1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002-2022 Free Software Foundation, Inc.
3 Contributed by Ben Elliston <bje@redhat.com>
4 and Andrew MacLeod <amacleod@redhat.com>
5 Adapted to use control dependence by Steven Bosscher, SUSE Labs.
6
7 This file is part of GCC.
8
9 GCC is free software; you can redistribute it and/or modify it
10 under the terms of the GNU General Public License as published by the
11 Free Software Foundation; either version 3, or (at your option) any
12 later version.
13
14 GCC is distributed in the hope that it will be useful, but WITHOUT
15 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
16 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
17 for more details.
18
19 You should have received a copy of the GNU General Public License
20 along with GCC; see the file COPYING3. If not see
21 <http://www.gnu.org/licenses/>. */
22
23 /* Dead code elimination.
24
25 References:
26
27 Building an Optimizing Compiler,
28 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
29
30 Advanced Compiler Design and Implementation,
31 Steven Muchnick, Morgan Kaufmann, 1997, Section 18.10.
32
33 Dead-code elimination is the removal of statements which have no
34 impact on the program's output. "Dead statements" have no impact
35 on the program's output, while "necessary statements" may have
36 impact on the output.
37
38 The algorithm consists of three phases:
39 1. Marking as necessary all statements known to be necessary,
40 e.g. most function calls, writing a value to memory, etc;
41 2. Propagating necessary statements, e.g., the statements
42 giving values to operands in necessary statements; and
43 3. Removing dead statements. */
44
45 #include "config.h"
46 #include "system.h"
47 #include "coretypes.h"
48 #include "backend.h"
49 #include "rtl.h"
50 #include "tree.h"
51 #include "gimple.h"
52 #include "cfghooks.h"
53 #include "tree-pass.h"
54 #include "ssa.h"
55 #include "gimple-pretty-print.h"
56 #include "fold-const.h"
57 #include "calls.h"
58 #include "cfganal.h"
59 #include "tree-eh.h"
60 #include "gimplify.h"
61 #include "gimple-iterator.h"
62 #include "tree-cfg.h"
63 #include "tree-ssa-loop-niter.h"
64 #include "tree-into-ssa.h"
65 #include "tree-dfa.h"
66 #include "cfgloop.h"
67 #include "tree-scalar-evolution.h"
68 #include "tree-ssa-propagate.h"
69 #include "gimple-fold.h"
70 #include "tree-ssa.h"
71
72 static struct stmt_stats
73 {
74 int total;
75 int total_phis;
76 int removed;
77 int removed_phis;
78 } stats;
79
80 #define STMT_NECESSARY GF_PLF_1
81
82 static vec<gimple *> worklist;
83
84 /* Vector indicating an SSA name has already been processed and marked
85 as necessary. */
86 static sbitmap processed;
87
88 /* Vector indicating that the last statement of a basic block has already
89 been marked as necessary. */
90 static sbitmap last_stmt_necessary;
91
92 /* Vector indicating that BB contains statements that are live. */
93 static sbitmap bb_contains_live_stmts;
94
95 /* Before we can determine whether a control branch is dead, we need to
96 compute which blocks are control dependent on which edges.
97
98 We expect each block to be control dependent on very few edges so we
99 use a bitmap for each block recording its edges. An array holds the
100 bitmap. The Ith bit in the bitmap is set if that block is dependent
101 on the Ith edge. */
102 static control_dependences *cd;
103
104 /* Vector indicating that a basic block has already had all the edges
105 processed that it is control dependent on. */
106 static sbitmap visited_control_parents;
107
108 /* TRUE if this pass alters the CFG (by removing control statements).
109 FALSE otherwise.
110
111 If this pass alters the CFG, then it will arrange for the dominators
112 to be recomputed. */
113 static bool cfg_altered;
114
115 /* When non-NULL holds map from basic block index into the postorder. */
116 static int *bb_postorder;
117
118
119 /* True if we should treat any stmt with a vdef as necessary. */
120
121 static inline bool
keep_all_vdefs_p()122 keep_all_vdefs_p ()
123 {
124 return optimize_debug;
125 }
126
127 /* If STMT is not already marked necessary, mark it, and add it to the
128 worklist if ADD_TO_WORKLIST is true. */
129
130 static inline void
mark_stmt_necessary(gimple * stmt,bool add_to_worklist)131 mark_stmt_necessary (gimple *stmt, bool add_to_worklist)
132 {
133 gcc_assert (stmt);
134
135 if (gimple_plf (stmt, STMT_NECESSARY))
136 return;
137
138 if (dump_file && (dump_flags & TDF_DETAILS))
139 {
140 fprintf (dump_file, "Marking useful stmt: ");
141 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
142 fprintf (dump_file, "\n");
143 }
144
145 gimple_set_plf (stmt, STMT_NECESSARY, true);
146 if (add_to_worklist)
147 worklist.safe_push (stmt);
148 if (add_to_worklist && bb_contains_live_stmts && !is_gimple_debug (stmt))
149 bitmap_set_bit (bb_contains_live_stmts, gimple_bb (stmt)->index);
150 }
151
152
153 /* Mark the statement defining operand OP as necessary. */
154
155 static inline void
mark_operand_necessary(tree op)156 mark_operand_necessary (tree op)
157 {
158 gimple *stmt;
159 int ver;
160
161 gcc_assert (op);
162
163 ver = SSA_NAME_VERSION (op);
164 if (bitmap_bit_p (processed, ver))
165 {
166 stmt = SSA_NAME_DEF_STMT (op);
167 gcc_assert (gimple_nop_p (stmt)
168 || gimple_plf (stmt, STMT_NECESSARY));
169 return;
170 }
171 bitmap_set_bit (processed, ver);
172
173 stmt = SSA_NAME_DEF_STMT (op);
174 gcc_assert (stmt);
175
176 if (gimple_plf (stmt, STMT_NECESSARY) || gimple_nop_p (stmt))
177 return;
178
179 if (dump_file && (dump_flags & TDF_DETAILS))
180 {
181 fprintf (dump_file, "marking necessary through ");
182 print_generic_expr (dump_file, op);
183 fprintf (dump_file, " stmt ");
184 print_gimple_stmt (dump_file, stmt, 0);
185 }
186
187 gimple_set_plf (stmt, STMT_NECESSARY, true);
188 if (bb_contains_live_stmts)
189 bitmap_set_bit (bb_contains_live_stmts, gimple_bb (stmt)->index);
190 worklist.safe_push (stmt);
191 }
192
193
194 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
195 it can make other statements necessary.
196
197 If AGGRESSIVE is false, control statements are conservatively marked as
198 necessary. */
199
200 static void
mark_stmt_if_obviously_necessary(gimple * stmt,bool aggressive)201 mark_stmt_if_obviously_necessary (gimple *stmt, bool aggressive)
202 {
203 /* Statements that are implicitly live. Most function calls, asm
204 and return statements are required. Labels and GIMPLE_BIND nodes
205 are kept because they are control flow, and we have no way of
206 knowing whether they can be removed. DCE can eliminate all the
207 other statements in a block, and CFG can then remove the block
208 and labels. */
209 switch (gimple_code (stmt))
210 {
211 case GIMPLE_PREDICT:
212 case GIMPLE_LABEL:
213 mark_stmt_necessary (stmt, false);
214 return;
215
216 case GIMPLE_ASM:
217 case GIMPLE_RESX:
218 case GIMPLE_RETURN:
219 mark_stmt_necessary (stmt, true);
220 return;
221
222 case GIMPLE_CALL:
223 {
224 tree callee = gimple_call_fndecl (stmt);
225 if (callee != NULL_TREE
226 && fndecl_built_in_p (callee, BUILT_IN_NORMAL))
227 switch (DECL_FUNCTION_CODE (callee))
228 {
229 case BUILT_IN_MALLOC:
230 case BUILT_IN_ALIGNED_ALLOC:
231 case BUILT_IN_CALLOC:
232 CASE_BUILT_IN_ALLOCA:
233 case BUILT_IN_STRDUP:
234 case BUILT_IN_STRNDUP:
235 case BUILT_IN_GOMP_ALLOC:
236 return;
237
238 default:;
239 }
240
241 if (callee != NULL_TREE
242 && flag_allocation_dce
243 && DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee))
244 return;
245
246 /* IFN_GOACC_LOOP calls are necessary in that they are used to
247 represent parameter (i.e. step, bound) of a lowered OpenACC
248 partitioned loop. But this kind of partitioned loop might not
249 survive from aggressive loop removal for it has loop exit and
250 is assumed to be finite. Therefore, we need to explicitly mark
251 these calls. (An example is libgomp.oacc-c-c++-common/pr84955.c) */
252 if (gimple_call_internal_p (stmt, IFN_GOACC_LOOP))
253 {
254 mark_stmt_necessary (stmt, true);
255 return;
256 }
257 break;
258 }
259
260 case GIMPLE_DEBUG:
261 /* Debug temps without a value are not useful. ??? If we could
262 easily locate the debug temp bind stmt for a use thereof,
263 would could refrain from marking all debug temps here, and
264 mark them only if they're used. */
265 if (gimple_debug_nonbind_marker_p (stmt)
266 || !gimple_debug_bind_p (stmt)
267 || gimple_debug_bind_has_value_p (stmt)
268 || TREE_CODE (gimple_debug_bind_get_var (stmt)) != DEBUG_EXPR_DECL)
269 mark_stmt_necessary (stmt, false);
270 return;
271
272 case GIMPLE_GOTO:
273 gcc_assert (!simple_goto_p (stmt));
274 mark_stmt_necessary (stmt, true);
275 return;
276
277 case GIMPLE_COND:
278 gcc_assert (EDGE_COUNT (gimple_bb (stmt)->succs) == 2);
279 /* Fall through. */
280
281 case GIMPLE_SWITCH:
282 if (! aggressive)
283 mark_stmt_necessary (stmt, true);
284 break;
285
286 case GIMPLE_ASSIGN:
287 /* Mark indirect CLOBBERs to be lazily removed if their SSA operands
288 do not prevail. That also makes control flow leading to them
289 not necessary in aggressive mode. */
290 if (gimple_clobber_p (stmt) && !zero_ssa_operands (stmt, SSA_OP_USE))
291 return;
292 break;
293
294 default:
295 break;
296 }
297
298 /* If the statement has volatile operands, it needs to be preserved.
299 Same for statements that can alter control flow in unpredictable
300 ways. */
301 if (gimple_has_side_effects (stmt) || is_ctrl_altering_stmt (stmt))
302 {
303 mark_stmt_necessary (stmt, true);
304 return;
305 }
306
307 /* If a statement could throw, it can be deemed necessary unless we
308 are allowed to remove dead EH. Test this after checking for
309 new/delete operators since we always elide their EH. */
310 if (!cfun->can_delete_dead_exceptions
311 && stmt_could_throw_p (cfun, stmt))
312 {
313 mark_stmt_necessary (stmt, true);
314 return;
315 }
316
317 if ((gimple_vdef (stmt) && keep_all_vdefs_p ())
318 || stmt_may_clobber_global_p (stmt, false))
319 {
320 mark_stmt_necessary (stmt, true);
321 return;
322 }
323
324 return;
325 }
326
327
328 /* Mark the last statement of BB as necessary. */
329
330 static void
mark_last_stmt_necessary(basic_block bb)331 mark_last_stmt_necessary (basic_block bb)
332 {
333 gimple *stmt = last_stmt (bb);
334
335 bitmap_set_bit (last_stmt_necessary, bb->index);
336 bitmap_set_bit (bb_contains_live_stmts, bb->index);
337
338 /* We actually mark the statement only if it is a control statement. */
339 if (stmt && is_ctrl_stmt (stmt))
340 mark_stmt_necessary (stmt, true);
341 }
342
343
344 /* Mark control dependent edges of BB as necessary. We have to do this only
345 once for each basic block so we set the appropriate bit after we're done.
346
347 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
348
349 static void
mark_control_dependent_edges_necessary(basic_block bb,bool ignore_self)350 mark_control_dependent_edges_necessary (basic_block bb, bool ignore_self)
351 {
352 bitmap_iterator bi;
353 unsigned edge_number;
354 bool skipped = false;
355
356 gcc_assert (bb != EXIT_BLOCK_PTR_FOR_FN (cfun));
357
358 if (bb == ENTRY_BLOCK_PTR_FOR_FN (cfun))
359 return;
360
361 EXECUTE_IF_SET_IN_BITMAP (cd->get_edges_dependent_on (bb->index),
362 0, edge_number, bi)
363 {
364 basic_block cd_bb = cd->get_edge_src (edge_number);
365
366 if (ignore_self && cd_bb == bb)
367 {
368 skipped = true;
369 continue;
370 }
371
372 if (!bitmap_bit_p (last_stmt_necessary, cd_bb->index))
373 mark_last_stmt_necessary (cd_bb);
374 }
375
376 if (!skipped)
377 bitmap_set_bit (visited_control_parents, bb->index);
378 }
379
380
381 /* Find obviously necessary statements. These are things like most function
382 calls, and stores to file level variables.
383
384 If EL is NULL, control statements are conservatively marked as
385 necessary. Otherwise it contains the list of edges used by control
386 dependence analysis. */
387
388 static void
find_obviously_necessary_stmts(bool aggressive)389 find_obviously_necessary_stmts (bool aggressive)
390 {
391 basic_block bb;
392 gimple_stmt_iterator gsi;
393 edge e;
394 gimple *phi, *stmt;
395 int flags;
396
397 FOR_EACH_BB_FN (bb, cfun)
398 {
399 /* PHI nodes are never inherently necessary. */
400 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
401 {
402 phi = gsi_stmt (gsi);
403 gimple_set_plf (phi, STMT_NECESSARY, false);
404 }
405
406 /* Check all statements in the block. */
407 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
408 {
409 stmt = gsi_stmt (gsi);
410 gimple_set_plf (stmt, STMT_NECESSARY, false);
411 mark_stmt_if_obviously_necessary (stmt, aggressive);
412 }
413 }
414
415 /* Pure and const functions are finite and thus have no infinite loops in
416 them. */
417 flags = flags_from_decl_or_type (current_function_decl);
418 if ((flags & (ECF_CONST|ECF_PURE)) && !(flags & ECF_LOOPING_CONST_OR_PURE))
419 return;
420
421 /* Prevent the empty possibly infinite loops from being removed. This is
422 needed to make the logic in remove_dead_stmt work to identify the
423 correct edge to keep when removing a controlling condition. */
424 if (aggressive)
425 {
426 if (mark_irreducible_loops ())
427 FOR_EACH_BB_FN (bb, cfun)
428 {
429 edge_iterator ei;
430 FOR_EACH_EDGE (e, ei, bb->succs)
431 if ((e->flags & EDGE_DFS_BACK)
432 && (e->flags & EDGE_IRREDUCIBLE_LOOP))
433 {
434 if (dump_file)
435 fprintf (dump_file, "Marking back edge of irreducible "
436 "loop %i->%i\n", e->src->index, e->dest->index);
437 mark_control_dependent_edges_necessary (e->dest, false);
438 }
439 }
440
441 for (auto loop : loops_list (cfun, 0))
442 /* For loops without an exit do not mark any condition. */
443 if (loop->exits->next->e && !finite_loop_p (loop))
444 {
445 if (dump_file)
446 fprintf (dump_file, "cannot prove finiteness of loop %i\n",
447 loop->num);
448 mark_control_dependent_edges_necessary (loop->latch, false);
449 }
450 }
451 }
452
453
454 /* Return true if REF is based on an aliased base, otherwise false. */
455
456 static bool
ref_may_be_aliased(tree ref)457 ref_may_be_aliased (tree ref)
458 {
459 gcc_assert (TREE_CODE (ref) != WITH_SIZE_EXPR);
460 while (handled_component_p (ref))
461 ref = TREE_OPERAND (ref, 0);
462 if ((TREE_CODE (ref) == MEM_REF || TREE_CODE (ref) == TARGET_MEM_REF)
463 && TREE_CODE (TREE_OPERAND (ref, 0)) == ADDR_EXPR)
464 ref = TREE_OPERAND (TREE_OPERAND (ref, 0), 0);
465 return !(DECL_P (ref)
466 && !may_be_aliased (ref));
467 }
468
469 static bitmap visited = NULL;
470 static unsigned int longest_chain = 0;
471 static unsigned int total_chain = 0;
472 static unsigned int nr_walks = 0;
473 static bool chain_ovfl = false;
474
475 /* Worker for the walker that marks reaching definitions of REF,
476 which is based on a non-aliased decl, necessary. It returns
477 true whenever the defining statement of the current VDEF is
478 a kill for REF, as no dominating may-defs are necessary for REF
479 anymore. DATA points to the basic-block that contains the
480 stmt that refers to REF. */
481
482 static bool
mark_aliased_reaching_defs_necessary_1(ao_ref * ref,tree vdef,void * data)483 mark_aliased_reaching_defs_necessary_1 (ao_ref *ref, tree vdef, void *data)
484 {
485 gimple *def_stmt = SSA_NAME_DEF_STMT (vdef);
486
487 /* All stmts we visit are necessary. */
488 if (! gimple_clobber_p (def_stmt))
489 mark_operand_necessary (vdef);
490
491 /* If the stmt lhs kills ref, then we can stop walking. */
492 if (gimple_has_lhs (def_stmt)
493 && TREE_CODE (gimple_get_lhs (def_stmt)) != SSA_NAME
494 /* The assignment is not necessarily carried out if it can throw
495 and we can catch it in the current function where we could inspect
496 the previous value.
497 ??? We only need to care about the RHS throwing. For aggregate
498 assignments or similar calls and non-call exceptions the LHS
499 might throw as well. */
500 && !stmt_can_throw_internal (cfun, def_stmt))
501 {
502 tree base, lhs = gimple_get_lhs (def_stmt);
503 poly_int64 size, offset, max_size;
504 bool reverse;
505 ao_ref_base (ref);
506 base
507 = get_ref_base_and_extent (lhs, &offset, &size, &max_size, &reverse);
508 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
509 so base == refd->base does not always hold. */
510 if (base == ref->base)
511 {
512 /* For a must-alias check we need to be able to constrain
513 the accesses properly. */
514 if (known_eq (size, max_size)
515 && known_subrange_p (ref->offset, ref->max_size, offset, size))
516 return true;
517 /* Or they need to be exactly the same. */
518 else if (ref->ref
519 /* Make sure there is no induction variable involved
520 in the references (gcc.c-torture/execute/pr42142.c).
521 The simplest way is to check if the kill dominates
522 the use. */
523 /* But when both are in the same block we cannot
524 easily tell whether we came from a backedge
525 unless we decide to compute stmt UIDs
526 (see PR58246). */
527 && (basic_block) data != gimple_bb (def_stmt)
528 && dominated_by_p (CDI_DOMINATORS, (basic_block) data,
529 gimple_bb (def_stmt))
530 && operand_equal_p (ref->ref, lhs, 0))
531 return true;
532 }
533 }
534
535 /* Otherwise keep walking. */
536 return false;
537 }
538
539 static void
mark_aliased_reaching_defs_necessary(gimple * stmt,tree ref)540 mark_aliased_reaching_defs_necessary (gimple *stmt, tree ref)
541 {
542 /* Should have been caught before calling this function. */
543 gcc_checking_assert (!keep_all_vdefs_p ());
544
545 unsigned int chain;
546 ao_ref refd;
547 gcc_assert (!chain_ovfl);
548 ao_ref_init (&refd, ref);
549 chain = walk_aliased_vdefs (&refd, gimple_vuse (stmt),
550 mark_aliased_reaching_defs_necessary_1,
551 gimple_bb (stmt), NULL);
552 if (chain > longest_chain)
553 longest_chain = chain;
554 total_chain += chain;
555 nr_walks++;
556 }
557
558 /* Worker for the walker that marks reaching definitions of REF, which
559 is not based on a non-aliased decl. For simplicity we need to end
560 up marking all may-defs necessary that are not based on a non-aliased
561 decl. The only job of this walker is to skip may-defs based on
562 a non-aliased decl. */
563
564 static bool
mark_all_reaching_defs_necessary_1(ao_ref * ref ATTRIBUTE_UNUSED,tree vdef,void * data ATTRIBUTE_UNUSED)565 mark_all_reaching_defs_necessary_1 (ao_ref *ref ATTRIBUTE_UNUSED,
566 tree vdef, void *data ATTRIBUTE_UNUSED)
567 {
568 gimple *def_stmt = SSA_NAME_DEF_STMT (vdef);
569
570 /* We have to skip already visited (and thus necessary) statements
571 to make the chaining work after we dropped back to simple mode. */
572 if (chain_ovfl
573 && bitmap_bit_p (processed, SSA_NAME_VERSION (vdef)))
574 {
575 gcc_assert (gimple_nop_p (def_stmt)
576 || gimple_plf (def_stmt, STMT_NECESSARY));
577 return false;
578 }
579
580 /* We want to skip stores to non-aliased variables. */
581 if (!chain_ovfl
582 && gimple_assign_single_p (def_stmt))
583 {
584 tree lhs = gimple_assign_lhs (def_stmt);
585 if (!ref_may_be_aliased (lhs))
586 return false;
587 }
588
589 /* We want to skip statments that do not constitute stores but have
590 a virtual definition. */
591 if (gcall *call = dyn_cast <gcall *> (def_stmt))
592 {
593 tree callee = gimple_call_fndecl (call);
594 if (callee != NULL_TREE
595 && fndecl_built_in_p (callee, BUILT_IN_NORMAL))
596 switch (DECL_FUNCTION_CODE (callee))
597 {
598 case BUILT_IN_MALLOC:
599 case BUILT_IN_ALIGNED_ALLOC:
600 case BUILT_IN_CALLOC:
601 CASE_BUILT_IN_ALLOCA:
602 case BUILT_IN_FREE:
603 case BUILT_IN_GOMP_ALLOC:
604 case BUILT_IN_GOMP_FREE:
605 return false;
606
607 default:;
608 }
609
610 if (callee != NULL_TREE
611 && (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee)
612 || DECL_IS_OPERATOR_DELETE_P (callee))
613 && gimple_call_from_new_or_delete (call))
614 return false;
615 }
616
617 if (! gimple_clobber_p (def_stmt))
618 mark_operand_necessary (vdef);
619
620 return false;
621 }
622
623 static void
mark_all_reaching_defs_necessary(gimple * stmt)624 mark_all_reaching_defs_necessary (gimple *stmt)
625 {
626 /* Should have been caught before calling this function. */
627 gcc_checking_assert (!keep_all_vdefs_p ());
628 walk_aliased_vdefs (NULL, gimple_vuse (stmt),
629 mark_all_reaching_defs_necessary_1, NULL, &visited);
630 }
631
632 /* Return true for PHI nodes with one or identical arguments
633 can be removed. */
634 static bool
degenerate_phi_p(gimple * phi)635 degenerate_phi_p (gimple *phi)
636 {
637 unsigned int i;
638 tree op = gimple_phi_arg_def (phi, 0);
639 for (i = 1; i < gimple_phi_num_args (phi); i++)
640 if (gimple_phi_arg_def (phi, i) != op)
641 return false;
642 return true;
643 }
644
645 /* Return that NEW_CALL and DELETE_CALL are a valid pair of new
646 and delete operators. */
647
648 static bool
valid_new_delete_pair_p(gimple * new_call,gimple * delete_call)649 valid_new_delete_pair_p (gimple *new_call, gimple *delete_call)
650 {
651 tree new_asm = DECL_ASSEMBLER_NAME (gimple_call_fndecl (new_call));
652 tree delete_asm = DECL_ASSEMBLER_NAME (gimple_call_fndecl (delete_call));
653 return valid_new_delete_pair_p (new_asm, delete_asm);
654 }
655
656 /* Propagate necessity using the operands of necessary statements.
657 Process the uses on each statement in the worklist, and add all
658 feeding statements which contribute to the calculation of this
659 value to the worklist.
660
661 In conservative mode, EL is NULL. */
662
663 static void
propagate_necessity(bool aggressive)664 propagate_necessity (bool aggressive)
665 {
666 gimple *stmt;
667
668 if (dump_file && (dump_flags & TDF_DETAILS))
669 fprintf (dump_file, "\nProcessing worklist:\n");
670
671 while (worklist.length () > 0)
672 {
673 /* Take STMT from worklist. */
674 stmt = worklist.pop ();
675
676 if (dump_file && (dump_flags & TDF_DETAILS))
677 {
678 fprintf (dump_file, "processing: ");
679 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
680 fprintf (dump_file, "\n");
681 }
682
683 if (aggressive)
684 {
685 /* Mark the last statement of the basic blocks on which the block
686 containing STMT is control dependent, but only if we haven't
687 already done so. */
688 basic_block bb = gimple_bb (stmt);
689 if (bb != ENTRY_BLOCK_PTR_FOR_FN (cfun)
690 && !bitmap_bit_p (visited_control_parents, bb->index))
691 mark_control_dependent_edges_necessary (bb, false);
692 }
693
694 if (gimple_code (stmt) == GIMPLE_PHI
695 /* We do not process virtual PHI nodes nor do we track their
696 necessity. */
697 && !virtual_operand_p (gimple_phi_result (stmt)))
698 {
699 /* PHI nodes are somewhat special in that each PHI alternative has
700 data and control dependencies. All the statements feeding the
701 PHI node's arguments are always necessary. In aggressive mode,
702 we also consider the control dependent edges leading to the
703 predecessor block associated with each PHI alternative as
704 necessary. */
705 gphi *phi = as_a <gphi *> (stmt);
706 size_t k;
707
708 for (k = 0; k < gimple_phi_num_args (stmt); k++)
709 {
710 tree arg = PHI_ARG_DEF (stmt, k);
711 if (TREE_CODE (arg) == SSA_NAME)
712 mark_operand_necessary (arg);
713 }
714
715 /* For PHI operands it matters from where the control flow arrives
716 to the BB. Consider the following example:
717
718 a=exp1;
719 b=exp2;
720 if (test)
721 ;
722 else
723 ;
724 c=PHI(a,b)
725
726 We need to mark control dependence of the empty basic blocks, since they
727 contains computation of PHI operands.
728
729 Doing so is too restrictive in the case the predecestor block is in
730 the loop. Consider:
731
732 if (b)
733 {
734 int i;
735 for (i = 0; i<1000; ++i)
736 ;
737 j = 0;
738 }
739 return j;
740
741 There is PHI for J in the BB containing return statement.
742 In this case the control dependence of predecestor block (that is
743 within the empty loop) also contains the block determining number
744 of iterations of the block that would prevent removing of empty
745 loop in this case.
746
747 This scenario can be avoided by splitting critical edges.
748 To save the critical edge splitting pass we identify how the control
749 dependence would look like if the edge was split.
750
751 Consider the modified CFG created from current CFG by splitting
752 edge B->C. In the postdominance tree of modified CFG, C' is
753 always child of C. There are two cases how chlids of C' can look
754 like:
755
756 1) C' is leaf
757
758 In this case the only basic block C' is control dependent on is B.
759
760 2) C' has single child that is B
761
762 In this case control dependence of C' is same as control
763 dependence of B in original CFG except for block B itself.
764 (since C' postdominate B in modified CFG)
765
766 Now how to decide what case happens? There are two basic options:
767
768 a) C postdominate B. Then C immediately postdominate B and
769 case 2 happens iff there is no other way from B to C except
770 the edge B->C.
771
772 There is other way from B to C iff there is succesor of B that
773 is not postdominated by B. Testing this condition is somewhat
774 expensive, because we need to iterate all succesors of B.
775 We are safe to assume that this does not happen: we will mark B
776 as needed when processing the other path from B to C that is
777 conrol dependent on B and marking control dependencies of B
778 itself is harmless because they will be processed anyway after
779 processing control statement in B.
780
781 b) C does not postdominate B. Always case 1 happens since there is
782 path from C to exit that does not go through B and thus also C'. */
783
784 if (aggressive && !degenerate_phi_p (stmt))
785 {
786 for (k = 0; k < gimple_phi_num_args (stmt); k++)
787 {
788 basic_block arg_bb = gimple_phi_arg_edge (phi, k)->src;
789
790 if (gimple_bb (stmt)
791 != get_immediate_dominator (CDI_POST_DOMINATORS, arg_bb))
792 {
793 if (!bitmap_bit_p (last_stmt_necessary, arg_bb->index))
794 mark_last_stmt_necessary (arg_bb);
795 }
796 else if (arg_bb != ENTRY_BLOCK_PTR_FOR_FN (cfun)
797 && !bitmap_bit_p (visited_control_parents,
798 arg_bb->index))
799 mark_control_dependent_edges_necessary (arg_bb, true);
800 }
801 }
802 }
803 else
804 {
805 /* Propagate through the operands. Examine all the USE, VUSE and
806 VDEF operands in this statement. Mark all the statements
807 which feed this statement's uses as necessary. */
808 ssa_op_iter iter;
809 tree use;
810
811 /* If this is a call to free which is directly fed by an
812 allocation function do not mark that necessary through
813 processing the argument. */
814 bool is_delete_operator
815 = (is_gimple_call (stmt)
816 && gimple_call_from_new_or_delete (as_a <gcall *> (stmt))
817 && gimple_call_operator_delete_p (as_a <gcall *> (stmt)));
818 if (is_delete_operator
819 || gimple_call_builtin_p (stmt, BUILT_IN_FREE)
820 || gimple_call_builtin_p (stmt, BUILT_IN_GOMP_FREE))
821 {
822 tree ptr = gimple_call_arg (stmt, 0);
823 gcall *def_stmt;
824 tree def_callee;
825 /* If the pointer we free is defined by an allocation
826 function do not add the call to the worklist. */
827 if (TREE_CODE (ptr) == SSA_NAME
828 && (def_stmt = dyn_cast <gcall *> (SSA_NAME_DEF_STMT (ptr)))
829 && (def_callee = gimple_call_fndecl (def_stmt))
830 && ((DECL_BUILT_IN_CLASS (def_callee) == BUILT_IN_NORMAL
831 && (DECL_FUNCTION_CODE (def_callee) == BUILT_IN_ALIGNED_ALLOC
832 || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_MALLOC
833 || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_CALLOC
834 || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_GOMP_ALLOC))
835 || (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (def_callee)
836 && gimple_call_from_new_or_delete (def_stmt))))
837 {
838 if (is_delete_operator
839 && !valid_new_delete_pair_p (def_stmt, stmt))
840 mark_operand_necessary (gimple_call_arg (stmt, 0));
841
842 /* Delete operators can have alignment and (or) size
843 as next arguments. When being a SSA_NAME, they
844 must be marked as necessary. Similarly GOMP_free. */
845 if (gimple_call_num_args (stmt) >= 2)
846 for (unsigned i = 1; i < gimple_call_num_args (stmt);
847 i++)
848 {
849 tree arg = gimple_call_arg (stmt, i);
850 if (TREE_CODE (arg) == SSA_NAME)
851 mark_operand_necessary (arg);
852 }
853
854 continue;
855 }
856 }
857
858 FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
859 mark_operand_necessary (use);
860
861 use = gimple_vuse (stmt);
862 if (!use)
863 continue;
864
865 /* No need to search for vdefs if we intrinsicly keep them all. */
866 if (keep_all_vdefs_p ())
867 continue;
868
869 /* If we dropped to simple mode make all immediately
870 reachable definitions necessary. */
871 if (chain_ovfl)
872 {
873 mark_all_reaching_defs_necessary (stmt);
874 continue;
875 }
876
877 /* For statements that may load from memory (have a VUSE) we
878 have to mark all reaching (may-)definitions as necessary.
879 We partition this task into two cases:
880 1) explicit loads based on decls that are not aliased
881 2) implicit loads (like calls) and explicit loads not
882 based on decls that are not aliased (like indirect
883 references or loads from globals)
884 For 1) we mark all reaching may-defs as necessary, stopping
885 at dominating kills. For 2) we want to mark all dominating
886 references necessary, but non-aliased ones which we handle
887 in 1). By keeping a global visited bitmap for references
888 we walk for 2) we avoid quadratic behavior for those. */
889
890 if (gcall *call = dyn_cast <gcall *> (stmt))
891 {
892 tree callee = gimple_call_fndecl (call);
893 unsigned i;
894
895 /* Calls to functions that are merely acting as barriers
896 or that only store to memory do not make any previous
897 stores necessary. */
898 if (callee != NULL_TREE
899 && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL
900 && (DECL_FUNCTION_CODE (callee) == BUILT_IN_MEMSET
901 || DECL_FUNCTION_CODE (callee) == BUILT_IN_MEMSET_CHK
902 || DECL_FUNCTION_CODE (callee) == BUILT_IN_MALLOC
903 || DECL_FUNCTION_CODE (callee) == BUILT_IN_ALIGNED_ALLOC
904 || DECL_FUNCTION_CODE (callee) == BUILT_IN_CALLOC
905 || DECL_FUNCTION_CODE (callee) == BUILT_IN_FREE
906 || DECL_FUNCTION_CODE (callee) == BUILT_IN_VA_END
907 || ALLOCA_FUNCTION_CODE_P (DECL_FUNCTION_CODE (callee))
908 || DECL_FUNCTION_CODE (callee) == BUILT_IN_STACK_SAVE
909 || DECL_FUNCTION_CODE (callee) == BUILT_IN_STACK_RESTORE
910 || DECL_FUNCTION_CODE (callee) == BUILT_IN_ASSUME_ALIGNED))
911 continue;
912
913 if (callee != NULL_TREE
914 && (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee)
915 || DECL_IS_OPERATOR_DELETE_P (callee))
916 && gimple_call_from_new_or_delete (call))
917 continue;
918
919 /* Calls implicitly load from memory, their arguments
920 in addition may explicitly perform memory loads. */
921 mark_all_reaching_defs_necessary (call);
922 for (i = 0; i < gimple_call_num_args (call); ++i)
923 {
924 tree arg = gimple_call_arg (call, i);
925 if (TREE_CODE (arg) == SSA_NAME
926 || is_gimple_min_invariant (arg))
927 continue;
928 if (TREE_CODE (arg) == WITH_SIZE_EXPR)
929 arg = TREE_OPERAND (arg, 0);
930 if (!ref_may_be_aliased (arg))
931 mark_aliased_reaching_defs_necessary (call, arg);
932 }
933 }
934 else if (gimple_assign_single_p (stmt))
935 {
936 tree rhs;
937 /* If this is a load mark things necessary. */
938 rhs = gimple_assign_rhs1 (stmt);
939 if (TREE_CODE (rhs) != SSA_NAME
940 && !is_gimple_min_invariant (rhs)
941 && TREE_CODE (rhs) != CONSTRUCTOR)
942 {
943 if (!ref_may_be_aliased (rhs))
944 mark_aliased_reaching_defs_necessary (stmt, rhs);
945 else
946 mark_all_reaching_defs_necessary (stmt);
947 }
948 }
949 else if (greturn *return_stmt = dyn_cast <greturn *> (stmt))
950 {
951 tree rhs = gimple_return_retval (return_stmt);
952 /* A return statement may perform a load. */
953 if (rhs
954 && TREE_CODE (rhs) != SSA_NAME
955 && !is_gimple_min_invariant (rhs)
956 && TREE_CODE (rhs) != CONSTRUCTOR)
957 {
958 if (!ref_may_be_aliased (rhs))
959 mark_aliased_reaching_defs_necessary (stmt, rhs);
960 else
961 mark_all_reaching_defs_necessary (stmt);
962 }
963 }
964 else if (gasm *asm_stmt = dyn_cast <gasm *> (stmt))
965 {
966 unsigned i;
967 mark_all_reaching_defs_necessary (stmt);
968 /* Inputs may perform loads. */
969 for (i = 0; i < gimple_asm_ninputs (asm_stmt); ++i)
970 {
971 tree op = TREE_VALUE (gimple_asm_input_op (asm_stmt, i));
972 if (TREE_CODE (op) != SSA_NAME
973 && !is_gimple_min_invariant (op)
974 && TREE_CODE (op) != CONSTRUCTOR
975 && !ref_may_be_aliased (op))
976 mark_aliased_reaching_defs_necessary (stmt, op);
977 }
978 }
979 else if (gimple_code (stmt) == GIMPLE_TRANSACTION)
980 {
981 /* The beginning of a transaction is a memory barrier. */
982 /* ??? If we were really cool, we'd only be a barrier
983 for the memories touched within the transaction. */
984 mark_all_reaching_defs_necessary (stmt);
985 }
986 else
987 gcc_unreachable ();
988
989 /* If we over-used our alias oracle budget drop to simple
990 mode. The cost metric allows quadratic behavior
991 (number of uses times number of may-defs queries) up to
992 a constant maximal number of queries and after that falls back to
993 super-linear complexity. */
994 if (/* Constant but quadratic for small functions. */
995 total_chain > 128 * 128
996 /* Linear in the number of may-defs. */
997 && total_chain > 32 * longest_chain
998 /* Linear in the number of uses. */
999 && total_chain > nr_walks * 32)
1000 {
1001 chain_ovfl = true;
1002 if (visited)
1003 bitmap_clear (visited);
1004 }
1005 }
1006 }
1007 }
1008
1009 /* Remove dead PHI nodes from block BB. */
1010
1011 static bool
remove_dead_phis(basic_block bb)1012 remove_dead_phis (basic_block bb)
1013 {
1014 bool something_changed = false;
1015 gphi *phi;
1016 gphi_iterator gsi;
1017
1018 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi);)
1019 {
1020 stats.total_phis++;
1021 phi = gsi.phi ();
1022
1023 /* We do not track necessity of virtual PHI nodes. Instead do
1024 very simple dead PHI removal here. */
1025 if (virtual_operand_p (gimple_phi_result (phi)))
1026 {
1027 /* Virtual PHI nodes with one or identical arguments
1028 can be removed. */
1029 if (degenerate_phi_p (phi))
1030 {
1031 tree vdef = gimple_phi_result (phi);
1032 tree vuse = gimple_phi_arg_def (phi, 0);
1033
1034 use_operand_p use_p;
1035 imm_use_iterator iter;
1036 gimple *use_stmt;
1037 FOR_EACH_IMM_USE_STMT (use_stmt, iter, vdef)
1038 FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
1039 SET_USE (use_p, vuse);
1040 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef)
1041 && TREE_CODE (vuse) == SSA_NAME)
1042 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse) = 1;
1043 }
1044 else
1045 gimple_set_plf (phi, STMT_NECESSARY, true);
1046 }
1047
1048 if (!gimple_plf (phi, STMT_NECESSARY))
1049 {
1050 something_changed = true;
1051 if (dump_file && (dump_flags & TDF_DETAILS))
1052 {
1053 fprintf (dump_file, "Deleting : ");
1054 print_gimple_stmt (dump_file, phi, 0, TDF_SLIM);
1055 fprintf (dump_file, "\n");
1056 }
1057
1058 remove_phi_node (&gsi, true);
1059 stats.removed_phis++;
1060 continue;
1061 }
1062
1063 gsi_next (&gsi);
1064 }
1065 return something_changed;
1066 }
1067
1068
1069 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1070 containing I so that we don't have to look it up. */
1071
1072 static void
remove_dead_stmt(gimple_stmt_iterator * i,basic_block bb,vec<edge> & to_remove_edges)1073 remove_dead_stmt (gimple_stmt_iterator *i, basic_block bb,
1074 vec<edge> &to_remove_edges)
1075 {
1076 gimple *stmt = gsi_stmt (*i);
1077
1078 if (dump_file && (dump_flags & TDF_DETAILS))
1079 {
1080 fprintf (dump_file, "Deleting : ");
1081 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
1082 fprintf (dump_file, "\n");
1083 }
1084
1085 stats.removed++;
1086
1087 /* If we have determined that a conditional branch statement contributes
1088 nothing to the program, then we not only remove it, but we need to update
1089 the CFG. We can chose any of edges out of BB as long as we are sure to not
1090 close infinite loops. This is done by always choosing the edge closer to
1091 exit in inverted_post_order_compute order. */
1092 if (is_ctrl_stmt (stmt))
1093 {
1094 edge_iterator ei;
1095 edge e = NULL, e2;
1096
1097 /* See if there is only one non-abnormal edge. */
1098 if (single_succ_p (bb))
1099 e = single_succ_edge (bb);
1100 /* Otherwise chose one that is closer to bb with live statement in it.
1101 To be able to chose one, we compute inverted post order starting from
1102 all BBs with live statements. */
1103 if (!e)
1104 {
1105 if (!bb_postorder)
1106 {
1107 auto_vec<int, 20> postorder;
1108 inverted_post_order_compute (&postorder,
1109 &bb_contains_live_stmts);
1110 bb_postorder = XNEWVEC (int, last_basic_block_for_fn (cfun));
1111 for (unsigned int i = 0; i < postorder.length (); ++i)
1112 bb_postorder[postorder[i]] = i;
1113 }
1114 FOR_EACH_EDGE (e2, ei, bb->succs)
1115 if (!e || e2->dest == EXIT_BLOCK_PTR_FOR_FN (cfun)
1116 || bb_postorder [e->dest->index]
1117 < bb_postorder [e2->dest->index])
1118 e = e2;
1119 }
1120 gcc_assert (e);
1121 e->probability = profile_probability::always ();
1122
1123 /* The edge is no longer associated with a conditional, so it does
1124 not have TRUE/FALSE flags.
1125 We are also safe to drop EH/ABNORMAL flags and turn them into
1126 normal control flow, because we know that all the destinations (including
1127 those odd edges) are equivalent for program execution. */
1128 e->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_EH | EDGE_ABNORMAL);
1129
1130 /* The lone outgoing edge from BB will be a fallthru edge. */
1131 e->flags |= EDGE_FALLTHRU;
1132
1133 /* Remove the remaining outgoing edges. */
1134 FOR_EACH_EDGE (e2, ei, bb->succs)
1135 if (e != e2)
1136 {
1137 /* If we made a BB unconditionally exit a loop or removed
1138 an entry into an irreducible region, then this transform
1139 alters the set of BBs in the loop. Schedule a fixup. */
1140 if (loop_exit_edge_p (bb->loop_father, e)
1141 || (e2->dest->flags & BB_IRREDUCIBLE_LOOP))
1142 loops_state_set (LOOPS_NEED_FIXUP);
1143 to_remove_edges.safe_push (e2);
1144 }
1145 }
1146
1147 /* If this is a store into a variable that is being optimized away,
1148 add a debug bind stmt if possible. */
1149 if (MAY_HAVE_DEBUG_BIND_STMTS
1150 && gimple_assign_single_p (stmt)
1151 && is_gimple_val (gimple_assign_rhs1 (stmt)))
1152 {
1153 tree lhs = gimple_assign_lhs (stmt);
1154 if ((VAR_P (lhs) || TREE_CODE (lhs) == PARM_DECL)
1155 && !DECL_IGNORED_P (lhs)
1156 && is_gimple_reg_type (TREE_TYPE (lhs))
1157 && !is_global_var (lhs)
1158 && !DECL_HAS_VALUE_EXPR_P (lhs))
1159 {
1160 tree rhs = gimple_assign_rhs1 (stmt);
1161 gdebug *note
1162 = gimple_build_debug_bind (lhs, unshare_expr (rhs), stmt);
1163 gsi_insert_after (i, note, GSI_SAME_STMT);
1164 }
1165 }
1166
1167 unlink_stmt_vdef (stmt);
1168 gsi_remove (i, true);
1169 release_defs (stmt);
1170 }
1171
1172 /* Helper for maybe_optimize_arith_overflow. Find in *TP if there are any
1173 uses of data (SSA_NAME) other than REALPART_EXPR referencing it. */
1174
1175 static tree
find_non_realpart_uses(tree * tp,int * walk_subtrees,void * data)1176 find_non_realpart_uses (tree *tp, int *walk_subtrees, void *data)
1177 {
1178 if (TYPE_P (*tp) || TREE_CODE (*tp) == REALPART_EXPR)
1179 *walk_subtrees = 0;
1180 if (*tp == (tree) data)
1181 return *tp;
1182 return NULL_TREE;
1183 }
1184
1185 /* If the IMAGPART_EXPR of the {ADD,SUB,MUL}_OVERFLOW result is never used,
1186 but REALPART_EXPR is, optimize the {ADD,SUB,MUL}_OVERFLOW internal calls
1187 into plain unsigned {PLUS,MINUS,MULT}_EXPR, and if needed reset debug
1188 uses. */
1189
1190 static void
maybe_optimize_arith_overflow(gimple_stmt_iterator * gsi,enum tree_code subcode)1191 maybe_optimize_arith_overflow (gimple_stmt_iterator *gsi,
1192 enum tree_code subcode)
1193 {
1194 gimple *stmt = gsi_stmt (*gsi);
1195 tree lhs = gimple_call_lhs (stmt);
1196
1197 if (lhs == NULL || TREE_CODE (lhs) != SSA_NAME)
1198 return;
1199
1200 imm_use_iterator imm_iter;
1201 use_operand_p use_p;
1202 bool has_debug_uses = false;
1203 bool has_realpart_uses = false;
1204 bool has_other_uses = false;
1205 FOR_EACH_IMM_USE_FAST (use_p, imm_iter, lhs)
1206 {
1207 gimple *use_stmt = USE_STMT (use_p);
1208 if (is_gimple_debug (use_stmt))
1209 has_debug_uses = true;
1210 else if (is_gimple_assign (use_stmt)
1211 && gimple_assign_rhs_code (use_stmt) == REALPART_EXPR
1212 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == lhs)
1213 has_realpart_uses = true;
1214 else
1215 {
1216 has_other_uses = true;
1217 break;
1218 }
1219 }
1220
1221 if (!has_realpart_uses || has_other_uses)
1222 return;
1223
1224 tree arg0 = gimple_call_arg (stmt, 0);
1225 tree arg1 = gimple_call_arg (stmt, 1);
1226 location_t loc = gimple_location (stmt);
1227 tree type = TREE_TYPE (TREE_TYPE (lhs));
1228 tree utype = type;
1229 if (!TYPE_UNSIGNED (type))
1230 utype = build_nonstandard_integer_type (TYPE_PRECISION (type), 1);
1231 tree result = fold_build2_loc (loc, subcode, utype,
1232 fold_convert_loc (loc, utype, arg0),
1233 fold_convert_loc (loc, utype, arg1));
1234 result = fold_convert_loc (loc, type, result);
1235
1236 if (has_debug_uses)
1237 {
1238 gimple *use_stmt;
1239 FOR_EACH_IMM_USE_STMT (use_stmt, imm_iter, lhs)
1240 {
1241 if (!gimple_debug_bind_p (use_stmt))
1242 continue;
1243 tree v = gimple_debug_bind_get_value (use_stmt);
1244 if (walk_tree (&v, find_non_realpart_uses, lhs, NULL))
1245 {
1246 gimple_debug_bind_reset_value (use_stmt);
1247 update_stmt (use_stmt);
1248 }
1249 }
1250 }
1251
1252 if (TREE_CODE (result) == INTEGER_CST && TREE_OVERFLOW (result))
1253 result = drop_tree_overflow (result);
1254 tree overflow = build_zero_cst (type);
1255 tree ctype = build_complex_type (type);
1256 if (TREE_CODE (result) == INTEGER_CST)
1257 result = build_complex (ctype, result, overflow);
1258 else
1259 result = build2_loc (gimple_location (stmt), COMPLEX_EXPR,
1260 ctype, result, overflow);
1261
1262 if (dump_file && (dump_flags & TDF_DETAILS))
1263 {
1264 fprintf (dump_file, "Transforming call: ");
1265 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
1266 fprintf (dump_file, "because the overflow result is never used into: ");
1267 print_generic_stmt (dump_file, result, TDF_SLIM);
1268 fprintf (dump_file, "\n");
1269 }
1270
1271 gimplify_and_update_call_from_tree (gsi, result);
1272 }
1273
1274 /* Returns whether the control parents of BB are preserved. */
1275
1276 static bool
control_parents_preserved_p(basic_block bb)1277 control_parents_preserved_p (basic_block bb)
1278 {
1279 /* If we marked the control parents from BB they are preserved. */
1280 if (bitmap_bit_p (visited_control_parents, bb->index))
1281 return true;
1282
1283 /* But they can also end up being marked from elsewhere. */
1284 bitmap_iterator bi;
1285 unsigned edge_number;
1286 EXECUTE_IF_SET_IN_BITMAP (cd->get_edges_dependent_on (bb->index),
1287 0, edge_number, bi)
1288 {
1289 basic_block cd_bb = cd->get_edge_src (edge_number);
1290 if (cd_bb != bb
1291 && !bitmap_bit_p (last_stmt_necessary, cd_bb->index))
1292 return false;
1293 }
1294 /* And cache the result. */
1295 bitmap_set_bit (visited_control_parents, bb->index);
1296 return true;
1297 }
1298
1299 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1300 contributes nothing to the program, and can be deleted. */
1301
1302 static bool
eliminate_unnecessary_stmts(bool aggressive)1303 eliminate_unnecessary_stmts (bool aggressive)
1304 {
1305 bool something_changed = false;
1306 basic_block bb;
1307 gimple_stmt_iterator gsi, psi;
1308 gimple *stmt;
1309 tree call;
1310 auto_vec<edge> to_remove_edges;
1311
1312 if (dump_file && (dump_flags & TDF_DETAILS))
1313 fprintf (dump_file, "\nEliminating unnecessary statements:\n");
1314
1315 clear_special_calls ();
1316
1317 /* Walking basic blocks and statements in reverse order avoids
1318 releasing SSA names before any other DEFs that refer to them are
1319 released. This helps avoid loss of debug information, as we get
1320 a chance to propagate all RHSs of removed SSAs into debug uses,
1321 rather than only the latest ones. E.g., consider:
1322
1323 x_3 = y_1 + z_2;
1324 a_5 = x_3 - b_4;
1325 # DEBUG a => a_5
1326
1327 If we were to release x_3 before a_5, when we reached a_5 and
1328 tried to substitute it into the debug stmt, we'd see x_3 there,
1329 but x_3's DEF, type, etc would have already been disconnected.
1330 By going backwards, the debug stmt first changes to:
1331
1332 # DEBUG a => x_3 - b_4
1333
1334 and then to:
1335
1336 # DEBUG a => y_1 + z_2 - b_4
1337
1338 as desired. */
1339 gcc_assert (dom_info_available_p (CDI_DOMINATORS));
1340 auto_vec<basic_block> h;
1341 h = get_all_dominated_blocks (CDI_DOMINATORS,
1342 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
1343
1344 while (h.length ())
1345 {
1346 bb = h.pop ();
1347
1348 /* Remove dead statements. */
1349 auto_bitmap debug_seen;
1350 for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi = psi)
1351 {
1352 stmt = gsi_stmt (gsi);
1353
1354 psi = gsi;
1355 gsi_prev (&psi);
1356
1357 stats.total++;
1358
1359 /* We can mark a call to free as not necessary if the
1360 defining statement of its argument is not necessary
1361 (and thus is getting removed). */
1362 if (gimple_plf (stmt, STMT_NECESSARY)
1363 && (gimple_call_builtin_p (stmt, BUILT_IN_FREE)
1364 || (is_gimple_call (stmt)
1365 && gimple_call_from_new_or_delete (as_a <gcall *> (stmt))
1366 && gimple_call_operator_delete_p (as_a <gcall *> (stmt)))))
1367 {
1368 tree ptr = gimple_call_arg (stmt, 0);
1369 if (TREE_CODE (ptr) == SSA_NAME)
1370 {
1371 gimple *def_stmt = SSA_NAME_DEF_STMT (ptr);
1372 if (!gimple_nop_p (def_stmt)
1373 && !gimple_plf (def_stmt, STMT_NECESSARY))
1374 gimple_set_plf (stmt, STMT_NECESSARY, false);
1375 }
1376 }
1377
1378 /* If GSI is not necessary then remove it. */
1379 if (!gimple_plf (stmt, STMT_NECESSARY))
1380 {
1381 /* Keep clobbers that we can keep live live. */
1382 if (gimple_clobber_p (stmt))
1383 {
1384 ssa_op_iter iter;
1385 use_operand_p use_p;
1386 bool dead = false;
1387 FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE)
1388 {
1389 tree name = USE_FROM_PTR (use_p);
1390 if (!SSA_NAME_IS_DEFAULT_DEF (name)
1391 && !bitmap_bit_p (processed, SSA_NAME_VERSION (name)))
1392 {
1393 dead = true;
1394 break;
1395 }
1396 }
1397 if (!dead
1398 /* When doing CD-DCE we have to ensure all controls
1399 of the stmt are still live. */
1400 && (!aggressive || control_parents_preserved_p (bb)))
1401 {
1402 bitmap_clear (debug_seen);
1403 continue;
1404 }
1405 }
1406 if (!is_gimple_debug (stmt))
1407 something_changed = true;
1408 remove_dead_stmt (&gsi, bb, to_remove_edges);
1409 continue;
1410 }
1411 else if (is_gimple_call (stmt))
1412 {
1413 tree name = gimple_call_lhs (stmt);
1414
1415 notice_special_calls (as_a <gcall *> (stmt));
1416
1417 /* When LHS of var = call (); is dead, simplify it into
1418 call (); saving one operand. */
1419 if (name
1420 && TREE_CODE (name) == SSA_NAME
1421 && !bitmap_bit_p (processed, SSA_NAME_VERSION (name))
1422 /* Avoid doing so for allocation calls which we
1423 did not mark as necessary, it will confuse the
1424 special logic we apply to malloc/free pair removal. */
1425 && (!(call = gimple_call_fndecl (stmt))
1426 || ((DECL_BUILT_IN_CLASS (call) != BUILT_IN_NORMAL
1427 || (DECL_FUNCTION_CODE (call) != BUILT_IN_ALIGNED_ALLOC
1428 && DECL_FUNCTION_CODE (call) != BUILT_IN_MALLOC
1429 && DECL_FUNCTION_CODE (call) != BUILT_IN_CALLOC
1430 && !ALLOCA_FUNCTION_CODE_P
1431 (DECL_FUNCTION_CODE (call))))
1432 && !DECL_IS_REPLACEABLE_OPERATOR_NEW_P (call))))
1433 {
1434 something_changed = true;
1435 if (dump_file && (dump_flags & TDF_DETAILS))
1436 {
1437 fprintf (dump_file, "Deleting LHS of call: ");
1438 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
1439 fprintf (dump_file, "\n");
1440 }
1441
1442 gimple_call_set_lhs (stmt, NULL_TREE);
1443 maybe_clean_or_replace_eh_stmt (stmt, stmt);
1444 update_stmt (stmt);
1445 release_ssa_name (name);
1446
1447 /* GOMP_SIMD_LANE (unless three argument) or ASAN_POISON
1448 without lhs is not needed. */
1449 if (gimple_call_internal_p (stmt))
1450 switch (gimple_call_internal_fn (stmt))
1451 {
1452 case IFN_GOMP_SIMD_LANE:
1453 if (gimple_call_num_args (stmt) >= 3
1454 && !integer_nonzerop (gimple_call_arg (stmt, 2)))
1455 break;
1456 /* FALLTHRU */
1457 case IFN_ASAN_POISON:
1458 remove_dead_stmt (&gsi, bb, to_remove_edges);
1459 break;
1460 default:
1461 break;
1462 }
1463 }
1464 else if (gimple_call_internal_p (stmt))
1465 switch (gimple_call_internal_fn (stmt))
1466 {
1467 case IFN_ADD_OVERFLOW:
1468 maybe_optimize_arith_overflow (&gsi, PLUS_EXPR);
1469 break;
1470 case IFN_SUB_OVERFLOW:
1471 maybe_optimize_arith_overflow (&gsi, MINUS_EXPR);
1472 break;
1473 case IFN_MUL_OVERFLOW:
1474 maybe_optimize_arith_overflow (&gsi, MULT_EXPR);
1475 break;
1476 default:
1477 break;
1478 }
1479 }
1480 else if (gimple_debug_bind_p (stmt))
1481 {
1482 /* We are only keeping the last debug-bind of a
1483 non-DEBUG_EXPR_DECL variable in a series of
1484 debug-bind stmts. */
1485 tree var = gimple_debug_bind_get_var (stmt);
1486 if (TREE_CODE (var) != DEBUG_EXPR_DECL
1487 && !bitmap_set_bit (debug_seen, DECL_UID (var)))
1488 remove_dead_stmt (&gsi, bb, to_remove_edges);
1489 continue;
1490 }
1491 bitmap_clear (debug_seen);
1492 }
1493
1494 /* Remove dead PHI nodes. */
1495 something_changed |= remove_dead_phis (bb);
1496 }
1497
1498
1499 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1500 rendered some PHI nodes unreachable while they are still in use.
1501 Mark them for renaming. */
1502 if (!to_remove_edges.is_empty ())
1503 {
1504 basic_block prev_bb;
1505
1506 /* Remove edges. We've delayed this to not get bogus debug stmts
1507 during PHI node removal. */
1508 for (unsigned i = 0; i < to_remove_edges.length (); ++i)
1509 remove_edge (to_remove_edges[i]);
1510 cfg_altered = true;
1511
1512 find_unreachable_blocks ();
1513
1514 /* Delete all unreachable basic blocks in reverse dominator order. */
1515 for (bb = EXIT_BLOCK_PTR_FOR_FN (cfun)->prev_bb;
1516 bb != ENTRY_BLOCK_PTR_FOR_FN (cfun); bb = prev_bb)
1517 {
1518 prev_bb = bb->prev_bb;
1519
1520 if (!bitmap_bit_p (bb_contains_live_stmts, bb->index)
1521 || !(bb->flags & BB_REACHABLE))
1522 {
1523 for (gphi_iterator gsi = gsi_start_phis (bb); !gsi_end_p (gsi);
1524 gsi_next (&gsi))
1525 if (virtual_operand_p (gimple_phi_result (gsi.phi ())))
1526 {
1527 bool found = false;
1528 imm_use_iterator iter;
1529
1530 FOR_EACH_IMM_USE_STMT (stmt, iter,
1531 gimple_phi_result (gsi.phi ()))
1532 {
1533 if (!(gimple_bb (stmt)->flags & BB_REACHABLE))
1534 continue;
1535 if (gimple_code (stmt) == GIMPLE_PHI
1536 || gimple_plf (stmt, STMT_NECESSARY))
1537 {
1538 found = true;
1539 break;
1540 }
1541 }
1542 if (found)
1543 mark_virtual_phi_result_for_renaming (gsi.phi ());
1544 }
1545
1546 if (!(bb->flags & BB_REACHABLE))
1547 {
1548 /* Speed up the removal of blocks that don't
1549 dominate others. Walking backwards, this should
1550 be the common case. ??? Do we need to recompute
1551 dominators because of cfg_altered? */
1552 if (!first_dom_son (CDI_DOMINATORS, bb))
1553 delete_basic_block (bb);
1554 else
1555 {
1556 h = get_all_dominated_blocks (CDI_DOMINATORS, bb);
1557
1558 while (h.length ())
1559 {
1560 bb = h.pop ();
1561 prev_bb = bb->prev_bb;
1562 /* Rearrangements to the CFG may have failed
1563 to update the dominators tree, so that
1564 formerly-dominated blocks are now
1565 otherwise reachable. */
1566 if (!!(bb->flags & BB_REACHABLE))
1567 continue;
1568 delete_basic_block (bb);
1569 }
1570
1571 h.release ();
1572 }
1573 }
1574 }
1575 }
1576 }
1577
1578 if (bb_postorder)
1579 free (bb_postorder);
1580 bb_postorder = NULL;
1581
1582 return something_changed;
1583 }
1584
1585
1586 /* Print out removed statement statistics. */
1587
1588 static void
print_stats(void)1589 print_stats (void)
1590 {
1591 float percg;
1592
1593 percg = ((float) stats.removed / (float) stats.total) * 100;
1594 fprintf (dump_file, "Removed %d of %d statements (%d%%)\n",
1595 stats.removed, stats.total, (int) percg);
1596
1597 if (stats.total_phis == 0)
1598 percg = 0;
1599 else
1600 percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100;
1601
1602 fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n",
1603 stats.removed_phis, stats.total_phis, (int) percg);
1604 }
1605
1606 /* Initialization for this pass. Set up the used data structures. */
1607
1608 static void
tree_dce_init(bool aggressive)1609 tree_dce_init (bool aggressive)
1610 {
1611 memset ((void *) &stats, 0, sizeof (stats));
1612
1613 if (aggressive)
1614 {
1615 last_stmt_necessary = sbitmap_alloc (last_basic_block_for_fn (cfun));
1616 bitmap_clear (last_stmt_necessary);
1617 bb_contains_live_stmts = sbitmap_alloc (last_basic_block_for_fn (cfun));
1618 bitmap_clear (bb_contains_live_stmts);
1619 }
1620
1621 processed = sbitmap_alloc (num_ssa_names + 1);
1622 bitmap_clear (processed);
1623
1624 worklist.create (64);
1625 cfg_altered = false;
1626 }
1627
1628 /* Cleanup after this pass. */
1629
1630 static void
tree_dce_done(bool aggressive)1631 tree_dce_done (bool aggressive)
1632 {
1633 if (aggressive)
1634 {
1635 delete cd;
1636 sbitmap_free (visited_control_parents);
1637 sbitmap_free (last_stmt_necessary);
1638 sbitmap_free (bb_contains_live_stmts);
1639 bb_contains_live_stmts = NULL;
1640 }
1641
1642 sbitmap_free (processed);
1643
1644 worklist.release ();
1645 }
1646
1647 /* Sort PHI argument values for make_forwarders_with_degenerate_phis. */
1648
1649 static int
sort_phi_args(const void * a_,const void * b_)1650 sort_phi_args (const void *a_, const void *b_)
1651 {
1652 auto *a = (const std::pair<edge, hashval_t> *) a_;
1653 auto *b = (const std::pair<edge, hashval_t> *) b_;
1654 hashval_t ha = a->second;
1655 hashval_t hb = b->second;
1656 if (ha < hb)
1657 return -1;
1658 else if (ha > hb)
1659 return 1;
1660 else if (a->first->dest_idx < b->first->dest_idx)
1661 return -1;
1662 else if (a->first->dest_idx > b->first->dest_idx)
1663 return 1;
1664 else
1665 return 0;
1666 }
1667
1668 /* Look for a non-virtual PHIs and make a forwarder block when all PHIs
1669 have the same argument on a set of edges. This is to not consider
1670 control dependences of individual edges for same values but only for
1671 the common set. */
1672
1673 static unsigned
make_forwarders_with_degenerate_phis(function * fn)1674 make_forwarders_with_degenerate_phis (function *fn)
1675 {
1676 unsigned todo = 0;
1677
1678 basic_block bb;
1679 FOR_EACH_BB_FN (bb, fn)
1680 {
1681 /* Only PHIs with three or more arguments have opportunities. */
1682 if (EDGE_COUNT (bb->preds) < 3)
1683 continue;
1684 /* Do not touch loop headers or blocks with abnormal predecessors.
1685 ??? This is to avoid creating valid loops here, see PR103458.
1686 We might want to improve things to either explicitely add those
1687 loops or at least consider blocks with no backedges. */
1688 if (bb->loop_father->header == bb
1689 || bb_has_abnormal_pred (bb))
1690 continue;
1691
1692 /* Take one PHI node as template to look for identical
1693 arguments. Build a vector of candidates forming sets
1694 of argument edges with equal values. Note optimality
1695 depends on the particular choice of the template PHI
1696 since equal arguments are unordered leaving other PHIs
1697 with more than one set of equal arguments within this
1698 argument range unsorted. We'd have to break ties by
1699 looking at other PHI nodes. */
1700 gphi_iterator gsi = gsi_start_nonvirtual_phis (bb);
1701 if (gsi_end_p (gsi))
1702 continue;
1703 gphi *phi = gsi.phi ();
1704 auto_vec<std::pair<edge, hashval_t>, 8> args;
1705 bool need_resort = false;
1706 for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i)
1707 {
1708 edge e = gimple_phi_arg_edge (phi, i);
1709 /* Skip abnormal edges since we cannot redirect them. */
1710 if (e->flags & EDGE_ABNORMAL)
1711 continue;
1712 /* Skip loop exit edges when we are in loop-closed SSA form
1713 since the forwarder we'd create does not have a PHI node. */
1714 if (loops_state_satisfies_p (LOOP_CLOSED_SSA)
1715 && loop_exit_edge_p (e->src->loop_father, e))
1716 continue;
1717
1718 tree arg = gimple_phi_arg_def (phi, i);
1719 if (!CONSTANT_CLASS_P (arg) && TREE_CODE (arg) != SSA_NAME)
1720 need_resort = true;
1721 args.safe_push (std::make_pair (e, iterative_hash_expr (arg, 0)));
1722 }
1723 if (args.length () < 2)
1724 continue;
1725 args.qsort (sort_phi_args);
1726 /* The above sorting can be different between -g and -g0, as e.g. decls
1727 can have different uids (-g could have bigger gaps in between them).
1728 So, only use that to determine which args are equal, then change
1729 second from hash value to smallest dest_idx of the edges which have
1730 equal argument and sort again. If all the phi arguments are
1731 constants or SSA_NAME, there is no need for the second sort, the hash
1732 values are stable in that case. */
1733 hashval_t hash = args[0].second;
1734 args[0].second = args[0].first->dest_idx;
1735 bool any_equal = false;
1736 for (unsigned i = 1; i < args.length (); ++i)
1737 if (hash == args[i].second
1738 && operand_equal_p (PHI_ARG_DEF_FROM_EDGE (phi, args[i - 1].first),
1739 PHI_ARG_DEF_FROM_EDGE (phi, args[i].first)))
1740 {
1741 args[i].second = args[i - 1].second;
1742 any_equal = true;
1743 }
1744 else
1745 {
1746 hash = args[i].second;
1747 args[i].second = args[i].first->dest_idx;
1748 }
1749 if (!any_equal)
1750 continue;
1751 if (need_resort)
1752 args.qsort (sort_phi_args);
1753
1754 /* From the candidates vector now verify true candidates for
1755 forwarders and create them. */
1756 gphi *vphi = get_virtual_phi (bb);
1757 unsigned start = 0;
1758 while (start < args.length () - 1)
1759 {
1760 unsigned i;
1761 for (i = start + 1; i < args.length (); ++i)
1762 if (args[start].second != args[i].second)
1763 break;
1764 /* args[start]..args[i-1] are equal. */
1765 if (start != i - 1)
1766 {
1767 /* Check all PHI nodes for argument equality. */
1768 bool equal = true;
1769 gphi_iterator gsi2 = gsi;
1770 gsi_next (&gsi2);
1771 for (; !gsi_end_p (gsi2); gsi_next (&gsi2))
1772 {
1773 gphi *phi2 = gsi2.phi ();
1774 if (virtual_operand_p (gimple_phi_result (phi2)))
1775 continue;
1776 tree start_arg
1777 = PHI_ARG_DEF_FROM_EDGE (phi2, args[start].first);
1778 for (unsigned j = start + 1; j < i; ++j)
1779 {
1780 if (!operand_equal_p (start_arg,
1781 PHI_ARG_DEF_FROM_EDGE
1782 (phi2, args[j].first)))
1783 {
1784 /* Another PHI might have a shorter set of
1785 equivalent args. Go for that. */
1786 i = j;
1787 if (j == start + 1)
1788 equal = false;
1789 break;
1790 }
1791 }
1792 if (!equal)
1793 break;
1794 }
1795 if (equal)
1796 {
1797 /* If we are asked to forward all edges the block
1798 has all degenerate PHIs. Do nothing in that case. */
1799 if (start == 0
1800 && i == args.length ()
1801 && args.length () == gimple_phi_num_args (phi))
1802 break;
1803 /* Instead of using make_forwarder_block we are
1804 rolling our own variant knowing that the forwarder
1805 does not need PHI nodes apart from eventually
1806 a virtual one. */
1807 auto_vec<tree, 8> vphi_args;
1808 if (vphi)
1809 {
1810 vphi_args.reserve_exact (i - start);
1811 for (unsigned j = start; j < i; ++j)
1812 vphi_args.quick_push
1813 (PHI_ARG_DEF_FROM_EDGE (vphi, args[j].first));
1814 }
1815 free_dominance_info (fn, CDI_DOMINATORS);
1816 basic_block forwarder = split_edge (args[start].first);
1817 for (unsigned j = start + 1; j < i; ++j)
1818 {
1819 edge e = args[j].first;
1820 redirect_edge_and_branch_force (e, forwarder);
1821 redirect_edge_var_map_clear (e);
1822 }
1823 if (vphi)
1824 {
1825 tree def = copy_ssa_name (vphi_args[0]);
1826 gphi *vphi_copy = create_phi_node (def, forwarder);
1827 for (unsigned j = start; j < i; ++j)
1828 add_phi_arg (vphi_copy, vphi_args[j - start],
1829 args[j].first, UNKNOWN_LOCATION);
1830 SET_PHI_ARG_DEF
1831 (vphi, single_succ_edge (forwarder)->dest_idx, def);
1832 }
1833 todo |= TODO_cleanup_cfg;
1834 }
1835 }
1836 /* Continue searching for more opportunities. */
1837 start = i;
1838 }
1839 }
1840 return todo;
1841 }
1842
1843 /* Main routine to eliminate dead code.
1844
1845 AGGRESSIVE controls the aggressiveness of the algorithm.
1846 In conservative mode, we ignore control dependence and simply declare
1847 all but the most trivially dead branches necessary. This mode is fast.
1848 In aggressive mode, control dependences are taken into account, which
1849 results in more dead code elimination, but at the cost of some time.
1850
1851 FIXME: Aggressive mode before PRE doesn't work currently because
1852 the dominance info is not invalidated after DCE1. This is
1853 not an issue right now because we only run aggressive DCE
1854 as the last tree SSA pass, but keep this in mind when you
1855 start experimenting with pass ordering. */
1856
1857 static unsigned int
perform_tree_ssa_dce(bool aggressive)1858 perform_tree_ssa_dce (bool aggressive)
1859 {
1860 bool something_changed = 0;
1861 unsigned todo = 0;
1862
1863 /* Preheaders are needed for SCEV to work.
1864 Simple lateches and recorded exits improve chances that loop will
1865 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1866 bool in_loop_pipeline = scev_initialized_p ();
1867 if (aggressive && ! in_loop_pipeline)
1868 {
1869 scev_initialize ();
1870 loop_optimizer_init (LOOPS_NORMAL
1871 | LOOPS_HAVE_RECORDED_EXITS);
1872 }
1873
1874 if (aggressive)
1875 todo |= make_forwarders_with_degenerate_phis (cfun);
1876
1877 calculate_dominance_info (CDI_DOMINATORS);
1878
1879 tree_dce_init (aggressive);
1880
1881 if (aggressive)
1882 {
1883 /* Compute control dependence. */
1884 calculate_dominance_info (CDI_POST_DOMINATORS);
1885 cd = new control_dependences ();
1886
1887 visited_control_parents =
1888 sbitmap_alloc (last_basic_block_for_fn (cfun));
1889 bitmap_clear (visited_control_parents);
1890
1891 mark_dfs_back_edges ();
1892 }
1893
1894 find_obviously_necessary_stmts (aggressive);
1895
1896 if (aggressive && ! in_loop_pipeline)
1897 {
1898 loop_optimizer_finalize ();
1899 scev_finalize ();
1900 }
1901
1902 longest_chain = 0;
1903 total_chain = 0;
1904 nr_walks = 0;
1905 chain_ovfl = false;
1906 visited = BITMAP_ALLOC (NULL);
1907 propagate_necessity (aggressive);
1908 BITMAP_FREE (visited);
1909
1910 something_changed |= eliminate_unnecessary_stmts (aggressive);
1911 something_changed |= cfg_altered;
1912
1913 /* We do not update postdominators, so free them unconditionally. */
1914 free_dominance_info (CDI_POST_DOMINATORS);
1915
1916 /* If we removed paths in the CFG, then we need to update
1917 dominators as well. I haven't investigated the possibility
1918 of incrementally updating dominators. */
1919 if (cfg_altered)
1920 free_dominance_info (CDI_DOMINATORS);
1921
1922 statistics_counter_event (cfun, "Statements deleted", stats.removed);
1923 statistics_counter_event (cfun, "PHI nodes deleted", stats.removed_phis);
1924
1925 /* Debugging dumps. */
1926 if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS)))
1927 print_stats ();
1928
1929 tree_dce_done (aggressive);
1930
1931 if (something_changed)
1932 {
1933 free_numbers_of_iterations_estimates (cfun);
1934 if (in_loop_pipeline)
1935 scev_reset ();
1936 todo |= TODO_update_ssa | TODO_cleanup_cfg;
1937 }
1938 return todo;
1939 }
1940
1941 /* Pass entry points. */
1942 static unsigned int
tree_ssa_dce(void)1943 tree_ssa_dce (void)
1944 {
1945 return perform_tree_ssa_dce (/*aggressive=*/false);
1946 }
1947
1948 static unsigned int
tree_ssa_cd_dce(void)1949 tree_ssa_cd_dce (void)
1950 {
1951 return perform_tree_ssa_dce (/*aggressive=*/optimize >= 2);
1952 }
1953
1954 namespace {
1955
1956 const pass_data pass_data_dce =
1957 {
1958 GIMPLE_PASS, /* type */
1959 "dce", /* name */
1960 OPTGROUP_NONE, /* optinfo_flags */
1961 TV_TREE_DCE, /* tv_id */
1962 ( PROP_cfg | PROP_ssa ), /* properties_required */
1963 0, /* properties_provided */
1964 0, /* properties_destroyed */
1965 0, /* todo_flags_start */
1966 0, /* todo_flags_finish */
1967 };
1968
1969 class pass_dce : public gimple_opt_pass
1970 {
1971 public:
pass_dce(gcc::context * ctxt)1972 pass_dce (gcc::context *ctxt)
1973 : gimple_opt_pass (pass_data_dce, ctxt)
1974 {}
1975
1976 /* opt_pass methods: */
clone()1977 opt_pass * clone () { return new pass_dce (m_ctxt); }
gate(function *)1978 virtual bool gate (function *) { return flag_tree_dce != 0; }
execute(function *)1979 virtual unsigned int execute (function *) { return tree_ssa_dce (); }
1980
1981 }; // class pass_dce
1982
1983 } // anon namespace
1984
1985 gimple_opt_pass *
make_pass_dce(gcc::context * ctxt)1986 make_pass_dce (gcc::context *ctxt)
1987 {
1988 return new pass_dce (ctxt);
1989 }
1990
1991 namespace {
1992
1993 const pass_data pass_data_cd_dce =
1994 {
1995 GIMPLE_PASS, /* type */
1996 "cddce", /* name */
1997 OPTGROUP_NONE, /* optinfo_flags */
1998 TV_TREE_CD_DCE, /* tv_id */
1999 ( PROP_cfg | PROP_ssa ), /* properties_required */
2000 0, /* properties_provided */
2001 0, /* properties_destroyed */
2002 0, /* todo_flags_start */
2003 0, /* todo_flags_finish */
2004 };
2005
2006 class pass_cd_dce : public gimple_opt_pass
2007 {
2008 public:
pass_cd_dce(gcc::context * ctxt)2009 pass_cd_dce (gcc::context *ctxt)
2010 : gimple_opt_pass (pass_data_cd_dce, ctxt), update_address_taken_p (false)
2011 {}
2012
2013 /* opt_pass methods: */
clone()2014 opt_pass * clone () { return new pass_cd_dce (m_ctxt); }
set_pass_param(unsigned n,bool param)2015 void set_pass_param (unsigned n, bool param)
2016 {
2017 gcc_assert (n == 0);
2018 update_address_taken_p = param;
2019 }
gate(function *)2020 virtual bool gate (function *) { return flag_tree_dce != 0; }
execute(function *)2021 virtual unsigned int execute (function *)
2022 {
2023 return (tree_ssa_cd_dce ()
2024 | (update_address_taken_p ? TODO_update_address_taken : 0));
2025 }
2026
2027 private:
2028 bool update_address_taken_p;
2029 }; // class pass_cd_dce
2030
2031 } // anon namespace
2032
2033 gimple_opt_pass *
make_pass_cd_dce(gcc::context * ctxt)2034 make_pass_cd_dce (gcc::context *ctxt)
2035 {
2036 return new pass_cd_dce (ctxt);
2037 }
2038
2039
2040 /* A cheap DCE interface. WORKLIST is a list of possibly dead stmts and
2041 is consumed by this function. The function has linear complexity in
2042 the number of dead stmts with a constant factor like the average SSA
2043 use operands number. */
2044
2045 void
simple_dce_from_worklist(bitmap worklist)2046 simple_dce_from_worklist (bitmap worklist)
2047 {
2048 while (! bitmap_empty_p (worklist))
2049 {
2050 /* Pop item. */
2051 unsigned i = bitmap_first_set_bit (worklist);
2052 bitmap_clear_bit (worklist, i);
2053
2054 tree def = ssa_name (i);
2055 /* Removed by somebody else or still in use. */
2056 if (! def || ! has_zero_uses (def))
2057 continue;
2058
2059 gimple *t = SSA_NAME_DEF_STMT (def);
2060 if (gimple_has_side_effects (t))
2061 continue;
2062
2063 /* The defining statement needs to be defining only this name.
2064 ASM is the only statement that can define more than one
2065 name. */
2066 if (is_a<gasm *>(t)
2067 && !single_ssa_def_operand (t, SSA_OP_ALL_DEFS))
2068 continue;
2069
2070 /* Don't remove statements that are needed for non-call
2071 eh to work. */
2072 if (stmt_unremovable_because_of_non_call_eh_p (cfun, t))
2073 continue;
2074
2075 /* Add uses to the worklist. */
2076 ssa_op_iter iter;
2077 use_operand_p use_p;
2078 FOR_EACH_PHI_OR_STMT_USE (use_p, t, iter, SSA_OP_USE)
2079 {
2080 tree use = USE_FROM_PTR (use_p);
2081 if (TREE_CODE (use) == SSA_NAME
2082 && ! SSA_NAME_IS_DEFAULT_DEF (use))
2083 bitmap_set_bit (worklist, SSA_NAME_VERSION (use));
2084 }
2085
2086 /* Remove stmt. */
2087 if (dump_file && (dump_flags & TDF_DETAILS))
2088 {
2089 fprintf (dump_file, "Removing dead stmt:");
2090 print_gimple_stmt (dump_file, t, 0);
2091 }
2092 gimple_stmt_iterator gsi = gsi_for_stmt (t);
2093 if (gimple_code (t) == GIMPLE_PHI)
2094 remove_phi_node (&gsi, true);
2095 else
2096 {
2097 unlink_stmt_vdef (t);
2098 gsi_remove (&gsi, true);
2099 release_defs (t);
2100 }
2101 }
2102 }
2103