1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002, 2003, 2004, 2005 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"
58 #include "basic-block.h"
61 #include "diagnostic.h"
62 #include "tree-flow.h"
63 #include "tree-gimple.h"
64 #include "tree-dump.h"
65 #include "tree-pass.h"
69 static struct stmt_stats
77 static varray_type worklist;
79 /* Vector indicating an SSA name has already been processed and marked
81 static sbitmap processed;
83 /* Vector indicating that last_stmt if a basic block has already been
84 marked as necessary. */
85 static sbitmap last_stmt_necessary;
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 /* Execute CODE for each edge (given number EDGE_NUMBER within the CODE)
101 for which the block with index N is control dependent. */
102 #define EXECUTE_IF_CONTROL_DEPENDENT(N, EDGE_NUMBER, CODE) \
104 bitmap_iterator bi; \
106 EXECUTE_IF_SET_IN_BITMAP (control_dependence_map[N], 0, EDGE_NUMBER, bi) \
112 /* Local function prototypes. */
113 static inline void set_control_dependence_map_bit (basic_block, int);
114 static inline void clear_control_dependence_bitmap (basic_block);
115 static void find_all_control_dependences (struct edge_list *);
116 static void find_control_dependence (struct edge_list *, int);
117 static inline basic_block find_pdom (basic_block);
119 static inline void mark_stmt_necessary (tree, bool);
120 static inline void mark_operand_necessary (tree, bool);
122 static void mark_stmt_if_obviously_necessary (tree, bool);
123 static void find_obviously_necessary_stmts (struct edge_list *);
125 static void mark_control_dependent_edges_necessary (basic_block, struct edge_list *);
126 static void propagate_necessity (struct edge_list *);
128 static void eliminate_unnecessary_stmts (void);
129 static void remove_dead_phis (basic_block);
130 static void remove_dead_stmt (block_stmt_iterator *, basic_block);
132 static void print_stats (void);
133 static void tree_dce_init (bool);
134 static void tree_dce_done (bool);
136 /* Indicate block BB is control dependent on an edge with index EDGE_INDEX. */
138 set_control_dependence_map_bit (basic_block bb, int edge_index)
140 if (bb == ENTRY_BLOCK_PTR)
142 gcc_assert (bb != EXIT_BLOCK_PTR);
143 bitmap_set_bit (control_dependence_map[bb->index], edge_index);
146 /* Clear all control dependences for block BB. */
148 void clear_control_dependence_bitmap (basic_block bb)
150 bitmap_clear (control_dependence_map[bb->index]);
153 /* Record all blocks' control dependences on all edges in the edge
154 list EL, ala Morgan, Section 3.6. */
157 find_all_control_dependences (struct edge_list *el)
161 for (i = 0; i < NUM_EDGES (el); ++i)
162 find_control_dependence (el, i);
165 /* Determine all blocks' control dependences on the given edge with edge_list
166 EL index EDGE_INDEX, ala Morgan, Section 3.6. */
169 find_control_dependence (struct edge_list *el, int edge_index)
171 basic_block current_block;
172 basic_block ending_block;
174 gcc_assert (INDEX_EDGE_PRED_BB (el, edge_index) != EXIT_BLOCK_PTR);
176 if (INDEX_EDGE_PRED_BB (el, edge_index) == ENTRY_BLOCK_PTR)
177 ending_block = ENTRY_BLOCK_PTR->next_bb;
179 ending_block = find_pdom (INDEX_EDGE_PRED_BB (el, edge_index));
181 for (current_block = INDEX_EDGE_SUCC_BB (el, edge_index);
182 current_block != ending_block && current_block != EXIT_BLOCK_PTR;
183 current_block = find_pdom (current_block))
185 edge e = INDEX_EDGE (el, edge_index);
187 /* For abnormal edges, we don't make current_block control
188 dependent because instructions that throw are always necessary
190 if (e->flags & EDGE_ABNORMAL)
193 set_control_dependence_map_bit (current_block, edge_index);
197 /* Find the immediate postdominator PDOM of the specified basic block BLOCK.
198 This function is necessary because some blocks have negative numbers. */
200 static inline basic_block
201 find_pdom (basic_block block)
203 gcc_assert (block != ENTRY_BLOCK_PTR);
205 if (block == EXIT_BLOCK_PTR)
206 return EXIT_BLOCK_PTR;
209 basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block);
211 return EXIT_BLOCK_PTR;
216 #define NECESSARY(stmt) stmt->common.asm_written_flag
218 /* If STMT is not already marked necessary, mark it, and add it to the
219 worklist if ADD_TO_WORKLIST is true. */
221 mark_stmt_necessary (tree stmt, bool add_to_worklist)
224 gcc_assert (!DECL_P (stmt));
226 if (NECESSARY (stmt))
229 if (dump_file && (dump_flags & TDF_DETAILS))
231 fprintf (dump_file, "Marking useful stmt: ");
232 print_generic_stmt (dump_file, stmt, TDF_SLIM);
233 fprintf (dump_file, "\n");
236 NECESSARY (stmt) = 1;
238 VARRAY_PUSH_TREE (worklist, stmt);
241 /* Mark the statement defining operand OP as necessary. PHIONLY is true
242 if we should only mark it necessary if it is a phi node. */
245 mark_operand_necessary (tree op, bool phionly)
252 ver = SSA_NAME_VERSION (op);
253 if (TEST_BIT (processed, ver))
255 SET_BIT (processed, ver);
257 stmt = SSA_NAME_DEF_STMT (op);
261 || IS_EMPTY_STMT (stmt)
262 || (phionly && TREE_CODE (stmt) != PHI_NODE))
265 NECESSARY (stmt) = 1;
266 VARRAY_PUSH_TREE (worklist, stmt);
270 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
271 it can make other statements necessary.
273 If AGGRESSIVE is false, control statements are conservatively marked as
277 mark_stmt_if_obviously_necessary (tree stmt, bool aggressive)
283 /* Statements that are implicitly live. Most function calls, asm and return
284 statements are required. Labels and BIND_EXPR nodes are kept because
285 they are control flow, and we have no way of knowing whether they can be
286 removed. DCE can eliminate all the other statements in a block, and CFG
287 can then remove the block and labels. */
288 switch (TREE_CODE (stmt))
292 case CASE_LABEL_EXPR:
293 mark_stmt_necessary (stmt, false);
299 mark_stmt_necessary (stmt, true);
303 /* Most, but not all function calls are required. Function calls that
304 produce no result and have no side effects (i.e. const pure
305 functions) are unnecessary. */
306 if (TREE_SIDE_EFFECTS (stmt))
307 mark_stmt_necessary (stmt, true);
311 op = get_call_expr_in (stmt);
312 if (op && TREE_SIDE_EFFECTS (op))
314 mark_stmt_necessary (stmt, true);
318 /* These values are mildly magic bits of the EH runtime. We can't
319 see the entire lifetime of these values until landing pads are
321 if (TREE_CODE (TREE_OPERAND (stmt, 0)) == EXC_PTR_EXPR
322 || TREE_CODE (TREE_OPERAND (stmt, 0)) == FILTER_EXPR)
324 mark_stmt_necessary (stmt, true);
330 gcc_assert (!simple_goto_p (stmt));
331 mark_stmt_necessary (stmt, true);
335 gcc_assert (EDGE_COUNT (bb_for_stmt (stmt)->succs) == 2);
340 mark_stmt_necessary (stmt, true);
347 ann = stmt_ann (stmt);
349 /* If the statement has volatile operands, it needs to be preserved.
350 Same for statements that can alter control flow in unpredictable
352 if (ann->has_volatile_ops || is_ctrl_altering_stmt (stmt))
354 mark_stmt_necessary (stmt, true);
358 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF)
360 if (is_global_var (SSA_NAME_VAR (def)))
362 mark_stmt_necessary (stmt, true);
366 if (is_hidden_global_store (stmt))
368 mark_stmt_necessary (stmt, true);
375 /* Find obviously necessary statements. These are things like most function
376 calls, and stores to file level variables.
378 If EL is NULL, control statements are conservatively marked as
379 necessary. Otherwise it contains the list of edges used by control
380 dependence analysis. */
383 find_obviously_necessary_stmts (struct edge_list *el)
386 block_stmt_iterator i;
393 /* Check any PHI nodes in the block. */
394 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
398 /* PHIs for virtual variables do not directly affect code
399 generation and need not be considered inherently necessary
400 regardless of the bits set in their decl.
402 Thus, we only need to mark PHIs for real variables which
403 need their result preserved as being inherently necessary. */
404 if (is_gimple_reg (PHI_RESULT (phi))
405 && is_global_var (SSA_NAME_VAR (PHI_RESULT (phi))))
406 mark_stmt_necessary (phi, true);
409 /* Check all statements in the block. */
410 for (i = bsi_start (bb); ! bsi_end_p (i); bsi_next (&i))
412 tree stmt = bsi_stmt (i);
413 NECESSARY (stmt) = 0;
414 mark_stmt_if_obviously_necessary (stmt, el != NULL);
420 /* Prevent the loops from being removed. We must keep the infinite loops,
421 and we currently do not have a means to recognize the finite ones. */
425 FOR_EACH_EDGE (e, ei, bb->succs)
426 if (e->flags & EDGE_DFS_BACK)
427 mark_control_dependent_edges_necessary (e->dest, el);
432 /* Make corresponding control dependent edges necessary. We only
433 have to do this once for each basic block, so we clear the bitmap
436 mark_control_dependent_edges_necessary (basic_block bb, struct edge_list *el)
438 unsigned edge_number;
440 gcc_assert (bb != EXIT_BLOCK_PTR);
442 if (bb == ENTRY_BLOCK_PTR)
445 EXECUTE_IF_CONTROL_DEPENDENT (bb->index, edge_number,
448 basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number);
450 if (TEST_BIT (last_stmt_necessary, cd_bb->index))
452 SET_BIT (last_stmt_necessary, cd_bb->index);
454 t = last_stmt (cd_bb);
455 if (t && is_ctrl_stmt (t))
456 mark_stmt_necessary (t, true);
460 /* Propagate necessity using the operands of necessary statements. Process
461 the uses on each statement in the worklist, and add all feeding statements
462 which contribute to the calculation of this value to the worklist.
464 In conservative mode, EL is NULL. */
467 propagate_necessity (struct edge_list *el)
470 bool aggressive = (el ? true : false);
472 if (dump_file && (dump_flags & TDF_DETAILS))
473 fprintf (dump_file, "\nProcessing worklist:\n");
475 while (VARRAY_ACTIVE_SIZE (worklist) > 0)
477 /* Take `i' from worklist. */
478 i = VARRAY_TOP_TREE (worklist);
479 VARRAY_POP (worklist);
481 if (dump_file && (dump_flags & TDF_DETAILS))
483 fprintf (dump_file, "processing: ");
484 print_generic_stmt (dump_file, i, TDF_SLIM);
485 fprintf (dump_file, "\n");
490 /* Mark the last statements of the basic blocks that the block
491 containing `i' is control dependent on, but only if we haven't
493 basic_block bb = bb_for_stmt (i);
494 if (bb != ENTRY_BLOCK_PTR
495 && ! TEST_BIT (visited_control_parents, bb->index))
497 SET_BIT (visited_control_parents, bb->index);
498 mark_control_dependent_edges_necessary (bb, el);
502 if (TREE_CODE (i) == PHI_NODE)
504 /* PHI nodes are somewhat special in that each PHI alternative has
505 data and control dependencies. All the statements feeding the
506 PHI node's arguments are always necessary. In aggressive mode,
507 we also consider the control dependent edges leading to the
508 predecessor block associated with each PHI alternative as
511 for (k = 0; k < PHI_NUM_ARGS (i); k++)
513 tree arg = PHI_ARG_DEF (i, k);
514 if (TREE_CODE (arg) == SSA_NAME)
515 mark_operand_necessary (arg, false);
520 for (k = 0; k < PHI_NUM_ARGS (i); k++)
522 basic_block arg_bb = PHI_ARG_EDGE (i, k)->src;
523 if (arg_bb != ENTRY_BLOCK_PTR
524 && ! TEST_BIT (visited_control_parents, arg_bb->index))
526 SET_BIT (visited_control_parents, arg_bb->index);
527 mark_control_dependent_edges_necessary (arg_bb, el);
534 /* Propagate through the operands. Examine all the USE, VUSE and
535 V_MAY_DEF operands in this statement. Mark all the statements
536 which feed this statement's uses as necessary. */
540 /* The operands of V_MAY_DEF expressions are also needed as they
541 represent potential definitions that may reach this
542 statement (V_MAY_DEF operands allow us to follow def-def
545 FOR_EACH_SSA_TREE_OPERAND (use, i, iter, SSA_OP_ALL_USES)
546 mark_operand_necessary (use, false);
552 /* Propagate necessity around virtual phi nodes used in kill operands.
553 The reason this isn't done during propagate_necessity is because we don't
554 want to keep phis around that are just there for must-defs, unless we
555 absolutely have to. After we've rewritten the reaching definitions to be
556 correct in the previous part of the fixup routine, we can simply propagate
557 around the information about which of these virtual phi nodes are really
558 used, and set the NECESSARY flag accordingly.
559 Note that we do the minimum here to ensure that we keep alive the phis that
560 are actually used in the corrected SSA form. In particular, some of these
561 phis may now have all of the same operand, and will be deleted by some
565 mark_really_necessary_kill_operand_phis (void)
570 /* Seed the worklist with the new virtual phi arguments and virtual
574 block_stmt_iterator bsi;
577 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
579 if (!is_gimple_reg (PHI_RESULT (phi)) && NECESSARY (phi))
581 for (i = 0; i < PHI_NUM_ARGS (phi); i++)
582 mark_operand_necessary (PHI_ARG_DEF (phi, i), true);
586 for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi))
588 tree stmt = bsi_stmt (bsi);
590 if (NECESSARY (stmt))
594 FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter,
595 SSA_OP_VIRTUAL_USES | SSA_OP_VIRTUAL_KILLS)
597 tree use = USE_FROM_PTR (use_p);
598 mark_operand_necessary (use, true);
604 /* Mark all virtual phis still in use as necessary, and all of their
605 arguments that are phis as necessary. */
606 while (VARRAY_ACTIVE_SIZE (worklist) > 0)
608 tree use = VARRAY_TOP_TREE (worklist);
609 VARRAY_POP (worklist);
611 for (i = 0; i < PHI_NUM_ARGS (use); i++)
612 mark_operand_necessary (PHI_ARG_DEF (use, i), true);
619 /* Eliminate unnecessary statements. Any instruction not marked as necessary
620 contributes nothing to the program, and can be deleted. */
623 eliminate_unnecessary_stmts (void)
626 block_stmt_iterator i;
628 if (dump_file && (dump_flags & TDF_DETAILS))
629 fprintf (dump_file, "\nEliminating unnecessary statements:\n");
631 clear_special_calls ();
634 /* Remove dead PHI nodes. */
635 remove_dead_phis (bb);
640 /* Remove dead statements. */
641 for (i = bsi_start (bb); ! bsi_end_p (i) ; )
643 tree t = bsi_stmt (i);
647 /* If `i' is not necessary then remove it. */
649 remove_dead_stmt (&i, bb);
652 tree call = get_call_expr_in (t);
654 notice_special_calls (call);
661 /* Remove dead PHI nodes from block BB. */
664 remove_dead_phis (basic_block bb)
669 phi = phi_nodes (bb);
674 if (! NECESSARY (phi))
676 tree next = PHI_CHAIN (phi);
678 if (dump_file && (dump_flags & TDF_DETAILS))
680 fprintf (dump_file, "Deleting : ");
681 print_generic_stmt (dump_file, phi, TDF_SLIM);
682 fprintf (dump_file, "\n");
685 remove_phi_node (phi, prev);
686 stats.removed_phis++;
692 phi = PHI_CHAIN (phi);
697 /* Remove dead statement pointed by iterator I. Receives the basic block BB
698 containing I so that we don't have to look it up. */
701 remove_dead_stmt (block_stmt_iterator *i, basic_block bb)
703 tree t = bsi_stmt (*i);
708 if (dump_file && (dump_flags & TDF_DETAILS))
710 fprintf (dump_file, "Deleting : ");
711 print_generic_stmt (dump_file, t, TDF_SLIM);
712 fprintf (dump_file, "\n");
717 /* If we have determined that a conditional branch statement contributes
718 nothing to the program, then we not only remove it, but we also change
719 the flow graph so that the current block will simply fall-thru to its
720 immediate post-dominator. The blocks we are circumventing will be
721 removed by cleaup_cfg if this change in the flow graph makes them
723 if (is_ctrl_stmt (t))
725 basic_block post_dom_bb;
727 /* The post dominance info has to be up-to-date. */
728 gcc_assert (dom_computed[CDI_POST_DOMINATORS] == DOM_OK);
729 /* Get the immediate post dominator of bb. */
730 post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
731 /* Some blocks don't have an immediate post dominator. This can happen
732 for example with infinite loops. Removing an infinite loop is an
733 inappropriate transformation anyway... */
740 /* If the post dominator block has PHI nodes, we might be unable
741 to compute the right PHI args for them. Since the control
742 statement is unnecessary, all edges can be regarded as
743 equivalent, but we have to get rid of the condition, since it
744 might reference a variable that was determined to be
745 unnecessary and thus removed. */
746 if (phi_nodes (post_dom_bb))
747 post_dom_bb = EDGE_SUCC (bb, 0)->dest;
750 /* Redirect the first edge out of BB to reach POST_DOM_BB. */
751 redirect_edge_and_branch (EDGE_SUCC (bb, 0), post_dom_bb);
752 PENDING_STMT (EDGE_SUCC (bb, 0)) = NULL;
754 EDGE_SUCC (bb, 0)->probability = REG_BR_PROB_BASE;
755 EDGE_SUCC (bb, 0)->count = bb->count;
757 /* The edge is no longer associated with a conditional, so it does
758 not have TRUE/FALSE flags. */
759 EDGE_SUCC (bb, 0)->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
761 /* If the edge reaches any block other than the exit, then it is a
762 fallthru edge; if it reaches the exit, then it is not a fallthru
764 if (post_dom_bb != EXIT_BLOCK_PTR)
765 EDGE_SUCC (bb, 0)->flags |= EDGE_FALLTHRU;
767 EDGE_SUCC (bb, 0)->flags &= ~EDGE_FALLTHRU;
769 /* Remove the remaining the outgoing edges. */
770 while (!single_succ_p (bb))
771 remove_edge (EDGE_SUCC (bb, 1));
774 FOR_EACH_SSA_DEF_OPERAND (def_p, t, iter,
775 SSA_OP_VIRTUAL_DEFS | SSA_OP_VIRTUAL_KILLS)
777 tree def = DEF_FROM_PTR (def_p);
778 mark_sym_for_renaming (SSA_NAME_VAR (def));
784 /* Print out removed statement statistics. */
789 if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS)))
793 percg = ((float) stats.removed / (float) stats.total) * 100;
794 fprintf (dump_file, "Removed %d of %d statements (%d%%)\n",
795 stats.removed, stats.total, (int) percg);
797 if (stats.total_phis == 0)
800 percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100;
802 fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n",
803 stats.removed_phis, stats.total_phis, (int) percg);
807 /* Initialization for this pass. Set up the used data structures. */
810 tree_dce_init (bool aggressive)
812 memset ((void *) &stats, 0, sizeof (stats));
818 control_dependence_map
819 = xmalloc (last_basic_block * sizeof (bitmap));
820 for (i = 0; i < last_basic_block; ++i)
821 control_dependence_map[i] = BITMAP_ALLOC (NULL);
823 last_stmt_necessary = sbitmap_alloc (last_basic_block);
824 sbitmap_zero (last_stmt_necessary);
827 processed = sbitmap_alloc (num_ssa_names + 1);
828 sbitmap_zero (processed);
830 VARRAY_TREE_INIT (worklist, 64, "work list");
833 /* Cleanup after this pass. */
836 tree_dce_done (bool aggressive)
842 for (i = 0; i < last_basic_block; ++i)
843 BITMAP_FREE (control_dependence_map[i]);
844 free (control_dependence_map);
846 sbitmap_free (visited_control_parents);
847 sbitmap_free (last_stmt_necessary);
850 sbitmap_free (processed);
853 /* Main routine to eliminate dead code.
855 AGGRESSIVE controls the aggressiveness of the algorithm.
856 In conservative mode, we ignore control dependence and simply declare
857 all but the most trivially dead branches necessary. This mode is fast.
858 In aggressive mode, control dependences are taken into account, which
859 results in more dead code elimination, but at the cost of some time.
861 FIXME: Aggressive mode before PRE doesn't work currently because
862 the dominance info is not invalidated after DCE1. This is
863 not an issue right now because we only run aggressive DCE
864 as the last tree SSA pass, but keep this in mind when you
865 start experimenting with pass ordering. */
868 perform_tree_ssa_dce (bool aggressive)
870 struct edge_list *el = NULL;
872 tree_dce_init (aggressive);
876 /* Compute control dependence. */
877 timevar_push (TV_CONTROL_DEPENDENCES);
878 calculate_dominance_info (CDI_POST_DOMINATORS);
879 el = create_edge_list ();
880 find_all_control_dependences (el);
881 timevar_pop (TV_CONTROL_DEPENDENCES);
883 visited_control_parents = sbitmap_alloc (last_basic_block);
884 sbitmap_zero (visited_control_parents);
886 mark_dfs_back_edges ();
889 find_obviously_necessary_stmts (el);
891 propagate_necessity (el);
893 mark_really_necessary_kill_operand_phis ();
894 eliminate_unnecessary_stmts ();
897 free_dominance_info (CDI_POST_DOMINATORS);
899 /* Debugging dumps. */
903 tree_dce_done (aggressive);
908 /* Pass entry points. */
912 perform_tree_ssa_dce (/*aggressive=*/false);
916 tree_ssa_cd_dce (void)
918 perform_tree_ssa_dce (/*aggressive=*/optimize >= 2);
924 return flag_tree_dce != 0;
927 struct tree_opt_pass pass_dce =
931 tree_ssa_dce, /* execute */
934 0, /* static_pass_number */
935 TV_TREE_DCE, /* tv_id */
936 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */
937 0, /* properties_provided */
938 0, /* properties_destroyed */
939 0, /* todo_flags_start */
941 | TODO_update_ssa_no_phi
944 | TODO_verify_ssa, /* todo_flags_finish */
948 struct tree_opt_pass pass_cd_dce =
952 tree_ssa_cd_dce, /* execute */
955 0, /* static_pass_number */
956 TV_TREE_CD_DCE, /* tv_id */
957 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */
958 0, /* properties_provided */
959 0, /* properties_destroyed */
960 0, /* todo_flags_start */
962 | TODO_update_ssa_no_phi
966 | TODO_verify_flow, /* todo_flags_finish */