1 /* Branch prediction routines for the GNU compiler.
2 Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc.
3
4 This file is part of GCC.
5
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
9 version.
10
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
14 for more details.
15
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
19 02111-1307, USA. */
20
21 /* References:
22
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. */
29
30
31 #include "config.h"
32 #include "system.h"
33 #include "tree.h"
34 #include "rtl.h"
35 #include "tm_p.h"
36 #include "hard-reg-set.h"
37 #include "basic-block.h"
38 #include "insn-config.h"
39 #include "regs.h"
40 #include "flags.h"
41 #include "output.h"
42 #include "function.h"
43 #include "except.h"
44 #include "toplev.h"
45 #include "recog.h"
46 #include "expr.h"
47 #include "predict.h"
48 #include "profile.h"
49 #include "real.h"
50 #include "params.h"
51 #include "target.h"
52 #include "loop.h"
53
54 /* real constants: 0, 1, 1-1/REG_BR_PROB_BASE, REG_BR_PROB_BASE,
55 1/REG_BR_PROB_BASE, 0.5, BB_FREQ_MAX. */
56 static REAL_VALUE_TYPE real_zero, real_one, real_almost_one, real_br_prob_base,
57 real_inv_br_prob_base, real_one_half, real_bb_freq_max;
58
59 /* Random guesstimation given names. */
60 #define PROB_VERY_UNLIKELY (REG_BR_PROB_BASE / 10 - 1)
61 #define PROB_EVEN (REG_BR_PROB_BASE / 2)
62 #define PROB_VERY_LIKELY (REG_BR_PROB_BASE - PROB_VERY_UNLIKELY)
63 #define PROB_ALWAYS (REG_BR_PROB_BASE)
64
65 static bool predicted_by_p PARAMS ((basic_block,
66 enum br_predictor));
67 static void combine_predictions_for_insn PARAMS ((rtx, basic_block));
68 static void dump_prediction PARAMS ((enum br_predictor, int,
69 basic_block, int));
70 static void estimate_loops_at_level PARAMS ((struct loop *loop));
71 static void propagate_freq PARAMS ((struct loop *));
72 static void estimate_bb_frequencies PARAMS ((struct loops *));
73 static void counts_to_freqs PARAMS ((void));
74 static void process_note_predictions PARAMS ((basic_block, int *,
75 dominance_info,
76 dominance_info));
77 static void process_note_prediction PARAMS ((basic_block, int *,
78 dominance_info,
79 dominance_info, 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));
83 static bool can_predict_insn_p PARAMS ((rtx));
84
85 /* Information we hold about each branch predictor.
86 Filled using information from predict.def. */
87
88 struct predictor_info
89 {
90 const char *const name; /* Name used in the debugging dumps. */
91 const int hitrate; /* Expected hitrate used by
92 predict_insn_def call. */
93 const int flags;
94 };
95
96 /* Use given predictor without Dempster-Shaffer theory if it matches
97 using first_match heuristics. */
98 #define PRED_FLAG_FIRST_MATCH 1
99
100 /* Recompute hitrate in percent to our representation. */
101
102 #define HITRATE(VAL) ((int) ((VAL) * REG_BR_PROB_BASE + 50) / 100)
103
104 #define DEF_PREDICTOR(ENUM, NAME, HITRATE, FLAGS) {NAME, HITRATE, FLAGS},
105 static const struct predictor_info predictor_info[]= {
106 #include "predict.def"
107
108 /* Upper bound on predictors. */
109 {NULL, 0, 0}
110 };
111 #undef DEF_PREDICTOR
112
113 /* Return true in case BB can be CPU intensive and should be optimized
114 for maximal perofmrance. */
115
116 bool
maybe_hot_bb_p(bb)117 maybe_hot_bb_p (bb)
118 basic_block bb;
119 {
120 if (profile_info.count_profiles_merged
121 && flag_branch_probabilities
122 && (bb->count
123 < profile_info.max_counter_in_program
124 / PARAM_VALUE (HOT_BB_COUNT_FRACTION)))
125 return false;
126 if (bb->frequency < BB_FREQ_MAX / PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION))
127 return false;
128 return true;
129 }
130
131 /* Return true in case BB is cold and should be optimized for size. */
132
133 bool
probably_cold_bb_p(bb)134 probably_cold_bb_p (bb)
135 basic_block bb;
136 {
137 if (profile_info.count_profiles_merged
138 && flag_branch_probabilities
139 && (bb->count
140 < profile_info.max_counter_in_program
141 / PARAM_VALUE (HOT_BB_COUNT_FRACTION)))
142 return true;
143 if (bb->frequency < BB_FREQ_MAX / PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION))
144 return true;
145 return false;
146 }
147
148 /* Return true in case BB is probably never executed. */
149 bool
probably_never_executed_bb_p(bb)150 probably_never_executed_bb_p (bb)
151 basic_block bb;
152 {
153 if (profile_info.count_profiles_merged
154 && flag_branch_probabilities)
155 return ((bb->count + profile_info.count_profiles_merged / 2)
156 / profile_info.count_profiles_merged) == 0;
157 return false;
158 }
159
160 /* Return true if the one of outgoing edges is already predicted by
161 PREDICTOR. */
162
163 static bool
predicted_by_p(bb,predictor)164 predicted_by_p (bb, predictor)
165 basic_block bb;
166 enum br_predictor predictor;
167 {
168 rtx note;
169 if (!INSN_P (bb->end))
170 return false;
171 for (note = REG_NOTES (bb->end); note; note = XEXP (note, 1))
172 if (REG_NOTE_KIND (note) == REG_BR_PRED
173 && INTVAL (XEXP (XEXP (note, 0), 0)) == (int)predictor)
174 return true;
175 return false;
176 }
177
178 void
predict_insn(insn,predictor,probability)179 predict_insn (insn, predictor, probability)
180 rtx insn;
181 int probability;
182 enum br_predictor predictor;
183 {
184 if (!any_condjump_p (insn))
185 abort ();
186 if (!flag_guess_branch_prob)
187 return;
188
189 REG_NOTES (insn)
190 = gen_rtx_EXPR_LIST (REG_BR_PRED,
191 gen_rtx_CONCAT (VOIDmode,
192 GEN_INT ((int) predictor),
193 GEN_INT ((int) probability)),
194 REG_NOTES (insn));
195 }
196
197 /* Predict insn by given predictor. */
198
199 void
predict_insn_def(insn,predictor,taken)200 predict_insn_def (insn, predictor, taken)
201 rtx insn;
202 enum br_predictor predictor;
203 enum prediction taken;
204 {
205 int probability = predictor_info[(int) predictor].hitrate;
206
207 if (taken != TAKEN)
208 probability = REG_BR_PROB_BASE - probability;
209
210 predict_insn (insn, predictor, probability);
211 }
212
213 /* Predict edge E with given probability if possible. */
214
215 void
predict_edge(e,predictor,probability)216 predict_edge (e, predictor, probability)
217 edge e;
218 int probability;
219 enum br_predictor predictor;
220 {
221 rtx last_insn;
222 last_insn = e->src->end;
223
224 /* We can store the branch prediction information only about
225 conditional jumps. */
226 if (!any_condjump_p (last_insn))
227 return;
228
229 /* We always store probability of branching. */
230 if (e->flags & EDGE_FALLTHRU)
231 probability = REG_BR_PROB_BASE - probability;
232
233 predict_insn (last_insn, predictor, probability);
234 }
235
236 /* Return true when we can store prediction on insn INSN.
237 At the moment we represent predictions only on conditional
238 jumps, not at computed jump or other complicated cases. */
239 static bool
can_predict_insn_p(insn)240 can_predict_insn_p (insn)
241 rtx insn;
242 {
243 return (GET_CODE (insn) == JUMP_INSN
244 && any_condjump_p (insn)
245 && BLOCK_FOR_INSN (insn)->succ->succ_next);
246 }
247
248 /* Predict edge E by given predictor if possible. */
249
250 void
predict_edge_def(e,predictor,taken)251 predict_edge_def (e, predictor, taken)
252 edge e;
253 enum br_predictor predictor;
254 enum prediction taken;
255 {
256 int probability = predictor_info[(int) predictor].hitrate;
257
258 if (taken != TAKEN)
259 probability = REG_BR_PROB_BASE - probability;
260
261 predict_edge (e, predictor, probability);
262 }
263
264 /* Invert all branch predictions or probability notes in the INSN. This needs
265 to be done each time we invert the condition used by the jump. */
266
267 void
invert_br_probabilities(insn)268 invert_br_probabilities (insn)
269 rtx insn;
270 {
271 rtx note;
272
273 for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
274 if (REG_NOTE_KIND (note) == REG_BR_PROB)
275 XEXP (note, 0) = GEN_INT (REG_BR_PROB_BASE - INTVAL (XEXP (note, 0)));
276 else if (REG_NOTE_KIND (note) == REG_BR_PRED)
277 XEXP (XEXP (note, 0), 1)
278 = GEN_INT (REG_BR_PROB_BASE - INTVAL (XEXP (XEXP (note, 0), 1)));
279 }
280
281 /* Dump information about the branch prediction to the output file. */
282
283 static void
dump_prediction(predictor,probability,bb,used)284 dump_prediction (predictor, probability, bb, used)
285 enum br_predictor predictor;
286 int probability;
287 basic_block bb;
288 int used;
289 {
290 edge e = bb->succ;
291
292 if (!rtl_dump_file)
293 return;
294
295 while (e && (e->flags & EDGE_FALLTHRU))
296 e = e->succ_next;
297
298 fprintf (rtl_dump_file, " %s heuristics%s: %.1f%%",
299 predictor_info[predictor].name,
300 used ? "" : " (ignored)", probability * 100.0 / REG_BR_PROB_BASE);
301
302 if (bb->count)
303 {
304 fprintf (rtl_dump_file, " exec ");
305 fprintf (rtl_dump_file, HOST_WIDEST_INT_PRINT_DEC, bb->count);
306 if (e)
307 {
308 fprintf (rtl_dump_file, " hit ");
309 fprintf (rtl_dump_file, HOST_WIDEST_INT_PRINT_DEC, e->count);
310 fprintf (rtl_dump_file, " (%.1f%%)", e->count * 100.0 / bb->count);
311 }
312 }
313
314 fprintf (rtl_dump_file, "\n");
315 }
316
317 /* Combine all REG_BR_PRED notes into single probability and attach REG_BR_PROB
318 note if not already present. Remove now useless REG_BR_PRED notes. */
319
320 static void
combine_predictions_for_insn(insn,bb)321 combine_predictions_for_insn (insn, bb)
322 rtx insn;
323 basic_block bb;
324 {
325 rtx prob_note = find_reg_note (insn, REG_BR_PROB, 0);
326 rtx *pnote = ®_NOTES (insn);
327 rtx note;
328 int best_probability = PROB_EVEN;
329 int best_predictor = END_PREDICTORS;
330 int combined_probability = REG_BR_PROB_BASE / 2;
331 int d;
332 bool first_match = false;
333 bool found = false;
334
335 if (rtl_dump_file)
336 fprintf (rtl_dump_file, "Predictions for insn %i bb %i\n", INSN_UID (insn),
337 bb->index);
338
339 /* We implement "first match" heuristics and use probability guessed
340 by predictor with smallest index. In the future we will use better
341 probability combination techniques. */
342 for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
343 if (REG_NOTE_KIND (note) == REG_BR_PRED)
344 {
345 int predictor = INTVAL (XEXP (XEXP (note, 0), 0));
346 int probability = INTVAL (XEXP (XEXP (note, 0), 1));
347
348 found = true;
349 if (best_predictor > predictor)
350 best_probability = probability, best_predictor = predictor;
351
352 d = (combined_probability * probability
353 + (REG_BR_PROB_BASE - combined_probability)
354 * (REG_BR_PROB_BASE - probability));
355
356 /* Use FP math to avoid overflows of 32bit integers. */
357 if (d == 0)
358 /* If one probability is 0% and one 100%, avoid division by zero. */
359 combined_probability = REG_BR_PROB_BASE / 2;
360 else
361 combined_probability = (((double) combined_probability) * probability
362 * REG_BR_PROB_BASE / d + 0.5);
363 }
364
365 /* Decide which heuristic to use. In case we didn't match anything,
366 use no_prediction heuristic, in case we did match, use either
367 first match or Dempster-Shaffer theory depending on the flags. */
368
369 if (predictor_info [best_predictor].flags & PRED_FLAG_FIRST_MATCH)
370 first_match = true;
371
372 if (!found)
373 dump_prediction (PRED_NO_PREDICTION, combined_probability, bb, true);
374 else
375 {
376 dump_prediction (PRED_DS_THEORY, combined_probability, bb, !first_match);
377 dump_prediction (PRED_FIRST_MATCH, best_probability, bb, first_match);
378 }
379
380 if (first_match)
381 combined_probability = best_probability;
382 dump_prediction (PRED_COMBINED, combined_probability, bb, true);
383
384 while (*pnote)
385 {
386 if (REG_NOTE_KIND (*pnote) == REG_BR_PRED)
387 {
388 int predictor = INTVAL (XEXP (XEXP (*pnote, 0), 0));
389 int probability = INTVAL (XEXP (XEXP (*pnote, 0), 1));
390
391 dump_prediction (predictor, probability, bb,
392 !first_match || best_predictor == predictor);
393 *pnote = XEXP (*pnote, 1);
394 }
395 else
396 pnote = &XEXP (*pnote, 1);
397 }
398
399 if (!prob_note)
400 {
401 REG_NOTES (insn)
402 = gen_rtx_EXPR_LIST (REG_BR_PROB,
403 GEN_INT (combined_probability), REG_NOTES (insn));
404
405 /* Save the prediction into CFG in case we are seeing non-degenerated
406 conditional jump. */
407 if (bb->succ->succ_next)
408 {
409 BRANCH_EDGE (bb)->probability = combined_probability;
410 FALLTHRU_EDGE (bb)->probability
411 = REG_BR_PROB_BASE - combined_probability;
412 }
413 }
414 }
415
416 /* Statically estimate the probability that a branch will be taken.
417 ??? In the next revision there will be a number of other predictors added
418 from the above references. Further, each heuristic will be factored out
419 into its own function for clarity (and to facilitate the combination of
420 predictions). */
421
422 void
estimate_probability(loops_info)423 estimate_probability (loops_info)
424 struct loops *loops_info;
425 {
426 dominance_info dominators, post_dominators;
427 basic_block bb;
428 int i;
429
430 connect_infinite_loops_to_exit ();
431 dominators = calculate_dominance_info (CDI_DOMINATORS);
432 post_dominators = calculate_dominance_info (CDI_POST_DOMINATORS);
433
434 /* Try to predict out blocks in a loop that are not part of a
435 natural loop. */
436 for (i = 1; i < loops_info->num; i++)
437 {
438 basic_block bb, *bbs;
439 int j;
440 int exits;
441 struct loop *loop = loops_info->parray[i];
442
443 flow_loop_scan (loops_info, loop, LOOP_EXIT_EDGES);
444 exits = loop->num_exits;
445
446 bbs = get_loop_body (loop);
447 for (j = 0; j < loop->num_nodes; j++)
448 {
449 int header_found = 0;
450 edge e;
451
452 bb = bbs[j];
453
454 /* Bypass loop heuristics on continue statement. These
455 statements construct loops via "non-loop" constructs
456 in the source language and are better to be handled
457 separately. */
458 if (!can_predict_insn_p (bb->end)
459 || predicted_by_p (bb, PRED_CONTINUE))
460 continue;
461
462 /* Loop branch heuristics - predict an edge back to a
463 loop's head as taken. */
464 for (e = bb->succ; e; e = e->succ_next)
465 if (e->dest == loop->header
466 && e->src == loop->latch)
467 {
468 header_found = 1;
469 predict_edge_def (e, PRED_LOOP_BRANCH, TAKEN);
470 }
471
472 /* Loop exit heuristics - predict an edge exiting the loop if the
473 conditinal has no loop header successors as not taken. */
474 if (!header_found)
475 for (e = bb->succ; e; e = e->succ_next)
476 if (e->dest->index < 0
477 || !flow_bb_inside_loop_p (loop, e->dest))
478 predict_edge
479 (e, PRED_LOOP_EXIT,
480 (REG_BR_PROB_BASE
481 - predictor_info [(int) PRED_LOOP_EXIT].hitrate)
482 / exits);
483 }
484 }
485
486 /* Attempt to predict conditional jumps using a number of heuristics. */
487 FOR_EACH_BB (bb)
488 {
489 rtx last_insn = bb->end;
490 rtx cond, earliest;
491 edge e;
492
493 if (! can_predict_insn_p (last_insn))
494 continue;
495
496 for (e = bb->succ; e; e = e->succ_next)
497 {
498 /* Predict early returns to be probable, as we've already taken
499 care for error returns and other are often used for fast paths
500 trought function. */
501 if ((e->dest == EXIT_BLOCK_PTR
502 || (e->dest->succ && !e->dest->succ->succ_next
503 && e->dest->succ->dest == EXIT_BLOCK_PTR))
504 && !predicted_by_p (bb, PRED_NULL_RETURN)
505 && !predicted_by_p (bb, PRED_CONST_RETURN)
506 && !predicted_by_p (bb, PRED_NEGATIVE_RETURN)
507 && !last_basic_block_p (e->dest))
508 predict_edge_def (e, PRED_EARLY_RETURN, TAKEN);
509
510 /* Look for block we are guarding (ie we dominate it,
511 but it doesn't postdominate us). */
512 if (e->dest != EXIT_BLOCK_PTR && e->dest != bb
513 && dominated_by_p (dominators, e->dest, e->src)
514 && !dominated_by_p (post_dominators, e->src, e->dest))
515 {
516 rtx insn;
517
518 /* The call heuristic claims that a guarded function call
519 is improbable. This is because such calls are often used
520 to signal exceptional situations such as printing error
521 messages. */
522 for (insn = e->dest->head; insn != NEXT_INSN (e->dest->end);
523 insn = NEXT_INSN (insn))
524 if (GET_CODE (insn) == CALL_INSN
525 /* Constant and pure calls are hardly used to signalize
526 something exceptional. */
527 && ! CONST_OR_PURE_CALL_P (insn))
528 {
529 predict_edge_def (e, PRED_CALL, NOT_TAKEN);
530 break;
531 }
532 }
533 }
534
535 cond = get_condition (last_insn, &earliest);
536 if (! cond)
537 continue;
538
539 /* Try "pointer heuristic."
540 A comparison ptr == 0 is predicted as false.
541 Similarly, a comparison ptr1 == ptr2 is predicted as false. */
542 if (GET_RTX_CLASS (GET_CODE (cond)) == '<'
543 && ((REG_P (XEXP (cond, 0)) && REG_POINTER (XEXP (cond, 0)))
544 || (REG_P (XEXP (cond, 1)) && REG_POINTER (XEXP (cond, 1)))))
545 {
546 if (GET_CODE (cond) == EQ)
547 predict_insn_def (last_insn, PRED_POINTER, NOT_TAKEN);
548 else if (GET_CODE (cond) == NE)
549 predict_insn_def (last_insn, PRED_POINTER, TAKEN);
550 }
551 else
552
553 /* Try "opcode heuristic."
554 EQ tests are usually false and NE tests are usually true. Also,
555 most quantities are positive, so we can make the appropriate guesses
556 about signed comparisons against zero. */
557 switch (GET_CODE (cond))
558 {
559 case CONST_INT:
560 /* Unconditional branch. */
561 predict_insn_def (last_insn, PRED_UNCONDITIONAL,
562 cond == const0_rtx ? NOT_TAKEN : TAKEN);
563 break;
564
565 case EQ:
566 case UNEQ:
567 /* Floating point comparisons appears to behave in a very
568 inpredictable way because of special role of = tests in
569 FP code. */
570 if (FLOAT_MODE_P (GET_MODE (XEXP (cond, 0))))
571 ;
572 /* Comparisons with 0 are often used for booleans and there is
573 nothing usefull to predict about them. */
574 else if (XEXP (cond, 1) == const0_rtx
575 || XEXP (cond, 0) == const0_rtx)
576 ;
577 else
578 predict_insn_def (last_insn, PRED_OPCODE_NONEQUAL, NOT_TAKEN);
579 break;
580
581 case NE:
582 case LTGT:
583 /* Floating point comparisons appears to behave in a very
584 inpredictable way because of special role of = tests in
585 FP code. */
586 if (FLOAT_MODE_P (GET_MODE (XEXP (cond, 0))))
587 ;
588 /* Comparisons with 0 are often used for booleans and there is
589 nothing usefull to predict about them. */
590 else if (XEXP (cond, 1) == const0_rtx
591 || XEXP (cond, 0) == const0_rtx)
592 ;
593 else
594 predict_insn_def (last_insn, PRED_OPCODE_NONEQUAL, TAKEN);
595 break;
596
597 case ORDERED:
598 predict_insn_def (last_insn, PRED_FPOPCODE, TAKEN);
599 break;
600
601 case UNORDERED:
602 predict_insn_def (last_insn, PRED_FPOPCODE, NOT_TAKEN);
603 break;
604
605 case LE:
606 case LT:
607 if (XEXP (cond, 1) == const0_rtx || XEXP (cond, 1) == const1_rtx
608 || XEXP (cond, 1) == constm1_rtx)
609 predict_insn_def (last_insn, PRED_OPCODE_POSITIVE, NOT_TAKEN);
610 break;
611
612 case GE:
613 case GT:
614 if (XEXP (cond, 1) == const0_rtx || XEXP (cond, 1) == const1_rtx
615 || XEXP (cond, 1) == constm1_rtx)
616 predict_insn_def (last_insn, PRED_OPCODE_POSITIVE, TAKEN);
617 break;
618
619 default:
620 break;
621 }
622 }
623
624 /* Attach the combined probability to each conditional jump. */
625 FOR_EACH_BB (bb)
626 if (GET_CODE (bb->end) == JUMP_INSN
627 && any_condjump_p (bb->end)
628 && bb->succ->succ_next != NULL)
629 combine_predictions_for_insn (bb->end, bb);
630
631 free_dominance_info (post_dominators);
632 free_dominance_info (dominators);
633
634 remove_fake_edges ();
635 estimate_bb_frequencies (loops_info);
636 }
637
638 /* __builtin_expect dropped tokens into the insn stream describing expected
639 values of registers. Generate branch probabilities based off these
640 values. */
641
642 void
expected_value_to_br_prob()643 expected_value_to_br_prob ()
644 {
645 rtx insn, cond, ev = NULL_RTX, ev_reg = NULL_RTX;
646
647 for (insn = get_insns (); insn ; insn = NEXT_INSN (insn))
648 {
649 switch (GET_CODE (insn))
650 {
651 case NOTE:
652 /* Look for expected value notes. */
653 if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_EXPECTED_VALUE)
654 {
655 ev = NOTE_EXPECTED_VALUE (insn);
656 ev_reg = XEXP (ev, 0);
657 delete_insn (insn);
658 }
659 continue;
660
661 case CODE_LABEL:
662 /* Never propagate across labels. */
663 ev = NULL_RTX;
664 continue;
665
666 case JUMP_INSN:
667 /* Look for simple conditional branches. If we haven't got an
668 expected value yet, no point going further. */
669 if (GET_CODE (insn) != JUMP_INSN || ev == NULL_RTX
670 || ! any_condjump_p (insn))
671 continue;
672 break;
673
674 default:
675 /* Look for insns that clobber the EV register. */
676 if (ev && reg_set_p (ev_reg, insn))
677 ev = NULL_RTX;
678 continue;
679 }
680
681 /* Collect the branch condition, hopefully relative to EV_REG. */
682 /* ??? At present we'll miss things like
683 (expected_value (eq r70 0))
684 (set r71 -1)
685 (set r80 (lt r70 r71))
686 (set pc (if_then_else (ne r80 0) ...))
687 as canonicalize_condition will render this to us as
688 (lt r70, r71)
689 Could use cselib to try and reduce this further. */
690 cond = XEXP (SET_SRC (pc_set (insn)), 0);
691 cond = canonicalize_condition (insn, cond, 0, NULL, ev_reg);
692 if (! cond || XEXP (cond, 0) != ev_reg
693 || GET_CODE (XEXP (cond, 1)) != CONST_INT)
694 continue;
695
696 /* Substitute and simplify. Given that the expression we're
697 building involves two constants, we should wind up with either
698 true or false. */
699 cond = gen_rtx_fmt_ee (GET_CODE (cond), VOIDmode,
700 XEXP (ev, 1), XEXP (cond, 1));
701 cond = simplify_rtx (cond);
702
703 /* Turn the condition into a scaled branch probability. */
704 if (cond != const_true_rtx && cond != const0_rtx)
705 abort ();
706 predict_insn_def (insn, PRED_BUILTIN_EXPECT,
707 cond == const_true_rtx ? TAKEN : NOT_TAKEN);
708 }
709 }
710
711 /* Check whether this is the last basic block of function. Commonly tehre
712 is one extra common cleanup block. */
713 static bool
last_basic_block_p(bb)714 last_basic_block_p (bb)
715 basic_block bb;
716 {
717 if (bb == EXIT_BLOCK_PTR)
718 return false;
719
720 return (bb->next_bb == EXIT_BLOCK_PTR
721 || (bb->next_bb->next_bb == EXIT_BLOCK_PTR
722 && bb->succ && !bb->succ->succ_next
723 && bb->succ->dest->next_bb == EXIT_BLOCK_PTR));
724 }
725
726 /* Sets branch probabilities according to PREDiction and FLAGS. HEADS[bb->index]
727 should be index of basic block in that we need to alter branch predictions
728 (i.e. the first of our dominators such that we do not post-dominate it)
729 (but we fill this information on demand, so -1 may be there in case this
730 was not needed yet). */
731
732 static void
process_note_prediction(bb,heads,dominators,post_dominators,pred,flags)733 process_note_prediction (bb, heads, dominators, post_dominators, pred, flags)
734 basic_block bb;
735 int *heads;
736 dominance_info dominators;
737 dominance_info post_dominators;
738 int pred;
739 int flags;
740 {
741 edge e;
742 int y;
743 bool taken;
744
745 taken = flags & IS_TAKEN;
746
747 if (heads[bb->index] < 0)
748 {
749 /* This is first time we need this field in heads array; so
750 find first dominator that we do not post-dominate (we are
751 using already known members of heads array). */
752 basic_block ai = bb;
753 basic_block next_ai = get_immediate_dominator (dominators, bb);
754 int head;
755
756 while (heads[next_ai->index] < 0)
757 {
758 if (!dominated_by_p (post_dominators, next_ai, bb))
759 break;
760 heads[next_ai->index] = ai->index;
761 ai = next_ai;
762 next_ai = get_immediate_dominator (dominators, next_ai);
763 }
764 if (!dominated_by_p (post_dominators, next_ai, bb))
765 head = next_ai->index;
766 else
767 head = heads[next_ai->index];
768 while (next_ai != bb)
769 {
770 next_ai = ai;
771 if (heads[ai->index] == ENTRY_BLOCK)
772 ai = ENTRY_BLOCK_PTR;
773 else
774 ai = BASIC_BLOCK (heads[ai->index]);
775 heads[next_ai->index] = head;
776 }
777 }
778 y = heads[bb->index];
779
780 /* Now find the edge that leads to our branch and aply the prediction. */
781
782 if (y == last_basic_block || !can_predict_insn_p (BASIC_BLOCK (y)->end))
783 return;
784 for (e = BASIC_BLOCK (y)->succ; e; e = e->succ_next)
785 if (e->dest->index >= 0
786 && dominated_by_p (post_dominators, e->dest, bb))
787 predict_edge_def (e, pred, taken);
788 }
789
790 /* Gathers NOTE_INSN_PREDICTIONs in given basic block and turns them
791 into branch probabilities. For description of heads array, see
792 process_note_prediction. */
793
794 static void
process_note_predictions(bb,heads,dominators,post_dominators)795 process_note_predictions (bb, heads, dominators, post_dominators)
796 basic_block bb;
797 int *heads;
798 dominance_info dominators;
799 dominance_info post_dominators;
800 {
801 rtx insn;
802 edge e;
803
804 /* Additionaly, we check here for blocks with no successors. */
805 int contained_noreturn_call = 0;
806 int was_bb_head = 0;
807 int noreturn_block = 1;
808
809 for (insn = bb->end; insn;
810 was_bb_head |= (insn == bb->head), insn = PREV_INSN (insn))
811 {
812 if (GET_CODE (insn) != NOTE)
813 {
814 if (was_bb_head)
815 break;
816 else
817 {
818 /* Noreturn calls cause program to exit, therefore they are
819 always predicted as not taken. */
820 if (GET_CODE (insn) == CALL_INSN
821 && find_reg_note (insn, REG_NORETURN, NULL))
822 contained_noreturn_call = 1;
823 continue;
824 }
825 }
826 if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_PREDICTION)
827 {
828 int alg = (int) NOTE_PREDICTION_ALG (insn);
829 /* Process single prediction note. */
830 process_note_prediction (bb,
831 heads,
832 dominators,
833 post_dominators,
834 alg, (int) NOTE_PREDICTION_FLAGS (insn));
835 delete_insn (insn);
836 }
837 }
838 for (e = bb->succ; e; e = e->succ_next)
839 if (!(e->flags & EDGE_FAKE))
840 noreturn_block = 0;
841 if (contained_noreturn_call)
842 {
843 /* This block ended from other reasons than because of return.
844 If it is because of noreturn call, this should certainly not
845 be taken. Otherwise it is probably some error recovery. */
846 process_note_prediction (bb,
847 heads,
848 dominators,
849 post_dominators, PRED_NORETURN, NOT_TAKEN);
850 }
851 }
852
853 /* Gathers NOTE_INSN_PREDICTIONs and turns them into
854 branch probabilities. */
855
856 void
note_prediction_to_br_prob()857 note_prediction_to_br_prob ()
858 {
859 basic_block bb;
860 dominance_info post_dominators, dominators;
861 int *heads;
862
863 /* To enable handling of noreturn blocks. */
864 add_noreturn_fake_exit_edges ();
865 connect_infinite_loops_to_exit ();
866
867 post_dominators = calculate_dominance_info (CDI_POST_DOMINATORS);
868 dominators = calculate_dominance_info (CDI_DOMINATORS);
869
870 heads = xmalloc (sizeof (int) * last_basic_block);
871 memset (heads, -1, sizeof (int) * last_basic_block);
872 heads[ENTRY_BLOCK_PTR->next_bb->index] = last_basic_block;
873
874 /* Process all prediction notes. */
875
876 FOR_EACH_BB (bb)
877 process_note_predictions (bb, heads, dominators, post_dominators);
878
879 free_dominance_info (post_dominators);
880 free_dominance_info (dominators);
881 free (heads);
882
883 remove_fake_edges ();
884 }
885
886 /* This is used to carry information about basic blocks. It is
887 attached to the AUX field of the standard CFG block. */
888
889 typedef struct block_info_def
890 {
891 /* Estimated frequency of execution of basic_block. */
892 REAL_VALUE_TYPE frequency;
893
894 /* To keep queue of basic blocks to process. */
895 basic_block next;
896
897 /* True if block needs to be visited in prop_freqency. */
898 int tovisit:1;
899
900 /* Number of predecessors we need to visit first. */
901 int npredecessors;
902 } *block_info;
903
904 /* Similar information for edges. */
905 typedef struct edge_info_def
906 {
907 /* In case edge is an loopback edge, the probability edge will be reached
908 in case header is. Estimated number of iterations of the loop can be
909 then computed as 1 / (1 - back_edge_prob). */
910 REAL_VALUE_TYPE back_edge_prob;
911 /* True if the edge is an loopback edge in the natural loop. */
912 int back_edge:1;
913 } *edge_info;
914
915 #define BLOCK_INFO(B) ((block_info) (B)->aux)
916 #define EDGE_INFO(E) ((edge_info) (E)->aux)
917
918 /* Helper function for estimate_bb_frequencies.
919 Propagate the frequencies for LOOP. */
920
921 static void
propagate_freq(loop)922 propagate_freq (loop)
923 struct loop *loop;
924 {
925 basic_block head = loop->header;
926 basic_block bb;
927 basic_block last;
928 edge e;
929 basic_block nextbb;
930
931 /* For each basic block we need to visit count number of his predecessors
932 we need to visit first. */
933 FOR_EACH_BB (bb)
934 {
935 if (BLOCK_INFO (bb)->tovisit)
936 {
937 int count = 0;
938
939 for (e = bb->pred; e; e = e->pred_next)
940 if (BLOCK_INFO (e->src)->tovisit && !(e->flags & EDGE_DFS_BACK))
941 count++;
942 else if (BLOCK_INFO (e->src)->tovisit
943 && rtl_dump_file && !EDGE_INFO (e)->back_edge)
944 fprintf (rtl_dump_file,
945 "Irreducible region hit, ignoring edge to %i->%i\n",
946 e->src->index, bb->index);
947 BLOCK_INFO (bb)->npredecessors = count;
948 }
949 }
950
951 memcpy (&BLOCK_INFO (head)->frequency, &real_one, sizeof (real_one));
952 last = head;
953 for (bb = head; bb; bb = nextbb)
954 {
955 REAL_VALUE_TYPE cyclic_probability, frequency;
956
957 memcpy (&cyclic_probability, &real_zero, sizeof (real_zero));
958 memcpy (&frequency, &real_zero, sizeof (real_zero));
959
960 nextbb = BLOCK_INFO (bb)->next;
961 BLOCK_INFO (bb)->next = NULL;
962
963 /* Compute frequency of basic block. */
964 if (bb != head)
965 {
966 #ifdef ENABLE_CHECKING
967 for (e = bb->pred; e; e = e->pred_next)
968 if (BLOCK_INFO (e->src)->tovisit && !(e->flags & EDGE_DFS_BACK))
969 abort ();
970 #endif
971
972 for (e = bb->pred; e; e = e->pred_next)
973 if (EDGE_INFO (e)->back_edge)
974 {
975 REAL_ARITHMETIC (cyclic_probability, PLUS_EXPR,
976 cyclic_probability,
977 EDGE_INFO (e)->back_edge_prob);
978 }
979 else if (!(e->flags & EDGE_DFS_BACK))
980 {
981 REAL_VALUE_TYPE tmp;
982
983 /* frequency += (e->probability
984 * BLOCK_INFO (e->src)->frequency /
985 REG_BR_PROB_BASE); */
986
987 REAL_VALUE_FROM_INT (tmp, e->probability, 0,
988 TYPE_MODE (double_type_node));
989 REAL_ARITHMETIC (tmp, MULT_EXPR, tmp,
990 BLOCK_INFO (e->src)->frequency);
991 REAL_ARITHMETIC (tmp, MULT_EXPR, tmp, real_inv_br_prob_base);
992 REAL_ARITHMETIC (frequency, PLUS_EXPR, frequency, tmp);
993 }
994
995 if (REAL_VALUES_IDENTICAL (cyclic_probability, real_zero))
996 memcpy (&BLOCK_INFO (bb)->frequency, &frequency, sizeof (frequency));
997 else
998 {
999 if (REAL_VALUES_LESS (real_almost_one, cyclic_probability))
1000 memcpy (&cyclic_probability, &real_almost_one, sizeof (real_zero));
1001
1002 /* BLOCK_INFO (bb)->frequency = frequency / (1 - cyclic_probability)
1003 */
1004
1005 REAL_ARITHMETIC (cyclic_probability, MINUS_EXPR, real_one,
1006 cyclic_probability);
1007 REAL_ARITHMETIC (BLOCK_INFO (bb)->frequency,
1008 RDIV_EXPR, frequency, cyclic_probability);
1009 }
1010 }
1011
1012 BLOCK_INFO (bb)->tovisit = 0;
1013
1014 /* Compute back edge frequencies. */
1015 for (e = bb->succ; e; e = e->succ_next)
1016 if (e->dest == head)
1017 {
1018 REAL_VALUE_TYPE tmp;
1019
1020 /* EDGE_INFO (e)->back_edge_prob
1021 = ((e->probability * BLOCK_INFO (bb)->frequency)
1022 / REG_BR_PROB_BASE); */
1023 REAL_VALUE_FROM_INT (tmp, e->probability, 0,
1024 TYPE_MODE (double_type_node));
1025 REAL_ARITHMETIC (tmp, MULT_EXPR, tmp,
1026 BLOCK_INFO (bb)->frequency);
1027 REAL_ARITHMETIC (EDGE_INFO (e)->back_edge_prob,
1028 MULT_EXPR, tmp, real_inv_br_prob_base);
1029
1030 }
1031
1032 /* Propagate to successor blocks. */
1033 for (e = bb->succ; e; e = e->succ_next)
1034 if (!(e->flags & EDGE_DFS_BACK)
1035 && BLOCK_INFO (e->dest)->npredecessors)
1036 {
1037 BLOCK_INFO (e->dest)->npredecessors--;
1038 if (!BLOCK_INFO (e->dest)->npredecessors)
1039 {
1040 if (!nextbb)
1041 nextbb = e->dest;
1042 else
1043 BLOCK_INFO (last)->next = e->dest;
1044
1045 last = e->dest;
1046 }
1047 }
1048 }
1049 }
1050
1051 /* Estimate probabilities of loopback edges in loops at same nest level. */
1052
1053 static void
estimate_loops_at_level(first_loop)1054 estimate_loops_at_level (first_loop)
1055 struct loop *first_loop;
1056 {
1057 struct loop *loop;
1058
1059 for (loop = first_loop; loop; loop = loop->next)
1060 {
1061 edge e;
1062 basic_block *bbs;
1063 int i;
1064
1065 estimate_loops_at_level (loop->inner);
1066
1067 if (loop->latch->succ) /* Do not do this for dummy function loop. */
1068 {
1069 /* Find current loop back edge and mark it. */
1070 e = loop_latch_edge (loop);
1071 EDGE_INFO (e)->back_edge = 1;
1072 }
1073
1074 bbs = get_loop_body (loop);
1075 for (i = 0; i < loop->num_nodes; i++)
1076 BLOCK_INFO (bbs[i])->tovisit = 1;
1077 free (bbs);
1078 propagate_freq (loop);
1079 }
1080 }
1081
1082 /* Convert counts measured by profile driven feedback to frequencies. */
1083
1084 static void
counts_to_freqs()1085 counts_to_freqs ()
1086 {
1087 HOST_WIDEST_INT count_max = 1;
1088 basic_block bb;
1089
1090 FOR_EACH_BB (bb)
1091 count_max = MAX (bb->count, count_max);
1092
1093 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
1094 bb->frequency = (bb->count * BB_FREQ_MAX + count_max / 2) / count_max;
1095 }
1096
1097 /* Return true if function is likely to be expensive, so there is no point to
1098 optimize performance of prologue, epilogue or do inlining at the expense
1099 of code size growth. THRESHOLD is the limit of number of isntructions
1100 function can execute at average to be still considered not expensive. */
1101
1102 bool
expensive_function_p(threshold)1103 expensive_function_p (threshold)
1104 int threshold;
1105 {
1106 unsigned int sum = 0;
1107 basic_block bb;
1108 unsigned int limit;
1109
1110 /* We can not compute accurately for large thresholds due to scaled
1111 frequencies. */
1112 if (threshold > BB_FREQ_MAX)
1113 abort ();
1114
1115 /* Frequencies are out of range. This either means that function contains
1116 internal loop executing more than BB_FREQ_MAX times or profile feedback
1117 is available and function has not been executed at all. */
1118 if (ENTRY_BLOCK_PTR->frequency == 0)
1119 return true;
1120
1121 /* Maximally BB_FREQ_MAX^2 so overflow won't happen. */
1122 limit = ENTRY_BLOCK_PTR->frequency * threshold;
1123 FOR_EACH_BB (bb)
1124 {
1125 rtx insn;
1126
1127 for (insn = bb->head; insn != NEXT_INSN (bb->end);
1128 insn = NEXT_INSN (insn))
1129 if (active_insn_p (insn))
1130 {
1131 sum += bb->frequency;
1132 if (sum > limit)
1133 return true;
1134 }
1135 }
1136
1137 return false;
1138 }
1139
1140 /* Estimate basic blocks frequency by given branch probabilities. */
1141
1142 static void
estimate_bb_frequencies(loops)1143 estimate_bb_frequencies (loops)
1144 struct loops *loops;
1145 {
1146 basic_block bb;
1147 REAL_VALUE_TYPE freq_max;
1148 enum machine_mode double_mode = TYPE_MODE (double_type_node);
1149
1150 if (flag_branch_probabilities)
1151 counts_to_freqs ();
1152 else
1153 {
1154 REAL_VALUE_FROM_INT (real_zero, 0, 0, double_mode);
1155 REAL_VALUE_FROM_INT (real_one, 1, 0, double_mode);
1156 REAL_VALUE_FROM_INT (real_br_prob_base, REG_BR_PROB_BASE, 0, double_mode);
1157 REAL_VALUE_FROM_INT (real_bb_freq_max, BB_FREQ_MAX, 0, double_mode);
1158 REAL_VALUE_FROM_INT (real_one_half, 2, 0, double_mode);
1159 REAL_ARITHMETIC (real_one_half, RDIV_EXPR, real_one, real_one_half);
1160 REAL_ARITHMETIC (real_inv_br_prob_base, RDIV_EXPR, real_one, real_br_prob_base);
1161 REAL_ARITHMETIC (real_almost_one, MINUS_EXPR, real_one, real_inv_br_prob_base);
1162
1163 mark_dfs_back_edges ();
1164 /* Fill in the probability values in flowgraph based on the REG_BR_PROB
1165 notes. */
1166 FOR_EACH_BB (bb)
1167 {
1168 rtx last_insn = bb->end;
1169
1170 if (!can_predict_insn_p (last_insn))
1171 {
1172 /* We can predict only conditional jumps at the moment.
1173 Expect each edge to be equally probable.
1174 ?? In the future we want to make abnormal edges improbable. */
1175 int nedges = 0;
1176 edge e;
1177
1178 for (e = bb->succ; e; e = e->succ_next)
1179 {
1180 nedges++;
1181 if (e->probability != 0)
1182 break;
1183 }
1184 if (!e)
1185 for (e = bb->succ; e; e = e->succ_next)
1186 e->probability = (REG_BR_PROB_BASE + nedges / 2) / nedges;
1187 }
1188 }
1189
1190 ENTRY_BLOCK_PTR->succ->probability = REG_BR_PROB_BASE;
1191
1192 /* Set up block info for each basic block. */
1193 alloc_aux_for_blocks (sizeof (struct block_info_def));
1194 alloc_aux_for_edges (sizeof (struct edge_info_def));
1195 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
1196 {
1197 edge e;
1198
1199 BLOCK_INFO (bb)->tovisit = 0;
1200 for (e = bb->succ; e; e = e->succ_next)
1201 {
1202 REAL_VALUE_FROM_INT (EDGE_INFO (e)->back_edge_prob,
1203 e->probability, 0, double_mode);
1204 REAL_ARITHMETIC (EDGE_INFO (e)->back_edge_prob,
1205 MULT_EXPR, EDGE_INFO (e)->back_edge_prob,
1206 real_inv_br_prob_base);
1207 }
1208 }
1209
1210 /* First compute probabilities locally for each loop from innermost
1211 to outermost to examine probabilities for back edges. */
1212 estimate_loops_at_level (loops->tree_root);
1213
1214 memcpy (&freq_max, &real_zero, sizeof (real_zero));
1215 FOR_EACH_BB (bb)
1216 if (REAL_VALUES_LESS
1217 (freq_max, BLOCK_INFO (bb)->frequency))
1218 memcpy (&freq_max, &BLOCK_INFO (bb)->frequency,
1219 sizeof (freq_max));
1220
1221 REAL_ARITHMETIC (freq_max, RDIV_EXPR, real_bb_freq_max, freq_max);
1222
1223 FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
1224 {
1225 REAL_VALUE_TYPE tmp;
1226
1227 REAL_ARITHMETIC (tmp, MULT_EXPR, BLOCK_INFO (bb)->frequency,
1228 freq_max);
1229 REAL_ARITHMETIC (tmp, PLUS_EXPR, tmp, real_one_half);
1230 bb->frequency = REAL_VALUE_UNSIGNED_FIX (tmp);
1231 }
1232
1233 free_aux_for_blocks ();
1234 free_aux_for_edges ();
1235 }
1236 compute_function_frequency ();
1237 if (flag_reorder_functions)
1238 choose_function_section ();
1239 }
1240
1241 /* Decide whether function is hot, cold or unlikely executed. */
1242 static void
compute_function_frequency()1243 compute_function_frequency ()
1244 {
1245 basic_block bb;
1246
1247 if (!profile_info.count_profiles_merged
1248 || !flag_branch_probabilities)
1249 return;
1250 cfun->function_frequency = FUNCTION_FREQUENCY_UNLIKELY_EXECUTED;
1251 FOR_EACH_BB (bb)
1252 {
1253 if (maybe_hot_bb_p (bb))
1254 {
1255 cfun->function_frequency = FUNCTION_FREQUENCY_HOT;
1256 return;
1257 }
1258 if (!probably_never_executed_bb_p (bb))
1259 cfun->function_frequency = FUNCTION_FREQUENCY_NORMAL;
1260 }
1261 }
1262
1263 /* Choose appropriate section for the function. */
1264 static void
choose_function_section()1265 choose_function_section ()
1266 {
1267 if (DECL_SECTION_NAME (current_function_decl)
1268 || !targetm.have_named_sections
1269 /* Theoretically we can split the gnu.linkonce text section too,
1270 but this requires more work as the frequency needs to match
1271 for all generated objects so we need to merge the frequency
1272 of all instances. For now just never set frequency for these. */
1273 || DECL_ONE_ONLY (current_function_decl))
1274 return;
1275 if (cfun->function_frequency == FUNCTION_FREQUENCY_HOT)
1276 DECL_SECTION_NAME (current_function_decl) =
1277 build_string (strlen (HOT_TEXT_SECTION_NAME), HOT_TEXT_SECTION_NAME);
1278 if (cfun->function_frequency == FUNCTION_FREQUENCY_UNLIKELY_EXECUTED)
1279 DECL_SECTION_NAME (current_function_decl) =
1280 build_string (strlen (UNLIKELY_EXECUTED_TEXT_SECTION_NAME),
1281 UNLIKELY_EXECUTED_TEXT_SECTION_NAME);
1282 }
1283