1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002-2020 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-ssa-propagate.h"
69 #include "gimple-fold.h"
71 static struct stmt_stats
79 #define STMT_NECESSARY GF_PLF_1
81 static vec
<gimple
*> worklist
;
83 /* Vector indicating an SSA name has already been processed and marked
85 static sbitmap processed
;
87 /* Vector indicating that the last statement of a basic block has already
88 been marked as necessary. */
89 static sbitmap last_stmt_necessary
;
91 /* Vector indicating that BB contains statements that are live. */
92 static sbitmap bb_contains_live_stmts
;
94 /* Before we can determine whether a control branch is dead, we need to
95 compute which blocks are control dependent on which edges.
97 We expect each block to be control dependent on very few edges so we
98 use a bitmap for each block recording its edges. An array holds the
99 bitmap. The Ith bit in the bitmap is set if that block is dependent
101 static control_dependences
*cd
;
103 /* Vector indicating that a basic block has already had all the edges
104 processed that it is control dependent on. */
105 static sbitmap visited_control_parents
;
107 /* TRUE if this pass alters the CFG (by removing control statements).
110 If this pass alters the CFG, then it will arrange for the dominators
112 static bool cfg_altered
;
114 /* When non-NULL holds map from basic block index into the postorder. */
115 static int *bb_postorder
;
118 /* True if we should treat any stmt with a vdef as necessary. */
123 return optimize_debug
;
126 /* If STMT is not already marked necessary, mark it, and add it to the
127 worklist if ADD_TO_WORKLIST is true. */
130 mark_stmt_necessary (gimple
*stmt
, bool add_to_worklist
)
134 if (gimple_plf (stmt
, STMT_NECESSARY
))
137 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
139 fprintf (dump_file
, "Marking useful stmt: ");
140 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
141 fprintf (dump_file
, "\n");
144 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
146 worklist
.safe_push (stmt
);
147 if (add_to_worklist
&& bb_contains_live_stmts
&& !is_gimple_debug (stmt
))
148 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
152 /* Mark the statement defining operand OP as necessary. */
155 mark_operand_necessary (tree op
)
162 ver
= SSA_NAME_VERSION (op
);
163 if (bitmap_bit_p (processed
, ver
))
165 stmt
= SSA_NAME_DEF_STMT (op
);
166 gcc_assert (gimple_nop_p (stmt
)
167 || gimple_plf (stmt
, STMT_NECESSARY
));
170 bitmap_set_bit (processed
, ver
);
172 stmt
= SSA_NAME_DEF_STMT (op
);
175 if (gimple_plf (stmt
, STMT_NECESSARY
) || gimple_nop_p (stmt
))
178 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
180 fprintf (dump_file
, "marking necessary through ");
181 print_generic_expr (dump_file
, op
);
182 fprintf (dump_file
, " stmt ");
183 print_gimple_stmt (dump_file
, stmt
, 0);
186 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
187 if (bb_contains_live_stmts
)
188 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
189 worklist
.safe_push (stmt
);
193 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
194 it can make other statements necessary.
196 If AGGRESSIVE is false, control statements are conservatively marked as
200 mark_stmt_if_obviously_necessary (gimple
*stmt
, bool aggressive
)
202 /* With non-call exceptions, we have to assume that all statements could
203 throw. If a statement could throw, it can be deemed necessary. */
204 if (stmt_unremovable_because_of_non_call_eh_p (cfun
, stmt
))
206 mark_stmt_necessary (stmt
, true);
210 /* Statements that are implicitly live. Most function calls, asm
211 and return statements are required. Labels and GIMPLE_BIND nodes
212 are kept because they are control flow, and we have no way of
213 knowing whether they can be removed. DCE can eliminate all the
214 other statements in a block, and CFG can then remove the block
216 switch (gimple_code (stmt
))
220 mark_stmt_necessary (stmt
, false);
226 mark_stmt_necessary (stmt
, true);
231 tree callee
= gimple_call_fndecl (stmt
);
232 if (callee
!= NULL_TREE
233 && fndecl_built_in_p (callee
, BUILT_IN_NORMAL
))
234 switch (DECL_FUNCTION_CODE (callee
))
236 case BUILT_IN_MALLOC
:
237 case BUILT_IN_ALIGNED_ALLOC
:
238 case BUILT_IN_CALLOC
:
239 CASE_BUILT_IN_ALLOCA
:
240 case BUILT_IN_STRDUP
:
241 case BUILT_IN_STRNDUP
:
242 case BUILT_IN_GOMP_ALLOC
:
248 if (callee
!= NULL_TREE
249 && flag_allocation_dce
250 && DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
))
253 /* Most, but not all function calls are required. Function calls that
254 produce no result and have no side effects (i.e. const pure
255 functions) are unnecessary. */
256 if (gimple_has_side_effects (stmt
))
258 mark_stmt_necessary (stmt
, true);
261 /* IFN_GOACC_LOOP calls are necessary in that they are used to
262 represent parameter (i.e. step, bound) of a lowered OpenACC
263 partitioned loop. But this kind of partitioned loop might not
264 survive from aggressive loop removal for it has loop exit and
265 is assumed to be finite. Therefore, we need to explicitly mark
266 these calls. (An example is libgomp.oacc-c-c++-common/pr84955.c) */
267 if (gimple_call_internal_p (stmt
, IFN_GOACC_LOOP
))
269 mark_stmt_necessary (stmt
, true);
272 if (!gimple_call_lhs (stmt
))
278 /* Debug temps without a value are not useful. ??? If we could
279 easily locate the debug temp bind stmt for a use thereof,
280 would could refrain from marking all debug temps here, and
281 mark them only if they're used. */
282 if (gimple_debug_nonbind_marker_p (stmt
)
283 || !gimple_debug_bind_p (stmt
)
284 || gimple_debug_bind_has_value_p (stmt
)
285 || TREE_CODE (gimple_debug_bind_get_var (stmt
)) != DEBUG_EXPR_DECL
)
286 mark_stmt_necessary (stmt
, false);
290 gcc_assert (!simple_goto_p (stmt
));
291 mark_stmt_necessary (stmt
, true);
295 gcc_assert (EDGE_COUNT (gimple_bb (stmt
)->succs
) == 2);
300 mark_stmt_necessary (stmt
, true);
304 if (gimple_clobber_p (stmt
))
312 /* If the statement has volatile operands, it needs to be preserved.
313 Same for statements that can alter control flow in unpredictable
315 if (gimple_has_volatile_ops (stmt
) || is_ctrl_altering_stmt (stmt
))
317 mark_stmt_necessary (stmt
, true);
321 if (stmt_may_clobber_global_p (stmt
))
323 mark_stmt_necessary (stmt
, true);
327 if (gimple_vdef (stmt
) && keep_all_vdefs_p ())
329 mark_stmt_necessary (stmt
, true);
337 /* Mark the last statement of BB as necessary. */
340 mark_last_stmt_necessary (basic_block bb
)
342 gimple
*stmt
= last_stmt (bb
);
344 bitmap_set_bit (last_stmt_necessary
, bb
->index
);
345 bitmap_set_bit (bb_contains_live_stmts
, bb
->index
);
347 /* We actually mark the statement only if it is a control statement. */
348 if (stmt
&& is_ctrl_stmt (stmt
))
349 mark_stmt_necessary (stmt
, true);
353 /* Mark control dependent edges of BB as necessary. We have to do this only
354 once for each basic block so we set the appropriate bit after we're done.
356 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
359 mark_control_dependent_edges_necessary (basic_block bb
, bool ignore_self
)
362 unsigned edge_number
;
363 bool skipped
= false;
365 gcc_assert (bb
!= EXIT_BLOCK_PTR_FOR_FN (cfun
));
367 if (bb
== ENTRY_BLOCK_PTR_FOR_FN (cfun
))
370 EXECUTE_IF_SET_IN_BITMAP (cd
->get_edges_dependent_on (bb
->index
),
373 basic_block cd_bb
= cd
->get_edge_src (edge_number
);
375 if (ignore_self
&& cd_bb
== bb
)
381 if (!bitmap_bit_p (last_stmt_necessary
, cd_bb
->index
))
382 mark_last_stmt_necessary (cd_bb
);
386 bitmap_set_bit (visited_control_parents
, bb
->index
);
390 /* Find obviously necessary statements. These are things like most function
391 calls, and stores to file level variables.
393 If EL is NULL, control statements are conservatively marked as
394 necessary. Otherwise it contains the list of edges used by control
395 dependence analysis. */
398 find_obviously_necessary_stmts (bool aggressive
)
401 gimple_stmt_iterator gsi
;
406 FOR_EACH_BB_FN (bb
, cfun
)
408 /* PHI nodes are never inherently necessary. */
409 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
411 phi
= gsi_stmt (gsi
);
412 gimple_set_plf (phi
, STMT_NECESSARY
, false);
415 /* Check all statements in the block. */
416 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
418 stmt
= gsi_stmt (gsi
);
419 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
420 mark_stmt_if_obviously_necessary (stmt
, aggressive
);
424 /* Pure and const functions are finite and thus have no infinite loops in
426 flags
= flags_from_decl_or_type (current_function_decl
);
427 if ((flags
& (ECF_CONST
|ECF_PURE
)) && !(flags
& ECF_LOOPING_CONST_OR_PURE
))
430 /* Prevent the empty possibly infinite loops from being removed. */
434 if (mark_irreducible_loops ())
435 FOR_EACH_BB_FN (bb
, cfun
)
438 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
439 if ((e
->flags
& EDGE_DFS_BACK
)
440 && (e
->flags
& EDGE_IRREDUCIBLE_LOOP
))
443 fprintf (dump_file
, "Marking back edge of irreducible loop %i->%i\n",
444 e
->src
->index
, e
->dest
->index
);
445 mark_control_dependent_edges_necessary (e
->dest
, false);
449 FOR_EACH_LOOP (loop
, 0)
450 if (!finite_loop_p (loop
))
453 fprintf (dump_file
, "cannot prove finiteness of loop %i\n", loop
->num
);
454 mark_control_dependent_edges_necessary (loop
->latch
, false);
460 /* Return true if REF is based on an aliased base, otherwise false. */
463 ref_may_be_aliased (tree ref
)
465 gcc_assert (TREE_CODE (ref
) != WITH_SIZE_EXPR
);
466 while (handled_component_p (ref
))
467 ref
= TREE_OPERAND (ref
, 0);
468 if (TREE_CODE (ref
) == MEM_REF
469 && TREE_CODE (TREE_OPERAND (ref
, 0)) == ADDR_EXPR
)
470 ref
= TREE_OPERAND (TREE_OPERAND (ref
, 0), 0);
471 return !(DECL_P (ref
)
472 && !may_be_aliased (ref
));
475 static bitmap visited
= NULL
;
476 static unsigned int longest_chain
= 0;
477 static unsigned int total_chain
= 0;
478 static unsigned int nr_walks
= 0;
479 static bool chain_ovfl
= false;
481 /* Worker for the walker that marks reaching definitions of REF,
482 which is based on a non-aliased decl, necessary. It returns
483 true whenever the defining statement of the current VDEF is
484 a kill for REF, as no dominating may-defs are necessary for REF
485 anymore. DATA points to the basic-block that contains the
486 stmt that refers to REF. */
489 mark_aliased_reaching_defs_necessary_1 (ao_ref
*ref
, tree vdef
, void *data
)
491 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
493 /* All stmts we visit are necessary. */
494 if (! gimple_clobber_p (def_stmt
))
495 mark_operand_necessary (vdef
);
497 /* If the stmt lhs kills ref, then we can stop walking. */
498 if (gimple_has_lhs (def_stmt
)
499 && TREE_CODE (gimple_get_lhs (def_stmt
)) != SSA_NAME
500 /* The assignment is not necessarily carried out if it can throw
501 and we can catch it in the current function where we could inspect
503 ??? We only need to care about the RHS throwing. For aggregate
504 assignments or similar calls and non-call exceptions the LHS
505 might throw as well. */
506 && !stmt_can_throw_internal (cfun
, def_stmt
))
508 tree base
, lhs
= gimple_get_lhs (def_stmt
);
509 poly_int64 size
, offset
, max_size
;
513 = get_ref_base_and_extent (lhs
, &offset
, &size
, &max_size
, &reverse
);
514 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
515 so base == refd->base does not always hold. */
516 if (base
== ref
->base
)
518 /* For a must-alias check we need to be able to constrain
519 the accesses properly. */
520 if (known_eq (size
, max_size
)
521 && known_subrange_p (ref
->offset
, ref
->max_size
, offset
, size
))
523 /* Or they need to be exactly the same. */
525 /* Make sure there is no induction variable involved
526 in the references (gcc.c-torture/execute/pr42142.c).
527 The simplest way is to check if the kill dominates
529 /* But when both are in the same block we cannot
530 easily tell whether we came from a backedge
531 unless we decide to compute stmt UIDs
533 && (basic_block
) data
!= gimple_bb (def_stmt
)
534 && dominated_by_p (CDI_DOMINATORS
, (basic_block
) data
,
535 gimple_bb (def_stmt
))
536 && operand_equal_p (ref
->ref
, lhs
, 0))
541 /* Otherwise keep walking. */
546 mark_aliased_reaching_defs_necessary (gimple
*stmt
, tree ref
)
548 /* Should have been caught before calling this function. */
549 gcc_checking_assert (!keep_all_vdefs_p ());
553 gcc_assert (!chain_ovfl
);
554 ao_ref_init (&refd
, ref
);
555 chain
= walk_aliased_vdefs (&refd
, gimple_vuse (stmt
),
556 mark_aliased_reaching_defs_necessary_1
,
557 gimple_bb (stmt
), NULL
);
558 if (chain
> longest_chain
)
559 longest_chain
= chain
;
560 total_chain
+= chain
;
564 /* Worker for the walker that marks reaching definitions of REF, which
565 is not based on a non-aliased decl. For simplicity we need to end
566 up marking all may-defs necessary that are not based on a non-aliased
567 decl. The only job of this walker is to skip may-defs based on
568 a non-aliased decl. */
571 mark_all_reaching_defs_necessary_1 (ao_ref
*ref ATTRIBUTE_UNUSED
,
572 tree vdef
, void *data ATTRIBUTE_UNUSED
)
574 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
576 /* We have to skip already visited (and thus necessary) statements
577 to make the chaining work after we dropped back to simple mode. */
579 && bitmap_bit_p (processed
, SSA_NAME_VERSION (vdef
)))
581 gcc_assert (gimple_nop_p (def_stmt
)
582 || gimple_plf (def_stmt
, STMT_NECESSARY
));
586 /* We want to skip stores to non-aliased variables. */
588 && gimple_assign_single_p (def_stmt
))
590 tree lhs
= gimple_assign_lhs (def_stmt
);
591 if (!ref_may_be_aliased (lhs
))
595 /* We want to skip statments that do not constitute stores but have
596 a virtual definition. */
597 if (gcall
*call
= dyn_cast
<gcall
*> (def_stmt
))
599 tree callee
= gimple_call_fndecl (call
);
600 if (callee
!= NULL_TREE
601 && fndecl_built_in_p (callee
, BUILT_IN_NORMAL
))
602 switch (DECL_FUNCTION_CODE (callee
))
604 case BUILT_IN_MALLOC
:
605 case BUILT_IN_ALIGNED_ALLOC
:
606 case BUILT_IN_CALLOC
:
607 CASE_BUILT_IN_ALLOCA
:
609 case BUILT_IN_GOMP_ALLOC
:
610 case BUILT_IN_GOMP_FREE
:
616 if (callee
!= NULL_TREE
617 && (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
)
618 || DECL_IS_OPERATOR_DELETE_P (callee
))
619 && gimple_call_from_new_or_delete (call
))
623 if (! gimple_clobber_p (def_stmt
))
624 mark_operand_necessary (vdef
);
630 mark_all_reaching_defs_necessary (gimple
*stmt
)
632 /* Should have been caught before calling this function. */
633 gcc_checking_assert (!keep_all_vdefs_p ());
634 walk_aliased_vdefs (NULL
, gimple_vuse (stmt
),
635 mark_all_reaching_defs_necessary_1
, NULL
, &visited
);
638 /* Return true for PHI nodes with one or identical arguments
641 degenerate_phi_p (gimple
*phi
)
644 tree op
= gimple_phi_arg_def (phi
, 0);
645 for (i
= 1; i
< gimple_phi_num_args (phi
); i
++)
646 if (gimple_phi_arg_def (phi
, i
) != op
)
651 /* Return that NEW_CALL and DELETE_CALL are a valid pair of new
652 and delete operators. */
655 valid_new_delete_pair_p (gimple
*new_call
, gimple
*delete_call
)
657 tree new_asm
= DECL_ASSEMBLER_NAME (gimple_call_fndecl (new_call
));
658 tree delete_asm
= DECL_ASSEMBLER_NAME (gimple_call_fndecl (delete_call
));
659 const char *new_name
= IDENTIFIER_POINTER (new_asm
);
660 const char *delete_name
= IDENTIFIER_POINTER (delete_asm
);
661 unsigned int new_len
= IDENTIFIER_LENGTH (new_asm
);
662 unsigned int delete_len
= IDENTIFIER_LENGTH (delete_asm
);
664 if (new_len
< 5 || delete_len
< 6)
666 if (new_name
[0] == '_')
667 ++new_name
, --new_len
;
668 if (new_name
[0] == '_')
669 ++new_name
, --new_len
;
670 if (delete_name
[0] == '_')
671 ++delete_name
, --delete_len
;
672 if (delete_name
[0] == '_')
673 ++delete_name
, --delete_len
;
674 if (new_len
< 4 || delete_len
< 5)
676 /* *_len is now just the length after initial underscores. */
677 if (new_name
[0] != 'Z' || new_name
[1] != 'n')
679 if (delete_name
[0] != 'Z' || delete_name
[1] != 'd')
681 /* _Znw must match _Zdl, _Zna must match _Zda. */
682 if ((new_name
[2] != 'w' || delete_name
[2] != 'l')
683 && (new_name
[2] != 'a' || delete_name
[2] != 'a'))
685 /* 'j', 'm' and 'y' correspond to size_t. */
686 if (new_name
[3] != 'j' && new_name
[3] != 'm' && new_name
[3] != 'y')
688 if (delete_name
[3] != 'P' || delete_name
[4] != 'v')
691 || (new_len
== 18 && !memcmp (new_name
+ 4, "RKSt9nothrow_t", 14)))
693 /* _ZnXY or _ZnXYRKSt9nothrow_t matches
694 _ZdXPv, _ZdXPvY and _ZdXPvRKSt9nothrow_t. */
697 if (delete_len
== 6 && delete_name
[5] == new_name
[3])
699 if (delete_len
== 19 && !memcmp (delete_name
+ 5, "RKSt9nothrow_t", 14))
702 else if ((new_len
== 19 && !memcmp (new_name
+ 4, "St11align_val_t", 15))
704 && !memcmp (new_name
+ 4, "St11align_val_tRKSt9nothrow_t", 29)))
706 /* _ZnXYSt11align_val_t or _ZnXYSt11align_val_tRKSt9nothrow_t matches
707 _ZdXPvSt11align_val_t or _ZdXPvYSt11align_val_t or or
708 _ZdXPvSt11align_val_tRKSt9nothrow_t. */
709 if (delete_len
== 20 && !memcmp (delete_name
+ 5, "St11align_val_t", 15))
712 && delete_name
[5] == new_name
[3]
713 && !memcmp (delete_name
+ 6, "St11align_val_t", 15))
716 && !memcmp (delete_name
+ 5, "St11align_val_tRKSt9nothrow_t", 29))
722 /* Propagate necessity using the operands of necessary statements.
723 Process the uses on each statement in the worklist, and add all
724 feeding statements which contribute to the calculation of this
725 value to the worklist.
727 In conservative mode, EL is NULL. */
730 propagate_necessity (bool aggressive
)
734 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
735 fprintf (dump_file
, "\nProcessing worklist:\n");
737 while (worklist
.length () > 0)
739 /* Take STMT from worklist. */
740 stmt
= worklist
.pop ();
742 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
744 fprintf (dump_file
, "processing: ");
745 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
746 fprintf (dump_file
, "\n");
751 /* Mark the last statement of the basic blocks on which the block
752 containing STMT is control dependent, but only if we haven't
754 basic_block bb
= gimple_bb (stmt
);
755 if (bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
756 && !bitmap_bit_p (visited_control_parents
, bb
->index
))
757 mark_control_dependent_edges_necessary (bb
, false);
760 if (gimple_code (stmt
) == GIMPLE_PHI
761 /* We do not process virtual PHI nodes nor do we track their
763 && !virtual_operand_p (gimple_phi_result (stmt
)))
765 /* PHI nodes are somewhat special in that each PHI alternative has
766 data and control dependencies. All the statements feeding the
767 PHI node's arguments are always necessary. In aggressive mode,
768 we also consider the control dependent edges leading to the
769 predecessor block associated with each PHI alternative as
771 gphi
*phi
= as_a
<gphi
*> (stmt
);
774 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
776 tree arg
= PHI_ARG_DEF (stmt
, k
);
777 if (TREE_CODE (arg
) == SSA_NAME
)
778 mark_operand_necessary (arg
);
781 /* For PHI operands it matters from where the control flow arrives
782 to the BB. Consider the following example:
792 We need to mark control dependence of the empty basic blocks, since they
793 contains computation of PHI operands.
795 Doing so is too restrictive in the case the predecestor block is in
801 for (i = 0; i<1000; ++i)
807 There is PHI for J in the BB containing return statement.
808 In this case the control dependence of predecestor block (that is
809 within the empty loop) also contains the block determining number
810 of iterations of the block that would prevent removing of empty
813 This scenario can be avoided by splitting critical edges.
814 To save the critical edge splitting pass we identify how the control
815 dependence would look like if the edge was split.
817 Consider the modified CFG created from current CFG by splitting
818 edge B->C. In the postdominance tree of modified CFG, C' is
819 always child of C. There are two cases how chlids of C' can look
824 In this case the only basic block C' is control dependent on is B.
826 2) C' has single child that is B
828 In this case control dependence of C' is same as control
829 dependence of B in original CFG except for block B itself.
830 (since C' postdominate B in modified CFG)
832 Now how to decide what case happens? There are two basic options:
834 a) C postdominate B. Then C immediately postdominate B and
835 case 2 happens iff there is no other way from B to C except
838 There is other way from B to C iff there is succesor of B that
839 is not postdominated by B. Testing this condition is somewhat
840 expensive, because we need to iterate all succesors of B.
841 We are safe to assume that this does not happen: we will mark B
842 as needed when processing the other path from B to C that is
843 conrol dependent on B and marking control dependencies of B
844 itself is harmless because they will be processed anyway after
845 processing control statement in B.
847 b) C does not postdominate B. Always case 1 happens since there is
848 path from C to exit that does not go through B and thus also C'. */
850 if (aggressive
&& !degenerate_phi_p (stmt
))
852 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
854 basic_block arg_bb
= gimple_phi_arg_edge (phi
, k
)->src
;
857 != get_immediate_dominator (CDI_POST_DOMINATORS
, arg_bb
))
859 if (!bitmap_bit_p (last_stmt_necessary
, arg_bb
->index
))
860 mark_last_stmt_necessary (arg_bb
);
862 else if (arg_bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
863 && !bitmap_bit_p (visited_control_parents
,
865 mark_control_dependent_edges_necessary (arg_bb
, true);
871 /* Propagate through the operands. Examine all the USE, VUSE and
872 VDEF operands in this statement. Mark all the statements
873 which feed this statement's uses as necessary. */
877 /* If this is a call to free which is directly fed by an
878 allocation function do not mark that necessary through
879 processing the argument. */
880 bool is_delete_operator
881 = (is_gimple_call (stmt
)
882 && gimple_call_from_new_or_delete (as_a
<gcall
*> (stmt
))
883 && gimple_call_operator_delete_p (as_a
<gcall
*> (stmt
)));
884 if (is_delete_operator
885 || gimple_call_builtin_p (stmt
, BUILT_IN_FREE
)
886 || gimple_call_builtin_p (stmt
, BUILT_IN_GOMP_FREE
))
888 tree ptr
= gimple_call_arg (stmt
, 0);
891 /* If the pointer we free is defined by an allocation
892 function do not add the call to the worklist. */
893 if (TREE_CODE (ptr
) == SSA_NAME
894 && (def_stmt
= dyn_cast
<gcall
*> (SSA_NAME_DEF_STMT (ptr
)))
895 && (def_callee
= gimple_call_fndecl (def_stmt
))
896 && ((DECL_BUILT_IN_CLASS (def_callee
) == BUILT_IN_NORMAL
897 && (DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_ALIGNED_ALLOC
898 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_MALLOC
899 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_CALLOC
900 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_GOMP_ALLOC
))
901 || (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (def_callee
)
902 && gimple_call_from_new_or_delete (def_stmt
))))
904 if (is_delete_operator
905 && !valid_new_delete_pair_p (def_stmt
, stmt
))
906 mark_operand_necessary (gimple_call_arg (stmt
, 0));
908 /* Delete operators can have alignment and (or) size
909 as next arguments. When being a SSA_NAME, they
910 must be marked as necessary. Similarly GOMP_free. */
911 if (gimple_call_num_args (stmt
) >= 2)
912 for (unsigned i
= 1; i
< gimple_call_num_args (stmt
);
915 tree arg
= gimple_call_arg (stmt
, i
);
916 if (TREE_CODE (arg
) == SSA_NAME
)
917 mark_operand_necessary (arg
);
924 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
925 mark_operand_necessary (use
);
927 use
= gimple_vuse (stmt
);
931 /* No need to search for vdefs if we intrinsicly keep them all. */
932 if (keep_all_vdefs_p ())
935 /* If we dropped to simple mode make all immediately
936 reachable definitions necessary. */
939 mark_all_reaching_defs_necessary (stmt
);
943 /* For statements that may load from memory (have a VUSE) we
944 have to mark all reaching (may-)definitions as necessary.
945 We partition this task into two cases:
946 1) explicit loads based on decls that are not aliased
947 2) implicit loads (like calls) and explicit loads not
948 based on decls that are not aliased (like indirect
949 references or loads from globals)
950 For 1) we mark all reaching may-defs as necessary, stopping
951 at dominating kills. For 2) we want to mark all dominating
952 references necessary, but non-aliased ones which we handle
953 in 1). By keeping a global visited bitmap for references
954 we walk for 2) we avoid quadratic behavior for those. */
956 if (gcall
*call
= dyn_cast
<gcall
*> (stmt
))
958 tree callee
= gimple_call_fndecl (call
);
961 /* Calls to functions that are merely acting as barriers
962 or that only store to memory do not make any previous
964 if (callee
!= NULL_TREE
965 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
966 && (DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET
967 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET_CHK
968 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MALLOC
969 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALIGNED_ALLOC
970 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_CALLOC
971 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_FREE
972 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_VA_END
973 || ALLOCA_FUNCTION_CODE_P (DECL_FUNCTION_CODE (callee
))
974 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_SAVE
975 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_RESTORE
976 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ASSUME_ALIGNED
))
979 if (callee
!= NULL_TREE
980 && (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
)
981 || DECL_IS_OPERATOR_DELETE_P (callee
))
982 && gimple_call_from_new_or_delete (call
))
985 /* Calls implicitly load from memory, their arguments
986 in addition may explicitly perform memory loads. */
987 mark_all_reaching_defs_necessary (call
);
988 for (i
= 0; i
< gimple_call_num_args (call
); ++i
)
990 tree arg
= gimple_call_arg (call
, i
);
991 if (TREE_CODE (arg
) == SSA_NAME
992 || is_gimple_min_invariant (arg
))
994 if (TREE_CODE (arg
) == WITH_SIZE_EXPR
)
995 arg
= TREE_OPERAND (arg
, 0);
996 if (!ref_may_be_aliased (arg
))
997 mark_aliased_reaching_defs_necessary (call
, arg
);
1000 else if (gimple_assign_single_p (stmt
))
1003 /* If this is a load mark things necessary. */
1004 rhs
= gimple_assign_rhs1 (stmt
);
1005 if (TREE_CODE (rhs
) != SSA_NAME
1006 && !is_gimple_min_invariant (rhs
)
1007 && TREE_CODE (rhs
) != CONSTRUCTOR
)
1009 if (!ref_may_be_aliased (rhs
))
1010 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
1012 mark_all_reaching_defs_necessary (stmt
);
1015 else if (greturn
*return_stmt
= dyn_cast
<greturn
*> (stmt
))
1017 tree rhs
= gimple_return_retval (return_stmt
);
1018 /* A return statement may perform a load. */
1020 && TREE_CODE (rhs
) != SSA_NAME
1021 && !is_gimple_min_invariant (rhs
)
1022 && TREE_CODE (rhs
) != CONSTRUCTOR
)
1024 if (!ref_may_be_aliased (rhs
))
1025 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
1027 mark_all_reaching_defs_necessary (stmt
);
1030 else if (gasm
*asm_stmt
= dyn_cast
<gasm
*> (stmt
))
1033 mark_all_reaching_defs_necessary (stmt
);
1034 /* Inputs may perform loads. */
1035 for (i
= 0; i
< gimple_asm_ninputs (asm_stmt
); ++i
)
1037 tree op
= TREE_VALUE (gimple_asm_input_op (asm_stmt
, i
));
1038 if (TREE_CODE (op
) != SSA_NAME
1039 && !is_gimple_min_invariant (op
)
1040 && TREE_CODE (op
) != CONSTRUCTOR
1041 && !ref_may_be_aliased (op
))
1042 mark_aliased_reaching_defs_necessary (stmt
, op
);
1045 else if (gimple_code (stmt
) == GIMPLE_TRANSACTION
)
1047 /* The beginning of a transaction is a memory barrier. */
1048 /* ??? If we were really cool, we'd only be a barrier
1049 for the memories touched within the transaction. */
1050 mark_all_reaching_defs_necessary (stmt
);
1055 /* If we over-used our alias oracle budget drop to simple
1056 mode. The cost metric allows quadratic behavior
1057 (number of uses times number of may-defs queries) up to
1058 a constant maximal number of queries and after that falls back to
1059 super-linear complexity. */
1060 if (/* Constant but quadratic for small functions. */
1061 total_chain
> 128 * 128
1062 /* Linear in the number of may-defs. */
1063 && total_chain
> 32 * longest_chain
1064 /* Linear in the number of uses. */
1065 && total_chain
> nr_walks
* 32)
1069 bitmap_clear (visited
);
1075 /* Remove dead PHI nodes from block BB. */
1078 remove_dead_phis (basic_block bb
)
1080 bool something_changed
= false;
1084 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);)
1089 /* We do not track necessity of virtual PHI nodes. Instead do
1090 very simple dead PHI removal here. */
1091 if (virtual_operand_p (gimple_phi_result (phi
)))
1093 /* Virtual PHI nodes with one or identical arguments
1095 if (degenerate_phi_p (phi
))
1097 tree vdef
= gimple_phi_result (phi
);
1098 tree vuse
= gimple_phi_arg_def (phi
, 0);
1100 use_operand_p use_p
;
1101 imm_use_iterator iter
;
1103 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, vdef
)
1104 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
1105 SET_USE (use_p
, vuse
);
1106 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef
)
1107 && TREE_CODE (vuse
) == SSA_NAME
)
1108 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse
) = 1;
1111 gimple_set_plf (phi
, STMT_NECESSARY
, true);
1114 if (!gimple_plf (phi
, STMT_NECESSARY
))
1116 something_changed
= true;
1117 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1119 fprintf (dump_file
, "Deleting : ");
1120 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
1121 fprintf (dump_file
, "\n");
1124 remove_phi_node (&gsi
, true);
1125 stats
.removed_phis
++;
1131 return something_changed
;
1135 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1136 containing I so that we don't have to look it up. */
1139 remove_dead_stmt (gimple_stmt_iterator
*i
, basic_block bb
,
1140 vec
<edge
> &to_remove_edges
)
1142 gimple
*stmt
= gsi_stmt (*i
);
1144 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1146 fprintf (dump_file
, "Deleting : ");
1147 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1148 fprintf (dump_file
, "\n");
1153 /* If we have determined that a conditional branch statement contributes
1154 nothing to the program, then we not only remove it, but we need to update
1155 the CFG. We can chose any of edges out of BB as long as we are sure to not
1156 close infinite loops. This is done by always choosing the edge closer to
1157 exit in inverted_post_order_compute order. */
1158 if (is_ctrl_stmt (stmt
))
1163 /* See if there is only one non-abnormal edge. */
1164 if (single_succ_p (bb
))
1165 e
= single_succ_edge (bb
);
1166 /* Otherwise chose one that is closer to bb with live statement in it.
1167 To be able to chose one, we compute inverted post order starting from
1168 all BBs with live statements. */
1173 auto_vec
<int, 20> postorder
;
1174 inverted_post_order_compute (&postorder
,
1175 &bb_contains_live_stmts
);
1176 bb_postorder
= XNEWVEC (int, last_basic_block_for_fn (cfun
));
1177 for (unsigned int i
= 0; i
< postorder
.length (); ++i
)
1178 bb_postorder
[postorder
[i
]] = i
;
1180 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1181 if (!e
|| e2
->dest
== EXIT_BLOCK_PTR_FOR_FN (cfun
)
1182 || bb_postorder
[e
->dest
->index
]
1183 < bb_postorder
[e2
->dest
->index
])
1187 e
->probability
= profile_probability::always ();
1189 /* The edge is no longer associated with a conditional, so it does
1190 not have TRUE/FALSE flags.
1191 We are also safe to drop EH/ABNORMAL flags and turn them into
1192 normal control flow, because we know that all the destinations (including
1193 those odd edges) are equivalent for program execution. */
1194 e
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
| EDGE_EH
| EDGE_ABNORMAL
);
1196 /* The lone outgoing edge from BB will be a fallthru edge. */
1197 e
->flags
|= EDGE_FALLTHRU
;
1199 /* Remove the remaining outgoing edges. */
1200 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1203 /* If we made a BB unconditionally exit a loop or removed
1204 an entry into an irreducible region, then this transform
1205 alters the set of BBs in the loop. Schedule a fixup. */
1206 if (loop_exit_edge_p (bb
->loop_father
, e
)
1207 || (e2
->dest
->flags
& BB_IRREDUCIBLE_LOOP
))
1208 loops_state_set (LOOPS_NEED_FIXUP
);
1209 to_remove_edges
.safe_push (e2
);
1213 /* If this is a store into a variable that is being optimized away,
1214 add a debug bind stmt if possible. */
1215 if (MAY_HAVE_DEBUG_BIND_STMTS
1216 && gimple_assign_single_p (stmt
)
1217 && is_gimple_val (gimple_assign_rhs1 (stmt
)))
1219 tree lhs
= gimple_assign_lhs (stmt
);
1220 if ((VAR_P (lhs
) || TREE_CODE (lhs
) == PARM_DECL
)
1221 && !DECL_IGNORED_P (lhs
)
1222 && is_gimple_reg_type (TREE_TYPE (lhs
))
1223 && !is_global_var (lhs
)
1224 && !DECL_HAS_VALUE_EXPR_P (lhs
))
1226 tree rhs
= gimple_assign_rhs1 (stmt
);
1228 = gimple_build_debug_bind (lhs
, unshare_expr (rhs
), stmt
);
1229 gsi_insert_after (i
, note
, GSI_SAME_STMT
);
1233 unlink_stmt_vdef (stmt
);
1234 gsi_remove (i
, true);
1235 release_defs (stmt
);
1238 /* Helper for maybe_optimize_arith_overflow. Find in *TP if there are any
1239 uses of data (SSA_NAME) other than REALPART_EXPR referencing it. */
1242 find_non_realpart_uses (tree
*tp
, int *walk_subtrees
, void *data
)
1244 if (TYPE_P (*tp
) || TREE_CODE (*tp
) == REALPART_EXPR
)
1246 if (*tp
== (tree
) data
)
1251 /* If the IMAGPART_EXPR of the {ADD,SUB,MUL}_OVERFLOW result is never used,
1252 but REALPART_EXPR is, optimize the {ADD,SUB,MUL}_OVERFLOW internal calls
1253 into plain unsigned {PLUS,MINUS,MULT}_EXPR, and if needed reset debug
1257 maybe_optimize_arith_overflow (gimple_stmt_iterator
*gsi
,
1258 enum tree_code subcode
)
1260 gimple
*stmt
= gsi_stmt (*gsi
);
1261 tree lhs
= gimple_call_lhs (stmt
);
1263 if (lhs
== NULL
|| TREE_CODE (lhs
) != SSA_NAME
)
1266 imm_use_iterator imm_iter
;
1267 use_operand_p use_p
;
1268 bool has_debug_uses
= false;
1269 bool has_realpart_uses
= false;
1270 bool has_other_uses
= false;
1271 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, lhs
)
1273 gimple
*use_stmt
= USE_STMT (use_p
);
1274 if (is_gimple_debug (use_stmt
))
1275 has_debug_uses
= true;
1276 else if (is_gimple_assign (use_stmt
)
1277 && gimple_assign_rhs_code (use_stmt
) == REALPART_EXPR
1278 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt
), 0) == lhs
)
1279 has_realpart_uses
= true;
1282 has_other_uses
= true;
1287 if (!has_realpart_uses
|| has_other_uses
)
1290 tree arg0
= gimple_call_arg (stmt
, 0);
1291 tree arg1
= gimple_call_arg (stmt
, 1);
1292 location_t loc
= gimple_location (stmt
);
1293 tree type
= TREE_TYPE (TREE_TYPE (lhs
));
1295 if (!TYPE_UNSIGNED (type
))
1296 utype
= build_nonstandard_integer_type (TYPE_PRECISION (type
), 1);
1297 tree result
= fold_build2_loc (loc
, subcode
, utype
,
1298 fold_convert_loc (loc
, utype
, arg0
),
1299 fold_convert_loc (loc
, utype
, arg1
));
1300 result
= fold_convert_loc (loc
, type
, result
);
1305 FOR_EACH_IMM_USE_STMT (use_stmt
, imm_iter
, lhs
)
1307 if (!gimple_debug_bind_p (use_stmt
))
1309 tree v
= gimple_debug_bind_get_value (use_stmt
);
1310 if (walk_tree (&v
, find_non_realpart_uses
, lhs
, NULL
))
1312 gimple_debug_bind_reset_value (use_stmt
);
1313 update_stmt (use_stmt
);
1318 if (TREE_CODE (result
) == INTEGER_CST
&& TREE_OVERFLOW (result
))
1319 result
= drop_tree_overflow (result
);
1320 tree overflow
= build_zero_cst (type
);
1321 tree ctype
= build_complex_type (type
);
1322 if (TREE_CODE (result
) == INTEGER_CST
)
1323 result
= build_complex (ctype
, result
, overflow
);
1325 result
= build2_loc (gimple_location (stmt
), COMPLEX_EXPR
,
1326 ctype
, result
, overflow
);
1328 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1330 fprintf (dump_file
, "Transforming call: ");
1331 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1332 fprintf (dump_file
, "because the overflow result is never used into: ");
1333 print_generic_stmt (dump_file
, result
, TDF_SLIM
);
1334 fprintf (dump_file
, "\n");
1337 if (!update_call_from_tree (gsi
, result
))
1338 gimplify_and_update_call_from_tree (gsi
, result
);
1341 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1342 contributes nothing to the program, and can be deleted. */
1345 eliminate_unnecessary_stmts (void)
1347 bool something_changed
= false;
1349 gimple_stmt_iterator gsi
, psi
;
1353 auto_vec
<edge
> to_remove_edges
;
1355 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1356 fprintf (dump_file
, "\nEliminating unnecessary statements:\n");
1358 clear_special_calls ();
1360 /* Walking basic blocks and statements in reverse order avoids
1361 releasing SSA names before any other DEFs that refer to them are
1362 released. This helps avoid loss of debug information, as we get
1363 a chance to propagate all RHSs of removed SSAs into debug uses,
1364 rather than only the latest ones. E.g., consider:
1370 If we were to release x_3 before a_5, when we reached a_5 and
1371 tried to substitute it into the debug stmt, we'd see x_3 there,
1372 but x_3's DEF, type, etc would have already been disconnected.
1373 By going backwards, the debug stmt first changes to:
1375 # DEBUG a => x_3 - b_4
1379 # DEBUG a => y_1 + z_2 - b_4
1382 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
1383 h
= get_all_dominated_blocks (CDI_DOMINATORS
,
1384 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun
)));
1390 /* Remove dead statements. */
1391 auto_bitmap debug_seen
;
1392 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi
= psi
)
1394 stmt
= gsi_stmt (gsi
);
1401 /* We can mark a call to free as not necessary if the
1402 defining statement of its argument is not necessary
1403 (and thus is getting removed). */
1404 if (gimple_plf (stmt
, STMT_NECESSARY
)
1405 && (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
)
1406 || (is_gimple_call (stmt
)
1407 && gimple_call_from_new_or_delete (as_a
<gcall
*> (stmt
))
1408 && gimple_call_operator_delete_p (as_a
<gcall
*> (stmt
)))))
1410 tree ptr
= gimple_call_arg (stmt
, 0);
1411 if (TREE_CODE (ptr
) == SSA_NAME
)
1413 gimple
*def_stmt
= SSA_NAME_DEF_STMT (ptr
);
1414 if (!gimple_nop_p (def_stmt
)
1415 && !gimple_plf (def_stmt
, STMT_NECESSARY
))
1416 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
1420 /* If GSI is not necessary then remove it. */
1421 if (!gimple_plf (stmt
, STMT_NECESSARY
))
1423 /* Keep clobbers that we can keep live live. */
1424 if (gimple_clobber_p (stmt
))
1427 use_operand_p use_p
;
1429 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_USE
)
1431 tree name
= USE_FROM_PTR (use_p
);
1432 if (!SSA_NAME_IS_DEFAULT_DEF (name
)
1433 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
)))
1441 bitmap_clear (debug_seen
);
1445 if (!is_gimple_debug (stmt
))
1446 something_changed
= true;
1447 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1450 else if (is_gimple_call (stmt
))
1452 tree name
= gimple_call_lhs (stmt
);
1454 notice_special_calls (as_a
<gcall
*> (stmt
));
1456 /* When LHS of var = call (); is dead, simplify it into
1457 call (); saving one operand. */
1459 && TREE_CODE (name
) == SSA_NAME
1460 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
))
1461 /* Avoid doing so for allocation calls which we
1462 did not mark as necessary, it will confuse the
1463 special logic we apply to malloc/free pair removal. */
1464 && (!(call
= gimple_call_fndecl (stmt
))
1465 || ((DECL_BUILT_IN_CLASS (call
) != BUILT_IN_NORMAL
1466 || (DECL_FUNCTION_CODE (call
) != BUILT_IN_ALIGNED_ALLOC
1467 && DECL_FUNCTION_CODE (call
) != BUILT_IN_MALLOC
1468 && DECL_FUNCTION_CODE (call
) != BUILT_IN_CALLOC
1469 && !ALLOCA_FUNCTION_CODE_P
1470 (DECL_FUNCTION_CODE (call
))))
1471 && !DECL_IS_REPLACEABLE_OPERATOR_NEW_P (call
))))
1473 something_changed
= true;
1474 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1476 fprintf (dump_file
, "Deleting LHS of call: ");
1477 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1478 fprintf (dump_file
, "\n");
1481 gimple_call_set_lhs (stmt
, NULL_TREE
);
1482 maybe_clean_or_replace_eh_stmt (stmt
, stmt
);
1484 release_ssa_name (name
);
1486 /* GOMP_SIMD_LANE (unless three argument) or ASAN_POISON
1487 without lhs is not needed. */
1488 if (gimple_call_internal_p (stmt
))
1489 switch (gimple_call_internal_fn (stmt
))
1491 case IFN_GOMP_SIMD_LANE
:
1492 if (gimple_call_num_args (stmt
) >= 3
1493 && !integer_nonzerop (gimple_call_arg (stmt
, 2)))
1496 case IFN_ASAN_POISON
:
1497 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1503 else if (gimple_call_internal_p (stmt
))
1504 switch (gimple_call_internal_fn (stmt
))
1506 case IFN_ADD_OVERFLOW
:
1507 maybe_optimize_arith_overflow (&gsi
, PLUS_EXPR
);
1509 case IFN_SUB_OVERFLOW
:
1510 maybe_optimize_arith_overflow (&gsi
, MINUS_EXPR
);
1512 case IFN_MUL_OVERFLOW
:
1513 maybe_optimize_arith_overflow (&gsi
, MULT_EXPR
);
1519 else if (gimple_debug_bind_p (stmt
))
1521 /* We are only keeping the last debug-bind of a
1522 non-DEBUG_EXPR_DECL variable in a series of
1523 debug-bind stmts. */
1524 tree var
= gimple_debug_bind_get_var (stmt
);
1525 if (TREE_CODE (var
) != DEBUG_EXPR_DECL
1526 && !bitmap_set_bit (debug_seen
, DECL_UID (var
)))
1527 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1530 bitmap_clear (debug_seen
);
1533 /* Remove dead PHI nodes. */
1534 something_changed
|= remove_dead_phis (bb
);
1539 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1540 rendered some PHI nodes unreachable while they are still in use.
1541 Mark them for renaming. */
1542 if (!to_remove_edges
.is_empty ())
1544 basic_block prev_bb
;
1546 /* Remove edges. We've delayed this to not get bogus debug stmts
1547 during PHI node removal. */
1548 for (unsigned i
= 0; i
< to_remove_edges
.length (); ++i
)
1549 remove_edge (to_remove_edges
[i
]);
1552 find_unreachable_blocks ();
1554 /* Delete all unreachable basic blocks in reverse dominator order. */
1555 for (bb
= EXIT_BLOCK_PTR_FOR_FN (cfun
)->prev_bb
;
1556 bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
); bb
= prev_bb
)
1558 prev_bb
= bb
->prev_bb
;
1560 if (!bitmap_bit_p (bb_contains_live_stmts
, bb
->index
)
1561 || !(bb
->flags
& BB_REACHABLE
))
1563 for (gphi_iterator gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
1565 if (virtual_operand_p (gimple_phi_result (gsi
.phi ())))
1568 imm_use_iterator iter
;
1570 FOR_EACH_IMM_USE_STMT (stmt
, iter
,
1571 gimple_phi_result (gsi
.phi ()))
1573 if (!(gimple_bb (stmt
)->flags
& BB_REACHABLE
))
1575 if (gimple_code (stmt
) == GIMPLE_PHI
1576 || gimple_plf (stmt
, STMT_NECESSARY
))
1579 BREAK_FROM_IMM_USE_STMT (iter
);
1583 mark_virtual_phi_result_for_renaming (gsi
.phi ());
1586 if (!(bb
->flags
& BB_REACHABLE
))
1588 /* Speed up the removal of blocks that don't
1589 dominate others. Walking backwards, this should
1590 be the common case. ??? Do we need to recompute
1591 dominators because of cfg_altered? */
1592 if (!first_dom_son (CDI_DOMINATORS
, bb
))
1593 delete_basic_block (bb
);
1596 h
= get_all_dominated_blocks (CDI_DOMINATORS
, bb
);
1601 prev_bb
= bb
->prev_bb
;
1602 /* Rearrangements to the CFG may have failed
1603 to update the dominators tree, so that
1604 formerly-dominated blocks are now
1605 otherwise reachable. */
1606 if (!!(bb
->flags
& BB_REACHABLE
))
1608 delete_basic_block (bb
);
1619 free (bb_postorder
);
1620 bb_postorder
= NULL
;
1622 return something_changed
;
1626 /* Print out removed statement statistics. */
1633 percg
= ((float) stats
.removed
/ (float) stats
.total
) * 100;
1634 fprintf (dump_file
, "Removed %d of %d statements (%d%%)\n",
1635 stats
.removed
, stats
.total
, (int) percg
);
1637 if (stats
.total_phis
== 0)
1640 percg
= ((float) stats
.removed_phis
/ (float) stats
.total_phis
) * 100;
1642 fprintf (dump_file
, "Removed %d of %d PHI nodes (%d%%)\n",
1643 stats
.removed_phis
, stats
.total_phis
, (int) percg
);
1646 /* Initialization for this pass. Set up the used data structures. */
1649 tree_dce_init (bool aggressive
)
1651 memset ((void *) &stats
, 0, sizeof (stats
));
1655 last_stmt_necessary
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1656 bitmap_clear (last_stmt_necessary
);
1657 bb_contains_live_stmts
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1658 bitmap_clear (bb_contains_live_stmts
);
1661 processed
= sbitmap_alloc (num_ssa_names
+ 1);
1662 bitmap_clear (processed
);
1664 worklist
.create (64);
1665 cfg_altered
= false;
1668 /* Cleanup after this pass. */
1671 tree_dce_done (bool aggressive
)
1676 sbitmap_free (visited_control_parents
);
1677 sbitmap_free (last_stmt_necessary
);
1678 sbitmap_free (bb_contains_live_stmts
);
1679 bb_contains_live_stmts
= NULL
;
1682 sbitmap_free (processed
);
1684 worklist
.release ();
1687 /* Main routine to eliminate dead code.
1689 AGGRESSIVE controls the aggressiveness of the algorithm.
1690 In conservative mode, we ignore control dependence and simply declare
1691 all but the most trivially dead branches necessary. This mode is fast.
1692 In aggressive mode, control dependences are taken into account, which
1693 results in more dead code elimination, but at the cost of some time.
1695 FIXME: Aggressive mode before PRE doesn't work currently because
1696 the dominance info is not invalidated after DCE1. This is
1697 not an issue right now because we only run aggressive DCE
1698 as the last tree SSA pass, but keep this in mind when you
1699 start experimenting with pass ordering. */
1702 perform_tree_ssa_dce (bool aggressive
)
1704 bool something_changed
= 0;
1706 calculate_dominance_info (CDI_DOMINATORS
);
1708 /* Preheaders are needed for SCEV to work.
1709 Simple lateches and recorded exits improve chances that loop will
1710 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1711 bool in_loop_pipeline
= scev_initialized_p ();
1712 if (aggressive
&& ! in_loop_pipeline
)
1715 loop_optimizer_init (LOOPS_NORMAL
1716 | LOOPS_HAVE_RECORDED_EXITS
);
1719 tree_dce_init (aggressive
);
1723 /* Compute control dependence. */
1724 calculate_dominance_info (CDI_POST_DOMINATORS
);
1725 cd
= new control_dependences ();
1727 visited_control_parents
=
1728 sbitmap_alloc (last_basic_block_for_fn (cfun
));
1729 bitmap_clear (visited_control_parents
);
1731 mark_dfs_back_edges ();
1734 find_obviously_necessary_stmts (aggressive
);
1736 if (aggressive
&& ! in_loop_pipeline
)
1738 loop_optimizer_finalize ();
1746 visited
= BITMAP_ALLOC (NULL
);
1747 propagate_necessity (aggressive
);
1748 BITMAP_FREE (visited
);
1750 something_changed
|= eliminate_unnecessary_stmts ();
1751 something_changed
|= cfg_altered
;
1753 /* We do not update postdominators, so free them unconditionally. */
1754 free_dominance_info (CDI_POST_DOMINATORS
);
1756 /* If we removed paths in the CFG, then we need to update
1757 dominators as well. I haven't investigated the possibility
1758 of incrementally updating dominators. */
1760 free_dominance_info (CDI_DOMINATORS
);
1762 statistics_counter_event (cfun
, "Statements deleted", stats
.removed
);
1763 statistics_counter_event (cfun
, "PHI nodes deleted", stats
.removed_phis
);
1765 /* Debugging dumps. */
1766 if (dump_file
&& (dump_flags
& (TDF_STATS
|TDF_DETAILS
)))
1769 tree_dce_done (aggressive
);
1771 if (something_changed
)
1773 free_numbers_of_iterations_estimates (cfun
);
1774 if (in_loop_pipeline
)
1776 return TODO_update_ssa
| TODO_cleanup_cfg
;
1781 /* Pass entry points. */
1785 return perform_tree_ssa_dce (/*aggressive=*/false);
1789 tree_ssa_cd_dce (void)
1791 return perform_tree_ssa_dce (/*aggressive=*/optimize
>= 2);
1796 const pass_data pass_data_dce
=
1798 GIMPLE_PASS
, /* type */
1800 OPTGROUP_NONE
, /* optinfo_flags */
1801 TV_TREE_DCE
, /* tv_id */
1802 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1803 0, /* properties_provided */
1804 0, /* properties_destroyed */
1805 0, /* todo_flags_start */
1806 0, /* todo_flags_finish */
1809 class pass_dce
: public gimple_opt_pass
1812 pass_dce (gcc::context
*ctxt
)
1813 : gimple_opt_pass (pass_data_dce
, ctxt
)
1816 /* opt_pass methods: */
1817 opt_pass
* clone () { return new pass_dce (m_ctxt
); }
1818 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1819 virtual unsigned int execute (function
*) { return tree_ssa_dce (); }
1821 }; // class pass_dce
1826 make_pass_dce (gcc::context
*ctxt
)
1828 return new pass_dce (ctxt
);
1833 const pass_data pass_data_cd_dce
=
1835 GIMPLE_PASS
, /* type */
1837 OPTGROUP_NONE
, /* optinfo_flags */
1838 TV_TREE_CD_DCE
, /* tv_id */
1839 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1840 0, /* properties_provided */
1841 0, /* properties_destroyed */
1842 0, /* todo_flags_start */
1843 0, /* todo_flags_finish */
1846 class pass_cd_dce
: public gimple_opt_pass
1849 pass_cd_dce (gcc::context
*ctxt
)
1850 : gimple_opt_pass (pass_data_cd_dce
, ctxt
)
1853 /* opt_pass methods: */
1854 opt_pass
* clone () { return new pass_cd_dce (m_ctxt
); }
1855 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1856 virtual unsigned int execute (function
*) { return tree_ssa_cd_dce (); }
1858 }; // class pass_cd_dce
1863 make_pass_cd_dce (gcc::context
*ctxt
)
1865 return new pass_cd_dce (ctxt
);
1869 /* A cheap DCE interface. WORKLIST is a list of possibly dead stmts and
1870 is consumed by this function. The function has linear complexity in
1871 the number of dead stmts with a constant factor like the average SSA
1872 use operands number. */
1875 simple_dce_from_worklist (bitmap worklist
)
1877 while (! bitmap_empty_p (worklist
))
1880 unsigned i
= bitmap_first_set_bit (worklist
);
1881 bitmap_clear_bit (worklist
, i
);
1883 tree def
= ssa_name (i
);
1884 /* Removed by somebody else or still in use. */
1885 if (! def
|| ! has_zero_uses (def
))
1888 gimple
*t
= SSA_NAME_DEF_STMT (def
);
1889 if (gimple_has_side_effects (t
))
1892 /* Add uses to the worklist. */
1894 use_operand_p use_p
;
1895 FOR_EACH_PHI_OR_STMT_USE (use_p
, t
, iter
, SSA_OP_USE
)
1897 tree use
= USE_FROM_PTR (use_p
);
1898 if (TREE_CODE (use
) == SSA_NAME
1899 && ! SSA_NAME_IS_DEFAULT_DEF (use
))
1900 bitmap_set_bit (worklist
, SSA_NAME_VERSION (use
));
1904 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1906 fprintf (dump_file
, "Removing dead stmt:");
1907 print_gimple_stmt (dump_file
, t
, 0);
1909 gimple_stmt_iterator gsi
= gsi_for_stmt (t
);
1910 if (gimple_code (t
) == GIMPLE_PHI
)
1911 remove_phi_node (&gsi
, true);
1914 gsi_remove (&gsi
, true);