1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007
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 2, 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 COPYING. If not, write to the Free
22 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
25 /* Dead code elimination.
29 Building an Optimizing Compiler,
30 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
32 Advanced Compiler Design and Implementation,
33 Steven Muchnick, Morgan Kaufmann, 1997, Section 18.10.
35 Dead-code elimination is the removal of statements which have no
36 impact on the program's output. "Dead statements" have no impact
37 on the program's output, while "necessary statements" may have
40 The algorithm consists of three phases:
41 1. Marking as necessary all statements known to be necessary,
42 e.g. most function calls, writing a value to memory, etc;
43 2. Propagating necessary statements, e.g., the statements
44 giving values to operands in necessary statements; and
45 3. Removing dead statements. */
49 #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 #include "tree-scalar-evolution.h"
71 static struct stmt_stats
79 static VEC(tree,heap) *worklist;
81 /* Vector indicating an SSA name has already been processed and marked
83 static sbitmap processed;
85 /* Vector indicating that last_stmt if a basic block has already been
86 marked as necessary. */
87 static sbitmap last_stmt_necessary;
89 /* Before we can determine whether a control branch is dead, we need to
90 compute which blocks are control dependent on which edges.
92 We expect each block to be control dependent on very few edges so we
93 use a bitmap for each block recording its edges. An array holds the
94 bitmap. The Ith bit in the bitmap is set if that block is dependent
96 static bitmap *control_dependence_map;
98 /* Vector indicating that a basic block has already had all the edges
99 processed that it is control dependent on. */
100 static sbitmap visited_control_parents;
102 /* TRUE if this pass alters the CFG (by removing control statements).
105 If this pass alters the CFG, then it will arrange for the dominators
107 static bool cfg_altered;
109 /* Execute code that follows the macro for each edge (given number
110 EDGE_NUMBER within the CODE) for which the block with index N is
111 control dependent. */
112 #define EXECUTE_IF_CONTROL_DEPENDENT(BI, N, EDGE_NUMBER) \
113 EXECUTE_IF_SET_IN_BITMAP (control_dependence_map[(N)], 0, \
117 /* Indicate block BB is control dependent on an edge with index EDGE_INDEX. */
119 set_control_dependence_map_bit (basic_block bb, int edge_index)
121 if (bb == ENTRY_BLOCK_PTR)
123 gcc_assert (bb != EXIT_BLOCK_PTR);
124 bitmap_set_bit (control_dependence_map[bb->index], edge_index);
127 /* Clear all control dependences for block BB. */
129 clear_control_dependence_bitmap (basic_block bb)
131 bitmap_clear (control_dependence_map[bb->index]);
135 /* Find the immediate postdominator PDOM of the specified basic block BLOCK.
136 This function is necessary because some blocks have negative numbers. */
138 static inline basic_block
139 find_pdom (basic_block block)
141 gcc_assert (block != ENTRY_BLOCK_PTR);
143 if (block == EXIT_BLOCK_PTR)
144 return EXIT_BLOCK_PTR;
147 basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block);
149 return EXIT_BLOCK_PTR;
155 /* Determine all blocks' control dependences on the given edge with edge_list
156 EL index EDGE_INDEX, ala Morgan, Section 3.6. */
159 find_control_dependence (struct edge_list *el, int edge_index)
161 basic_block current_block;
162 basic_block ending_block;
164 gcc_assert (INDEX_EDGE_PRED_BB (el, edge_index) != EXIT_BLOCK_PTR);
166 if (INDEX_EDGE_PRED_BB (el, edge_index) == ENTRY_BLOCK_PTR)
167 ending_block = single_succ (ENTRY_BLOCK_PTR);
169 ending_block = find_pdom (INDEX_EDGE_PRED_BB (el, edge_index));
171 for (current_block = INDEX_EDGE_SUCC_BB (el, edge_index);
172 current_block != ending_block && current_block != EXIT_BLOCK_PTR;
173 current_block = find_pdom (current_block))
175 edge e = INDEX_EDGE (el, edge_index);
177 /* For abnormal edges, we don't make current_block control
178 dependent because instructions that throw are always necessary
180 if (e->flags & EDGE_ABNORMAL)
183 set_control_dependence_map_bit (current_block, edge_index);
188 /* Record all blocks' control dependences on all edges in the edge
189 list EL, ala Morgan, Section 3.6. */
192 find_all_control_dependences (struct edge_list *el)
196 for (i = 0; i < NUM_EDGES (el); ++i)
197 find_control_dependence (el, i);
201 #define NECESSARY(stmt) stmt->base.asm_written_flag
203 /* If STMT is not already marked necessary, mark it, and add it to the
204 worklist if ADD_TO_WORKLIST is true. */
206 mark_stmt_necessary (tree stmt, bool add_to_worklist)
209 gcc_assert (!DECL_P (stmt));
211 if (NECESSARY (stmt))
214 if (dump_file && (dump_flags & TDF_DETAILS))
216 fprintf (dump_file, "Marking useful stmt: ");
217 print_generic_stmt (dump_file, stmt, TDF_SLIM);
218 fprintf (dump_file, "\n");
221 NECESSARY (stmt) = 1;
223 VEC_safe_push (tree, heap, worklist, stmt);
227 /* Mark the statement defining operand OP as necessary. */
230 mark_operand_necessary (tree op)
237 ver = SSA_NAME_VERSION (op);
238 if (TEST_BIT (processed, ver))
240 SET_BIT (processed, ver);
242 stmt = SSA_NAME_DEF_STMT (op);
245 if (NECESSARY (stmt) || IS_EMPTY_STMT (stmt))
248 NECESSARY (stmt) = 1;
249 VEC_safe_push (tree, heap, worklist, stmt);
253 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
254 it can make other statements necessary.
256 If AGGRESSIVE is false, control statements are conservatively marked as
260 mark_stmt_if_obviously_necessary (tree stmt, bool aggressive)
265 /* With non-call exceptions, we have to assume that all statements could
266 throw. If a statement may throw, it is inherently necessary. */
267 if (flag_non_call_exceptions
268 && tree_could_throw_p (stmt))
270 mark_stmt_necessary (stmt, true);
274 /* Statements that are implicitly live. Most function calls, asm and return
275 statements are required. Labels and BIND_EXPR nodes are kept because
276 they are control flow, and we have no way of knowing whether they can be
277 removed. DCE can eliminate all the other statements in a block, and CFG
278 can then remove the block and labels. */
279 switch (TREE_CODE (stmt))
283 case CASE_LABEL_EXPR:
284 mark_stmt_necessary (stmt, false);
290 case CHANGE_DYNAMIC_TYPE_EXPR:
291 mark_stmt_necessary (stmt, true);
295 /* Most, but not all function calls are required. Function calls that
296 produce no result and have no side effects (i.e. const pure
297 functions) are unnecessary. */
298 if (TREE_SIDE_EFFECTS (stmt))
299 mark_stmt_necessary (stmt, true);
302 case GIMPLE_MODIFY_STMT:
303 op = get_call_expr_in (stmt);
304 if (op && TREE_SIDE_EFFECTS (op))
306 mark_stmt_necessary (stmt, true);
310 /* These values are mildly magic bits of the EH runtime. We can't
311 see the entire lifetime of these values until landing pads are
313 if (TREE_CODE (GIMPLE_STMT_OPERAND (stmt, 0)) == EXC_PTR_EXPR
314 || TREE_CODE (GIMPLE_STMT_OPERAND (stmt, 0)) == FILTER_EXPR)
316 mark_stmt_necessary (stmt, true);
322 gcc_assert (!simple_goto_p (stmt));
323 mark_stmt_necessary (stmt, true);
327 gcc_assert (EDGE_COUNT (bb_for_stmt (stmt)->succs) == 2);
332 mark_stmt_necessary (stmt, true);
339 ann = stmt_ann (stmt);
341 /* If the statement has volatile operands, it needs to be preserved.
342 Same for statements that can alter control flow in unpredictable
344 if (ann->has_volatile_ops || is_ctrl_altering_stmt (stmt))
346 mark_stmt_necessary (stmt, true);
350 if (is_hidden_global_store (stmt))
352 mark_stmt_necessary (stmt, true);
360 /* Make corresponding control dependent edges necessary. We only
361 have to do this once for each basic block, so we clear the bitmap
364 mark_control_dependent_edges_necessary (basic_block bb, struct edge_list *el)
367 unsigned edge_number;
369 gcc_assert (bb != EXIT_BLOCK_PTR);
371 if (bb == ENTRY_BLOCK_PTR)
374 EXECUTE_IF_CONTROL_DEPENDENT (bi, bb->index, edge_number)
377 basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number);
379 if (TEST_BIT (last_stmt_necessary, cd_bb->index))
381 SET_BIT (last_stmt_necessary, cd_bb->index);
383 t = last_stmt (cd_bb);
384 if (t && is_ctrl_stmt (t))
385 mark_stmt_necessary (t, true);
390 /* Find obviously necessary statements. These are things like most function
391 calls, and stores to file level variables.
393 If EL is NULL, control statements are conservatively marked as
394 necessary. Otherwise it contains the list of edges used by control
395 dependence analysis. */
398 find_obviously_necessary_stmts (struct edge_list *el)
401 block_stmt_iterator i;
408 /* PHI nodes are never inherently necessary. */
409 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
412 /* Check all statements in the block. */
413 for (i = bsi_start (bb); ! bsi_end_p (i); bsi_next (&i))
415 tree stmt = bsi_stmt (i);
416 NECESSARY (stmt) = 0;
417 mark_stmt_if_obviously_necessary (stmt, el != NULL);
423 /* Prevent the loops from being removed. We must keep the infinite loops,
424 and we currently do not have a means to recognize the finite ones. */
428 FOR_EACH_EDGE (e, ei, bb->succs)
429 if (e->flags & EDGE_DFS_BACK)
430 mark_control_dependent_edges_necessary (e->dest, el);
436 /* Propagate necessity using the operands of necessary statements.
437 Process the uses on each statement in the worklist, and add all
438 feeding statements which contribute to the calculation of this
439 value to the worklist.
441 In conservative mode, EL is NULL. */
444 propagate_necessity (struct edge_list *el)
447 bool aggressive = (el ? true : false);
449 if (dump_file && (dump_flags & TDF_DETAILS))
450 fprintf (dump_file, "\nProcessing worklist:\n");
452 while (VEC_length (tree, worklist) > 0)
454 /* Take STMT from worklist. */
455 stmt = VEC_pop (tree, worklist);
457 if (dump_file && (dump_flags & TDF_DETAILS))
459 fprintf (dump_file, "processing: ");
460 print_generic_stmt (dump_file, stmt, TDF_SLIM);
461 fprintf (dump_file, "\n");
466 /* Mark the last statements of the basic blocks that the block
467 containing STMT is control dependent on, but only if we haven't
469 basic_block bb = bb_for_stmt (stmt);
470 if (bb != ENTRY_BLOCK_PTR
471 && ! TEST_BIT (visited_control_parents, bb->index))
473 SET_BIT (visited_control_parents, bb->index);
474 mark_control_dependent_edges_necessary (bb, el);
478 if (TREE_CODE (stmt) == PHI_NODE)
480 /* PHI nodes are somewhat special in that each PHI alternative has
481 data and control dependencies. All the statements feeding the
482 PHI node's arguments are always necessary. In aggressive mode,
483 we also consider the control dependent edges leading to the
484 predecessor block associated with each PHI alternative as
488 for (k = 0; k < PHI_NUM_ARGS (stmt); k++)
490 tree arg = PHI_ARG_DEF (stmt, k);
491 if (TREE_CODE (arg) == SSA_NAME)
492 mark_operand_necessary (arg);
497 for (k = 0; k < PHI_NUM_ARGS (stmt); k++)
499 basic_block arg_bb = PHI_ARG_EDGE (stmt, k)->src;
500 if (arg_bb != ENTRY_BLOCK_PTR
501 && ! TEST_BIT (visited_control_parents, arg_bb->index))
503 SET_BIT (visited_control_parents, arg_bb->index);
504 mark_control_dependent_edges_necessary (arg_bb, el);
511 /* Propagate through the operands. Examine all the USE, VUSE and
512 VDEF operands in this statement. Mark all the statements
513 which feed this statement's uses as necessary. The
514 operands of VDEF expressions are also needed as they
515 represent potential definitions that may reach this
516 statement (VDEF operands allow us to follow def-def
521 FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_ALL_USES)
522 mark_operand_necessary (use);
528 /* Remove dead PHI nodes from block BB. */
531 remove_dead_phis (basic_block bb)
534 bool something_changed = false;
537 phi = phi_nodes (bb);
542 if (! NECESSARY (phi))
544 tree next = PHI_CHAIN (phi);
546 something_changed = true;
547 if (dump_file && (dump_flags & TDF_DETAILS))
549 fprintf (dump_file, "Deleting : ");
550 print_generic_stmt (dump_file, phi, TDF_SLIM);
551 fprintf (dump_file, "\n");
554 remove_phi_node (phi, prev, true);
555 stats.removed_phis++;
561 phi = PHI_CHAIN (phi);
564 return something_changed;
568 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
569 containing I so that we don't have to look it up. */
572 remove_dead_stmt (block_stmt_iterator *i, basic_block bb)
574 tree t = bsi_stmt (*i);
576 if (dump_file && (dump_flags & TDF_DETAILS))
578 fprintf (dump_file, "Deleting : ");
579 print_generic_stmt (dump_file, t, TDF_SLIM);
580 fprintf (dump_file, "\n");
585 /* If we have determined that a conditional branch statement contributes
586 nothing to the program, then we not only remove it, but we also change
587 the flow graph so that the current block will simply fall-thru to its
588 immediate post-dominator. The blocks we are circumventing will be
589 removed by cleanup_tree_cfg if this change in the flow graph makes them
591 if (is_ctrl_stmt (t))
593 basic_block post_dom_bb;
595 /* The post dominance info has to be up-to-date. */
596 gcc_assert (dom_info_state (CDI_POST_DOMINATORS) == DOM_OK);
597 /* Get the immediate post dominator of bb. */
598 post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
600 /* There are three particularly problematical cases.
602 1. Blocks that do not have an immediate post dominator. This
603 can happen with infinite loops.
605 2. Blocks that are only post dominated by the exit block. These
606 can also happen for infinite loops as we create fake edges
607 in the dominator tree.
609 3. If the post dominator has PHI nodes we may be able to compute
610 the right PHI args for them.
612 In each of these cases we must remove the control statement
613 as it may reference SSA_NAMEs which are going to be removed and
614 we remove all but one outgoing edge from the block. */
616 || post_dom_bb == EXIT_BLOCK_PTR
617 || phi_nodes (post_dom_bb))
621 /* Redirect the first edge out of BB to reach POST_DOM_BB. */
622 redirect_edge_and_branch (EDGE_SUCC (bb, 0), post_dom_bb);
623 PENDING_STMT (EDGE_SUCC (bb, 0)) = NULL;
625 /* It is not sufficient to set cfg_altered below during edge
626 removal, in case BB has two successors and one of them
630 EDGE_SUCC (bb, 0)->probability = REG_BR_PROB_BASE;
631 EDGE_SUCC (bb, 0)->count = bb->count;
633 /* The edge is no longer associated with a conditional, so it does
634 not have TRUE/FALSE flags. */
635 EDGE_SUCC (bb, 0)->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
637 /* The lone outgoing edge from BB will be a fallthru edge. */
638 EDGE_SUCC (bb, 0)->flags |= EDGE_FALLTHRU;
640 /* Remove the remaining the outgoing edges. */
641 while (!single_succ_p (bb))
643 /* FIXME. When we remove the edge, we modify the CFG, which
644 in turn modifies the dominator and post-dominator tree.
645 Is it safe to postpone recomputing the dominator and
646 post-dominator tree until the end of this pass given that
647 the post-dominators are used above? */
649 remove_edge (EDGE_SUCC (bb, 1));
653 bsi_remove (i, true);
658 /* Eliminate unnecessary statements. Any instruction not marked as necessary
659 contributes nothing to the program, and can be deleted. */
662 eliminate_unnecessary_stmts (void)
664 bool something_changed = false;
666 block_stmt_iterator i;
668 if (dump_file && (dump_flags & TDF_DETAILS))
669 fprintf (dump_file, "\nEliminating unnecessary statements:\n");
671 clear_special_calls ();
674 /* Remove dead PHI nodes. */
675 something_changed |= remove_dead_phis (bb);
680 /* Remove dead statements. */
681 for (i = bsi_start (bb); ! bsi_end_p (i) ; )
683 tree t = bsi_stmt (i);
687 /* If `i' is not necessary then remove it. */
690 remove_dead_stmt (&i, bb);
691 something_changed = true;
695 tree call = get_call_expr_in (t);
700 /* When LHS of var = call (); is dead, simplify it into
701 call (); saving one operand. */
702 if (TREE_CODE (t) == GIMPLE_MODIFY_STMT
703 && (TREE_CODE ((name = GIMPLE_STMT_OPERAND (t, 0)))
705 && !TEST_BIT (processed, SSA_NAME_VERSION (name)))
707 tree oldlhs = GIMPLE_STMT_OPERAND (t, 0);
708 something_changed = true;
709 if (dump_file && (dump_flags & TDF_DETAILS))
711 fprintf (dump_file, "Deleting LHS of call: ");
712 print_generic_stmt (dump_file, t, TDF_SLIM);
713 fprintf (dump_file, "\n");
715 push_stmt_changes (bsi_stmt_ptr (i));
716 TREE_BLOCK (call) = TREE_BLOCK (t);
717 bsi_replace (&i, call, false);
718 maybe_clean_or_replace_eh_stmt (t, call);
719 mark_symbols_for_renaming (call);
720 pop_stmt_changes (bsi_stmt_ptr (i));
721 release_ssa_name (oldlhs);
723 notice_special_calls (call);
730 return something_changed;
734 /* Print out removed statement statistics. */
739 if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS)))
743 percg = ((float) stats.removed / (float) stats.total) * 100;
744 fprintf (dump_file, "Removed %d of %d statements (%d%%)\n",
745 stats.removed, stats.total, (int) percg);
747 if (stats.total_phis == 0)
750 percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100;
752 fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n",
753 stats.removed_phis, stats.total_phis, (int) percg);
757 /* Initialization for this pass. Set up the used data structures. */
760 tree_dce_init (bool aggressive)
762 memset ((void *) &stats, 0, sizeof (stats));
768 control_dependence_map = XNEWVEC (bitmap, last_basic_block);
769 for (i = 0; i < last_basic_block; ++i)
770 control_dependence_map[i] = BITMAP_ALLOC (NULL);
772 last_stmt_necessary = sbitmap_alloc (last_basic_block);
773 sbitmap_zero (last_stmt_necessary);
776 processed = sbitmap_alloc (num_ssa_names + 1);
777 sbitmap_zero (processed);
779 worklist = VEC_alloc (tree, heap, 64);
783 /* Cleanup after this pass. */
786 tree_dce_done (bool aggressive)
792 for (i = 0; i < last_basic_block; ++i)
793 BITMAP_FREE (control_dependence_map[i]);
794 free (control_dependence_map);
796 sbitmap_free (visited_control_parents);
797 sbitmap_free (last_stmt_necessary);
800 sbitmap_free (processed);
802 VEC_free (tree, heap, worklist);
805 /* Main routine to eliminate dead code.
807 AGGRESSIVE controls the aggressiveness of the algorithm.
808 In conservative mode, we ignore control dependence and simply declare
809 all but the most trivially dead branches necessary. This mode is fast.
810 In aggressive mode, control dependences are taken into account, which
811 results in more dead code elimination, but at the cost of some time.
813 FIXME: Aggressive mode before PRE doesn't work currently because
814 the dominance info is not invalidated after DCE1. This is
815 not an issue right now because we only run aggressive DCE
816 as the last tree SSA pass, but keep this in mind when you
817 start experimenting with pass ordering. */
820 perform_tree_ssa_dce (bool aggressive)
822 struct edge_list *el = NULL;
823 bool something_changed = 0;
825 tree_dce_init (aggressive);
829 /* Compute control dependence. */
830 timevar_push (TV_CONTROL_DEPENDENCES);
831 calculate_dominance_info (CDI_POST_DOMINATORS);
832 el = create_edge_list ();
833 find_all_control_dependences (el);
834 timevar_pop (TV_CONTROL_DEPENDENCES);
836 visited_control_parents = sbitmap_alloc (last_basic_block);
837 sbitmap_zero (visited_control_parents);
839 mark_dfs_back_edges ();
842 find_obviously_necessary_stmts (el);
844 propagate_necessity (el);
846 something_changed |= eliminate_unnecessary_stmts ();
847 something_changed |= cfg_altered;
849 /* We do not update postdominators, so free them unconditionally. */
850 free_dominance_info (CDI_POST_DOMINATORS);
852 /* If we removed paths in the CFG, then we need to update
853 dominators as well. I haven't investigated the possibility
854 of incrementally updating dominators. */
856 free_dominance_info (CDI_DOMINATORS);
858 /* Debugging dumps. */
862 tree_dce_done (aggressive);
866 if (something_changed)
867 return (TODO_update_ssa | TODO_cleanup_cfg | TODO_ggc_collect
868 | TODO_remove_unused_locals);
873 /* Pass entry points. */
877 return perform_tree_ssa_dce (/*aggressive=*/false);
881 tree_ssa_dce_loop (void)
884 todo = perform_tree_ssa_dce (/*aggressive=*/false);
887 free_numbers_of_iterations_estimates ();
894 tree_ssa_cd_dce (void)
896 return perform_tree_ssa_dce (/*aggressive=*/optimize >= 2);
902 return flag_tree_dce != 0;
905 struct tree_opt_pass pass_dce =
909 tree_ssa_dce, /* execute */
912 0, /* static_pass_number */
913 TV_TREE_DCE, /* tv_id */
914 PROP_cfg | PROP_ssa, /* properties_required */
915 0, /* properties_provided */
916 0, /* properties_destroyed */
917 0, /* todo_flags_start */
918 TODO_dump_func | TODO_verify_ssa, /* todo_flags_finish */
922 struct tree_opt_pass pass_dce_loop =
924 "dceloop", /* name */
926 tree_ssa_dce_loop, /* execute */
929 0, /* static_pass_number */
930 TV_TREE_DCE, /* tv_id */
931 PROP_cfg | PROP_ssa, /* properties_required */
932 0, /* properties_provided */
933 0, /* properties_destroyed */
934 0, /* todo_flags_start */
935 TODO_dump_func | 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, /* properties_required */
949 0, /* properties_provided */
950 0, /* properties_destroyed */
951 0, /* todo_flags_start */
952 TODO_dump_func | TODO_verify_ssa
953 | TODO_verify_flow, /* todo_flags_finish */