xref: /freebsd-10.0-release/contrib/gcc/predict.def

/* Definitions for the branch prediction routines in the GNU compiler.
   Copyright (C) 2001, 2003, 2004 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 2, 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 COPYING.  If not, write to the Free
Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301, USA.  */

/* 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 loop unroller 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)

/* Hints dropped by user via __builtin_expect feature.  */
DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY,
	       PRED_FLAG_FIRST_MATCH)

/* Branch containing goto is probably not taken.  */
DEF_PREDICTOR (PRED_CONTINUE, "continue", HITRATE (56), 0)

/* Branch to basic block containing call marked by noreturn attribute.  */
DEF_PREDICTOR (PRED_NORETURN, "noreturn call", HITRATE (99),
	       PRED_FLAG_FIRST_MATCH)

/* Loopback edge is taken.  */
DEF_PREDICTOR (PRED_LOOP_BRANCH, "loop branch", HITRATE (89),
	       PRED_FLAG_FIRST_MATCH)

/* Edge causing loop to terminate is probably not taken.  */
DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", HITRATE (90),
	       PRED_FLAG_FIRST_MATCH)

/* Condition emitted by preconditiong code to ensure that variable
   setting number of iterations is greater than initial value of iterator.  */
DEF_PREDICTOR (PRED_LOOP_CONDITION, "loop condition", PROB_VERY_LIKELY, 0)

/* Preconditioning makes linear list of branches.  */
DEF_PREDICTOR (PRED_LOOP_PRECONDITIONING, "loop preconditioning", PROB_VERY_LIKELY, 0)

/* Copied condition for the first iteration of loop is probably true.  */
DEF_PREDICTOR (PRED_LOOP_HEADER, "loop header", HITRATE (64), 0)

/* Pointers are usually not NULL.  */
DEF_PREDICTOR (PRED_POINTER, "pointer", HITRATE (81), 0)
DEF_PREDICTOR (PRED_TREE_POINTER, "pointer (on trees)", HITRATE (81), 0)

/* NE is probable, EQ not etc...  */
DEF_PREDICTOR (PRED_OPCODE_POSITIVE, "opcode values positive", HITRATE (79), 0)
DEF_PREDICTOR (PRED_OPCODE_NONEQUAL, "opcode values nonequal", HITRATE (71), 0)
DEF_PREDICTOR (PRED_FPOPCODE, "fp_opcode", HITRATE (90), 0)
DEF_PREDICTOR (PRED_TREE_OPCODE_POSITIVE, "opcode values positive (on trees)", HITRATE (79), 0)
DEF_PREDICTOR (PRED_TREE_OPCODE_NONEQUAL, "opcode values nonequal (on trees)", HITRATE (71), 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 (70), 0)

/* Branch causing function to terminate is probably not taken.  */
DEF_PREDICTOR (PRED_EARLY_RETURN, "early return", HITRATE (67), 0)
DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (67), 0)

/* Branch containing goto is probably not taken.  */
DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (70), 0)

/* Branch ending with return constant is probably not taken.  */
DEF_PREDICTOR (PRED_CONST_RETURN, "const return", HITRATE (95), 0)

/* Branch ending with return negative constant is probably not taken.  */
DEF_PREDICTOR (PRED_NEGATIVE_RETURN, "negative return", HITRATE (96), 0)

/* Branch ending with return; is probably not taken */
DEF_PREDICTOR (PRED_NULL_RETURN, "null return", HITRATE (90), 0)

/* Branches to a mudflap bounds check are extremely unlikely.  */
DEF_PREDICTOR (PRED_MUDFLAP, "mudflap check", HITRATE (99), 0)