Merge branch 'vendor/GCC47'
[dragonfly.git] / contrib / gcc-4.7 / gcc / tree-ssa-dce.c
CommitLineData
e4b17023
JM
1/* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
3 Free Software Foundation, Inc.
4 Contributed by Ben Elliston <bje@redhat.com>
5 and Andrew MacLeod <amacleod@redhat.com>
6 Adapted to use control dependence by Steven Bosscher, SUSE Labs.
7
8This file is part of GCC.
9
10GCC is free software; you can redistribute it and/or modify it
11under the terms of the GNU General Public License as published by the
12Free Software Foundation; either version 3, or (at your option) any
13later version.
14
15GCC is distributed in the hope that it will be useful, but WITHOUT
16ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
17FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
18for more details.
19
20You should have received a copy of the GNU General Public License
21along with GCC; see the file COPYING3. If not see
22<http://www.gnu.org/licenses/>. */
23
24/* Dead code elimination.
25
26 References:
27
28 Building an Optimizing Compiler,
29 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
30
31 Advanced Compiler Design and Implementation,
32 Steven Muchnick, Morgan Kaufmann, 1997, Section 18.10.
33
34 Dead-code elimination is the removal of statements which have no
35 impact on the program's output. "Dead statements" have no impact
36 on the program's output, while "necessary statements" may have
37 impact on the output.
38
39 The algorithm consists of three phases:
40 1. Marking as necessary all statements known to be necessary,
41 e.g. most function calls, writing a value to memory, etc;
42 2. Propagating necessary statements, e.g., the statements
43 giving values to operands in necessary statements; and
44 3. Removing dead statements. */
45
46#include "config.h"
47#include "system.h"
48#include "coretypes.h"
49#include "tm.h"
50
51#include "tree.h"
52#include "tree-pretty-print.h"
53#include "gimple-pretty-print.h"
54#include "basic-block.h"
55#include "tree-flow.h"
56#include "gimple.h"
57#include "tree-dump.h"
58#include "tree-pass.h"
59#include "timevar.h"
60#include "flags.h"
61#include "cfgloop.h"
62#include "tree-scalar-evolution.h"
63
64static struct stmt_stats
65{
66 int total;
67 int total_phis;
68 int removed;
69 int removed_phis;
70} stats;
71
72#define STMT_NECESSARY GF_PLF_1
73
74static VEC(gimple,heap) *worklist;
75
76/* Vector indicating an SSA name has already been processed and marked
77 as necessary. */
78static sbitmap processed;
79
80/* Vector indicating that the last statement of a basic block has already
81 been marked as necessary. */
82static sbitmap last_stmt_necessary;
83
84/* Vector indicating that BB contains statements that are live. */
85static sbitmap bb_contains_live_stmts;
86
87/* Before we can determine whether a control branch is dead, we need to
88 compute which blocks are control dependent on which edges.
89
90 We expect each block to be control dependent on very few edges so we
91 use a bitmap for each block recording its edges. An array holds the
92 bitmap. The Ith bit in the bitmap is set if that block is dependent
93 on the Ith edge. */
94static bitmap *control_dependence_map;
95
96/* Vector indicating that a basic block has already had all the edges
97 processed that it is control dependent on. */
98static sbitmap visited_control_parents;
99
100/* TRUE if this pass alters the CFG (by removing control statements).
101 FALSE otherwise.
102
103 If this pass alters the CFG, then it will arrange for the dominators
104 to be recomputed. */
105static bool cfg_altered;
106
107/* Execute code that follows the macro for each edge (given number
108 EDGE_NUMBER within the CODE) for which the block with index N is
109 control dependent. */
110#define EXECUTE_IF_CONTROL_DEPENDENT(BI, N, EDGE_NUMBER) \
111 EXECUTE_IF_SET_IN_BITMAP (control_dependence_map[(N)], 0, \
112 (EDGE_NUMBER), (BI))
113
114
115/* Indicate block BB is control dependent on an edge with index EDGE_INDEX. */
116static inline void
117set_control_dependence_map_bit (basic_block bb, int edge_index)
118{
119 if (bb == ENTRY_BLOCK_PTR)
120 return;
121 gcc_assert (bb != EXIT_BLOCK_PTR);
122 bitmap_set_bit (control_dependence_map[bb->index], edge_index);
123}
124
125/* Clear all control dependences for block BB. */
126static inline void
127clear_control_dependence_bitmap (basic_block bb)
128{
129 bitmap_clear (control_dependence_map[bb->index]);
130}
131
132
133/* Find the immediate postdominator PDOM of the specified basic block BLOCK.
134 This function is necessary because some blocks have negative numbers. */
135
136static inline basic_block
137find_pdom (basic_block block)
138{
139 gcc_assert (block != ENTRY_BLOCK_PTR);
140
141 if (block == EXIT_BLOCK_PTR)
142 return EXIT_BLOCK_PTR;
143 else
144 {
145 basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block);
146 if (! bb)
147 return EXIT_BLOCK_PTR;
148 return bb;
149 }
150}
151
152
153/* Determine all blocks' control dependences on the given edge with edge_list
154 EL index EDGE_INDEX, ala Morgan, Section 3.6. */
155
156static void
157find_control_dependence (struct edge_list *el, int edge_index)
158{
159 basic_block current_block;
160 basic_block ending_block;
161
162 gcc_assert (INDEX_EDGE_PRED_BB (el, edge_index) != EXIT_BLOCK_PTR);
163
164 if (INDEX_EDGE_PRED_BB (el, edge_index) == ENTRY_BLOCK_PTR)
165 ending_block = single_succ (ENTRY_BLOCK_PTR);
166 else
167 ending_block = find_pdom (INDEX_EDGE_PRED_BB (el, edge_index));
168
169 for (current_block = INDEX_EDGE_SUCC_BB (el, edge_index);
170 current_block != ending_block && current_block != EXIT_BLOCK_PTR;
171 current_block = find_pdom (current_block))
172 {
173 edge e = INDEX_EDGE (el, edge_index);
174
175 /* For abnormal edges, we don't make current_block control
176 dependent because instructions that throw are always necessary
177 anyway. */
178 if (e->flags & EDGE_ABNORMAL)
179 continue;
180
181 set_control_dependence_map_bit (current_block, edge_index);
182 }
183}
184
185
186/* Record all blocks' control dependences on all edges in the edge
187 list EL, ala Morgan, Section 3.6. */
188
189static void
190find_all_control_dependences (struct edge_list *el)
191{
192 int i;
193
194 for (i = 0; i < NUM_EDGES (el); ++i)
195 find_control_dependence (el, i);
196}
197
198/* If STMT is not already marked necessary, mark it, and add it to the
199 worklist if ADD_TO_WORKLIST is true. */
200
201static inline void
202mark_stmt_necessary (gimple stmt, bool add_to_worklist)
203{
204 gcc_assert (stmt);
205
206 if (gimple_plf (stmt, STMT_NECESSARY))
207 return;
208
209 if (dump_file && (dump_flags & TDF_DETAILS))
210 {
211 fprintf (dump_file, "Marking useful stmt: ");
212 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
213 fprintf (dump_file, "\n");
214 }
215
216 gimple_set_plf (stmt, STMT_NECESSARY, true);
217 if (add_to_worklist)
218 VEC_safe_push (gimple, heap, worklist, stmt);
219 if (bb_contains_live_stmts && !is_gimple_debug (stmt))
220 SET_BIT (bb_contains_live_stmts, gimple_bb (stmt)->index);
221}
222
223
224/* Mark the statement defining operand OP as necessary. */
225
226static inline void
227mark_operand_necessary (tree op)
228{
229 gimple stmt;
230 int ver;
231
232 gcc_assert (op);
233
234 ver = SSA_NAME_VERSION (op);
235 if (TEST_BIT (processed, ver))
236 {
237 stmt = SSA_NAME_DEF_STMT (op);
238 gcc_assert (gimple_nop_p (stmt)
239 || gimple_plf (stmt, STMT_NECESSARY));
240 return;
241 }
242 SET_BIT (processed, ver);
243
244 stmt = SSA_NAME_DEF_STMT (op);
245 gcc_assert (stmt);
246
247 if (gimple_plf (stmt, STMT_NECESSARY) || gimple_nop_p (stmt))
248 return;
249
250 if (dump_file && (dump_flags & TDF_DETAILS))
251 {
252 fprintf (dump_file, "marking necessary through ");
253 print_generic_expr (dump_file, op, 0);
254 fprintf (dump_file, " stmt ");
255 print_gimple_stmt (dump_file, stmt, 0, 0);
256 }
257
258 gimple_set_plf (stmt, STMT_NECESSARY, true);
259 if (bb_contains_live_stmts)
260 SET_BIT (bb_contains_live_stmts, gimple_bb (stmt)->index);
261 VEC_safe_push (gimple, heap, worklist, stmt);
262}
263
264
265/* Mark STMT as necessary if it obviously is. Add it to the worklist if
266 it can make other statements necessary.
267
268 If AGGRESSIVE is false, control statements are conservatively marked as
269 necessary. */
270
271static void
272mark_stmt_if_obviously_necessary (gimple stmt, bool aggressive)
273{
274 /* With non-call exceptions, we have to assume that all statements could
275 throw. If a statement may throw, it is inherently necessary. */
276 if (cfun->can_throw_non_call_exceptions && stmt_could_throw_p (stmt))
277 {
278 mark_stmt_necessary (stmt, true);
279 return;
280 }
281
282 /* Statements that are implicitly live. Most function calls, asm
283 and return statements are required. Labels and GIMPLE_BIND nodes
284 are kept because they are control flow, and we have no way of
285 knowing whether they can be removed. DCE can eliminate all the
286 other statements in a block, and CFG can then remove the block
287 and labels. */
288 switch (gimple_code (stmt))
289 {
290 case GIMPLE_PREDICT:
291 case GIMPLE_LABEL:
292 mark_stmt_necessary (stmt, false);
293 return;
294
295 case GIMPLE_ASM:
296 case GIMPLE_RESX:
297 case GIMPLE_RETURN:
298 mark_stmt_necessary (stmt, true);
299 return;
300
301 case GIMPLE_CALL:
302 {
303 tree callee = gimple_call_fndecl (stmt);
304 if (callee != NULL_TREE
305 && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL)
306 switch (DECL_FUNCTION_CODE (callee))
307 {
308 case BUILT_IN_MALLOC:
309 case BUILT_IN_CALLOC:
310 case BUILT_IN_ALLOCA:
311 case BUILT_IN_ALLOCA_WITH_ALIGN:
312 return;
313
314 default:;
315 }
316 /* Most, but not all function calls are required. Function calls that
317 produce no result and have no side effects (i.e. const pure
318 functions) are unnecessary. */
319 if (gimple_has_side_effects (stmt))
320 {
321 mark_stmt_necessary (stmt, true);
322 return;
323 }
324 if (!gimple_call_lhs (stmt))
325 return;
326 break;
327 }
328
329 case GIMPLE_DEBUG:
330 /* Debug temps without a value are not useful. ??? If we could
331 easily locate the debug temp bind stmt for a use thereof,
332 would could refrain from marking all debug temps here, and
333 mark them only if they're used. */
334 if (!gimple_debug_bind_p (stmt)
335 || gimple_debug_bind_has_value_p (stmt)
336 || TREE_CODE (gimple_debug_bind_get_var (stmt)) != DEBUG_EXPR_DECL)
337 mark_stmt_necessary (stmt, false);
338 return;
339
340 case GIMPLE_GOTO:
341 gcc_assert (!simple_goto_p (stmt));
342 mark_stmt_necessary (stmt, true);
343 return;
344
345 case GIMPLE_COND:
346 gcc_assert (EDGE_COUNT (gimple_bb (stmt)->succs) == 2);
347 /* Fall through. */
348
349 case GIMPLE_SWITCH:
350 if (! aggressive)
351 mark_stmt_necessary (stmt, true);
352 break;
353
354 case GIMPLE_ASSIGN:
355 if (TREE_CODE (gimple_assign_lhs (stmt)) == SSA_NAME
356 && TREE_CLOBBER_P (gimple_assign_rhs1 (stmt)))
357 return;
358 break;
359
360 default:
361 break;
362 }
363
364 /* If the statement has volatile operands, it needs to be preserved.
365 Same for statements that can alter control flow in unpredictable
366 ways. */
367 if (gimple_has_volatile_ops (stmt) || is_ctrl_altering_stmt (stmt))
368 {
369 mark_stmt_necessary (stmt, true);
370 return;
371 }
372
373 if (is_hidden_global_store (stmt))
374 {
375 mark_stmt_necessary (stmt, true);
376 return;
377 }
378
379 return;
380}
381
382
383/* Mark the last statement of BB as necessary. */
384
385static void
386mark_last_stmt_necessary (basic_block bb)
387{
388 gimple stmt = last_stmt (bb);
389
390 SET_BIT (last_stmt_necessary, bb->index);
391 SET_BIT (bb_contains_live_stmts, bb->index);
392
393 /* We actually mark the statement only if it is a control statement. */
394 if (stmt && is_ctrl_stmt (stmt))
395 mark_stmt_necessary (stmt, true);
396}
397
398
399/* Mark control dependent edges of BB as necessary. We have to do this only
400 once for each basic block so we set the appropriate bit after we're done.
401
402 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
403
404static void
405mark_control_dependent_edges_necessary (basic_block bb, struct edge_list *el,
406 bool ignore_self)
407{
408 bitmap_iterator bi;
409 unsigned edge_number;
410 bool skipped = false;
411
412 gcc_assert (bb != EXIT_BLOCK_PTR);
413
414 if (bb == ENTRY_BLOCK_PTR)
415 return;
416
417 EXECUTE_IF_CONTROL_DEPENDENT (bi, bb->index, edge_number)
418 {
419 basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number);
420
421 if (ignore_self && cd_bb == bb)
422 {
423 skipped = true;
424 continue;
425 }
426
427 if (!TEST_BIT (last_stmt_necessary, cd_bb->index))
428 mark_last_stmt_necessary (cd_bb);
429 }
430
431 if (!skipped)
432 SET_BIT (visited_control_parents, bb->index);
433}
434
435
436/* Find obviously necessary statements. These are things like most function
437 calls, and stores to file level variables.
438
439 If EL is NULL, control statements are conservatively marked as
440 necessary. Otherwise it contains the list of edges used by control
441 dependence analysis. */
442
443static void
444find_obviously_necessary_stmts (struct edge_list *el)
445{
446 basic_block bb;
447 gimple_stmt_iterator gsi;
448 edge e;
449 gimple phi, stmt;
450 int flags;
451
452 FOR_EACH_BB (bb)
453 {
454 /* PHI nodes are never inherently necessary. */
455 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
456 {
457 phi = gsi_stmt (gsi);
458 gimple_set_plf (phi, STMT_NECESSARY, false);
459 }
460
461 /* Check all statements in the block. */
462 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
463 {
464 stmt = gsi_stmt (gsi);
465 gimple_set_plf (stmt, STMT_NECESSARY, false);
466 mark_stmt_if_obviously_necessary (stmt, el != NULL);
467 }
468 }
469
470 /* Pure and const functions are finite and thus have no infinite loops in
471 them. */
472 flags = flags_from_decl_or_type (current_function_decl);
473 if ((flags & (ECF_CONST|ECF_PURE)) && !(flags & ECF_LOOPING_CONST_OR_PURE))
474 return;
475
476 /* Prevent the empty possibly infinite loops from being removed. */
477 if (el)
478 {
479 loop_iterator li;
480 struct loop *loop;
481 scev_initialize ();
482 if (mark_irreducible_loops ())
483 FOR_EACH_BB (bb)
484 {
485 edge_iterator ei;
486 FOR_EACH_EDGE (e, ei, bb->succs)
487 if ((e->flags & EDGE_DFS_BACK)
488 && (e->flags & EDGE_IRREDUCIBLE_LOOP))
489 {
490 if (dump_file)
491 fprintf (dump_file, "Marking back edge of irreducible loop %i->%i\n",
492 e->src->index, e->dest->index);
493 mark_control_dependent_edges_necessary (e->dest, el, false);
494 }
495 }
496
497 FOR_EACH_LOOP (li, loop, 0)
498 if (!finite_loop_p (loop))
499 {
500 if (dump_file)
501 fprintf (dump_file, "can not prove finiteness of loop %i\n", loop->num);
502 mark_control_dependent_edges_necessary (loop->latch, el, false);
503 }
504 scev_finalize ();
505 }
506}
507
508
509/* Return true if REF is based on an aliased base, otherwise false. */
510
511static bool
512ref_may_be_aliased (tree ref)
513{
514 gcc_assert (TREE_CODE (ref) != WITH_SIZE_EXPR);
515 while (handled_component_p (ref))
516 ref = TREE_OPERAND (ref, 0);
517 if (TREE_CODE (ref) == MEM_REF
518 && TREE_CODE (TREE_OPERAND (ref, 0)) == ADDR_EXPR)
519 ref = TREE_OPERAND (TREE_OPERAND (ref, 0), 0);
520 return !(DECL_P (ref)
521 && !may_be_aliased (ref));
522}
523
524static bitmap visited = NULL;
525static unsigned int longest_chain = 0;
526static unsigned int total_chain = 0;
527static unsigned int nr_walks = 0;
528static bool chain_ovfl = false;
529
530/* Worker for the walker that marks reaching definitions of REF,
531 which is based on a non-aliased decl, necessary. It returns
532 true whenever the defining statement of the current VDEF is
533 a kill for REF, as no dominating may-defs are necessary for REF
534 anymore. DATA points to the basic-block that contains the
535 stmt that refers to REF. */
536
537static bool
538mark_aliased_reaching_defs_necessary_1 (ao_ref *ref, tree vdef, void *data)
539{
540 gimple def_stmt = SSA_NAME_DEF_STMT (vdef);
541
542 /* All stmts we visit are necessary. */
543 mark_operand_necessary (vdef);
544
545 /* If the stmt lhs kills ref, then we can stop walking. */
546 if (gimple_has_lhs (def_stmt)
547 && TREE_CODE (gimple_get_lhs (def_stmt)) != SSA_NAME
548 /* The assignment is not necessarily carried out if it can throw
549 and we can catch it in the current function where we could inspect
550 the previous value.
551 ??? We only need to care about the RHS throwing. For aggregate
552 assignments or similar calls and non-call exceptions the LHS
553 might throw as well. */
554 && !stmt_can_throw_internal (def_stmt))
555 {
556 tree base, lhs = gimple_get_lhs (def_stmt);
557 HOST_WIDE_INT size, offset, max_size;
558 ao_ref_base (ref);
559 base = get_ref_base_and_extent (lhs, &offset, &size, &max_size);
560 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
561 so base == refd->base does not always hold. */
562 if (base == ref->base)
563 {
564 /* For a must-alias check we need to be able to constrain
565 the accesses properly. */
566 if (size != -1 && size == max_size
567 && ref->max_size != -1)
568 {
569 if (offset <= ref->offset
570 && offset + size >= ref->offset + ref->max_size)
571 return true;
572 }
573 /* Or they need to be exactly the same. */
574 else if (ref->ref
575 /* Make sure there is no induction variable involved
576 in the references (gcc.c-torture/execute/pr42142.c).
577 The simplest way is to check if the kill dominates
578 the use. */
95d28233
JM
579 /* But when both are in the same block we cannot
580 easily tell whether we came from a backedge
581 unless we decide to compute stmt UIDs
582 (see PR58246). */
583 && (basic_block) data != gimple_bb (def_stmt)
e4b17023
JM
584 && dominated_by_p (CDI_DOMINATORS, (basic_block) data,
585 gimple_bb (def_stmt))
586 && operand_equal_p (ref->ref, lhs, 0))
587 return true;
588 }
589 }
590
591 /* Otherwise keep walking. */
592 return false;
593}
594
595static void
596mark_aliased_reaching_defs_necessary (gimple stmt, tree ref)
597{
598 unsigned int chain;
599 ao_ref refd;
600 gcc_assert (!chain_ovfl);
601 ao_ref_init (&refd, ref);
602 chain = walk_aliased_vdefs (&refd, gimple_vuse (stmt),
603 mark_aliased_reaching_defs_necessary_1,
604 gimple_bb (stmt), NULL);
605 if (chain > longest_chain)
606 longest_chain = chain;
607 total_chain += chain;
608 nr_walks++;
609}
610
611/* Worker for the walker that marks reaching definitions of REF, which
612 is not based on a non-aliased decl. For simplicity we need to end
613 up marking all may-defs necessary that are not based on a non-aliased
614 decl. The only job of this walker is to skip may-defs based on
615 a non-aliased decl. */
616
617static bool
618mark_all_reaching_defs_necessary_1 (ao_ref *ref ATTRIBUTE_UNUSED,
619 tree vdef, void *data ATTRIBUTE_UNUSED)
620{
621 gimple def_stmt = SSA_NAME_DEF_STMT (vdef);
622
623 /* We have to skip already visited (and thus necessary) statements
624 to make the chaining work after we dropped back to simple mode. */
625 if (chain_ovfl
626 && TEST_BIT (processed, SSA_NAME_VERSION (vdef)))
627 {
628 gcc_assert (gimple_nop_p (def_stmt)
629 || gimple_plf (def_stmt, STMT_NECESSARY));
630 return false;
631 }
632
633 /* We want to skip stores to non-aliased variables. */
634 if (!chain_ovfl
635 && gimple_assign_single_p (def_stmt))
636 {
637 tree lhs = gimple_assign_lhs (def_stmt);
638 if (!ref_may_be_aliased (lhs))
639 return false;
640 }
641
642 /* We want to skip statments that do not constitute stores but have
643 a virtual definition. */
644 if (is_gimple_call (def_stmt))
645 {
646 tree callee = gimple_call_fndecl (def_stmt);
647 if (callee != NULL_TREE
648 && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL)
649 switch (DECL_FUNCTION_CODE (callee))
650 {
651 case BUILT_IN_MALLOC:
652 case BUILT_IN_CALLOC:
653 case BUILT_IN_ALLOCA:
654 case BUILT_IN_ALLOCA_WITH_ALIGN:
655 case BUILT_IN_FREE:
656 return false;
657
658 default:;
659 }
660 }
661
662 mark_operand_necessary (vdef);
663
664 return false;
665}
666
667static void
668mark_all_reaching_defs_necessary (gimple stmt)
669{
670 walk_aliased_vdefs (NULL, gimple_vuse (stmt),
671 mark_all_reaching_defs_necessary_1, NULL, &visited);
672}
673
674/* Return true for PHI nodes with one or identical arguments
675 can be removed. */
676static bool
677degenerate_phi_p (gimple phi)
678{
679 unsigned int i;
680 tree op = gimple_phi_arg_def (phi, 0);
681 for (i = 1; i < gimple_phi_num_args (phi); i++)
682 if (gimple_phi_arg_def (phi, i) != op)
683 return false;
684 return true;
685}
686
687/* Propagate necessity using the operands of necessary statements.
688 Process the uses on each statement in the worklist, and add all
689 feeding statements which contribute to the calculation of this
690 value to the worklist.
691
692 In conservative mode, EL is NULL. */
693
694static void
695propagate_necessity (struct edge_list *el)
696{
697 gimple stmt;
698 bool aggressive = (el ? true : false);
699
700 if (dump_file && (dump_flags & TDF_DETAILS))
701 fprintf (dump_file, "\nProcessing worklist:\n");
702
703 while (VEC_length (gimple, worklist) > 0)
704 {
705 /* Take STMT from worklist. */
706 stmt = VEC_pop (gimple, worklist);
707
708 if (dump_file && (dump_flags & TDF_DETAILS))
709 {
710 fprintf (dump_file, "processing: ");
711 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
712 fprintf (dump_file, "\n");
713 }
714
715 if (aggressive)
716 {
717 /* Mark the last statement of the basic blocks on which the block
718 containing STMT is control dependent, but only if we haven't
719 already done so. */
720 basic_block bb = gimple_bb (stmt);
721 if (bb != ENTRY_BLOCK_PTR
722 && !TEST_BIT (visited_control_parents, bb->index))
723 mark_control_dependent_edges_necessary (bb, el, false);
724 }
725
726 if (gimple_code (stmt) == GIMPLE_PHI
727 /* We do not process virtual PHI nodes nor do we track their
728 necessity. */
729 && is_gimple_reg (gimple_phi_result (stmt)))
730 {
731 /* PHI nodes are somewhat special in that each PHI alternative has
732 data and control dependencies. All the statements feeding the
733 PHI node's arguments are always necessary. In aggressive mode,
734 we also consider the control dependent edges leading to the
735 predecessor block associated with each PHI alternative as
736 necessary. */
737 size_t k;
738
739 for (k = 0; k < gimple_phi_num_args (stmt); k++)
740 {
741 tree arg = PHI_ARG_DEF (stmt, k);
742 if (TREE_CODE (arg) == SSA_NAME)
743 mark_operand_necessary (arg);
744 }
745
746 /* For PHI operands it matters from where the control flow arrives
747 to the BB. Consider the following example:
748
749 a=exp1;
750 b=exp2;
751 if (test)
752 ;
753 else
754 ;
755 c=PHI(a,b)
756
757 We need to mark control dependence of the empty basic blocks, since they
758 contains computation of PHI operands.
759
760 Doing so is too restrictive in the case the predecestor block is in
761 the loop. Consider:
762
763 if (b)
764 {
765 int i;
766 for (i = 0; i<1000; ++i)
767 ;
768 j = 0;
769 }
770 return j;
771
772 There is PHI for J in the BB containing return statement.
773 In this case the control dependence of predecestor block (that is
774 within the empty loop) also contains the block determining number
775 of iterations of the block that would prevent removing of empty
776 loop in this case.
777
778 This scenario can be avoided by splitting critical edges.
779 To save the critical edge splitting pass we identify how the control
780 dependence would look like if the edge was split.
781
782 Consider the modified CFG created from current CFG by splitting
783 edge B->C. In the postdominance tree of modified CFG, C' is
784 always child of C. There are two cases how chlids of C' can look
785 like:
786
787 1) C' is leaf
788
789 In this case the only basic block C' is control dependent on is B.
790
791 2) C' has single child that is B
792
793 In this case control dependence of C' is same as control
794 dependence of B in original CFG except for block B itself.
795 (since C' postdominate B in modified CFG)
796
797 Now how to decide what case happens? There are two basic options:
798
799 a) C postdominate B. Then C immediately postdominate B and
800 case 2 happens iff there is no other way from B to C except
801 the edge B->C.
802
803 There is other way from B to C iff there is succesor of B that
804 is not postdominated by B. Testing this condition is somewhat
805 expensive, because we need to iterate all succesors of B.
806 We are safe to assume that this does not happen: we will mark B
807 as needed when processing the other path from B to C that is
808 conrol dependent on B and marking control dependencies of B
809 itself is harmless because they will be processed anyway after
810 processing control statement in B.
811
812 b) C does not postdominate B. Always case 1 happens since there is
813 path from C to exit that does not go through B and thus also C'. */
814
815 if (aggressive && !degenerate_phi_p (stmt))
816 {
817 for (k = 0; k < gimple_phi_num_args (stmt); k++)
818 {
819 basic_block arg_bb = gimple_phi_arg_edge (stmt, k)->src;
820
821 if (gimple_bb (stmt)
822 != get_immediate_dominator (CDI_POST_DOMINATORS, arg_bb))
823 {
824 if (!TEST_BIT (last_stmt_necessary, arg_bb->index))
825 mark_last_stmt_necessary (arg_bb);
826 }
827 else if (arg_bb != ENTRY_BLOCK_PTR
828 && !TEST_BIT (visited_control_parents,
829 arg_bb->index))
830 mark_control_dependent_edges_necessary (arg_bb, el, true);
831 }
832 }
833 }
834 else
835 {
836 /* Propagate through the operands. Examine all the USE, VUSE and
837 VDEF operands in this statement. Mark all the statements
838 which feed this statement's uses as necessary. */
839 ssa_op_iter iter;
840 tree use;
841
842 /* If this is a call to free which is directly fed by an
843 allocation function do not mark that necessary through
844 processing the argument. */
845 if (gimple_call_builtin_p (stmt, BUILT_IN_FREE))
846 {
847 tree ptr = gimple_call_arg (stmt, 0);
848 gimple def_stmt;
849 tree def_callee;
850 /* If the pointer we free is defined by an allocation
851 function do not add the call to the worklist. */
852 if (TREE_CODE (ptr) == SSA_NAME
853 && is_gimple_call (def_stmt = SSA_NAME_DEF_STMT (ptr))
854 && (def_callee = gimple_call_fndecl (def_stmt))
855 && DECL_BUILT_IN_CLASS (def_callee) == BUILT_IN_NORMAL
856 && (DECL_FUNCTION_CODE (def_callee) == BUILT_IN_MALLOC
857 || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_CALLOC))
858 continue;
859 }
860
861 FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
862 mark_operand_necessary (use);
863
864 use = gimple_vuse (stmt);
865 if (!use)
866 continue;
867
868 /* If we dropped to simple mode make all immediately
869 reachable definitions necessary. */
870 if (chain_ovfl)
871 {
872 mark_all_reaching_defs_necessary (stmt);
873 continue;
874 }
875
876 /* For statements that may load from memory (have a VUSE) we
877 have to mark all reaching (may-)definitions as necessary.
878 We partition this task into two cases:
879 1) explicit loads based on decls that are not aliased
880 2) implicit loads (like calls) and explicit loads not
881 based on decls that are not aliased (like indirect
882 references or loads from globals)
883 For 1) we mark all reaching may-defs as necessary, stopping
884 at dominating kills. For 2) we want to mark all dominating
885 references necessary, but non-aliased ones which we handle
886 in 1). By keeping a global visited bitmap for references
887 we walk for 2) we avoid quadratic behavior for those. */
888
889 if (is_gimple_call (stmt))
890 {
891 tree callee = gimple_call_fndecl (stmt);
892 unsigned i;
893
894 /* Calls to functions that are merely acting as barriers
895 or that only store to memory do not make any previous
896 stores necessary. */
897 if (callee != NULL_TREE
898 && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL
899 && (DECL_FUNCTION_CODE (callee) == BUILT_IN_MEMSET
900 || DECL_FUNCTION_CODE (callee) == BUILT_IN_MEMSET_CHK
901 || DECL_FUNCTION_CODE (callee) == BUILT_IN_MALLOC
902 || DECL_FUNCTION_CODE (callee) == BUILT_IN_CALLOC
903 || DECL_FUNCTION_CODE (callee) == BUILT_IN_FREE
904 || DECL_FUNCTION_CODE (callee) == BUILT_IN_VA_END
905 || DECL_FUNCTION_CODE (callee) == BUILT_IN_ALLOCA
906 || (DECL_FUNCTION_CODE (callee)
907 == BUILT_IN_ALLOCA_WITH_ALIGN)
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 /* Calls implicitly load from memory, their arguments
914 in addition may explicitly perform memory loads. */
915 mark_all_reaching_defs_necessary (stmt);
916 for (i = 0; i < gimple_call_num_args (stmt); ++i)
917 {
918 tree arg = gimple_call_arg (stmt, i);
919 if (TREE_CODE (arg) == SSA_NAME
920 || is_gimple_min_invariant (arg))
921 continue;
922 if (TREE_CODE (arg) == WITH_SIZE_EXPR)
923 arg = TREE_OPERAND (arg, 0);
924 if (!ref_may_be_aliased (arg))
925 mark_aliased_reaching_defs_necessary (stmt, arg);
926 }
927 }
928 else if (gimple_assign_single_p (stmt))
929 {
930 tree rhs;
931 /* If this is a load mark things necessary. */
932 rhs = gimple_assign_rhs1 (stmt);
933 if (TREE_CODE (rhs) != SSA_NAME
934 && !is_gimple_min_invariant (rhs)
935 && TREE_CODE (rhs) != CONSTRUCTOR)
936 {
937 if (!ref_may_be_aliased (rhs))
938 mark_aliased_reaching_defs_necessary (stmt, rhs);
939 else
940 mark_all_reaching_defs_necessary (stmt);
941 }
942 }
943 else if (gimple_code (stmt) == GIMPLE_RETURN)
944 {
945 tree rhs = gimple_return_retval (stmt);
946 /* A return statement may perform a load. */
947 if (rhs
948 && TREE_CODE (rhs) != SSA_NAME
949 && !is_gimple_min_invariant (rhs)
950 && TREE_CODE (rhs) != CONSTRUCTOR)
951 {
952 if (!ref_may_be_aliased (rhs))
953 mark_aliased_reaching_defs_necessary (stmt, rhs);
954 else
955 mark_all_reaching_defs_necessary (stmt);
956 }
957 }
958 else if (gimple_code (stmt) == GIMPLE_ASM)
959 {
960 unsigned i;
961 mark_all_reaching_defs_necessary (stmt);
962 /* Inputs may perform loads. */
963 for (i = 0; i < gimple_asm_ninputs (stmt); ++i)
964 {
965 tree op = TREE_VALUE (gimple_asm_input_op (stmt, i));
966 if (TREE_CODE (op) != SSA_NAME
967 && !is_gimple_min_invariant (op)
968 && TREE_CODE (op) != CONSTRUCTOR
969 && !ref_may_be_aliased (op))
970 mark_aliased_reaching_defs_necessary (stmt, op);
971 }
972 }
973 else if (gimple_code (stmt) == GIMPLE_TRANSACTION)
974 {
975 /* The beginning of a transaction is a memory barrier. */
976 /* ??? If we were really cool, we'd only be a barrier
977 for the memories touched within the transaction. */
978 mark_all_reaching_defs_necessary (stmt);
979 }
980 else
981 gcc_unreachable ();
982
983 /* If we over-used our alias oracle budget drop to simple
984 mode. The cost metric allows quadratic behavior
985 (number of uses times number of may-defs queries) up to
986 a constant maximal number of queries and after that falls back to
987 super-linear complexity. */
988 if (/* Constant but quadratic for small functions. */
989 total_chain > 128 * 128
990 /* Linear in the number of may-defs. */
991 && total_chain > 32 * longest_chain
992 /* Linear in the number of uses. */
993 && total_chain > nr_walks * 32)
994 {
995 chain_ovfl = true;
996 if (visited)
997 bitmap_clear (visited);
998 }
999 }
1000 }
1001}
1002
1003/* Replace all uses of NAME by underlying variable and mark it
1004 for renaming. */
1005
1006void
1007mark_virtual_operand_for_renaming (tree name)
1008{
1009 bool used = false;
1010 imm_use_iterator iter;
1011 use_operand_p use_p;
1012 gimple stmt;
1013 tree name_var;
1014
1015 name_var = SSA_NAME_VAR (name);
1016 FOR_EACH_IMM_USE_STMT (stmt, iter, name)
1017 {
1018 FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
1019 SET_USE (use_p, name_var);
1020 update_stmt (stmt);
1021 used = true;
1022 }
1023 if (used)
1024 mark_sym_for_renaming (name_var);
1025}
1026
1027/* Replace all uses of result of PHI by underlying variable and mark it
1028 for renaming. */
1029
1030void
1031mark_virtual_phi_result_for_renaming (gimple phi)
1032{
1033 if (dump_file && (dump_flags & TDF_DETAILS))
1034 {
1035 fprintf (dump_file, "Marking result for renaming : ");
1036 print_gimple_stmt (dump_file, phi, 0, TDF_SLIM);
1037 fprintf (dump_file, "\n");
1038 }
1039
1040 mark_virtual_operand_for_renaming (gimple_phi_result (phi));
1041}
1042
1043
1044/* Remove dead PHI nodes from block BB. */
1045
1046static bool
1047remove_dead_phis (basic_block bb)
1048{
1049 bool something_changed = false;
1050 gimple_seq phis;
1051 gimple phi;
1052 gimple_stmt_iterator gsi;
1053 phis = phi_nodes (bb);
1054
1055 for (gsi = gsi_start (phis); !gsi_end_p (gsi);)
1056 {
1057 stats.total_phis++;
1058 phi = gsi_stmt (gsi);
1059
1060 /* We do not track necessity of virtual PHI nodes. Instead do
1061 very simple dead PHI removal here. */
1062 if (!is_gimple_reg (gimple_phi_result (phi)))
1063 {
1064 /* Virtual PHI nodes with one or identical arguments
1065 can be removed. */
1066 if (degenerate_phi_p (phi))
1067 {
1068 tree vdef = gimple_phi_result (phi);
1069 tree vuse = gimple_phi_arg_def (phi, 0);
1070
1071 use_operand_p use_p;
1072 imm_use_iterator iter;
1073 gimple use_stmt;
1074 FOR_EACH_IMM_USE_STMT (use_stmt, iter, vdef)
1075 FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
1076 SET_USE (use_p, vuse);
1077 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef)
1078 && TREE_CODE (vuse) == SSA_NAME)
1079 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse) = 1;
1080 }
1081 else
1082 gimple_set_plf (phi, STMT_NECESSARY, true);
1083 }
1084
1085 if (!gimple_plf (phi, STMT_NECESSARY))
1086 {
1087 something_changed = true;
1088 if (dump_file && (dump_flags & TDF_DETAILS))
1089 {
1090 fprintf (dump_file, "Deleting : ");
1091 print_gimple_stmt (dump_file, phi, 0, TDF_SLIM);
1092 fprintf (dump_file, "\n");
1093 }
1094
1095 remove_phi_node (&gsi, true);
1096 stats.removed_phis++;
1097 continue;
1098 }
1099
1100 gsi_next (&gsi);
1101 }
1102 return something_changed;
1103}
1104
1105/* Forward edge E to respective POST_DOM_BB and update PHIs. */
1106
1107static edge
1108forward_edge_to_pdom (edge e, basic_block post_dom_bb)
1109{
1110 gimple_stmt_iterator gsi;
1111 edge e2 = NULL;
1112 edge_iterator ei;
1113
1114 if (dump_file && (dump_flags & TDF_DETAILS))
1115 fprintf (dump_file, "Redirecting edge %i->%i to %i\n", e->src->index,
1116 e->dest->index, post_dom_bb->index);
1117
1118 e2 = redirect_edge_and_branch (e, post_dom_bb);
1119 cfg_altered = true;
1120
1121 /* If edge was already around, no updating is neccesary. */
1122 if (e2 != e)
1123 return e2;
1124
1125 if (!gimple_seq_empty_p (phi_nodes (post_dom_bb)))
1126 {
1127 /* We are sure that for every live PHI we are seeing control dependent BB.
1128 This means that we can pick any edge to duplicate PHI args from. */
1129 FOR_EACH_EDGE (e2, ei, post_dom_bb->preds)
1130 if (e2 != e)
1131 break;
1132 for (gsi = gsi_start_phis (post_dom_bb); !gsi_end_p (gsi);)
1133 {
1134 gimple phi = gsi_stmt (gsi);
1135 tree op;
1136 source_location locus;
1137
1138 /* PHIs for virtuals have no control dependency relation on them.
1139 We are lost here and must force renaming of the symbol. */
1140 if (!is_gimple_reg (gimple_phi_result (phi)))
1141 {
1142 mark_virtual_phi_result_for_renaming (phi);
1143 remove_phi_node (&gsi, true);
1144 continue;
1145 }
1146
1147 /* Dead PHI do not imply control dependency. */
1148 if (!gimple_plf (phi, STMT_NECESSARY))
1149 {
1150 gsi_next (&gsi);
1151 continue;
1152 }
1153
1154 op = gimple_phi_arg_def (phi, e2->dest_idx);
1155 locus = gimple_phi_arg_location (phi, e2->dest_idx);
1156 add_phi_arg (phi, op, e, locus);
1157 /* The resulting PHI if not dead can only be degenerate. */
1158 gcc_assert (degenerate_phi_p (phi));
1159 gsi_next (&gsi);
1160 }
1161 }
1162 return e;
1163}
1164
1165/* Remove dead statement pointed to by iterator I. Receives the basic block BB
1166 containing I so that we don't have to look it up. */
1167
1168static void
1169remove_dead_stmt (gimple_stmt_iterator *i, basic_block bb)
1170{
1171 gimple stmt = gsi_stmt (*i);
1172
1173 if (dump_file && (dump_flags & TDF_DETAILS))
1174 {
1175 fprintf (dump_file, "Deleting : ");
1176 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
1177 fprintf (dump_file, "\n");
1178 }
1179
1180 stats.removed++;
1181
1182 /* If we have determined that a conditional branch statement contributes
1183 nothing to the program, then we not only remove it, but we also change
1184 the flow graph so that the current block will simply fall-thru to its
1185 immediate post-dominator. The blocks we are circumventing will be
1186 removed by cleanup_tree_cfg if this change in the flow graph makes them
1187 unreachable. */
1188 if (is_ctrl_stmt (stmt))
1189 {
1190 basic_block post_dom_bb;
1191 edge e, e2;
1192 edge_iterator ei;
1193
1194 post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
1195
1196 e = find_edge (bb, post_dom_bb);
1197
1198 /* If edge is already there, try to use it. This avoids need to update
1199 PHI nodes. Also watch for cases where post dominator does not exists
1200 or is exit block. These can happen for infinite loops as we create
1201 fake edges in the dominator tree. */
1202 if (e)
1203 ;
1204 else if (! post_dom_bb || post_dom_bb == EXIT_BLOCK_PTR)
1205 e = EDGE_SUCC (bb, 0);
1206 else
1207 e = forward_edge_to_pdom (EDGE_SUCC (bb, 0), post_dom_bb);
1208 gcc_assert (e);
1209 e->probability = REG_BR_PROB_BASE;
1210 e->count = bb->count;
1211
1212 /* The edge is no longer associated with a conditional, so it does
1213 not have TRUE/FALSE flags. */
1214 e->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
1215
1216 /* The lone outgoing edge from BB will be a fallthru edge. */
1217 e->flags |= EDGE_FALLTHRU;
1218
1219 /* Remove the remaining outgoing edges. */
1220 for (ei = ei_start (bb->succs); (e2 = ei_safe_edge (ei)); )
1221 if (e != e2)
1222 {
1223 cfg_altered = true;
1224 remove_edge (e2);
1225 }
1226 else
1227 ei_next (&ei);
1228 }
1229
1230 /* If this is a store into a variable that is being optimized away,
1231 add a debug bind stmt if possible. */
1232 if (MAY_HAVE_DEBUG_STMTS
1233 && gimple_assign_single_p (stmt)
1234 && is_gimple_val (gimple_assign_rhs1 (stmt)))
1235 {
1236 tree lhs = gimple_assign_lhs (stmt);
1237 if ((TREE_CODE (lhs) == VAR_DECL || TREE_CODE (lhs) == PARM_DECL)
1238 && !DECL_IGNORED_P (lhs)
1239 && is_gimple_reg_type (TREE_TYPE (lhs))
1240 && !is_global_var (lhs)
1241 && !DECL_HAS_VALUE_EXPR_P (lhs))
1242 {
1243 tree rhs = gimple_assign_rhs1 (stmt);
1244 gimple note
1245 = gimple_build_debug_bind (lhs, unshare_expr (rhs), stmt);
1246 gsi_insert_after (i, note, GSI_SAME_STMT);
1247 }
1248 }
1249
1250 unlink_stmt_vdef (stmt);
1251 gsi_remove (i, true);
1252 release_defs (stmt);
1253}
1254
1255/* Eliminate unnecessary statements. Any instruction not marked as necessary
1256 contributes nothing to the program, and can be deleted. */
1257
1258static bool
1259eliminate_unnecessary_stmts (void)
1260{
1261 bool something_changed = false;
1262 basic_block bb;
1263 gimple_stmt_iterator gsi, psi;
1264 gimple stmt;
1265 tree call;
1266 VEC (basic_block, heap) *h;
1267
1268 if (dump_file && (dump_flags & TDF_DETAILS))
1269 fprintf (dump_file, "\nEliminating unnecessary statements:\n");
1270
1271 clear_special_calls ();
1272
1273 /* Walking basic blocks and statements in reverse order avoids
1274 releasing SSA names before any other DEFs that refer to them are
1275 released. This helps avoid loss of debug information, as we get
1276 a chance to propagate all RHSs of removed SSAs into debug uses,
1277 rather than only the latest ones. E.g., consider:
1278
1279 x_3 = y_1 + z_2;
1280 a_5 = x_3 - b_4;
1281 # DEBUG a => a_5
1282
1283 If we were to release x_3 before a_5, when we reached a_5 and
1284 tried to substitute it into the debug stmt, we'd see x_3 there,
1285 but x_3's DEF, type, etc would have already been disconnected.
1286 By going backwards, the debug stmt first changes to:
1287
1288 # DEBUG a => x_3 - b_4
1289
1290 and then to:
1291
1292 # DEBUG a => y_1 + z_2 - b_4
1293
1294 as desired. */
1295 gcc_assert (dom_info_available_p (CDI_DOMINATORS));
1296 h = get_all_dominated_blocks (CDI_DOMINATORS, single_succ (ENTRY_BLOCK_PTR));
1297
1298 while (VEC_length (basic_block, h))
1299 {
1300 bb = VEC_pop (basic_block, h);
1301
1302 /* Remove dead statements. */
1303 for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi = psi)
1304 {
1305 stmt = gsi_stmt (gsi);
1306
1307 psi = gsi;
1308 gsi_prev (&psi);
1309
1310 stats.total++;
1311
1312 /* We can mark a call to free as not necessary if the
95d28233
JM
1313 defining statement of its argument is not necessary
1314 (and thus is getting removed). */
1315 if (gimple_plf (stmt, STMT_NECESSARY)
1316 && gimple_call_builtin_p (stmt, BUILT_IN_FREE))
e4b17023
JM
1317 {
1318 tree ptr = gimple_call_arg (stmt, 0);
95d28233
JM
1319 if (TREE_CODE (ptr) == SSA_NAME)
1320 {
1321 gimple def_stmt = SSA_NAME_DEF_STMT (ptr);
1322 if (!gimple_nop_p (def_stmt)
1323 && !gimple_plf (def_stmt, STMT_NECESSARY))
1324 gimple_set_plf (stmt, STMT_NECESSARY, false);
1325 }
e4b17023
JM
1326 }
1327
1328 /* If GSI is not necessary then remove it. */
1329 if (!gimple_plf (stmt, STMT_NECESSARY))
1330 {
1331 if (!is_gimple_debug (stmt))
1332 something_changed = true;
1333 remove_dead_stmt (&gsi, bb);
1334 }
1335 else if (is_gimple_call (stmt))
1336 {
1337 tree name = gimple_call_lhs (stmt);
1338
1339 notice_special_calls (stmt);
1340
1341 /* When LHS of var = call (); is dead, simplify it into
1342 call (); saving one operand. */
1343 if (name
1344 && TREE_CODE (name) == SSA_NAME
1345 && !TEST_BIT (processed, SSA_NAME_VERSION (name))
1346 /* Avoid doing so for allocation calls which we
1347 did not mark as necessary, it will confuse the
1348 special logic we apply to malloc/free pair removal. */
1349 && (!(call = gimple_call_fndecl (stmt))
1350 || DECL_BUILT_IN_CLASS (call) != BUILT_IN_NORMAL
1351 || (DECL_FUNCTION_CODE (call) != BUILT_IN_MALLOC
1352 && DECL_FUNCTION_CODE (call) != BUILT_IN_CALLOC
1353 && DECL_FUNCTION_CODE (call) != BUILT_IN_ALLOCA
1354 && (DECL_FUNCTION_CODE (call)
1355 != BUILT_IN_ALLOCA_WITH_ALIGN))))
1356 {
1357 something_changed = true;
1358 if (dump_file && (dump_flags & TDF_DETAILS))
1359 {
1360 fprintf (dump_file, "Deleting LHS of call: ");
1361 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
1362 fprintf (dump_file, "\n");
1363 }
1364
1365 gimple_call_set_lhs (stmt, NULL_TREE);
1366 maybe_clean_or_replace_eh_stmt (stmt, stmt);
1367 update_stmt (stmt);
1368 release_ssa_name (name);
1369 }
1370 }
1371 }
1372 }
1373
1374 VEC_free (basic_block, heap, h);
1375
1376 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1377 rendered some PHI nodes unreachable while they are still in use.
1378 Mark them for renaming. */
1379 if (cfg_altered)
1380 {
1381 basic_block prev_bb;
1382
1383 find_unreachable_blocks ();
1384
1385 /* Delete all unreachable basic blocks in reverse dominator order. */
1386 for (bb = EXIT_BLOCK_PTR->prev_bb; bb != ENTRY_BLOCK_PTR; bb = prev_bb)
1387 {
1388 prev_bb = bb->prev_bb;
1389
1390 if (!TEST_BIT (bb_contains_live_stmts, bb->index)
1391 || !(bb->flags & BB_REACHABLE))
1392 {
1393 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
1394 if (!is_gimple_reg (gimple_phi_result (gsi_stmt (gsi))))
1395 {
1396 bool found = false;
1397 imm_use_iterator iter;
1398
1399 FOR_EACH_IMM_USE_STMT (stmt, iter, gimple_phi_result (gsi_stmt (gsi)))
1400 {
1401 if (!(gimple_bb (stmt)->flags & BB_REACHABLE))
1402 continue;
1403 if (gimple_code (stmt) == GIMPLE_PHI
1404 || gimple_plf (stmt, STMT_NECESSARY))
1405 {
1406 found = true;
1407 BREAK_FROM_IMM_USE_STMT (iter);
1408 }
1409 }
1410 if (found)
1411 mark_virtual_phi_result_for_renaming (gsi_stmt (gsi));
1412 }
1413
1414 if (!(bb->flags & BB_REACHABLE))
1415 {
1416 /* Speed up the removal of blocks that don't
1417 dominate others. Walking backwards, this should
1418 be the common case. ??? Do we need to recompute
1419 dominators because of cfg_altered? */
1420 if (!MAY_HAVE_DEBUG_STMTS
1421 || !first_dom_son (CDI_DOMINATORS, bb))
1422 delete_basic_block (bb);
1423 else
1424 {
1425 h = get_all_dominated_blocks (CDI_DOMINATORS, bb);
1426
1427 while (VEC_length (basic_block, h))
1428 {
1429 bb = VEC_pop (basic_block, h);
1430 prev_bb = bb->prev_bb;
1431 /* Rearrangements to the CFG may have failed
1432 to update the dominators tree, so that
1433 formerly-dominated blocks are now
1434 otherwise reachable. */
1435 if (!!(bb->flags & BB_REACHABLE))
1436 continue;
1437 delete_basic_block (bb);
1438 }
1439
1440 VEC_free (basic_block, heap, h);
1441 }
1442 }
1443 }
1444 }
1445 }
1446 FOR_EACH_BB (bb)
1447 {
1448 /* Remove dead PHI nodes. */
1449 something_changed |= remove_dead_phis (bb);
1450 }
1451
1452 return something_changed;
1453}
1454
1455
1456/* Print out removed statement statistics. */
1457
1458static void
1459print_stats (void)
1460{
1461 float percg;
1462
1463 percg = ((float) stats.removed / (float) stats.total) * 100;
1464 fprintf (dump_file, "Removed %d of %d statements (%d%%)\n",
1465 stats.removed, stats.total, (int) percg);
1466
1467 if (stats.total_phis == 0)
1468 percg = 0;
1469 else
1470 percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100;
1471
1472 fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n",
1473 stats.removed_phis, stats.total_phis, (int) percg);
1474}
1475
1476/* Initialization for this pass. Set up the used data structures. */
1477
1478static void
1479tree_dce_init (bool aggressive)
1480{
1481 memset ((void *) &stats, 0, sizeof (stats));
1482
1483 if (aggressive)
1484 {
1485 int i;
1486
1487 control_dependence_map = XNEWVEC (bitmap, last_basic_block);
1488 for (i = 0; i < last_basic_block; ++i)
1489 control_dependence_map[i] = BITMAP_ALLOC (NULL);
1490
1491 last_stmt_necessary = sbitmap_alloc (last_basic_block);
1492 sbitmap_zero (last_stmt_necessary);
1493 bb_contains_live_stmts = sbitmap_alloc (last_basic_block);
1494 sbitmap_zero (bb_contains_live_stmts);
1495 }
1496
1497 processed = sbitmap_alloc (num_ssa_names + 1);
1498 sbitmap_zero (processed);
1499
1500 worklist = VEC_alloc (gimple, heap, 64);
1501 cfg_altered = false;
1502}
1503
1504/* Cleanup after this pass. */
1505
1506static void
1507tree_dce_done (bool aggressive)
1508{
1509 if (aggressive)
1510 {
1511 int i;
1512
1513 for (i = 0; i < last_basic_block; ++i)
1514 BITMAP_FREE (control_dependence_map[i]);
1515 free (control_dependence_map);
1516
1517 sbitmap_free (visited_control_parents);
1518 sbitmap_free (last_stmt_necessary);
1519 sbitmap_free (bb_contains_live_stmts);
1520 bb_contains_live_stmts = NULL;
1521 }
1522
1523 sbitmap_free (processed);
1524
1525 VEC_free (gimple, heap, worklist);
1526}
1527
1528/* Main routine to eliminate dead code.
1529
1530 AGGRESSIVE controls the aggressiveness of the algorithm.
1531 In conservative mode, we ignore control dependence and simply declare
1532 all but the most trivially dead branches necessary. This mode is fast.
1533 In aggressive mode, control dependences are taken into account, which
1534 results in more dead code elimination, but at the cost of some time.
1535
1536 FIXME: Aggressive mode before PRE doesn't work currently because
1537 the dominance info is not invalidated after DCE1. This is
1538 not an issue right now because we only run aggressive DCE
1539 as the last tree SSA pass, but keep this in mind when you
1540 start experimenting with pass ordering. */
1541
1542static unsigned int
1543perform_tree_ssa_dce (bool aggressive)
1544{
1545 struct edge_list *el = NULL;
1546 bool something_changed = 0;
1547
1548 calculate_dominance_info (CDI_DOMINATORS);
1549
1550 /* Preheaders are needed for SCEV to work.
1551 Simple lateches and recorded exits improve chances that loop will
1552 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1553 if (aggressive)
1554 loop_optimizer_init (LOOPS_NORMAL
1555 | LOOPS_HAVE_RECORDED_EXITS);
1556
1557 tree_dce_init (aggressive);
1558
1559 if (aggressive)
1560 {
1561 /* Compute control dependence. */
1562 timevar_push (TV_CONTROL_DEPENDENCES);
1563 calculate_dominance_info (CDI_POST_DOMINATORS);
1564 el = create_edge_list ();
1565 find_all_control_dependences (el);
1566 timevar_pop (TV_CONTROL_DEPENDENCES);
1567
1568 visited_control_parents = sbitmap_alloc (last_basic_block);
1569 sbitmap_zero (visited_control_parents);
1570
1571 mark_dfs_back_edges ();
1572 }
1573
1574 find_obviously_necessary_stmts (el);
1575
1576 if (aggressive)
1577 loop_optimizer_finalize ();
1578
1579 longest_chain = 0;
1580 total_chain = 0;
1581 nr_walks = 0;
1582 chain_ovfl = false;
1583 visited = BITMAP_ALLOC (NULL);
1584 propagate_necessity (el);
1585 BITMAP_FREE (visited);
1586
1587 something_changed |= eliminate_unnecessary_stmts ();
1588 something_changed |= cfg_altered;
1589
1590 /* We do not update postdominators, so free them unconditionally. */
1591 free_dominance_info (CDI_POST_DOMINATORS);
1592
1593 /* If we removed paths in the CFG, then we need to update
1594 dominators as well. I haven't investigated the possibility
1595 of incrementally updating dominators. */
1596 if (cfg_altered)
1597 free_dominance_info (CDI_DOMINATORS);
1598
1599 statistics_counter_event (cfun, "Statements deleted", stats.removed);
1600 statistics_counter_event (cfun, "PHI nodes deleted", stats.removed_phis);
1601
1602 /* Debugging dumps. */
1603 if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS)))
1604 print_stats ();
1605
1606 tree_dce_done (aggressive);
1607
1608 free_edge_list (el);
1609
1610 if (something_changed)
1611 return (TODO_update_ssa | TODO_cleanup_cfg | TODO_ggc_collect
1612 | TODO_remove_unused_locals);
1613 else
1614 return 0;
1615}
1616
1617/* Pass entry points. */
1618static unsigned int
1619tree_ssa_dce (void)
1620{
1621 return perform_tree_ssa_dce (/*aggressive=*/false);
1622}
1623
1624static unsigned int
1625tree_ssa_dce_loop (void)
1626{
1627 unsigned int todo;
1628 todo = perform_tree_ssa_dce (/*aggressive=*/false);
1629 if (todo)
1630 {
1631 free_numbers_of_iterations_estimates ();
1632 scev_reset ();
1633 }
1634 return todo;
1635}
1636
1637static unsigned int
1638tree_ssa_cd_dce (void)
1639{
1640 return perform_tree_ssa_dce (/*aggressive=*/optimize >= 2);
1641}
1642
1643static bool
1644gate_dce (void)
1645{
1646 return flag_tree_dce != 0;
1647}
1648
1649struct gimple_opt_pass pass_dce =
1650{
1651 {
1652 GIMPLE_PASS,
1653 "dce", /* name */
1654 gate_dce, /* gate */
1655 tree_ssa_dce, /* execute */
1656 NULL, /* sub */
1657 NULL, /* next */
1658 0, /* static_pass_number */
1659 TV_TREE_DCE, /* tv_id */
1660 PROP_cfg | PROP_ssa, /* properties_required */
1661 0, /* properties_provided */
1662 0, /* properties_destroyed */
1663 0, /* todo_flags_start */
1664 TODO_verify_ssa /* todo_flags_finish */
1665 }
1666};
1667
1668struct gimple_opt_pass pass_dce_loop =
1669{
1670 {
1671 GIMPLE_PASS,
1672 "dceloop", /* name */
1673 gate_dce, /* gate */
1674 tree_ssa_dce_loop, /* execute */
1675 NULL, /* sub */
1676 NULL, /* next */
1677 0, /* static_pass_number */
1678 TV_TREE_DCE, /* tv_id */
1679 PROP_cfg | PROP_ssa, /* properties_required */
1680 0, /* properties_provided */
1681 0, /* properties_destroyed */
1682 0, /* todo_flags_start */
1683 TODO_verify_ssa /* todo_flags_finish */
1684 }
1685};
1686
1687struct gimple_opt_pass pass_cd_dce =
1688{
1689 {
1690 GIMPLE_PASS,
1691 "cddce", /* name */
1692 gate_dce, /* gate */
1693 tree_ssa_cd_dce, /* execute */
1694 NULL, /* sub */
1695 NULL, /* next */
1696 0, /* static_pass_number */
1697 TV_TREE_CD_DCE, /* tv_id */
1698 PROP_cfg | PROP_ssa, /* properties_required */
1699 0, /* properties_provided */
1700 0, /* properties_destroyed */
1701 0, /* todo_flags_start */
1702 TODO_verify_ssa
1703 | TODO_verify_flow /* todo_flags_finish */
1704 }
1705};