1 | /* Definitions for the branch prediction routines in the GNU compiler. |
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2 | Copyright (C) 2001-2014 Free Software Foundation, Inc. |
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3 | |
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4 | This file is part of GCC. |
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5 | |
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6 | GCC is free software; you can redistribute it and/or modify it under |
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7 | the terms of the GNU General Public License as published by the Free |
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8 | Software Foundation; either version 3, or (at your option) any later |
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9 | version. |
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10 | |
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11 | GCC is distributed in the hope that it will be useful, but WITHOUT ANY |
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12 | WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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13 | FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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14 | for more details. |
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15 | |
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16 | You should have received a copy of the GNU General Public License |
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17 | along with GCC; see the file COPYING3. If not see |
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18 | <http://www.gnu.org/licenses/>. */ |
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19 | |
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20 | /* Before including this file, you should define a macro: |
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21 | |
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22 | DEF_PREDICTOR (ENUM, NAME, HITRATE) |
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23 | |
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24 | This macro will be called once for each predictor. The ENUM will |
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25 | be of type `enum predictor', and will enumerate all supported |
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26 | predictors. The order of DEF_PREDICTOR calls is important, as |
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27 | in the first match combining heuristics, the predictor appearing |
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28 | first in this file will win. |
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29 | |
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30 | NAME is used in the debugging output to determine predictor type. |
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31 | |
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32 | HITRATE is the probability that edge predicted by predictor as taken |
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33 | will be really taken (so it should be always above |
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34 | REG_BR_PROB_BASE / 2). */ |
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35 | |
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36 | |
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37 | /* A value used as final outcome of all heuristics. */ |
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38 | DEF_PREDICTOR (PRED_COMBINED, "combined", PROB_ALWAYS, 0) |
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39 | |
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40 | /* An outcome estimated by Dempster-Shaffer theory. */ |
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41 | DEF_PREDICTOR (PRED_DS_THEORY, "DS theory", PROB_ALWAYS, 0) |
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42 | |
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43 | /* A combined heuristics using probability determined by first |
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44 | matching heuristics from this list. */ |
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45 | DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS, 0) |
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46 | |
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47 | /* Heuristic applying when no heuristic below applies. */ |
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48 | DEF_PREDICTOR (PRED_NO_PREDICTION, "no prediction", PROB_ALWAYS, 0) |
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49 | |
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50 | /* Mark unconditional jump as taken. */ |
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51 | DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS, |
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52 | PRED_FLAG_FIRST_MATCH) |
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53 | |
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54 | /* Use number of loop iterations determined by # of iterations |
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55 | analysis to set probability. We don't want to use Dempster-Shaffer |
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56 | theory here, as the predictions is exact. */ |
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57 | DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_ALWAYS, |
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58 | PRED_FLAG_FIRST_MATCH) |
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59 | |
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60 | /* Assume that any given atomic operation has low contention, |
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61 | and thus the compare-and-swap operation succeeds. */ |
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62 | DEF_PREDICTOR (PRED_COMPARE_AND_SWAP, "compare and swap", PROB_VERY_LIKELY, |
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63 | PRED_FLAG_FIRST_MATCH) |
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64 | |
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65 | /* Hints dropped by user via __builtin_expect feature. Note: the |
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66 | probability of PROB_VERY_LIKELY is now overwritten by param |
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67 | builtin_expect_probability with a default value of HITRATE(90). |
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68 | Refer to param.def for details. */ |
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69 | DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY, |
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70 | PRED_FLAG_FIRST_MATCH) |
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71 | |
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72 | /* Use number of loop iterations guessed by the contents of the loop. */ |
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73 | DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations", |
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74 | PROB_ALWAYS, PRED_FLAG_FIRST_MATCH) |
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75 | |
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76 | /* Branch containing goto is probably not taken. */ |
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77 | DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (50), 0) |
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78 | |
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79 | /* Branch to basic block containing call marked by noreturn attribute. */ |
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80 | DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY, |
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81 | PRED_FLAG_FIRST_MATCH) |
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82 | |
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83 | /* Branch to basic block containing call marked by cold function attribute. */ |
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84 | DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY, |
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85 | PRED_FLAG_FIRST_MATCH) |
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86 | |
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87 | /* Loopback edge is taken. */ |
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88 | DEF_PREDICTOR (PRED_LOOP_BRANCH, "loop branch", HITRATE (86), |
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89 | PRED_FLAG_FIRST_MATCH) |
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90 | |
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91 | /* Edge causing loop to terminate is probably not taken. */ |
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92 | DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (91), |
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93 | PRED_FLAG_FIRST_MATCH) |
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94 | |
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95 | /* Pointers are usually not NULL. */ |
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96 | DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (85), 0) |
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97 | DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (85), 0) |
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98 | |
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99 | /* NE is probable, EQ not etc... */ |
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100 | DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (79), 0) |
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101 | DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (71), 0) |
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102 | DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0) |
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103 | DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", HITRATE (73), 0) |
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104 | DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", HITRATE (72), 0) |
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105 | DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0) |
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106 | |
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107 | /* Branch guarding call is probably taken. */ |
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108 | DEF_PREDICTOR (PRED_CALL, "call", HITRATE (71), 0) |
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109 | |
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110 | /* Branch causing function to terminate is probably not taken. */ |
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111 | DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (61), 0) |
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112 | |
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113 | /* Branch containing goto is probably not taken. */ |
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114 | DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (70), 0) |
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115 | |
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116 | /* Branch ending with return constant is probably not taken. */ |
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117 | DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (67), 0) |
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118 | |
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119 | /* Branch ending with return negative constant is probably not taken. */ |
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120 | DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (96), 0) |
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121 | |
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122 | /* Branch ending with return; is probably not taken */ |
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123 | DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (90), 0) |
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124 | |
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125 | /* Branches to compare induction variable to a loop bound is |
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126 | extremely likely. */ |
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127 | DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv compare", |
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128 | PROB_VERY_LIKELY, 0) |
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129 | |
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130 | /* Use number of loop iterations determined by # of iterations analysis |
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131 | to set probability of branches that compares IV to loop bound variable. */ |
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132 | DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_VERY_LIKELY, |
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133 | PRED_FLAG_FIRST_MATCH) |
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134 | |
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135 | /* Branches to hot labels are likely. */ |
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136 | DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (85), 0) |
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137 | |
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138 | /* Branches to cold labels are extremely unlikely. */ |
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139 | DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", PROB_VERY_LIKELY, |
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140 | PRED_FLAG_FIRST_MATCH) |
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141 | |
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142 | |
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143 | /* The following predictors are used in Fortran. */ |
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144 | |
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145 | /* Branch leading to an integer overflow are extremely unlikely. */ |
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146 | DEF_PREDICTOR (PRED_FORTRAN_OVERFLOW, "overflow", PROB_ALWAYS, |
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147 | PRED_FLAG_FIRST_MATCH) |
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148 | |
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149 | /* Branch leading to a failure status are unlikely. This can occur for out |
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150 | of memory or when trying to allocate an already allocated allocated or |
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151 | deallocating an already deallocated allocatable. This predictor only |
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152 | occurs when the user explicitly asked for a return status. By default, |
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153 | the code aborts, which is handled via PRED_NORETURN. */ |
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154 | DEF_PREDICTOR (PRED_FORTRAN_FAIL_ALLOC, "fail alloc", PROB_VERY_LIKELY, 0) |
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155 | |
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156 | /* Branch leading to an I/O failure status are unlikely. This predictor is |
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157 | used for I/O failures such as for invalid unit numbers. This predictor |
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158 | only occurs when the user explicitly asked for a return status. By default, |
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159 | the code aborts, which is handled via PRED_NORETURN. */ |
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160 | DEF_PREDICTOR (PRED_FORTRAN_FAIL_IO, "fail alloc", HITRATE(85), 0) |
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161 | |
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162 | /* Branch leading to a run-time warning message which is printed only once |
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163 | are unlikely. The print-warning branch itself can be likely or unlikely. */ |
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164 | DEF_PREDICTOR (PRED_FORTRAN_WARN_ONCE, "warn once", HITRATE (75), 0) |
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165 | |
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166 | /* Branch belonging to a zero-sized array. */ |
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167 | DEF_PREDICTOR (PRED_FORTRAN_SIZE_ZERO, "zero-sized array", HITRATE(70), 0) |
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168 | |
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169 | /* Branch belonging to an invalid bound index, in a context where it is |
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170 | standard conform and well defined but rather pointless and, hence, rather |
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171 | unlikely to occur. */ |
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172 | DEF_PREDICTOR (PRED_FORTRAN_INVALID_BOUND, "zero-sized array", HITRATE(90), 0) |
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173 | |
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174 | /* Branch belonging to the handling of absent optional arguments. This |
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175 | predictor is used when an optional dummy argument, associated with an |
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176 | absent argument, is passed on as actual argument to another procedure, |
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177 | which in turn has an optional argument. */ |
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178 | DEF_PREDICTOR (PRED_FORTRAN_ABSENT_DUMMY, "absent dummy", HITRATE(60), 0) |
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