| /* Definitions for the branch prediction routines in the GNU compiler. |
| Copyright (C) 2001-2017 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 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) |
| |
| /* 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_ALWAYS, |
| 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) |
| |
| /* Use number of loop iterations guessed by the contents of the loop. */ |
| DEF_PREDICTOR (PRED_LOOP_ITERATIONS_GUESSED, "guessed loop iterations", |
| PROB_ALWAYS, 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_ALWAYS, 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 (85), |
| 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 (72), 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 (83), |
| 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 (64), 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 (64), 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) |
| |
| /* PRED_CALL is not very reliable predictor and it turns out to be even |
| less reliable for indirect calls and polymorphic calls. For spec2k6 |
| the predictio nis slightly in the direction of taking the call. */ |
| DEF_PREDICTOR (PRED_INDIR_CALL, "indirect call", HITRATE (86), 0) |
| DEF_PREDICTOR (PRED_POLYMORPHIC_CALL, "polymorphic call", HITRATE (59), 0) |
| |
| /* Recursive calls are usually not taken or the function will recurse |
| indefinitely. */ |
| DEF_PREDICTOR (PRED_RECURSIVE_CALL, "recursive call", HITRATE (75), 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 (69), 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 (91), 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 (98), 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_VERY_LIKELY, |
| 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 (66), 0) |
| |
| /* Same but for loops containing recursion. */ |
| DEF_PREDICTOR (PRED_LOOP_GUARD_WITH_RECURSION, "loop guard with recursion", |
| HITRATE (85), 0) |
| |
| /* Branches to hot labels are likely. */ |
| DEF_PREDICTOR (PRED_HOT_LABEL, "hot label", HITRATE (85), 0) |
| |
| /* Branches to cold labels are extremely unlikely. */ |
| DEF_PREDICTOR (PRED_COLD_LABEL, "cold label", PROB_VERY_LIKELY, |
| PRED_FLAG_FIRST_MATCH) |
| |
| |
| /* 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) |