Introduce gimple_call
[official-gcc.git] / gcc / tree-ssa-dce.c
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1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002-2014 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.
7 This file is part of GCC.
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.
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.
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/>. */
23 /* Dead code elimination.
25 References:
27 Building an Optimizing Compiler,
28 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
30 Advanced Compiler Design and Implementation,
31 Steven Muchnick, Morgan Kaufmann, 1997, Section 18.10.
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.
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. */
45 #include "config.h"
46 #include "system.h"
47 #include "coretypes.h"
48 #include "tm.h"
50 #include "tree.h"
51 #include "calls.h"
52 #include "gimple-pretty-print.h"
53 #include "basic-block.h"
54 #include "tree-ssa-alias.h"
55 #include "internal-fn.h"
56 #include "tree-eh.h"
57 #include "gimple-expr.h"
58 #include "is-a.h"
59 #include "gimple.h"
60 #include "gimplify.h"
61 #include "gimple-iterator.h"
62 #include "gimple-ssa.h"
63 #include "tree-cfg.h"
64 #include "tree-phinodes.h"
65 #include "ssa-iterators.h"
66 #include "stringpool.h"
67 #include "tree-ssanames.h"
68 #include "tree-ssa-loop-niter.h"
69 #include "tree-into-ssa.h"
70 #include "expr.h"
71 #include "tree-dfa.h"
72 #include "tree-pass.h"
73 #include "flags.h"
74 #include "cfgloop.h"
75 #include "tree-scalar-evolution.h"
77 static struct stmt_stats
79 int total;
80 int total_phis;
81 int removed;
82 int removed_phis;
83 } stats;
85 #define STMT_NECESSARY GF_PLF_1
87 static vec<gimple> worklist;
89 /* Vector indicating an SSA name has already been processed and marked
90 as necessary. */
91 static sbitmap processed;
93 /* Vector indicating that the last statement of a basic block has already
94 been marked as necessary. */
95 static sbitmap last_stmt_necessary;
97 /* Vector indicating that BB contains statements that are live. */
98 static sbitmap bb_contains_live_stmts;
100 /* Before we can determine whether a control branch is dead, we need to
101 compute which blocks are control dependent on which edges.
103 We expect each block to be control dependent on very few edges so we
104 use a bitmap for each block recording its edges. An array holds the
105 bitmap. The Ith bit in the bitmap is set if that block is dependent
106 on the Ith edge. */
107 static control_dependences *cd;
109 /* Vector indicating that a basic block has already had all the edges
110 processed that it is control dependent on. */
111 static sbitmap visited_control_parents;
113 /* TRUE if this pass alters the CFG (by removing control statements).
114 FALSE otherwise.
116 If this pass alters the CFG, then it will arrange for the dominators
117 to be recomputed. */
118 static bool cfg_altered;
121 /* If STMT is not already marked necessary, mark it, and add it to the
122 worklist if ADD_TO_WORKLIST is true. */
124 static inline void
125 mark_stmt_necessary (gimple stmt, bool add_to_worklist)
127 gcc_assert (stmt);
129 if (gimple_plf (stmt, STMT_NECESSARY))
130 return;
132 if (dump_file && (dump_flags & TDF_DETAILS))
134 fprintf (dump_file, "Marking useful stmt: ");
135 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
136 fprintf (dump_file, "\n");
139 gimple_set_plf (stmt, STMT_NECESSARY, true);
140 if (add_to_worklist)
141 worklist.safe_push (stmt);
142 if (bb_contains_live_stmts && !is_gimple_debug (stmt))
143 bitmap_set_bit (bb_contains_live_stmts, gimple_bb (stmt)->index);
147 /* Mark the statement defining operand OP as necessary. */
149 static inline void
150 mark_operand_necessary (tree op)
152 gimple stmt;
153 int ver;
155 gcc_assert (op);
157 ver = SSA_NAME_VERSION (op);
158 if (bitmap_bit_p (processed, ver))
160 stmt = SSA_NAME_DEF_STMT (op);
161 gcc_assert (gimple_nop_p (stmt)
162 || gimple_plf (stmt, STMT_NECESSARY));
163 return;
165 bitmap_set_bit (processed, ver);
167 stmt = SSA_NAME_DEF_STMT (op);
168 gcc_assert (stmt);
170 if (gimple_plf (stmt, STMT_NECESSARY) || gimple_nop_p (stmt))
171 return;
173 if (dump_file && (dump_flags & TDF_DETAILS))
175 fprintf (dump_file, "marking necessary through ");
176 print_generic_expr (dump_file, op, 0);
177 fprintf (dump_file, " stmt ");
178 print_gimple_stmt (dump_file, stmt, 0, 0);
181 gimple_set_plf (stmt, STMT_NECESSARY, true);
182 if (bb_contains_live_stmts)
183 bitmap_set_bit (bb_contains_live_stmts, gimple_bb (stmt)->index);
184 worklist.safe_push (stmt);
188 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
189 it can make other statements necessary.
191 If AGGRESSIVE is false, control statements are conservatively marked as
192 necessary. */
194 static void
195 mark_stmt_if_obviously_necessary (gimple stmt, bool aggressive)
197 /* With non-call exceptions, we have to assume that all statements could
198 throw. If a statement could throw, it can be deemed necessary. */
199 if (cfun->can_throw_non_call_exceptions
200 && !cfun->can_delete_dead_exceptions
201 && stmt_could_throw_p (stmt))
203 mark_stmt_necessary (stmt, true);
204 return;
207 /* Statements that are implicitly live. Most function calls, asm
208 and return statements are required. Labels and GIMPLE_BIND nodes
209 are kept because they are control flow, and we have no way of
210 knowing whether they can be removed. DCE can eliminate all the
211 other statements in a block, and CFG can then remove the block
212 and labels. */
213 switch (gimple_code (stmt))
215 case GIMPLE_PREDICT:
216 case GIMPLE_LABEL:
217 mark_stmt_necessary (stmt, false);
218 return;
220 case GIMPLE_ASM:
221 case GIMPLE_RESX:
222 case GIMPLE_RETURN:
223 mark_stmt_necessary (stmt, true);
224 return;
226 case GIMPLE_CALL:
228 tree callee = gimple_call_fndecl (stmt);
229 if (callee != NULL_TREE
230 && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL)
231 switch (DECL_FUNCTION_CODE (callee))
233 case BUILT_IN_MALLOC:
234 case BUILT_IN_ALIGNED_ALLOC:
235 case BUILT_IN_CALLOC:
236 case BUILT_IN_ALLOCA:
237 case BUILT_IN_ALLOCA_WITH_ALIGN:
238 return;
240 default:;
242 /* Most, but not all function calls are required. Function calls that
243 produce no result and have no side effects (i.e. const pure
244 functions) are unnecessary. */
245 if (gimple_has_side_effects (stmt))
247 mark_stmt_necessary (stmt, true);
248 return;
250 if (!gimple_call_lhs (stmt))
251 return;
252 break;
255 case GIMPLE_DEBUG:
256 /* Debug temps without a value are not useful. ??? If we could
257 easily locate the debug temp bind stmt for a use thereof,
258 would could refrain from marking all debug temps here, and
259 mark them only if they're used. */
260 if (!gimple_debug_bind_p (stmt)
261 || gimple_debug_bind_has_value_p (stmt)
262 || TREE_CODE (gimple_debug_bind_get_var (stmt)) != DEBUG_EXPR_DECL)
263 mark_stmt_necessary (stmt, false);
264 return;
266 case GIMPLE_GOTO:
267 gcc_assert (!simple_goto_p (stmt));
268 mark_stmt_necessary (stmt, true);
269 return;
271 case GIMPLE_COND:
272 gcc_assert (EDGE_COUNT (gimple_bb (stmt)->succs) == 2);
273 /* Fall through. */
275 case GIMPLE_SWITCH:
276 if (! aggressive)
277 mark_stmt_necessary (stmt, true);
278 break;
280 case GIMPLE_ASSIGN:
281 if (TREE_CODE (gimple_assign_lhs (stmt)) == SSA_NAME
282 && TREE_CLOBBER_P (gimple_assign_rhs1 (stmt)))
283 return;
284 break;
286 default:
287 break;
290 /* If the statement has volatile operands, it needs to be preserved.
291 Same for statements that can alter control flow in unpredictable
292 ways. */
293 if (gimple_has_volatile_ops (stmt) || is_ctrl_altering_stmt (stmt))
295 mark_stmt_necessary (stmt, true);
296 return;
299 if (stmt_may_clobber_global_p (stmt))
301 mark_stmt_necessary (stmt, true);
302 return;
305 return;
309 /* Mark the last statement of BB as necessary. */
311 static void
312 mark_last_stmt_necessary (basic_block bb)
314 gimple stmt = last_stmt (bb);
316 bitmap_set_bit (last_stmt_necessary, bb->index);
317 bitmap_set_bit (bb_contains_live_stmts, bb->index);
319 /* We actually mark the statement only if it is a control statement. */
320 if (stmt && is_ctrl_stmt (stmt))
321 mark_stmt_necessary (stmt, true);
325 /* Mark control dependent edges of BB as necessary. We have to do this only
326 once for each basic block so we set the appropriate bit after we're done.
328 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
330 static void
331 mark_control_dependent_edges_necessary (basic_block bb, bool ignore_self)
333 bitmap_iterator bi;
334 unsigned edge_number;
335 bool skipped = false;
337 gcc_assert (bb != EXIT_BLOCK_PTR_FOR_FN (cfun));
339 if (bb == ENTRY_BLOCK_PTR_FOR_FN (cfun))
340 return;
342 EXECUTE_IF_SET_IN_BITMAP (cd->get_edges_dependent_on (bb->index),
343 0, edge_number, bi)
345 basic_block cd_bb = cd->get_edge (edge_number)->src;
347 if (ignore_self && cd_bb == bb)
349 skipped = true;
350 continue;
353 if (!bitmap_bit_p (last_stmt_necessary, cd_bb->index))
354 mark_last_stmt_necessary (cd_bb);
357 if (!skipped)
358 bitmap_set_bit (visited_control_parents, bb->index);
362 /* Find obviously necessary statements. These are things like most function
363 calls, and stores to file level variables.
365 If EL is NULL, control statements are conservatively marked as
366 necessary. Otherwise it contains the list of edges used by control
367 dependence analysis. */
369 static void
370 find_obviously_necessary_stmts (bool aggressive)
372 basic_block bb;
373 gimple_stmt_iterator gsi;
374 edge e;
375 gimple phi, stmt;
376 int flags;
378 FOR_EACH_BB_FN (bb, cfun)
380 /* PHI nodes are never inherently necessary. */
381 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
383 phi = gsi_stmt (gsi);
384 gimple_set_plf (phi, STMT_NECESSARY, false);
387 /* Check all statements in the block. */
388 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
390 stmt = gsi_stmt (gsi);
391 gimple_set_plf (stmt, STMT_NECESSARY, false);
392 mark_stmt_if_obviously_necessary (stmt, aggressive);
396 /* Pure and const functions are finite and thus have no infinite loops in
397 them. */
398 flags = flags_from_decl_or_type (current_function_decl);
399 if ((flags & (ECF_CONST|ECF_PURE)) && !(flags & ECF_LOOPING_CONST_OR_PURE))
400 return;
402 /* Prevent the empty possibly infinite loops from being removed. */
403 if (aggressive)
405 struct loop *loop;
406 scev_initialize ();
407 if (mark_irreducible_loops ())
408 FOR_EACH_BB_FN (bb, cfun)
410 edge_iterator ei;
411 FOR_EACH_EDGE (e, ei, bb->succs)
412 if ((e->flags & EDGE_DFS_BACK)
413 && (e->flags & EDGE_IRREDUCIBLE_LOOP))
415 if (dump_file)
416 fprintf (dump_file, "Marking back edge of irreducible loop %i->%i\n",
417 e->src->index, e->dest->index);
418 mark_control_dependent_edges_necessary (e->dest, false);
422 FOR_EACH_LOOP (loop, 0)
423 if (!finite_loop_p (loop))
425 if (dump_file)
426 fprintf (dump_file, "can not prove finiteness of loop %i\n", loop->num);
427 mark_control_dependent_edges_necessary (loop->latch, false);
429 scev_finalize ();
434 /* Return true if REF is based on an aliased base, otherwise false. */
436 static bool
437 ref_may_be_aliased (tree ref)
439 gcc_assert (TREE_CODE (ref) != WITH_SIZE_EXPR);
440 while (handled_component_p (ref))
441 ref = TREE_OPERAND (ref, 0);
442 if (TREE_CODE (ref) == MEM_REF
443 && TREE_CODE (TREE_OPERAND (ref, 0)) == ADDR_EXPR)
444 ref = TREE_OPERAND (TREE_OPERAND (ref, 0), 0);
445 return !(DECL_P (ref)
446 && !may_be_aliased (ref));
449 static bitmap visited = NULL;
450 static unsigned int longest_chain = 0;
451 static unsigned int total_chain = 0;
452 static unsigned int nr_walks = 0;
453 static bool chain_ovfl = false;
455 /* Worker for the walker that marks reaching definitions of REF,
456 which is based on a non-aliased decl, necessary. It returns
457 true whenever the defining statement of the current VDEF is
458 a kill for REF, as no dominating may-defs are necessary for REF
459 anymore. DATA points to the basic-block that contains the
460 stmt that refers to REF. */
462 static bool
463 mark_aliased_reaching_defs_necessary_1 (ao_ref *ref, tree vdef, void *data)
465 gimple def_stmt = SSA_NAME_DEF_STMT (vdef);
467 /* All stmts we visit are necessary. */
468 mark_operand_necessary (vdef);
470 /* If the stmt lhs kills ref, then we can stop walking. */
471 if (gimple_has_lhs (def_stmt)
472 && TREE_CODE (gimple_get_lhs (def_stmt)) != SSA_NAME
473 /* The assignment is not necessarily carried out if it can throw
474 and we can catch it in the current function where we could inspect
475 the previous value.
476 ??? We only need to care about the RHS throwing. For aggregate
477 assignments or similar calls and non-call exceptions the LHS
478 might throw as well. */
479 && !stmt_can_throw_internal (def_stmt))
481 tree base, lhs = gimple_get_lhs (def_stmt);
482 HOST_WIDE_INT size, offset, max_size;
483 ao_ref_base (ref);
484 base = get_ref_base_and_extent (lhs, &offset, &size, &max_size);
485 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
486 so base == refd->base does not always hold. */
487 if (base == ref->base)
489 /* For a must-alias check we need to be able to constrain
490 the accesses properly. */
491 if (size != -1 && size == max_size
492 && ref->max_size != -1)
494 if (offset <= ref->offset
495 && offset + size >= ref->offset + ref->max_size)
496 return true;
498 /* Or they need to be exactly the same. */
499 else if (ref->ref
500 /* Make sure there is no induction variable involved
501 in the references (gcc.c-torture/execute/pr42142.c).
502 The simplest way is to check if the kill dominates
503 the use. */
504 /* But when both are in the same block we cannot
505 easily tell whether we came from a backedge
506 unless we decide to compute stmt UIDs
507 (see PR58246). */
508 && (basic_block) data != gimple_bb (def_stmt)
509 && dominated_by_p (CDI_DOMINATORS, (basic_block) data,
510 gimple_bb (def_stmt))
511 && operand_equal_p (ref->ref, lhs, 0))
512 return true;
516 /* Otherwise keep walking. */
517 return false;
520 static void
521 mark_aliased_reaching_defs_necessary (gimple stmt, tree ref)
523 unsigned int chain;
524 ao_ref refd;
525 gcc_assert (!chain_ovfl);
526 ao_ref_init (&refd, ref);
527 chain = walk_aliased_vdefs (&refd, gimple_vuse (stmt),
528 mark_aliased_reaching_defs_necessary_1,
529 gimple_bb (stmt), NULL);
530 if (chain > longest_chain)
531 longest_chain = chain;
532 total_chain += chain;
533 nr_walks++;
536 /* Worker for the walker that marks reaching definitions of REF, which
537 is not based on a non-aliased decl. For simplicity we need to end
538 up marking all may-defs necessary that are not based on a non-aliased
539 decl. The only job of this walker is to skip may-defs based on
540 a non-aliased decl. */
542 static bool
543 mark_all_reaching_defs_necessary_1 (ao_ref *ref ATTRIBUTE_UNUSED,
544 tree vdef, void *data ATTRIBUTE_UNUSED)
546 gimple def_stmt = SSA_NAME_DEF_STMT (vdef);
548 /* We have to skip already visited (and thus necessary) statements
549 to make the chaining work after we dropped back to simple mode. */
550 if (chain_ovfl
551 && bitmap_bit_p (processed, SSA_NAME_VERSION (vdef)))
553 gcc_assert (gimple_nop_p (def_stmt)
554 || gimple_plf (def_stmt, STMT_NECESSARY));
555 return false;
558 /* We want to skip stores to non-aliased variables. */
559 if (!chain_ovfl
560 && gimple_assign_single_p (def_stmt))
562 tree lhs = gimple_assign_lhs (def_stmt);
563 if (!ref_may_be_aliased (lhs))
564 return false;
567 /* We want to skip statments that do not constitute stores but have
568 a virtual definition. */
569 if (is_gimple_call (def_stmt))
571 tree callee = gimple_call_fndecl (def_stmt);
572 if (callee != NULL_TREE
573 && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL)
574 switch (DECL_FUNCTION_CODE (callee))
576 case BUILT_IN_MALLOC:
577 case BUILT_IN_ALIGNED_ALLOC:
578 case BUILT_IN_CALLOC:
579 case BUILT_IN_ALLOCA:
580 case BUILT_IN_ALLOCA_WITH_ALIGN:
581 case BUILT_IN_FREE:
582 return false;
584 default:;
588 mark_operand_necessary (vdef);
590 return false;
593 static void
594 mark_all_reaching_defs_necessary (gimple stmt)
596 walk_aliased_vdefs (NULL, gimple_vuse (stmt),
597 mark_all_reaching_defs_necessary_1, NULL, &visited);
600 /* Return true for PHI nodes with one or identical arguments
601 can be removed. */
602 static bool
603 degenerate_phi_p (gimple phi)
605 unsigned int i;
606 tree op = gimple_phi_arg_def (phi, 0);
607 for (i = 1; i < gimple_phi_num_args (phi); i++)
608 if (gimple_phi_arg_def (phi, i) != op)
609 return false;
610 return true;
613 /* Propagate necessity using the operands of necessary statements.
614 Process the uses on each statement in the worklist, and add all
615 feeding statements which contribute to the calculation of this
616 value to the worklist.
618 In conservative mode, EL is NULL. */
620 static void
621 propagate_necessity (bool aggressive)
623 gimple stmt;
625 if (dump_file && (dump_flags & TDF_DETAILS))
626 fprintf (dump_file, "\nProcessing worklist:\n");
628 while (worklist.length () > 0)
630 /* Take STMT from worklist. */
631 stmt = worklist.pop ();
633 if (dump_file && (dump_flags & TDF_DETAILS))
635 fprintf (dump_file, "processing: ");
636 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
637 fprintf (dump_file, "\n");
640 if (aggressive)
642 /* Mark the last statement of the basic blocks on which the block
643 containing STMT is control dependent, but only if we haven't
644 already done so. */
645 basic_block bb = gimple_bb (stmt);
646 if (bb != ENTRY_BLOCK_PTR_FOR_FN (cfun)
647 && !bitmap_bit_p (visited_control_parents, bb->index))
648 mark_control_dependent_edges_necessary (bb, false);
651 if (gimple_code (stmt) == GIMPLE_PHI
652 /* We do not process virtual PHI nodes nor do we track their
653 necessity. */
654 && !virtual_operand_p (gimple_phi_result (stmt)))
656 /* PHI nodes are somewhat special in that each PHI alternative has
657 data and control dependencies. All the statements feeding the
658 PHI node's arguments are always necessary. In aggressive mode,
659 we also consider the control dependent edges leading to the
660 predecessor block associated with each PHI alternative as
661 necessary. */
662 size_t k;
664 for (k = 0; k < gimple_phi_num_args (stmt); k++)
666 tree arg = PHI_ARG_DEF (stmt, k);
667 if (TREE_CODE (arg) == SSA_NAME)
668 mark_operand_necessary (arg);
671 /* For PHI operands it matters from where the control flow arrives
672 to the BB. Consider the following example:
674 a=exp1;
675 b=exp2;
676 if (test)
678 else
680 c=PHI(a,b)
682 We need to mark control dependence of the empty basic blocks, since they
683 contains computation of PHI operands.
685 Doing so is too restrictive in the case the predecestor block is in
686 the loop. Consider:
688 if (b)
690 int i;
691 for (i = 0; i<1000; ++i)
693 j = 0;
695 return j;
697 There is PHI for J in the BB containing return statement.
698 In this case the control dependence of predecestor block (that is
699 within the empty loop) also contains the block determining number
700 of iterations of the block that would prevent removing of empty
701 loop in this case.
703 This scenario can be avoided by splitting critical edges.
704 To save the critical edge splitting pass we identify how the control
705 dependence would look like if the edge was split.
707 Consider the modified CFG created from current CFG by splitting
708 edge B->C. In the postdominance tree of modified CFG, C' is
709 always child of C. There are two cases how chlids of C' can look
710 like:
712 1) C' is leaf
714 In this case the only basic block C' is control dependent on is B.
716 2) C' has single child that is B
718 In this case control dependence of C' is same as control
719 dependence of B in original CFG except for block B itself.
720 (since C' postdominate B in modified CFG)
722 Now how to decide what case happens? There are two basic options:
724 a) C postdominate B. Then C immediately postdominate B and
725 case 2 happens iff there is no other way from B to C except
726 the edge B->C.
728 There is other way from B to C iff there is succesor of B that
729 is not postdominated by B. Testing this condition is somewhat
730 expensive, because we need to iterate all succesors of B.
731 We are safe to assume that this does not happen: we will mark B
732 as needed when processing the other path from B to C that is
733 conrol dependent on B and marking control dependencies of B
734 itself is harmless because they will be processed anyway after
735 processing control statement in B.
737 b) C does not postdominate B. Always case 1 happens since there is
738 path from C to exit that does not go through B and thus also C'. */
740 if (aggressive && !degenerate_phi_p (stmt))
742 for (k = 0; k < gimple_phi_num_args (stmt); k++)
744 basic_block arg_bb = gimple_phi_arg_edge (stmt, k)->src;
746 if (gimple_bb (stmt)
747 != get_immediate_dominator (CDI_POST_DOMINATORS, arg_bb))
749 if (!bitmap_bit_p (last_stmt_necessary, arg_bb->index))
750 mark_last_stmt_necessary (arg_bb);
752 else if (arg_bb != ENTRY_BLOCK_PTR_FOR_FN (cfun)
753 && !bitmap_bit_p (visited_control_parents,
754 arg_bb->index))
755 mark_control_dependent_edges_necessary (arg_bb, true);
759 else
761 /* Propagate through the operands. Examine all the USE, VUSE and
762 VDEF operands in this statement. Mark all the statements
763 which feed this statement's uses as necessary. */
764 ssa_op_iter iter;
765 tree use;
767 /* If this is a call to free which is directly fed by an
768 allocation function do not mark that necessary through
769 processing the argument. */
770 if (gimple_call_builtin_p (stmt, BUILT_IN_FREE))
772 tree ptr = gimple_call_arg (stmt, 0);
773 gimple def_stmt;
774 tree def_callee;
775 /* If the pointer we free is defined by an allocation
776 function do not add the call to the worklist. */
777 if (TREE_CODE (ptr) == SSA_NAME
778 && is_gimple_call (def_stmt = SSA_NAME_DEF_STMT (ptr))
779 && (def_callee = gimple_call_fndecl (def_stmt))
780 && DECL_BUILT_IN_CLASS (def_callee) == BUILT_IN_NORMAL
781 && (DECL_FUNCTION_CODE (def_callee) == BUILT_IN_ALIGNED_ALLOC
782 || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_MALLOC
783 || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_CALLOC))
784 continue;
787 FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
788 mark_operand_necessary (use);
790 use = gimple_vuse (stmt);
791 if (!use)
792 continue;
794 /* If we dropped to simple mode make all immediately
795 reachable definitions necessary. */
796 if (chain_ovfl)
798 mark_all_reaching_defs_necessary (stmt);
799 continue;
802 /* For statements that may load from memory (have a VUSE) we
803 have to mark all reaching (may-)definitions as necessary.
804 We partition this task into two cases:
805 1) explicit loads based on decls that are not aliased
806 2) implicit loads (like calls) and explicit loads not
807 based on decls that are not aliased (like indirect
808 references or loads from globals)
809 For 1) we mark all reaching may-defs as necessary, stopping
810 at dominating kills. For 2) we want to mark all dominating
811 references necessary, but non-aliased ones which we handle
812 in 1). By keeping a global visited bitmap for references
813 we walk for 2) we avoid quadratic behavior for those. */
815 if (is_gimple_call (stmt))
817 tree callee = gimple_call_fndecl (stmt);
818 unsigned i;
820 /* Calls to functions that are merely acting as barriers
821 or that only store to memory do not make any previous
822 stores necessary. */
823 if (callee != NULL_TREE
824 && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL
825 && (DECL_FUNCTION_CODE (callee) == BUILT_IN_MEMSET
826 || DECL_FUNCTION_CODE (callee) == BUILT_IN_MEMSET_CHK
827 || DECL_FUNCTION_CODE (callee) == BUILT_IN_MALLOC
828 || DECL_FUNCTION_CODE (callee) == BUILT_IN_ALIGNED_ALLOC
829 || DECL_FUNCTION_CODE (callee) == BUILT_IN_CALLOC
830 || DECL_FUNCTION_CODE (callee) == BUILT_IN_FREE
831 || DECL_FUNCTION_CODE (callee) == BUILT_IN_VA_END
832 || DECL_FUNCTION_CODE (callee) == BUILT_IN_ALLOCA
833 || (DECL_FUNCTION_CODE (callee)
834 == BUILT_IN_ALLOCA_WITH_ALIGN)
835 || DECL_FUNCTION_CODE (callee) == BUILT_IN_STACK_SAVE
836 || DECL_FUNCTION_CODE (callee) == BUILT_IN_STACK_RESTORE
837 || DECL_FUNCTION_CODE (callee) == BUILT_IN_ASSUME_ALIGNED))
838 continue;
840 /* Calls implicitly load from memory, their arguments
841 in addition may explicitly perform memory loads. */
842 mark_all_reaching_defs_necessary (stmt);
843 for (i = 0; i < gimple_call_num_args (stmt); ++i)
845 tree arg = gimple_call_arg (stmt, i);
846 if (TREE_CODE (arg) == SSA_NAME
847 || is_gimple_min_invariant (arg))
848 continue;
849 if (TREE_CODE (arg) == WITH_SIZE_EXPR)
850 arg = TREE_OPERAND (arg, 0);
851 if (!ref_may_be_aliased (arg))
852 mark_aliased_reaching_defs_necessary (stmt, arg);
855 else if (gimple_assign_single_p (stmt))
857 tree rhs;
858 /* If this is a load mark things necessary. */
859 rhs = gimple_assign_rhs1 (stmt);
860 if (TREE_CODE (rhs) != SSA_NAME
861 && !is_gimple_min_invariant (rhs)
862 && TREE_CODE (rhs) != CONSTRUCTOR)
864 if (!ref_may_be_aliased (rhs))
865 mark_aliased_reaching_defs_necessary (stmt, rhs);
866 else
867 mark_all_reaching_defs_necessary (stmt);
870 else if (gimple_code (stmt) == GIMPLE_RETURN)
872 tree rhs = gimple_return_retval (stmt);
873 /* A return statement may perform a load. */
874 if (rhs
875 && TREE_CODE (rhs) != SSA_NAME
876 && !is_gimple_min_invariant (rhs)
877 && TREE_CODE (rhs) != CONSTRUCTOR)
879 if (!ref_may_be_aliased (rhs))
880 mark_aliased_reaching_defs_necessary (stmt, rhs);
881 else
882 mark_all_reaching_defs_necessary (stmt);
885 else if (gimple_code (stmt) == GIMPLE_ASM)
887 unsigned i;
888 mark_all_reaching_defs_necessary (stmt);
889 /* Inputs may perform loads. */
890 for (i = 0; i < gimple_asm_ninputs (stmt); ++i)
892 tree op = TREE_VALUE (gimple_asm_input_op (stmt, i));
893 if (TREE_CODE (op) != SSA_NAME
894 && !is_gimple_min_invariant (op)
895 && TREE_CODE (op) != CONSTRUCTOR
896 && !ref_may_be_aliased (op))
897 mark_aliased_reaching_defs_necessary (stmt, op);
900 else if (gimple_code (stmt) == GIMPLE_TRANSACTION)
902 /* The beginning of a transaction is a memory barrier. */
903 /* ??? If we were really cool, we'd only be a barrier
904 for the memories touched within the transaction. */
905 mark_all_reaching_defs_necessary (stmt);
907 else
908 gcc_unreachable ();
910 /* If we over-used our alias oracle budget drop to simple
911 mode. The cost metric allows quadratic behavior
912 (number of uses times number of may-defs queries) up to
913 a constant maximal number of queries and after that falls back to
914 super-linear complexity. */
915 if (/* Constant but quadratic for small functions. */
916 total_chain > 128 * 128
917 /* Linear in the number of may-defs. */
918 && total_chain > 32 * longest_chain
919 /* Linear in the number of uses. */
920 && total_chain > nr_walks * 32)
922 chain_ovfl = true;
923 if (visited)
924 bitmap_clear (visited);
930 /* Remove dead PHI nodes from block BB. */
932 static bool
933 remove_dead_phis (basic_block bb)
935 bool something_changed = false;
936 gimple_phi phi;
937 gimple_phi_iterator gsi;
939 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi);)
941 stats.total_phis++;
942 phi = gsi.phi ();
944 /* We do not track necessity of virtual PHI nodes. Instead do
945 very simple dead PHI removal here. */
946 if (virtual_operand_p (gimple_phi_result (phi)))
948 /* Virtual PHI nodes with one or identical arguments
949 can be removed. */
950 if (degenerate_phi_p (phi))
952 tree vdef = gimple_phi_result (phi);
953 tree vuse = gimple_phi_arg_def (phi, 0);
955 use_operand_p use_p;
956 imm_use_iterator iter;
957 gimple use_stmt;
958 FOR_EACH_IMM_USE_STMT (use_stmt, iter, vdef)
959 FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
960 SET_USE (use_p, vuse);
961 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef)
962 && TREE_CODE (vuse) == SSA_NAME)
963 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse) = 1;
965 else
966 gimple_set_plf (phi, STMT_NECESSARY, true);
969 if (!gimple_plf (phi, STMT_NECESSARY))
971 something_changed = true;
972 if (dump_file && (dump_flags & TDF_DETAILS))
974 fprintf (dump_file, "Deleting : ");
975 print_gimple_stmt (dump_file, phi, 0, TDF_SLIM);
976 fprintf (dump_file, "\n");
979 remove_phi_node (&gsi, true);
980 stats.removed_phis++;
981 continue;
984 gsi_next (&gsi);
986 return something_changed;
989 /* Forward edge E to respective POST_DOM_BB and update PHIs. */
991 static edge
992 forward_edge_to_pdom (edge e, basic_block post_dom_bb)
994 gimple_phi_iterator gsi;
995 edge e2 = NULL;
996 edge_iterator ei;
998 if (dump_file && (dump_flags & TDF_DETAILS))
999 fprintf (dump_file, "Redirecting edge %i->%i to %i\n", e->src->index,
1000 e->dest->index, post_dom_bb->index);
1002 e2 = redirect_edge_and_branch (e, post_dom_bb);
1003 cfg_altered = true;
1005 /* If edge was already around, no updating is necessary. */
1006 if (e2 != e)
1007 return e2;
1009 if (!gimple_seq_empty_p (phi_nodes (post_dom_bb)))
1011 /* We are sure that for every live PHI we are seeing control dependent BB.
1012 This means that we can pick any edge to duplicate PHI args from. */
1013 FOR_EACH_EDGE (e2, ei, post_dom_bb->preds)
1014 if (e2 != e)
1015 break;
1016 for (gsi = gsi_start_phis (post_dom_bb); !gsi_end_p (gsi);)
1018 gimple_phi phi = gsi.phi ();
1019 tree op;
1020 source_location locus;
1022 /* PHIs for virtuals have no control dependency relation on them.
1023 We are lost here and must force renaming of the symbol. */
1024 if (virtual_operand_p (gimple_phi_result (phi)))
1026 mark_virtual_phi_result_for_renaming (phi);
1027 remove_phi_node (&gsi, true);
1028 continue;
1031 /* Dead PHI do not imply control dependency. */
1032 if (!gimple_plf (phi, STMT_NECESSARY))
1034 gsi_next (&gsi);
1035 continue;
1038 op = gimple_phi_arg_def (phi, e2->dest_idx);
1039 locus = gimple_phi_arg_location (phi, e2->dest_idx);
1040 add_phi_arg (phi, op, e, locus);
1041 /* The resulting PHI if not dead can only be degenerate. */
1042 gcc_assert (degenerate_phi_p (phi));
1043 gsi_next (&gsi);
1046 return e;
1049 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1050 containing I so that we don't have to look it up. */
1052 static void
1053 remove_dead_stmt (gimple_stmt_iterator *i, basic_block bb)
1055 gimple stmt = gsi_stmt (*i);
1057 if (dump_file && (dump_flags & TDF_DETAILS))
1059 fprintf (dump_file, "Deleting : ");
1060 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
1061 fprintf (dump_file, "\n");
1064 stats.removed++;
1066 /* If we have determined that a conditional branch statement contributes
1067 nothing to the program, then we not only remove it, but we also change
1068 the flow graph so that the current block will simply fall-thru to its
1069 immediate post-dominator. The blocks we are circumventing will be
1070 removed by cleanup_tree_cfg if this change in the flow graph makes them
1071 unreachable. */
1072 if (is_ctrl_stmt (stmt))
1074 basic_block post_dom_bb;
1075 edge e, e2;
1076 edge_iterator ei;
1078 post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
1080 e = find_edge (bb, post_dom_bb);
1082 /* If edge is already there, try to use it. This avoids need to update
1083 PHI nodes. Also watch for cases where post dominator does not exists
1084 or is exit block. These can happen for infinite loops as we create
1085 fake edges in the dominator tree. */
1086 if (e)
1088 else if (! post_dom_bb || post_dom_bb == EXIT_BLOCK_PTR_FOR_FN (cfun))
1089 e = EDGE_SUCC (bb, 0);
1090 else
1091 e = forward_edge_to_pdom (EDGE_SUCC (bb, 0), post_dom_bb);
1092 gcc_assert (e);
1093 e->probability = REG_BR_PROB_BASE;
1094 e->count = bb->count;
1096 /* The edge is no longer associated with a conditional, so it does
1097 not have TRUE/FALSE flags. */
1098 e->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
1100 /* The lone outgoing edge from BB will be a fallthru edge. */
1101 e->flags |= EDGE_FALLTHRU;
1103 /* Remove the remaining outgoing edges. */
1104 for (ei = ei_start (bb->succs); (e2 = ei_safe_edge (ei)); )
1105 if (e != e2)
1107 cfg_altered = true;
1108 remove_edge (e2);
1110 else
1111 ei_next (&ei);
1114 /* If this is a store into a variable that is being optimized away,
1115 add a debug bind stmt if possible. */
1116 if (MAY_HAVE_DEBUG_STMTS
1117 && gimple_assign_single_p (stmt)
1118 && is_gimple_val (gimple_assign_rhs1 (stmt)))
1120 tree lhs = gimple_assign_lhs (stmt);
1121 if ((TREE_CODE (lhs) == VAR_DECL || TREE_CODE (lhs) == PARM_DECL)
1122 && !DECL_IGNORED_P (lhs)
1123 && is_gimple_reg_type (TREE_TYPE (lhs))
1124 && !is_global_var (lhs)
1125 && !DECL_HAS_VALUE_EXPR_P (lhs))
1127 tree rhs = gimple_assign_rhs1 (stmt);
1128 gimple note
1129 = gimple_build_debug_bind (lhs, unshare_expr (rhs), stmt);
1130 gsi_insert_after (i, note, GSI_SAME_STMT);
1134 unlink_stmt_vdef (stmt);
1135 gsi_remove (i, true);
1136 release_defs (stmt);
1139 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1140 contributes nothing to the program, and can be deleted. */
1142 static bool
1143 eliminate_unnecessary_stmts (void)
1145 bool something_changed = false;
1146 basic_block bb;
1147 gimple_stmt_iterator gsi, psi;
1148 gimple stmt;
1149 tree call;
1150 vec<basic_block> h;
1152 if (dump_file && (dump_flags & TDF_DETAILS))
1153 fprintf (dump_file, "\nEliminating unnecessary statements:\n");
1155 clear_special_calls ();
1157 /* Walking basic blocks and statements in reverse order avoids
1158 releasing SSA names before any other DEFs that refer to them are
1159 released. This helps avoid loss of debug information, as we get
1160 a chance to propagate all RHSs of removed SSAs into debug uses,
1161 rather than only the latest ones. E.g., consider:
1163 x_3 = y_1 + z_2;
1164 a_5 = x_3 - b_4;
1165 # DEBUG a => a_5
1167 If we were to release x_3 before a_5, when we reached a_5 and
1168 tried to substitute it into the debug stmt, we'd see x_3 there,
1169 but x_3's DEF, type, etc would have already been disconnected.
1170 By going backwards, the debug stmt first changes to:
1172 # DEBUG a => x_3 - b_4
1174 and then to:
1176 # DEBUG a => y_1 + z_2 - b_4
1178 as desired. */
1179 gcc_assert (dom_info_available_p (CDI_DOMINATORS));
1180 h = get_all_dominated_blocks (CDI_DOMINATORS,
1181 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)));
1183 while (h.length ())
1185 bb = h.pop ();
1187 /* Remove dead statements. */
1188 for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi = psi)
1190 stmt = gsi_stmt (gsi);
1192 psi = gsi;
1193 gsi_prev (&psi);
1195 stats.total++;
1197 /* We can mark a call to free as not necessary if the
1198 defining statement of its argument is not necessary
1199 (and thus is getting removed). */
1200 if (gimple_plf (stmt, STMT_NECESSARY)
1201 && gimple_call_builtin_p (stmt, BUILT_IN_FREE))
1203 tree ptr = gimple_call_arg (stmt, 0);
1204 if (TREE_CODE (ptr) == SSA_NAME)
1206 gimple def_stmt = SSA_NAME_DEF_STMT (ptr);
1207 if (!gimple_nop_p (def_stmt)
1208 && !gimple_plf (def_stmt, STMT_NECESSARY))
1209 gimple_set_plf (stmt, STMT_NECESSARY, false);
1213 /* If GSI is not necessary then remove it. */
1214 if (!gimple_plf (stmt, STMT_NECESSARY))
1216 if (!is_gimple_debug (stmt))
1217 something_changed = true;
1218 remove_dead_stmt (&gsi, bb);
1220 else if (is_gimple_call (stmt))
1222 tree name = gimple_call_lhs (stmt);
1224 notice_special_calls (as_a <gimple_call> (stmt));
1226 /* When LHS of var = call (); is dead, simplify it into
1227 call (); saving one operand. */
1228 if (name
1229 && TREE_CODE (name) == SSA_NAME
1230 && !bitmap_bit_p (processed, SSA_NAME_VERSION (name))
1231 /* Avoid doing so for allocation calls which we
1232 did not mark as necessary, it will confuse the
1233 special logic we apply to malloc/free pair removal. */
1234 && (!(call = gimple_call_fndecl (stmt))
1235 || DECL_BUILT_IN_CLASS (call) != BUILT_IN_NORMAL
1236 || (DECL_FUNCTION_CODE (call) != BUILT_IN_ALIGNED_ALLOC
1237 && DECL_FUNCTION_CODE (call) != BUILT_IN_MALLOC
1238 && DECL_FUNCTION_CODE (call) != BUILT_IN_CALLOC
1239 && DECL_FUNCTION_CODE (call) != BUILT_IN_ALLOCA
1240 && (DECL_FUNCTION_CODE (call)
1241 != BUILT_IN_ALLOCA_WITH_ALIGN))))
1243 something_changed = true;
1244 if (dump_file && (dump_flags & TDF_DETAILS))
1246 fprintf (dump_file, "Deleting LHS of call: ");
1247 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
1248 fprintf (dump_file, "\n");
1251 gimple_call_set_lhs (stmt, NULL_TREE);
1252 maybe_clean_or_replace_eh_stmt (stmt, stmt);
1253 update_stmt (stmt);
1254 release_ssa_name (name);
1260 h.release ();
1262 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1263 rendered some PHI nodes unreachable while they are still in use.
1264 Mark them for renaming. */
1265 if (cfg_altered)
1267 basic_block prev_bb;
1269 find_unreachable_blocks ();
1271 /* Delete all unreachable basic blocks in reverse dominator order. */
1272 for (bb = EXIT_BLOCK_PTR_FOR_FN (cfun)->prev_bb;
1273 bb != ENTRY_BLOCK_PTR_FOR_FN (cfun); bb = prev_bb)
1275 prev_bb = bb->prev_bb;
1277 if (!bitmap_bit_p (bb_contains_live_stmts, bb->index)
1278 || !(bb->flags & BB_REACHABLE))
1280 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
1281 if (virtual_operand_p (gimple_phi_result (gsi_stmt (gsi))))
1283 bool found = false;
1284 imm_use_iterator iter;
1286 FOR_EACH_IMM_USE_STMT (stmt, iter, gimple_phi_result (gsi_stmt (gsi)))
1288 if (!(gimple_bb (stmt)->flags & BB_REACHABLE))
1289 continue;
1290 if (gimple_code (stmt) == GIMPLE_PHI
1291 || gimple_plf (stmt, STMT_NECESSARY))
1293 found = true;
1294 BREAK_FROM_IMM_USE_STMT (iter);
1297 if (found)
1298 mark_virtual_phi_result_for_renaming (gsi_stmt (gsi));
1301 if (!(bb->flags & BB_REACHABLE))
1303 /* Speed up the removal of blocks that don't
1304 dominate others. Walking backwards, this should
1305 be the common case. ??? Do we need to recompute
1306 dominators because of cfg_altered? */
1307 if (!MAY_HAVE_DEBUG_STMTS
1308 || !first_dom_son (CDI_DOMINATORS, bb))
1309 delete_basic_block (bb);
1310 else
1312 h = get_all_dominated_blocks (CDI_DOMINATORS, bb);
1314 while (h.length ())
1316 bb = h.pop ();
1317 prev_bb = bb->prev_bb;
1318 /* Rearrangements to the CFG may have failed
1319 to update the dominators tree, so that
1320 formerly-dominated blocks are now
1321 otherwise reachable. */
1322 if (!!(bb->flags & BB_REACHABLE))
1323 continue;
1324 delete_basic_block (bb);
1327 h.release ();
1333 FOR_EACH_BB_FN (bb, cfun)
1335 /* Remove dead PHI nodes. */
1336 something_changed |= remove_dead_phis (bb);
1339 return something_changed;
1343 /* Print out removed statement statistics. */
1345 static void
1346 print_stats (void)
1348 float percg;
1350 percg = ((float) stats.removed / (float) stats.total) * 100;
1351 fprintf (dump_file, "Removed %d of %d statements (%d%%)\n",
1352 stats.removed, stats.total, (int) percg);
1354 if (stats.total_phis == 0)
1355 percg = 0;
1356 else
1357 percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100;
1359 fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n",
1360 stats.removed_phis, stats.total_phis, (int) percg);
1363 /* Initialization for this pass. Set up the used data structures. */
1365 static void
1366 tree_dce_init (bool aggressive)
1368 memset ((void *) &stats, 0, sizeof (stats));
1370 if (aggressive)
1372 last_stmt_necessary = sbitmap_alloc (last_basic_block_for_fn (cfun));
1373 bitmap_clear (last_stmt_necessary);
1374 bb_contains_live_stmts = sbitmap_alloc (last_basic_block_for_fn (cfun));
1375 bitmap_clear (bb_contains_live_stmts);
1378 processed = sbitmap_alloc (num_ssa_names + 1);
1379 bitmap_clear (processed);
1381 worklist.create (64);
1382 cfg_altered = false;
1385 /* Cleanup after this pass. */
1387 static void
1388 tree_dce_done (bool aggressive)
1390 if (aggressive)
1392 delete cd;
1393 sbitmap_free (visited_control_parents);
1394 sbitmap_free (last_stmt_necessary);
1395 sbitmap_free (bb_contains_live_stmts);
1396 bb_contains_live_stmts = NULL;
1399 sbitmap_free (processed);
1401 worklist.release ();
1404 /* Main routine to eliminate dead code.
1406 AGGRESSIVE controls the aggressiveness of the algorithm.
1407 In conservative mode, we ignore control dependence and simply declare
1408 all but the most trivially dead branches necessary. This mode is fast.
1409 In aggressive mode, control dependences are taken into account, which
1410 results in more dead code elimination, but at the cost of some time.
1412 FIXME: Aggressive mode before PRE doesn't work currently because
1413 the dominance info is not invalidated after DCE1. This is
1414 not an issue right now because we only run aggressive DCE
1415 as the last tree SSA pass, but keep this in mind when you
1416 start experimenting with pass ordering. */
1418 static unsigned int
1419 perform_tree_ssa_dce (bool aggressive)
1421 bool something_changed = 0;
1423 calculate_dominance_info (CDI_DOMINATORS);
1425 /* Preheaders are needed for SCEV to work.
1426 Simple lateches and recorded exits improve chances that loop will
1427 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1428 if (aggressive)
1429 loop_optimizer_init (LOOPS_NORMAL
1430 | LOOPS_HAVE_RECORDED_EXITS);
1432 tree_dce_init (aggressive);
1434 if (aggressive)
1436 /* Compute control dependence. */
1437 calculate_dominance_info (CDI_POST_DOMINATORS);
1438 cd = new control_dependences (create_edge_list ());
1440 visited_control_parents =
1441 sbitmap_alloc (last_basic_block_for_fn (cfun));
1442 bitmap_clear (visited_control_parents);
1444 mark_dfs_back_edges ();
1447 find_obviously_necessary_stmts (aggressive);
1449 if (aggressive)
1450 loop_optimizer_finalize ();
1452 longest_chain = 0;
1453 total_chain = 0;
1454 nr_walks = 0;
1455 chain_ovfl = false;
1456 visited = BITMAP_ALLOC (NULL);
1457 propagate_necessity (aggressive);
1458 BITMAP_FREE (visited);
1460 something_changed |= eliminate_unnecessary_stmts ();
1461 something_changed |= cfg_altered;
1463 /* We do not update postdominators, so free them unconditionally. */
1464 free_dominance_info (CDI_POST_DOMINATORS);
1466 /* If we removed paths in the CFG, then we need to update
1467 dominators as well. I haven't investigated the possibility
1468 of incrementally updating dominators. */
1469 if (cfg_altered)
1470 free_dominance_info (CDI_DOMINATORS);
1472 statistics_counter_event (cfun, "Statements deleted", stats.removed);
1473 statistics_counter_event (cfun, "PHI nodes deleted", stats.removed_phis);
1475 /* Debugging dumps. */
1476 if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS)))
1477 print_stats ();
1479 tree_dce_done (aggressive);
1481 if (something_changed)
1483 free_numbers_of_iterations_estimates ();
1484 if (scev_initialized_p ())
1485 scev_reset ();
1486 return TODO_update_ssa | TODO_cleanup_cfg;
1488 return 0;
1491 /* Pass entry points. */
1492 static unsigned int
1493 tree_ssa_dce (void)
1495 return perform_tree_ssa_dce (/*aggressive=*/false);
1498 static unsigned int
1499 tree_ssa_cd_dce (void)
1501 return perform_tree_ssa_dce (/*aggressive=*/optimize >= 2);
1504 namespace {
1506 const pass_data pass_data_dce =
1508 GIMPLE_PASS, /* type */
1509 "dce", /* name */
1510 OPTGROUP_NONE, /* optinfo_flags */
1511 TV_TREE_DCE, /* tv_id */
1512 ( PROP_cfg | PROP_ssa ), /* properties_required */
1513 0, /* properties_provided */
1514 0, /* properties_destroyed */
1515 0, /* todo_flags_start */
1516 0, /* todo_flags_finish */
1519 class pass_dce : public gimple_opt_pass
1521 public:
1522 pass_dce (gcc::context *ctxt)
1523 : gimple_opt_pass (pass_data_dce, ctxt)
1526 /* opt_pass methods: */
1527 opt_pass * clone () { return new pass_dce (m_ctxt); }
1528 virtual bool gate (function *) { return flag_tree_dce != 0; }
1529 virtual unsigned int execute (function *) { return tree_ssa_dce (); }
1531 }; // class pass_dce
1533 } // anon namespace
1535 gimple_opt_pass *
1536 make_pass_dce (gcc::context *ctxt)
1538 return new pass_dce (ctxt);
1541 namespace {
1543 const pass_data pass_data_cd_dce =
1545 GIMPLE_PASS, /* type */
1546 "cddce", /* name */
1547 OPTGROUP_NONE, /* optinfo_flags */
1548 TV_TREE_CD_DCE, /* tv_id */
1549 ( PROP_cfg | PROP_ssa ), /* properties_required */
1550 0, /* properties_provided */
1551 0, /* properties_destroyed */
1552 0, /* todo_flags_start */
1553 0, /* todo_flags_finish */
1556 class pass_cd_dce : public gimple_opt_pass
1558 public:
1559 pass_cd_dce (gcc::context *ctxt)
1560 : gimple_opt_pass (pass_data_cd_dce, ctxt)
1563 /* opt_pass methods: */
1564 opt_pass * clone () { return new pass_cd_dce (m_ctxt); }
1565 virtual bool gate (function *) { return flag_tree_dce != 0; }
1566 virtual unsigned int execute (function *) { return tree_ssa_cd_dce (); }
1568 }; // class pass_cd_dce
1570 } // anon namespace
1572 gimple_opt_pass *
1573 make_pass_cd_dce (gcc::context *ctxt)
1575 return new pass_cd_dce (ctxt);