gcc/predict.def

   1 /* Definitions for the branch prediction routines in the GNU compiler.
   2    Copyright (C) 2001-2015 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 /* Assume that any given atomic operation has low contention,
  61    and thus the compare-and-swap operation succeeds. */
  62 DEF_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.  */
  69 DEF_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.  */
  73 DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations",
  74                PROB_ALWAYS, PRED_FLAG_FIRST_MATCH)
  75
  76 /* Branch containing goto is probably not taken.  */
  77 DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (50), 0)
  78
  79 /* Branch to basic block containing call marked by noreturn attribute.  */
  80 DEF_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.  */
  84 DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY,
  85                PRED_FLAG_FIRST_MATCH)
  86
  87 /* Loopback edge is taken.  */
  88 DEF_PREDICTOR (PRED_LOOP_BRANCH, "loop branch", HITRATE (86),
  89                PRED_FLAG_FIRST_MATCH)
  90
  91 /* Edge causing loop to terminate is probably not taken.  */
  92 DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (91),
  93                PRED_FLAG_FIRST_MATCH)
  94
  95 /* Pointers are usually not NULL.  */
  96 DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (85), 0)
  97 DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (85), 0)
  98
  99 /* NE is probable, EQ not etc...  */
 100 DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (79), 0)
 101 DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (71), 0)
 102 DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0)
 103 DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", HITRATE (73), 0)
 104 DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", HITRATE (72), 0)
 105 DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0)
 106
 107 /* Branch guarding call is probably taken.  */
 108 DEF_PREDICTOR (PRED_CALL, "call", HITRATE (71), 0)
 109
 110 /* Branch causing function to terminate is probably not taken.  */
 111 DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (61), 0)
 112
 113 /* Branch containing goto is probably not taken.  */
 114 DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (70), 0)
 115
 116 /* Branch ending with return constant is probably not taken.  */
 117 DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (67), 0)
 118
 119 /* Branch ending with return negative constant is probably not taken.  */
 120 DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (96), 0)
 121
 122 /* Branch ending with return; is probably not taken */
 123 DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (90), 0)
 124
 125 /* Branches to compare induction variable to a loop bound is
 126    extremely likely.  */
 127 DEF_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.  */
 132 DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_VERY_LIKELY,
 133                PRED_FLAG_FIRST_MATCH)
 134
 135 /* Branches to hot labels are likely.  */
 136 DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (85), 0)
 137
 138 /* Branches to cold labels are extremely unlikely.  */
 139 DEF_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.  */
 146 DEF_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.  */
 154 DEF_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.  */
 160 DEF_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.  */
 164 DEF_PREDICTOR (PRED_FORTRAN_WARN_ONCE, "warn once", HITRATE (75), 0)
 165
 166 /* Branch belonging to a zero-sized array.  */
 167 DEF_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.  */
 172 DEF_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.  */
 178 DEF_PREDICTOR (PRED_FORTRAN_ABSENT_DUMMY, "absent dummy", HITRATE(60), 0)