forked from illumos/gcc
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predict.c
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predict.c
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/* Branch prediction routines for the GNU compiler.
Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2007, 2008, 2009
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/>. */
/* References:
[1] "Branch Prediction for Free"
Ball and Larus; PLDI '93.
[2] "Static Branch Frequency and Program Profile Analysis"
Wu and Larus; MICRO-27.
[3] "Corpus-based Static Branch Prediction"
Calder, Grunwald, Lindsay, Martin, Mozer, and Zorn; PLDI '95. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "rtl.h"
#include "tm_p.h"
#include "hard-reg-set.h"
#include "basic-block.h"
#include "insn-config.h"
#include "regs.h"
#include "flags.h"
#include "output.h"
#include "function.h"
#include "except.h"
#include "toplev.h"
#include "recog.h"
#include "expr.h"
#include "predict.h"
#include "coverage.h"
#include "sreal.h"
#include "params.h"
#include "target.h"
#include "cfgloop.h"
#include "tree-flow.h"
#include "ggc.h"
#include "tree-dump.h"
#include "tree-pass.h"
#include "timevar.h"
#include "tree-scalar-evolution.h"
#include "cfgloop.h"
#include "pointer-set.h"
/* real constants: 0, 1, 1-1/REG_BR_PROB_BASE, REG_BR_PROB_BASE,
1/REG_BR_PROB_BASE, 0.5, BB_FREQ_MAX. */
static sreal real_zero, real_one, real_almost_one, real_br_prob_base,
real_inv_br_prob_base, real_one_half, real_bb_freq_max;
/* Random guesstimation given names.
PROV_VERY_UNLIKELY should be small enough so basic block predicted
by it gets bellow HOT_BB_FREQUENCY_FRANCTION. */
#define PROB_VERY_UNLIKELY (REG_BR_PROB_BASE / 2000 - 1)
#define PROB_EVEN (REG_BR_PROB_BASE / 2)
#define PROB_VERY_LIKELY (REG_BR_PROB_BASE - PROB_VERY_UNLIKELY)
#define PROB_ALWAYS (REG_BR_PROB_BASE)
static void combine_predictions_for_insn (rtx, basic_block);
static void dump_prediction (FILE *, enum br_predictor, int, basic_block, int);
static void predict_paths_leading_to (basic_block, enum br_predictor, enum prediction);
static void choose_function_section (void);
static bool can_predict_insn_p (const_rtx);
/* Information we hold about each branch predictor.
Filled using information from predict.def. */
struct predictor_info
{
const char *const name; /* Name used in the debugging dumps. */
const int hitrate; /* Expected hitrate used by
predict_insn_def call. */
const int flags;
};
/* Use given predictor without Dempster-Shaffer theory if it matches
using first_match heuristics. */
#define PRED_FLAG_FIRST_MATCH 1
/* Recompute hitrate in percent to our representation. */
#define HITRATE(VAL) ((int) ((VAL) * REG_BR_PROB_BASE + 50) / 100)
#define DEF_PREDICTOR(ENUM, NAME, HITRATE, FLAGS) {NAME, HITRATE, FLAGS},
static const struct predictor_info predictor_info[]= {
#include "predict.def"
/* Upper bound on predictors. */
{NULL, 0, 0}
};
#undef DEF_PREDICTOR
/* Return TRUE if frequency FREQ is considered to be hot. */
static inline bool
maybe_hot_frequency_p (int freq)
{
if (!profile_info || !flag_branch_probabilities)
{
if (cfun->function_frequency == FUNCTION_FREQUENCY_UNLIKELY_EXECUTED)
return false;
if (cfun->function_frequency == FUNCTION_FREQUENCY_HOT)
return true;
}
if (profile_status == PROFILE_ABSENT)
return true;
if (freq < BB_FREQ_MAX / PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION))
return false;
return true;
}
/* Return TRUE if frequency FREQ is considered to be hot. */
static inline bool
maybe_hot_count_p (gcov_type count)
{
if (profile_status != PROFILE_READ)
return true;
/* Code executed at most once is not hot. */
if (profile_info->runs >= count)
return false;
return (count
> profile_info->sum_max / PARAM_VALUE (HOT_BB_COUNT_FRACTION));
}
/* Return true in case BB can be CPU intensive and should be optimized
for maximal performance. */
bool
maybe_hot_bb_p (const_basic_block bb)
{
if (profile_status == PROFILE_READ)
return maybe_hot_count_p (bb->count);
return maybe_hot_frequency_p (bb->frequency);
}
/* Return true if the call can be hot. */
bool
cgraph_maybe_hot_edge_p (struct cgraph_edge *edge)
{
if (profile_info && flag_branch_probabilities
&& (edge->count
<= profile_info->sum_max / PARAM_VALUE (HOT_BB_COUNT_FRACTION)))
return false;
if (lookup_attribute ("cold", DECL_ATTRIBUTES (edge->callee->decl))
|| lookup_attribute ("cold", DECL_ATTRIBUTES (edge->caller->decl)))
return false;
if (lookup_attribute ("hot", DECL_ATTRIBUTES (edge->caller->decl)))
return true;
if (flag_guess_branch_prob
&& edge->frequency <= (CGRAPH_FREQ_BASE
/ PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION)))
return false;
return true;
}
/* Return true in case BB can be CPU intensive and should be optimized
for maximal performance. */
bool
maybe_hot_edge_p (edge e)
{
if (profile_status == PROFILE_READ)
return maybe_hot_count_p (e->count);
return maybe_hot_frequency_p (EDGE_FREQUENCY (e));
}
/* Return true in case BB is probably never executed. */
bool
probably_never_executed_bb_p (const_basic_block bb)
{
if (profile_info && flag_branch_probabilities)
return ((bb->count + profile_info->runs / 2) / profile_info->runs) == 0;
if ((!profile_info || !flag_branch_probabilities)
&& cfun->function_frequency == FUNCTION_FREQUENCY_UNLIKELY_EXECUTED)
return true;
return false;
}
/* Return true when current function should always be optimized for size. */
bool
optimize_function_for_size_p (struct function *fun)
{
return (optimize_size
|| (fun && (fun->function_frequency
== FUNCTION_FREQUENCY_UNLIKELY_EXECUTED)));
}
/* Return true when current function should always be optimized for speed. */
bool
optimize_function_for_speed_p (struct function *fun)
{
return !optimize_function_for_size_p (fun);
}
/* Return TRUE when BB should be optimized for size. */
bool
optimize_bb_for_size_p (const_basic_block bb)
{
return optimize_function_for_size_p (cfun) || !maybe_hot_bb_p (bb);
}
/* Return TRUE when BB should be optimized for speed. */
bool
optimize_bb_for_speed_p (const_basic_block bb)
{
return !optimize_bb_for_size_p (bb);
}
/* Return TRUE when BB should be optimized for size. */
bool
optimize_edge_for_size_p (edge e)
{
return optimize_function_for_size_p (cfun) || !maybe_hot_edge_p (e);
}
/* Return TRUE when BB should be optimized for speed. */
bool
optimize_edge_for_speed_p (edge e)
{
return !optimize_edge_for_size_p (e);
}
/* Return TRUE when BB should be optimized for size. */
bool
optimize_insn_for_size_p (void)
{
return optimize_function_for_size_p (cfun) || !crtl->maybe_hot_insn_p;
}
/* Return TRUE when BB should be optimized for speed. */
bool
optimize_insn_for_speed_p (void)
{
return !optimize_insn_for_size_p ();
}
/* Return TRUE when LOOP should be optimized for size. */
bool
optimize_loop_for_size_p (struct loop *loop)
{
return optimize_bb_for_size_p (loop->header);
}
/* Return TRUE when LOOP should be optimized for speed. */
bool
optimize_loop_for_speed_p (struct loop *loop)
{
return optimize_bb_for_speed_p (loop->header);
}
/* Return TRUE when LOOP nest should be optimized for speed. */
bool
optimize_loop_nest_for_speed_p (struct loop *loop)
{
struct loop *l = loop;
if (optimize_loop_for_speed_p (loop))
return true;
l = loop->inner;
while (l && l != loop)
{
if (optimize_loop_for_speed_p (l))
return true;
if (l->inner)
l = l->inner;
else if (l->next)
l = l->next;
else
{
while (l != loop && !l->next)
l = loop_outer (l);
if (l != loop)
l = l->next;
}
}
return false;
}
/* Return TRUE when LOOP nest should be optimized for size. */
bool
optimize_loop_nest_for_size_p (struct loop *loop)
{
return !optimize_loop_nest_for_speed_p (loop);
}
/* Return true when edge E is likely to be well predictable by branch
predictor. */
bool
predictable_edge_p (edge e)
{
if (profile_status == PROFILE_ABSENT)
return false;
if ((e->probability
<= PARAM_VALUE (PARAM_PREDICTABLE_BRANCH_OUTCOME) * REG_BR_PROB_BASE / 100)
|| (REG_BR_PROB_BASE - e->probability
<= PARAM_VALUE (PARAM_PREDICTABLE_BRANCH_OUTCOME) * REG_BR_PROB_BASE / 100))
return true;
return false;
}
/* Set RTL expansion for BB profile. */
void
rtl_profile_for_bb (basic_block bb)
{
crtl->maybe_hot_insn_p = maybe_hot_bb_p (bb);
}
/* Set RTL expansion for edge profile. */
void
rtl_profile_for_edge (edge e)
{
crtl->maybe_hot_insn_p = maybe_hot_edge_p (e);
}
/* Set RTL expansion to default mode (i.e. when profile info is not known). */
void
default_rtl_profile (void)
{
crtl->maybe_hot_insn_p = true;
}
/* Return true if the one of outgoing edges is already predicted by
PREDICTOR. */
bool
rtl_predicted_by_p (const_basic_block bb, enum br_predictor predictor)
{
rtx note;
if (!INSN_P (BB_END (bb)))
return false;
for (note = REG_NOTES (BB_END (bb)); note; note = XEXP (note, 1))
if (REG_NOTE_KIND (note) == REG_BR_PRED
&& INTVAL (XEXP (XEXP (note, 0), 0)) == (int)predictor)
return true;
return false;
}
/* This map contains for a basic block the list of predictions for the
outgoing edges. */
static struct pointer_map_t *bb_predictions;
/* Return true if the one of outgoing edges is already predicted by
PREDICTOR. */
bool
gimple_predicted_by_p (const_basic_block bb, enum br_predictor predictor)
{
struct edge_prediction *i;
void **preds = pointer_map_contains (bb_predictions, bb);
if (!preds)
return false;
for (i = (struct edge_prediction *) *preds; i; i = i->ep_next)
if (i->ep_predictor == predictor)
return true;
return false;
}
/* Return true when the probability of edge is reliable.
The profile guessing code is good at predicting branch outcome (ie.
taken/not taken), that is predicted right slightly over 75% of time.
It is however notoriously poor on predicting the probability itself.
In general the profile appear a lot flatter (with probabilities closer
to 50%) than the reality so it is bad idea to use it to drive optimization
such as those disabling dynamic branch prediction for well predictable
branches.
There are two exceptions - edges leading to noreturn edges and edges
predicted by number of iterations heuristics are predicted well. This macro
should be able to distinguish those, but at the moment it simply check for
noreturn heuristic that is only one giving probability over 99% or bellow
1%. In future we might want to propagate reliability information across the
CFG if we find this information useful on multiple places. */
static bool
probability_reliable_p (int prob)
{
return (profile_status == PROFILE_READ
|| (profile_status == PROFILE_GUESSED
&& (prob <= HITRATE (1) || prob >= HITRATE (99))));
}
/* Same predicate as above, working on edges. */
bool
edge_probability_reliable_p (const_edge e)
{
return probability_reliable_p (e->probability);
}
/* Same predicate as edge_probability_reliable_p, working on notes. */
bool
br_prob_note_reliable_p (const_rtx note)
{
gcc_assert (REG_NOTE_KIND (note) == REG_BR_PROB);
return probability_reliable_p (INTVAL (XEXP (note, 0)));
}
static void
predict_insn (rtx insn, enum br_predictor predictor, int probability)
{
gcc_assert (any_condjump_p (insn));
if (!flag_guess_branch_prob)
return;
add_reg_note (insn, REG_BR_PRED,
gen_rtx_CONCAT (VOIDmode,
GEN_INT ((int) predictor),
GEN_INT ((int) probability)));
}
/* Predict insn by given predictor. */
void
predict_insn_def (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. */
void
rtl_predict_edge (edge e, enum br_predictor predictor, int probability)
{
rtx last_insn;
last_insn = BB_END (e->src);
/* We can store the branch prediction information only about
conditional jumps. */
if (!any_condjump_p (last_insn))
return;
/* We always store probability of branching. */
if (e->flags & EDGE_FALLTHRU)
probability = REG_BR_PROB_BASE - probability;
predict_insn (last_insn, predictor, probability);
}
/* Predict edge E with the given PROBABILITY. */
void
gimple_predict_edge (edge e, enum br_predictor predictor, int probability)
{
gcc_assert (profile_status != PROFILE_GUESSED);
if ((e->src != ENTRY_BLOCK_PTR && EDGE_COUNT (e->src->succs) > 1)
&& flag_guess_branch_prob && optimize)
{
struct edge_prediction *i = XNEW (struct edge_prediction);
void **preds = pointer_map_insert (bb_predictions, e->src);
i->ep_next = (struct edge_prediction *) *preds;
*preds = i;
i->ep_probability = probability;
i->ep_predictor = predictor;
i->ep_edge = e;
}
}
/* Remove all predictions on given basic block that are attached
to edge E. */
void
remove_predictions_associated_with_edge (edge e)
{
void **preds;
if (!bb_predictions)
return;
preds = pointer_map_contains (bb_predictions, e->src);
if (preds)
{
struct edge_prediction **prediction = (struct edge_prediction **) preds;
struct edge_prediction *next;
while (*prediction)
{
if ((*prediction)->ep_edge == e)
{
next = (*prediction)->ep_next;
free (*prediction);
*prediction = next;
}
else
prediction = &((*prediction)->ep_next);
}
}
}
/* Clears the list of predictions stored for BB. */
static void
clear_bb_predictions (basic_block bb)
{
void **preds = pointer_map_contains (bb_predictions, bb);
struct edge_prediction *pred, *next;
if (!preds)
return;
for (pred = (struct edge_prediction *) *preds; pred; pred = next)
{
next = pred->ep_next;
free (pred);
}
*preds = NULL;
}
/* Return true when we can store prediction on insn INSN.
At the moment we represent predictions only on conditional
jumps, not at computed jump or other complicated cases. */
static bool
can_predict_insn_p (const_rtx insn)
{
return (JUMP_P (insn)
&& any_condjump_p (insn)
&& EDGE_COUNT (BLOCK_FOR_INSN (insn)->succs) >= 2);
}
/* Predict edge E by given predictor if possible. */
void
predict_edge_def (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 (rtx insn)
{
rtx note;
for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
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)));
}
/* Dump information about the branch prediction to the output file. */
static void
dump_prediction (FILE *file, enum br_predictor predictor, int probability,
basic_block bb, int used)
{
edge e;
edge_iterator ei;
if (!file)
return;
FOR_EACH_EDGE (e, ei, bb->succs)
if (! (e->flags & EDGE_FALLTHRU))
break;
fprintf (file, " %s heuristics%s: %.1f%%",
predictor_info[predictor].name,
used ? "" : " (ignored)", probability * 100.0 / REG_BR_PROB_BASE);
if (bb->count)
{
fprintf (file, " exec ");
fprintf (file, HOST_WIDEST_INT_PRINT_DEC, bb->count);
if (e)
{
fprintf (file, " hit ");
fprintf (file, HOST_WIDEST_INT_PRINT_DEC, e->count);
fprintf (file, " (%.1f%%)", e->count * 100.0 / bb->count);
}
}
fprintf (file, "\n");
}
/* We can not predict the probabilities of outgoing edges of bb. Set them
evenly and hope for the best. */
static void
set_even_probabilities (basic_block bb)
{
int nedges = 0;
edge e;
edge_iterator ei;
FOR_EACH_EDGE (e, ei, bb->succs)
if (!(e->flags & (EDGE_EH | EDGE_FAKE)))
nedges ++;
FOR_EACH_EDGE (e, ei, bb->succs)
if (!(e->flags & (EDGE_EH | EDGE_FAKE)))
e->probability = (REG_BR_PROB_BASE + nedges / 2) / nedges;
else
e->probability = 0;
}
/* 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 (rtx insn, basic_block bb)
{
rtx prob_note;
rtx *pnote;
rtx note;
int best_probability = PROB_EVEN;
enum br_predictor best_predictor = END_PREDICTORS;
int combined_probability = REG_BR_PROB_BASE / 2;
int d;
bool first_match = false;
bool found = false;
if (!can_predict_insn_p (insn))
{
set_even_probabilities (bb);
return;
}
prob_note = find_reg_note (insn, REG_BR_PROB, 0);
pnote = ®_NOTES (insn);
if (dump_file)
fprintf (dump_file, "Predictions for insn %i bb %i\n", INSN_UID (insn),
bb->index);
/* We implement "first match" heuristics and use probability guessed
by predictor with smallest index. */
for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
if (REG_NOTE_KIND (note) == REG_BR_PRED)
{
enum br_predictor predictor = ((enum br_predictor)
INTVAL (XEXP (XEXP (note, 0), 0)));
int probability = INTVAL (XEXP (XEXP (note, 0), 1));
found = true;
if (best_predictor > predictor)
best_probability = probability, best_predictor = predictor;
d = (combined_probability * probability
+ (REG_BR_PROB_BASE - combined_probability)
* (REG_BR_PROB_BASE - probability));
/* Use FP math to avoid overflows of 32bit integers. */
if (d == 0)
/* If one probability is 0% and one 100%, avoid division by zero. */
combined_probability = REG_BR_PROB_BASE / 2;
else
combined_probability = (((double) combined_probability) * probability
* REG_BR_PROB_BASE / d + 0.5);
}
/* Decide which heuristic to use. In case we didn't match anything,
use no_prediction heuristic, in case we did match, use either
first match or Dempster-Shaffer theory depending on the flags. */
if (predictor_info [best_predictor].flags & PRED_FLAG_FIRST_MATCH)
first_match = true;
if (!found)
dump_prediction (dump_file, PRED_NO_PREDICTION,
combined_probability, bb, true);
else
{
dump_prediction (dump_file, PRED_DS_THEORY, combined_probability,
bb, !first_match);
dump_prediction (dump_file, PRED_FIRST_MATCH, best_probability,
bb, first_match);
}
if (first_match)
combined_probability = best_probability;
dump_prediction (dump_file, PRED_COMBINED, combined_probability, bb, true);
while (*pnote)
{
if (REG_NOTE_KIND (*pnote) == REG_BR_PRED)
{
enum br_predictor predictor = ((enum br_predictor)
INTVAL (XEXP (XEXP (*pnote, 0), 0)));
int probability = INTVAL (XEXP (XEXP (*pnote, 0), 1));
dump_prediction (dump_file, predictor, probability, bb,
!first_match || best_predictor == predictor);
*pnote = XEXP (*pnote, 1);
}
else
pnote = &XEXP (*pnote, 1);
}
if (!prob_note)
{
add_reg_note (insn, REG_BR_PROB, GEN_INT (combined_probability));
/* Save the prediction into CFG in case we are seeing non-degenerated
conditional jump. */
if (!single_succ_p (bb))
{
BRANCH_EDGE (bb)->probability = combined_probability;
FALLTHRU_EDGE (bb)->probability
= REG_BR_PROB_BASE - combined_probability;
}
}
else if (!single_succ_p (bb))
{
int prob = INTVAL (XEXP (prob_note, 0));
BRANCH_EDGE (bb)->probability = prob;
FALLTHRU_EDGE (bb)->probability = REG_BR_PROB_BASE - prob;
}
else
single_succ_edge (bb)->probability = REG_BR_PROB_BASE;
}
/* Combine predictions into single probability and store them into CFG.
Remove now useless prediction entries. */
static void
combine_predictions_for_bb (basic_block bb)
{
int best_probability = PROB_EVEN;
enum br_predictor best_predictor = END_PREDICTORS;
int combined_probability = REG_BR_PROB_BASE / 2;
int d;
bool first_match = false;
bool found = false;
struct edge_prediction *pred;
int nedges = 0;
edge e, first = NULL, second = NULL;
edge_iterator ei;
void **preds;
FOR_EACH_EDGE (e, ei, bb->succs)
if (!(e->flags & (EDGE_EH | EDGE_FAKE)))
{
nedges ++;
if (first && !second)
second = e;
if (!first)
first = e;
}
/* When there is no successor or only one choice, prediction is easy.
We are lazy for now and predict only basic blocks with two outgoing
edges. It is possible to predict generic case too, but we have to
ignore first match heuristics and do more involved combining. Implement
this later. */
if (nedges != 2)
{
if (!bb->count)
set_even_probabilities (bb);
clear_bb_predictions (bb);
if (dump_file)
fprintf (dump_file, "%i edges in bb %i predicted to even probabilities\n",
nedges, bb->index);
return;
}
if (dump_file)
fprintf (dump_file, "Predictions for bb %i\n", bb->index);
preds = pointer_map_contains (bb_predictions, bb);
if (preds)
{
/* We implement "first match" heuristics and use probability guessed
by predictor with smallest index. */
for (pred = (struct edge_prediction *) *preds; pred; pred = pred->ep_next)
{
enum br_predictor predictor = pred->ep_predictor;
int probability = pred->ep_probability;
if (pred->ep_edge != first)
probability = REG_BR_PROB_BASE - probability;
found = true;
/* First match heuristics would be widly confused if we predicted
both directions. */
if (best_predictor > predictor)
{
struct edge_prediction *pred2;
int prob = probability;
for (pred2 = (struct edge_prediction *) *preds; pred2; pred2 = pred2->ep_next)
if (pred2 != pred && pred2->ep_predictor == pred->ep_predictor)
{
int probability2 = pred->ep_probability;
if (pred2->ep_edge != first)
probability2 = REG_BR_PROB_BASE - probability2;
if ((probability < REG_BR_PROB_BASE / 2) !=
(probability2 < REG_BR_PROB_BASE / 2))
break;
/* If the same predictor later gave better result, go for it! */
if ((probability >= REG_BR_PROB_BASE / 2 && (probability2 > probability))
|| (probability <= REG_BR_PROB_BASE / 2 && (probability2 < probability)))
prob = probability2;
}
if (!pred2)
best_probability = prob, best_predictor = predictor;
}
d = (combined_probability * probability
+ (REG_BR_PROB_BASE - combined_probability)
* (REG_BR_PROB_BASE - probability));
/* Use FP math to avoid overflows of 32bit integers. */
if (d == 0)
/* If one probability is 0% and one 100%, avoid division by zero. */
combined_probability = REG_BR_PROB_BASE / 2;
else
combined_probability = (((double) combined_probability)
* probability
* REG_BR_PROB_BASE / d + 0.5);
}
}
/* Decide which heuristic to use. In case we didn't match anything,
use no_prediction heuristic, in case we did match, use either
first match or Dempster-Shaffer theory depending on the flags. */
if (predictor_info [best_predictor].flags & PRED_FLAG_FIRST_MATCH)
first_match = true;
if (!found)
dump_prediction (dump_file, PRED_NO_PREDICTION, combined_probability, bb, true);
else
{
dump_prediction (dump_file, PRED_DS_THEORY, combined_probability, bb,
!first_match);
dump_prediction (dump_file, PRED_FIRST_MATCH, best_probability, bb,
first_match);
}
if (first_match)
combined_probability = best_probability;
dump_prediction (dump_file, PRED_COMBINED, combined_probability, bb, true);
if (preds)
{
for (pred = (struct edge_prediction *) *preds; pred; pred = pred->ep_next)
{
enum br_predictor predictor = pred->ep_predictor;
int probability = pred->ep_probability;
if (pred->ep_edge != EDGE_SUCC (bb, 0))
probability = REG_BR_PROB_BASE - probability;
dump_prediction (dump_file, predictor, probability, bb,
!first_match || best_predictor == predictor);
}
}
clear_bb_predictions (bb);
if (!bb->count)
{
first->probability = combined_probability;
second->probability = REG_BR_PROB_BASE - combined_probability;
}
}
/* Predict edge probabilities by exploiting loop structure. */
static void
predict_loops (void)
{
loop_iterator li;
struct loop *loop;
/* Try to predict out blocks in a loop that are not part of a
natural loop. */
FOR_EACH_LOOP (li, loop, 0)
{
basic_block bb, *bbs;
unsigned j, n_exits;
VEC (edge, heap) *exits;
struct tree_niter_desc niter_desc;
edge ex;
exits = get_loop_exit_edges (loop);
n_exits = VEC_length (edge, exits);
for (j = 0; VEC_iterate (edge, exits, j, ex); j++)
{
tree niter = NULL;
HOST_WIDE_INT nitercst;
int max = PARAM_VALUE (PARAM_MAX_PREDICTED_ITERATIONS);
int probability;
enum br_predictor predictor;
if (number_of_iterations_exit (loop, ex, &niter_desc, false))
niter = niter_desc.niter;
if (!niter || TREE_CODE (niter_desc.niter) != INTEGER_CST)
niter = loop_niter_by_eval (loop, ex);
if (TREE_CODE (niter) == INTEGER_CST)
{
if (host_integerp (niter, 1)
&& compare_tree_int (niter, max-1) == -1)
nitercst = tree_low_cst (niter, 1) + 1;
else
nitercst = max;
predictor = PRED_LOOP_ITERATIONS;
}
/* If we have just one exit and we can derive some information about
the number of iterations of the loop from the statements inside
the loop, use it to predict this exit. */
else if (n_exits == 1)
{
nitercst = estimated_loop_iterations_int (loop, false);
if (nitercst < 0)
continue;
if (nitercst > max)
nitercst = max;
predictor = PRED_LOOP_ITERATIONS_GUESSED;
}
else
continue;
probability = ((REG_BR_PROB_BASE + nitercst / 2) / nitercst);
predict_edge (ex, predictor, probability);
}
VEC_free (edge, heap, exits);
bbs = get_loop_body (loop);
for (j = 0; j < loop->num_nodes; j++)
{
int header_found = 0;
edge e;
edge_iterator ei;
bb = bbs[j];
/* Bypass loop heuristics on continue statement. These
statements construct loops via "non-loop" constructs
in the source language and are better to be handled
separately. */
if (predicted_by_p (bb, PRED_CONTINUE))
continue;
/* Loop branch heuristics - predict an edge back to a
loop's head as taken. */
if (bb == loop->latch)
{
e = find_edge (loop->latch, loop->header);
if (e)
{
header_found = 1;
predict_edge_def (e, PRED_LOOP_BRANCH, TAKEN);
}