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 && dominated_by_p (CDI_DOMINATORS
, (basic_block
) data
,
580 gimple_bb (def_stmt
))
581 && operand_equal_p (ref
->ref
, lhs
, 0))
586 /* Otherwise keep walking. */
591 mark_aliased_reaching_defs_necessary (gimple stmt
, tree ref
)
595 gcc_assert (!chain_ovfl
);
596 ao_ref_init (&refd
, ref
);
597 chain
= walk_aliased_vdefs (&refd
, gimple_vuse (stmt
),
598 mark_aliased_reaching_defs_necessary_1
,
599 gimple_bb (stmt
), NULL
);
600 if (chain
> longest_chain
)
601 longest_chain
= chain
;
602 total_chain
+= chain
;
606 /* Worker for the walker that marks reaching definitions of REF, which
607 is not based on a non-aliased decl. For simplicity we need to end
608 up marking all may-defs necessary that are not based on a non-aliased
609 decl. The only job of this walker is to skip may-defs based on
610 a non-aliased decl. */
613 mark_all_reaching_defs_necessary_1 (ao_ref
*ref ATTRIBUTE_UNUSED
,
614 tree vdef
, void *data ATTRIBUTE_UNUSED
)
616 gimple def_stmt
= SSA_NAME_DEF_STMT (vdef
);
618 /* We have to skip already visited (and thus necessary) statements
619 to make the chaining work after we dropped back to simple mode. */
621 && TEST_BIT (processed
, SSA_NAME_VERSION (vdef
)))
623 gcc_assert (gimple_nop_p (def_stmt
)
624 || gimple_plf (def_stmt
, STMT_NECESSARY
));
628 /* We want to skip stores to non-aliased variables. */
630 && gimple_assign_single_p (def_stmt
))
632 tree lhs
= gimple_assign_lhs (def_stmt
);
633 if (!ref_may_be_aliased (lhs
))
637 /* We want to skip statments that do not constitute stores but have
638 a virtual definition. */
639 if (is_gimple_call (def_stmt
))
641 tree callee
= gimple_call_fndecl (def_stmt
);
642 if (callee
!= NULL_TREE
643 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
)
644 switch (DECL_FUNCTION_CODE (callee
))
646 case BUILT_IN_MALLOC
:
647 case BUILT_IN_CALLOC
:
648 case BUILT_IN_ALLOCA
:
649 case BUILT_IN_ALLOCA_WITH_ALIGN
:
657 mark_operand_necessary (vdef
);
663 mark_all_reaching_defs_necessary (gimple stmt
)
665 walk_aliased_vdefs (NULL
, gimple_vuse (stmt
),
666 mark_all_reaching_defs_necessary_1
, NULL
, &visited
);
669 /* Return true for PHI nodes with one or identical arguments
672 degenerate_phi_p (gimple phi
)
675 tree op
= gimple_phi_arg_def (phi
, 0);
676 for (i
= 1; i
< gimple_phi_num_args (phi
); i
++)
677 if (gimple_phi_arg_def (phi
, i
) != op
)
682 /* Propagate necessity using the operands of necessary statements.
683 Process the uses on each statement in the worklist, and add all
684 feeding statements which contribute to the calculation of this
685 value to the worklist.
687 In conservative mode, EL is NULL. */
690 propagate_necessity (struct edge_list
*el
)
693 bool aggressive
= (el
? true : false);
695 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
696 fprintf (dump_file
, "\nProcessing worklist:\n");
698 while (VEC_length (gimple
, worklist
) > 0)
700 /* Take STMT from worklist. */
701 stmt
= VEC_pop (gimple
, worklist
);
703 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
705 fprintf (dump_file
, "processing: ");
706 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
707 fprintf (dump_file
, "\n");
712 /* Mark the last statement of the basic blocks on which the block
713 containing STMT is control dependent, but only if we haven't
715 basic_block bb
= gimple_bb (stmt
);
716 if (bb
!= ENTRY_BLOCK_PTR
717 && !TEST_BIT (visited_control_parents
, bb
->index
))
718 mark_control_dependent_edges_necessary (bb
, el
, false);
721 if (gimple_code (stmt
) == GIMPLE_PHI
722 /* We do not process virtual PHI nodes nor do we track their
724 && is_gimple_reg (gimple_phi_result (stmt
)))
726 /* PHI nodes are somewhat special in that each PHI alternative has
727 data and control dependencies. All the statements feeding the
728 PHI node's arguments are always necessary. In aggressive mode,
729 we also consider the control dependent edges leading to the
730 predecessor block associated with each PHI alternative as
734 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
736 tree arg
= PHI_ARG_DEF (stmt
, k
);
737 if (TREE_CODE (arg
) == SSA_NAME
)
738 mark_operand_necessary (arg
);
741 /* For PHI operands it matters from where the control flow arrives
742 to the BB. Consider the following example:
752 We need to mark control dependence of the empty basic blocks, since they
753 contains computation of PHI operands.
755 Doing so is too restrictive in the case the predecestor block is in
761 for (i = 0; i<1000; ++i)
767 There is PHI for J in the BB containing return statement.
768 In this case the control dependence of predecestor block (that is
769 within the empty loop) also contains the block determining number
770 of iterations of the block that would prevent removing of empty
773 This scenario can be avoided by splitting critical edges.
774 To save the critical edge splitting pass we identify how the control
775 dependence would look like if the edge was split.
777 Consider the modified CFG created from current CFG by splitting
778 edge B->C. In the postdominance tree of modified CFG, C' is
779 always child of C. There are two cases how chlids of C' can look
784 In this case the only basic block C' is control dependent on is B.
786 2) C' has single child that is B
788 In this case control dependence of C' is same as control
789 dependence of B in original CFG except for block B itself.
790 (since C' postdominate B in modified CFG)
792 Now how to decide what case happens? There are two basic options:
794 a) C postdominate B. Then C immediately postdominate B and
795 case 2 happens iff there is no other way from B to C except
798 There is other way from B to C iff there is succesor of B that
799 is not postdominated by B. Testing this condition is somewhat
800 expensive, because we need to iterate all succesors of B.
801 We are safe to assume that this does not happen: we will mark B
802 as needed when processing the other path from B to C that is
803 conrol dependent on B and marking control dependencies of B
804 itself is harmless because they will be processed anyway after
805 processing control statement in B.
807 b) C does not postdominate B. Always case 1 happens since there is
808 path from C to exit that does not go through B and thus also C'. */
810 if (aggressive
&& !degenerate_phi_p (stmt
))
812 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
814 basic_block arg_bb
= gimple_phi_arg_edge (stmt
, k
)->src
;
817 != get_immediate_dominator (CDI_POST_DOMINATORS
, arg_bb
))
819 if (!TEST_BIT (last_stmt_necessary
, arg_bb
->index
))
820 mark_last_stmt_necessary (arg_bb
);
822 else if (arg_bb
!= ENTRY_BLOCK_PTR
823 && !TEST_BIT (visited_control_parents
,
825 mark_control_dependent_edges_necessary (arg_bb
, el
, true);
831 /* Propagate through the operands. Examine all the USE, VUSE and
832 VDEF operands in this statement. Mark all the statements
833 which feed this statement's uses as necessary. */
837 /* If this is a call to free which is directly fed by an
838 allocation function do not mark that necessary through
839 processing the argument. */
840 if (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
))
842 tree ptr
= gimple_call_arg (stmt
, 0);
845 /* If the pointer we free is defined by an allocation
846 function do not add the call to the worklist. */
847 if (TREE_CODE (ptr
) == SSA_NAME
848 && is_gimple_call (def_stmt
= SSA_NAME_DEF_STMT (ptr
))
849 && (def_callee
= gimple_call_fndecl (def_stmt
))
850 && DECL_BUILT_IN_CLASS (def_callee
) == BUILT_IN_NORMAL
851 && (DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_MALLOC
852 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_CALLOC
))
856 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
857 mark_operand_necessary (use
);
859 use
= gimple_vuse (stmt
);
863 /* If we dropped to simple mode make all immediately
864 reachable definitions necessary. */
867 mark_all_reaching_defs_necessary (stmt
);
871 /* For statements that may load from memory (have a VUSE) we
872 have to mark all reaching (may-)definitions as necessary.
873 We partition this task into two cases:
874 1) explicit loads based on decls that are not aliased
875 2) implicit loads (like calls) and explicit loads not
876 based on decls that are not aliased (like indirect
877 references or loads from globals)
878 For 1) we mark all reaching may-defs as necessary, stopping
879 at dominating kills. For 2) we want to mark all dominating
880 references necessary, but non-aliased ones which we handle
881 in 1). By keeping a global visited bitmap for references
882 we walk for 2) we avoid quadratic behavior for those. */
884 if (is_gimple_call (stmt
))
886 tree callee
= gimple_call_fndecl (stmt
);
889 /* Calls to functions that are merely acting as barriers
890 or that only store to memory do not make any previous
892 if (callee
!= NULL_TREE
893 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
894 && (DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET
895 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET_CHK
896 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MALLOC
897 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_CALLOC
898 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_FREE
899 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_VA_END
900 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALLOCA
901 || (DECL_FUNCTION_CODE (callee
)
902 == BUILT_IN_ALLOCA_WITH_ALIGN
)
903 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_SAVE
904 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_RESTORE
905 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ASSUME_ALIGNED
))
908 /* Calls implicitly load from memory, their arguments
909 in addition may explicitly perform memory loads. */
910 mark_all_reaching_defs_necessary (stmt
);
911 for (i
= 0; i
< gimple_call_num_args (stmt
); ++i
)
913 tree arg
= gimple_call_arg (stmt
, i
);
914 if (TREE_CODE (arg
) == SSA_NAME
915 || is_gimple_min_invariant (arg
))
917 if (TREE_CODE (arg
) == WITH_SIZE_EXPR
)
918 arg
= TREE_OPERAND (arg
, 0);
919 if (!ref_may_be_aliased (arg
))
920 mark_aliased_reaching_defs_necessary (stmt
, arg
);
923 else if (gimple_assign_single_p (stmt
))
926 /* If this is a load mark things necessary. */
927 rhs
= gimple_assign_rhs1 (stmt
);
928 if (TREE_CODE (rhs
) != SSA_NAME
929 && !is_gimple_min_invariant (rhs
)
930 && TREE_CODE (rhs
) != CONSTRUCTOR
)
932 if (!ref_may_be_aliased (rhs
))
933 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
935 mark_all_reaching_defs_necessary (stmt
);
938 else if (gimple_code (stmt
) == GIMPLE_RETURN
)
940 tree rhs
= gimple_return_retval (stmt
);
941 /* A return statement may perform a load. */
943 && TREE_CODE (rhs
) != SSA_NAME
944 && !is_gimple_min_invariant (rhs
)
945 && TREE_CODE (rhs
) != CONSTRUCTOR
)
947 if (!ref_may_be_aliased (rhs
))
948 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
950 mark_all_reaching_defs_necessary (stmt
);
953 else if (gimple_code (stmt
) == GIMPLE_ASM
)
956 mark_all_reaching_defs_necessary (stmt
);
957 /* Inputs may perform loads. */
958 for (i
= 0; i
< gimple_asm_ninputs (stmt
); ++i
)
960 tree op
= TREE_VALUE (gimple_asm_input_op (stmt
, i
));
961 if (TREE_CODE (op
) != SSA_NAME
962 && !is_gimple_min_invariant (op
)
963 && TREE_CODE (op
) != CONSTRUCTOR
964 && !ref_may_be_aliased (op
))
965 mark_aliased_reaching_defs_necessary (stmt
, op
);
971 /* If we over-used our alias oracle budget drop to simple
972 mode. The cost metric allows quadratic behavior
973 (number of uses times number of may-defs queries) up to
974 a constant maximal number of queries and after that falls back to
975 super-linear complexity. */
976 if (/* Constant but quadratic for small functions. */
977 total_chain
> 128 * 128
978 /* Linear in the number of may-defs. */
979 && total_chain
> 32 * longest_chain
980 /* Linear in the number of uses. */
981 && total_chain
> nr_walks
* 32)
985 bitmap_clear (visited
);
991 /* Replace all uses of NAME by underlying variable and mark it
995 mark_virtual_operand_for_renaming (tree name
)
998 imm_use_iterator iter
;
1003 name_var
= SSA_NAME_VAR (name
);
1004 FOR_EACH_IMM_USE_STMT (stmt
, iter
, name
)
1006 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
1007 SET_USE (use_p
, name_var
);
1012 mark_sym_for_renaming (name_var
);
1015 /* Replace all uses of result of PHI by underlying variable and mark it
1019 mark_virtual_phi_result_for_renaming (gimple phi
)
1021 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1023 fprintf (dump_file
, "Marking result for renaming : ");
1024 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
1025 fprintf (dump_file
, "\n");
1028 mark_virtual_operand_for_renaming (gimple_phi_result (phi
));
1032 /* Remove dead PHI nodes from block BB. */
1035 remove_dead_phis (basic_block bb
)
1037 bool something_changed
= false;
1040 gimple_stmt_iterator gsi
;
1041 phis
= phi_nodes (bb
);
1043 for (gsi
= gsi_start (phis
); !gsi_end_p (gsi
);)
1046 phi
= gsi_stmt (gsi
);
1048 /* We do not track necessity of virtual PHI nodes. Instead do
1049 very simple dead PHI removal here. */
1050 if (!is_gimple_reg (gimple_phi_result (phi
)))
1052 /* Virtual PHI nodes with one or identical arguments
1054 if (degenerate_phi_p (phi
))
1056 tree vdef
= gimple_phi_result (phi
);
1057 tree vuse
= gimple_phi_arg_def (phi
, 0);
1059 use_operand_p use_p
;
1060 imm_use_iterator iter
;
1062 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, vdef
)
1063 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
1064 SET_USE (use_p
, vuse
);
1065 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef
)
1066 && TREE_CODE (vuse
) == SSA_NAME
)
1067 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse
) = 1;
1070 gimple_set_plf (phi
, STMT_NECESSARY
, true);
1073 if (!gimple_plf (phi
, STMT_NECESSARY
))
1075 something_changed
= true;
1076 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1078 fprintf (dump_file
, "Deleting : ");
1079 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
1080 fprintf (dump_file
, "\n");
1083 remove_phi_node (&gsi
, true);
1084 stats
.removed_phis
++;
1090 return something_changed
;
1093 /* Forward edge E to respective POST_DOM_BB and update PHIs. */
1096 forward_edge_to_pdom (edge e
, basic_block post_dom_bb
)
1098 gimple_stmt_iterator gsi
;
1102 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1103 fprintf (dump_file
, "Redirecting edge %i->%i to %i\n", e
->src
->index
,
1104 e
->dest
->index
, post_dom_bb
->index
);
1106 e2
= redirect_edge_and_branch (e
, post_dom_bb
);
1109 /* If edge was already around, no updating is neccesary. */
1113 if (!gimple_seq_empty_p (phi_nodes (post_dom_bb
)))
1115 /* We are sure that for every live PHI we are seeing control dependent BB.
1116 This means that we can pick any edge to duplicate PHI args from. */
1117 FOR_EACH_EDGE (e2
, ei
, post_dom_bb
->preds
)
1120 for (gsi
= gsi_start_phis (post_dom_bb
); !gsi_end_p (gsi
);)
1122 gimple phi
= gsi_stmt (gsi
);
1124 source_location locus
;
1126 /* PHIs for virtuals have no control dependency relation on them.
1127 We are lost here and must force renaming of the symbol. */
1128 if (!is_gimple_reg (gimple_phi_result (phi
)))
1130 mark_virtual_phi_result_for_renaming (phi
);
1131 remove_phi_node (&gsi
, true);
1135 /* Dead PHI do not imply control dependency. */
1136 if (!gimple_plf (phi
, STMT_NECESSARY
))
1142 op
= gimple_phi_arg_def (phi
, e2
->dest_idx
);
1143 locus
= gimple_phi_arg_location (phi
, e2
->dest_idx
);
1144 add_phi_arg (phi
, op
, e
, locus
);
1145 /* The resulting PHI if not dead can only be degenerate. */
1146 gcc_assert (degenerate_phi_p (phi
));
1153 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1154 containing I so that we don't have to look it up. */
1157 remove_dead_stmt (gimple_stmt_iterator
*i
, basic_block bb
)
1159 gimple stmt
= gsi_stmt (*i
);
1161 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1163 fprintf (dump_file
, "Deleting : ");
1164 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1165 fprintf (dump_file
, "\n");
1170 /* If we have determined that a conditional branch statement contributes
1171 nothing to the program, then we not only remove it, but we also change
1172 the flow graph so that the current block will simply fall-thru to its
1173 immediate post-dominator. The blocks we are circumventing will be
1174 removed by cleanup_tree_cfg if this change in the flow graph makes them
1176 if (is_ctrl_stmt (stmt
))
1178 basic_block post_dom_bb
;
1182 post_dom_bb
= get_immediate_dominator (CDI_POST_DOMINATORS
, bb
);
1184 e
= find_edge (bb
, post_dom_bb
);
1186 /* If edge is already there, try to use it. This avoids need to update
1187 PHI nodes. Also watch for cases where post dominator does not exists
1188 or is exit block. These can happen for infinite loops as we create
1189 fake edges in the dominator tree. */
1192 else if (! post_dom_bb
|| post_dom_bb
== EXIT_BLOCK_PTR
)
1193 e
= EDGE_SUCC (bb
, 0);
1195 e
= forward_edge_to_pdom (EDGE_SUCC (bb
, 0), post_dom_bb
);
1197 e
->probability
= REG_BR_PROB_BASE
;
1198 e
->count
= bb
->count
;
1200 /* The edge is no longer associated with a conditional, so it does
1201 not have TRUE/FALSE flags. */
1202 e
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
);
1204 /* The lone outgoing edge from BB will be a fallthru edge. */
1205 e
->flags
|= EDGE_FALLTHRU
;
1207 /* Remove the remaining outgoing edges. */
1208 for (ei
= ei_start (bb
->succs
); (e2
= ei_safe_edge (ei
)); )
1218 /* If this is a store into a variable that is being optimized away,
1219 add a debug bind stmt if possible. */
1220 if (MAY_HAVE_DEBUG_STMTS
1221 && gimple_assign_single_p (stmt
)
1222 && is_gimple_val (gimple_assign_rhs1 (stmt
)))
1224 tree lhs
= gimple_assign_lhs (stmt
);
1225 if ((TREE_CODE (lhs
) == VAR_DECL
|| TREE_CODE (lhs
) == PARM_DECL
)
1226 && !DECL_IGNORED_P (lhs
)
1227 && is_gimple_reg_type (TREE_TYPE (lhs
))
1228 && !is_global_var (lhs
)
1229 && !DECL_HAS_VALUE_EXPR_P (lhs
))
1231 tree rhs
= gimple_assign_rhs1 (stmt
);
1233 = gimple_build_debug_bind (lhs
, unshare_expr (rhs
), stmt
);
1234 gsi_insert_after (i
, note
, GSI_SAME_STMT
);
1238 unlink_stmt_vdef (stmt
);
1239 gsi_remove (i
, true);
1240 release_defs (stmt
);
1243 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1244 contributes nothing to the program, and can be deleted. */
1247 eliminate_unnecessary_stmts (void)
1249 bool something_changed
= false;
1251 gimple_stmt_iterator gsi
, psi
;
1254 VEC (basic_block
, heap
) *h
;
1256 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1257 fprintf (dump_file
, "\nEliminating unnecessary statements:\n");
1259 clear_special_calls ();
1261 /* Walking basic blocks and statements in reverse order avoids
1262 releasing SSA names before any other DEFs that refer to them are
1263 released. This helps avoid loss of debug information, as we get
1264 a chance to propagate all RHSs of removed SSAs into debug uses,
1265 rather than only the latest ones. E.g., consider:
1271 If we were to release x_3 before a_5, when we reached a_5 and
1272 tried to substitute it into the debug stmt, we'd see x_3 there,
1273 but x_3's DEF, type, etc would have already been disconnected.
1274 By going backwards, the debug stmt first changes to:
1276 # DEBUG a => x_3 - b_4
1280 # DEBUG a => y_1 + z_2 - b_4
1283 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
1284 h
= get_all_dominated_blocks (CDI_DOMINATORS
, single_succ (ENTRY_BLOCK_PTR
));
1286 while (VEC_length (basic_block
, h
))
1288 bb
= VEC_pop (basic_block
, h
);
1290 /* Remove dead statements. */
1291 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi
= psi
)
1293 stmt
= gsi_stmt (gsi
);
1300 /* We can mark a call to free as not necessary if the
1301 defining statement of its argument is an allocation
1302 function and that is not necessary itself. */
1303 if (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
))
1305 tree ptr
= gimple_call_arg (stmt
, 0);
1308 if (TREE_CODE (ptr
) != SSA_NAME
)
1310 def_stmt
= SSA_NAME_DEF_STMT (ptr
);
1311 if (!is_gimple_call (def_stmt
)
1312 || gimple_plf (def_stmt
, STMT_NECESSARY
))
1314 callee2
= gimple_call_fndecl (def_stmt
);
1315 if (callee2
== NULL_TREE
1316 || DECL_BUILT_IN_CLASS (callee2
) != BUILT_IN_NORMAL
1317 || (DECL_FUNCTION_CODE (callee2
) != BUILT_IN_MALLOC
1318 && DECL_FUNCTION_CODE (callee2
) != BUILT_IN_CALLOC
))
1320 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
1323 /* If GSI is not necessary then remove it. */
1324 if (!gimple_plf (stmt
, STMT_NECESSARY
))
1326 if (!is_gimple_debug (stmt
))
1327 something_changed
= true;
1328 remove_dead_stmt (&gsi
, bb
);
1330 else if (is_gimple_call (stmt
))
1332 tree name
= gimple_call_lhs (stmt
);
1334 notice_special_calls (stmt
);
1336 /* When LHS of var = call (); is dead, simplify it into
1337 call (); saving one operand. */
1339 && TREE_CODE (name
) == SSA_NAME
1340 && !TEST_BIT (processed
, SSA_NAME_VERSION (name
))
1341 /* Avoid doing so for allocation calls which we
1342 did not mark as necessary, it will confuse the
1343 special logic we apply to malloc/free pair removal. */
1344 && (!(call
= gimple_call_fndecl (stmt
))
1345 || DECL_BUILT_IN_CLASS (call
) != BUILT_IN_NORMAL
1346 || (DECL_FUNCTION_CODE (call
) != BUILT_IN_MALLOC
1347 && DECL_FUNCTION_CODE (call
) != BUILT_IN_CALLOC
1348 && DECL_FUNCTION_CODE (call
) != BUILT_IN_ALLOCA
1349 && (DECL_FUNCTION_CODE (call
)
1350 != BUILT_IN_ALLOCA_WITH_ALIGN
))))
1352 something_changed
= true;
1353 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1355 fprintf (dump_file
, "Deleting LHS of call: ");
1356 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1357 fprintf (dump_file
, "\n");
1360 gimple_call_set_lhs (stmt
, NULL_TREE
);
1361 maybe_clean_or_replace_eh_stmt (stmt
, stmt
);
1363 release_ssa_name (name
);
1369 VEC_free (basic_block
, heap
, h
);
1371 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1372 rendered some PHI nodes unreachable while they are still in use.
1373 Mark them for renaming. */
1376 basic_block prev_bb
;
1378 find_unreachable_blocks ();
1380 /* Delete all unreachable basic blocks in reverse dominator order. */
1381 for (bb
= EXIT_BLOCK_PTR
->prev_bb
; bb
!= ENTRY_BLOCK_PTR
; bb
= prev_bb
)
1383 prev_bb
= bb
->prev_bb
;
1385 if (!TEST_BIT (bb_contains_live_stmts
, bb
->index
)
1386 || !(bb
->flags
& BB_REACHABLE
))
1388 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
1389 if (!is_gimple_reg (gimple_phi_result (gsi_stmt (gsi
))))
1392 imm_use_iterator iter
;
1394 FOR_EACH_IMM_USE_STMT (stmt
, iter
, gimple_phi_result (gsi_stmt (gsi
)))
1396 if (!(gimple_bb (stmt
)->flags
& BB_REACHABLE
))
1398 if (gimple_code (stmt
) == GIMPLE_PHI
1399 || gimple_plf (stmt
, STMT_NECESSARY
))
1402 BREAK_FROM_IMM_USE_STMT (iter
);
1406 mark_virtual_phi_result_for_renaming (gsi_stmt (gsi
));
1409 if (!(bb
->flags
& BB_REACHABLE
))
1411 /* Speed up the removal of blocks that don't
1412 dominate others. Walking backwards, this should
1413 be the common case. ??? Do we need to recompute
1414 dominators because of cfg_altered? */
1415 if (!MAY_HAVE_DEBUG_STMTS
1416 || !first_dom_son (CDI_DOMINATORS
, bb
))
1417 delete_basic_block (bb
);
1420 h
= get_all_dominated_blocks (CDI_DOMINATORS
, bb
);
1422 while (VEC_length (basic_block
, h
))
1424 bb
= VEC_pop (basic_block
, h
);
1425 prev_bb
= bb
->prev_bb
;
1426 /* Rearrangements to the CFG may have failed
1427 to update the dominators tree, so that
1428 formerly-dominated blocks are now
1429 otherwise reachable. */
1430 if (!!(bb
->flags
& BB_REACHABLE
))
1432 delete_basic_block (bb
);
1435 VEC_free (basic_block
, heap
, h
);
1443 /* Remove dead PHI nodes. */
1444 something_changed
|= remove_dead_phis (bb
);
1447 return something_changed
;
1451 /* Print out removed statement statistics. */
1458 percg
= ((float) stats
.removed
/ (float) stats
.total
) * 100;
1459 fprintf (dump_file
, "Removed %d of %d statements (%d%%)\n",
1460 stats
.removed
, stats
.total
, (int) percg
);
1462 if (stats
.total_phis
== 0)
1465 percg
= ((float) stats
.removed_phis
/ (float) stats
.total_phis
) * 100;
1467 fprintf (dump_file
, "Removed %d of %d PHI nodes (%d%%)\n",
1468 stats
.removed_phis
, stats
.total_phis
, (int) percg
);
1471 /* Initialization for this pass. Set up the used data structures. */
1474 tree_dce_init (bool aggressive
)
1476 memset ((void *) &stats
, 0, sizeof (stats
));
1482 control_dependence_map
= XNEWVEC (bitmap
, last_basic_block
);
1483 for (i
= 0; i
< last_basic_block
; ++i
)
1484 control_dependence_map
[i
] = BITMAP_ALLOC (NULL
);
1486 last_stmt_necessary
= sbitmap_alloc (last_basic_block
);
1487 sbitmap_zero (last_stmt_necessary
);
1488 bb_contains_live_stmts
= sbitmap_alloc (last_basic_block
);
1489 sbitmap_zero (bb_contains_live_stmts
);
1492 processed
= sbitmap_alloc (num_ssa_names
+ 1);
1493 sbitmap_zero (processed
);
1495 worklist
= VEC_alloc (gimple
, heap
, 64);
1496 cfg_altered
= false;
1499 /* Cleanup after this pass. */
1502 tree_dce_done (bool aggressive
)
1508 for (i
= 0; i
< last_basic_block
; ++i
)
1509 BITMAP_FREE (control_dependence_map
[i
]);
1510 free (control_dependence_map
);
1512 sbitmap_free (visited_control_parents
);
1513 sbitmap_free (last_stmt_necessary
);
1514 sbitmap_free (bb_contains_live_stmts
);
1515 bb_contains_live_stmts
= NULL
;
1518 sbitmap_free (processed
);
1520 VEC_free (gimple
, heap
, worklist
);
1523 /* Main routine to eliminate dead code.
1525 AGGRESSIVE controls the aggressiveness of the algorithm.
1526 In conservative mode, we ignore control dependence and simply declare
1527 all but the most trivially dead branches necessary. This mode is fast.
1528 In aggressive mode, control dependences are taken into account, which
1529 results in more dead code elimination, but at the cost of some time.
1531 FIXME: Aggressive mode before PRE doesn't work currently because
1532 the dominance info is not invalidated after DCE1. This is
1533 not an issue right now because we only run aggressive DCE
1534 as the last tree SSA pass, but keep this in mind when you
1535 start experimenting with pass ordering. */
1538 perform_tree_ssa_dce (bool aggressive
)
1540 struct edge_list
*el
= NULL
;
1541 bool something_changed
= 0;
1543 calculate_dominance_info (CDI_DOMINATORS
);
1545 /* Preheaders are needed for SCEV to work.
1546 Simple lateches and recorded exits improve chances that loop will
1547 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1549 loop_optimizer_init (LOOPS_NORMAL
1550 | LOOPS_HAVE_RECORDED_EXITS
);
1552 tree_dce_init (aggressive
);
1556 /* Compute control dependence. */
1557 timevar_push (TV_CONTROL_DEPENDENCES
);
1558 calculate_dominance_info (CDI_POST_DOMINATORS
);
1559 el
= create_edge_list ();
1560 find_all_control_dependences (el
);
1561 timevar_pop (TV_CONTROL_DEPENDENCES
);
1563 visited_control_parents
= sbitmap_alloc (last_basic_block
);
1564 sbitmap_zero (visited_control_parents
);
1566 mark_dfs_back_edges ();
1569 find_obviously_necessary_stmts (el
);
1572 loop_optimizer_finalize ();
1578 visited
= BITMAP_ALLOC (NULL
);
1579 propagate_necessity (el
);
1580 BITMAP_FREE (visited
);
1582 something_changed
|= eliminate_unnecessary_stmts ();
1583 something_changed
|= cfg_altered
;
1585 /* We do not update postdominators, so free them unconditionally. */
1586 free_dominance_info (CDI_POST_DOMINATORS
);
1588 /* If we removed paths in the CFG, then we need to update
1589 dominators as well. I haven't investigated the possibility
1590 of incrementally updating dominators. */
1592 free_dominance_info (CDI_DOMINATORS
);
1594 statistics_counter_event (cfun
, "Statements deleted", stats
.removed
);
1595 statistics_counter_event (cfun
, "PHI nodes deleted", stats
.removed_phis
);
1597 /* Debugging dumps. */
1598 if (dump_file
&& (dump_flags
& (TDF_STATS
|TDF_DETAILS
)))
1601 tree_dce_done (aggressive
);
1603 free_edge_list (el
);
1605 if (something_changed
)
1606 return (TODO_update_ssa
| TODO_cleanup_cfg
| TODO_ggc_collect
1607 | TODO_remove_unused_locals
);
1612 /* Pass entry points. */
1616 return perform_tree_ssa_dce (/*aggressive=*/false);
1620 tree_ssa_dce_loop (void)
1623 todo
= perform_tree_ssa_dce (/*aggressive=*/false);
1626 free_numbers_of_iterations_estimates ();
1633 tree_ssa_cd_dce (void)
1635 return perform_tree_ssa_dce (/*aggressive=*/optimize
>= 2);
1641 return flag_tree_dce
!= 0;
1644 struct gimple_opt_pass pass_dce
=
1649 gate_dce
, /* gate */
1650 tree_ssa_dce
, /* execute */
1653 0, /* static_pass_number */
1654 TV_TREE_DCE
, /* tv_id */
1655 PROP_cfg
| PROP_ssa
, /* properties_required */
1656 0, /* properties_provided */
1657 0, /* properties_destroyed */
1658 0, /* todo_flags_start */
1659 TODO_verify_ssa
/* todo_flags_finish */
1663 struct gimple_opt_pass pass_dce_loop
=
1667 "dceloop", /* name */
1668 gate_dce
, /* gate */
1669 tree_ssa_dce_loop
, /* execute */
1672 0, /* static_pass_number */
1673 TV_TREE_DCE
, /* tv_id */
1674 PROP_cfg
| PROP_ssa
, /* properties_required */
1675 0, /* properties_provided */
1676 0, /* properties_destroyed */
1677 0, /* todo_flags_start */
1678 TODO_verify_ssa
/* todo_flags_finish */
1682 struct gimple_opt_pass pass_cd_dce
=
1687 gate_dce
, /* gate */
1688 tree_ssa_cd_dce
, /* execute */
1691 0, /* static_pass_number */
1692 TV_TREE_CD_DCE
, /* tv_id */
1693 PROP_cfg
| PROP_ssa
, /* properties_required */
1694 0, /* properties_provided */
1695 0, /* properties_destroyed */
1696 0, /* todo_flags_start */
1698 | TODO_verify_flow
/* todo_flags_finish */