is always safe for this macro to not be defined.  It exists so
+that alias analysis can understand machine-dependent addresses.
+
+The typical use of this macro is to handle addresses containing
+a label_ref or symbol_ref within an UNSPEC@.
+@end defmac
+
+@hook TARGET_LEGITIMIZE_ADDRESS
+This hook is given an invalid memory address @var{x} for an
+operand of mode @var{mode} and should try to return a valid memory
+address.
+
+@findex break_out_memory_refs
+@var{x} will always be the result of a call to @code{break_out_memory_refs},
+and @var{oldx} will be the operand that was given to that function to produce
+@var{x}.
+
+The code of the hook should not alter the substructure of
+@var{x}.  If it transforms @var{x} into a more legitimate form, it
+should return the new @var{x}.
+
+It is not necessary for this hook to come up with a legitimate address.
+The compiler has standard ways of doing so in all cases.  In fact, it
+is safe to omit this hook or make it return @var{x} if it cannot find
+a valid way to legitimize the address.  But often a machine-dependent
+strategy can generate better code.
+@end deftypefn
+
+@defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win})
+A C compound statement that attempts to replace @var{x}, which is an address
+that needs reloading, with a valid memory address for an operand of mode
+@var{mode}.  @var{win} will be a C statement label elsewhere in the code.
+It is not necessary to define this macro, but it might be useful for
+performance reasons.
+
+For example, on the i386, it is sometimes possible to use a single
+reload register instead of two by reloading a sum of two pseudo
+registers into a register.  On the other hand, for number of RISC
+processors offsets are limited so that often an intermediate address
+needs to be generated in order to address a stack slot.  By defining
+@code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses
+generated for adjacent some stack slots can be made identical, and thus
+be shared.
+
+@emph{Note}: This macro should be used with caution.  It is necessary
+to know something of how reload works in order to effectively use this,
+and it is quite easy to produce macros that build in too much knowledge
+of reload internals.
+
+@emph{Note}: This macro must be able to reload an address created by a
+previous invocation of this macro.  If it fails to handle such addresses
+then the compiler may generate incorrect code or abort.
+
+@findex push_reload
+The macro definition should use @code{push_reload} to indicate parts that
+need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually
+suitable to be passed unaltered to @code{push_reload}.
+
+The code generated by this macro must not alter the substructure of
+@var{x}.  If it transforms @var{x} into a more legitimate form, it
+should assign @var{x} (which will always be a C variable) a new value.
+This also applies to parts that you change indirectly by calling
+@code{push_reload}.
+
+@findex strict_memory_address_p
+The macro definition may use @code{strict_memory_address_p} to test if
+the address has become legitimate.
+
+@findex copy_rtx
+If you want to change only a part of @var{x}, one standard way of doing
+this is to use @code{copy_rtx}.  Note, however, that it unshares only a
+single level of rtl.  Thus, if the part to be changed is not at the
+top level, you'll need to replace first the top level.
+It is not necessary for this macro to come up with a legitimate
+address;  but often a machine-dependent strategy can generate better code.
+@end defmac
+
+@hook TARGET_MODE_DEPENDENT_ADDRESS_P
+This hook returns @code{true} if memory address @var{addr} can have
+different meanings depending on the machine mode of the memory
+reference it is used for or if the address is valid for some modes
+but not others.
+
+Autoincrement and autodecrement addresses typically have mode-dependent
+effects because the amount of the increment or decrement is the size
+of the operand being addressed.  Some machines have other mode-dependent
+addresses.  Many RISC machines have no mode-dependent addresses.
+
+You may assume that @var{addr} is a valid address for the machine.
+
+The default version of this hook returns @code{false}.
+@end deftypefn
+
+@defmac GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label})
+A C statement or compound statement with a conditional @code{goto
+@var{label};} executed if memory address @var{x} (an RTX) can have
+different meanings depending on the machine mode of the memory
+reference it is used for or if the address is valid for some modes
+but not others.
+
+Autoincrement and autodecrement addresses typically have mode-dependent
+effects because the amount of the increment or decrement is the size
+of the operand being addressed.  Some machines have other mode-dependent
+addresses.  Many RISC machines have no mode-dependent addresses.
+
+You may assume that @var{addr} is a valid address for the machine.
+
+These are obsolete macros, replaced by the
+@code{TARGET_MODE_DEPENDENT_ADDRESS_P} target hook.
+@end defmac
+
+@defmac LEGITIMATE_CONSTANT_P (@var{x})
+A C expression that is nonzero if @var{x} is a legitimate constant for
+an immediate operand on the target machine.  You can assume that
+@var{x} satisfies @code{CONSTANT_P}, so you need not check this.  In fact,
+@samp{1} is a suitable definition for this macro on machines where
+anything @code{CONSTANT_P} is valid.
+@end defmac
+
+@hook TARGET_DELEGITIMIZE_ADDRESS
+This hook is used to undo the possibly obfuscating effects of the
+@code{LEGITIMIZE_ADDRESS} and @code{LEGITIMIZE_RELOAD_ADDRESS} target
+macros.  Some backend implementations of these macros wrap symbol
+references inside an @code{UNSPEC} rtx to represent PIC or similar
+addressing modes.  This target hook allows GCC's optimizers to understand
+the semantics of these opaque @code{UNSPEC}s by converting them back
+into their original form.
+@end deftypefn
+
+@hook TARGET_CANNOT_FORCE_CONST_MEM
+This hook should return true if @var{x} is of a form that cannot (or
+should not) be spilled to the constant pool.  The default version of
+this hook returns false.
+
+The primary reason to define this hook is to prevent reload from
+deciding that a non-legitimate constant would be better reloaded
+from the constant pool instead of spilling and reloading a register
+holding the constant.  This restriction is often true of addresses
+of TLS symbols for various targets.
+@end deftypefn
+
+@hook TARGET_USE_BLOCKS_FOR_CONSTANT_P
+This hook should return true if pool entries for constant @var{x} can
+be placed in an @code{object_block} structure.  @var{mode} is the mode
+of @var{x}.
+
+The default version returns false for all constants.
+@end deftypefn
+
+@hook TARGET_BUILTIN_RECIPROCAL
+This hook should return the DECL of a function that implements reciprocal of
+the builtin function with builtin function code @var{fn}, or
+@code{NULL_TREE} if such a function is not available.  @var{md_fn} is true
+when @var{fn} is a code of a machine-dependent builtin function.  When
+@var{sqrt} is true, additional optimizations that apply only to the reciprocal
+of a square root function are performed, and only reciprocals of @code{sqrt}
+function are valid.
+@end deftypefn
+
+@hook TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD
+This hook should return the DECL of a function @var{f} that given an
+address @var{addr} as an argument returns a mask @var{m} that can be
+used to extract from two vectors the relevant data that resides in
+@var{addr} in case @var{addr} is not properly aligned.
+
+The autovectorizer, when vectorizing a load operation from an address
+@var{addr} that may be unaligned, will generate two vector loads from
+the two aligned addresses around @var{addr}. It then generates a
+@code{REALIGN_LOAD} operation to extract the relevant data from the
+two loaded vectors. The first two arguments to @code{REALIGN_LOAD},
+@var{v1} and @var{v2}, are the two vectors, each of size @var{VS}, and
+the third argument, @var{OFF}, defines how the data will be extracted
+from these two vectors: if @var{OFF} is 0, then the returned vector is
+@var{v2}; otherwise, the returned vector is composed from the last
+@var{VS}-@var{OFF} elements of @var{v1} concatenated to the first
+@var{OFF} elements of @var{v2}.
+
+If this hook is defined, the autovectorizer will generate a call
+to @var{f} (using the DECL tree that this hook returns) and will
+use the return value of @var{f} as the argument @var{OFF} to
+@code{REALIGN_LOAD}. Therefore, the mask @var{m} returned by @var{f}
+should comply with the semantics expected by @code{REALIGN_LOAD}
+described above.
+If this hook is not defined, then @var{addr} will be used as
+the argument @var{OFF} to @code{REALIGN_LOAD}, in which case the low
+log2(@var{VS}) @minus{} 1 bits of @var{addr} will be considered.
+@end deftypefn
+
+@hook TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_EVEN
+This hook should return the DECL of a function @var{f} that implements
+widening multiplication of the even elements of two input vectors of type @var{x}.
+
+If this hook is defined, the autovectorizer will use it along with the
+@code{TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_ODD} target hook when vectorizing
+widening multiplication in cases that the order of the results does not have to be
+preserved (e.g.@: used only by a reduction computation). Otherwise, the
+@code{widen_mult_hi/lo} idioms will be used.
+@end deftypefn
+
+@hook TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_ODD
+This hook should return the DECL of a function @var{f} that implements
+widening multiplication of the odd elements of two input vectors of type @var{x}.
+
+If this hook is defined, the autovectorizer will use it along with the
+@code{TARGET_VECTORIZE_BUILTIN_MUL_WIDEN_EVEN} target hook when vectorizing
+widening multiplication in cases that the order of the results does not have to be
+preserved (e.g.@: used only by a reduction computation). Otherwise, the
+@code{widen_mult_hi/lo} idioms will be used.
+@end deftypefn
+
+@hook TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST
+Returns cost of different scalar or vector statements for vectorization cost model.
+For vector memory operations the cost may depend on type (@var{vectype}) and 
+misalignment value (@var{misalign}).
+@end deftypefn
+
+@hook TARGET_VECTORIZE_VECTOR_ALIGNMENT_REACHABLE
+Return true if vector alignment is reachable (by peeling N iterations) for the given type.
+@end deftypefn
+
+@hook TARGET_VECTORIZE_BUILTIN_VEC_PERM
+Target builtin that implements vector permute.
+@end deftypefn
+
+@hook TARGET_VECTORIZE_BUILTIN_VEC_PERM_OK
+Return true if a vector created for @code{builtin_vec_perm} is valid.
+@end deftypefn
+
+@hook TARGET_VECTORIZE_BUILTIN_CONVERSION
+This hook should return the DECL of a function that implements conversion of the
+input vector of type @var{src_type} to type @var{dest_type}.
+The value of @var{code} is one of the enumerators in @code{enum tree_code} and
+specifies how the conversion is to be applied
+(truncation, rounding, etc.).
+
+If this hook is defined, the autovectorizer will use the
+@code{TARGET_VECTORIZE_BUILTIN_CONVERSION} target hook when vectorizing
+conversion. Otherwise, it will return @code{NULL_TREE}.
+@end deftypefn
+
+@hook TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION
+This hook should return the decl of a function that implements the
+vectorized variant of the builtin function with builtin function code
+@var{code} or @code{NULL_TREE} if such a function is not available.
+The value of @var{fndecl} is the builtin function declaration.  The
+return type of the vectorized function shall be of vector type
+@var{vec_type_out} and the argument types should be @var{vec_type_in}.
+@end deftypefn
+
+@hook TARGET_VECTORIZE_SUPPORT_VECTOR_MISALIGNMENT
+This hook should return true if the target supports misaligned vector
+store/load of a specific factor denoted in the @var{misalignment}
+parameter.  The vector store/load should be of machine mode @var{mode} and
+the elements in the vectors should be of type @var{type}.  @var{is_packed}
+parameter is true if the memory access is defined in a packed struct.
+@end deftypefn
+
+@hook TARGET_VECTORIZE_PREFERRED_SIMD_MODE
+This hook should return the preferred mode for vectorizing scalar
+mode @var{mode}.  The default is
+equal to @code{word_mode}, because the vectorizer can do some
+transformations even in absence of specialized @acronym{SIMD} hardware.
+@end deftypefn
+
+@hook TARGET_VECTORIZE_AUTOVECTORIZE_VECTOR_SIZES
+This hook should return a mask of sizes that should be iterated over
+after trying to autovectorize using the vector size derived from the
+mode returned by @code{TARGET_VECTORIZE_PREFERRED_SIMD_MODE}.
+The default is zero which means to not iterate over other vector sizes.
+@end deftypefn
+
+@node Anchored Addresses
+@section Anchored Addresses
+@cindex anchored addresses
+@cindex @option{-fsection-anchors}
+
+GCC usually addresses every static object as a separate entity.
+For example, if we have:
+
+@smallexample
+static int a, b, c;
+int foo (void) @{ return a + b + c; @}
+@end smallexample
+
+the code for @code{foo} will usually calculate three separate symbolic
+addresses: those of @code{a}, @code{b} and @code{c}.  On some targets,
+it would be better to calculate just one symbolic address and access
+the three variables relative to it.  The equivalent pseudocode would
+be something like:
+
+@smallexample
+int foo (void)
+@{
+  register int *xr = &x;
+  return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
+@}
+@end smallexample
+
+(which isn't valid C).  We refer to shared addresses like @code{x} as
+``section anchors''.  Their use is controlled by @option{-fsection-anchors}.
+
+The hooks below describe the target properties that GCC needs to know
+in order to make effective use of section anchors.  It won't use
+section anchors at all unless either @code{TARGET_MIN_ANCHOR_OFFSET}
+or @code{TARGET_MAX_ANCHOR_OFFSET} is set to a nonzero value.
+
+@hook TARGET_MIN_ANCHOR_OFFSET
+The minimum offset that should be applied to a section anchor.
+On most targets, it should be the smallest offset that can be
+applied to a base register while still giving a legitimate address
+for every mode.  The default value is 0.
+@end deftypevr
+
+@hook TARGET_MAX_ANCHOR_OFFSET
+Like @code{TARGET_MIN_ANCHOR_OFFSET}, but the maximum (inclusive)
+offset that should be applied to section anchors.  The default
+value is 0.
+@end deftypevr
+
+@hook TARGET_ASM_OUTPUT_ANCHOR
+Write the assembly code to define section anchor @var{x}, which is a
+@code{SYMBOL_REF} for which @samp{SYMBOL_REF_ANCHOR_P (@var{x})} is true.
+The hook is called with the assembly output position set to the beginning
+of @code{SYMBOL_REF_BLOCK (@var{x})}.
+
+If @code{ASM_OUTPUT_DEF} is available, the hook's default definition uses
+it to define the symbol as @samp{. + SYMBOL_REF_BLOCK_OFFSET (@var{x})}.
+If @code{ASM_OUTPUT_DEF} is not available, the hook's default definition
+is @code{NULL}, which disables the use of section anchors altogether.
+@end deftypefn
+
+@hook TARGET_USE_ANCHORS_FOR_SYMBOL_P
+Return true if GCC should attempt to use anchors to access @code{SYMBOL_REF}
+@var{x}.  You can assume @samp{SYMBOL_REF_HAS_BLOCK_INFO_P (@var{x})} and
+@samp{!SYMBOL_REF_ANCHOR_P (@var{x})}.
+
+The default version is correct for most targets, but you might need to
+intercept this hook to handle things like target-specific attributes
+or target-specific sections.
+@end deftypefn
+
+@node Condition Code
+@section Condition Code Status
+@cindex condition code status
+
+The macros in this section can be split in two families, according to the
+two ways of representing condition codes in GCC.
+
+The first representation is the so called @code{(cc0)} representation
+(@pxref{Jump Patterns}), where all instructions can have an implicit
+clobber of the condition codes.  The second is the condition code
+register representation, which provides better schedulability for
+architectures that do have a condition code register, but on which
+most instructions do not affect it.  The latter category includes
+most RISC machines.
+
+The implicit clobbering poses a strong restriction on the placement of
+the definition and use of the condition code, which need to be in adjacent
+insns for machines using @code{(cc0)}.  This can prevent important
+optimizations on some machines.  For example, on the IBM RS/6000, there
+is a delay for taken branches unless the condition code register is set
+three instructions earlier than the conditional branch.  The instruction
+scheduler cannot perform this optimization if it is not permitted to
+separate the definition and use of the condition code register.
+
+For this reason, it is possible and suggested to use a register to
+represent the condition code for new ports.  If there is a specific
+condition code register in the machine, use a hard register.  If the
+condition code or comparison result can be placed in any general register,
+or if there are multiple condition registers, use a pseudo register.
+Registers used to store the condition code value will usually have a mode
+that is in class @code{MODE_CC}.
+
+Alternatively, you can use @code{BImode} if the comparison operator is
+specified already in the compare instruction.  In this case, you are not
+interested in most macros in this section.
+
+@menu
+* CC0 Condition Codes::      Old style representation of condition codes.
+* MODE_CC Condition Codes::  Modern representation of condition codes.
+* Cond Exec Macros::         Macros to control conditional execution.
+@end menu
+
+@node CC0 Condition Codes
+@subsection Representation of condition codes using @code{(cc0)}
+@findex cc0
+
+@findex cc_status
+The file @file{conditions.h} defines a variable @code{cc_status} to
+describe how the condition code was computed (in case the interpretation of
+the condition code depends on the instruction that it was set by).  This
+variable contains the RTL expressions on which the condition code is
+currently based, and several standard flags.
+
+Sometimes additional machine-specific flags must be defined in the machine
+description header file.  It can also add additional machine-specific
+information by defining @code{CC_STATUS_MDEP}.
+
+@defmac CC_STATUS_MDEP
+C code for a data type which is used for declaring the @code{mdep}
+component of @code{cc_status}.  It defaults to @code{int}.
+
+This macro is not used on machines that do not use @code{cc0}.
+@end defmac
+
+@defmac CC_STATUS_MDEP_INIT
+A C expression to initialize the @code{mdep} field to ``empty''.
+The default definition does nothing, since most machines don't use
+the field anyway.  If you want to use the field, you should probably
+define this macro to initialize it.
+
+This macro is not used on machines that do not use @code{cc0}.
+@end defmac
+
+@defmac NOTICE_UPDATE_CC (@var{exp}, @var{insn})
+A C compound statement to set the components of @code{cc_status}
+appropriately for an insn @var{insn} whose body is @var{exp}.  It is
+this macro's responsibility to recognize insns that set the condition
+code as a byproduct of other activity as well as those that explicitly
+set @code{(cc0)}.
+
+This macro is not used on machines that do not use @code{cc0}.
+
+If there are insns that do not set the condition code but do alter
+other machine registers, this macro must check to see whether they
+invalidate the expressions that the condition code is recorded as
+reflecting.  For example, on the 68000, insns that store in address
+registers do not set the condition code, which means that usually
+@code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such
+insns.  But suppose that the previous insn set the condition code
+based on location @samp{a4@@(102)} and the current insn stores a new
+value in @samp{a4}.  Although the condition code is not changed by
+this, it will no longer be true that it reflects the contents of
+@samp{a4@@(102)}.  Therefore, @code{NOTICE_UPDATE_CC} must alter
+@code{cc_status} in this case to say that nothing is known about the
+condition code value.
+
+The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal
+with the results of peephole optimization: insns whose patterns are
+@code{parallel} RTXs containing various @code{reg}, @code{mem} or
+constants which are just the operands.  The RTL structure of these
+insns is not sufficient to indicate what the insns actually do.  What
+@code{NOTICE_UPDATE_CC} should do when it sees one is just to run
+@code{CC_STATUS_INIT}.
+
+A possible definition of @code{NOTICE_UPDATE_CC} is to call a function
+that looks at an attribute (@pxref{Insn Attributes}) named, for example,
+@samp{cc}.  This avoids having detailed information about patterns in
+two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}.
+@end defmac
+
+@node MODE_CC Condition Codes
+@subsection Representation of condition codes using registers
+@findex CCmode
+@findex MODE_CC
+
+@defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y})
+On many machines, the condition code may be produced by other instructions
+than compares, for example the branch can use directly the condition
+code set by a subtract instruction.  However, on some machines
+when the condition code is set this way some bits (such as the overflow
+bit) are not set in the same way as a test instruction, so that a different
+branch instruction must be used for some conditional branches.  When
+this happens, use the machine mode of the condition code register to
+record different formats of the condition code register.  Modes can
+also be used to record which compare instruction (e.g. a signed or an
+unsigned comparison) produced the condition codes.
+
+If other modes than @code{CCmode} are required, add them to
+@file{@var{machine}-modes.def} and define @code{SELECT_CC_MODE} to choose
+a mode given an operand of a compare.  This is needed because the modes
+have to be chosen not only during RTL generation but also, for example,
+by instruction combination.  The result of @code{SELECT_CC_MODE} should
+be consistent with the mode used in the patterns; for example to support
+the case of the add on the SPARC discussed above, we have the pattern
+
+@smallexample
+(define_insn ""
+  [(set (reg:CC_NOOV 0)
+        (compare:CC_NOOV
+          (plus:SI (match_operand:SI 0 "register_operand" "%r")
+                   (match_operand:SI 1 "arith_operand" "rI"))
+          (const_int 0)))]
+  ""
+  "@dots{}")
+@end smallexample
+
+@noindent
+together with a @code{SELECT_CC_MODE} that returns @code{CC_NOOVmode}
+for comparisons whose argument is a @code{plus}:
+
+@smallexample
+#define SELECT_CC_MODE(OP,X,Y) \
+  (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT          \
+   ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode)    \
+   : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS    \
+       || GET_CODE (X) == NEG) \
+      ? CC_NOOVmode : CCmode))
+@end smallexample
+
+Another reason to use modes is to retain information on which operands
+were used by the comparison; see @code{REVERSIBLE_CC_MODE} later in
+this section.
+
+You should define this macro if and only if you define extra CC modes
+in @file{@var{machine}-modes.def}.
+@end defmac
+
+@defmac CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1})
+On some machines not all possible comparisons are defined, but you can
+convert an invalid comparison into a valid one.  For example, the Alpha
+does not have a @code{GT} comparison, but you can use an @code{LT}
+comparison instead and swap the order of the operands.
+
+On such machines, define this macro to be a C statement to do any
+required conversions.  @var{code} is the initial comparison code
+and @var{op0} and @var{op1} are the left and right operands of the
+comparison, respectively.  You should modify @var{code}, @var{op0}, and
+@var{op1} as required.
+
+GCC will not assume that the comparison resulting from this macro is
+valid but will see if the resulting insn matches a pattern in the
+@file{md} file.
+
+You need not define this macro if it would never change the comparison
+code or operands.
+@end defmac
+
+@defmac REVERSIBLE_CC_MODE (@var{mode})
+A C expression whose value is one if it is always safe to reverse a
+comparison whose mode is @var{mode}.  If @code{SELECT_CC_MODE}
+can ever return @var{mode} for a floating-point inequality comparison,
+then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero.
+
+You need not define this macro if it would always returns zero or if the
+floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}.
+For example, here is the definition used on the SPARC, where floating-point
+inequality comparisons are always given @code{CCFPEmode}:
+
+@smallexample
+#define REVERSIBLE_CC_MODE(MODE)  ((MODE) != CCFPEmode)
+@end smallexample
+@end defmac
+
+@defmac REVERSE_CONDITION (@var{code}, @var{mode})
+A C expression whose value is reversed condition code of the @var{code} for
+comparison done in CC_MODE @var{mode}.  The macro is used only in case
+@code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero.  Define this macro in case
+machine has some non-standard way how to reverse certain conditionals.  For
+instance in case all floating point conditions are non-trapping, compiler may
+freely convert unordered compares to ordered one.  Then definition may look
+like:
+
+@smallexample
+#define REVERSE_CONDITION(CODE, MODE) \
+   ((MODE) != CCFPmode ? reverse_condition (CODE) \
+    : reverse_condition_maybe_unordered (CODE))
+@end smallexample
+@end defmac
+
+@hook TARGET_FIXED_CONDITION_CODE_REGS
+On targets which do not use @code{(cc0)}, and which use a hard
+register rather than a pseudo-register to hold condition codes, the
+regular CSE passes are often not able to identify cases in which the
+hard register is set to a common value.  Use this hook to enable a
+small pass which optimizes such cases.  This hook should return true
+to enable this pass, and it should set the integers to which its
+arguments point to the hard register numbers used for condition codes.
+When there is only one such register, as is true on most systems, the
+integer pointed to by @var{p2} should be set to
+@code{INVALID_REGNUM}.
+
+The default version of this hook returns false.
+@end deftypefn
+
+@hook TARGET_CC_MODES_COMPATIBLE
+On targets which use multiple condition code modes in class
+@code{MODE_CC}, it is sometimes the case that a comparison can be
+validly done in more than one mode.  On such a system, define this
+target hook to take two mode arguments and to return a mode in which
+both comparisons may be validly done.  If there is no such mode,
+return @code{VOIDmode}.
+
+The default version of this hook checks whether the modes are the
+same.  If they are, it returns that mode.  If they are different, it
+returns @code{VOIDmode}.
+@end deftypefn
+
+@node Cond Exec Macros
+@subsection Macros to control conditional execution
+@findex conditional execution
+@findex predication
+
+There is one macro that may need to be defined for targets
+supporting conditional execution, independent of how they
+represent conditional branches.
+
+@defmac REVERSE_CONDEXEC_PREDICATES_P (@var{op1}, @var{op2})
+A C expression that returns true if the conditional execution predicate
+@var{op1}, a comparison operation, is the inverse of @var{op2} and vice
+versa.  Define this to return 0 if the target has conditional execution
+predicates that cannot be reversed safely.  There is no need to validate
+that the arguments of op1 and op2 are the same, this is done separately.
+If no expansion is specified, this macro is defined as follows:
+
+@smallexample
+#define REVERSE_CONDEXEC_PREDICATES_P (x, y) \
+   (GET_CODE ((x)) == reversed_comparison_code ((y), NULL))
+@end smallexample
+@end defmac
+
+@node Costs
+@section Describing Relative Costs of Operations
+@cindex costs of instructions
+@cindex relative costs
+@cindex speed of instructions
+
+These macros let you describe the relative speed of various operations
+on the target machine.
+
+@defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to})
+A C expression for the cost of moving data of mode @var{mode} from a
+register in class @var{from} to one in class @var{to}.  The classes are
+expressed using the enumeration values such as @code{GENERAL_REGS}.  A
+value of 2 is the default; other values are interpreted relative to
+that.
+
+It is not required that the cost always equal 2 when @var{from} is the
+same as @var{to}; on some machines it is expensive to move between
+registers if they are not general registers.
+
+If reload sees an insn consisting of a single @code{set} between two
+hard registers, and if @code{REGISTER_MOVE_COST} applied to their
+classes returns a value of 2, reload does not check to ensure that the
+constraints of the insn are met.  Setting a cost of other than 2 will
+allow reload to verify that the constraints are met.  You should do this
+if the @samp{mov@var{m}} pattern's constraints do not allow such copying.
+
+These macros are obsolete, new ports should use the target hook
+@code{TARGET_REGISTER_MOVE_COST} instead.
+@end defmac
+
+@hook TARGET_REGISTER_MOVE_COST
+This target hook should return the cost of moving data of mode @var{mode}
+from a register in class @var{from} to one in class @var{to}.  The classes
+are expressed using the enumeration values such as @code{GENERAL_REGS}.
+A value of 2 is the default; other values are interpreted relative to
+that.
+
+It is not required that the cost always equal 2 when @var{from} is the
+same as @var{to}; on some machines it is expensive to move between
+registers if they are not general registers.
+
+If reload sees an insn consisting of a single @code{set} between two
+hard registers, and if @code{TARGET_REGISTER_MOVE_COST} applied to their
+classes returns a value of 2, reload does not check to ensure that the
+constraints of the insn are met.  Setting a cost of other than 2 will
+allow reload to verify that the constraints are met.  You should do this
+if the @samp{mov@var{m}} pattern's constraints do not allow such copying.
+
+The default version of this function returns 2.
+@end deftypefn
+
+@defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in})
+A C expression for the cost of moving data of mode @var{mode} between a
+register of class @var{class} and memory; @var{in} is zero if the value
+is to be written to memory, nonzero if it is to be read in.  This cost
+is relative to those in @code{REGISTER_MOVE_COST}.  If moving between
+registers and memory is more expensive than between two registers, you
+should define this macro to express the relative cost.
+
+If you do not define this macro, GCC uses a default cost of 4 plus
+the cost of copying via a secondary reload register, if one is
+needed.  If your machine requires a secondary reload register to copy
+between memory and a register of @var{class} but the reload mechanism is
+more complex than copying via an intermediate, define this macro to
+reflect the actual cost of the move.
+
+GCC defines the function @code{memory_move_secondary_cost} if
+secondary reloads are needed.  It computes the costs due to copying via
+a secondary register.  If your machine copies from memory using a
+secondary register in the conventional way but the default base value of
+4 is not correct for your machine, define this macro to add some other
+value to the result of that function.  The arguments to that function
+are the same as to this macro.
+
+These macros are obsolete, new ports should use the target hook
+@code{TARGET_MEMORY_MOVE_COST} instead.
+@end defmac
+
+@hook TARGET_MEMORY_MOVE_COST
+This target hook should return the cost of moving data of mode @var{mode}
+between a register of class @var{rclass} and memory; @var{in} is @code{false}
+if the value is to be written to memory, @code{true} if it is to be read in.
+This cost is relative to those in @code{TARGET_REGISTER_MOVE_COST}.
+If moving between registers and memory is more expensive than between two
+registers, you should add this target hook to express the relative cost.
+
+If you do not add this target hook, GCC uses a default cost of 4 plus
+the cost of copying via a secondary reload register, if one is
+needed.  If your machine requires a secondary reload register to copy
+between memory and a register of @var{rclass} but the reload mechanism is
+more complex than copying via an intermediate, use this target hook to
+reflect the actual cost of the move.
+
+GCC defines the function @code{memory_move_secondary_cost} if
+secondary reloads are needed.  It computes the costs due to copying via
+a secondary register.  If your machine copies from memory using a
+secondary register in the conventional way but the default base value of
+4 is not correct for your machine, use this target hook to add some other
+value to the result of that function.  The arguments to that function
+are the same as to this target hook.
+@end deftypefn
+
+@defmac BRANCH_COST (@var{speed_p}, @var{predictable_p})
+A C expression for the cost of a branch instruction.  A value of 1 is
+the default; other values are interpreted relative to that. Parameter
+@var{speed_p} is true when the branch in question should be optimized
+for speed.  When it is false, @code{BRANCH_COST} should return a value
+optimal for code size rather than performance.  @var{predictable_p} is
+true for well-predicted branches. On many architectures the
+@code{BRANCH_COST} can be reduced then.
+@end defmac
+
+Here are additional macros which do not specify precise relative costs,
+but only that certain actions are more expensive than GCC would
+ordinarily expect.
+
+@defmac SLOW_BYTE_ACCESS
+Define this macro as a C expression which is nonzero if accessing less
+than a word of memory (i.e.@: a @code{char} or a @code{short}) is no
+faster than accessing a word of memory, i.e., if such access
+require more than one instruction or if there is no difference in cost
+between byte and (aligned) word loads.
+
+When this macro is not defined, the compiler will access a field by
+finding the smallest containing object; when it is defined, a fullword
+load will be used if alignment permits.  Unless bytes accesses are
+faster than word accesses, using word accesses is preferable since it
+may eliminate subsequent memory access if subsequent accesses occur to
+other fields in the same word of the structure, but to different bytes.
+@end defmac
+
+@defmac SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment})
+Define this macro to be the value 1 if memory accesses described by the
+@var{mode} and @var{alignment} parameters have a cost many times greater
+than aligned accesses, for example if they are emulated in a trap
+handler.
+
+When this macro is nonzero, the compiler will act as if
+@code{STRICT_ALIGNMENT} were nonzero when generating code for block
+moves.  This can cause significantly more instructions to be produced.
+Therefore, do not set this macro nonzero if unaligned accesses only add a
+cycle or two to the time for a memory access.
+
+If the value of this macro is always zero, it need not be defined.  If
+this macro is defined, it should produce a nonzero value when
+@code{STRICT_ALIGNMENT} is nonzero.
+@end defmac
+
+@defmac MOVE_RATIO (@var{speed})
+The threshold of number of scalar memory-to-memory move insns, @emph{below}
+which a sequence of insns should be generated instead of a
+string move insn or a library call.  Increasing the value will always
+make code faster, but eventually incurs high cost in increased code size.
+
+Note that on machines where the corresponding move insn is a
+@code{define_expand} that emits a sequence of insns, this macro counts
+the number of such sequences.
+
+The parameter @var{speed} is true if the code is currently being
+optimized for speed rather than size.
+
+If you don't define this, a reasonable default is used.
+@end defmac
+
+@defmac MOVE_BY_PIECES_P (@var{size}, @var{alignment})
+A C expression used to determine whether @code{move_by_pieces} will be used to
+copy a chunk of memory, or whether some other block move mechanism
+will be used.  Defaults to 1 if @code{move_by_pieces_ninsns} returns less
+than @code{MOVE_RATIO}.
+@end defmac
+
+@defmac MOVE_MAX_PIECES
+A C expression used by @code{move_by_pieces} to determine the largest unit
+a load or store used to copy memory is.  Defaults to @code{MOVE_MAX}.
+@end defmac
+
+@defmac CLEAR_RATIO (@var{speed})
+The threshold of number of scalar move insns, @emph{below} which a sequence
+of insns should be generated to clear memory instead of a string clear insn
+or a library call.  Increasing the value will always make code faster, but
+eventually incurs high cost in increased code size.
+
+The parameter @var{speed} is true if the code is currently being
+optimized for speed rather than size.
+
+If you don't define this, a reasonable default is used.
+@end defmac
+
+@defmac CLEAR_BY_PIECES_P (@var{size}, @var{alignment})
+A C expression used to determine whether @code{clear_by_pieces} will be used
+to clear a chunk of memory, or whether some other block clear mechanism
+will be used.  Defaults to 1 if @code{move_by_pieces_ninsns} returns less
+than @code{CLEAR_RATIO}.
+@end defmac
+
+@defmac SET_RATIO (@var{speed})
+The threshold of number of scalar move insns, @emph{below} which a sequence
+of insns should be generated to set memory to a constant value, instead of
+a block set insn or a library call.  
+Increasing the value will always make code faster, but
+eventually incurs high cost in increased code size.
+
+The parameter @var{speed} is true if the code is currently being
+optimized for speed rather than size.
+
+If you don't define this, it defaults to the value of @code{MOVE_RATIO}.
+@end defmac
+
+@defmac SET_BY_PIECES_P (@var{size}, @var{alignment})
+A C expression used to determine whether @code{store_by_pieces} will be
+used to set a chunk of memory to a constant value, or whether some 
+other mechanism will be used.  Used by @code{__builtin_memset} when 
+storing values other than constant zero.
+Defaults to 1 if @code{move_by_pieces_ninsns} returns less
+than @code{SET_RATIO}.
+@end defmac
+
+@defmac STORE_BY_PIECES_P (@var{size}, @var{alignment})
+A C expression used to determine whether @code{store_by_pieces} will be
+used to set a chunk of memory to a constant string value, or whether some
+other mechanism will be used.  Used by @code{__builtin_strcpy} when
+called with a constant source string.
+Defaults to 1 if @code{move_by_pieces_ninsns} returns less
+than @code{MOVE_RATIO}.
+@end defmac
+
+@defmac USE_LOAD_POST_INCREMENT (@var{mode})
+A C expression used to determine whether a load postincrement is a good
+thing to use for a given mode.  Defaults to the value of
+@code{HAVE_POST_INCREMENT}.
+@end defmac
+
+@defmac USE_LOAD_POST_DECREMENT (@var{mode})
+A C expression used to determine whether a load postdecrement is a good
+thing to use for a given mode.  Defaults to the value of
+@code{HAVE_POST_DECREMENT}.
+@end defmac
+
+@defmac USE_LOAD_PRE_INCREMENT (@var{mode})
+A C expression used to determine whether a load preincrement is a good
+thing to use for a given mode.  Defaults to the value of
+@code{HAVE_PRE_INCREMENT}.
+@end defmac
+
+@defmac USE_LOAD_PRE_DECREMENT (@var{mode})
+A C expression used to determine whether a load predecrement is a good
+thing to use for a given mode.  Defaults to the value of
+@code{HAVE_PRE_DECREMENT}.
+@end defmac
+
+@defmac USE_STORE_POST_INCREMENT (@var{mode})
+A C expression used to determine whether a store postincrement is a good
+thing to use for a given mode.  Defaults to the value of
+@code{HAVE_POST_INCREMENT}.
+@end defmac
+
+@defmac USE_STORE_POST_DECREMENT (@var{mode})
+A C expression used to determine whether a store postdecrement is a good
+thing to use for a given mode.  Defaults to the value of
+@code{HAVE_POST_DECREMENT}.
+@end defmac
+
+@defmac USE_STORE_PRE_INCREMENT (@var{mode})
+This macro is used to determine whether a store preincrement is a good
+thing to use for a given mode.  Defaults to the value of
+@code{HAVE_PRE_INCREMENT}.
+@end defmac
+
+@defmac USE_STORE_PRE_DECREMENT (@var{mode})
+This macro is used to determine whether a store predecrement is a good
+thing to use for a given mode.  Defaults to the value of
+@code{HAVE_PRE_DECREMENT}.
+@end defmac
+
+@defmac NO_FUNCTION_CSE
+Define this macro if it is as good or better to call a constant
+function address than to call an address kept in a register.
+@end defmac
+
+@defmac RANGE_TEST_NON_SHORT_CIRCUIT
+Define this macro if a non-short-circuit operation produced by
+@samp{fold_range_test ()} is optimal.  This macro defaults to true if
+@code{BRANCH_COST} is greater than or equal to the value 2.
+@end defmac
+
+@hook TARGET_RTX_COSTS
+This target hook describes the relative costs of RTL expressions.
+
+The cost may depend on the precise form of the expression, which is
+available for examination in @var{x}, and the rtx code of the expression
+in which it is contained, found in @var{outer_code}.  @var{code} is the
+expression code---redundant, since it can be obtained with
+@code{GET_CODE (@var{x})}.
+
+In implementing this hook, you can use the construct
+@code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast
+instructions.
+
+On entry to the hook, @code{*@var{total}} contains a default estimate
+for the cost of the expression.  The hook should modify this value as
+necessary.  Traditionally, the default costs are @code{COSTS_N_INSNS (5)}
+for multiplications, @code{COSTS_N_INSNS (7)} for division and modulus
+operations, and @code{COSTS_N_INSNS (1)} for all other operations.
+
+When optimizing for code size, i.e.@: when @code{speed} is
+false, this target hook should be used to estimate the relative
+size cost of an expression, again relative to @code{COSTS_N_INSNS}.
+
+The hook returns true when all subexpressions of @var{x} have been
+processed, and false when @code{rtx_cost} should recurse.
+@end deftypefn
+
+@hook TARGET_ADDRESS_COST
+This hook computes the cost of an addressing mode that contains
+@var{address}.  If not defined, the cost is computed from
+the @var{address} expression and the @code{TARGET_RTX_COST} hook.
+
+For most CISC machines, the default cost is a good approximation of the
+true cost of the addressing mode.  However, on RISC machines, all
+instructions normally have the same length and execution time.  Hence
+all addresses will have equal costs.
+
+In cases where more than one form of an address is known, the form with
+the lowest cost will be used.  If multiple forms have the same, lowest,
+cost, the one that is the most complex will be used.
+
+For example, suppose an address that is equal to the sum of a register
+and a constant is used twice in the same basic block.  When this macro
+is not defined, the address will be computed in a register and memory
+references will be indirect through that register.  On machines where
+the cost of the addressing mode containing the sum is no higher than
+that of a simple indirect reference, this will produce an additional
+instruction and possibly require an additional register.  Proper
+specification of this macro eliminates this overhead for such machines.
+
+This hook is never called with an invalid address.
+
+On machines where an address involving more than one register is as
+cheap as an address computation involving only one register, defining
+@code{TARGET_ADDRESS_COST} to reflect this can cause two registers to
+be live over a region of code where only one would have been if
+@code{TARGET_ADDRESS_COST} were not defined in that manner.  This effect
+should be considered in the definition of this macro.  Equivalent costs
+should probably only be given to addresses with different numbers of
+registers on machines with lots of registers.
+@end deftypefn
+
+@node Scheduling
+@section Adjusting the Instruction Scheduler
+
+The instruction scheduler may need a fair amount of machine-specific
+adjustment in order to produce good code.  GCC provides several target
+hooks for this purpose.  It is usually enough to define just a few of
+them: try the first ones in this list first.
+
+@hook TARGET_SCHED_ISSUE_RATE
+This hook returns the maximum number of instructions that can ever
+issue at the same time on the target machine.  The default is one.
+Although the insn scheduler can define itself the possibility of issue
+an insn on the same cycle, the value can serve as an additional
+constraint to issue insns on the same simulated processor cycle (see
+hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}).
+This value must be constant over the entire compilation.  If you need
+it to vary depending on what the instructions are, you must use
+@samp{TARGET_SCHED_VARIABLE_ISSUE}.
+@end deftypefn
+
+@hook TARGET_SCHED_VARIABLE_ISSUE
+This hook is executed by the scheduler after it has scheduled an insn
+from the ready list.  It should return the number of insns which can
+still be issued in the current cycle.  The default is
+@samp{@w{@var{more} - 1}} for insns other than @code{CLOBBER} and
+@code{USE}, which normally are not counted against the issue rate.
+You should define this hook if some insns take more machine resources
+than others, so that fewer insns can follow them in the same cycle.
+@var{file} is either a null pointer, or a stdio stream to write any
+debug output to.  @var{verbose} is the verbose level provided by
+@option{-fsched-verbose-@var{n}}.  @var{insn} is the instruction that
+was scheduled.
+@end deftypefn
+
+@hook TARGET_SCHED_ADJUST_COST
+This function corrects the value of @var{cost} based on the
+relationship between @var{insn} and @var{dep_insn} through the
+dependence @var{link}.  It should return the new value.  The default
+is to make no adjustment to @var{cost}.  This can be used for example
+to specify to the scheduler using the traditional pipeline description
+that an output- or anti-dependence does not incur the same cost as a
+data-dependence.  If the scheduler using the automaton based pipeline
+description, the cost of anti-dependence is zero and the cost of
+output-dependence is maximum of one and the difference of latency
+times of the first and the second insns.  If these values are not
+acceptable, you could use the hook to modify them too.  See also
+@pxref{Processor pipeline description}.
+@end deftypefn
+
+@hook TARGET_SCHED_ADJUST_PRIORITY
+This hook adjusts the integer scheduling priority @var{priority} of
+@var{insn}.  It should return the new priority.  Increase the priority to
+execute @var{insn} earlier, reduce the priority to execute @var{insn}
+later.  Do not define this hook if you do not need to adjust the
+scheduling priorities of insns.
+@end deftypefn
+
+@hook TARGET_SCHED_REORDER
+This hook is executed by the scheduler after it has scheduled the ready
+list, to allow the machine description to reorder it (for example to
+combine two small instructions together on @samp{VLIW} machines).
+@var{file} is either a null pointer, or a stdio stream to write any
+debug output to.  @var{verbose} is the verbose level provided by
+@option{-fsched-verbose-@var{n}}.  @var{ready} is a pointer to the ready
+list of instructions that are ready to be scheduled.  @var{n_readyp} is
+a pointer to the number of elements in the ready list.  The scheduler
+reads the ready list in reverse order, starting with
+@var{ready}[@var{*n_readyp} @minus{} 1] and going to @var{ready}[0].  @var{clock}
+is the timer tick of the scheduler.  You may modify the ready list and
+the number of ready insns.  The return value is the number of insns that
+can issue this cycle; normally this is just @code{issue_rate}.  See also
+@samp{TARGET_SCHED_REORDER2}.
+@end deftypefn
+
+@hook TARGET_SCHED_REORDER2
+Like @samp{TARGET_SCHED_REORDER}, but called at a different time.  That
+function is called whenever the scheduler starts a new cycle.  This one
+is called once per iteration over a cycle, immediately after
+@samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and
+return the number of insns to be scheduled in the same cycle.  Defining
+this hook can be useful if there are frequent situations where
+scheduling one insn causes other insns to become ready in the same
+cycle.  These other insns can then be taken into account properly.
+@end deftypefn
+
+@hook TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK
+This hook is called after evaluation forward dependencies of insns in
+chain given by two parameter values (@var{head} and @var{tail}
+correspondingly) but before insns scheduling of the insn chain.  For
+example, it can be used for better insn classification if it requires
+analysis of dependencies.  This hook can use backward and forward
+dependencies of the insn scheduler because they are already
+calculated.
+@end deftypefn
+
+@hook TARGET_SCHED_INIT
+This hook is executed by the scheduler at the beginning of each block of
+instructions that are to be scheduled.  @var{file} is either a null
+pointer, or a stdio stream to write any debug output to.  @var{verbose}
+is the verbose level provided by @option{-fsched-verbose-@var{n}}.
+@var{max_ready} is the maximum number of insns in the current scheduling
+region that can be live at the same time.  This can be used to allocate
+scratch space if it is needed, e.g.@: by @samp{TARGET_SCHED_REORDER}.
+@end deftypefn
+
+@hook TARGET_SCHED_FINISH
+This hook is executed by the scheduler at the end of each block of
+instructions that are to be scheduled.  It can be used to perform
+cleanup of any actions done by the other scheduling hooks.  @var{file}
+is either a null pointer, or a stdio stream to write any debug output
+to.  @var{verbose} is the verbose level provided by
+@option{-fsched-verbose-@var{n}}.
+@end deftypefn
+
+@hook TARGET_SCHED_INIT_GLOBAL
+This hook is executed by the scheduler after function level initializations.
+@var{file} is either a null pointer, or a stdio stream to write any debug output to.
+@var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}.
+@var{old_max_uid} is the maximum insn uid when scheduling begins.
+@end deftypefn
+
+@hook TARGET_SCHED_FINISH_GLOBAL
+This is the cleanup hook corresponding to @code{TARGET_SCHED_INIT_GLOBAL}.
+@var{file} is either a null pointer, or a stdio stream to write any debug output to.
+@var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}.
+@end deftypefn
+
+@hook TARGET_SCHED_DFA_PRE_CYCLE_INSN
+The hook returns an RTL insn.  The automaton state used in the
+pipeline hazard recognizer is changed as if the insn were scheduled
+when the new simulated processor cycle starts.  Usage of the hook may
+simplify the automaton pipeline description for some @acronym{VLIW}
+processors.  If the hook is defined, it is used only for the automaton
+based pipeline description.  The default is not to change the state
+when the new simulated processor cycle starts.
+@end deftypefn
+
+@hook TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN
+The hook can be used to initialize data used by the previous hook.
+@end deftypefn
+
+@hook TARGET_SCHED_DFA_POST_CYCLE_INSN
+The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
+to changed the state as if the insn were scheduled when the new
+simulated processor cycle finishes.
+@end deftypefn
+
+@hook TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN
+The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but
+used to initialize data used by the previous hook.
+@end deftypefn
+
+@hook TARGET_SCHED_DFA_PRE_ADVANCE_CYCLE
+The hook to notify target that the current simulated cycle is about to finish.
+The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
+to change the state in more complicated situations - e.g., when advancing
+state on a single insn is not enough.
+@end deftypefn
+
+@hook TARGET_SCHED_DFA_POST_ADVANCE_CYCLE
+The hook to notify target that new simulated cycle has just started.
+The hook is analogous to @samp{TARGET_SCHED_DFA_POST_CYCLE_INSN} but used
+to change the state in more complicated situations - e.g., when advancing
+state on a single insn is not enough.
+@end deftypefn
+
+@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD
+This hook controls better choosing an insn from the ready insn queue
+for the @acronym{DFA}-based insn scheduler.  Usually the scheduler
+chooses the first insn from the queue.  If the hook returns a positive
+value, an additional scheduler code tries all permutations of
+@samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()}
+subsequent ready insns to choose an insn whose issue will result in
+maximal number of issued insns on the same cycle.  For the
+@acronym{VLIW} processor, the code could actually solve the problem of
+packing simple insns into the @acronym{VLIW} insn.  Of course, if the
+rules of @acronym{VLIW} packing are described in the automaton.
+
+This code also could be used for superscalar @acronym{RISC}
+processors.  Let us consider a superscalar @acronym{RISC} processor
+with 3 pipelines.  Some insns can be executed in pipelines @var{A} or
+@var{B}, some insns can be executed only in pipelines @var{B} or
+@var{C}, and one insn can be executed in pipeline @var{B}.  The
+processor may issue the 1st insn into @var{A} and the 2nd one into
+@var{B}.  In this case, the 3rd insn will wait for freeing @var{B}
+until the next cycle.  If the scheduler issues the 3rd insn the first,
+the processor could issue all 3 insns per cycle.
+
+Actually this code demonstrates advantages of the automaton based
+pipeline hazard recognizer.  We try quickly and easy many insn
+schedules to choose the best one.
+
+The default is no multipass scheduling.
+@end deftypefn
+
+@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD
+
+This hook controls what insns from the ready insn queue will be
+considered for the multipass insn scheduling.  If the hook returns
+zero for @var{insn}, the insn will be not chosen to
+be issued.
+
+The default is that any ready insns can be chosen to be issued.
+@end deftypefn
+
+@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BEGIN
+This hook prepares the target backend for a new round of multipass
+scheduling.
+@end deftypefn
+
+@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_ISSUE
+This hook is called when multipass scheduling evaluates instruction INSN.
+@end deftypefn
+
+@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BACKTRACK
+This is called when multipass scheduling backtracks from evaluation of
+an instruction.
+@end deftypefn
+
+@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_END
+This hook notifies the target about the result of the concluded current
+round of multipass scheduling.
+@end deftypefn
+
+@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_INIT
+This hook initializes target-specific data used in multipass scheduling.
+@end deftypefn
+
+@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_FINI
+This hook finalizes target-specific data used in multipass scheduling.
+@end deftypefn
+
+@hook TARGET_SCHED_DFA_NEW_CYCLE
+This hook is called by the insn scheduler before issuing @var{insn}
+on cycle @var{clock}.  If the hook returns nonzero,
+@var{insn} is not issued on this processor cycle.  Instead,
+the processor cycle is advanced.  If *@var{sort_p}
+is zero, the insn ready queue is not sorted on the new cycle
+start as usually.  @var{dump} and @var{verbose} specify the file and
+verbosity level to use for debugging output.
+@var{last_clock} and @var{clock} are, respectively, the
+processor cycle on which the previous insn has been issued,
+and the current processor cycle.
+@end deftypefn
+
+@hook TARGET_SCHED_IS_COSTLY_DEPENDENCE
+This hook is used to define which dependences are considered costly by
+the target, so costly that it is not advisable to schedule the insns that
+are involved in the dependence too close to one another.  The parameters
+to this hook are as follows:  The first parameter @var{_dep} is the dependence
+being evaluated.  The second parameter @var{cost} is the cost of the
+dependence as estimated by the scheduler, and the third
+parameter @var{distance} is the distance in cycles between the two insns.
+The hook returns @code{true} if considering the distance between the two
+insns the dependence between them is considered costly by the target,
+and @code{false} otherwise.
+
+Defining this hook can be useful in multiple-issue out-of-order machines,
+where (a) it's practically hopeless to predict the actual data/resource
+delays, however: (b) there's a better chance to predict the actual grouping
+that will be formed, and (c) correctly emulating the grouping can be very
+important.  In such targets one may want to allow issuing dependent insns
+closer to one another---i.e., closer than the dependence distance;  however,
+not in cases of ``costly dependences'', which this hooks allows to define.
+@end deftypefn
+
+@hook TARGET_SCHED_H_I_D_EXTENDED
+This hook is called by the insn scheduler after emitting a new instruction to
+the instruction stream.  The hook notifies a target backend to extend its
+per instruction data structures.
+@end deftypefn
+
+@hook TARGET_SCHED_ALLOC_SCHED_CONTEXT
+Return a pointer to a store large enough to hold target scheduling context.
+@end deftypefn
+
+@hook TARGET_SCHED_INIT_SCHED_CONTEXT
+Initialize store pointed to by @var{tc} to hold target scheduling context.
+It @var{clean_p} is true then initialize @var{tc} as if scheduler is at the
+beginning of the block.  Otherwise, copy the current context into @var{tc}.
+@end deftypefn
+
+@hook TARGET_SCHED_SET_SCHED_CONTEXT
+Copy target scheduling context pointed to by @var{tc} to the current context.
+@end deftypefn
+
+@hook TARGET_SCHED_CLEAR_SCHED_CONTEXT
+Deallocate internal data in target scheduling context pointed to by @var{tc}.
+@end deftypefn
+
+@hook TARGET_SCHED_FREE_SCHED_CONTEXT
+Deallocate a store for target scheduling context pointed to by @var{tc}.
+@end deftypefn
+
+@hook TARGET_SCHED_SPECULATE_INSN
+This hook is called by the insn scheduler when @var{insn} has only
+speculative dependencies and therefore can be scheduled speculatively.
+The hook is used to check if the pattern of @var{insn} has a speculative
+version and, in case of successful check, to generate that speculative
+pattern.  The hook should return 1, if the instruction has a speculative form,
+or @minus{}1, if it doesn't.  @var{request} describes the type of requested
+speculation.  If the return value equals 1 then @var{new_pat} is assigned
+the generated speculative pattern.
+@end deftypefn
+
+@hook TARGET_SCHED_NEEDS_BLOCK_P
+This hook is called by the insn scheduler during generation of recovery code
+for @var{insn}.  It should return @code{true}, if the corresponding check
+instruction should branch to recovery code, or @code{false} otherwise.
+@end deftypefn
+
+@hook TARGET_SCHED_GEN_SPEC_CHECK
+This hook is called by the insn scheduler to generate a pattern for recovery
+check instruction.  If @var{mutate_p} is zero, then @var{insn} is a
+speculative instruction for which the check should be generated.
+@var{label} is either a label of a basic block, where recovery code should
+be emitted, or a null pointer, when requested check doesn't branch to
+recovery code (a simple check).  If @var{mutate_p} is nonzero, then
+a pattern for a branchy check corresponding to a simple check denoted by
+@var{insn} should be generated.  In this case @var{label} can't be null.
+@end deftypefn
+
+@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD_SPEC
+This hook is used as a workaround for
+@samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD} not being
+called on the first instruction of the ready list.  The hook is used to
+discard speculative instructions that stand first in the ready list from
+being scheduled on the current cycle.  If the hook returns @code{false},
+@var{insn} will not be chosen to be issued.
+For non-speculative instructions,
+the hook should always return @code{true}.  For example, in the ia64 backend
+the hook is used to cancel data speculative insns when the ALAT table
+is nearly full.
+@end deftypefn
+
+@hook TARGET_SCHED_SET_SCHED_FLAGS
+This hook is used by the insn scheduler to find out what features should be
+enabled/used.
+The structure *@var{spec_info} should be filled in by the target.
+The structure describes speculation types that can be used in the scheduler.
+@end deftypefn
+
+@hook TARGET_SCHED_SMS_RES_MII
+This hook is called by the swing modulo scheduler to calculate a
+resource-based lower bound which is based on the resources available in
+the machine and the resources required by each instruction.  The target
+backend can use @var{g} to calculate such bound.  A very simple lower
+bound will be used in case this hook is not implemented: the total number
+of instructions divided by the issue rate.
+@end deftypefn
+
+@hook TARGET_SCHED_DISPATCH
+This hook is called by Haifa Scheduler.  It returns true if dispatch scheduling
+is supported in hardware and the condition specified in the parameter is true.
+@end deftypefn
+
+@hook TARGET_SCHED_DISPATCH_DO
+This hook is called by Haifa Scheduler.  It performs the operation specified
+in its second parameter.
+@end deftypefn
+
+@node Sections
+@section Dividing the Output into Sections (Texts, Data, @dots{})
+@c the above section title is WAY too long.  maybe cut the part between
+@c the (...)?  --mew 10feb93
+
+An object file is divided into sections containing different types of
+data.  In the most common case, there are three sections: the @dfn{text
+section}, which holds instructions and read-only data; the @dfn{data
+section}, which holds initialized writable data; and the @dfn{bss
+section}, which holds uninitialized data.  Some systems have other kinds
+of sections.
+
+@file{varasm.c} provides several well-known sections, such as
+@code{text_section}, @code{data_section} and @code{bss_section}.
+The normal way of controlling a @code{@var{foo}_section} variable
+is to define the associated @code{@var{FOO}_SECTION_ASM_OP} macro,
+as described below.  The macros are only read once, when @file{varasm.c}
+initializes itself, so their values must be run-time constants.
+They may however depend on command-line flags.
+
+@emph{Note:} Some run-time files, such @file{crtstuff.c}, also make
+use of the @code{@var{FOO}_SECTION_ASM_OP} macros, and expect them
+to be string literals.
+
+Some assemblers require a different string to be written every time a
+section is selected.  If your assembler falls into this category, you
+should define the @code{TARGET_ASM_INIT_SECTIONS} hook and use
+@code{get_unnamed_section} to set up the sections.
+
+You must always create a @code{text_section}, either by defining
+@code{TEXT_SECTION_ASM_OP} or by initializing @code{text_section}
+in @code{TARGET_ASM_INIT_SECTIONS}.  The same is true of
+@code{data_section} and @code{DATA_SECTION_ASM_OP}.  If you do not
+create a distinct @code{readonly_data_section}, the default is to
+reuse @code{text_section}.
+
+All the other @file{varasm.c} sections are optional, and are null
+if the target does not provide them.
+
+@defmac TEXT_SECTION_ASM_OP
+A C expression whose value is a string, including spacing, containing the
+assembler operation that should precede instructions and read-only data.
+Normally @code{"\t.text"} is right.
+@end defmac
+
+@defmac HOT_TEXT_SECTION_NAME
+If defined, a C string constant for the name of the section containing most
+frequently executed functions of the program.  If not defined, GCC will provide
+a default definition if the target supports named sections.
+@end defmac
+
+@defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME
+If defined, a C string constant for the name of the section containing unlikely
+executed functions in the program.
+@end defmac
+
+@defmac DATA_SECTION_ASM_OP
+A C expression whose value is a string, including spacing, containing the
+assembler operation to identify the following data as writable initialized
+data.  Normally @code{"\t.data"} is right.
+@end defmac
+
+@defmac SDATA_SECTION_ASM_OP
+If defined, a C expression whose value is a string, including spacing,
+containing the assembler operation to identify the following data as
+initialized, writable small data.
+@end defmac
+
+@defmac READONLY_DATA_SECTION_ASM_OP
+A C expression whose value is a string, including spacing, containing the
+assembler operation to identify the following data as read-only initialized
+data.
+@end defmac
+
+@defmac BSS_SECTION_ASM_OP
+If defined, a C expression whose value is a string, including spacing,
+containing the assembler operation to identify the following data as
+uninitialized global data.  If not defined, and neither
+@code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined,
+uninitialized global data will be output in the data section if
+@option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be
+used.
+@end defmac
+
+@defmac SBSS_SECTION_ASM_OP
+If defined, a C expression whose value is a string, including spacing,
+containing the assembler operation to identify the following data as
+uninitialized, writable small data.
+@end defmac
+
+@defmac TLS_COMMON_ASM_OP
+If defined, a C expression whose value is a string containing the
+assembler operation to identify the following data as thread-local
+common data.  The default is @code{".tls_common"}.
+@end defmac
+
+@defmac TLS_SECTION_ASM_FLAG
+If defined, a C expression whose value is a character constant
+containing the flag used to mark a section as a TLS section.  The
+default is @code{'T'}.
+@end defmac
+
+@defmac INIT_SECTION_ASM_OP
+If defined, a C expression whose value is a string, including spacing,
+containing the assembler operation to identify the following data as
+initialization code.  If not defined, GCC will assume such a section does
+not exist.  This section has no corresponding @code{init_section}
+variable; it is used entirely in runtime code.
+@end defmac
+
+@defmac FINI_SECTION_ASM_OP
+If defined, a C expression whose value is a string, including spacing,
+containing the assembler operation to identify the following data as
+finalization code.  If not defined, GCC will assume such a section does
+not exist.  This section has no corresponding @code{fini_section}
+variable; it is used entirely in runtime code.
+@end defmac
+
+@defmac INIT_ARRAY_SECTION_ASM_OP
+If defined, a C expression whose value is a string, including spacing,
+containing the assembler operation to identify the following data as
+part of the @code{.init_array} (or equivalent) section.  If not
+defined, GCC will assume such a section does not exist.  Do not define
+both this macro and @code{INIT_SECTION_ASM_OP}.
+@end defmac
+
+@defmac FINI_ARRAY_SECTION_ASM_OP
+If defined, a C expression whose value is a string, including spacing,
+containing the assembler operation to identify the following data as
+part of the @code{.fini_array} (or equivalent) section.  If not
+defined, GCC will assume such a section does not exist.  Do not define
+both this macro and @code{FINI_SECTION_ASM_OP}.
+@end defmac
+
+@defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function})
+If defined, an ASM statement that switches to a different section
+via @var{section_op}, calls @var{function}, and switches back to
+the text section.  This is used in @file{crtstuff.c} if
+@code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls
+to initialization and finalization functions from the init and fini
+sections.  By default, this macro uses a simple function call.  Some
+ports need hand-crafted assembly code to avoid dependencies on
+registers initialized in the function prologue or to ensure that
+constant pools don't end up too far way in the text section.
+@end defmac
+
+@defmac TARGET_LIBGCC_SDATA_SECTION
+If defined, a string which names the section into which small
+variables defined in crtstuff and libgcc should go.  This is useful
+when the target has options for optimizing access to small data, and
+you want the crtstuff and libgcc routines to be conservative in what
+they expect of your application yet liberal in what your application
+expects.  For example, for targets with a @code{.sdata} section (like
+MIPS), you could compile crtstuff with @code{-G 0} so that it doesn't
+require small data support from your application, but use this macro
+to put small data into @code{.sdata} so that your application can
+access these variables whether it uses small data or not.
+@end defmac
+
+@defmac FORCE_CODE_SECTION_ALIGN
+If defined, an ASM statement that aligns a code section to some
+arbitrary boundary.  This is used to force all fragments of the
+@code{.init} and @code{.fini} sections to have to same alignment
+and thus prevent the linker from having to add any padding.
+@end defmac
+
+@defmac JUMP_TABLES_IN_TEXT_SECTION
+Define this macro to be an expression with a nonzero value if jump
+tables (for @code{tablejump} insns) should be output in the text
+section, along with the assembler instructions.  Otherwise, the
+readonly data section is used.
+
+This macro is irrelevant if there is no separate readonly data section.
+@end defmac
+
+@hook TARGET_ASM_INIT_SECTIONS
+Define this hook if you need to do something special to set up the
+@file{varasm.c} sections, or if your target has some special sections
+of its own that you need to create.
+
+GCC calls this hook after processing the command line, but before writing
+any assembly code, and before calling any of the section-returning hooks
+described below.
+@end deftypefn
+
+@hook TARGET_ASM_RELOC_RW_MASK
+Return a mask describing how relocations should be treated when
+selecting sections.  Bit 1 should be set if global relocations
+should be placed in a read-write section; bit 0 should be set if
+local relocations should be placed in a read-write section.
+
+The default version of this function returns 3 when @option{-fpic}
+is in effect, and 0 otherwise.  The hook is typically redefined
+when the target cannot support (some kinds of) dynamic relocations
+in read-only sections even in executables.
+@end deftypefn
+
+@hook TARGET_ASM_SELECT_SECTION
+Return the section into which @var{exp} should be placed.  You can
+assume that @var{exp} is either a @code{VAR_DECL} node or a constant of
+some sort.  @var{reloc} indicates whether the initial value of @var{exp}
+requires link-time relocations.  Bit 0 is set when variable contains
+local relocations only, while bit 1 is set for global relocations.
+@var{align} is the constant alignment in bits.
+
+The default version of this function takes care of putting read-only
+variables in @code{readonly_data_section}.
+
+See also @var{USE_SELECT_SECTION_FOR_FUNCTIONS}.
+@end deftypefn
+
+@defmac USE_SELECT_SECTION_FOR_FUNCTIONS
+Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called
+for @code{FUNCTION_DECL}s as well as for variables and constants.
+
+In the case of a @code{FUNCTION_DECL}, @var{reloc} will be zero if the
+function has been determined to be likely to be called, and nonzero if
+it is unlikely to be called.
+@end defmac
+
+@hook TARGET_ASM_UNIQUE_SECTION
+Build up a unique section name, expressed as a @code{STRING_CST} node,
+and assign it to @samp{DECL_SECTION_NAME (@var{decl})}.
+As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether
+the initial value of @var{exp} requires link-time relocations.
+
+The default version of this function appends the symbol name to the
+ELF section name that would normally be used for the symbol.  For
+example, the function @code{foo} would be placed in @code{.text.foo}.
+Whatever the actual target object format, this is often good enough.
+@end deftypefn
+
+@hook TARGET_ASM_FUNCTION_RODATA_SECTION
+Return the readonly data section associated with
+@samp{DECL_SECTION_NAME (@var{decl})}.
+The default version of this function selects @code{.gnu.linkonce.r.name} if
+the function's section is @code{.gnu.linkonce.t.name}, @code{.rodata.name}
+if function is in @code{.text.name}, and the normal readonly-data section
+otherwise.
+@end deftypefn
+
+@hook TARGET_ASM_SELECT_RTX_SECTION
+Return the section into which a constant @var{x}, of mode @var{mode},
+should be placed.  You can assume that @var{x} is some kind of
+constant in RTL@.  The argument @var{mode} is redundant except in the
+case of a @code{const_int} rtx.  @var{align} is the constant alignment
+in bits.
+
+The default version of this function takes care of putting symbolic
+constants in @code{flag_pic} mode in @code{data_section} and everything
+else in @code{readonly_data_section}.
+@end deftypefn
+
+@hook TARGET_MANGLE_DECL_ASSEMBLER_NAME
+Define this hook if you need to postprocess the assembler name generated
+by target-independent code.  The @var{id} provided to this hook will be
+the computed name (e.g., the macro @code{DECL_NAME} of the @var{decl} in C,
+or the mangled name of the @var{decl} in C++).  The return value of the
+hook is an @code{IDENTIFIER_NODE} for the appropriate mangled name on
+your target system.  The default implementation of this hook just
+returns the @var{id} provided.
+@end deftypefn
+
+@hook TARGET_ENCODE_SECTION_INFO
+Define this hook if references to a symbol or a constant must be
+treated differently depending on something about the variable or
+function named by the symbol (such as what section it is in).
+
+The hook is executed immediately after rtl has been created for
+@var{decl}, which may be a variable or function declaration or
+an entry in the constant pool.  In either case, @var{rtl} is the
+rtl in question.  Do @emph{not} use @code{DECL_RTL (@var{decl})}
+in this hook; that field may not have been initialized yet.
+
+In the case of a constant, it is safe to assume that the rtl is
+a @code{mem} whose address is a @code{symbol_ref}.  Most decls
+will also have this form, but that is not guaranteed.  Global
+register variables, for instance, will have a @code{reg} for their
+rtl.  (Normally the right thing to do with such unusual rtl is
+leave it alone.)
+
+The @var{new_decl_p} argument will be true if this is the first time
+that @code{TARGET_ENCODE_SECTION_INFO} has been invoked on this decl.  It will
+be false for subsequent invocations, which will happen for duplicate
+declarations.  Whether or not anything must be done for the duplicate
+declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}.
+@var{new_decl_p} is always true when the hook is called for a constant.
+
+@cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO}
+The usual thing for this hook to do is to record flags in the
+@code{symbol_ref}, using @code{SYMBOL_REF_FLAG} or @code{SYMBOL_REF_FLAGS}.
+Historically, the name string was modified if it was necessary to
+encode more than one bit of information, but this practice is now
+discouraged; use @code{SYMBOL_REF_FLAGS}.
+
+The default definition of this hook, @code{default_encode_section_info}
+in @file{varasm.c}, sets a number of commonly-useful bits in
+@code{SYMBOL_REF_FLAGS}.  Check whether the default does what you need
+before overriding it.
+@end deftypefn
+
+@hook TARGET_STRIP_NAME_ENCODING
+Decode @var{name} and return the real name part, sans
+the characters that @code{TARGET_ENCODE_SECTION_INFO}
+may have added.
+@end deftypefn
+
+@hook TARGET_IN_SMALL_DATA_P
+Returns true if @var{exp} should be placed into a ``small data'' section.
+The default version of this hook always returns false.
+@end deftypefn
+
+@hook TARGET_HAVE_SRODATA_SECTION
+Contains the value true if the target places read-only
+``small data'' into a separate section.  The default value is false.
+@end deftypevr
+
+@hook TARGET_PROFILE_BEFORE_PROLOGUE
+
+@hook TARGET_BINDS_LOCAL_P
+Returns true if @var{exp} names an object for which name resolution
+rules must resolve to the current ``module'' (dynamic shared library
+or executable image).
+
+The default version of this hook implements the name resolution rules
+for ELF, which has a looser model of global name binding than other
+currently supported object file formats.
+@end deftypefn
+
+@hook TARGET_HAVE_TLS
+Contains the value true if the target supports thread-local storage.
+The default value is false.
+@end deftypevr
+
+
+@node PIC
+@section Position Independent Code
+@cindex position independent code
+@cindex PIC
+
+This section describes macros that help implement generation of position
+independent code.  Simply defining these macros is not enough to
+generate valid PIC; you must also add support to the hook
+@code{TARGET_LEGITIMATE_ADDRESS_P} and to the macro
+@code{PRINT_OPERAND_ADDRESS}, as well as @code{LEGITIMIZE_ADDRESS}.  You
+must modify the definition of @samp{movsi} to do something appropriate
+when the source operand contains a symbolic address.  You may also
+need to alter the handling of switch statements so that they use
+relative addresses.
+@c i rearranged the order of the macros above to try to force one of 
+@c them to the next line, to eliminate an overfull hbox. --mew 10feb93
+
+@defmac PIC_OFFSET_TABLE_REGNUM
+The register number of the register used to address a table of static
+data addresses in memory.  In some cases this register is defined by a
+processor's ``application binary interface'' (ABI)@.  When this macro
+is defined, RTL is generated for this register once, as with the stack
+pointer and frame pointer registers.  If this macro is not defined, it
+is up to the machine-dependent files to allocate such a register (if
+necessary).  Note that this register must be fixed when in use (e.g.@:
+when @code{flag_pic} is true).
+@end defmac
+
+@defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED
+A C expression that is nonzero if the register defined by
+@code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls.  If not defined,
+the default is zero.  Do not define
+this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined.
+@end defmac
+
+@defmac LEGITIMATE_PIC_OPERAND_P (@var{x})
+A C expression that is nonzero if @var{x} is a legitimate immediate
+operand on the target machine when generating position independent code.
+You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not
+check this.  You can also assume @var{flag_pic} is true, so you need not
+check it either.  You need not define this macro if all constants
+(including @code{SYMBOL_REF}) can be immediate operands when generating
+position independent code.
+@end defmac
+
+@node Assembler Format
+@section Defining the Output Assembler Language
+
+This section describes macros whose principal purpose is to describe how
+to write instructions in assembler language---rather than what the
+instructions do.
+
+@menu
+* File Framework::       Structural information for the assembler file.
+* Data Output::          Output of constants (numbers, strings, addresses).
+* Uninitialized Data::   Output of uninitialized variables.
+* Label Output::         Output and generation of labels.
+* Initialization::       General principles of initialization
+                         and termination routines.
+* Macros for Initialization::
+                         Specific macros that control the handling of
+                         initialization and termination routines.
+* Instruction Output::   Output of actual instructions.
+* Dispatch Tables::      Output of jump tables.
+* Exception Region Output:: Output of exception region code.
+* Alignment Output::     Pseudo ops for alignment and skipping data.
+@end menu
+
+@node File Framework
+@subsection The Overall Framework of an Assembler File
+@cindex assembler format
+@cindex output of assembler code
+
+@c prevent bad page break with this line
+This describes the overall framework of an assembly file.
+
+@findex default_file_start
+@hook TARGET_ASM_FILE_START
+Output to @code{asm_out_file} any text which the assembler expects to
+find at the beginning of a file.  The default behavior is controlled
+by two flags, documented below.  Unless your target's assembler is
+quite unusual, if you override the default, you should call
+@code{default_file_start} at some point in your target hook.  This
+lets other target files rely on these variables.
+@end deftypefn
+
+@hook TARGET_ASM_FILE_START_APP_OFF
+If this flag is true, the text of the macro @code{ASM_APP_OFF} will be
+printed as the very first line in the assembly file, unless
+@option{-fverbose-asm} is in effect.  (If that macro has been defined
+to the empty string, this variable has no effect.)  With the normal
+definition of @code{ASM_APP_OFF}, the effect is to notify the GNU
+assembler that it need not bother stripping comments or extra
+whitespace from its input.  This allows it to work a bit faster.
+
+The default is false.  You should not set it to true unless you have
+verified that your port does not generate any extra whitespace or
+comments that will cause GAS to issue errors in NO_APP mode.
+@end deftypevr
+
+@hook TARGET_ASM_FILE_START_FILE_DIRECTIVE
+If this flag is true, @code{output_file_directive} will be called
+for the primary source file, immediately after printing
+@code{ASM_APP_OFF} (if that is enabled).  Most ELF assemblers expect
+this to be done.  The default is false.
+@end deftypevr
+
+@hook TARGET_ASM_FILE_END
+Output to @code{asm_out_file} any text which the assembler expects
+to find at the end of a file.  The default is to output nothing.
+@end deftypefn
+
+@deftypefun void file_end_indicate_exec_stack ()
+Some systems use a common convention, the @samp{.note.GNU-stack}
+special section, to indicate whether or not an object file relies on
+the stack being executable.  If your system uses this convention, you
+should define @code{TARGET_ASM_FILE_END} to this function.  If you
+need to do other things in that hook, have your hook function call
+this function.
+@end deftypefun
+
+@hook TARGET_ASM_LTO_START
+Output to @code{asm_out_file} any text which the assembler expects
+to find at the start of an LTO section.  The default is to output
+nothing.
+@end deftypefn
+
+@hook TARGET_ASM_LTO_END
+Output to @code{asm_out_file} any text which the assembler expects
+to find at the end of an LTO section.  The default is to output
+nothing.
+@end deftypefn
+
+@hook TARGET_ASM_CODE_END
+Output to @code{asm_out_file} any text which is needed before emitting
+unwind info and debug info at the end of a file.  Some targets emit
+here PIC setup thunks that cannot be emitted at the end of file,
+because they couldn't have unwind info then.  The default is to output
+nothing.
+@end deftypefn
+
+@defmac ASM_COMMENT_START
+A C string constant describing how to begin a comment in the target
+assembler language.  The compiler assumes that the comment will end at
+the end of the line.
+@end defmac
+
+@defmac ASM_APP_ON
+A C string constant for text to be output before each @code{asm}
+statement or group of consecutive ones.  Normally this is
+@code{"#APP"}, which is a comment that has no effect on most
+assemblers but tells the GNU assembler that it must check the lines
+that follow for all valid assembler constructs.
+@end defmac
+
+@defmac ASM_APP_OFF
+A C string constant for text to be output after each @code{asm}
+statement or group of consecutive ones.  Normally this is
+@code{"#NO_APP"}, which tells the GNU assembler to resume making the
+time-saving assumptions that are valid for ordinary compiler output.
+@end defmac
+
+@defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name})
+A C statement to output COFF information or DWARF debugging information
+which indicates that filename @var{name} is the current source file to
+the stdio stream @var{stream}.
+
+This macro need not be defined if the standard form of output
+for the file format in use is appropriate.
+@end defmac
+
+@hook TARGET_ASM_OUTPUT_SOURCE_FILENAME
+
+@defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string})
+A C statement to output the string @var{string} to the stdio stream
+@var{stream}.  If you do not call the function @code{output_quoted_string}
+in your config files, GCC will only call it to output filenames to
+the assembler source.  So you can use it to canonicalize the format
+of the filename using this macro.
+@end defmac
+
+@defmac ASM_OUTPUT_IDENT (@var{stream}, @var{string})
+A C statement to output something to the assembler file to handle a
+@samp{#ident} directive containing the text @var{string}.  If this
+macro is not defined, nothing is output for a @samp{#ident} directive.
+@end defmac
+
+@hook TARGET_ASM_NAMED_SECTION
+Output assembly directives to switch to section @var{name}.  The section
+should have attributes as specified by @var{flags}, which is a bit mask
+of the @code{SECTION_*} flags defined in @file{output.h}.  If @var{decl}
+is non-NULL, it is the @code{VAR_DECL} or @code{FUNCTION_DECL} with which
+this section is associated.
+@end deftypefn
+
+@hook TARGET_ASM_FUNCTION_SECTION
+Return preferred text (sub)section for function @var{decl}.
+Main purpose of this function is to separate cold, normal and hot
+functions. @var{startup} is true when function is known to be used only 
+at startup (from static constructors or it is @code{main()}).
+@var{exit} is true when function is known to be used only at exit
+(from static destructors).
+Return NULL if function should go to default text section.
+@end deftypefn
+
+@hook TARGET_ASM_FUNCTION_SWITCHED_TEXT_SECTIONS
+
+@hook TARGET_HAVE_NAMED_SECTIONS
+This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}.
+It must not be modified by command-line option processing.
+@end deftypevr
+
+@anchor{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}
+@hook TARGET_HAVE_SWITCHABLE_BSS_SECTIONS
+This flag is true if we can create zeroed data by switching to a BSS
+section and then using @code{ASM_OUTPUT_SKIP} to allocate the space.
+This is true on most ELF targets.
+@end deftypevr
+
+@hook TARGET_SECTION_TYPE_FLAGS
+Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION}
+based on a variable or function decl, a section name, and whether or not the
+declaration's initializer may contain runtime relocations.  @var{decl} may be
+null, in which case read-write data should be assumed.
+
+The default version of this function handles choosing code vs data,
+read-only vs read-write data, and @code{flag_pic}.  You should only
+need to override this if your target has special flags that might be
+set via @code{__attribute__}.
+@end deftypefn
+
+@hook TARGET_ASM_RECORD_GCC_SWITCHES
+Provides the target with the ability to record the gcc command line
+switches that have been passed to the compiler, and options that are
+enabled.  The @var{type} argument specifies what is being recorded.
+It can take the following values:
+
+@table @gcctabopt
+@item SWITCH_TYPE_PASSED
+@var{text} is a command line switch that has been set by the user.
+
+@item SWITCH_TYPE_ENABLED
+@var{text} is an option which has been enabled.  This might be as a
+direct result of a command line switch, or because it is enabled by
+default or because it has been enabled as a side effect of a different
+command line switch.  For example, the @option{-O2} switch enables
+various different individual optimization passes.
+
+@item SWITCH_TYPE_DESCRIPTIVE
+@var{text} is either NULL or some descriptive text which should be
+ignored.  If @var{text} is NULL then it is being used to warn the
+target hook that either recording is starting or ending.  The first
+time @var{type} is SWITCH_TYPE_DESCRIPTIVE and @var{text} is NULL, the
+warning is for start up and the second time the warning is for
+wind down.  This feature is to allow the target hook to make any
+necessary preparations before it starts to record switches and to
+perform any necessary tidying up after it has finished recording
+switches.
+
+@item SWITCH_TYPE_LINE_START
+This option can be ignored by this target hook.
+
+@item  SWITCH_TYPE_LINE_END
+This option can be ignored by this target hook.
+@end table
+
+The hook's return value must be zero.  Other return values may be
+supported in the future.
+
+By default this hook is set to NULL, but an example implementation is
+provided for ELF based targets.  Called @var{elf_record_gcc_switches},
+it records the switches as ASCII text inside a new, string mergeable
+section in the assembler output file.  The name of the new section is
+provided by the @code{TARGET_ASM_RECORD_GCC_SWITCHES_SECTION} target
+hook.
+@end deftypefn
+
+@hook TARGET_ASM_RECORD_GCC_SWITCHES_SECTION
+This is the name of the section that will be created by the example
+ELF implementation of the @code{TARGET_ASM_RECORD_GCC_SWITCHES} target
+hook.
+@end deftypevr
+
+@need 2000
+@node Data Output
+@subsection Output of Data
+
+
+@hook TARGET_ASM_BYTE_OP
+@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP
+@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP
+@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP
+@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP
+@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP
+@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP
+@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP
+@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP
+These hooks specify assembly directives for creating certain kinds
+of integer object.  The @code{TARGET_ASM_BYTE_OP} directive creates a
+byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an
+aligned two-byte object, and so on.  Any of the hooks may be
+@code{NULL}, indicating that no suitable directive is available.
+
+The compiler will print these strings at the start of a new line,
+followed immediately by the object's initial value.  In most cases,
+the string should contain a tab, a pseudo-op, and then another tab.
+@end deftypevr
+
+@hook TARGET_ASM_INTEGER
+The @code{assemble_integer} function uses this hook to output an
+integer object.  @var{x} is the object's value, @var{size} is its size
+in bytes and @var{aligned_p} indicates whether it is aligned.  The
+function should return @code{true} if it was able to output the
+object.  If it returns false, @code{assemble_integer} will try to
+split the object into smaller parts.
+
+The default implementation of this hook will use the
+@code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false}
+when the relevant string is @code{NULL}.
+@end deftypefn
+
+@hook TARGET_ASM_OUTPUT_ADDR_CONST_EXTRA
+A target hook to recognize @var{rtx} patterns that @code{output_addr_const}
+can't deal with, and output assembly code to @var{file} corresponding to
+the pattern @var{x}.  This may be used to allow machine-dependent
+@code{UNSPEC}s to appear within constants.
+
+If target hook fails to recognize a pattern, it must return @code{false},
+so that a standard error message is printed.  If it prints an error message
+itself, by calling, for example, @code{output_operand_lossage}, it may just
+return @code{true}.
+@end deftypefn
+
+@defmac OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail})
+A C statement to recognize @var{rtx} patterns that
+@code{output_addr_const} can't deal with, and output assembly code to
+@var{stream} corresponding to the pattern @var{x}.  This may be used to
+allow machine-dependent @code{UNSPEC}s to appear within constants.
+
+If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must
+@code{goto fail}, so that a standard error message is printed.  If it
+prints an error message itself, by calling, for example,
+@code{output_operand_lossage}, it may just complete normally.
+@end defmac
+
+@defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len})
+A C statement to output to the stdio stream @var{stream} an assembler
+instruction to assemble a string constant containing the @var{len}
+bytes at @var{ptr}.  @var{ptr} will be a C expression of type
+@code{char *} and @var{len} a C expression of type @code{int}.
+
+If the assembler has a @code{.ascii} pseudo-op as found in the
+Berkeley Unix assembler, do not define the macro
+@code{ASM_OUTPUT_ASCII}.
+@end defmac
+
+@defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n})
+A C statement to output word @var{n} of a function descriptor for
+@var{decl}.  This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS}
+is defined, and is otherwise unused.
+@end defmac
+
+@defmac CONSTANT_POOL_BEFORE_FUNCTION
+You may define this macro as a C expression.  You should define the
+expression to have a nonzero value if GCC should output the constant
+pool for a function before the code for the function, or a zero value if
+GCC should output the constant pool after the function.  If you do
+not define this macro, the usual case, GCC will output the constant
+pool before the function.
+@end defmac
+
+@defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size})
+A C statement to output assembler commands to define the start of the
+constant pool for a function.  @var{funname} is a string giving
+the name of the function.  Should the return type of the function
+be required, it can be obtained via @var{fundecl}.  @var{size}
+is the size, in bytes, of the constant pool that will be written
+immediately after this call.
+
+If no constant-pool prefix is required, the usual case, this macro need
+not be defined.
+@end defmac
+
+@defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto})
+A C statement (with or without semicolon) to output a constant in the
+constant pool, if it needs special treatment.  (This macro need not do
+anything for RTL expressions that can be output normally.)
+
+The argument @var{file} is the standard I/O stream to output the
+assembler code on.  @var{x} is the RTL expression for the constant to
+output, and @var{mode} is the machine mode (in case @var{x} is a
+@samp{const_int}).  @var{align} is the required alignment for the value
+@var{x}; you should output an assembler directive to force this much
+alignment.
+
+The argument @var{labelno} is a number to use in an internal label for
+the address of this pool entry.  The definition of this macro is
+responsible for outputting the label definition at the proper place.
+Here is how to do this:
+
+@smallexample
+@code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno});
+@end smallexample
+
+When you output a pool entry specially, you should end with a
+@code{goto} to the label @var{jumpto}.  This will prevent the same pool
+entry from being output a second time in the usual manner.
+
+You need not define this macro if it would do nothing.
+@end defmac
+
+@defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size})
+A C statement to output assembler commands to at the end of the constant
+pool for a function.  @var{funname} is a string giving the name of the
+function.  Should the return type of the function be required, you can
+obtain it via @var{fundecl}.  @var{size} is the size, in bytes, of the
+constant pool that GCC wrote immediately before this call.
+
+If no constant-pool epilogue is required, the usual case, you need not
+define this macro.
+@end defmac
+
+@defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}, @var{STR})
+Define this macro as a C expression which is nonzero if @var{C} is
+used as a logical line separator by the assembler.  @var{STR} points
+to the position in the string where @var{C} was found; this can be used if
+a line separator uses multiple characters.
+
+If you do not define this macro, the default is that only
+the character @samp{;} is treated as a logical line separator.
+@end defmac
+
+@hook TARGET_ASM_OPEN_PAREN
+These target hooks are C string constants, describing the syntax in the
+assembler for grouping arithmetic expressions.  If not overridden, they
+default to normal parentheses, which is correct for most assemblers.
+@end deftypevr
+
+These macros are provided by @file{real.h} for writing the definitions
+of @code{ASM_OUTPUT_DOUBLE} and the like:
+
+@defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l})
+@defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l})
+@defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l})
+@defmacx REAL_VALUE_TO_TARGET_DECIMAL32 (@var{x}, @var{l})
+@defmacx REAL_VALUE_TO_TARGET_DECIMAL64 (@var{x}, @var{l})
+@defmacx REAL_VALUE_TO_TARGET_DECIMAL128 (@var{x}, @var{l})
+These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the
+target's floating point representation, and store its bit pattern in
+the variable @var{l}.  For @code{REAL_VALUE_TO_TARGET_SINGLE} and
+@code{REAL_VALUE_TO_TARGET_DECIMAL32}, this variable should be a
+simple @code{long int}.  For the others, it should be an array of
+@code{long int}.  The number of elements in this array is determined
+by the size of the desired target floating point data type: 32 bits of
+it go in each @code{long int} array element.  Each array element holds
+32 bits of the result, even if @code{long int} is wider than 32 bits
+on the host machine.
+
+The array element values are designed so that you can print them out
+using @code{fprintf} in the order they should appear in the target
+machine's memory.
+@end defmac
+
+@node Uninitialized Data
+@subsection Output of Uninitialized Variables
+
+Each of the macros in this section is used to do the whole job of
+outputting a single uninitialized variable.
+
+@defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} the assembler definition of a common-label named
+@var{name} whose size is @var{size} bytes.  The variable @var{rounded}
+is the size rounded up to whatever alignment the caller wants.  It is
+possible that @var{size} may be zero, for instance if a struct with no
+other member than a zero-length array is defined.  In this case, the
+backend must output a symbol definition that allocates at least one
+byte, both so that the address of the resulting object does not compare
+equal to any other, and because some object formats cannot even express
+the concept of a zero-sized common symbol, as that is how they represent
+an ordinary undefined external.
+
+Use the expression @code{assemble_name (@var{stream}, @var{name})} to
+output the name itself; before and after that, output the additional
+assembler syntax for defining the name, and a newline.
+
+This macro controls how the assembler definitions of uninitialized
+common global variables are output.
+@end defmac
+
+@defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment})
+Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a
+separate, explicit argument.  If you define this macro, it is used in
+place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in
+handling the required alignment of the variable.  The alignment is specified
+as the number of bits.
+@end defmac
+
+@defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
+Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the
+variable to be output, if there is one, or @code{NULL_TREE} if there
+is no corresponding variable.  If you define this macro, GCC will use it
+in place of both @code{ASM_OUTPUT_COMMON} and
+@code{ASM_OUTPUT_ALIGNED_COMMON}.  Define this macro when you need to see
+the variable's decl in order to chose what to output.
+@end defmac
+
+@defmac ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} the assembler definition of uninitialized global @var{decl} named
+@var{name} whose size is @var{size} bytes.  The variable @var{rounded}
+is the size rounded up to whatever alignment the caller wants.
+
+Try to use function @code{asm_output_bss} defined in @file{varasm.c} when
+defining this macro.  If unable, use the expression
+@code{assemble_name (@var{stream}, @var{name})} to output the name itself;
+before and after that, output the additional assembler syntax for defining
+the name, and a newline.
+
+There are two ways of handling global BSS@.  One is to define either
+this macro or its aligned counterpart, @code{ASM_OUTPUT_ALIGNED_BSS}.
+The other is to have @code{TARGET_ASM_SELECT_SECTION} return a
+switchable BSS section (@pxref{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}).
+You do not need to do both.
+
+Some languages do not have @code{common} data, and require a
+non-common form of global BSS in order to handle uninitialized globals
+efficiently.  C++ is one example of this.  However, if the target does
+not support global BSS, the front end may choose to make globals
+common in order to save space in the object file.
+@end defmac
+
+@defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
+Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a
+separate, explicit argument.  If you define this macro, it is used in
+place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in
+handling the required alignment of the variable.  The alignment is specified
+as the number of bits.
+
+Try to use function @code{asm_output_aligned_bss} defined in file
+@file{varasm.c} when defining this macro.
+@end defmac
+
+@defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} the assembler definition of a local-common-label named
+@var{name} whose size is @var{size} bytes.  The variable @var{rounded}
+is the size rounded up to whatever alignment the caller wants.
+
+Use the expression @code{assemble_name (@var{stream}, @var{name})} to
+output the name itself; before and after that, output the additional
+assembler syntax for defining the name, and a newline.
+
+This macro controls how the assembler definitions of uninitialized
+static variables are output.
+@end defmac
+
+@defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment})
+Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a
+separate, explicit argument.  If you define this macro, it is used in
+place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in
+handling the required alignment of the variable.  The alignment is specified
+as the number of bits.
+@end defmac
+
+@defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
+Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the
+variable to be output, if there is one, or @code{NULL_TREE} if there
+is no corresponding variable.  If you define this macro, GCC will use it
+in place of both @code{ASM_OUTPUT_DECL} and
+@code{ASM_OUTPUT_ALIGNED_DECL}.  Define this macro when you need to see
+the variable's decl in order to chose what to output.
+@end defmac
+
+@node Label Output
+@subsection Output and Generation of Labels
+
+@c prevent bad page break with this line
+This is about outputting labels.
+
+@findex assemble_name
+@defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} the assembler definition of a label named @var{name}.
+Use the expression @code{assemble_name (@var{stream}, @var{name})} to
+output the name itself; before and after that, output the additional
+assembler syntax for defining the name, and a newline.  A default
+definition of this macro is provided which is correct for most systems.
+@end defmac
+
+@defmac ASM_OUTPUT_FUNCTION_LABEL (@var{stream}, @var{name}, @var{decl})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} the assembler definition of a label named @var{name} of
+a function.
+Use the expression @code{assemble_name (@var{stream}, @var{name})} to
+output the name itself; before and after that, output the additional
+assembler syntax for defining the name, and a newline.  A default
+definition of this macro is provided which is correct for most systems.
+
+If this macro is not defined, then the function name is defined in the
+usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
+@end defmac
+
+@findex assemble_name_raw
+@defmac ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{name})
+Identical to @code{ASM_OUTPUT_LABEL}, except that @var{name} is known
+to refer to a compiler-generated label.  The default definition uses
+@code{assemble_name_raw}, which is like @code{assemble_name} except
+that it is more efficient.
+@end defmac
+
+@defmac SIZE_ASM_OP
+A C string containing the appropriate assembler directive to specify the
+size of a symbol, without any arguments.  On systems that use ELF, the
+default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other
+systems, the default is not to define this macro.
+
+Define this macro only if it is correct to use the default definitions
+of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE}
+for your system.  If you need your own custom definitions of those
+macros, or if you do not need explicit symbol sizes at all, do not
+define this macro.
+@end defmac
+
+@defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} a directive telling the assembler that the size of the
+symbol @var{name} is @var{size}.  @var{size} is a @code{HOST_WIDE_INT}.
+If you define @code{SIZE_ASM_OP}, a default definition of this macro is
+provided.
+@end defmac
+
+@defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} a directive telling the assembler to calculate the size of
+the symbol @var{name} by subtracting its address from the current
+address.
+
+If you define @code{SIZE_ASM_OP}, a default definition of this macro is
+provided.  The default assumes that the assembler recognizes a special
+@samp{.} symbol as referring to the current address, and can calculate
+the difference between this and another symbol.  If your assembler does
+not recognize @samp{.} or cannot do calculations with it, you will need
+to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique.
+@end defmac
+
+@defmac TYPE_ASM_OP
+A C string containing the appropriate assembler directive to specify the
+type of a symbol, without any arguments.  On systems that use ELF, the
+default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other
+systems, the default is not to define this macro.
+
+Define this macro only if it is correct to use the default definition of
+@code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system.  If you need your own
+custom definition of this macro, or if you do not need explicit symbol
+types at all, do not define this macro.
+@end defmac
+
+@defmac TYPE_OPERAND_FMT
+A C string which specifies (using @code{printf} syntax) the format of
+the second operand to @code{TYPE_ASM_OP}.  On systems that use ELF, the
+default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems,
+the default is not to define this macro.
+
+Define this macro only if it is correct to use the default definition of
+@code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system.  If you need your own
+custom definition of this macro, or if you do not need explicit symbol
+types at all, do not define this macro.
+@end defmac
+
+@defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} a directive telling the assembler that the type of the
+symbol @var{name} is @var{type}.  @var{type} is a C string; currently,
+that string is always either @samp{"function"} or @samp{"object"}, but
+you should not count on this.
+
+If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default
+definition of this macro is provided.
+@end defmac
+
+@defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} any text necessary for declaring the name @var{name} of a
+function which is being defined.  This macro is responsible for
+outputting the label definition (perhaps using
+@code{ASM_OUTPUT_FUNCTION_LABEL}).  The argument @var{decl} is the
+@code{FUNCTION_DECL} tree node representing the function.
+
+If this macro is not defined, then the function name is defined in the
+usual manner as a label (by means of @code{ASM_OUTPUT_FUNCTION_LABEL}).
+
+You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
+of this macro.
+@end defmac
+
+@defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} any text necessary for declaring the size of a function
+which is being defined.  The argument @var{name} is the name of the
+function.  The argument @var{decl} is the @code{FUNCTION_DECL} tree node
+representing the function.
+
+If this macro is not defined, then the function size is not defined.
+
+You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition
+of this macro.
+@end defmac
+
+@defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} any text necessary for declaring the name @var{name} of an
+initialized variable which is being defined.  This macro must output the
+label definition (perhaps using @code{ASM_OUTPUT_LABEL}).  The argument
+@var{decl} is the @code{VAR_DECL} tree node representing the variable.
+
+If this macro is not defined, then the variable name is defined in the
+usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
+
+You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or
+@code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro.
+@end defmac
+
+@hook TARGET_ASM_DECLARE_CONSTANT_NAME
+A target hook to output to the stdio stream @var{file} any text necessary
+for declaring the name @var{name} of a constant which is being defined.  This
+target hook is responsible for outputting the label definition (perhaps using
+@code{assemble_label}).  The argument @var{exp} is the value of the constant,
+and @var{size} is the size of the constant in bytes.  The @var{name}
+will be an internal label.
+
+The default version of this target hook, define the @var{name} in the
+usual manner as a label (by means of @code{assemble_label}).
+
+You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in this target hook.
+@end deftypefn
+
+@defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} any text necessary for claiming a register @var{regno}
+for a global variable @var{decl} with name @var{name}.
+
+If you don't define this macro, that is equivalent to defining it to do
+nothing.
+@end defmac
+
+@defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend})
+A C statement (sans semicolon) to finish up declaring a variable name
+once the compiler has processed its initializer fully and thus has had a
+chance to determine the size of an array when controlled by an
+initializer.  This is used on systems where it's necessary to declare
+something about the size of the object.
+
+If you don't define this macro, that is equivalent to defining it to do
+nothing.
+
+You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or
+@code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro.
+@end defmac
+
+@hook TARGET_ASM_GLOBALIZE_LABEL
+This target hook is a function to output to the stdio stream
+@var{stream} some commands that will make the label @var{name} global;
+that is, available for reference from other files.
+
+The default implementation relies on a proper definition of
+@code{GLOBAL_ASM_OP}.
+@end deftypefn
+
+@hook TARGET_ASM_GLOBALIZE_DECL_NAME
+This target hook is a function to output to the stdio stream
+@var{stream} some commands that will make the name associated with @var{decl}
+global; that is, available for reference from other files.
+
+The default implementation uses the TARGET_ASM_GLOBALIZE_LABEL target hook.
+@end deftypefn
+
+@defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} some commands that will make the label @var{name} weak;
+that is, available for reference from other files but only used if
+no other definition is available.  Use the expression
+@code{assemble_name (@var{stream}, @var{name})} to output the name
+itself; before and after that, output the additional assembler syntax
+for making that name weak, and a newline.
+
+If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not
+support weak symbols and you should not define the @code{SUPPORTS_WEAK}
+macro.
+@end defmac
+
+@defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value})
+Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and
+@code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function
+or variable decl.  If @var{value} is not @code{NULL}, this C statement
+should output to the stdio stream @var{stream} assembler code which
+defines (equates) the weak symbol @var{name} to have the value
+@var{value}.  If @var{value} is @code{NULL}, it should output commands
+to make @var{name} weak.
+@end defmac
+
+@defmac ASM_OUTPUT_WEAKREF (@var{stream}, @var{decl}, @var{name}, @var{value})
+Outputs a directive that enables @var{name} to be used to refer to
+symbol @var{value} with weak-symbol semantics.  @code{decl} is the
+declaration of @code{name}.
+@end defmac
+
+@defmac SUPPORTS_WEAK
+A preprocessor constant expression which evaluates to true if the target
+supports weak symbols.
+
+If you don't define this macro, @file{defaults.h} provides a default
+definition.  If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL}
+is defined, the default definition is @samp{1}; otherwise, it is @samp{0}.
+@end defmac
+
+@defmac TARGET_SUPPORTS_WEAK
+A C expression which evaluates to true if the target supports weak symbols.
+
+If you don't define this macro, @file{defaults.h} provides a default
+definition.  The default definition is @samp{(SUPPORTS_WEAK)}.  Define
+this macro if you want to control weak symbol support with a compiler
+flag such as @option{-melf}.
+@end defmac
+
+@defmac MAKE_DECL_ONE_ONLY (@var{decl})
+A C statement (sans semicolon) to mark @var{decl} to be emitted as a
+public symbol such that extra copies in multiple translation units will
+be discarded by the linker.  Define this macro if your object file
+format provides support for this concept, such as the @samp{COMDAT}
+section flags in the Microsoft Windows PE/COFF format, and this support
+requires changes to @var{decl}, such as putting it in a separate section.
+@end defmac
+
+@defmac SUPPORTS_ONE_ONLY
+A C expression which evaluates to true if the target supports one-only
+semantics.
+
+If you don't define this macro, @file{varasm.c} provides a default
+definition.  If @code{MAKE_DECL_ONE_ONLY} is defined, the default
+definition is @samp{1}; otherwise, it is @samp{0}.  Define this macro if
+you want to control one-only symbol support with a compiler flag, or if
+setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to
+be emitted as one-only.
+@end defmac
+
+@hook TARGET_ASM_ASSEMBLE_VISIBILITY
+This target hook is a function to output to @var{asm_out_file} some
+commands that will make the symbol(s) associated with @var{decl} have
+hidden, protected or internal visibility as specified by @var{visibility}.
+@end deftypefn
+
+@defmac TARGET_WEAK_NOT_IN_ARCHIVE_TOC
+A C expression that evaluates to true if the target's linker expects
+that weak symbols do not appear in a static archive's table of contents.
+The default is @code{0}.
+
+Leaving weak symbols out of an archive's table of contents means that,
+if a symbol will only have a definition in one translation unit and
+will have undefined references from other translation units, that
+symbol should not be weak.  Defining this macro to be nonzero will
+thus have the effect that certain symbols that would normally be weak
+(explicit template instantiations, and vtables for polymorphic classes
+with noninline key methods) will instead be nonweak.
+
+The C++ ABI requires this macro to be zero.  Define this macro for
+targets where full C++ ABI compliance is impossible and where linker
+restrictions require weak symbols to be left out of a static archive's
+table of contents.
+@end defmac
+
+@defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} any text necessary for declaring the name of an external
+symbol named @var{name} which is referenced in this compilation but
+not defined.  The value of @var{decl} is the tree node for the
+declaration.
+
+This macro need not be defined if it does not need to output anything.
+The GNU assembler and most Unix assemblers don't require anything.
+@end defmac
+
+@hook TARGET_ASM_EXTERNAL_LIBCALL
+This target hook is a function to output to @var{asm_out_file} an assembler
+pseudo-op to declare a library function name external.  The name of the
+library function is given by @var{symref}, which is a @code{symbol_ref}.
+@end deftypefn
+
+@hook TARGET_ASM_MARK_DECL_PRESERVED
+This target hook is a function to output to @var{asm_out_file} an assembler
+directive to annotate @var{symbol} as used.  The Darwin target uses the
+.no_dead_code_strip directive.
+@end deftypefn
+
+@defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} a reference in assembler syntax to a label named
+@var{name}.  This should add @samp{_} to the front of the name, if that
+is customary on your operating system, as it is in most Berkeley Unix
+systems.  This macro is used in @code{assemble_name}.
+@end defmac
+
+@hook TARGET_MANGLE_ASSEMBLER_NAME
+
+@defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
+A C statement (sans semicolon) to output a reference to
+@code{SYMBOL_REF} @var{sym}.  If not defined, @code{assemble_name}
+will be used to output the name of the symbol.  This macro may be used
+to modify the way a symbol is referenced depending on information
+encoded by @code{TARGET_ENCODE_SECTION_INFO}.
+@end defmac
+
+@defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf})
+A C statement (sans semicolon) to output a reference to @var{buf}, the
+result of @code{ASM_GENERATE_INTERNAL_LABEL}.  If not defined,
+@code{assemble_name} will be used to output the name of the symbol.
+This macro is not used by @code{output_asm_label}, or the @code{%l}
+specifier that calls it; the intention is that this macro should be set
+when it is necessary to output a label differently when its address is
+being taken.
+@end defmac
+
+@hook TARGET_ASM_INTERNAL_LABEL
+A function to output to the stdio stream @var{stream} a label whose
+name is made from the string @var{prefix} and the number @var{labelno}.
+
+It is absolutely essential that these labels be distinct from the labels
+used for user-level functions and variables.  Otherwise, certain programs
+will have name conflicts with internal labels.
+
+It is desirable to exclude internal labels from the symbol table of the
+object file.  Most assemblers have a naming convention for labels that
+should be excluded; on many systems, the letter @samp{L} at the
+beginning of a label has this effect.  You should find out what
+convention your system uses, and follow it.
+
+The default version of this function utilizes @code{ASM_GENERATE_INTERNAL_LABEL}.
+@end deftypefn
+
+@defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num})
+A C statement to output to the stdio stream @var{stream} a debug info
+label whose name is made from the string @var{prefix} and the number
+@var{num}.  This is useful for VLIW targets, where debug info labels
+may need to be treated differently than branch target labels.  On some
+systems, branch target labels must be at the beginning of instruction
+bundles, but debug info labels can occur in the middle of instruction
+bundles.
+
+If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be
+used.
+@end defmac
+
+@defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num})
+A C statement to store into the string @var{string} a label whose name
+is made from the string @var{prefix} and the number @var{num}.
+
+This string, when output subsequently by @code{assemble_name}, should
+produce the output that @code{(*targetm.asm_out.internal_label)} would produce
+with the same @var{prefix} and @var{num}.
+
+If the string begins with @samp{*}, then @code{assemble_name} will
+output the rest of the string unchanged.  It is often convenient for
+@code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way.  If the
+string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets
+to output the string, and may change it.  (Of course,
+@code{ASM_OUTPUT_LABELREF} is also part of your machine description, so
+you should know what it does on your machine.)
+@end defmac
+
+@defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number})
+A C expression to assign to @var{outvar} (which is a variable of type
+@code{char *}) a newly allocated string made from the string
+@var{name} and the number @var{number}, with some suitable punctuation
+added.  Use @code{alloca} to get space for the string.
+
+The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to
+produce an assembler label for an internal static variable whose name is
+@var{name}.  Therefore, the string must be such as to result in valid
+assembler code.  The argument @var{number} is different each time this
+macro is executed; it prevents conflicts between similarly-named
+internal static variables in different scopes.
+
+Ideally this string should not be a valid C identifier, to prevent any
+conflict with the user's own symbols.  Most assemblers allow periods
+or percent signs in assembler symbols; putting at least one of these
+between the name and the number will suffice.
+
+If this macro is not defined, a default definition will be provided
+which is correct for most systems.
+@end defmac
+
+@defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value})
+A C statement to output to the stdio stream @var{stream} assembler code
+which defines (equates) the symbol @var{name} to have the value @var{value}.
+
+@findex SET_ASM_OP
+If @code{SET_ASM_OP} is defined, a default definition is provided which is
+correct for most systems.
+@end defmac
+
+@defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value})
+A C statement to output to the stdio stream @var{stream} assembler code
+which defines (equates) the symbol whose tree node is @var{decl_of_name}
+to have the value of the tree node @var{decl_of_value}.  This macro will
+be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if
+the tree nodes are available.
+
+@findex SET_ASM_OP
+If @code{SET_ASM_OP} is defined, a default definition is provided which is
+correct for most systems.
+@end defmac
+
+@defmac TARGET_DEFERRED_OUTPUT_DEFS (@var{decl_of_name}, @var{decl_of_value})
+A C statement that evaluates to true if the assembler code which defines
+(equates) the symbol whose tree node is @var{decl_of_name} to have the value
+of the tree node @var{decl_of_value} should be emitted near the end of the
+current compilation unit.  The default is to not defer output of defines.
+This macro affects defines output by @samp{ASM_OUTPUT_DEF} and
+@samp{ASM_OUTPUT_DEF_FROM_DECLS}.
+@end defmac
+
+@defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value})
+A C statement to output to the stdio stream @var{stream} assembler code
+which defines (equates) the weak symbol @var{name} to have the value
+@var{value}.  If @var{value} is @code{NULL}, it defines @var{name} as
+an undefined weak symbol.
+
+Define this macro if the target only supports weak aliases; define
+@code{ASM_OUTPUT_DEF} instead if possible.
+@end defmac
+
+@defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name})
+Define this macro to override the default assembler names used for
+Objective-C methods.
+
+The default name is a unique method number followed by the name of the
+class (e.g.@: @samp{_1_Foo}).  For methods in categories, the name of
+the category is also included in the assembler name (e.g.@:
+@samp{_1_Foo_Bar}).
+
+These names are safe on most systems, but make debugging difficult since
+the method's selector is not present in the name.  Therefore, particular
+systems define other ways of computing names.
+
+@var{buf} is an expression of type @code{char *} which gives you a
+buffer in which to store the name; its length is as long as
+@var{class_name}, @var{cat_name} and @var{sel_name} put together, plus
+50 characters extra.
+
+The argument @var{is_inst} specifies whether the method is an instance
+method or a class method; @var{class_name} is the name of the class;
+@var{cat_name} is the name of the category (or @code{NULL} if the method is not
+in a category); and @var{sel_name} is the name of the selector.
+
+On systems where the assembler can handle quoted names, you can use this
+macro to provide more human-readable names.
+@end defmac
+
+@defmac ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} commands to declare that the label @var{name} is an
+Objective-C class reference.  This is only needed for targets whose
+linkers have special support for NeXT-style runtimes.
+@end defmac
+
+@defmac ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name})
+A C statement (sans semicolon) to output to the stdio stream
+@var{stream} commands to declare that the label @var{name} is an
+unresolved Objective-C class reference.  This is only needed for targets
+whose linkers have special support for NeXT-style runtimes.
+@end defmac
+
+@node Initialization
+@subsection How Initialization Functions Are Handled
+@cindex initialization routines
+@cindex termination routines
+@cindex constructors, output of
+@cindex destructors, output of
+
+The compiled code for certain languages includes @dfn{constructors}
+(also called @dfn{initialization routines})---functions to initialize
+data in the program when the program is started.  These functions need
+to be called before the program is ``started''---that is to say, before
+@code{main} is called.
+
+Compiling some languages generates @dfn{destructors} (also called
+@dfn{termination routines}) that should be called when the program
+terminates.
+
+To make the initialization and termination functions work, the compiler
+must output something in the assembler code to cause those functions to
+be called at the appropriate time.  When you port the compiler to a new
+system, you need to specify how to do this.
+
+There are two major ways that GCC currently supports the execution of
+initialization and termination functions.  Each way has two variants.
+Much of the structure is common to all four variations.
+
+@findex __CTOR_LIST__
+@findex __DTOR_LIST__
+The linker must build two lists of these functions---a list of
+initialization functions, called @code{__CTOR_LIST__}, and a list of
+termination functions, called @code{__DTOR_LIST__}.
+
+Each list always begins with an ignored function pointer (which may hold
+0, @minus{}1, or a count of the function pointers after it, depending on
+the environment).  This is followed by a series of zero or more function
+pointers to constructors (or destructors), followed by a function
+pointer containing zero.
+
+Depending on the operating system and its executable file format, either
+@file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup
+time and exit time.  Constructors are called in reverse order of the
+list; destructors in forward order.
+
+The best way to handle static constructors works only for object file
+formats which provide arbitrarily-named sections.  A section is set
+aside for a list of constructors, and another for a list of destructors.
+Traditionally these are called @samp{.ctors} and @samp{.dtors}.  Each
+object file that defines an initialization function also puts a word in
+the constructor section to point to that function.  The linker
+accumulates all these words into one contiguous @samp{.ctors} section.
+Termination functions are handled similarly.
+
+This method will be chosen as the default by @file{target-def.h} if
+@code{TARGET_ASM_NAMED_SECTION} is defined.  A target that does not
+support arbitrary sections, but does support special designated
+constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP}
+and @code{DTORS_SECTION_ASM_OP} to achieve the same effect.
+
+When arbitrary sections are available, there are two variants, depending
+upon how the code in @file{crtstuff.c} is called.  On systems that
+support a @dfn{.init} section which is executed at program startup,
+parts of @file{crtstuff.c} are compiled into that section.  The
+program is linked by the @command{gcc} driver like this:
+
+@smallexample
+ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o
+@end smallexample
+
+The prologue of a function (@code{__init}) appears in the @code{.init}
+section of @file{crti.o}; the epilogue appears in @file{crtn.o}.  Likewise
+for the function @code{__fini} in the @dfn{.fini} section.  Normally these
+files are provided by the operating system or by the GNU C library, but
+are provided by GCC for a few targets.
+
+The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets)
+compiled from @file{crtstuff.c}.  They contain, among other things, code
+fragments within the @code{.init} and @code{.fini} sections that branch
+to routines in the @code{.text} section.  The linker will pull all parts
+of a section together, which results in a complete @code{__init} function
+that invokes the routines we need at startup.
+
+To use this variant, you must define the @code{INIT_SECTION_ASM_OP}
+macro properly.
+
+If no init section is available, when GCC compiles any function called
+@code{main} (or more accurately, any function designated as a program
+entry point by the language front end calling @code{expand_main_function}),
+it inserts a procedure call to @code{__main} as the first executable code
+after the function prologue.  The @code{__main} function is defined
+in @file{libgcc2.c} and runs the global constructors.
+
+In file formats that don't support arbitrary sections, there are again
+two variants.  In the simplest variant, the GNU linker (GNU @code{ld})
+and an `a.out' format must be used.  In this case,
+@code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs}
+entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__},
+and with the address of the void function containing the initialization
+code as its value.  The GNU linker recognizes this as a request to add
+the value to a @dfn{set}; the values are accumulated, and are eventually
+placed in the executable as a vector in the format described above, with
+a leading (ignored) count and a trailing zero element.
+@code{TARGET_ASM_DESTRUCTOR} is handled similarly.  Since no init
+section is available, the absence of @code{INIT_SECTION_ASM_OP} causes
+the compilation of @code{main} to call @code{__main} as above, starting
+the initialization process.
+
+The last variant uses neither arbitrary sections nor the GNU linker.
+This is preferable when you want to do dynamic linking and when using
+file formats which the GNU linker does not support, such as `ECOFF'@.  In
+this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and
+termination functions are recognized simply by their names.  This requires
+an extra program in the linkage step, called @command{collect2}.  This program
+pretends to be the linker, for use with GCC; it does its job by running
+the ordinary linker, but also arranges to include the vectors of
+initialization and termination functions.  These functions are called
+via @code{__main} as described above.  In order to use this method,
+@code{use_collect2} must be defined in the target in @file{config.gcc}.
+
+@ifinfo
+The following section describes the specific macros that control and
+customize the handling of initialization and termination functions.
+@end ifinfo
+
+@node Macros for Initialization
+@subsection Macros Controlling Initialization Routines
+
+Here are the macros that control how the compiler handles initialization
+and termination functions:
+
+@defmac INIT_SECTION_ASM_OP
+If defined, a C string constant, including spacing, for the assembler
+operation to identify the following data as initialization code.  If not
+defined, GCC will assume such a section does not exist.  When you are
+using special sections for initialization and termination functions, this
+macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to
+run the initialization functions.
+@end defmac
+
+@defmac HAS_INIT_SECTION
+If defined, @code{main} will not call @code{__main} as described above.
+This macro should be defined for systems that control start-up code
+on a symbol-by-symbol basis, such as OSF/1, and should not
+be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}.
+@end defmac
+
+@defmac LD_INIT_SWITCH
+If defined, a C string constant for a switch that tells the linker that
+the following symbol is an initialization routine.
+@end defmac
+
+@defmac LD_FINI_SWITCH
+If defined, a C string constant for a switch that tells the linker that
+the following symbol is a finalization routine.
+@end defmac
+
+@defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func})
+If defined, a C statement that will write a function that can be
+automatically called when a shared library is loaded.  The function
+should call @var{func}, which takes no arguments.  If not defined, and
+the object format requires an explicit initialization function, then a
+function called @code{_GLOBAL__DI} will be generated.
+
+This function and the following one are used by collect2 when linking a
+shared library that needs constructors or destructors, or has DWARF2
+exception tables embedded in the code.
+@end defmac
+
+@defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func})
+If defined, a C statement that will write a function that can be
+automatically called when a shared library is unloaded.  The function
+should call @var{func}, which takes no arguments.  If not defined, and
+the object format requires an explicit finalization function, then a
+function called @code{_GLOBAL__DD} will be generated.
+@end defmac
+
+@defmac INVOKE__main
+If defined, @code{main} will call @code{__main} despite the presence of
+@code{INIT_SECTION_ASM_OP}.  This macro should be defined for systems
+where the init section is not actually run automatically, but is still
+useful for collecting the lists of constructors and destructors.
+@end defmac
+
+@defmac SUPPORTS_INIT_PRIORITY
+If nonzero, the C++ @code{init_priority} attribute is supported and the
+compiler should emit instructions to control the order of initialization
+of objects.  If zero, the compiler will issue an error message upon
+encountering an @code{init_priority} attribute.
+@end defmac
+
+@hook TARGET_HAVE_CTORS_DTORS
+This value is true if the target supports some ``native'' method of
+collecting constructors and destructors to be run at startup and exit.
+It is false if we must use @command{collect2}.
+@end deftypevr
+
+@hook TARGET_ASM_CONSTRUCTOR
+If defined, a function that outputs assembler code to arrange to call
+the function referenced by @var{symbol} at initialization time.
+
+Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking
+no arguments and with no return value.  If the target supports initialization
+priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY};
+otherwise it must be @code{DEFAULT_INIT_PRIORITY}.
+
+If this macro is not defined by the target, a suitable default will
+be chosen if (1) the target supports arbitrary section names, (2) the
+target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2}
+is not defined.
+@end deftypefn
+
+@hook TARGET_ASM_DESTRUCTOR
+This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination
+functions rather than initialization functions.
+@end deftypefn
+
+If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine
+generated for the generated object file will have static linkage.
+
+If your system uses @command{collect2} as the means of processing
+constructors, then that program normally uses @command{nm} to scan
+an object file for constructor functions to be called.
+
+On certain kinds of systems, you can define this macro to make
+@command{collect2} work faster (and, in some cases, make it work at all):
+
+@defmac OBJECT_FORMAT_COFF
+Define this macro if the system uses COFF (Common Object File Format)
+object files, so that @command{collect2} can assume this format and scan
+object files directly for dynamic constructor/destructor functions.
+
+This macro is effective only in a native compiler; @command{collect2} as
+part of a cross compiler always uses @command{nm} for the target machine.
+@end defmac
+
+@defmac REAL_NM_FILE_NAME
+Define this macro as a C string constant containing the file name to use
+to execute @command{nm}.  The default is to search the path normally for
+@command{nm}.
+@end defmac
+
+@defmac NM_FLAGS
+@command{collect2} calls @command{nm} to scan object files for static
+constructors and destructors and LTO info.  By default, @option{-n} is
+passed.  Define @code{NM_FLAGS} to a C string constant if other options
+are needed to get the same output format as GNU @command{nm -n}
+produces.
+@end defmac
+
+If your system supports shared libraries and has a program to list the
+dynamic dependencies of a given library or executable, you can define
+these macros to enable support for running initialization and
+termination functions in shared libraries:
+
+@defmac LDD_SUFFIX
+Define this macro to a C string constant containing the name of the program
+which lists dynamic dependencies, like @command{ldd} under SunOS 4.
+@end defmac
+
+@defmac PARSE_LDD_OUTPUT (@var{ptr})
+Define this macro to be C code that extracts filenames from the output
+of the program denoted by @code{LDD_SUFFIX}.  @var{ptr} is a variable
+of type @code{char *} that points to the beginning of a line of output
+from @code{LDD_SUFFIX}.  If the line lists a dynamic dependency, the
+code must advance @var{ptr} to the beginning of the filename on that
+line.  Otherwise, it must set @var{ptr} to @code{NULL}.
+@end defmac
+
+@defmac SHLIB_SUFFIX
+Define this macro to a C string constant containing the default shared
+library extension of the target (e.g., @samp{".so"}).  @command{collect2}
+strips version information after this suffix when generating global
+constructor and destructor names.  This define is only needed on targets
+that use @command{collect2} to process constructors and destructors.
+@end defmac
+
+@node Instruction Output
+@subsection Output of Assembler Instructions
+
+@c prevent bad page break with this line
+This describes assembler instruction output.
+
+@defmac REGISTER_NAMES
+A C initializer containing the assembler's names for the machine
+registers, each one as a C string constant.  This is what translates
+register numbers in the compiler into assembler language.
+@end defmac
+
+@defmac ADDITIONAL_REGISTER_NAMES
+If defined, a C initializer for an array of structures containing a name
+and a register number.  This macro defines additional names for hard
+registers, thus allowing the @code{asm} option in declarations to refer
+to registers using alternate names.
+@end defmac
+
+@defmac OVERLAPPING_REGISTER_NAMES
+If defined, a C initializer for an array of structures containing a
+name, a register number and a count of the number of consecutive
+machine registers the name overlaps.  This macro defines additional
+names for hard registers, thus allowing the @code{asm} option in
+declarations to refer to registers using alternate names.  Unlike
+@code{ADDITIONAL_REGISTER_NAMES}, this macro should be used when the
+register name implies multiple underlying registers.
+
+This macro should be used when it is important that a clobber in an
+@code{asm} statement clobbers all the underlying values implied by the
+register name.  For example, on ARM, clobbering the double-precision
+VFP register ``d0'' implies clobbering both single-precision registers
+``s0'' and ``s1''.
+@end defmac
+
+@defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr})
+Define this macro if you are using an unusual assembler that
+requires different names for the machine instructions.
+
+The definition is a C statement or statements which output an
+assembler instruction opcode to the stdio stream @var{stream}.  The
+macro-operand @var{ptr} is a variable of type @code{char *} which
+points to the opcode name in its ``internal'' form---the form that is
+written in the machine description.  The definition should output the
+opcode name to @var{stream}, performing any translation you desire, and
+increment the variable @var{ptr} to point at the end of the opcode
+so that it will not be output twice.
+
+In fact, your macro definition may process less than the entire opcode
+name, or more than the opcode name; but if you want to process text
+that includes @samp{%}-sequences to substitute operands, you must take
+care of the substitution yourself.  Just be sure to increment
+@var{ptr} over whatever text should not be output normally.
+
+@findex recog_data.operand
+If you need to look at the operand values, they can be found as the
+elements of @code{recog_data.operand}.
+
+If the macro definition does nothing, the instruction is output
+in the usual way.
+@end defmac
+
+@defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands})
+If defined, a C statement to be executed just prior to the output of
+assembler code for @var{insn}, to modify the extracted operands so
+they will be output differently.
+
+Here the argument @var{opvec} is the vector containing the operands
+extracted from @var{insn}, and @var{noperands} is the number of
+elements of the vector which contain meaningful data for this insn.
+The contents of this vector are what will be used to convert the insn
+template into assembler code, so you can change the assembler output
+by changing the contents of the vector.
+
+This macro is useful when various assembler syntaxes share a single
+file of instruction patterns; by defining this macro differently, you
+can cause a large class of instructions to be output differently (such
+as with rearranged operands).  Naturally, variations in assembler
+syntax affecting individual insn patterns ought to be handled by
+writing conditional output routines in those patterns.
+
+If this macro is not defined, it is equivalent to a null statement.
+@end defmac
+
+@hook TARGET_ASM_FINAL_POSTSCAN_INSN
+If defined, this target hook is a function which is executed just after the
+output of assembler code for @var{insn}, to change the mode of the assembler
+if necessary.
+
+Here the argument @var{opvec} is the vector containing the operands
+extracted from @var{insn}, and @var{noperands} is the number of
+elements of the vector which contain meaningful data for this insn.
+The contents of this vector are what was used to convert the insn
+template into assembler code, so you can change the assembler mode
+by checking the contents of the vector.
+@end deftypefn
+
+@defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code})
+A C compound statement to output to stdio stream @var{stream} the
+assembler syntax for an instruction operand @var{x}.  @var{x} is an
+RTL expression.
+
+@var{code} is a value that can be used to specify one of several ways
+of printing the operand.  It is used when identical operands must be
+printed differently depending on the context.  @var{code} comes from
+the @samp{%} specification that was used to request printing of the
+operand.  If the specification was just @samp{%@var{digit}} then
+@var{code} is 0; if the specification was @samp{%@var{ltr}
+@var{digit}} then @var{code} is the ASCII code for @var{ltr}.
+
+@findex reg_names
+If @var{x} is a register, this macro should print the register's name.
+The names can be found in an array @code{reg_names} whose type is
+@code{char *[]}.  @code{reg_names} is initialized from
+@code{REGISTER_NAMES}.
+
+When the machine description has a specification @samp{%@var{punct}}
+(a @samp{%} followed by a punctuation character), this macro is called
+with a null pointer for @var{x} and the punctuation character for
+@var{code}.
+@end defmac
+
+@defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code})
+A C expression which evaluates to true if @var{code} is a valid
+punctuation character for use in the @code{PRINT_OPERAND} macro.  If
+@code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no
+punctuation characters (except for the standard one, @samp{%}) are used
+in this way.
+@end defmac
+
+@defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x})
+A C compound statement to output to stdio stream @var{stream} the
+assembler syntax for an instruction operand that is a memory reference
+whose address is @var{x}.  @var{x} is an RTL expression.
+
+@cindex @code{TARGET_ENCODE_SECTION_INFO} usage
+On some machines, the syntax for a symbolic address depends on the
+section that the address refers to.  On these machines, define the hook
+@code{TARGET_ENCODE_SECTION_INFO} to store the information into the
+@code{symbol_ref}, and then check for it here.  @xref{Assembler
+Format}.
+@end defmac
+
+@findex dbr_sequence_length
+@defmac DBR_OUTPUT_SEQEND (@var{file})
+A C statement, to be executed after all slot-filler instructions have
+been output.  If necessary, call @code{dbr_sequence_length} to
+determine the number of slots filled in a sequence (zero if not
+currently outputting a sequence), to decide how many no-ops to output,
+or whatever.
+
+Don't define this macro if it has nothing to do, but it is helpful in
+reading assembly output if the extent of the delay sequence is made
+explicit (e.g.@: with white space).
+@end defmac
+
+@findex final_sequence
+Note that output routines for instructions with delay slots must be
+prepared to deal with not being output as part of a sequence
+(i.e.@: when the scheduling pass is not run, or when no slot fillers could be
+found.)  The variable @code{final_sequence} is null when not
+processing a sequence, otherwise it contains the @code{sequence} rtx
+being output.
+
+@findex asm_fprintf
+@defmac REGISTER_PREFIX
+@defmacx LOCAL_LABEL_PREFIX
+@defmacx USER_LABEL_PREFIX
+@defmacx IMMEDIATE_PREFIX
+If defined, C string expressions to be used for the @samp{%R}, @samp{%L},
+@samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see
+@file{final.c}).  These are useful when a single @file{md} file must
+support multiple assembler formats.  In that case, the various @file{tm.h}
+files can define these macros differently.
+@end defmac
+
+@defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format})
+If defined this macro should expand to a series of @code{case}
+statements which will be parsed inside the @code{switch} statement of
+the @code{asm_fprintf} function.  This allows targets to define extra
+printf formats which may useful when generating their assembler
+statements.  Note that uppercase letters are reserved for future
+generic extensions to asm_fprintf, and so are not available to target
+specific code.  The output file is given by the parameter @var{file}.
+The varargs input pointer is @var{argptr} and the rest of the format
+string, starting the character after the one that is being switched
+upon, is pointed to by @var{format}.
+@end defmac
+
+@defmac ASSEMBLER_DIALECT
+If your target supports multiple dialects of assembler language (such as
+different opcodes), define this macro as a C expression that gives the
+numeric index of the assembler language dialect to use, with zero as the
+first variant.
+
+If this macro is defined, you may use constructs of the form
+@smallexample
+@samp{@{option0|option1|option2@dots{}@}}
+@end smallexample
+@noindent
+in the output templates of patterns (@pxref{Output Template}) or in the
+first argument of @code{asm_fprintf}.  This construct outputs
+@samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of
+@code{ASSEMBLER_DIALECT} is zero, one, two, etc.  Any special characters
+within these strings retain their usual meaning.  If there are fewer
+alternatives within the braces than the value of
+@code{ASSEMBLER_DIALECT}, the construct outputs nothing.
+
+If you do not define this macro, the characters @samp{@{}, @samp{|} and
+@samp{@}} do not have any special meaning when used in templates or
+operands to @code{asm_fprintf}.
+
+Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX},
+@code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express
+the variations in assembler language syntax with that mechanism.  Define
+@code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax
+if the syntax variant are larger and involve such things as different
+opcodes or operand order.
+@end defmac
+
+@defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno})
+A C expression to output to @var{stream} some assembler code
+which will push hard register number @var{regno} onto the stack.
+The code need not be optimal, since this macro is used only when
+profiling.
+@end defmac
+
+@defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno})
+A C expression to output to @var{stream} some assembler code
+which will pop hard register number @var{regno} off of the stack.
+The code need not be optimal, since this macro is used only when
+profiling.
+@end defmac
+
+@node Dispatch Tables
+@subsection Output of Dispatch Tables
+
+@c prevent bad page break with this line
+This concerns dispatch tables.
+
+@cindex dispatch table
+@defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel})
+A C statement to output to the stdio stream @var{stream} an assembler
+pseudo-instruction to generate a difference between two labels.
+@var{value} and @var{rel} are the numbers of two internal labels.  The
+definitions of these labels are output using
+@code{(*targetm.asm_out.internal_label)}, and they must be printed in the same
+way here.  For example,
+
+@smallexample
+fprintf (@var{stream}, "\t.word L%d-L%d\n",
+         @var{value}, @var{rel})
+@end smallexample
+
+You must provide this macro on machines where the addresses in a
+dispatch table are relative to the table's own address.  If defined, GCC
+will also use this macro on all machines when producing PIC@.
+@var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the
+mode and flags can be read.
+@end defmac
+
+@defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value})
+This macro should be provided on machines where the addresses
+in a dispatch table are absolute.
+
+The definition should be a C statement to output to the stdio stream
+@var{stream} an assembler pseudo-instruction to generate a reference to
+a label.  @var{value} is the number of an internal label whose
+definition is output using @code{(*targetm.asm_out.internal_label)}.
+For example,
+
+@smallexample
+fprintf (@var{stream}, "\t.word L%d\n", @var{value})
+@end smallexample
+@end defmac
+
+@defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table})
+Define this if the label before a jump-table needs to be output
+specially.  The first three arguments are the same as for
+@code{(*targetm.asm_out.internal_label)}; the fourth argument is the
+jump-table which follows (a @code{jump_insn} containing an
+@code{addr_vec} or @code{addr_diff_vec}).
+
+This feature is used on system V to output a @code{swbeg} statement
+for the table.
+
+If this macro is not defined, these labels are output with
+@code{(*targetm.asm_out.internal_label)}.
+@end defmac
+
+@defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table})
+Define this if something special must be output at the end of a
+jump-table.  The definition should be a C statement to be executed
+after the assembler code for the table is written.  It should write
+the appropriate code to stdio stream @var{stream}.  The argument
+@var{table} is the jump-table insn, and @var{num} is the label-number
+of the preceding label.
+
+If this macro is not defined, nothing special is output at the end of
+the jump-table.
+@end defmac
+
+@hook TARGET_ASM_EMIT_UNWIND_LABEL
+This target hook emits a label at the beginning of each FDE@.  It
+should be defined on targets where FDEs need special labels, and it
+should write the appropriate label, for the FDE associated with the
+function declaration @var{decl}, to the stdio stream @var{stream}.
+The third argument, @var{for_eh}, is a boolean: true if this is for an
+exception table.  The fourth argument, @var{empty}, is a boolean:
+true if this is a placeholder label for an omitted FDE@.
+
+The default is that FDEs are not given nonlocal labels.
+@end deftypefn
+
+@hook TARGET_ASM_EMIT_EXCEPT_TABLE_LABEL
+This target hook emits a label at the beginning of the exception table.
+It should be defined on targets where it is desirable for the table
+to be broken up according to function.
+
+The default is that no label is emitted.
+@end deftypefn
+
+@hook TARGET_ASM_EMIT_EXCEPT_PERSONALITY
+
+@hook TARGET_ASM_UNWIND_EMIT
+This target hook emits assembly directives required to unwind the
+given instruction.  This is only used when @code{TARGET_EXCEPT_UNWIND_INFO}
+returns @code{UI_TARGET}.
+@end deftypefn
+
+@hook TARGET_ASM_UNWIND_EMIT_BEFORE_INSN
+
+@node Exception Region Output
+@subsection Assembler Commands for Exception Regions
+
+@c prevent bad page break with this line
+
+This describes commands marking the start and the end of an exception
+region.
+
+@defmac EH_FRAME_SECTION_NAME
+If defined, a C string constant for the name of the section containing
+exception handling frame unwind information.  If not defined, GCC will
+provide a default definition if the target supports named sections.
+@file{crtstuff.c} uses this macro to switch to the appropriate section.
+
+You should define this symbol if your target supports DWARF 2 frame
+unwind information and the default definition does not work.
+@end defmac
+
+@defmac EH_FRAME_IN_DATA_SECTION
+If defined, DWARF 2 frame unwind information will be placed in the
+data section even though the target supports named sections.  This
+might be necessary, for instance, if the system linker does garbage
+collection and sections cannot be marked as not to be collected.
+
+Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is
+also defined.
+@end defmac
+
+@defmac EH_TABLES_CAN_BE_READ_ONLY
+Define this macro to 1 if your target is such that no frame unwind
+information encoding used with non-PIC code will ever require a
+runtime relocation, but the linker may not support merging read-only
+and read-write sections into a single read-write section.
+@end defmac
+
+@defmac MASK_RETURN_ADDR
+An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so
+that it does not contain any extraneous set bits in it.
+@end defmac
+
+@defmac DWARF2_UNWIND_INFO
+Define this macro to 0 if your target supports DWARF 2 frame unwind
+information, but it does not yet work with exception handling.
+Otherwise, if your target supports this information (if it defines
+@code{INCOMING_RETURN_ADDR_RTX} and either @code{UNALIGNED_INT_ASM_OP}
+or @code{OBJECT_FORMAT_ELF}), GCC will provide a default definition of 1.
+@end defmac
+
+@hook TARGET_EXCEPT_UNWIND_INFO
+This hook defines the mechanism that will be used for exception handling
+by the target.  If the target has ABI specified unwind tables, the hook
+should return @code{UI_TARGET}.  If the target is to use the
+@code{setjmp}/@code{longjmp}-based exception handling scheme, the hook
+should return @code{UI_SJLJ}.  If the target supports DWARF 2 frame unwind
+information, the hook should return @code{UI_DWARF2}.
+
+A target may, if exceptions are disabled, choose to return @code{UI_NONE}.
+This may end up simplifying other parts of target-specific code.  The
+default implementation of this hook never returns @code{UI_NONE}.
+
+Note that the value returned by this hook should be constant.  It should
+not depend on anything except the command-line switches described by
+@var{opts}.  In particular, the
+setting @code{UI_SJLJ} must be fixed at compiler start-up as C pre-processor
+macros and builtin functions related to exception handling are set up
+depending on this setting.
+
+The default implementation of the hook first honors the
+@option{--enable-sjlj-exceptions} configure option, then
+@code{DWARF2_UNWIND_INFO}, and finally defaults to @code{UI_SJLJ}.  If
+@code{DWARF2_UNWIND_INFO} depends on command-line options, the target
+must define this hook so that @var{opts} is used correctly.
+@end deftypefn
+
+@hook TARGET_UNWIND_TABLES_DEFAULT
+This variable should be set to @code{true} if the target ABI requires unwinding
+tables even when exceptions are not used.  It must not be modified by
+command-line option processing.
+@end deftypevr
+
+@defmac DONT_USE_BUILTIN_SETJMP
+Define this macro to 1 if the @code{setjmp}/@code{longjmp}-based scheme
+should use the @code{setjmp}/@code{longjmp} functions from the C library
+instead of the @code{__builtin_setjmp}/@code{__builtin_longjmp} machinery.
+@end defmac
+
+@defmac DWARF_CIE_DATA_ALIGNMENT
+This macro need only be defined if the target might save registers in the
+function prologue at an offset to the stack pointer that is not aligned to
+@code{UNITS_PER_WORD}.  The definition should be the negative minimum
+alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive
+minimum alignment otherwise.  @xref{SDB and DWARF}.  Only applicable if
+the target supports DWARF 2 frame unwind information.
+@end defmac
+
+@hook TARGET_TERMINATE_DW2_EH_FRAME_INFO
+Contains the value true if the target should add a zero word onto the
+end of a Dwarf-2 frame info section when used for exception handling.
+Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and
+true otherwise.
+@end deftypevr
+
+@hook TARGET_DWARF_REGISTER_SPAN
+Given a register, this hook should return a parallel of registers to
+represent where to find the register pieces.  Define this hook if the
+register and its mode are represented in Dwarf in non-contiguous
+locations, or if the register should be represented in more than one
+register in Dwarf.  Otherwise, this hook should return @code{NULL_RTX}.
+If not defined, the default is to return @code{NULL_RTX}.
+@end deftypefn
+
+@hook TARGET_INIT_DWARF_REG_SIZES_EXTRA
+If some registers are represented in Dwarf-2 unwind information in
+multiple pieces, define this hook to fill in information about the
+sizes of those pieces in the table used by the unwinder at runtime.
+It will be called by @code{expand_builtin_init_dwarf_reg_sizes} after
+filling in a single size corresponding to each hard register;
+@var{address} is the address of the table.
+@end deftypefn
+
+@hook TARGET_ASM_TTYPE
+This hook is used to output a reference from a frame unwinding table to
+the type_info object identified by @var{sym}.  It should return @code{true}
+if the reference was output.  Returning @code{false} will cause the
+reference to be output using the normal Dwarf2 routines.
+@end deftypefn
+
+@hook TARGET_ARM_EABI_UNWINDER
+This flag should be set to @code{true} on targets that use an ARM EABI
+based unwinding library, and @code{false} on other targets.  This effects
+the format of unwinding tables, and how the unwinder in entered after
+running a cleanup.  The default is @code{false}.
+@end deftypevr
+
+@node Alignment Output
+@subsection Assembler Commands for Alignment
+
+@c prevent bad page break with this line
+This describes commands for alignment.
+
+@defmac JUMP_ALIGN (@var{label})
+The alignment (log base 2) to put in front of @var{label}, which is
+a common destination of jumps and has no fallthru incoming edge.
+
+This macro need not be defined if you don't want any special alignment
+to be done at such a time.  Most machine descriptions do not currently
+define the macro.
+
+Unless it's necessary to inspect the @var{label} parameter, it is better
+to set the variable @var{align_jumps} in the target's
+@code{TARGET_OPTION_OVERRIDE}.  Otherwise, you should try to honor the user's
+selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation.
+@end defmac
+
+@hook TARGET_ASM_JUMP_ALIGN_MAX_SKIP
+The maximum number of bytes to skip before @var{label} when applying
+@code{JUMP_ALIGN}.  This works only if
+@code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
+@end deftypefn
+
+@defmac LABEL_ALIGN_AFTER_BARRIER (@var{label})
+The alignment (log base 2) to put in front of @var{label}, which follows
+a @code{BARRIER}.
+
+This macro need not be defined if you don't want any special alignment
+to be done at such a time.  Most machine descriptions do not currently
+define the macro.
+@end defmac
+
+@hook TARGET_ASM_LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP
+The maximum number of bytes to skip before @var{label} when applying
+@code{LABEL_ALIGN_AFTER_BARRIER}.  This works only if
+@code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined.
+@end deftypefn
+
+@defmac LOOP_ALIGN (@var{label})
+The alignment (log base 2) to put in front of @var{label}, which follows
+a @code{NOTE_INSN_LOOP_BEG} note.
+
+This macro need not be defined if you don't want any special alignment
+to be done at such a time.  Most machine descriptions do not currently
+define the macro.
+
+Unless it's necessary to inspect the @var{label} parameter, it is better
+to set the variable @code{align_loops} in the target's
+@code{TARGET_OPTION_OVERRIDE}.  Otherwise, you should try to honor the user's
+selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation.
+@end defmac
+
+@hook TARGET_ASM_LOOP_ALIGN_MAX_SKIP
+The maximum number of bytes to skip when applying @code{LOOP_ALIGN} to
+@var{label}.  This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is
+defined.
+@end deftypefn
+
+@defmac LABEL_ALIGN (@var{label})
+The alignment (log base 2) to put in front of @var{label}.
+If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment,
+the maximum of the specified values is used.
+
+Unless it's necessary to inspect the @var{label} parameter, it is better
+to set the variable @code{align_labels} in the target's
+@code{TARGET_OPTION_OVERRIDE}.  Otherwise, you should try to honor the user's
+selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation.
+@end defmac
+
+@hook TARGET_ASM_LABEL_ALIGN_MAX_SKIP
+The maximum number of bytes to skip when applying @code{LABEL_ALIGN}
+to @var{label}.  This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN}
+is defined.
+@end deftypefn
+
+@defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes})
+A C statement to output to the stdio stream @var{stream} an assembler
+instruction to advance the location counter by @var{nbytes} bytes.
+Those bytes should be zero when loaded.  @var{nbytes} will be a C
+expression of type @code{unsigned HOST_WIDE_INT}.
+@end defmac
+
+@defmac ASM_NO_SKIP_IN_TEXT
+Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the
+text section because it fails to put zeros in the bytes that are skipped.
+This is true on many Unix systems, where the pseudo--op to skip bytes
+produces no-op instructions rather than zeros when used in the text
+section.
+@end defmac
+
+@defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power})
+A C statement to output to the stdio stream @var{stream} an assembler
+command to advance the location counter to a multiple of 2 to the
+@var{power} bytes.  @var{power} will be a C expression of type @code{int}.
+@end defmac
+
+@defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power})
+Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used
+for padding, if necessary.
+@end defmac
+
+@defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip})
+A C statement to output to the stdio stream @var{stream} an assembler
+command to advance the location counter to a multiple of 2 to the
+@var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to
+satisfy the alignment request.  @var{power} and @var{max_skip} will be
+a C expression of type @code{int}.
+@end defmac
+
+@need 3000
+@node Debugging Info
+@section Controlling Debugging Information Format
+
+@c prevent bad page break with this line
+This describes how to specify debugging information.
+
+@menu
+* All Debuggers::      Macros that affect all debugging formats uniformly.
+* DBX Options::        Macros enabling specific options in DBX format.
+* DBX Hooks::          Hook macros for varying DBX format.
+* File Names and DBX:: Macros controlling output of file names in DBX format.
+* SDB and DWARF::      Macros for SDB (COFF) and DWARF formats.
+* VMS Debug::          Macros for VMS debug format.
+@end menu
+
+@node All Debuggers
+@subsection Macros Affecting All Debugging Formats
+
+@c prevent bad page break with this line
+These macros affect all debugging formats.
+
+@defmac DBX_REGISTER_NUMBER (@var{regno})
+A C expression that returns the DBX register number for the compiler
+register number @var{regno}.  In the default macro provided, the value
+of this expression will be @var{regno} itself.  But sometimes there are
+some registers that the compiler knows about and DBX does not, or vice
+versa.  In such cases, some register may need to have one number in the
+compiler and another for DBX@.
+
+If two registers have consecutive numbers inside GCC, and they can be
+used as a pair to hold a multiword value, then they @emph{must} have
+consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}.
+Otherwise, debuggers will be unable to access such a pair, because they
+expect register pairs to be consecutive in their own numbering scheme.
+
+If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that
+does not preserve register pairs, then what you must do instead is
+redefine the actual register numbering scheme.
+@end defmac
+
+@defmac DEBUGGER_AUTO_OFFSET (@var{x})
+A C expression that returns the integer offset value for an automatic
+variable having address @var{x} (an RTL expression).  The default
+computation assumes that @var{x} is based on the frame-pointer and
+gives the offset from the frame-pointer.  This is required for targets
+that produce debugging output for DBX or COFF-style debugging output
+for SDB and allow the frame-pointer to be eliminated when the
+@option{-g} options is used.
+@end defmac
+
+@defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x})
+A C expression that returns the integer offset value for an argument
+having address @var{x} (an RTL expression).  The nominal offset is
+@var{offset}.
+@end defmac
+
+@defmac PREFERRED_DEBUGGING_TYPE
+A C expression that returns the type of debugging output GCC should
+produce when the user specifies just @option{-g}.  Define
+this if you have arranged for GCC to support more than one format of
+debugging output.  Currently, the allowable values are @code{DBX_DEBUG},
+@code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG},
+@code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}.
+
+When the user specifies @option{-ggdb}, GCC normally also uses the
+value of this macro to select the debugging output format, but with two
+exceptions.  If @code{DWARF2_DEBUGGING_INFO} is defined, GCC uses the
+value @code{DWARF2_DEBUG}.  Otherwise, if @code{DBX_DEBUGGING_INFO} is
+defined, GCC uses @code{DBX_DEBUG}.
+
+The value of this macro only affects the default debugging output; the
+user can always get a specific type of output by using @option{-gstabs},
+@option{-gcoff}, @option{-gdwarf-2}, @option{-gxcoff}, or @option{-gvms}.
+@end defmac
+
+@node DBX Options
+@subsection Specific Options for DBX Output
+
+@c prevent bad page break with this line
+These are specific options for DBX output.
+
+@defmac DBX_DEBUGGING_INFO
+Define this macro if GCC should produce debugging output for DBX
+in response to the @option{-g} option.
+@end defmac
+
+@defmac XCOFF_DEBUGGING_INFO
+Define this macro if GCC should produce XCOFF format debugging output
+in response to the @option{-g} option.  This is a variant of DBX format.
+@end defmac
+
+@defmac DEFAULT_GDB_EXTENSIONS
+Define this macro to control whether GCC should by default generate
+GDB's extended version of DBX debugging information (assuming DBX-format
+debugging information is enabled at all).  If you don't define the
+macro, the default is 1: always generate the extended information
+if there is any occasion to.
+@end defmac
+
+@defmac DEBUG_SYMS_TEXT
+Define this macro if all @code{.stabs} commands should be output while
+in the text section.
+@end defmac
+
+@defmac ASM_STABS_OP
+A C string constant, including spacing, naming the assembler pseudo op to
+use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol.
+If you don't define this macro, @code{"\t.stabs\t"} is used.  This macro
+applies only to DBX debugging information format.
+@end defmac
+
+@defmac ASM_STABD_OP
+A C string constant, including spacing, naming the assembler pseudo op to
+use instead of @code{"\t.stabd\t"} to define a debugging symbol whose
+value is the current location.  If you don't define this macro,
+@code{"\t.stabd\t"} is used.  This macro applies only to DBX debugging
+information format.
+@end defmac
+
+@defmac ASM_STABN_OP
+A C string constant, including spacing, naming the assembler pseudo op to
+use instead of @code{"\t.stabn\t"} to define a debugging symbol with no
+name.  If you don't define this macro, @code{"\t.stabn\t"} is used.  This
+macro applies only to DBX debugging information format.
+@end defmac
+
+@defmac DBX_NO_XREFS
+Define this macro if DBX on your system does not support the construct
+@samp{xs@var{tagname}}.  On some systems, this construct is used to
+describe a forward reference to a structure named @var{tagname}.
+On other systems, this construct is not supported at all.
+@end defmac
+
+@defmac DBX_CONTIN_LENGTH
+A symbol name in DBX-format debugging information is normally
+continued (split into two separate @code{.stabs} directives) when it
+exceeds a certain length (by default, 80 characters).  On some
+operating systems, DBX requires this splitting; on others, splitting
+must not be done.  You can inhibit splitting by defining this macro
+with the value zero.  You can override the default splitting-length by
+defining this macro as an expression for the length you desire.
+@end defmac
+
+@defmac DBX_CONTIN_CHAR
+Normally continuation is indicated by adding a @samp{\} character to
+the end of a @code{.stabs} string when a continuation follows.  To use
+a different character instead, define this macro as a character
+constant for the character you want to use.  Do not define this macro
+if backslash is correct for your system.
+@end defmac
+
+@defmac DBX_STATIC_STAB_DATA_SECTION
+Define this macro if it is necessary to go to the data section before
+outputting the @samp{.stabs} pseudo-op for a non-global static
+variable.
+@end defmac
+
+@defmac DBX_TYPE_DECL_STABS_CODE
+The value to use in the ``code'' field of the @code{.stabs} directive
+for a typedef.  The default is @code{N_LSYM}.
+@end defmac
+
+@defmac DBX_STATIC_CONST_VAR_CODE
+The value to use in the ``code'' field of the @code{.stabs} directive
+for a static variable located in the text section.  DBX format does not
+provide any ``right'' way to do this.  The default is @code{N_FUN}.
+@end defmac
+
+@defmac DBX_REGPARM_STABS_CODE
+The value to use in the ``code'' field of the @code{.stabs} directive
+for a parameter passed in registers.  DBX format does not provide any
+``right'' way to do this.  The default is @code{N_RSYM}.
+@end defmac
+
+@defmac DBX_REGPARM_STABS_LETTER
+The letter to use in DBX symbol data to identify a symbol as a parameter
+passed in registers.  DBX format does not customarily provide any way to
+do this.  The default is @code{'P'}.
+@end defmac
+
+@defmac DBX_FUNCTION_FIRST
+Define this macro if the DBX information for a function and its
+arguments should precede the assembler code for the function.  Normally,
+in DBX format, the debugging information entirely follows the assembler
+code.
+@end defmac
+
+@defmac DBX_BLOCKS_FUNCTION_RELATIVE
+Define this macro, with value 1, if the value of a symbol describing
+the scope of a block (@code{N_LBRAC} or @code{N_RBRAC}) should be
+relative to the start of the enclosing function.  Normally, GCC uses
+an absolute address.
+@end defmac
+
+@defmac DBX_LINES_FUNCTION_RELATIVE
+Define this macro, with value 1, if the value of a symbol indicating
+the current line number (@code{N_SLINE}) should be relative to the
+start of the enclosing function.  Normally, GCC uses an absolute address.
+@end defmac
+
+@defmac DBX_USE_BINCL
+Define this macro if GCC should generate @code{N_BINCL} and
+@code{N_EINCL} stabs for included header files, as on Sun systems.  This
+macro also directs GCC to output a type number as a pair of a file
+number and a type number within the file.  Normally, GCC does not
+generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single
+number for a type number.
+@end defmac
+
+@node DBX Hooks
+@subsection Open-Ended Hooks for DBX Format
+
+@c prevent bad page break with this line
+These are hooks for DBX format.
+
+@defmac DBX_OUTPUT_LBRAC (@var{stream}, @var{name})
+Define this macro to say how to output to @var{stream} the debugging
+information for the start of a scope level for variable names.  The
+argument @var{name} is the name of an assembler symbol (for use with
+@code{assemble_name}) whose value is the address where the scope begins.
+@end defmac
+
+@defmac DBX_OUTPUT_RBRAC (@var{stream}, @var{name})
+Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level.
+@end defmac
+
+@defmac DBX_OUTPUT_NFUN (@var{stream}, @var{lscope_label}, @var{decl})
+Define this macro if the target machine requires special handling to
+output an @code{N_FUN} entry for the function @var{decl}.
+@end defmac
+
+@defmac DBX_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}, @var{counter})
+A C statement to output DBX debugging information before code for line
+number @var{line} of the current source file to the stdio stream
+@var{stream}.  @var{counter} is the number of time the macro was
+invoked, including the current invocation; it is intended to generate
+unique labels in the assembly output.
+
+This macro should not be defined if the default output is correct, or
+if it can be made correct by defining @code{DBX_LINES_FUNCTION_RELATIVE}.
+@end defmac
+
+@defmac NO_DBX_FUNCTION_END
+Some stabs encapsulation formats (in particular ECOFF), cannot handle the
+@code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct.
+On those machines, define this macro to turn this feature off without
+disturbing the rest of the gdb extensions.
+@end defmac
+
+@defmac NO_DBX_BNSYM_ENSYM
+Some assemblers cannot handle the @code{.stabd BNSYM/ENSYM,0,0} gdb dbx
+extension construct.  On those machines, define this macro to turn this
+feature off without disturbing the rest of the gdb extensions.
+@end defmac
+
+@node File Names and DBX
+@subsection File Names in DBX Format
+
+@c prevent bad page break with this line
+This describes file names in DBX format.
+
+@defmac DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name})
+A C statement to output DBX debugging information to the stdio stream
+@var{stream}, which indicates that file @var{name} is the main source
+file---the file specified as the input file for compilation.
+This macro is called only once, at the beginning of compilation.
+
+This macro need not be defined if the standard form of output
+for DBX debugging information is appropriate.
+
+It may be necessary to refer to a label equal to the beginning of the
+text section.  You can use @samp{assemble_name (stream, ltext_label_name)}
+to do so.  If you do this, you must also set the variable
+@var{used_ltext_label_name} to @code{true}.
+@end defmac
+
+@defmac NO_DBX_MAIN_SOURCE_DIRECTORY
+Define this macro, with value 1, if GCC should not emit an indication
+of the current directory for compilation and current source language at
+the beginning of the file.
+@end defmac
+
+@defmac NO_DBX_GCC_MARKER
+Define this macro, with value 1, if GCC should not emit an indication
+that this object file was compiled by GCC@.  The default is to emit
+an @code{N_OPT} stab at the beginning of every source file, with
+@samp{gcc2_compiled.} for the string and value 0.
+@end defmac
+
+@defmac DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name})
+A C statement to output DBX debugging information at the end of
+compilation of the main source file @var{name}.  Output should be
+written to the stdio stream @var{stream}.
+
+If you don't define this macro, nothing special is output at the end
+of compilation, which is correct for most machines.
+@end defmac
+
+@defmac DBX_OUTPUT_NULL_N_SO_AT_MAIN_SOURCE_FILE_END
+Define this macro @emph{instead of} defining
+@code{DBX_OUTPUT_MAIN_SOURCE_FILE_END}, if what needs to be output at
+the end of compilation is an @code{N_SO} stab with an empty string,
+whose value is the highest absolute text address in the file.
+@end defmac
+
+@need 2000
+@node SDB and DWARF
+@subsection Macros for SDB and DWARF Output
+
+@c prevent bad page break with this line
+Here are macros for SDB and DWARF output.
+
+@defmac SDB_DEBUGGING_INFO
+Define this macro if GCC should produce COFF-style debugging output
+for SDB in response to the @option{-g} option.
+@end defmac
+
+@defmac DWARF2_DEBUGGING_INFO
+Define this macro if GCC should produce dwarf version 2 format
+debugging output in response to the @option{-g} option.
+
+@hook TARGET_DWARF_CALLING_CONVENTION
+Define this to enable the dwarf attribute @code{DW_AT_calling_convention} to
+be emitted for each function.  Instead of an integer return the enum
+value for the @code{DW_CC_} tag.
+@end deftypefn
+
+To support optional call frame debugging information, you must also
+define @code{INCOMING_RETURN_ADDR_RTX} and either set
+@code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the
+prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save}
+as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't.
+@end defmac
+
+@defmac DWARF2_FRAME_INFO
+Define this macro to a nonzero value if GCC should always output
+Dwarf 2 frame information.  If @code{TARGET_EXCEPT_UNWIND_INFO}
+(@pxref{Exception Region Output}) returns @code{UI_DWARF2}, and
+exceptions are enabled, GCC will output this information not matter
+how you define @code{DWARF2_FRAME_INFO}.
+@end defmac
+
+@hook TARGET_DEBUG_UNWIND_INFO
+This hook defines the mechanism that will be used for describing frame
+unwind information to the debugger.  Normally the hook will return
+@code{UI_DWARF2} if DWARF 2 debug information is enabled, and
+return @code{UI_NONE} otherwise.
+
+A target may return @code{UI_DWARF2} even when DWARF 2 debug information
+is disabled in order to always output DWARF 2 frame information.
+
+A target may return @code{UI_TARGET} if it has ABI specified unwind tables.
+This will suppress generation of the normal debug frame unwind information.
+@end deftypefn
+
+@defmac DWARF2_ASM_LINE_DEBUG_INFO
+Define this macro to be a nonzero value if the assembler can generate Dwarf 2
+line debug info sections.  This will result in much more compact line number
+tables, and hence is desirable if it works.
+@end defmac
+
+@hook TARGET_WANT_DEBUG_PUB_SECTIONS
+
+@hook TARGET_DELAY_SCHED2
+
+@hook TARGET_DELAY_VARTRACK
+
+@defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
+A C statement to issue assembly directives that create a difference
+@var{lab1} minus @var{lab2}, using an integer of the given @var{size}.
+@end defmac
+
+@defmac ASM_OUTPUT_DWARF_VMS_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
+A C statement to issue assembly directives that create a difference
+between the two given labels in system defined units, e.g. instruction
+slots on IA64 VMS, using an integer of the given size.
+@end defmac
+
+@defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label}, @var{section})
+A C statement to issue assembly directives that create a
+section-relative reference to the given @var{label}, using an integer of the
+given @var{size}.  The label is known to be defined in the given @var{section}.
+@end defmac
+
+@defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label})
+A C statement to issue assembly directives that create a self-relative
+reference to the given @var{label}, using an integer of the given @var{size}.
+@end defmac
+
+@defmac ASM_OUTPUT_DWARF_TABLE_REF (@var{label})
+A C statement to issue assembly directives that create a reference to
+the DWARF table identifier @var{label} from the current section.  This
+is used on some systems to avoid garbage collecting a DWARF table which
+is referenced by a function.
+@end defmac
+
+@hook TARGET_ASM_OUTPUT_DWARF_DTPREL
+If defined, this target hook is a function which outputs a DTP-relative
+reference to the given TLS symbol of the specified size.
+@end deftypefn
+
+@defmac PUT_SDB_@dots{}
+Define these macros to override the assembler syntax for the special
+SDB assembler directives.  See @file{sdbout.c} for a list of these
+macros and their arguments.  If the standard syntax is used, you need
+not define them yourself.
+@end defmac
+
+@defmac SDB_DELIM
+Some assemblers do not support a semicolon as a delimiter, even between
+SDB assembler directives.  In that case, define this macro to be the
+delimiter to use (usually @samp{\n}).  It is not necessary to define
+a new set of @code{PUT_SDB_@var{op}} macros if this is the only change
+required.
+@end defmac
+
+@defmac SDB_ALLOW_UNKNOWN_REFERENCES
+Define this macro to allow references to unknown structure,
+union, or enumeration tags to be emitted.  Standard COFF does not
+allow handling of unknown references, MIPS ECOFF has support for
+it.
+@end defmac
+
+@defmac SDB_ALLOW_FORWARD_REFERENCES
+Define this macro to allow references to structure, union, or
+enumeration tags that have not yet been seen to be handled.  Some
+assemblers choke if forward tags are used, while some require it.
+@end defmac
+
+@defmac SDB_OUTPUT_SOURCE_LINE (@var{stream}, @var{line})
+A C statement to output SDB debugging information before code for line
+number @var{line} of the current source file to the stdio stream
+@var{stream}.  The default is to emit an @code{.ln} directive.
+@end defmac
+
+@need 2000
+@node VMS Debug
+@subsection Macros for VMS Debug Format
+
+@c prevent bad page break with this line
+Here are macros for VMS debug format.
+
+@defmac VMS_DEBUGGING_INFO
+Define this macro if GCC should produce debugging output for VMS
+in response to the @option{-g} option.  The default behavior for VMS
+is to generate minimal debug info for a traceback in the absence of
+@option{-g} unless explicitly overridden with @option{-g0}.  This
+behavior is controlled by @code{TARGET_OPTION_OPTIMIZATION} and
+@code{TARGET_OPTION_OVERRIDE}.
+@end defmac
+
+@node Floating Point
+@section Cross Compilation and Floating Point
+@cindex cross compilation and floating point
+@cindex floating point and cross compilation
+
+While all modern machines use twos-complement representation for integers,
+there are a variety of representations for floating point numbers.  This
+means that in a cross-compiler the representation of floating point numbers
+in the compiled program may be different from that used in the machine
+doing the compilation.
+
+Because different representation systems may offer different amounts of
+range and precision, all floating point constants must be represented in
+the target machine's format.  Therefore, the cross compiler cannot
+safely use the host machine's floating point arithmetic; it must emulate
+the target's arithmetic.  To ensure consistency, GCC always uses
+emulation to work with floating point values, even when the host and
+target floating point formats are identical.
+
+The following macros are provided by @file{real.h} for the compiler to
+use.  All parts of the compiler which generate or optimize
+floating-point calculations must use these macros.  They may evaluate
+their operands more than once, so operands must not have side effects.
+
+@defmac REAL_VALUE_TYPE
+The C data type to be used to hold a floating point value in the target
+machine's format.  Typically this is a @code{struct} containing an
+array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque
+quantity.
+@end defmac
+
+@deftypefn Macro int REAL_VALUES_EQUAL (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
+Compares for equality the two values, @var{x} and @var{y}.  If the target
+floating point format supports negative zeroes and/or NaNs,
+@samp{REAL_VALUES_EQUAL (-0.0, 0.0)} is true, and
+@samp{REAL_VALUES_EQUAL (NaN, NaN)} is false.
+@end deftypefn
+
+@deftypefn Macro int REAL_VALUES_LESS (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
+Tests whether @var{x} is less than @var{y}.
+@end deftypefn
+
+@deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x})
+Truncates @var{x} to a signed integer, rounding toward zero.
+@end deftypefn
+
+@deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x})
+Truncates @var{x} to an unsigned integer, rounding toward zero.  If
+@var{x} is negative, returns zero.
+@end deftypefn
+
+@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, enum machine_mode @var{mode})
+Converts @var{string} into a floating point number in the target machine's
+representation for mode @var{mode}.  This routine can handle both
+decimal and hexadecimal floating point constants, using the syntax
+defined by the C language for both.
+@end deftypefn
+
+@deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x})
+Returns 1 if @var{x} is negative (including negative zero), 0 otherwise.
+@end deftypefn
+
+@deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x})
+Determines whether @var{x} represents infinity (positive or negative).
+@end deftypefn
+
+@deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x})
+Determines whether @var{x} represents a ``NaN'' (not-a-number).
+@end deftypefn
+
+@deftypefn Macro void REAL_ARITHMETIC (REAL_VALUE_TYPE @var{output}, enum tree_code @var{code}, REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y})
+Calculates an arithmetic operation on the two floating point values
+@var{x} and @var{y}, storing the result in @var{output} (which must be a
+variable).
+
+The operation to be performed is specified by @var{code}.  Only the
+following codes are supported: @code{PLUS_EXPR}, @code{MINUS_EXPR},
+@code{MULT_EXPR}, @code{RDIV_EXPR}, @code{MAX_EXPR}, @code{MIN_EXPR}.
+
+If @code{REAL_ARITHMETIC} is asked to evaluate division by zero and the
+target's floating point format cannot represent infinity, it will call
+@code{abort}.  Callers should check for this situation first, using
+@code{MODE_HAS_INFINITIES}.  @xref{Storage Layout}.
+@end deftypefn
+
+@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x})
+Returns the negative of the floating point value @var{x}.
+@end deftypefn
+
+@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x})
+Returns the absolute value of @var{x}.
+@end deftypefn
+
+@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_TRUNCATE (REAL_VALUE_TYPE @var{mode}, enum machine_mode @var{x})
+Truncates the floating point value @var{x} to fit in @var{mode}.  The
+return value is still a full-size @code{REAL_VALUE_TYPE}, but it has an
+appropriate bit pattern to be output as a floating constant whose
+precision accords with mode @var{mode}.
+@end deftypefn
+
+@deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x})
+Converts a floating point value @var{x} into a double-precision integer
+which is then stored into @var{low} and @var{high}.  If the value is not
+integral, it is truncated.
+@end deftypefn
+
+@deftypefn Macro void REAL_VALUE_FROM_INT (REAL_VALUE_TYPE @var{x}, HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, enum machine_mode @var{mode})
+Converts a double-precision integer found in @var{low} and @var{high},
+into a floating point value which is then stored into @var{x}.  The
+value is truncated to fit in mode @var{mode}.
+@end deftypefn
+
+@node Mode Switching
+@section Mode Switching Instructions
+@cindex mode switching
+The following macros control mode switching optimizations:
+
+@defmac OPTIMIZE_MODE_SWITCHING (@var{entity})
+Define this macro if the port needs extra instructions inserted for mode
+switching in an optimizing compilation.
+
+For an example, the SH4 can perform both single and double precision
+floating point operations, but to perform a single precision operation,
+the FPSCR PR bit has to be cleared, while for a double precision
+operation, this bit has to be set.  Changing the PR bit requires a general
+purpose register as a scratch register, hence these FPSCR sets have to
+be inserted before reload, i.e.@: you can't put this into instruction emitting
+or @code{TARGET_MACHINE_DEPENDENT_REORG}.
+
+You can have multiple entities that are mode-switched, and select at run time
+which entities actually need it.  @code{OPTIMIZE_MODE_SWITCHING} should
+return nonzero for any @var{entity} that needs mode-switching.
+If you define this macro, you also have to define
+@code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED},
+@code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}.
+@code{MODE_AFTER}, @code{MODE_ENTRY}, and @code{MODE_EXIT}
+are optional.
+@end defmac
+
+@defmac NUM_MODES_FOR_MODE_SWITCHING
+If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as
+initializer for an array of integers.  Each initializer element
+N refers to an entity that needs mode switching, and specifies the number
+of different modes that might need to be set for this entity.
+The position of the initializer in the initializer---starting counting at
+zero---determines the integer that is used to refer to the mode-switched
+entity in question.
+In macros that take mode arguments / yield a mode result, modes are
+represented as numbers 0 @dots{} N @minus{} 1.  N is used to specify that no mode
+switch is needed / supplied.
+@end defmac
+
+@defmac MODE_NEEDED (@var{entity}, @var{insn})
+@var{entity} is an integer specifying a mode-switched entity.  If
+@code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to
+return an integer value not larger than the corresponding element in
+@code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must
+be switched into prior to the execution of @var{insn}.
+@end defmac
+
+@defmac MODE_AFTER (@var{mode}, @var{insn})
+If this macro is defined, it is evaluated for every @var{insn} during
+mode switching.  It determines the mode that an insn results in (if
+different from the incoming mode).
+@end defmac
+
+@defmac MODE_ENTRY (@var{entity})
+If this macro is defined, it is evaluated for every @var{entity} that needs
+mode switching.  It should evaluate to an integer, which is a mode that
+@var{entity} is assumed to be switched to at function entry.  If @code{MODE_ENTRY}
+is defined then @code{MODE_EXIT} must be defined.
+@end defmac
+
+@defmac MODE_EXIT (@var{entity})
+If this macro is defined, it is evaluated for every @var{entity} that needs
+mode switching.  It should evaluate to an integer, which is a mode that
+@var{entity} is assumed to be switched to at function exit.  If @code{MODE_EXIT}
+is defined then @code{MODE_ENTRY} must be defined.
+@end defmac
+
+@defmac MODE_PRIORITY_TO_MODE (@var{entity}, @var{n})
+This macro specifies the order in which modes for @var{entity} are processed.
+0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the
+lowest.  The value of the macro should be an integer designating a mode
+for @var{entity}.  For any fixed @var{entity}, @code{mode_priority_to_mode}
+(@var{entity}, @var{n}) shall be a bijection in 0 @dots{}
+@code{num_modes_for_mode_switching[@var{entity}] - 1}.
+@end defmac
+
+@defmac EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live})
+Generate one or more insns to set @var{entity} to @var{mode}.
+@var{hard_reg_live} is the set of hard registers live at the point where
+the insn(s) are to be inserted.
+@end defmac
+
+@node Target Attributes
+@section Defining target-specific uses of @code{__attribute__}
+@cindex target attributes
+@cindex machine attributes
+@cindex attributes, target-specific
+
+Target-specific attributes may be defined for functions, data and types.
+These are described using the following target hooks; they also need to
+be documented in @file{extend.texi}.
+
+@hook TARGET_ATTRIBUTE_TABLE
+If defined, this target hook points to an array of @samp{struct
+attribute_spec} (defined in @file{tree.h}) specifying the machine
+specific attributes for this target and some of the restrictions on the
+entities to which these attributes are applied and the arguments they
+take.
+@end deftypevr
+
+@hook TARGET_ATTRIBUTE_TAKES_IDENTIFIER_P
+If defined, this target hook is a function which returns true if the
+machine-specific attribute named @var{name} expects an identifier
+given as its first argument to be passed on as a plain identifier, not
+subjected to name lookup.  If this is not defined, the default is
+false for all machine-specific attributes.
+@end deftypefn
+
+@hook TARGET_COMP_TYPE_ATTRIBUTES
+If defined, this target hook is a function which returns zero if the attributes on
+@var{type1} and @var{type2} are incompatible, one if they are compatible,
+and two if they are nearly compatible (which causes a warning to be
+generated).  If this is not defined, machine-specific attributes are
+supposed always to be compatible.
+@end deftypefn
+
+@hook TARGET_SET_DEFAULT_TYPE_ATTRIBUTES
+If defined, this target hook is a function which assigns default attributes to
+the newly defined @var{type}.
+@end deftypefn
+
+@hook TARGET_MERGE_TYPE_ATTRIBUTES
+Define this target hook if the merging of type attributes needs special
+handling.  If defined, the result is a list of the combined
+@code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}.  It is assumed
+that @code{comptypes} has already been called and returned 1.  This
+function may call @code{merge_attributes} to handle machine-independent
+merging.
+@end deftypefn
+
+@hook TARGET_MERGE_DECL_ATTRIBUTES
+Define this target hook if the merging of decl attributes needs special
+handling.  If defined, the result is a list of the combined
+@code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}.
+@var{newdecl} is a duplicate declaration of @var{olddecl}.  Examples of
+when this is needed are when one attribute overrides another, or when an
+attribute is nullified by a subsequent definition.  This function may
+call @code{merge_attributes} to handle machine-independent merging.
+
+@findex TARGET_DLLIMPORT_DECL_ATTRIBUTES
+If the only target-specific handling you require is @samp{dllimport}
+for Microsoft Windows targets, you should define the macro
+@code{TARGET_DLLIMPORT_DECL_ATTRIBUTES} to @code{1}.  The compiler
+will then define a function called
+@code{merge_dllimport_decl_attributes} which can then be defined as
+the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}.  You can also
+add @code{handle_dll_attribute} in the attribute table for your port
+to perform initial processing of the @samp{dllimport} and
+@samp{dllexport} attributes.  This is done in @file{i386/cygwin.h} and
+@file{i386/i386.c}, for example.
+@end deftypefn
+
+@hook TARGET_VALID_DLLIMPORT_ATTRIBUTE_P
+
+@defmac TARGET_DECLSPEC
+Define this macro to a nonzero value if you want to treat
+@code{__declspec(X)} as equivalent to @code{__attribute((X))}.  By
+default, this behavior is enabled only for targets that define
+@code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}.  The current implementation
+of @code{__declspec} is via a built-in macro, but you should not rely
+on this implementation detail.
+@end defmac
+
+@hook TARGET_INSERT_ATTRIBUTES
+Define this target hook if you want to be able to add attributes to a decl
+when it is being created.  This is normally useful for back ends which
+wish to implement a pragma by using the attributes which correspond to
+the pragma's effect.  The @var{node} argument is the decl which is being
+created.  The @var{attr_ptr} argument is a pointer to the attribute list
+for this decl.  The list itself should not be modified, since it may be
+shared with other decls, but attributes may be chained on the head of
+the list and @code{*@var{attr_ptr}} modified to point to the new
+attributes, or a copy of the list may be made if further changes are
+needed.
+@end deftypefn
+
+@hook TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P
+@cindex inlining
+This target hook returns @code{true} if it is ok to inline @var{fndecl}
+into the current function, despite its having target-specific
+attributes, @code{false} otherwise.  By default, if a function has a
+target specific attribute attached to it, it will not be inlined.
+@end deftypefn
+
+@hook TARGET_OPTION_VALID_ATTRIBUTE_P
+This hook is called to parse the @code{attribute(option("..."))}, and
+it allows the function to set different target machine compile time
+options for the current function that might be different than the
+options specified on the command line.  The hook should return
+@code{true} if the options are valid.
+
+The hook should set the @var{DECL_FUNCTION_SPECIFIC_TARGET} field in
+the function declaration to hold a pointer to a target specific
+@var{struct cl_target_option} structure.
+@end deftypefn
+
+@hook TARGET_OPTION_SAVE
+This hook is called to save any additional target specific information
+in the @var{struct cl_target_option} structure for function specific
+options.
+@xref{Option file format}.
+@end deftypefn
+
+@hook TARGET_OPTION_RESTORE
+This hook is called to restore any additional target specific
+information in the @var{struct cl_target_option} structure for
+function specific options.
+@end deftypefn
+
+@hook TARGET_OPTION_PRINT
+This hook is called to print any additional target specific
+information in the @var{struct cl_target_option} structure for
+function specific options.
+@end deftypefn
+
+@hook TARGET_OPTION_PRAGMA_PARSE
+This target hook parses the options for @code{#pragma GCC option} to
+set the machine specific options for functions that occur later in the
+input stream.  The options should be the same as handled by the
+@code{TARGET_OPTION_VALID_ATTRIBUTE_P} hook.
+@end deftypefn
+
+@hook TARGET_OPTION_OVERRIDE
+Sometimes certain combinations of command options do not make sense on
+a particular target machine.  You can override the hook
+@code{TARGET_OPTION_OVERRIDE} to take account of this.  This hooks is called
+once just after all the command options have been parsed.
+
+Don't use this hook to turn on various extra optimizations for
+@option{-O}.  That is what @code{TARGET_OPTION_OPTIMIZATION} is for.
+
+If you need to do something whenever the optimization level is
+changed via the optimize attribute or pragma, see
+@code{TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE}
+@end deftypefn
+
+@hook TARGET_CAN_INLINE_P
+This target hook returns @code{false} if the @var{caller} function
+cannot inline @var{callee}, based on target specific information.  By
+default, inlining is not allowed if the callee function has function
+specific target options and the caller does not use the same options.
+@end deftypefn
+
+@node Emulated TLS
+@section Emulating TLS
+@cindex Emulated TLS
+
+For targets whose psABI does not provide Thread Local Storage via
+specific relocations and instruction sequences, an emulation layer is
+used.  A set of target hooks allows this emulation layer to be
+configured for the requirements of a particular target.  For instance
+the psABI may in fact specify TLS support in terms of an emulation
+layer.
+
+The emulation layer works by creating a control object for every TLS
+object.  To access the TLS object, a lookup function is provided
+which, when given the address of the control object, will return the
+address of the current thread's instance of the TLS object.
+
+@hook TARGET_EMUTLS_GET_ADDRESS
+Contains the name of the helper function that uses a TLS control
+object to locate a TLS instance.  The default causes libgcc's
+emulated TLS helper function to be used.
+@end deftypevr
+
+@hook TARGET_EMUTLS_REGISTER_COMMON
+Contains the name of the helper function that should be used at
+program startup to register TLS objects that are implicitly
+initialized to zero.  If this is @code{NULL}, all TLS objects will
+have explicit initializers.  The default causes libgcc's emulated TLS
+registration function to be used.
+@end deftypevr
+
+@hook TARGET_EMUTLS_VAR_SECTION
+Contains the name of the section in which TLS control variables should
+be placed.  The default of @code{NULL} allows these to be placed in
+any section.
+@end deftypevr
+
+@hook TARGET_EMUTLS_TMPL_SECTION
+Contains the name of the section in which TLS initializers should be
+placed.  The default of @code{NULL} allows these to be placed in any
+section.
+@end deftypevr
+
+@hook TARGET_EMUTLS_VAR_PREFIX
+Contains the prefix to be prepended to TLS control variable names.
+The default of @code{NULL} uses a target-specific prefix.
+@end deftypevr
+
+@hook TARGET_EMUTLS_TMPL_PREFIX
+Contains the prefix to be prepended to TLS initializer objects.  The
+default of @code{NULL} uses a target-specific prefix.
+@end deftypevr
+
+@hook TARGET_EMUTLS_VAR_FIELDS
+Specifies a function that generates the FIELD_DECLs for a TLS control
+object type.  @var{type} is the RECORD_TYPE the fields are for and
+@var{name} should be filled with the structure tag, if the default of
+@code{__emutls_object} is unsuitable.  The default creates a type suitable
+for libgcc's emulated TLS function.
+@end deftypefn
+
+@hook TARGET_EMUTLS_VAR_INIT
+Specifies a function that generates the CONSTRUCTOR to initialize a
+TLS control object.  @var{var} is the TLS control object, @var{decl}
+is the TLS object and @var{tmpl_addr} is the address of the
+initializer.  The default initializes libgcc's emulated TLS control object.
+@end deftypefn
+
+@hook TARGET_EMUTLS_VAR_ALIGN_FIXED
+Specifies whether the alignment of TLS control variable objects is
+fixed and should not be increased as some backends may do to optimize
+single objects.  The default is false.
+@end deftypevr
+
+@hook TARGET_EMUTLS_DEBUG_FORM_TLS_ADDRESS
+Specifies whether a DWARF @code{DW_OP_form_tls_address} location descriptor
+may be used to describe emulated TLS control objects.
+@end deftypevr
+
+@node MIPS Coprocessors
+@section Defining coprocessor specifics for MIPS targets.
+@cindex MIPS coprocessor-definition macros
+
+The MIPS specification allows MIPS implementations to have as many as 4
+coprocessors, each with as many as 32 private registers.  GCC supports
+accessing these registers and transferring values between the registers
+and memory using asm-ized variables.  For example:
+
+@smallexample
+  register unsigned int cp0count asm ("c0r1");
+  unsigned int d;
+
+  d = cp0count + 3;
+@end smallexample
+
+(``c0r1'' is the default name of register 1 in coprocessor 0; alternate
+names may be added as described below, or the default names may be
+overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.)
+
+Coprocessor registers are assumed to be epilogue-used; sets to them will
+be preserved even if it does not appear that the register is used again
+later in the function.
+
+Another note: according to the MIPS spec, coprocessor 1 (if present) is
+the FPU@.  One accesses COP1 registers through standard mips
+floating-point support; they are not included in this mechanism.
+
+There is one macro used in defining the MIPS coprocessor interface which
+you may want to override in subtargets; it is described below.
+
+@defmac ALL_COP_ADDITIONAL_REGISTER_NAMES
+A comma-separated list (with leading comma) of pairs describing the
+alternate names of coprocessor registers.  The format of each entry should be
+@smallexample
+@{ @var{alternatename}, @var{register_number}@}
+@end smallexample
+Default: empty.
+@end defmac
+
+@node PCH Target
+@section Parameters for Precompiled Header Validity Checking
+@cindex parameters, precompiled headers
+
+@hook TARGET_GET_PCH_VALIDITY
+This hook returns a pointer to the data needed by
+@code{TARGET_PCH_VALID_P} and sets
+@samp{*@var{sz}} to the size of the data in bytes.
+@end deftypefn
+
+@hook TARGET_PCH_VALID_P
+This hook checks whether the options used to create a PCH file are
+compatible with the current settings.  It returns @code{NULL}
+if so and a suitable error message if not.  Error messages will
+be presented to the user and must be localized using @samp{_(@var{msg})}.
+
+@var{data} is the data that was returned by @code{TARGET_GET_PCH_VALIDITY}
+when the PCH file was created and @var{sz} is the size of that data in bytes.
+It's safe to assume that the data was created by the same version of the
+compiler, so no format checking is needed.
+
+The default definition of @code{default_pch_valid_p} should be
+suitable for most targets.
+@end deftypefn
+
+@hook TARGET_CHECK_PCH_TARGET_FLAGS
+If this hook is nonnull, the default implementation of
+@code{TARGET_PCH_VALID_P} will use it to check for compatible values
+of @code{target_flags}.  @var{pch_flags} specifies the value that
+@code{target_flags} had when the PCH file was created.  The return
+value is the same as for @code{TARGET_PCH_VALID_P}.
+@end deftypefn
+
+@node C++ ABI
+@section C++ ABI parameters
+@cindex parameters, c++ abi
+
+@hook TARGET_CXX_GUARD_TYPE
+Define this hook to override the integer type used for guard variables.
+These are used to implement one-time construction of static objects.  The
+default is long_long_integer_type_node.
+@end deftypefn
+
+@hook TARGET_CXX_GUARD_MASK_BIT
+This hook determines how guard variables are used.  It should return
+@code{false} (the default) if the first byte should be used.  A return value of
+@code{true} indicates that only the least significant bit should be used.
+@end deftypefn
+
+@hook TARGET_CXX_GET_COOKIE_SIZE
+This hook returns the size of the cookie to use when allocating an array
+whose elements have the indicated @var{type}.  Assumes that it is already
+known that a cookie is needed.  The default is
+@code{max(sizeof (size_t), alignof(type))}, as defined in section 2.7 of the
+IA64/Generic C++ ABI@.
+@end deftypefn
+
+@hook TARGET_CXX_COOKIE_HAS_SIZE
+This hook should return @code{true} if the element size should be stored in
+array cookies.  The default is to return @code{false}.
+@end deftypefn
+
+@hook TARGET_CXX_IMPORT_EXPORT_CLASS
+If defined by a backend this hook allows the decision made to export
+class @var{type} to be overruled.  Upon entry @var{import_export}
+will contain 1 if the class is going to be exported, @minus{}1 if it is going
+to be imported and 0 otherwise.  This function should return the
+modified value and perform any other actions necessary to support the
+backend's targeted operating system.
+@end deftypefn
+
+@hook TARGET_CXX_CDTOR_RETURNS_THIS
+This hook should return @code{true} if constructors and destructors return
+the address of the object created/destroyed.  The default is to return
+@code{false}.
+@end deftypefn
+
+@hook TARGET_CXX_KEY_METHOD_MAY_BE_INLINE
+This hook returns true if the key method for a class (i.e., the method
+which, if defined in the current translation unit, causes the virtual
+table to be emitted) may be an inline function.  Under the standard
+Itanium C++ ABI the key method may be an inline function so long as
+the function is not declared inline in the class definition.  Under
+some variants of the ABI, an inline function can never be the key
+method.  The default is to return @code{true}.
+@end deftypefn
+
+@hook TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY
+
+@hook TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT
+This hook returns true (the default) if virtual tables and other
+similar implicit class data objects are always COMDAT if they have
+external linkage.  If this hook returns false, then class data for
+classes whose virtual table will be emitted in only one translation
+unit will not be COMDAT.
+@end deftypefn
+
+@hook TARGET_CXX_LIBRARY_RTTI_COMDAT
+This hook returns true (the default) if the RTTI information for
+the basic types which is defined in the C++ runtime should always
+be COMDAT, false if it should not be COMDAT.
+@end deftypefn
+
+@hook TARGET_CXX_USE_AEABI_ATEXIT
+This hook returns true if @code{__aeabi_atexit} (as defined by the ARM EABI)
+should be used to register static destructors when @option{-fuse-cxa-atexit}
+is in effect.  The default is to return false to use @code{__cxa_atexit}.
+@end deftypefn
+
+@hook TARGET_CXX_USE_ATEXIT_FOR_CXA_ATEXIT
+This hook returns true if the target @code{atexit} function can be used
+in the same manner as @code{__cxa_atexit} to register C++ static
+destructors. This requires that @code{atexit}-registered functions in
+shared libraries are run in the correct order when the libraries are
+unloaded. The default is to return false.
+@end deftypefn
+
+@hook TARGET_CXX_ADJUST_CLASS_AT_DEFINITION
+
+@node Named Address Spaces
+@section Adding support for named address spaces
+@cindex named address spaces
+
+The draft technical report of the ISO/IEC JTC1 S22 WG14 N1275
+standards committee, @cite{Programming Languages - C - Extensions to
+support embedded processors}, specifies a syntax for embedded
+processors to specify alternate address spaces.  You can configure a
+GCC port to support section 5.1 of the draft report to add support for
+address spaces other than the default address space.  These address
+spaces are new keywords that are similar to the @code{volatile} and
+@code{const} type attributes.
+
+Pointers to named address spaces can have a different size than
+pointers to the generic address space.
+
+For example, the SPU port uses the @code{__ea} address space to refer
+to memory in the host processor, rather than memory local to the SPU
+processor.  Access to memory in the @code{__ea} address space involves
+issuing DMA operations to move data between the host processor and the
+local processor memory address space.  Pointers in the @code{__ea}
+address space are either 32 bits or 64 bits based on the
+@option{-mea32} or @option{-mea64} switches (native SPU pointers are
+always 32 bits).
+
+Internally, address spaces are represented as a small integer in the
+range 0 to 15 with address space 0 being reserved for the generic
+address space.
+
+To register a named address space qualifier keyword with the C front end,
+the target may call the @code{c_register_addr_space} routine.  For example,
+the SPU port uses the following to declare @code{__ea} as the keyword for
+named address space #1:
+@smallexample
+#define ADDR_SPACE_EA 1
+c_register_addr_space ("__ea", ADDR_SPACE_EA);
+@end smallexample
+
+@hook TARGET_ADDR_SPACE_POINTER_MODE
+Define this to return the machine mode to use for pointers to
+@var{address_space} if the target supports named address spaces.
+The default version of this hook returns @code{ptr_mode} for the
+generic address space only.
+@end deftypefn
+
+@hook TARGET_ADDR_SPACE_ADDRESS_MODE
+Define this to return the machine mode to use for addresses in
+@var{address_space} if the target supports named address spaces.
+The default version of this hook returns @code{Pmode} for the
+generic address space only.
+@end deftypefn
+
+@hook TARGET_ADDR_SPACE_VALID_POINTER_MODE
+Define this to return nonzero if the port can handle pointers
+with machine mode @var{mode} to address space @var{as}.  This target
+hook is the same as the @code{TARGET_VALID_POINTER_MODE} target hook,
+except that it includes explicit named address space support.  The default
+version of this hook returns true for the modes returned by either the
+@code{TARGET_ADDR_SPACE_POINTER_MODE} or @code{TARGET_ADDR_SPACE_ADDRESS_MODE}
+target hooks for the given address space.
+@end deftypefn
+
+@hook TARGET_ADDR_SPACE_LEGITIMATE_ADDRESS_P
+Define this to return true if @var{exp} is a valid address for mode
+@var{mode} in the named address space @var{as}.  The @var{strict}
+parameter says whether strict addressing is in effect after reload has
+finished.  This target hook is the same as the
+@code{TARGET_LEGITIMATE_ADDRESS_P} target hook, except that it includes
+explicit named address space support.
+@end deftypefn
+
+@hook TARGET_ADDR_SPACE_LEGITIMIZE_ADDRESS
+Define this to modify an invalid address @var{x} to be a valid address
+with mode @var{mode} in the named address space @var{as}.  This target
+hook is the same as the @code{TARGET_LEGITIMIZE_ADDRESS} target hook,
+except that it includes explicit named address space support.
+@end deftypefn
+
+@hook TARGET_ADDR_SPACE_SUBSET_P
+Define this to return whether the @var{subset} named address space is
+contained within the @var{superset} named address space.  Pointers to
+a named address space that is a subset of another named address space
+will be converted automatically without a cast if used together in
+arithmetic operations.  Pointers to a superset address space can be
+converted to pointers to a subset address space via explicit casts.
+@end deftypefn
+
+@hook TARGET_ADDR_SPACE_CONVERT
+Define this to convert the pointer expression represented by the RTL
+@var{op} with type @var{from_type} that points to a named address
+space to a new pointer expression with type @var{to_type} that points
+to a different named address space.  When this hook it called, it is
+guaranteed that one of the two address spaces is a subset of the other,
+as determined by the @code{TARGET_ADDR_SPACE_SUBSET_P} target hook.
+@end deftypefn
+
+@node Misc
+@section Miscellaneous Parameters
+@cindex parameters, miscellaneous
+
+@c prevent bad page break with this line
+Here are several miscellaneous parameters.
+
+@defmac HAS_LONG_COND_BRANCH
+Define this boolean macro to indicate whether or not your architecture
+has conditional branches that can span all of memory.  It is used in
+conjunction with an optimization that partitions hot and cold basic
+blocks into separate sections of the executable.  If this macro is
+set to false, gcc will convert any conditional branches that attempt
+to cross between sections into unconditional branches or indirect jumps.
+@end defmac
+
+@defmac HAS_LONG_UNCOND_BRANCH
+Define this boolean macro to indicate whether or not your architecture
+has unconditional branches that can span all of memory.  It is used in
+conjunction with an optimization that partitions hot and cold basic
+blocks into separate sections of the executable.  If this macro is
+set to false, gcc will convert any unconditional branches that attempt
+to cross between sections into indirect jumps.
+@end defmac
+
+@defmac CASE_VECTOR_MODE
+An alias for a machine mode name.  This is the machine mode that
+elements of a jump-table should have.
+@end defmac
+
+@defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body})
+Optional: return the preferred mode for an @code{addr_diff_vec}
+when the minimum and maximum offset are known.  If you define this,
+it enables extra code in branch shortening to deal with @code{addr_diff_vec}.
+To make this work, you also have to define @code{INSN_ALIGN} and
+make the alignment for @code{addr_diff_vec} explicit.
+The @var{body} argument is provided so that the offset_unsigned and scale
+flags can be updated.
+@end defmac
+
+@defmac CASE_VECTOR_PC_RELATIVE
+Define this macro to be a C expression to indicate when jump-tables
+should contain relative addresses.  You need not define this macro if
+jump-tables never contain relative addresses, or jump-tables should
+contain relative addresses only when @option{-fPIC} or @option{-fPIC}
+is in effect.
+@end defmac
+
+@hook TARGET_CASE_VALUES_THRESHOLD
+This function return the smallest number of different values for which it
+is best to use a jump-table instead of a tree of conditional branches.
+The default is four for machines with a @code{casesi} instruction and
+five otherwise.  This is best for most machines.
+@end deftypefn
+
+@defmac CASE_USE_BIT_TESTS
+Define this macro to be a C expression to indicate whether C switch
+statements may be implemented by a sequence of bit tests.  This is
+advantageous on processors that can efficiently implement left shift
+of 1 by the number of bits held in a register, but inappropriate on
+targets that would require a loop.  By default, this macro returns
+@code{true} if the target defines an @code{ashlsi3} pattern, and
+@code{false} otherwise.
+@end defmac
+
+@defmac WORD_REGISTER_OPERATIONS
+Define this macro if operations between registers with integral mode
+smaller than a word are always performed on the entire register.
+Most RISC machines have this property and most CISC machines do not.
+@end defmac
+
+@defmac LOAD_EXTEND_OP (@var{mem_mode})
+Define this macro to be a C expression indicating when insns that read
+memory in @var{mem_mode}, an integral mode narrower than a word, set the
+bits outside of @var{mem_mode} to be either the sign-extension or the
+zero-extension of the data read.  Return @code{SIGN_EXTEND} for values
+of @var{mem_mode} for which the
+insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and
+@code{UNKNOWN} for other modes.
+
+This macro is not called with @var{mem_mode} non-integral or with a width
+greater than or equal to @code{BITS_PER_WORD}, so you may return any
+value in this case.  Do not define this macro if it would always return
+@code{UNKNOWN}.  On machines where this macro is defined, you will normally
+define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}.
+
+You may return a non-@code{UNKNOWN} value even if for some hard registers
+the sign extension is not performed, if for the @code{REGNO_REG_CLASS}
+of these hard registers @code{CANNOT_CHANGE_MODE_CLASS} returns nonzero
+when the @var{from} mode is @var{mem_mode} and the @var{to} mode is any
+integral mode larger than this but not larger than @code{word_mode}.
+
+You must return @code{UNKNOWN} if for some hard registers that allow this
+mode, @code{CANNOT_CHANGE_MODE_CLASS} says that they cannot change to
+@code{word_mode}, but that they can change to another integral mode that
+is larger then @var{mem_mode} but still smaller than @code{word_mode}.
+@end defmac
+
+@defmac SHORT_IMMEDIATES_SIGN_EXTEND
+Define this macro if loading short immediate values into registers sign
+extends.
+@end defmac
+
+@defmac FIXUNS_TRUNC_LIKE_FIX_TRUNC
+Define this macro if the same instructions that convert a floating
+point number to a signed fixed point number also convert validly to an
+unsigned one.
+@end defmac
+
+@hook TARGET_MIN_DIVISIONS_FOR_RECIP_MUL
+When @option{-ffast-math} is in effect, GCC tries to optimize
+divisions by the same divisor, by turning them into multiplications by
+the reciprocal.  This target hook specifies the minimum number of divisions
+that should be there for GCC to perform the optimization for a variable
+of mode @var{mode}.  The default implementation returns 3 if the machine
+has an instruction for the division, and 2 if it does not.
+@end deftypefn
+
+@defmac MOVE_MAX
+The maximum number of bytes that a single instruction can move quickly
+between memory and registers or between two memory locations.
+@end defmac
+
+@defmac MAX_MOVE_MAX
+The maximum number of bytes that a single instruction can move quickly
+between memory and registers or between two memory locations.  If this
+is undefined, the default is @code{MOVE_MAX}.  Otherwise, it is the
+constant value that is the largest value that @code{MOVE_MAX} can have
+at run-time.
+@end defmac
+
+@defmac SHIFT_COUNT_TRUNCATED
+A C expression that is nonzero if on this machine the number of bits
+actually used for the count of a shift operation is equal to the number
+of bits needed to represent the size of the object being shifted.  When
+this macro is nonzero, the compiler will assume that it is safe to omit
+a sign-extend, zero-extend, and certain bitwise `and' instructions that
+truncates the count of a shift operation.  On machines that have
+instructions that act on bit-fields at variable positions, which may
+include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED}
+also enables deletion of truncations of the values that serve as
+arguments to bit-field instructions.
+
+If both types of instructions truncate the count (for shifts) and
+position (for bit-field operations), or if no variable-position bit-field
+instructions exist, you should define this macro.
+
+However, on some machines, such as the 80386 and the 680x0, truncation
+only applies to shift operations and not the (real or pretended)
+bit-field operations.  Define @code{SHIFT_COUNT_TRUNCATED} to be zero on
+such machines.  Instead, add patterns to the @file{md} file that include
+the implied truncation of the shift instructions.
+
+You need not define this macro if it would always have the value of zero.
+@end defmac
+
+@anchor{TARGET_SHIFT_TRUNCATION_MASK}
+@hook TARGET_SHIFT_TRUNCATION_MASK
+This function describes how the standard shift patterns for @var{mode}
+deal with shifts by negative amounts or by more than the width of the mode.
+@xref{shift patterns}.
+
+On many machines, the shift patterns will apply a mask @var{m} to the
+shift count, meaning that a fixed-width shift of @var{x} by @var{y} is
+equivalent to an arbitrary-width shift of @var{x} by @var{y & m}.  If
+this is true for mode @var{mode}, the function should return @var{m},
+otherwise it should return 0.  A return value of 0 indicates that no
+particular behavior is guaranteed.
+
+Note that, unlike @code{SHIFT_COUNT_TRUNCATED}, this function does
+@emph{not} apply to general shift rtxes; it applies only to instructions
+that are generated by the named shift patterns.
+
+The default implementation of this function returns
+@code{GET_MODE_BITSIZE (@var{mode}) - 1} if @code{SHIFT_COUNT_TRUNCATED}
+and 0 otherwise.  This definition is always safe, but if
+@code{SHIFT_COUNT_TRUNCATED} is false, and some shift patterns
+nevertheless truncate the shift count, you may get better code
+by overriding it.
+@end deftypefn
+
+@defmac TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec})
+A C expression which is nonzero if on this machine it is safe to
+``convert'' an integer of @var{inprec} bits to one of @var{outprec}
+bits (where @var{outprec} is smaller than @var{inprec}) by merely
+operating on it as if it had only @var{outprec} bits.
+
+On many machines, this expression can be 1.
+
+@c rearranged this, removed the phrase "it is reported that".  this was
+@c to fix an overfull hbox.  --mew 10feb93
+When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for
+modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result.
+If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in
+such cases may improve things.
+@end defmac
+
+@hook TARGET_MODE_REP_EXTENDED
+The representation of an integral mode can be such that the values
+are always extended to a wider integral mode.  Return
+@code{SIGN_EXTEND} if values of @var{mode} are represented in
+sign-extended form to @var{rep_mode}.  Return @code{UNKNOWN}
+otherwise.  (Currently, none of the targets use zero-extended
+representation this way so unlike @code{LOAD_EXTEND_OP},
+@code{TARGET_MODE_REP_EXTENDED} is expected to return either
+@code{SIGN_EXTEND} or @code{UNKNOWN}.  Also no target extends
+@var{mode} to @var{rep_mode} so that @var{rep_mode} is not the next
+widest integral mode and currently we take advantage of this fact.)
+
+Similarly to @code{LOAD_EXTEND_OP} you may return a non-@code{UNKNOWN}
+value even if the extension is not performed on certain hard registers
+as long as for the @code{REGNO_REG_CLASS} of these hard registers
+@code{CANNOT_CHANGE_MODE_CLASS} returns nonzero.
+
+Note that @code{TARGET_MODE_REP_EXTENDED} and @code{LOAD_EXTEND_OP}
+describe two related properties.  If you define
+@code{TARGET_MODE_REP_EXTENDED (mode, word_mode)} you probably also want
+to define @code{LOAD_EXTEND_OP (mode)} to return the same type of
+extension.
+
+In order to enforce the representation of @code{mode},
+@code{TRULY_NOOP_TRUNCATION} should return false when truncating to
+@code{mode}.
+@end deftypefn
+
+@defmac STORE_FLAG_VALUE
+A C expression describing the value returned by a comparison operator
+with an integral mode and stored by a store-flag instruction
+(@samp{cstore@var{mode}4}) when the condition is true.  This description must
+apply to @emph{all} the @samp{cstore@var{mode}4} patterns and all the
+comparison operators whose results have a @code{MODE_INT} mode.
+
+A value of 1 or @minus{}1 means that the instruction implementing the
+comparison operator returns exactly 1 or @minus{}1 when the comparison is true
+and 0 when the comparison is false.  Otherwise, the value indicates
+which bits of the result are guaranteed to be 1 when the comparison is
+true.  This value is interpreted in the mode of the comparison
+operation, which is given by the mode of the first operand in the
+@samp{cstore@var{mode}4} pattern.  Either the low bit or the sign bit of
+@code{STORE_FLAG_VALUE} be on.  Presently, only those bits are used by
+the compiler.
+
+If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will
+generate code that depends only on the specified bits.  It can also
+replace comparison operators with equivalent operations if they cause
+the required bits to be set, even if the remaining bits are undefined.
+For example, on a machine whose comparison operators return an
+@code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as
+@samp{0x80000000}, saying that just the sign bit is relevant, the
+expression
+
+@smallexample
+(ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0))
+@end smallexample
+
+@noindent
+can be converted to
+
+@smallexample
+(ashift:SI @var{x} (const_int @var{n}))
+@end smallexample
+
+@noindent
+where @var{n} is the appropriate shift count to move the bit being
+tested into the sign bit.
+
+There is no way to describe a machine that always sets the low-order bit
+for a true value, but does not guarantee the value of any other bits,
+but we do not know of any machine that has such an instruction.  If you
+are trying to port GCC to such a machine, include an instruction to
+perform a logical-and of the result with 1 in the pattern for the
+comparison operators and let us know at @email{gcc@@gcc.gnu.org}.
+
+Often, a machine will have multiple instructions that obtain a value
+from a comparison (or the condition codes).  Here are rules to guide the
+choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions
+to be used:
+
+@itemize @bullet
+@item
+Use the shortest sequence that yields a valid definition for
+@code{STORE_FLAG_VALUE}.  It is more efficient for the compiler to
+``normalize'' the value (convert it to, e.g., 1 or 0) than for the
+comparison operators to do so because there may be opportunities to
+combine the normalization with other operations.
+
+@item
+For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being
+slightly preferred on machines with expensive jumps and 1 preferred on
+other machines.
+
+@item
+As a second choice, choose a value of @samp{0x80000001} if instructions
+exist that set both the sign and low-order bits but do not define the
+others.
+
+@item
+Otherwise, use a value of @samp{0x80000000}.
+@end itemize
+
+Many machines can produce both the value chosen for
+@code{STORE_FLAG_VALUE} and its negation in the same number of
+instructions.  On those machines, you should also define a pattern for
+those cases, e.g., one matching
+
+@smallexample
+(set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C})))
+@end smallexample
+
+Some machines can also perform @code{and} or @code{plus} operations on
+condition code values with less instructions than the corresponding
+@samp{cstore@var{mode}4} insn followed by @code{and} or @code{plus}.  On those
+machines, define the appropriate patterns.  Use the names @code{incscc}
+and @code{decscc}, respectively, for the patterns which perform
+@code{plus} or @code{minus} operations on condition code values.  See
+@file{rs6000.md} for some examples.  The GNU Superoptimizer can be used to
+find such instruction sequences on other machines.
+
+If this macro is not defined, the default value, 1, is used.  You need
+not define @code{STORE_FLAG_VALUE} if the machine has no store-flag
+instructions, or if the value generated by these instructions is 1.
+@end defmac
+
+@defmac FLOAT_STORE_FLAG_VALUE (@var{mode})
+A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is
+returned when comparison operators with floating-point results are true.
+Define this macro on machines that have comparison operations that return
+floating-point values.  If there are no such operations, do not define
+this macro.
+@end defmac
+
+@defmac VECTOR_STORE_FLAG_VALUE (@var{mode})
+A C expression that gives a rtx representing the nonzero true element
+for vector comparisons.  The returned rtx should be valid for the inner
+mode of @var{mode} which is guaranteed to be a vector mode.  Define
+this macro on machines that have vector comparison operations that
+return a vector result.  If there are no such operations, do not define
+this macro.  Typically, this macro is defined as @code{const1_rtx} or
+@code{constm1_rtx}.  This macro may return @code{NULL_RTX} to prevent
+the compiler optimizing such vector comparison operations for the
+given mode.
+@end defmac
+
+@defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
+@defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
+A C expression that indicates whether the architecture defines a value
+for @code{clz} or @code{ctz} with a zero operand.  
+A result of @code{0} indicates the value is undefined.
+If the value is defined for only the RTL expression, the macro should
+evaluate to @code{1}; if the value applies also to the corresponding optab
+entry (which is normally the case if it expands directly into
+the corresponding RTL), then the macro should evaluate to @code{2}.  
+In the cases where the value is defined, @var{value} should be set to
+this value.  
+
+If this macro is not defined, the value of @code{clz} or
+@code{ctz} at zero is assumed to be undefined.
+
+This macro must be defined if the target's expansion for @code{ffs}
+relies on a particular value to get correct results.  Otherwise it
+is not necessary, though it may be used to optimize some corner cases, and
+to provide a default expansion for the @code{ffs} optab.
+
+Note that regardless of this macro the ``definedness'' of @code{clz}
+and @code{ctz} at zero do @emph{not} extend to the builtin functions
+visible to the user.  Thus one may be free to adjust the value at will
+to match the target expansion of these operations without fear of
+breaking the API@.
+@end defmac
+
+@defmac Pmode
+An alias for the machine mode for pointers.  On most machines, define
+this to be the integer mode corresponding to the width of a hardware
+pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines.
+On some machines you must define this to be one of the partial integer
+modes, such as @code{PSImode}.
+
+The width of @code{Pmode} must be at least as large as the value of
+@code{POINTER_SIZE}.  If it is not equal, you must define the macro
+@code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended
+to @code{Pmode}.
+@end defmac
+
+@defmac FUNCTION_MODE
+An alias for the machine mode used for memory references to functions
+being called, in @code{call} RTL expressions.  On most CISC machines,
+where an instruction can begin at any byte address, this should be 
+@code{QImode}.  On most RISC machines, where all instructions have fixed
+size and alignment, this should be a mode with the same size and alignment
+as the machine instruction words - typically @code{SImode} or @code{HImode}.
+@end defmac
+
+@defmac STDC_0_IN_SYSTEM_HEADERS
+In normal operation, the preprocessor expands @code{__STDC__} to the
+constant 1, to signify that GCC conforms to ISO Standard C@.  On some
+hosts, like Solaris, the system compiler uses a different convention,
+where @code{__STDC__} is normally 0, but is 1 if the user specifies
+strict conformance to the C Standard.
+
+Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host
+convention when processing system header files, but when processing user
+files @code{__STDC__} will always expand to 1.
+@end defmac
+
+@defmac NO_IMPLICIT_EXTERN_C
+Define this macro if the system header files support C++ as well as C@.
+This macro inhibits the usual method of using system header files in
+C++, which is to pretend that the file's contents are enclosed in
+@samp{extern "C" @{@dots{}@}}.
+@end defmac
+
+@findex #pragma
+@findex pragma
+@defmac REGISTER_TARGET_PRAGMAS ()
+Define this macro if you want to implement any target-specific pragmas.
+If defined, it is a C expression which makes a series of calls to
+@code{c_register_pragma} or @code{c_register_pragma_with_expansion}
+for each pragma.  The macro may also do any
+setup required for the pragmas.
+
+The primary reason to define this macro is to provide compatibility with
+other compilers for the same target.  In general, we discourage
+definition of target-specific pragmas for GCC@.
+
+If the pragma can be implemented by attributes then you should consider
+defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well.
+
+Preprocessor macros that appear on pragma lines are not expanded.  All
+@samp{#pragma} directives that do not match any registered pragma are
+silently ignored, unless the user specifies @option{-Wunknown-pragmas}.
+@end defmac
+
+@deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
+@deftypefunx void c_register_pragma_with_expansion (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
+
+Each call to @code{c_register_pragma} or
+@code{c_register_pragma_with_expansion} establishes one pragma.  The
+@var{callback} routine will be called when the preprocessor encounters a
+pragma of the form
+
+@smallexample
+#pragma [@var{space}] @var{name} @dots{}
+@end smallexample
+
+@var{space} is the case-sensitive namespace of the pragma, or
+@code{NULL} to put the pragma in the global namespace.  The callback
+routine receives @var{pfile} as its first argument, which can be passed
+on to cpplib's functions if necessary.  You can lex tokens after the
+@var{name} by calling @code{pragma_lex}.  Tokens that are not read by the
+callback will be silently ignored.  The end of the line is indicated by
+a token of type @code{CPP_EOF}.  Macro expansion occurs on the
+arguments of pragmas registered with
+@code{c_register_pragma_with_expansion} but not on the arguments of
+pragmas registered with @code{c_register_pragma}.
+
+Note that the use of @code{pragma_lex} is specific to the C and C++
+compilers.  It will not work in the Java or Fortran compilers, or any
+other language compilers for that matter.  Thus if @code{pragma_lex} is going
+to be called from target-specific code, it must only be done so when
+building the C and C++ compilers.  This can be done by defining the
+variables @code{c_target_objs} and @code{cxx_target_objs} in the
+target entry in the @file{config.gcc} file.  These variables should name
+the target-specific, language-specific object file which contains the
+code that uses @code{pragma_lex}.  Note it will also be necessary to add a
+rule to the makefile fragment pointed to by @code{tmake_file} that shows
+how to build this object file.
+@end deftypefun
+
+@defmac HANDLE_PRAGMA_PACK_WITH_EXPANSION
+Define this macro if macros should be expanded in the
+arguments of @samp{#pragma pack}.
+@end defmac
+
+@hook TARGET_HANDLE_PRAGMA_EXTERN_PREFIX
+
+@defmac TARGET_DEFAULT_PACK_STRUCT
+If your target requires a structure packing default other than 0 (meaning
+the machine default), define this macro to the necessary value (in bytes).
+This must be a value that would also be valid to use with
+@samp{#pragma pack()} (that is, a small power of two).
+@end defmac
+
+@defmac DOLLARS_IN_IDENTIFIERS
+Define this macro to control use of the character @samp{$} in
+identifier names for the C family of languages.  0 means @samp{$} is
+not allowed by default; 1 means it is allowed.  1 is the default;
+there is no need to define this macro in that case.
+@end defmac
+
+@defmac NO_DOLLAR_IN_LABEL
+Define this macro if the assembler does not accept the character
+@samp{$} in label names.  By default constructors and destructors in
+G++ have @samp{$} in the identifiers.  If this macro is defined,
+@samp{.} is used instead.
+@end defmac
+
+@defmac NO_DOT_IN_LABEL
+Define this macro if the assembler does not accept the character
+@samp{.} in label names.  By default constructors and destructors in G++
+have names that use @samp{.}.  If this macro is defined, these names
+are rewritten to avoid @samp{.}.
+@end defmac
+
+@defmac INSN_SETS_ARE_DELAYED (@var{insn})
+Define this macro as a C expression that is nonzero if it is safe for the
+delay slot scheduler to place instructions in the delay slot of @var{insn},
+even if they appear to use a resource set or clobbered in @var{insn}.
+@var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that
+every @code{call_insn} has this behavior.  On machines where some @code{insn}
+or @code{jump_insn} is really a function call and hence has this behavior,
+you should define this macro.
+
+You need not define this macro if it would always return zero.
+@end defmac
+
+@defmac INSN_REFERENCES_ARE_DELAYED (@var{insn})
+Define this macro as a C expression that is nonzero if it is safe for the
+delay slot scheduler to place instructions in the delay slot of @var{insn},
+even if they appear to set or clobber a resource referenced in @var{insn}.
+@var{insn} is always a @code{jump_insn} or an @code{insn}.  On machines where
+some @code{insn} or @code{jump_insn} is really a function call and its operands
+are registers whose use is actually in the subroutine it calls, you should
+define this macro.  Doing so allows the delay slot scheduler to move
+instructions which copy arguments into the argument registers into the delay
+slot of @var{insn}.
+
+You need not define this macro if it would always return zero.
+@end defmac
+
+@defmac MULTIPLE_SYMBOL_SPACES
+Define this macro as a C expression that is nonzero if, in some cases,
+global symbols from one translation unit may not be bound to undefined
+symbols in another translation unit without user intervention.  For
+instance, under Microsoft Windows symbols must be explicitly imported
+from shared libraries (DLLs).
+
+You need not define this macro if it would always evaluate to zero.
+@end defmac
+
+@hook TARGET_MD_ASM_CLOBBERS
+This target hook should add to @var{clobbers} @code{STRING_CST} trees for
+any hard regs the port wishes to automatically clobber for an asm.
+It should return the result of the last @code{tree_cons} used to add a
+clobber.  The @var{outputs}, @var{inputs} and @var{clobber} lists are the
+corresponding parameters to the asm and may be inspected to avoid
+clobbering a register that is an input or output of the asm.  You can use
+@code{tree_overlaps_hard_reg_set}, declared in @file{tree.h}, to test
+for overlap with regards to asm-declared registers.
+@end deftypefn
+
+@defmac MATH_LIBRARY
+Define this macro as a C string constant for the linker argument to link
+in the system math library, minus the initial @samp{"-l"}, or
+@samp{""} if the target does not have a
+separate math library.
+
+You need only define this macro if the default of @samp{"m"} is wrong.
+@end defmac
+
+@defmac LIBRARY_PATH_ENV
+Define this macro as a C string constant for the environment variable that
+specifies where the linker should look for libraries.
+
+You need only define this macro if the default of @samp{"LIBRARY_PATH"}
+is wrong.
+@end defmac
+
+@defmac TARGET_POSIX_IO
+Define this macro if the target supports the following POSIX@ file
+functions, access, mkdir and  file locking with fcntl / F_SETLKW@.
+Defining @code{TARGET_POSIX_IO} will enable the test coverage code
+to use file locking when exiting a program, which avoids race conditions
+if the program has forked. It will also create directories at run-time
+for cross-profiling.
+@end defmac
+
+@defmac MAX_CONDITIONAL_EXECUTE
+
+A C expression for the maximum number of instructions to execute via
+conditional execution instructions instead of a branch.  A value of
+@code{BRANCH_COST}+1 is the default if the machine does not use cc0, and
+1 if it does use cc0.
+@end defmac
+
+@defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr})
+Used if the target needs to perform machine-dependent modifications on the
+conditionals used for turning basic blocks into conditionally executed code.
+@var{ce_info} points to a data structure, @code{struct ce_if_block}, which
+contains information about the currently processed blocks.  @var{true_expr}
+and @var{false_expr} are the tests that are used for converting the
+then-block and the else-block, respectively.  Set either @var{true_expr} or
+@var{false_expr} to a null pointer if the tests cannot be converted.
+@end defmac
+
+@defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr})
+Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated
+if-statements into conditions combined by @code{and} and @code{or} operations.
+@var{bb} contains the basic block that contains the test that is currently
+being processed and about to be turned into a condition.
+@end defmac
+
+@defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn})
+A C expression to modify the @var{PATTERN} of an @var{INSN} that is to
+be converted to conditional execution format.  @var{ce_info} points to
+a data structure, @code{struct ce_if_block}, which contains information
+about the currently processed blocks.
+@end defmac
+
+@defmac IFCVT_MODIFY_FINAL (@var{ce_info})
+A C expression to perform any final machine dependent modifications in
+converting code to conditional execution.  The involved basic blocks
+can be found in the @code{struct ce_if_block} structure that is pointed
+to by @var{ce_info}.
+@end defmac
+
+@defmac IFCVT_MODIFY_CANCEL (@var{ce_info})
+A C expression to cancel any machine dependent modifications in
+converting code to conditional execution.  The involved basic blocks
+can be found in the @code{struct ce_if_block} structure that is pointed
+to by @var{ce_info}.
+@end defmac
+
+@defmac IFCVT_INIT_EXTRA_FIELDS (@var{ce_info})
+A C expression to initialize any extra fields in a @code{struct ce_if_block}
+structure, which are defined by the @code{IFCVT_EXTRA_FIELDS} macro.
+@end defmac
+
+@defmac IFCVT_EXTRA_FIELDS
+If defined, it should expand to a set of field declarations that will be
+added to the @code{struct ce_if_block} structure.  These should be initialized
+by the @code{IFCVT_INIT_EXTRA_FIELDS} macro.
+@end defmac
+
+@hook TARGET_MACHINE_DEPENDENT_REORG
+If non-null, this hook performs a target-specific pass over the
+instruction stream.  The compiler will run it at all optimization levels,
+just before the point at which it normally does delayed-branch scheduling.
+
+The exact purpose of the hook varies from target to target.  Some use
+it to do transformations that are necessary for correctness, such as
+laying out in-function constant pools or avoiding hardware hazards.
+Others use it as an opportunity to do some machine-dependent optimizations.
+
+You need not implement the hook if it has nothing to do.  The default
+definition is null.
+@end deftypefn
+
+@hook TARGET_INIT_BUILTINS
+Define this hook if you have any machine-specific built-in functions
+that need to be defined.  It should be a function that performs the
+necessary setup.
+
+Machine specific built-in functions can be useful to expand special machine
+instructions that would otherwise not normally be generated because
+they have no equivalent in the source language (for example, SIMD vector
+instructions or prefetch instructions).
+
+To create a built-in function, call the function
+@code{lang_hooks.builtin_function}
+which is defined by the language front end.  You can use any type nodes set
+up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2};
+only language front ends that use those two functions will call
+@samp{TARGET_INIT_BUILTINS}.
+@end deftypefn
+
+@hook TARGET_BUILTIN_DECL
+Define this hook if you have any machine-specific built-in functions
+that need to be defined.  It should be a function that returns the
+builtin function declaration for the builtin function code @var{code}.
+If there is no such builtin and it cannot be initialized at this time
+if @var{initialize_p} is true the function should return @code{NULL_TREE}.
+If @var{code} is out of range the function should return
+@code{error_mark_node}.
+@end deftypefn
+
+@hook TARGET_EXPAND_BUILTIN
+
+Expand a call to a machine specific built-in function that was set up by
+@samp{TARGET_INIT_BUILTINS}.  @var{exp} is the expression for the
+function call; the result should go to @var{target} if that is
+convenient, and have mode @var{mode} if that is convenient.
+@var{subtarget} may be used as the target for computing one of
+@var{exp}'s operands.  @var{ignore} is nonzero if the value is to be
+ignored.  This function should return the result of the call to the
+built-in function.
+@end deftypefn
+
+@hook TARGET_RESOLVE_OVERLOADED_BUILTIN
+Select a replacement for a machine specific built-in function that
+was set up by @samp{TARGET_INIT_BUILTINS}.  This is done
+@emph{before} regular type checking, and so allows the target to
+implement a crude form of function overloading.  @var{fndecl} is the
+declaration of the built-in function.  @var{arglist} is the list of
+arguments passed to the built-in function.  The result is a
+complete expression that implements the operation, usually
+another @code{CALL_EXPR}.
+@var{arglist} really has type @samp{VEC(tree,gc)*}
+@end deftypefn
+
+@hook TARGET_FOLD_BUILTIN
+Fold a call to a machine specific built-in function that was set up by
+@samp{TARGET_INIT_BUILTINS}.  @var{fndecl} is the declaration of the
+built-in function.  @var{n_args} is the number of arguments passed to
+the function; the arguments themselves are pointed to by @var{argp}.
+The result is another tree containing a simplified expression for the
+call's result.  If @var{ignore} is true the value will be ignored.
+@end deftypefn
+
+@hook TARGET_INVALID_WITHIN_DOLOOP
+
+Take an instruction in @var{insn} and return NULL if it is valid within a
+low-overhead loop, otherwise return a string explaining why doloop
+could not be applied.
+
+Many targets use special registers for low-overhead looping. For any
+instruction that clobbers these this function should return a string indicating
+the reason why the doloop could not be applied.
+By default, the RTL loop optimizer does not use a present doloop pattern for
+loops containing function calls or branch on table instructions.
+@end deftypefn
+
+@defmac MD_CAN_REDIRECT_BRANCH (@var{branch1}, @var{branch2})
+
+Take a branch insn in @var{branch1} and another in @var{branch2}.
+Return true if redirecting @var{branch1} to the destination of
+@var{branch2} is possible.
+
+On some targets, branches may have a limited range.  Optimizing the
+filling of delay slots can result in branches being redirected, and this
+may in turn cause a branch offset to overflow.
+@end defmac
+
+@hook TARGET_COMMUTATIVE_P
+This target hook returns @code{true} if @var{x} is considered to be commutative.
+Usually, this is just COMMUTATIVE_P (@var{x}), but the HP PA doesn't consider
+PLUS to be commutative inside a MEM@.  @var{outer_code} is the rtx code
+of the enclosing rtl, if known, otherwise it is UNKNOWN.
+@end deftypefn
+
+@hook TARGET_ALLOCATE_INITIAL_VALUE
+
+When the initial value of a hard register has been copied in a pseudo
+register, it is often not necessary to actually allocate another register
+to this pseudo register, because the original hard register or a stack slot
+it has been saved into can be used.  @code{TARGET_ALLOCATE_INITIAL_VALUE}
+is called at the start of register allocation once for each hard register
+that had its initial value copied by using
+@code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}.
+Possible values are @code{NULL_RTX}, if you don't want
+to do any special allocation, a @code{REG} rtx---that would typically be
+the hard register itself, if it is known not to be clobbered---or a
+@code{MEM}.
+If you are returning a @code{MEM}, this is only a hint for the allocator;
+it might decide to use another register anyways.
+You may use @code{current_function_leaf_function} in the hook, functions
+that use @code{REG_N_SETS}, to determine if the hard
+register in question will not be clobbered.
+The default value of this hook is @code{NULL}, which disables any special
+allocation.
+@end deftypefn
+
+@hook TARGET_UNSPEC_MAY_TRAP_P
+This target hook returns nonzero if @var{x}, an @code{unspec} or
+@code{unspec_volatile} operation, might cause a trap.  Targets can use
+this hook to enhance precision of analysis for @code{unspec} and
+@code{unspec_volatile} operations.  You may call @code{may_trap_p_1}
+to analyze inner elements of @var{x} in which case @var{flags} should be
+passed along.
+@end deftypefn
+
+@hook TARGET_SET_CURRENT_FUNCTION
+The compiler invokes this hook whenever it changes its current function 
+context (@code{cfun}).  You can define this function if
+the back end needs to perform any initialization or reset actions on a
+per-function basis.  For example, it may be used to implement function
+attributes that affect register usage or code generation patterns.
+The argument @var{decl} is the declaration for the new function context,
+and may be null to indicate that the compiler has left a function context
+and is returning to processing at the top level.
+The default hook function does nothing.
+
+GCC sets @code{cfun} to a dummy function context during initialization of
+some parts of the back end.  The hook function is not invoked in this
+situation; you need not worry about the hook being invoked recursively,
+or when the back end is in a partially-initialized state.
+@code{cfun} might be @code{NULL} to indicate processing at top level,
+outside of any function scope.
+@end deftypefn
+
+@defmac TARGET_OBJECT_SUFFIX
+Define this macro to be a C string representing the suffix for object
+files on your target machine.  If you do not define this macro, GCC will
+use @samp{.o} as the suffix for object files.
+@end defmac
+
+@defmac TARGET_EXECUTABLE_SUFFIX
+Define this macro to be a C string representing the suffix to be
+automatically added to executable files on your target machine.  If you
+do not define this macro, GCC will use the null string as the suffix for
+executable files.
+@end defmac
+
+@defmac COLLECT_EXPORT_LIST
+If defined, @code{collect2} will scan the individual object files
+specified on its command line and create an export list for the linker.
+Define this macro for systems like AIX, where the linker discards
+object files that are not referenced from @code{main} and uses export
+lists.
+@end defmac
+
+@defmac MODIFY_JNI_METHOD_CALL (@var{mdecl})
+Define this macro to a C expression representing a variant of the
+method call @var{mdecl}, if Java Native Interface (JNI) methods
+must be invoked differently from other methods on your target.
+For example, on 32-bit Microsoft Windows, JNI methods must be invoked using
+the @code{stdcall} calling convention and this macro is then
+defined as this expression:
+
+@smallexample
+build_type_attribute_variant (@var{mdecl},
+                              build_tree_list
+                              (get_identifier ("stdcall"),
+                               NULL))
+@end smallexample
+@end defmac
+
+@hook TARGET_CANNOT_MODIFY_JUMPS_P
+This target hook returns @code{true} past the point in which new jump
+instructions could be created.  On machines that require a register for
+every jump such as the SHmedia ISA of SH5, this point would typically be
+reload, so this target hook should be defined to a function such as:
+
+@smallexample
+static bool
+cannot_modify_jumps_past_reload_p ()
+@{
+  return (reload_completed || reload_in_progress);
+@}
+@end smallexample
+@end deftypefn
+
+@hook TARGET_BRANCH_TARGET_REGISTER_CLASS
+This target hook returns a register class for which branch target register
+optimizations should be applied.  All registers in this class should be
+usable interchangeably.  After reload, registers in this class will be
+re-allocated and loads will be hoisted out of loops and be subjected
+to inter-block scheduling.
+@end deftypefn
+
+@hook TARGET_BRANCH_TARGET_REGISTER_CALLEE_SAVED
+Branch target register optimization will by default exclude callee-saved
+registers
+that are not already live during the current function; if this target hook
+returns true, they will be included.  The target code must than make sure
+that all target registers in the class returned by
+@samp{TARGET_BRANCH_TARGET_REGISTER_CLASS} that might need saving are
+saved.  @var{after_prologue_epilogue_gen} indicates if prologues and
+epilogues have already been generated.  Note, even if you only return
+true when @var{after_prologue_epilogue_gen} is false, you still are likely
+to have to make special provisions in @code{INITIAL_ELIMINATION_OFFSET}
+to reserve space for caller-saved target registers.
+@end deftypefn
+
+@hook TARGET_HAVE_CONDITIONAL_EXECUTION
+This target hook returns true if the target supports conditional execution.
+This target hook is required only when the target has several different
+modes and they have different conditional execution capability, such as ARM.
+@end deftypefn
+
+@hook TARGET_LOOP_UNROLL_ADJUST
+This target hook returns a new value for the number of times @var{loop}
+should be unrolled. The parameter @var{nunroll} is the number of times
+the loop is to be unrolled. The parameter @var{loop} is a pointer to
+the loop, which is going to be checked for unrolling. This target hook
+is required only when the target has special constraints like maximum
+number of memory accesses.
+@end deftypefn
+
+@defmac POWI_MAX_MULTS
+If defined, this macro is interpreted as a signed integer C expression
+that specifies the maximum number of floating point multiplications
+that should be emitted when expanding exponentiation by an integer
+constant inline.  When this value is defined, exponentiation requiring
+more than this number of multiplications is implemented by calling the
+system library's @code{pow}, @code{powf} or @code{powl} routines.
+The default value places no upper bound on the multiplication count.
+@end defmac
+
+@deftypefn Macro void TARGET_EXTRA_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
+This target hook should register any extra include files for the
+target.  The parameter @var{stdinc} indicates if normal include files
+are present.  The parameter @var{sysroot} is the system root directory.
+The parameter @var{iprefix} is the prefix for the gcc directory.
+@end deftypefn
+
+@deftypefn Macro void TARGET_EXTRA_PRE_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
+This target hook should register any extra include files for the
+target before any standard headers.  The parameter @var{stdinc}
+indicates if normal include files are present.  The parameter
+@var{sysroot} is the system root directory.  The parameter
+@var{iprefix} is the prefix for the gcc directory.
+@end deftypefn
+
+@deftypefn Macro void TARGET_OPTF (char *@var{path})
+This target hook should register special include paths for the target.
+The parameter @var{path} is the include to register.  On Darwin
+systems, this is used for Framework includes, which have semantics
+that are different from @option{-I}.
+@end deftypefn
+
+@defmac bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree @var{fndecl})
+This target macro returns @code{true} if it is safe to use a local alias
+for a virtual function @var{fndecl} when constructing thunks,
+@code{false} otherwise.  By default, the macro returns @code{true} for all
+functions, if a target supports aliases (i.e.@: defines
+@code{ASM_OUTPUT_DEF}), @code{false} otherwise,
+@end defmac
+
+@defmac TARGET_FORMAT_TYPES
+If defined, this macro is the name of a global variable containing
+target-specific format checking information for the @option{-Wformat}
+option.  The default is to have no target-specific format checks.
+@end defmac
+
+@defmac TARGET_N_FORMAT_TYPES
+If defined, this macro is the number of entries in
+@code{TARGET_FORMAT_TYPES}.
+@end defmac
+
+@defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES
+If defined, this macro is the name of a global variable containing
+target-specific format overrides for the @option{-Wformat} option. The
+default is to have no target-specific format overrides. If defined,
+@code{TARGET_FORMAT_TYPES} must be defined, too.
+@end defmac
+
+@defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES_COUNT
+If defined, this macro specifies the number of entries in
+@code{TARGET_OVERRIDES_FORMAT_ATTRIBUTES}.
+@end defmac
+
+@defmac TARGET_OVERRIDES_FORMAT_INIT
+If defined, this macro specifies the optional initialization
+routine for target specific customizations of the system printf
+and scanf formatter settings.
+@end defmac
+
+@hook TARGET_RELAXED_ORDERING
+If set to @code{true}, means that the target's memory model does not
+guarantee that loads which do not depend on one another will access
+main memory in the order of the instruction stream; if ordering is
+important, an explicit memory barrier must be used.  This is true of
+many recent processors which implement a policy of ``relaxed,''
+``weak,'' or ``release'' memory consistency, such as Alpha, PowerPC,
+and ia64.  The default is @code{false}.
+@end deftypevr
+
+@hook TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN
+If defined, this macro returns the diagnostic message when it is
+illegal to pass argument @var{val} to function @var{funcdecl}
+with prototype @var{typelist}.
+@end deftypefn
+
+@hook TARGET_INVALID_CONVERSION
+If defined, this macro returns the diagnostic message when it is
+invalid to convert from @var{fromtype} to @var{totype}, or @code{NULL}
+if validity should be determined by the front end.
+@end deftypefn
+
+@hook TARGET_INVALID_UNARY_OP
+If defined, this macro returns the diagnostic message when it is
+invalid to apply operation @var{op} (where unary plus is denoted by
+@code{CONVERT_EXPR}) to an operand of type @var{type}, or @code{NULL}
+if validity should be determined by the front end.
+@end deftypefn
+
+@hook TARGET_INVALID_BINARY_OP
+If defined, this macro returns the diagnostic message when it is
+invalid to apply operation @var{op} to operands of types @var{type1}
+and @var{type2}, or @code{NULL} if validity should be determined by
+the front end.
+@end deftypefn
+
+@hook TARGET_INVALID_PARAMETER_TYPE
+If defined, this macro returns the diagnostic message when it is
+invalid for functions to include parameters of type @var{type}, 
+or @code{NULL} if validity should be determined by
+the front end.  This is currently used only by the C and C++ front ends.
+@end deftypefn
+
+@hook TARGET_INVALID_RETURN_TYPE
+If defined, this macro returns the diagnostic message when it is
+invalid for functions to have return type @var{type}, 
+or @code{NULL} if validity should be determined by
+the front end.  This is currently used only by the C and C++ front ends.
+@end deftypefn
+
+@hook TARGET_PROMOTED_TYPE
+If defined, this target hook returns the type to which values of 
+@var{type} should be promoted when they appear in expressions, 
+analogous to the integer promotions, or @code{NULL_TREE} to use the
+front end's normal promotion rules.  This hook is useful when there are
+target-specific types with special promotion rules.
+This is currently used only by the C and C++ front ends.
+@end deftypefn
+
+@hook TARGET_CONVERT_TO_TYPE
+If defined, this hook returns the result of converting @var{expr} to 
+@var{type}.  It should return the converted expression, 
+or @code{NULL_TREE} to apply the front end's normal conversion rules.
+This hook is useful when there are target-specific types with special 
+conversion rules.
+This is currently used only by the C and C++ front ends.
+@end deftypefn
+
+@defmac TARGET_USE_JCR_SECTION
+This macro determines whether to use the JCR section to register Java
+classes. By default, TARGET_USE_JCR_SECTION is defined to 1 if both
+SUPPORTS_WEAK and TARGET_HAVE_NAMED_SECTIONS are true, else 0.
+@end defmac
+
+@defmac OBJC_JBLEN
+This macro determines the size of the objective C jump buffer for the
+NeXT runtime. By default, OBJC_JBLEN is defined to an innocuous value.
+@end defmac
+
+@defmac LIBGCC2_UNWIND_ATTRIBUTE
+Define this macro if any target-specific attributes need to be attached
+to the functions in @file{libgcc} that provide low-level support for 
+call stack unwinding.  It is used in declarations in @file{unwind-generic.h}
+and the associated definitions of those functions.
+@end defmac
+
+@hook TARGET_UPDATE_STACK_BOUNDARY
+Define this macro to update the current function stack boundary if
+necessary.
+@end deftypefn
+
+@hook TARGET_GET_DRAP_RTX
+This hook should return an rtx for Dynamic Realign Argument Pointer (DRAP) if a
+different argument pointer register is needed to access the function's
+argument list due to stack realignment.  Return @code{NULL} if no DRAP
+is needed.
+@end deftypefn
+
+@hook TARGET_ALLOCATE_STACK_SLOTS_FOR_ARGS
+When optimization is disabled, this hook indicates whether or not
+arguments should be allocated to stack slots.  Normally, GCC allocates
+stacks slots for arguments when not optimizing in order to make
+debugging easier.  However, when a function is declared with
+@code{__attribute__((naked))}, there is no stack frame, and the compiler
+cannot safely move arguments from the registers in which they are passed
+to the stack.  Therefore, this hook should return true in general, but
+false for naked functions.  The default implementation always returns true.
+@end deftypefn
+
+@hook TARGET_CONST_ANCHOR
+On some architectures it can take multiple instructions to synthesize
+a constant.  If there is another constant already in a register that
+is close enough in value then it is preferable that the new constant
+is computed from this register using immediate addition or
+subtraction.  We accomplish this through CSE.  Besides the value of
+the constant we also add a lower and an upper constant anchor to the
+available expressions.  These are then queried when encountering new
+constants.  The anchors are computed by rounding the constant up and
+down to a multiple of the value of @code{TARGET_CONST_ANCHOR}.
+@code{TARGET_CONST_ANCHOR} should be the maximum positive value
+accepted by immediate-add plus one.  We currently assume that the
+value of @code{TARGET_CONST_ANCHOR} is a power of 2.  For example, on
+MIPS, where add-immediate takes a 16-bit signed value,
+@code{TARGET_CONST_ANCHOR} is set to @samp{0x8000}.  The default value
+is zero, which disables this optimization.  @end deftypevr