1 /* Branch prediction routines for the GNU compiler.
2 Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005
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 2, 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 COPYING. If not, write to the Free
19 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
24 [1] "Branch Prediction for Free"
25 Ball and Larus; PLDI '93.
26 [2] "Static Branch Frequency and Program Profile Analysis"
27 Wu and Larus; MICRO-27.
28 [3] "Corpus-based Static Branch Prediction"
29 Calder, Grunwald, Lindsay, Martin, Mozer, and Zorn; PLDI '95. */
34 #include "coretypes.h"
39 #include "hard-reg-set.h"
40 #include "basic-block.h"
41 #include "insn-config.h"
56 #include "tree-flow.h"
58 #include "tree-dump.h"
59 #include "tree-pass.h"
61 #include "tree-scalar-evolution.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 #define PROB_VERY_UNLIKELY (REG_BR_PROB_BASE / 100 - 1)
71 #define PROB_EVEN (REG_BR_PROB_BASE / 2)
72 #define PROB_VERY_LIKELY (REG_BR_PROB_BASE - PROB_VERY_UNLIKELY)
73 #define PROB_ALWAYS (REG_BR_PROB_BASE)
75 static void combine_predictions_for_insn (rtx
, basic_block
);
76 static void dump_prediction (FILE *, enum br_predictor
, int, basic_block
, int);
77 static void predict_paths_leading_to (basic_block
, int *, enum br_predictor
, enum prediction
);
78 static bool last_basic_block_p (basic_block
);
79 static void compute_function_frequency (void);
80 static void choose_function_section (void);
81 static bool can_predict_insn_p (rtx
);
82 static void estimate_bb_frequencies (void);
84 /* Information we hold about each branch predictor.
85 Filled using information from predict.def. */
89 const char *const name
; /* Name used in the debugging dumps. */
90 const int hitrate
; /* Expected hitrate used by
91 predict_insn_def call. */
95 /* Use given predictor without Dempster-Shaffer theory if it matches
96 using first_match heuristics. */
97 #define PRED_FLAG_FIRST_MATCH 1
99 /* Recompute hitrate in percent to our representation. */
101 #define HITRATE(VAL) ((int) ((VAL) * REG_BR_PROB_BASE + 50) / 100)
103 #define DEF_PREDICTOR(ENUM, NAME, HITRATE, FLAGS) {NAME, HITRATE, FLAGS},
104 static const struct predictor_info predictor_info
[]= {
105 #include "predict.def"
107 /* Upper bound on predictors. */
112 /* Return true in case BB can be CPU intensive and should be optimized
113 for maximal performance. */
116 maybe_hot_bb_p (basic_block bb
)
118 if (profile_info
&& flag_branch_probabilities
120 < profile_info
->sum_max
/ PARAM_VALUE (HOT_BB_COUNT_FRACTION
)))
122 if (bb
->frequency
< BB_FREQ_MAX
/ PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION
))
127 /* Return true in case BB is cold and should be optimized for size. */
130 probably_cold_bb_p (basic_block bb
)
132 if (profile_info
&& flag_branch_probabilities
134 < profile_info
->sum_max
/ PARAM_VALUE (HOT_BB_COUNT_FRACTION
)))
136 if (bb
->frequency
< BB_FREQ_MAX
/ PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION
))
141 /* Return true in case BB is probably never executed. */
143 probably_never_executed_bb_p (basic_block bb
)
145 if (profile_info
&& flag_branch_probabilities
)
146 return ((bb
->count
+ profile_info
->runs
/ 2) / profile_info
->runs
) == 0;
150 /* Return true if the one of outgoing edges is already predicted by
154 rtl_predicted_by_p (basic_block bb
, enum br_predictor predictor
)
157 if (!INSN_P (BB_END (bb
)))
159 for (note
= REG_NOTES (BB_END (bb
)); note
; note
= XEXP (note
, 1))
160 if (REG_NOTE_KIND (note
) == REG_BR_PRED
161 && INTVAL (XEXP (XEXP (note
, 0), 0)) == (int)predictor
)
166 /* Return true if the one of outgoing edges is already predicted by
170 tree_predicted_by_p (basic_block bb
, enum br_predictor predictor
)
172 struct edge_prediction
*i
;
173 for (i
= bb
->predictions
; i
; i
= i
->ep_next
)
174 if (i
->ep_predictor
== predictor
)
179 /* Return true when the probability of edge is reliable.
181 The profile guessing code is good at predicting branch outcome (ie.
182 taken/not taken), that is predicted right slightly over 75% of time.
183 It is however notoriously poor on predicting the probability itself.
184 In general the profile appear a lot flatter (with probabilities closer
185 to 50%) than the reality so it is bad idea to use it to drive optimization
186 such as those disabling dynamic branch prediction for well predictable
189 There are two exceptions - edges leading to noreturn edges and edges
190 predicted by number of iterations heuristics are predicted well. This macro
191 should be able to distinguish those, but at the moment it simply check for
192 noreturn heuristic that is only one giving probability over 99% or bellow
193 1%. In future we might want to propagate reliability information across the
194 CFG if we find this information useful on multiple places. */
196 probability_reliable_p (int prob
)
198 return (profile_status
== PROFILE_READ
199 || (profile_status
== PROFILE_GUESSED
200 && (prob
<= HITRATE (1) || prob
>= HITRATE (99))));
203 /* Same predicate as above, working on edges. */
205 edge_probability_reliable_p (edge e
)
207 return probability_reliable_p (e
->probability
);
210 /* Same predicate as edge_probability_reliable_p, working on notes. */
212 br_prob_note_reliable_p (rtx note
)
214 gcc_assert (REG_NOTE_KIND (note
) == REG_BR_PROB
);
215 return probability_reliable_p (INTVAL (XEXP (note
, 0)));
219 predict_insn (rtx insn
, enum br_predictor predictor
, int probability
)
221 gcc_assert (any_condjump_p (insn
));
222 if (!flag_guess_branch_prob
)
226 = gen_rtx_EXPR_LIST (REG_BR_PRED
,
227 gen_rtx_CONCAT (VOIDmode
,
228 GEN_INT ((int) predictor
),
229 GEN_INT ((int) probability
)),
233 /* Predict insn by given predictor. */
236 predict_insn_def (rtx insn
, enum br_predictor predictor
,
237 enum prediction taken
)
239 int probability
= predictor_info
[(int) predictor
].hitrate
;
242 probability
= REG_BR_PROB_BASE
- probability
;
244 predict_insn (insn
, predictor
, probability
);
247 /* Predict edge E with given probability if possible. */
250 rtl_predict_edge (edge e
, enum br_predictor predictor
, int probability
)
253 last_insn
= BB_END (e
->src
);
255 /* We can store the branch prediction information only about
256 conditional jumps. */
257 if (!any_condjump_p (last_insn
))
260 /* We always store probability of branching. */
261 if (e
->flags
& EDGE_FALLTHRU
)
262 probability
= REG_BR_PROB_BASE
- probability
;
264 predict_insn (last_insn
, predictor
, probability
);
267 /* Predict edge E with the given PROBABILITY. */
269 tree_predict_edge (edge e
, enum br_predictor predictor
, int probability
)
271 gcc_assert (profile_status
!= PROFILE_GUESSED
);
272 if ((e
->src
!= ENTRY_BLOCK_PTR
&& EDGE_COUNT (e
->src
->succs
) > 1)
273 && flag_guess_branch_prob
&& optimize
)
275 struct edge_prediction
*i
= ggc_alloc (sizeof (struct edge_prediction
));
277 i
->ep_next
= e
->src
->predictions
;
278 e
->src
->predictions
= i
;
279 i
->ep_probability
= probability
;
280 i
->ep_predictor
= predictor
;
285 /* Remove all predictions on given basic block that are attached
288 remove_predictions_associated_with_edge (edge e
)
290 if (e
->src
->predictions
)
292 struct edge_prediction
**prediction
= &e
->src
->predictions
;
295 if ((*prediction
)->ep_edge
== e
)
296 *prediction
= (*prediction
)->ep_next
;
298 prediction
= &((*prediction
)->ep_next
);
303 /* Return true when we can store prediction on insn INSN.
304 At the moment we represent predictions only on conditional
305 jumps, not at computed jump or other complicated cases. */
307 can_predict_insn_p (rtx insn
)
309 return (JUMP_P (insn
)
310 && any_condjump_p (insn
)
311 && EDGE_COUNT (BLOCK_FOR_INSN (insn
)->succs
) >= 2);
314 /* Predict edge E by given predictor if possible. */
317 predict_edge_def (edge e
, enum br_predictor predictor
,
318 enum prediction taken
)
320 int probability
= predictor_info
[(int) predictor
].hitrate
;
323 probability
= REG_BR_PROB_BASE
- probability
;
325 predict_edge (e
, predictor
, probability
);
328 /* Invert all branch predictions or probability notes in the INSN. This needs
329 to be done each time we invert the condition used by the jump. */
332 invert_br_probabilities (rtx insn
)
336 for (note
= REG_NOTES (insn
); note
; note
= XEXP (note
, 1))
337 if (REG_NOTE_KIND (note
) == REG_BR_PROB
)
338 XEXP (note
, 0) = GEN_INT (REG_BR_PROB_BASE
- INTVAL (XEXP (note
, 0)));
339 else if (REG_NOTE_KIND (note
) == REG_BR_PRED
)
340 XEXP (XEXP (note
, 0), 1)
341 = GEN_INT (REG_BR_PROB_BASE
- INTVAL (XEXP (XEXP (note
, 0), 1)));
344 /* Dump information about the branch prediction to the output file. */
347 dump_prediction (FILE *file
, enum br_predictor predictor
, int probability
,
348 basic_block bb
, int used
)
356 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
357 if (! (e
->flags
& EDGE_FALLTHRU
))
360 fprintf (file
, " %s heuristics%s: %.1f%%",
361 predictor_info
[predictor
].name
,
362 used
? "" : " (ignored)", probability
* 100.0 / REG_BR_PROB_BASE
);
366 fprintf (file
, " exec ");
367 fprintf (file
, HOST_WIDEST_INT_PRINT_DEC
, bb
->count
);
370 fprintf (file
, " hit ");
371 fprintf (file
, HOST_WIDEST_INT_PRINT_DEC
, e
->count
);
372 fprintf (file
, " (%.1f%%)", e
->count
* 100.0 / bb
->count
);
376 fprintf (file
, "\n");
379 /* We can not predict the probabilities of outgoing edges of bb. Set them
380 evenly and hope for the best. */
382 set_even_probabilities (basic_block bb
)
388 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
389 if (!(e
->flags
& (EDGE_EH
| EDGE_FAKE
)))
391 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
392 if (!(e
->flags
& (EDGE_EH
| EDGE_FAKE
)))
393 e
->probability
= (REG_BR_PROB_BASE
+ nedges
/ 2) / nedges
;
398 /* Combine all REG_BR_PRED notes into single probability and attach REG_BR_PROB
399 note if not already present. Remove now useless REG_BR_PRED notes. */
402 combine_predictions_for_insn (rtx insn
, basic_block bb
)
407 int best_probability
= PROB_EVEN
;
408 int best_predictor
= END_PREDICTORS
;
409 int combined_probability
= REG_BR_PROB_BASE
/ 2;
411 bool first_match
= false;
414 if (!can_predict_insn_p (insn
))
416 set_even_probabilities (bb
);
420 prob_note
= find_reg_note (insn
, REG_BR_PROB
, 0);
421 pnote
= ®_NOTES (insn
);
423 fprintf (dump_file
, "Predictions for insn %i bb %i\n", INSN_UID (insn
),
426 /* We implement "first match" heuristics and use probability guessed
427 by predictor with smallest index. */
428 for (note
= REG_NOTES (insn
); note
; note
= XEXP (note
, 1))
429 if (REG_NOTE_KIND (note
) == REG_BR_PRED
)
431 int predictor
= INTVAL (XEXP (XEXP (note
, 0), 0));
432 int probability
= INTVAL (XEXP (XEXP (note
, 0), 1));
435 if (best_predictor
> predictor
)
436 best_probability
= probability
, best_predictor
= predictor
;
438 d
= (combined_probability
* probability
439 + (REG_BR_PROB_BASE
- combined_probability
)
440 * (REG_BR_PROB_BASE
- probability
));
442 /* Use FP math to avoid overflows of 32bit integers. */
444 /* If one probability is 0% and one 100%, avoid division by zero. */
445 combined_probability
= REG_BR_PROB_BASE
/ 2;
447 combined_probability
= (((double) combined_probability
) * probability
448 * REG_BR_PROB_BASE
/ d
+ 0.5);
451 /* Decide which heuristic to use. In case we didn't match anything,
452 use no_prediction heuristic, in case we did match, use either
453 first match or Dempster-Shaffer theory depending on the flags. */
455 if (predictor_info
[best_predictor
].flags
& PRED_FLAG_FIRST_MATCH
)
459 dump_prediction (dump_file
, PRED_NO_PREDICTION
,
460 combined_probability
, bb
, true);
463 dump_prediction (dump_file
, PRED_DS_THEORY
, combined_probability
,
465 dump_prediction (dump_file
, PRED_FIRST_MATCH
, best_probability
,
470 combined_probability
= best_probability
;
471 dump_prediction (dump_file
, PRED_COMBINED
, combined_probability
, bb
, true);
475 if (REG_NOTE_KIND (*pnote
) == REG_BR_PRED
)
477 int predictor
= INTVAL (XEXP (XEXP (*pnote
, 0), 0));
478 int probability
= INTVAL (XEXP (XEXP (*pnote
, 0), 1));
480 dump_prediction (dump_file
, predictor
, probability
, bb
,
481 !first_match
|| best_predictor
== predictor
);
482 *pnote
= XEXP (*pnote
, 1);
485 pnote
= &XEXP (*pnote
, 1);
491 = gen_rtx_EXPR_LIST (REG_BR_PROB
,
492 GEN_INT (combined_probability
), REG_NOTES (insn
));
494 /* Save the prediction into CFG in case we are seeing non-degenerated
496 if (!single_succ_p (bb
))
498 BRANCH_EDGE (bb
)->probability
= combined_probability
;
499 FALLTHRU_EDGE (bb
)->probability
500 = REG_BR_PROB_BASE
- combined_probability
;
503 else if (!single_succ_p (bb
))
505 int prob
= INTVAL (XEXP (prob_note
, 0));
507 BRANCH_EDGE (bb
)->probability
= prob
;
508 FALLTHRU_EDGE (bb
)->probability
= REG_BR_PROB_BASE
- prob
;
511 single_succ_edge (bb
)->probability
= REG_BR_PROB_BASE
;
514 /* Combine predictions into single probability and store them into CFG.
515 Remove now useless prediction entries. */
518 combine_predictions_for_bb (basic_block bb
)
520 int best_probability
= PROB_EVEN
;
521 int best_predictor
= END_PREDICTORS
;
522 int combined_probability
= REG_BR_PROB_BASE
/ 2;
524 bool first_match
= false;
526 struct edge_prediction
*pred
;
528 edge e
, first
= NULL
, second
= NULL
;
531 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
532 if (!(e
->flags
& (EDGE_EH
| EDGE_FAKE
)))
535 if (first
&& !second
)
541 /* When there is no successor or only one choice, prediction is easy.
543 We are lazy for now and predict only basic blocks with two outgoing
544 edges. It is possible to predict generic case too, but we have to
545 ignore first match heuristics and do more involved combining. Implement
550 set_even_probabilities (bb
);
551 bb
->predictions
= NULL
;
553 fprintf (dump_file
, "%i edges in bb %i predicted to even probabilities\n",
559 fprintf (dump_file
, "Predictions for bb %i\n", bb
->index
);
561 /* We implement "first match" heuristics and use probability guessed
562 by predictor with smallest index. */
563 for (pred
= bb
->predictions
; pred
; pred
= pred
->ep_next
)
565 int predictor
= pred
->ep_predictor
;
566 int probability
= pred
->ep_probability
;
568 if (pred
->ep_edge
!= first
)
569 probability
= REG_BR_PROB_BASE
- probability
;
572 if (best_predictor
> predictor
)
573 best_probability
= probability
, best_predictor
= predictor
;
575 d
= (combined_probability
* probability
576 + (REG_BR_PROB_BASE
- combined_probability
)
577 * (REG_BR_PROB_BASE
- probability
));
579 /* Use FP math to avoid overflows of 32bit integers. */
581 /* If one probability is 0% and one 100%, avoid division by zero. */
582 combined_probability
= REG_BR_PROB_BASE
/ 2;
584 combined_probability
= (((double) combined_probability
) * probability
585 * REG_BR_PROB_BASE
/ d
+ 0.5);
588 /* Decide which heuristic to use. In case we didn't match anything,
589 use no_prediction heuristic, in case we did match, use either
590 first match or Dempster-Shaffer theory depending on the flags. */
592 if (predictor_info
[best_predictor
].flags
& PRED_FLAG_FIRST_MATCH
)
596 dump_prediction (dump_file
, PRED_NO_PREDICTION
, combined_probability
, bb
, true);
599 dump_prediction (dump_file
, PRED_DS_THEORY
, combined_probability
, bb
,
601 dump_prediction (dump_file
, PRED_FIRST_MATCH
, best_probability
, bb
,
606 combined_probability
= best_probability
;
607 dump_prediction (dump_file
, PRED_COMBINED
, combined_probability
, bb
, true);
609 for (pred
= bb
->predictions
; pred
; pred
= pred
->ep_next
)
611 int predictor
= pred
->ep_predictor
;
612 int probability
= pred
->ep_probability
;
614 if (pred
->ep_edge
!= EDGE_SUCC (bb
, 0))
615 probability
= REG_BR_PROB_BASE
- probability
;
616 dump_prediction (dump_file
, predictor
, probability
, bb
,
617 !first_match
|| best_predictor
== predictor
);
619 bb
->predictions
= NULL
;
623 first
->probability
= combined_probability
;
624 second
->probability
= REG_BR_PROB_BASE
- combined_probability
;
628 /* Predict edge probabilities by exploiting loop structure. */
637 /* Try to predict out blocks in a loop that are not part of a
639 for (i
= 1; i
< current_loops
->num
; i
++)
641 basic_block bb
, *bbs
;
643 struct loop
*loop
= current_loops
->parray
[i
];
644 VEC (edge
, heap
) *exits
;
645 struct tree_niter_desc niter_desc
;
648 exits
= get_loop_exit_edges (loop
);
649 n_exits
= VEC_length (edge
, exits
);
651 for (j
= 0; VEC_iterate (edge
, exits
, j
, ex
); j
++)
655 if (number_of_iterations_exit (loop
, ex
, &niter_desc
, false))
656 niter
= niter_desc
.niter
;
657 if (!niter
|| TREE_CODE (niter_desc
.niter
) != INTEGER_CST
)
658 niter
= loop_niter_by_eval (loop
, ex
);
660 if (TREE_CODE (niter
) == INTEGER_CST
)
663 int max
= PARAM_VALUE (PARAM_MAX_PREDICTED_ITERATIONS
);
664 if (host_integerp (niter
, 1)
665 && tree_int_cst_lt (niter
,
666 build_int_cstu (NULL_TREE
, max
- 1)))
668 HOST_WIDE_INT nitercst
= tree_low_cst (niter
, 1) + 1;
669 probability
= ((REG_BR_PROB_BASE
+ nitercst
/ 2)
673 probability
= ((REG_BR_PROB_BASE
+ max
/ 2) / max
);
675 predict_edge (ex
, PRED_LOOP_ITERATIONS
, probability
);
678 VEC_free (edge
, heap
, exits
);
680 bbs
= get_loop_body (loop
);
682 for (j
= 0; j
< loop
->num_nodes
; j
++)
684 int header_found
= 0;
690 /* Bypass loop heuristics on continue statement. These
691 statements construct loops via "non-loop" constructs
692 in the source language and are better to be handled
694 if (predicted_by_p (bb
, PRED_CONTINUE
))
697 /* Loop branch heuristics - predict an edge back to a
698 loop's head as taken. */
699 if (bb
== loop
->latch
)
701 e
= find_edge (loop
->latch
, loop
->header
);
705 predict_edge_def (e
, PRED_LOOP_BRANCH
, TAKEN
);
709 /* Loop exit heuristics - predict an edge exiting the loop if the
710 conditional has no loop header successors as not taken. */
713 /* For loop with many exits we don't want to predict all exits
714 with the pretty large probability, because if all exits are
715 considered in row, the loop would be predicted to iterate
716 almost never. The code to divide probability by number of
717 exits is very rough. It should compute the number of exits
718 taken in each patch through function (not the overall number
719 of exits that might be a lot higher for loops with wide switch
720 statements in them) and compute n-th square root.
722 We limit the minimal probability by 2% to avoid
723 EDGE_PROBABILITY_RELIABLE from trusting the branch prediction
724 as this was causing regression in perl benchmark containing such
727 int probability
= ((REG_BR_PROB_BASE
728 - predictor_info
[(int) PRED_LOOP_EXIT
].hitrate
)
730 if (probability
< HITRATE (2))
731 probability
= HITRATE (2);
732 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
733 if (e
->dest
->index
< NUM_FIXED_BLOCKS
734 || !flow_bb_inside_loop_p (loop
, e
->dest
))
735 predict_edge (e
, PRED_LOOP_EXIT
, probability
);
739 /* Free basic blocks from get_loop_body. */
746 /* Attempt to predict probabilities of BB outgoing edges using local
749 bb_estimate_probability_locally (basic_block bb
)
751 rtx last_insn
= BB_END (bb
);
754 if (! can_predict_insn_p (last_insn
))
756 cond
= get_condition (last_insn
, NULL
, false, false);
760 /* Try "pointer heuristic."
761 A comparison ptr == 0 is predicted as false.
762 Similarly, a comparison ptr1 == ptr2 is predicted as false. */
763 if (COMPARISON_P (cond
)
764 && ((REG_P (XEXP (cond
, 0)) && REG_POINTER (XEXP (cond
, 0)))
765 || (REG_P (XEXP (cond
, 1)) && REG_POINTER (XEXP (cond
, 1)))))
767 if (GET_CODE (cond
) == EQ
)
768 predict_insn_def (last_insn
, PRED_POINTER
, NOT_TAKEN
);
769 else if (GET_CODE (cond
) == NE
)
770 predict_insn_def (last_insn
, PRED_POINTER
, TAKEN
);
774 /* Try "opcode heuristic."
775 EQ tests are usually false and NE tests are usually true. Also,
776 most quantities are positive, so we can make the appropriate guesses
777 about signed comparisons against zero. */
778 switch (GET_CODE (cond
))
781 /* Unconditional branch. */
782 predict_insn_def (last_insn
, PRED_UNCONDITIONAL
,
783 cond
== const0_rtx
? NOT_TAKEN
: TAKEN
);
788 /* Floating point comparisons appears to behave in a very
789 unpredictable way because of special role of = tests in
791 if (FLOAT_MODE_P (GET_MODE (XEXP (cond
, 0))))
793 /* Comparisons with 0 are often used for booleans and there is
794 nothing useful to predict about them. */
795 else if (XEXP (cond
, 1) == const0_rtx
796 || XEXP (cond
, 0) == const0_rtx
)
799 predict_insn_def (last_insn
, PRED_OPCODE_NONEQUAL
, NOT_TAKEN
);
804 /* Floating point comparisons appears to behave in a very
805 unpredictable way because of special role of = tests in
807 if (FLOAT_MODE_P (GET_MODE (XEXP (cond
, 0))))
809 /* Comparisons with 0 are often used for booleans and there is
810 nothing useful to predict about them. */
811 else if (XEXP (cond
, 1) == const0_rtx
812 || XEXP (cond
, 0) == const0_rtx
)
815 predict_insn_def (last_insn
, PRED_OPCODE_NONEQUAL
, TAKEN
);
819 predict_insn_def (last_insn
, PRED_FPOPCODE
, TAKEN
);
823 predict_insn_def (last_insn
, PRED_FPOPCODE
, NOT_TAKEN
);
828 if (XEXP (cond
, 1) == const0_rtx
|| XEXP (cond
, 1) == const1_rtx
829 || XEXP (cond
, 1) == constm1_rtx
)
830 predict_insn_def (last_insn
, PRED_OPCODE_POSITIVE
, NOT_TAKEN
);
835 if (XEXP (cond
, 1) == const0_rtx
|| XEXP (cond
, 1) == const1_rtx
836 || XEXP (cond
, 1) == constm1_rtx
)
837 predict_insn_def (last_insn
, PRED_OPCODE_POSITIVE
, TAKEN
);
845 /* Set edge->probability for each successor edge of BB. */
847 guess_outgoing_edge_probabilities (basic_block bb
)
849 bb_estimate_probability_locally (bb
);
850 combine_predictions_for_insn (BB_END (bb
), bb
);
853 /* Return constant EXPR will likely have at execution time, NULL if unknown.
854 The function is used by builtin_expect branch predictor so the evidence
855 must come from this construct and additional possible constant folding.
857 We may want to implement more involved value guess (such as value range
858 propagation based prediction), but such tricks shall go to new
862 expr_expected_value (tree expr
, bitmap visited
)
864 if (TREE_CONSTANT (expr
))
866 else if (TREE_CODE (expr
) == SSA_NAME
)
868 tree def
= SSA_NAME_DEF_STMT (expr
);
870 /* If we were already here, break the infinite cycle. */
871 if (bitmap_bit_p (visited
, SSA_NAME_VERSION (expr
)))
873 bitmap_set_bit (visited
, SSA_NAME_VERSION (expr
));
875 if (TREE_CODE (def
) == PHI_NODE
)
877 /* All the arguments of the PHI node must have the same constant
880 tree val
= NULL
, new_val
;
882 for (i
= 0; i
< PHI_NUM_ARGS (def
); i
++)
884 tree arg
= PHI_ARG_DEF (def
, i
);
886 /* If this PHI has itself as an argument, we cannot
887 determine the string length of this argument. However,
888 if we can find an expected constant value for the other
889 PHI args then we can still be sure that this is
890 likely a constant. So be optimistic and just
891 continue with the next argument. */
892 if (arg
== PHI_RESULT (def
))
895 new_val
= expr_expected_value (arg
, visited
);
900 else if (!operand_equal_p (val
, new_val
, false))
905 if (TREE_CODE (def
) != MODIFY_EXPR
|| TREE_OPERAND (def
, 0) != expr
)
907 return expr_expected_value (TREE_OPERAND (def
, 1), visited
);
909 else if (TREE_CODE (expr
) == CALL_EXPR
)
911 tree decl
= get_callee_fndecl (expr
);
914 if (DECL_BUILT_IN_CLASS (decl
) == BUILT_IN_NORMAL
915 && DECL_FUNCTION_CODE (decl
) == BUILT_IN_EXPECT
)
917 tree arglist
= TREE_OPERAND (expr
, 1);
920 if (arglist
== NULL_TREE
921 || TREE_CHAIN (arglist
) == NULL_TREE
)
923 val
= TREE_VALUE (TREE_CHAIN (TREE_OPERAND (expr
, 1)));
924 if (TREE_CONSTANT (val
))
926 return TREE_VALUE (TREE_CHAIN (TREE_OPERAND (expr
, 1)));
929 if (BINARY_CLASS_P (expr
) || COMPARISON_CLASS_P (expr
))
932 op0
= expr_expected_value (TREE_OPERAND (expr
, 0), visited
);
935 op1
= expr_expected_value (TREE_OPERAND (expr
, 1), visited
);
938 res
= fold_build2 (TREE_CODE (expr
), TREE_TYPE (expr
), op0
, op1
);
939 if (TREE_CONSTANT (res
))
943 if (UNARY_CLASS_P (expr
))
946 op0
= expr_expected_value (TREE_OPERAND (expr
, 0), visited
);
949 res
= fold_build1 (TREE_CODE (expr
), TREE_TYPE (expr
), op0
);
950 if (TREE_CONSTANT (res
))
957 /* Get rid of all builtin_expect calls we no longer need. */
959 strip_builtin_expect (void)
964 block_stmt_iterator bi
;
965 for (bi
= bsi_start (bb
); !bsi_end_p (bi
); bsi_next (&bi
))
967 tree stmt
= bsi_stmt (bi
);
971 if (TREE_CODE (stmt
) == MODIFY_EXPR
972 && TREE_CODE (TREE_OPERAND (stmt
, 1)) == CALL_EXPR
973 && (fndecl
= get_callee_fndecl (TREE_OPERAND (stmt
, 1)))
974 && DECL_BUILT_IN_CLASS (fndecl
) == BUILT_IN_NORMAL
975 && DECL_FUNCTION_CODE (fndecl
) == BUILT_IN_EXPECT
976 && (arglist
= TREE_OPERAND (TREE_OPERAND (stmt
, 1), 1))
977 && TREE_CHAIN (arglist
))
979 TREE_OPERAND (stmt
, 1) = TREE_VALUE (arglist
);
986 /* Predict using opcode of the last statement in basic block. */
988 tree_predict_by_opcode (basic_block bb
)
990 tree stmt
= last_stmt (bb
);
999 if (!stmt
|| TREE_CODE (stmt
) != COND_EXPR
)
1001 FOR_EACH_EDGE (then_edge
, ei
, bb
->succs
)
1002 if (then_edge
->flags
& EDGE_TRUE_VALUE
)
1004 cond
= TREE_OPERAND (stmt
, 0);
1005 if (!COMPARISON_CLASS_P (cond
))
1007 op0
= TREE_OPERAND (cond
, 0);
1008 type
= TREE_TYPE (op0
);
1009 visited
= BITMAP_ALLOC (NULL
);
1010 val
= expr_expected_value (cond
, visited
);
1011 BITMAP_FREE (visited
);
1014 if (integer_zerop (val
))
1015 predict_edge_def (then_edge
, PRED_BUILTIN_EXPECT
, NOT_TAKEN
);
1017 predict_edge_def (then_edge
, PRED_BUILTIN_EXPECT
, TAKEN
);
1020 /* Try "pointer heuristic."
1021 A comparison ptr == 0 is predicted as false.
1022 Similarly, a comparison ptr1 == ptr2 is predicted as false. */
1023 if (POINTER_TYPE_P (type
))
1025 if (TREE_CODE (cond
) == EQ_EXPR
)
1026 predict_edge_def (then_edge
, PRED_TREE_POINTER
, NOT_TAKEN
);
1027 else if (TREE_CODE (cond
) == NE_EXPR
)
1028 predict_edge_def (then_edge
, PRED_TREE_POINTER
, TAKEN
);
1032 /* Try "opcode heuristic."
1033 EQ tests are usually false and NE tests are usually true. Also,
1034 most quantities are positive, so we can make the appropriate guesses
1035 about signed comparisons against zero. */
1036 switch (TREE_CODE (cond
))
1040 /* Floating point comparisons appears to behave in a very
1041 unpredictable way because of special role of = tests in
1043 if (FLOAT_TYPE_P (type
))
1045 /* Comparisons with 0 are often used for booleans and there is
1046 nothing useful to predict about them. */
1047 else if (integer_zerop (op0
)
1048 || integer_zerop (TREE_OPERAND (cond
, 1)))
1051 predict_edge_def (then_edge
, PRED_TREE_OPCODE_NONEQUAL
, NOT_TAKEN
);
1056 /* Floating point comparisons appears to behave in a very
1057 unpredictable way because of special role of = tests in
1059 if (FLOAT_TYPE_P (type
))
1061 /* Comparisons with 0 are often used for booleans and there is
1062 nothing useful to predict about them. */
1063 else if (integer_zerop (op0
)
1064 || integer_zerop (TREE_OPERAND (cond
, 1)))
1067 predict_edge_def (then_edge
, PRED_TREE_OPCODE_NONEQUAL
, TAKEN
);
1071 predict_edge_def (then_edge
, PRED_TREE_FPOPCODE
, TAKEN
);
1074 case UNORDERED_EXPR
:
1075 predict_edge_def (then_edge
, PRED_TREE_FPOPCODE
, NOT_TAKEN
);
1080 if (integer_zerop (TREE_OPERAND (cond
, 1))
1081 || integer_onep (TREE_OPERAND (cond
, 1))
1082 || integer_all_onesp (TREE_OPERAND (cond
, 1))
1083 || real_zerop (TREE_OPERAND (cond
, 1))
1084 || real_onep (TREE_OPERAND (cond
, 1))
1085 || real_minus_onep (TREE_OPERAND (cond
, 1)))
1086 predict_edge_def (then_edge
, PRED_TREE_OPCODE_POSITIVE
, NOT_TAKEN
);
1091 if (integer_zerop (TREE_OPERAND (cond
, 1))
1092 || integer_onep (TREE_OPERAND (cond
, 1))
1093 || integer_all_onesp (TREE_OPERAND (cond
, 1))
1094 || real_zerop (TREE_OPERAND (cond
, 1))
1095 || real_onep (TREE_OPERAND (cond
, 1))
1096 || real_minus_onep (TREE_OPERAND (cond
, 1)))
1097 predict_edge_def (then_edge
, PRED_TREE_OPCODE_POSITIVE
, TAKEN
);
1105 /* Try to guess whether the value of return means error code. */
1106 static enum br_predictor
1107 return_prediction (tree val
, enum prediction
*prediction
)
1111 return PRED_NO_PREDICTION
;
1112 /* Different heuristics for pointers and scalars. */
1113 if (POINTER_TYPE_P (TREE_TYPE (val
)))
1115 /* NULL is usually not returned. */
1116 if (integer_zerop (val
))
1118 *prediction
= NOT_TAKEN
;
1119 return PRED_NULL_RETURN
;
1122 else if (INTEGRAL_TYPE_P (TREE_TYPE (val
)))
1124 /* Negative return values are often used to indicate
1126 if (TREE_CODE (val
) == INTEGER_CST
1127 && tree_int_cst_sgn (val
) < 0)
1129 *prediction
= NOT_TAKEN
;
1130 return PRED_NEGATIVE_RETURN
;
1132 /* Constant return values seems to be commonly taken.
1133 Zero/one often represent booleans so exclude them from the
1135 if (TREE_CONSTANT (val
)
1136 && (!integer_zerop (val
) && !integer_onep (val
)))
1138 *prediction
= TAKEN
;
1139 return PRED_NEGATIVE_RETURN
;
1142 return PRED_NO_PREDICTION
;
1145 /* Find the basic block with return expression and look up for possible
1146 return value trying to apply RETURN_PREDICTION heuristics. */
1148 apply_return_prediction (int *heads
)
1150 tree return_stmt
= NULL
;
1154 int phi_num_args
, i
;
1155 enum br_predictor pred
;
1156 enum prediction direction
;
1159 FOR_EACH_EDGE (e
, ei
, EXIT_BLOCK_PTR
->preds
)
1161 return_stmt
= last_stmt (e
->src
);
1162 if (TREE_CODE (return_stmt
) == RETURN_EXPR
)
1167 return_val
= TREE_OPERAND (return_stmt
, 0);
1170 if (TREE_CODE (return_val
) == MODIFY_EXPR
)
1171 return_val
= TREE_OPERAND (return_val
, 1);
1172 if (TREE_CODE (return_val
) != SSA_NAME
1173 || !SSA_NAME_DEF_STMT (return_val
)
1174 || TREE_CODE (SSA_NAME_DEF_STMT (return_val
)) != PHI_NODE
)
1176 for (phi
= SSA_NAME_DEF_STMT (return_val
); phi
; phi
= PHI_CHAIN (phi
))
1177 if (PHI_RESULT (phi
) == return_val
)
1181 phi_num_args
= PHI_NUM_ARGS (phi
);
1182 pred
= return_prediction (PHI_ARG_DEF (phi
, 0), &direction
);
1184 /* Avoid the degenerate case where all return values form the function
1185 belongs to same category (ie they are all positive constants)
1186 so we can hardly say something about them. */
1187 for (i
= 1; i
< phi_num_args
; i
++)
1188 if (pred
!= return_prediction (PHI_ARG_DEF (phi
, i
), &direction
))
1190 if (i
!= phi_num_args
)
1191 for (i
= 0; i
< phi_num_args
; i
++)
1193 pred
= return_prediction (PHI_ARG_DEF (phi
, i
), &direction
);
1194 if (pred
!= PRED_NO_PREDICTION
)
1195 predict_paths_leading_to (PHI_ARG_EDGE (phi
, i
)->src
, heads
, pred
,
1200 /* Look for basic block that contains unlikely to happen events
1201 (such as noreturn calls) and mark all paths leading to execution
1202 of this basic blocks as unlikely. */
1205 tree_bb_level_predictions (void)
1210 heads
= XCNEWVEC (int, last_basic_block
);
1211 heads
[ENTRY_BLOCK_PTR
->next_bb
->index
] = last_basic_block
;
1213 apply_return_prediction (heads
);
1217 block_stmt_iterator bsi
= bsi_last (bb
);
1219 for (bsi
= bsi_start (bb
); !bsi_end_p (bsi
); bsi_next (&bsi
))
1221 tree stmt
= bsi_stmt (bsi
);
1222 switch (TREE_CODE (stmt
))
1225 if (TREE_CODE (TREE_OPERAND (stmt
, 1)) == CALL_EXPR
)
1227 stmt
= TREE_OPERAND (stmt
, 1);
1233 if (call_expr_flags (stmt
) & ECF_NORETURN
)
1234 predict_paths_leading_to (bb
, heads
, PRED_NORETURN
,
1246 /* Predict branch probabilities and estimate profile of the tree CFG. */
1248 tree_estimate_probability (void)
1252 loop_optimizer_init (0);
1253 if (current_loops
&& dump_file
&& (dump_flags
& TDF_DETAILS
))
1254 flow_loops_dump (dump_file
, NULL
, 0);
1256 add_noreturn_fake_exit_edges ();
1257 connect_infinite_loops_to_exit ();
1258 calculate_dominance_info (CDI_DOMINATORS
);
1259 calculate_dominance_info (CDI_POST_DOMINATORS
);
1261 tree_bb_level_predictions ();
1263 mark_irreducible_loops ();
1272 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
1274 /* Predict early returns to be probable, as we've already taken
1275 care for error returns and other cases are often used for
1276 fast paths through function. */
1277 if (e
->dest
== EXIT_BLOCK_PTR
1278 && TREE_CODE (last_stmt (bb
)) == RETURN_EXPR
1279 && !single_pred_p (bb
))
1284 FOR_EACH_EDGE (e1
, ei1
, bb
->preds
)
1285 if (!predicted_by_p (e1
->src
, PRED_NULL_RETURN
)
1286 && !predicted_by_p (e1
->src
, PRED_CONST_RETURN
)
1287 && !predicted_by_p (e1
->src
, PRED_NEGATIVE_RETURN
)
1288 && !last_basic_block_p (e1
->src
))
1289 predict_edge_def (e1
, PRED_TREE_EARLY_RETURN
, NOT_TAKEN
);
1292 /* Look for block we are guarding (ie we dominate it,
1293 but it doesn't postdominate us). */
1294 if (e
->dest
!= EXIT_BLOCK_PTR
&& e
->dest
!= bb
1295 && dominated_by_p (CDI_DOMINATORS
, e
->dest
, e
->src
)
1296 && !dominated_by_p (CDI_POST_DOMINATORS
, e
->src
, e
->dest
))
1298 block_stmt_iterator bi
;
1300 /* The call heuristic claims that a guarded function call
1301 is improbable. This is because such calls are often used
1302 to signal exceptional situations such as printing error
1304 for (bi
= bsi_start (e
->dest
); !bsi_end_p (bi
);
1307 tree stmt
= bsi_stmt (bi
);
1308 if ((TREE_CODE (stmt
) == CALL_EXPR
1309 || (TREE_CODE (stmt
) == MODIFY_EXPR
1310 && TREE_CODE (TREE_OPERAND (stmt
, 1)) == CALL_EXPR
))
1311 /* Constant and pure calls are hardly used to signalize
1312 something exceptional. */
1313 && TREE_SIDE_EFFECTS (stmt
))
1315 predict_edge_def (e
, PRED_CALL
, NOT_TAKEN
);
1321 tree_predict_by_opcode (bb
);
1324 combine_predictions_for_bb (bb
);
1326 strip_builtin_expect ();
1327 estimate_bb_frequencies ();
1328 free_dominance_info (CDI_POST_DOMINATORS
);
1329 remove_fake_exit_edges ();
1330 loop_optimizer_finalize ();
1331 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1332 dump_tree_cfg (dump_file
, dump_flags
);
1333 if (profile_status
== PROFILE_ABSENT
)
1334 profile_status
= PROFILE_GUESSED
;
1338 /* Check whether this is the last basic block of function. Commonly
1339 there is one extra common cleanup block. */
1341 last_basic_block_p (basic_block bb
)
1343 if (bb
== EXIT_BLOCK_PTR
)
1346 return (bb
->next_bb
== EXIT_BLOCK_PTR
1347 || (bb
->next_bb
->next_bb
== EXIT_BLOCK_PTR
1348 && single_succ_p (bb
)
1349 && single_succ (bb
)->next_bb
== EXIT_BLOCK_PTR
));
1352 /* Sets branch probabilities according to PREDiction and
1353 FLAGS. HEADS[bb->index] should be index of basic block in that we
1354 need to alter branch predictions (i.e. the first of our dominators
1355 such that we do not post-dominate it) (but we fill this information
1356 on demand, so -1 may be there in case this was not needed yet). */
1359 predict_paths_leading_to (basic_block bb
, int *heads
, enum br_predictor pred
,
1360 enum prediction taken
)
1366 if (heads
[bb
->index
] == ENTRY_BLOCK
)
1368 /* This is first time we need this field in heads array; so
1369 find first dominator that we do not post-dominate (we are
1370 using already known members of heads array). */
1371 basic_block ai
= bb
;
1372 basic_block next_ai
= get_immediate_dominator (CDI_DOMINATORS
, bb
);
1375 while (heads
[next_ai
->index
] == ENTRY_BLOCK
)
1377 if (!dominated_by_p (CDI_POST_DOMINATORS
, next_ai
, bb
))
1379 heads
[next_ai
->index
] = ai
->index
;
1381 next_ai
= get_immediate_dominator (CDI_DOMINATORS
, next_ai
);
1383 if (!dominated_by_p (CDI_POST_DOMINATORS
, next_ai
, bb
))
1384 head
= next_ai
->index
;
1386 head
= heads
[next_ai
->index
];
1387 while (next_ai
!= bb
)
1390 ai
= BASIC_BLOCK (heads
[ai
->index
]);
1391 heads
[next_ai
->index
] = head
;
1394 y
= heads
[bb
->index
];
1396 /* Now find the edge that leads to our branch and aply the prediction. */
1398 if (y
== last_basic_block
)
1400 FOR_EACH_EDGE (e
, ei
, BASIC_BLOCK (y
)->succs
)
1401 if (e
->dest
->index
>= NUM_FIXED_BLOCKS
1402 && dominated_by_p (CDI_POST_DOMINATORS
, e
->dest
, bb
))
1403 predict_edge_def (e
, pred
, taken
);
1406 /* This is used to carry information about basic blocks. It is
1407 attached to the AUX field of the standard CFG block. */
1409 typedef struct block_info_def
1411 /* Estimated frequency of execution of basic_block. */
1414 /* To keep queue of basic blocks to process. */
1417 /* Number of predecessors we need to visit first. */
1421 /* Similar information for edges. */
1422 typedef struct edge_info_def
1424 /* In case edge is a loopback edge, the probability edge will be reached
1425 in case header is. Estimated number of iterations of the loop can be
1426 then computed as 1 / (1 - back_edge_prob). */
1427 sreal back_edge_prob
;
1428 /* True if the edge is a loopback edge in the natural loop. */
1429 unsigned int back_edge
:1;
1432 #define BLOCK_INFO(B) ((block_info) (B)->aux)
1433 #define EDGE_INFO(E) ((edge_info) (E)->aux)
1435 /* Helper function for estimate_bb_frequencies.
1436 Propagate the frequencies in blocks marked in
1437 TOVISIT, starting in HEAD. */
1440 propagate_freq (basic_block head
, bitmap tovisit
)
1449 /* For each basic block we need to visit count number of his predecessors
1450 we need to visit first. */
1451 EXECUTE_IF_SET_IN_BITMAP (tovisit
, 0, i
, bi
)
1456 /* The outermost "loop" includes the exit block, which we can not
1457 look up via BASIC_BLOCK. Detect this and use EXIT_BLOCK_PTR
1458 directly. Do the same for the entry block. */
1459 bb
= BASIC_BLOCK (i
);
1461 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
1463 bool visit
= bitmap_bit_p (tovisit
, e
->src
->index
);
1465 if (visit
&& !(e
->flags
& EDGE_DFS_BACK
))
1467 else if (visit
&& dump_file
&& !EDGE_INFO (e
)->back_edge
)
1469 "Irreducible region hit, ignoring edge to %i->%i\n",
1470 e
->src
->index
, bb
->index
);
1472 BLOCK_INFO (bb
)->npredecessors
= count
;
1475 memcpy (&BLOCK_INFO (head
)->frequency
, &real_one
, sizeof (real_one
));
1477 for (bb
= head
; bb
; bb
= nextbb
)
1480 sreal cyclic_probability
, frequency
;
1482 memcpy (&cyclic_probability
, &real_zero
, sizeof (real_zero
));
1483 memcpy (&frequency
, &real_zero
, sizeof (real_zero
));
1485 nextbb
= BLOCK_INFO (bb
)->next
;
1486 BLOCK_INFO (bb
)->next
= NULL
;
1488 /* Compute frequency of basic block. */
1491 #ifdef ENABLE_CHECKING
1492 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
1493 gcc_assert (!bitmap_bit_p (tovisit
, e
->src
->index
)
1494 || (e
->flags
& EDGE_DFS_BACK
));
1497 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
1498 if (EDGE_INFO (e
)->back_edge
)
1500 sreal_add (&cyclic_probability
, &cyclic_probability
,
1501 &EDGE_INFO (e
)->back_edge_prob
);
1503 else if (!(e
->flags
& EDGE_DFS_BACK
))
1507 /* frequency += (e->probability
1508 * BLOCK_INFO (e->src)->frequency /
1509 REG_BR_PROB_BASE); */
1511 sreal_init (&tmp
, e
->probability
, 0);
1512 sreal_mul (&tmp
, &tmp
, &BLOCK_INFO (e
->src
)->frequency
);
1513 sreal_mul (&tmp
, &tmp
, &real_inv_br_prob_base
);
1514 sreal_add (&frequency
, &frequency
, &tmp
);
1517 if (sreal_compare (&cyclic_probability
, &real_zero
) == 0)
1519 memcpy (&BLOCK_INFO (bb
)->frequency
, &frequency
,
1520 sizeof (frequency
));
1524 if (sreal_compare (&cyclic_probability
, &real_almost_one
) > 0)
1526 memcpy (&cyclic_probability
, &real_almost_one
,
1527 sizeof (real_almost_one
));
1530 /* BLOCK_INFO (bb)->frequency = frequency
1531 / (1 - cyclic_probability) */
1533 sreal_sub (&cyclic_probability
, &real_one
, &cyclic_probability
);
1534 sreal_div (&BLOCK_INFO (bb
)->frequency
,
1535 &frequency
, &cyclic_probability
);
1539 bitmap_clear_bit (tovisit
, bb
->index
);
1541 e
= find_edge (bb
, head
);
1546 /* EDGE_INFO (e)->back_edge_prob
1547 = ((e->probability * BLOCK_INFO (bb)->frequency)
1548 / REG_BR_PROB_BASE); */
1550 sreal_init (&tmp
, e
->probability
, 0);
1551 sreal_mul (&tmp
, &tmp
, &BLOCK_INFO (bb
)->frequency
);
1552 sreal_mul (&EDGE_INFO (e
)->back_edge_prob
,
1553 &tmp
, &real_inv_br_prob_base
);
1556 /* Propagate to successor blocks. */
1557 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
1558 if (!(e
->flags
& EDGE_DFS_BACK
)
1559 && BLOCK_INFO (e
->dest
)->npredecessors
)
1561 BLOCK_INFO (e
->dest
)->npredecessors
--;
1562 if (!BLOCK_INFO (e
->dest
)->npredecessors
)
1567 BLOCK_INFO (last
)->next
= e
->dest
;
1575 /* Estimate probabilities of loopback edges in loops at same nest level. */
1578 estimate_loops_at_level (struct loop
*first_loop
)
1582 for (loop
= first_loop
; loop
; loop
= loop
->next
)
1587 bitmap tovisit
= BITMAP_ALLOC (NULL
);
1589 estimate_loops_at_level (loop
->inner
);
1591 /* Find current loop back edge and mark it. */
1592 e
= loop_latch_edge (loop
);
1593 EDGE_INFO (e
)->back_edge
= 1;
1595 bbs
= get_loop_body (loop
);
1596 for (i
= 0; i
< loop
->num_nodes
; i
++)
1597 bitmap_set_bit (tovisit
, bbs
[i
]->index
);
1599 propagate_freq (loop
->header
, tovisit
);
1600 BITMAP_FREE (tovisit
);
1604 /* Propates frequencies through structure of loops. */
1607 estimate_loops (void)
1609 bitmap tovisit
= BITMAP_ALLOC (NULL
);
1612 /* Start by estimating the frequencies in the loops. */
1614 estimate_loops_at_level (current_loops
->tree_root
->inner
);
1616 /* Now propagate the frequencies through all the blocks. */
1619 bitmap_set_bit (tovisit
, bb
->index
);
1621 propagate_freq (ENTRY_BLOCK_PTR
, tovisit
);
1622 BITMAP_FREE (tovisit
);
1625 /* Convert counts measured by profile driven feedback to frequencies.
1626 Return nonzero iff there was any nonzero execution count. */
1629 counts_to_freqs (void)
1631 gcov_type count_max
, true_count_max
= 0;
1635 true_count_max
= MAX (bb
->count
, true_count_max
);
1637 count_max
= MAX (true_count_max
, 1);
1638 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR
, NULL
, next_bb
)
1639 bb
->frequency
= (bb
->count
* BB_FREQ_MAX
+ count_max
/ 2) / count_max
;
1640 return true_count_max
;
1643 /* Return true if function is likely to be expensive, so there is no point to
1644 optimize performance of prologue, epilogue or do inlining at the expense
1645 of code size growth. THRESHOLD is the limit of number of instructions
1646 function can execute at average to be still considered not expensive. */
1649 expensive_function_p (int threshold
)
1651 unsigned int sum
= 0;
1655 /* We can not compute accurately for large thresholds due to scaled
1657 gcc_assert (threshold
<= BB_FREQ_MAX
);
1659 /* Frequencies are out of range. This either means that function contains
1660 internal loop executing more than BB_FREQ_MAX times or profile feedback
1661 is available and function has not been executed at all. */
1662 if (ENTRY_BLOCK_PTR
->frequency
== 0)
1665 /* Maximally BB_FREQ_MAX^2 so overflow won't happen. */
1666 limit
= ENTRY_BLOCK_PTR
->frequency
* threshold
;
1671 for (insn
= BB_HEAD (bb
); insn
!= NEXT_INSN (BB_END (bb
));
1672 insn
= NEXT_INSN (insn
))
1673 if (active_insn_p (insn
))
1675 sum
+= bb
->frequency
;
1684 /* Estimate basic blocks frequency by given branch probabilities. */
1687 estimate_bb_frequencies (void)
1692 if (!flag_branch_probabilities
|| !counts_to_freqs ())
1694 static int real_values_initialized
= 0;
1696 if (!real_values_initialized
)
1698 real_values_initialized
= 1;
1699 sreal_init (&real_zero
, 0, 0);
1700 sreal_init (&real_one
, 1, 0);
1701 sreal_init (&real_br_prob_base
, REG_BR_PROB_BASE
, 0);
1702 sreal_init (&real_bb_freq_max
, BB_FREQ_MAX
, 0);
1703 sreal_init (&real_one_half
, 1, -1);
1704 sreal_div (&real_inv_br_prob_base
, &real_one
, &real_br_prob_base
);
1705 sreal_sub (&real_almost_one
, &real_one
, &real_inv_br_prob_base
);
1708 mark_dfs_back_edges ();
1710 single_succ_edge (ENTRY_BLOCK_PTR
)->probability
= REG_BR_PROB_BASE
;
1712 /* Set up block info for each basic block. */
1713 alloc_aux_for_blocks (sizeof (struct block_info_def
));
1714 alloc_aux_for_edges (sizeof (struct edge_info_def
));
1715 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR
, NULL
, next_bb
)
1720 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
1722 sreal_init (&EDGE_INFO (e
)->back_edge_prob
, e
->probability
, 0);
1723 sreal_mul (&EDGE_INFO (e
)->back_edge_prob
,
1724 &EDGE_INFO (e
)->back_edge_prob
,
1725 &real_inv_br_prob_base
);
1729 /* First compute probabilities locally for each loop from innermost
1730 to outermost to examine probabilities for back edges. */
1733 memcpy (&freq_max
, &real_zero
, sizeof (real_zero
));
1735 if (sreal_compare (&freq_max
, &BLOCK_INFO (bb
)->frequency
) < 0)
1736 memcpy (&freq_max
, &BLOCK_INFO (bb
)->frequency
, sizeof (freq_max
));
1738 sreal_div (&freq_max
, &real_bb_freq_max
, &freq_max
);
1739 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR
, NULL
, next_bb
)
1743 sreal_mul (&tmp
, &BLOCK_INFO (bb
)->frequency
, &freq_max
);
1744 sreal_add (&tmp
, &tmp
, &real_one_half
);
1745 bb
->frequency
= sreal_to_int (&tmp
);
1748 free_aux_for_blocks ();
1749 free_aux_for_edges ();
1751 compute_function_frequency ();
1752 if (flag_reorder_functions
)
1753 choose_function_section ();
1756 /* Decide whether function is hot, cold or unlikely executed. */
1758 compute_function_frequency (void)
1762 if (!profile_info
|| !flag_branch_probabilities
)
1764 cfun
->function_frequency
= FUNCTION_FREQUENCY_UNLIKELY_EXECUTED
;
1767 if (maybe_hot_bb_p (bb
))
1769 cfun
->function_frequency
= FUNCTION_FREQUENCY_HOT
;
1772 if (!probably_never_executed_bb_p (bb
))
1773 cfun
->function_frequency
= FUNCTION_FREQUENCY_NORMAL
;
1777 /* Choose appropriate section for the function. */
1779 choose_function_section (void)
1781 if (DECL_SECTION_NAME (current_function_decl
)
1782 || !targetm
.have_named_sections
1783 /* Theoretically we can split the gnu.linkonce text section too,
1784 but this requires more work as the frequency needs to match
1785 for all generated objects so we need to merge the frequency
1786 of all instances. For now just never set frequency for these. */
1787 || DECL_ONE_ONLY (current_function_decl
))
1790 /* If we are doing the partitioning optimization, let the optimization
1791 choose the correct section into which to put things. */
1793 if (flag_reorder_blocks_and_partition
)
1796 if (cfun
->function_frequency
== FUNCTION_FREQUENCY_HOT
)
1797 DECL_SECTION_NAME (current_function_decl
) =
1798 build_string (strlen (HOT_TEXT_SECTION_NAME
), HOT_TEXT_SECTION_NAME
);
1799 if (cfun
->function_frequency
== FUNCTION_FREQUENCY_UNLIKELY_EXECUTED
)
1800 DECL_SECTION_NAME (current_function_decl
) =
1801 build_string (strlen (UNLIKELY_EXECUTED_TEXT_SECTION_NAME
),
1802 UNLIKELY_EXECUTED_TEXT_SECTION_NAME
);
1806 gate_estimate_probability (void)
1808 return flag_guess_branch_prob
;
1811 struct tree_opt_pass pass_profile
=
1813 "profile", /* name */
1814 gate_estimate_probability
, /* gate */
1815 tree_estimate_probability
, /* execute */
1818 0, /* static_pass_number */
1819 TV_BRANCH_PROB
, /* tv_id */
1820 PROP_cfg
, /* properties_required */
1821 0, /* properties_provided */
1822 0, /* properties_destroyed */
1823 0, /* todo_flags_start */
1824 TODO_ggc_collect
| TODO_verify_ssa
, /* todo_flags_finish */