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.
8 This file is part of GCC.
10 GCC is free software; you can redistribute it and/or modify it
11 under the terms of the GNU General Public License as published by the
12 Free Software Foundation; either version 3, or (at your option) any
15 GCC is distributed in the hope that it will be useful, but WITHOUT
16 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
17 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
20 You should have received a copy of the GNU General Public License
21 along with GCC; see the file COPYING3. If not see
22 <http://www.gnu.org/licenses/>. */
24 /* Dead code elimination.
28 Building an Optimizing Compiler,
29 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
31 Advanced Compiler Design and Implementation,
32 Steven Muchnick, Morgan Kaufmann, 1997, Section 18.10.
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
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. */
48 #include "coretypes.h"
52 #include "tree-pretty-print.h"
53 #include "gimple-pretty-print.h"
54 #include "basic-block.h"
55 #include "tree-flow.h"
57 #include "tree-dump.h"
58 #include "tree-pass.h"
62 #include "tree-scalar-evolution.h"
64 static struct stmt_stats
72 #define STMT_NECESSARY GF_PLF_1
74 static VEC(gimple,heap) *worklist;
76 /* Vector indicating an SSA name has already been processed and marked
78 static sbitmap processed;
80 /* Vector indicating that the last statement of a basic block has already
81 been marked as necessary. */
82 static sbitmap last_stmt_necessary;
84 /* Vector indicating that BB contains statements that are live. */
85 static sbitmap bb_contains_live_stmts;
87 /* Before we can determine whether a control branch is dead, we need to
88 compute which blocks are control dependent on which edges.
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
94 static bitmap *control_dependence_map;
96 /* Vector indicating that a basic block has already had all the edges
97 processed that it is control dependent on. */
98 static sbitmap visited_control_parents;
100 /* TRUE if this pass alters the CFG (by removing control statements).
103 If this pass alters the CFG, then it will arrange for the dominators
105 static bool cfg_altered;
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, \
115 /* Indicate block BB is control dependent on an edge with index EDGE_INDEX. */
117 set_control_dependence_map_bit (basic_block bb, int edge_index)
119 if (bb == ENTRY_BLOCK_PTR)
121 gcc_assert (bb != EXIT_BLOCK_PTR);
122 bitmap_set_bit (control_dependence_map[bb->index], edge_index);
125 /* Clear all control dependences for block BB. */
127 clear_control_dependence_bitmap (basic_block bb)
129 bitmap_clear (control_dependence_map[bb->index]);
133 /* Find the immediate postdominator PDOM of the specified basic block BLOCK.
134 This function is necessary because some blocks have negative numbers. */
136 static inline basic_block
137 find_pdom (basic_block block)
139 gcc_assert (block != ENTRY_BLOCK_PTR);
141 if (block == EXIT_BLOCK_PTR)
142 return EXIT_BLOCK_PTR;
145 basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block);
147 return EXIT_BLOCK_PTR;
153 /* Determine all blocks' control dependences on the given edge with edge_list
154 EL index EDGE_INDEX, ala Morgan, Section 3.6. */
157 find_control_dependence (struct edge_list *el, int edge_index)
159 basic_block current_block;
160 basic_block ending_block;
162 gcc_assert (INDEX_EDGE_PRED_BB (el, edge_index) != EXIT_BLOCK_PTR);
164 if (INDEX_EDGE_PRED_BB (el, edge_index) == ENTRY_BLOCK_PTR)
165 ending_block = single_succ (ENTRY_BLOCK_PTR);
167 ending_block = find_pdom (INDEX_EDGE_PRED_BB (el, edge_index));
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))
173 edge e = INDEX_EDGE (el, edge_index);
175 /* For abnormal edges, we don't make current_block control
176 dependent because instructions that throw are always necessary
178 if (e->flags & EDGE_ABNORMAL)
181 set_control_dependence_map_bit (current_block, edge_index);
186 /* Record all blocks' control dependences on all edges in the edge
187 list EL, ala Morgan, Section 3.6. */
190 find_all_control_dependences (struct edge_list *el)
194 for (i = 0; i < NUM_EDGES (el); ++i)
195 find_control_dependence (el, i);
198 /* If STMT is not already marked necessary, mark it, and add it to the
199 worklist if ADD_TO_WORKLIST is true. */
202 mark_stmt_necessary (gimple stmt, bool add_to_worklist)
206 if (gimple_plf (stmt, STMT_NECESSARY))
209 if (dump_file && (dump_flags & TDF_DETAILS))
211 fprintf (dump_file, "Marking useful stmt: ");
212 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
213 fprintf (dump_file, "\n");
216 gimple_set_plf (stmt, STMT_NECESSARY, true);
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);
224 /* Mark the statement defining operand OP as necessary. */
227 mark_operand_necessary (tree op)
234 ver = SSA_NAME_VERSION (op);
235 if (TEST_BIT (processed, ver))
237 stmt = SSA_NAME_DEF_STMT (op);
238 gcc_assert (gimple_nop_p (stmt)
239 || gimple_plf (stmt, STMT_NECESSARY));
242 SET_BIT (processed, ver);
244 stmt = SSA_NAME_DEF_STMT (op);
247 if (gimple_plf (stmt, STMT_NECESSARY) || gimple_nop_p (stmt))
250 if (dump_file && (dump_flags & TDF_DETAILS))
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);
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);
265 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
266 it can make other statements necessary.
268 If AGGRESSIVE is false, control statements are conservatively marked as
272 mark_stmt_if_obviously_necessary (gimple stmt, bool aggressive)
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))
278 mark_stmt_necessary (stmt, true);
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
288 switch (gimple_code (stmt))
292 mark_stmt_necessary (stmt, false);
298 mark_stmt_necessary (stmt, true);
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))
308 case BUILT_IN_MALLOC:
309 case BUILT_IN_CALLOC:
310 case BUILT_IN_ALLOCA:
311 case BUILT_IN_ALLOCA_WITH_ALIGN:
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))
321 mark_stmt_necessary (stmt, true);
324 if (!gimple_call_lhs (stmt))
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);
341 gcc_assert (!simple_goto_p (stmt));
342 mark_stmt_necessary (stmt, true);
346 gcc_assert (EDGE_COUNT (gimple_bb (stmt)->succs) == 2);
351 mark_stmt_necessary (stmt, true);
355 if (TREE_CODE (gimple_assign_lhs (stmt)) == SSA_NAME
356 && TREE_CLOBBER_P (gimple_assign_rhs1 (stmt)))
364 /* If the statement has volatile operands, it needs to be preserved.
365 Same for statements that can alter control flow in unpredictable
367 if (gimple_has_volatile_ops (stmt) || is_ctrl_altering_stmt (stmt))
369 mark_stmt_necessary (stmt, true);
373 if (is_hidden_global_store (stmt))
375 mark_stmt_necessary (stmt, true);
383 /* Mark the last statement of BB as necessary. */
386 mark_last_stmt_necessary (basic_block bb)
388 gimple stmt = last_stmt (bb);
390 SET_BIT (last_stmt_necessary, bb->index);
391 SET_BIT (bb_contains_live_stmts, bb->index);
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);
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.
402 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
405 mark_control_dependent_edges_necessary (basic_block bb, struct edge_list *el,
409 unsigned edge_number;
410 bool skipped = false;
412 gcc_assert (bb != EXIT_BLOCK_PTR);
414 if (bb == ENTRY_BLOCK_PTR)
417 EXECUTE_IF_CONTROL_DEPENDENT (bi, bb->index, edge_number)
419 basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number);
421 if (ignore_self && cd_bb == bb)
427 if (!TEST_BIT (last_stmt_necessary, cd_bb->index))
428 mark_last_stmt_necessary (cd_bb);
432 SET_BIT (visited_control_parents, bb->index);
436 /* Find obviously necessary statements. These are things like most function
437 calls, and stores to file level variables.
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. */
444 find_obviously_necessary_stmts (struct edge_list *el)
447 gimple_stmt_iterator gsi;
454 /* PHI nodes are never inherently necessary. */
455 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
457 phi = gsi_stmt (gsi);
458 gimple_set_plf (phi, STMT_NECESSARY, false);
461 /* Check all statements in the block. */
462 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
464 stmt = gsi_stmt (gsi);
465 gimple_set_plf (stmt, STMT_NECESSARY, false);
466 mark_stmt_if_obviously_necessary (stmt, el != NULL);
470 /* Pure and const functions are finite and thus have no infinite loops in
472 flags = flags_from_decl_or_type (current_function_decl);
473 if ((flags & (ECF_CONST|ECF_PURE)) && !(flags & ECF_LOOPING_CONST_OR_PURE))
476 /* Prevent the empty possibly infinite loops from being removed. */
482 if (mark_irreducible_loops ())
486 FOR_EACH_EDGE (e, ei, bb->succs)
487 if ((e->flags & EDGE_DFS_BACK)
488 && (e->flags & EDGE_IRREDUCIBLE_LOOP))
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);
497 FOR_EACH_LOOP (li, loop, 0)
498 if (!finite_loop_p (loop))
501 fprintf (dump_file, "can not prove finiteness of loop %i\n", loop->num);
502 mark_control_dependent_edges_necessary (loop->latch, el, false);
509 /* Return true if REF is based on an aliased base, otherwise false. */
512 ref_may_be_aliased (tree ref)
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));
524 static bitmap visited = NULL;
525 static unsigned int longest_chain = 0;
526 static unsigned int total_chain = 0;
527 static unsigned int nr_walks = 0;
528 static bool chain_ovfl = false;
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. */
538 mark_aliased_reaching_defs_necessary_1 (ao_ref *ref, tree vdef, void *data)
540 gimple def_stmt = SSA_NAME_DEF_STMT (vdef);
542 /* All stmts we visit are necessary. */
543 mark_operand_necessary (vdef);
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
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))
556 tree base, lhs = gimple_get_lhs (def_stmt);
557 HOST_WIDE_INT size, offset, max_size;
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)
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)
569 if (offset <= ref->offset
570 && offset + size >= ref->offset + ref->max_size)
573 /* Or they need to be exactly the same. */
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
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
583 && (basic_block) data != gimple_bb (def_stmt)
584 && dominated_by_p (CDI_DOMINATORS, (basic_block) data,
585 gimple_bb (def_stmt))
586 && operand_equal_p (ref->ref, lhs, 0))
591 /* Otherwise keep walking. */
596 mark_aliased_reaching_defs_necessary (gimple stmt, tree ref)
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;
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. */
618 mark_all_reaching_defs_necessary_1 (ao_ref *ref ATTRIBUTE_UNUSED,
619 tree vdef, void *data ATTRIBUTE_UNUSED)
621 gimple def_stmt = SSA_NAME_DEF_STMT (vdef);
623 /* We have to skip already visited (and thus necessary) statements
624 to make the chaining work after we dropped back to simple mode. */
626 && TEST_BIT (processed, SSA_NAME_VERSION (vdef)))
628 gcc_assert (gimple_nop_p (def_stmt)
629 || gimple_plf (def_stmt, STMT_NECESSARY));
633 /* We want to skip stores to non-aliased variables. */
635 && gimple_assign_single_p (def_stmt))
637 tree lhs = gimple_assign_lhs (def_stmt);
638 if (!ref_may_be_aliased (lhs))
642 /* We want to skip statments that do not constitute stores but have
643 a virtual definition. */
644 if (is_gimple_call (def_stmt))
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))
651 case BUILT_IN_MALLOC:
652 case BUILT_IN_CALLOC:
653 case BUILT_IN_ALLOCA:
654 case BUILT_IN_ALLOCA_WITH_ALIGN:
662 mark_operand_necessary (vdef);
668 mark_all_reaching_defs_necessary (gimple stmt)
670 walk_aliased_vdefs (NULL, gimple_vuse (stmt),
671 mark_all_reaching_defs_necessary_1, NULL, &visited);
674 /* Return true for PHI nodes with one or identical arguments
677 degenerate_phi_p (gimple phi)
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)
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.
692 In conservative mode, EL is NULL. */
695 propagate_necessity (struct edge_list *el)
698 bool aggressive = (el ? true : false);
700 if (dump_file && (dump_flags & TDF_DETAILS))
701 fprintf (dump_file, "\nProcessing worklist:\n");
703 while (VEC_length (gimple, worklist) > 0)
705 /* Take STMT from worklist. */
706 stmt = VEC_pop (gimple, worklist);
708 if (dump_file && (dump_flags & TDF_DETAILS))
710 fprintf (dump_file, "processing: ");
711 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
712 fprintf (dump_file, "\n");
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
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);
726 if (gimple_code (stmt) == GIMPLE_PHI
727 /* We do not process virtual PHI nodes nor do we track their
729 && is_gimple_reg (gimple_phi_result (stmt)))
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
739 for (k = 0; k < gimple_phi_num_args (stmt); k++)
741 tree arg = PHI_ARG_DEF (stmt, k);
742 if (TREE_CODE (arg) == SSA_NAME)
743 mark_operand_necessary (arg);
746 /* For PHI operands it matters from where the control flow arrives
747 to the BB. Consider the following example:
757 We need to mark control dependence of the empty basic blocks, since they
758 contains computation of PHI operands.
760 Doing so is too restrictive in the case the predecestor block is in
766 for (i = 0; i<1000; ++i)
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
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.
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
789 In this case the only basic block C' is control dependent on is B.
791 2) C' has single child that is B
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)
797 Now how to decide what case happens? There are two basic options:
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
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.
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'. */
815 if (aggressive && !degenerate_phi_p (stmt))
817 for (k = 0; k < gimple_phi_num_args (stmt); k++)
819 basic_block arg_bb = gimple_phi_arg_edge (stmt, k)->src;
822 != get_immediate_dominator (CDI_POST_DOMINATORS, arg_bb))
824 if (!TEST_BIT (last_stmt_necessary, arg_bb->index))
825 mark_last_stmt_necessary (arg_bb);
827 else if (arg_bb != ENTRY_BLOCK_PTR
828 && !TEST_BIT (visited_control_parents,
830 mark_control_dependent_edges_necessary (arg_bb, el, true);
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. */
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))
847 tree ptr = gimple_call_arg (stmt, 0);
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))
861 FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
862 mark_operand_necessary (use);
864 use = gimple_vuse (stmt);
868 /* If we dropped to simple mode make all immediately
869 reachable definitions necessary. */
872 mark_all_reaching_defs_necessary (stmt);
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. */
889 if (is_gimple_call (stmt))
891 tree callee = gimple_call_fndecl (stmt);
894 /* Calls to functions that are merely acting as barriers
895 or that only store to memory do not make any previous
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))
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)
918 tree arg = gimple_call_arg (stmt, i);
919 if (TREE_CODE (arg) == SSA_NAME
920 || is_gimple_min_invariant (arg))
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);
928 else if (gimple_assign_single_p (stmt))
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)
937 if (!ref_may_be_aliased (rhs))
938 mark_aliased_reaching_defs_necessary (stmt, rhs);
940 mark_all_reaching_defs_necessary (stmt);
943 else if (gimple_code (stmt) == GIMPLE_RETURN)
945 tree rhs = gimple_return_retval (stmt);
946 /* A return statement may perform a load. */
948 && TREE_CODE (rhs) != SSA_NAME
949 && !is_gimple_min_invariant (rhs)
950 && TREE_CODE (rhs) != CONSTRUCTOR)
952 if (!ref_may_be_aliased (rhs))
953 mark_aliased_reaching_defs_necessary (stmt, rhs);
955 mark_all_reaching_defs_necessary (stmt);
958 else if (gimple_code (stmt) == GIMPLE_ASM)
961 mark_all_reaching_defs_necessary (stmt);
962 /* Inputs may perform loads. */
963 for (i = 0; i < gimple_asm_ninputs (stmt); ++i)
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);
973 else if (gimple_code (stmt) == GIMPLE_TRANSACTION)
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);
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)
997 bitmap_clear (visited);
1003 /* Replace all uses of NAME by underlying variable and mark it
1007 mark_virtual_operand_for_renaming (tree name)
1010 imm_use_iterator iter;
1011 use_operand_p use_p;
1015 name_var = SSA_NAME_VAR (name);
1016 FOR_EACH_IMM_USE_STMT (stmt, iter, name)
1018 FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
1019 SET_USE (use_p, name_var);
1024 mark_sym_for_renaming (name_var);
1027 /* Replace all uses of result of PHI by underlying variable and mark it
1031 mark_virtual_phi_result_for_renaming (gimple phi)
1033 if (dump_file && (dump_flags & TDF_DETAILS))
1035 fprintf (dump_file, "Marking result for renaming : ");
1036 print_gimple_stmt (dump_file, phi, 0, TDF_SLIM);
1037 fprintf (dump_file, "\n");
1040 mark_virtual_operand_for_renaming (gimple_phi_result (phi));
1044 /* Remove dead PHI nodes from block BB. */
1047 remove_dead_phis (basic_block bb)
1049 bool something_changed = false;
1052 gimple_stmt_iterator gsi;
1053 phis = phi_nodes (bb);
1055 for (gsi = gsi_start (phis); !gsi_end_p (gsi);)
1058 phi = gsi_stmt (gsi);
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)))
1064 /* Virtual PHI nodes with one or identical arguments
1066 if (degenerate_phi_p (phi))
1068 tree vdef = gimple_phi_result (phi);
1069 tree vuse = gimple_phi_arg_def (phi, 0);
1071 use_operand_p use_p;
1072 imm_use_iterator iter;
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;
1082 gimple_set_plf (phi, STMT_NECESSARY, true);
1085 if (!gimple_plf (phi, STMT_NECESSARY))
1087 something_changed = true;
1088 if (dump_file && (dump_flags & TDF_DETAILS))
1090 fprintf (dump_file, "Deleting : ");
1091 print_gimple_stmt (dump_file, phi, 0, TDF_SLIM);
1092 fprintf (dump_file, "\n");
1095 remove_phi_node (&gsi, true);
1096 stats.removed_phis++;
1102 return something_changed;
1105 /* Forward edge E to respective POST_DOM_BB and update PHIs. */
1108 forward_edge_to_pdom (edge e, basic_block post_dom_bb)
1110 gimple_stmt_iterator gsi;
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);
1118 e2 = redirect_edge_and_branch (e, post_dom_bb);
1121 /* If edge was already around, no updating is neccesary. */
1125 if (!gimple_seq_empty_p (phi_nodes (post_dom_bb)))
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)
1132 for (gsi = gsi_start_phis (post_dom_bb); !gsi_end_p (gsi);)
1134 gimple phi = gsi_stmt (gsi);
1136 source_location locus;
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)))
1142 mark_virtual_phi_result_for_renaming (phi);
1143 remove_phi_node (&gsi, true);
1147 /* Dead PHI do not imply control dependency. */
1148 if (!gimple_plf (phi, STMT_NECESSARY))
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));
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. */
1169 remove_dead_stmt (gimple_stmt_iterator *i, basic_block bb)
1171 gimple stmt = gsi_stmt (*i);
1173 if (dump_file && (dump_flags & TDF_DETAILS))
1175 fprintf (dump_file, "Deleting : ");
1176 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
1177 fprintf (dump_file, "\n");
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
1188 if (is_ctrl_stmt (stmt))
1190 basic_block post_dom_bb;
1194 post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
1196 e = find_edge (bb, post_dom_bb);
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. */
1204 else if (! post_dom_bb || post_dom_bb == EXIT_BLOCK_PTR)
1205 e = EDGE_SUCC (bb, 0);
1207 e = forward_edge_to_pdom (EDGE_SUCC (bb, 0), post_dom_bb);
1209 e->probability = REG_BR_PROB_BASE;
1210 e->count = bb->count;
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);
1216 /* The lone outgoing edge from BB will be a fallthru edge. */
1217 e->flags |= EDGE_FALLTHRU;
1219 /* Remove the remaining outgoing edges. */
1220 for (ei = ei_start (bb->succs); (e2 = ei_safe_edge (ei)); )
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)))
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))
1243 tree rhs = gimple_assign_rhs1 (stmt);
1245 = gimple_build_debug_bind (lhs, unshare_expr (rhs), stmt);
1246 gsi_insert_after (i, note, GSI_SAME_STMT);
1250 unlink_stmt_vdef (stmt);
1251 gsi_remove (i, true);
1252 release_defs (stmt);
1255 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1256 contributes nothing to the program, and can be deleted. */
1259 eliminate_unnecessary_stmts (void)
1261 bool something_changed = false;
1263 gimple_stmt_iterator gsi, psi;
1266 VEC (basic_block, heap) *h;
1268 if (dump_file && (dump_flags & TDF_DETAILS))
1269 fprintf (dump_file, "\nEliminating unnecessary statements:\n");
1271 clear_special_calls ();
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:
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:
1288 # DEBUG a => x_3 - b_4
1292 # DEBUG a => y_1 + z_2 - b_4
1295 gcc_assert (dom_info_available_p (CDI_DOMINATORS));
1296 h = get_all_dominated_blocks (CDI_DOMINATORS, single_succ (ENTRY_BLOCK_PTR));
1298 while (VEC_length (basic_block, h))
1300 bb = VEC_pop (basic_block, h);
1302 /* Remove dead statements. */
1303 for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi = psi)
1305 stmt = gsi_stmt (gsi);
1312 /* We can mark a call to free as not necessary if the
1313 defining statement of its argument is an allocation
1314 function and that is not necessary itself. */
1315 if (gimple_call_builtin_p (stmt, BUILT_IN_FREE))
1317 tree ptr = gimple_call_arg (stmt, 0);
1320 if (TREE_CODE (ptr) != SSA_NAME)
1322 def_stmt = SSA_NAME_DEF_STMT (ptr);
1323 if (!is_gimple_call (def_stmt)
1324 || gimple_plf (def_stmt, STMT_NECESSARY))
1326 callee2 = gimple_call_fndecl (def_stmt);
1327 if (callee2 == NULL_TREE
1328 || DECL_BUILT_IN_CLASS (callee2) != BUILT_IN_NORMAL
1329 || (DECL_FUNCTION_CODE (callee2) != BUILT_IN_MALLOC
1330 && DECL_FUNCTION_CODE (callee2) != BUILT_IN_CALLOC))
1332 gimple_set_plf (stmt, STMT_NECESSARY, false);
1335 /* If GSI is not necessary then remove it. */
1336 if (!gimple_plf (stmt, STMT_NECESSARY))
1338 if (!is_gimple_debug (stmt))
1339 something_changed = true;
1340 remove_dead_stmt (&gsi, bb);
1342 else if (is_gimple_call (stmt))
1344 tree name = gimple_call_lhs (stmt);
1346 notice_special_calls (stmt);
1348 /* When LHS of var = call (); is dead, simplify it into
1349 call (); saving one operand. */
1351 && TREE_CODE (name) == SSA_NAME
1352 && !TEST_BIT (processed, SSA_NAME_VERSION (name))
1353 /* Avoid doing so for allocation calls which we
1354 did not mark as necessary, it will confuse the
1355 special logic we apply to malloc/free pair removal. */
1356 && (!(call = gimple_call_fndecl (stmt))
1357 || DECL_BUILT_IN_CLASS (call) != BUILT_IN_NORMAL
1358 || (DECL_FUNCTION_CODE (call) != BUILT_IN_MALLOC
1359 && DECL_FUNCTION_CODE (call) != BUILT_IN_CALLOC
1360 && DECL_FUNCTION_CODE (call) != BUILT_IN_ALLOCA
1361 && (DECL_FUNCTION_CODE (call)
1362 != BUILT_IN_ALLOCA_WITH_ALIGN))))
1364 something_changed = true;
1365 if (dump_file && (dump_flags & TDF_DETAILS))
1367 fprintf (dump_file, "Deleting LHS of call: ");
1368 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
1369 fprintf (dump_file, "\n");
1372 gimple_call_set_lhs (stmt, NULL_TREE);
1373 maybe_clean_or_replace_eh_stmt (stmt, stmt);
1375 release_ssa_name (name);
1381 VEC_free (basic_block, heap, h);
1383 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1384 rendered some PHI nodes unreachable while they are still in use.
1385 Mark them for renaming. */
1388 basic_block prev_bb;
1390 find_unreachable_blocks ();
1392 /* Delete all unreachable basic blocks in reverse dominator order. */
1393 for (bb = EXIT_BLOCK_PTR->prev_bb; bb != ENTRY_BLOCK_PTR; bb = prev_bb)
1395 prev_bb = bb->prev_bb;
1397 if (!TEST_BIT (bb_contains_live_stmts, bb->index)
1398 || !(bb->flags & BB_REACHABLE))
1400 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
1401 if (!is_gimple_reg (gimple_phi_result (gsi_stmt (gsi))))
1404 imm_use_iterator iter;
1406 FOR_EACH_IMM_USE_STMT (stmt, iter, gimple_phi_result (gsi_stmt (gsi)))
1408 if (!(gimple_bb (stmt)->flags & BB_REACHABLE))
1410 if (gimple_code (stmt) == GIMPLE_PHI
1411 || gimple_plf (stmt, STMT_NECESSARY))
1414 BREAK_FROM_IMM_USE_STMT (iter);
1418 mark_virtual_phi_result_for_renaming (gsi_stmt (gsi));
1421 if (!(bb->flags & BB_REACHABLE))
1423 /* Speed up the removal of blocks that don't
1424 dominate others. Walking backwards, this should
1425 be the common case. ??? Do we need to recompute
1426 dominators because of cfg_altered? */
1427 if (!MAY_HAVE_DEBUG_STMTS
1428 || !first_dom_son (CDI_DOMINATORS, bb))
1429 delete_basic_block (bb);
1432 h = get_all_dominated_blocks (CDI_DOMINATORS, bb);
1434 while (VEC_length (basic_block, h))
1436 bb = VEC_pop (basic_block, h);
1437 prev_bb = bb->prev_bb;
1438 /* Rearrangements to the CFG may have failed
1439 to update the dominators tree, so that
1440 formerly-dominated blocks are now
1441 otherwise reachable. */
1442 if (!!(bb->flags & BB_REACHABLE))
1444 delete_basic_block (bb);
1447 VEC_free (basic_block, heap, h);
1455 /* Remove dead PHI nodes. */
1456 something_changed |= remove_dead_phis (bb);
1459 return something_changed;
1463 /* Print out removed statement statistics. */
1470 percg = ((float) stats.removed / (float) stats.total) * 100;
1471 fprintf (dump_file, "Removed %d of %d statements (%d%%)\n",
1472 stats.removed, stats.total, (int) percg);
1474 if (stats.total_phis == 0)
1477 percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100;
1479 fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n",
1480 stats.removed_phis, stats.total_phis, (int) percg);
1483 /* Initialization for this pass. Set up the used data structures. */
1486 tree_dce_init (bool aggressive)
1488 memset ((void *) &stats, 0, sizeof (stats));
1494 control_dependence_map = XNEWVEC (bitmap, last_basic_block);
1495 for (i = 0; i < last_basic_block; ++i)
1496 control_dependence_map[i] = BITMAP_ALLOC (NULL);
1498 last_stmt_necessary = sbitmap_alloc (last_basic_block);
1499 sbitmap_zero (last_stmt_necessary);
1500 bb_contains_live_stmts = sbitmap_alloc (last_basic_block);
1501 sbitmap_zero (bb_contains_live_stmts);
1504 processed = sbitmap_alloc (num_ssa_names + 1);
1505 sbitmap_zero (processed);
1507 worklist = VEC_alloc (gimple, heap, 64);
1508 cfg_altered = false;
1511 /* Cleanup after this pass. */
1514 tree_dce_done (bool aggressive)
1520 for (i = 0; i < last_basic_block; ++i)
1521 BITMAP_FREE (control_dependence_map[i]);
1522 free (control_dependence_map);
1524 sbitmap_free (visited_control_parents);
1525 sbitmap_free (last_stmt_necessary);
1526 sbitmap_free (bb_contains_live_stmts);
1527 bb_contains_live_stmts = NULL;
1530 sbitmap_free (processed);
1532 VEC_free (gimple, heap, worklist);
1535 /* Main routine to eliminate dead code.
1537 AGGRESSIVE controls the aggressiveness of the algorithm.
1538 In conservative mode, we ignore control dependence and simply declare
1539 all but the most trivially dead branches necessary. This mode is fast.
1540 In aggressive mode, control dependences are taken into account, which
1541 results in more dead code elimination, but at the cost of some time.
1543 FIXME: Aggressive mode before PRE doesn't work currently because
1544 the dominance info is not invalidated after DCE1. This is
1545 not an issue right now because we only run aggressive DCE
1546 as the last tree SSA pass, but keep this in mind when you
1547 start experimenting with pass ordering. */
1550 perform_tree_ssa_dce (bool aggressive)
1552 struct edge_list *el = NULL;
1553 bool something_changed = 0;
1555 calculate_dominance_info (CDI_DOMINATORS);
1557 /* Preheaders are needed for SCEV to work.
1558 Simple lateches and recorded exits improve chances that loop will
1559 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1561 loop_optimizer_init (LOOPS_NORMAL
1562 | LOOPS_HAVE_RECORDED_EXITS);
1564 tree_dce_init (aggressive);
1568 /* Compute control dependence. */
1569 timevar_push (TV_CONTROL_DEPENDENCES);
1570 calculate_dominance_info (CDI_POST_DOMINATORS);
1571 el = create_edge_list ();
1572 find_all_control_dependences (el);
1573 timevar_pop (TV_CONTROL_DEPENDENCES);
1575 visited_control_parents = sbitmap_alloc (last_basic_block);
1576 sbitmap_zero (visited_control_parents);
1578 mark_dfs_back_edges ();
1581 find_obviously_necessary_stmts (el);
1584 loop_optimizer_finalize ();
1590 visited = BITMAP_ALLOC (NULL);
1591 propagate_necessity (el);
1592 BITMAP_FREE (visited);
1594 something_changed |= eliminate_unnecessary_stmts ();
1595 something_changed |= cfg_altered;
1597 /* We do not update postdominators, so free them unconditionally. */
1598 free_dominance_info (CDI_POST_DOMINATORS);
1600 /* If we removed paths in the CFG, then we need to update
1601 dominators as well. I haven't investigated the possibility
1602 of incrementally updating dominators. */
1604 free_dominance_info (CDI_DOMINATORS);
1606 statistics_counter_event (cfun, "Statements deleted", stats.removed);
1607 statistics_counter_event (cfun, "PHI nodes deleted", stats.removed_phis);
1609 /* Debugging dumps. */
1610 if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS)))
1613 tree_dce_done (aggressive);
1615 free_edge_list (el);
1617 if (something_changed)
1618 return (TODO_update_ssa | TODO_cleanup_cfg | TODO_ggc_collect
1619 | TODO_remove_unused_locals);
1624 /* Pass entry points. */
1628 return perform_tree_ssa_dce (/*aggressive=*/false);
1632 tree_ssa_dce_loop (void)
1635 todo = perform_tree_ssa_dce (/*aggressive=*/false);
1638 free_numbers_of_iterations_estimates ();
1645 tree_ssa_cd_dce (void)
1647 return perform_tree_ssa_dce (/*aggressive=*/optimize >= 2);
1653 return flag_tree_dce != 0;
1656 struct gimple_opt_pass pass_dce =
1661 gate_dce, /* gate */
1662 tree_ssa_dce, /* execute */
1665 0, /* static_pass_number */
1666 TV_TREE_DCE, /* tv_id */
1667 PROP_cfg | PROP_ssa, /* properties_required */
1668 0, /* properties_provided */
1669 0, /* properties_destroyed */
1670 0, /* todo_flags_start */
1671 TODO_verify_ssa /* todo_flags_finish */
1675 struct gimple_opt_pass pass_dce_loop =
1679 "dceloop", /* name */
1680 gate_dce, /* gate */
1681 tree_ssa_dce_loop, /* execute */
1684 0, /* static_pass_number */
1685 TV_TREE_DCE, /* tv_id */
1686 PROP_cfg | PROP_ssa, /* properties_required */
1687 0, /* properties_provided */
1688 0, /* properties_destroyed */
1689 0, /* todo_flags_start */
1690 TODO_verify_ssa /* todo_flags_finish */
1694 struct gimple_opt_pass pass_cd_dce =
1699 gate_dce, /* gate */
1700 tree_ssa_cd_dce, /* execute */
1703 0, /* static_pass_number */
1704 TV_TREE_CD_DCE, /* tv_id */
1705 PROP_cfg | PROP_ssa, /* properties_required */
1706 0, /* properties_provided */
1707 0, /* properties_destroyed */
1708 0, /* todo_flags_start */
1710 | TODO_verify_flow /* todo_flags_finish */