/* Definitions for the branch prediction routines in the GNU compiler. | |

Copyright (C) 2001-2021 Free Software Foundation, Inc. | |

This file is part of GCC. | |

GCC is free software; you can redistribute it and/or modify it under | |

the terms of the GNU General Public License as published by the Free | |

Software Foundation; either version 3, or (at your option) any later | |

version. | |

GCC is distributed in the hope that it will be useful, but WITHOUT ANY | |

WARRANTY; without even the implied warranty of MERCHANTABILITY or | |

FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |

for more details. | |

You should have received a copy of the GNU General Public License | |

along with GCC; see the file COPYING3. If not see | |

<http://www.gnu.org/licenses/>. */ | |

/* Before including this file, you should define a macro: | |

DEF_PREDICTOR (ENUM, NAME, HITRATE) | |

This macro will be called once for each predictor. The ENUM will | |

be of type `enum br_predictor', and will enumerate all supported | |

predictors. The order of DEF_PREDICTOR calls is important, as | |

in the first match combining heuristics, the predictor appearing | |

first in this file will win. | |

NAME is used in the debugging output to determine predictor type. | |

HITRATE is the probability that edge predicted by predictor as taken | |

will be really taken (so it should be always above | |

REG_BR_PROB_BASE / 2). */ | |

/* A value used as final outcome of all heuristics. */ | |

DEF_PREDICTOR (PRED_COMBINED, "combined", PROB_ALWAYS, 0) | |

/* An outcome estimated by Dempster-Shaffer theory. */ | |

DEF_PREDICTOR (PRED_DS_THEORY, "DS theory", PROB_ALWAYS, 0) | |

/* A combined heuristics using probability determined by first | |

matching heuristics from this list. */ | |

DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS, 0) | |

/* Heuristic applying when no heuristic below applies. */ | |

DEF_PREDICTOR (PRED_NO_PREDICTION, "no prediction", PROB_ALWAYS, 0) | |

/* Mark unconditional jump as taken. */ | |

DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS, | |

PRED_FLAG_FIRST_MATCH) | |

/* Return value of malloc function is almost always non-null. */ | |

DEF_PREDICTOR (PRED_MALLOC_NONNULL, "malloc returned non-NULL", \ | |

PROB_VERY_LIKELY, PRED_FLAG_FIRST_MATCH) | |

/* Use number of loop iterations determined by # of iterations | |

analysis to set probability. We don't want to use Dempster-Shaffer | |

theory here, as the predictions is exact. */ | |

DEF_PREDICTOR (PRED_LOOP_ITERATIONS, "loop iterations", PROB_UNINITIALIZED, | |

PRED_FLAG_FIRST_MATCH) | |

/* Assume that any given atomic operation has low contention, | |

and thus the compare-and-swap operation succeeds. */ | |

DEF_PREDICTOR (PRED_COMPARE_AND_SWAP, "compare and swap", PROB_VERY_LIKELY, | |

PRED_FLAG_FIRST_MATCH) | |

/* Hints dropped by user via __builtin_expect feature. Note: the | |

probability of PROB_VERY_LIKELY is now overwritten by param | |

builtin_expect_probability with a default value of HITRATE(90). | |

Refer to param.def for details. */ | |

DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY, | |

PRED_FLAG_FIRST_MATCH) | |

/* Hints provided by user via __builtin_expect_with_probability. */ | |

DEF_PREDICTOR (PRED_BUILTIN_EXPECT_WITH_PROBABILITY, | |

"__builtin_expect_with_probability", PROB_UNINITIALIZED, | |

PRED_FLAG_FIRST_MATCH) | |

/* Branches to hot labels are likely. */ | |

DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (90), | |

PRED_FLAG_FIRST_MATCH) | |

/* Branches to cold labels are extremely unlikely. */ | |

DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", HITRATE (90), | |

PRED_FLAG_FIRST_MATCH) | |

/* Use number of loop iterations guessed by the contents of the loop. */ | |

DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations", | |

PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH) | |

/* Use number of loop iterations guessed by the contents of the loop. */ | |

DEF_PREDICTOR (PRED_LOOP_ITERATIONS_MAX, "guessed loop iterations", | |

PROB_UNINITIALIZED, PRED_FLAG_FIRST_MATCH) | |

/* Branch containing goto is probably not taken. */ | |

DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (67), 0) | |

/* Branch to basic block containing call marked by noreturn attribute. */ | |

DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_VERY_LIKELY, | |

PRED_FLAG_FIRST_MATCH) | |

/* Branch to basic block containing call marked by cold function attribute. */ | |

DEF_PREDICTOR (PRED_COLD_FUNCTION, "cold function call", PROB_VERY_LIKELY, | |

PRED_FLAG_FIRST_MATCH) | |

/* Edge causing loop to terminate is probably not taken. */ | |

DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (89), | |

PRED_FLAG_FIRST_MATCH) | |

/* Same as LOOP_EXIT but for loops containing recursive call. */ | |

DEF_PREDICTOR (PRED_LOOP_EXIT_WITH_RECURSION, "loop exit with recursion", | |

HITRATE (78), PRED_FLAG_FIRST_MATCH) | |

/* Edge causing loop to terminate by computing value used by later | |

conditional. */ | |

DEF_PREDICTOR (PRED_LOOP_EXTRA_EXIT, "extra loop exit", HITRATE (67), | |

PRED_FLAG_FIRST_MATCH) | |

/* Pointers are usually not NULL. */ | |

DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (70), 0) | |

DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (70), 0) | |

/* NE is probable, EQ not etc... */ | |

DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (59), 0) | |

DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (66), 0) | |

DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0) | |

DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", | |

HITRATE (59), 0) | |

DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", | |

HITRATE (66), 0) | |

DEF_PREDICTOR (PRED_TREE_FPOPCODE, "fp_opcode (on trees)", HITRATE (90), 0) | |

/* Branch guarding call is probably taken. */ | |

DEF_PREDICTOR (PRED_CALL, "call", HITRATE (67), 0) | |

/* Call predictors are for now ignored, lets leave the predictor | |

to measure its benefit. */ | |

DEF_PREDICTOR (PRED_INDIR_CALL, "indirect call", PROB_EVEN, 0) | |

DEF_PREDICTOR (PRED_POLYMORPHIC_CALL, "polymorphic call", PROB_EVEN, 0) | |

DEF_PREDICTOR (PRED_RECURSIVE_CALL, "recursive call", PROB_EVEN, 0) | |

/* Branch causing function to terminate is probably not taken. */ | |

DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (66), | |

0) | |

/* Branch containing goto is probably not taken. */ | |

DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (66), 0) | |

/* Branch ending with return constant is probably not taken. */ | |

DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (65), 0) | |

/* Branch ending with return negative constant is probably not taken. */ | |

DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (98), 0) | |

/* Branch ending with return; is probably not taken */ | |

DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (71), 0) | |

/* Branches to compare induction variable to a loop bound is | |

extremely likely. */ | |

DEF_PREDICTOR (PRED_LOOP_IV_COMPARE_GUESS, "guess loop iv compare", | |

HITRATE (64), 0) | |

/* Use number of loop iterations determined by # of iterations analysis | |

to set probability of branches that compares IV to loop bound variable. */ | |

DEF_PREDICTOR (PRED_LOOP_IV_COMPARE, "loop iv compare", PROB_UNINITIALIZED, | |

PRED_FLAG_FIRST_MATCH) | |

/* In the following code | |

for (loop1) | |

if (cond) | |

for (loop2) | |

body; | |

guess that cond is unlikely. */ | |

DEF_PREDICTOR (PRED_LOOP_GUARD, "loop guard", HITRATE (73), 0) | |

/* Same but for loops containing recursion. */ | |

DEF_PREDICTOR (PRED_LOOP_GUARD_WITH_RECURSION, "loop guard with recursion", | |

HITRATE (85), 0) | |

/* The following predictors are used in Fortran. */ | |

/* Branch leading to an integer overflow are extremely unlikely. */ | |

DEF_PREDICTOR (PRED_FORTRAN_OVERFLOW, "Fortran overflow", PROB_ALWAYS, | |

PRED_FLAG_FIRST_MATCH) | |

/* Branch leading to a failure status are unlikely. This can occur for out | |

of memory. This predictor only occurs when the user explicitly asked | |

for a return status. By default, the code aborts, | |

which is handled via PRED_NORETURN. */ | |

DEF_PREDICTOR (PRED_FORTRAN_FAIL_ALLOC, "Fortran fail alloc", | |

PROB_VERY_LIKELY, 0) | |

/* Predictor is used for an allocation of an already allocated memory or | |

deallocating an already deallocated allocatable. */ | |

DEF_PREDICTOR (PRED_FORTRAN_REALLOC, "Fortran repeated allocation/deallocation", | |

PROB_LIKELY, 0) | |

/* Branch leading to an I/O failure status are unlikely. This predictor is | |

used for I/O failures such as for invalid unit numbers. This predictor | |

only occurs when the user explicitly asked for a return status. By default, | |

the code aborts, which is handled via PRED_NORETURN. */ | |

DEF_PREDICTOR (PRED_FORTRAN_FAIL_IO, "Fortran fail IO", HITRATE (85), 0) | |

/* Branch leading to a run-time warning message which is printed only once | |

are unlikely. The print-warning branch itself can be likely or unlikely. */ | |

DEF_PREDICTOR (PRED_FORTRAN_WARN_ONCE, "Fortran warn once", HITRATE (75), 0) | |

/* Branch belonging to a zero-sized array. */ | |

DEF_PREDICTOR (PRED_FORTRAN_SIZE_ZERO, "Fortran zero-sized array", \ | |

HITRATE (99), 0) | |

/* Branch belonging to an invalid bound index, in a context where it is | |

standard conform and well defined but rather pointless and, hence, rather | |

unlikely to occur. */ | |

DEF_PREDICTOR (PRED_FORTRAN_INVALID_BOUND, "Fortran invalid bound", \ | |

HITRATE (90), 0) | |

/* Branch belonging to the handling of absent optional arguments. This | |

predictor is used when an optional dummy argument, associated with an | |

absent argument, is passed on as actual argument to another procedure, | |

which in turn has an optional argument. */ | |

DEF_PREDICTOR (PRED_FORTRAN_ABSENT_DUMMY, "Fortran absent dummy", \ | |

HITRATE (60), 0) | |

/* Fortran DO statement generates a pre-header guard: | |

empty = (step > 0 ? to < from : to > from), which can be predicted | |

to be very likely. */ | |

DEF_PREDICTOR (PRED_FORTRAN_LOOP_PREHEADER, "Fortran loop preheader", \ | |

HITRATE (99), 0) | |

/* Fortran assumed size arrays can be non-contiguous, so they need | |

to be repacked. */ | |

DEF_PREDICTOR (PRED_FORTRAN_CONTIGUOUS, "Fortran contiguous", \ | |

HITRATE (75), 0) | |