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"
52 /* These RTL headers are needed for basic-block.h. */
55 #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 VEC(tree,heap) *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 static bitmap *control_dependence_map;
95 /* Vector indicating that a basic block has already had all the edges
96 processed that it is control dependent on. */
97 static sbitmap visited_control_parents;
99 /* Execute CODE for each edge (given number EDGE_NUMBER within the CODE)
100 for which the block with index N is control dependent. */
101 #define EXECUTE_IF_CONTROL_DEPENDENT(N, EDGE_NUMBER, CODE) \
103 bitmap_iterator bi; \
105 EXECUTE_IF_SET_IN_BITMAP (control_dependence_map[N], 0, EDGE_NUMBER, bi) \
111 /* Local function prototypes. */
112 static inline void set_control_dependence_map_bit (basic_block, int);
113 static inline void clear_control_dependence_bitmap (basic_block);
114 static void find_all_control_dependences (struct edge_list *);
115 static void find_control_dependence (struct edge_list *, int);
116 static inline basic_block find_pdom (basic_block);
118 static inline void mark_stmt_necessary (tree, bool);
119 static inline void mark_operand_necessary (tree, bool);
121 static void mark_stmt_if_obviously_necessary (tree, bool);
122 static void find_obviously_necessary_stmts (struct edge_list *);
124 static void mark_control_dependent_edges_necessary (basic_block, struct edge_list *);
125 static void propagate_necessity (struct edge_list *);
127 static void eliminate_unnecessary_stmts (void);
128 static void remove_dead_phis (basic_block);
129 static void remove_dead_stmt (block_stmt_iterator *, basic_block);
131 static void print_stats (void);
132 static void tree_dce_init (bool);
133 static void tree_dce_done (bool);
135 /* Indicate block BB is control dependent on an edge with index EDGE_INDEX. */
137 set_control_dependence_map_bit (basic_block bb, int edge_index)
139 if (bb == ENTRY_BLOCK_PTR)
141 gcc_assert (bb != EXIT_BLOCK_PTR);
142 bitmap_set_bit (control_dependence_map[bb->index], edge_index);
145 /* Clear all control dependences for block BB. */
147 void clear_control_dependence_bitmap (basic_block bb)
149 bitmap_clear (control_dependence_map[bb->index]);
152 /* Record all blocks' control dependences on all edges in the edge
153 list EL, ala Morgan, Section 3.6. */
156 find_all_control_dependences (struct edge_list *el)
160 for (i = 0; i < NUM_EDGES (el); ++i)
161 find_control_dependence (el, i);
164 /* Determine all blocks' control dependences on the given edge with edge_list
165 EL index EDGE_INDEX, ala Morgan, Section 3.6. */
168 find_control_dependence (struct edge_list *el, int edge_index)
170 basic_block current_block;
171 basic_block ending_block;
173 gcc_assert (INDEX_EDGE_PRED_BB (el, edge_index) != EXIT_BLOCK_PTR);
175 if (INDEX_EDGE_PRED_BB (el, edge_index) == ENTRY_BLOCK_PTR)
176 ending_block = ENTRY_BLOCK_PTR->next_bb;
178 ending_block = find_pdom (INDEX_EDGE_PRED_BB (el, edge_index));
180 for (current_block = INDEX_EDGE_SUCC_BB (el, edge_index);
181 current_block != ending_block && current_block != EXIT_BLOCK_PTR;
182 current_block = find_pdom (current_block))
184 edge e = INDEX_EDGE (el, edge_index);
186 /* For abnormal edges, we don't make current_block control
187 dependent because instructions that throw are always necessary
189 if (e->flags & EDGE_ABNORMAL)
192 set_control_dependence_map_bit (current_block, edge_index);
196 /* Find the immediate postdominator PDOM of the specified basic block BLOCK.
197 This function is necessary because some blocks have negative numbers. */
199 static inline basic_block
200 find_pdom (basic_block block)
202 gcc_assert (block != ENTRY_BLOCK_PTR);
204 if (block == EXIT_BLOCK_PTR)
205 return EXIT_BLOCK_PTR;
208 basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block);
210 return EXIT_BLOCK_PTR;
215 #define NECESSARY(stmt) stmt->common.asm_written_flag
217 /* If STMT is not already marked necessary, mark it, and add it to the
218 worklist if ADD_TO_WORKLIST is true. */
220 mark_stmt_necessary (tree stmt, bool add_to_worklist)
223 gcc_assert (!DECL_P (stmt));
225 if (NECESSARY (stmt))
228 if (dump_file && (dump_flags & TDF_DETAILS))
230 fprintf (dump_file, "Marking useful stmt: ");
231 print_generic_stmt (dump_file, stmt, TDF_SLIM);
232 fprintf (dump_file, "\n");
235 NECESSARY (stmt) = 1;
237 VEC_safe_push (tree, heap, worklist, stmt);
240 /* Mark the statement defining operand OP as necessary. PHIONLY is true
241 if we should only mark it necessary if it is a phi node. */
244 mark_operand_necessary (tree op, bool phionly)
251 ver = SSA_NAME_VERSION (op);
252 if (TEST_BIT (processed, ver))
254 SET_BIT (processed, ver);
256 stmt = SSA_NAME_DEF_STMT (op);
260 || IS_EMPTY_STMT (stmt)
261 || (phionly && TREE_CODE (stmt) != PHI_NODE))
264 NECESSARY (stmt) = 1;
265 VEC_safe_push (tree, heap, worklist, stmt);
269 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
270 it can make other statements necessary.
272 If AGGRESSIVE is false, control statements are conservatively marked as
276 mark_stmt_if_obviously_necessary (tree stmt, bool aggressive)
282 /* Statements that are implicitly live. Most function calls, asm and return
283 statements are required. Labels and BIND_EXPR nodes are kept because
284 they are control flow, and we have no way of knowing whether they can be
285 removed. DCE can eliminate all the other statements in a block, and CFG
286 can then remove the block and labels. */
287 switch (TREE_CODE (stmt))
291 case CASE_LABEL_EXPR:
292 mark_stmt_necessary (stmt, false);
298 mark_stmt_necessary (stmt, true);
302 /* Most, but not all function calls are required. Function calls that
303 produce no result and have no side effects (i.e. const pure
304 functions) are unnecessary. */
305 if (TREE_SIDE_EFFECTS (stmt))
306 mark_stmt_necessary (stmt, true);
310 op = get_call_expr_in (stmt);
311 if (op && TREE_SIDE_EFFECTS (op))
313 mark_stmt_necessary (stmt, true);
317 /* These values are mildly magic bits of the EH runtime. We can't
318 see the entire lifetime of these values until landing pads are
320 if (TREE_CODE (TREE_OPERAND (stmt, 0)) == EXC_PTR_EXPR
321 || TREE_CODE (TREE_OPERAND (stmt, 0)) == FILTER_EXPR)
323 mark_stmt_necessary (stmt, true);
329 gcc_assert (!simple_goto_p (stmt));
330 mark_stmt_necessary (stmt, true);
334 gcc_assert (EDGE_COUNT (bb_for_stmt (stmt)->succs) == 2);
339 mark_stmt_necessary (stmt, true);
346 ann = stmt_ann (stmt);
348 /* If the statement has volatile operands, it needs to be preserved.
349 Same for statements that can alter control flow in unpredictable
351 if (ann->has_volatile_ops || is_ctrl_altering_stmt (stmt))
353 mark_stmt_necessary (stmt, true);
357 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF)
359 if (is_global_var (SSA_NAME_VAR (def)))
361 mark_stmt_necessary (stmt, true);
365 if (is_hidden_global_store (stmt))
367 mark_stmt_necessary (stmt, true);
374 /* Find obviously necessary statements. These are things like most function
375 calls, and stores to file level variables.
377 If EL is NULL, control statements are conservatively marked as
378 necessary. Otherwise it contains the list of edges used by control
379 dependence analysis. */
382 find_obviously_necessary_stmts (struct edge_list *el)
385 block_stmt_iterator i;
392 /* Check any PHI nodes in the block. */
393 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
397 /* PHIs for virtual variables do not directly affect code
398 generation and need not be considered inherently necessary
399 regardless of the bits set in their decl.
401 Thus, we only need to mark PHIs for real variables which
402 need their result preserved as being inherently necessary. */
403 if (is_gimple_reg (PHI_RESULT (phi))
404 && is_global_var (SSA_NAME_VAR (PHI_RESULT (phi))))
405 mark_stmt_necessary (phi, true);
408 /* Check all statements in the block. */
409 for (i = bsi_start (bb); ! bsi_end_p (i); bsi_next (&i))
411 tree stmt = bsi_stmt (i);
412 NECESSARY (stmt) = 0;
413 mark_stmt_if_obviously_necessary (stmt, el != NULL);
419 /* Prevent the loops from being removed. We must keep the infinite loops,
420 and we currently do not have a means to recognize the finite ones. */
424 FOR_EACH_EDGE (e, ei, bb->succs)
425 if (e->flags & EDGE_DFS_BACK)
426 mark_control_dependent_edges_necessary (e->dest, el);
431 /* Make corresponding control dependent edges necessary. We only
432 have to do this once for each basic block, so we clear the bitmap
435 mark_control_dependent_edges_necessary (basic_block bb, struct edge_list *el)
437 unsigned edge_number;
439 gcc_assert (bb != EXIT_BLOCK_PTR);
441 if (bb == ENTRY_BLOCK_PTR)
444 EXECUTE_IF_CONTROL_DEPENDENT (bb->index, edge_number,
447 basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number);
449 if (TEST_BIT (last_stmt_necessary, cd_bb->index))
451 SET_BIT (last_stmt_necessary, cd_bb->index);
453 t = last_stmt (cd_bb);
454 if (t && is_ctrl_stmt (t))
455 mark_stmt_necessary (t, true);
459 /* Propagate necessity using the operands of necessary statements. Process
460 the uses on each statement in the worklist, and add all feeding statements
461 which contribute to the calculation of this value to the worklist.
463 In conservative mode, EL is NULL. */
466 propagate_necessity (struct edge_list *el)
469 bool aggressive = (el ? true : false);
471 if (dump_file && (dump_flags & TDF_DETAILS))
472 fprintf (dump_file, "\nProcessing worklist:\n");
474 while (VEC_length (tree, worklist) > 0)
476 /* Take `i' from worklist. */
477 i = VEC_pop (tree, worklist);
479 if (dump_file && (dump_flags & TDF_DETAILS))
481 fprintf (dump_file, "processing: ");
482 print_generic_stmt (dump_file, i, TDF_SLIM);
483 fprintf (dump_file, "\n");
488 /* Mark the last statements of the basic blocks that the block
489 containing `i' is control dependent on, but only if we haven't
491 basic_block bb = bb_for_stmt (i);
492 if (bb != ENTRY_BLOCK_PTR
493 && ! TEST_BIT (visited_control_parents, bb->index))
495 SET_BIT (visited_control_parents, bb->index);
496 mark_control_dependent_edges_necessary (bb, el);
500 if (TREE_CODE (i) == PHI_NODE)
502 /* PHI nodes are somewhat special in that each PHI alternative has
503 data and control dependencies. All the statements feeding the
504 PHI node's arguments are always necessary. In aggressive mode,
505 we also consider the control dependent edges leading to the
506 predecessor block associated with each PHI alternative as
509 for (k = 0; k < PHI_NUM_ARGS (i); k++)
511 tree arg = PHI_ARG_DEF (i, k);
512 if (TREE_CODE (arg) == SSA_NAME)
513 mark_operand_necessary (arg, false);
518 for (k = 0; k < PHI_NUM_ARGS (i); k++)
520 basic_block arg_bb = PHI_ARG_EDGE (i, k)->src;
521 if (arg_bb != ENTRY_BLOCK_PTR
522 && ! TEST_BIT (visited_control_parents, arg_bb->index))
524 SET_BIT (visited_control_parents, arg_bb->index);
525 mark_control_dependent_edges_necessary (arg_bb, el);
532 /* Propagate through the operands. Examine all the USE, VUSE and
533 V_MAY_DEF operands in this statement. Mark all the statements
534 which feed this statement's uses as necessary. */
538 /* The operands of V_MAY_DEF expressions are also needed as they
539 represent potential definitions that may reach this
540 statement (V_MAY_DEF operands allow us to follow def-def
543 FOR_EACH_SSA_TREE_OPERAND (use, i, iter, SSA_OP_ALL_USES)
544 mark_operand_necessary (use, false);
550 /* Propagate necessity around virtual phi nodes used in kill operands.
551 The reason this isn't done during propagate_necessity is because we don't
552 want to keep phis around that are just there for must-defs, unless we
553 absolutely have to. After we've rewritten the reaching definitions to be
554 correct in the previous part of the fixup routine, we can simply propagate
555 around the information about which of these virtual phi nodes are really
556 used, and set the NECESSARY flag accordingly.
557 Note that we do the minimum here to ensure that we keep alive the phis that
558 are actually used in the corrected SSA form. In particular, some of these
559 phis may now have all of the same operand, and will be deleted by some
563 mark_really_necessary_kill_operand_phis (void)
568 /* Seed the worklist with the new virtual phi arguments and virtual
572 block_stmt_iterator bsi;
575 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
577 if (!is_gimple_reg (PHI_RESULT (phi)) && NECESSARY (phi))
579 for (i = 0; i < PHI_NUM_ARGS (phi); i++)
580 mark_operand_necessary (PHI_ARG_DEF (phi, i), true);
584 for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi))
586 tree stmt = bsi_stmt (bsi);
588 if (NECESSARY (stmt))
592 FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter,
593 SSA_OP_VIRTUAL_USES | SSA_OP_VIRTUAL_KILLS)
595 tree use = USE_FROM_PTR (use_p);
596 mark_operand_necessary (use, true);
602 /* Mark all virtual phis still in use as necessary, and all of their
603 arguments that are phis as necessary. */
604 while (VEC_length (tree, worklist) > 0)
606 tree use = VEC_pop (tree, worklist);
608 for (i = 0; i < PHI_NUM_ARGS (use); i++)
609 mark_operand_necessary (PHI_ARG_DEF (use, i), true);
616 /* Eliminate unnecessary statements. Any instruction not marked as necessary
617 contributes nothing to the program, and can be deleted. */
620 eliminate_unnecessary_stmts (void)
623 block_stmt_iterator i;
625 if (dump_file && (dump_flags & TDF_DETAILS))
626 fprintf (dump_file, "\nEliminating unnecessary statements:\n");
628 clear_special_calls ();
631 /* Remove dead PHI nodes. */
632 remove_dead_phis (bb);
637 /* Remove dead statements. */
638 for (i = bsi_start (bb); ! bsi_end_p (i) ; )
640 tree t = bsi_stmt (i);
644 /* If `i' is not necessary then remove it. */
646 remove_dead_stmt (&i, bb);
649 tree call = get_call_expr_in (t);
651 notice_special_calls (call);
658 /* Remove dead PHI nodes from block BB. */
661 remove_dead_phis (basic_block bb)
666 phi = phi_nodes (bb);
671 if (! NECESSARY (phi))
673 tree next = PHI_CHAIN (phi);
675 if (dump_file && (dump_flags & TDF_DETAILS))
677 fprintf (dump_file, "Deleting : ");
678 print_generic_stmt (dump_file, phi, TDF_SLIM);
679 fprintf (dump_file, "\n");
682 remove_phi_node (phi, prev);
683 stats.removed_phis++;
689 phi = PHI_CHAIN (phi);
694 /* Remove dead statement pointed by iterator I. Receives the basic block BB
695 containing I so that we don't have to look it up. */
698 remove_dead_stmt (block_stmt_iterator *i, basic_block bb)
700 tree t = bsi_stmt (*i);
705 if (dump_file && (dump_flags & TDF_DETAILS))
707 fprintf (dump_file, "Deleting : ");
708 print_generic_stmt (dump_file, t, TDF_SLIM);
709 fprintf (dump_file, "\n");
714 /* If we have determined that a conditional branch statement contributes
715 nothing to the program, then we not only remove it, but we also change
716 the flow graph so that the current block will simply fall-thru to its
717 immediate post-dominator. The blocks we are circumventing will be
718 removed by cleaup_tree_cfg if this change in the flow graph makes them
720 if (is_ctrl_stmt (t))
722 basic_block post_dom_bb;
724 /* The post dominance info has to be up-to-date. */
725 gcc_assert (dom_computed[CDI_POST_DOMINATORS] == DOM_OK);
726 /* Get the immediate post dominator of bb. */
727 post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
728 /* Some blocks don't have an immediate post dominator. This can happen
729 for example with infinite loops. Removing an infinite loop is an
730 inappropriate transformation anyway... */
737 /* If the post dominator block has PHI nodes, we might be unable
738 to compute the right PHI args for them. Since the control
739 statement is unnecessary, all edges can be regarded as
740 equivalent, but we have to get rid of the condition, since it
741 might reference a variable that was determined to be
742 unnecessary and thus removed. */
743 if (phi_nodes (post_dom_bb))
744 post_dom_bb = EDGE_SUCC (bb, 0)->dest;
747 /* Redirect the first edge out of BB to reach POST_DOM_BB. */
748 redirect_edge_and_branch (EDGE_SUCC (bb, 0), post_dom_bb);
749 PENDING_STMT (EDGE_SUCC (bb, 0)) = NULL;
751 EDGE_SUCC (bb, 0)->probability = REG_BR_PROB_BASE;
752 EDGE_SUCC (bb, 0)->count = bb->count;
754 /* The edge is no longer associated with a conditional, so it does
755 not have TRUE/FALSE flags. */
756 EDGE_SUCC (bb, 0)->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 EDGE_SUCC (bb, 0)->flags |= EDGE_FALLTHRU;
764 EDGE_SUCC (bb, 0)->flags &= ~EDGE_FALLTHRU;
766 /* Remove the remaining the outgoing edges. */
767 while (!single_succ_p (bb))
768 remove_edge (EDGE_SUCC (bb, 1));
771 FOR_EACH_SSA_DEF_OPERAND (def_p, t, iter, SSA_OP_VIRTUAL_DEFS)
773 tree def = DEF_FROM_PTR (def_p);
774 mark_sym_for_renaming (SSA_NAME_VAR (def));
780 /* Print out removed statement statistics. */
785 if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS)))
789 percg = ((float) stats.removed / (float) stats.total) * 100;
790 fprintf (dump_file, "Removed %d of %d statements (%d%%)\n",
791 stats.removed, stats.total, (int) percg);
793 if (stats.total_phis == 0)
796 percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100;
798 fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n",
799 stats.removed_phis, stats.total_phis, (int) percg);
803 /* Initialization for this pass. Set up the used data structures. */
806 tree_dce_init (bool aggressive)
808 memset ((void *) &stats, 0, sizeof (stats));
814 control_dependence_map
815 = xmalloc (last_basic_block * sizeof (bitmap));
816 for (i = 0; i < last_basic_block; ++i)
817 control_dependence_map[i] = BITMAP_ALLOC (NULL);
819 last_stmt_necessary = sbitmap_alloc (last_basic_block);
820 sbitmap_zero (last_stmt_necessary);
823 processed = sbitmap_alloc (num_ssa_names + 1);
824 sbitmap_zero (processed);
826 worklist = VEC_alloc (tree, heap, 64);
829 /* Cleanup after this pass. */
832 tree_dce_done (bool aggressive)
838 for (i = 0; i < last_basic_block; ++i)
839 BITMAP_FREE (control_dependence_map[i]);
840 free (control_dependence_map);
842 sbitmap_free (visited_control_parents);
843 sbitmap_free (last_stmt_necessary);
846 sbitmap_free (processed);
848 VEC_free (tree, heap, worklist);
851 /* Main routine to eliminate dead code.
853 AGGRESSIVE controls the aggressiveness of the algorithm.
854 In conservative mode, we ignore control dependence and simply declare
855 all but the most trivially dead branches necessary. This mode is fast.
856 In aggressive mode, control dependences are taken into account, which
857 results in more dead code elimination, but at the cost of some time.
859 FIXME: Aggressive mode before PRE doesn't work currently because
860 the dominance info is not invalidated after DCE1. This is
861 not an issue right now because we only run aggressive DCE
862 as the last tree SSA pass, but keep this in mind when you
863 start experimenting with pass ordering. */
866 perform_tree_ssa_dce (bool aggressive)
868 struct edge_list *el = NULL;
870 tree_dce_init (aggressive);
874 /* Compute control dependence. */
875 timevar_push (TV_CONTROL_DEPENDENCES);
876 calculate_dominance_info (CDI_POST_DOMINATORS);
877 el = create_edge_list ();
878 find_all_control_dependences (el);
879 timevar_pop (TV_CONTROL_DEPENDENCES);
881 visited_control_parents = sbitmap_alloc (last_basic_block);
882 sbitmap_zero (visited_control_parents);
884 mark_dfs_back_edges ();
887 find_obviously_necessary_stmts (el);
889 propagate_necessity (el);
891 mark_really_necessary_kill_operand_phis ();
892 eliminate_unnecessary_stmts ();
895 free_dominance_info (CDI_POST_DOMINATORS);
897 /* Debugging dumps. */
901 tree_dce_done (aggressive);
906 /* Pass entry points. */
910 perform_tree_ssa_dce (/*aggressive=*/false);
914 tree_ssa_cd_dce (void)
916 perform_tree_ssa_dce (/*aggressive=*/optimize >= 2);
922 return flag_tree_dce != 0;
925 struct tree_opt_pass pass_dce =
929 tree_ssa_dce, /* execute */
932 0, /* static_pass_number */
933 TV_TREE_DCE, /* tv_id */
934 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */
935 0, /* properties_provided */
936 0, /* properties_destroyed */
937 0, /* todo_flags_start */
939 | TODO_update_ssa_no_phi
942 | TODO_verify_ssa, /* todo_flags_finish */
946 struct tree_opt_pass pass_cd_dce =
950 tree_ssa_cd_dce, /* execute */
953 0, /* static_pass_number */
954 TV_TREE_CD_DCE, /* tv_id */
955 PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */
956 0, /* properties_provided */
957 0, /* properties_destroyed */
958 0, /* todo_flags_start */
960 | TODO_update_ssa_no_phi
964 | TODO_verify_flow, /* todo_flags_finish */