/* Branch prediction routines for the GNU compiler.
Copyright (C) 2000, 2001 Free Software Foundation, Inc.
- This file is part of GCC.
+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 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.
+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, 59 Temple Place - Suite 330, Boston, MA
- 02111-1307, USA. */
+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, 59 Temple Place - Suite 330, Boston, MA
+02111-1307, USA. */
/* References:
[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.
-
-*/
+ Calder, Grunwald, Lindsay, Martin, Mozer, and Zorn; PLDI '95. */
#include "config.h"
/* 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. */
/* Recompute hitrate in percent to our representation. */
-#define HITRATE(VAL) ((int)((VAL) * REG_BR_PROB_BASE + 50) / 100)
+#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[] = {
+static const struct predictor_info predictor_info[]= {
#include "predict.def"
/* Upper bound on predictors. */
{
if (!any_condjump_p (insn))
abort ();
+
REG_NOTES (insn)
= gen_rtx_EXPR_LIST (REG_BR_PRED,
gen_rtx_CONCAT (VOIDmode,
}
/* Predict insn by given predictor. */
+
void
predict_insn_def (insn, predictor, taken)
rtx insn;
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
predict_edge (e, predictor, probability)
edge e;
}
/* Predict edge E by given predictor if possible. */
+
void
predict_edge_def (e, predictor, taken)
edge e;
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);
- }
+ 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 (predictor, probability, bb, used)
enum br_predictor predictor;
fprintf (rtl_dump_file, " %s heuristics%s: %.1f%%",
predictor_info[predictor].name,
- used ? "" : " (ignored)",
- probability * 100.0 / REG_BR_PROB_BASE);
+ used ? "" : " (ignored)", probability * 100.0 / REG_BR_PROB_BASE);
if (bb->count)
{
fprintf (rtl_dump_file, " exec ");
- fprintf (rtl_dump_file, HOST_WIDEST_INT_PRINT_DEC,
- (HOST_WIDEST_INT) bb->count);
+ fprintf (rtl_dump_file, HOST_WIDEST_INT_PRINT_DEC, bb->count);
fprintf (rtl_dump_file, " hit ");
- fprintf (rtl_dump_file, HOST_WIDEST_INT_PRINT_DEC,
- (HOST_WIDEST_INT) e->count);
- fprintf (rtl_dump_file, " (%.1f%%)",
- e->count * 100.0 / bb->count);
+ fprintf (rtl_dump_file, HOST_WIDEST_INT_PRINT_DEC, e->count);
+ fprintf (rtl_dump_file, " (%.1f%%)", 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;
{
rtx prob_note = find_reg_note (insn, REG_BR_PROB, 0);
rtx *pnote = ®_NOTES (insn);
- rtx note = REG_NOTES (insn);
+ rtx note;
int best_probability = PROB_EVEN;
int best_predictor = END_PREDICTORS;
int combined_probability = REG_BR_PROB_BASE / 2;
/* We implement "first match" heuristics and use probability guessed
by predictor with smallest index. In the future we will use better
probability combination techniques. */
- while (note)
- {
- if (REG_NOTE_KIND (note) == REG_BR_PRED)
- {
- int 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));
- /* An FP math to avoid overflows of 32bit integers. */
- combined_probability = (((double)combined_probability) * probability
- * REG_BR_PROB_BASE / d + 0.5);
- }
- note = XEXP (note, 1);
- }
-
- /* Decide heuristic to use. In case we didn't match anything, use
- no_prediction heuristic, in case we did match, use either
+ for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
+ if (REG_NOTE_KIND (note) == REG_BR_PRED)
+ {
+ int 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. */
+ 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)
dump_prediction (PRED_NO_PREDICTION, combined_probability, bb, true);
else
{
- dump_prediction (PRED_DS_THEORY, combined_probability, bb,
- !first_match);
+ dump_prediction (PRED_DS_THEORY, combined_probability, bb, !first_match);
dump_prediction (PRED_FIRST_MATCH, best_probability, bb, first_match);
}
else
pnote = &XEXP (*pnote, 1);
}
+
if (!prob_note)
{
REG_NOTES (insn)
= gen_rtx_EXPR_LIST (REG_BR_PROB,
GEN_INT (combined_probability), REG_NOTES (insn));
+
/* Save the prediction into CFG in case we are seeing non-degenerated
conditional jump. */
if (bb->succ->succ_next)
{
BRANCH_EDGE (bb)->probability = combined_probability;
- FALLTHRU_EDGE (bb)->probability = REG_BR_PROB_BASE - combined_probability;
+ FALLTHRU_EDGE (bb)->probability
+ = REG_BR_PROB_BASE - combined_probability;
}
}
}
flow_loop_scan (loops_info, loop, LOOP_EXIT_EDGES);
exits = loop->num_exits;
- for (j = loop->first->index;
- j <= loop->last->index;
- ++j)
- {
- if (TEST_BIT (loop->nodes, j))
- {
- int header_found = 0;
- edge e;
-
- /* Loop branch heuristics - predict as taken an edge back to
- a loop's head. */
+ for (j = loop->first->index; j <= loop->last->index; ++j)
+ if (TEST_BIT (loop->nodes, j))
+ {
+ int header_found = 0;
+ edge e;
+
+ /* Loop branch heuristics - predict an edge back to a
+ loop's head as taken. */
+ for (e = BASIC_BLOCK(j)->succ; e; e = e->succ_next)
+ if (e->dest == loop->header
+ && e->src == loop->latch)
+ {
+ header_found = 1;
+ predict_edge_def (e, PRED_LOOP_BRANCH, TAKEN);
+ }
+
+ /* Loop exit heuristics - predict an edge exiting the loop if the
+ conditinal has no loop header successors as not taken. */
+ if (!header_found)
for (e = BASIC_BLOCK(j)->succ; e; e = e->succ_next)
- if (e->dest == loop->header
- && e->src == loop->latch)
- {
- header_found = 1;
- predict_edge_def (e, PRED_LOOP_BRANCH, TAKEN);
- }
- /* Loop exit heuristics - predict as not taken an edge
- exiting the loop if the conditinal has no loop header
- successors. */
- if (!header_found)
- for (e = BASIC_BLOCK(j)->succ; e; e = e->succ_next)
- if (e->dest->index < 0
- || !TEST_BIT (loop->nodes, e->dest->index))
- predict_edge (e, PRED_LOOP_EXIT,
- (REG_BR_PROB_BASE
- - predictor_info [(int)PRED_LOOP_EXIT].hitrate)
- / exits);
- }
- }
+ if (e->dest->index < 0
+ || !TEST_BIT (loop->nodes, e->dest->index))
+ predict_edge
+ (e, PRED_LOOP_EXIT,
+ (REG_BR_PROB_BASE
+ - predictor_info [(int)PRED_LOOP_EXIT].hitrate)
+ / exits);
+ }
}
/* Attempt to predict conditional jumps using a number of heuristics. */
rtx cond, earliest;
edge e;
- /* If block has no successor, predict all possible paths to
- it as improbable, as the block contains a call to a noreturn
- function and thus can be executed only once. */
+ /* If block has no successor, predict all possible paths to it as
+ improbable, as the block contains a call to a noreturn function and
+ thus can be executed only once. */
if (bb->succ == NULL && !found_noreturn)
{
int y;
/* ??? Postdominator claims each noreturn block to be postdominated
by each, so we need to run only once. This needs to be changed
- once postdominace algorithm is updated to say something more sane.
- */
+ once postdominace algorithm is updated to say something more
+ sane. */
found_noreturn = 1;
for (y = 0; y < n_basic_blocks; y++)
if (!TEST_BIT (post_dominators[y], i))
- {
- for (e = BASIC_BLOCK (y)->succ; e; e = e->succ_next)
+ for (e = BASIC_BLOCK (y)->succ; e; e = e->succ_next)
if (e->dest->index >= 0
&& TEST_BIT (post_dominators[e->dest->index], i))
predict_edge_def (e, PRED_NORETURN, NOT_TAKEN);
- }
}
- if (GET_CODE (last_insn) != JUMP_INSN
- || ! any_condjump_p (last_insn))
+ if (GET_CODE (last_insn) != JUMP_INSN || ! any_condjump_p (last_insn))
continue;
for (e = bb->succ; e; e = e->succ_next)
/* Look for block we are guarding (ie we dominate it,
but it doesn't postdominate us). */
- if (e->dest != EXIT_BLOCK_PTR
- && e->dest != bb
+ if (e->dest != EXIT_BLOCK_PTR && e->dest != bb
&& TEST_BIT (dominators[e->dest->index], e->src->index)
&& !TEST_BIT (post_dominators[e->src->index], e->dest->index))
{
rtx insn;
+
/* The call heuristic claims that a guarded function call
is improbable. This is because such calls are often used
to signal exceptional situations such as printing error
if (GET_RTX_CLASS (GET_CODE (cond)) == '<'
&& ((REG_P (XEXP (cond, 0)) && REG_POINTER (XEXP (cond, 0)))
|| (REG_P (XEXP (cond, 1)) && REG_POINTER (XEXP (cond, 1)))))
- switch (GET_CODE (cond))
- {
- case EQ:
+ {
+ if (GET_CODE (cond) == EQ)
predict_insn_def (last_insn, PRED_POINTER, NOT_TAKEN);
- break;
- case NE:
+ else if (GET_CODE (cond) == NE)
predict_insn_def (last_insn, PRED_POINTER, TAKEN);
- break;
- default:
- break;
- }
+ }
else
+
/* Try "opcode heuristic."
EQ tests are usually false and NE tests are usually true. Also,
most quantities are positive, so we can make the appropriate guesses
;
/* Comparisons with 0 are often used for booleans and there is
nothing usefull to predict about them. */
- else if (XEXP (cond, 1) == const0_rtx || XEXP (cond, 0) == const0_rtx)
+ else if (XEXP (cond, 1) == const0_rtx
+ || XEXP (cond, 0) == const0_rtx)
;
else
predict_insn_def (last_insn, PRED_OPCODE_NONEQUAL, NOT_TAKEN);
break;
+
case NE:
case LTGT:
/* Floating point comparisons appears to behave in a very
;
/* Comparisons with 0 are often used for booleans and there is
nothing usefull to predict about them. */
- else if (XEXP (cond, 1) == const0_rtx || XEXP (cond, 0) == const0_rtx)
+ else if (XEXP (cond, 1) == const0_rtx
+ || XEXP (cond, 0) == const0_rtx)
;
else
predict_insn_def (last_insn, PRED_OPCODE_NONEQUAL, TAKEN);
break;
+
case ORDERED:
predict_insn_def (last_insn, PRED_FPOPCODE, TAKEN);
break;
+
case UNORDERED:
predict_insn_def (last_insn, PRED_FPOPCODE, NOT_TAKEN);
break;
+
case LE:
case LT:
if (XEXP (cond, 1) == const0_rtx || XEXP (cond, 1) == const1_rtx
|| XEXP (cond, 1) == constm1_rtx)
predict_insn_def (last_insn, PRED_OPCODE_POSITIVE, NOT_TAKEN);
break;
+
case GE:
case GT:
if (XEXP (cond, 1) == const0_rtx || XEXP (cond, 1) == const1_rtx
/* Attach the combined probability to each conditional jump. */
for (i = 0; i < n_basic_blocks; i++)
- {
- rtx last_insn = BLOCK_END (i);
+ if (GET_CODE (BLOCK_END (i)) == JUMP_INSN
+ && any_condjump_p (BLOCK_END (i)))
+ combine_predictions_for_insn (BLOCK_END (i), BASIC_BLOCK (i));
- if (GET_CODE (last_insn) != JUMP_INSN
- || ! any_condjump_p (last_insn))
- continue;
- combine_predictions_for_insn (last_insn, BASIC_BLOCK (i));
- }
sbitmap_vector_free (post_dominators);
sbitmap_vector_free (dominators);
estimate_bb_frequencies (loops_info);
}
\f
-/* __builtin_expect dropped tokens into the insn stream describing
- expected values of registers. Generate branch probabilities
- based off these values. */
+/* __builtin_expect dropped tokens into the insn stream describing expected
+ values of registers. Generate branch probabilities based off these
+ values. */
void
expected_value_to_br_prob ()
ev = NULL_RTX;
continue;
- default:
- /* Look for insns that clobber the EV register. */
- if (ev && reg_set_p (ev_reg, insn))
- ev = NULL_RTX;
- continue;
-
case JUMP_INSN:
/* Look for simple conditional branches. If we haven't got an
expected value yet, no point going further. */
- if (GET_CODE (insn) != JUMP_INSN || ev == NULL_RTX)
- continue;
- if (! any_condjump_p (insn))
+ if (GET_CODE (insn) != JUMP_INSN || ev == NULL_RTX
+ || ! any_condjump_p (insn))
continue;
break;
+
+ default:
+ /* Look for insns that clobber the EV register. */
+ if (ev && reg_set_p (ev_reg, insn))
+ ev = NULL_RTX;
+ continue;
}
/* Collect the branch condition, hopefully relative to EV_REG. */
Could use cselib to try and reduce this further. */
cond = XEXP (SET_SRC (pc_set (insn)), 0);
cond = canonicalize_condition (insn, cond, 0, NULL, ev_reg);
- if (! cond
- || XEXP (cond, 0) != ev_reg
+ if (! cond || XEXP (cond, 0) != ev_reg
|| GET_CODE (XEXP (cond, 1)) != CONST_INT)
continue;
/* Helper function for estimate_bb_frequencies.
Propagate the frequencies for loops headed by HEAD. */
+
static void
propagate_freq (head)
basic_block head;
if (BLOCK_INFO (bb)->tovisit)
{
int count = 0;
+
for (e = bb->pred; e; e = e->pred_next)
if (BLOCK_INFO (e->src)->tovisit && !(e->flags & EDGE_DFS_BACK))
count++;
BLOCK_INFO (head)->frequency = 1;
for (; bb; bb = nextbb)
{
- volatile double cyclic_probability = 0, frequency = 0;
+ double cyclic_probability = 0, frequency = 0;
nextbb = BLOCK_INFO (bb)->next;
BLOCK_INFO (bb)->next = NULL;
/* Compute back edge frequencies. */
for (e = bb->succ; e; e = e->succ_next)
if (e->dest == head)
- EDGE_INFO (e)->back_edge_prob = (e->probability
- * BLOCK_INFO (bb)->frequency
- / REG_BR_PROB_BASE);
+ EDGE_INFO (e)->back_edge_prob
+ = ((e->probability * BLOCK_INFO (bb)->frequency)
+ / REG_BR_PROB_BASE);
/* Propagate to successor blocks. */
for (e = bb->succ; e; e = e->succ_next)
nextbb = e->dest;
else
BLOCK_INFO (last)->next = e->dest;
+
last = e->dest;
}
}
}
/* Estimate probabilities of loopback edges in loops at same nest level. */
+
static void
estimate_loops_at_level (first_loop)
struct loop *first_loop;
estimate_loops_at_level (loop->inner);
/* Find current loop back edge and mark it. */
- for (e = loop->latch->succ; e->dest != loop->header; e = e->succ_next);
+ for (e = loop->latch->succ; e->dest != loop->header; e = e->succ_next)
+ ;
EDGE_INFO (e)->back_edge = 1;
for (l = loop->next; l; l = l->next)
if (l->header == loop->header)
break;
+
if (l)
continue;
}
EXECUTE_IF_SET_IN_SBITMAP (l->nodes, 0, n,
BLOCK_INFO (BASIC_BLOCK (n))->tovisit = 1
);
+
propagate_freq (loop->header);
}
}
/* Convert counts measured by profile driven feedback to frequencies. */
+
static void
counts_to_freqs ()
{
int i;
for (i = 0; i < n_basic_blocks; i++)
- if (BASIC_BLOCK (i)->count > count_max)
- count_max = BASIC_BLOCK (i)->count;
+ count_max = MAX (BASIC_BLOCK (i)->count, count_max);
for (i = -2; i < n_basic_blocks; i++)
{
basic_block bb;
+
if (i == -2)
bb = ENTRY_BLOCK_PTR;
else if (i == -1)
bb = EXIT_BLOCK_PTR;
else
bb = BASIC_BLOCK (i);
- bb->frequency = ((bb->count * BB_FREQ_MAX + count_max / 2)
- / count_max);
+
+ bb->frequency = (bb->count * BB_FREQ_MAX + count_max / 2) / count_max;
}
}
-/* Return true if function is likely to be expensive, so there is no point
- to optimizer performance of prologue, epilogue or do inlining at the
- expense of code size growth. THRESHOLD is the limit of number
- of isntructions function can execute at average to be still considered
- not expensive. */
+/* Return true if function is likely to be expensive, so there is no point to
+ optimize performance of prologue, epilogue or do inlining at the expense
+ of code size growth. THRESHOLD is the limit of number of isntructions
+ function can execute at average to be still considered not expensive. */
+
bool
expensive_function_p (threshold)
int threshold;
for (insn = bb->head; insn != NEXT_INSN (bb->end);
insn = NEXT_INSN (insn))
- {
- if (active_insn_p (insn))
- {
- sum += bb->frequency;
- if (sum > limit)
- return true;
- }
+ if (active_insn_p (insn))
+ {
+ sum += bb->frequency;
+ if (sum > limit)
+ return true;
}
}
+
return false;
}
/* Estimate basic blocks frequency by given branch probabilities. */
+
static void
estimate_bb_frequencies (loops)
struct loops *loops;
fallthru->probability = REG_BR_PROB_BASE - probability;
}
}
+
ENTRY_BLOCK_PTR->succ->probability = REG_BR_PROB_BASE;
/* Set up block info for each basic block. */
bb = EXIT_BLOCK_PTR;
else
bb = BASIC_BLOCK (i);
+
BLOCK_INFO (bb)->tovisit = 0;
for (e = bb->succ; e; e = e->succ_next)
EDGE_INFO (e)->back_edge_prob = ((double) e->probability
/ REG_BR_PROB_BASE);
}
+
/* First compute probabilities locally for each loop from innermost
to outermost to examine probabilities for back edges. */
estimate_loops_at_level (loops->tree_root);
/* Now fake loop around whole function to finalize probabilities. */
for (i = 0; i < n_basic_blocks; i++)
BLOCK_INFO (BASIC_BLOCK (i))->tovisit = 1;
+
BLOCK_INFO (ENTRY_BLOCK_PTR)->tovisit = 1;
BLOCK_INFO (EXIT_BLOCK_PTR)->tovisit = 1;
propagate_freq (ENTRY_BLOCK_PTR);
for (i = 0; i < n_basic_blocks; i++)
if (BLOCK_INFO (BASIC_BLOCK (i))->frequency > freq_max)
freq_max = BLOCK_INFO (BASIC_BLOCK (i))->frequency;
+
for (i = -2; i < n_basic_blocks; i++)
{
basic_block bb;
+
if (i == -2)
bb = ENTRY_BLOCK_PTR;
else if (i == -1)
bb = EXIT_BLOCK_PTR;
else
bb = BASIC_BLOCK (i);
- bb->frequency = (BLOCK_INFO (bb)->frequency * BB_FREQ_MAX / freq_max
- + 0.5);
+ bb->frequency
+ = BLOCK_INFO (bb)->frequency * BB_FREQ_MAX / freq_max + 0.5;
}
free_aux_for_blocks ();
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