1 /* Branch prediction routines for the GNU compiler.
2 Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2007, 2008, 2009, 2010
3 Free Software Foundation, Inc.
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify it under
8 the terms of the GNU General Public License as published by the Free
9 Software Foundation; either version 3, or (at your option) any later
12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING3. If not see
19 <http://www.gnu.org/licenses/>. */
23 [1] "Branch Prediction for Free"
24 Ball and Larus; PLDI '93.
25 [2] "Static Branch Frequency and Program Profile Analysis"
26 Wu and Larus; MICRO-27.
27 [3] "Corpus-based Static Branch Prediction"
28 Calder, Grunwald, Lindsay, Martin, Mozer, and Zorn; PLDI '95. */
33 #include "coretypes.h"
38 #include "hard-reg-set.h"
39 #include "basic-block.h"
40 #include "insn-config.h"
46 #include "diagnostic-core.h"
55 #include "tree-flow.h"
57 #include "tree-dump.h"
58 #include "tree-pass.h"
60 #include "tree-scalar-evolution.h"
62 #include "pointer-set.h"
64 /* real constants: 0, 1, 1-1/REG_BR_PROB_BASE, REG_BR_PROB_BASE,
65 1/REG_BR_PROB_BASE, 0.5, BB_FREQ_MAX. */
66 static sreal real_zero
, real_one
, real_almost_one
, real_br_prob_base
,
67 real_inv_br_prob_base
, real_one_half
, real_bb_freq_max
;
69 /* Random guesstimation given names.
70 PROV_VERY_UNLIKELY should be small enough so basic block predicted
71 by it gets bellow HOT_BB_FREQUENCY_FRANCTION. */
72 #define PROB_VERY_UNLIKELY (REG_BR_PROB_BASE / 2000 - 1)
73 #define PROB_EVEN (REG_BR_PROB_BASE / 2)
74 #define PROB_VERY_LIKELY (REG_BR_PROB_BASE - PROB_VERY_UNLIKELY)
75 #define PROB_ALWAYS (REG_BR_PROB_BASE)
77 static void combine_predictions_for_insn (rtx
, basic_block
);
78 static void dump_prediction (FILE *, enum br_predictor
, int, basic_block
, int);
79 static void predict_paths_leading_to (basic_block
, enum br_predictor
, enum prediction
);
80 static void predict_paths_leading_to_edge (edge
, enum br_predictor
, enum prediction
);
81 static bool can_predict_insn_p (const_rtx
);
83 /* Information we hold about each branch predictor.
84 Filled using information from predict.def. */
88 const char *const name
; /* Name used in the debugging dumps. */
89 const int hitrate
; /* Expected hitrate used by
90 predict_insn_def call. */
94 /* Use given predictor without Dempster-Shaffer theory if it matches
95 using first_match heuristics. */
96 #define PRED_FLAG_FIRST_MATCH 1
98 /* Recompute hitrate in percent to our representation. */
100 #define HITRATE(VAL) ((int) ((VAL) * REG_BR_PROB_BASE + 50) / 100)
102 #define DEF_PREDICTOR(ENUM, NAME, HITRATE, FLAGS) {NAME, HITRATE, FLAGS},
103 static const struct predictor_info predictor_info
[]= {
104 #include "predict.def"
106 /* Upper bound on predictors. */
111 /* Return TRUE if frequency FREQ is considered to be hot. */
114 maybe_hot_frequency_p (int freq
)
116 struct cgraph_node
*node
= cgraph_get_node (current_function_decl
);
117 if (!profile_info
|| !flag_branch_probabilities
)
119 if (node
->frequency
== NODE_FREQUENCY_UNLIKELY_EXECUTED
)
121 if (node
->frequency
== NODE_FREQUENCY_HOT
)
124 if (profile_status
== PROFILE_ABSENT
)
126 if (node
->frequency
== NODE_FREQUENCY_EXECUTED_ONCE
127 && freq
< (ENTRY_BLOCK_PTR
->frequency
* 2 / 3))
129 if (freq
< ENTRY_BLOCK_PTR
->frequency
/ PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION
))
134 /* Return TRUE if frequency FREQ is considered to be hot. */
137 maybe_hot_count_p (gcov_type count
)
139 if (profile_status
!= PROFILE_READ
)
141 /* Code executed at most once is not hot. */
142 if (profile_info
->runs
>= count
)
145 > profile_info
->sum_max
/ PARAM_VALUE (HOT_BB_COUNT_FRACTION
));
148 /* Return true in case BB can be CPU intensive and should be optimized
149 for maximal performance. */
152 maybe_hot_bb_p (const_basic_block bb
)
154 if (profile_status
== PROFILE_READ
)
155 return maybe_hot_count_p (bb
->count
);
156 return maybe_hot_frequency_p (bb
->frequency
);
159 /* Return true if the call can be hot. */
162 cgraph_maybe_hot_edge_p (struct cgraph_edge
*edge
)
164 if (profile_info
&& flag_branch_probabilities
166 <= profile_info
->sum_max
/ PARAM_VALUE (HOT_BB_COUNT_FRACTION
)))
168 if (edge
->caller
->frequency
== NODE_FREQUENCY_UNLIKELY_EXECUTED
169 || edge
->callee
->frequency
== NODE_FREQUENCY_UNLIKELY_EXECUTED
)
171 if (edge
->caller
->frequency
> NODE_FREQUENCY_UNLIKELY_EXECUTED
172 && edge
->callee
->frequency
<= NODE_FREQUENCY_EXECUTED_ONCE
)
176 if (edge
->caller
->frequency
== NODE_FREQUENCY_HOT
)
178 if (edge
->caller
->frequency
== NODE_FREQUENCY_EXECUTED_ONCE
179 && edge
->frequency
< CGRAPH_FREQ_BASE
* 3 / 2)
181 if (flag_guess_branch_prob
182 && edge
->frequency
<= (CGRAPH_FREQ_BASE
183 / PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION
)))
188 /* Return true in case BB can be CPU intensive and should be optimized
189 for maximal performance. */
192 maybe_hot_edge_p (edge e
)
194 if (profile_status
== PROFILE_READ
)
195 return maybe_hot_count_p (e
->count
);
196 return maybe_hot_frequency_p (EDGE_FREQUENCY (e
));
200 /* Return true in case BB is probably never executed. */
203 probably_never_executed_bb_p (const_basic_block bb
)
205 if (profile_info
&& flag_branch_probabilities
)
206 return ((bb
->count
+ profile_info
->runs
/ 2) / profile_info
->runs
) == 0;
207 if ((!profile_info
|| !flag_branch_probabilities
)
208 && (cgraph_get_node (current_function_decl
)->frequency
209 == NODE_FREQUENCY_UNLIKELY_EXECUTED
))
214 /* Return true if NODE should be optimized for size. */
217 cgraph_optimize_for_size_p (struct cgraph_node
*node
)
221 if (node
&& (node
->frequency
== NODE_FREQUENCY_UNLIKELY_EXECUTED
))
227 /* Return true when current function should always be optimized for size. */
230 optimize_function_for_size_p (struct function
*fun
)
234 if (!fun
|| !fun
->decl
)
236 return cgraph_optimize_for_size_p (cgraph_get_node (fun
->decl
));
239 /* Return true when current function should always be optimized for speed. */
242 optimize_function_for_speed_p (struct function
*fun
)
244 return !optimize_function_for_size_p (fun
);
247 /* Return TRUE when BB should be optimized for size. */
250 optimize_bb_for_size_p (const_basic_block bb
)
252 return optimize_function_for_size_p (cfun
) || !maybe_hot_bb_p (bb
);
255 /* Return TRUE when BB should be optimized for speed. */
258 optimize_bb_for_speed_p (const_basic_block bb
)
260 return !optimize_bb_for_size_p (bb
);
263 /* Return TRUE when BB should be optimized for size. */
266 optimize_edge_for_size_p (edge e
)
268 return optimize_function_for_size_p (cfun
) || !maybe_hot_edge_p (e
);
271 /* Return TRUE when BB should be optimized for speed. */
274 optimize_edge_for_speed_p (edge e
)
276 return !optimize_edge_for_size_p (e
);
279 /* Return TRUE when BB should be optimized for size. */
282 optimize_insn_for_size_p (void)
284 return optimize_function_for_size_p (cfun
) || !crtl
->maybe_hot_insn_p
;
287 /* Return TRUE when BB should be optimized for speed. */
290 optimize_insn_for_speed_p (void)
292 return !optimize_insn_for_size_p ();
295 /* Return TRUE when LOOP should be optimized for size. */
298 optimize_loop_for_size_p (struct loop
*loop
)
300 return optimize_bb_for_size_p (loop
->header
);
303 /* Return TRUE when LOOP should be optimized for speed. */
306 optimize_loop_for_speed_p (struct loop
*loop
)
308 return optimize_bb_for_speed_p (loop
->header
);
311 /* Return TRUE when LOOP nest should be optimized for speed. */
314 optimize_loop_nest_for_speed_p (struct loop
*loop
)
316 struct loop
*l
= loop
;
317 if (optimize_loop_for_speed_p (loop
))
320 while (l
&& l
!= loop
)
322 if (optimize_loop_for_speed_p (l
))
330 while (l
!= loop
&& !l
->next
)
339 /* Return TRUE when LOOP nest should be optimized for size. */
342 optimize_loop_nest_for_size_p (struct loop
*loop
)
344 return !optimize_loop_nest_for_speed_p (loop
);
347 /* Return true when edge E is likely to be well predictable by branch
351 predictable_edge_p (edge e
)
353 if (profile_status
== PROFILE_ABSENT
)
356 <= PARAM_VALUE (PARAM_PREDICTABLE_BRANCH_OUTCOME
) * REG_BR_PROB_BASE
/ 100)
357 || (REG_BR_PROB_BASE
- e
->probability
358 <= PARAM_VALUE (PARAM_PREDICTABLE_BRANCH_OUTCOME
) * REG_BR_PROB_BASE
/ 100))
364 /* Set RTL expansion for BB profile. */
367 rtl_profile_for_bb (basic_block bb
)
369 crtl
->maybe_hot_insn_p
= maybe_hot_bb_p (bb
);
372 /* Set RTL expansion for edge profile. */
375 rtl_profile_for_edge (edge e
)
377 crtl
->maybe_hot_insn_p
= maybe_hot_edge_p (e
);
380 /* Set RTL expansion to default mode (i.e. when profile info is not known). */
382 default_rtl_profile (void)
384 crtl
->maybe_hot_insn_p
= true;
387 /* Return true if the one of outgoing edges is already predicted by
391 rtl_predicted_by_p (const_basic_block bb
, enum br_predictor predictor
)
394 if (!INSN_P (BB_END (bb
)))
396 for (note
= REG_NOTES (BB_END (bb
)); note
; note
= XEXP (note
, 1))
397 if (REG_NOTE_KIND (note
) == REG_BR_PRED
398 && INTVAL (XEXP (XEXP (note
, 0), 0)) == (int)predictor
)
403 /* This map contains for a basic block the list of predictions for the
406 static struct pointer_map_t
*bb_predictions
;
408 /* Structure representing predictions in tree level. */
410 struct edge_prediction
{
411 struct edge_prediction
*ep_next
;
413 enum br_predictor ep_predictor
;
417 /* Return true if the one of outgoing edges is already predicted by
421 gimple_predicted_by_p (const_basic_block bb
, enum br_predictor predictor
)
423 struct edge_prediction
*i
;
424 void **preds
= pointer_map_contains (bb_predictions
, bb
);
429 for (i
= (struct edge_prediction
*) *preds
; i
; i
= i
->ep_next
)
430 if (i
->ep_predictor
== predictor
)
435 /* Return true when the probability of edge is reliable.
437 The profile guessing code is good at predicting branch outcome (ie.
438 taken/not taken), that is predicted right slightly over 75% of time.
439 It is however notoriously poor on predicting the probability itself.
440 In general the profile appear a lot flatter (with probabilities closer
441 to 50%) than the reality so it is bad idea to use it to drive optimization
442 such as those disabling dynamic branch prediction for well predictable
445 There are two exceptions - edges leading to noreturn edges and edges
446 predicted by number of iterations heuristics are predicted well. This macro
447 should be able to distinguish those, but at the moment it simply check for
448 noreturn heuristic that is only one giving probability over 99% or bellow
449 1%. In future we might want to propagate reliability information across the
450 CFG if we find this information useful on multiple places. */
452 probability_reliable_p (int prob
)
454 return (profile_status
== PROFILE_READ
455 || (profile_status
== PROFILE_GUESSED
456 && (prob
<= HITRATE (1) || prob
>= HITRATE (99))));
459 /* Same predicate as above, working on edges. */
461 edge_probability_reliable_p (const_edge e
)
463 return probability_reliable_p (e
->probability
);
466 /* Same predicate as edge_probability_reliable_p, working on notes. */
468 br_prob_note_reliable_p (const_rtx note
)
470 gcc_assert (REG_NOTE_KIND (note
) == REG_BR_PROB
);
471 return probability_reliable_p (INTVAL (XEXP (note
, 0)));
475 predict_insn (rtx insn
, enum br_predictor predictor
, int probability
)
477 gcc_assert (any_condjump_p (insn
));
478 if (!flag_guess_branch_prob
)
481 add_reg_note (insn
, REG_BR_PRED
,
482 gen_rtx_CONCAT (VOIDmode
,
483 GEN_INT ((int) predictor
),
484 GEN_INT ((int) probability
)));
487 /* Predict insn by given predictor. */
490 predict_insn_def (rtx insn
, enum br_predictor predictor
,
491 enum prediction taken
)
493 int probability
= predictor_info
[(int) predictor
].hitrate
;
496 probability
= REG_BR_PROB_BASE
- probability
;
498 predict_insn (insn
, predictor
, probability
);
501 /* Predict edge E with given probability if possible. */
504 rtl_predict_edge (edge e
, enum br_predictor predictor
, int probability
)
507 last_insn
= BB_END (e
->src
);
509 /* We can store the branch prediction information only about
510 conditional jumps. */
511 if (!any_condjump_p (last_insn
))
514 /* We always store probability of branching. */
515 if (e
->flags
& EDGE_FALLTHRU
)
516 probability
= REG_BR_PROB_BASE
- probability
;
518 predict_insn (last_insn
, predictor
, probability
);
521 /* Predict edge E with the given PROBABILITY. */
523 gimple_predict_edge (edge e
, enum br_predictor predictor
, int probability
)
525 gcc_assert (profile_status
!= PROFILE_GUESSED
);
526 if ((e
->src
!= ENTRY_BLOCK_PTR
&& EDGE_COUNT (e
->src
->succs
) > 1)
527 && flag_guess_branch_prob
&& optimize
)
529 struct edge_prediction
*i
= XNEW (struct edge_prediction
);
530 void **preds
= pointer_map_insert (bb_predictions
, e
->src
);
532 i
->ep_next
= (struct edge_prediction
*) *preds
;
534 i
->ep_probability
= probability
;
535 i
->ep_predictor
= predictor
;
540 /* Remove all predictions on given basic block that are attached
543 remove_predictions_associated_with_edge (edge e
)
550 preds
= pointer_map_contains (bb_predictions
, e
->src
);
554 struct edge_prediction
**prediction
= (struct edge_prediction
**) preds
;
555 struct edge_prediction
*next
;
559 if ((*prediction
)->ep_edge
== e
)
561 next
= (*prediction
)->ep_next
;
566 prediction
= &((*prediction
)->ep_next
);
571 /* Clears the list of predictions stored for BB. */
574 clear_bb_predictions (basic_block bb
)
576 void **preds
= pointer_map_contains (bb_predictions
, bb
);
577 struct edge_prediction
*pred
, *next
;
582 for (pred
= (struct edge_prediction
*) *preds
; pred
; pred
= next
)
584 next
= pred
->ep_next
;
590 /* Return true when we can store prediction on insn INSN.
591 At the moment we represent predictions only on conditional
592 jumps, not at computed jump or other complicated cases. */
594 can_predict_insn_p (const_rtx insn
)
596 return (JUMP_P (insn
)
597 && any_condjump_p (insn
)
598 && EDGE_COUNT (BLOCK_FOR_INSN (insn
)->succs
) >= 2);
601 /* Predict edge E by given predictor if possible. */
604 predict_edge_def (edge e
, enum br_predictor predictor
,
605 enum prediction taken
)
607 int probability
= predictor_info
[(int) predictor
].hitrate
;
610 probability
= REG_BR_PROB_BASE
- probability
;
612 predict_edge (e
, predictor
, probability
);
615 /* Invert all branch predictions or probability notes in the INSN. This needs
616 to be done each time we invert the condition used by the jump. */
619 invert_br_probabilities (rtx insn
)
623 for (note
= REG_NOTES (insn
); note
; note
= XEXP (note
, 1))
624 if (REG_NOTE_KIND (note
) == REG_BR_PROB
)
625 XEXP (note
, 0) = GEN_INT (REG_BR_PROB_BASE
- INTVAL (XEXP (note
, 0)));
626 else if (REG_NOTE_KIND (note
) == REG_BR_PRED
)
627 XEXP (XEXP (note
, 0), 1)
628 = GEN_INT (REG_BR_PROB_BASE
- INTVAL (XEXP (XEXP (note
, 0), 1)));
631 /* Dump information about the branch prediction to the output file. */
634 dump_prediction (FILE *file
, enum br_predictor predictor
, int probability
,
635 basic_block bb
, int used
)
643 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
644 if (! (e
->flags
& EDGE_FALLTHRU
))
647 fprintf (file
, " %s heuristics%s: %.1f%%",
648 predictor_info
[predictor
].name
,
649 used
? "" : " (ignored)", probability
* 100.0 / REG_BR_PROB_BASE
);
653 fprintf (file
, " exec ");
654 fprintf (file
, HOST_WIDEST_INT_PRINT_DEC
, bb
->count
);
657 fprintf (file
, " hit ");
658 fprintf (file
, HOST_WIDEST_INT_PRINT_DEC
, e
->count
);
659 fprintf (file
, " (%.1f%%)", e
->count
* 100.0 / bb
->count
);
663 fprintf (file
, "\n");
666 /* We can not predict the probabilities of outgoing edges of bb. Set them
667 evenly and hope for the best. */
669 set_even_probabilities (basic_block bb
)
675 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
676 if (!(e
->flags
& (EDGE_EH
| EDGE_FAKE
)))
678 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
679 if (!(e
->flags
& (EDGE_EH
| EDGE_FAKE
)))
680 e
->probability
= (REG_BR_PROB_BASE
+ nedges
/ 2) / nedges
;
685 /* Combine all REG_BR_PRED notes into single probability and attach REG_BR_PROB
686 note if not already present. Remove now useless REG_BR_PRED notes. */
689 combine_predictions_for_insn (rtx insn
, basic_block bb
)
694 int best_probability
= PROB_EVEN
;
695 enum br_predictor best_predictor
= END_PREDICTORS
;
696 int combined_probability
= REG_BR_PROB_BASE
/ 2;
698 bool first_match
= false;
701 if (!can_predict_insn_p (insn
))
703 set_even_probabilities (bb
);
707 prob_note
= find_reg_note (insn
, REG_BR_PROB
, 0);
708 pnote
= ®_NOTES (insn
);
710 fprintf (dump_file
, "Predictions for insn %i bb %i\n", INSN_UID (insn
),
713 /* We implement "first match" heuristics and use probability guessed
714 by predictor with smallest index. */
715 for (note
= REG_NOTES (insn
); note
; note
= XEXP (note
, 1))
716 if (REG_NOTE_KIND (note
) == REG_BR_PRED
)
718 enum br_predictor predictor
= ((enum br_predictor
)
719 INTVAL (XEXP (XEXP (note
, 0), 0)));
720 int probability
= INTVAL (XEXP (XEXP (note
, 0), 1));
723 if (best_predictor
> predictor
)
724 best_probability
= probability
, best_predictor
= predictor
;
726 d
= (combined_probability
* probability
727 + (REG_BR_PROB_BASE
- combined_probability
)
728 * (REG_BR_PROB_BASE
- probability
));
730 /* Use FP math to avoid overflows of 32bit integers. */
732 /* If one probability is 0% and one 100%, avoid division by zero. */
733 combined_probability
= REG_BR_PROB_BASE
/ 2;
735 combined_probability
= (((double) combined_probability
) * probability
736 * REG_BR_PROB_BASE
/ d
+ 0.5);
739 /* Decide which heuristic to use. In case we didn't match anything,
740 use no_prediction heuristic, in case we did match, use either
741 first match or Dempster-Shaffer theory depending on the flags. */
743 if (predictor_info
[best_predictor
].flags
& PRED_FLAG_FIRST_MATCH
)
747 dump_prediction (dump_file
, PRED_NO_PREDICTION
,
748 combined_probability
, bb
, true);
751 dump_prediction (dump_file
, PRED_DS_THEORY
, combined_probability
,
753 dump_prediction (dump_file
, PRED_FIRST_MATCH
, best_probability
,
758 combined_probability
= best_probability
;
759 dump_prediction (dump_file
, PRED_COMBINED
, combined_probability
, bb
, true);
763 if (REG_NOTE_KIND (*pnote
) == REG_BR_PRED
)
765 enum br_predictor predictor
= ((enum br_predictor
)
766 INTVAL (XEXP (XEXP (*pnote
, 0), 0)));
767 int probability
= INTVAL (XEXP (XEXP (*pnote
, 0), 1));
769 dump_prediction (dump_file
, predictor
, probability
, bb
,
770 !first_match
|| best_predictor
== predictor
);
771 *pnote
= XEXP (*pnote
, 1);
774 pnote
= &XEXP (*pnote
, 1);
779 add_reg_note (insn
, REG_BR_PROB
, GEN_INT (combined_probability
));
781 /* Save the prediction into CFG in case we are seeing non-degenerated
783 if (!single_succ_p (bb
))
785 BRANCH_EDGE (bb
)->probability
= combined_probability
;
786 FALLTHRU_EDGE (bb
)->probability
787 = REG_BR_PROB_BASE
- combined_probability
;
790 else if (!single_succ_p (bb
))
792 int prob
= INTVAL (XEXP (prob_note
, 0));
794 BRANCH_EDGE (bb
)->probability
= prob
;
795 FALLTHRU_EDGE (bb
)->probability
= REG_BR_PROB_BASE
- prob
;
798 single_succ_edge (bb
)->probability
= REG_BR_PROB_BASE
;
801 /* Combine predictions into single probability and store them into CFG.
802 Remove now useless prediction entries. */
805 combine_predictions_for_bb (basic_block bb
)
807 int best_probability
= PROB_EVEN
;
808 enum br_predictor best_predictor
= END_PREDICTORS
;
809 int combined_probability
= REG_BR_PROB_BASE
/ 2;
811 bool first_match
= false;
813 struct edge_prediction
*pred
;
815 edge e
, first
= NULL
, second
= NULL
;
819 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
820 if (!(e
->flags
& (EDGE_EH
| EDGE_FAKE
)))
823 if (first
&& !second
)
829 /* When there is no successor or only one choice, prediction is easy.
831 We are lazy for now and predict only basic blocks with two outgoing
832 edges. It is possible to predict generic case too, but we have to
833 ignore first match heuristics and do more involved combining. Implement
838 set_even_probabilities (bb
);
839 clear_bb_predictions (bb
);
841 fprintf (dump_file
, "%i edges in bb %i predicted to even probabilities\n",
847 fprintf (dump_file
, "Predictions for bb %i\n", bb
->index
);
849 preds
= pointer_map_contains (bb_predictions
, bb
);
852 /* We implement "first match" heuristics and use probability guessed
853 by predictor with smallest index. */
854 for (pred
= (struct edge_prediction
*) *preds
; pred
; pred
= pred
->ep_next
)
856 enum br_predictor predictor
= pred
->ep_predictor
;
857 int probability
= pred
->ep_probability
;
859 if (pred
->ep_edge
!= first
)
860 probability
= REG_BR_PROB_BASE
- probability
;
863 /* First match heuristics would be widly confused if we predicted
865 if (best_predictor
> predictor
)
867 struct edge_prediction
*pred2
;
868 int prob
= probability
;
870 for (pred2
= (struct edge_prediction
*) *preds
; pred2
; pred2
= pred2
->ep_next
)
871 if (pred2
!= pred
&& pred2
->ep_predictor
== pred
->ep_predictor
)
873 int probability2
= pred
->ep_probability
;
875 if (pred2
->ep_edge
!= first
)
876 probability2
= REG_BR_PROB_BASE
- probability2
;
878 if ((probability
< REG_BR_PROB_BASE
/ 2) !=
879 (probability2
< REG_BR_PROB_BASE
/ 2))
882 /* If the same predictor later gave better result, go for it! */
883 if ((probability
>= REG_BR_PROB_BASE
/ 2 && (probability2
> probability
))
884 || (probability
<= REG_BR_PROB_BASE
/ 2 && (probability2
< probability
)))
888 best_probability
= prob
, best_predictor
= predictor
;
891 d
= (combined_probability
* probability
892 + (REG_BR_PROB_BASE
- combined_probability
)
893 * (REG_BR_PROB_BASE
- probability
));
895 /* Use FP math to avoid overflows of 32bit integers. */
897 /* If one probability is 0% and one 100%, avoid division by zero. */
898 combined_probability
= REG_BR_PROB_BASE
/ 2;
900 combined_probability
= (((double) combined_probability
)
902 * REG_BR_PROB_BASE
/ d
+ 0.5);
906 /* Decide which heuristic to use. In case we didn't match anything,
907 use no_prediction heuristic, in case we did match, use either
908 first match or Dempster-Shaffer theory depending on the flags. */
910 if (predictor_info
[best_predictor
].flags
& PRED_FLAG_FIRST_MATCH
)
914 dump_prediction (dump_file
, PRED_NO_PREDICTION
, combined_probability
, bb
, true);
917 dump_prediction (dump_file
, PRED_DS_THEORY
, combined_probability
, bb
,
919 dump_prediction (dump_file
, PRED_FIRST_MATCH
, best_probability
, bb
,
924 combined_probability
= best_probability
;
925 dump_prediction (dump_file
, PRED_COMBINED
, combined_probability
, bb
, true);
929 for (pred
= (struct edge_prediction
*) *preds
; pred
; pred
= pred
->ep_next
)
931 enum br_predictor predictor
= pred
->ep_predictor
;
932 int probability
= pred
->ep_probability
;
934 if (pred
->ep_edge
!= EDGE_SUCC (bb
, 0))
935 probability
= REG_BR_PROB_BASE
- probability
;
936 dump_prediction (dump_file
, predictor
, probability
, bb
,
937 !first_match
|| best_predictor
== predictor
);
940 clear_bb_predictions (bb
);
944 first
->probability
= combined_probability
;
945 second
->probability
= REG_BR_PROB_BASE
- combined_probability
;
949 /* Predict edge probabilities by exploiting loop structure. */
957 /* Try to predict out blocks in a loop that are not part of a
959 FOR_EACH_LOOP (li
, loop
, 0)
961 basic_block bb
, *bbs
;
963 VEC (edge
, heap
) *exits
;
964 struct tree_niter_desc niter_desc
;
967 exits
= get_loop_exit_edges (loop
);
968 n_exits
= VEC_length (edge
, exits
);
970 FOR_EACH_VEC_ELT (edge
, exits
, j
, ex
)
973 HOST_WIDE_INT nitercst
;
974 int max
= PARAM_VALUE (PARAM_MAX_PREDICTED_ITERATIONS
);
976 enum br_predictor predictor
;
978 if (number_of_iterations_exit (loop
, ex
, &niter_desc
, false))
979 niter
= niter_desc
.niter
;
980 if (!niter
|| TREE_CODE (niter_desc
.niter
) != INTEGER_CST
)
981 niter
= loop_niter_by_eval (loop
, ex
);
983 if (TREE_CODE (niter
) == INTEGER_CST
)
985 if (host_integerp (niter
, 1)
986 && compare_tree_int (niter
, max
-1) == -1)
987 nitercst
= tree_low_cst (niter
, 1) + 1;
990 predictor
= PRED_LOOP_ITERATIONS
;
992 /* If we have just one exit and we can derive some information about
993 the number of iterations of the loop from the statements inside
994 the loop, use it to predict this exit. */
995 else if (n_exits
== 1)
997 nitercst
= max_stmt_executions_int (loop
, false);
1003 predictor
= PRED_LOOP_ITERATIONS_GUESSED
;
1008 probability
= ((REG_BR_PROB_BASE
+ nitercst
/ 2) / nitercst
);
1009 predict_edge (ex
, predictor
, probability
);
1011 VEC_free (edge
, heap
, exits
);
1013 bbs
= get_loop_body (loop
);
1015 for (j
= 0; j
< loop
->num_nodes
; j
++)
1017 int header_found
= 0;
1023 /* Bypass loop heuristics on continue statement. These
1024 statements construct loops via "non-loop" constructs
1025 in the source language and are better to be handled
1027 if (predicted_by_p (bb
, PRED_CONTINUE
))
1030 /* Loop branch heuristics - predict an edge back to a
1031 loop's head as taken. */
1032 if (bb
== loop
->latch
)
1034 e
= find_edge (loop
->latch
, loop
->header
);
1038 predict_edge_def (e
, PRED_LOOP_BRANCH
, TAKEN
);
1042 /* Loop exit heuristics - predict an edge exiting the loop if the
1043 conditional has no loop header successors as not taken. */
1045 /* If we already used more reliable loop exit predictors, do not
1046 bother with PRED_LOOP_EXIT. */
1047 && !predicted_by_p (bb
, PRED_LOOP_ITERATIONS_GUESSED
)
1048 && !predicted_by_p (bb
, PRED_LOOP_ITERATIONS
))
1050 /* For loop with many exits we don't want to predict all exits
1051 with the pretty large probability, because if all exits are
1052 considered in row, the loop would be predicted to iterate
1053 almost never. The code to divide probability by number of
1054 exits is very rough. It should compute the number of exits
1055 taken in each patch through function (not the overall number
1056 of exits that might be a lot higher for loops with wide switch
1057 statements in them) and compute n-th square root.
1059 We limit the minimal probability by 2% to avoid
1060 EDGE_PROBABILITY_RELIABLE from trusting the branch prediction
1061 as this was causing regression in perl benchmark containing such
1064 int probability
= ((REG_BR_PROB_BASE
1065 - predictor_info
[(int) PRED_LOOP_EXIT
].hitrate
)
1067 if (probability
< HITRATE (2))
1068 probability
= HITRATE (2);
1069 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
1070 if (e
->dest
->index
< NUM_FIXED_BLOCKS
1071 || !flow_bb_inside_loop_p (loop
, e
->dest
))
1072 predict_edge (e
, PRED_LOOP_EXIT
, probability
);
1076 /* Free basic blocks from get_loop_body. */
1081 /* Attempt to predict probabilities of BB outgoing edges using local
1084 bb_estimate_probability_locally (basic_block bb
)
1086 rtx last_insn
= BB_END (bb
);
1089 if (! can_predict_insn_p (last_insn
))
1091 cond
= get_condition (last_insn
, NULL
, false, false);
1095 /* Try "pointer heuristic."
1096 A comparison ptr == 0 is predicted as false.
1097 Similarly, a comparison ptr1 == ptr2 is predicted as false. */
1098 if (COMPARISON_P (cond
)
1099 && ((REG_P (XEXP (cond
, 0)) && REG_POINTER (XEXP (cond
, 0)))
1100 || (REG_P (XEXP (cond
, 1)) && REG_POINTER (XEXP (cond
, 1)))))
1102 if (GET_CODE (cond
) == EQ
)
1103 predict_insn_def (last_insn
, PRED_POINTER
, NOT_TAKEN
);
1104 else if (GET_CODE (cond
) == NE
)
1105 predict_insn_def (last_insn
, PRED_POINTER
, TAKEN
);
1109 /* Try "opcode heuristic."
1110 EQ tests are usually false and NE tests are usually true. Also,
1111 most quantities are positive, so we can make the appropriate guesses
1112 about signed comparisons against zero. */
1113 switch (GET_CODE (cond
))
1116 /* Unconditional branch. */
1117 predict_insn_def (last_insn
, PRED_UNCONDITIONAL
,
1118 cond
== const0_rtx
? NOT_TAKEN
: TAKEN
);
1123 /* Floating point comparisons appears to behave in a very
1124 unpredictable way because of special role of = tests in
1126 if (FLOAT_MODE_P (GET_MODE (XEXP (cond
, 0))))
1128 /* Comparisons with 0 are often used for booleans and there is
1129 nothing useful to predict about them. */
1130 else if (XEXP (cond
, 1) == const0_rtx
1131 || XEXP (cond
, 0) == const0_rtx
)
1134 predict_insn_def (last_insn
, PRED_OPCODE_NONEQUAL
, NOT_TAKEN
);
1139 /* Floating point comparisons appears to behave in a very
1140 unpredictable way because of special role of = tests in
1142 if (FLOAT_MODE_P (GET_MODE (XEXP (cond
, 0))))
1144 /* Comparisons with 0 are often used for booleans and there is
1145 nothing useful to predict about them. */
1146 else if (XEXP (cond
, 1) == const0_rtx
1147 || XEXP (cond
, 0) == const0_rtx
)
1150 predict_insn_def (last_insn
, PRED_OPCODE_NONEQUAL
, TAKEN
);
1154 predict_insn_def (last_insn
, PRED_FPOPCODE
, TAKEN
);
1158 predict_insn_def (last_insn
, PRED_FPOPCODE
, NOT_TAKEN
);
1163 if (XEXP (cond
, 1) == const0_rtx
|| XEXP (cond
, 1) == const1_rtx
1164 || XEXP (cond
, 1) == constm1_rtx
)
1165 predict_insn_def (last_insn
, PRED_OPCODE_POSITIVE
, NOT_TAKEN
);
1170 if (XEXP (cond
, 1) == const0_rtx
|| XEXP (cond
, 1) == const1_rtx
1171 || XEXP (cond
, 1) == constm1_rtx
)
1172 predict_insn_def (last_insn
, PRED_OPCODE_POSITIVE
, TAKEN
);
1180 /* Set edge->probability for each successor edge of BB. */
1182 guess_outgoing_edge_probabilities (basic_block bb
)
1184 bb_estimate_probability_locally (bb
);
1185 combine_predictions_for_insn (BB_END (bb
), bb
);
1188 static tree
expr_expected_value (tree
, bitmap
);
1190 /* Helper function for expr_expected_value. */
1193 expr_expected_value_1 (tree type
, tree op0
, enum tree_code code
,
1194 tree op1
, bitmap visited
)
1198 if (get_gimple_rhs_class (code
) == GIMPLE_SINGLE_RHS
)
1200 if (TREE_CONSTANT (op0
))
1203 if (code
!= SSA_NAME
)
1206 def
= SSA_NAME_DEF_STMT (op0
);
1208 /* If we were already here, break the infinite cycle. */
1209 if (!bitmap_set_bit (visited
, SSA_NAME_VERSION (op0
)))
1212 if (gimple_code (def
) == GIMPLE_PHI
)
1214 /* All the arguments of the PHI node must have the same constant
1216 int i
, n
= gimple_phi_num_args (def
);
1217 tree val
= NULL
, new_val
;
1219 for (i
= 0; i
< n
; i
++)
1221 tree arg
= PHI_ARG_DEF (def
, i
);
1223 /* If this PHI has itself as an argument, we cannot
1224 determine the string length of this argument. However,
1225 if we can find an expected constant value for the other
1226 PHI args then we can still be sure that this is
1227 likely a constant. So be optimistic and just
1228 continue with the next argument. */
1229 if (arg
== PHI_RESULT (def
))
1232 new_val
= expr_expected_value (arg
, visited
);
1237 else if (!operand_equal_p (val
, new_val
, false))
1242 if (is_gimple_assign (def
))
1244 if (gimple_assign_lhs (def
) != op0
)
1247 return expr_expected_value_1 (TREE_TYPE (gimple_assign_lhs (def
)),
1248 gimple_assign_rhs1 (def
),
1249 gimple_assign_rhs_code (def
),
1250 gimple_assign_rhs2 (def
),
1254 if (is_gimple_call (def
))
1256 tree decl
= gimple_call_fndecl (def
);
1259 if (DECL_BUILT_IN_CLASS (decl
) == BUILT_IN_NORMAL
)
1260 switch (DECL_FUNCTION_CODE (decl
))
1262 case BUILT_IN_EXPECT
:
1265 if (gimple_call_num_args (def
) != 2)
1267 val
= gimple_call_arg (def
, 0);
1268 if (TREE_CONSTANT (val
))
1270 return gimple_call_arg (def
, 1);
1273 case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_N
:
1274 case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_1
:
1275 case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_2
:
1276 case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_4
:
1277 case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_8
:
1278 case BUILT_IN_SYNC_BOOL_COMPARE_AND_SWAP_16
:
1279 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE
:
1280 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_N
:
1281 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_1
:
1282 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_2
:
1283 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_4
:
1284 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_8
:
1285 case BUILT_IN_ATOMIC_COMPARE_EXCHANGE_16
:
1286 /* Assume that any given atomic operation has low contention,
1287 and thus the compare-and-swap operation succeeds. */
1288 return boolean_true_node
;
1295 if (get_gimple_rhs_class (code
) == GIMPLE_BINARY_RHS
)
1298 op0
= expr_expected_value (op0
, visited
);
1301 op1
= expr_expected_value (op1
, visited
);
1304 res
= fold_build2 (code
, type
, op0
, op1
);
1305 if (TREE_CONSTANT (res
))
1309 if (get_gimple_rhs_class (code
) == GIMPLE_UNARY_RHS
)
1312 op0
= expr_expected_value (op0
, visited
);
1315 res
= fold_build1 (code
, type
, op0
);
1316 if (TREE_CONSTANT (res
))
1323 /* Return constant EXPR will likely have at execution time, NULL if unknown.
1324 The function is used by builtin_expect branch predictor so the evidence
1325 must come from this construct and additional possible constant folding.
1327 We may want to implement more involved value guess (such as value range
1328 propagation based prediction), but such tricks shall go to new
1332 expr_expected_value (tree expr
, bitmap visited
)
1334 enum tree_code code
;
1337 if (TREE_CONSTANT (expr
))
1340 extract_ops_from_tree (expr
, &code
, &op0
, &op1
);
1341 return expr_expected_value_1 (TREE_TYPE (expr
),
1342 op0
, code
, op1
, visited
);
1346 /* Get rid of all builtin_expect calls and GIMPLE_PREDICT statements
1347 we no longer need. */
1349 strip_predict_hints (void)
1357 gimple_stmt_iterator bi
;
1358 for (bi
= gsi_start_bb (bb
); !gsi_end_p (bi
);)
1360 gimple stmt
= gsi_stmt (bi
);
1362 if (gimple_code (stmt
) == GIMPLE_PREDICT
)
1364 gsi_remove (&bi
, true);
1367 else if (gimple_code (stmt
) == GIMPLE_CALL
)
1369 tree fndecl
= gimple_call_fndecl (stmt
);
1372 && DECL_BUILT_IN_CLASS (fndecl
) == BUILT_IN_NORMAL
1373 && DECL_FUNCTION_CODE (fndecl
) == BUILT_IN_EXPECT
1374 && gimple_call_num_args (stmt
) == 2)
1376 var
= gimple_call_lhs (stmt
);
1380 = gimple_build_assign (var
, gimple_call_arg (stmt
, 0));
1381 gsi_replace (&bi
, ass_stmt
, true);
1385 gsi_remove (&bi
, true);
1396 /* Predict using opcode of the last statement in basic block. */
1398 tree_predict_by_opcode (basic_block bb
)
1400 gimple stmt
= last_stmt (bb
);
1409 if (!stmt
|| gimple_code (stmt
) != GIMPLE_COND
)
1411 FOR_EACH_EDGE (then_edge
, ei
, bb
->succs
)
1412 if (then_edge
->flags
& EDGE_TRUE_VALUE
)
1414 op0
= gimple_cond_lhs (stmt
);
1415 op1
= gimple_cond_rhs (stmt
);
1416 cmp
= gimple_cond_code (stmt
);
1417 type
= TREE_TYPE (op0
);
1418 visited
= BITMAP_ALLOC (NULL
);
1419 val
= expr_expected_value_1 (boolean_type_node
, op0
, cmp
, op1
, visited
);
1420 BITMAP_FREE (visited
);
1423 if (integer_zerop (val
))
1424 predict_edge_def (then_edge
, PRED_BUILTIN_EXPECT
, NOT_TAKEN
);
1426 predict_edge_def (then_edge
, PRED_BUILTIN_EXPECT
, TAKEN
);
1429 /* Try "pointer heuristic."
1430 A comparison ptr == 0 is predicted as false.
1431 Similarly, a comparison ptr1 == ptr2 is predicted as false. */
1432 if (POINTER_TYPE_P (type
))
1435 predict_edge_def (then_edge
, PRED_TREE_POINTER
, NOT_TAKEN
);
1436 else if (cmp
== NE_EXPR
)
1437 predict_edge_def (then_edge
, PRED_TREE_POINTER
, TAKEN
);
1441 /* Try "opcode heuristic."
1442 EQ tests are usually false and NE tests are usually true. Also,
1443 most quantities are positive, so we can make the appropriate guesses
1444 about signed comparisons against zero. */
1449 /* Floating point comparisons appears to behave in a very
1450 unpredictable way because of special role of = tests in
1452 if (FLOAT_TYPE_P (type
))
1454 /* Comparisons with 0 are often used for booleans and there is
1455 nothing useful to predict about them. */
1456 else if (integer_zerop (op0
) || integer_zerop (op1
))
1459 predict_edge_def (then_edge
, PRED_TREE_OPCODE_NONEQUAL
, NOT_TAKEN
);
1464 /* Floating point comparisons appears to behave in a very
1465 unpredictable way because of special role of = tests in
1467 if (FLOAT_TYPE_P (type
))
1469 /* Comparisons with 0 are often used for booleans and there is
1470 nothing useful to predict about them. */
1471 else if (integer_zerop (op0
)
1472 || integer_zerop (op1
))
1475 predict_edge_def (then_edge
, PRED_TREE_OPCODE_NONEQUAL
, TAKEN
);
1479 predict_edge_def (then_edge
, PRED_TREE_FPOPCODE
, TAKEN
);
1482 case UNORDERED_EXPR
:
1483 predict_edge_def (then_edge
, PRED_TREE_FPOPCODE
, NOT_TAKEN
);
1488 if (integer_zerop (op1
)
1489 || integer_onep (op1
)
1490 || integer_all_onesp (op1
)
1493 || real_minus_onep (op1
))
1494 predict_edge_def (then_edge
, PRED_TREE_OPCODE_POSITIVE
, NOT_TAKEN
);
1499 if (integer_zerop (op1
)
1500 || integer_onep (op1
)
1501 || integer_all_onesp (op1
)
1504 || real_minus_onep (op1
))
1505 predict_edge_def (then_edge
, PRED_TREE_OPCODE_POSITIVE
, TAKEN
);
1513 /* Try to guess whether the value of return means error code. */
1515 static enum br_predictor
1516 return_prediction (tree val
, enum prediction
*prediction
)
1520 return PRED_NO_PREDICTION
;
1521 /* Different heuristics for pointers and scalars. */
1522 if (POINTER_TYPE_P (TREE_TYPE (val
)))
1524 /* NULL is usually not returned. */
1525 if (integer_zerop (val
))
1527 *prediction
= NOT_TAKEN
;
1528 return PRED_NULL_RETURN
;
1531 else if (INTEGRAL_TYPE_P (TREE_TYPE (val
)))
1533 /* Negative return values are often used to indicate
1535 if (TREE_CODE (val
) == INTEGER_CST
1536 && tree_int_cst_sgn (val
) < 0)
1538 *prediction
= NOT_TAKEN
;
1539 return PRED_NEGATIVE_RETURN
;
1541 /* Constant return values seems to be commonly taken.
1542 Zero/one often represent booleans so exclude them from the
1544 if (TREE_CONSTANT (val
)
1545 && (!integer_zerop (val
) && !integer_onep (val
)))
1547 *prediction
= TAKEN
;
1548 return PRED_CONST_RETURN
;
1551 return PRED_NO_PREDICTION
;
1554 /* Find the basic block with return expression and look up for possible
1555 return value trying to apply RETURN_PREDICTION heuristics. */
1557 apply_return_prediction (void)
1559 gimple return_stmt
= NULL
;
1563 int phi_num_args
, i
;
1564 enum br_predictor pred
;
1565 enum prediction direction
;
1568 FOR_EACH_EDGE (e
, ei
, EXIT_BLOCK_PTR
->preds
)
1570 return_stmt
= last_stmt (e
->src
);
1572 && gimple_code (return_stmt
) == GIMPLE_RETURN
)
1577 return_val
= gimple_return_retval (return_stmt
);
1580 if (TREE_CODE (return_val
) != SSA_NAME
1581 || !SSA_NAME_DEF_STMT (return_val
)
1582 || gimple_code (SSA_NAME_DEF_STMT (return_val
)) != GIMPLE_PHI
)
1584 phi
= SSA_NAME_DEF_STMT (return_val
);
1585 phi_num_args
= gimple_phi_num_args (phi
);
1586 pred
= return_prediction (PHI_ARG_DEF (phi
, 0), &direction
);
1588 /* Avoid the degenerate case where all return values form the function
1589 belongs to same category (ie they are all positive constants)
1590 so we can hardly say something about them. */
1591 for (i
= 1; i
< phi_num_args
; i
++)
1592 if (pred
!= return_prediction (PHI_ARG_DEF (phi
, i
), &direction
))
1594 if (i
!= phi_num_args
)
1595 for (i
= 0; i
< phi_num_args
; i
++)
1597 pred
= return_prediction (PHI_ARG_DEF (phi
, i
), &direction
);
1598 if (pred
!= PRED_NO_PREDICTION
)
1599 predict_paths_leading_to_edge (gimple_phi_arg_edge (phi
, i
), pred
,
1604 /* Look for basic block that contains unlikely to happen events
1605 (such as noreturn calls) and mark all paths leading to execution
1606 of this basic blocks as unlikely. */
1609 tree_bb_level_predictions (void)
1612 bool has_return_edges
= false;
1616 FOR_EACH_EDGE (e
, ei
, EXIT_BLOCK_PTR
->preds
)
1617 if (!(e
->flags
& (EDGE_ABNORMAL
| EDGE_FAKE
| EDGE_EH
)))
1619 has_return_edges
= true;
1623 apply_return_prediction ();
1627 gimple_stmt_iterator gsi
;
1629 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
1631 gimple stmt
= gsi_stmt (gsi
);
1634 if (is_gimple_call (stmt
))
1636 if ((gimple_call_flags (stmt
) & ECF_NORETURN
)
1637 && has_return_edges
)
1638 predict_paths_leading_to (bb
, PRED_NORETURN
,
1640 decl
= gimple_call_fndecl (stmt
);
1642 && lookup_attribute ("cold",
1643 DECL_ATTRIBUTES (decl
)))
1644 predict_paths_leading_to (bb
, PRED_COLD_FUNCTION
,
1647 else if (gimple_code (stmt
) == GIMPLE_PREDICT
)
1649 predict_paths_leading_to (bb
, gimple_predict_predictor (stmt
),
1650 gimple_predict_outcome (stmt
));
1651 /* Keep GIMPLE_PREDICT around so early inlining will propagate
1652 hints to callers. */
1658 #ifdef ENABLE_CHECKING
1660 /* Callback for pointer_map_traverse, asserts that the pointer map is
1664 assert_is_empty (const void *key ATTRIBUTE_UNUSED
, void **value
,
1665 void *data ATTRIBUTE_UNUSED
)
1667 gcc_assert (!*value
);
1672 /* Predict branch probabilities and estimate profile for basic block BB. */
1675 tree_estimate_probability_bb (basic_block bb
)
1681 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
1683 /* Predict early returns to be probable, as we've already taken
1684 care for error returns and other cases are often used for
1685 fast paths through function.
1687 Since we've already removed the return statements, we are
1688 looking for CFG like:
1698 if (e
->dest
!= bb
->next_bb
1699 && e
->dest
!= EXIT_BLOCK_PTR
1700 && single_succ_p (e
->dest
)
1701 && single_succ_edge (e
->dest
)->dest
== EXIT_BLOCK_PTR
1702 && (last
= last_stmt (e
->dest
)) != NULL
1703 && gimple_code (last
) == GIMPLE_RETURN
)
1708 if (single_succ_p (bb
))
1710 FOR_EACH_EDGE (e1
, ei1
, bb
->preds
)
1711 if (!predicted_by_p (e1
->src
, PRED_NULL_RETURN
)
1712 && !predicted_by_p (e1
->src
, PRED_CONST_RETURN
)
1713 && !predicted_by_p (e1
->src
, PRED_NEGATIVE_RETURN
))
1714 predict_edge_def (e1
, PRED_TREE_EARLY_RETURN
, NOT_TAKEN
);
1717 if (!predicted_by_p (e
->src
, PRED_NULL_RETURN
)
1718 && !predicted_by_p (e
->src
, PRED_CONST_RETURN
)
1719 && !predicted_by_p (e
->src
, PRED_NEGATIVE_RETURN
))
1720 predict_edge_def (e
, PRED_TREE_EARLY_RETURN
, NOT_TAKEN
);
1723 /* Look for block we are guarding (ie we dominate it,
1724 but it doesn't postdominate us). */
1725 if (e
->dest
!= EXIT_BLOCK_PTR
&& e
->dest
!= bb
1726 && dominated_by_p (CDI_DOMINATORS
, e
->dest
, e
->src
)
1727 && !dominated_by_p (CDI_POST_DOMINATORS
, e
->src
, e
->dest
))
1729 gimple_stmt_iterator bi
;
1731 /* The call heuristic claims that a guarded function call
1732 is improbable. This is because such calls are often used
1733 to signal exceptional situations such as printing error
1735 for (bi
= gsi_start_bb (e
->dest
); !gsi_end_p (bi
);
1738 gimple stmt
= gsi_stmt (bi
);
1739 if (is_gimple_call (stmt
)
1740 /* Constant and pure calls are hardly used to signalize
1741 something exceptional. */
1742 && gimple_has_side_effects (stmt
))
1744 predict_edge_def (e
, PRED_CALL
, NOT_TAKEN
);
1750 tree_predict_by_opcode (bb
);
1753 /* Predict branch probabilities and estimate profile of the tree CFG.
1754 This function can be called from the loop optimizers to recompute
1755 the profile information. */
1758 tree_estimate_probability (void)
1762 add_noreturn_fake_exit_edges ();
1763 connect_infinite_loops_to_exit ();
1764 /* We use loop_niter_by_eval, which requires that the loops have
1766 create_preheaders (CP_SIMPLE_PREHEADERS
);
1767 calculate_dominance_info (CDI_POST_DOMINATORS
);
1769 bb_predictions
= pointer_map_create ();
1770 tree_bb_level_predictions ();
1771 record_loop_exits ();
1773 if (number_of_loops () > 1)
1777 tree_estimate_probability_bb (bb
);
1780 combine_predictions_for_bb (bb
);
1782 #ifdef ENABLE_CHECKING
1783 pointer_map_traverse (bb_predictions
, assert_is_empty
, NULL
);
1785 pointer_map_destroy (bb_predictions
);
1786 bb_predictions
= NULL
;
1788 estimate_bb_frequencies ();
1789 free_dominance_info (CDI_POST_DOMINATORS
);
1790 remove_fake_exit_edges ();
1793 /* Predict branch probabilities and estimate profile of the tree CFG.
1794 This is the driver function for PASS_PROFILE. */
1797 tree_estimate_probability_driver (void)
1801 loop_optimizer_init (0);
1802 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1803 flow_loops_dump (dump_file
, NULL
, 0);
1805 mark_irreducible_loops ();
1807 nb_loops
= number_of_loops ();
1811 tree_estimate_probability ();
1816 loop_optimizer_finalize ();
1817 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1818 gimple_dump_cfg (dump_file
, dump_flags
);
1819 if (profile_status
== PROFILE_ABSENT
)
1820 profile_status
= PROFILE_GUESSED
;
1824 /* Predict edges to successors of CUR whose sources are not postdominated by
1825 BB by PRED and recurse to all postdominators. */
1828 predict_paths_for_bb (basic_block cur
, basic_block bb
,
1829 enum br_predictor pred
,
1830 enum prediction taken
,
1837 /* We are looking for all edges forming edge cut induced by
1838 set of all blocks postdominated by BB. */
1839 FOR_EACH_EDGE (e
, ei
, cur
->preds
)
1840 if (e
->src
->index
>= NUM_FIXED_BLOCKS
1841 && !dominated_by_p (CDI_POST_DOMINATORS
, e
->src
, bb
))
1847 /* Ignore fake edges and eh, we predict them as not taken anyway. */
1848 if (e
->flags
& (EDGE_EH
| EDGE_FAKE
))
1850 gcc_assert (bb
== cur
|| dominated_by_p (CDI_POST_DOMINATORS
, cur
, bb
));
1852 /* See if there is an edge from e->src that is not abnormal
1853 and does not lead to BB. */
1854 FOR_EACH_EDGE (e2
, ei2
, e
->src
->succs
)
1856 && !(e2
->flags
& (EDGE_EH
| EDGE_FAKE
))
1857 && !dominated_by_p (CDI_POST_DOMINATORS
, e2
->dest
, bb
))
1863 /* If there is non-abnormal path leaving e->src, predict edge
1864 using predictor. Otherwise we need to look for paths
1867 The second may lead to infinite loop in the case we are predicitng
1868 regions that are only reachable by abnormal edges. We simply
1869 prevent visiting given BB twice. */
1871 predict_edge_def (e
, pred
, taken
);
1872 else if (bitmap_set_bit (visited
, e
->src
->index
))
1873 predict_paths_for_bb (e
->src
, e
->src
, pred
, taken
, visited
);
1875 for (son
= first_dom_son (CDI_POST_DOMINATORS
, cur
);
1877 son
= next_dom_son (CDI_POST_DOMINATORS
, son
))
1878 predict_paths_for_bb (son
, bb
, pred
, taken
, visited
);
1881 /* Sets branch probabilities according to PREDiction and
1885 predict_paths_leading_to (basic_block bb
, enum br_predictor pred
,
1886 enum prediction taken
)
1888 bitmap visited
= BITMAP_ALLOC (NULL
);
1889 predict_paths_for_bb (bb
, bb
, pred
, taken
, visited
);
1890 BITMAP_FREE (visited
);
1893 /* Like predict_paths_leading_to but take edge instead of basic block. */
1896 predict_paths_leading_to_edge (edge e
, enum br_predictor pred
,
1897 enum prediction taken
)
1899 bool has_nonloop_edge
= false;
1903 basic_block bb
= e
->src
;
1904 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1905 if (e2
->dest
!= e
->src
&& e2
->dest
!= e
->dest
1906 && !(e
->flags
& (EDGE_EH
| EDGE_FAKE
))
1907 && !dominated_by_p (CDI_POST_DOMINATORS
, e
->src
, e2
->dest
))
1909 has_nonloop_edge
= true;
1912 if (!has_nonloop_edge
)
1914 bitmap visited
= BITMAP_ALLOC (NULL
);
1915 predict_paths_for_bb (bb
, bb
, pred
, taken
, visited
);
1916 BITMAP_FREE (visited
);
1919 predict_edge_def (e
, pred
, taken
);
1922 /* This is used to carry information about basic blocks. It is
1923 attached to the AUX field of the standard CFG block. */
1925 typedef struct block_info_def
1927 /* Estimated frequency of execution of basic_block. */
1930 /* To keep queue of basic blocks to process. */
1933 /* Number of predecessors we need to visit first. */
1937 /* Similar information for edges. */
1938 typedef struct edge_info_def
1940 /* In case edge is a loopback edge, the probability edge will be reached
1941 in case header is. Estimated number of iterations of the loop can be
1942 then computed as 1 / (1 - back_edge_prob). */
1943 sreal back_edge_prob
;
1944 /* True if the edge is a loopback edge in the natural loop. */
1945 unsigned int back_edge
:1;
1948 #define BLOCK_INFO(B) ((block_info) (B)->aux)
1949 #define EDGE_INFO(E) ((edge_info) (E)->aux)
1951 /* Helper function for estimate_bb_frequencies.
1952 Propagate the frequencies in blocks marked in
1953 TOVISIT, starting in HEAD. */
1956 propagate_freq (basic_block head
, bitmap tovisit
)
1965 /* For each basic block we need to visit count number of his predecessors
1966 we need to visit first. */
1967 EXECUTE_IF_SET_IN_BITMAP (tovisit
, 0, i
, bi
)
1972 bb
= BASIC_BLOCK (i
);
1974 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
1976 bool visit
= bitmap_bit_p (tovisit
, e
->src
->index
);
1978 if (visit
&& !(e
->flags
& EDGE_DFS_BACK
))
1980 else if (visit
&& dump_file
&& !EDGE_INFO (e
)->back_edge
)
1982 "Irreducible region hit, ignoring edge to %i->%i\n",
1983 e
->src
->index
, bb
->index
);
1985 BLOCK_INFO (bb
)->npredecessors
= count
;
1986 /* When function never returns, we will never process exit block. */
1987 if (!count
&& bb
== EXIT_BLOCK_PTR
)
1988 bb
->count
= bb
->frequency
= 0;
1991 memcpy (&BLOCK_INFO (head
)->frequency
, &real_one
, sizeof (real_one
));
1993 for (bb
= head
; bb
; bb
= nextbb
)
1996 sreal cyclic_probability
, frequency
;
1998 memcpy (&cyclic_probability
, &real_zero
, sizeof (real_zero
));
1999 memcpy (&frequency
, &real_zero
, sizeof (real_zero
));
2001 nextbb
= BLOCK_INFO (bb
)->next
;
2002 BLOCK_INFO (bb
)->next
= NULL
;
2004 /* Compute frequency of basic block. */
2007 #ifdef ENABLE_CHECKING
2008 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
2009 gcc_assert (!bitmap_bit_p (tovisit
, e
->src
->index
)
2010 || (e
->flags
& EDGE_DFS_BACK
));
2013 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
2014 if (EDGE_INFO (e
)->back_edge
)
2016 sreal_add (&cyclic_probability
, &cyclic_probability
,
2017 &EDGE_INFO (e
)->back_edge_prob
);
2019 else if (!(e
->flags
& EDGE_DFS_BACK
))
2023 /* frequency += (e->probability
2024 * BLOCK_INFO (e->src)->frequency /
2025 REG_BR_PROB_BASE); */
2027 sreal_init (&tmp
, e
->probability
, 0);
2028 sreal_mul (&tmp
, &tmp
, &BLOCK_INFO (e
->src
)->frequency
);
2029 sreal_mul (&tmp
, &tmp
, &real_inv_br_prob_base
);
2030 sreal_add (&frequency
, &frequency
, &tmp
);
2033 if (sreal_compare (&cyclic_probability
, &real_zero
) == 0)
2035 memcpy (&BLOCK_INFO (bb
)->frequency
, &frequency
,
2036 sizeof (frequency
));
2040 if (sreal_compare (&cyclic_probability
, &real_almost_one
) > 0)
2042 memcpy (&cyclic_probability
, &real_almost_one
,
2043 sizeof (real_almost_one
));
2046 /* BLOCK_INFO (bb)->frequency = frequency
2047 / (1 - cyclic_probability) */
2049 sreal_sub (&cyclic_probability
, &real_one
, &cyclic_probability
);
2050 sreal_div (&BLOCK_INFO (bb
)->frequency
,
2051 &frequency
, &cyclic_probability
);
2055 bitmap_clear_bit (tovisit
, bb
->index
);
2057 e
= find_edge (bb
, head
);
2062 /* EDGE_INFO (e)->back_edge_prob
2063 = ((e->probability * BLOCK_INFO (bb)->frequency)
2064 / REG_BR_PROB_BASE); */
2066 sreal_init (&tmp
, e
->probability
, 0);
2067 sreal_mul (&tmp
, &tmp
, &BLOCK_INFO (bb
)->frequency
);
2068 sreal_mul (&EDGE_INFO (e
)->back_edge_prob
,
2069 &tmp
, &real_inv_br_prob_base
);
2072 /* Propagate to successor blocks. */
2073 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
2074 if (!(e
->flags
& EDGE_DFS_BACK
)
2075 && BLOCK_INFO (e
->dest
)->npredecessors
)
2077 BLOCK_INFO (e
->dest
)->npredecessors
--;
2078 if (!BLOCK_INFO (e
->dest
)->npredecessors
)
2083 BLOCK_INFO (last
)->next
= e
->dest
;
2091 /* Estimate probabilities of loopback edges in loops at same nest level. */
2094 estimate_loops_at_level (struct loop
*first_loop
)
2098 for (loop
= first_loop
; loop
; loop
= loop
->next
)
2103 bitmap tovisit
= BITMAP_ALLOC (NULL
);
2105 estimate_loops_at_level (loop
->inner
);
2107 /* Find current loop back edge and mark it. */
2108 e
= loop_latch_edge (loop
);
2109 EDGE_INFO (e
)->back_edge
= 1;
2111 bbs
= get_loop_body (loop
);
2112 for (i
= 0; i
< loop
->num_nodes
; i
++)
2113 bitmap_set_bit (tovisit
, bbs
[i
]->index
);
2115 propagate_freq (loop
->header
, tovisit
);
2116 BITMAP_FREE (tovisit
);
2120 /* Propagates frequencies through structure of loops. */
2123 estimate_loops (void)
2125 bitmap tovisit
= BITMAP_ALLOC (NULL
);
2128 /* Start by estimating the frequencies in the loops. */
2129 if (number_of_loops () > 1)
2130 estimate_loops_at_level (current_loops
->tree_root
->inner
);
2132 /* Now propagate the frequencies through all the blocks. */
2135 bitmap_set_bit (tovisit
, bb
->index
);
2137 propagate_freq (ENTRY_BLOCK_PTR
, tovisit
);
2138 BITMAP_FREE (tovisit
);
2141 /* Convert counts measured by profile driven feedback to frequencies.
2142 Return nonzero iff there was any nonzero execution count. */
2145 counts_to_freqs (void)
2147 gcov_type count_max
, true_count_max
= 0;
2150 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR
, NULL
, next_bb
)
2151 true_count_max
= MAX (bb
->count
, true_count_max
);
2153 count_max
= MAX (true_count_max
, 1);
2154 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR
, NULL
, next_bb
)
2155 bb
->frequency
= (bb
->count
* BB_FREQ_MAX
+ count_max
/ 2) / count_max
;
2157 return true_count_max
;
2160 /* Return true if function is likely to be expensive, so there is no point to
2161 optimize performance of prologue, epilogue or do inlining at the expense
2162 of code size growth. THRESHOLD is the limit of number of instructions
2163 function can execute at average to be still considered not expensive. */
2166 expensive_function_p (int threshold
)
2168 unsigned int sum
= 0;
2172 /* We can not compute accurately for large thresholds due to scaled
2174 gcc_assert (threshold
<= BB_FREQ_MAX
);
2176 /* Frequencies are out of range. This either means that function contains
2177 internal loop executing more than BB_FREQ_MAX times or profile feedback
2178 is available and function has not been executed at all. */
2179 if (ENTRY_BLOCK_PTR
->frequency
== 0)
2182 /* Maximally BB_FREQ_MAX^2 so overflow won't happen. */
2183 limit
= ENTRY_BLOCK_PTR
->frequency
* threshold
;
2188 for (insn
= BB_HEAD (bb
); insn
!= NEXT_INSN (BB_END (bb
));
2189 insn
= NEXT_INSN (insn
))
2190 if (active_insn_p (insn
))
2192 sum
+= bb
->frequency
;
2201 /* Estimate basic blocks frequency by given branch probabilities. */
2204 estimate_bb_frequencies (void)
2209 if (profile_status
!= PROFILE_READ
|| !counts_to_freqs ())
2211 static int real_values_initialized
= 0;
2213 if (!real_values_initialized
)
2215 real_values_initialized
= 1;
2216 sreal_init (&real_zero
, 0, 0);
2217 sreal_init (&real_one
, 1, 0);
2218 sreal_init (&real_br_prob_base
, REG_BR_PROB_BASE
, 0);
2219 sreal_init (&real_bb_freq_max
, BB_FREQ_MAX
, 0);
2220 sreal_init (&real_one_half
, 1, -1);
2221 sreal_div (&real_inv_br_prob_base
, &real_one
, &real_br_prob_base
);
2222 sreal_sub (&real_almost_one
, &real_one
, &real_inv_br_prob_base
);
2225 mark_dfs_back_edges ();
2227 single_succ_edge (ENTRY_BLOCK_PTR
)->probability
= REG_BR_PROB_BASE
;
2229 /* Set up block info for each basic block. */
2230 alloc_aux_for_blocks (sizeof (struct block_info_def
));
2231 alloc_aux_for_edges (sizeof (struct edge_info_def
));
2232 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR
, NULL
, next_bb
)
2237 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
2239 sreal_init (&EDGE_INFO (e
)->back_edge_prob
, e
->probability
, 0);
2240 sreal_mul (&EDGE_INFO (e
)->back_edge_prob
,
2241 &EDGE_INFO (e
)->back_edge_prob
,
2242 &real_inv_br_prob_base
);
2246 /* First compute probabilities locally for each loop from innermost
2247 to outermost to examine probabilities for back edges. */
2250 memcpy (&freq_max
, &real_zero
, sizeof (real_zero
));
2252 if (sreal_compare (&freq_max
, &BLOCK_INFO (bb
)->frequency
) < 0)
2253 memcpy (&freq_max
, &BLOCK_INFO (bb
)->frequency
, sizeof (freq_max
));
2255 sreal_div (&freq_max
, &real_bb_freq_max
, &freq_max
);
2256 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR
, NULL
, next_bb
)
2260 sreal_mul (&tmp
, &BLOCK_INFO (bb
)->frequency
, &freq_max
);
2261 sreal_add (&tmp
, &tmp
, &real_one_half
);
2262 bb
->frequency
= sreal_to_int (&tmp
);
2265 free_aux_for_blocks ();
2266 free_aux_for_edges ();
2268 compute_function_frequency ();
2271 /* Decide whether function is hot, cold or unlikely executed. */
2273 compute_function_frequency (void)
2276 struct cgraph_node
*node
= cgraph_get_node (current_function_decl
);
2277 if (DECL_STATIC_CONSTRUCTOR (current_function_decl
)
2278 || MAIN_NAME_P (DECL_NAME (current_function_decl
)))
2279 node
->only_called_at_startup
= true;
2280 if (DECL_STATIC_DESTRUCTOR (current_function_decl
))
2281 node
->only_called_at_exit
= true;
2283 if (!profile_info
|| !flag_branch_probabilities
)
2285 int flags
= flags_from_decl_or_type (current_function_decl
);
2286 if (lookup_attribute ("cold", DECL_ATTRIBUTES (current_function_decl
))
2288 node
->frequency
= NODE_FREQUENCY_UNLIKELY_EXECUTED
;
2289 else if (lookup_attribute ("hot", DECL_ATTRIBUTES (current_function_decl
))
2291 node
->frequency
= NODE_FREQUENCY_HOT
;
2292 else if (flags
& ECF_NORETURN
)
2293 node
->frequency
= NODE_FREQUENCY_EXECUTED_ONCE
;
2294 else if (MAIN_NAME_P (DECL_NAME (current_function_decl
)))
2295 node
->frequency
= NODE_FREQUENCY_EXECUTED_ONCE
;
2296 else if (DECL_STATIC_CONSTRUCTOR (current_function_decl
)
2297 || DECL_STATIC_DESTRUCTOR (current_function_decl
))
2298 node
->frequency
= NODE_FREQUENCY_EXECUTED_ONCE
;
2301 node
->frequency
= NODE_FREQUENCY_UNLIKELY_EXECUTED
;
2304 if (maybe_hot_bb_p (bb
))
2306 node
->frequency
= NODE_FREQUENCY_HOT
;
2309 if (!probably_never_executed_bb_p (bb
))
2310 node
->frequency
= NODE_FREQUENCY_NORMAL
;
2315 gate_estimate_probability (void)
2317 return flag_guess_branch_prob
;
2320 /* Build PREDICT_EXPR. */
2322 build_predict_expr (enum br_predictor predictor
, enum prediction taken
)
2324 tree t
= build1 (PREDICT_EXPR
, void_type_node
,
2325 build_int_cst (integer_type_node
, predictor
));
2326 SET_PREDICT_EXPR_OUTCOME (t
, taken
);
2331 predictor_name (enum br_predictor predictor
)
2333 return predictor_info
[predictor
].name
;
2336 struct gimple_opt_pass pass_profile
=
2340 "profile_estimate", /* name */
2341 gate_estimate_probability
, /* gate */
2342 tree_estimate_probability_driver
, /* execute */
2345 0, /* static_pass_number */
2346 TV_BRANCH_PROB
, /* tv_id */
2347 PROP_cfg
, /* properties_required */
2348 0, /* properties_provided */
2349 0, /* properties_destroyed */
2350 0, /* todo_flags_start */
2351 TODO_ggc_collect
| TODO_verify_ssa
/* todo_flags_finish */
2355 struct gimple_opt_pass pass_strip_predict_hints
=
2359 "*strip_predict_hints", /* name */
2361 strip_predict_hints
, /* execute */
2364 0, /* static_pass_number */
2365 TV_BRANCH_PROB
, /* tv_id */
2366 PROP_cfg
, /* properties_required */
2367 0, /* properties_provided */
2368 0, /* properties_destroyed */
2369 0, /* todo_flags_start */
2370 TODO_ggc_collect
| TODO_verify_ssa
/* todo_flags_finish */
2374 /* Rebuild function frequencies. Passes are in general expected to
2375 maintain profile by hand, however in some cases this is not possible:
2376 for example when inlining several functions with loops freuqencies might run
2377 out of scale and thus needs to be recomputed. */
2380 rebuild_frequencies (void)
2382 timevar_push (TV_REBUILD_FREQUENCIES
);
2383 if (profile_status
== PROFILE_GUESSED
)
2385 loop_optimizer_init (0);
2386 add_noreturn_fake_exit_edges ();
2387 mark_irreducible_loops ();
2388 connect_infinite_loops_to_exit ();
2389 estimate_bb_frequencies ();
2390 remove_fake_exit_edges ();
2391 loop_optimizer_finalize ();
2393 else if (profile_status
== PROFILE_READ
)
2397 timevar_pop (TV_REBUILD_FREQUENCIES
);