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1 723 jeremybenn
#!/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, 2003 Free Software Foundation, Inc.
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#
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# This file is part of GCC.
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#
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# GCC 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 3, or (at your option)
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# any later version.
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#
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# GCC 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 GCC; see the file COPYING.  If not, write to
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# the Free Software Foundation, 51 Franklin Street, Fifth Floor,
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# Boston, MA 02110-1301, 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 executions 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 *.bp dumps.  You need to pass the -db 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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    phits[name]=phits[name] "+(("hit")<"count"/2)*("count"-("hit"))+(("hit")>="count"/2)*("hit")"
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    #BC crashes on long strings.  Irritating.
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    if (length(counts[name]) > 2000)
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      counts[name] = longeval(counts[name])
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    if (length(hits[name]) > 2000)
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      hits[name] = longeval(hits[name])
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    if (length(phits[name]) > 2000)
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      phits[name] = longeval(phits[name])
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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["combined"])
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  maxbranches = branches["combined"]
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  max = names["combined"]
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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 ("%-26s %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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