1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002-2017 Free Software Foundation, Inc.
3 Contributed by Ben Elliston <bje@redhat.com>
4 and Andrew MacLeod <amacleod@redhat.com>
5 Adapted to use control dependence by Steven Bosscher, SUSE Labs.
7 This file is part of GCC.
9 GCC is free software; you can redistribute it and/or modify it
10 under the terms of the GNU General Public License as published by the
11 Free Software Foundation; either version 3, or (at your option) any
14 GCC is distributed in the hope that it will be useful, but WITHOUT
15 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
16 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
19 You should have received a copy of the GNU General Public License
20 along with GCC; see the file COPYING3. If not see
21 <http://www.gnu.org/licenses/>. */
23 /* Dead code elimination.
27 Building an Optimizing Compiler,
28 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
30 Advanced Compiler Design and Implementation,
31 Steven Muchnick, Morgan Kaufmann, 1997, Section 18.10.
33 Dead-code elimination is the removal of statements which have no
34 impact on the program's output. "Dead statements" have no impact
35 on the program's output, while "necessary statements" may have
38 The algorithm consists of three phases:
39 1. Marking as necessary all statements known to be necessary,
40 e.g. most function calls, writing a value to memory, etc;
41 2. Propagating necessary statements, e.g., the statements
42 giving values to operands in necessary statements; and
43 3. Removing dead statements. */
47 #include "coretypes.h"
53 #include "tree-pass.h"
55 #include "gimple-pretty-print.h"
56 #include "fold-const.h"
61 #include "gimple-iterator.h"
63 #include "tree-ssa-loop-niter.h"
64 #include "tree-into-ssa.h"
67 #include "tree-scalar-evolution.h"
68 #include "tree-chkp.h"
69 #include "tree-ssa-propagate.h"
70 #include "gimple-fold.h"
72 static struct stmt_stats
80 #define STMT_NECESSARY GF_PLF_1
82 static vec
<gimple
*> worklist
;
84 /* Vector indicating an SSA name has already been processed and marked
86 static sbitmap processed
;
88 /* Vector indicating that the last statement of a basic block has already
89 been marked as necessary. */
90 static sbitmap last_stmt_necessary
;
92 /* Vector indicating that BB contains statements that are live. */
93 static sbitmap bb_contains_live_stmts
;
95 /* Before we can determine whether a control branch is dead, we need to
96 compute which blocks are control dependent on which edges.
98 We expect each block to be control dependent on very few edges so we
99 use a bitmap for each block recording its edges. An array holds the
100 bitmap. The Ith bit in the bitmap is set if that block is dependent
102 static control_dependences
*cd
;
104 /* Vector indicating that a basic block has already had all the edges
105 processed that it is control dependent on. */
106 static sbitmap visited_control_parents
;
108 /* TRUE if this pass alters the CFG (by removing control statements).
111 If this pass alters the CFG, then it will arrange for the dominators
113 static bool cfg_altered
;
115 /* When non-NULL holds map from basic block index into the postorder. */
116 static int *bb_postorder
;
119 /* If STMT is not already marked necessary, mark it, and add it to the
120 worklist if ADD_TO_WORKLIST is true. */
123 mark_stmt_necessary (gimple
*stmt
, bool add_to_worklist
)
127 if (gimple_plf (stmt
, STMT_NECESSARY
))
130 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
132 fprintf (dump_file
, "Marking useful stmt: ");
133 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
134 fprintf (dump_file
, "\n");
137 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
139 worklist
.safe_push (stmt
);
140 if (add_to_worklist
&& bb_contains_live_stmts
&& !is_gimple_debug (stmt
))
141 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
145 /* Mark the statement defining operand OP as necessary. */
148 mark_operand_necessary (tree op
)
155 ver
= SSA_NAME_VERSION (op
);
156 if (bitmap_bit_p (processed
, ver
))
158 stmt
= SSA_NAME_DEF_STMT (op
);
159 gcc_assert (gimple_nop_p (stmt
)
160 || gimple_plf (stmt
, STMT_NECESSARY
));
163 bitmap_set_bit (processed
, ver
);
165 stmt
= SSA_NAME_DEF_STMT (op
);
168 if (gimple_plf (stmt
, STMT_NECESSARY
) || gimple_nop_p (stmt
))
171 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
173 fprintf (dump_file
, "marking necessary through ");
174 print_generic_expr (dump_file
, op
, 0);
175 fprintf (dump_file
, " stmt ");
176 print_gimple_stmt (dump_file
, stmt
, 0, 0);
179 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
180 if (bb_contains_live_stmts
)
181 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
182 worklist
.safe_push (stmt
);
186 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
187 it can make other statements necessary.
189 If AGGRESSIVE is false, control statements are conservatively marked as
193 mark_stmt_if_obviously_necessary (gimple
*stmt
, bool aggressive
)
195 /* With non-call exceptions, we have to assume that all statements could
196 throw. If a statement could throw, it can be deemed necessary. */
197 if (cfun
->can_throw_non_call_exceptions
198 && !cfun
->can_delete_dead_exceptions
199 && stmt_could_throw_p (stmt
))
201 mark_stmt_necessary (stmt
, true);
205 /* Statements that are implicitly live. Most function calls, asm
206 and return statements are required. Labels and GIMPLE_BIND nodes
207 are kept because they are control flow, and we have no way of
208 knowing whether they can be removed. DCE can eliminate all the
209 other statements in a block, and CFG can then remove the block
211 switch (gimple_code (stmt
))
215 mark_stmt_necessary (stmt
, false);
221 mark_stmt_necessary (stmt
, true);
226 tree callee
= gimple_call_fndecl (stmt
);
227 if (callee
!= NULL_TREE
228 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
)
229 switch (DECL_FUNCTION_CODE (callee
))
231 case BUILT_IN_MALLOC
:
232 case BUILT_IN_ALIGNED_ALLOC
:
233 case BUILT_IN_CALLOC
:
234 case BUILT_IN_ALLOCA
:
235 case BUILT_IN_ALLOCA_WITH_ALIGN
:
236 case BUILT_IN_STRDUP
:
237 case BUILT_IN_STRNDUP
:
242 /* Most, but not all function calls are required. Function calls that
243 produce no result and have no side effects (i.e. const pure
244 functions) are unnecessary. */
245 if (gimple_has_side_effects (stmt
))
247 mark_stmt_necessary (stmt
, true);
250 if (!gimple_call_lhs (stmt
))
256 /* Debug temps without a value are not useful. ??? If we could
257 easily locate the debug temp bind stmt for a use thereof,
258 would could refrain from marking all debug temps here, and
259 mark them only if they're used. */
260 if (!gimple_debug_bind_p (stmt
)
261 || gimple_debug_bind_has_value_p (stmt
)
262 || TREE_CODE (gimple_debug_bind_get_var (stmt
)) != DEBUG_EXPR_DECL
)
263 mark_stmt_necessary (stmt
, false);
267 gcc_assert (!simple_goto_p (stmt
));
268 mark_stmt_necessary (stmt
, true);
272 gcc_assert (EDGE_COUNT (gimple_bb (stmt
)->succs
) == 2);
277 mark_stmt_necessary (stmt
, true);
281 if (gimple_clobber_p (stmt
))
289 /* If the statement has volatile operands, it needs to be preserved.
290 Same for statements that can alter control flow in unpredictable
292 if (gimple_has_volatile_ops (stmt
) || is_ctrl_altering_stmt (stmt
))
294 mark_stmt_necessary (stmt
, true);
298 if (stmt_may_clobber_global_p (stmt
))
300 mark_stmt_necessary (stmt
, true);
308 /* Mark the last statement of BB as necessary. */
311 mark_last_stmt_necessary (basic_block bb
)
313 gimple
*stmt
= last_stmt (bb
);
315 bitmap_set_bit (last_stmt_necessary
, bb
->index
);
316 bitmap_set_bit (bb_contains_live_stmts
, bb
->index
);
318 /* We actually mark the statement only if it is a control statement. */
319 if (stmt
&& is_ctrl_stmt (stmt
))
320 mark_stmt_necessary (stmt
, true);
324 /* Mark control dependent edges of BB as necessary. We have to do this only
325 once for each basic block so we set the appropriate bit after we're done.
327 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
330 mark_control_dependent_edges_necessary (basic_block bb
, bool ignore_self
)
333 unsigned edge_number
;
334 bool skipped
= false;
336 gcc_assert (bb
!= EXIT_BLOCK_PTR_FOR_FN (cfun
));
338 if (bb
== ENTRY_BLOCK_PTR_FOR_FN (cfun
))
341 EXECUTE_IF_SET_IN_BITMAP (cd
->get_edges_dependent_on (bb
->index
),
344 basic_block cd_bb
= cd
->get_edge_src (edge_number
);
346 if (ignore_self
&& cd_bb
== bb
)
352 if (!bitmap_bit_p (last_stmt_necessary
, cd_bb
->index
))
353 mark_last_stmt_necessary (cd_bb
);
357 bitmap_set_bit (visited_control_parents
, bb
->index
);
361 /* Find obviously necessary statements. These are things like most function
362 calls, and stores to file level variables.
364 If EL is NULL, control statements are conservatively marked as
365 necessary. Otherwise it contains the list of edges used by control
366 dependence analysis. */
369 find_obviously_necessary_stmts (bool aggressive
)
372 gimple_stmt_iterator gsi
;
377 FOR_EACH_BB_FN (bb
, cfun
)
379 /* PHI nodes are never inherently necessary. */
380 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
382 phi
= gsi_stmt (gsi
);
383 gimple_set_plf (phi
, STMT_NECESSARY
, false);
386 /* Check all statements in the block. */
387 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
389 stmt
= gsi_stmt (gsi
);
390 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
391 mark_stmt_if_obviously_necessary (stmt
, aggressive
);
395 /* Pure and const functions are finite and thus have no infinite loops in
397 flags
= flags_from_decl_or_type (current_function_decl
);
398 if ((flags
& (ECF_CONST
|ECF_PURE
)) && !(flags
& ECF_LOOPING_CONST_OR_PURE
))
401 /* Prevent the empty possibly infinite loops from being removed. */
405 if (mark_irreducible_loops ())
406 FOR_EACH_BB_FN (bb
, cfun
)
409 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
410 if ((e
->flags
& EDGE_DFS_BACK
)
411 && (e
->flags
& EDGE_IRREDUCIBLE_LOOP
))
414 fprintf (dump_file
, "Marking back edge of irreducible loop %i->%i\n",
415 e
->src
->index
, e
->dest
->index
);
416 mark_control_dependent_edges_necessary (e
->dest
, false);
420 FOR_EACH_LOOP (loop
, 0)
421 if (!finite_loop_p (loop
))
424 fprintf (dump_file
, "can not prove finiteness of loop %i\n", loop
->num
);
425 mark_control_dependent_edges_necessary (loop
->latch
, false);
431 /* Return true if REF is based on an aliased base, otherwise false. */
434 ref_may_be_aliased (tree ref
)
436 gcc_assert (TREE_CODE (ref
) != WITH_SIZE_EXPR
);
437 while (handled_component_p (ref
))
438 ref
= TREE_OPERAND (ref
, 0);
439 if (TREE_CODE (ref
) == MEM_REF
440 && TREE_CODE (TREE_OPERAND (ref
, 0)) == ADDR_EXPR
)
441 ref
= TREE_OPERAND (TREE_OPERAND (ref
, 0), 0);
442 return !(DECL_P (ref
)
443 && !may_be_aliased (ref
));
446 static bitmap visited
= NULL
;
447 static unsigned int longest_chain
= 0;
448 static unsigned int total_chain
= 0;
449 static unsigned int nr_walks
= 0;
450 static bool chain_ovfl
= false;
452 /* Worker for the walker that marks reaching definitions of REF,
453 which is based on a non-aliased decl, necessary. It returns
454 true whenever the defining statement of the current VDEF is
455 a kill for REF, as no dominating may-defs are necessary for REF
456 anymore. DATA points to the basic-block that contains the
457 stmt that refers to REF. */
460 mark_aliased_reaching_defs_necessary_1 (ao_ref
*ref
, tree vdef
, void *data
)
462 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
464 /* All stmts we visit are necessary. */
465 if (! gimple_clobber_p (def_stmt
))
466 mark_operand_necessary (vdef
);
468 /* If the stmt lhs kills ref, then we can stop walking. */
469 if (gimple_has_lhs (def_stmt
)
470 && TREE_CODE (gimple_get_lhs (def_stmt
)) != SSA_NAME
471 /* The assignment is not necessarily carried out if it can throw
472 and we can catch it in the current function where we could inspect
474 ??? We only need to care about the RHS throwing. For aggregate
475 assignments or similar calls and non-call exceptions the LHS
476 might throw as well. */
477 && !stmt_can_throw_internal (def_stmt
))
479 tree base
, lhs
= gimple_get_lhs (def_stmt
);
480 HOST_WIDE_INT size
, offset
, max_size
;
484 = get_ref_base_and_extent (lhs
, &offset
, &size
, &max_size
, &reverse
);
485 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
486 so base == refd->base does not always hold. */
487 if (base
== ref
->base
)
489 /* For a must-alias check we need to be able to constrain
490 the accesses properly. */
491 if (size
!= -1 && size
== max_size
492 && ref
->max_size
!= -1)
494 if (offset
<= ref
->offset
495 && offset
+ size
>= ref
->offset
+ ref
->max_size
)
498 /* Or they need to be exactly the same. */
500 /* Make sure there is no induction variable involved
501 in the references (gcc.c-torture/execute/pr42142.c).
502 The simplest way is to check if the kill dominates
504 /* But when both are in the same block we cannot
505 easily tell whether we came from a backedge
506 unless we decide to compute stmt UIDs
508 && (basic_block
) data
!= gimple_bb (def_stmt
)
509 && dominated_by_p (CDI_DOMINATORS
, (basic_block
) data
,
510 gimple_bb (def_stmt
))
511 && operand_equal_p (ref
->ref
, lhs
, 0))
516 /* Otherwise keep walking. */
521 mark_aliased_reaching_defs_necessary (gimple
*stmt
, tree ref
)
525 gcc_assert (!chain_ovfl
);
526 ao_ref_init (&refd
, ref
);
527 chain
= walk_aliased_vdefs (&refd
, gimple_vuse (stmt
),
528 mark_aliased_reaching_defs_necessary_1
,
529 gimple_bb (stmt
), NULL
);
530 if (chain
> longest_chain
)
531 longest_chain
= chain
;
532 total_chain
+= chain
;
536 /* Worker for the walker that marks reaching definitions of REF, which
537 is not based on a non-aliased decl. For simplicity we need to end
538 up marking all may-defs necessary that are not based on a non-aliased
539 decl. The only job of this walker is to skip may-defs based on
540 a non-aliased decl. */
543 mark_all_reaching_defs_necessary_1 (ao_ref
*ref ATTRIBUTE_UNUSED
,
544 tree vdef
, void *data ATTRIBUTE_UNUSED
)
546 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
548 /* We have to skip already visited (and thus necessary) statements
549 to make the chaining work after we dropped back to simple mode. */
551 && bitmap_bit_p (processed
, SSA_NAME_VERSION (vdef
)))
553 gcc_assert (gimple_nop_p (def_stmt
)
554 || gimple_plf (def_stmt
, STMT_NECESSARY
));
558 /* We want to skip stores to non-aliased variables. */
560 && gimple_assign_single_p (def_stmt
))
562 tree lhs
= gimple_assign_lhs (def_stmt
);
563 if (!ref_may_be_aliased (lhs
))
567 /* We want to skip statments that do not constitute stores but have
568 a virtual definition. */
569 if (is_gimple_call (def_stmt
))
571 tree callee
= gimple_call_fndecl (def_stmt
);
572 if (callee
!= NULL_TREE
573 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
)
574 switch (DECL_FUNCTION_CODE (callee
))
576 case BUILT_IN_MALLOC
:
577 case BUILT_IN_ALIGNED_ALLOC
:
578 case BUILT_IN_CALLOC
:
579 case BUILT_IN_ALLOCA
:
580 case BUILT_IN_ALLOCA_WITH_ALIGN
:
588 if (! gimple_clobber_p (def_stmt
))
589 mark_operand_necessary (vdef
);
595 mark_all_reaching_defs_necessary (gimple
*stmt
)
597 walk_aliased_vdefs (NULL
, gimple_vuse (stmt
),
598 mark_all_reaching_defs_necessary_1
, NULL
, &visited
);
601 /* Return true for PHI nodes with one or identical arguments
604 degenerate_phi_p (gimple
*phi
)
607 tree op
= gimple_phi_arg_def (phi
, 0);
608 for (i
= 1; i
< gimple_phi_num_args (phi
); i
++)
609 if (gimple_phi_arg_def (phi
, i
) != op
)
614 /* Propagate necessity using the operands of necessary statements.
615 Process the uses on each statement in the worklist, and add all
616 feeding statements which contribute to the calculation of this
617 value to the worklist.
619 In conservative mode, EL is NULL. */
622 propagate_necessity (bool aggressive
)
626 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
627 fprintf (dump_file
, "\nProcessing worklist:\n");
629 while (worklist
.length () > 0)
631 /* Take STMT from worklist. */
632 stmt
= worklist
.pop ();
634 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
636 fprintf (dump_file
, "processing: ");
637 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
638 fprintf (dump_file
, "\n");
643 /* Mark the last statement of the basic blocks on which the block
644 containing STMT is control dependent, but only if we haven't
646 basic_block bb
= gimple_bb (stmt
);
647 if (bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
648 && !bitmap_bit_p (visited_control_parents
, bb
->index
))
649 mark_control_dependent_edges_necessary (bb
, false);
652 if (gimple_code (stmt
) == GIMPLE_PHI
653 /* We do not process virtual PHI nodes nor do we track their
655 && !virtual_operand_p (gimple_phi_result (stmt
)))
657 /* PHI nodes are somewhat special in that each PHI alternative has
658 data and control dependencies. All the statements feeding the
659 PHI node's arguments are always necessary. In aggressive mode,
660 we also consider the control dependent edges leading to the
661 predecessor block associated with each PHI alternative as
663 gphi
*phi
= as_a
<gphi
*> (stmt
);
666 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
668 tree arg
= PHI_ARG_DEF (stmt
, k
);
669 if (TREE_CODE (arg
) == SSA_NAME
)
670 mark_operand_necessary (arg
);
673 /* For PHI operands it matters from where the control flow arrives
674 to the BB. Consider the following example:
684 We need to mark control dependence of the empty basic blocks, since they
685 contains computation of PHI operands.
687 Doing so is too restrictive in the case the predecestor block is in
693 for (i = 0; i<1000; ++i)
699 There is PHI for J in the BB containing return statement.
700 In this case the control dependence of predecestor block (that is
701 within the empty loop) also contains the block determining number
702 of iterations of the block that would prevent removing of empty
705 This scenario can be avoided by splitting critical edges.
706 To save the critical edge splitting pass we identify how the control
707 dependence would look like if the edge was split.
709 Consider the modified CFG created from current CFG by splitting
710 edge B->C. In the postdominance tree of modified CFG, C' is
711 always child of C. There are two cases how chlids of C' can look
716 In this case the only basic block C' is control dependent on is B.
718 2) C' has single child that is B
720 In this case control dependence of C' is same as control
721 dependence of B in original CFG except for block B itself.
722 (since C' postdominate B in modified CFG)
724 Now how to decide what case happens? There are two basic options:
726 a) C postdominate B. Then C immediately postdominate B and
727 case 2 happens iff there is no other way from B to C except
730 There is other way from B to C iff there is succesor of B that
731 is not postdominated by B. Testing this condition is somewhat
732 expensive, because we need to iterate all succesors of B.
733 We are safe to assume that this does not happen: we will mark B
734 as needed when processing the other path from B to C that is
735 conrol dependent on B and marking control dependencies of B
736 itself is harmless because they will be processed anyway after
737 processing control statement in B.
739 b) C does not postdominate B. Always case 1 happens since there is
740 path from C to exit that does not go through B and thus also C'. */
742 if (aggressive
&& !degenerate_phi_p (stmt
))
744 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
746 basic_block arg_bb
= gimple_phi_arg_edge (phi
, k
)->src
;
749 != get_immediate_dominator (CDI_POST_DOMINATORS
, arg_bb
))
751 if (!bitmap_bit_p (last_stmt_necessary
, arg_bb
->index
))
752 mark_last_stmt_necessary (arg_bb
);
754 else if (arg_bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
755 && !bitmap_bit_p (visited_control_parents
,
757 mark_control_dependent_edges_necessary (arg_bb
, true);
763 /* Propagate through the operands. Examine all the USE, VUSE and
764 VDEF operands in this statement. Mark all the statements
765 which feed this statement's uses as necessary. */
769 /* If this is a call to free which is directly fed by an
770 allocation function do not mark that necessary through
771 processing the argument. */
772 if (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
))
774 tree ptr
= gimple_call_arg (stmt
, 0);
777 /* If the pointer we free is defined by an allocation
778 function do not add the call to the worklist. */
779 if (TREE_CODE (ptr
) == SSA_NAME
780 && is_gimple_call (def_stmt
= SSA_NAME_DEF_STMT (ptr
))
781 && (def_callee
= gimple_call_fndecl (def_stmt
))
782 && DECL_BUILT_IN_CLASS (def_callee
) == BUILT_IN_NORMAL
783 && (DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_ALIGNED_ALLOC
784 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_MALLOC
785 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_CALLOC
786 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_STRDUP
787 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_STRNDUP
))
789 gimple
*bounds_def_stmt
;
792 /* For instrumented calls we should also check used
793 bounds are returned by the same allocation call. */
794 if (!gimple_call_with_bounds_p (stmt
)
795 || ((bounds
= gimple_call_arg (stmt
, 1))
796 && TREE_CODE (bounds
) == SSA_NAME
797 && (bounds_def_stmt
= SSA_NAME_DEF_STMT (bounds
))
798 && chkp_gimple_call_builtin_p (bounds_def_stmt
,
799 BUILT_IN_CHKP_BNDRET
)
800 && gimple_call_arg (bounds_def_stmt
, 0) == ptr
))
805 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
806 mark_operand_necessary (use
);
808 use
= gimple_vuse (stmt
);
812 /* If we dropped to simple mode make all immediately
813 reachable definitions necessary. */
816 mark_all_reaching_defs_necessary (stmt
);
820 /* For statements that may load from memory (have a VUSE) we
821 have to mark all reaching (may-)definitions as necessary.
822 We partition this task into two cases:
823 1) explicit loads based on decls that are not aliased
824 2) implicit loads (like calls) and explicit loads not
825 based on decls that are not aliased (like indirect
826 references or loads from globals)
827 For 1) we mark all reaching may-defs as necessary, stopping
828 at dominating kills. For 2) we want to mark all dominating
829 references necessary, but non-aliased ones which we handle
830 in 1). By keeping a global visited bitmap for references
831 we walk for 2) we avoid quadratic behavior for those. */
833 if (is_gimple_call (stmt
))
835 tree callee
= gimple_call_fndecl (stmt
);
838 /* Calls to functions that are merely acting as barriers
839 or that only store to memory do not make any previous
841 if (callee
!= NULL_TREE
842 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
843 && (DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET
844 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET_CHK
845 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MALLOC
846 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALIGNED_ALLOC
847 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_CALLOC
848 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_FREE
849 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_VA_END
850 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALLOCA
851 || (DECL_FUNCTION_CODE (callee
)
852 == BUILT_IN_ALLOCA_WITH_ALIGN
)
853 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_SAVE
854 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_RESTORE
855 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ASSUME_ALIGNED
))
858 /* Calls implicitly load from memory, their arguments
859 in addition may explicitly perform memory loads. */
860 mark_all_reaching_defs_necessary (stmt
);
861 for (i
= 0; i
< gimple_call_num_args (stmt
); ++i
)
863 tree arg
= gimple_call_arg (stmt
, i
);
864 if (TREE_CODE (arg
) == SSA_NAME
865 || is_gimple_min_invariant (arg
))
867 if (TREE_CODE (arg
) == WITH_SIZE_EXPR
)
868 arg
= TREE_OPERAND (arg
, 0);
869 if (!ref_may_be_aliased (arg
))
870 mark_aliased_reaching_defs_necessary (stmt
, arg
);
873 else if (gimple_assign_single_p (stmt
))
876 /* If this is a load mark things necessary. */
877 rhs
= gimple_assign_rhs1 (stmt
);
878 if (TREE_CODE (rhs
) != SSA_NAME
879 && !is_gimple_min_invariant (rhs
)
880 && TREE_CODE (rhs
) != CONSTRUCTOR
)
882 if (!ref_may_be_aliased (rhs
))
883 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
885 mark_all_reaching_defs_necessary (stmt
);
888 else if (greturn
*return_stmt
= dyn_cast
<greturn
*> (stmt
))
890 tree rhs
= gimple_return_retval (return_stmt
);
891 /* A return statement may perform a load. */
893 && TREE_CODE (rhs
) != SSA_NAME
894 && !is_gimple_min_invariant (rhs
)
895 && TREE_CODE (rhs
) != CONSTRUCTOR
)
897 if (!ref_may_be_aliased (rhs
))
898 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
900 mark_all_reaching_defs_necessary (stmt
);
903 else if (gasm
*asm_stmt
= dyn_cast
<gasm
*> (stmt
))
906 mark_all_reaching_defs_necessary (stmt
);
907 /* Inputs may perform loads. */
908 for (i
= 0; i
< gimple_asm_ninputs (asm_stmt
); ++i
)
910 tree op
= TREE_VALUE (gimple_asm_input_op (asm_stmt
, i
));
911 if (TREE_CODE (op
) != SSA_NAME
912 && !is_gimple_min_invariant (op
)
913 && TREE_CODE (op
) != CONSTRUCTOR
914 && !ref_may_be_aliased (op
))
915 mark_aliased_reaching_defs_necessary (stmt
, op
);
918 else if (gimple_code (stmt
) == GIMPLE_TRANSACTION
)
920 /* The beginning of a transaction is a memory barrier. */
921 /* ??? If we were really cool, we'd only be a barrier
922 for the memories touched within the transaction. */
923 mark_all_reaching_defs_necessary (stmt
);
928 /* If we over-used our alias oracle budget drop to simple
929 mode. The cost metric allows quadratic behavior
930 (number of uses times number of may-defs queries) up to
931 a constant maximal number of queries and after that falls back to
932 super-linear complexity. */
933 if (/* Constant but quadratic for small functions. */
934 total_chain
> 128 * 128
935 /* Linear in the number of may-defs. */
936 && total_chain
> 32 * longest_chain
937 /* Linear in the number of uses. */
938 && total_chain
> nr_walks
* 32)
942 bitmap_clear (visited
);
948 /* Remove dead PHI nodes from block BB. */
951 remove_dead_phis (basic_block bb
)
953 bool something_changed
= false;
957 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);)
962 /* We do not track necessity of virtual PHI nodes. Instead do
963 very simple dead PHI removal here. */
964 if (virtual_operand_p (gimple_phi_result (phi
)))
966 /* Virtual PHI nodes with one or identical arguments
968 if (degenerate_phi_p (phi
))
970 tree vdef
= gimple_phi_result (phi
);
971 tree vuse
= gimple_phi_arg_def (phi
, 0);
974 imm_use_iterator iter
;
976 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, vdef
)
977 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
978 SET_USE (use_p
, vuse
);
979 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef
)
980 && TREE_CODE (vuse
) == SSA_NAME
)
981 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse
) = 1;
984 gimple_set_plf (phi
, STMT_NECESSARY
, true);
987 if (!gimple_plf (phi
, STMT_NECESSARY
))
989 something_changed
= true;
990 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
992 fprintf (dump_file
, "Deleting : ");
993 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
994 fprintf (dump_file
, "\n");
997 remove_phi_node (&gsi
, true);
998 stats
.removed_phis
++;
1004 return something_changed
;
1008 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1009 containing I so that we don't have to look it up. */
1012 remove_dead_stmt (gimple_stmt_iterator
*i
, basic_block bb
)
1014 gimple
*stmt
= gsi_stmt (*i
);
1016 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1018 fprintf (dump_file
, "Deleting : ");
1019 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1020 fprintf (dump_file
, "\n");
1025 /* If we have determined that a conditional branch statement contributes
1026 nothing to the program, then we not only remove it, but we need to update
1027 the CFG. We can chose any of edges out of BB as long as we are sure to not
1028 close infinite loops. This is done by always choosing the edge closer to
1029 exit in inverted_post_order_compute order. */
1030 if (is_ctrl_stmt (stmt
))
1035 /* See if there is only one non-abnormal edge. */
1036 if (single_succ_p (bb
))
1037 e
= single_succ_edge (bb
);
1038 /* Otherwise chose one that is closer to bb with live statement in it.
1039 To be able to chose one, we compute inverted post order starting from
1040 all BBs with live statements. */
1045 int *postorder
= XNEWVEC (int, n_basic_blocks_for_fn (cfun
));
1047 = inverted_post_order_compute (postorder
,
1048 &bb_contains_live_stmts
);
1049 bb_postorder
= XNEWVEC (int, last_basic_block_for_fn (cfun
));
1050 for (int i
= 0; i
< postorder_num
; ++i
)
1051 bb_postorder
[postorder
[i
]] = i
;
1054 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1055 if (!e
|| e2
->dest
== EXIT_BLOCK_PTR_FOR_FN (cfun
)
1056 || bb_postorder
[e
->dest
->index
]
1057 < bb_postorder
[e2
->dest
->index
])
1061 e
->probability
= REG_BR_PROB_BASE
;
1062 e
->count
= bb
->count
;
1064 /* The edge is no longer associated with a conditional, so it does
1065 not have TRUE/FALSE flags.
1066 We are also safe to drop EH/ABNORMAL flags and turn them into
1067 normal control flow, because we know that all the destinations (including
1068 those odd edges) are equivalent for program execution. */
1069 e
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
| EDGE_EH
| EDGE_ABNORMAL
);
1071 /* The lone outgoing edge from BB will be a fallthru edge. */
1072 e
->flags
|= EDGE_FALLTHRU
;
1074 /* Remove the remaining outgoing edges. */
1075 for (ei
= ei_start (bb
->succs
); (e2
= ei_safe_edge (ei
)); )
1079 /* If we made a BB unconditionally exit a loop or removed
1080 an entry into an irreducible region, then this transform
1081 alters the set of BBs in the loop. Schedule a fixup. */
1082 if (loop_exit_edge_p (bb
->loop_father
, e
)
1083 || (e2
->dest
->flags
& BB_IRREDUCIBLE_LOOP
))
1084 loops_state_set (LOOPS_NEED_FIXUP
);
1091 /* If this is a store into a variable that is being optimized away,
1092 add a debug bind stmt if possible. */
1093 if (MAY_HAVE_DEBUG_STMTS
1094 && gimple_assign_single_p (stmt
)
1095 && is_gimple_val (gimple_assign_rhs1 (stmt
)))
1097 tree lhs
= gimple_assign_lhs (stmt
);
1098 if ((VAR_P (lhs
) || TREE_CODE (lhs
) == PARM_DECL
)
1099 && !DECL_IGNORED_P (lhs
)
1100 && is_gimple_reg_type (TREE_TYPE (lhs
))
1101 && !is_global_var (lhs
)
1102 && !DECL_HAS_VALUE_EXPR_P (lhs
))
1104 tree rhs
= gimple_assign_rhs1 (stmt
);
1106 = gimple_build_debug_bind (lhs
, unshare_expr (rhs
), stmt
);
1107 gsi_insert_after (i
, note
, GSI_SAME_STMT
);
1111 unlink_stmt_vdef (stmt
);
1112 gsi_remove (i
, true);
1113 release_defs (stmt
);
1116 /* Helper for maybe_optimize_arith_overflow. Find in *TP if there are any
1117 uses of data (SSA_NAME) other than REALPART_EXPR referencing it. */
1120 find_non_realpart_uses (tree
*tp
, int *walk_subtrees
, void *data
)
1122 if (TYPE_P (*tp
) || TREE_CODE (*tp
) == REALPART_EXPR
)
1124 if (*tp
== (tree
) data
)
1129 /* If the IMAGPART_EXPR of the {ADD,SUB,MUL}_OVERFLOW result is never used,
1130 but REALPART_EXPR is, optimize the {ADD,SUB,MUL}_OVERFLOW internal calls
1131 into plain unsigned {PLUS,MINUS,MULT}_EXPR, and if needed reset debug
1135 maybe_optimize_arith_overflow (gimple_stmt_iterator
*gsi
,
1136 enum tree_code subcode
)
1138 gimple
*stmt
= gsi_stmt (*gsi
);
1139 tree lhs
= gimple_call_lhs (stmt
);
1141 if (lhs
== NULL
|| TREE_CODE (lhs
) != SSA_NAME
)
1144 imm_use_iterator imm_iter
;
1145 use_operand_p use_p
;
1146 bool has_debug_uses
= false;
1147 bool has_realpart_uses
= false;
1148 bool has_other_uses
= false;
1149 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, lhs
)
1151 gimple
*use_stmt
= USE_STMT (use_p
);
1152 if (is_gimple_debug (use_stmt
))
1153 has_debug_uses
= true;
1154 else if (is_gimple_assign (use_stmt
)
1155 && gimple_assign_rhs_code (use_stmt
) == REALPART_EXPR
1156 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt
), 0) == lhs
)
1157 has_realpart_uses
= true;
1160 has_other_uses
= true;
1165 if (!has_realpart_uses
|| has_other_uses
)
1168 tree arg0
= gimple_call_arg (stmt
, 0);
1169 tree arg1
= gimple_call_arg (stmt
, 1);
1170 location_t loc
= gimple_location (stmt
);
1171 tree type
= TREE_TYPE (TREE_TYPE (lhs
));
1173 if (!TYPE_UNSIGNED (type
))
1174 utype
= build_nonstandard_integer_type (TYPE_PRECISION (type
), 1);
1175 tree result
= fold_build2_loc (loc
, subcode
, utype
,
1176 fold_convert_loc (loc
, utype
, arg0
),
1177 fold_convert_loc (loc
, utype
, arg1
));
1178 result
= fold_convert_loc (loc
, type
, result
);
1183 FOR_EACH_IMM_USE_STMT (use_stmt
, imm_iter
, lhs
)
1185 if (!gimple_debug_bind_p (use_stmt
))
1187 tree v
= gimple_debug_bind_get_value (use_stmt
);
1188 if (walk_tree (&v
, find_non_realpart_uses
, lhs
, NULL
))
1190 gimple_debug_bind_reset_value (use_stmt
);
1191 update_stmt (use_stmt
);
1196 if (TREE_CODE (result
) == INTEGER_CST
&& TREE_OVERFLOW (result
))
1197 result
= drop_tree_overflow (result
);
1198 tree overflow
= build_zero_cst (type
);
1199 tree ctype
= build_complex_type (type
);
1200 if (TREE_CODE (result
) == INTEGER_CST
)
1201 result
= build_complex (ctype
, result
, overflow
);
1203 result
= build2_loc (gimple_location (stmt
), COMPLEX_EXPR
,
1204 ctype
, result
, overflow
);
1206 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1208 fprintf (dump_file
, "Transforming call: ");
1209 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1210 fprintf (dump_file
, "because the overflow result is never used into: ");
1211 print_generic_stmt (dump_file
, result
, TDF_SLIM
);
1212 fprintf (dump_file
, "\n");
1215 if (!update_call_from_tree (gsi
, result
))
1216 gimplify_and_update_call_from_tree (gsi
, result
);
1219 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1220 contributes nothing to the program, and can be deleted. */
1223 eliminate_unnecessary_stmts (void)
1225 bool something_changed
= false;
1227 gimple_stmt_iterator gsi
, psi
;
1232 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1233 fprintf (dump_file
, "\nEliminating unnecessary statements:\n");
1235 clear_special_calls ();
1237 /* Walking basic blocks and statements in reverse order avoids
1238 releasing SSA names before any other DEFs that refer to them are
1239 released. This helps avoid loss of debug information, as we get
1240 a chance to propagate all RHSs of removed SSAs into debug uses,
1241 rather than only the latest ones. E.g., consider:
1247 If we were to release x_3 before a_5, when we reached a_5 and
1248 tried to substitute it into the debug stmt, we'd see x_3 there,
1249 but x_3's DEF, type, etc would have already been disconnected.
1250 By going backwards, the debug stmt first changes to:
1252 # DEBUG a => x_3 - b_4
1256 # DEBUG a => y_1 + z_2 - b_4
1259 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
1260 h
= get_all_dominated_blocks (CDI_DOMINATORS
,
1261 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun
)));
1267 /* Remove dead statements. */
1268 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi
= psi
)
1270 stmt
= gsi_stmt (gsi
);
1277 /* We can mark a call to free as not necessary if the
1278 defining statement of its argument is not necessary
1279 (and thus is getting removed). */
1280 if (gimple_plf (stmt
, STMT_NECESSARY
)
1281 && gimple_call_builtin_p (stmt
, BUILT_IN_FREE
))
1283 tree ptr
= gimple_call_arg (stmt
, 0);
1284 if (TREE_CODE (ptr
) == SSA_NAME
)
1286 gimple
*def_stmt
= SSA_NAME_DEF_STMT (ptr
);
1287 if (!gimple_nop_p (def_stmt
)
1288 && !gimple_plf (def_stmt
, STMT_NECESSARY
))
1289 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
1291 /* We did not propagate necessity for free calls fed
1292 by allocation function to allow unnecessary
1293 alloc-free sequence elimination. For instrumented
1294 calls it also means we did not mark bounds producer
1295 as necessary and it is time to do it in case free
1296 call is not removed. */
1297 if (gimple_call_with_bounds_p (stmt
))
1299 gimple
*bounds_def_stmt
;
1300 tree bounds
= gimple_call_arg (stmt
, 1);
1301 gcc_assert (TREE_CODE (bounds
) == SSA_NAME
);
1302 bounds_def_stmt
= SSA_NAME_DEF_STMT (bounds
);
1304 && !gimple_plf (bounds_def_stmt
, STMT_NECESSARY
))
1305 gimple_set_plf (bounds_def_stmt
, STMT_NECESSARY
,
1306 gimple_plf (stmt
, STMT_NECESSARY
));
1310 /* If GSI is not necessary then remove it. */
1311 if (!gimple_plf (stmt
, STMT_NECESSARY
))
1313 /* Keep clobbers that we can keep live live. */
1314 if (gimple_clobber_p (stmt
))
1317 use_operand_p use_p
;
1319 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_USE
)
1321 tree name
= USE_FROM_PTR (use_p
);
1322 if (!SSA_NAME_IS_DEFAULT_DEF (name
)
1323 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
)))
1332 if (!is_gimple_debug (stmt
))
1333 something_changed
= true;
1334 remove_dead_stmt (&gsi
, bb
);
1336 else if (is_gimple_call (stmt
))
1338 tree name
= gimple_call_lhs (stmt
);
1340 notice_special_calls (as_a
<gcall
*> (stmt
));
1342 /* When LHS of var = call (); is dead, simplify it into
1343 call (); saving one operand. */
1345 && TREE_CODE (name
) == SSA_NAME
1346 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
))
1347 /* Avoid doing so for allocation calls which we
1348 did not mark as necessary, it will confuse the
1349 special logic we apply to malloc/free pair removal. */
1350 && (!(call
= gimple_call_fndecl (stmt
))
1351 || DECL_BUILT_IN_CLASS (call
) != BUILT_IN_NORMAL
1352 || (DECL_FUNCTION_CODE (call
) != BUILT_IN_ALIGNED_ALLOC
1353 && DECL_FUNCTION_CODE (call
) != BUILT_IN_MALLOC
1354 && DECL_FUNCTION_CODE (call
) != BUILT_IN_CALLOC
1355 && DECL_FUNCTION_CODE (call
) != BUILT_IN_ALLOCA
1356 && (DECL_FUNCTION_CODE (call
)
1357 != BUILT_IN_ALLOCA_WITH_ALIGN
)))
1358 /* Avoid doing so for bndret calls for the same reason. */
1359 && !chkp_gimple_call_builtin_p (stmt
, BUILT_IN_CHKP_BNDRET
))
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
);
1374 /* GOMP_SIMD_LANE or ASAN_POISON without lhs is not
1376 if (gimple_call_internal_p (stmt
))
1377 switch (gimple_call_internal_fn (stmt
))
1379 case IFN_GOMP_SIMD_LANE
:
1380 case IFN_ASAN_POISON
:
1381 remove_dead_stmt (&gsi
, bb
);
1387 else if (gimple_call_internal_p (stmt
))
1388 switch (gimple_call_internal_fn (stmt
))
1390 case IFN_ADD_OVERFLOW
:
1391 maybe_optimize_arith_overflow (&gsi
, PLUS_EXPR
);
1393 case IFN_SUB_OVERFLOW
:
1394 maybe_optimize_arith_overflow (&gsi
, MINUS_EXPR
);
1396 case IFN_MUL_OVERFLOW
:
1397 maybe_optimize_arith_overflow (&gsi
, MULT_EXPR
);
1408 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1409 rendered some PHI nodes unreachable while they are still in use.
1410 Mark them for renaming. */
1413 basic_block prev_bb
;
1415 find_unreachable_blocks ();
1417 /* Delete all unreachable basic blocks in reverse dominator order. */
1418 for (bb
= EXIT_BLOCK_PTR_FOR_FN (cfun
)->prev_bb
;
1419 bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
); bb
= prev_bb
)
1421 prev_bb
= bb
->prev_bb
;
1423 if (!bitmap_bit_p (bb_contains_live_stmts
, bb
->index
)
1424 || !(bb
->flags
& BB_REACHABLE
))
1426 for (gphi_iterator gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
1428 if (virtual_operand_p (gimple_phi_result (gsi
.phi ())))
1431 imm_use_iterator iter
;
1433 FOR_EACH_IMM_USE_STMT (stmt
, iter
,
1434 gimple_phi_result (gsi
.phi ()))
1436 if (!(gimple_bb (stmt
)->flags
& BB_REACHABLE
))
1438 if (gimple_code (stmt
) == GIMPLE_PHI
1439 || gimple_plf (stmt
, STMT_NECESSARY
))
1442 BREAK_FROM_IMM_USE_STMT (iter
);
1446 mark_virtual_phi_result_for_renaming (gsi
.phi ());
1449 if (!(bb
->flags
& BB_REACHABLE
))
1451 /* Speed up the removal of blocks that don't
1452 dominate others. Walking backwards, this should
1453 be the common case. ??? Do we need to recompute
1454 dominators because of cfg_altered? */
1455 if (!MAY_HAVE_DEBUG_STMTS
1456 || !first_dom_son (CDI_DOMINATORS
, bb
))
1457 delete_basic_block (bb
);
1460 h
= get_all_dominated_blocks (CDI_DOMINATORS
, bb
);
1465 prev_bb
= bb
->prev_bb
;
1466 /* Rearrangements to the CFG may have failed
1467 to update the dominators tree, so that
1468 formerly-dominated blocks are now
1469 otherwise reachable. */
1470 if (!!(bb
->flags
& BB_REACHABLE
))
1472 delete_basic_block (bb
);
1481 FOR_EACH_BB_FN (bb
, cfun
)
1483 /* Remove dead PHI nodes. */
1484 something_changed
|= remove_dead_phis (bb
);
1488 free (bb_postorder
);
1489 bb_postorder
= NULL
;
1491 return something_changed
;
1495 /* Print out removed statement statistics. */
1502 percg
= ((float) stats
.removed
/ (float) stats
.total
) * 100;
1503 fprintf (dump_file
, "Removed %d of %d statements (%d%%)\n",
1504 stats
.removed
, stats
.total
, (int) percg
);
1506 if (stats
.total_phis
== 0)
1509 percg
= ((float) stats
.removed_phis
/ (float) stats
.total_phis
) * 100;
1511 fprintf (dump_file
, "Removed %d of %d PHI nodes (%d%%)\n",
1512 stats
.removed_phis
, stats
.total_phis
, (int) percg
);
1515 /* Initialization for this pass. Set up the used data structures. */
1518 tree_dce_init (bool aggressive
)
1520 memset ((void *) &stats
, 0, sizeof (stats
));
1524 last_stmt_necessary
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1525 bitmap_clear (last_stmt_necessary
);
1526 bb_contains_live_stmts
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1527 bitmap_clear (bb_contains_live_stmts
);
1530 processed
= sbitmap_alloc (num_ssa_names
+ 1);
1531 bitmap_clear (processed
);
1533 worklist
.create (64);
1534 cfg_altered
= false;
1537 /* Cleanup after this pass. */
1540 tree_dce_done (bool aggressive
)
1545 sbitmap_free (visited_control_parents
);
1546 sbitmap_free (last_stmt_necessary
);
1547 sbitmap_free (bb_contains_live_stmts
);
1548 bb_contains_live_stmts
= NULL
;
1551 sbitmap_free (processed
);
1553 worklist
.release ();
1556 /* Main routine to eliminate dead code.
1558 AGGRESSIVE controls the aggressiveness of the algorithm.
1559 In conservative mode, we ignore control dependence and simply declare
1560 all but the most trivially dead branches necessary. This mode is fast.
1561 In aggressive mode, control dependences are taken into account, which
1562 results in more dead code elimination, but at the cost of some time.
1564 FIXME: Aggressive mode before PRE doesn't work currently because
1565 the dominance info is not invalidated after DCE1. This is
1566 not an issue right now because we only run aggressive DCE
1567 as the last tree SSA pass, but keep this in mind when you
1568 start experimenting with pass ordering. */
1571 perform_tree_ssa_dce (bool aggressive
)
1573 bool something_changed
= 0;
1575 calculate_dominance_info (CDI_DOMINATORS
);
1577 /* Preheaders are needed for SCEV to work.
1578 Simple lateches and recorded exits improve chances that loop will
1579 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1580 bool in_loop_pipeline
= scev_initialized_p ();
1581 if (aggressive
&& ! in_loop_pipeline
)
1584 loop_optimizer_init (LOOPS_NORMAL
1585 | LOOPS_HAVE_RECORDED_EXITS
);
1588 tree_dce_init (aggressive
);
1592 /* Compute control dependence. */
1593 calculate_dominance_info (CDI_POST_DOMINATORS
);
1594 cd
= new control_dependences ();
1596 visited_control_parents
=
1597 sbitmap_alloc (last_basic_block_for_fn (cfun
));
1598 bitmap_clear (visited_control_parents
);
1600 mark_dfs_back_edges ();
1603 find_obviously_necessary_stmts (aggressive
);
1605 if (aggressive
&& ! in_loop_pipeline
)
1607 loop_optimizer_finalize ();
1615 visited
= BITMAP_ALLOC (NULL
);
1616 propagate_necessity (aggressive
);
1617 BITMAP_FREE (visited
);
1619 something_changed
|= eliminate_unnecessary_stmts ();
1620 something_changed
|= cfg_altered
;
1622 /* We do not update postdominators, so free them unconditionally. */
1623 free_dominance_info (CDI_POST_DOMINATORS
);
1625 /* If we removed paths in the CFG, then we need to update
1626 dominators as well. I haven't investigated the possibility
1627 of incrementally updating dominators. */
1629 free_dominance_info (CDI_DOMINATORS
);
1631 statistics_counter_event (cfun
, "Statements deleted", stats
.removed
);
1632 statistics_counter_event (cfun
, "PHI nodes deleted", stats
.removed_phis
);
1634 /* Debugging dumps. */
1635 if (dump_file
&& (dump_flags
& (TDF_STATS
|TDF_DETAILS
)))
1638 tree_dce_done (aggressive
);
1640 if (something_changed
)
1642 free_numbers_of_iterations_estimates (cfun
);
1643 if (in_loop_pipeline
)
1645 return TODO_update_ssa
| TODO_cleanup_cfg
;
1650 /* Pass entry points. */
1654 return perform_tree_ssa_dce (/*aggressive=*/false);
1658 tree_ssa_cd_dce (void)
1660 return perform_tree_ssa_dce (/*aggressive=*/optimize
>= 2);
1665 const pass_data pass_data_dce
=
1667 GIMPLE_PASS
, /* type */
1669 OPTGROUP_NONE
, /* optinfo_flags */
1670 TV_TREE_DCE
, /* tv_id */
1671 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1672 0, /* properties_provided */
1673 0, /* properties_destroyed */
1674 0, /* todo_flags_start */
1675 0, /* todo_flags_finish */
1678 class pass_dce
: public gimple_opt_pass
1681 pass_dce (gcc::context
*ctxt
)
1682 : gimple_opt_pass (pass_data_dce
, ctxt
)
1685 /* opt_pass methods: */
1686 opt_pass
* clone () { return new pass_dce (m_ctxt
); }
1687 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1688 virtual unsigned int execute (function
*) { return tree_ssa_dce (); }
1690 }; // class pass_dce
1695 make_pass_dce (gcc::context
*ctxt
)
1697 return new pass_dce (ctxt
);
1702 const pass_data pass_data_cd_dce
=
1704 GIMPLE_PASS
, /* type */
1706 OPTGROUP_NONE
, /* optinfo_flags */
1707 TV_TREE_CD_DCE
, /* tv_id */
1708 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1709 0, /* properties_provided */
1710 0, /* properties_destroyed */
1711 0, /* todo_flags_start */
1712 0, /* todo_flags_finish */
1715 class pass_cd_dce
: public gimple_opt_pass
1718 pass_cd_dce (gcc::context
*ctxt
)
1719 : gimple_opt_pass (pass_data_cd_dce
, ctxt
)
1722 /* opt_pass methods: */
1723 opt_pass
* clone () { return new pass_cd_dce (m_ctxt
); }
1724 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1725 virtual unsigned int execute (function
*) { return tree_ssa_cd_dce (); }
1727 }; // class pass_cd_dce
1732 make_pass_cd_dce (gcc::context
*ctxt
)
1734 return new pass_cd_dce (ctxt
);