1/* Definitions for the branch prediction routines in the GNU compiler. 2 Copyright (C) 2001-2016 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_ALWAYS, 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_ALWAYS, PRED_FLAG_FIRST_MATCH) 75 76/* Branch containing goto is probably not taken. */ 77DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (50), 0) 78 79/* Branch to basic block containing call marked by noreturn attribute. */ 80DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY, 81 PRED_FLAG_FIRST_MATCH) 82 83/* Branch to basic block containing call marked by cold function attribute. */ 84DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY, 85 PRED_FLAG_FIRST_MATCH) 86 87/* Loopback edge is taken. */ 88DEF_PREDICTOR (PRED_LOOP_BRANCH, "loop branch", HITRATE (86), 89 PRED_FLAG_FIRST_MATCH) 90 91/* Edge causing loop to terminate is probably not taken. */ 92DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (91), 93 PRED_FLAG_FIRST_MATCH) 94 95/* Pointers are usually not NULL. */ 96DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (85), 0) 97DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (85), 0) 98 99/* NE is probable, EQ not etc... */ 100DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (79), 0) 101DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (71), 0) 102DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0) 103DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", HITRATE (73), 0) 104DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", HITRATE (72), 0) 105DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0) 106 107/* Branch guarding call is probably taken. */ 108DEF_PREDICTOR (PRED_CALL, "call", HITRATE (71), 0) 109 110/* Branch causing function to terminate is probably not taken. */ 111DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (61), 0) 112 113/* Branch containing goto is probably not taken. */ 114DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (70), 0) 115 116/* Branch ending with return constant is probably not taken. */ 117DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (67), 0) 118 119/* Branch ending with return negative constant is probably not taken. */ 120DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (96), 0) 121 122/* Branch ending with return; is probably not taken */ 123DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (90), 0) 124 125/* Branches to compare induction variable to a loop bound is 126 extremely likely. */ 127DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv compare", 128 PROB_VERY_LIKELY, 0) 129 130/* Use number of loop iterations determined by # of iterations analysis 131 to set probability of branches that compares IV to loop bound variable. */ 132DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_VERY_LIKELY, 133 PRED_FLAG_FIRST_MATCH) 134 135/* Branches to hot labels are likely. */ 136DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (85), 0) 137 138/* Branches to cold labels are extremely unlikely. */ 139DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", PROB_VERY_LIKELY, 140 PRED_FLAG_FIRST_MATCH) 141 142 143/* The following predictors are used in Fortran. */ 144 145/* Branch leading to an integer overflow are extremely unlikely. */ 146DEF_PREDICTOR (PRED_FORTRAN_OVERFLOW, "overflow", PROB_ALWAYS, 147 PRED_FLAG_FIRST_MATCH) 148 149/* Branch leading to a failure status are unlikely. This can occur for out 150 of memory or when trying to allocate an already allocated allocated or 151 deallocating an already deallocated allocatable. This predictor only 152 occurs when the user explicitly asked for a return status. By default, 153 the code aborts, which is handled via PRED_NORETURN. */ 154DEF_PREDICTOR (PRED_FORTRAN_FAIL_ALLOC, "fail alloc", PROB_VERY_LIKELY, 0) 155 156/* Branch leading to an I/O failure status are unlikely. This predictor is 157 used for I/O failures such as for invalid unit numbers. This predictor 158 only occurs when the user explicitly asked for a return status. By default, 159 the code aborts, which is handled via PRED_NORETURN. */ 160DEF_PREDICTOR (PRED_FORTRAN_FAIL_IO, "fail alloc", HITRATE(85), 0) 161 162/* Branch leading to a run-time warning message which is printed only once 163 are unlikely. The print-warning branch itself can be likely or unlikely. */ 164DEF_PREDICTOR (PRED_FORTRAN_WARN_ONCE, "warn once", HITRATE (75), 0) 165 166/* Branch belonging to a zero-sized array. */ 167DEF_PREDICTOR (PRED_FORTRAN_SIZE_ZERO, "zero-sized array", HITRATE(70), 0) 168 169/* Branch belonging to an invalid bound index, in a context where it is 170 standard conform and well defined but rather pointless and, hence, rather 171 unlikely to occur. */ 172DEF_PREDICTOR (PRED_FORTRAN_INVALID_BOUND, "zero-sized array", HITRATE(90), 0) 173 174/* Branch belonging to the handling of absent optional arguments. This 175 predictor is used when an optional dummy argument, associated with an 176 absent argument, is passed on as actual argument to another procedure, 177 which in turn has an optional argument. */ 178DEF_PREDICTOR (PRED_FORTRAN_ABSENT_DUMMY, "absent dummy", HITRATE(60), 0) 179