| | 1 | /* Definitions for the branch prediction routines in the GNU compiler. |
| | 2 | Copyright (C) 2001, 2003 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 2, 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 COPYING. If not, write to the Free |
| | 18 | Software Foundation, 59 Temple Place - Suite 330, Boston, MA |
| | 19 | 02111-1307, USA. */ |
| | 20 | |
| | 21 | /* Before including this file, you should define a macro: |
| | 22 | |
| | 23 | DEF_PREDICTOR (ENUM, NAME, HITRATE) |
| | 24 | |
| | 25 | This macro will be called once for each predictor. The ENUM will |
| | 26 | be of type `enum predictor', and will enumerate all supported |
| | 27 | predictors. The order of DEF_PREDICTOR calls is important, as |
| | 28 | in the first match combining heuristics, the predictor appearing |
| | 29 | first in this file will win. |
| | 30 | |
| | 31 | NAME is used in the debugging output to determine predictor type. |
| | 32 | |
| | 33 | HITRATE is the probability that edge predicted by predictor as taken |
| | 34 | will be really taken (so it should be always above |
| | 35 | REG_BR_PROB_BASE / 2). */ |
| | 36 | |
| | 37 | |
| | 38 | /* A value used as final outcome of all heuristics. */ |
| | 39 | DEF_PREDICTOR (PRED_COMBINED, "combined", PROB_ALWAYS, 0) |
| | 40 | |
| | 41 | /* An outcome estimated by Dempster-Shaffer theory. */ |
| | 42 | DEF_PREDICTOR (PRED_DS_THEORY, "DS theory", PROB_ALWAYS, 0) |
| | 43 | |
| | 44 | /* An combined heuristics using probability determined by first |
| | 45 | matching heuristics from this list. */ |
| | 46 | DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS, 0) |
| | 47 | |
| | 48 | /* Heuristic applying when no heuristic below applies. */ |
| | 49 | DEF_PREDICTOR (PRED_NO_PREDICTION, "no prediction", PROB_ALWAYS, 0) |
| | 50 | |
| | 51 | /* Mark unconditional jump as taken. */ |
| | 52 | DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS, |
| | 53 | PRED_FLAG_FIRST_MATCH) |
| | 54 | |
| | 55 | /* Use number of loop iterations determined by loop unroller to set |
| | 56 | probability. We don't want to use Dempster-Shaffer theory here, |
| | 57 | as the predictions is exact. */ |
| | 58 | DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_ALWAYS, |
| | 59 | PRED_FLAG_FIRST_MATCH) |
| | 60 | |
| | 61 | /* Hints dropped by user via __builtin_expect feature. */ |
| | 62 | DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY, |
| | 63 | PRED_FLAG_FIRST_MATCH) |
| | 64 | |
| | 65 | /* Branch containing goto is probably not taken. */ |
| | 66 | DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (56), 0) |
| | 67 | |
| | 68 | /* Branch to basic block containing call marked by noreturn attribute. */ |
| | 69 | DEF_PREDICTOR (PRED_NORETURN, "noreturn call", HITRATE (99), |
| | 70 | PRED_FLAG_FIRST_MATCH) |
| | 71 | |
| | 72 | /* Loopback edge is taken. */ |
| | 73 | DEF_PREDICTOR (PRED_LOOP_BRANCH, "loop branch", HITRATE (89), |
| | 74 | PRED_FLAG_FIRST_MATCH) |
| | 75 | |
| | 76 | /* Edge causing loop to terminate is probably not taken. */ |
| | 77 | DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (90), |
| | 78 | PRED_FLAG_FIRST_MATCH) |
| | 79 | |
| | 80 | /* Condition emitted by preconditiong code to ensure that variable |
| | 81 | setting number of iterations is greater than initial value of iterator. */ |
| | 82 | DEF_PREDICTOR (PRED_LOOP_CONDITION, "loop condition", PROB_VERY_LIKELY, 0) |
| | 83 | |
| | 84 | /* Preconditioning makes linear list of branches. */ |
| | 85 | DEF_PREDICTOR (PRED_LOOP_PRECONDITIONING, "loop preconditioning", PROB_VERY_LIKELY, 0) |
| | 86 | |
| | 87 | /* Copied condition for the first iteration of loop is probably true. */ |
| | 88 | DEF_PREDICTOR (PRED_LOOP_HEADER, "loop header", HITRATE (64), 0) |
| | 89 | |
| | 90 | /* Pointers are usually not NULL. */ |
| | 91 | DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (81), 0) |
| | 92 | |
| | 93 | /* NE is probable, EQ not etc... */ |
| | 94 | DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (79), 0) |
| | 95 | DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (71), 0) |
| | 96 | DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0) |
| | 97 | |
| | 98 | /* Branch guarding call is probably taken. */ |
| | 99 | DEF_PREDICTOR (PRED_CALL, "call", HITRATE (70), 0) |
| | 100 | |
| | 101 | /* Branch causing function to terminate is probably not taken. */ |
| | 102 | DEF_PREDICTOR (PRED_EARLY_RETURN, "early return", HITRATE (67), 0) |
| | 103 | |
| | 104 | /* Branch containing goto is probably not taken. */ |
| | 105 | DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (70), 0) |
| | 106 | |
| | 107 | /* Branch ending with return constant is probably not taken. */ |
| | 108 | DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (95), 0) |
| | 109 | |
| | 110 | /* Branch ending with return negative constant is probably not taken. */ |
| | 111 | DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (96), 0) |
| | 112 | |
| | 113 | /* Branch ending with return; is probably not taken */ |
| | 114 | DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (90), 0) |
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