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 could throw, it can be deemed necessary. */
276 if (cfun
->can_throw_non_call_exceptions
277 && !cfun
->can_delete_dead_exceptions
278 && stmt_could_throw_p (stmt
))
280 mark_stmt_necessary (stmt
, true);
284 /* Statements that are implicitly live. Most function calls, asm
285 and return statements are required. Labels and GIMPLE_BIND nodes
286 are kept because they are control flow, and we have no way of
287 knowing whether they can be removed. DCE can eliminate all the
288 other statements in a block, and CFG can then remove the block
290 switch (gimple_code (stmt
))
294 mark_stmt_necessary (stmt
, false);
300 mark_stmt_necessary (stmt
, true);
305 tree callee
= gimple_call_fndecl (stmt
);
306 if (callee
!= NULL_TREE
307 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
)
308 switch (DECL_FUNCTION_CODE (callee
))
310 case BUILT_IN_MALLOC
:
311 case BUILT_IN_CALLOC
:
312 case BUILT_IN_ALLOCA
:
313 case BUILT_IN_ALLOCA_WITH_ALIGN
:
318 /* Most, but not all function calls are required. Function calls that
319 produce no result and have no side effects (i.e. const pure
320 functions) are unnecessary. */
321 if (gimple_has_side_effects (stmt
))
323 mark_stmt_necessary (stmt
, true);
326 if (!gimple_call_lhs (stmt
))
332 /* Debug temps without a value are not useful. ??? If we could
333 easily locate the debug temp bind stmt for a use thereof,
334 would could refrain from marking all debug temps here, and
335 mark them only if they're used. */
336 if (!gimple_debug_bind_p (stmt
)
337 || gimple_debug_bind_has_value_p (stmt
)
338 || TREE_CODE (gimple_debug_bind_get_var (stmt
)) != DEBUG_EXPR_DECL
)
339 mark_stmt_necessary (stmt
, false);
343 gcc_assert (!simple_goto_p (stmt
));
344 mark_stmt_necessary (stmt
, true);
348 gcc_assert (EDGE_COUNT (gimple_bb (stmt
)->succs
) == 2);
353 mark_stmt_necessary (stmt
, true);
357 if (TREE_CODE (gimple_assign_lhs (stmt
)) == SSA_NAME
358 && TREE_CLOBBER_P (gimple_assign_rhs1 (stmt
)))
366 /* If the statement has volatile operands, it needs to be preserved.
367 Same for statements that can alter control flow in unpredictable
369 if (gimple_has_volatile_ops (stmt
) || is_ctrl_altering_stmt (stmt
))
371 mark_stmt_necessary (stmt
, true);
375 if (stmt_may_clobber_global_p (stmt
))
377 mark_stmt_necessary (stmt
, true);
385 /* Mark the last statement of BB as necessary. */
388 mark_last_stmt_necessary (basic_block bb
)
390 gimple stmt
= last_stmt (bb
);
392 SET_BIT (last_stmt_necessary
, bb
->index
);
393 SET_BIT (bb_contains_live_stmts
, bb
->index
);
395 /* We actually mark the statement only if it is a control statement. */
396 if (stmt
&& is_ctrl_stmt (stmt
))
397 mark_stmt_necessary (stmt
, true);
401 /* Mark control dependent edges of BB as necessary. We have to do this only
402 once for each basic block so we set the appropriate bit after we're done.
404 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
407 mark_control_dependent_edges_necessary (basic_block bb
, struct edge_list
*el
,
411 unsigned edge_number
;
412 bool skipped
= false;
414 gcc_assert (bb
!= EXIT_BLOCK_PTR
);
416 if (bb
== ENTRY_BLOCK_PTR
)
419 EXECUTE_IF_CONTROL_DEPENDENT (bi
, bb
->index
, edge_number
)
421 basic_block cd_bb
= INDEX_EDGE_PRED_BB (el
, edge_number
);
423 if (ignore_self
&& cd_bb
== bb
)
429 if (!TEST_BIT (last_stmt_necessary
, cd_bb
->index
))
430 mark_last_stmt_necessary (cd_bb
);
434 SET_BIT (visited_control_parents
, bb
->index
);
438 /* Find obviously necessary statements. These are things like most function
439 calls, and stores to file level variables.
441 If EL is NULL, control statements are conservatively marked as
442 necessary. Otherwise it contains the list of edges used by control
443 dependence analysis. */
446 find_obviously_necessary_stmts (struct edge_list
*el
)
449 gimple_stmt_iterator gsi
;
456 /* PHI nodes are never inherently necessary. */
457 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
459 phi
= gsi_stmt (gsi
);
460 gimple_set_plf (phi
, STMT_NECESSARY
, false);
463 /* Check all statements in the block. */
464 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
466 stmt
= gsi_stmt (gsi
);
467 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
468 mark_stmt_if_obviously_necessary (stmt
, el
!= NULL
);
472 /* Pure and const functions are finite and thus have no infinite loops in
474 flags
= flags_from_decl_or_type (current_function_decl
);
475 if ((flags
& (ECF_CONST
|ECF_PURE
)) && !(flags
& ECF_LOOPING_CONST_OR_PURE
))
478 /* Prevent the empty possibly infinite loops from being removed. */
484 if (mark_irreducible_loops ())
488 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
489 if ((e
->flags
& EDGE_DFS_BACK
)
490 && (e
->flags
& EDGE_IRREDUCIBLE_LOOP
))
493 fprintf (dump_file
, "Marking back edge of irreducible loop %i->%i\n",
494 e
->src
->index
, e
->dest
->index
);
495 mark_control_dependent_edges_necessary (e
->dest
, el
, false);
499 FOR_EACH_LOOP (li
, loop
, 0)
500 if (!finite_loop_p (loop
))
503 fprintf (dump_file
, "can not prove finiteness of loop %i\n", loop
->num
);
504 mark_control_dependent_edges_necessary (loop
->latch
, el
, false);
511 /* Return true if REF is based on an aliased base, otherwise false. */
514 ref_may_be_aliased (tree ref
)
516 gcc_assert (TREE_CODE (ref
) != WITH_SIZE_EXPR
);
517 while (handled_component_p (ref
))
518 ref
= TREE_OPERAND (ref
, 0);
519 if (TREE_CODE (ref
) == MEM_REF
520 && TREE_CODE (TREE_OPERAND (ref
, 0)) == ADDR_EXPR
)
521 ref
= TREE_OPERAND (TREE_OPERAND (ref
, 0), 0);
522 return !(DECL_P (ref
)
523 && !may_be_aliased (ref
));
526 static bitmap visited
= NULL
;
527 static unsigned int longest_chain
= 0;
528 static unsigned int total_chain
= 0;
529 static unsigned int nr_walks
= 0;
530 static bool chain_ovfl
= false;
532 /* Worker for the walker that marks reaching definitions of REF,
533 which is based on a non-aliased decl, necessary. It returns
534 true whenever the defining statement of the current VDEF is
535 a kill for REF, as no dominating may-defs are necessary for REF
536 anymore. DATA points to the basic-block that contains the
537 stmt that refers to REF. */
540 mark_aliased_reaching_defs_necessary_1 (ao_ref
*ref
, tree vdef
, void *data
)
542 gimple def_stmt
= SSA_NAME_DEF_STMT (vdef
);
544 /* All stmts we visit are necessary. */
545 mark_operand_necessary (vdef
);
547 /* If the stmt lhs kills ref, then we can stop walking. */
548 if (gimple_has_lhs (def_stmt
)
549 && TREE_CODE (gimple_get_lhs (def_stmt
)) != SSA_NAME
550 /* The assignment is not necessarily carried out if it can throw
551 and we can catch it in the current function where we could inspect
553 ??? We only need to care about the RHS throwing. For aggregate
554 assignments or similar calls and non-call exceptions the LHS
555 might throw as well. */
556 && !stmt_can_throw_internal (def_stmt
))
558 tree base
, lhs
= gimple_get_lhs (def_stmt
);
559 HOST_WIDE_INT size
, offset
, max_size
;
561 base
= get_ref_base_and_extent (lhs
, &offset
, &size
, &max_size
);
562 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
563 so base == refd->base does not always hold. */
564 if (base
== ref
->base
)
566 /* For a must-alias check we need to be able to constrain
567 the accesses properly. */
568 if (size
!= -1 && size
== max_size
569 && ref
->max_size
!= -1)
571 if (offset
<= ref
->offset
572 && offset
+ size
>= ref
->offset
+ ref
->max_size
)
575 /* Or they need to be exactly the same. */
577 /* Make sure there is no induction variable involved
578 in the references (gcc.c-torture/execute/pr42142.c).
579 The simplest way is to check if the kill dominates
581 && dominated_by_p (CDI_DOMINATORS
, (basic_block
) data
,
582 gimple_bb (def_stmt
))
583 && operand_equal_p (ref
->ref
, lhs
, 0))
588 /* Otherwise keep walking. */
593 mark_aliased_reaching_defs_necessary (gimple stmt
, tree ref
)
597 gcc_assert (!chain_ovfl
);
598 ao_ref_init (&refd
, ref
);
599 chain
= walk_aliased_vdefs (&refd
, gimple_vuse (stmt
),
600 mark_aliased_reaching_defs_necessary_1
,
601 gimple_bb (stmt
), NULL
);
602 if (chain
> longest_chain
)
603 longest_chain
= chain
;
604 total_chain
+= chain
;
608 /* Worker for the walker that marks reaching definitions of REF, which
609 is not based on a non-aliased decl. For simplicity we need to end
610 up marking all may-defs necessary that are not based on a non-aliased
611 decl. The only job of this walker is to skip may-defs based on
612 a non-aliased decl. */
615 mark_all_reaching_defs_necessary_1 (ao_ref
*ref ATTRIBUTE_UNUSED
,
616 tree vdef
, void *data ATTRIBUTE_UNUSED
)
618 gimple def_stmt
= SSA_NAME_DEF_STMT (vdef
);
620 /* We have to skip already visited (and thus necessary) statements
621 to make the chaining work after we dropped back to simple mode. */
623 && TEST_BIT (processed
, SSA_NAME_VERSION (vdef
)))
625 gcc_assert (gimple_nop_p (def_stmt
)
626 || gimple_plf (def_stmt
, STMT_NECESSARY
));
630 /* We want to skip stores to non-aliased variables. */
632 && gimple_assign_single_p (def_stmt
))
634 tree lhs
= gimple_assign_lhs (def_stmt
);
635 if (!ref_may_be_aliased (lhs
))
639 /* We want to skip statments that do not constitute stores but have
640 a virtual definition. */
641 if (is_gimple_call (def_stmt
))
643 tree callee
= gimple_call_fndecl (def_stmt
);
644 if (callee
!= NULL_TREE
645 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
)
646 switch (DECL_FUNCTION_CODE (callee
))
648 case BUILT_IN_MALLOC
:
649 case BUILT_IN_CALLOC
:
650 case BUILT_IN_ALLOCA
:
651 case BUILT_IN_ALLOCA_WITH_ALIGN
:
659 mark_operand_necessary (vdef
);
665 mark_all_reaching_defs_necessary (gimple stmt
)
667 walk_aliased_vdefs (NULL
, gimple_vuse (stmt
),
668 mark_all_reaching_defs_necessary_1
, NULL
, &visited
);
671 /* Return true for PHI nodes with one or identical arguments
674 degenerate_phi_p (gimple phi
)
677 tree op
= gimple_phi_arg_def (phi
, 0);
678 for (i
= 1; i
< gimple_phi_num_args (phi
); i
++)
679 if (gimple_phi_arg_def (phi
, i
) != op
)
684 /* Propagate necessity using the operands of necessary statements.
685 Process the uses on each statement in the worklist, and add all
686 feeding statements which contribute to the calculation of this
687 value to the worklist.
689 In conservative mode, EL is NULL. */
692 propagate_necessity (struct edge_list
*el
)
695 bool aggressive
= (el
? true : false);
697 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
698 fprintf (dump_file
, "\nProcessing worklist:\n");
700 while (VEC_length (gimple
, worklist
) > 0)
702 /* Take STMT from worklist. */
703 stmt
= VEC_pop (gimple
, worklist
);
705 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
707 fprintf (dump_file
, "processing: ");
708 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
709 fprintf (dump_file
, "\n");
714 /* Mark the last statement of the basic blocks on which the block
715 containing STMT is control dependent, but only if we haven't
717 basic_block bb
= gimple_bb (stmt
);
718 if (bb
!= ENTRY_BLOCK_PTR
719 && !TEST_BIT (visited_control_parents
, bb
->index
))
720 mark_control_dependent_edges_necessary (bb
, el
, false);
723 if (gimple_code (stmt
) == GIMPLE_PHI
724 /* We do not process virtual PHI nodes nor do we track their
726 && is_gimple_reg (gimple_phi_result (stmt
)))
728 /* PHI nodes are somewhat special in that each PHI alternative has
729 data and control dependencies. All the statements feeding the
730 PHI node's arguments are always necessary. In aggressive mode,
731 we also consider the control dependent edges leading to the
732 predecessor block associated with each PHI alternative as
736 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
738 tree arg
= PHI_ARG_DEF (stmt
, k
);
739 if (TREE_CODE (arg
) == SSA_NAME
)
740 mark_operand_necessary (arg
);
743 /* For PHI operands it matters from where the control flow arrives
744 to the BB. Consider the following example:
754 We need to mark control dependence of the empty basic blocks, since they
755 contains computation of PHI operands.
757 Doing so is too restrictive in the case the predecestor block is in
763 for (i = 0; i<1000; ++i)
769 There is PHI for J in the BB containing return statement.
770 In this case the control dependence of predecestor block (that is
771 within the empty loop) also contains the block determining number
772 of iterations of the block that would prevent removing of empty
775 This scenario can be avoided by splitting critical edges.
776 To save the critical edge splitting pass we identify how the control
777 dependence would look like if the edge was split.
779 Consider the modified CFG created from current CFG by splitting
780 edge B->C. In the postdominance tree of modified CFG, C' is
781 always child of C. There are two cases how chlids of C' can look
786 In this case the only basic block C' is control dependent on is B.
788 2) C' has single child that is B
790 In this case control dependence of C' is same as control
791 dependence of B in original CFG except for block B itself.
792 (since C' postdominate B in modified CFG)
794 Now how to decide what case happens? There are two basic options:
796 a) C postdominate B. Then C immediately postdominate B and
797 case 2 happens iff there is no other way from B to C except
800 There is other way from B to C iff there is succesor of B that
801 is not postdominated by B. Testing this condition is somewhat
802 expensive, because we need to iterate all succesors of B.
803 We are safe to assume that this does not happen: we will mark B
804 as needed when processing the other path from B to C that is
805 conrol dependent on B and marking control dependencies of B
806 itself is harmless because they will be processed anyway after
807 processing control statement in B.
809 b) C does not postdominate B. Always case 1 happens since there is
810 path from C to exit that does not go through B and thus also C'. */
812 if (aggressive
&& !degenerate_phi_p (stmt
))
814 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
816 basic_block arg_bb
= gimple_phi_arg_edge (stmt
, k
)->src
;
819 != get_immediate_dominator (CDI_POST_DOMINATORS
, arg_bb
))
821 if (!TEST_BIT (last_stmt_necessary
, arg_bb
->index
))
822 mark_last_stmt_necessary (arg_bb
);
824 else if (arg_bb
!= ENTRY_BLOCK_PTR
825 && !TEST_BIT (visited_control_parents
,
827 mark_control_dependent_edges_necessary (arg_bb
, el
, true);
833 /* Propagate through the operands. Examine all the USE, VUSE and
834 VDEF operands in this statement. Mark all the statements
835 which feed this statement's uses as necessary. */
839 /* If this is a call to free which is directly fed by an
840 allocation function do not mark that necessary through
841 processing the argument. */
842 if (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
))
844 tree ptr
= gimple_call_arg (stmt
, 0);
847 /* If the pointer we free is defined by an allocation
848 function do not add the call to the worklist. */
849 if (TREE_CODE (ptr
) == SSA_NAME
850 && is_gimple_call (def_stmt
= SSA_NAME_DEF_STMT (ptr
))
851 && (def_callee
= gimple_call_fndecl (def_stmt
))
852 && DECL_BUILT_IN_CLASS (def_callee
) == BUILT_IN_NORMAL
853 && (DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_MALLOC
854 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_CALLOC
))
858 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
859 mark_operand_necessary (use
);
861 use
= gimple_vuse (stmt
);
865 /* If we dropped to simple mode make all immediately
866 reachable definitions necessary. */
869 mark_all_reaching_defs_necessary (stmt
);
873 /* For statements that may load from memory (have a VUSE) we
874 have to mark all reaching (may-)definitions as necessary.
875 We partition this task into two cases:
876 1) explicit loads based on decls that are not aliased
877 2) implicit loads (like calls) and explicit loads not
878 based on decls that are not aliased (like indirect
879 references or loads from globals)
880 For 1) we mark all reaching may-defs as necessary, stopping
881 at dominating kills. For 2) we want to mark all dominating
882 references necessary, but non-aliased ones which we handle
883 in 1). By keeping a global visited bitmap for references
884 we walk for 2) we avoid quadratic behavior for those. */
886 if (is_gimple_call (stmt
))
888 tree callee
= gimple_call_fndecl (stmt
);
891 /* Calls to functions that are merely acting as barriers
892 or that only store to memory do not make any previous
894 if (callee
!= NULL_TREE
895 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
896 && (DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET
897 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET_CHK
898 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MALLOC
899 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_CALLOC
900 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_FREE
901 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_VA_END
902 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALLOCA
903 || (DECL_FUNCTION_CODE (callee
)
904 == BUILT_IN_ALLOCA_WITH_ALIGN
)
905 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_SAVE
906 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_RESTORE
907 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ASSUME_ALIGNED
))
910 /* Calls implicitly load from memory, their arguments
911 in addition may explicitly perform memory loads. */
912 mark_all_reaching_defs_necessary (stmt
);
913 for (i
= 0; i
< gimple_call_num_args (stmt
); ++i
)
915 tree arg
= gimple_call_arg (stmt
, i
);
916 if (TREE_CODE (arg
) == SSA_NAME
917 || is_gimple_min_invariant (arg
))
919 if (TREE_CODE (arg
) == WITH_SIZE_EXPR
)
920 arg
= TREE_OPERAND (arg
, 0);
921 if (!ref_may_be_aliased (arg
))
922 mark_aliased_reaching_defs_necessary (stmt
, arg
);
925 else if (gimple_assign_single_p (stmt
))
928 /* If this is a load mark things necessary. */
929 rhs
= gimple_assign_rhs1 (stmt
);
930 if (TREE_CODE (rhs
) != SSA_NAME
931 && !is_gimple_min_invariant (rhs
)
932 && TREE_CODE (rhs
) != CONSTRUCTOR
)
934 if (!ref_may_be_aliased (rhs
))
935 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
937 mark_all_reaching_defs_necessary (stmt
);
940 else if (gimple_code (stmt
) == GIMPLE_RETURN
)
942 tree rhs
= gimple_return_retval (stmt
);
943 /* A return statement may perform a load. */
945 && TREE_CODE (rhs
) != SSA_NAME
946 && !is_gimple_min_invariant (rhs
)
947 && TREE_CODE (rhs
) != CONSTRUCTOR
)
949 if (!ref_may_be_aliased (rhs
))
950 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
952 mark_all_reaching_defs_necessary (stmt
);
955 else if (gimple_code (stmt
) == GIMPLE_ASM
)
958 mark_all_reaching_defs_necessary (stmt
);
959 /* Inputs may perform loads. */
960 for (i
= 0; i
< gimple_asm_ninputs (stmt
); ++i
)
962 tree op
= TREE_VALUE (gimple_asm_input_op (stmt
, i
));
963 if (TREE_CODE (op
) != SSA_NAME
964 && !is_gimple_min_invariant (op
)
965 && TREE_CODE (op
) != CONSTRUCTOR
966 && !ref_may_be_aliased (op
))
967 mark_aliased_reaching_defs_necessary (stmt
, op
);
970 else if (gimple_code (stmt
) == GIMPLE_TRANSACTION
)
972 /* The beginning of a transaction is a memory barrier. */
973 /* ??? If we were really cool, we'd only be a barrier
974 for the memories touched within the transaction. */
975 mark_all_reaching_defs_necessary (stmt
);
980 /* If we over-used our alias oracle budget drop to simple
981 mode. The cost metric allows quadratic behavior
982 (number of uses times number of may-defs queries) up to
983 a constant maximal number of queries and after that falls back to
984 super-linear complexity. */
985 if (/* Constant but quadratic for small functions. */
986 total_chain
> 128 * 128
987 /* Linear in the number of may-defs. */
988 && total_chain
> 32 * longest_chain
989 /* Linear in the number of uses. */
990 && total_chain
> nr_walks
* 32)
994 bitmap_clear (visited
);
1000 /* Replace all uses of NAME by underlying variable and mark it
1004 mark_virtual_operand_for_renaming (tree name
)
1007 imm_use_iterator iter
;
1008 use_operand_p use_p
;
1012 name_var
= SSA_NAME_VAR (name
);
1013 FOR_EACH_IMM_USE_STMT (stmt
, iter
, name
)
1015 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
1016 SET_USE (use_p
, name_var
);
1021 mark_sym_for_renaming (name_var
);
1024 /* Replace all uses of result of PHI by underlying variable and mark it
1028 mark_virtual_phi_result_for_renaming (gimple phi
)
1030 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1032 fprintf (dump_file
, "Marking result for renaming : ");
1033 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
1034 fprintf (dump_file
, "\n");
1037 mark_virtual_operand_for_renaming (gimple_phi_result (phi
));
1041 /* Remove dead PHI nodes from block BB. */
1044 remove_dead_phis (basic_block bb
)
1046 bool something_changed
= false;
1048 gimple_stmt_iterator gsi
;
1050 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);)
1053 phi
= gsi_stmt (gsi
);
1055 /* We do not track necessity of virtual PHI nodes. Instead do
1056 very simple dead PHI removal here. */
1057 if (!is_gimple_reg (gimple_phi_result (phi
)))
1059 /* Virtual PHI nodes with one or identical arguments
1061 if (degenerate_phi_p (phi
))
1063 tree vdef
= gimple_phi_result (phi
);
1064 tree vuse
= gimple_phi_arg_def (phi
, 0);
1066 use_operand_p use_p
;
1067 imm_use_iterator iter
;
1069 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, vdef
)
1070 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
1071 SET_USE (use_p
, vuse
);
1072 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef
)
1073 && TREE_CODE (vuse
) == SSA_NAME
)
1074 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse
) = 1;
1077 gimple_set_plf (phi
, STMT_NECESSARY
, true);
1080 if (!gimple_plf (phi
, STMT_NECESSARY
))
1082 something_changed
= true;
1083 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1085 fprintf (dump_file
, "Deleting : ");
1086 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
1087 fprintf (dump_file
, "\n");
1090 remove_phi_node (&gsi
, true);
1091 stats
.removed_phis
++;
1097 return something_changed
;
1100 /* Forward edge E to respective POST_DOM_BB and update PHIs. */
1103 forward_edge_to_pdom (edge e
, basic_block post_dom_bb
)
1105 gimple_stmt_iterator gsi
;
1109 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1110 fprintf (dump_file
, "Redirecting edge %i->%i to %i\n", e
->src
->index
,
1111 e
->dest
->index
, post_dom_bb
->index
);
1113 e2
= redirect_edge_and_branch (e
, post_dom_bb
);
1116 /* If edge was already around, no updating is neccesary. */
1120 if (!gimple_seq_empty_p (phi_nodes (post_dom_bb
)))
1122 /* We are sure that for every live PHI we are seeing control dependent BB.
1123 This means that we can pick any edge to duplicate PHI args from. */
1124 FOR_EACH_EDGE (e2
, ei
, post_dom_bb
->preds
)
1127 for (gsi
= gsi_start_phis (post_dom_bb
); !gsi_end_p (gsi
);)
1129 gimple phi
= gsi_stmt (gsi
);
1131 source_location locus
;
1134 /* PHIs for virtuals have no control dependency relation on them.
1135 We are lost here and must force renaming of the symbol. */
1136 if (!is_gimple_reg (gimple_phi_result (phi
)))
1138 mark_virtual_phi_result_for_renaming (phi
);
1139 remove_phi_node (&gsi
, true);
1143 /* Dead PHI do not imply control dependency. */
1144 if (!gimple_plf (phi
, STMT_NECESSARY
))
1150 op
= gimple_phi_arg_def (phi
, e2
->dest_idx
);
1151 locus
= gimple_phi_arg_location (phi
, e2
->dest_idx
);
1152 block
= gimple_phi_arg_block (phi
, e2
->dest_idx
);
1153 add_phi_arg (phi
, op
, e
, locus
, block
);
1154 /* The resulting PHI if not dead can only be degenerate. */
1155 gcc_assert (degenerate_phi_p (phi
));
1162 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1163 containing I so that we don't have to look it up. */
1166 remove_dead_stmt (gimple_stmt_iterator
*i
, basic_block bb
)
1168 gimple stmt
= gsi_stmt (*i
);
1170 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1172 fprintf (dump_file
, "Deleting : ");
1173 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1174 fprintf (dump_file
, "\n");
1179 /* If we have determined that a conditional branch statement contributes
1180 nothing to the program, then we not only remove it, but we also change
1181 the flow graph so that the current block will simply fall-thru to its
1182 immediate post-dominator. The blocks we are circumventing will be
1183 removed by cleanup_tree_cfg if this change in the flow graph makes them
1185 if (is_ctrl_stmt (stmt
))
1187 basic_block post_dom_bb
;
1191 post_dom_bb
= get_immediate_dominator (CDI_POST_DOMINATORS
, bb
);
1193 e
= find_edge (bb
, post_dom_bb
);
1195 /* If edge is already there, try to use it. This avoids need to update
1196 PHI nodes. Also watch for cases where post dominator does not exists
1197 or is exit block. These can happen for infinite loops as we create
1198 fake edges in the dominator tree. */
1201 else if (! post_dom_bb
|| post_dom_bb
== EXIT_BLOCK_PTR
)
1202 e
= EDGE_SUCC (bb
, 0);
1204 e
= forward_edge_to_pdom (EDGE_SUCC (bb
, 0), post_dom_bb
);
1206 e
->probability
= REG_BR_PROB_BASE
;
1207 e
->count
= bb
->count
;
1209 /* The edge is no longer associated with a conditional, so it does
1210 not have TRUE/FALSE flags. */
1211 e
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
);
1213 /* The lone outgoing edge from BB will be a fallthru edge. */
1214 e
->flags
|= EDGE_FALLTHRU
;
1216 /* Remove the remaining outgoing edges. */
1217 for (ei
= ei_start (bb
->succs
); (e2
= ei_safe_edge (ei
)); )
1227 /* If this is a store into a variable that is being optimized away,
1228 add a debug bind stmt if possible. */
1229 if (MAY_HAVE_DEBUG_STMTS
1230 && gimple_assign_single_p (stmt
)
1231 && is_gimple_val (gimple_assign_rhs1 (stmt
)))
1233 tree lhs
= gimple_assign_lhs (stmt
);
1234 if ((TREE_CODE (lhs
) == VAR_DECL
|| TREE_CODE (lhs
) == PARM_DECL
)
1235 && !DECL_IGNORED_P (lhs
)
1236 && is_gimple_reg_type (TREE_TYPE (lhs
))
1237 && !is_global_var (lhs
)
1238 && !DECL_HAS_VALUE_EXPR_P (lhs
))
1240 tree rhs
= gimple_assign_rhs1 (stmt
);
1242 = gimple_build_debug_bind (lhs
, unshare_expr (rhs
), stmt
);
1243 gsi_insert_after (i
, note
, GSI_SAME_STMT
);
1247 unlink_stmt_vdef (stmt
);
1248 gsi_remove (i
, true);
1249 release_defs (stmt
);
1252 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1253 contributes nothing to the program, and can be deleted. */
1256 eliminate_unnecessary_stmts (void)
1258 bool something_changed
= false;
1260 gimple_stmt_iterator gsi
, psi
;
1263 VEC (basic_block
, heap
) *h
;
1265 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1266 fprintf (dump_file
, "\nEliminating unnecessary statements:\n");
1268 clear_special_calls ();
1270 /* Walking basic blocks and statements in reverse order avoids
1271 releasing SSA names before any other DEFs that refer to them are
1272 released. This helps avoid loss of debug information, as we get
1273 a chance to propagate all RHSs of removed SSAs into debug uses,
1274 rather than only the latest ones. E.g., consider:
1280 If we were to release x_3 before a_5, when we reached a_5 and
1281 tried to substitute it into the debug stmt, we'd see x_3 there,
1282 but x_3's DEF, type, etc would have already been disconnected.
1283 By going backwards, the debug stmt first changes to:
1285 # DEBUG a => x_3 - b_4
1289 # DEBUG a => y_1 + z_2 - b_4
1292 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
1293 h
= get_all_dominated_blocks (CDI_DOMINATORS
, single_succ (ENTRY_BLOCK_PTR
));
1295 while (VEC_length (basic_block
, h
))
1297 bb
= VEC_pop (basic_block
, h
);
1299 /* Remove dead statements. */
1300 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi
= psi
)
1302 stmt
= gsi_stmt (gsi
);
1309 /* We can mark a call to free as not necessary if the
1310 defining statement of its argument is an allocation
1311 function and that is not necessary itself. */
1312 if (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
))
1314 tree ptr
= gimple_call_arg (stmt
, 0);
1317 if (TREE_CODE (ptr
) != SSA_NAME
)
1319 def_stmt
= SSA_NAME_DEF_STMT (ptr
);
1320 if (!is_gimple_call (def_stmt
)
1321 || gimple_plf (def_stmt
, STMT_NECESSARY
))
1323 callee2
= gimple_call_fndecl (def_stmt
);
1324 if (callee2
== NULL_TREE
1325 || DECL_BUILT_IN_CLASS (callee2
) != BUILT_IN_NORMAL
1326 || (DECL_FUNCTION_CODE (callee2
) != BUILT_IN_MALLOC
1327 && DECL_FUNCTION_CODE (callee2
) != BUILT_IN_CALLOC
))
1329 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
1332 /* If GSI is not necessary then remove it. */
1333 if (!gimple_plf (stmt
, STMT_NECESSARY
))
1335 if (!is_gimple_debug (stmt
))
1336 something_changed
= true;
1337 remove_dead_stmt (&gsi
, bb
);
1339 else if (is_gimple_call (stmt
))
1341 tree name
= gimple_call_lhs (stmt
);
1343 notice_special_calls (stmt
);
1345 /* When LHS of var = call (); is dead, simplify it into
1346 call (); saving one operand. */
1348 && TREE_CODE (name
) == SSA_NAME
1349 && !TEST_BIT (processed
, SSA_NAME_VERSION (name
))
1350 /* Avoid doing so for allocation calls which we
1351 did not mark as necessary, it will confuse the
1352 special logic we apply to malloc/free pair removal. */
1353 && (!(call
= gimple_call_fndecl (stmt
))
1354 || DECL_BUILT_IN_CLASS (call
) != BUILT_IN_NORMAL
1355 || (DECL_FUNCTION_CODE (call
) != BUILT_IN_MALLOC
1356 && DECL_FUNCTION_CODE (call
) != BUILT_IN_CALLOC
1357 && DECL_FUNCTION_CODE (call
) != BUILT_IN_ALLOCA
1358 && (DECL_FUNCTION_CODE (call
)
1359 != BUILT_IN_ALLOCA_WITH_ALIGN
))))
1361 something_changed
= true;
1362 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1364 fprintf (dump_file
, "Deleting LHS of call: ");
1365 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1366 fprintf (dump_file
, "\n");
1369 gimple_call_set_lhs (stmt
, NULL_TREE
);
1370 maybe_clean_or_replace_eh_stmt (stmt
, stmt
);
1372 release_ssa_name (name
);
1378 VEC_free (basic_block
, heap
, h
);
1380 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1381 rendered some PHI nodes unreachable while they are still in use.
1382 Mark them for renaming. */
1385 basic_block prev_bb
;
1387 find_unreachable_blocks ();
1389 /* Delete all unreachable basic blocks in reverse dominator order. */
1390 for (bb
= EXIT_BLOCK_PTR
->prev_bb
; bb
!= ENTRY_BLOCK_PTR
; bb
= prev_bb
)
1392 prev_bb
= bb
->prev_bb
;
1394 if (!TEST_BIT (bb_contains_live_stmts
, bb
->index
)
1395 || !(bb
->flags
& BB_REACHABLE
))
1397 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
1398 if (!is_gimple_reg (gimple_phi_result (gsi_stmt (gsi
))))
1401 imm_use_iterator iter
;
1403 FOR_EACH_IMM_USE_STMT (stmt
, iter
, gimple_phi_result (gsi_stmt (gsi
)))
1405 if (!(gimple_bb (stmt
)->flags
& BB_REACHABLE
))
1407 if (gimple_code (stmt
) == GIMPLE_PHI
1408 || gimple_plf (stmt
, STMT_NECESSARY
))
1411 BREAK_FROM_IMM_USE_STMT (iter
);
1415 mark_virtual_phi_result_for_renaming (gsi_stmt (gsi
));
1418 if (!(bb
->flags
& BB_REACHABLE
))
1420 /* Speed up the removal of blocks that don't
1421 dominate others. Walking backwards, this should
1422 be the common case. ??? Do we need to recompute
1423 dominators because of cfg_altered? */
1424 if (!MAY_HAVE_DEBUG_STMTS
1425 || !first_dom_son (CDI_DOMINATORS
, bb
))
1426 delete_basic_block (bb
);
1429 h
= get_all_dominated_blocks (CDI_DOMINATORS
, bb
);
1431 while (VEC_length (basic_block
, h
))
1433 bb
= VEC_pop (basic_block
, h
);
1434 prev_bb
= bb
->prev_bb
;
1435 /* Rearrangements to the CFG may have failed
1436 to update the dominators tree, so that
1437 formerly-dominated blocks are now
1438 otherwise reachable. */
1439 if (!!(bb
->flags
& BB_REACHABLE
))
1441 delete_basic_block (bb
);
1444 VEC_free (basic_block
, heap
, h
);
1452 /* Remove dead PHI nodes. */
1453 something_changed
|= remove_dead_phis (bb
);
1456 return something_changed
;
1460 /* Print out removed statement statistics. */
1467 percg
= ((float) stats
.removed
/ (float) stats
.total
) * 100;
1468 fprintf (dump_file
, "Removed %d of %d statements (%d%%)\n",
1469 stats
.removed
, stats
.total
, (int) percg
);
1471 if (stats
.total_phis
== 0)
1474 percg
= ((float) stats
.removed_phis
/ (float) stats
.total_phis
) * 100;
1476 fprintf (dump_file
, "Removed %d of %d PHI nodes (%d%%)\n",
1477 stats
.removed_phis
, stats
.total_phis
, (int) percg
);
1480 /* Initialization for this pass. Set up the used data structures. */
1483 tree_dce_init (bool aggressive
)
1485 memset ((void *) &stats
, 0, sizeof (stats
));
1491 control_dependence_map
= XNEWVEC (bitmap
, last_basic_block
);
1492 for (i
= 0; i
< last_basic_block
; ++i
)
1493 control_dependence_map
[i
] = BITMAP_ALLOC (NULL
);
1495 last_stmt_necessary
= sbitmap_alloc (last_basic_block
);
1496 sbitmap_zero (last_stmt_necessary
);
1497 bb_contains_live_stmts
= sbitmap_alloc (last_basic_block
);
1498 sbitmap_zero (bb_contains_live_stmts
);
1501 processed
= sbitmap_alloc (num_ssa_names
+ 1);
1502 sbitmap_zero (processed
);
1504 worklist
= VEC_alloc (gimple
, heap
, 64);
1505 cfg_altered
= false;
1508 /* Cleanup after this pass. */
1511 tree_dce_done (bool aggressive
)
1517 for (i
= 0; i
< last_basic_block
; ++i
)
1518 BITMAP_FREE (control_dependence_map
[i
]);
1519 free (control_dependence_map
);
1521 sbitmap_free (visited_control_parents
);
1522 sbitmap_free (last_stmt_necessary
);
1523 sbitmap_free (bb_contains_live_stmts
);
1524 bb_contains_live_stmts
= NULL
;
1527 sbitmap_free (processed
);
1529 VEC_free (gimple
, heap
, worklist
);
1532 /* Main routine to eliminate dead code.
1534 AGGRESSIVE controls the aggressiveness of the algorithm.
1535 In conservative mode, we ignore control dependence and simply declare
1536 all but the most trivially dead branches necessary. This mode is fast.
1537 In aggressive mode, control dependences are taken into account, which
1538 results in more dead code elimination, but at the cost of some time.
1540 FIXME: Aggressive mode before PRE doesn't work currently because
1541 the dominance info is not invalidated after DCE1. This is
1542 not an issue right now because we only run aggressive DCE
1543 as the last tree SSA pass, but keep this in mind when you
1544 start experimenting with pass ordering. */
1547 perform_tree_ssa_dce (bool aggressive
)
1549 struct edge_list
*el
= NULL
;
1550 bool something_changed
= 0;
1552 calculate_dominance_info (CDI_DOMINATORS
);
1554 /* Preheaders are needed for SCEV to work.
1555 Simple lateches and recorded exits improve chances that loop will
1556 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1558 loop_optimizer_init (LOOPS_NORMAL
1559 | LOOPS_HAVE_RECORDED_EXITS
);
1561 tree_dce_init (aggressive
);
1565 /* Compute control dependence. */
1566 timevar_push (TV_CONTROL_DEPENDENCES
);
1567 calculate_dominance_info (CDI_POST_DOMINATORS
);
1568 el
= create_edge_list ();
1569 find_all_control_dependences (el
);
1570 timevar_pop (TV_CONTROL_DEPENDENCES
);
1572 visited_control_parents
= sbitmap_alloc (last_basic_block
);
1573 sbitmap_zero (visited_control_parents
);
1575 mark_dfs_back_edges ();
1578 find_obviously_necessary_stmts (el
);
1581 loop_optimizer_finalize ();
1587 visited
= BITMAP_ALLOC (NULL
);
1588 propagate_necessity (el
);
1589 BITMAP_FREE (visited
);
1591 something_changed
|= eliminate_unnecessary_stmts ();
1592 something_changed
|= cfg_altered
;
1594 /* We do not update postdominators, so free them unconditionally. */
1595 free_dominance_info (CDI_POST_DOMINATORS
);
1597 /* If we removed paths in the CFG, then we need to update
1598 dominators as well. I haven't investigated the possibility
1599 of incrementally updating dominators. */
1601 free_dominance_info (CDI_DOMINATORS
);
1603 statistics_counter_event (cfun
, "Statements deleted", stats
.removed
);
1604 statistics_counter_event (cfun
, "PHI nodes deleted", stats
.removed_phis
);
1606 /* Debugging dumps. */
1607 if (dump_file
&& (dump_flags
& (TDF_STATS
|TDF_DETAILS
)))
1610 tree_dce_done (aggressive
);
1612 free_edge_list (el
);
1614 if (something_changed
)
1615 return (TODO_update_ssa
| TODO_cleanup_cfg
| TODO_ggc_collect
1616 | TODO_remove_unused_locals
);
1621 /* Pass entry points. */
1625 return perform_tree_ssa_dce (/*aggressive=*/false);
1629 tree_ssa_dce_loop (void)
1632 todo
= perform_tree_ssa_dce (/*aggressive=*/false);
1635 free_numbers_of_iterations_estimates ();
1642 tree_ssa_cd_dce (void)
1644 return perform_tree_ssa_dce (/*aggressive=*/optimize
>= 2);
1650 return flag_tree_dce
!= 0;
1653 struct gimple_opt_pass pass_dce
=
1658 gate_dce
, /* gate */
1659 tree_ssa_dce
, /* execute */
1662 0, /* static_pass_number */
1663 TV_TREE_DCE
, /* tv_id */
1664 PROP_cfg
| PROP_ssa
, /* properties_required */
1665 0, /* properties_provided */
1666 0, /* properties_destroyed */
1667 0, /* todo_flags_start */
1668 TODO_verify_ssa
/* todo_flags_finish */
1672 struct gimple_opt_pass pass_dce_loop
=
1676 "dceloop", /* name */
1677 gate_dce
, /* gate */
1678 tree_ssa_dce_loop
, /* execute */
1681 0, /* static_pass_number */
1682 TV_TREE_DCE
, /* tv_id */
1683 PROP_cfg
| PROP_ssa
, /* properties_required */
1684 0, /* properties_provided */
1685 0, /* properties_destroyed */
1686 0, /* todo_flags_start */
1687 TODO_verify_ssa
/* todo_flags_finish */
1691 struct gimple_opt_pass pass_cd_dce
=
1696 gate_dce
, /* gate */
1697 tree_ssa_cd_dce
, /* execute */
1700 0, /* static_pass_number */
1701 TV_TREE_CD_DCE
, /* tv_id */
1702 PROP_cfg
| PROP_ssa
, /* properties_required */
1703 0, /* properties_provided */
1704 0, /* properties_destroyed */
1705 0, /* todo_flags_start */
1707 | TODO_verify_flow
/* todo_flags_finish */