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#!/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)"))
}
}
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