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148bd232 | 1 | /* Definitions for the branch prediction routines in the GNU compiler. |
fbd26352 | 2 | Copyright (C) 2001-2019 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 | |
c03de6c9 | 25 | be of type `enum br_predictor', and will enumerate all supported |
13488c51 | 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 | |
ba9d6f44 | 54 | /* Return value of malloc function is almost always non-null. */ |
55 | DEF_PREDICTOR (PRED_MALLOC_NONNULL, "malloc returned non-NULL", \ | |
56 | PROB_VERY_LIKELY, PRED_FLAG_FIRST_MATCH) | |
57 | ||
d500fef3 | 58 | /* Use number of loop iterations determined by # of iterations |
59 | analysis to set probability. We don't want to use Dempster-Shaffer | |
60 | theory here, as the predictions is exact. */ | |
8d7738e1 | 61 | DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_UNINITIALIZED, |
eb429644 | 62 | PRED_FLAG_FIRST_MATCH) |
f6664fee | 63 | |
c83059be | 64 | /* Assume that any given atomic operation has low contention, |
65 | and thus the compare-and-swap operation succeeds. */ | |
66 | DEF_PREDICTOR (PRED_COMPARE_AND_SWAP, "compare and swap", PROB_VERY_LIKELY, | |
67 | PRED_FLAG_FIRST_MATCH) | |
68 | ||
21853731 | 69 | /* Hints dropped by user via __builtin_expect feature. Note: the |
70 | probability of PROB_VERY_LIKELY is now overwritten by param | |
71 | builtin_expect_probability with a default value of HITRATE(90). | |
72 | Refer to param.def for details. */ | |
eb429644 | 73 | DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY, |
74 | PRED_FLAG_FIRST_MATCH) | |
f6664fee | 75 | |
01107f42 | 76 | /* Hints provided by user via __builtin_expect_with_probability. */ |
77 | DEF_PREDICTOR (PRED_BUILTIN_EXPECT_WITH_PROBABILITY, | |
78 | "__builtin_expect_with_probability", PROB_UNINITIALIZED, | |
79 | PRED_FLAG_FIRST_MATCH) | |
80 | ||
c914d1b3 | 81 | /* Branches to hot labels are likely. */ |
82 | DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (90), | |
83 | PRED_FLAG_FIRST_MATCH) | |
84 | ||
85 | /* Branches to cold labels are extremely unlikely. */ | |
86 | DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", HITRATE (90), | |
87 | PRED_FLAG_FIRST_MATCH) | |
88 | ||
d500fef3 | 89 | /* Use number of loop iterations guessed by the contents of the loop. */ |
90 | DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations", | |
8d7738e1 | 91 | PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH) |
d500fef3 | 92 | |
d07b2b6f | 93 | /* Use number of loop iterations guessed by the contents of the loop. */ |
94 | DEF_PREDICTOR (PRED_LOOP_ITERATIONS_MAX, "guessed loop iterations", | |
8d7738e1 | 95 | PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH) |
d07b2b6f | 96 | |
cd0fe062 | 97 | /* Branch containing goto is probably not taken. */ |
d3cb49c9 | 98 | DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (67), 0) |
cd0fe062 | 99 | |
f6664fee | 100 | /* Branch to basic block containing call marked by noreturn attribute. */ |
fc29fdf5 | 101 | DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY, |
49493a4e | 102 | PRED_FLAG_FIRST_MATCH) |
f6664fee | 103 | |
5de92639 | 104 | /* Branch to basic block containing call marked by cold function attribute. */ |
fc29fdf5 | 105 | DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY, |
5de92639 | 106 | PRED_FLAG_FIRST_MATCH) |
107 | ||
9cb8e99f | 108 | /* Edge causing loop to terminate is probably not taken. */ |
2bbcff9a | 109 | DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (89), |
49493a4e | 110 | PRED_FLAG_FIRST_MATCH) |
f6664fee | 111 | |
cbcc4297 | 112 | /* Same as LOOP_EXIT but for loops containing recursive call. */ |
113 | DEF_PREDICTOR (PRED_LOOP_EXIT_WITH_RECURSION, "loop exit with recursion", | |
2bbcff9a | 114 | HITRATE (78), PRED_FLAG_FIRST_MATCH) |
cbcc4297 | 115 | |
d3cb49c9 | 116 | /* Edge causing loop to terminate by computing value used by later |
117 | conditional. */ | |
2bbcff9a | 118 | DEF_PREDICTOR (PRED_LOOP_EXTRA_EXIT, "extra loop exit", HITRATE (67), |
76f8f901 | 119 | PRED_FLAG_FIRST_MATCH) |
120 | ||
f6664fee | 121 | /* Pointers are usually not NULL. */ |
d3cb49c9 | 122 | DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (70), 0) |
123 | DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (70), 0) | |
f6664fee | 124 | |
125 | /* NE is probable, EQ not etc... */ | |
2bbcff9a | 126 | DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (59), 0) |
d3cb49c9 | 127 | DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (66), 0) |
ba38e12b | 128 | DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0) |
cbcc4297 | 129 | DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", |
2bbcff9a | 130 | HITRATE (59), 0) |
cbcc4297 | 131 | DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", |
132 | HITRATE (66), 0) | |
4ee9c684 | 133 | DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0) |
f6664fee | 134 | |
135 | /* Branch guarding call is probably taken. */ | |
84a4920a | 136 | DEF_PREDICTOR (PRED_CALL, "call", HITRATE (67), 0) |
1cb6c2eb | 137 | |
3a600fec | 138 | /* Call predictors are for now ignored, lets leave the predictor |
139 | to measure its benefit. */ | |
140 | DEF_PREDICTOR (PRED_INDIR_CALL, "indirect call", PROB_EVEN, 0) | |
141 | DEF_PREDICTOR (PRED_POLYMORPHIC_CALL, "polymorphic call", PROB_EVEN, 0) | |
142 | DEF_PREDICTOR (PRED_RECURSIVE_CALL, "recursive call", PROB_EVEN, 0) | |
89beffc9 | 143 | |
c65f167e | 144 | /* Branch causing function to terminate is probably not taken. */ |
145 | DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (66), | |
146 | 0) | |
d3cb49c9 | 147 | |
38ef3642 | 148 | /* Branch containing goto is probably not taken. */ |
149 | DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (66), 0) | |
cd0fe062 | 150 | |
151 | /* Branch ending with return constant is probably not taken. */ | |
2bbcff9a | 152 | DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (65), 0) |
cd0fe062 | 153 | |
154 | /* Branch ending with return negative constant is probably not taken. */ | |
d3cb49c9 | 155 | DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (98), 0) |
cd0fe062 | 156 | |
157 | /* Branch ending with return; is probably not taken */ | |
2bbcff9a | 158 | DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (71), 0) |
0ec80471 | 159 | |
fd757b76 | 160 | /* Branches to compare induction variable to a loop bound is |
161 | extremely likely. */ | |
162 | DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv compare", | |
2bbcff9a | 163 | HITRATE (64), 0) |
fd757b76 | 164 | |
165 | /* Use number of loop iterations determined by # of iterations analysis | |
166 | to set probability of branches that compares IV to loop bound variable. */ | |
8d7738e1 | 167 | DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_UNINITIALIZED, |
fd757b76 | 168 | PRED_FLAG_FIRST_MATCH) |
758a38ab | 169 | |
e09883e4 | 170 | /* In the following code |
171 | for (loop1) | |
172 | if (cond) | |
173 | for (loop2) | |
174 | body; | |
175 | guess that cond is unlikely. */ | |
2bbcff9a | 176 | DEF_PREDICTOR (PRED_LOOP_GUARD, "loop guard", HITRATE (73), 0) |
e09883e4 | 177 | |
cbcc4297 | 178 | /* Same but for loops containing recursion. */ |
179 | DEF_PREDICTOR (PRED_LOOP_GUARD_WITH_RECURSION, "loop guard with recursion", | |
180 | HITRATE (85), 0) | |
181 | ||
c83059be | 182 | /* The following predictors are used in Fortran. */ |
183 | ||
184 | /* Branch leading to an integer overflow are extremely unlikely. */ | |
a3475f4c | 185 | DEF_PREDICTOR (PRED_FORTRAN_OVERFLOW, "Fortran overflow", PROB_ALWAYS, |
c83059be | 186 | PRED_FLAG_FIRST_MATCH) |
187 | ||
188 | /* Branch leading to a failure status are unlikely. This can occur for out | |
9f478225 | 189 | of memory. This predictor only occurs when the user explicitly asked |
190 | for a return status. By default, the code aborts, | |
191 | which is handled via PRED_NORETURN. */ | |
d879f5ad | 192 | DEF_PREDICTOR (PRED_FORTRAN_FAIL_ALLOC, "Fortran fail alloc", |
193 | PROB_VERY_LIKELY, 0) | |
9f478225 | 194 | |
195 | /* Predictor is used for an allocation of an already allocated memory or | |
196 | deallocating an already deallocated allocatable. */ | |
d879f5ad | 197 | DEF_PREDICTOR (PRED_FORTRAN_REALLOC, "Fortran repeated allocation/deallocation", |
198 | PROB_LIKELY, 0) | |
c83059be | 199 | |
200 | /* Branch leading to an I/O failure status are unlikely. This predictor is | |
201 | used for I/O failures such as for invalid unit numbers. This predictor | |
202 | only occurs when the user explicitly asked for a return status. By default, | |
203 | the code aborts, which is handled via PRED_NORETURN. */ | |
a3475f4c | 204 | DEF_PREDICTOR (PRED_FORTRAN_FAIL_IO, "Fortran fail IO", HITRATE (85), 0) |
c83059be | 205 | |
206 | /* Branch leading to a run-time warning message which is printed only once | |
207 | are unlikely. The print-warning branch itself can be likely or unlikely. */ | |
a3475f4c | 208 | DEF_PREDICTOR (PRED_FORTRAN_WARN_ONCE, "Fortran warn once", HITRATE (75), 0) |
c83059be | 209 | |
210 | /* Branch belonging to a zero-sized array. */ | |
a3475f4c | 211 | DEF_PREDICTOR (PRED_FORTRAN_SIZE_ZERO, "Fortran zero-sized array", \ |
212 | HITRATE (99), 0) | |
c83059be | 213 | |
214 | /* Branch belonging to an invalid bound index, in a context where it is | |
215 | standard conform and well defined but rather pointless and, hence, rather | |
216 | unlikely to occur. */ | |
a3475f4c | 217 | DEF_PREDICTOR (PRED_FORTRAN_INVALID_BOUND, "Fortran invalid bound", \ |
218 | HITRATE (90), 0) | |
c83059be | 219 | |
220 | /* Branch belonging to the handling of absent optional arguments. This | |
221 | predictor is used when an optional dummy argument, associated with an | |
222 | absent argument, is passed on as actual argument to another procedure, | |
223 | which in turn has an optional argument. */ | |
a3475f4c | 224 | DEF_PREDICTOR (PRED_FORTRAN_ABSENT_DUMMY, "Fortran absent dummy", \ |
225 | HITRATE (60), 0) | |
db48d95b | 226 | |
227 | /* Fortran DO statement generates a pre-header guard: | |
228 | empty = (step > 0 ? to < from : to > from), which can be predicted | |
229 | to be very likely. */ | |
230 | DEF_PREDICTOR (PRED_FORTRAN_LOOP_PREHEADER, "Fortran loop preheader", \ | |
231 | HITRATE (99), 0) | |
73835b3d | 232 | |
233 | /* Fortran assumed size arrays can be non-contiguous, so they need | |
234 | to be repacked. */ | |
235 | ||
236 | DEF_PREDICTOR (PRED_FORTRAN_CONTIGUOUS, "Fortran contiguous", \ | |
237 | HITRATE (75), 0) | |
238 |