1 /* Branch prediction routines for the GNU compiler.
2 Copyright (C) 2000-2016 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify it under
7 the terms of the GNU General Public License as published by the Free
8 Software Foundation; either version 3, or (at your option) any later
11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
22 [1] "Branch Prediction for Free"
23 Ball and Larus; PLDI '93.
24 [2] "Static Branch Frequency and Program Profile Analysis"
25 Wu and Larus; MICRO-27.
26 [3] "Corpus-based Static Branch Prediction"
27 Calder, Grunwald, Lindsay, Martin, Mozer, and Zorn; PLDI '95. */
32 #include "coretypes.h"
38 #include "tree-pass.h"
43 #include "diagnostic-core.h"
44 #include "gimple-predict.h"
45 #include "fold-const.h"
52 #include "gimple-iterator.h"
54 #include "tree-ssa-loop-niter.h"
55 #include "tree-ssa-loop.h"
56 #include "tree-scalar-evolution.h"
58 /* real constants: 0, 1, 1-1/REG_BR_PROB_BASE, REG_BR_PROB_BASE,
59 1/REG_BR_PROB_BASE, 0.5, BB_FREQ_MAX. */
60 static sreal real_almost_one
, real_br_prob_base
,
61 real_inv_br_prob_base
, real_one_half
, real_bb_freq_max
;
63 static void combine_predictions_for_insn (rtx_insn
*, basic_block
);
64 static void dump_prediction (FILE *, enum br_predictor
, int, basic_block
, int);
65 static void predict_paths_leading_to (basic_block
, enum br_predictor
, enum prediction
);
66 static void predict_paths_leading_to_edge (edge
, enum br_predictor
, enum prediction
);
67 static bool can_predict_insn_p (const rtx_insn
*);
69 /* Information we hold about each branch predictor.
70 Filled using information from predict.def. */
74 const char *const name
; /* Name used in the debugging dumps. */
75 const int hitrate
; /* Expected hitrate used by
76 predict_insn_def call. */
80 /* Use given predictor without Dempster-Shaffer theory if it matches
81 using first_match heuristics. */
82 #define PRED_FLAG_FIRST_MATCH 1
84 /* Recompute hitrate in percent to our representation. */
86 #define HITRATE(VAL) ((int) ((VAL) * REG_BR_PROB_BASE + 50) / 100)
88 #define DEF_PREDICTOR(ENUM, NAME, HITRATE, FLAGS) {NAME, HITRATE, FLAGS},
89 static const struct predictor_info predictor_info
[]= {
90 #include "predict.def"
92 /* Upper bound on predictors. */
97 /* Return TRUE if frequency FREQ is considered to be hot. */
100 maybe_hot_frequency_p (struct function
*fun
, int freq
)
102 struct cgraph_node
*node
= cgraph_node::get (fun
->decl
);
104 || !opt_for_fn (fun
->decl
, flag_branch_probabilities
))
106 if (node
->frequency
== NODE_FREQUENCY_UNLIKELY_EXECUTED
)
108 if (node
->frequency
== NODE_FREQUENCY_HOT
)
111 if (profile_status_for_fn (fun
) == PROFILE_ABSENT
)
113 if (node
->frequency
== NODE_FREQUENCY_EXECUTED_ONCE
114 && freq
< (ENTRY_BLOCK_PTR_FOR_FN (fun
)->frequency
* 2 / 3))
116 if (PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION
) == 0)
118 if (freq
< (ENTRY_BLOCK_PTR_FOR_FN (fun
)->frequency
119 / PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION
)))
124 static gcov_type min_count
= -1;
126 /* Determine the threshold for hot BB counts. */
129 get_hot_bb_threshold ()
131 gcov_working_set_t
*ws
;
134 ws
= find_working_set (PARAM_VALUE (HOT_BB_COUNT_WS_PERMILLE
));
136 min_count
= ws
->min_counter
;
141 /* Set the threshold for hot BB counts. */
144 set_hot_bb_threshold (gcov_type min
)
149 /* Return TRUE if frequency FREQ is considered to be hot. */
152 maybe_hot_count_p (struct function
*fun
, gcov_type count
)
154 if (fun
&& profile_status_for_fn (fun
) != PROFILE_READ
)
156 /* Code executed at most once is not hot. */
157 if (profile_info
->runs
>= count
)
159 return (count
>= get_hot_bb_threshold ());
162 /* Return true in case BB can be CPU intensive and should be optimized
163 for maximal performance. */
166 maybe_hot_bb_p (struct function
*fun
, const_basic_block bb
)
168 gcc_checking_assert (fun
);
169 if (profile_status_for_fn (fun
) == PROFILE_READ
)
170 return maybe_hot_count_p (fun
, bb
->count
);
171 return maybe_hot_frequency_p (fun
, bb
->frequency
);
174 /* Return true in case BB can be CPU intensive and should be optimized
175 for maximal performance. */
178 maybe_hot_edge_p (edge e
)
180 if (profile_status_for_fn (cfun
) == PROFILE_READ
)
181 return maybe_hot_count_p (cfun
, e
->count
);
182 return maybe_hot_frequency_p (cfun
, EDGE_FREQUENCY (e
));
185 /* Return true if profile COUNT and FREQUENCY, or function FUN static
186 node frequency reflects never being executed. */
189 probably_never_executed (struct function
*fun
,
190 gcov_type count
, int frequency
)
192 gcc_checking_assert (fun
);
193 if (profile_status_for_fn (fun
) == PROFILE_READ
)
195 int unlikely_count_fraction
= PARAM_VALUE (UNLIKELY_BB_COUNT_FRACTION
);
196 if (count
* unlikely_count_fraction
>= profile_info
->runs
)
200 if (!ENTRY_BLOCK_PTR_FOR_FN (fun
)->frequency
)
202 if (ENTRY_BLOCK_PTR_FOR_FN (fun
)->count
)
204 gcov_type computed_count
;
205 /* Check for possibility of overflow, in which case entry bb count
206 is large enough to do the division first without losing much
208 if (ENTRY_BLOCK_PTR_FOR_FN (fun
)->count
< REG_BR_PROB_BASE
*
211 gcov_type scaled_count
212 = frequency
* ENTRY_BLOCK_PTR_FOR_FN (fun
)->count
*
213 unlikely_count_fraction
;
214 computed_count
= RDIV (scaled_count
,
215 ENTRY_BLOCK_PTR_FOR_FN (fun
)->frequency
);
219 computed_count
= RDIV (ENTRY_BLOCK_PTR_FOR_FN (fun
)->count
,
220 ENTRY_BLOCK_PTR_FOR_FN (fun
)->frequency
);
221 computed_count
*= frequency
* unlikely_count_fraction
;
223 if (computed_count
>= profile_info
->runs
)
228 if ((!profile_info
|| !(opt_for_fn (fun
->decl
, flag_branch_probabilities
)))
229 && (cgraph_node::get (fun
->decl
)->frequency
230 == NODE_FREQUENCY_UNLIKELY_EXECUTED
))
236 /* Return true in case BB is probably never executed. */
239 probably_never_executed_bb_p (struct function
*fun
, const_basic_block bb
)
241 return probably_never_executed (fun
, bb
->count
, bb
->frequency
);
245 /* Return true in case edge E is probably never executed. */
248 probably_never_executed_edge_p (struct function
*fun
, edge e
)
250 return probably_never_executed (fun
, e
->count
, EDGE_FREQUENCY (e
));
253 /* Return true when current function should always be optimized for size. */
256 optimize_function_for_size_p (struct function
*fun
)
258 if (!fun
|| !fun
->decl
)
259 return optimize_size
;
260 cgraph_node
*n
= cgraph_node::get (fun
->decl
);
261 return n
&& n
->optimize_for_size_p ();
264 /* Return true when current function should always be optimized for speed. */
267 optimize_function_for_speed_p (struct function
*fun
)
269 return !optimize_function_for_size_p (fun
);
272 /* Return the optimization type that should be used for the function FUN. */
275 function_optimization_type (struct function
*fun
)
277 return (optimize_function_for_speed_p (fun
)
279 : OPTIMIZE_FOR_SIZE
);
282 /* Return TRUE when BB should be optimized for size. */
285 optimize_bb_for_size_p (const_basic_block bb
)
287 return (optimize_function_for_size_p (cfun
)
288 || (bb
&& !maybe_hot_bb_p (cfun
, bb
)));
291 /* Return TRUE when BB should be optimized for speed. */
294 optimize_bb_for_speed_p (const_basic_block bb
)
296 return !optimize_bb_for_size_p (bb
);
299 /* Return the optimization type that should be used for block BB. */
302 bb_optimization_type (const_basic_block bb
)
304 return (optimize_bb_for_speed_p (bb
)
306 : OPTIMIZE_FOR_SIZE
);
309 /* Return TRUE when BB should be optimized for size. */
312 optimize_edge_for_size_p (edge e
)
314 return optimize_function_for_size_p (cfun
) || !maybe_hot_edge_p (e
);
317 /* Return TRUE when BB should be optimized for speed. */
320 optimize_edge_for_speed_p (edge e
)
322 return !optimize_edge_for_size_p (e
);
325 /* Return TRUE when BB should be optimized for size. */
328 optimize_insn_for_size_p (void)
330 return optimize_function_for_size_p (cfun
) || !crtl
->maybe_hot_insn_p
;
333 /* Return TRUE when BB should be optimized for speed. */
336 optimize_insn_for_speed_p (void)
338 return !optimize_insn_for_size_p ();
341 /* Return TRUE when LOOP should be optimized for size. */
344 optimize_loop_for_size_p (struct loop
*loop
)
346 return optimize_bb_for_size_p (loop
->header
);
349 /* Return TRUE when LOOP should be optimized for speed. */
352 optimize_loop_for_speed_p (struct loop
*loop
)
354 return optimize_bb_for_speed_p (loop
->header
);
357 /* Return TRUE when LOOP nest should be optimized for speed. */
360 optimize_loop_nest_for_speed_p (struct loop
*loop
)
362 struct loop
*l
= loop
;
363 if (optimize_loop_for_speed_p (loop
))
366 while (l
&& l
!= loop
)
368 if (optimize_loop_for_speed_p (l
))
376 while (l
!= loop
&& !l
->next
)
385 /* Return TRUE when LOOP nest should be optimized for size. */
388 optimize_loop_nest_for_size_p (struct loop
*loop
)
390 return !optimize_loop_nest_for_speed_p (loop
);
393 /* Return true when edge E is likely to be well predictable by branch
397 predictable_edge_p (edge e
)
399 if (profile_status_for_fn (cfun
) == PROFILE_ABSENT
)
402 <= PARAM_VALUE (PARAM_PREDICTABLE_BRANCH_OUTCOME
) * REG_BR_PROB_BASE
/ 100)
403 || (REG_BR_PROB_BASE
- e
->probability
404 <= PARAM_VALUE (PARAM_PREDICTABLE_BRANCH_OUTCOME
) * REG_BR_PROB_BASE
/ 100))
410 /* Set RTL expansion for BB profile. */
413 rtl_profile_for_bb (basic_block bb
)
415 crtl
->maybe_hot_insn_p
= maybe_hot_bb_p (cfun
, bb
);
418 /* Set RTL expansion for edge profile. */
421 rtl_profile_for_edge (edge e
)
423 crtl
->maybe_hot_insn_p
= maybe_hot_edge_p (e
);
426 /* Set RTL expansion to default mode (i.e. when profile info is not known). */
428 default_rtl_profile (void)
430 crtl
->maybe_hot_insn_p
= true;
433 /* Return true if the one of outgoing edges is already predicted by
437 rtl_predicted_by_p (const_basic_block bb
, enum br_predictor predictor
)
440 if (!INSN_P (BB_END (bb
)))
442 for (note
= REG_NOTES (BB_END (bb
)); note
; note
= XEXP (note
, 1))
443 if (REG_NOTE_KIND (note
) == REG_BR_PRED
444 && INTVAL (XEXP (XEXP (note
, 0), 0)) == (int)predictor
)
449 /* Structure representing predictions in tree level. */
451 struct edge_prediction
{
452 struct edge_prediction
*ep_next
;
454 enum br_predictor ep_predictor
;
458 /* This map contains for a basic block the list of predictions for the
461 static hash_map
<const_basic_block
, edge_prediction
*> *bb_predictions
;
463 /* Return true if the one of outgoing edges is already predicted by
467 gimple_predicted_by_p (const_basic_block bb
, enum br_predictor predictor
)
469 struct edge_prediction
*i
;
470 edge_prediction
**preds
= bb_predictions
->get (bb
);
475 for (i
= *preds
; i
; i
= i
->ep_next
)
476 if (i
->ep_predictor
== predictor
)
481 /* Return true when the probability of edge is reliable.
483 The profile guessing code is good at predicting branch outcome (ie.
484 taken/not taken), that is predicted right slightly over 75% of time.
485 It is however notoriously poor on predicting the probability itself.
486 In general the profile appear a lot flatter (with probabilities closer
487 to 50%) than the reality so it is bad idea to use it to drive optimization
488 such as those disabling dynamic branch prediction for well predictable
491 There are two exceptions - edges leading to noreturn edges and edges
492 predicted by number of iterations heuristics are predicted well. This macro
493 should be able to distinguish those, but at the moment it simply check for
494 noreturn heuristic that is only one giving probability over 99% or bellow
495 1%. In future we might want to propagate reliability information across the
496 CFG if we find this information useful on multiple places. */
498 probability_reliable_p (int prob
)
500 return (profile_status_for_fn (cfun
) == PROFILE_READ
501 || (profile_status_for_fn (cfun
) == PROFILE_GUESSED
502 && (prob
<= HITRATE (1) || prob
>= HITRATE (99))));
505 /* Same predicate as above, working on edges. */
507 edge_probability_reliable_p (const_edge e
)
509 return probability_reliable_p (e
->probability
);
512 /* Same predicate as edge_probability_reliable_p, working on notes. */
514 br_prob_note_reliable_p (const_rtx note
)
516 gcc_assert (REG_NOTE_KIND (note
) == REG_BR_PROB
);
517 return probability_reliable_p (XINT (note
, 0));
521 predict_insn (rtx_insn
*insn
, enum br_predictor predictor
, int probability
)
523 gcc_assert (any_condjump_p (insn
));
524 if (!flag_guess_branch_prob
)
527 add_reg_note (insn
, REG_BR_PRED
,
528 gen_rtx_CONCAT (VOIDmode
,
529 GEN_INT ((int) predictor
),
530 GEN_INT ((int) probability
)));
533 /* Predict insn by given predictor. */
536 predict_insn_def (rtx_insn
*insn
, enum br_predictor predictor
,
537 enum prediction taken
)
539 int probability
= predictor_info
[(int) predictor
].hitrate
;
542 probability
= REG_BR_PROB_BASE
- probability
;
544 predict_insn (insn
, predictor
, probability
);
547 /* Predict edge E with given probability if possible. */
550 rtl_predict_edge (edge e
, enum br_predictor predictor
, int probability
)
553 last_insn
= BB_END (e
->src
);
555 /* We can store the branch prediction information only about
556 conditional jumps. */
557 if (!any_condjump_p (last_insn
))
560 /* We always store probability of branching. */
561 if (e
->flags
& EDGE_FALLTHRU
)
562 probability
= REG_BR_PROB_BASE
- probability
;
564 predict_insn (last_insn
, predictor
, probability
);
567 /* Predict edge E with the given PROBABILITY. */
569 gimple_predict_edge (edge e
, enum br_predictor predictor
, int probability
)
571 gcc_assert (profile_status_for_fn (cfun
) != PROFILE_GUESSED
);
572 if ((e
->src
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
) && EDGE_COUNT (e
->src
->succs
) >
574 && flag_guess_branch_prob
&& optimize
)
576 struct edge_prediction
*i
= XNEW (struct edge_prediction
);
577 edge_prediction
*&preds
= bb_predictions
->get_or_insert (e
->src
);
581 i
->ep_probability
= probability
;
582 i
->ep_predictor
= predictor
;
587 /* Remove all predictions on given basic block that are attached
590 remove_predictions_associated_with_edge (edge e
)
595 edge_prediction
**preds
= bb_predictions
->get (e
->src
);
599 struct edge_prediction
**prediction
= preds
;
600 struct edge_prediction
*next
;
604 if ((*prediction
)->ep_edge
== e
)
606 next
= (*prediction
)->ep_next
;
611 prediction
= &((*prediction
)->ep_next
);
616 /* Clears the list of predictions stored for BB. */
619 clear_bb_predictions (basic_block bb
)
621 edge_prediction
**preds
= bb_predictions
->get (bb
);
622 struct edge_prediction
*pred
, *next
;
627 for (pred
= *preds
; pred
; pred
= next
)
629 next
= pred
->ep_next
;
635 /* Return true when we can store prediction on insn INSN.
636 At the moment we represent predictions only on conditional
637 jumps, not at computed jump or other complicated cases. */
639 can_predict_insn_p (const rtx_insn
*insn
)
641 return (JUMP_P (insn
)
642 && any_condjump_p (insn
)
643 && EDGE_COUNT (BLOCK_FOR_INSN (insn
)->succs
) >= 2);
646 /* Predict edge E by given predictor if possible. */
649 predict_edge_def (edge e
, enum br_predictor predictor
,
650 enum prediction taken
)
652 int probability
= predictor_info
[(int) predictor
].hitrate
;
655 probability
= REG_BR_PROB_BASE
- probability
;
657 predict_edge (e
, predictor
, probability
);
660 /* Invert all branch predictions or probability notes in the INSN. This needs
661 to be done each time we invert the condition used by the jump. */
664 invert_br_probabilities (rtx insn
)
668 for (note
= REG_NOTES (insn
); note
; note
= XEXP (note
, 1))
669 if (REG_NOTE_KIND (note
) == REG_BR_PROB
)
670 XINT (note
, 0) = REG_BR_PROB_BASE
- XINT (note
, 0);
671 else if (REG_NOTE_KIND (note
) == REG_BR_PRED
)
672 XEXP (XEXP (note
, 0), 1)
673 = GEN_INT (REG_BR_PROB_BASE
- INTVAL (XEXP (XEXP (note
, 0), 1)));
676 /* Dump information about the branch prediction to the output file. */
679 dump_prediction (FILE *file
, enum br_predictor predictor
, int probability
,
680 basic_block bb
, int used
)
688 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
689 if (! (e
->flags
& EDGE_FALLTHRU
))
692 fprintf (file
, " %s heuristics%s: %.1f%%",
693 predictor_info
[predictor
].name
,
694 used
? "" : " (ignored)", probability
* 100.0 / REG_BR_PROB_BASE
);
698 fprintf (file
, " exec %" PRId64
, bb
->count
);
701 fprintf (file
, " hit %" PRId64
, e
->count
);
702 fprintf (file
, " (%.1f%%)", e
->count
* 100.0 / bb
->count
);
706 fprintf (file
, "\n");
709 /* We can not predict the probabilities of outgoing edges of bb. Set them
710 evenly and hope for the best. */
712 set_even_probabilities (basic_block bb
)
718 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
719 if (!(e
->flags
& (EDGE_EH
| EDGE_FAKE
)))
721 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
722 if (!(e
->flags
& (EDGE_EH
| EDGE_FAKE
)))
723 e
->probability
= (REG_BR_PROB_BASE
+ nedges
/ 2) / nedges
;
728 /* Combine all REG_BR_PRED notes into single probability and attach REG_BR_PROB
729 note if not already present. Remove now useless REG_BR_PRED notes. */
732 combine_predictions_for_insn (rtx_insn
*insn
, basic_block bb
)
737 int best_probability
= PROB_EVEN
;
738 enum br_predictor best_predictor
= END_PREDICTORS
;
739 int combined_probability
= REG_BR_PROB_BASE
/ 2;
741 bool first_match
= false;
744 if (!can_predict_insn_p (insn
))
746 set_even_probabilities (bb
);
750 prob_note
= find_reg_note (insn
, REG_BR_PROB
, 0);
751 pnote
= ®_NOTES (insn
);
753 fprintf (dump_file
, "Predictions for insn %i bb %i\n", INSN_UID (insn
),
756 /* We implement "first match" heuristics and use probability guessed
757 by predictor with smallest index. */
758 for (note
= REG_NOTES (insn
); note
; note
= XEXP (note
, 1))
759 if (REG_NOTE_KIND (note
) == REG_BR_PRED
)
761 enum br_predictor predictor
= ((enum br_predictor
)
762 INTVAL (XEXP (XEXP (note
, 0), 0)));
763 int probability
= INTVAL (XEXP (XEXP (note
, 0), 1));
766 if (best_predictor
> predictor
)
767 best_probability
= probability
, best_predictor
= predictor
;
769 d
= (combined_probability
* probability
770 + (REG_BR_PROB_BASE
- combined_probability
)
771 * (REG_BR_PROB_BASE
- probability
));
773 /* Use FP math to avoid overflows of 32bit integers. */
775 /* If one probability is 0% and one 100%, avoid division by zero. */
776 combined_probability
= REG_BR_PROB_BASE
/ 2;
778 combined_probability
= (((double) combined_probability
) * probability
779 * REG_BR_PROB_BASE
/ d
+ 0.5);
782 /* Decide which heuristic to use. In case we didn't match anything,
783 use no_prediction heuristic, in case we did match, use either
784 first match or Dempster-Shaffer theory depending on the flags. */
786 if (predictor_info
[best_predictor
].flags
& PRED_FLAG_FIRST_MATCH
)
790 dump_prediction (dump_file
, PRED_NO_PREDICTION
,
791 combined_probability
, bb
, true);
794 dump_prediction (dump_file
, PRED_DS_THEORY
, combined_probability
,
796 dump_prediction (dump_file
, PRED_FIRST_MATCH
, best_probability
,
801 combined_probability
= best_probability
;
802 dump_prediction (dump_file
, PRED_COMBINED
, combined_probability
, bb
, true);
806 if (REG_NOTE_KIND (*pnote
) == REG_BR_PRED
)
808 enum br_predictor predictor
= ((enum br_predictor
)
809 INTVAL (XEXP (XEXP (*pnote
, 0), 0)));
810 int probability
= INTVAL (XEXP (XEXP (*pnote
, 0), 1));
812 dump_prediction (dump_file
, predictor
, probability
, bb
,
813 !first_match
|| best_predictor
== predictor
);
814 *pnote
= XEXP (*pnote
, 1);
817 pnote
= &XEXP (*pnote
, 1);
822 add_int_reg_note (insn
, REG_BR_PROB
, combined_probability
);
824 /* Save the prediction into CFG in case we are seeing non-degenerated
826 if (!single_succ_p (bb
))
828 BRANCH_EDGE (bb
)->probability
= combined_probability
;
829 FALLTHRU_EDGE (bb
)->probability
830 = REG_BR_PROB_BASE
- combined_probability
;
833 else if (!single_succ_p (bb
))
835 int prob
= XINT (prob_note
, 0);
837 BRANCH_EDGE (bb
)->probability
= prob
;
838 FALLTHRU_EDGE (bb
)->probability
= REG_BR_PROB_BASE
- prob
;
841 single_succ_edge (bb
)->probability
= REG_BR_PROB_BASE
;
844 /* Combine predictions into single probability and store them into CFG.
845 Remove now useless prediction entries. */
848 combine_predictions_for_bb (basic_block bb
)
850 int best_probability
= PROB_EVEN
;
851 enum br_predictor best_predictor
= END_PREDICTORS
;
852 int combined_probability
= REG_BR_PROB_BASE
/ 2;
854 bool first_match
= false;
856 struct edge_prediction
*pred
;
858 edge e
, first
= NULL
, second
= NULL
;
861 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
862 if (!(e
->flags
& (EDGE_EH
| EDGE_FAKE
)))
865 if (first
&& !second
)
871 /* When there is no successor or only one choice, prediction is easy.
873 We are lazy for now and predict only basic blocks with two outgoing
874 edges. It is possible to predict generic case too, but we have to
875 ignore first match heuristics and do more involved combining. Implement
880 set_even_probabilities (bb
);
881 clear_bb_predictions (bb
);
883 fprintf (dump_file
, "%i edges in bb %i predicted to even probabilities\n",
889 fprintf (dump_file
, "Predictions for bb %i\n", bb
->index
);
891 edge_prediction
**preds
= bb_predictions
->get (bb
);
894 /* We implement "first match" heuristics and use probability guessed
895 by predictor with smallest index. */
896 for (pred
= *preds
; pred
; pred
= pred
->ep_next
)
898 enum br_predictor predictor
= pred
->ep_predictor
;
899 int probability
= pred
->ep_probability
;
901 if (pred
->ep_edge
!= first
)
902 probability
= REG_BR_PROB_BASE
- probability
;
905 /* First match heuristics would be widly confused if we predicted
907 if (best_predictor
> predictor
)
909 struct edge_prediction
*pred2
;
910 int prob
= probability
;
912 for (pred2
= (struct edge_prediction
*) *preds
;
913 pred2
; pred2
= pred2
->ep_next
)
914 if (pred2
!= pred
&& pred2
->ep_predictor
== pred
->ep_predictor
)
916 int probability2
= pred
->ep_probability
;
918 if (pred2
->ep_edge
!= first
)
919 probability2
= REG_BR_PROB_BASE
- probability2
;
921 if ((probability
< REG_BR_PROB_BASE
/ 2) !=
922 (probability2
< REG_BR_PROB_BASE
/ 2))
925 /* If the same predictor later gave better result, go for it! */
926 if ((probability
>= REG_BR_PROB_BASE
/ 2 && (probability2
> probability
))
927 || (probability
<= REG_BR_PROB_BASE
/ 2 && (probability2
< probability
)))
931 best_probability
= prob
, best_predictor
= predictor
;
934 d
= (combined_probability
* probability
935 + (REG_BR_PROB_BASE
- combined_probability
)
936 * (REG_BR_PROB_BASE
- probability
));
938 /* Use FP math to avoid overflows of 32bit integers. */
940 /* If one probability is 0% and one 100%, avoid division by zero. */
941 combined_probability
= REG_BR_PROB_BASE
/ 2;
943 combined_probability
= (((double) combined_probability
)
945 * REG_BR_PROB_BASE
/ d
+ 0.5);
949 /* Decide which heuristic to use. In case we didn't match anything,
950 use no_prediction heuristic, in case we did match, use either
951 first match or Dempster-Shaffer theory depending on the flags. */
953 if (predictor_info
[best_predictor
].flags
& PRED_FLAG_FIRST_MATCH
)
957 dump_prediction (dump_file
, PRED_NO_PREDICTION
, combined_probability
, bb
, true);
960 dump_prediction (dump_file
, PRED_DS_THEORY
, combined_probability
, bb
,
962 dump_prediction (dump_file
, PRED_FIRST_MATCH
, best_probability
, bb
,
967 combined_probability
= best_probability
;
968 dump_prediction (dump_file
, PRED_COMBINED
, combined_probability
, bb
, true);
972 for (pred
= (struct edge_prediction
*) *preds
; pred
; pred
= pred
->ep_next
)
974 enum br_predictor predictor
= pred
->ep_predictor
;
975 int probability
= pred
->ep_probability
;
977 if (pred
->ep_edge
!= EDGE_SUCC (bb
, 0))
978 probability
= REG_BR_PROB_BASE
- probability
;
979 dump_prediction (dump_file
, predictor
, probability
, bb
,
980 !first_match
|| best_predictor
== predictor
);
983 clear_bb_predictions (bb
);
987 first
->probability
= combined_probability
;
988 second
->probability
= REG_BR_PROB_BASE
- combined_probability
;
992 /* Check if T1 and T2 satisfy the IV_COMPARE condition.
993 Return the SSA_NAME if the condition satisfies, NULL otherwise.
995 T1 and T2 should be one of the following cases:
996 1. T1 is SSA_NAME, T2 is NULL
997 2. T1 is SSA_NAME, T2 is INTEGER_CST between [-4, 4]
998 3. T2 is SSA_NAME, T1 is INTEGER_CST between [-4, 4] */
1001 strips_small_constant (tree t1
, tree t2
)
1008 else if (TREE_CODE (t1
) == SSA_NAME
)
1010 else if (tree_fits_shwi_p (t1
))
1011 value
= tree_to_shwi (t1
);
1017 else if (tree_fits_shwi_p (t2
))
1018 value
= tree_to_shwi (t2
);
1019 else if (TREE_CODE (t2
) == SSA_NAME
)
1027 if (value
<= 4 && value
>= -4)
1033 /* Return the SSA_NAME in T or T's operands.
1034 Return NULL if SSA_NAME cannot be found. */
1037 get_base_value (tree t
)
1039 if (TREE_CODE (t
) == SSA_NAME
)
1042 if (!BINARY_CLASS_P (t
))
1045 switch (TREE_OPERAND_LENGTH (t
))
1048 return strips_small_constant (TREE_OPERAND (t
, 0), NULL
);
1050 return strips_small_constant (TREE_OPERAND (t
, 0),
1051 TREE_OPERAND (t
, 1));
1057 /* Check the compare STMT in LOOP. If it compares an induction
1058 variable to a loop invariant, return true, and save
1059 LOOP_INVARIANT, COMPARE_CODE and LOOP_STEP.
1060 Otherwise return false and set LOOP_INVAIANT to NULL. */
1063 is_comparison_with_loop_invariant_p (gcond
*stmt
, struct loop
*loop
,
1064 tree
*loop_invariant
,
1065 enum tree_code
*compare_code
,
1069 tree op0
, op1
, bound
, base
;
1071 enum tree_code code
;
1074 code
= gimple_cond_code (stmt
);
1075 *loop_invariant
= NULL
;
1091 op0
= gimple_cond_lhs (stmt
);
1092 op1
= gimple_cond_rhs (stmt
);
1094 if ((TREE_CODE (op0
) != SSA_NAME
&& TREE_CODE (op0
) != INTEGER_CST
)
1095 || (TREE_CODE (op1
) != SSA_NAME
&& TREE_CODE (op1
) != INTEGER_CST
))
1097 if (!simple_iv (loop
, loop_containing_stmt (stmt
), op0
, &iv0
, true))
1099 if (!simple_iv (loop
, loop_containing_stmt (stmt
), op1
, &iv1
, true))
1101 if (TREE_CODE (iv0
.step
) != INTEGER_CST
1102 || TREE_CODE (iv1
.step
) != INTEGER_CST
)
1104 if ((integer_zerop (iv0
.step
) && integer_zerop (iv1
.step
))
1105 || (!integer_zerop (iv0
.step
) && !integer_zerop (iv1
.step
)))
1108 if (integer_zerop (iv0
.step
))
1110 if (code
!= NE_EXPR
&& code
!= EQ_EXPR
)
1111 code
= invert_tree_comparison (code
, false);
1114 if (tree_fits_shwi_p (iv1
.step
))
1123 if (tree_fits_shwi_p (iv0
.step
))
1129 if (TREE_CODE (bound
) != INTEGER_CST
)
1130 bound
= get_base_value (bound
);
1133 if (TREE_CODE (base
) != INTEGER_CST
)
1134 base
= get_base_value (base
);
1138 *loop_invariant
= bound
;
1139 *compare_code
= code
;
1141 *loop_iv_base
= base
;
1145 /* Compare two SSA_NAMEs: returns TRUE if T1 and T2 are value coherent. */
1148 expr_coherent_p (tree t1
, tree t2
)
1151 tree ssa_name_1
= NULL
;
1152 tree ssa_name_2
= NULL
;
1154 gcc_assert (TREE_CODE (t1
) == SSA_NAME
|| TREE_CODE (t1
) == INTEGER_CST
);
1155 gcc_assert (TREE_CODE (t2
) == SSA_NAME
|| TREE_CODE (t2
) == INTEGER_CST
);
1160 if (TREE_CODE (t1
) == INTEGER_CST
&& TREE_CODE (t2
) == INTEGER_CST
)
1162 if (TREE_CODE (t1
) == INTEGER_CST
|| TREE_CODE (t2
) == INTEGER_CST
)
1165 /* Check to see if t1 is expressed/defined with t2. */
1166 stmt
= SSA_NAME_DEF_STMT (t1
);
1167 gcc_assert (stmt
!= NULL
);
1168 if (is_gimple_assign (stmt
))
1170 ssa_name_1
= SINGLE_SSA_TREE_OPERAND (stmt
, SSA_OP_USE
);
1171 if (ssa_name_1
&& ssa_name_1
== t2
)
1175 /* Check to see if t2 is expressed/defined with t1. */
1176 stmt
= SSA_NAME_DEF_STMT (t2
);
1177 gcc_assert (stmt
!= NULL
);
1178 if (is_gimple_assign (stmt
))
1180 ssa_name_2
= SINGLE_SSA_TREE_OPERAND (stmt
, SSA_OP_USE
);
1181 if (ssa_name_2
&& ssa_name_2
== t1
)
1185 /* Compare if t1 and t2's def_stmts are identical. */
1186 if (ssa_name_2
!= NULL
&& ssa_name_1
== ssa_name_2
)
1192 /* Predict branch probability of BB when BB contains a branch that compares
1193 an induction variable in LOOP with LOOP_IV_BASE_VAR to LOOP_BOUND_VAR. The
1194 loop exit is compared using LOOP_BOUND_CODE, with step of LOOP_BOUND_STEP.
1197 for (int i = 0; i < bound; i++) {
1204 In this loop, we will predict the branch inside the loop to be taken. */
1207 predict_iv_comparison (struct loop
*loop
, basic_block bb
,
1208 tree loop_bound_var
,
1209 tree loop_iv_base_var
,
1210 enum tree_code loop_bound_code
,
1211 int loop_bound_step
)
1214 tree compare_var
, compare_base
;
1215 enum tree_code compare_code
;
1216 tree compare_step_var
;
1220 if (predicted_by_p (bb
, PRED_LOOP_ITERATIONS_GUESSED
)
1221 || predicted_by_p (bb
, PRED_LOOP_ITERATIONS
)
1222 || predicted_by_p (bb
, PRED_LOOP_EXIT
))
1225 stmt
= last_stmt (bb
);
1226 if (!stmt
|| gimple_code (stmt
) != GIMPLE_COND
)
1228 if (!is_comparison_with_loop_invariant_p (as_a
<gcond
*> (stmt
),
1235 /* Find the taken edge. */
1236 FOR_EACH_EDGE (then_edge
, ei
, bb
->succs
)
1237 if (then_edge
->flags
& EDGE_TRUE_VALUE
)
1240 /* When comparing an IV to a loop invariant, NE is more likely to be
1241 taken while EQ is more likely to be not-taken. */
1242 if (compare_code
== NE_EXPR
)
1244 predict_edge_def (then_edge
, PRED_LOOP_IV_COMPARE_GUESS
, TAKEN
);
1247 else if (compare_code
== EQ_EXPR
)
1249 predict_edge_def (then_edge
, PRED_LOOP_IV_COMPARE_GUESS
, NOT_TAKEN
);
1253 if (!expr_coherent_p (loop_iv_base_var
, compare_base
))
1256 /* If loop bound, base and compare bound are all constants, we can
1257 calculate the probability directly. */
1258 if (tree_fits_shwi_p (loop_bound_var
)
1259 && tree_fits_shwi_p (compare_var
)
1260 && tree_fits_shwi_p (compare_base
))
1263 bool overflow
, overall_overflow
= false;
1264 widest_int compare_count
, tem
;
1266 /* (loop_bound - base) / compare_step */
1267 tem
= wi::sub (wi::to_widest (loop_bound_var
),
1268 wi::to_widest (compare_base
), SIGNED
, &overflow
);
1269 overall_overflow
|= overflow
;
1270 widest_int loop_count
= wi::div_trunc (tem
,
1271 wi::to_widest (compare_step_var
),
1273 overall_overflow
|= overflow
;
1275 if (!wi::neg_p (wi::to_widest (compare_step_var
))
1276 ^ (compare_code
== LT_EXPR
|| compare_code
== LE_EXPR
))
1278 /* (loop_bound - compare_bound) / compare_step */
1279 tem
= wi::sub (wi::to_widest (loop_bound_var
),
1280 wi::to_widest (compare_var
), SIGNED
, &overflow
);
1281 overall_overflow
|= overflow
;
1282 compare_count
= wi::div_trunc (tem
, wi::to_widest (compare_step_var
),
1284 overall_overflow
|= overflow
;
1288 /* (compare_bound - base) / compare_step */
1289 tem
= wi::sub (wi::to_widest (compare_var
),
1290 wi::to_widest (compare_base
), SIGNED
, &overflow
);
1291 overall_overflow
|= overflow
;
1292 compare_count
= wi::div_trunc (tem
, wi::to_widest (compare_step_var
),
1294 overall_overflow
|= overflow
;
1296 if (compare_code
== LE_EXPR
|| compare_code
== GE_EXPR
)
1298 if (loop_bound_code
== LE_EXPR
|| loop_bound_code
== GE_EXPR
)
1300 if (wi::neg_p (compare_count
))
1302 if (wi::neg_p (loop_count
))
1304 if (loop_count
== 0)
1306 else if (wi::cmps (compare_count
, loop_count
) == 1)
1307 probability
= REG_BR_PROB_BASE
;
1310 tem
= compare_count
* REG_BR_PROB_BASE
;
1311 tem
= wi::udiv_trunc (tem
, loop_count
);
1312 probability
= tem
.to_uhwi ();
1315 if (!overall_overflow
)
1316 predict_edge (then_edge
, PRED_LOOP_IV_COMPARE
, probability
);
1321 if (expr_coherent_p (loop_bound_var
, compare_var
))
1323 if ((loop_bound_code
== LT_EXPR
|| loop_bound_code
== LE_EXPR
)
1324 && (compare_code
== LT_EXPR
|| compare_code
== LE_EXPR
))
1325 predict_edge_def (then_edge
, PRED_LOOP_IV_COMPARE_GUESS
, TAKEN
);
1326 else if ((loop_bound_code
== GT_EXPR
|| loop_bound_code
== GE_EXPR
)
1327 && (compare_code
== GT_EXPR
|| compare_code
== GE_EXPR
))
1328 predict_edge_def (then_edge
, PRED_LOOP_IV_COMPARE_GUESS
, TAKEN
);
1329 else if (loop_bound_code
== NE_EXPR
)
1331 /* If the loop backedge condition is "(i != bound)", we do
1332 the comparison based on the step of IV:
1333 * step < 0 : backedge condition is like (i > bound)
1334 * step > 0 : backedge condition is like (i < bound) */
1335 gcc_assert (loop_bound_step
!= 0);
1336 if (loop_bound_step
> 0
1337 && (compare_code
== LT_EXPR
1338 || compare_code
== LE_EXPR
))
1339 predict_edge_def (then_edge
, PRED_LOOP_IV_COMPARE_GUESS
, TAKEN
);
1340 else if (loop_bound_step
< 0
1341 && (compare_code
== GT_EXPR
1342 || compare_code
== GE_EXPR
))
1343 predict_edge_def (then_edge
, PRED_LOOP_IV_COMPARE_GUESS
, TAKEN
);
1345 predict_edge_def (then_edge
, PRED_LOOP_IV_COMPARE_GUESS
, NOT_TAKEN
);
1348 /* The branch is predicted not-taken if loop_bound_code is
1349 opposite with compare_code. */
1350 predict_edge_def (then_edge
, PRED_LOOP_IV_COMPARE_GUESS
, NOT_TAKEN
);
1352 else if (expr_coherent_p (loop_iv_base_var
, compare_var
))
1355 for (i = s; i < h; i++)
1357 The branch should be predicted taken. */
1358 if (loop_bound_step
> 0
1359 && (compare_code
== GT_EXPR
|| compare_code
== GE_EXPR
))
1360 predict_edge_def (then_edge
, PRED_LOOP_IV_COMPARE_GUESS
, TAKEN
);
1361 else if (loop_bound_step
< 0
1362 && (compare_code
== LT_EXPR
|| compare_code
== LE_EXPR
))
1363 predict_edge_def (then_edge
, PRED_LOOP_IV_COMPARE_GUESS
, TAKEN
);
1365 predict_edge_def (then_edge
, PRED_LOOP_IV_COMPARE_GUESS
, NOT_TAKEN
);
1369 /* Predict for extra loop exits that will lead to EXIT_EDGE. The extra loop
1370 exits are resulted from short-circuit conditions that will generate an
1373 if (foo() || global > 10)
1376 This will be translated into:
1381 if foo() goto BB6 else goto BB5
1383 if global > 10 goto BB6 else goto BB7
1387 iftmp = (PHI 0(BB5), 1(BB6))
1388 if iftmp == 1 goto BB8 else goto BB3
1390 outside of the loop...
1392 The edge BB7->BB8 is loop exit because BB8 is outside of the loop.
1393 From the dataflow, we can infer that BB4->BB6 and BB5->BB6 are also loop
1394 exits. This function takes BB7->BB8 as input, and finds out the extra loop
1395 exits to predict them using PRED_LOOP_EXIT. */
1398 predict_extra_loop_exits (edge exit_edge
)
1401 bool check_value_one
;
1402 gimple
*lhs_def_stmt
;
1404 tree cmp_rhs
, cmp_lhs
;
1408 last
= last_stmt (exit_edge
->src
);
1411 cmp_stmt
= dyn_cast
<gcond
*> (last
);
1415 cmp_rhs
= gimple_cond_rhs (cmp_stmt
);
1416 cmp_lhs
= gimple_cond_lhs (cmp_stmt
);
1417 if (!TREE_CONSTANT (cmp_rhs
)
1418 || !(integer_zerop (cmp_rhs
) || integer_onep (cmp_rhs
)))
1420 if (TREE_CODE (cmp_lhs
) != SSA_NAME
)
1423 /* If check_value_one is true, only the phi_args with value '1' will lead
1424 to loop exit. Otherwise, only the phi_args with value '0' will lead to
1426 check_value_one
= (((integer_onep (cmp_rhs
))
1427 ^ (gimple_cond_code (cmp_stmt
) == EQ_EXPR
))
1428 ^ ((exit_edge
->flags
& EDGE_TRUE_VALUE
) != 0));
1430 lhs_def_stmt
= SSA_NAME_DEF_STMT (cmp_lhs
);
1434 phi_stmt
= dyn_cast
<gphi
*> (lhs_def_stmt
);
1438 for (i
= 0; i
< gimple_phi_num_args (phi_stmt
); i
++)
1442 tree val
= gimple_phi_arg_def (phi_stmt
, i
);
1443 edge e
= gimple_phi_arg_edge (phi_stmt
, i
);
1445 if (!TREE_CONSTANT (val
) || !(integer_zerop (val
) || integer_onep (val
)))
1447 if ((check_value_one
^ integer_onep (val
)) == 1)
1449 if (EDGE_COUNT (e
->src
->succs
) != 1)
1451 predict_paths_leading_to_edge (e
, PRED_LOOP_EXIT
, NOT_TAKEN
);
1455 FOR_EACH_EDGE (e1
, ei
, e
->src
->preds
)
1456 predict_paths_leading_to_edge (e1
, PRED_LOOP_EXIT
, NOT_TAKEN
);
1460 /* Predict edge probabilities by exploiting loop structure. */
1463 predict_loops (void)
1467 /* Try to predict out blocks in a loop that are not part of a
1469 FOR_EACH_LOOP (loop
, 0)
1471 basic_block bb
, *bbs
;
1472 unsigned j
, n_exits
;
1474 struct tree_niter_desc niter_desc
;
1476 struct nb_iter_bound
*nb_iter
;
1477 enum tree_code loop_bound_code
= ERROR_MARK
;
1478 tree loop_bound_step
= NULL
;
1479 tree loop_bound_var
= NULL
;
1480 tree loop_iv_base
= NULL
;
1483 exits
= get_loop_exit_edges (loop
);
1484 n_exits
= exits
.length ();
1491 FOR_EACH_VEC_ELT (exits
, j
, ex
)
1494 HOST_WIDE_INT nitercst
;
1495 int max
= PARAM_VALUE (PARAM_MAX_PREDICTED_ITERATIONS
);
1497 enum br_predictor predictor
;
1499 predict_extra_loop_exits (ex
);
1501 if (number_of_iterations_exit (loop
, ex
, &niter_desc
, false, false))
1502 niter
= niter_desc
.niter
;
1503 if (!niter
|| TREE_CODE (niter_desc
.niter
) != INTEGER_CST
)
1504 niter
= loop_niter_by_eval (loop
, ex
);
1506 if (TREE_CODE (niter
) == INTEGER_CST
)
1508 if (tree_fits_uhwi_p (niter
)
1510 && compare_tree_int (niter
, max
- 1) == -1)
1511 nitercst
= tree_to_uhwi (niter
) + 1;
1514 predictor
= PRED_LOOP_ITERATIONS
;
1516 /* If we have just one exit and we can derive some information about
1517 the number of iterations of the loop from the statements inside
1518 the loop, use it to predict this exit. */
1519 else if (n_exits
== 1)
1521 nitercst
= estimated_stmt_executions_int (loop
);
1527 predictor
= PRED_LOOP_ITERATIONS_GUESSED
;
1532 /* If the prediction for number of iterations is zero, do not
1533 predict the exit edges. */
1537 probability
= ((REG_BR_PROB_BASE
+ nitercst
/ 2) / nitercst
);
1538 predict_edge (ex
, predictor
, probability
);
1542 /* Find information about loop bound variables. */
1543 for (nb_iter
= loop
->bounds
; nb_iter
;
1544 nb_iter
= nb_iter
->next
)
1546 && gimple_code (nb_iter
->stmt
) == GIMPLE_COND
)
1548 stmt
= as_a
<gcond
*> (nb_iter
->stmt
);
1551 if (!stmt
&& last_stmt (loop
->header
)
1552 && gimple_code (last_stmt (loop
->header
)) == GIMPLE_COND
)
1553 stmt
= as_a
<gcond
*> (last_stmt (loop
->header
));
1555 is_comparison_with_loop_invariant_p (stmt
, loop
,
1561 bbs
= get_loop_body (loop
);
1563 for (j
= 0; j
< loop
->num_nodes
; j
++)
1565 int header_found
= 0;
1571 /* Bypass loop heuristics on continue statement. These
1572 statements construct loops via "non-loop" constructs
1573 in the source language and are better to be handled
1575 if (predicted_by_p (bb
, PRED_CONTINUE
))
1578 /* Loop branch heuristics - predict an edge back to a
1579 loop's head as taken. */
1580 if (bb
== loop
->latch
)
1582 e
= find_edge (loop
->latch
, loop
->header
);
1586 predict_edge_def (e
, PRED_LOOP_BRANCH
, TAKEN
);
1590 /* Loop exit heuristics - predict an edge exiting the loop if the
1591 conditional has no loop header successors as not taken. */
1593 /* If we already used more reliable loop exit predictors, do not
1594 bother with PRED_LOOP_EXIT. */
1595 && !predicted_by_p (bb
, PRED_LOOP_ITERATIONS_GUESSED
)
1596 && !predicted_by_p (bb
, PRED_LOOP_ITERATIONS
))
1598 /* For loop with many exits we don't want to predict all exits
1599 with the pretty large probability, because if all exits are
1600 considered in row, the loop would be predicted to iterate
1601 almost never. The code to divide probability by number of
1602 exits is very rough. It should compute the number of exits
1603 taken in each patch through function (not the overall number
1604 of exits that might be a lot higher for loops with wide switch
1605 statements in them) and compute n-th square root.
1607 We limit the minimal probability by 2% to avoid
1608 EDGE_PROBABILITY_RELIABLE from trusting the branch prediction
1609 as this was causing regression in perl benchmark containing such
1612 int probability
= ((REG_BR_PROB_BASE
1613 - predictor_info
[(int) PRED_LOOP_EXIT
].hitrate
)
1615 if (probability
< HITRATE (2))
1616 probability
= HITRATE (2);
1617 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
1618 if (e
->dest
->index
< NUM_FIXED_BLOCKS
1619 || !flow_bb_inside_loop_p (loop
, e
->dest
))
1620 predict_edge (e
, PRED_LOOP_EXIT
, probability
);
1623 predict_iv_comparison (loop
, bb
, loop_bound_var
, loop_iv_base
,
1625 tree_to_shwi (loop_bound_step
));
1628 /* Free basic blocks from get_loop_body. */
1633 /* Attempt to predict probabilities of BB outgoing edges using local
1636 bb_estimate_probability_locally (basic_block bb
)
1638 rtx_insn
*last_insn
= BB_END (bb
);
1641 if (! can_predict_insn_p (last_insn
))
1643 cond
= get_condition (last_insn
, NULL
, false, false);
1647 /* Try "pointer heuristic."
1648 A comparison ptr == 0 is predicted as false.
1649 Similarly, a comparison ptr1 == ptr2 is predicted as false. */
1650 if (COMPARISON_P (cond
)
1651 && ((REG_P (XEXP (cond
, 0)) && REG_POINTER (XEXP (cond
, 0)))
1652 || (REG_P (XEXP (cond
, 1)) && REG_POINTER (XEXP (cond
, 1)))))
1654 if (GET_CODE (cond
) == EQ
)
1655 predict_insn_def (last_insn
, PRED_POINTER
, NOT_TAKEN
);
1656 else if (GET_CODE (cond
) == NE
)
1657 predict_insn_def (last_insn
, PRED_POINTER
, TAKEN
);
1661 /* Try "opcode heuristic."
1662 EQ tests are usually false and NE tests are usually true. Also,
1663 most quantities are positive, so we can make the appropriate guesses
1664 about signed comparisons against zero. */
1665 switch (GET_CODE (cond
))
1668 /* Unconditional branch. */
1669 predict_insn_def (last_insn
, PRED_UNCONDITIONAL
,
1670 cond
== const0_rtx
? NOT_TAKEN
: TAKEN
);
1675 /* Floating point comparisons appears to behave in a very
1676 unpredictable way because of special role of = tests in
1678 if (FLOAT_MODE_P (GET_MODE (XEXP (cond
, 0))))
1680 /* Comparisons with 0 are often used for booleans and there is
1681 nothing useful to predict about them. */
1682 else if (XEXP (cond
, 1) == const0_rtx
1683 || XEXP (cond
, 0) == const0_rtx
)
1686 predict_insn_def (last_insn
, PRED_OPCODE_NONEQUAL
, NOT_TAKEN
);
1691 /* Floating point comparisons appears to behave in a very
1692 unpredictable way because of special role of = tests in
1694 if (FLOAT_MODE_P (GET_MODE (XEXP (cond
, 0))))
1696 /* Comparisons with 0 are often used for booleans and there is
1697 nothing useful to predict about them. */
1698 else if (XEXP (cond
, 1) == const0_rtx
1699 || XEXP (cond
, 0) == const0_rtx
)
1702 predict_insn_def (last_insn
, PRED_OPCODE_NONEQUAL
, TAKEN
);
1706 predict_insn_def (last_insn
, PRED_FPOPCODE
, TAKEN
);
1710 predict_insn_def (last_insn
, PRED_FPOPCODE
, NOT_TAKEN
);
1715 if (XEXP (cond
, 1) == const0_rtx
|| XEXP (cond
, 1) == const1_rtx
1716 || XEXP (cond
, 1) == constm1_rtx
)
1717 predict_insn_def (last_insn
, PRED_OPCODE_POSITIVE
, NOT_TAKEN
);
1722 if (XEXP (cond
, 1) == const0_rtx
|| XEXP (cond
, 1) == const1_rtx
1723 || XEXP (cond
, 1) == constm1_rtx
)
1724 predict_insn_def (last_insn
, PRED_OPCODE_POSITIVE
, TAKEN
);
1732 /* Set edge->probability for each successor edge of BB. */
1734 guess_outgoing_edge_probabilities (basic_block bb
)
1736 bb_estimate_probability_locally (bb
);
1737 combine_predictions_for_insn (BB_END (bb
), bb
);
1740 static tree
expr_expected_value (tree
, bitmap
, enum br_predictor
*predictor
);
1742 /* Helper function for expr_expected_value. */
1745 expr_expected_value_1 (tree type
, tree op0
, enum tree_code code
,
1746 tree op1
, bitmap visited
, enum br_predictor
*predictor
)
1751 *predictor
= PRED_UNCONDITIONAL
;
1753 if (get_gimple_rhs_class (code
) == GIMPLE_SINGLE_RHS
)
1755 if (TREE_CONSTANT (op0
))
1758 if (code
!= SSA_NAME
)
1761 def
= SSA_NAME_DEF_STMT (op0
);
1763 /* If we were already here, break the infinite cycle. */
1764 if (!bitmap_set_bit (visited
, SSA_NAME_VERSION (op0
)))
1767 if (gimple_code (def
) == GIMPLE_PHI
)
1769 /* All the arguments of the PHI node must have the same constant
1771 int i
, n
= gimple_phi_num_args (def
);
1772 tree val
= NULL
, new_val
;
1774 for (i
= 0; i
< n
; i
++)
1776 tree arg
= PHI_ARG_DEF (def
, i
);
1777 enum br_predictor predictor2
;
1779 /* If this PHI has itself as an argument, we cannot
1780 determine the string length of this argument. However,
1781 if we can find an expected constant value for the other
1782 PHI args then we can still be sure that this is
1783 likely a constant. So be optimistic and just
1784 continue with the next argument. */
1785 if (arg
== PHI_RESULT (def
))
1788 new_val
= expr_expected_value (arg
, visited
, &predictor2
);
1790 /* It is difficult to combine value predictors. Simply assume
1791 that later predictor is weaker and take its prediction. */
1792 if (predictor
&& *predictor
< predictor2
)
1793 *predictor
= predictor2
;
1798 else if (!operand_equal_p (val
, new_val
, false))
1803 if (is_gimple_assign (def
))
1805 if (gimple_assign_lhs (def
) != op0
)
1808 return expr_expected_value_1 (TREE_TYPE (gimple_assign_lhs (def
)),
1809 gimple_assign_rhs1 (def
),
1810 gimple_assign_rhs_code (def
),
1811 gimple_assign_rhs2 (def
),
1812 visited
, predictor
);
1815 if (is_gimple_call (def
))
1817 tree decl
= gimple_call_fndecl (def
);
1820 if (gimple_call_internal_p (def
)
1821 && gimple_call_internal_fn (def
) == IFN_BUILTIN_EXPECT
)
1823 gcc_assert (gimple_call_num_args (def
) == 3);
1824 tree val
= gimple_call_arg (def
, 0);
1825 if (TREE_CONSTANT (val
))
1829 tree val2
= gimple_call_arg (def
, 2);
1830 gcc_assert (TREE_CODE (val2
) == INTEGER_CST
1831 && tree_fits_uhwi_p (val2
)
1832 && tree_to_uhwi (val2
) < END_PREDICTORS
);
1833 *predictor
= (enum br_predictor
) tree_to_uhwi (val2
);
1835 return gimple_call_arg (def
, 1);
1839 if (DECL_BUILT_IN_CLASS (decl
) == BUILT_IN_NORMAL
)
1840 switch (DECL_FUNCTION_CODE (decl
))
1842 case BUILT_IN_EXPECT
:
1845 if (gimple_call_num_args (def
) != 2)
1847 val
= gimple_call_arg (def
, 0);
1848 if (TREE_CONSTANT (val
))
1851 *predictor
= PRED_BUILTIN_EXPECT
;
1852 return gimple_call_arg (def
, 1);
1855 case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_N
:
1856 case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_1
:
1857 case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_2
:
1858 case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_4
:
1859 case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_8
:
1860 case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_16
:
1861 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE
:
1862 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_N
:
1863 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_1
:
1864 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_2
:
1865 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_4
:
1866 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_8
:
1867 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_16
:
1868 /* Assume that any given atomic operation has low contention,
1869 and thus the compare-and-swap operation succeeds. */
1871 *predictor
= PRED_COMPARE_AND_SWAP
;
1872 return boolean_true_node
;
1881 if (get_gimple_rhs_class (code
) == GIMPLE_BINARY_RHS
)
1884 enum br_predictor predictor2
;
1885 op0
= expr_expected_value (op0
, visited
, predictor
);
1888 op1
= expr_expected_value (op1
, visited
, &predictor2
);
1889 if (predictor
&& *predictor
< predictor2
)
1890 *predictor
= predictor2
;
1893 res
= fold_build2 (code
, type
, op0
, op1
);
1894 if (TREE_CONSTANT (res
))
1898 if (get_gimple_rhs_class (code
) == GIMPLE_UNARY_RHS
)
1901 op0
= expr_expected_value (op0
, visited
, predictor
);
1904 res
= fold_build1 (code
, type
, op0
);
1905 if (TREE_CONSTANT (res
))
1912 /* Return constant EXPR will likely have at execution time, NULL if unknown.
1913 The function is used by builtin_expect branch predictor so the evidence
1914 must come from this construct and additional possible constant folding.
1916 We may want to implement more involved value guess (such as value range
1917 propagation based prediction), but such tricks shall go to new
1921 expr_expected_value (tree expr
, bitmap visited
,
1922 enum br_predictor
*predictor
)
1924 enum tree_code code
;
1927 if (TREE_CONSTANT (expr
))
1930 *predictor
= PRED_UNCONDITIONAL
;
1934 extract_ops_from_tree (expr
, &code
, &op0
, &op1
);
1935 return expr_expected_value_1 (TREE_TYPE (expr
),
1936 op0
, code
, op1
, visited
, predictor
);
1939 /* Predict using opcode of the last statement in basic block. */
1941 tree_predict_by_opcode (basic_block bb
)
1943 gimple
*stmt
= last_stmt (bb
);
1951 enum br_predictor predictor
;
1953 if (!stmt
|| gimple_code (stmt
) != GIMPLE_COND
)
1955 FOR_EACH_EDGE (then_edge
, ei
, bb
->succs
)
1956 if (then_edge
->flags
& EDGE_TRUE_VALUE
)
1958 op0
= gimple_cond_lhs (stmt
);
1959 op1
= gimple_cond_rhs (stmt
);
1960 cmp
= gimple_cond_code (stmt
);
1961 type
= TREE_TYPE (op0
);
1962 visited
= BITMAP_ALLOC (NULL
);
1963 val
= expr_expected_value_1 (boolean_type_node
, op0
, cmp
, op1
, visited
,
1965 BITMAP_FREE (visited
);
1966 if (val
&& TREE_CODE (val
) == INTEGER_CST
)
1968 if (predictor
== PRED_BUILTIN_EXPECT
)
1970 int percent
= PARAM_VALUE (BUILTIN_EXPECT_PROBABILITY
);
1972 gcc_assert (percent
>= 0 && percent
<= 100);
1973 if (integer_zerop (val
))
1974 percent
= 100 - percent
;
1975 predict_edge (then_edge
, PRED_BUILTIN_EXPECT
, HITRATE (percent
));
1978 predict_edge (then_edge
, predictor
,
1979 integer_zerop (val
) ? NOT_TAKEN
: TAKEN
);
1981 /* Try "pointer heuristic."
1982 A comparison ptr == 0 is predicted as false.
1983 Similarly, a comparison ptr1 == ptr2 is predicted as false. */
1984 if (POINTER_TYPE_P (type
))
1987 predict_edge_def (then_edge
, PRED_TREE_POINTER
, NOT_TAKEN
);
1988 else if (cmp
== NE_EXPR
)
1989 predict_edge_def (then_edge
, PRED_TREE_POINTER
, TAKEN
);
1993 /* Try "opcode heuristic."
1994 EQ tests are usually false and NE tests are usually true. Also,
1995 most quantities are positive, so we can make the appropriate guesses
1996 about signed comparisons against zero. */
2001 /* Floating point comparisons appears to behave in a very
2002 unpredictable way because of special role of = tests in
2004 if (FLOAT_TYPE_P (type
))
2006 /* Comparisons with 0 are often used for booleans and there is
2007 nothing useful to predict about them. */
2008 else if (integer_zerop (op0
) || integer_zerop (op1
))
2011 predict_edge_def (then_edge
, PRED_TREE_OPCODE_NONEQUAL
, NOT_TAKEN
);
2016 /* Floating point comparisons appears to behave in a very
2017 unpredictable way because of special role of = tests in
2019 if (FLOAT_TYPE_P (type
))
2021 /* Comparisons with 0 are often used for booleans and there is
2022 nothing useful to predict about them. */
2023 else if (integer_zerop (op0
)
2024 || integer_zerop (op1
))
2027 predict_edge_def (then_edge
, PRED_TREE_OPCODE_NONEQUAL
, TAKEN
);
2031 predict_edge_def (then_edge
, PRED_TREE_FPOPCODE
, TAKEN
);
2034 case UNORDERED_EXPR
:
2035 predict_edge_def (then_edge
, PRED_TREE_FPOPCODE
, NOT_TAKEN
);
2040 if (integer_zerop (op1
)
2041 || integer_onep (op1
)
2042 || integer_all_onesp (op1
)
2045 || real_minus_onep (op1
))
2046 predict_edge_def (then_edge
, PRED_TREE_OPCODE_POSITIVE
, NOT_TAKEN
);
2051 if (integer_zerop (op1
)
2052 || integer_onep (op1
)
2053 || integer_all_onesp (op1
)
2056 || real_minus_onep (op1
))
2057 predict_edge_def (then_edge
, PRED_TREE_OPCODE_POSITIVE
, TAKEN
);
2065 /* Try to guess whether the value of return means error code. */
2067 static enum br_predictor
2068 return_prediction (tree val
, enum prediction
*prediction
)
2072 return PRED_NO_PREDICTION
;
2073 /* Different heuristics for pointers and scalars. */
2074 if (POINTER_TYPE_P (TREE_TYPE (val
)))
2076 /* NULL is usually not returned. */
2077 if (integer_zerop (val
))
2079 *prediction
= NOT_TAKEN
;
2080 return PRED_NULL_RETURN
;
2083 else if (INTEGRAL_TYPE_P (TREE_TYPE (val
)))
2085 /* Negative return values are often used to indicate
2087 if (TREE_CODE (val
) == INTEGER_CST
2088 && tree_int_cst_sgn (val
) < 0)
2090 *prediction
= NOT_TAKEN
;
2091 return PRED_NEGATIVE_RETURN
;
2093 /* Constant return values seems to be commonly taken.
2094 Zero/one often represent booleans so exclude them from the
2096 if (TREE_CONSTANT (val
)
2097 && (!integer_zerop (val
) && !integer_onep (val
)))
2099 *prediction
= TAKEN
;
2100 return PRED_CONST_RETURN
;
2103 return PRED_NO_PREDICTION
;
2106 /* Find the basic block with return expression and look up for possible
2107 return value trying to apply RETURN_PREDICTION heuristics. */
2109 apply_return_prediction (void)
2111 greturn
*return_stmt
= NULL
;
2115 int phi_num_args
, i
;
2116 enum br_predictor pred
;
2117 enum prediction direction
;
2120 FOR_EACH_EDGE (e
, ei
, EXIT_BLOCK_PTR_FOR_FN (cfun
)->preds
)
2122 gimple
*last
= last_stmt (e
->src
);
2124 && gimple_code (last
) == GIMPLE_RETURN
)
2126 return_stmt
= as_a
<greturn
*> (last
);
2132 return_val
= gimple_return_retval (return_stmt
);
2135 if (TREE_CODE (return_val
) != SSA_NAME
2136 || !SSA_NAME_DEF_STMT (return_val
)
2137 || gimple_code (SSA_NAME_DEF_STMT (return_val
)) != GIMPLE_PHI
)
2139 phi
= as_a
<gphi
*> (SSA_NAME_DEF_STMT (return_val
));
2140 phi_num_args
= gimple_phi_num_args (phi
);
2141 pred
= return_prediction (PHI_ARG_DEF (phi
, 0), &direction
);
2143 /* Avoid the degenerate case where all return values form the function
2144 belongs to same category (ie they are all positive constants)
2145 so we can hardly say something about them. */
2146 for (i
= 1; i
< phi_num_args
; i
++)
2147 if (pred
!= return_prediction (PHI_ARG_DEF (phi
, i
), &direction
))
2149 if (i
!= phi_num_args
)
2150 for (i
= 0; i
< phi_num_args
; i
++)
2152 pred
= return_prediction (PHI_ARG_DEF (phi
, i
), &direction
);
2153 if (pred
!= PRED_NO_PREDICTION
)
2154 predict_paths_leading_to_edge (gimple_phi_arg_edge (phi
, i
), pred
,
2159 /* Look for basic block that contains unlikely to happen events
2160 (such as noreturn calls) and mark all paths leading to execution
2161 of this basic blocks as unlikely. */
2164 tree_bb_level_predictions (void)
2167 bool has_return_edges
= false;
2171 FOR_EACH_EDGE (e
, ei
, EXIT_BLOCK_PTR_FOR_FN (cfun
)->preds
)
2172 if (!(e
->flags
& (EDGE_ABNORMAL
| EDGE_FAKE
| EDGE_EH
)))
2174 has_return_edges
= true;
2178 apply_return_prediction ();
2180 FOR_EACH_BB_FN (bb
, cfun
)
2182 gimple_stmt_iterator gsi
;
2184 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
2186 gimple
*stmt
= gsi_stmt (gsi
);
2189 if (is_gimple_call (stmt
))
2191 if ((gimple_call_flags (stmt
) & ECF_NORETURN
)
2192 && has_return_edges
)
2193 predict_paths_leading_to (bb
, PRED_NORETURN
,
2195 decl
= gimple_call_fndecl (stmt
);
2197 && lookup_attribute ("cold",
2198 DECL_ATTRIBUTES (decl
)))
2199 predict_paths_leading_to (bb
, PRED_COLD_FUNCTION
,
2202 else if (gimple_code (stmt
) == GIMPLE_PREDICT
)
2204 predict_paths_leading_to (bb
, gimple_predict_predictor (stmt
),
2205 gimple_predict_outcome (stmt
));
2206 /* Keep GIMPLE_PREDICT around so early inlining will propagate
2207 hints to callers. */
2213 /* Callback for hash_map::traverse, asserts that the pointer map is
2217 assert_is_empty (const_basic_block
const &, edge_prediction
*const &value
,
2220 gcc_assert (!value
);
2224 /* Predict branch probabilities and estimate profile for basic block BB. */
2227 tree_estimate_probability_bb (basic_block bb
)
2233 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
2235 /* Predict edges to user labels with attributes. */
2236 if (e
->dest
!= EXIT_BLOCK_PTR_FOR_FN (cfun
))
2238 gimple_stmt_iterator gi
;
2239 for (gi
= gsi_start_bb (e
->dest
); !gsi_end_p (gi
); gsi_next (&gi
))
2241 glabel
*label_stmt
= dyn_cast
<glabel
*> (gsi_stmt (gi
));
2246 decl
= gimple_label_label (label_stmt
);
2247 if (DECL_ARTIFICIAL (decl
))
2250 /* Finally, we have a user-defined label. */
2251 if (lookup_attribute ("cold", DECL_ATTRIBUTES (decl
)))
2252 predict_edge_def (e
, PRED_COLD_LABEL
, NOT_TAKEN
);
2253 else if (lookup_attribute ("hot", DECL_ATTRIBUTES (decl
)))
2254 predict_edge_def (e
, PRED_HOT_LABEL
, TAKEN
);
2258 /* Predict early returns to be probable, as we've already taken
2259 care for error returns and other cases are often used for
2260 fast paths through function.
2262 Since we've already removed the return statements, we are
2263 looking for CFG like:
2273 if (e
->dest
!= bb
->next_bb
2274 && e
->dest
!= EXIT_BLOCK_PTR_FOR_FN (cfun
)
2275 && single_succ_p (e
->dest
)
2276 && single_succ_edge (e
->dest
)->dest
== EXIT_BLOCK_PTR_FOR_FN (cfun
)
2277 && (last
= last_stmt (e
->dest
)) != NULL
2278 && gimple_code (last
) == GIMPLE_RETURN
)
2283 if (single_succ_p (bb
))
2285 FOR_EACH_EDGE (e1
, ei1
, bb
->preds
)
2286 if (!predicted_by_p (e1
->src
, PRED_NULL_RETURN
)
2287 && !predicted_by_p (e1
->src
, PRED_CONST_RETURN
)
2288 && !predicted_by_p (e1
->src
, PRED_NEGATIVE_RETURN
))
2289 predict_edge_def (e1
, PRED_TREE_EARLY_RETURN
, NOT_TAKEN
);
2292 if (!predicted_by_p (e
->src
, PRED_NULL_RETURN
)
2293 && !predicted_by_p (e
->src
, PRED_CONST_RETURN
)
2294 && !predicted_by_p (e
->src
, PRED_NEGATIVE_RETURN
))
2295 predict_edge_def (e
, PRED_TREE_EARLY_RETURN
, NOT_TAKEN
);
2298 /* Look for block we are guarding (ie we dominate it,
2299 but it doesn't postdominate us). */
2300 if (e
->dest
!= EXIT_BLOCK_PTR_FOR_FN (cfun
) && e
->dest
!= bb
2301 && dominated_by_p (CDI_DOMINATORS
, e
->dest
, e
->src
)
2302 && !dominated_by_p (CDI_POST_DOMINATORS
, e
->src
, e
->dest
))
2304 gimple_stmt_iterator bi
;
2306 /* The call heuristic claims that a guarded function call
2307 is improbable. This is because such calls are often used
2308 to signal exceptional situations such as printing error
2310 for (bi
= gsi_start_bb (e
->dest
); !gsi_end_p (bi
);
2313 gimple
*stmt
= gsi_stmt (bi
);
2314 if (is_gimple_call (stmt
)
2315 /* Constant and pure calls are hardly used to signalize
2316 something exceptional. */
2317 && gimple_has_side_effects (stmt
))
2319 predict_edge_def (e
, PRED_CALL
, NOT_TAKEN
);
2325 tree_predict_by_opcode (bb
);
2328 /* Predict branch probabilities and estimate profile of the tree CFG.
2329 This function can be called from the loop optimizers to recompute
2330 the profile information. */
2333 tree_estimate_probability (void)
2337 add_noreturn_fake_exit_edges ();
2338 connect_infinite_loops_to_exit ();
2339 /* We use loop_niter_by_eval, which requires that the loops have
2341 create_preheaders (CP_SIMPLE_PREHEADERS
);
2342 calculate_dominance_info (CDI_POST_DOMINATORS
);
2344 bb_predictions
= new hash_map
<const_basic_block
, edge_prediction
*>;
2345 tree_bb_level_predictions ();
2346 record_loop_exits ();
2348 if (number_of_loops (cfun
) > 1)
2351 FOR_EACH_BB_FN (bb
, cfun
)
2352 tree_estimate_probability_bb (bb
);
2354 FOR_EACH_BB_FN (bb
, cfun
)
2355 combine_predictions_for_bb (bb
);
2358 bb_predictions
->traverse
<void *, assert_is_empty
> (NULL
);
2360 delete bb_predictions
;
2361 bb_predictions
= NULL
;
2363 estimate_bb_frequencies (false);
2364 free_dominance_info (CDI_POST_DOMINATORS
);
2365 remove_fake_exit_edges ();
2368 /* Predict edges to successors of CUR whose sources are not postdominated by
2369 BB by PRED and recurse to all postdominators. */
2372 predict_paths_for_bb (basic_block cur
, basic_block bb
,
2373 enum br_predictor pred
,
2374 enum prediction taken
,
2381 /* We are looking for all edges forming edge cut induced by
2382 set of all blocks postdominated by BB. */
2383 FOR_EACH_EDGE (e
, ei
, cur
->preds
)
2384 if (e
->src
->index
>= NUM_FIXED_BLOCKS
2385 && !dominated_by_p (CDI_POST_DOMINATORS
, e
->src
, bb
))
2391 /* Ignore fake edges and eh, we predict them as not taken anyway. */
2392 if (e
->flags
& (EDGE_EH
| EDGE_FAKE
))
2394 gcc_assert (bb
== cur
|| dominated_by_p (CDI_POST_DOMINATORS
, cur
, bb
));
2396 /* See if there is an edge from e->src that is not abnormal
2397 and does not lead to BB. */
2398 FOR_EACH_EDGE (e2
, ei2
, e
->src
->succs
)
2400 && !(e2
->flags
& (EDGE_EH
| EDGE_FAKE
))
2401 && !dominated_by_p (CDI_POST_DOMINATORS
, e2
->dest
, bb
))
2407 /* If there is non-abnormal path leaving e->src, predict edge
2408 using predictor. Otherwise we need to look for paths
2411 The second may lead to infinite loop in the case we are predicitng
2412 regions that are only reachable by abnormal edges. We simply
2413 prevent visiting given BB twice. */
2415 predict_edge_def (e
, pred
, taken
);
2416 else if (bitmap_set_bit (visited
, e
->src
->index
))
2417 predict_paths_for_bb (e
->src
, e
->src
, pred
, taken
, visited
);
2419 for (son
= first_dom_son (CDI_POST_DOMINATORS
, cur
);
2421 son
= next_dom_son (CDI_POST_DOMINATORS
, son
))
2422 predict_paths_for_bb (son
, bb
, pred
, taken
, visited
);
2425 /* Sets branch probabilities according to PREDiction and
2429 predict_paths_leading_to (basic_block bb
, enum br_predictor pred
,
2430 enum prediction taken
)
2432 bitmap visited
= BITMAP_ALLOC (NULL
);
2433 predict_paths_for_bb (bb
, bb
, pred
, taken
, visited
);
2434 BITMAP_FREE (visited
);
2437 /* Like predict_paths_leading_to but take edge instead of basic block. */
2440 predict_paths_leading_to_edge (edge e
, enum br_predictor pred
,
2441 enum prediction taken
)
2443 bool has_nonloop_edge
= false;
2447 basic_block bb
= e
->src
;
2448 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
2449 if (e2
->dest
!= e
->src
&& e2
->dest
!= e
->dest
2450 && !(e
->flags
& (EDGE_EH
| EDGE_FAKE
))
2451 && !dominated_by_p (CDI_POST_DOMINATORS
, e
->src
, e2
->dest
))
2453 has_nonloop_edge
= true;
2456 if (!has_nonloop_edge
)
2458 bitmap visited
= BITMAP_ALLOC (NULL
);
2459 predict_paths_for_bb (bb
, bb
, pred
, taken
, visited
);
2460 BITMAP_FREE (visited
);
2463 predict_edge_def (e
, pred
, taken
);
2466 /* This is used to carry information about basic blocks. It is
2467 attached to the AUX field of the standard CFG block. */
2471 /* Estimated frequency of execution of basic_block. */
2474 /* To keep queue of basic blocks to process. */
2477 /* Number of predecessors we need to visit first. */
2481 /* Similar information for edges. */
2482 struct edge_prob_info
2484 /* In case edge is a loopback edge, the probability edge will be reached
2485 in case header is. Estimated number of iterations of the loop can be
2486 then computed as 1 / (1 - back_edge_prob). */
2487 sreal back_edge_prob
;
2488 /* True if the edge is a loopback edge in the natural loop. */
2489 unsigned int back_edge
:1;
2492 #define BLOCK_INFO(B) ((block_info *) (B)->aux)
2494 #define EDGE_INFO(E) ((edge_prob_info *) (E)->aux)
2496 /* Helper function for estimate_bb_frequencies.
2497 Propagate the frequencies in blocks marked in
2498 TOVISIT, starting in HEAD. */
2501 propagate_freq (basic_block head
, bitmap tovisit
)
2510 /* For each basic block we need to visit count number of his predecessors
2511 we need to visit first. */
2512 EXECUTE_IF_SET_IN_BITMAP (tovisit
, 0, i
, bi
)
2517 bb
= BASIC_BLOCK_FOR_FN (cfun
, i
);
2519 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
2521 bool visit
= bitmap_bit_p (tovisit
, e
->src
->index
);
2523 if (visit
&& !(e
->flags
& EDGE_DFS_BACK
))
2525 else if (visit
&& dump_file
&& !EDGE_INFO (e
)->back_edge
)
2527 "Irreducible region hit, ignoring edge to %i->%i\n",
2528 e
->src
->index
, bb
->index
);
2530 BLOCK_INFO (bb
)->npredecessors
= count
;
2531 /* When function never returns, we will never process exit block. */
2532 if (!count
&& bb
== EXIT_BLOCK_PTR_FOR_FN (cfun
))
2533 bb
->count
= bb
->frequency
= 0;
2536 BLOCK_INFO (head
)->frequency
= 1;
2538 for (bb
= head
; bb
; bb
= nextbb
)
2541 sreal cyclic_probability
= 0;
2542 sreal frequency
= 0;
2544 nextbb
= BLOCK_INFO (bb
)->next
;
2545 BLOCK_INFO (bb
)->next
= NULL
;
2547 /* Compute frequency of basic block. */
2551 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
2552 gcc_assert (!bitmap_bit_p (tovisit
, e
->src
->index
)
2553 || (e
->flags
& EDGE_DFS_BACK
));
2555 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
2556 if (EDGE_INFO (e
)->back_edge
)
2558 cyclic_probability
+= EDGE_INFO (e
)->back_edge_prob
;
2560 else if (!(e
->flags
& EDGE_DFS_BACK
))
2562 /* frequency += (e->probability
2563 * BLOCK_INFO (e->src)->frequency /
2564 REG_BR_PROB_BASE); */
2566 sreal tmp
= e
->probability
;
2567 tmp
*= BLOCK_INFO (e
->src
)->frequency
;
2568 tmp
*= real_inv_br_prob_base
;
2572 if (cyclic_probability
== 0)
2574 BLOCK_INFO (bb
)->frequency
= frequency
;
2578 if (cyclic_probability
> real_almost_one
)
2579 cyclic_probability
= real_almost_one
;
2581 /* BLOCK_INFO (bb)->frequency = frequency
2582 / (1 - cyclic_probability) */
2584 cyclic_probability
= sreal (1) - cyclic_probability
;
2585 BLOCK_INFO (bb
)->frequency
= frequency
/ cyclic_probability
;
2589 bitmap_clear_bit (tovisit
, bb
->index
);
2591 e
= find_edge (bb
, head
);
2594 /* EDGE_INFO (e)->back_edge_prob
2595 = ((e->probability * BLOCK_INFO (bb)->frequency)
2596 / REG_BR_PROB_BASE); */
2598 sreal tmp
= e
->probability
;
2599 tmp
*= BLOCK_INFO (bb
)->frequency
;
2600 EDGE_INFO (e
)->back_edge_prob
= tmp
* real_inv_br_prob_base
;
2603 /* Propagate to successor blocks. */
2604 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
2605 if (!(e
->flags
& EDGE_DFS_BACK
)
2606 && BLOCK_INFO (e
->dest
)->npredecessors
)
2608 BLOCK_INFO (e
->dest
)->npredecessors
--;
2609 if (!BLOCK_INFO (e
->dest
)->npredecessors
)
2614 BLOCK_INFO (last
)->next
= e
->dest
;
2622 /* Estimate frequencies in loops at same nest level. */
2625 estimate_loops_at_level (struct loop
*first_loop
)
2629 for (loop
= first_loop
; loop
; loop
= loop
->next
)
2634 bitmap tovisit
= BITMAP_ALLOC (NULL
);
2636 estimate_loops_at_level (loop
->inner
);
2638 /* Find current loop back edge and mark it. */
2639 e
= loop_latch_edge (loop
);
2640 EDGE_INFO (e
)->back_edge
= 1;
2642 bbs
= get_loop_body (loop
);
2643 for (i
= 0; i
< loop
->num_nodes
; i
++)
2644 bitmap_set_bit (tovisit
, bbs
[i
]->index
);
2646 propagate_freq (loop
->header
, tovisit
);
2647 BITMAP_FREE (tovisit
);
2651 /* Propagates frequencies through structure of loops. */
2654 estimate_loops (void)
2656 bitmap tovisit
= BITMAP_ALLOC (NULL
);
2659 /* Start by estimating the frequencies in the loops. */
2660 if (number_of_loops (cfun
) > 1)
2661 estimate_loops_at_level (current_loops
->tree_root
->inner
);
2663 /* Now propagate the frequencies through all the blocks. */
2664 FOR_ALL_BB_FN (bb
, cfun
)
2666 bitmap_set_bit (tovisit
, bb
->index
);
2668 propagate_freq (ENTRY_BLOCK_PTR_FOR_FN (cfun
), tovisit
);
2669 BITMAP_FREE (tovisit
);
2672 /* Drop the profile for NODE to guessed, and update its frequency based on
2673 whether it is expected to be hot given the CALL_COUNT. */
2676 drop_profile (struct cgraph_node
*node
, gcov_type call_count
)
2678 struct function
*fn
= DECL_STRUCT_FUNCTION (node
->decl
);
2679 /* In the case where this was called by another function with a
2680 dropped profile, call_count will be 0. Since there are no
2681 non-zero call counts to this function, we don't know for sure
2682 whether it is hot, and therefore it will be marked normal below. */
2683 bool hot
= maybe_hot_count_p (NULL
, call_count
);
2687 "Dropping 0 profile for %s/%i. %s based on calls.\n",
2688 node
->name (), node
->order
,
2689 hot
? "Function is hot" : "Function is normal");
2690 /* We only expect to miss profiles for functions that are reached
2691 via non-zero call edges in cases where the function may have
2692 been linked from another module or library (COMDATs and extern
2693 templates). See the comments below for handle_missing_profiles.
2694 Also, only warn in cases where the missing counts exceed the
2695 number of training runs. In certain cases with an execv followed
2696 by a no-return call the profile for the no-return call is not
2697 dumped and there can be a mismatch. */
2698 if (!DECL_COMDAT (node
->decl
) && !DECL_EXTERNAL (node
->decl
)
2699 && call_count
> profile_info
->runs
)
2701 if (flag_profile_correction
)
2705 "Missing counts for called function %s/%i\n",
2706 node
->name (), node
->order
);
2709 warning (0, "Missing counts for called function %s/%i",
2710 node
->name (), node
->order
);
2713 profile_status_for_fn (fn
)
2714 = (flag_guess_branch_prob
? PROFILE_GUESSED
: PROFILE_ABSENT
);
2716 = hot
? NODE_FREQUENCY_HOT
: NODE_FREQUENCY_NORMAL
;
2719 /* In the case of COMDAT routines, multiple object files will contain the same
2720 function and the linker will select one for the binary. In that case
2721 all the other copies from the profile instrument binary will be missing
2722 profile counts. Look for cases where this happened, due to non-zero
2723 call counts going to 0-count functions, and drop the profile to guessed
2724 so that we can use the estimated probabilities and avoid optimizing only
2727 The other case where the profile may be missing is when the routine
2728 is not going to be emitted to the object file, e.g. for "extern template"
2729 class methods. Those will be marked DECL_EXTERNAL. Emit a warning in
2730 all other cases of non-zero calls to 0-count functions. */
2733 handle_missing_profiles (void)
2735 struct cgraph_node
*node
;
2736 int unlikely_count_fraction
= PARAM_VALUE (UNLIKELY_BB_COUNT_FRACTION
);
2737 vec
<struct cgraph_node
*> worklist
;
2738 worklist
.create (64);
2740 /* See if 0 count function has non-0 count callers. In this case we
2741 lost some profile. Drop its function profile to PROFILE_GUESSED. */
2742 FOR_EACH_DEFINED_FUNCTION (node
)
2744 struct cgraph_edge
*e
;
2745 gcov_type call_count
= 0;
2746 gcov_type max_tp_first_run
= 0;
2747 struct function
*fn
= DECL_STRUCT_FUNCTION (node
->decl
);
2751 for (e
= node
->callers
; e
; e
= e
->next_caller
)
2753 call_count
+= e
->count
;
2755 if (e
->caller
->tp_first_run
> max_tp_first_run
)
2756 max_tp_first_run
= e
->caller
->tp_first_run
;
2759 /* If time profile is missing, let assign the maximum that comes from
2760 caller functions. */
2761 if (!node
->tp_first_run
&& max_tp_first_run
)
2762 node
->tp_first_run
= max_tp_first_run
+ 1;
2766 && (call_count
* unlikely_count_fraction
>= profile_info
->runs
))
2768 drop_profile (node
, call_count
);
2769 worklist
.safe_push (node
);
2773 /* Propagate the profile dropping to other 0-count COMDATs that are
2774 potentially called by COMDATs we already dropped the profile on. */
2775 while (worklist
.length () > 0)
2777 struct cgraph_edge
*e
;
2779 node
= worklist
.pop ();
2780 for (e
= node
->callees
; e
; e
= e
->next_caller
)
2782 struct cgraph_node
*callee
= e
->callee
;
2783 struct function
*fn
= DECL_STRUCT_FUNCTION (callee
->decl
);
2785 if (callee
->count
> 0)
2787 if (DECL_COMDAT (callee
->decl
) && fn
&& fn
->cfg
2788 && profile_status_for_fn (fn
) == PROFILE_READ
)
2790 drop_profile (node
, 0);
2791 worklist
.safe_push (callee
);
2795 worklist
.release ();
2798 /* Convert counts measured by profile driven feedback to frequencies.
2799 Return nonzero iff there was any nonzero execution count. */
2802 counts_to_freqs (void)
2804 gcov_type count_max
, true_count_max
= 0;
2807 /* Don't overwrite the estimated frequencies when the profile for
2808 the function is missing. We may drop this function PROFILE_GUESSED
2809 later in drop_profile (). */
2810 if (!flag_auto_profile
&& !ENTRY_BLOCK_PTR_FOR_FN (cfun
)->count
)
2813 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR_FOR_FN (cfun
), NULL
, next_bb
)
2814 true_count_max
= MAX (bb
->count
, true_count_max
);
2816 count_max
= MAX (true_count_max
, 1);
2817 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR_FOR_FN (cfun
), NULL
, next_bb
)
2818 bb
->frequency
= (bb
->count
* BB_FREQ_MAX
+ count_max
/ 2) / count_max
;
2820 return true_count_max
;
2823 /* Return true if function is likely to be expensive, so there is no point to
2824 optimize performance of prologue, epilogue or do inlining at the expense
2825 of code size growth. THRESHOLD is the limit of number of instructions
2826 function can execute at average to be still considered not expensive. */
2829 expensive_function_p (int threshold
)
2831 unsigned int sum
= 0;
2835 /* We can not compute accurately for large thresholds due to scaled
2837 gcc_assert (threshold
<= BB_FREQ_MAX
);
2839 /* Frequencies are out of range. This either means that function contains
2840 internal loop executing more than BB_FREQ_MAX times or profile feedback
2841 is available and function has not been executed at all. */
2842 if (ENTRY_BLOCK_PTR_FOR_FN (cfun
)->frequency
== 0)
2845 /* Maximally BB_FREQ_MAX^2 so overflow won't happen. */
2846 limit
= ENTRY_BLOCK_PTR_FOR_FN (cfun
)->frequency
* threshold
;
2847 FOR_EACH_BB_FN (bb
, cfun
)
2851 FOR_BB_INSNS (bb
, insn
)
2852 if (active_insn_p (insn
))
2854 sum
+= bb
->frequency
;
2863 /* Estimate and propagate basic block frequencies using the given branch
2864 probabilities. If FORCE is true, the frequencies are used to estimate
2865 the counts even when there are already non-zero profile counts. */
2868 estimate_bb_frequencies (bool force
)
2873 if (force
|| profile_status_for_fn (cfun
) != PROFILE_READ
|| !counts_to_freqs ())
2875 static int real_values_initialized
= 0;
2877 if (!real_values_initialized
)
2879 real_values_initialized
= 1;
2880 real_br_prob_base
= REG_BR_PROB_BASE
;
2881 real_bb_freq_max
= BB_FREQ_MAX
;
2882 real_one_half
= sreal (1, -1);
2883 real_inv_br_prob_base
= sreal (1) / real_br_prob_base
;
2884 real_almost_one
= sreal (1) - real_inv_br_prob_base
;
2887 mark_dfs_back_edges ();
2889 single_succ_edge (ENTRY_BLOCK_PTR_FOR_FN (cfun
))->probability
=
2892 /* Set up block info for each basic block. */
2893 alloc_aux_for_blocks (sizeof (block_info
));
2894 alloc_aux_for_edges (sizeof (edge_prob_info
));
2895 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR_FOR_FN (cfun
), NULL
, next_bb
)
2900 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
2902 EDGE_INFO (e
)->back_edge_prob
= e
->probability
;
2903 EDGE_INFO (e
)->back_edge_prob
*= real_inv_br_prob_base
;
2907 /* First compute frequencies locally for each loop from innermost
2908 to outermost to examine frequencies for back edges. */
2912 FOR_EACH_BB_FN (bb
, cfun
)
2913 if (freq_max
< BLOCK_INFO (bb
)->frequency
)
2914 freq_max
= BLOCK_INFO (bb
)->frequency
;
2916 freq_max
= real_bb_freq_max
/ freq_max
;
2917 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR_FOR_FN (cfun
), NULL
, next_bb
)
2919 sreal tmp
= BLOCK_INFO (bb
)->frequency
* freq_max
+ real_one_half
;
2920 bb
->frequency
= tmp
.to_int ();
2923 free_aux_for_blocks ();
2924 free_aux_for_edges ();
2926 compute_function_frequency ();
2929 /* Decide whether function is hot, cold or unlikely executed. */
2931 compute_function_frequency (void)
2934 struct cgraph_node
*node
= cgraph_node::get (current_function_decl
);
2936 if (DECL_STATIC_CONSTRUCTOR (current_function_decl
)
2937 || MAIN_NAME_P (DECL_NAME (current_function_decl
)))
2938 node
->only_called_at_startup
= true;
2939 if (DECL_STATIC_DESTRUCTOR (current_function_decl
))
2940 node
->only_called_at_exit
= true;
2942 if (profile_status_for_fn (cfun
) != PROFILE_READ
)
2944 int flags
= flags_from_decl_or_type (current_function_decl
);
2945 if (lookup_attribute ("cold", DECL_ATTRIBUTES (current_function_decl
))
2947 node
->frequency
= NODE_FREQUENCY_UNLIKELY_EXECUTED
;
2948 else if (lookup_attribute ("hot", DECL_ATTRIBUTES (current_function_decl
))
2950 node
->frequency
= NODE_FREQUENCY_HOT
;
2951 else if (flags
& ECF_NORETURN
)
2952 node
->frequency
= NODE_FREQUENCY_EXECUTED_ONCE
;
2953 else if (MAIN_NAME_P (DECL_NAME (current_function_decl
)))
2954 node
->frequency
= NODE_FREQUENCY_EXECUTED_ONCE
;
2955 else if (DECL_STATIC_CONSTRUCTOR (current_function_decl
)
2956 || DECL_STATIC_DESTRUCTOR (current_function_decl
))
2957 node
->frequency
= NODE_FREQUENCY_EXECUTED_ONCE
;
2961 /* Only first time try to drop function into unlikely executed.
2962 After inlining the roundoff errors may confuse us.
2963 Ipa-profile pass will drop functions only called from unlikely
2964 functions to unlikely and that is most of what we care about. */
2965 if (!cfun
->after_inlining
)
2966 node
->frequency
= NODE_FREQUENCY_UNLIKELY_EXECUTED
;
2967 FOR_EACH_BB_FN (bb
, cfun
)
2969 if (maybe_hot_bb_p (cfun
, bb
))
2971 node
->frequency
= NODE_FREQUENCY_HOT
;
2974 if (!probably_never_executed_bb_p (cfun
, bb
))
2975 node
->frequency
= NODE_FREQUENCY_NORMAL
;
2979 /* Build PREDICT_EXPR. */
2981 build_predict_expr (enum br_predictor predictor
, enum prediction taken
)
2983 tree t
= build1 (PREDICT_EXPR
, void_type_node
,
2984 build_int_cst (integer_type_node
, predictor
));
2985 SET_PREDICT_EXPR_OUTCOME (t
, taken
);
2990 predictor_name (enum br_predictor predictor
)
2992 return predictor_info
[predictor
].name
;
2995 /* Predict branch probabilities and estimate profile of the tree CFG. */
2999 const pass_data pass_data_profile
=
3001 GIMPLE_PASS
, /* type */
3002 "profile_estimate", /* name */
3003 OPTGROUP_NONE
, /* optinfo_flags */
3004 TV_BRANCH_PROB
, /* tv_id */
3005 PROP_cfg
, /* properties_required */
3006 0, /* properties_provided */
3007 0, /* properties_destroyed */
3008 0, /* todo_flags_start */
3009 0, /* todo_flags_finish */
3012 class pass_profile
: public gimple_opt_pass
3015 pass_profile (gcc::context
*ctxt
)
3016 : gimple_opt_pass (pass_data_profile
, ctxt
)
3019 /* opt_pass methods: */
3020 virtual bool gate (function
*) { return flag_guess_branch_prob
; }
3021 virtual unsigned int execute (function
*);
3023 }; // class pass_profile
3026 pass_profile::execute (function
*fun
)
3030 if (profile_status_for_fn (cfun
) == PROFILE_GUESSED
)
3033 loop_optimizer_init (LOOPS_NORMAL
);
3034 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
3035 flow_loops_dump (dump_file
, NULL
, 0);
3037 mark_irreducible_loops ();
3039 nb_loops
= number_of_loops (fun
);
3043 tree_estimate_probability ();
3048 loop_optimizer_finalize ();
3049 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
3050 gimple_dump_cfg (dump_file
, dump_flags
);
3051 if (profile_status_for_fn (fun
) == PROFILE_ABSENT
)
3052 profile_status_for_fn (fun
) = PROFILE_GUESSED
;
3059 make_pass_profile (gcc::context
*ctxt
)
3061 return new pass_profile (ctxt
);
3066 const pass_data pass_data_strip_predict_hints
=
3068 GIMPLE_PASS
, /* type */
3069 "*strip_predict_hints", /* name */
3070 OPTGROUP_NONE
, /* optinfo_flags */
3071 TV_BRANCH_PROB
, /* tv_id */
3072 PROP_cfg
, /* properties_required */
3073 0, /* properties_provided */
3074 0, /* properties_destroyed */
3075 0, /* todo_flags_start */
3076 0, /* todo_flags_finish */
3079 class pass_strip_predict_hints
: public gimple_opt_pass
3082 pass_strip_predict_hints (gcc::context
*ctxt
)
3083 : gimple_opt_pass (pass_data_strip_predict_hints
, ctxt
)
3086 /* opt_pass methods: */
3087 opt_pass
* clone () { return new pass_strip_predict_hints (m_ctxt
); }
3088 virtual unsigned int execute (function
*);
3090 }; // class pass_strip_predict_hints
3092 /* Get rid of all builtin_expect calls and GIMPLE_PREDICT statements
3093 we no longer need. */
3095 pass_strip_predict_hints::execute (function
*fun
)
3101 FOR_EACH_BB_FN (bb
, fun
)
3103 gimple_stmt_iterator bi
;
3104 for (bi
= gsi_start_bb (bb
); !gsi_end_p (bi
);)
3106 gimple
*stmt
= gsi_stmt (bi
);
3108 if (gimple_code (stmt
) == GIMPLE_PREDICT
)
3110 gsi_remove (&bi
, true);
3113 else if (is_gimple_call (stmt
))
3115 tree fndecl
= gimple_call_fndecl (stmt
);
3118 && DECL_BUILT_IN_CLASS (fndecl
) == BUILT_IN_NORMAL
3119 && DECL_FUNCTION_CODE (fndecl
) == BUILT_IN_EXPECT
3120 && gimple_call_num_args (stmt
) == 2)
3121 || (gimple_call_internal_p (stmt
)
3122 && gimple_call_internal_fn (stmt
) == IFN_BUILTIN_EXPECT
))
3124 var
= gimple_call_lhs (stmt
);
3128 = gimple_build_assign (var
, gimple_call_arg (stmt
, 0));
3129 gsi_replace (&bi
, ass_stmt
, true);
3133 gsi_remove (&bi
, true);
3147 make_pass_strip_predict_hints (gcc::context
*ctxt
)
3149 return new pass_strip_predict_hints (ctxt
);
3152 /* Rebuild function frequencies. Passes are in general expected to
3153 maintain profile by hand, however in some cases this is not possible:
3154 for example when inlining several functions with loops freuqencies might run
3155 out of scale and thus needs to be recomputed. */
3158 rebuild_frequencies (void)
3160 timevar_push (TV_REBUILD_FREQUENCIES
);
3162 /* When the max bb count in the function is small, there is a higher
3163 chance that there were truncation errors in the integer scaling
3164 of counts by inlining and other optimizations. This could lead
3165 to incorrect classification of code as being cold when it isn't.
3166 In that case, force the estimation of bb counts/frequencies from the
3167 branch probabilities, rather than computing frequencies from counts,
3168 which may also lead to frequencies incorrectly reduced to 0. There
3169 is less precision in the probabilities, so we only do this for small
3171 gcov_type count_max
= 0;
3173 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR_FOR_FN (cfun
), NULL
, next_bb
)
3174 count_max
= MAX (bb
->count
, count_max
);
3176 if (profile_status_for_fn (cfun
) == PROFILE_GUESSED
3177 || (!flag_auto_profile
&& profile_status_for_fn (cfun
) == PROFILE_READ
3178 && count_max
< REG_BR_PROB_BASE
/10))
3180 loop_optimizer_init (0);
3181 add_noreturn_fake_exit_edges ();
3182 mark_irreducible_loops ();
3183 connect_infinite_loops_to_exit ();
3184 estimate_bb_frequencies (true);
3185 remove_fake_exit_edges ();
3186 loop_optimizer_finalize ();
3188 else if (profile_status_for_fn (cfun
) == PROFILE_READ
)
3192 timevar_pop (TV_REBUILD_FREQUENCIES
);