#include "toplev.h"
#include "recog.h"
#include "expr.h"
-
+#include "predict.h"
/* Random guesstimation given names. */
#define PROB_NEVER (0)
#define PROB_VERY_LIKELY (REG_BR_PROB_BASE - PROB_VERY_UNLIKELY)
#define PROB_ALWAYS (REG_BR_PROB_BASE)
-static void predict_insn PARAMS ((rtx, int));
-static void predict_edge PARAMS ((edge, int));
+static void combine_predictions_for_insn PARAMS ((rtx, basic_block));
+static void dump_prediction PARAMS ((enum br_predictor, int,
+ basic_block));
-static void
-predict_insn (insn, probability)
- rtx insn;
- int probability;
+/* Information we hold about each branch predictor.
+ Filled using information from predict.def. */
+struct predictor_info
{
- rtx note = find_reg_note (insn, REG_BR_PROB, 0);
+ const char *name; /* Name used in the debugging dumps. */
+ int hitrate; /* Expected hitrate used by
+ predict_insn_def call. */
+};
- /* Implement "first match" heruistics. In case we already predicted
- insn somehow, keep it predicted that way. In future we would like
- to rather store all predictions and then combine them. */
- if (note)
- return;
+#define DEF_PREDICTOR(ENUM, NAME, HITRATE) {NAME, HITRATE},
+struct predictor_info predictor_info[] = {
+#include "predict.def"
+
+ /* Upper bound on non-language-specific builtins. */
+ {NULL, 0}
+};
+#undef DEF_PREDICTOR
+void
+predict_insn (insn, predictor, probability)
+ rtx insn;
+ int probability;
+ enum br_predictor predictor;
+{
if (!any_condjump_p (insn))
abort ();
REG_NOTES (insn)
- = gen_rtx_EXPR_LIST (REG_BR_PROB,
- GEN_INT (probability), REG_NOTES (insn));
+ = gen_rtx_EXPR_LIST (REG_BR_PRED,
+ gen_rtx_CONCAT (VOIDmode,
+ GEN_INT ((int) predictor),
+ GEN_INT ((int) probability)),
+ REG_NOTES (insn));
+}
+
+/* Predict insn by given predictor. */
+void
+predict_insn_def (insn, predictor, taken)
+ rtx insn;
+ enum br_predictor predictor;
+ enum prediction taken;
+{
+ int probability = predictor_info[(int) predictor].hitrate;
+ if (taken != TAKEN)
+ probability = REG_BR_PROB_BASE - probability;
+ predict_insn (insn, predictor, probability);
}
/* Predict edge E with given probability if possible. */
-static void
-predict_edge (e, probability)
+void
+predict_edge (e, predictor, probability)
edge e;
int probability;
+ enum br_predictor predictor;
{
rtx last_insn;
last_insn = e->src->end;
if (e->flags & EDGE_FALLTHRU)
probability = REG_BR_PROB_BASE - probability;
- predict_insn (last_insn, probability);
+ predict_insn (last_insn, predictor, probability);
+}
+
+/* Predict edge E by given predictor if possible. */
+void
+predict_edge_def (e, predictor, taken)
+ edge e;
+ enum br_predictor predictor;
+ enum prediction taken;
+{
+ int probability = predictor_info[(int) predictor].hitrate;
+
+ if (taken != TAKEN)
+ probability = REG_BR_PROB_BASE - probability;
+ predict_edge (e, predictor, probability);
+}
+
+/* Invert all branch predictions or probability notes in the INSN. This needs
+ to be done each time we invert the condition used by the jump. */
+void
+invert_br_probabilities (insn)
+ rtx insn;
+{
+ rtx note = REG_NOTES (insn);
+
+ while (note)
+ {
+ if (REG_NOTE_KIND (note) == REG_BR_PROB)
+ XEXP (note, 0) = GEN_INT (REG_BR_PROB_BASE - INTVAL (XEXP (note, 0)));
+ else if (REG_NOTE_KIND (note) == REG_BR_PRED)
+ XEXP (XEXP (note, 0), 1)
+ = GEN_INT (REG_BR_PROB_BASE - INTVAL (XEXP (XEXP (note, 0), 1)));
+ note = XEXP (note, 1);
+ }
+}
+
+/* Dump information about the branch prediction to the output file. */
+static void
+dump_prediction (predictor, probability, bb)
+ enum br_predictor predictor;
+ int probability;
+ basic_block bb;
+{
+ edge e = bb->succ;
+
+ if (!rtl_dump_file)
+ return;
+
+ while (e->flags & EDGE_FALLTHRU)
+ e = e->succ_next;
+
+ fprintf (rtl_dump_file, " %s heuristics: %.1f%%",
+ predictor_info[predictor].name,
+ probability * 100.0 / REG_BR_PROB_BASE);
+
+ if (bb->count)
+ fprintf (rtl_dump_file, " exec %i hit %i (%.1f%%)",
+ bb->count, e->count, e->count * 100.0 / bb->count);
+ fprintf (rtl_dump_file, "\n");
+}
+
+/* Combine all REG_BR_PRED notes into single probability and attach REG_BR_PROB
+ note if not already present. Remove now useless REG_BR_PRED notes. */
+static void
+combine_predictions_for_insn (insn, bb)
+ rtx insn;
+ basic_block bb;
+{
+ rtx prob_note = find_reg_note (insn, REG_BR_PROB, 0);
+ rtx *pnote = ®_NOTES (insn);
+ int best_probability = PROB_EVEN;
+ int best_predictor = END_PREDICTORS;
+
+ if (rtl_dump_file)
+ fprintf (rtl_dump_file, "Predictions for insn %i\n", INSN_UID (insn));
+
+ /* We implement "first match" heuristics and use probability guessed
+ by predictor with smallest index. In future we will use better
+ probability combination techniques. */
+ while (*pnote)
+ {
+ rtx *next_pnote = &XEXP (*pnote, 1);
+ if (REG_NOTE_KIND (*pnote) == REG_BR_PRED)
+ {
+ int predictor = INTVAL (XEXP (XEXP (*pnote, 0), 0));
+ int probability = INTVAL (XEXP (XEXP (*pnote, 0), 1));
+
+ dump_prediction (predictor, probability, bb);
+ if (best_predictor > predictor)
+ best_probability = probability, best_predictor = predictor;
+ *pnote = XEXP (*pnote, 1);
+ }
+ pnote = next_pnote;
+ }
+ dump_prediction (PRED_FIRST_MATCH, best_probability, bb);
+ if (!prob_note)
+ {
+ REG_NOTES (insn)
+ = gen_rtx_EXPR_LIST (REG_BR_PROB,
+ GEN_INT (best_probability), REG_NOTES (insn));
+ }
}
/* Statically estimate the probability that a branch will be taken.
if (e->dest == loops_info->array[i].header)
{
header_found = 1;
- predict_edge (e, PROB_VERY_LIKELY);
+ predict_edge_def (e, PRED_LOOP_BRANCH, TAKEN);
}
/* Loop exit heruistics - predict as not taken an edge exiting
the loop if the conditinal has no loop header successors */
for (e = BASIC_BLOCK(j)->succ; e; e = e->succ_next)
if (e->dest->index <= 0
|| !TEST_BIT (loops_info->array[i].nodes, e->dest->index))
- predict_edge (e, PROB_UNLIKELY);
+ predict_edge_def (e, PRED_LOOP_EXIT, NOT_TAKEN);
}
}
}
/* ??? Ought to do the same for any subgraph with no exit. */
for (e = BASIC_BLOCK (i)->succ; e; e = e->succ_next)
if (e->dest->succ == NULL)
- predict_edge (e, PROB_NEVER);
+ predict_edge_def (e, PRED_NORETURN, NOT_TAKEN);
cond = get_condition (last_insn, &earliest);
if (! cond)
|| (GET_CODE (XEXP (cond, 1)) == REG
&& REG_POINTER (XEXP (cond, 1)))))
- predict_insn (last_insn, PROB_UNLIKELY);
+ predict_insn_def (last_insn, PRED_POINTER, NOT_TAKEN);
break;
case NE:
if (GET_CODE (XEXP (cond, 0)) == REG
&& (XEXP (cond, 1) == const0_rtx
|| (GET_CODE (XEXP (cond, 1)) == REG
&& REG_POINTER (XEXP (cond, 1)))))
- predict_insn (last_insn, PROB_LIKELY);
+ predict_insn_def (last_insn, PRED_POINTER, TAKEN);
break;
default:
{
case CONST_INT:
/* Unconditional branch. */
- predict_insn (last_insn,
- cond == const0_rtx ? PROB_NEVER : PROB_ALWAYS);
+ predict_insn_def (last_insn, PRED_UNCONDITIONAL,
+ cond == const0_rtx ? NOT_TAKEN : TAKEN);
break;
case EQ:
case UNEQ:
- predict_insn (last_insn, PROB_UNLIKELY);
+ predict_insn_def (last_insn, PRED_OPCODE, NOT_TAKEN);
break;
case NE:
case LTGT:
- predict_insn (last_insn, PROB_LIKELY);
+ predict_insn_def (last_insn, PRED_OPCODE, TAKEN);
break;
case ORDERED:
- predict_insn (last_insn, PROB_LIKELY);
+ predict_insn_def (last_insn, PRED_OPCODE, TAKEN);
break;
case UNORDERED:
- predict_insn (last_insn, PROB_UNLIKELY);
+ predict_insn_def (last_insn, PRED_OPCODE, NOT_TAKEN);
break;
case LE:
case LT:
if (XEXP (cond, 1) == const0_rtx)
- predict_insn (last_insn, PROB_UNLIKELY);
+ predict_insn_def (last_insn, PRED_OPCODE, NOT_TAKEN);
break;
case GE:
case GT:
if (XEXP (cond, 1) == const0_rtx
|| (GET_CODE (XEXP (cond, 1)) == CONST_INT
&& INTVAL (XEXP (cond, 1)) == -1))
- predict_insn (last_insn, PROB_LIKELY);
+ predict_insn_def (last_insn, PRED_OPCODE, TAKEN);
break;
default:
break;
}
}
+
+ /* Attach the combined probability to each conditional jump. */
+ for (i = 0; i < n_basic_blocks - 1; i++)
+ {
+ rtx last_insn = BLOCK_END (i);
+
+ if (GET_CODE (last_insn) != JUMP_INSN
+ || ! any_condjump_p (last_insn))
+ continue;
+ combine_predictions_for_insn (last_insn, BASIC_BLOCK (i));
+ }
}
\f
/* __builtin_expect dropped tokens into the insn stream describing
expected value yet, no point going further. */
if (GET_CODE (insn) != JUMP_INSN || ev == NULL_RTX)
continue;
- if (! condjump_p (insn) || simplejump_p (insn))
+ if (! any_condjump_p (insn))
continue;
break;
}
/* Turn the condition into a scaled branch probability. */
if (cond != const1_rtx && cond != const0_rtx)
abort ();
- predict_insn (insn,
- cond == const1_rtx ? PROB_VERY_LIKELY : PROB_VERY_UNLIKELY);
+ predict_insn_def (insn, PRED_BUILTIN_EXPECT,
+ cond == const1_rtx ? TAKEN : NOT_TAKEN);
}
}
--- /dev/null
+/* This file contains the definitions and documentation for the
+ builtins used in the GNU compiler.
+ Copyright (C) 2001 Free Software Foundation, Inc.
+
+This file is part of GNU CC.
+
+GNU CC 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.
+
+GNU CC 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 GNU CC; see the file COPYING. If not, write to
+the Free Software Foundation, 59 Temple Place - Suite 330,
+Boston, MA 02111-1307, 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). */
+
+
+DEF_PREDICTOR (PRED_FIRST_MATCH, "first match", PROB_ALWAYS)
+DEF_PREDICTOR (PRED_UNCONDITIONAL, "unconditional jump", PROB_ALWAYS)
+DEF_PREDICTOR (PRED_BUILTIN_EXPECT, "__builtin_expect", PROB_VERY_LIKELY)
+DEF_PREDICTOR (PRED_NORETURN, "noreturn call", PROB_ALWAYS)
+DEF_PREDICTOR (PRED_LOOP_BRANCH, "loop branch", PROB_VERY_LIKELY)
+DEF_PREDICTOR (PRED_LOOP_EXIT, "loop exit", PROB_LIKELY)
+DEF_PREDICTOR (PRED_LOOP_HEADER, "loop header", PROB_LIKELY)
+DEF_PREDICTOR (PRED_POINTER, "pointer", PROB_LIKELY)
+DEF_PREDICTOR (PRED_OPCODE, "opcode", PROB_LIKELY)
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