gcc/predict.def

   1 /* Definitions for the branch prediction routines in the GNU compiler.
   2    Copyright (C) 2001-2013 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 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 /* 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.  */
  57 DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_ALWAYS,
  58                PRED_FLAG_FIRST_MATCH)
  59
  60 /* Hints dropped by user via __builtin_expect feature.  Note: the
  61    probability of PROB_VERY_LIKELY is now overwritten by param
  62    builtin_expect_probability with a default value of HITRATE(90).
  63    Refer to param.def for details.  */
  64 DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY,
  65                PRED_FLAG_FIRST_MATCH)
  66
  67 /* Use number of loop iterations guessed by the contents of the loop.  */
  68 DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations",
  69                PROB_ALWAYS, PRED_FLAG_FIRST_MATCH)
  70
  71 /* Branch containing goto is probably not taken.  */
  72 DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (50), 0)
  73
  74 /* Branch to basic block containing call marked by noreturn attribute.  */
  75 DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY,
  76                PRED_FLAG_FIRST_MATCH)
  77
  78 /* Branch to basic block containing call marked by cold function attribute.  */
  79 DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY,
  80                PRED_FLAG_FIRST_MATCH)
  81
  82 /* Loopback edge is taken.  */
  83 DEF_PREDICTOR (PRED_LOOP_BRANCH, "loop branch", HITRATE (86),
  84                PRED_FLAG_FIRST_MATCH)
  85
  86 /* Edge causing loop to terminate is probably not taken.  */
  87 DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (91),
  88                PRED_FLAG_FIRST_MATCH)
  89
  90 /* Pointers are usually not NULL.  */
  91 DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (85), 0)
  92 DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (85), 0)
  93
  94 /* NE is probable, EQ not etc...  */
  95 DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (79), 0)
  96 DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (71), 0)
  97 DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0)
  98 DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", HITRATE (73), 0)
  99 DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", HITRATE (72), 0)
 100 DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0)
 101
 102 /* Branch guarding call is probably taken.  */
 103 DEF_PREDICTOR (PRED_CALL, "call", HITRATE (71), 0)
 104
 105 /* Branch causing function to terminate is probably not taken.  */
 106 DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (61), 0)
 107
 108 /* Branch containing goto is probably not taken.  */
 109 DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (70), 0)
 110
 111 /* Branch ending with return constant is probably not taken.  */
 112 DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (67), 0)
 113
 114 /* Branch ending with return negative constant is probably not taken.  */
 115 DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (96), 0)
 116
 117 /* Branch ending with return; is probably not taken */
 118 DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (90), 0)
 119
 120 /* Branches to compare induction variable to a loop bound is
 121    extremely likely.  */
 122 DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv compare",
 123                PROB_VERY_LIKELY, 0)
 124
 125 /* Use number of loop iterations determined by # of iterations analysis
 126    to set probability of branches that compares IV to loop bound variable.  */
 127 DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_VERY_LIKELY,
 128                PRED_FLAG_FIRST_MATCH)
 129
 130 /* Branches to hot labels are likely.  */
 131 DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (85), 0)
 132
 133 /* Branches to cold labels are extremely unlikely.  */
 134 DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", PROB_VERY_LIKELY,
 135                PRED_FLAG_FIRST_MATCH)