1 /* Definitions for the branch prediction routines in the GNU compiler. 2 Copyright (C) 2001-2022 Free Software Foundation, Inc. 3 4 This file is part of GCC. 5 6 GCC is free software; you can redistribute it and/or modify it under 7 the terms of the GNU General Public License as published by the Free 8 Software Foundation; either version 3, or (at your option) any later 9 version. 10 11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY 12 WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with GCC; see the file COPYING3. If not see 18 <http://www.gnu.org/licenses/>. */ 19 20 /* Before including this file, you should define a macro: 21 22 DEF_PREDICTOR (ENUM, NAME, HITRATE) 23 24 This macro will be called once for each predictor. The ENUM will 25 be of type `enum br_predictor', and will enumerate all supported 26 predictors. The order of DEF_PREDICTOR calls is important, as 27 in the first match combining heuristics, the predictor appearing 28 first in this file will win. 29 30 NAME is used in the debugging output to determine predictor type. 31 32 HITRATE is the probability that edge predicted by predictor as taken 33 will be really taken (so it should be always above 34 REG_BR_PROB_BASE / 2). */ 35 36 37 /* A value used as final outcome of all heuristics. */ 38 DEF_PREDICTOR (PRED_COMBINED, "combined", PROB_ALWAYS, 0) 39 40 /* An outcome estimated by Dempster-Shaffer theory. */ 41 DEF_PREDICTOR (PRED_DS_THEORY, "DS theory", PROB_ALWAYS, 0) 42 43 /* A combined heuristics using probability determined by first 44 matching heuristics from this list. */ 45 DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS, 0) 46 47 /* Heuristic applying when no heuristic below applies. */ 48 DEF_PREDICTOR (PRED_NO_PREDICTION, "no prediction", PROB_ALWAYS, 0) 49 50 /* Mark unconditional jump as taken. */ 51 DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS, 52 PRED_FLAG_FIRST_MATCH) 53 54 /* Return value of malloc function is almost always non-null. */ 55 DEF_PREDICTOR (PRED_MALLOC_NONNULL, "malloc returned non-NULL", \ 56 PROB_VERY_LIKELY, PRED_FLAG_FIRST_MATCH) 57 58 /* Use number of loop iterations determined by # of iterations 59 analysis to set probability. We don't want to use Dempster-Shaffer 60 theory here, as the predictions is exact. */ 61 DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_UNINITIALIZED, 62 PRED_FLAG_FIRST_MATCH) 63 64 /* Assume that any given atomic operation has low contention, 65 and thus the compare-and-swap operation succeeds. */ 66 DEF_PREDICTOR (PRED_COMPARE_AND_SWAP, "compare and swap", PROB_VERY_LIKELY, 67 PRED_FLAG_FIRST_MATCH) 68 69 /* Hints dropped by user via __builtin_expect feature. Note: the 70 probability of PROB_VERY_LIKELY is now overwritten by param 71 builtin_expect_probability with a default value of HITRATE(90). 72 Refer to param.def for details. */ 73 DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY, 74 PRED_FLAG_FIRST_MATCH) 75 76 /* Hints provided by user via __builtin_expect_with_probability. */ 77 DEF_PREDICTOR (PRED_BUILTIN_EXPECT_WITH_PROBABILITY, 78 "__builtin_expect_with_probability", PROB_UNINITIALIZED, 79 PRED_FLAG_FIRST_MATCH) 80 81 /* Branches to hot labels are likely. */ 82 DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (90), 83 PRED_FLAG_FIRST_MATCH) 84 85 /* Branches to cold labels are extremely unlikely. */ 86 DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", HITRATE (90), 87 PRED_FLAG_FIRST_MATCH) 88 89 /* Use number of loop iterations guessed by the contents of the loop. */ 90 DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations", 91 PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH) 92 93 /* Use number of loop iterations guessed by the contents of the loop. */ 94 DEF_PREDICTOR (PRED_LOOP_ITERATIONS_MAX, "guessed loop iterations", 95 PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH) 96 97 /* Branch containing goto is probably not taken. */ 98 DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (67), 0) 99 100 /* Branch to basic block containing call marked by noreturn attribute. */ 101 DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY, 102 PRED_FLAG_FIRST_MATCH) 103 104 /* Branch to basic block containing call marked by cold function attribute. */ 105 DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY, 106 PRED_FLAG_FIRST_MATCH) 107 108 /* Edge causing loop to terminate is probably not taken. */ 109 DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (89), 110 PRED_FLAG_FIRST_MATCH) 111 112 /* Same as LOOP_EXIT but for loops containing recursive call. */ 113 DEF_PREDICTOR (PRED_LOOP_EXIT_WITH_RECURSION, "loop exit with recursion", 114 HITRATE (78), PRED_FLAG_FIRST_MATCH) 115 116 /* Edge causing loop to terminate by computing value used by later 117 conditional. */ 118 DEF_PREDICTOR (PRED_LOOP_EXTRA_EXIT, "extra loop exit", HITRATE (67), 119 PRED_FLAG_FIRST_MATCH) 120 121 /* Pointers are usually not NULL. */ 122 DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (70), 0) 123 DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (70), 0) 124 125 /* NE is probable, EQ not etc... */ 126 DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (59), 0) 127 DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (66), 0) 128 DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0) 129 DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", 130 HITRATE (59), 0) 131 DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", 132 HITRATE (66), 0) 133 DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0) 134 135 /* Branch guarding call is probably taken. */ 136 DEF_PREDICTOR (PRED_CALL, "call", HITRATE (67), 0) 137 138 /* Call predictors are for now ignored, lets leave the predictor 139 to measure its benefit. */ 140 DEF_PREDICTOR (PRED_INDIR_CALL, "indirect call", PROB_EVEN, 0) 141 DEF_PREDICTOR (PRED_POLYMORPHIC_CALL, "polymorphic call", PROB_EVEN, 0) 142 DEF_PREDICTOR (PRED_RECURSIVE_CALL, "recursive call", PROB_EVEN, 0) 143 144 /* Branch causing function to terminate is probably not taken. */ 145 DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (66), 146 0) 147 148 /* Branch containing goto is probably not taken. */ 149 DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (66), 0) 150 151 /* Branch ending with return constant is probably not taken. */ 152 DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (65), 0) 153 154 /* Branch ending with return negative constant is probably not taken. */ 155 DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (98), 0) 156 157 /* Branch ending with return; is probably not taken */ 158 DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (71), 0) 159 160 /* Branches to compare induction variable to a loop bound is 161 extremely likely. */ 162 DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv compare", 163 HITRATE (64), 0) 164 165 /* Use number of loop iterations determined by # of iterations analysis 166 to set probability of branches that compares IV to loop bound variable. */ 167 DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_UNINITIALIZED, 168 PRED_FLAG_FIRST_MATCH) 169 170 /* In the following code 171 for (loop1) 172 if (cond) 173 for (loop2) 174 body; 175 guess that cond is unlikely. */ 176 DEF_PREDICTOR (PRED_LOOP_GUARD, "loop guard", HITRATE (73), 0) 177 178 /* Same but for loops containing recursion. */ 179 DEF_PREDICTOR (PRED_LOOP_GUARD_WITH_RECURSION, "loop guard with recursion", 180 HITRATE (85), 0) 181 182 /* The following predictors are used in Fortran. */ 183 184 /* Branch leading to an integer overflow are extremely unlikely. */ 185 DEF_PREDICTOR (PRED_FORTRAN_OVERFLOW, "Fortran overflow", PROB_ALWAYS, 186 PRED_FLAG_FIRST_MATCH) 187 188 /* Branch leading to a failure status are unlikely. This can occur for out 189 of memory. This predictor only occurs when the user explicitly asked 190 for a return status. By default, the code aborts, 191 which is handled via PRED_NORETURN. */ 192 DEF_PREDICTOR (PRED_FORTRAN_FAIL_ALLOC, "Fortran fail alloc", 193 PROB_VERY_LIKELY, 0) 194 195 /* Predictor is used for an allocation of an already allocated memory or 196 deallocating an already deallocated allocatable. */ 197 DEF_PREDICTOR (PRED_FORTRAN_REALLOC, "Fortran repeated allocation/deallocation", 198 PROB_LIKELY, 0) 199 200 /* Branch leading to an I/O failure status are unlikely. This predictor is 201 used for I/O failures such as for invalid unit numbers. This predictor 202 only occurs when the user explicitly asked for a return status. By default, 203 the code aborts, which is handled via PRED_NORETURN. */ 204 DEF_PREDICTOR (PRED_FORTRAN_FAIL_IO, "Fortran fail IO", HITRATE (85), 0) 205 206 /* Branch leading to a run-time warning message which is printed only once 207 are unlikely. The print-warning branch itself can be likely or unlikely. */ 208 DEF_PREDICTOR (PRED_FORTRAN_WARN_ONCE, "Fortran warn once", HITRATE (75), 0) 209 210 /* Branch belonging to a zero-sized array. */ 211 DEF_PREDICTOR (PRED_FORTRAN_SIZE_ZERO, "Fortran zero-sized array", \ 212 HITRATE (99), 0) 213 214 /* Branch belonging to an invalid bound index, in a context where it is 215 standard conform and well defined but rather pointless and, hence, rather 216 unlikely to occur. */ 217 DEF_PREDICTOR (PRED_FORTRAN_INVALID_BOUND, "Fortran invalid bound", \ 218 HITRATE (90), 0) 219 220 /* Branch belonging to the handling of absent optional arguments. This 221 predictor is used when an optional dummy argument, associated with an 222 absent argument, is passed on as actual argument to another procedure, 223 which in turn has an optional argument. */ 224 DEF_PREDICTOR (PRED_FORTRAN_ABSENT_DUMMY, "Fortran absent dummy", \ 225 HITRATE (60), 0) 226 227 /* Fortran DO statement generates a pre-header guard: 228 empty = (step > 0 ? to < from : to > from), which can be predicted 229 to be very likely. */ 230 DEF_PREDICTOR (PRED_FORTRAN_LOOP_PREHEADER, "Fortran loop preheader", \ 231 HITRATE (99), 0) 232 233 /* Fortran assumed size arrays can be non-contiguous, so they need 234 to be repacked. */ 235 236 DEF_PREDICTOR (PRED_FORTRAN_CONTIGUOUS, "Fortran contiguous", \ 237 HITRATE (75), 0) 238 239
Indexes created Wed Mar 04 15:26:31 UTC 2026