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1 /* Definitions for the branch prediction routines in the GNU compiler.
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2 Copyright (C) 2001, 2003, 2004, 2007, 2008 Free Software Foundation, Inc.
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3
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4 This file is part of GCC.
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5
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6 GCC is free software; you can redistribute it and/or modify it under
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7 the terms of the GNU General Public License as published by the Free
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8 Software Foundation; either version 3, or (at your option) any later
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9 version.
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10
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11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
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13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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14 for more details.
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15
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16 You should have received a copy of the GNU General Public License
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17 along with GCC; see the file COPYING3. If not see
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18 <http://www.gnu.org/licenses/>. */
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19
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20 /* Before including this file, you should define a macro:
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21
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22 DEF_PREDICTOR (ENUM, NAME, HITRATE)
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23
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24 This macro will be called once for each predictor. The ENUM will
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25 be of type `enum predictor', and will enumerate all supported
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26 predictors. The order of DEF_PREDICTOR calls is important, as
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27 in the first match combining heuristics, the predictor appearing
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28 first in this file will win.
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29
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30 NAME is used in the debugging output to determine predictor type.
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31
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32 HITRATE is the probability that edge predicted by predictor as taken
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33 will be really taken (so it should be always above
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34 REG_BR_PROB_BASE / 2). */
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35
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36
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37 /* A value used as final outcome of all heuristics. */
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38 DEF_PREDICTOR (PRED_COMBINED, "combined", PROB_ALWAYS, 0)
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39
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40 /* An outcome estimated by Dempster-Shaffer theory. */
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41 DEF_PREDICTOR (PRED_DS_THEORY, "DS theory", PROB_ALWAYS, 0)
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42
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43 /* A combined heuristics using probability determined by first
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44 matching heuristics from this list. */
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45 DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS, 0)
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46
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47 /* Heuristic applying when no heuristic below applies. */
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48 DEF_PREDICTOR (PRED_NO_PREDICTION, "no prediction", PROB_ALWAYS, 0)
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49
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50 /* Mark unconditional jump as taken. */
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51 DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS,
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52 PRED_FLAG_FIRST_MATCH)
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53
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54 /* Use number of loop iterations determined by # of iterations
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55 analysis to set probability. We don't want to use Dempster-Shaffer
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56 theory here, as the predictions is exact. */
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57 DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_ALWAYS,
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58 PRED_FLAG_FIRST_MATCH)
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59
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60 /* Hints dropped by user via __builtin_expect feature. */
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61 DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY,
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62 PRED_FLAG_FIRST_MATCH)
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63
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64 /* Use number of loop iterations guessed by the contents of the loop. */
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65 DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations",
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66 PROB_ALWAYS, PRED_FLAG_FIRST_MATCH)
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67
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68 /* Branch containing goto is probably not taken. */
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69 DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (50), 0)
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70
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71 /* Branch to basic block containing call marked by noreturn attribute. */
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72 DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY,
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73 PRED_FLAG_FIRST_MATCH)
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74
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75 /* Branch to basic block containing call marked by cold function attribute. */
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76 DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY,
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77 PRED_FLAG_FIRST_MATCH)
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78
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79 /* Loopback edge is taken. */
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80 DEF_PREDICTOR (PRED_LOOP_BRANCH, "loop branch", HITRATE (86),
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81 PRED_FLAG_FIRST_MATCH)
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82
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83 /* Edge causing loop to terminate is probably not taken. */
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84 DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (91),
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85 PRED_FLAG_FIRST_MATCH)
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86
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87 /* Pointers are usually not NULL. */
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88 DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (85), 0)
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89 DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (85), 0)
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90
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91 /* NE is probable, EQ not etc... */
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92 DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (79), 0)
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93 DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (71), 0)
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94 DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0)
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95 DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", HITRATE (73), 0)
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96 DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", HITRATE (72), 0)
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97 DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0)
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98
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99 /* Branch guarding call is probably taken. */
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100 DEF_PREDICTOR (PRED_CALL, "call", HITRATE (71), 0)
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101
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102 /* Branch causing function to terminate is probably not taken. */
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103 DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (61), 0)
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104
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105 /* Branch containing goto is probably not taken. */
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106 DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (70), 0)
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107
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108 /* Branch ending with return constant is probably not taken. */
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109 DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (67), 0)
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110
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111 /* Branch ending with return negative constant is probably not taken. */
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112 DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (96), 0)
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113
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114 /* Branch ending with return; is probably not taken */
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115 DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (90), 0)
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116
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117 /* Branches to a mudflap bounds check are extremely unlikely. */
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118 DEF_PREDICTOR (PRED_MUDFLAP, "mudflap check", PROB_VERY_LIKELY, 0)
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