--- /dev/null
+#!/usr/bin/awk -f
+# Script to analyze experimental results of our branch prediction heursitics
+# Contributed by Jan Hubicka, SuSE inc.
+# Copyright (C) 2001 Free Software Foundation, Inc.
+#
+# This file is part of GNU CC.
+#
+# GNU CC 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.
+#
+# GNU CC 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 GNU CC; see the file COPYING. If not, write to
+# the Free Software Foundation, 59 Temple Place - Suite 330,
+# Boston, MA 02111-1307, USA.
+#
+#
+# This script is used to calculate two basic properties of the branch prediction
+# heursitics - coverage and hitrate. Coverage is number of executions of given
+# branch matched by the heuristics and hitrate is probability that once branch is
+# predicted as taken it is really taken.
+#
+# These values are usefull to determine quality of given heuristics and 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 *.life dumps. You need to pass -df swtich to compiler as well
+# as -fbranch-probabilities to get results of profiling noted in the dumps.
+# Ensure that there is no "Arc profiling: some edge counts were bad." warnings.
+# Keep the -fprofile-arcs switch to ensure that CFGs match.
+# step 3: Run this script to concatetation of 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 script does use bc to perform long arithmetic.
+# step 4: Read the results. Basically following table is printed:
+# (this is just example from very early stages 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 heuristics called "first match" is heuristics 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 usefull.
+# On the other hand, "exit block" heuristics (predicting exit edges as not
+# taken) have good hitrate, but poor coverage, so only 3 branches has been
+# predicted. The "loop header" heuristics have problem, 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
+ if (int (hit) < (int (count) / 2))
+ hit = count - hit;
+ phits[name]=phits[name] "+" hit
+
+ #BC crashes on long strings. Irritating.
+ if (length(counts[name]) > 4000)
+ {
+ counts[name] = longeval (counts[name])
+ hits[name] = longeval (hits[name])
+ phits[name] = longeval (phits[name])
+ }
+ }
+END {
+ # Heuristics called combined predicts just everything.
+ maxcounts = longeval (counts["first match"])
+ maxbranches = branches["first match"]
+ max = names["firat match"]
+ printf("HEURISTICS BRANCHES (REL) HITRATE COVERAGE (REL)\n")
+ for (i = 0; i < nnames ; i++)
+ {
+ name = names[i]
+ counts[name] = longeval (counts[name])
+ printf ("%-27s %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)"))
+ }
+}
projects / gcc.git / commitdiff