1/* Definitions for the branch prediction routines in the GNU compiler.
2 Copyright (C) 2001-2017 Free Software Foundation, Inc.
3
4This file is part of GCC.
5
6GCC is free software; you can redistribute it and/or modify it under
7the terms of the GNU General Public License as published by the Free
8Software Foundation; either version 3, or (at your option) any later
9version.
10
11GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12WARRANTY; without even the implied warranty of MERCHANTABILITY or
13FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14for more details.
15
16You should have received a copy of the GNU General Public License
17along with GCC; see the file COPYING3. If not see
18<http://www.gnu.org/licenses/>. */
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). */
35
36
37/* A value used as final outcome of all heuristics. */
38DEF_PREDICTOR (PRED_COMBINED, "combined", PROB_ALWAYS, 0)
39
40/* An outcome estimated by Dempster-Shaffer theory. */
41DEF_PREDICTOR (PRED_DS_THEORY, "DS theory", PROB_ALWAYS, 0)
42
43/* A combined heuristics using probability determined by first
44 matching heuristics from this list. */
45DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS, 0)
46
47/* Heuristic applying when no heuristic below applies. */
48DEF_PREDICTOR (PRED_NO_PREDICTION, "no prediction", PROB_ALWAYS, 0)
49
50/* Mark unconditional jump as taken. */
51DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS,
52 PRED_FLAG_FIRST_MATCH)
53
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. */
57DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_ALWAYS,
58 PRED_FLAG_FIRST_MATCH)
59
60/* Assume that any given atomic operation has low contention,
61 and thus the compare-and-swap operation succeeds. */
62DEF_PREDICTOR (PRED_COMPARE_AND_SWAP, "compare and swap", PROB_VERY_LIKELY,
63 PRED_FLAG_FIRST_MATCH)
64
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. */
69DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY,
70 PRED_FLAG_FIRST_MATCH)
71
72/* Use number of loop iterations guessed by the contents of the loop. */
73DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations",
74 PROB_ALWAYS, PRED_FLAG_FIRST_MATCH)
75
76/* Use number of loop iterations guessed by the contents of the loop. */
77DEF_PREDICTOR (PRED_LOOP_ITERATIONS_MAX, "guessed loop iterations",
78 PROB_ALWAYS, PRED_FLAG_FIRST_MATCH)
79
80/* Branch containing goto is probably not taken. */
81DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (67), 0)
82
83/* Branch to basic block containing call marked by noreturn attribute. */
84DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY,
85 PRED_FLAG_FIRST_MATCH)
86
87/* Branch to basic block containing call marked by cold function attribute. */
88DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY,
89 PRED_FLAG_FIRST_MATCH)
90
91/* Edge causing loop to terminate is probably not taken. */
92DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (85),
93 PRED_FLAG_FIRST_MATCH)
94
95/* Same as LOOP_EXIT but for loops containing recursive call. */
96DEF_PREDICTOR (PRED_LOOP_EXIT_WITH_RECURSION, "loop exit with recursion",
97 HITRATE (72), PRED_FLAG_FIRST_MATCH)
98
99/* Edge causing loop to terminate by computing value used by later
100 conditional. */
101DEF_PREDICTOR (PRED_LOOP_EXTRA_EXIT, "extra loop exit", HITRATE (83),
102 PRED_FLAG_FIRST_MATCH)
103
104/* Pointers are usually not NULL. */
105DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (70), 0)
106DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (70), 0)
107
108/* NE is probable, EQ not etc... */
109DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (64), 0)
110DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (66), 0)
111DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0)
112DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)",
113 HITRATE (64), 0)
114DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)",
115 HITRATE (66), 0)
116DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0)
117
118/* Branch guarding call is probably taken. */
119DEF_PREDICTOR (PRED_CALL, "call", HITRATE (67), 0)
120
121/* PRED_CALL is not very reliable predictor and it turns out to be even
122 less reliable for indirect calls and polymorphic calls. For spec2k6
123 the predictio nis slightly in the direction of taking the call. */
124DEF_PREDICTOR (PRED_INDIR_CALL, "indirect call", HITRATE (86), 0)
125DEF_PREDICTOR (PRED_POLYMORPHIC_CALL, "polymorphic call", HITRATE (59), 0)
126
127/* Recursive calls are usually not taken or the function will recurse
128 indefinitely. */
129DEF_PREDICTOR (PRED_RECURSIVE_CALL, "recursive call", HITRATE (75), 0)
130
131/* Branch causing function to terminate is probably not taken. */
132DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (66),
133 0)
134
135/* Branch containing goto is probably not taken. */
136DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (66), 0)
137
138/* Branch ending with return constant is probably not taken. */
139DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (69), 0)
140
141/* Branch ending with return negative constant is probably not taken. */
142DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (98), 0)
143
144/* Branch ending with return; is probably not taken */
145DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (91), 0)
146
147/* Branches to compare induction variable to a loop bound is
148 extremely likely. */
149DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv compare",
150 HITRATE (98), 0)
151
152/* Use number of loop iterations determined by # of iterations analysis
153 to set probability of branches that compares IV to loop bound variable. */
154DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_VERY_LIKELY,
155 PRED_FLAG_FIRST_MATCH)
156
157/* In the following code
158 for (loop1)
159 if (cond)
160 for (loop2)
161 body;
162 guess that cond is unlikely. */
163DEF_PREDICTOR (PRED_LOOP_GUARD, "loop guard", HITRATE (66), 0)
164
165/* Same but for loops containing recursion. */
166DEF_PREDICTOR (PRED_LOOP_GUARD_WITH_RECURSION, "loop guard with recursion",
167 HITRATE (85), 0)
168
169/* Branches to hot labels are likely. */
170DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (85), 0)
171
172/* Branches to cold labels are extremely unlikely. */
173DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", PROB_VERY_LIKELY,
174 PRED_FLAG_FIRST_MATCH)
175
176
177/* The following predictors are used in Fortran. */
178
179/* Branch leading to an integer overflow are extremely unlikely. */
180DEF_PREDICTOR (PRED_FORTRAN_OVERFLOW, "Fortran overflow", PROB_ALWAYS,
181 PRED_FLAG_FIRST_MATCH)
182
183/* Branch leading to a failure status are unlikely. This can occur for out
184 of memory. This predictor only occurs when the user explicitly asked
185 for a return status. By default, the code aborts,
186 which is handled via PRED_NORETURN. */
187DEF_PREDICTOR (PRED_FORTRAN_FAIL_ALLOC, "Fortran fail alloc",
188 PROB_VERY_LIKELY, 0)
189
190/* Predictor is used for an allocation of an already allocated memory or
191 deallocating an already deallocated allocatable. */
192DEF_PREDICTOR (PRED_FORTRAN_REALLOC, "Fortran repeated allocation/deallocation",
193 PROB_LIKELY, 0)
194
195/* Branch leading to an I/O failure status are unlikely. This predictor is
196 used for I/O failures such as for invalid unit numbers. This predictor
197 only occurs when the user explicitly asked for a return status. By default,
198 the code aborts, which is handled via PRED_NORETURN. */
199DEF_PREDICTOR (PRED_FORTRAN_FAIL_IO, "Fortran fail IO", HITRATE (85), 0)
200
201/* Branch leading to a run-time warning message which is printed only once
202 are unlikely. The print-warning branch itself can be likely or unlikely. */
203DEF_PREDICTOR (PRED_FORTRAN_WARN_ONCE, "Fortran warn once", HITRATE (75), 0)
204
205/* Branch belonging to a zero-sized array. */
206DEF_PREDICTOR (PRED_FORTRAN_SIZE_ZERO, "Fortran zero-sized array", \
207 HITRATE (99), 0)
208
209/* Branch belonging to an invalid bound index, in a context where it is
210 standard conform and well defined but rather pointless and, hence, rather
211 unlikely to occur. */
212DEF_PREDICTOR (PRED_FORTRAN_INVALID_BOUND, "Fortran invalid bound", \
213 HITRATE (90), 0)
214
215/* Branch belonging to the handling of absent optional arguments. This
216 predictor is used when an optional dummy argument, associated with an
217 absent argument, is passed on as actual argument to another procedure,
218 which in turn has an optional argument. */
219DEF_PREDICTOR (PRED_FORTRAN_ABSENT_DUMMY, "Fortran absent dummy", \
220 HITRATE (60), 0)
221
222/* Fortran DO statement generates a pre-header guard:
223 empty = (step > 0 ? to < from : to > from), which can be predicted
224 to be very likely. */
225DEF_PREDICTOR (PRED_FORTRAN_LOOP_PREHEADER, "Fortran loop preheader", \
226 HITRATE (99), 0)
227