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Diffstat (limited to 'contrib/analyze_brprob')
| -rwxr-xr-x | contrib/analyze_brprob | 146 |
1 files changed, 146 insertions, 0 deletions
diff --git a/contrib/analyze_brprob b/contrib/analyze_brprob new file mode 100755 index 000000000..093c1dea7 --- /dev/null +++ b/contrib/analyze_brprob @@ -0,0 +1,146 @@ +#!/usr/bin/awk -f +# Script to analyze experimental results of our branch prediction heuristics +# Contributed by Jan Hubicka, SuSE Inc. +# Copyright (C) 2001, 2003 Free Software Foundation, Inc. +# +# This file is part of GCC. +# +# GCC is free software; you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 3, or (at your option) +# any later version. +# +# GCC is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with GCC; see the file COPYING. If not, write to +# the Free Software Foundation, 51 Franklin Street, Fifth Floor, +# Boston, MA 02110-1301, USA. +# +# +# This script is used to calculate two basic properties of the branch prediction +# heuristics - coverage and hitrate. Coverage is number of executions of a given +# branch matched by the heuristics and hitrate is probability that once branch is +# predicted as taken it is really taken. +# +# These values are useful to determine the quality of given heuristics. Hitrate +# may be directly used in predict.c. +# +# Usage: +# Step 1: Compile and profile your program. You need to use -fprofile-arcs +# flag to get the profiles +# Step 2: Generate log files. The information about given heuristics are +# saved into *.bp dumps. You need to pass the -db switch to the compiler as well +# as -fbranch-probabilities to get the results of profiling noted in the dumps. +# Ensure that there are no "Arc profiling: some edge counts were bad." warnings. +# Step 3: Run this script to concatenate all *.life files: +# analyze_brprob `find . -name *.life` +# the information is collected and print once all files are parsed. This +# may take a while. +# Note that the script does use bc to perform long arithmetic. +# Step 4: Read the results. Basically the following table is printed: +# (this is just an example from a very early stage of branch prediction pass +# development, so please don't take these numbers seriously) +# +#HEURISTICS BRANCHES (REL) HITRATE COVERAGE (REL) +#opcode 2889 83.7% 94.96%/ 97.62% 7516383 75.3% +#pointer 246 7.1% 99.69%/ 99.86% 118791 1.2% +#loop header 449 13.0% 98.32%/ 99.07% 43553 0.4% +#first match 3450 100.0% 89.92%/ 97.27% 9979782 100.0% +#loop exit 924 26.8% 88.95%/ 95.58% 9026266 90.4% +#error return 150 4.3% 64.48%/ 86.81% 453542 4.5% +#call 803 23.3% 51.66%/ 98.61% 3614037 36.2% +#loop branch 51 1.5% 99.26%/ 99.27% 26854 0.3% +#noreturn call 951 27.6% 100.00%/100.00% 1759809 17.6% +# +# The heuristic called "first match" is a heuristic used by GCC branch +# prediction pass and it predicts 89.92% branches correctly. +# +# The quality of heuristics can be rated using both, coverage and hitrate +# parameters. For example "loop branch" heuristics (predicting loopback edge +# as taken) have both very high hitrate and coverage, so it is very useful. +# On the other hand, "exit block" heuristics (predicting exit edges as not +# taken) have good hitrate, but poor coverage, so only 3 branches have been +# predicted. The "loop header" heuristic has problems, since it tends to +# misspredict. +# +# The implementation of this script is somewhat brute force. My awk skills +# are limited. + +function longeval(e) +{ + e = "echo \"scale = 2 ;"e"\" | bc" + e | getline res + close (e) + return res +} + +BEGIN {nnames = 0} + +/^ .* heuristics: .*.$/ { + name=$0 + sub (/^ /,"",name) + sub (/ heuristics: .*.$/,"",name) + if (!(name in branches)) + { + names[nnames] = name + branches[name]=0 + counts[name]=0 + hits[name]=0 + phits[name]=0 + nnames++ + } + branches[name]+=1 + } + +/^ .* heuristics: .*. exec [0-9]* hit [0-9]* (.*.)$/ { + name=$0 + sub (/^ /,"",name) + sub (/ heuristics: .*. exec [0-9]* hit [0-9]* (.*.)$/,"",name) + pred=$0 + sub (/^ .* heuristics: /,"",pred) + sub (/. exec [0-9]* hit [0-9]* (.*.)$/,"",pred) + count=$0 + sub (/^ .* heuristics: .*. exec /,"",count) + sub (/ hit [0-9]* (.*.)$/,"",count) + hit=$0 + sub (/^ .* heuristics: .*. exec [0-9]* hit /,"",hit) + sub (/ (.*.)$/,"",hit) + + if (int(pred) < 50.0) + { + hit = count"-"hit; + } + counts[name]=counts[name] "+" count + hits[name]=hits[name] "+" hit + phits[name]=phits[name] "+(("hit")<"count"/2)*("count"-("hit"))+(("hit")>="count"/2)*("hit")" + + #BC crashes on long strings. Irritating. + if (length(counts[name]) > 2000) + counts[name] = longeval(counts[name]) + if (length(hits[name]) > 2000) + hits[name] = longeval(hits[name]) + if (length(phits[name]) > 2000) + phits[name] = longeval(phits[name]) + } +END { + # Heuristics called combined predicts just everything. + maxcounts = longeval(counts["combined"]) + maxbranches = branches["combined"] + max = names["combined"] + printf("HEURISTICS BRANCHES (REL) HITRATE COVERAGE (REL)\n") + for (i = 0; i < nnames ; i++) + { + name = names[i] + counts[name] = longeval(counts[name]) + printf ("%-26s %8i %5.1f%% %6s%% / %6s%% %12s %5.1f%%\n", + name, + branches[name], branches[name] * 100 / maxbranches, + longeval("("hits[name]") * 100 /(" counts[name]"-0.00001)"), + longeval("("phits[name]") * 100 /(" counts[name]"-0.00001)"), + counts[name], longeval(counts[name]" * 100 / ("maxcounts"-0.00001)")) + } +} |