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
);
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 in case BB can be CPU intensive and should be optimized
112 for maximal performance. */
115 maybe_hot_bb_p (basic_block bb
)
117 if (profile_info
&& flag_branch_probabilities
119 < profile_info
->sum_max
/ PARAM_VALUE (HOT_BB_COUNT_FRACTION
)))
121 if (bb
->frequency
< BB_FREQ_MAX
/ PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION
))
126 /* Return true in case BB is cold and should be optimized for size. */
129 probably_cold_bb_p (basic_block bb
)
131 if (profile_info
&& flag_branch_probabilities
133 < profile_info
->sum_max
/ PARAM_VALUE (HOT_BB_COUNT_FRACTION
)))
135 if (bb
->frequency
< BB_FREQ_MAX
/ PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION
))
140 /* Return true in case BB is probably never executed. */
142 probably_never_executed_bb_p (basic_block bb
)
144 if (profile_info
&& flag_branch_probabilities
)
145 return ((bb
->count
+ profile_info
->runs
/ 2) / profile_info
->runs
) == 0;
149 /* Return true if the one of outgoing edges is already predicted by
153 rtl_predicted_by_p (basic_block bb
, enum br_predictor predictor
)
156 if (!INSN_P (BB_END (bb
)))
158 for (note
= REG_NOTES (BB_END (bb
)); note
; note
= XEXP (note
, 1))
159 if (REG_NOTE_KIND (note
) == REG_BR_PRED
160 && INTVAL (XEXP (XEXP (note
, 0), 0)) == (int)predictor
)
165 /* Return true if the one of outgoing edges is already predicted by
169 tree_predicted_by_p (basic_block bb
, enum br_predictor predictor
)
171 struct edge_prediction
*i
;
172 for (i
= bb
->predictions
; i
; i
= i
->ep_next
)
173 if (i
->ep_predictor
== predictor
)
178 /* Return true when the probability of edge is reliable.
180 The profile guessing code is good at predicting branch outcome (ie.
181 taken/not taken), that is predicted right slightly over 75% of time.
182 It is however notoriously poor on predicting the probability itself.
183 In general the profile appear a lot flatter (with probabilities closer
184 to 50%) than the reality so it is bad idea to use it to drive optimization
185 such as those disabling dynamic branch prediction for well predictable
188 There are two exceptions - edges leading to noreturn edges and edges
189 predicted by number of iterations heuristics are predicted well. This macro
190 should be able to distinguish those, but at the moment it simply check for
191 noreturn heuristic that is only one giving probability over 99% or bellow
192 1%. In future we might want to propagate reliability information across the
193 CFG if we find this information useful on multiple places. */
195 probability_reliable_p (int prob
)
197 return (profile_status
== PROFILE_READ
198 || (profile_status
== PROFILE_GUESSED
199 && (prob
<= HITRATE (1) || prob
>= HITRATE (99))));
202 /* Same predicate as above, working on edges. */
204 edge_probability_reliable_p (edge e
)
206 return probability_reliable_p (e
->probability
);
209 /* Same predicate as edge_probability_reliable_p, working on notes. */
211 br_prob_note_reliable_p (rtx note
)
213 gcc_assert (REG_NOTE_KIND (note
) == REG_BR_PROB
);
214 return probability_reliable_p (INTVAL (XEXP (note
, 0)));
218 predict_insn (rtx insn
, enum br_predictor predictor
, int probability
)
220 gcc_assert (any_condjump_p (insn
));
221 if (!flag_guess_branch_prob
)
225 = gen_rtx_EXPR_LIST (REG_BR_PRED
,
226 gen_rtx_CONCAT (VOIDmode
,
227 GEN_INT ((int) predictor
),
228 GEN_INT ((int) probability
)),
232 /* Predict insn by given predictor. */
235 predict_insn_def (rtx insn
, enum br_predictor predictor
,
236 enum prediction taken
)
238 int probability
= predictor_info
[(int) predictor
].hitrate
;
241 probability
= REG_BR_PROB_BASE
- probability
;
243 predict_insn (insn
, predictor
, probability
);
246 /* Predict edge E with given probability if possible. */
249 rtl_predict_edge (edge e
, enum br_predictor predictor
, int probability
)
252 last_insn
= BB_END (e
->src
);
254 /* We can store the branch prediction information only about
255 conditional jumps. */
256 if (!any_condjump_p (last_insn
))
259 /* We always store probability of branching. */
260 if (e
->flags
& EDGE_FALLTHRU
)
261 probability
= REG_BR_PROB_BASE
- probability
;
263 predict_insn (last_insn
, predictor
, probability
);
266 /* Predict edge E with the given PROBABILITY. */
268 tree_predict_edge (edge e
, enum br_predictor predictor
, int probability
)
270 gcc_assert (profile_status
!= PROFILE_GUESSED
);
271 if ((e
->src
!= ENTRY_BLOCK_PTR
&& EDGE_COUNT (e
->src
->succs
) > 1)
272 && flag_guess_branch_prob
&& optimize
)
274 struct edge_prediction
*i
= ggc_alloc (sizeof (struct edge_prediction
));
276 i
->ep_next
= e
->src
->predictions
;
277 e
->src
->predictions
= i
;
278 i
->ep_probability
= probability
;
279 i
->ep_predictor
= predictor
;
284 /* Remove all predictions on given basic block that are attached
287 remove_predictions_associated_with_edge (edge e
)
289 if (e
->src
->predictions
)
291 struct edge_prediction
**prediction
= &e
->src
->predictions
;
294 if ((*prediction
)->ep_edge
== e
)
295 *prediction
= (*prediction
)->ep_next
;
297 prediction
= &((*prediction
)->ep_next
);
302 /* Return true when we can store prediction on insn INSN.
303 At the moment we represent predictions only on conditional
304 jumps, not at computed jump or other complicated cases. */
306 can_predict_insn_p (rtx insn
)
308 return (JUMP_P (insn
)
309 && any_condjump_p (insn
)
310 && EDGE_COUNT (BLOCK_FOR_INSN (insn
)->succs
) >= 2);
313 /* Predict edge E by given predictor if possible. */
316 predict_edge_def (edge e
, enum br_predictor predictor
,
317 enum prediction taken
)
319 int probability
= predictor_info
[(int) predictor
].hitrate
;
322 probability
= REG_BR_PROB_BASE
- probability
;
324 predict_edge (e
, predictor
, probability
);
327 /* Invert all branch predictions or probability notes in the INSN. This needs
328 to be done each time we invert the condition used by the jump. */
331 invert_br_probabilities (rtx insn
)
335 for (note
= REG_NOTES (insn
); note
; note
= XEXP (note
, 1))
336 if (REG_NOTE_KIND (note
) == REG_BR_PROB
)
337 XEXP (note
, 0) = GEN_INT (REG_BR_PROB_BASE
- INTVAL (XEXP (note
, 0)));
338 else if (REG_NOTE_KIND (note
) == REG_BR_PRED
)
339 XEXP (XEXP (note
, 0), 1)
340 = GEN_INT (REG_BR_PROB_BASE
- INTVAL (XEXP (XEXP (note
, 0), 1)));
343 /* Dump information about the branch prediction to the output file. */
346 dump_prediction (FILE *file
, enum br_predictor predictor
, int probability
,
347 basic_block bb
, int used
)
355 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
356 if (! (e
->flags
& EDGE_FALLTHRU
))
359 fprintf (file
, " %s heuristics%s: %.1f%%",
360 predictor_info
[predictor
].name
,
361 used
? "" : " (ignored)", probability
* 100.0 / REG_BR_PROB_BASE
);
365 fprintf (file
, " exec ");
366 fprintf (file
, HOST_WIDEST_INT_PRINT_DEC
, bb
->count
);
369 fprintf (file
, " hit ");
370 fprintf (file
, HOST_WIDEST_INT_PRINT_DEC
, e
->count
);
371 fprintf (file
, " (%.1f%%)", e
->count
* 100.0 / bb
->count
);
375 fprintf (file
, "\n");
378 /* We can not predict the probabilities of outgoing edges of bb. Set them
379 evenly and hope for the best. */
381 set_even_probabilities (basic_block bb
)
387 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
388 if (!(e
->flags
& (EDGE_EH
| EDGE_FAKE
)))
390 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
391 if (!(e
->flags
& (EDGE_EH
| EDGE_FAKE
)))
392 e
->probability
= (REG_BR_PROB_BASE
+ nedges
/ 2) / nedges
;
397 /* Combine all REG_BR_PRED notes into single probability and attach REG_BR_PROB
398 note if not already present. Remove now useless REG_BR_PRED notes. */
401 combine_predictions_for_insn (rtx insn
, basic_block bb
)
406 int best_probability
= PROB_EVEN
;
407 int best_predictor
= END_PREDICTORS
;
408 int combined_probability
= REG_BR_PROB_BASE
/ 2;
410 bool first_match
= false;
413 if (!can_predict_insn_p (insn
))
415 set_even_probabilities (bb
);
419 prob_note
= find_reg_note (insn
, REG_BR_PROB
, 0);
420 pnote
= ®_NOTES (insn
);
422 fprintf (dump_file
, "Predictions for insn %i bb %i\n", INSN_UID (insn
),
425 /* We implement "first match" heuristics and use probability guessed
426 by predictor with smallest index. */
427 for (note
= REG_NOTES (insn
); note
; note
= XEXP (note
, 1))
428 if (REG_NOTE_KIND (note
) == REG_BR_PRED
)
430 int predictor
= INTVAL (XEXP (XEXP (note
, 0), 0));
431 int probability
= INTVAL (XEXP (XEXP (note
, 0), 1));
434 if (best_predictor
> predictor
)
435 best_probability
= probability
, best_predictor
= predictor
;
437 d
= (combined_probability
* probability
438 + (REG_BR_PROB_BASE
- combined_probability
)
439 * (REG_BR_PROB_BASE
- probability
));
441 /* Use FP math to avoid overflows of 32bit integers. */
443 /* If one probability is 0% and one 100%, avoid division by zero. */
444 combined_probability
= REG_BR_PROB_BASE
/ 2;
446 combined_probability
= (((double) combined_probability
) * probability
447 * REG_BR_PROB_BASE
/ d
+ 0.5);
450 /* Decide which heuristic to use. In case we didn't match anything,
451 use no_prediction heuristic, in case we did match, use either
452 first match or Dempster-Shaffer theory depending on the flags. */
454 if (predictor_info
[best_predictor
].flags
& PRED_FLAG_FIRST_MATCH
)
458 dump_prediction (dump_file
, PRED_NO_PREDICTION
,
459 combined_probability
, bb
, true);
462 dump_prediction (dump_file
, PRED_DS_THEORY
, combined_probability
,
464 dump_prediction (dump_file
, PRED_FIRST_MATCH
, best_probability
,
469 combined_probability
= best_probability
;
470 dump_prediction (dump_file
, PRED_COMBINED
, combined_probability
, bb
, true);
474 if (REG_NOTE_KIND (*pnote
) == REG_BR_PRED
)
476 int predictor
= INTVAL (XEXP (XEXP (*pnote
, 0), 0));
477 int probability
= INTVAL (XEXP (XEXP (*pnote
, 0), 1));
479 dump_prediction (dump_file
, predictor
, probability
, bb
,
480 !first_match
|| best_predictor
== predictor
);
481 *pnote
= XEXP (*pnote
, 1);
484 pnote
= &XEXP (*pnote
, 1);
490 = gen_rtx_EXPR_LIST (REG_BR_PROB
,
491 GEN_INT (combined_probability
), REG_NOTES (insn
));
493 /* Save the prediction into CFG in case we are seeing non-degenerated
495 if (!single_succ_p (bb
))
497 BRANCH_EDGE (bb
)->probability
= combined_probability
;
498 FALLTHRU_EDGE (bb
)->probability
499 = REG_BR_PROB_BASE
- combined_probability
;
502 else if (!single_succ_p (bb
))
504 int prob
= INTVAL (XEXP (prob_note
, 0));
506 BRANCH_EDGE (bb
)->probability
= prob
;
507 FALLTHRU_EDGE (bb
)->probability
= REG_BR_PROB_BASE
- prob
;
510 single_succ_edge (bb
)->probability
= REG_BR_PROB_BASE
;
513 /* Combine predictions into single probability and store them into CFG.
514 Remove now useless prediction entries. */
517 combine_predictions_for_bb (basic_block bb
)
519 int best_probability
= PROB_EVEN
;
520 int best_predictor
= END_PREDICTORS
;
521 int combined_probability
= REG_BR_PROB_BASE
/ 2;
523 bool first_match
= false;
525 struct edge_prediction
*pred
;
527 edge e
, first
= NULL
, second
= NULL
;
530 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
531 if (!(e
->flags
& (EDGE_EH
| EDGE_FAKE
)))
534 if (first
&& !second
)
540 /* When there is no successor or only one choice, prediction is easy.
542 We are lazy for now and predict only basic blocks with two outgoing
543 edges. It is possible to predict generic case too, but we have to
544 ignore first match heuristics and do more involved combining. Implement
549 set_even_probabilities (bb
);
550 bb
->predictions
= NULL
;
552 fprintf (dump_file
, "%i edges in bb %i predicted to even probabilities\n",
558 fprintf (dump_file
, "Predictions for bb %i\n", bb
->index
);
560 /* We implement "first match" heuristics and use probability guessed
561 by predictor with smallest index. */
562 for (pred
= bb
->predictions
; pred
; pred
= pred
->ep_next
)
564 int predictor
= pred
->ep_predictor
;
565 int probability
= pred
->ep_probability
;
567 if (pred
->ep_edge
!= first
)
568 probability
= REG_BR_PROB_BASE
- probability
;
571 if (best_predictor
> predictor
)
572 best_probability
= probability
, best_predictor
= predictor
;
574 d
= (combined_probability
* probability
575 + (REG_BR_PROB_BASE
- combined_probability
)
576 * (REG_BR_PROB_BASE
- probability
));
578 /* Use FP math to avoid overflows of 32bit integers. */
580 /* If one probability is 0% and one 100%, avoid division by zero. */
581 combined_probability
= REG_BR_PROB_BASE
/ 2;
583 combined_probability
= (((double) combined_probability
) * probability
584 * REG_BR_PROB_BASE
/ d
+ 0.5);
587 /* Decide which heuristic to use. In case we didn't match anything,
588 use no_prediction heuristic, in case we did match, use either
589 first match or Dempster-Shaffer theory depending on the flags. */
591 if (predictor_info
[best_predictor
].flags
& PRED_FLAG_FIRST_MATCH
)
595 dump_prediction (dump_file
, PRED_NO_PREDICTION
, combined_probability
, bb
, true);
598 dump_prediction (dump_file
, PRED_DS_THEORY
, combined_probability
, bb
,
600 dump_prediction (dump_file
, PRED_FIRST_MATCH
, best_probability
, bb
,
605 combined_probability
= best_probability
;
606 dump_prediction (dump_file
, PRED_COMBINED
, combined_probability
, bb
, true);
608 for (pred
= bb
->predictions
; pred
; pred
= pred
->ep_next
)
610 int predictor
= pred
->ep_predictor
;
611 int probability
= pred
->ep_probability
;
613 if (pred
->ep_edge
!= EDGE_SUCC (bb
, 0))
614 probability
= REG_BR_PROB_BASE
- probability
;
615 dump_prediction (dump_file
, predictor
, probability
, bb
,
616 !first_match
|| best_predictor
== predictor
);
618 bb
->predictions
= NULL
;
622 first
->probability
= combined_probability
;
623 second
->probability
= REG_BR_PROB_BASE
- combined_probability
;
627 /* Predict edge probabilities by exploiting loop structure. */
637 /* Try to predict out blocks in a loop that are not part of a
639 FOR_EACH_LOOP (li
, loop
, 0)
641 basic_block bb
, *bbs
;
643 VEC (edge
, heap
) *exits
;
644 struct tree_niter_desc niter_desc
;
647 exits
= get_loop_exit_edges (loop
);
648 n_exits
= VEC_length (edge
, exits
);
650 for (j
= 0; VEC_iterate (edge
, exits
, j
, ex
); j
++)
654 if (number_of_iterations_exit (loop
, ex
, &niter_desc
, false))
655 niter
= niter_desc
.niter
;
656 if (!niter
|| TREE_CODE (niter_desc
.niter
) != INTEGER_CST
)
657 niter
= loop_niter_by_eval (loop
, ex
);
659 if (TREE_CODE (niter
) == INTEGER_CST
)
662 int max
= PARAM_VALUE (PARAM_MAX_PREDICTED_ITERATIONS
);
663 if (host_integerp (niter
, 1)
664 && compare_tree_int (niter
, max
-1) == -1)
666 HOST_WIDE_INT nitercst
= tree_low_cst (niter
, 1) + 1;
667 probability
= ((REG_BR_PROB_BASE
+ nitercst
/ 2)
671 probability
= ((REG_BR_PROB_BASE
+ max
/ 2) / max
);
673 predict_edge (ex
, PRED_LOOP_ITERATIONS
, probability
);
676 VEC_free (edge
, heap
, exits
);
678 bbs
= get_loop_body (loop
);
680 for (j
= 0; j
< loop
->num_nodes
; j
++)
682 int header_found
= 0;
688 /* Bypass loop heuristics on continue statement. These
689 statements construct loops via "non-loop" constructs
690 in the source language and are better to be handled
692 if (predicted_by_p (bb
, PRED_CONTINUE
))
695 /* Loop branch heuristics - predict an edge back to a
696 loop's head as taken. */
697 if (bb
== loop
->latch
)
699 e
= find_edge (loop
->latch
, loop
->header
);
703 predict_edge_def (e
, PRED_LOOP_BRANCH
, TAKEN
);
707 /* Loop exit heuristics - predict an edge exiting the loop if the
708 conditional has no loop header successors as not taken. */
711 /* For loop with many exits we don't want to predict all exits
712 with the pretty large probability, because if all exits are
713 considered in row, the loop would be predicted to iterate
714 almost never. The code to divide probability by number of
715 exits is very rough. It should compute the number of exits
716 taken in each patch through function (not the overall number
717 of exits that might be a lot higher for loops with wide switch
718 statements in them) and compute n-th square root.
720 We limit the minimal probability by 2% to avoid
721 EDGE_PROBABILITY_RELIABLE from trusting the branch prediction
722 as this was causing regression in perl benchmark containing such
725 int probability
= ((REG_BR_PROB_BASE
726 - predictor_info
[(int) PRED_LOOP_EXIT
].hitrate
)
728 if (probability
< HITRATE (2))
729 probability
= HITRATE (2);
730 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
731 if (e
->dest
->index
< NUM_FIXED_BLOCKS
732 || !flow_bb_inside_loop_p (loop
, e
->dest
))
733 predict_edge (e
, PRED_LOOP_EXIT
, probability
);
737 /* Free basic blocks from get_loop_body. */
744 /* Attempt to predict probabilities of BB outgoing edges using local
747 bb_estimate_probability_locally (basic_block bb
)
749 rtx last_insn
= BB_END (bb
);
752 if (! can_predict_insn_p (last_insn
))
754 cond
= get_condition (last_insn
, NULL
, false, false);
758 /* Try "pointer heuristic."
759 A comparison ptr == 0 is predicted as false.
760 Similarly, a comparison ptr1 == ptr2 is predicted as false. */
761 if (COMPARISON_P (cond
)
762 && ((REG_P (XEXP (cond
, 0)) && REG_POINTER (XEXP (cond
, 0)))
763 || (REG_P (XEXP (cond
, 1)) && REG_POINTER (XEXP (cond
, 1)))))
765 if (GET_CODE (cond
) == EQ
)
766 predict_insn_def (last_insn
, PRED_POINTER
, NOT_TAKEN
);
767 else if (GET_CODE (cond
) == NE
)
768 predict_insn_def (last_insn
, PRED_POINTER
, TAKEN
);
772 /* Try "opcode heuristic."
773 EQ tests are usually false and NE tests are usually true. Also,
774 most quantities are positive, so we can make the appropriate guesses
775 about signed comparisons against zero. */
776 switch (GET_CODE (cond
))
779 /* Unconditional branch. */
780 predict_insn_def (last_insn
, PRED_UNCONDITIONAL
,
781 cond
== const0_rtx
? NOT_TAKEN
: TAKEN
);
786 /* Floating point comparisons appears to behave in a very
787 unpredictable way because of special role of = tests in
789 if (FLOAT_MODE_P (GET_MODE (XEXP (cond
, 0))))
791 /* Comparisons with 0 are often used for booleans and there is
792 nothing useful to predict about them. */
793 else if (XEXP (cond
, 1) == const0_rtx
794 || XEXP (cond
, 0) == const0_rtx
)
797 predict_insn_def (last_insn
, PRED_OPCODE_NONEQUAL
, NOT_TAKEN
);
802 /* Floating point comparisons appears to behave in a very
803 unpredictable way because of special role of = tests in
805 if (FLOAT_MODE_P (GET_MODE (XEXP (cond
, 0))))
807 /* Comparisons with 0 are often used for booleans and there is
808 nothing useful to predict about them. */
809 else if (XEXP (cond
, 1) == const0_rtx
810 || XEXP (cond
, 0) == const0_rtx
)
813 predict_insn_def (last_insn
, PRED_OPCODE_NONEQUAL
, TAKEN
);
817 predict_insn_def (last_insn
, PRED_FPOPCODE
, TAKEN
);
821 predict_insn_def (last_insn
, PRED_FPOPCODE
, NOT_TAKEN
);
826 if (XEXP (cond
, 1) == const0_rtx
|| XEXP (cond
, 1) == const1_rtx
827 || XEXP (cond
, 1) == constm1_rtx
)
828 predict_insn_def (last_insn
, PRED_OPCODE_POSITIVE
, NOT_TAKEN
);
833 if (XEXP (cond
, 1) == const0_rtx
|| XEXP (cond
, 1) == const1_rtx
834 || XEXP (cond
, 1) == constm1_rtx
)
835 predict_insn_def (last_insn
, PRED_OPCODE_POSITIVE
, TAKEN
);
843 /* Set edge->probability for each successor edge of BB. */
845 guess_outgoing_edge_probabilities (basic_block bb
)
847 bb_estimate_probability_locally (bb
);
848 combine_predictions_for_insn (BB_END (bb
), bb
);
851 /* Return constant EXPR will likely have at execution time, NULL if unknown.
852 The function is used by builtin_expect branch predictor so the evidence
853 must come from this construct and additional possible constant folding.
855 We may want to implement more involved value guess (such as value range
856 propagation based prediction), but such tricks shall go to new
860 expr_expected_value (tree expr
, bitmap visited
)
862 if (TREE_CONSTANT (expr
))
864 else if (TREE_CODE (expr
) == SSA_NAME
)
866 tree def
= SSA_NAME_DEF_STMT (expr
);
868 /* If we were already here, break the infinite cycle. */
869 if (bitmap_bit_p (visited
, SSA_NAME_VERSION (expr
)))
871 bitmap_set_bit (visited
, SSA_NAME_VERSION (expr
));
873 if (TREE_CODE (def
) == PHI_NODE
)
875 /* All the arguments of the PHI node must have the same constant
878 tree val
= NULL
, new_val
;
880 for (i
= 0; i
< PHI_NUM_ARGS (def
); i
++)
882 tree arg
= PHI_ARG_DEF (def
, i
);
884 /* If this PHI has itself as an argument, we cannot
885 determine the string length of this argument. However,
886 if we can find an expected constant value for the other
887 PHI args then we can still be sure that this is
888 likely a constant. So be optimistic and just
889 continue with the next argument. */
890 if (arg
== PHI_RESULT (def
))
893 new_val
= expr_expected_value (arg
, visited
);
898 else if (!operand_equal_p (val
, new_val
, false))
903 if (TREE_CODE (def
) != GIMPLE_MODIFY_STMT
904 || GIMPLE_STMT_OPERAND (def
, 0) != expr
)
906 return expr_expected_value (GIMPLE_STMT_OPERAND (def
, 1), visited
);
908 else if (TREE_CODE (expr
) == CALL_EXPR
)
910 tree decl
= get_callee_fndecl (expr
);
913 if (DECL_BUILT_IN_CLASS (decl
) == BUILT_IN_NORMAL
914 && DECL_FUNCTION_CODE (decl
) == BUILT_IN_EXPECT
)
916 tree arglist
= TREE_OPERAND (expr
, 1);
919 if (arglist
== NULL_TREE
920 || TREE_CHAIN (arglist
) == NULL_TREE
)
922 val
= TREE_VALUE (TREE_CHAIN (TREE_OPERAND (expr
, 1)));
923 if (TREE_CONSTANT (val
))
925 return TREE_VALUE (TREE_CHAIN (TREE_OPERAND (expr
, 1)));
928 if (BINARY_CLASS_P (expr
) || COMPARISON_CLASS_P (expr
))
931 op0
= expr_expected_value (TREE_OPERAND (expr
, 0), visited
);
934 op1
= expr_expected_value (TREE_OPERAND (expr
, 1), visited
);
937 res
= fold_build2 (TREE_CODE (expr
), TREE_TYPE (expr
), op0
, op1
);
938 if (TREE_CONSTANT (res
))
942 if (UNARY_CLASS_P (expr
))
945 op0
= expr_expected_value (TREE_OPERAND (expr
, 0), visited
);
948 res
= fold_build1 (TREE_CODE (expr
), TREE_TYPE (expr
), op0
);
949 if (TREE_CONSTANT (res
))
956 /* Get rid of all builtin_expect calls we no longer need. */
958 strip_builtin_expect (void)
963 block_stmt_iterator bi
;
964 for (bi
= bsi_start (bb
); !bsi_end_p (bi
); bsi_next (&bi
))
966 tree stmt
= bsi_stmt (bi
);
970 if (TREE_CODE (stmt
) == GIMPLE_MODIFY_STMT
971 && TREE_CODE (GIMPLE_STMT_OPERAND (stmt
, 1)) == CALL_EXPR
972 && (fndecl
= get_callee_fndecl (GIMPLE_STMT_OPERAND (stmt
, 1)))
973 && DECL_BUILT_IN_CLASS (fndecl
) == BUILT_IN_NORMAL
974 && DECL_FUNCTION_CODE (fndecl
) == BUILT_IN_EXPECT
975 && (arglist
= TREE_OPERAND (GIMPLE_STMT_OPERAND (stmt
, 1), 1))
976 && TREE_CHAIN (arglist
))
978 GIMPLE_STMT_OPERAND (stmt
, 1) = TREE_VALUE (arglist
);
985 /* Predict using opcode of the last statement in basic block. */
987 tree_predict_by_opcode (basic_block bb
)
989 tree stmt
= last_stmt (bb
);
998 if (!stmt
|| TREE_CODE (stmt
) != COND_EXPR
)
1000 FOR_EACH_EDGE (then_edge
, ei
, bb
->succs
)
1001 if (then_edge
->flags
& EDGE_TRUE_VALUE
)
1003 cond
= TREE_OPERAND (stmt
, 0);
1004 if (!COMPARISON_CLASS_P (cond
))
1006 op0
= TREE_OPERAND (cond
, 0);
1007 type
= TREE_TYPE (op0
);
1008 visited
= BITMAP_ALLOC (NULL
);
1009 val
= expr_expected_value (cond
, visited
);
1010 BITMAP_FREE (visited
);
1013 if (integer_zerop (val
))
1014 predict_edge_def (then_edge
, PRED_BUILTIN_EXPECT
, NOT_TAKEN
);
1016 predict_edge_def (then_edge
, PRED_BUILTIN_EXPECT
, TAKEN
);
1019 /* Try "pointer heuristic."
1020 A comparison ptr == 0 is predicted as false.
1021 Similarly, a comparison ptr1 == ptr2 is predicted as false. */
1022 if (POINTER_TYPE_P (type
))
1024 if (TREE_CODE (cond
) == EQ_EXPR
)
1025 predict_edge_def (then_edge
, PRED_TREE_POINTER
, NOT_TAKEN
);
1026 else if (TREE_CODE (cond
) == NE_EXPR
)
1027 predict_edge_def (then_edge
, PRED_TREE_POINTER
, TAKEN
);
1031 /* Try "opcode heuristic."
1032 EQ tests are usually false and NE tests are usually true. Also,
1033 most quantities are positive, so we can make the appropriate guesses
1034 about signed comparisons against zero. */
1035 switch (TREE_CODE (cond
))
1039 /* Floating point comparisons appears to behave in a very
1040 unpredictable way because of special role of = tests in
1042 if (FLOAT_TYPE_P (type
))
1044 /* Comparisons with 0 are often used for booleans and there is
1045 nothing useful to predict about them. */
1046 else if (integer_zerop (op0
)
1047 || integer_zerop (TREE_OPERAND (cond
, 1)))
1050 predict_edge_def (then_edge
, PRED_TREE_OPCODE_NONEQUAL
, NOT_TAKEN
);
1055 /* Floating point comparisons appears to behave in a very
1056 unpredictable way because of special role of = tests in
1058 if (FLOAT_TYPE_P (type
))
1060 /* Comparisons with 0 are often used for booleans and there is
1061 nothing useful to predict about them. */
1062 else if (integer_zerop (op0
)
1063 || integer_zerop (TREE_OPERAND (cond
, 1)))
1066 predict_edge_def (then_edge
, PRED_TREE_OPCODE_NONEQUAL
, TAKEN
);
1070 predict_edge_def (then_edge
, PRED_TREE_FPOPCODE
, TAKEN
);
1073 case UNORDERED_EXPR
:
1074 predict_edge_def (then_edge
, PRED_TREE_FPOPCODE
, NOT_TAKEN
);
1079 if (integer_zerop (TREE_OPERAND (cond
, 1))
1080 || integer_onep (TREE_OPERAND (cond
, 1))
1081 || integer_all_onesp (TREE_OPERAND (cond
, 1))
1082 || real_zerop (TREE_OPERAND (cond
, 1))
1083 || real_onep (TREE_OPERAND (cond
, 1))
1084 || real_minus_onep (TREE_OPERAND (cond
, 1)))
1085 predict_edge_def (then_edge
, PRED_TREE_OPCODE_POSITIVE
, NOT_TAKEN
);
1090 if (integer_zerop (TREE_OPERAND (cond
, 1))
1091 || integer_onep (TREE_OPERAND (cond
, 1))
1092 || integer_all_onesp (TREE_OPERAND (cond
, 1))
1093 || real_zerop (TREE_OPERAND (cond
, 1))
1094 || real_onep (TREE_OPERAND (cond
, 1))
1095 || real_minus_onep (TREE_OPERAND (cond
, 1)))
1096 predict_edge_def (then_edge
, PRED_TREE_OPCODE_POSITIVE
, TAKEN
);
1104 /* Try to guess whether the value of return means error code. */
1105 static enum br_predictor
1106 return_prediction (tree val
, enum prediction
*prediction
)
1110 return PRED_NO_PREDICTION
;
1111 /* Different heuristics for pointers and scalars. */
1112 if (POINTER_TYPE_P (TREE_TYPE (val
)))
1114 /* NULL is usually not returned. */
1115 if (integer_zerop (val
))
1117 *prediction
= NOT_TAKEN
;
1118 return PRED_NULL_RETURN
;
1121 else if (INTEGRAL_TYPE_P (TREE_TYPE (val
)))
1123 /* Negative return values are often used to indicate
1125 if (TREE_CODE (val
) == INTEGER_CST
1126 && tree_int_cst_sgn (val
) < 0)
1128 *prediction
= NOT_TAKEN
;
1129 return PRED_NEGATIVE_RETURN
;
1131 /* Constant return values seems to be commonly taken.
1132 Zero/one often represent booleans so exclude them from the
1134 if (TREE_CONSTANT (val
)
1135 && (!integer_zerop (val
) && !integer_onep (val
)))
1137 *prediction
= TAKEN
;
1138 return PRED_NEGATIVE_RETURN
;
1141 return PRED_NO_PREDICTION
;
1144 /* Find the basic block with return expression and look up for possible
1145 return value trying to apply RETURN_PREDICTION heuristics. */
1147 apply_return_prediction (int *heads
)
1149 tree return_stmt
= NULL
;
1153 int phi_num_args
, i
;
1154 enum br_predictor pred
;
1155 enum prediction direction
;
1158 FOR_EACH_EDGE (e
, ei
, EXIT_BLOCK_PTR
->preds
)
1160 return_stmt
= last_stmt (e
->src
);
1161 if (TREE_CODE (return_stmt
) == RETURN_EXPR
)
1166 return_val
= TREE_OPERAND (return_stmt
, 0);
1169 if (TREE_CODE (return_val
) == GIMPLE_MODIFY_STMT
)
1170 return_val
= GIMPLE_STMT_OPERAND (return_val
, 1);
1171 if (TREE_CODE (return_val
) != SSA_NAME
1172 || !SSA_NAME_DEF_STMT (return_val
)
1173 || TREE_CODE (SSA_NAME_DEF_STMT (return_val
)) != PHI_NODE
)
1175 for (phi
= SSA_NAME_DEF_STMT (return_val
); phi
; phi
= PHI_CHAIN (phi
))
1176 if (PHI_RESULT (phi
) == return_val
)
1180 phi_num_args
= PHI_NUM_ARGS (phi
);
1181 pred
= return_prediction (PHI_ARG_DEF (phi
, 0), &direction
);
1183 /* Avoid the degenerate case where all return values form the function
1184 belongs to same category (ie they are all positive constants)
1185 so we can hardly say something about them. */
1186 for (i
= 1; i
< phi_num_args
; i
++)
1187 if (pred
!= return_prediction (PHI_ARG_DEF (phi
, i
), &direction
))
1189 if (i
!= phi_num_args
)
1190 for (i
= 0; i
< phi_num_args
; i
++)
1192 pred
= return_prediction (PHI_ARG_DEF (phi
, i
), &direction
);
1193 if (pred
!= PRED_NO_PREDICTION
)
1194 predict_paths_leading_to (PHI_ARG_EDGE (phi
, i
)->src
, heads
, pred
,
1199 /* Look for basic block that contains unlikely to happen events
1200 (such as noreturn calls) and mark all paths leading to execution
1201 of this basic blocks as unlikely. */
1204 tree_bb_level_predictions (void)
1209 heads
= XCNEWVEC (int, last_basic_block
);
1210 heads
[ENTRY_BLOCK_PTR
->next_bb
->index
] = last_basic_block
;
1212 apply_return_prediction (heads
);
1216 block_stmt_iterator bsi
= bsi_last (bb
);
1218 for (bsi
= bsi_start (bb
); !bsi_end_p (bsi
); bsi_next (&bsi
))
1220 tree stmt
= bsi_stmt (bsi
);
1221 switch (TREE_CODE (stmt
))
1223 case GIMPLE_MODIFY_STMT
:
1224 if (TREE_CODE (GIMPLE_STMT_OPERAND (stmt
, 1)) == CALL_EXPR
)
1226 stmt
= GIMPLE_STMT_OPERAND (stmt
, 1);
1232 if (call_expr_flags (stmt
) & ECF_NORETURN
)
1233 predict_paths_leading_to (bb
, heads
, PRED_NORETURN
,
1245 /* Predict branch probabilities and estimate profile of the tree CFG. */
1247 tree_estimate_probability (void)
1251 loop_optimizer_init (0);
1252 if (current_loops
&& dump_file
&& (dump_flags
& TDF_DETAILS
))
1253 flow_loops_dump (dump_file
, NULL
, 0);
1255 add_noreturn_fake_exit_edges ();
1256 connect_infinite_loops_to_exit ();
1257 calculate_dominance_info (CDI_DOMINATORS
);
1258 calculate_dominance_info (CDI_POST_DOMINATORS
);
1260 tree_bb_level_predictions ();
1262 mark_irreducible_loops ();
1271 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
1273 /* Predict early returns to be probable, as we've already taken
1274 care for error returns and other cases are often used for
1275 fast paths through function. */
1276 if (e
->dest
== EXIT_BLOCK_PTR
1277 && TREE_CODE (last_stmt (bb
)) == RETURN_EXPR
1278 && !single_pred_p (bb
))
1283 FOR_EACH_EDGE (e1
, ei1
, bb
->preds
)
1284 if (!predicted_by_p (e1
->src
, PRED_NULL_RETURN
)
1285 && !predicted_by_p (e1
->src
, PRED_CONST_RETURN
)
1286 && !predicted_by_p (e1
->src
, PRED_NEGATIVE_RETURN
)
1287 && !last_basic_block_p (e1
->src
))
1288 predict_edge_def (e1
, PRED_TREE_EARLY_RETURN
, NOT_TAKEN
);
1291 /* Look for block we are guarding (ie we dominate it,
1292 but it doesn't postdominate us). */
1293 if (e
->dest
!= EXIT_BLOCK_PTR
&& e
->dest
!= bb
1294 && dominated_by_p (CDI_DOMINATORS
, e
->dest
, e
->src
)
1295 && !dominated_by_p (CDI_POST_DOMINATORS
, e
->src
, e
->dest
))
1297 block_stmt_iterator bi
;
1299 /* The call heuristic claims that a guarded function call
1300 is improbable. This is because such calls are often used
1301 to signal exceptional situations such as printing error
1303 for (bi
= bsi_start (e
->dest
); !bsi_end_p (bi
);
1306 tree stmt
= bsi_stmt (bi
);
1307 if ((TREE_CODE (stmt
) == CALL_EXPR
1308 || (TREE_CODE (stmt
) == GIMPLE_MODIFY_STMT
1309 && TREE_CODE (GIMPLE_STMT_OPERAND (stmt
, 1))
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 /* Propagates 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
;
1641 return true_count_max
;
1644 /* Return true if function is likely to be expensive, so there is no point to
1645 optimize performance of prologue, epilogue or do inlining at the expense
1646 of code size growth. THRESHOLD is the limit of number of instructions
1647 function can execute at average to be still considered not expensive. */
1650 expensive_function_p (int threshold
)
1652 unsigned int sum
= 0;
1656 /* We can not compute accurately for large thresholds due to scaled
1658 gcc_assert (threshold
<= BB_FREQ_MAX
);
1660 /* Frequencies are out of range. This either means that function contains
1661 internal loop executing more than BB_FREQ_MAX times or profile feedback
1662 is available and function has not been executed at all. */
1663 if (ENTRY_BLOCK_PTR
->frequency
== 0)
1666 /* Maximally BB_FREQ_MAX^2 so overflow won't happen. */
1667 limit
= ENTRY_BLOCK_PTR
->frequency
* threshold
;
1672 for (insn
= BB_HEAD (bb
); insn
!= NEXT_INSN (BB_END (bb
));
1673 insn
= NEXT_INSN (insn
))
1674 if (active_insn_p (insn
))
1676 sum
+= bb
->frequency
;
1685 /* Estimate basic blocks frequency by given branch probabilities. */
1688 estimate_bb_frequencies (void)
1693 if (!flag_branch_probabilities
|| !counts_to_freqs ())
1695 static int real_values_initialized
= 0;
1697 if (!real_values_initialized
)
1699 real_values_initialized
= 1;
1700 sreal_init (&real_zero
, 0, 0);
1701 sreal_init (&real_one
, 1, 0);
1702 sreal_init (&real_br_prob_base
, REG_BR_PROB_BASE
, 0);
1703 sreal_init (&real_bb_freq_max
, BB_FREQ_MAX
, 0);
1704 sreal_init (&real_one_half
, 1, -1);
1705 sreal_div (&real_inv_br_prob_base
, &real_one
, &real_br_prob_base
);
1706 sreal_sub (&real_almost_one
, &real_one
, &real_inv_br_prob_base
);
1709 mark_dfs_back_edges ();
1711 single_succ_edge (ENTRY_BLOCK_PTR
)->probability
= REG_BR_PROB_BASE
;
1713 /* Set up block info for each basic block. */
1714 alloc_aux_for_blocks (sizeof (struct block_info_def
));
1715 alloc_aux_for_edges (sizeof (struct edge_info_def
));
1716 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR
, NULL
, next_bb
)
1721 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
1723 sreal_init (&EDGE_INFO (e
)->back_edge_prob
, e
->probability
, 0);
1724 sreal_mul (&EDGE_INFO (e
)->back_edge_prob
,
1725 &EDGE_INFO (e
)->back_edge_prob
,
1726 &real_inv_br_prob_base
);
1730 /* First compute probabilities locally for each loop from innermost
1731 to outermost to examine probabilities for back edges. */
1734 memcpy (&freq_max
, &real_zero
, sizeof (real_zero
));
1736 if (sreal_compare (&freq_max
, &BLOCK_INFO (bb
)->frequency
) < 0)
1737 memcpy (&freq_max
, &BLOCK_INFO (bb
)->frequency
, sizeof (freq_max
));
1739 sreal_div (&freq_max
, &real_bb_freq_max
, &freq_max
);
1740 FOR_BB_BETWEEN (bb
, ENTRY_BLOCK_PTR
, NULL
, next_bb
)
1744 sreal_mul (&tmp
, &BLOCK_INFO (bb
)->frequency
, &freq_max
);
1745 sreal_add (&tmp
, &tmp
, &real_one_half
);
1746 bb
->frequency
= sreal_to_int (&tmp
);
1749 free_aux_for_blocks ();
1750 free_aux_for_edges ();
1752 compute_function_frequency ();
1753 if (flag_reorder_functions
)
1754 choose_function_section ();
1757 /* Decide whether function is hot, cold or unlikely executed. */
1759 compute_function_frequency (void)
1763 if (!profile_info
|| !flag_branch_probabilities
)
1765 cfun
->function_frequency
= FUNCTION_FREQUENCY_UNLIKELY_EXECUTED
;
1768 if (maybe_hot_bb_p (bb
))
1770 cfun
->function_frequency
= FUNCTION_FREQUENCY_HOT
;
1773 if (!probably_never_executed_bb_p (bb
))
1774 cfun
->function_frequency
= FUNCTION_FREQUENCY_NORMAL
;
1778 /* Choose appropriate section for the function. */
1780 choose_function_section (void)
1782 if (DECL_SECTION_NAME (current_function_decl
)
1783 || !targetm
.have_named_sections
1784 /* Theoretically we can split the gnu.linkonce text section too,
1785 but this requires more work as the frequency needs to match
1786 for all generated objects so we need to merge the frequency
1787 of all instances. For now just never set frequency for these. */
1788 || DECL_ONE_ONLY (current_function_decl
))
1791 /* If we are doing the partitioning optimization, let the optimization
1792 choose the correct section into which to put things. */
1794 if (flag_reorder_blocks_and_partition
)
1797 if (cfun
->function_frequency
== FUNCTION_FREQUENCY_HOT
)
1798 DECL_SECTION_NAME (current_function_decl
) =
1799 build_string (strlen (HOT_TEXT_SECTION_NAME
), HOT_TEXT_SECTION_NAME
);
1800 if (cfun
->function_frequency
== FUNCTION_FREQUENCY_UNLIKELY_EXECUTED
)
1801 DECL_SECTION_NAME (current_function_decl
) =
1802 build_string (strlen (UNLIKELY_EXECUTED_TEXT_SECTION_NAME
),
1803 UNLIKELY_EXECUTED_TEXT_SECTION_NAME
);
1807 gate_estimate_probability (void)
1809 return flag_guess_branch_prob
;
1812 struct tree_opt_pass pass_profile
=
1814 "profile", /* name */
1815 gate_estimate_probability
, /* gate */
1816 tree_estimate_probability
, /* execute */
1819 0, /* static_pass_number */
1820 TV_BRANCH_PROB
, /* tv_id */
1821 PROP_cfg
, /* properties_required */
1822 0, /* properties_provided */
1823 0, /* properties_destroyed */
1824 0, /* todo_flags_start */
1825 TODO_ggc_collect
| TODO_verify_ssa
, /* todo_flags_finish */