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21f1c577 | 1 | /* Definitions for the branch prediction routines in the GNU compiler. |
8d9254fc | 2 | Copyright (C) 2001-2020 Free Software Foundation, Inc. |
4db384c9 | 3 | |
1322177d | 4 | This file is part of GCC. |
4db384c9 | 5 | |
1322177d LB |
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 | |
9dcd6f09 | 8 | Software Foundation; either version 3, or (at your option) any later |
1322177d | 9 | version. |
4db384c9 | 10 | |
1322177d LB |
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. | |
4db384c9 JH |
15 | |
16 | You should have received a copy of the GNU General Public License | |
9dcd6f09 NC |
17 | along with GCC; see the file COPYING3. If not see |
18 | <http://www.gnu.org/licenses/>. */ | |
4db384c9 JH |
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 | |
7a096965 | 25 | be of type `enum br_predictor', and will enumerate all supported |
4db384c9 JH |
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). */ | |
b8698a0f | 35 | |
4db384c9 | 36 | |
d195b46f | 37 | /* A value used as final outcome of all heuristics. */ |
134d3a2e JH |
38 | DEF_PREDICTOR (PRED_COMBINED, "combined", PROB_ALWAYS, 0) |
39 | ||
d195b46f JH |
40 | /* An outcome estimated by Dempster-Shaffer theory. */ |
41 | DEF_PREDICTOR (PRED_DS_THEORY, "DS theory", PROB_ALWAYS, 0) | |
42 | ||
569b7f6a | 43 | /* A combined heuristics using probability determined by first |
923cbdc3 | 44 | matching heuristics from this list. */ |
134d3a2e | 45 | DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS, 0) |
923cbdc3 | 46 | |
ff7cc307 | 47 | /* Heuristic applying when no heuristic below applies. */ |
d195b46f JH |
48 | DEF_PREDICTOR (PRED_NO_PREDICTION, "no prediction", PROB_ALWAYS, 0) |
49 | ||
923cbdc3 | 50 | /* Mark unconditional jump as taken. */ |
134d3a2e JH |
51 | DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS, |
52 | PRED_FLAG_FIRST_MATCH) | |
923cbdc3 | 53 | |
806562fd ML |
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 | ||
4839cb59 ZD |
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. */ | |
e2a1e6a4 | 61 | DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_UNINITIALIZED, |
134d3a2e | 62 | PRED_FLAG_FIRST_MATCH) |
923cbdc3 | 63 | |
ed9c79e1 JJ |
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 | ||
942df739 RX |
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. */ | |
134d3a2e JH |
73 | DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY, |
74 | PRED_FLAG_FIRST_MATCH) | |
923cbdc3 | 75 | |
1e9168b2 ML |
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 | ||
b3282dfe ML |
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 | ||
4839cb59 ZD |
89 | /* Use number of loop iterations guessed by the contents of the loop. */ |
90 | DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations", | |
e2a1e6a4 | 91 | PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH) |
4839cb59 | 92 | |
429d2750 JH |
93 | /* Use number of loop iterations guessed by the contents of the loop. */ |
94 | DEF_PREDICTOR (PRED_LOOP_ITERATIONS_MAX, "guessed loop iterations", | |
e2a1e6a4 | 95 | PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH) |
429d2750 | 96 | |
969d70ca | 97 | /* Branch containing goto is probably not taken. */ |
d1fcc2bd | 98 | DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (67), 0) |
969d70ca | 99 | |
923cbdc3 | 100 | /* Branch to basic block containing call marked by noreturn attribute. */ |
277b4867 | 101 | DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY, |
8b7e92f9 | 102 | PRED_FLAG_FIRST_MATCH) |
923cbdc3 | 103 | |
52bf96d2 | 104 | /* Branch to basic block containing call marked by cold function attribute. */ |
277b4867 | 105 | DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY, |
52bf96d2 JH |
106 | PRED_FLAG_FIRST_MATCH) |
107 | ||
991b6592 | 108 | /* Edge causing loop to terminate is probably not taken. */ |
664d17c6 | 109 | DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (89), |
8b7e92f9 | 110 | PRED_FLAG_FIRST_MATCH) |
923cbdc3 | 111 | |
9bb86f40 JH |
112 | /* Same as LOOP_EXIT but for loops containing recursive call. */ |
113 | DEF_PREDICTOR (PRED_LOOP_EXIT_WITH_RECURSION, "loop exit with recursion", | |
664d17c6 | 114 | HITRATE (78), PRED_FLAG_FIRST_MATCH) |
9bb86f40 | 115 | |
d1fcc2bd JH |
116 | /* Edge causing loop to terminate by computing value used by later |
117 | conditional. */ | |
664d17c6 | 118 | DEF_PREDICTOR (PRED_LOOP_EXTRA_EXIT, "extra loop exit", HITRATE (67), |
050fb209 JH |
119 | PRED_FLAG_FIRST_MATCH) |
120 | ||
923cbdc3 | 121 | /* Pointers are usually not NULL. */ |
d1fcc2bd JH |
122 | DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (70), 0) |
123 | DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (70), 0) | |
923cbdc3 JH |
124 | |
125 | /* NE is probable, EQ not etc... */ | |
664d17c6 | 126 | DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (59), 0) |
d1fcc2bd | 127 | DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (66), 0) |
0dd0e980 | 128 | DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0) |
9bb86f40 | 129 | DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", |
664d17c6 | 130 | HITRATE (59), 0) |
9bb86f40 JH |
131 | DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", |
132 | HITRATE (66), 0) | |
6de9cd9a | 133 | DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0) |
923cbdc3 JH |
134 | |
135 | /* Branch guarding call is probably taken. */ | |
ad730fac | 136 | DEF_PREDICTOR (PRED_CALL, "call", HITRATE (67), 0) |
2c512374 | 137 | |
813d6db9 ML |
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) | |
888ed1a3 | 143 | |
e59a1c22 ML |
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) | |
d1fcc2bd | 147 | |
7fef86d3 JH |
148 | /* Branch containing goto is probably not taken. */ |
149 | DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (66), 0) | |
969d70ca JH |
150 | |
151 | /* Branch ending with return constant is probably not taken. */ | |
664d17c6 | 152 | DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (65), 0) |
969d70ca JH |
153 | |
154 | /* Branch ending with return negative constant is probably not taken. */ | |
d1fcc2bd | 155 | DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (98), 0) |
969d70ca JH |
156 | |
157 | /* Branch ending with return; is probably not taken */ | |
664d17c6 | 158 | DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (71), 0) |
242229bb | 159 | |
9c04723a DC |
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", | |
664d17c6 | 163 | HITRATE (64), 0) |
9c04723a DC |
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. */ | |
e2a1e6a4 | 167 | DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_UNINITIALIZED, |
9c04723a | 168 | PRED_FLAG_FIRST_MATCH) |
e45abe1f | 169 | |
7805417a JH |
170 | /* In the following code |
171 | for (loop1) | |
172 | if (cond) | |
173 | for (loop2) | |
174 | body; | |
175 | guess that cond is unlikely. */ | |
664d17c6 | 176 | DEF_PREDICTOR (PRED_LOOP_GUARD, "loop guard", HITRATE (73), 0) |
7805417a | 177 | |
9bb86f40 JH |
178 | /* Same but for loops containing recursion. */ |
179 | DEF_PREDICTOR (PRED_LOOP_GUARD_WITH_RECURSION, "loop guard with recursion", | |
180 | HITRATE (85), 0) | |
181 | ||
ed9c79e1 JJ |
182 | /* The following predictors are used in Fortran. */ |
183 | ||
184 | /* Branch leading to an integer overflow are extremely unlikely. */ | |
8b051d2e | 185 | DEF_PREDICTOR (PRED_FORTRAN_OVERFLOW, "Fortran overflow", PROB_ALWAYS, |
ed9c79e1 JJ |
186 | PRED_FLAG_FIRST_MATCH) |
187 | ||
188 | /* Branch leading to a failure status are unlikely. This can occur for out | |
7f7fa20f ML |
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. */ | |
a5824361 ML |
192 | DEF_PREDICTOR (PRED_FORTRAN_FAIL_ALLOC, "Fortran fail alloc", |
193 | PROB_VERY_LIKELY, 0) | |
7f7fa20f ML |
194 | |
195 | /* Predictor is used for an allocation of an already allocated memory or | |
196 | deallocating an already deallocated allocatable. */ | |
a5824361 ML |
197 | DEF_PREDICTOR (PRED_FORTRAN_REALLOC, "Fortran repeated allocation/deallocation", |
198 | PROB_LIKELY, 0) | |
ed9c79e1 JJ |
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. */ | |
8b051d2e | 204 | DEF_PREDICTOR (PRED_FORTRAN_FAIL_IO, "Fortran fail IO", HITRATE (85), 0) |
ed9c79e1 JJ |
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. */ | |
8b051d2e | 208 | DEF_PREDICTOR (PRED_FORTRAN_WARN_ONCE, "Fortran warn once", HITRATE (75), 0) |
ed9c79e1 JJ |
209 | |
210 | /* Branch belonging to a zero-sized array. */ | |
8b051d2e ML |
211 | DEF_PREDICTOR (PRED_FORTRAN_SIZE_ZERO, "Fortran zero-sized array", \ |
212 | HITRATE (99), 0) | |
ed9c79e1 JJ |
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. */ | |
8b051d2e ML |
217 | DEF_PREDICTOR (PRED_FORTRAN_INVALID_BOUND, "Fortran invalid bound", \ |
218 | HITRATE (90), 0) | |
ed9c79e1 JJ |
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. */ | |
8b051d2e ML |
224 | DEF_PREDICTOR (PRED_FORTRAN_ABSENT_DUMMY, "Fortran absent dummy", \ |
225 | HITRATE (60), 0) | |
68fa96d6 ML |
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) | |
5d9c602d TK |
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 |