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author kent <kent@cr.ie.u-ryukyu.ac.jp>
date Fri, 17 Jul 2009 14:47:48 +0900
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1 #!/usr/bin/awk -f
2 # Script to analyze experimental results of our branch prediction heuristics
3 # Contributed by Jan Hubicka, SuSE Inc.
4 # Copyright (C) 2001, 2003 Free Software Foundation, Inc.
5 #
6 # This file is part of GCC.
7 #
8 # GCC is free software; you can redistribute it and/or modify
9 # it under the terms of the GNU General Public License as published by
10 # the Free Software Foundation; either version 3, or (at your option)
11 # any later version.
12 #
13 # GCC is distributed in the hope that it will be useful,
14 # but WITHOUT ANY WARRANTY; without even the implied warranty of
15 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 # GNU General Public License for more details.
17 #
18 # You should have received a copy of the GNU General Public License
19 # along with GCC; see the file COPYING. If not, write to
20 # the Free Software Foundation, 51 Franklin Street, Fifth Floor,
21 # Boston, MA 02110-1301, USA.
22 #
23 #
24 # This script is used to calculate two basic properties of the branch prediction
25 # heuristics - coverage and hitrate. Coverage is number of executions of a given
26 # branch matched by the heuristics and hitrate is probability that once branch is
27 # predicted as taken it is really taken.
28 #
29 # These values are useful to determine the quality of given heuristics. Hitrate
30 # may be directly used in predict.c.
31 #
32 # Usage:
33 # Step 1: Compile and profile your program. You need to use -fprofile-arcs
34 # flag to get the profiles
35 # Step 2: Generate log files. The information about given heuristics are
36 # saved into *.bp dumps. You need to pass the -db switch to the compiler as well
37 # as -fbranch-probabilities to get the results of profiling noted in the dumps.
38 # Ensure that there are no "Arc profiling: some edge counts were bad." warnings.
39 # Step 3: Run this script to concatenate all *.life files:
40 # analyze_brprob `find . -name *.life`
41 # the information is collected and print once all files are parsed. This
42 # may take a while.
43 # Note that the script does use bc to perform long arithmetic.
44 # Step 4: Read the results. Basically the following table is printed:
45 # (this is just an example from a very early stage of branch prediction pass
46 # development, so please don't take these numbers seriously)
47 #
48 #HEURISTICS BRANCHES (REL) HITRATE COVERAGE (REL)
49 #opcode 2889 83.7% 94.96%/ 97.62% 7516383 75.3%
50 #pointer 246 7.1% 99.69%/ 99.86% 118791 1.2%
51 #loop header 449 13.0% 98.32%/ 99.07% 43553 0.4%
52 #first match 3450 100.0% 89.92%/ 97.27% 9979782 100.0%
53 #loop exit 924 26.8% 88.95%/ 95.58% 9026266 90.4%
54 #error return 150 4.3% 64.48%/ 86.81% 453542 4.5%
55 #call 803 23.3% 51.66%/ 98.61% 3614037 36.2%
56 #loop branch 51 1.5% 99.26%/ 99.27% 26854 0.3%
57 #noreturn call 951 27.6% 100.00%/100.00% 1759809 17.6%
58 #
59 # The heuristic called "first match" is a heuristic used by GCC branch
60 # prediction pass and it predicts 89.92% branches correctly.
61 #
62 # The quality of heuristics can be rated using both, coverage and hitrate
63 # parameters. For example "loop branch" heuristics (predicting loopback edge
64 # as taken) have both very high hitrate and coverage, so it is very useful.
65 # On the other hand, "exit block" heuristics (predicting exit edges as not
66 # taken) have good hitrate, but poor coverage, so only 3 branches have been
67 # predicted. The "loop header" heuristic has problems, since it tends to
68 # misspredict.
69 #
70 # The implementation of this script is somewhat brute force. My awk skills
71 # are limited.
72
73 function longeval(e)
74 {
75 e = "echo \"scale = 2 ;"e"\" | bc"
76 e | getline res
77 close (e)
78 return res
79 }
80
81 BEGIN {nnames = 0}
82
83 /^ .* heuristics: .*.$/ {
84 name=$0
85 sub (/^ /,"",name)
86 sub (/ heuristics: .*.$/,"",name)
87 if (!(name in branches))
88 {
89 names[nnames] = name
90 branches[name]=0
91 counts[name]=0
92 hits[name]=0
93 phits[name]=0
94 nnames++
95 }
96 branches[name]+=1
97 }
98
99 /^ .* heuristics: .*. exec [0-9]* hit [0-9]* (.*.)$/ {
100 name=$0
101 sub (/^ /,"",name)
102 sub (/ heuristics: .*. exec [0-9]* hit [0-9]* (.*.)$/,"",name)
103 pred=$0
104 sub (/^ .* heuristics: /,"",pred)
105 sub (/. exec [0-9]* hit [0-9]* (.*.)$/,"",pred)
106 count=$0
107 sub (/^ .* heuristics: .*. exec /,"",count)
108 sub (/ hit [0-9]* (.*.)$/,"",count)
109 hit=$0
110 sub (/^ .* heuristics: .*. exec [0-9]* hit /,"",hit)
111 sub (/ (.*.)$/,"",hit)
112
113 if (int(pred) < 50.0)
114 {
115 hit = count"-"hit;
116 }
117 counts[name]=counts[name] "+" count
118 hits[name]=hits[name] "+" hit
119 phits[name]=phits[name] "+(("hit")<"count"/2)*("count"-("hit"))+(("hit")>="count"/2)*("hit")"
120
121 #BC crashes on long strings. Irritating.
122 if (length(counts[name]) > 2000)
123 counts[name] = longeval(counts[name])
124 if (length(hits[name]) > 2000)
125 hits[name] = longeval(hits[name])
126 if (length(phits[name]) > 2000)
127 phits[name] = longeval(phits[name])
128 }
129 END {
130 # Heuristics called combined predicts just everything.
131 maxcounts = longeval(counts["combined"])
132 maxbranches = branches["combined"]
133 max = names["combined"]
134 printf("HEURISTICS BRANCHES (REL) HITRATE COVERAGE (REL)\n")
135 for (i = 0; i < nnames ; i++)
136 {
137 name = names[i]
138 counts[name] = longeval(counts[name])
139 printf ("%-26s %8i %5.1f%% %6s%% / %6s%% %12s %5.1f%%\n",
140 name,
141 branches[name], branches[name] * 100 / maxbranches,
142 longeval("("hits[name]") * 100 /(" counts[name]"-0.00001)"),
143 longeval("("phits[name]") * 100 /(" counts[name]"-0.00001)"),
144 counts[name], longeval(counts[name]" * 100 / ("maxcounts"-0.00001)"))
145 }
146 }