1 /* Branch prediction routines for the GNU compiler.
2 Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify it under
7 the terms of the GNU General Public License as published by the Free
8 Software Foundation; either version 2, or (at your option) any later
11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING. If not, write to the Free
18 Software Foundation, 59 Temple Place - Suite 330, Boston, MA
23 [1] "Branch Prediction for Free"
24 Ball and Larus; PLDI '93.
25 [2] "Static Branch Frequency and Program Profile Analysis"
26 Wu and Larus; MICRO-27.
27 [3] "Corpus-based Static Branch Prediction"
28 Calder, Grunwald, Lindsay, Martin, Mozer, and Zorn; PLDI '95. */
36 #include "hard-reg-set.h"
37 #include "basic-block.h"
38 #include "insn-config.h"
53 /* real constants: 0, 1, 1-1/REG_BR_PROB_BASE, REG_BR_PROB_BASE, 0.5,
55 static REAL_VALUE_TYPE real_zero, real_one, real_almost_one, real_br_prob_base,
56 real_one_half, real_bb_freq_max;
58 /* Random guesstimation given names. */
59 #define PROB_NEVER (0)
60 #define PROB_VERY_UNLIKELY (REG_BR_PROB_BASE / 10 - 1)
61 #define PROB_UNLIKELY (REG_BR_PROB_BASE * 4 / 10 - 1)
62 #define PROB_EVEN (REG_BR_PROB_BASE / 2)
63 #define PROB_LIKELY (REG_BR_PROB_BASE - PROB_UNLIKELY)
64 #define PROB_VERY_LIKELY (REG_BR_PROB_BASE - PROB_VERY_UNLIKELY)
65 #define PROB_ALWAYS (REG_BR_PROB_BASE)
67 static bool predicted_by_p PARAMS ((basic_block,
69 static void combine_predictions_for_insn PARAMS ((rtx, basic_block));
70 static void dump_prediction PARAMS ((enum br_predictor, int,
72 static void estimate_loops_at_level PARAMS ((struct loop *loop));
73 static void propagate_freq PARAMS ((basic_block));
74 static void estimate_bb_frequencies PARAMS ((struct loops *));
75 static void counts_to_freqs PARAMS ((void));
76 static void process_note_predictions PARAMS ((basic_block, int *, int *,
78 static void process_note_prediction PARAMS ((basic_block, int *, int *,
79 sbitmap *, int, int));
80 static bool last_basic_block_p PARAMS ((basic_block));
81 static void compute_function_frequency PARAMS ((void));
82 static void choose_function_section PARAMS ((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 perofmrance. */
119 if (profile_info.count_profiles_merged
120 && flag_branch_probabilities
122 < profile_info.max_counter_in_program
123 / PARAM_VALUE (HOT_BB_COUNT_FRACTION)))
125 if (bb->frequency < BB_FREQ_MAX / PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION))
130 /* Return true in case BB is cold and should be optimized for size. */
133 probably_cold_bb_p (bb)
136 if (profile_info.count_profiles_merged
137 && flag_branch_probabilities
139 < profile_info.max_counter_in_program
140 / PARAM_VALUE (HOT_BB_COUNT_FRACTION)))
142 if (bb->frequency < BB_FREQ_MAX / PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION))
147 /* Return true in case BB is probably never executed. */
149 probably_never_executed_bb_p (bb)
152 if (profile_info.count_profiles_merged
153 && flag_branch_probabilities)
154 return ((bb->count + profile_info.count_profiles_merged / 2)
155 / profile_info.count_profiles_merged) == 0;
159 /* Return true if the one of outgoing edges is already predicted by
163 predicted_by_p (bb, predictor)
165 enum br_predictor predictor;
168 if (!INSN_P (bb->end))
170 for (note = REG_NOTES (bb->end); note; note = XEXP (note, 1))
171 if (REG_NOTE_KIND (note) == REG_BR_PRED
172 && INTVAL (XEXP (XEXP (note, 0), 0)) == (int)predictor)
178 predict_insn (insn, predictor, probability)
181 enum br_predictor predictor;
183 if (!any_condjump_p (insn))
187 = gen_rtx_EXPR_LIST (REG_BR_PRED,
188 gen_rtx_CONCAT (VOIDmode,
189 GEN_INT ((int) predictor),
190 GEN_INT ((int) probability)),
194 /* Predict insn by given predictor. */
197 predict_insn_def (insn, predictor, taken)
199 enum br_predictor predictor;
200 enum prediction taken;
202 int probability = predictor_info[(int) predictor].hitrate;
205 probability = REG_BR_PROB_BASE - probability;
207 predict_insn (insn, predictor, probability);
210 /* Predict edge E with given probability if possible. */
213 predict_edge (e, predictor, probability)
216 enum br_predictor predictor;
219 last_insn = e->src->end;
221 /* We can store the branch prediction information only about
222 conditional jumps. */
223 if (!any_condjump_p (last_insn))
226 /* We always store probability of branching. */
227 if (e->flags & EDGE_FALLTHRU)
228 probability = REG_BR_PROB_BASE - probability;
230 predict_insn (last_insn, predictor, probability);
233 /* Predict edge E by given predictor if possible. */
236 predict_edge_def (e, predictor, taken)
238 enum br_predictor predictor;
239 enum prediction taken;
241 int probability = predictor_info[(int) predictor].hitrate;
244 probability = REG_BR_PROB_BASE - probability;
246 predict_edge (e, predictor, probability);
249 /* Invert all branch predictions or probability notes in the INSN. This needs
250 to be done each time we invert the condition used by the jump. */
253 invert_br_probabilities (insn)
258 for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
259 if (REG_NOTE_KIND (note) == REG_BR_PROB)
260 XEXP (note, 0) = GEN_INT (REG_BR_PROB_BASE - INTVAL (XEXP (note, 0)));
261 else if (REG_NOTE_KIND (note) == REG_BR_PRED)
262 XEXP (XEXP (note, 0), 1)
263 = GEN_INT (REG_BR_PROB_BASE - INTVAL (XEXP (XEXP (note, 0), 1)));
266 /* Dump information about the branch prediction to the output file. */
269 dump_prediction (predictor, probability, bb, used)
270 enum br_predictor predictor;
280 while (e && (e->flags & EDGE_FALLTHRU))
283 fprintf (rtl_dump_file, " %s heuristics%s: %.1f%%",
284 predictor_info[predictor].name,
285 used ? "" : " (ignored)", probability * 100.0 / REG_BR_PROB_BASE);
289 fprintf (rtl_dump_file, " exec ");
290 fprintf (rtl_dump_file, HOST_WIDEST_INT_PRINT_DEC, bb->count);
293 fprintf (rtl_dump_file, " hit ");
294 fprintf (rtl_dump_file, HOST_WIDEST_INT_PRINT_DEC, e->count);
295 fprintf (rtl_dump_file, " (%.1f%%)", e->count * 100.0 / bb->count);
299 fprintf (rtl_dump_file, "\n");
302 /* Combine all REG_BR_PRED notes into single probability and attach REG_BR_PROB
303 note if not already present. Remove now useless REG_BR_PRED notes. */
306 combine_predictions_for_insn (insn, bb)
310 rtx prob_note = find_reg_note (insn, REG_BR_PROB, 0);
311 rtx *pnote = ®_NOTES (insn);
313 int best_probability = PROB_EVEN;
314 int best_predictor = END_PREDICTORS;
315 int combined_probability = REG_BR_PROB_BASE / 2;
317 bool first_match = false;
321 fprintf (rtl_dump_file, "Predictions for insn %i bb %i\n", INSN_UID (insn),
324 /* We implement "first match" heuristics and use probability guessed
325 by predictor with smallest index. In the future we will use better
326 probability combination techniques. */
327 for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
328 if (REG_NOTE_KIND (note) == REG_BR_PRED)
330 int predictor = INTVAL (XEXP (XEXP (note, 0), 0));
331 int probability = INTVAL (XEXP (XEXP (note, 0), 1));
334 if (best_predictor > predictor)
335 best_probability = probability, best_predictor = predictor;
337 d = (combined_probability * probability
338 + (REG_BR_PROB_BASE - combined_probability)
339 * (REG_BR_PROB_BASE - probability));
341 /* Use FP math to avoid overflows of 32bit integers. */
343 /* If one probability is 0% and one 100%, avoid division by zero. */
344 combined_probability = REG_BR_PROB_BASE / 2;
346 combined_probability = (((double) combined_probability) * probability
347 * REG_BR_PROB_BASE / d + 0.5);
350 /* Decide which heuristic to use. In case we didn't match anything,
351 use no_prediction heuristic, in case we did match, use either
352 first match or Dempster-Shaffer theory depending on the flags. */
354 if (predictor_info [best_predictor].flags & PRED_FLAG_FIRST_MATCH)
358 dump_prediction (PRED_NO_PREDICTION, combined_probability, bb, true);
361 dump_prediction (PRED_DS_THEORY, combined_probability, bb, !first_match);
362 dump_prediction (PRED_FIRST_MATCH, best_probability, bb, first_match);
366 combined_probability = best_probability;
367 dump_prediction (PRED_COMBINED, combined_probability, bb, true);
371 if (REG_NOTE_KIND (*pnote) == REG_BR_PRED)
373 int predictor = INTVAL (XEXP (XEXP (*pnote, 0), 0));
374 int probability = INTVAL (XEXP (XEXP (*pnote, 0), 1));
376 dump_prediction (predictor, probability, bb,
377 !first_match || best_predictor == predictor);
378 *pnote = XEXP (*pnote, 1);
381 pnote = &XEXP (*pnote, 1);
387 = gen_rtx_EXPR_LIST (REG_BR_PROB,
388 GEN_INT (combined_probability), REG_NOTES (insn));
390 /* Save the prediction into CFG in case we are seeing non-degenerated
392 if (bb->succ->succ_next)
394 BRANCH_EDGE (bb)->probability = combined_probability;
395 FALLTHRU_EDGE (bb)->probability
396 = REG_BR_PROB_BASE - combined_probability;
401 /* Statically estimate the probability that a branch will be taken.
402 ??? In the next revision there will be a number of other predictors added
403 from the above references. Further, each heuristic will be factored out
404 into its own function for clarity (and to facilitate the combination of
408 estimate_probability (loops_info)
409 struct loops *loops_info;
411 sbitmap *dominators, *post_dominators;
415 dominators = sbitmap_vector_alloc (n_basic_blocks, n_basic_blocks);
416 post_dominators = sbitmap_vector_alloc (n_basic_blocks, n_basic_blocks);
417 calculate_dominance_info (NULL, dominators, CDI_DOMINATORS);
418 calculate_dominance_info (NULL, post_dominators, CDI_POST_DOMINATORS);
420 /* Try to predict out blocks in a loop that are not part of a
422 for (i = 0; i < loops_info->num; i++)
425 struct loop *loop = &loops_info->array[i];
427 flow_loop_scan (loops_info, loop, LOOP_EXIT_EDGES);
428 exits = loop->num_exits;
430 FOR_BB_BETWEEN (bb, loop->first, loop->last->next_bb, next_bb)
431 if (TEST_BIT (loop->nodes, bb->index))
433 int header_found = 0;
436 /* Bypass loop heuristics on continue statement. These
437 statements construct loops via "non-loop" constructs
438 in the source language and are better to be handled
440 if (predicted_by_p (bb, PRED_CONTINUE))
443 /* Loop branch heuristics - predict an edge back to a
444 loop's head as taken. */
445 for (e = bb->succ; e; e = e->succ_next)
446 if (e->dest == loop->header
447 && e->src == loop->latch)
450 predict_edge_def (e, PRED_LOOP_BRANCH, TAKEN);
453 /* Loop exit heuristics - predict an edge exiting the loop if the
454 conditinal has no loop header successors as not taken. */
456 for (e = bb->succ; e; e = e->succ_next)
457 if (e->dest->index < 0
458 || !TEST_BIT (loop->nodes, e->dest->index))
462 - predictor_info [(int) PRED_LOOP_EXIT].hitrate)
467 /* Attempt to predict conditional jumps using a number of heuristics. */
470 rtx last_insn = bb->end;
474 if (GET_CODE (last_insn) != JUMP_INSN || ! any_condjump_p (last_insn))
477 for (e = bb->succ; e; e = e->succ_next)
479 /* Predict early returns to be probable, as we've already taken
480 care for error returns and other are often used for fast paths
482 if ((e->dest == EXIT_BLOCK_PTR
483 || (e->dest->succ && !e->dest->succ->succ_next
484 && e->dest->succ->dest == EXIT_BLOCK_PTR))
485 && !predicted_by_p (bb, PRED_NULL_RETURN)
486 && !predicted_by_p (bb, PRED_CONST_RETURN)
487 && !predicted_by_p (bb, PRED_NEGATIVE_RETURN)
488 && !last_basic_block_p (e->dest))
489 predict_edge_def (e, PRED_EARLY_RETURN, TAKEN);
491 /* Look for block we are guarding (ie we dominate it,
492 but it doesn't postdominate us). */
493 if (e->dest != EXIT_BLOCK_PTR && e->dest != bb
494 && TEST_BIT (dominators[e->dest->index], e->src->index)
495 && !TEST_BIT (post_dominators[e->src->index], e->dest->index))
499 /* The call heuristic claims that a guarded function call
500 is improbable. This is because such calls are often used
501 to signal exceptional situations such as printing error
503 for (insn = e->dest->head; insn != NEXT_INSN (e->dest->end);
504 insn = NEXT_INSN (insn))
505 if (GET_CODE (insn) == CALL_INSN
506 /* Constant and pure calls are hardly used to signalize
507 something exceptional. */
508 && ! CONST_OR_PURE_CALL_P (insn))
510 predict_edge_def (e, PRED_CALL, NOT_TAKEN);
516 cond = get_condition (last_insn, &earliest);
520 /* Try "pointer heuristic."
521 A comparison ptr == 0 is predicted as false.
522 Similarly, a comparison ptr1 == ptr2 is predicted as false. */
523 if (GET_RTX_CLASS (GET_CODE (cond)) == '<'
524 && ((REG_P (XEXP (cond, 0)) && REG_POINTER (XEXP (cond, 0)))
525 || (REG_P (XEXP (cond, 1)) && REG_POINTER (XEXP (cond, 1)))))
527 if (GET_CODE (cond) == EQ)
528 predict_insn_def (last_insn, PRED_POINTER, NOT_TAKEN);
529 else if (GET_CODE (cond) == NE)
530 predict_insn_def (last_insn, PRED_POINTER, TAKEN);
534 /* Try "opcode heuristic."
535 EQ tests are usually false and NE tests are usually true. Also,
536 most quantities are positive, so we can make the appropriate guesses
537 about signed comparisons against zero. */
538 switch (GET_CODE (cond))
541 /* Unconditional branch. */
542 predict_insn_def (last_insn, PRED_UNCONDITIONAL,
543 cond == const0_rtx ? NOT_TAKEN : TAKEN);
548 /* Floating point comparisons appears to behave in a very
549 inpredictable way because of special role of = tests in
551 if (FLOAT_MODE_P (GET_MODE (XEXP (cond, 0))))
553 /* Comparisons with 0 are often used for booleans and there is
554 nothing usefull to predict about them. */
555 else if (XEXP (cond, 1) == const0_rtx
556 || XEXP (cond, 0) == const0_rtx)
559 predict_insn_def (last_insn, PRED_OPCODE_NONEQUAL, NOT_TAKEN);
564 /* Floating point comparisons appears to behave in a very
565 inpredictable way because of special role of = tests in
567 if (FLOAT_MODE_P (GET_MODE (XEXP (cond, 0))))
569 /* Comparisons with 0 are often used for booleans and there is
570 nothing usefull to predict about them. */
571 else if (XEXP (cond, 1) == const0_rtx
572 || XEXP (cond, 0) == const0_rtx)
575 predict_insn_def (last_insn, PRED_OPCODE_NONEQUAL, TAKEN);
579 predict_insn_def (last_insn, PRED_FPOPCODE, TAKEN);
583 predict_insn_def (last_insn, PRED_FPOPCODE, NOT_TAKEN);
588 if (XEXP (cond, 1) == const0_rtx || XEXP (cond, 1) == const1_rtx
589 || XEXP (cond, 1) == constm1_rtx)
590 predict_insn_def (last_insn, PRED_OPCODE_POSITIVE, NOT_TAKEN);
595 if (XEXP (cond, 1) == const0_rtx || XEXP (cond, 1) == const1_rtx
596 || XEXP (cond, 1) == constm1_rtx)
597 predict_insn_def (last_insn, PRED_OPCODE_POSITIVE, TAKEN);
605 /* Attach the combined probability to each conditional jump. */
607 if (GET_CODE (bb->end) == JUMP_INSN
608 && any_condjump_p (bb->end)
609 && bb->succ->succ_next != NULL)
610 combine_predictions_for_insn (bb->end, bb);
612 sbitmap_vector_free (post_dominators);
613 sbitmap_vector_free (dominators);
615 estimate_bb_frequencies (loops_info);
618 /* __builtin_expect dropped tokens into the insn stream describing expected
619 values of registers. Generate branch probabilities based off these
623 expected_value_to_br_prob ()
625 rtx insn, cond, ev = NULL_RTX, ev_reg = NULL_RTX;
627 for (insn = get_insns (); insn ; insn = NEXT_INSN (insn))
629 switch (GET_CODE (insn))
632 /* Look for expected value notes. */
633 if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_EXPECTED_VALUE)
635 ev = NOTE_EXPECTED_VALUE (insn);
636 ev_reg = XEXP (ev, 0);
642 /* Never propagate across labels. */
647 /* Look for simple conditional branches. If we haven't got an
648 expected value yet, no point going further. */
649 if (GET_CODE (insn) != JUMP_INSN || ev == NULL_RTX
650 || ! any_condjump_p (insn))
655 /* Look for insns that clobber the EV register. */
656 if (ev && reg_set_p (ev_reg, insn))
661 /* Collect the branch condition, hopefully relative to EV_REG. */
662 /* ??? At present we'll miss things like
663 (expected_value (eq r70 0))
665 (set r80 (lt r70 r71))
666 (set pc (if_then_else (ne r80 0) ...))
667 as canonicalize_condition will render this to us as
669 Could use cselib to try and reduce this further. */
670 cond = XEXP (SET_SRC (pc_set (insn)), 0);
671 cond = canonicalize_condition (insn, cond, 0, NULL, ev_reg);
672 if (! cond || XEXP (cond, 0) != ev_reg
673 || GET_CODE (XEXP (cond, 1)) != CONST_INT)
676 /* Substitute and simplify. Given that the expression we're
677 building involves two constants, we should wind up with either
679 cond = gen_rtx_fmt_ee (GET_CODE (cond), VOIDmode,
680 XEXP (ev, 1), XEXP (cond, 1));
681 cond = simplify_rtx (cond);
683 /* Turn the condition into a scaled branch probability. */
684 if (cond != const_true_rtx && cond != const0_rtx)
686 predict_insn_def (insn, PRED_BUILTIN_EXPECT,
687 cond == const_true_rtx ? TAKEN : NOT_TAKEN);
691 /* Check whether this is the last basic block of function. Commonly tehre
692 is one extra common cleanup block. */
694 last_basic_block_p (bb)
697 if (bb == EXIT_BLOCK_PTR)
700 return (bb->next_bb == EXIT_BLOCK_PTR
701 || (bb->next_bb->next_bb == EXIT_BLOCK_PTR
702 && bb->succ && !bb->succ->succ_next
703 && bb->succ->dest->next_bb == EXIT_BLOCK_PTR));
706 /* Sets branch probabilities according to PREDiction and FLAGS. HEADS[bb->index]
707 should be index of basic block in that we need to alter branch predictions
708 (i.e. the first of our dominators such that we do not post-dominate it)
709 (but we fill this information on demand, so -1 may be there in case this
710 was not needed yet). */
713 process_note_prediction (bb, heads, dominators, post_dominators, pred, flags)
717 sbitmap *post_dominators;
725 taken = flags & IS_TAKEN;
727 if (heads[bb->index] < 0)
729 /* This is first time we need this field in heads array; so
730 find first dominator that we do not post-dominate (we are
731 using already known members of heads array). */
733 int next_ai = dominators[bb->index];
736 while (heads[next_ai] < 0)
738 if (!TEST_BIT (post_dominators[next_ai], bb->index))
742 next_ai = dominators[next_ai];
744 if (!TEST_BIT (post_dominators[next_ai], bb->index))
747 head = heads[next_ai];
748 while (next_ai != bb->index)
752 heads[next_ai] = head;
755 y = heads[bb->index];
757 /* Now find the edge that leads to our branch and aply the prediction. */
759 if (y == n_basic_blocks)
761 for (e = BASIC_BLOCK (y)->succ; e; e = e->succ_next)
762 if (e->dest->index >= 0
763 && TEST_BIT (post_dominators[e->dest->index], bb->index))
764 predict_edge_def (e, pred, taken);
767 /* Gathers NOTE_INSN_PREDICTIONs in given basic block and turns them
768 into branch probabilities. For description of heads array, see
769 process_note_prediction. */
772 process_note_predictions (bb, heads, dominators, post_dominators)
776 sbitmap *post_dominators;
781 /* Additionaly, we check here for blocks with no successors. */
782 int contained_noreturn_call = 0;
784 int noreturn_block = 1;
786 for (insn = bb->end; insn;
787 was_bb_head |= (insn == bb->head), insn = PREV_INSN (insn))
789 if (GET_CODE (insn) != NOTE)
795 /* Noreturn calls cause program to exit, therefore they are
796 always predicted as not taken. */
797 if (GET_CODE (insn) == CALL_INSN
798 && find_reg_note (insn, REG_NORETURN, NULL))
799 contained_noreturn_call = 1;
803 if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_PREDICTION)
805 int alg = (int) NOTE_PREDICTION_ALG (insn);
806 /* Process single prediction note. */
807 process_note_prediction (bb,
811 alg, (int) NOTE_PREDICTION_FLAGS (insn));
815 for (e = bb->succ; e; e = e->succ_next)
816 if (!(e->flags & EDGE_FAKE))
818 if (contained_noreturn_call)
820 /* This block ended from other reasons than because of return.
821 If it is because of noreturn call, this should certainly not
822 be taken. Otherwise it is probably some error recovery. */
823 process_note_prediction (bb,
826 post_dominators, PRED_NORETURN, NOT_TAKEN);
830 /* Gathers NOTE_INSN_PREDICTIONs and turns them into
831 branch probabilities. */
834 note_prediction_to_br_prob ()
837 sbitmap *post_dominators;
838 int *dominators, *heads;
840 /* To enable handling of noreturn blocks. */
841 add_noreturn_fake_exit_edges ();
842 connect_infinite_loops_to_exit ();
844 dominators = xmalloc (sizeof (int) * n_basic_blocks);
845 memset (dominators, -1, sizeof (int) * n_basic_blocks);
846 post_dominators = sbitmap_vector_alloc (n_basic_blocks, n_basic_blocks);
847 calculate_dominance_info (NULL, post_dominators, CDI_POST_DOMINATORS);
848 calculate_dominance_info (dominators, NULL, CDI_DOMINATORS);
850 heads = xmalloc (sizeof (int) * n_basic_blocks);
851 memset (heads, -1, sizeof (int) * n_basic_blocks);
852 heads[ENTRY_BLOCK_PTR->next_bb->index] = n_basic_blocks;
854 /* Process all prediction notes. */
857 process_note_predictions (bb, heads, dominators, post_dominators);
859 sbitmap_vector_free (post_dominators);
863 remove_fake_edges ();
866 /* This is used to carry information about basic blocks. It is
867 attached to the AUX field of the standard CFG block. */
869 typedef struct block_info_def
871 /* Estimated frequency of execution of basic_block. */
872 REAL_VALUE_TYPE frequency;
874 /* To keep queue of basic blocks to process. */
877 /* True if block needs to be visited in prop_freqency. */
880 /* Number of predecessors we need to visit first. */
884 /* Similar information for edges. */
885 typedef struct edge_info_def
887 /* In case edge is an loopback edge, the probability edge will be reached
888 in case header is. Estimated number of iterations of the loop can be
889 then computed as 1 / (1 - back_edge_prob). */
890 REAL_VALUE_TYPE back_edge_prob;
891 /* True if the edge is an loopback edge in the natural loop. */
895 #define BLOCK_INFO(B) ((block_info) (B)->aux)
896 #define EDGE_INFO(E) ((edge_info) (E)->aux)
898 /* Helper function for estimate_bb_frequencies.
899 Propagate the frequencies for loops headed by HEAD. */
902 propagate_freq (head)
910 /* For each basic block we need to visit count number of his predecessors
911 we need to visit first. */
914 if (BLOCK_INFO (bb)->tovisit)
918 for (e = bb->pred; e; e = e->pred_next)
919 if (BLOCK_INFO (e->src)->tovisit && !(e->flags & EDGE_DFS_BACK))
921 else if (BLOCK_INFO (e->src)->tovisit
922 && rtl_dump_file && !EDGE_INFO (e)->back_edge)
923 fprintf (rtl_dump_file,
924 "Irreducible region hit, ignoring edge to %i->%i\n",
925 e->src->index, bb->index);
926 BLOCK_INFO (bb)->npredecessors = count;
930 memcpy (&BLOCK_INFO (head)->frequency, &real_one, sizeof (real_one));
932 for (bb = head; bb; bb = nextbb)
934 REAL_VALUE_TYPE cyclic_probability, frequency;
936 memcpy (&cyclic_probability, &real_zero, sizeof (real_zero));
937 memcpy (&frequency, &real_zero, sizeof (real_zero));
939 nextbb = BLOCK_INFO (bb)->next;
940 BLOCK_INFO (bb)->next = NULL;
942 /* Compute frequency of basic block. */
945 #ifdef ENABLE_CHECKING
946 for (e = bb->pred; e; e = e->pred_next)
947 if (BLOCK_INFO (e->src)->tovisit && !(e->flags & EDGE_DFS_BACK))
951 for (e = bb->pred; e; e = e->pred_next)
952 if (EDGE_INFO (e)->back_edge)
954 REAL_ARITHMETIC (cyclic_probability, PLUS_EXPR,
956 EDGE_INFO (e)->back_edge_prob);
958 else if (!(e->flags & EDGE_DFS_BACK))
962 /* frequency += (e->probability
963 * BLOCK_INFO (e->src)->frequency /
964 REG_BR_PROB_BASE); */
966 REAL_VALUE_FROM_INT (tmp, e->probability, 0,
967 TYPE_MODE (double_type_node));
968 REAL_ARITHMETIC (tmp, MULT_EXPR, tmp,
969 BLOCK_INFO (e->src)->frequency);
970 REAL_ARITHMETIC (tmp, RDIV_EXPR, tmp, real_br_prob_base);
971 REAL_ARITHMETIC (frequency, PLUS_EXPR, frequency, tmp);
974 if (REAL_VALUES_LESS (real_almost_one, cyclic_probability))
975 memcpy (&cyclic_probability, &real_almost_one, sizeof (real_zero));
977 /* BLOCK_INFO (bb)->frequency = frequency / (1 - cyclic_probability)
980 REAL_ARITHMETIC (cyclic_probability, MINUS_EXPR, real_one,
982 REAL_ARITHMETIC (BLOCK_INFO (bb)->frequency,
983 RDIV_EXPR, frequency, cyclic_probability);
986 BLOCK_INFO (bb)->tovisit = 0;
988 /* Compute back edge frequencies. */
989 for (e = bb->succ; e; e = e->succ_next)
994 /* EDGE_INFO (e)->back_edge_prob
995 = ((e->probability * BLOCK_INFO (bb)->frequency)
996 / REG_BR_PROB_BASE); */
997 REAL_VALUE_FROM_INT (tmp, e->probability, 0,
998 TYPE_MODE (double_type_node));
999 REAL_ARITHMETIC (tmp, MULT_EXPR, tmp,
1000 BLOCK_INFO (bb)->frequency);
1001 REAL_ARITHMETIC (EDGE_INFO (e)->back_edge_prob,
1002 RDIV_EXPR, tmp, real_br_prob_base);
1006 /* Propagate to successor blocks. */
1007 for (e = bb->succ; e; e = e->succ_next)
1008 if (!(e->flags & EDGE_DFS_BACK)
1009 && BLOCK_INFO (e->dest)->npredecessors)
1011 BLOCK_INFO (e->dest)->npredecessors--;
1012 if (!BLOCK_INFO (e->dest)->npredecessors)
1017 BLOCK_INFO (last)->next = e->dest;
1025 /* Estimate probabilities of loopback edges in loops at same nest level. */
1028 estimate_loops_at_level (first_loop)
1029 struct loop *first_loop;
1031 struct loop *l, *loop = first_loop;
1033 for (loop = first_loop; loop; loop = loop->next)
1038 estimate_loops_at_level (loop->inner);
1040 /* Find current loop back edge and mark it. */
1041 for (e = loop->latch->succ; e->dest != loop->header; e = e->succ_next)
1044 EDGE_INFO (e)->back_edge = 1;
1046 /* In case the loop header is shared, ensure that it is the last
1047 one sharing the same header, so we avoid redundant work. */
1050 for (l = loop->next; l; l = l->next)
1051 if (l->header == loop->header)
1058 /* Now merge all nodes of all loops with given header as not visited. */
1059 for (l = loop->shared ? first_loop : loop; l != loop->next; l = l->next)
1060 if (loop->header == l->header)
1061 EXECUTE_IF_SET_IN_SBITMAP (l->nodes, 0, n,
1062 BLOCK_INFO (BASIC_BLOCK (n))->tovisit = 1
1065 propagate_freq (loop->header);
1069 /* Convert counts measured by profile driven feedback to frequencies. */
1074 HOST_WIDEST_INT count_max = 1;
1078 count_max = MAX (bb->count, count_max);
1080 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
1081 bb->frequency = (bb->count * BB_FREQ_MAX + count_max / 2) / count_max;
1084 /* Return true if function is likely to be expensive, so there is no point to
1085 optimize performance of prologue, epilogue or do inlining at the expense
1086 of code size growth. THRESHOLD is the limit of number of isntructions
1087 function can execute at average to be still considered not expensive. */
1090 expensive_function_p (threshold)
1093 unsigned int sum = 0;
1097 /* We can not compute accurately for large thresholds due to scaled
1099 if (threshold > BB_FREQ_MAX)
1102 /* Frequencies are out of range. This either means that function contains
1103 internal loop executing more than BB_FREQ_MAX times or profile feedback
1104 is available and function has not been executed at all. */
1105 if (ENTRY_BLOCK_PTR->frequency == 0)
1108 /* Maximally BB_FREQ_MAX^2 so overflow won't happen. */
1109 limit = ENTRY_BLOCK_PTR->frequency * threshold;
1114 for (insn = bb->head; insn != NEXT_INSN (bb->end);
1115 insn = NEXT_INSN (insn))
1116 if (active_insn_p (insn))
1118 sum += bb->frequency;
1127 /* Estimate basic blocks frequency by given branch probabilities. */
1130 estimate_bb_frequencies (loops)
1131 struct loops *loops;
1134 REAL_VALUE_TYPE freq_max;
1135 enum machine_mode double_mode = TYPE_MODE (double_type_node);
1137 if (flag_branch_probabilities)
1141 REAL_VALUE_FROM_INT (real_zero, 0, 0, double_mode);
1142 REAL_VALUE_FROM_INT (real_one, 1, 0, double_mode);
1143 REAL_VALUE_FROM_INT (real_br_prob_base, REG_BR_PROB_BASE, 0, double_mode);
1144 REAL_VALUE_FROM_INT (real_bb_freq_max, BB_FREQ_MAX, 0, double_mode);
1145 REAL_VALUE_FROM_INT (real_one_half, 2, 0, double_mode);
1147 REAL_ARITHMETIC (real_one_half, RDIV_EXPR, real_one, real_one_half);
1149 REAL_ARITHMETIC (real_almost_one, RDIV_EXPR, real_one, real_br_prob_base);
1150 REAL_ARITHMETIC (real_almost_one, MINUS_EXPR, real_one, real_almost_one);
1152 mark_dfs_back_edges ();
1153 /* Fill in the probability values in flowgraph based on the REG_BR_PROB
1157 rtx last_insn = bb->end;
1159 if (GET_CODE (last_insn) != JUMP_INSN || !any_condjump_p (last_insn)
1160 /* Avoid handling of conditional jumps jumping to fallthru edge. */
1161 || bb->succ->succ_next == NULL)
1163 /* We can predict only conditional jumps at the moment.
1164 Expect each edge to be equally probable.
1165 ?? In the future we want to make abnormal edges improbable. */
1169 for (e = bb->succ; e; e = e->succ_next)
1172 if (e->probability != 0)
1176 for (e = bb->succ; e; e = e->succ_next)
1177 e->probability = (REG_BR_PROB_BASE + nedges / 2) / nedges;
1181 ENTRY_BLOCK_PTR->succ->probability = REG_BR_PROB_BASE;
1183 /* Set up block info for each basic block. */
1184 alloc_aux_for_blocks (sizeof (struct block_info_def));
1185 alloc_aux_for_edges (sizeof (struct edge_info_def));
1186 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
1190 BLOCK_INFO (bb)->tovisit = 0;
1191 for (e = bb->succ; e; e = e->succ_next)
1193 REAL_VALUE_FROM_INT (EDGE_INFO (e)->back_edge_prob,
1194 e->probability, 0, double_mode);
1195 REAL_ARITHMETIC (EDGE_INFO (e)->back_edge_prob,
1196 RDIV_EXPR, EDGE_INFO (e)->back_edge_prob,
1201 /* First compute probabilities locally for each loop from innermost
1202 to outermost to examine probabilities for back edges. */
1203 estimate_loops_at_level (loops->tree_root);
1205 /* Now fake loop around whole function to finalize probabilities. */
1206 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
1207 BLOCK_INFO (bb)->tovisit = 1;
1209 BLOCK_INFO (ENTRY_BLOCK_PTR)->tovisit = 1;
1210 BLOCK_INFO (EXIT_BLOCK_PTR)->tovisit = 1;
1211 propagate_freq (ENTRY_BLOCK_PTR);
1213 memcpy (&freq_max, &real_zero, sizeof (real_zero));
1215 if (REAL_VALUES_LESS
1216 (freq_max, BLOCK_INFO (bb)->frequency))
1217 memcpy (&freq_max, &BLOCK_INFO (bb)->frequency,
1220 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
1222 REAL_VALUE_TYPE tmp;
1224 REAL_ARITHMETIC (tmp, MULT_EXPR, BLOCK_INFO (bb)->frequency,
1226 REAL_ARITHMETIC (tmp, RDIV_EXPR, tmp, freq_max);
1227 REAL_ARITHMETIC (tmp, PLUS_EXPR, tmp, real_one_half);
1228 bb->frequency = REAL_VALUE_UNSIGNED_FIX (tmp);
1231 free_aux_for_blocks ();
1232 free_aux_for_edges ();
1234 compute_function_frequency ();
1235 if (flag_reorder_functions)
1236 choose_function_section ();
1239 /* Decide whether function is hot, cold or unlikely executed. */
1241 compute_function_frequency ()
1245 if (!profile_info.count_profiles_merged
1246 || !flag_branch_probabilities)
1248 cfun->function_frequency = FUNCTION_FREQUENCY_UNLIKELY_EXECUTED;
1251 if (maybe_hot_bb_p (bb))
1253 cfun->function_frequency = FUNCTION_FREQUENCY_HOT;
1256 if (!probably_never_executed_bb_p (bb))
1257 cfun->function_frequency = FUNCTION_FREQUENCY_NORMAL;
1261 /* Choose appropriate section for the function. */
1263 choose_function_section ()
1265 if (DECL_SECTION_NAME (current_function_decl)
1266 || !targetm.have_named_sections)
1268 if (cfun->function_frequency == FUNCTION_FREQUENCY_HOT)
1269 DECL_SECTION_NAME (current_function_decl) =
1270 build_string (strlen (HOT_TEXT_SECTION_NAME), HOT_TEXT_SECTION_NAME);
1271 if (cfun->function_frequency == FUNCTION_FREQUENCY_UNLIKELY_EXECUTED)
1272 DECL_SECTION_NAME (current_function_decl) =
1273 build_string (strlen (UNLIKELY_EXECUTED_TEXT_SECTION_NAME),
1274 UNLIKELY_EXECUTED_TEXT_SECTION_NAME);