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