1 /* Definitions for the branch prediction routines in the GNU compiler.
2 Copyright (C) 2001, 2003, 2004, 2007, 2008, 2012
3 Free Software Foundation, Inc.
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify it under
8 the terms of the GNU General Public License as published by the Free
9 Software Foundation; either version 3, or (at your option) any later
12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING3. If not see
19 <http://www.gnu.org/licenses/>. */
21 /* Before including this file, you should define a macro:
23 DEF_PREDICTOR (ENUM, NAME, HITRATE)
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.
31 NAME is used in the debugging output to determine predictor type.
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). */
38 /* A value used as final outcome of all heuristics. */
39 DEF_PREDICTOR (PRED_COMBINED, "combined", PROB_ALWAYS, 0)
41 /* An outcome estimated by Dempster-Shaffer theory. */
42 DEF_PREDICTOR (PRED_DS_THEORY, "DS theory", PROB_ALWAYS, 0)
44 /* A combined heuristics using probability determined by first
45 matching heuristics from this list. */
46 DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS, 0)
48 /* Heuristic applying when no heuristic below applies. */
49 DEF_PREDICTOR (PRED_NO_PREDICTION, "no prediction", PROB_ALWAYS, 0)
51 /* Mark unconditional jump as taken. */
52 DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS,
53 PRED_FLAG_FIRST_MATCH)
55 /* Use number of loop iterations determined by # of iterations
56 analysis to set probability. We don't want to use Dempster-Shaffer
57 theory here, as the predictions is exact. */
58 DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_ALWAYS,
59 PRED_FLAG_FIRST_MATCH)
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)
65 /* Use number of loop iterations guessed by the contents of the loop. */
66 DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations",
67 PROB_ALWAYS, PRED_FLAG_FIRST_MATCH)
69 /* Branch containing goto is probably not taken. */
70 DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (50), 0)
72 /* Branch to basic block containing call marked by noreturn attribute. */
73 DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY,
74 PRED_FLAG_FIRST_MATCH)
76 /* Branch to basic block containing call marked by cold function attribute. */
77 DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY,
78 PRED_FLAG_FIRST_MATCH)
80 /* Loopback edge is taken. */
81 DEF_PREDICTOR (PRED_LOOP_BRANCH, "loop branch", HITRATE (86),
82 PRED_FLAG_FIRST_MATCH)
84 /* Edge causing loop to terminate is probably not taken. */
85 DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (91),
86 PRED_FLAG_FIRST_MATCH)
88 /* Pointers are usually not NULL. */
89 DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (85), 0)
90 DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (85), 0)
92 /* NE is probable, EQ not etc... */
93 DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (79), 0)
94 DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (71), 0)
95 DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0)
96 DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", HITRATE (73), 0)
97 DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", HITRATE (72), 0)
98 DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0)
100 /* Branch guarding call is probably taken. */
101 DEF_PREDICTOR (PRED_CALL, "call", HITRATE (71), 0)
103 /* Branch causing function to terminate is probably not taken. */
104 DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (61), 0)
106 /* Branch containing goto is probably not taken. */
107 DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (70), 0)
109 /* Branch ending with return constant is probably not taken. */
110 DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (67), 0)
112 /* Branch ending with return negative constant is probably not taken. */
113 DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (96), 0)
115 /* Branch ending with return; is probably not taken */
116 DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (90), 0)
118 /* Branches to a mudflap bounds check are extremely unlikely. */
119 DEF_PREDICTOR (PRED_MUDFLAP, "mudflap check", PROB_VERY_LIKELY, 0)
121 /* Branches to compare induction variable to a loop bound is
123 DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv compare",
126 /* Use number of loop iterations determined by # of iterations analysis
127 to set probability of branches that compares IV to loop bound variable. */
128 DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_VERY_LIKELY,
129 PRED_FLAG_FIRST_MATCH)
131 /* Branches to hot labels are likely. */
132 DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (85), 0)
134 /* Branches to cold labels are extremely unlikely. */
135 DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", PROB_VERY_LIKELY,
136 PRED_FLAG_FIRST_MATCH)