149 lines
5.7 KiB
Awk
Executable File
149 lines
5.7 KiB
Awk
Executable File
#!/usr/bin/awk -f
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# Script to analyze experimental results of our branch prediction heuristics
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# Contributed by Jan Hubicka, SuSE Inc.
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# Copyright (C) 2001 Free Software Foundation, Inc.
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#
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# This file is part of GNU CC.
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#
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# GNU CC is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2, or (at your option)
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# any later version.
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#
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# GNU CC is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with GNU CC; see the file COPYING. If not, write to
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# the Free Software Foundation, 59 Temple Place - Suite 330,
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# Boston, MA 02111-1307, USA.
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#
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#
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# This script is used to calculate two basic properties of the branch prediction
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# heuristics - coverage and hitrate. Coverage is number of execution of a given
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# branch matched by the heuristics and hitrate is probability that once branch is
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# predicted as taken it is really taken.
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#
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# These values are useful to determine the quality of given heuristics. Hitrate
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# may be directly used in predict.c.
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#
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# Usage:
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# Step 1: compile and profile your program. You need to use -fprofile-arcs
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# flag to get the profiles
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# Step 2: Generate log files. The information about given heuristics are
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# saved into *.life dumps. You need to pass the -df switch to the compiler as well
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# as -fbranch-probabilities to get the results of profiling noted in the dumps.
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# Ensure that there are no "Arc profiling: some edge counts were bad." warnings.
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# Step 3: Run this script to concatenate all *.life files:
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# analyze_brprob `find . -name *.life`
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# the information is collected and print once all files are parsed. This
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# may take a while.
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# Note that the script does use bc to perform long arithmetic.
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# Step 4: Read the results. Basically the following table is printed:
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# (this is just an example from a very early stage of branch prediction pass
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# development, so please don't take these numbers seriously)
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#
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#HEURISTICS BRANCHES (REL) HITRATE COVERAGE (REL)
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#opcode 2889 83.7% 94.96%/ 97.62% 7516383 75.3%
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#pointer 246 7.1% 99.69%/ 99.86% 118791 1.2%
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#loop header 449 13.0% 98.32%/ 99.07% 43553 0.4%
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#first match 3450 100.0% 89.92%/ 97.27% 9979782 100.0%
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#loop exit 924 26.8% 88.95%/ 95.58% 9026266 90.4%
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#error return 150 4.3% 64.48%/ 86.81% 453542 4.5%
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#call 803 23.3% 51.66%/ 98.61% 3614037 36.2%
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#loop branch 51 1.5% 99.26%/ 99.27% 26854 0.3%
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#noreturn call 951 27.6% 100.00%/100.00% 1759809 17.6%
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#
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# The heuristic called "first match" is a heuristic used by GCC branch
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# prediction pass and it predicts 89.92% branches correctly.
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#
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# The quality of heuristics can be rated using both, coverage and hitrate
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# parameters. For example "loop branch" heuristics (predicting loopback edge
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# as taken) have both very high hitrate and coverage, so it is very useful.
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# On the other hand, "exit block" heuristics (predicting exit edges as not
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# taken) have good hitrate, but poor coverage, so only 3 branches have been
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# predicted. The "loop header" heuristic has problems, since it tends to
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# misspredict.
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#
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# The implementation of this script is somewhat brute force. My awk skills
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# are limited.
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function longeval(e)
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{
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e = "echo \"scale = 2 ;"e"\" | bc"
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e | getline res
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close (e)
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return res
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}
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BEGIN {nnames = 0}
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/^ .* heuristics: .*.$/ {
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name=$0
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sub (/^ /,"",name)
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sub (/ heuristics: .*.$/,"",name)
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if (!(name in branches))
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{
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names[nnames] = name
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branches[name]=0
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counts[name]=0
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hits[name]=0
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phits[name]=0
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nnames++
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}
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branches[name]+=1
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}
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/^ .* heuristics: .*. exec [0-9]* hit [0-9]* (.*.)$/ {
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name=$0
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sub (/^ /,"",name)
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sub (/ heuristics: .*. exec [0-9]* hit [0-9]* (.*.)$/,"",name)
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pred=$0
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sub (/^ .* heuristics: /,"",pred)
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sub (/. exec [0-9]* hit [0-9]* (.*.)$/,"",pred)
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count=$0
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sub (/^ .* heuristics: .*. exec /,"",count)
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sub (/ hit [0-9]* (.*.)$/,"",count)
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hit=$0
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sub (/^ .* heuristics: .*. exec [0-9]* hit /,"",hit)
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sub (/ (.*.)$/,"",hit)
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if (int(pred) < 50.0)
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{
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hit = count - hit;
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}
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counts[name]=counts[name] "+" count
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hits[name]=hits[name] "+" hit
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if (int (hit) < (int (count) / 2))
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hit = count - hit;
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phits[name]=phits[name] "+" hit
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#BC crashes on long strings. Irritating.
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if (length(counts[name]) > 4000)
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{
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counts[name] = longeval(counts[name])
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hits[name] = longeval(hits[name])
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phits[name] = longeval(phits[name])
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}
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}
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END {
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# Heuristics called combined predicts just everything.
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maxcounts = longeval(counts["first match"])
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maxbranches = branches["first match"]
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max = names["first match"]
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printf("HEURISTICS BRANCHES (REL) HITRATE COVERAGE (REL)\n")
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for (i = 0; i < nnames ; i++)
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{
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name = names[i]
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counts[name] = longeval(counts[name])
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printf ("%-27s %8i %5.1f%% %6s%%/%6s%% %12s %5.1f%%\n",
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name,
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branches[name], branches[name] * 100 / maxbranches,
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longeval("("hits[name]") * 100 /(" counts[name]"-0.00001)"),
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longeval("("phits[name]") * 100 /(" counts[name]"-0.00001)"),
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counts[name], longeval(counts[name]" * 100 / ("maxcounts"-0.00001)"))
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}
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}
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