Subversion Repositories openrisc_me

#!/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 2, 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)"))

   }

}