1 | /* Loop unswitching. |
2 | Copyright (C) 2004-2017 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 |
7 | under the terms of the GNU General Public License as published by the |
8 | Free Software Foundation; either version 3, or (at your option) any |
9 | later version. |
10 | |
11 | GCC is distributed in the hope that it will be useful, but WITHOUT |
12 | ANY 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 COPYING3. If not see |
18 | <http://www.gnu.org/licenses/>. */ |
19 | |
20 | #include "config.h" |
21 | #include "system.h" |
22 | #include "coretypes.h" |
23 | #include "backend.h" |
24 | #include "tree.h" |
25 | #include "gimple.h" |
26 | #include "tree-pass.h" |
27 | #include "ssa.h" |
28 | #include "fold-const.h" |
29 | #include "gimplify.h" |
30 | #include "tree-cfg.h" |
31 | #include "tree-ssa.h" |
32 | #include "tree-ssa-loop-niter.h" |
33 | #include "tree-ssa-loop.h" |
34 | #include "tree-into-ssa.h" |
35 | #include "cfgloop.h" |
36 | #include "params.h" |
37 | #include "tree-inline.h" |
38 | #include "gimple-iterator.h" |
39 | #include "cfghooks.h" |
40 | #include "tree-ssa-loop-manip.h" |
41 | |
42 | /* This file implements the loop unswitching, i.e. transformation of loops like |
43 | |
44 | while (A) |
45 | { |
46 | if (inv) |
47 | B; |
48 | |
49 | X; |
50 | |
51 | if (!inv) |
52 | C; |
53 | } |
54 | |
55 | where inv is the loop invariant, into |
56 | |
57 | if (inv) |
58 | { |
59 | while (A) |
60 | { |
61 | B; |
62 | X; |
63 | } |
64 | } |
65 | else |
66 | { |
67 | while (A) |
68 | { |
69 | X; |
70 | C; |
71 | } |
72 | } |
73 | |
74 | Inv is considered invariant iff the values it compares are both invariant; |
75 | tree-ssa-loop-im.c ensures that all the suitable conditions are in this |
76 | shape. */ |
77 | |
78 | static struct loop *tree_unswitch_loop (struct loop *, basic_block, tree); |
79 | static bool tree_unswitch_single_loop (struct loop *, int); |
80 | static tree tree_may_unswitch_on (basic_block, struct loop *); |
81 | static bool tree_unswitch_outer_loop (struct loop *); |
82 | static edge find_loop_guard (struct loop *); |
83 | static bool empty_bb_without_guard_p (struct loop *, basic_block); |
84 | static bool used_outside_loop_p (struct loop *, tree); |
85 | static void hoist_guard (struct loop *, edge); |
86 | static bool check_exit_phi (struct loop *); |
87 | static tree get_vop_from_header (struct loop *); |
88 | |
89 | /* Main entry point. Perform loop unswitching on all suitable loops. */ |
90 | |
91 | unsigned int |
92 | tree_ssa_unswitch_loops (void) |
93 | { |
94 | struct loop *loop; |
95 | bool changed = false; |
96 | |
97 | /* Go through all loops starting from innermost. */ |
98 | FOR_EACH_LOOP (loop, LI_FROM_INNERMOST) |
99 | { |
100 | if (!loop->inner) |
101 | /* Unswitch innermost loop. */ |
102 | changed |= tree_unswitch_single_loop (loop, 0); |
103 | else |
104 | changed |= tree_unswitch_outer_loop (loop); |
105 | } |
106 | |
107 | if (changed) |
108 | return TODO_cleanup_cfg; |
109 | return 0; |
110 | } |
111 | |
112 | /* Return TRUE if an SSA_NAME maybe undefined and is therefore |
113 | unsuitable for unswitching. STMT is the statement we are |
114 | considering for unswitching and LOOP is the loop it appears in. */ |
115 | |
116 | static bool |
117 | is_maybe_undefined (const tree name, gimple *stmt, struct loop *loop) |
118 | { |
119 | /* The loop header is the only block we can trivially determine that |
120 | will always be executed. If the comparison is in the loop |
121 | header, we know it's OK to unswitch on it. */ |
122 | if (gimple_bb (stmt) == loop->header) |
123 | return false; |
124 | |
125 | auto_bitmap visited_ssa; |
126 | auto_vec<tree> worklist; |
127 | worklist.safe_push (name); |
128 | bitmap_set_bit (visited_ssa, SSA_NAME_VERSION (name)); |
129 | while (!worklist.is_empty ()) |
130 | { |
131 | tree t = worklist.pop (); |
132 | |
133 | /* If it's obviously undefined, avoid further computations. */ |
134 | if (ssa_undefined_value_p (t, true)) |
135 | return true; |
136 | |
137 | if (ssa_defined_default_def_p (t)) |
138 | continue; |
139 | |
140 | gimple *def = SSA_NAME_DEF_STMT (t); |
141 | |
142 | /* Check that all the PHI args are fully defined. */ |
143 | if (gphi *phi = dyn_cast <gphi *> (def)) |
144 | { |
145 | for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i) |
146 | { |
147 | tree t = gimple_phi_arg_def (phi, i); |
148 | /* If an SSA has already been seen, it may be a loop, |
149 | but we can continue and ignore this use. Otherwise, |
150 | add the SSA_NAME to the queue and visit it later. */ |
151 | if (TREE_CODE (t) == SSA_NAME |
152 | && bitmap_set_bit (visited_ssa, SSA_NAME_VERSION (t))) |
153 | worklist.safe_push (t); |
154 | } |
155 | continue; |
156 | } |
157 | |
158 | /* Uses in stmts always executed when the region header executes |
159 | are fine. */ |
160 | if (dominated_by_p (CDI_DOMINATORS, loop->header, gimple_bb (def))) |
161 | continue; |
162 | |
163 | /* Handle calls and memory loads conservatively. */ |
164 | if (!is_gimple_assign (def) |
165 | || (gimple_assign_single_p (def) |
166 | && gimple_vuse (def))) |
167 | return true; |
168 | |
169 | /* Check that any SSA names used to define NAME are also fully |
170 | defined. */ |
171 | use_operand_p use_p; |
172 | ssa_op_iter iter; |
173 | FOR_EACH_SSA_USE_OPERAND (use_p, def, iter, SSA_OP_USE) |
174 | { |
175 | tree t = USE_FROM_PTR (use_p); |
176 | /* If an SSA has already been seen, it may be a loop, |
177 | but we can continue and ignore this use. Otherwise, |
178 | add the SSA_NAME to the queue and visit it later. */ |
179 | if (bitmap_set_bit (visited_ssa, SSA_NAME_VERSION (t))) |
180 | worklist.safe_push (t); |
181 | } |
182 | } |
183 | return false; |
184 | } |
185 | |
186 | /* Checks whether we can unswitch LOOP on condition at end of BB -- one of its |
187 | basic blocks (for what it means see comments below). */ |
188 | |
189 | static tree |
190 | tree_may_unswitch_on (basic_block bb, struct loop *loop) |
191 | { |
192 | gimple *last, *def; |
193 | gcond *stmt; |
194 | tree cond, use; |
195 | basic_block def_bb; |
196 | ssa_op_iter iter; |
197 | |
198 | /* BB must end in a simple conditional jump. */ |
199 | last = last_stmt (bb); |
200 | if (!last || gimple_code (last) != GIMPLE_COND) |
201 | return NULL_TREE; |
202 | stmt = as_a <gcond *> (last); |
203 | |
204 | /* To keep the things simple, we do not directly remove the conditions, |
205 | but just replace tests with 0 != 0 resp. 1 != 0. Prevent the infinite |
206 | loop where we would unswitch again on such a condition. */ |
207 | if (gimple_cond_true_p (stmt) || gimple_cond_false_p (stmt)) |
208 | return NULL_TREE; |
209 | |
210 | /* Condition must be invariant. */ |
211 | FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE) |
212 | { |
213 | def = SSA_NAME_DEF_STMT (use); |
214 | def_bb = gimple_bb (def); |
215 | if (def_bb |
216 | && flow_bb_inside_loop_p (loop, def_bb)) |
217 | return NULL_TREE; |
218 | /* Unswitching on undefined values would introduce undefined |
219 | behavior that the original program might never exercise. */ |
220 | if (is_maybe_undefined (use, stmt, loop)) |
221 | return NULL_TREE; |
222 | } |
223 | |
224 | cond = build2 (gimple_cond_code (stmt), boolean_type_node, |
225 | gimple_cond_lhs (stmt), gimple_cond_rhs (stmt)); |
226 | |
227 | return cond; |
228 | } |
229 | |
230 | /* Simplifies COND using checks in front of the entry of the LOOP. Just very |
231 | simplish (sufficient to prevent us from duplicating loop in unswitching |
232 | unnecessarily). */ |
233 | |
234 | static tree |
235 | simplify_using_entry_checks (struct loop *loop, tree cond) |
236 | { |
237 | edge e = loop_preheader_edge (loop); |
238 | gimple *stmt; |
239 | |
240 | while (1) |
241 | { |
242 | stmt = last_stmt (e->src); |
243 | if (stmt |
244 | && gimple_code (stmt) == GIMPLE_COND |
245 | && gimple_cond_code (stmt) == TREE_CODE (cond) |
246 | && operand_equal_p (gimple_cond_lhs (stmt), |
247 | TREE_OPERAND (cond, 0), 0) |
248 | && operand_equal_p (gimple_cond_rhs (stmt), |
249 | TREE_OPERAND (cond, 1), 0)) |
250 | return (e->flags & EDGE_TRUE_VALUE |
251 | ? boolean_true_node |
252 | : boolean_false_node); |
253 | |
254 | if (!single_pred_p (e->src)) |
255 | return cond; |
256 | |
257 | e = single_pred_edge (e->src); |
258 | if (e->src == ENTRY_BLOCK_PTR_FOR_FN (cfun)) |
259 | return cond; |
260 | } |
261 | } |
262 | |
263 | /* Unswitch single LOOP. NUM is number of unswitchings done; we do not allow |
264 | it to grow too much, it is too easy to create example on that the code would |
265 | grow exponentially. */ |
266 | |
267 | static bool |
268 | tree_unswitch_single_loop (struct loop *loop, int num) |
269 | { |
270 | basic_block *bbs; |
271 | struct loop *nloop; |
272 | unsigned i, found; |
273 | tree cond = NULL_TREE; |
274 | gimple *stmt; |
275 | bool changed = false; |
276 | HOST_WIDE_INT iterations; |
277 | |
278 | /* Perform initial tests if unswitch is eligible. */ |
279 | if (num == 0) |
280 | { |
281 | /* Do not unswitch in cold regions. */ |
282 | if (optimize_loop_for_size_p (loop)) |
283 | { |
284 | if (dump_file && (dump_flags & TDF_DETAILS)) |
285 | fprintf (dump_file, ";; Not unswitching cold loops\n" ); |
286 | return false; |
287 | } |
288 | |
289 | /* The loop should not be too large, to limit code growth. */ |
290 | if (tree_num_loop_insns (loop, &eni_size_weights) |
291 | > (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS)) |
292 | { |
293 | if (dump_file && (dump_flags & TDF_DETAILS)) |
294 | fprintf (dump_file, ";; Not unswitching, loop too big\n" ); |
295 | return false; |
296 | } |
297 | |
298 | /* If the loop is not expected to iterate, there is no need |
299 | for unswitching. */ |
300 | iterations = estimated_loop_iterations_int (loop); |
301 | if (iterations < 0) |
302 | iterations = likely_max_loop_iterations_int (loop); |
303 | if (iterations >= 0 && iterations <= 1) |
304 | { |
305 | if (dump_file && (dump_flags & TDF_DETAILS)) |
306 | fprintf (dump_file, ";; Not unswitching, loop is not expected" |
307 | " to iterate\n" ); |
308 | return false; |
309 | } |
310 | } |
311 | |
312 | i = 0; |
313 | bbs = get_loop_body (loop); |
314 | found = loop->num_nodes; |
315 | |
316 | while (1) |
317 | { |
318 | /* Find a bb to unswitch on. */ |
319 | for (; i < loop->num_nodes; i++) |
320 | if ((cond = tree_may_unswitch_on (bbs[i], loop))) |
321 | break; |
322 | |
323 | if (i == loop->num_nodes) |
324 | { |
325 | if (dump_file |
326 | && num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL) |
327 | && (dump_flags & TDF_DETAILS)) |
328 | fprintf (dump_file, ";; Not unswitching anymore, hit max level\n" ); |
329 | |
330 | if (found == loop->num_nodes) |
331 | { |
332 | free (bbs); |
333 | return changed; |
334 | } |
335 | break; |
336 | } |
337 | |
338 | cond = simplify_using_entry_checks (loop, cond); |
339 | stmt = last_stmt (bbs[i]); |
340 | if (integer_nonzerop (cond)) |
341 | { |
342 | /* Remove false path. */ |
343 | gimple_cond_set_condition_from_tree (as_a <gcond *> (stmt), |
344 | boolean_true_node); |
345 | changed = true; |
346 | } |
347 | else if (integer_zerop (cond)) |
348 | { |
349 | /* Remove true path. */ |
350 | gimple_cond_set_condition_from_tree (as_a <gcond *> (stmt), |
351 | boolean_false_node); |
352 | changed = true; |
353 | } |
354 | /* Do not unswitch too much. */ |
355 | else if (num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL)) |
356 | { |
357 | i++; |
358 | continue; |
359 | } |
360 | /* In nested tree_unswitch_single_loop first optimize all conditions |
361 | using entry checks, then discover still reachable blocks in the |
362 | loop and find the condition only among those still reachable bbs. */ |
363 | else if (num != 0) |
364 | { |
365 | if (found == loop->num_nodes) |
366 | found = i; |
367 | i++; |
368 | continue; |
369 | } |
370 | else |
371 | { |
372 | found = i; |
373 | break; |
374 | } |
375 | |
376 | update_stmt (stmt); |
377 | i++; |
378 | } |
379 | |
380 | if (num != 0) |
381 | { |
382 | basic_block *tos, *worklist; |
383 | |
384 | /* When called recursively, first do a quick discovery |
385 | of reachable bbs after the above changes and only |
386 | consider conditions in still reachable bbs. */ |
387 | tos = worklist = XNEWVEC (basic_block, loop->num_nodes); |
388 | |
389 | for (i = 0; i < loop->num_nodes; i++) |
390 | bbs[i]->flags &= ~BB_REACHABLE; |
391 | |
392 | /* Start with marking header. */ |
393 | *tos++ = bbs[0]; |
394 | bbs[0]->flags |= BB_REACHABLE; |
395 | |
396 | /* Iterate: find everything reachable from what we've already seen |
397 | within the same innermost loop. Don't look through false edges |
398 | if condition is always true or true edges if condition is |
399 | always false. */ |
400 | while (tos != worklist) |
401 | { |
402 | basic_block b = *--tos; |
403 | edge e; |
404 | edge_iterator ei; |
405 | int flags = 0; |
406 | |
407 | if (EDGE_COUNT (b->succs) == 2) |
408 | { |
409 | gimple *stmt = last_stmt (b); |
410 | if (stmt |
411 | && gimple_code (stmt) == GIMPLE_COND) |
412 | { |
413 | gcond *cond_stmt = as_a <gcond *> (stmt); |
414 | if (gimple_cond_true_p (cond_stmt)) |
415 | flags = EDGE_FALSE_VALUE; |
416 | else if (gimple_cond_false_p (cond_stmt)) |
417 | flags = EDGE_TRUE_VALUE; |
418 | } |
419 | } |
420 | |
421 | FOR_EACH_EDGE (e, ei, b->succs) |
422 | { |
423 | basic_block dest = e->dest; |
424 | |
425 | if (dest->loop_father == loop |
426 | && !(dest->flags & BB_REACHABLE) |
427 | && !(e->flags & flags)) |
428 | { |
429 | *tos++ = dest; |
430 | dest->flags |= BB_REACHABLE; |
431 | } |
432 | } |
433 | } |
434 | |
435 | free (worklist); |
436 | |
437 | /* Find a bb to unswitch on. */ |
438 | for (; found < loop->num_nodes; found++) |
439 | if ((bbs[found]->flags & BB_REACHABLE) |
440 | && (cond = tree_may_unswitch_on (bbs[found], loop))) |
441 | break; |
442 | |
443 | if (found == loop->num_nodes) |
444 | { |
445 | free (bbs); |
446 | return changed; |
447 | } |
448 | } |
449 | |
450 | if (dump_file && (dump_flags & TDF_DETAILS)) |
451 | fprintf (dump_file, ";; Unswitching loop\n" ); |
452 | |
453 | initialize_original_copy_tables (); |
454 | /* Unswitch the loop on this condition. */ |
455 | nloop = tree_unswitch_loop (loop, bbs[found], cond); |
456 | if (!nloop) |
457 | { |
458 | free_original_copy_tables (); |
459 | free (bbs); |
460 | return changed; |
461 | } |
462 | |
463 | /* Update the SSA form after unswitching. */ |
464 | update_ssa (TODO_update_ssa); |
465 | free_original_copy_tables (); |
466 | |
467 | /* Invoke itself on modified loops. */ |
468 | tree_unswitch_single_loop (nloop, num + 1); |
469 | tree_unswitch_single_loop (loop, num + 1); |
470 | free (bbs); |
471 | return true; |
472 | } |
473 | |
474 | /* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON. We only support |
475 | unswitching of innermost loops. COND is the condition determining which |
476 | loop is entered -- the new loop is entered if COND is true. Returns NULL |
477 | if impossible, new loop otherwise. */ |
478 | |
479 | static struct loop * |
480 | tree_unswitch_loop (struct loop *loop, |
481 | basic_block unswitch_on, tree cond) |
482 | { |
483 | profile_probability prob_true; |
484 | edge edge_true, edge_false; |
485 | |
486 | /* Some sanity checking. */ |
487 | gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on)); |
488 | gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2); |
489 | gcc_assert (loop->inner == NULL); |
490 | |
491 | extract_true_false_edges_from_block (unswitch_on, &edge_true, &edge_false); |
492 | prob_true = edge_true->probability; |
493 | return loop_version (loop, unshare_expr (cond), |
494 | NULL, prob_true, |
495 | prob_true.invert (), |
496 | prob_true, prob_true.invert (), |
497 | false); |
498 | } |
499 | |
500 | /* Unswitch outer loops by hoisting invariant guard on |
501 | inner loop without code duplication. */ |
502 | static bool |
503 | tree_unswitch_outer_loop (struct loop *loop) |
504 | { |
505 | edge exit, guard; |
506 | HOST_WIDE_INT iterations; |
507 | |
508 | gcc_assert (loop->inner); |
509 | if (loop->inner->next) |
510 | return false; |
511 | /* Accept loops with single exit only which is not from inner loop. */ |
512 | exit = single_exit (loop); |
513 | if (!exit || exit->src->loop_father != loop) |
514 | return false; |
515 | /* Check that phi argument of exit edge is not defined inside loop. */ |
516 | if (!check_exit_phi (loop)) |
517 | return false; |
518 | /* If the loop is not expected to iterate, there is no need |
519 | for unswitching. */ |
520 | iterations = estimated_loop_iterations_int (loop); |
521 | if (iterations < 0) |
522 | iterations = likely_max_loop_iterations_int (loop); |
523 | if (iterations >= 0 && iterations <= 1) |
524 | { |
525 | if (dump_file && (dump_flags & TDF_DETAILS)) |
526 | fprintf (dump_file, ";; Not unswitching, loop is not expected" |
527 | " to iterate\n" ); |
528 | return false; |
529 | } |
530 | |
531 | bool changed = false; |
532 | while ((guard = find_loop_guard (loop))) |
533 | { |
534 | if (! changed) |
535 | rewrite_virtuals_into_loop_closed_ssa (loop); |
536 | hoist_guard (loop, guard); |
537 | changed = true; |
538 | } |
539 | return changed; |
540 | } |
541 | |
542 | /* Checks if the body of the LOOP is within an invariant guard. If this |
543 | is the case, returns the edge that jumps over the real body of the loop, |
544 | otherwise returns NULL. */ |
545 | |
546 | static edge |
547 | find_loop_guard (struct loop *loop) |
548 | { |
549 | basic_block = loop->header; |
550 | edge guard_edge, te, fe; |
551 | basic_block *body = NULL; |
552 | unsigned i; |
553 | tree use; |
554 | ssa_op_iter iter; |
555 | |
556 | /* We check for the following situation: |
557 | |
558 | while (1) |
559 | { |
560 | [header]] |
561 | loop_phi_nodes; |
562 | something1; |
563 | if (cond1) |
564 | body; |
565 | nvar = phi(orig, bvar) ... for all variables changed in body; |
566 | [guard_end] |
567 | something2; |
568 | if (cond2) |
569 | break; |
570 | something3; |
571 | } |
572 | |
573 | where: |
574 | |
575 | 1) cond1 is loop invariant |
576 | 2) If cond1 is false, then the loop is essentially empty; i.e., |
577 | a) nothing in something1, something2 and something3 has side |
578 | effects |
579 | b) anything defined in something1, something2 and something3 |
580 | is not used outside of the loop. */ |
581 | |
582 | gcond *cond; |
583 | do |
584 | { |
585 | basic_block next = NULL; |
586 | if (single_succ_p (header)) |
587 | next = single_succ (header); |
588 | else |
589 | { |
590 | cond = dyn_cast <gcond *> (last_stmt (header)); |
591 | if (! cond) |
592 | return NULL; |
593 | extract_true_false_edges_from_block (header, &te, &fe); |
594 | /* Make sure to skip earlier hoisted guards that are left |
595 | in place as if (true). */ |
596 | if (gimple_cond_true_p (cond)) |
597 | next = te->dest; |
598 | else if (gimple_cond_false_p (cond)) |
599 | next = fe->dest; |
600 | else |
601 | break; |
602 | } |
603 | /* Never traverse a backedge. */ |
604 | if (header->loop_father->header == next) |
605 | return NULL; |
606 | header = next; |
607 | } |
608 | while (1); |
609 | if (!flow_bb_inside_loop_p (loop, te->dest) |
610 | || !flow_bb_inside_loop_p (loop, fe->dest)) |
611 | return NULL; |
612 | |
613 | if (just_once_each_iteration_p (loop, te->dest) |
614 | || (single_succ_p (te->dest) |
615 | && just_once_each_iteration_p (loop, single_succ (te->dest)))) |
616 | { |
617 | if (just_once_each_iteration_p (loop, fe->dest)) |
618 | return NULL; |
619 | guard_edge = te; |
620 | } |
621 | else if (just_once_each_iteration_p (loop, fe->dest) |
622 | || (single_succ_p (fe->dest) |
623 | && just_once_each_iteration_p (loop, single_succ (fe->dest)))) |
624 | guard_edge = fe; |
625 | else |
626 | return NULL; |
627 | |
628 | /* Guard edge must skip inner loop. */ |
629 | if (!dominated_by_p (CDI_DOMINATORS, loop->inner->header, |
630 | guard_edge == fe ? te->dest : fe->dest)) |
631 | { |
632 | if (dump_file && (dump_flags & TDF_DETAILS)) |
633 | fprintf (dump_file, "Guard edge %d --> %d is not around the loop!\n" , |
634 | guard_edge->src->index, guard_edge->dest->index); |
635 | return NULL; |
636 | } |
637 | if (guard_edge->dest == loop->latch) |
638 | { |
639 | if (dump_file && (dump_flags & TDF_DETAILS)) |
640 | fprintf (dump_file, "Guard edge destination is loop latch.\n" ); |
641 | return NULL; |
642 | } |
643 | |
644 | if (dump_file && (dump_flags & TDF_DETAILS)) |
645 | fprintf (dump_file, |
646 | "Considering guard %d -> %d in loop %d\n" , |
647 | guard_edge->src->index, guard_edge->dest->index, loop->num); |
648 | /* Check if condition operands do not have definitions inside loop since |
649 | any bb copying is not performed. */ |
650 | FOR_EACH_SSA_TREE_OPERAND (use, cond, iter, SSA_OP_USE) |
651 | { |
652 | gimple *def = SSA_NAME_DEF_STMT (use); |
653 | basic_block def_bb = gimple_bb (def); |
654 | if (def_bb |
655 | && flow_bb_inside_loop_p (loop, def_bb)) |
656 | { |
657 | if (dump_file && (dump_flags & TDF_DETAILS)) |
658 | fprintf (dump_file, " guard operands have definitions" |
659 | " inside loop\n" ); |
660 | return NULL; |
661 | } |
662 | } |
663 | |
664 | body = get_loop_body (loop); |
665 | for (i = 0; i < loop->num_nodes; i++) |
666 | { |
667 | basic_block bb = body[i]; |
668 | if (bb->loop_father != loop) |
669 | continue; |
670 | if (bb->flags & BB_IRREDUCIBLE_LOOP) |
671 | { |
672 | if (dump_file && (dump_flags & TDF_DETAILS)) |
673 | fprintf (dump_file, "Block %d is marked as irreducible in loop\n" , |
674 | bb->index); |
675 | guard_edge = NULL; |
676 | goto end; |
677 | } |
678 | if (!empty_bb_without_guard_p (loop, bb)) |
679 | { |
680 | if (dump_file && (dump_flags & TDF_DETAILS)) |
681 | fprintf (dump_file, " block %d has side effects\n" , bb->index); |
682 | guard_edge = NULL; |
683 | goto end; |
684 | } |
685 | } |
686 | |
687 | if (dump_file && (dump_flags & TDF_DETAILS)) |
688 | fprintf (dump_file, " suitable to hoist\n" ); |
689 | end: |
690 | if (body) |
691 | free (body); |
692 | return guard_edge; |
693 | } |
694 | |
695 | /* Returns true if |
696 | 1) no statement in BB has side effects |
697 | 2) assuming that edge GUARD is always taken, all definitions in BB |
698 | are noy used outside of the loop. |
699 | KNOWN_INVARIANTS is a set of ssa names we know to be invariant, and |
700 | PROCESSED is a set of ssa names for that we already tested whether they |
701 | are invariant or not. */ |
702 | |
703 | static bool |
704 | empty_bb_without_guard_p (struct loop *loop, basic_block bb) |
705 | { |
706 | basic_block exit_bb = single_exit (loop)->src; |
707 | bool may_be_used_outside = (bb == exit_bb |
708 | || !dominated_by_p (CDI_DOMINATORS, bb, exit_bb)); |
709 | tree name; |
710 | ssa_op_iter op_iter; |
711 | |
712 | /* Phi nodes do not have side effects, but their results might be used |
713 | outside of the loop. */ |
714 | if (may_be_used_outside) |
715 | { |
716 | for (gphi_iterator gsi = gsi_start_phis (bb); |
717 | !gsi_end_p (gsi); gsi_next (&gsi)) |
718 | { |
719 | gphi *phi = gsi.phi (); |
720 | name = PHI_RESULT (phi); |
721 | if (virtual_operand_p (name)) |
722 | continue; |
723 | |
724 | if (used_outside_loop_p (loop, name)) |
725 | return false; |
726 | } |
727 | } |
728 | |
729 | for (gimple_stmt_iterator gsi = gsi_start_bb (bb); |
730 | !gsi_end_p (gsi); gsi_next (&gsi)) |
731 | { |
732 | gimple *stmt = gsi_stmt (gsi); |
733 | if (gimple_has_side_effects (stmt)) |
734 | return false; |
735 | |
736 | if (gimple_vdef(stmt)) |
737 | return false; |
738 | |
739 | FOR_EACH_SSA_TREE_OPERAND (name, stmt, op_iter, SSA_OP_DEF) |
740 | { |
741 | if (may_be_used_outside |
742 | && used_outside_loop_p (loop, name)) |
743 | return false; |
744 | } |
745 | } |
746 | return true; |
747 | } |
748 | |
749 | /* Return true if NAME is used outside of LOOP. */ |
750 | |
751 | static bool |
752 | used_outside_loop_p (struct loop *loop, tree name) |
753 | { |
754 | imm_use_iterator it; |
755 | use_operand_p use; |
756 | |
757 | FOR_EACH_IMM_USE_FAST (use, it, name) |
758 | { |
759 | gimple *stmt = USE_STMT (use); |
760 | if (!flow_bb_inside_loop_p (loop, gimple_bb (stmt))) |
761 | return true; |
762 | } |
763 | |
764 | return false; |
765 | } |
766 | |
767 | /* Return argument for loop preheader edge in header virtual phi if any. */ |
768 | |
769 | static tree |
770 | (struct loop *loop) |
771 | { |
772 | for (gphi_iterator gsi = gsi_start_phis (loop->header); |
773 | !gsi_end_p (gsi); gsi_next (&gsi)) |
774 | { |
775 | gphi *phi = gsi.phi (); |
776 | if (!virtual_operand_p (gimple_phi_result (phi))) |
777 | continue; |
778 | return PHI_ARG_DEF_FROM_EDGE (phi, loop_preheader_edge (loop)); |
779 | } |
780 | return NULL_TREE; |
781 | } |
782 | |
783 | /* Move the check of GUARD outside of LOOP. */ |
784 | |
785 | static void |
786 | hoist_guard (struct loop *loop, edge guard) |
787 | { |
788 | edge exit = single_exit (loop); |
789 | edge preh = loop_preheader_edge (loop); |
790 | basic_block = preh->src; |
791 | basic_block bb; |
792 | edge te, fe, e, new_edge; |
793 | gimple *stmt; |
794 | basic_block guard_bb = guard->src; |
795 | edge not_guard; |
796 | gimple_stmt_iterator gsi; |
797 | int flags = 0; |
798 | bool fix_dom_of_exit; |
799 | gcond *cond_stmt, *new_cond_stmt; |
800 | |
801 | bb = get_immediate_dominator (CDI_DOMINATORS, exit->dest); |
802 | fix_dom_of_exit = flow_bb_inside_loop_p (loop, bb); |
803 | gsi = gsi_last_bb (guard_bb); |
804 | stmt = gsi_stmt (gsi); |
805 | gcc_assert (gimple_code (stmt) == GIMPLE_COND); |
806 | cond_stmt = as_a <gcond *> (stmt); |
807 | extract_true_false_edges_from_block (guard_bb, &te, &fe); |
808 | /* Insert guard to PRE_HEADER. */ |
809 | if (!empty_block_p (pre_header)) |
810 | gsi = gsi_last_bb (pre_header); |
811 | else |
812 | gsi = gsi_start_bb (pre_header); |
813 | /* Create copy of COND_STMT. */ |
814 | new_cond_stmt = gimple_build_cond (gimple_cond_code (cond_stmt), |
815 | gimple_cond_lhs (cond_stmt), |
816 | gimple_cond_rhs (cond_stmt), |
817 | NULL_TREE, NULL_TREE); |
818 | gsi_insert_after (&gsi, new_cond_stmt, GSI_NEW_STMT); |
819 | /* Convert COND_STMT to true/false conditional. */ |
820 | if (guard == te) |
821 | gimple_cond_make_false (cond_stmt); |
822 | else |
823 | gimple_cond_make_true (cond_stmt); |
824 | update_stmt (cond_stmt); |
825 | /* Create new loop pre-header. */ |
826 | e = split_block (pre_header, last_stmt (pre_header)); |
827 | if (dump_file && (dump_flags & TDF_DETAILS)) |
828 | { |
829 | fprintf (dump_file, " Moving guard %i->%i (prob " , |
830 | guard->src->index, guard->dest->index); |
831 | guard->probability.dump (dump_file); |
832 | fprintf (dump_file, ") to bb %i, new preheader is %i\n" , |
833 | e->src->index, e->dest->index); |
834 | } |
835 | |
836 | gcc_assert (loop_preheader_edge (loop)->src == e->dest); |
837 | |
838 | if (guard == fe) |
839 | { |
840 | e->flags = EDGE_TRUE_VALUE; |
841 | flags |= EDGE_FALSE_VALUE; |
842 | not_guard = te; |
843 | } |
844 | else |
845 | { |
846 | e->flags = EDGE_FALSE_VALUE; |
847 | flags |= EDGE_TRUE_VALUE; |
848 | not_guard = fe; |
849 | } |
850 | new_edge = make_edge (pre_header, exit->dest, flags); |
851 | |
852 | /* Determine the probability that we skip the loop. Assume that loop has |
853 | same average number of iterations regardless outcome of guard. */ |
854 | new_edge->probability = guard->probability; |
855 | profile_count skip_count = guard->src->count.nonzero_p () |
856 | ? guard->count ().apply_scale (pre_header->count, |
857 | guard->src->count) |
858 | : guard->count ().apply_probability (new_edge->probability); |
859 | |
860 | if (skip_count > e->count ()) |
861 | { |
862 | fprintf (dump_file, " Capping count; expect profile inconsistency\n" ); |
863 | skip_count = e->count (); |
864 | } |
865 | if (dump_file && (dump_flags & TDF_DETAILS)) |
866 | { |
867 | fprintf (dump_file, " Estimated probability of skipping loop is " ); |
868 | new_edge->probability.dump (dump_file); |
869 | fprintf (dump_file, "\n" ); |
870 | } |
871 | |
872 | /* Update profile after the transform: |
873 | |
874 | First decrease count of path from newly hoisted loop guard |
875 | to loop header... */ |
876 | e->probability = new_edge->probability.invert (); |
877 | e->dest->count = e->count (); |
878 | |
879 | /* ... now update profile to represent that original guard will be optimized |
880 | away ... */ |
881 | guard->probability = profile_probability::never (); |
882 | not_guard->probability = profile_probability::always (); |
883 | |
884 | /* ... finally scale everything in the loop except for guarded basic blocks |
885 | where profile does not change. */ |
886 | basic_block *body = get_loop_body (loop); |
887 | |
888 | if (dump_file && (dump_flags & TDF_DETAILS)) |
889 | fprintf (dump_file, " Scaling nonguarded BBs in loop:" ); |
890 | for (unsigned int i = 0; i < loop->num_nodes; i++) |
891 | { |
892 | basic_block bb = body[i]; |
893 | if (!dominated_by_p (CDI_DOMINATORS, bb, not_guard->dest)) |
894 | { |
895 | if (dump_file && (dump_flags & TDF_DETAILS)) |
896 | fprintf (dump_file, " %i" , bb->index); |
897 | if (e->probability.initialized_p ()) |
898 | scale_bbs_frequencies (&bb, 1, e->probability); |
899 | } |
900 | } |
901 | |
902 | if (fix_dom_of_exit) |
903 | set_immediate_dominator (CDI_DOMINATORS, exit->dest, pre_header); |
904 | /* Add NEW_ADGE argument for all phi in post-header block. */ |
905 | bb = exit->dest; |
906 | for (gphi_iterator gsi = gsi_start_phis (bb); |
907 | !gsi_end_p (gsi); gsi_next (&gsi)) |
908 | { |
909 | gphi *phi = gsi.phi (); |
910 | tree arg; |
911 | if (virtual_operand_p (gimple_phi_result (phi))) |
912 | { |
913 | arg = get_vop_from_header (loop); |
914 | if (arg == NULL_TREE) |
915 | /* Use exit edge argument. */ |
916 | arg = PHI_ARG_DEF_FROM_EDGE (phi, exit); |
917 | add_phi_arg (phi, arg, new_edge, UNKNOWN_LOCATION); |
918 | } |
919 | else |
920 | { |
921 | /* Use exit edge argument. */ |
922 | arg = PHI_ARG_DEF_FROM_EDGE (phi, exit); |
923 | add_phi_arg (phi, arg, new_edge, UNKNOWN_LOCATION); |
924 | } |
925 | } |
926 | |
927 | if (dump_file && (dump_flags & TDF_DETAILS)) |
928 | fprintf (dump_file, "\n guard hoisted.\n" ); |
929 | |
930 | free (body); |
931 | } |
932 | |
933 | /* Return true if phi argument for exit edge can be used |
934 | for edge around loop. */ |
935 | |
936 | static bool |
937 | check_exit_phi (struct loop *loop) |
938 | { |
939 | edge exit = single_exit (loop); |
940 | basic_block = loop_preheader_edge (loop)->src; |
941 | |
942 | for (gphi_iterator gsi = gsi_start_phis (exit->dest); |
943 | !gsi_end_p (gsi); gsi_next (&gsi)) |
944 | { |
945 | gphi *phi = gsi.phi (); |
946 | tree arg; |
947 | gimple *def; |
948 | basic_block def_bb; |
949 | if (virtual_operand_p (gimple_phi_result (phi))) |
950 | continue; |
951 | arg = PHI_ARG_DEF_FROM_EDGE (phi, exit); |
952 | if (TREE_CODE (arg) != SSA_NAME) |
953 | continue; |
954 | def = SSA_NAME_DEF_STMT (arg); |
955 | if (!def) |
956 | continue; |
957 | def_bb = gimple_bb (def); |
958 | if (!def_bb) |
959 | continue; |
960 | if (!dominated_by_p (CDI_DOMINATORS, pre_header, def_bb)) |
961 | /* Definition inside loop! */ |
962 | return false; |
963 | /* Check loop closed phi invariant. */ |
964 | if (!flow_bb_inside_loop_p (def_bb->loop_father, pre_header)) |
965 | return false; |
966 | } |
967 | return true; |
968 | } |
969 | |
970 | /* Loop unswitching pass. */ |
971 | |
972 | namespace { |
973 | |
974 | const pass_data pass_data_tree_unswitch = |
975 | { |
976 | GIMPLE_PASS, /* type */ |
977 | "unswitch" , /* name */ |
978 | OPTGROUP_LOOP, /* optinfo_flags */ |
979 | TV_TREE_LOOP_UNSWITCH, /* tv_id */ |
980 | PROP_cfg, /* properties_required */ |
981 | 0, /* properties_provided */ |
982 | 0, /* properties_destroyed */ |
983 | 0, /* todo_flags_start */ |
984 | 0, /* todo_flags_finish */ |
985 | }; |
986 | |
987 | class pass_tree_unswitch : public gimple_opt_pass |
988 | { |
989 | public: |
990 | pass_tree_unswitch (gcc::context *ctxt) |
991 | : gimple_opt_pass (pass_data_tree_unswitch, ctxt) |
992 | {} |
993 | |
994 | /* opt_pass methods: */ |
995 | virtual bool gate (function *) { return flag_unswitch_loops != 0; } |
996 | virtual unsigned int execute (function *); |
997 | |
998 | }; // class pass_tree_unswitch |
999 | |
1000 | unsigned int |
1001 | pass_tree_unswitch::execute (function *fun) |
1002 | { |
1003 | if (number_of_loops (fun) <= 1) |
1004 | return 0; |
1005 | |
1006 | return tree_ssa_unswitch_loops (); |
1007 | } |
1008 | |
1009 | } // anon namespace |
1010 | |
1011 | gimple_opt_pass * |
1012 | make_pass_tree_unswitch (gcc::context *ctxt) |
1013 | { |
1014 | return new pass_tree_unswitch (ctxt); |
1015 | } |
1016 | |
1017 | |
1018 | |