1/* Definitions for the branch prediction routines in the GNU compiler. 2 Copyright (C) 2001-2018 Free Software Foundation, Inc. 3 4This file is part of GCC. 5 6GCC is free software; you can redistribute it and/or modify it under 7the terms of the GNU General Public License as published by the Free 8Software Foundation; either version 3, or (at your option) any later 9version. 10 11GCC is distributed in the hope that it will be useful, but WITHOUT ANY 12WARRANTY; without even the implied warranty of MERCHANTABILITY or 13FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14for more details. 15 16You should have received a copy of the GNU General Public License 17along 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 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. */ 38DEF_PREDICTOR (PRED_COMBINED, "combined", PROB_ALWAYS, 0) 39 40/* An outcome estimated by Dempster-Shaffer theory. */ 41DEF_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. */ 45DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS, 0) 46 47/* Heuristic applying when no heuristic below applies. */ 48DEF_PREDICTOR (PRED_NO_PREDICTION, "no prediction", PROB_ALWAYS, 0) 49 50/* Mark unconditional jump as taken. */ 51DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS, 52 PRED_FLAG_FIRST_MATCH) 53 54/* Use number of loop iterations determined by # of iterations 55 analysis to set probability. We don't want to use Dempster-Shaffer 56 theory here, as the predictions is exact. */ 57DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_UNINITIALIZED, 58 PRED_FLAG_FIRST_MATCH) 59 60/* Assume that any given atomic operation has low contention, 61 and thus the compare-and-swap operation succeeds. */ 62DEF_PREDICTOR (PRED_COMPARE_AND_SWAP, "compare and swap", PROB_VERY_LIKELY, 63 PRED_FLAG_FIRST_MATCH) 64 65/* Hints dropped by user via __builtin_expect feature. Note: the 66 probability of PROB_VERY_LIKELY is now overwritten by param 67 builtin_expect_probability with a default value of HITRATE(90). 68 Refer to param.def for details. */ 69DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY, 70 PRED_FLAG_FIRST_MATCH) 71 72/* Use number of loop iterations guessed by the contents of the loop. */ 73DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations", 74 PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH) 75 76/* Use number of loop iterations guessed by the contents of the loop. */ 77DEF_PREDICTOR (PRED_LOOP_ITERATIONS_MAX, "guessed loop iterations", 78 PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH) 79 80/* Branch containing goto is probably not taken. */ 81DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (67), 0) 82 83/* Branch to basic block containing call marked by noreturn attribute. */ 84DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY, 85 PRED_FLAG_FIRST_MATCH) 86 87/* Branch to basic block containing call marked by cold function attribute. */ 88DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY, 89 PRED_FLAG_FIRST_MATCH) 90 91/* Edge causing loop to terminate is probably not taken. */ 92DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (89), 93 PRED_FLAG_FIRST_MATCH) 94 95/* Same as LOOP_EXIT but for loops containing recursive call. */ 96DEF_PREDICTOR (PRED_LOOP_EXIT_WITH_RECURSION, "loop exit with recursion", 97 HITRATE (78), PRED_FLAG_FIRST_MATCH) 98 99/* Edge causing loop to terminate by computing value used by later 100 conditional. */ 101DEF_PREDICTOR (PRED_LOOP_EXTRA_EXIT, "extra loop exit", HITRATE (67), 102 PRED_FLAG_FIRST_MATCH) 103 104/* Pointers are usually not NULL. */ 105DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (70), 0) 106DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (70), 0) 107 108/* NE is probable, EQ not etc... */ 109DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (59), 0) 110DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (66), 0) 111DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0) 112DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", 113 HITRATE (59), 0) 114DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", 115 HITRATE (66), 0) 116DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0) 117 118/* Branch guarding call is probably taken. */ 119DEF_PREDICTOR (PRED_CALL, "call", HITRATE (67), 0) 120 121/* Call predictors are for now ignored, lets leave the predictor 122 to measure its benefit. */ 123DEF_PREDICTOR (PRED_INDIR_CALL, "indirect call", PROB_EVEN, 0) 124DEF_PREDICTOR (PRED_POLYMORPHIC_CALL, "polymorphic call", PROB_EVEN, 0) 125DEF_PREDICTOR (PRED_RECURSIVE_CALL, "recursive call", PROB_EVEN, 0) 126 127/* Branch causing function to terminate is probably not taken. */ 128DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (66), 129 0) 130 131/* Branch containing goto is probably not taken. */ 132DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (66), 0) 133 134/* Branch ending with return constant is probably not taken. */ 135DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (65), 0) 136 137/* Branch ending with return negative constant is probably not taken. */ 138DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (98), 0) 139 140/* Branch ending with return; is probably not taken */ 141DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (71), 0) 142 143/* Branches to compare induction variable to a loop bound is 144 extremely likely. */ 145DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv compare", 146 HITRATE (64), 0) 147 148/* Use number of loop iterations determined by # of iterations analysis 149 to set probability of branches that compares IV to loop bound variable. */ 150DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_UNINITIALIZED, 151 PRED_FLAG_FIRST_MATCH) 152 153/* In the following code 154 for (loop1) 155 if (cond) 156 for (loop2) 157 body; 158 guess that cond is unlikely. */ 159DEF_PREDICTOR (PRED_LOOP_GUARD, "loop guard", HITRATE (73), 0) 160 161/* Same but for loops containing recursion. */ 162DEF_PREDICTOR (PRED_LOOP_GUARD_WITH_RECURSION, "loop guard with recursion", 163 HITRATE (85), 0) 164 165/* Branches to hot labels are likely. */ 166DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (85), 0) 167 168/* Branches to cold labels are extremely unlikely. */ 169DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", PROB_VERY_LIKELY, 170 PRED_FLAG_FIRST_MATCH) 171 172 173/* The following predictors are used in Fortran. */ 174 175/* Branch leading to an integer overflow are extremely unlikely. */ 176DEF_PREDICTOR (PRED_FORTRAN_OVERFLOW, "Fortran overflow", PROB_ALWAYS, 177 PRED_FLAG_FIRST_MATCH) 178 179/* Branch leading to a failure status are unlikely. This can occur for out 180 of memory. This predictor only occurs when the user explicitly asked 181 for a return status. By default, the code aborts, 182 which is handled via PRED_NORETURN. */ 183DEF_PREDICTOR (PRED_FORTRAN_FAIL_ALLOC, "Fortran fail alloc", 184 PROB_VERY_LIKELY, 0) 185 186/* Predictor is used for an allocation of an already allocated memory or 187 deallocating an already deallocated allocatable. */ 188DEF_PREDICTOR (PRED_FORTRAN_REALLOC, "Fortran repeated allocation/deallocation", 189 PROB_LIKELY, 0) 190 191/* Branch leading to an I/O failure status are unlikely. This predictor is 192 used for I/O failures such as for invalid unit numbers. This predictor 193 only occurs when the user explicitly asked for a return status. By default, 194 the code aborts, which is handled via PRED_NORETURN. */ 195DEF_PREDICTOR (PRED_FORTRAN_FAIL_IO, "Fortran fail IO", HITRATE (85), 0) 196 197/* Branch leading to a run-time warning message which is printed only once 198 are unlikely. The print-warning branch itself can be likely or unlikely. */ 199DEF_PREDICTOR (PRED_FORTRAN_WARN_ONCE, "Fortran warn once", HITRATE (75), 0) 200 201/* Branch belonging to a zero-sized array. */ 202DEF_PREDICTOR (PRED_FORTRAN_SIZE_ZERO, "Fortran zero-sized array", \ 203 HITRATE (99), 0) 204 205/* Branch belonging to an invalid bound index, in a context where it is 206 standard conform and well defined but rather pointless and, hence, rather 207 unlikely to occur. */ 208DEF_PREDICTOR (PRED_FORTRAN_INVALID_BOUND, "Fortran invalid bound", \ 209 HITRATE (90), 0) 210 211/* Branch belonging to the handling of absent optional arguments. This 212 predictor is used when an optional dummy argument, associated with an 213 absent argument, is passed on as actual argument to another procedure, 214 which in turn has an optional argument. */ 215DEF_PREDICTOR (PRED_FORTRAN_ABSENT_DUMMY, "Fortran absent dummy", \ 216 HITRATE (60), 0) 217 218/* Fortran DO statement generates a pre-header guard: 219 empty = (step > 0 ? to < from : to > from), which can be predicted 220 to be very likely. */ 221DEF_PREDICTOR (PRED_FORTRAN_LOOP_PREHEADER, "Fortran loop preheader", \ 222 HITRATE (99), 0) 223