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148bd232 | 1 | /* Definitions for the branch prediction routines in the GNU compiler. |
f1717362 | 2 | Copyright (C) 2001-2016 Free Software Foundation, Inc. |
13488c51 | 3 | |
f12b58b3 | 4 | This file is part of GCC. |
13488c51 | 5 | |
f12b58b3 | 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 | |
8c4c00c1 | 8 | Software Foundation; either version 3, or (at your option) any later |
f12b58b3 | 9 | version. |
13488c51 | 10 | |
f12b58b3 | 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. | |
13488c51 | 15 | |
16 | You should have received a copy of the GNU General Public License | |
8c4c00c1 | 17 | along with GCC; see the file COPYING3. If not see |
18 | <http://www.gnu.org/licenses/>. */ | |
13488c51 | 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). */ | |
48e1416a | 35 | |
13488c51 | 36 | |
49d7c0db | 37 | /* A value used as final outcome of all heuristics. */ |
eb429644 | 38 | DEF_PREDICTOR (PRED_COMBINED, "combined", PROB_ALWAYS, 0) |
39 | ||
49d7c0db | 40 | /* An outcome estimated by Dempster-Shaffer theory. */ |
41 | DEF_PREDICTOR (PRED_DS_THEORY, "DS theory", PROB_ALWAYS, 0) | |
42 | ||
77aa6362 | 43 | /* A combined heuristics using probability determined by first |
f6664fee | 44 | matching heuristics from this list. */ |
eb429644 | 45 | DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS, 0) |
f6664fee | 46 | |
424da949 | 47 | /* Heuristic applying when no heuristic below applies. */ |
49d7c0db | 48 | DEF_PREDICTOR (PRED_NO_PREDICTION, "no prediction", PROB_ALWAYS, 0) |
49 | ||
f6664fee | 50 | /* Mark unconditional jump as taken. */ |
eb429644 | 51 | DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS, |
52 | PRED_FLAG_FIRST_MATCH) | |
f6664fee | 53 | |
d500fef3 | 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. */ | |
eb429644 | 57 | DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_ALWAYS, |
58 | PRED_FLAG_FIRST_MATCH) | |
f6664fee | 59 | |
c83059be | 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 | ||
21853731 | 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. */ | |
eb429644 | 69 | DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY, |
70 | PRED_FLAG_FIRST_MATCH) | |
f6664fee | 71 | |
d500fef3 | 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 | ||
cd0fe062 | 76 | /* Branch containing goto is probably not taken. */ |
4a1849e3 | 77 | DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (50), 0) |
cd0fe062 | 78 | |
f6664fee | 79 | /* Branch to basic block containing call marked by noreturn attribute. */ |
fc29fdf5 | 80 | DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY, |
49493a4e | 81 | PRED_FLAG_FIRST_MATCH) |
f6664fee | 82 | |
5de92639 | 83 | /* Branch to basic block containing call marked by cold function attribute. */ |
fc29fdf5 | 84 | DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY, |
5de92639 | 85 | PRED_FLAG_FIRST_MATCH) |
86 | ||
f6664fee | 87 | /* Loopback edge is taken. */ |
4a4e4487 | 88 | DEF_PREDICTOR (PRED_LOOP_BRANCH, "loop branch", HITRATE (86), |
49493a4e | 89 | PRED_FLAG_FIRST_MATCH) |
f6664fee | 90 | |
9cb8e99f | 91 | /* Edge causing loop to terminate is probably not taken. */ |
4a4e4487 | 92 | DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (91), |
49493a4e | 93 | PRED_FLAG_FIRST_MATCH) |
f6664fee | 94 | |
f6664fee | 95 | /* Pointers are usually not NULL. */ |
4a4e4487 | 96 | DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (85), 0) |
97 | DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (85), 0) | |
f6664fee | 98 | |
99 | /* NE is probable, EQ not etc... */ | |
7c7b2e74 | 100 | DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (79), 0) |
101 | DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (71), 0) | |
ba38e12b | 102 | DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0) |
f3cb8b1d | 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) | |
4ee9c684 | 105 | DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0) |
f6664fee | 106 | |
107 | /* Branch guarding call is probably taken. */ | |
f3cb8b1d | 108 | DEF_PREDICTOR (PRED_CALL, "call", HITRATE (71), 0) |
f6664fee | 109 | |
110 | /* Branch causing function to terminate is probably not taken. */ | |
f3cb8b1d | 111 | DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (61), 0) |
cd0fe062 | 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. */ | |
5331f35a | 117 | DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (67), 0) |
cd0fe062 | 118 | |
119 | /* Branch ending with return negative constant is probably not taken. */ | |
5331f35a | 120 | DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (96), 0) |
cd0fe062 | 121 | |
122 | /* Branch ending with return; is probably not taken */ | |
f3cb8b1d | 123 | DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (90), 0) |
0ec80471 | 124 | |
fd757b76 | 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) | |
758a38ab | 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) | |
c83059be | 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) |