1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002-2021 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 /* Statements that are implicitly live. Most function calls, asm
203 and return statements are required. Labels and GIMPLE_BIND nodes
204 are kept because they are control flow, and we have no way of
205 knowing whether they can be removed. DCE can eliminate all the
206 other statements in a block, and CFG can then remove the block
208 switch (gimple_code (stmt
))
212 mark_stmt_necessary (stmt
, false);
218 mark_stmt_necessary (stmt
, true);
223 tree callee
= gimple_call_fndecl (stmt
);
224 if (callee
!= NULL_TREE
225 && fndecl_built_in_p (callee
, BUILT_IN_NORMAL
))
226 switch (DECL_FUNCTION_CODE (callee
))
228 case BUILT_IN_MALLOC
:
229 case BUILT_IN_ALIGNED_ALLOC
:
230 case BUILT_IN_CALLOC
:
231 CASE_BUILT_IN_ALLOCA
:
232 case BUILT_IN_STRDUP
:
233 case BUILT_IN_STRNDUP
:
234 case BUILT_IN_GOMP_ALLOC
:
240 if (callee
!= NULL_TREE
241 && flag_allocation_dce
242 && DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
))
245 /* IFN_GOACC_LOOP calls are necessary in that they are used to
246 represent parameter (i.e. step, bound) of a lowered OpenACC
247 partitioned loop. But this kind of partitioned loop might not
248 survive from aggressive loop removal for it has loop exit and
249 is assumed to be finite. Therefore, we need to explicitly mark
250 these calls. (An example is libgomp.oacc-c-c++-common/pr84955.c) */
251 if (gimple_call_internal_p (stmt
, IFN_GOACC_LOOP
))
253 mark_stmt_necessary (stmt
, true);
260 /* Debug temps without a value are not useful. ??? If we could
261 easily locate the debug temp bind stmt for a use thereof,
262 would could refrain from marking all debug temps here, and
263 mark them only if they're used. */
264 if (gimple_debug_nonbind_marker_p (stmt
)
265 || !gimple_debug_bind_p (stmt
)
266 || gimple_debug_bind_has_value_p (stmt
)
267 || TREE_CODE (gimple_debug_bind_get_var (stmt
)) != DEBUG_EXPR_DECL
)
268 mark_stmt_necessary (stmt
, false);
272 gcc_assert (!simple_goto_p (stmt
));
273 mark_stmt_necessary (stmt
, true);
277 gcc_assert (EDGE_COUNT (gimple_bb (stmt
)->succs
) == 2);
282 mark_stmt_necessary (stmt
, true);
286 if (gimple_clobber_p (stmt
))
294 /* If the statement has volatile operands, it needs to be preserved.
295 Same for statements that can alter control flow in unpredictable
297 if (gimple_has_side_effects (stmt
) || is_ctrl_altering_stmt (stmt
))
299 mark_stmt_necessary (stmt
, true);
303 /* If a statement could throw, it can be deemed necessary unless we
304 are allowed to remove dead EH. Test this after checking for
305 new/delete operators since we always elide their EH. */
306 if (!cfun
->can_delete_dead_exceptions
307 && stmt_could_throw_p (cfun
, stmt
))
309 mark_stmt_necessary (stmt
, true);
313 if ((gimple_vdef (stmt
) && keep_all_vdefs_p ())
314 || stmt_may_clobber_global_p (stmt
))
316 mark_stmt_necessary (stmt
, true);
324 /* Mark the last statement of BB as necessary. */
327 mark_last_stmt_necessary (basic_block bb
)
329 gimple
*stmt
= last_stmt (bb
);
331 bitmap_set_bit (last_stmt_necessary
, bb
->index
);
332 bitmap_set_bit (bb_contains_live_stmts
, bb
->index
);
334 /* We actually mark the statement only if it is a control statement. */
335 if (stmt
&& is_ctrl_stmt (stmt
))
336 mark_stmt_necessary (stmt
, true);
340 /* Mark control dependent edges of BB as necessary. We have to do this only
341 once for each basic block so we set the appropriate bit after we're done.
343 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
346 mark_control_dependent_edges_necessary (basic_block bb
, bool ignore_self
)
349 unsigned edge_number
;
350 bool skipped
= false;
352 gcc_assert (bb
!= EXIT_BLOCK_PTR_FOR_FN (cfun
));
354 if (bb
== ENTRY_BLOCK_PTR_FOR_FN (cfun
))
357 EXECUTE_IF_SET_IN_BITMAP (cd
->get_edges_dependent_on (bb
->index
),
360 basic_block cd_bb
= cd
->get_edge_src (edge_number
);
362 if (ignore_self
&& cd_bb
== bb
)
368 if (!bitmap_bit_p (last_stmt_necessary
, cd_bb
->index
))
369 mark_last_stmt_necessary (cd_bb
);
373 bitmap_set_bit (visited_control_parents
, bb
->index
);
377 /* Find obviously necessary statements. These are things like most function
378 calls, and stores to file level variables.
380 If EL is NULL, control statements are conservatively marked as
381 necessary. Otherwise it contains the list of edges used by control
382 dependence analysis. */
385 find_obviously_necessary_stmts (bool aggressive
)
388 gimple_stmt_iterator gsi
;
393 FOR_EACH_BB_FN (bb
, cfun
)
395 /* PHI nodes are never inherently necessary. */
396 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
398 phi
= gsi_stmt (gsi
);
399 gimple_set_plf (phi
, STMT_NECESSARY
, false);
402 /* Check all statements in the block. */
403 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
405 stmt
= gsi_stmt (gsi
);
406 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
407 mark_stmt_if_obviously_necessary (stmt
, aggressive
);
411 /* Pure and const functions are finite and thus have no infinite loops in
413 flags
= flags_from_decl_or_type (current_function_decl
);
414 if ((flags
& (ECF_CONST
|ECF_PURE
)) && !(flags
& ECF_LOOPING_CONST_OR_PURE
))
417 /* Prevent the empty possibly infinite loops from being removed. */
420 if (mark_irreducible_loops ())
421 FOR_EACH_BB_FN (bb
, cfun
)
424 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
425 if ((e
->flags
& EDGE_DFS_BACK
)
426 && (e
->flags
& EDGE_IRREDUCIBLE_LOOP
))
429 fprintf (dump_file
, "Marking back edge of irreducible loop %i->%i\n",
430 e
->src
->index
, e
->dest
->index
);
431 mark_control_dependent_edges_necessary (e
->dest
, false);
435 for (auto loop
: loops_list (cfun
, 0))
436 if (!finite_loop_p (loop
))
439 fprintf (dump_file
, "cannot prove finiteness of loop %i\n", loop
->num
);
440 mark_control_dependent_edges_necessary (loop
->latch
, false);
446 /* Return true if REF is based on an aliased base, otherwise false. */
449 ref_may_be_aliased (tree ref
)
451 gcc_assert (TREE_CODE (ref
) != WITH_SIZE_EXPR
);
452 while (handled_component_p (ref
))
453 ref
= TREE_OPERAND (ref
, 0);
454 if ((TREE_CODE (ref
) == MEM_REF
|| TREE_CODE (ref
) == TARGET_MEM_REF
)
455 && TREE_CODE (TREE_OPERAND (ref
, 0)) == ADDR_EXPR
)
456 ref
= TREE_OPERAND (TREE_OPERAND (ref
, 0), 0);
457 return !(DECL_P (ref
)
458 && !may_be_aliased (ref
));
461 static bitmap visited
= NULL
;
462 static unsigned int longest_chain
= 0;
463 static unsigned int total_chain
= 0;
464 static unsigned int nr_walks
= 0;
465 static bool chain_ovfl
= false;
467 /* Worker for the walker that marks reaching definitions of REF,
468 which is based on a non-aliased decl, necessary. It returns
469 true whenever the defining statement of the current VDEF is
470 a kill for REF, as no dominating may-defs are necessary for REF
471 anymore. DATA points to the basic-block that contains the
472 stmt that refers to REF. */
475 mark_aliased_reaching_defs_necessary_1 (ao_ref
*ref
, tree vdef
, void *data
)
477 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
479 /* All stmts we visit are necessary. */
480 if (! gimple_clobber_p (def_stmt
))
481 mark_operand_necessary (vdef
);
483 /* If the stmt lhs kills ref, then we can stop walking. */
484 if (gimple_has_lhs (def_stmt
)
485 && TREE_CODE (gimple_get_lhs (def_stmt
)) != SSA_NAME
486 /* The assignment is not necessarily carried out if it can throw
487 and we can catch it in the current function where we could inspect
489 ??? We only need to care about the RHS throwing. For aggregate
490 assignments or similar calls and non-call exceptions the LHS
491 might throw as well. */
492 && !stmt_can_throw_internal (cfun
, def_stmt
))
494 tree base
, lhs
= gimple_get_lhs (def_stmt
);
495 poly_int64 size
, offset
, max_size
;
499 = get_ref_base_and_extent (lhs
, &offset
, &size
, &max_size
, &reverse
);
500 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
501 so base == refd->base does not always hold. */
502 if (base
== ref
->base
)
504 /* For a must-alias check we need to be able to constrain
505 the accesses properly. */
506 if (known_eq (size
, max_size
)
507 && known_subrange_p (ref
->offset
, ref
->max_size
, offset
, size
))
509 /* Or they need to be exactly the same. */
511 /* Make sure there is no induction variable involved
512 in the references (gcc.c-torture/execute/pr42142.c).
513 The simplest way is to check if the kill dominates
515 /* But when both are in the same block we cannot
516 easily tell whether we came from a backedge
517 unless we decide to compute stmt UIDs
519 && (basic_block
) data
!= gimple_bb (def_stmt
)
520 && dominated_by_p (CDI_DOMINATORS
, (basic_block
) data
,
521 gimple_bb (def_stmt
))
522 && operand_equal_p (ref
->ref
, lhs
, 0))
527 /* Otherwise keep walking. */
532 mark_aliased_reaching_defs_necessary (gimple
*stmt
, tree ref
)
534 /* Should have been caught before calling this function. */
535 gcc_checking_assert (!keep_all_vdefs_p ());
539 gcc_assert (!chain_ovfl
);
540 ao_ref_init (&refd
, ref
);
541 chain
= walk_aliased_vdefs (&refd
, gimple_vuse (stmt
),
542 mark_aliased_reaching_defs_necessary_1
,
543 gimple_bb (stmt
), NULL
);
544 if (chain
> longest_chain
)
545 longest_chain
= chain
;
546 total_chain
+= chain
;
550 /* Worker for the walker that marks reaching definitions of REF, which
551 is not based on a non-aliased decl. For simplicity we need to end
552 up marking all may-defs necessary that are not based on a non-aliased
553 decl. The only job of this walker is to skip may-defs based on
554 a non-aliased decl. */
557 mark_all_reaching_defs_necessary_1 (ao_ref
*ref ATTRIBUTE_UNUSED
,
558 tree vdef
, void *data ATTRIBUTE_UNUSED
)
560 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
562 /* We have to skip already visited (and thus necessary) statements
563 to make the chaining work after we dropped back to simple mode. */
565 && bitmap_bit_p (processed
, SSA_NAME_VERSION (vdef
)))
567 gcc_assert (gimple_nop_p (def_stmt
)
568 || gimple_plf (def_stmt
, STMT_NECESSARY
));
572 /* We want to skip stores to non-aliased variables. */
574 && gimple_assign_single_p (def_stmt
))
576 tree lhs
= gimple_assign_lhs (def_stmt
);
577 if (!ref_may_be_aliased (lhs
))
581 /* We want to skip statments that do not constitute stores but have
582 a virtual definition. */
583 if (gcall
*call
= dyn_cast
<gcall
*> (def_stmt
))
585 tree callee
= gimple_call_fndecl (call
);
586 if (callee
!= NULL_TREE
587 && fndecl_built_in_p (callee
, BUILT_IN_NORMAL
))
588 switch (DECL_FUNCTION_CODE (callee
))
590 case BUILT_IN_MALLOC
:
591 case BUILT_IN_ALIGNED_ALLOC
:
592 case BUILT_IN_CALLOC
:
593 CASE_BUILT_IN_ALLOCA
:
595 case BUILT_IN_GOMP_ALLOC
:
596 case BUILT_IN_GOMP_FREE
:
602 if (callee
!= NULL_TREE
603 && (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
)
604 || DECL_IS_OPERATOR_DELETE_P (callee
))
605 && gimple_call_from_new_or_delete (call
))
609 if (! gimple_clobber_p (def_stmt
))
610 mark_operand_necessary (vdef
);
616 mark_all_reaching_defs_necessary (gimple
*stmt
)
618 /* Should have been caught before calling this function. */
619 gcc_checking_assert (!keep_all_vdefs_p ());
620 walk_aliased_vdefs (NULL
, gimple_vuse (stmt
),
621 mark_all_reaching_defs_necessary_1
, NULL
, &visited
);
624 /* Return true for PHI nodes with one or identical arguments
627 degenerate_phi_p (gimple
*phi
)
630 tree op
= gimple_phi_arg_def (phi
, 0);
631 for (i
= 1; i
< gimple_phi_num_args (phi
); i
++)
632 if (gimple_phi_arg_def (phi
, i
) != op
)
637 /* Return that NEW_CALL and DELETE_CALL are a valid pair of new
638 and delete operators. */
641 valid_new_delete_pair_p (gimple
*new_call
, gimple
*delete_call
)
643 tree new_asm
= DECL_ASSEMBLER_NAME (gimple_call_fndecl (new_call
));
644 tree delete_asm
= DECL_ASSEMBLER_NAME (gimple_call_fndecl (delete_call
));
645 return valid_new_delete_pair_p (new_asm
, delete_asm
);
648 /* Propagate necessity using the operands of necessary statements.
649 Process the uses on each statement in the worklist, and add all
650 feeding statements which contribute to the calculation of this
651 value to the worklist.
653 In conservative mode, EL is NULL. */
656 propagate_necessity (bool aggressive
)
660 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
661 fprintf (dump_file
, "\nProcessing worklist:\n");
663 while (worklist
.length () > 0)
665 /* Take STMT from worklist. */
666 stmt
= worklist
.pop ();
668 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
670 fprintf (dump_file
, "processing: ");
671 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
672 fprintf (dump_file
, "\n");
677 /* Mark the last statement of the basic blocks on which the block
678 containing STMT is control dependent, but only if we haven't
680 basic_block bb
= gimple_bb (stmt
);
681 if (bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
682 && !bitmap_bit_p (visited_control_parents
, bb
->index
))
683 mark_control_dependent_edges_necessary (bb
, false);
686 if (gimple_code (stmt
) == GIMPLE_PHI
687 /* We do not process virtual PHI nodes nor do we track their
689 && !virtual_operand_p (gimple_phi_result (stmt
)))
691 /* PHI nodes are somewhat special in that each PHI alternative has
692 data and control dependencies. All the statements feeding the
693 PHI node's arguments are always necessary. In aggressive mode,
694 we also consider the control dependent edges leading to the
695 predecessor block associated with each PHI alternative as
697 gphi
*phi
= as_a
<gphi
*> (stmt
);
700 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
702 tree arg
= PHI_ARG_DEF (stmt
, k
);
703 if (TREE_CODE (arg
) == SSA_NAME
)
704 mark_operand_necessary (arg
);
707 /* For PHI operands it matters from where the control flow arrives
708 to the BB. Consider the following example:
718 We need to mark control dependence of the empty basic blocks, since they
719 contains computation of PHI operands.
721 Doing so is too restrictive in the case the predecestor block is in
727 for (i = 0; i<1000; ++i)
733 There is PHI for J in the BB containing return statement.
734 In this case the control dependence of predecestor block (that is
735 within the empty loop) also contains the block determining number
736 of iterations of the block that would prevent removing of empty
739 This scenario can be avoided by splitting critical edges.
740 To save the critical edge splitting pass we identify how the control
741 dependence would look like if the edge was split.
743 Consider the modified CFG created from current CFG by splitting
744 edge B->C. In the postdominance tree of modified CFG, C' is
745 always child of C. There are two cases how chlids of C' can look
750 In this case the only basic block C' is control dependent on is B.
752 2) C' has single child that is B
754 In this case control dependence of C' is same as control
755 dependence of B in original CFG except for block B itself.
756 (since C' postdominate B in modified CFG)
758 Now how to decide what case happens? There are two basic options:
760 a) C postdominate B. Then C immediately postdominate B and
761 case 2 happens iff there is no other way from B to C except
764 There is other way from B to C iff there is succesor of B that
765 is not postdominated by B. Testing this condition is somewhat
766 expensive, because we need to iterate all succesors of B.
767 We are safe to assume that this does not happen: we will mark B
768 as needed when processing the other path from B to C that is
769 conrol dependent on B and marking control dependencies of B
770 itself is harmless because they will be processed anyway after
771 processing control statement in B.
773 b) C does not postdominate B. Always case 1 happens since there is
774 path from C to exit that does not go through B and thus also C'. */
776 if (aggressive
&& !degenerate_phi_p (stmt
))
778 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
780 basic_block arg_bb
= gimple_phi_arg_edge (phi
, k
)->src
;
783 != get_immediate_dominator (CDI_POST_DOMINATORS
, arg_bb
))
785 if (!bitmap_bit_p (last_stmt_necessary
, arg_bb
->index
))
786 mark_last_stmt_necessary (arg_bb
);
788 else if (arg_bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
789 && !bitmap_bit_p (visited_control_parents
,
791 mark_control_dependent_edges_necessary (arg_bb
, true);
797 /* Propagate through the operands. Examine all the USE, VUSE and
798 VDEF operands in this statement. Mark all the statements
799 which feed this statement's uses as necessary. */
803 /* If this is a call to free which is directly fed by an
804 allocation function do not mark that necessary through
805 processing the argument. */
806 bool is_delete_operator
807 = (is_gimple_call (stmt
)
808 && gimple_call_from_new_or_delete (as_a
<gcall
*> (stmt
))
809 && gimple_call_operator_delete_p (as_a
<gcall
*> (stmt
)));
810 if (is_delete_operator
811 || gimple_call_builtin_p (stmt
, BUILT_IN_FREE
)
812 || gimple_call_builtin_p (stmt
, BUILT_IN_GOMP_FREE
))
814 tree ptr
= gimple_call_arg (stmt
, 0);
817 /* If the pointer we free is defined by an allocation
818 function do not add the call to the worklist. */
819 if (TREE_CODE (ptr
) == SSA_NAME
820 && (def_stmt
= dyn_cast
<gcall
*> (SSA_NAME_DEF_STMT (ptr
)))
821 && (def_callee
= gimple_call_fndecl (def_stmt
))
822 && ((DECL_BUILT_IN_CLASS (def_callee
) == BUILT_IN_NORMAL
823 && (DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_ALIGNED_ALLOC
824 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_MALLOC
825 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_CALLOC
826 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_GOMP_ALLOC
))
827 || (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (def_callee
)
828 && gimple_call_from_new_or_delete (def_stmt
))))
830 if (is_delete_operator
831 && !valid_new_delete_pair_p (def_stmt
, stmt
))
832 mark_operand_necessary (gimple_call_arg (stmt
, 0));
834 /* Delete operators can have alignment and (or) size
835 as next arguments. When being a SSA_NAME, they
836 must be marked as necessary. Similarly GOMP_free. */
837 if (gimple_call_num_args (stmt
) >= 2)
838 for (unsigned i
= 1; i
< gimple_call_num_args (stmt
);
841 tree arg
= gimple_call_arg (stmt
, i
);
842 if (TREE_CODE (arg
) == SSA_NAME
)
843 mark_operand_necessary (arg
);
850 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
851 mark_operand_necessary (use
);
853 use
= gimple_vuse (stmt
);
857 /* No need to search for vdefs if we intrinsicly keep them all. */
858 if (keep_all_vdefs_p ())
861 /* If we dropped to simple mode make all immediately
862 reachable definitions necessary. */
865 mark_all_reaching_defs_necessary (stmt
);
869 /* For statements that may load from memory (have a VUSE) we
870 have to mark all reaching (may-)definitions as necessary.
871 We partition this task into two cases:
872 1) explicit loads based on decls that are not aliased
873 2) implicit loads (like calls) and explicit loads not
874 based on decls that are not aliased (like indirect
875 references or loads from globals)
876 For 1) we mark all reaching may-defs as necessary, stopping
877 at dominating kills. For 2) we want to mark all dominating
878 references necessary, but non-aliased ones which we handle
879 in 1). By keeping a global visited bitmap for references
880 we walk for 2) we avoid quadratic behavior for those. */
882 if (gcall
*call
= dyn_cast
<gcall
*> (stmt
))
884 tree callee
= gimple_call_fndecl (call
);
887 /* Calls to functions that are merely acting as barriers
888 or that only store to memory do not make any previous
890 if (callee
!= NULL_TREE
891 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
892 && (DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET
893 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET_CHK
894 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MALLOC
895 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALIGNED_ALLOC
896 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_CALLOC
897 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_FREE
898 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_VA_END
899 || ALLOCA_FUNCTION_CODE_P (DECL_FUNCTION_CODE (callee
))
900 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_SAVE
901 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_RESTORE
902 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ASSUME_ALIGNED
))
905 if (callee
!= NULL_TREE
906 && (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
)
907 || DECL_IS_OPERATOR_DELETE_P (callee
))
908 && gimple_call_from_new_or_delete (call
))
911 /* Calls implicitly load from memory, their arguments
912 in addition may explicitly perform memory loads. */
913 mark_all_reaching_defs_necessary (call
);
914 for (i
= 0; i
< gimple_call_num_args (call
); ++i
)
916 tree arg
= gimple_call_arg (call
, i
);
917 if (TREE_CODE (arg
) == SSA_NAME
918 || is_gimple_min_invariant (arg
))
920 if (TREE_CODE (arg
) == WITH_SIZE_EXPR
)
921 arg
= TREE_OPERAND (arg
, 0);
922 if (!ref_may_be_aliased (arg
))
923 mark_aliased_reaching_defs_necessary (call
, arg
);
926 else if (gimple_assign_single_p (stmt
))
929 /* If this is a load mark things necessary. */
930 rhs
= gimple_assign_rhs1 (stmt
);
931 if (TREE_CODE (rhs
) != SSA_NAME
932 && !is_gimple_min_invariant (rhs
)
933 && TREE_CODE (rhs
) != CONSTRUCTOR
)
935 if (!ref_may_be_aliased (rhs
))
936 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
938 mark_all_reaching_defs_necessary (stmt
);
941 else if (greturn
*return_stmt
= dyn_cast
<greturn
*> (stmt
))
943 tree rhs
= gimple_return_retval (return_stmt
);
944 /* A return statement may perform a load. */
946 && TREE_CODE (rhs
) != SSA_NAME
947 && !is_gimple_min_invariant (rhs
)
948 && TREE_CODE (rhs
) != CONSTRUCTOR
)
950 if (!ref_may_be_aliased (rhs
))
951 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
953 mark_all_reaching_defs_necessary (stmt
);
956 else if (gasm
*asm_stmt
= dyn_cast
<gasm
*> (stmt
))
959 mark_all_reaching_defs_necessary (stmt
);
960 /* Inputs may perform loads. */
961 for (i
= 0; i
< gimple_asm_ninputs (asm_stmt
); ++i
)
963 tree op
= TREE_VALUE (gimple_asm_input_op (asm_stmt
, i
));
964 if (TREE_CODE (op
) != SSA_NAME
965 && !is_gimple_min_invariant (op
)
966 && TREE_CODE (op
) != CONSTRUCTOR
967 && !ref_may_be_aliased (op
))
968 mark_aliased_reaching_defs_necessary (stmt
, op
);
971 else if (gimple_code (stmt
) == GIMPLE_TRANSACTION
)
973 /* The beginning of a transaction is a memory barrier. */
974 /* ??? If we were really cool, we'd only be a barrier
975 for the memories touched within the transaction. */
976 mark_all_reaching_defs_necessary (stmt
);
981 /* If we over-used our alias oracle budget drop to simple
982 mode. The cost metric allows quadratic behavior
983 (number of uses times number of may-defs queries) up to
984 a constant maximal number of queries and after that falls back to
985 super-linear complexity. */
986 if (/* Constant but quadratic for small functions. */
987 total_chain
> 128 * 128
988 /* Linear in the number of may-defs. */
989 && total_chain
> 32 * longest_chain
990 /* Linear in the number of uses. */
991 && total_chain
> nr_walks
* 32)
995 bitmap_clear (visited
);
1001 /* Remove dead PHI nodes from block BB. */
1004 remove_dead_phis (basic_block bb
)
1006 bool something_changed
= false;
1010 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);)
1015 /* We do not track necessity of virtual PHI nodes. Instead do
1016 very simple dead PHI removal here. */
1017 if (virtual_operand_p (gimple_phi_result (phi
)))
1019 /* Virtual PHI nodes with one or identical arguments
1021 if (degenerate_phi_p (phi
))
1023 tree vdef
= gimple_phi_result (phi
);
1024 tree vuse
= gimple_phi_arg_def (phi
, 0);
1026 use_operand_p use_p
;
1027 imm_use_iterator iter
;
1029 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, vdef
)
1030 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
1031 SET_USE (use_p
, vuse
);
1032 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef
)
1033 && TREE_CODE (vuse
) == SSA_NAME
)
1034 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse
) = 1;
1037 gimple_set_plf (phi
, STMT_NECESSARY
, true);
1040 if (!gimple_plf (phi
, STMT_NECESSARY
))
1042 something_changed
= true;
1043 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1045 fprintf (dump_file
, "Deleting : ");
1046 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
1047 fprintf (dump_file
, "\n");
1050 remove_phi_node (&gsi
, true);
1051 stats
.removed_phis
++;
1057 return something_changed
;
1061 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1062 containing I so that we don't have to look it up. */
1065 remove_dead_stmt (gimple_stmt_iterator
*i
, basic_block bb
,
1066 vec
<edge
> &to_remove_edges
)
1068 gimple
*stmt
= gsi_stmt (*i
);
1070 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1072 fprintf (dump_file
, "Deleting : ");
1073 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1074 fprintf (dump_file
, "\n");
1079 /* If we have determined that a conditional branch statement contributes
1080 nothing to the program, then we not only remove it, but we need to update
1081 the CFG. We can chose any of edges out of BB as long as we are sure to not
1082 close infinite loops. This is done by always choosing the edge closer to
1083 exit in inverted_post_order_compute order. */
1084 if (is_ctrl_stmt (stmt
))
1089 /* See if there is only one non-abnormal edge. */
1090 if (single_succ_p (bb
))
1091 e
= single_succ_edge (bb
);
1092 /* Otherwise chose one that is closer to bb with live statement in it.
1093 To be able to chose one, we compute inverted post order starting from
1094 all BBs with live statements. */
1099 auto_vec
<int, 20> postorder
;
1100 inverted_post_order_compute (&postorder
,
1101 &bb_contains_live_stmts
);
1102 bb_postorder
= XNEWVEC (int, last_basic_block_for_fn (cfun
));
1103 for (unsigned int i
= 0; i
< postorder
.length (); ++i
)
1104 bb_postorder
[postorder
[i
]] = i
;
1106 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1107 if (!e
|| e2
->dest
== EXIT_BLOCK_PTR_FOR_FN (cfun
)
1108 || bb_postorder
[e
->dest
->index
]
1109 < bb_postorder
[e2
->dest
->index
])
1113 e
->probability
= profile_probability::always ();
1115 /* The edge is no longer associated with a conditional, so it does
1116 not have TRUE/FALSE flags.
1117 We are also safe to drop EH/ABNORMAL flags and turn them into
1118 normal control flow, because we know that all the destinations (including
1119 those odd edges) are equivalent for program execution. */
1120 e
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
| EDGE_EH
| EDGE_ABNORMAL
);
1122 /* The lone outgoing edge from BB will be a fallthru edge. */
1123 e
->flags
|= EDGE_FALLTHRU
;
1125 /* Remove the remaining outgoing edges. */
1126 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1129 /* If we made a BB unconditionally exit a loop or removed
1130 an entry into an irreducible region, then this transform
1131 alters the set of BBs in the loop. Schedule a fixup. */
1132 if (loop_exit_edge_p (bb
->loop_father
, e
)
1133 || (e2
->dest
->flags
& BB_IRREDUCIBLE_LOOP
))
1134 loops_state_set (LOOPS_NEED_FIXUP
);
1135 to_remove_edges
.safe_push (e2
);
1139 /* If this is a store into a variable that is being optimized away,
1140 add a debug bind stmt if possible. */
1141 if (MAY_HAVE_DEBUG_BIND_STMTS
1142 && gimple_assign_single_p (stmt
)
1143 && is_gimple_val (gimple_assign_rhs1 (stmt
)))
1145 tree lhs
= gimple_assign_lhs (stmt
);
1146 if ((VAR_P (lhs
) || TREE_CODE (lhs
) == PARM_DECL
)
1147 && !DECL_IGNORED_P (lhs
)
1148 && is_gimple_reg_type (TREE_TYPE (lhs
))
1149 && !is_global_var (lhs
)
1150 && !DECL_HAS_VALUE_EXPR_P (lhs
))
1152 tree rhs
= gimple_assign_rhs1 (stmt
);
1154 = gimple_build_debug_bind (lhs
, unshare_expr (rhs
), stmt
);
1155 gsi_insert_after (i
, note
, GSI_SAME_STMT
);
1159 unlink_stmt_vdef (stmt
);
1160 gsi_remove (i
, true);
1161 release_defs (stmt
);
1164 /* Helper for maybe_optimize_arith_overflow. Find in *TP if there are any
1165 uses of data (SSA_NAME) other than REALPART_EXPR referencing it. */
1168 find_non_realpart_uses (tree
*tp
, int *walk_subtrees
, void *data
)
1170 if (TYPE_P (*tp
) || TREE_CODE (*tp
) == REALPART_EXPR
)
1172 if (*tp
== (tree
) data
)
1177 /* If the IMAGPART_EXPR of the {ADD,SUB,MUL}_OVERFLOW result is never used,
1178 but REALPART_EXPR is, optimize the {ADD,SUB,MUL}_OVERFLOW internal calls
1179 into plain unsigned {PLUS,MINUS,MULT}_EXPR, and if needed reset debug
1183 maybe_optimize_arith_overflow (gimple_stmt_iterator
*gsi
,
1184 enum tree_code subcode
)
1186 gimple
*stmt
= gsi_stmt (*gsi
);
1187 tree lhs
= gimple_call_lhs (stmt
);
1189 if (lhs
== NULL
|| TREE_CODE (lhs
) != SSA_NAME
)
1192 imm_use_iterator imm_iter
;
1193 use_operand_p use_p
;
1194 bool has_debug_uses
= false;
1195 bool has_realpart_uses
= false;
1196 bool has_other_uses
= false;
1197 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, lhs
)
1199 gimple
*use_stmt
= USE_STMT (use_p
);
1200 if (is_gimple_debug (use_stmt
))
1201 has_debug_uses
= true;
1202 else if (is_gimple_assign (use_stmt
)
1203 && gimple_assign_rhs_code (use_stmt
) == REALPART_EXPR
1204 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt
), 0) == lhs
)
1205 has_realpart_uses
= true;
1208 has_other_uses
= true;
1213 if (!has_realpart_uses
|| has_other_uses
)
1216 tree arg0
= gimple_call_arg (stmt
, 0);
1217 tree arg1
= gimple_call_arg (stmt
, 1);
1218 location_t loc
= gimple_location (stmt
);
1219 tree type
= TREE_TYPE (TREE_TYPE (lhs
));
1221 if (!TYPE_UNSIGNED (type
))
1222 utype
= build_nonstandard_integer_type (TYPE_PRECISION (type
), 1);
1223 tree result
= fold_build2_loc (loc
, subcode
, utype
,
1224 fold_convert_loc (loc
, utype
, arg0
),
1225 fold_convert_loc (loc
, utype
, arg1
));
1226 result
= fold_convert_loc (loc
, type
, result
);
1231 FOR_EACH_IMM_USE_STMT (use_stmt
, imm_iter
, lhs
)
1233 if (!gimple_debug_bind_p (use_stmt
))
1235 tree v
= gimple_debug_bind_get_value (use_stmt
);
1236 if (walk_tree (&v
, find_non_realpart_uses
, lhs
, NULL
))
1238 gimple_debug_bind_reset_value (use_stmt
);
1239 update_stmt (use_stmt
);
1244 if (TREE_CODE (result
) == INTEGER_CST
&& TREE_OVERFLOW (result
))
1245 result
= drop_tree_overflow (result
);
1246 tree overflow
= build_zero_cst (type
);
1247 tree ctype
= build_complex_type (type
);
1248 if (TREE_CODE (result
) == INTEGER_CST
)
1249 result
= build_complex (ctype
, result
, overflow
);
1251 result
= build2_loc (gimple_location (stmt
), COMPLEX_EXPR
,
1252 ctype
, result
, overflow
);
1254 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1256 fprintf (dump_file
, "Transforming call: ");
1257 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1258 fprintf (dump_file
, "because the overflow result is never used into: ");
1259 print_generic_stmt (dump_file
, result
, TDF_SLIM
);
1260 fprintf (dump_file
, "\n");
1263 gimplify_and_update_call_from_tree (gsi
, result
);
1266 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1267 contributes nothing to the program, and can be deleted. */
1270 eliminate_unnecessary_stmts (void)
1272 bool something_changed
= false;
1274 gimple_stmt_iterator gsi
, psi
;
1277 auto_vec
<edge
> to_remove_edges
;
1279 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1280 fprintf (dump_file
, "\nEliminating unnecessary statements:\n");
1282 clear_special_calls ();
1284 /* Walking basic blocks and statements in reverse order avoids
1285 releasing SSA names before any other DEFs that refer to them are
1286 released. This helps avoid loss of debug information, as we get
1287 a chance to propagate all RHSs of removed SSAs into debug uses,
1288 rather than only the latest ones. E.g., consider:
1294 If we were to release x_3 before a_5, when we reached a_5 and
1295 tried to substitute it into the debug stmt, we'd see x_3 there,
1296 but x_3's DEF, type, etc would have already been disconnected.
1297 By going backwards, the debug stmt first changes to:
1299 # DEBUG a => x_3 - b_4
1303 # DEBUG a => y_1 + z_2 - b_4
1306 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
1307 auto_vec
<basic_block
> h
;
1308 h
= get_all_dominated_blocks (CDI_DOMINATORS
,
1309 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun
)));
1315 /* Remove dead statements. */
1316 auto_bitmap debug_seen
;
1317 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi
= psi
)
1319 stmt
= gsi_stmt (gsi
);
1326 /* We can mark a call to free as not necessary if the
1327 defining statement of its argument is not necessary
1328 (and thus is getting removed). */
1329 if (gimple_plf (stmt
, STMT_NECESSARY
)
1330 && (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
)
1331 || (is_gimple_call (stmt
)
1332 && gimple_call_from_new_or_delete (as_a
<gcall
*> (stmt
))
1333 && gimple_call_operator_delete_p (as_a
<gcall
*> (stmt
)))))
1335 tree ptr
= gimple_call_arg (stmt
, 0);
1336 if (TREE_CODE (ptr
) == SSA_NAME
)
1338 gimple
*def_stmt
= SSA_NAME_DEF_STMT (ptr
);
1339 if (!gimple_nop_p (def_stmt
)
1340 && !gimple_plf (def_stmt
, STMT_NECESSARY
))
1341 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
1345 /* If GSI is not necessary then remove it. */
1346 if (!gimple_plf (stmt
, STMT_NECESSARY
))
1348 /* Keep clobbers that we can keep live live. */
1349 if (gimple_clobber_p (stmt
))
1352 use_operand_p use_p
;
1354 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_USE
)
1356 tree name
= USE_FROM_PTR (use_p
);
1357 if (!SSA_NAME_IS_DEFAULT_DEF (name
)
1358 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
)))
1366 bitmap_clear (debug_seen
);
1370 if (!is_gimple_debug (stmt
))
1371 something_changed
= true;
1372 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1375 else if (is_gimple_call (stmt
))
1377 tree name
= gimple_call_lhs (stmt
);
1379 notice_special_calls (as_a
<gcall
*> (stmt
));
1381 /* When LHS of var = call (); is dead, simplify it into
1382 call (); saving one operand. */
1384 && TREE_CODE (name
) == SSA_NAME
1385 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
))
1386 /* Avoid doing so for allocation calls which we
1387 did not mark as necessary, it will confuse the
1388 special logic we apply to malloc/free pair removal. */
1389 && (!(call
= gimple_call_fndecl (stmt
))
1390 || ((DECL_BUILT_IN_CLASS (call
) != BUILT_IN_NORMAL
1391 || (DECL_FUNCTION_CODE (call
) != BUILT_IN_ALIGNED_ALLOC
1392 && DECL_FUNCTION_CODE (call
) != BUILT_IN_MALLOC
1393 && DECL_FUNCTION_CODE (call
) != BUILT_IN_CALLOC
1394 && !ALLOCA_FUNCTION_CODE_P
1395 (DECL_FUNCTION_CODE (call
))))
1396 && !DECL_IS_REPLACEABLE_OPERATOR_NEW_P (call
))))
1398 something_changed
= true;
1399 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1401 fprintf (dump_file
, "Deleting LHS of call: ");
1402 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1403 fprintf (dump_file
, "\n");
1406 gimple_call_set_lhs (stmt
, NULL_TREE
);
1407 maybe_clean_or_replace_eh_stmt (stmt
, stmt
);
1409 release_ssa_name (name
);
1411 /* GOMP_SIMD_LANE (unless three argument) or ASAN_POISON
1412 without lhs is not needed. */
1413 if (gimple_call_internal_p (stmt
))
1414 switch (gimple_call_internal_fn (stmt
))
1416 case IFN_GOMP_SIMD_LANE
:
1417 if (gimple_call_num_args (stmt
) >= 3
1418 && !integer_nonzerop (gimple_call_arg (stmt
, 2)))
1421 case IFN_ASAN_POISON
:
1422 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1428 else if (gimple_call_internal_p (stmt
))
1429 switch (gimple_call_internal_fn (stmt
))
1431 case IFN_ADD_OVERFLOW
:
1432 maybe_optimize_arith_overflow (&gsi
, PLUS_EXPR
);
1434 case IFN_SUB_OVERFLOW
:
1435 maybe_optimize_arith_overflow (&gsi
, MINUS_EXPR
);
1437 case IFN_MUL_OVERFLOW
:
1438 maybe_optimize_arith_overflow (&gsi
, MULT_EXPR
);
1444 else if (gimple_debug_bind_p (stmt
))
1446 /* We are only keeping the last debug-bind of a
1447 non-DEBUG_EXPR_DECL variable in a series of
1448 debug-bind stmts. */
1449 tree var
= gimple_debug_bind_get_var (stmt
);
1450 if (TREE_CODE (var
) != DEBUG_EXPR_DECL
1451 && !bitmap_set_bit (debug_seen
, DECL_UID (var
)))
1452 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1455 bitmap_clear (debug_seen
);
1458 /* Remove dead PHI nodes. */
1459 something_changed
|= remove_dead_phis (bb
);
1463 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1464 rendered some PHI nodes unreachable while they are still in use.
1465 Mark them for renaming. */
1466 if (!to_remove_edges
.is_empty ())
1468 basic_block prev_bb
;
1470 /* Remove edges. We've delayed this to not get bogus debug stmts
1471 during PHI node removal. */
1472 for (unsigned i
= 0; i
< to_remove_edges
.length (); ++i
)
1473 remove_edge (to_remove_edges
[i
]);
1476 find_unreachable_blocks ();
1478 /* Delete all unreachable basic blocks in reverse dominator order. */
1479 for (bb
= EXIT_BLOCK_PTR_FOR_FN (cfun
)->prev_bb
;
1480 bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
); bb
= prev_bb
)
1482 prev_bb
= bb
->prev_bb
;
1484 if (!bitmap_bit_p (bb_contains_live_stmts
, bb
->index
)
1485 || !(bb
->flags
& BB_REACHABLE
))
1487 for (gphi_iterator gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
1489 if (virtual_operand_p (gimple_phi_result (gsi
.phi ())))
1492 imm_use_iterator iter
;
1494 FOR_EACH_IMM_USE_STMT (stmt
, iter
,
1495 gimple_phi_result (gsi
.phi ()))
1497 if (!(gimple_bb (stmt
)->flags
& BB_REACHABLE
))
1499 if (gimple_code (stmt
) == GIMPLE_PHI
1500 || gimple_plf (stmt
, STMT_NECESSARY
))
1507 mark_virtual_phi_result_for_renaming (gsi
.phi ());
1510 if (!(bb
->flags
& BB_REACHABLE
))
1512 /* Speed up the removal of blocks that don't
1513 dominate others. Walking backwards, this should
1514 be the common case. ??? Do we need to recompute
1515 dominators because of cfg_altered? */
1516 if (!first_dom_son (CDI_DOMINATORS
, bb
))
1517 delete_basic_block (bb
);
1520 h
= get_all_dominated_blocks (CDI_DOMINATORS
, bb
);
1525 prev_bb
= bb
->prev_bb
;
1526 /* Rearrangements to the CFG may have failed
1527 to update the dominators tree, so that
1528 formerly-dominated blocks are now
1529 otherwise reachable. */
1530 if (!!(bb
->flags
& BB_REACHABLE
))
1532 delete_basic_block (bb
);
1543 free (bb_postorder
);
1544 bb_postorder
= NULL
;
1546 return something_changed
;
1550 /* Print out removed statement statistics. */
1557 percg
= ((float) stats
.removed
/ (float) stats
.total
) * 100;
1558 fprintf (dump_file
, "Removed %d of %d statements (%d%%)\n",
1559 stats
.removed
, stats
.total
, (int) percg
);
1561 if (stats
.total_phis
== 0)
1564 percg
= ((float) stats
.removed_phis
/ (float) stats
.total_phis
) * 100;
1566 fprintf (dump_file
, "Removed %d of %d PHI nodes (%d%%)\n",
1567 stats
.removed_phis
, stats
.total_phis
, (int) percg
);
1570 /* Initialization for this pass. Set up the used data structures. */
1573 tree_dce_init (bool aggressive
)
1575 memset ((void *) &stats
, 0, sizeof (stats
));
1579 last_stmt_necessary
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1580 bitmap_clear (last_stmt_necessary
);
1581 bb_contains_live_stmts
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1582 bitmap_clear (bb_contains_live_stmts
);
1585 processed
= sbitmap_alloc (num_ssa_names
+ 1);
1586 bitmap_clear (processed
);
1588 worklist
.create (64);
1589 cfg_altered
= false;
1592 /* Cleanup after this pass. */
1595 tree_dce_done (bool aggressive
)
1600 sbitmap_free (visited_control_parents
);
1601 sbitmap_free (last_stmt_necessary
);
1602 sbitmap_free (bb_contains_live_stmts
);
1603 bb_contains_live_stmts
= NULL
;
1606 sbitmap_free (processed
);
1608 worklist
.release ();
1611 /* Main routine to eliminate dead code.
1613 AGGRESSIVE controls the aggressiveness of the algorithm.
1614 In conservative mode, we ignore control dependence and simply declare
1615 all but the most trivially dead branches necessary. This mode is fast.
1616 In aggressive mode, control dependences are taken into account, which
1617 results in more dead code elimination, but at the cost of some time.
1619 FIXME: Aggressive mode before PRE doesn't work currently because
1620 the dominance info is not invalidated after DCE1. This is
1621 not an issue right now because we only run aggressive DCE
1622 as the last tree SSA pass, but keep this in mind when you
1623 start experimenting with pass ordering. */
1626 perform_tree_ssa_dce (bool aggressive
)
1628 bool something_changed
= 0;
1630 calculate_dominance_info (CDI_DOMINATORS
);
1632 /* Preheaders are needed for SCEV to work.
1633 Simple lateches and recorded exits improve chances that loop will
1634 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1635 bool in_loop_pipeline
= scev_initialized_p ();
1636 if (aggressive
&& ! in_loop_pipeline
)
1639 loop_optimizer_init (LOOPS_NORMAL
1640 | LOOPS_HAVE_RECORDED_EXITS
);
1643 tree_dce_init (aggressive
);
1647 /* Compute control dependence. */
1648 calculate_dominance_info (CDI_POST_DOMINATORS
);
1649 cd
= new control_dependences ();
1651 visited_control_parents
=
1652 sbitmap_alloc (last_basic_block_for_fn (cfun
));
1653 bitmap_clear (visited_control_parents
);
1655 mark_dfs_back_edges ();
1658 find_obviously_necessary_stmts (aggressive
);
1660 if (aggressive
&& ! in_loop_pipeline
)
1662 loop_optimizer_finalize ();
1670 visited
= BITMAP_ALLOC (NULL
);
1671 propagate_necessity (aggressive
);
1672 BITMAP_FREE (visited
);
1674 something_changed
|= eliminate_unnecessary_stmts ();
1675 something_changed
|= cfg_altered
;
1677 /* We do not update postdominators, so free them unconditionally. */
1678 free_dominance_info (CDI_POST_DOMINATORS
);
1680 /* If we removed paths in the CFG, then we need to update
1681 dominators as well. I haven't investigated the possibility
1682 of incrementally updating dominators. */
1684 free_dominance_info (CDI_DOMINATORS
);
1686 statistics_counter_event (cfun
, "Statements deleted", stats
.removed
);
1687 statistics_counter_event (cfun
, "PHI nodes deleted", stats
.removed_phis
);
1689 /* Debugging dumps. */
1690 if (dump_file
&& (dump_flags
& (TDF_STATS
|TDF_DETAILS
)))
1693 tree_dce_done (aggressive
);
1695 if (something_changed
)
1697 free_numbers_of_iterations_estimates (cfun
);
1698 if (in_loop_pipeline
)
1700 return TODO_update_ssa
| TODO_cleanup_cfg
;
1705 /* Pass entry points. */
1709 return perform_tree_ssa_dce (/*aggressive=*/false);
1713 tree_ssa_cd_dce (void)
1715 return perform_tree_ssa_dce (/*aggressive=*/optimize
>= 2);
1720 const pass_data pass_data_dce
=
1722 GIMPLE_PASS
, /* type */
1724 OPTGROUP_NONE
, /* optinfo_flags */
1725 TV_TREE_DCE
, /* tv_id */
1726 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1727 0, /* properties_provided */
1728 0, /* properties_destroyed */
1729 0, /* todo_flags_start */
1730 0, /* todo_flags_finish */
1733 class pass_dce
: public gimple_opt_pass
1736 pass_dce (gcc::context
*ctxt
)
1737 : gimple_opt_pass (pass_data_dce
, ctxt
)
1740 /* opt_pass methods: */
1741 opt_pass
* clone () { return new pass_dce (m_ctxt
); }
1742 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1743 virtual unsigned int execute (function
*) { return tree_ssa_dce (); }
1745 }; // class pass_dce
1750 make_pass_dce (gcc::context
*ctxt
)
1752 return new pass_dce (ctxt
);
1757 const pass_data pass_data_cd_dce
=
1759 GIMPLE_PASS
, /* type */
1761 OPTGROUP_NONE
, /* optinfo_flags */
1762 TV_TREE_CD_DCE
, /* tv_id */
1763 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1764 0, /* properties_provided */
1765 0, /* properties_destroyed */
1766 0, /* todo_flags_start */
1767 0, /* todo_flags_finish */
1770 class pass_cd_dce
: public gimple_opt_pass
1773 pass_cd_dce (gcc::context
*ctxt
)
1774 : gimple_opt_pass (pass_data_cd_dce
, ctxt
), update_address_taken_p (false)
1777 /* opt_pass methods: */
1778 opt_pass
* clone () { return new pass_cd_dce (m_ctxt
); }
1779 void set_pass_param (unsigned n
, bool param
)
1781 gcc_assert (n
== 0);
1782 update_address_taken_p
= param
;
1784 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1785 virtual unsigned int execute (function
*)
1787 return (tree_ssa_cd_dce ()
1788 | (update_address_taken_p
? TODO_update_address_taken
: 0));
1792 bool update_address_taken_p
;
1793 }; // class pass_cd_dce
1798 make_pass_cd_dce (gcc::context
*ctxt
)
1800 return new pass_cd_dce (ctxt
);
1804 /* A cheap DCE interface. WORKLIST is a list of possibly dead stmts and
1805 is consumed by this function. The function has linear complexity in
1806 the number of dead stmts with a constant factor like the average SSA
1807 use operands number. */
1810 simple_dce_from_worklist (bitmap worklist
)
1812 while (! bitmap_empty_p (worklist
))
1815 unsigned i
= bitmap_first_set_bit (worklist
);
1816 bitmap_clear_bit (worklist
, i
);
1818 tree def
= ssa_name (i
);
1819 /* Removed by somebody else or still in use. */
1820 if (! def
|| ! has_zero_uses (def
))
1823 gimple
*t
= SSA_NAME_DEF_STMT (def
);
1824 if (gimple_has_side_effects (t
))
1827 /* Add uses to the worklist. */
1829 use_operand_p use_p
;
1830 FOR_EACH_PHI_OR_STMT_USE (use_p
, t
, iter
, SSA_OP_USE
)
1832 tree use
= USE_FROM_PTR (use_p
);
1833 if (TREE_CODE (use
) == SSA_NAME
1834 && ! SSA_NAME_IS_DEFAULT_DEF (use
))
1835 bitmap_set_bit (worklist
, SSA_NAME_VERSION (use
));
1839 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1841 fprintf (dump_file
, "Removing dead stmt:");
1842 print_gimple_stmt (dump_file
, t
, 0);
1844 gimple_stmt_iterator gsi
= gsi_for_stmt (t
);
1845 if (gimple_code (t
) == GIMPLE_PHI
)
1846 remove_phi_node (&gsi
, true);
1849 gsi_remove (&gsi
, true);