1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002, 2003, 2004 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 2, or (at your option) any
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
19 You should have received a copy of the GNU General Public License
20 along with GCC; see the file COPYING. If not, write to the Free
21 Software Foundation, 59 Temple Place - Suite 330, Boston, MA
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"
53 /* These RTL headers are needed for basic-block.h. */
56 #include "hard-reg-set.h"
57 #include "basic-block.h"
60 #include "diagnostic.h"
61 #include "tree-flow.h"
62 #include "tree-gimple.h"
63 #include "tree-dump.h"
64 #include "tree-pass.h"
68 static struct stmt_stats
76 static varray_type worklist;
78 /* Vector indicating an SSA name has already been processed and marked
80 static sbitmap processed;
82 /* Vector indicating that last_stmt if a basic block has already been
83 marked as necessary. */
84 static sbitmap last_stmt_necessary;
86 /* Before we can determine whether a control branch is dead, we need to
87 compute which blocks are control dependent on which edges.
89 We expect each block to be control dependent on very few edges so we
90 use a bitmap for each block recording its edges. An array holds the
91 bitmap. The Ith bit in the bitmap is set if that block is dependent
93 bitmap *control_dependence_map;
95 /* Execute CODE for each edge (given number EDGE_NUMBER within the CODE)
96 for which the block with index N is control dependent. */
97 #define EXECUTE_IF_CONTROL_DEPENDENT(N, EDGE_NUMBER, CODE) \
101 EXECUTE_IF_SET_IN_BITMAP (control_dependence_map[N], 0, EDGE_NUMBER, bi) \
107 /* Local function prototypes. */
108 static inline void set_control_dependence_map_bit (basic_block, int);
109 static inline void clear_control_dependence_bitmap (basic_block);
110 static void find_all_control_dependences (struct edge_list *);
111 static void find_control_dependence (struct edge_list *, int);
112 static inline basic_block find_pdom (basic_block);
114 static inline void mark_stmt_necessary (tree, bool);
115 static inline void mark_operand_necessary (tree);
117 static void mark_stmt_if_obviously_necessary (tree, bool);
118 static void find_obviously_necessary_stmts (struct edge_list *);
120 static void mark_control_dependent_edges_necessary (basic_block, struct edge_list *);
121 static void propagate_necessity (struct edge_list *);
123 static void eliminate_unnecessary_stmts (void);
124 static void remove_dead_phis (basic_block);
125 static void remove_dead_stmt (block_stmt_iterator *, basic_block);
127 static void print_stats (void);
128 static void tree_dce_init (bool);
129 static void tree_dce_done (bool);
131 /* Indicate block BB is control dependent on an edge with index EDGE_INDEX. */
133 set_control_dependence_map_bit (basic_block bb, int edge_index)
135 if (bb == ENTRY_BLOCK_PTR)
137 gcc_assert (bb != EXIT_BLOCK_PTR);
138 bitmap_set_bit (control_dependence_map[bb->index], edge_index);
141 /* Clear all control dependences for block BB. */
143 void clear_control_dependence_bitmap (basic_block bb)
145 bitmap_clear (control_dependence_map[bb->index]);
148 /* Record all blocks' control dependences on all edges in the edge
149 list EL, ala Morgan, Section 3.6. */
152 find_all_control_dependences (struct edge_list *el)
156 for (i = 0; i < NUM_EDGES (el); ++i)
157 find_control_dependence (el, i);
160 /* Determine all blocks' control dependences on the given edge with edge_list
161 EL index EDGE_INDEX, ala Morgan, Section 3.6. */
164 find_control_dependence (struct edge_list *el, int edge_index)
166 basic_block current_block;
167 basic_block ending_block;
169 gcc_assert (INDEX_EDGE_PRED_BB (el, edge_index) != EXIT_BLOCK_PTR);
171 if (INDEX_EDGE_PRED_BB (el, edge_index) == ENTRY_BLOCK_PTR)
172 ending_block = ENTRY_BLOCK_PTR->next_bb;
174 ending_block = find_pdom (INDEX_EDGE_PRED_BB (el, edge_index));
176 for (current_block = INDEX_EDGE_SUCC_BB (el, edge_index);
177 current_block != ending_block && current_block != EXIT_BLOCK_PTR;
178 current_block = find_pdom (current_block))
180 edge e = INDEX_EDGE (el, edge_index);
182 /* For abnormal edges, we don't make current_block control
183 dependent because instructions that throw are always necessary
185 if (e->flags & EDGE_ABNORMAL)
188 set_control_dependence_map_bit (current_block, edge_index);
192 /* Find the immediate postdominator PDOM of the specified basic block BLOCK.
193 This function is necessary because some blocks have negative numbers. */
195 static inline basic_block
196 find_pdom (basic_block block)
198 gcc_assert (block != ENTRY_BLOCK_PTR);
200 if (block == EXIT_BLOCK_PTR)
201 return EXIT_BLOCK_PTR;
204 basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block);
206 return EXIT_BLOCK_PTR;
211 #define NECESSARY(stmt) stmt->common.asm_written_flag
213 /* If STMT is not already marked necessary, mark it, and add it to the
214 worklist if ADD_TO_WORKLIST is true. */
216 mark_stmt_necessary (tree stmt, bool add_to_worklist)
219 gcc_assert (stmt != error_mark_node);
220 gcc_assert (!DECL_P (stmt));
222 if (NECESSARY (stmt))
225 if (dump_file && (dump_flags & TDF_DETAILS))
227 fprintf (dump_file, "Marking useful stmt: ");
228 print_generic_stmt (dump_file, stmt, TDF_SLIM);
229 fprintf (dump_file, "\n");
232 NECESSARY (stmt) = 1;
234 VARRAY_PUSH_TREE (worklist, stmt);
237 /* Mark the statement defining operand OP as necessary. */
240 mark_operand_necessary (tree op)
247 ver = SSA_NAME_VERSION (op);
248 if (TEST_BIT (processed, ver))
250 SET_BIT (processed, ver);
252 stmt = SSA_NAME_DEF_STMT (op);
256 || IS_EMPTY_STMT (stmt))
259 NECESSARY (stmt) = 1;
260 VARRAY_PUSH_TREE (worklist, stmt);
264 /* Mark STMT as necessary if it is obviously is. Add it to the worklist if
265 it can make other statements necessary.
267 If AGGRESSIVE is false, control statements are conservatively marked as
271 mark_stmt_if_obviously_necessary (tree stmt, bool aggressive)
273 v_may_def_optype v_may_defs;
274 v_must_def_optype v_must_defs;
279 /* Statements that are implicitly live. Most function calls, asm and return
280 statements are required. Labels and BIND_EXPR nodes are kept because
281 they are control flow, and we have no way of knowing whether they can be
282 removed. DCE can eliminate all the other statements in a block, and CFG
283 can then remove the block and labels. */
284 switch (TREE_CODE (stmt))
288 case CASE_LABEL_EXPR:
289 mark_stmt_necessary (stmt, false);
295 mark_stmt_necessary (stmt, true);
299 /* Most, but not all function calls are required. Function calls that
300 produce no result and have no side effects (i.e. const pure
301 functions) are unnecessary. */
302 if (TREE_SIDE_EFFECTS (stmt))
303 mark_stmt_necessary (stmt, true);
307 op = get_call_expr_in (stmt);
308 if (op && TREE_SIDE_EFFECTS (op))
310 mark_stmt_necessary (stmt, true);
314 /* These values are mildly magic bits of the EH runtime. We can't
315 see the entire lifetime of these values until landing pads are
317 if (TREE_CODE (TREE_OPERAND (stmt, 0)) == EXC_PTR_EXPR
318 || TREE_CODE (TREE_OPERAND (stmt, 0)) == FILTER_EXPR)
320 mark_stmt_necessary (stmt, true);
326 if (! simple_goto_p (stmt))
327 mark_stmt_necessary (stmt, true);
331 if (GOTO_DESTINATION (COND_EXPR_THEN (stmt))
332 == GOTO_DESTINATION (COND_EXPR_ELSE (stmt)))
334 /* A COND_EXPR is obviously dead if the target labels are the same.
335 We cannot kill the statement at this point, so to prevent the
336 statement from being marked necessary, we replace the condition
337 with a constant. The stmt is killed later on in cfg_cleanup. */
338 COND_EXPR_COND (stmt) = integer_zero_node;
346 mark_stmt_necessary (stmt, true);
353 ann = stmt_ann (stmt);
355 /* If the statement has volatile operands, it needs to be preserved.
356 Same for statements that can alter control flow in unpredictable
358 if (ann->has_volatile_ops || is_ctrl_altering_stmt (stmt))
360 mark_stmt_necessary (stmt, true);
364 get_stmt_operands (stmt);
366 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF)
368 if (is_global_var (SSA_NAME_VAR (def)))
370 mark_stmt_necessary (stmt, true);
375 /* Check virtual definitions. If we get here, the only virtual
376 definitions we should see are those generated by assignment
378 v_may_defs = V_MAY_DEF_OPS (ann);
379 v_must_defs = V_MUST_DEF_OPS (ann);
380 if (NUM_V_MAY_DEFS (v_may_defs) > 0 || NUM_V_MUST_DEFS (v_must_defs) > 0)
384 gcc_assert (TREE_CODE (stmt) == MODIFY_EXPR);
386 /* Note that we must not check the individual virtual operands
387 here. In particular, if this is an aliased store, we could
388 end up with something like the following (SSA notation
389 redacted for brevity):
394 p_1 = (i_2 > 3) ? &x : p_1;
396 # x_4 = V_MAY_DEF <x_3>
402 Notice that the store to '*p_1' should be preserved, if we
403 were to check the virtual definitions in that store, we would
404 not mark it needed. This is because 'x' is not a global
407 Therefore, we check the base address of the LHS. If the
408 address is a pointer, we check if its name tag or type tag is
409 a global variable. Otherwise, we check if the base variable
411 lhs = TREE_OPERAND (stmt, 0);
412 if (REFERENCE_CLASS_P (lhs))
413 lhs = get_base_address (lhs);
415 if (lhs == NULL_TREE)
417 /* If LHS is NULL, it means that we couldn't get the base
418 address of the reference. In which case, we should not
419 remove this store. */
420 mark_stmt_necessary (stmt, true);
422 else if (DECL_P (lhs))
424 /* If the store is to a global symbol, we need to keep it. */
425 if (is_global_var (lhs))
426 mark_stmt_necessary (stmt, true);
428 else if (TREE_CODE (lhs) == INDIRECT_REF
429 || TREE_CODE (lhs) == ALIGN_INDIRECT_REF
430 || TREE_CODE (lhs) == MISALIGNED_INDIRECT_REF)
432 tree ptr = TREE_OPERAND (lhs, 0);
433 struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr);
434 tree nmt = (pi) ? pi->name_mem_tag : NULL_TREE;
435 tree tmt = var_ann (SSA_NAME_VAR (ptr))->type_mem_tag;
437 /* If either the name tag or the type tag for PTR is a
438 global variable, then the store is necessary. */
439 if ((nmt && is_global_var (nmt))
440 || (tmt && is_global_var (tmt)))
442 mark_stmt_necessary (stmt, true);
453 /* Find obviously necessary statements. These are things like most function
454 calls, and stores to file level variables.
456 If EL is NULL, control statements are conservatively marked as
457 necessary. Otherwise it contains the list of edges used by control
458 dependence analysis. */
461 find_obviously_necessary_stmts (struct edge_list *el)
464 block_stmt_iterator i;
471 /* Check any PHI nodes in the block. */
472 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
476 /* PHIs for virtual variables do not directly affect code
477 generation and need not be considered inherently necessary
478 regardless of the bits set in their decl.
480 Thus, we only need to mark PHIs for real variables which
481 need their result preserved as being inherently necessary. */
482 if (is_gimple_reg (PHI_RESULT (phi))
483 && is_global_var (SSA_NAME_VAR (PHI_RESULT (phi))))
484 mark_stmt_necessary (phi, true);
487 /* Check all statements in the block. */
488 for (i = bsi_start (bb); ! bsi_end_p (i); bsi_next (&i))
490 tree stmt = bsi_stmt (i);
491 NECESSARY (stmt) = 0;
492 mark_stmt_if_obviously_necessary (stmt, el != NULL);
495 /* Mark this basic block as `not visited'. A block will be marked
496 visited when the edges that it is control dependent on have been
498 bb->flags &= ~BB_VISITED;
503 /* Prevent the loops from being removed. We must keep the infinite loops,
504 and we currently do not have a means to recognize the finite ones. */
507 for (e = bb->succ; e; e = e->succ_next)
508 if (e->flags & EDGE_DFS_BACK)
509 mark_control_dependent_edges_necessary (e->dest, el);
514 /* Make corresponding control dependent edges necessary. We only
515 have to do this once for each basic block, so we clear the bitmap
518 mark_control_dependent_edges_necessary (basic_block bb, struct edge_list *el)
522 gcc_assert (bb != EXIT_BLOCK_PTR);
524 if (bb == ENTRY_BLOCK_PTR)
527 EXECUTE_IF_CONTROL_DEPENDENT (bb->index, edge_number,
530 basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number);
532 if (TEST_BIT (last_stmt_necessary, cd_bb->index))
534 SET_BIT (last_stmt_necessary, cd_bb->index);
536 t = last_stmt (cd_bb);
537 if (t && is_ctrl_stmt (t))
538 mark_stmt_necessary (t, true);
542 /* Propagate necessity using the operands of necessary statements. Process
543 the uses on each statement in the worklist, and add all feeding statements
544 which contribute to the calculation of this value to the worklist.
546 In conservative mode, EL is NULL. */
549 propagate_necessity (struct edge_list *el)
552 bool aggressive = (el ? true : false);
554 if (dump_file && (dump_flags & TDF_DETAILS))
555 fprintf (dump_file, "\nProcessing worklist:\n");
557 while (VARRAY_ACTIVE_SIZE (worklist) > 0)
559 /* Take `i' from worklist. */
560 i = VARRAY_TOP_TREE (worklist);
561 VARRAY_POP (worklist);
563 if (dump_file && (dump_flags & TDF_DETAILS))
565 fprintf (dump_file, "processing: ");
566 print_generic_stmt (dump_file, i, TDF_SLIM);
567 fprintf (dump_file, "\n");
572 /* Mark the last statements of the basic blocks that the block
573 containing `i' is control dependent on, but only if we haven't
575 basic_block bb = bb_for_stmt (i);
576 if (! (bb->flags & BB_VISITED))
578 bb->flags |= BB_VISITED;
579 mark_control_dependent_edges_necessary (bb, el);
583 if (TREE_CODE (i) == PHI_NODE)
585 /* PHI nodes are somewhat special in that each PHI alternative has
586 data and control dependencies. All the statements feeding the
587 PHI node's arguments are always necessary. In aggressive mode,
588 we also consider the control dependent edges leading to the
589 predecessor block associated with each PHI alternative as
592 for (k = 0; k < PHI_NUM_ARGS (i); k++)
594 tree arg = PHI_ARG_DEF (i, k);
595 if (TREE_CODE (arg) == SSA_NAME)
596 mark_operand_necessary (arg);
601 for (k = 0; k < PHI_NUM_ARGS (i); k++)
603 basic_block arg_bb = PHI_ARG_EDGE (i, k)->src;
604 if (! (arg_bb->flags & BB_VISITED))
606 arg_bb->flags |= BB_VISITED;
607 mark_control_dependent_edges_necessary (arg_bb, el);
614 /* Propagate through the operands. Examine all the USE, VUSE and
615 V_MAY_DEF operands in this statement. Mark all the statements
616 which feed this statement's uses as necessary. */
620 get_stmt_operands (i);
622 /* The operands of V_MAY_DEF expressions are also needed as they
623 represent potential definitions that may reach this
624 statement (V_MAY_DEF operands allow us to follow def-def
627 FOR_EACH_SSA_TREE_OPERAND (use, i, iter, SSA_OP_ALL_USES)
628 mark_operand_necessary (use);
633 /* Eliminate unnecessary statements. Any instruction not marked as necessary
634 contributes nothing to the program, and can be deleted. */
637 eliminate_unnecessary_stmts (void)
640 block_stmt_iterator i;
642 if (dump_file && (dump_flags & TDF_DETAILS))
643 fprintf (dump_file, "\nEliminating unnecessary statements:\n");
645 clear_special_calls ();
648 /* Remove dead PHI nodes. */
649 remove_dead_phis (bb);
651 /* Remove dead statements. */
652 for (i = bsi_start (bb); ! bsi_end_p (i) ; )
654 tree t = bsi_stmt (i);
658 /* If `i' is not necessary then remove it. */
660 remove_dead_stmt (&i, bb);
663 tree call = get_call_expr_in (t);
665 notice_special_calls (call);
672 /* Remove dead PHI nodes from block BB. */
675 remove_dead_phis (basic_block bb)
680 phi = phi_nodes (bb);
685 if (! NECESSARY (phi))
687 tree next = PHI_CHAIN (phi);
689 if (dump_file && (dump_flags & TDF_DETAILS))
691 fprintf (dump_file, "Deleting : ");
692 print_generic_stmt (dump_file, phi, TDF_SLIM);
693 fprintf (dump_file, "\n");
696 remove_phi_node (phi, prev, bb);
697 stats.removed_phis++;
703 phi = PHI_CHAIN (phi);
708 /* Remove dead statement pointed by iterator I. Receives the basic block BB
709 containing I so that we don't have to look it up. */
712 remove_dead_stmt (block_stmt_iterator *i, basic_block bb)
714 tree t = bsi_stmt (*i);
716 if (dump_file && (dump_flags & TDF_DETAILS))
718 fprintf (dump_file, "Deleting : ");
719 print_generic_stmt (dump_file, t, TDF_SLIM);
720 fprintf (dump_file, "\n");
725 /* If we have determined that a conditional branch statement contributes
726 nothing to the program, then we not only remove it, but we also change
727 the flow graph so that the current block will simply fall-thru to its
728 immediate post-dominator. The blocks we are circumventing will be
729 removed by cleaup_cfg if this change in the flow graph makes them
731 if (is_ctrl_stmt (t))
733 basic_block post_dom_bb;
735 /* The post dominance info has to be up-to-date. */
736 gcc_assert (dom_computed[CDI_POST_DOMINATORS] == DOM_OK);
737 /* Get the immediate post dominator of bb. */
738 post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
739 /* Some blocks don't have an immediate post dominator. This can happen
740 for example with infinite loops. Removing an infinite loop is an
741 inappropriate transformation anyway... */
748 /* Redirect the first edge out of BB to reach POST_DOM_BB. */
749 redirect_edge_and_branch (bb->succ, post_dom_bb);
750 PENDING_STMT (bb->succ) = NULL;
751 bb->succ->probability = REG_BR_PROB_BASE;
752 bb->succ->count = bb->count;
754 /* The edge is no longer associated with a conditional, so it does
755 not have TRUE/FALSE flags. */
756 bb->succ->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
758 /* If the edge reaches any block other than the exit, then it is a
759 fallthru edge; if it reaches the exit, then it is not a fallthru
761 if (post_dom_bb != EXIT_BLOCK_PTR)
762 bb->succ->flags |= EDGE_FALLTHRU;
764 bb->succ->flags &= ~EDGE_FALLTHRU;
766 /* Remove the remaining the outgoing edges. */
767 for (e = bb->succ->succ_next; e != NULL;)
779 /* Print out removed statement statistics. */
784 if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS)))
788 percg = ((float) stats.removed / (float) stats.total) * 100;
789 fprintf (dump_file, "Removed %d of %d statements (%d%%)\n",
790 stats.removed, stats.total, (int) percg);
792 if (stats.total_phis == 0)
795 percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100;
797 fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n",
798 stats.removed_phis, stats.total_phis, (int) percg);
802 /* Initialization for this pass. Set up the used data structures. */
805 tree_dce_init (bool aggressive)
807 memset ((void *) &stats, 0, sizeof (stats));
813 control_dependence_map
814 = xmalloc (last_basic_block * sizeof (bitmap));
815 for (i = 0; i < last_basic_block; ++i)
816 control_dependence_map[i] = BITMAP_XMALLOC ();
818 last_stmt_necessary = sbitmap_alloc (last_basic_block);
819 sbitmap_zero (last_stmt_necessary);
822 processed = sbitmap_alloc (num_ssa_names + 1);
823 sbitmap_zero (processed);
825 VARRAY_TREE_INIT (worklist, 64, "work list");
828 /* Cleanup after this pass. */
831 tree_dce_done (bool aggressive)
837 for (i = 0; i < last_basic_block; ++i)
838 BITMAP_XFREE (control_dependence_map[i]);
839 free (control_dependence_map);
841 sbitmap_free (last_stmt_necessary);
844 sbitmap_free (processed);
847 /* Main routine to eliminate dead code.
849 AGGRESSIVE controls the aggressiveness of the algorithm.
850 In conservative mode, we ignore control dependence and simply declare
851 all but the most trivially dead branches necessary. This mode is fast.
852 In aggressive mode, control dependences are taken into account, which
853 results in more dead code elimination, but at the cost of some time.
855 FIXME: Aggressive mode before PRE doesn't work currently because
856 the dominance info is not invalidated after DCE1. This is
857 not an issue right now because we only run aggressive DCE
858 as the last tree SSA pass, but keep this in mind when you
859 start experimenting with pass ordering. */
862 perform_tree_ssa_dce (bool aggressive)
864 struct edge_list *el = NULL;
866 tree_dce_init (aggressive);
870 /* Compute control dependence. */
871 timevar_push (TV_CONTROL_DEPENDENCES);
872 calculate_dominance_info (CDI_POST_DOMINATORS);
873 el = create_edge_list ();
874 find_all_control_dependences (el);
875 timevar_pop (TV_CONTROL_DEPENDENCES);
877 mark_dfs_back_edges ();
880 find_obviously_necessary_stmts (el);
882 propagate_necessity (el);
884 eliminate_unnecessary_stmts ();
887 free_dominance_info (CDI_POST_DOMINATORS);
891 /* Debugging dumps. */
894 dump_function_to_file (current_function_decl, dump_file, dump_flags);
898 tree_dce_done (aggressive);
903 /* Pass entry points. */
907 perform_tree_ssa_dce (/*aggressive=*/false);
911 tree_ssa_cd_dce (void)
913 perform_tree_ssa_dce (/*aggressive=*/optimize >= 2);
919 return flag_tree_dce != 0;
922 struct tree_opt_pass pass_dce =
926 tree_ssa_dce, /* execute */
929 0, /* static_pass_number */
930 TV_TREE_DCE, /* tv_id */
931 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */
932 0, /* properties_provided */
933 0, /* properties_destroyed */
934 0, /* todo_flags_start */
935 TODO_ggc_collect | TODO_verify_ssa, /* todo_flags_finish */
939 struct tree_opt_pass pass_cd_dce =
943 tree_ssa_cd_dce, /* execute */
946 0, /* static_pass_number */
947 TV_TREE_CD_DCE, /* tv_id */
948 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */
949 0, /* properties_provided */
950 0, /* properties_destroyed */
951 0, /* todo_flags_start */
952 TODO_ggc_collect | TODO_verify_ssa | TODO_verify_flow,
953 /* todo_flags_finish */