1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002-2023 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"
72 static struct stmt_stats
80 #define STMT_NECESSARY GF_PLF_1
82 static vec
<gimple
*> worklist
;
84 /* Vector indicating an SSA name has already been processed and marked
86 static sbitmap processed
;
88 /* Vector indicating that the last statement of a basic block has already
89 been marked as necessary. */
90 static sbitmap last_stmt_necessary
;
92 /* Vector indicating that BB contains statements that are live. */
93 static sbitmap bb_contains_live_stmts
;
95 /* Before we can determine whether a control branch is dead, we need to
96 compute which blocks are control dependent on which edges.
98 We expect each block to be control dependent on very few edges so we
99 use a bitmap for each block recording its edges. An array holds the
100 bitmap. The Ith bit in the bitmap is set if that block is dependent
102 static control_dependences
*cd
;
104 /* Vector indicating that a basic block has already had all the edges
105 processed that it is control dependent on. */
106 static sbitmap visited_control_parents
;
108 /* TRUE if this pass alters the CFG (by removing control statements).
111 If this pass alters the CFG, then it will arrange for the dominators
113 static bool cfg_altered
;
115 /* When non-NULL holds map from basic block index into the postorder. */
116 static int *bb_postorder
;
119 /* True if we should treat any stmt with a vdef as necessary. */
124 return optimize_debug
;
127 /* If STMT is not already marked necessary, mark it, and add it to the
128 worklist if ADD_TO_WORKLIST is true. */
131 mark_stmt_necessary (gimple
*stmt
, bool add_to_worklist
)
135 if (gimple_plf (stmt
, STMT_NECESSARY
))
138 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
140 fprintf (dump_file
, "Marking useful stmt: ");
141 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
142 fprintf (dump_file
, "\n");
145 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
147 worklist
.safe_push (stmt
);
148 if (add_to_worklist
&& bb_contains_live_stmts
&& !is_gimple_debug (stmt
))
149 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
153 /* Mark the statement defining operand OP as necessary. */
156 mark_operand_necessary (tree op
)
163 ver
= SSA_NAME_VERSION (op
);
164 if (bitmap_bit_p (processed
, ver
))
166 stmt
= SSA_NAME_DEF_STMT (op
);
167 gcc_assert (gimple_nop_p (stmt
)
168 || gimple_plf (stmt
, STMT_NECESSARY
));
171 bitmap_set_bit (processed
, ver
);
173 stmt
= SSA_NAME_DEF_STMT (op
);
176 if (gimple_plf (stmt
, STMT_NECESSARY
) || gimple_nop_p (stmt
))
179 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
181 fprintf (dump_file
, "marking necessary through ");
182 print_generic_expr (dump_file
, op
);
183 fprintf (dump_file
, " stmt ");
184 print_gimple_stmt (dump_file
, stmt
, 0);
187 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
188 if (bb_contains_live_stmts
)
189 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
190 worklist
.safe_push (stmt
);
194 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
195 it can make other statements necessary.
197 If AGGRESSIVE is false, control statements are conservatively marked as
201 mark_stmt_if_obviously_necessary (gimple
*stmt
, bool aggressive
)
203 /* Statements that are implicitly live. Most function calls, asm
204 and return statements are required. Labels and GIMPLE_BIND nodes
205 are kept because they are control flow, and we have no way of
206 knowing whether they can be removed. DCE can eliminate all the
207 other statements in a block, and CFG can then remove the block
209 switch (gimple_code (stmt
))
213 mark_stmt_necessary (stmt
, false);
219 mark_stmt_necessary (stmt
, true);
224 /* Never elide a noreturn call we pruned control-flow for. */
225 if ((gimple_call_flags (stmt
) & ECF_NORETURN
)
226 && gimple_call_ctrl_altering_p (stmt
))
228 mark_stmt_necessary (stmt
, true);
232 tree callee
= gimple_call_fndecl (stmt
);
233 if (callee
!= NULL_TREE
234 && fndecl_built_in_p (callee
, BUILT_IN_NORMAL
))
235 switch (DECL_FUNCTION_CODE (callee
))
237 case BUILT_IN_MALLOC
:
238 case BUILT_IN_ALIGNED_ALLOC
:
239 case BUILT_IN_CALLOC
:
240 CASE_BUILT_IN_ALLOCA
:
241 case BUILT_IN_STRDUP
:
242 case BUILT_IN_STRNDUP
:
243 case BUILT_IN_GOMP_ALLOC
:
249 if (callee
!= NULL_TREE
250 && flag_allocation_dce
251 && DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
))
254 /* IFN_GOACC_LOOP calls are necessary in that they are used to
255 represent parameter (i.e. step, bound) of a lowered OpenACC
256 partitioned loop. But this kind of partitioned loop might not
257 survive from aggressive loop removal for it has loop exit and
258 is assumed to be finite. Therefore, we need to explicitly mark
259 these calls. (An example is libgomp.oacc-c-c++-common/pr84955.c) */
260 if (gimple_call_internal_p (stmt
, IFN_GOACC_LOOP
))
262 mark_stmt_necessary (stmt
, true);
269 /* Debug temps without a value are not useful. ??? If we could
270 easily locate the debug temp bind stmt for a use thereof,
271 would could refrain from marking all debug temps here, and
272 mark them only if they're used. */
273 if (gimple_debug_nonbind_marker_p (stmt
)
274 || !gimple_debug_bind_p (stmt
)
275 || gimple_debug_bind_has_value_p (stmt
)
276 || TREE_CODE (gimple_debug_bind_get_var (stmt
)) != DEBUG_EXPR_DECL
)
277 mark_stmt_necessary (stmt
, false);
281 gcc_assert (!simple_goto_p (stmt
));
282 mark_stmt_necessary (stmt
, true);
286 gcc_assert (EDGE_COUNT (gimple_bb (stmt
)->succs
) == 2);
291 mark_stmt_necessary (stmt
, true);
295 /* Mark indirect CLOBBERs to be lazily removed if their SSA operands
296 do not prevail. That also makes control flow leading to them
297 not necessary in aggressive mode. */
298 if (gimple_clobber_p (stmt
) && !zero_ssa_operands (stmt
, SSA_OP_USE
))
306 /* If the statement has volatile operands, it needs to be preserved.
307 Same for statements that can alter control flow in unpredictable
309 if (gimple_has_side_effects (stmt
) || is_ctrl_altering_stmt (stmt
))
311 mark_stmt_necessary (stmt
, true);
315 /* If a statement could throw, it can be deemed necessary unless we
316 are allowed to remove dead EH. Test this after checking for
317 new/delete operators since we always elide their EH. */
318 if (!cfun
->can_delete_dead_exceptions
319 && stmt_could_throw_p (cfun
, stmt
))
321 mark_stmt_necessary (stmt
, true);
325 if ((gimple_vdef (stmt
) && keep_all_vdefs_p ())
326 || stmt_may_clobber_global_p (stmt
, false))
328 mark_stmt_necessary (stmt
, true);
336 /* Mark the last statement of BB as necessary. */
339 mark_last_stmt_necessary (basic_block bb
)
341 if (!bitmap_set_bit (last_stmt_necessary
, bb
->index
))
344 bitmap_set_bit (bb_contains_live_stmts
, bb
->index
);
346 /* We actually mark the statement only if it is a control statement. */
347 gimple
*stmt
= *gsi_last_bb (bb
);
348 if (stmt
&& is_ctrl_stmt (stmt
))
350 mark_stmt_necessary (stmt
, true);
357 /* Mark control dependent edges of BB as necessary. We have to do this only
358 once for each basic block so we set the appropriate bit after we're done.
360 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
363 mark_control_dependent_edges_necessary (basic_block bb
, bool ignore_self
)
366 unsigned edge_number
;
367 bool skipped
= false;
369 gcc_assert (bb
!= EXIT_BLOCK_PTR_FOR_FN (cfun
));
371 if (bb
== ENTRY_BLOCK_PTR_FOR_FN (cfun
))
374 EXECUTE_IF_SET_IN_BITMAP (cd
->get_edges_dependent_on (bb
->index
),
377 basic_block cd_bb
= cd
->get_edge_src (edge_number
);
379 if (ignore_self
&& cd_bb
== bb
)
385 if (!mark_last_stmt_necessary (cd_bb
))
386 mark_control_dependent_edges_necessary (cd_bb
, false);
390 bitmap_set_bit (visited_control_parents
, bb
->index
);
394 /* Find obviously necessary statements. These are things like most function
395 calls, and stores to file level variables.
397 If EL is NULL, control statements are conservatively marked as
398 necessary. Otherwise it contains the list of edges used by control
399 dependence analysis. */
402 find_obviously_necessary_stmts (bool aggressive
)
405 gimple_stmt_iterator gsi
;
410 FOR_EACH_BB_FN (bb
, cfun
)
412 /* PHI nodes are never inherently necessary. */
413 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
415 phi
= gsi_stmt (gsi
);
416 gimple_set_plf (phi
, STMT_NECESSARY
, false);
419 /* Check all statements in the block. */
420 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
422 stmt
= gsi_stmt (gsi
);
423 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
424 mark_stmt_if_obviously_necessary (stmt
, aggressive
);
428 /* Pure and const functions are finite and thus have no infinite loops in
430 flags
= flags_from_decl_or_type (current_function_decl
);
431 if ((flags
& (ECF_CONST
|ECF_PURE
)) && !(flags
& ECF_LOOPING_CONST_OR_PURE
))
434 /* Prevent the empty possibly infinite loops from being removed. This is
435 needed to make the logic in remove_dead_stmt work to identify the
436 correct edge to keep when removing a controlling condition. */
439 if (mark_irreducible_loops ())
440 FOR_EACH_BB_FN (bb
, cfun
)
443 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
444 if ((e
->flags
& EDGE_DFS_BACK
)
445 && (e
->flags
& EDGE_IRREDUCIBLE_LOOP
))
448 fprintf (dump_file
, "Marking back edge of irreducible "
449 "loop %i->%i\n", e
->src
->index
, e
->dest
->index
);
450 mark_control_dependent_edges_necessary (e
->dest
, false);
454 for (auto loop
: loops_list (cfun
, 0))
455 /* For loops without an exit do not mark any condition. */
456 if (loop
->exits
->next
->e
&& !finite_loop_p (loop
))
459 fprintf (dump_file
, "cannot prove finiteness of loop %i\n",
461 mark_control_dependent_edges_necessary (loop
->latch
, false);
467 /* Return true if REF is based on an aliased base, otherwise false. */
470 ref_may_be_aliased (tree ref
)
472 gcc_assert (TREE_CODE (ref
) != WITH_SIZE_EXPR
);
473 while (handled_component_p (ref
))
474 ref
= TREE_OPERAND (ref
, 0);
475 if ((TREE_CODE (ref
) == MEM_REF
|| TREE_CODE (ref
) == TARGET_MEM_REF
)
476 && TREE_CODE (TREE_OPERAND (ref
, 0)) == ADDR_EXPR
)
477 ref
= TREE_OPERAND (TREE_OPERAND (ref
, 0), 0);
478 return !(DECL_P (ref
)
479 && !may_be_aliased (ref
));
482 static bitmap visited
= NULL
;
483 static unsigned int longest_chain
= 0;
484 static unsigned int total_chain
= 0;
485 static unsigned int nr_walks
= 0;
486 static bool chain_ovfl
= false;
488 /* Worker for the walker that marks reaching definitions of REF,
489 which is based on a non-aliased decl, necessary. It returns
490 true whenever the defining statement of the current VDEF is
491 a kill for REF, as no dominating may-defs are necessary for REF
492 anymore. DATA points to the basic-block that contains the
493 stmt that refers to REF. */
496 mark_aliased_reaching_defs_necessary_1 (ao_ref
*ref
, tree vdef
, void *data
)
498 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
500 /* All stmts we visit are necessary. */
501 if (! gimple_clobber_p (def_stmt
))
502 mark_operand_necessary (vdef
);
504 /* If the stmt lhs kills ref, then we can stop walking. */
505 if (gimple_has_lhs (def_stmt
)
506 && TREE_CODE (gimple_get_lhs (def_stmt
)) != SSA_NAME
507 /* The assignment is not necessarily carried out if it can throw
508 and we can catch it in the current function where we could inspect
510 ??? We only need to care about the RHS throwing. For aggregate
511 assignments or similar calls and non-call exceptions the LHS
512 might throw as well. */
513 && !stmt_can_throw_internal (cfun
, def_stmt
))
515 tree base
, lhs
= gimple_get_lhs (def_stmt
);
516 poly_int64 size
, offset
, max_size
;
520 = get_ref_base_and_extent (lhs
, &offset
, &size
, &max_size
, &reverse
);
521 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
522 so base == refd->base does not always hold. */
523 if (base
== ref
->base
)
525 /* For a must-alias check we need to be able to constrain
526 the accesses properly. */
527 if (known_eq (size
, max_size
)
528 && known_subrange_p (ref
->offset
, ref
->max_size
, offset
, size
))
530 /* Or they need to be exactly the same. */
532 /* Make sure there is no induction variable involved
533 in the references (gcc.c-torture/execute/pr42142.c).
534 The simplest way is to check if the kill dominates
536 /* But when both are in the same block we cannot
537 easily tell whether we came from a backedge
538 unless we decide to compute stmt UIDs
540 && (basic_block
) data
!= gimple_bb (def_stmt
)
541 && dominated_by_p (CDI_DOMINATORS
, (basic_block
) data
,
542 gimple_bb (def_stmt
))
543 && operand_equal_p (ref
->ref
, lhs
, 0))
548 /* Otherwise keep walking. */
553 mark_aliased_reaching_defs_necessary (gimple
*stmt
, tree ref
)
555 /* Should have been caught before calling this function. */
556 gcc_checking_assert (!keep_all_vdefs_p ());
560 gcc_assert (!chain_ovfl
);
561 ao_ref_init (&refd
, ref
);
562 chain
= walk_aliased_vdefs (&refd
, gimple_vuse (stmt
),
563 mark_aliased_reaching_defs_necessary_1
,
564 gimple_bb (stmt
), NULL
);
565 if (chain
> longest_chain
)
566 longest_chain
= chain
;
567 total_chain
+= chain
;
571 /* Worker for the walker that marks reaching definitions of REF, which
572 is not based on a non-aliased decl. For simplicity we need to end
573 up marking all may-defs necessary that are not based on a non-aliased
574 decl. The only job of this walker is to skip may-defs based on
575 a non-aliased decl. */
578 mark_all_reaching_defs_necessary_1 (ao_ref
*ref ATTRIBUTE_UNUSED
,
579 tree vdef
, void *data ATTRIBUTE_UNUSED
)
581 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
583 /* We have to skip already visited (and thus necessary) statements
584 to make the chaining work after we dropped back to simple mode. */
586 && bitmap_bit_p (processed
, SSA_NAME_VERSION (vdef
)))
588 gcc_assert (gimple_nop_p (def_stmt
)
589 || gimple_plf (def_stmt
, STMT_NECESSARY
));
593 /* We want to skip stores to non-aliased variables. */
595 && gimple_assign_single_p (def_stmt
))
597 tree lhs
= gimple_assign_lhs (def_stmt
);
598 if (!ref_may_be_aliased (lhs
))
602 /* We want to skip statments that do not constitute stores but have
603 a virtual definition. */
604 if (gcall
*call
= dyn_cast
<gcall
*> (def_stmt
))
606 tree callee
= gimple_call_fndecl (call
);
607 if (callee
!= NULL_TREE
608 && fndecl_built_in_p (callee
, BUILT_IN_NORMAL
))
609 switch (DECL_FUNCTION_CODE (callee
))
611 case BUILT_IN_MALLOC
:
612 case BUILT_IN_ALIGNED_ALLOC
:
613 case BUILT_IN_CALLOC
:
614 CASE_BUILT_IN_ALLOCA
:
616 case BUILT_IN_GOMP_ALLOC
:
617 case BUILT_IN_GOMP_FREE
:
623 if (callee
!= NULL_TREE
624 && (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
)
625 || DECL_IS_OPERATOR_DELETE_P (callee
))
626 && gimple_call_from_new_or_delete (call
))
630 if (! gimple_clobber_p (def_stmt
))
631 mark_operand_necessary (vdef
);
637 mark_all_reaching_defs_necessary (gimple
*stmt
)
639 /* Should have been caught before calling this function. */
640 gcc_checking_assert (!keep_all_vdefs_p ());
641 walk_aliased_vdefs (NULL
, gimple_vuse (stmt
),
642 mark_all_reaching_defs_necessary_1
, NULL
, &visited
);
645 /* Return true for PHI nodes with one or identical arguments
648 degenerate_phi_p (gimple
*phi
)
651 tree op
= gimple_phi_arg_def (phi
, 0);
652 for (i
= 1; i
< gimple_phi_num_args (phi
); i
++)
653 if (gimple_phi_arg_def (phi
, i
) != op
)
658 /* Return that NEW_CALL and DELETE_CALL are a valid pair of new
659 and delete operators. */
662 valid_new_delete_pair_p (gimple
*new_call
, gimple
*delete_call
)
664 tree new_asm
= DECL_ASSEMBLER_NAME (gimple_call_fndecl (new_call
));
665 tree delete_asm
= DECL_ASSEMBLER_NAME (gimple_call_fndecl (delete_call
));
666 return valid_new_delete_pair_p (new_asm
, delete_asm
);
669 /* Propagate necessity using the operands of necessary statements.
670 Process the uses on each statement in the worklist, and add all
671 feeding statements which contribute to the calculation of this
672 value to the worklist.
674 In conservative mode, EL is NULL. */
677 propagate_necessity (bool aggressive
)
681 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
682 fprintf (dump_file
, "\nProcessing worklist:\n");
684 while (worklist
.length () > 0)
686 /* Take STMT from worklist. */
687 stmt
= worklist
.pop ();
689 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
691 fprintf (dump_file
, "processing: ");
692 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
693 fprintf (dump_file
, "\n");
698 /* Mark the last statement of the basic blocks on which the block
699 containing STMT is control dependent, but only if we haven't
701 basic_block bb
= gimple_bb (stmt
);
702 if (bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
703 && !bitmap_bit_p (visited_control_parents
, bb
->index
))
704 mark_control_dependent_edges_necessary (bb
, false);
707 if (gimple_code (stmt
) == GIMPLE_PHI
708 /* We do not process virtual PHI nodes nor do we track their
710 && !virtual_operand_p (gimple_phi_result (stmt
)))
712 /* PHI nodes are somewhat special in that each PHI alternative has
713 data and control dependencies. All the statements feeding the
714 PHI node's arguments are always necessary. In aggressive mode,
715 we also consider the control dependent edges leading to the
716 predecessor block associated with each PHI alternative as
718 gphi
*phi
= as_a
<gphi
*> (stmt
);
721 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
723 tree arg
= PHI_ARG_DEF (stmt
, k
);
724 if (TREE_CODE (arg
) == SSA_NAME
)
725 mark_operand_necessary (arg
);
728 /* For PHI operands it matters from where the control flow arrives
729 to the BB. Consider the following example:
739 We need to mark control dependence of the empty basic blocks, since they
740 contains computation of PHI operands.
742 Doing so is too restrictive in the case the predecestor block is in
748 for (i = 0; i<1000; ++i)
754 There is PHI for J in the BB containing return statement.
755 In this case the control dependence of predecestor block (that is
756 within the empty loop) also contains the block determining number
757 of iterations of the block that would prevent removing of empty
760 This scenario can be avoided by splitting critical edges.
761 To save the critical edge splitting pass we identify how the control
762 dependence would look like if the edge was split.
764 Consider the modified CFG created from current CFG by splitting
765 edge B->C. In the postdominance tree of modified CFG, C' is
766 always child of C. There are two cases how chlids of C' can look
771 In this case the only basic block C' is control dependent on is B.
773 2) C' has single child that is B
775 In this case control dependence of C' is same as control
776 dependence of B in original CFG except for block B itself.
777 (since C' postdominate B in modified CFG)
779 Now how to decide what case happens? There are two basic options:
781 a) C postdominate B. Then C immediately postdominate B and
782 case 2 happens iff there is no other way from B to C except
785 There is other way from B to C iff there is succesor of B that
786 is not postdominated by B. Testing this condition is somewhat
787 expensive, because we need to iterate all succesors of B.
788 We are safe to assume that this does not happen: we will mark B
789 as needed when processing the other path from B to C that is
790 conrol dependent on B and marking control dependencies of B
791 itself is harmless because they will be processed anyway after
792 processing control statement in B.
794 b) C does not postdominate B. Always case 1 happens since there is
795 path from C to exit that does not go through B and thus also C'. */
797 if (aggressive
&& !degenerate_phi_p (stmt
))
799 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
801 basic_block arg_bb
= gimple_phi_arg_edge (phi
, k
)->src
;
804 != get_immediate_dominator (CDI_POST_DOMINATORS
, arg_bb
))
806 if (!mark_last_stmt_necessary (arg_bb
))
807 mark_control_dependent_edges_necessary (arg_bb
, false);
809 else if (arg_bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
810 && !bitmap_bit_p (visited_control_parents
,
812 mark_control_dependent_edges_necessary (arg_bb
, true);
818 /* Propagate through the operands. Examine all the USE, VUSE and
819 VDEF operands in this statement. Mark all the statements
820 which feed this statement's uses as necessary. */
824 /* If this is a call to free which is directly fed by an
825 allocation function do not mark that necessary through
826 processing the argument. */
827 bool is_delete_operator
828 = (is_gimple_call (stmt
)
829 && gimple_call_from_new_or_delete (as_a
<gcall
*> (stmt
))
830 && gimple_call_operator_delete_p (as_a
<gcall
*> (stmt
)));
831 if (is_delete_operator
832 || gimple_call_builtin_p (stmt
, BUILT_IN_FREE
)
833 || gimple_call_builtin_p (stmt
, BUILT_IN_GOMP_FREE
))
835 tree ptr
= gimple_call_arg (stmt
, 0);
838 /* If the pointer we free is defined by an allocation
839 function do not add the call to the worklist. */
840 if (TREE_CODE (ptr
) == SSA_NAME
841 && (def_stmt
= dyn_cast
<gcall
*> (SSA_NAME_DEF_STMT (ptr
)))
842 && (def_callee
= gimple_call_fndecl (def_stmt
))
843 && ((DECL_BUILT_IN_CLASS (def_callee
) == BUILT_IN_NORMAL
844 && (DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_ALIGNED_ALLOC
845 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_MALLOC
846 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_CALLOC
847 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_GOMP_ALLOC
))
848 || (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (def_callee
)
849 && gimple_call_from_new_or_delete (def_stmt
))))
851 if (is_delete_operator
852 && !valid_new_delete_pair_p (def_stmt
, stmt
))
853 mark_operand_necessary (gimple_call_arg (stmt
, 0));
855 /* Delete operators can have alignment and (or) size
856 as next arguments. When being a SSA_NAME, they
857 must be marked as necessary. Similarly GOMP_free. */
858 if (gimple_call_num_args (stmt
) >= 2)
859 for (unsigned i
= 1; i
< gimple_call_num_args (stmt
);
862 tree arg
= gimple_call_arg (stmt
, i
);
863 if (TREE_CODE (arg
) == SSA_NAME
)
864 mark_operand_necessary (arg
);
871 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
872 mark_operand_necessary (use
);
874 use
= gimple_vuse (stmt
);
878 /* No need to search for vdefs if we intrinsicly keep them all. */
879 if (keep_all_vdefs_p ())
882 /* If we dropped to simple mode make all immediately
883 reachable definitions necessary. */
886 mark_all_reaching_defs_necessary (stmt
);
890 /* For statements that may load from memory (have a VUSE) we
891 have to mark all reaching (may-)definitions as necessary.
892 We partition this task into two cases:
893 1) explicit loads based on decls that are not aliased
894 2) implicit loads (like calls) and explicit loads not
895 based on decls that are not aliased (like indirect
896 references or loads from globals)
897 For 1) we mark all reaching may-defs as necessary, stopping
898 at dominating kills. For 2) we want to mark all dominating
899 references necessary, but non-aliased ones which we handle
900 in 1). By keeping a global visited bitmap for references
901 we walk for 2) we avoid quadratic behavior for those. */
903 if (gcall
*call
= dyn_cast
<gcall
*> (stmt
))
905 tree callee
= gimple_call_fndecl (call
);
908 /* Calls to functions that are merely acting as barriers
909 or that only store to memory do not make any previous
911 if (callee
!= NULL_TREE
912 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
913 && (DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET
914 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET_CHK
915 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MALLOC
916 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALIGNED_ALLOC
917 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_CALLOC
918 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_FREE
919 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_VA_END
920 || ALLOCA_FUNCTION_CODE_P (DECL_FUNCTION_CODE (callee
))
921 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_SAVE
922 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_RESTORE
923 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ASSUME_ALIGNED
))
926 if (callee
!= NULL_TREE
927 && (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
)
928 || DECL_IS_OPERATOR_DELETE_P (callee
))
929 && gimple_call_from_new_or_delete (call
))
932 /* Calls implicitly load from memory, their arguments
933 in addition may explicitly perform memory loads. */
934 mark_all_reaching_defs_necessary (call
);
935 for (i
= 0; i
< gimple_call_num_args (call
); ++i
)
937 tree arg
= gimple_call_arg (call
, i
);
938 if (TREE_CODE (arg
) == SSA_NAME
939 || is_gimple_min_invariant (arg
))
941 if (TREE_CODE (arg
) == WITH_SIZE_EXPR
)
942 arg
= TREE_OPERAND (arg
, 0);
943 if (!ref_may_be_aliased (arg
))
944 mark_aliased_reaching_defs_necessary (call
, arg
);
947 else if (gimple_assign_single_p (stmt
))
950 /* If this is a load mark things necessary. */
951 rhs
= gimple_assign_rhs1 (stmt
);
952 if (TREE_CODE (rhs
) != SSA_NAME
953 && !is_gimple_min_invariant (rhs
)
954 && TREE_CODE (rhs
) != CONSTRUCTOR
)
956 if (!ref_may_be_aliased (rhs
))
957 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
959 mark_all_reaching_defs_necessary (stmt
);
962 else if (greturn
*return_stmt
= dyn_cast
<greturn
*> (stmt
))
964 tree rhs
= gimple_return_retval (return_stmt
);
965 /* A return statement may perform a load. */
967 && TREE_CODE (rhs
) != SSA_NAME
968 && !is_gimple_min_invariant (rhs
)
969 && TREE_CODE (rhs
) != CONSTRUCTOR
)
971 if (!ref_may_be_aliased (rhs
))
972 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
974 mark_all_reaching_defs_necessary (stmt
);
977 else if (gasm
*asm_stmt
= dyn_cast
<gasm
*> (stmt
))
980 mark_all_reaching_defs_necessary (stmt
);
981 /* Inputs may perform loads. */
982 for (i
= 0; i
< gimple_asm_ninputs (asm_stmt
); ++i
)
984 tree op
= TREE_VALUE (gimple_asm_input_op (asm_stmt
, i
));
985 if (TREE_CODE (op
) != SSA_NAME
986 && !is_gimple_min_invariant (op
)
987 && TREE_CODE (op
) != CONSTRUCTOR
988 && !ref_may_be_aliased (op
))
989 mark_aliased_reaching_defs_necessary (stmt
, op
);
992 else if (gimple_code (stmt
) == GIMPLE_TRANSACTION
)
994 /* The beginning of a transaction is a memory barrier. */
995 /* ??? If we were really cool, we'd only be a barrier
996 for the memories touched within the transaction. */
997 mark_all_reaching_defs_necessary (stmt
);
1002 /* If we over-used our alias oracle budget drop to simple
1003 mode. The cost metric allows quadratic behavior
1004 (number of uses times number of may-defs queries) up to
1005 a constant maximal number of queries and after that falls back to
1006 super-linear complexity. */
1007 if (/* Constant but quadratic for small functions. */
1008 total_chain
> 128 * 128
1009 /* Linear in the number of may-defs. */
1010 && total_chain
> 32 * longest_chain
1011 /* Linear in the number of uses. */
1012 && total_chain
> nr_walks
* 32)
1016 bitmap_clear (visited
);
1022 /* Remove dead PHI nodes from block BB. */
1025 remove_dead_phis (basic_block bb
)
1027 bool something_changed
= false;
1031 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);)
1036 /* We do not track necessity of virtual PHI nodes. Instead do
1037 very simple dead PHI removal here. */
1038 if (virtual_operand_p (gimple_phi_result (phi
)))
1040 /* Virtual PHI nodes with one or identical arguments
1042 if (!loops_state_satisfies_p (LOOP_CLOSED_SSA
)
1043 && degenerate_phi_p (phi
))
1045 tree vdef
= gimple_phi_result (phi
);
1046 tree vuse
= gimple_phi_arg_def (phi
, 0);
1048 use_operand_p use_p
;
1049 imm_use_iterator iter
;
1051 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, vdef
)
1052 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
1053 SET_USE (use_p
, vuse
);
1054 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef
)
1055 && TREE_CODE (vuse
) == SSA_NAME
)
1056 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse
) = 1;
1059 gimple_set_plf (phi
, STMT_NECESSARY
, true);
1062 if (!gimple_plf (phi
, STMT_NECESSARY
))
1064 something_changed
= true;
1065 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1067 fprintf (dump_file
, "Deleting : ");
1068 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
1069 fprintf (dump_file
, "\n");
1072 remove_phi_node (&gsi
, true);
1073 stats
.removed_phis
++;
1079 return something_changed
;
1083 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1084 containing I so that we don't have to look it up. */
1087 remove_dead_stmt (gimple_stmt_iterator
*i
, basic_block bb
,
1088 vec
<edge
> &to_remove_edges
)
1090 gimple
*stmt
= gsi_stmt (*i
);
1092 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1094 fprintf (dump_file
, "Deleting : ");
1095 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1096 fprintf (dump_file
, "\n");
1101 /* If we have determined that a conditional branch statement contributes
1102 nothing to the program, then we not only remove it, but we need to update
1103 the CFG. We can chose any of edges out of BB as long as we are sure to not
1104 close infinite loops. This is done by always choosing the edge closer to
1105 exit in inverted_rev_post_order_compute order. */
1106 if (is_ctrl_stmt (stmt
))
1111 /* See if there is only one non-abnormal edge. */
1112 if (single_succ_p (bb
))
1113 e
= single_succ_edge (bb
);
1114 /* Otherwise chose one that is closer to bb with live statement in it.
1115 To be able to chose one, we compute inverted post order starting from
1116 all BBs with live statements. */
1121 int *rpo
= XNEWVEC (int, n_basic_blocks_for_fn (cfun
));
1122 int n
= inverted_rev_post_order_compute (cfun
, rpo
,
1123 &bb_contains_live_stmts
);
1124 bb_postorder
= XNEWVEC (int, last_basic_block_for_fn (cfun
));
1125 for (int i
= 0; i
< n
; ++i
)
1126 bb_postorder
[rpo
[i
]] = i
;
1129 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1130 if (!e
|| e2
->dest
== EXIT_BLOCK_PTR_FOR_FN (cfun
)
1131 || bb_postorder
[e
->dest
->index
]
1132 >= bb_postorder
[e2
->dest
->index
])
1136 e
->probability
= profile_probability::always ();
1138 /* The edge is no longer associated with a conditional, so it does
1139 not have TRUE/FALSE flags.
1140 We are also safe to drop EH/ABNORMAL flags and turn them into
1141 normal control flow, because we know that all the destinations (including
1142 those odd edges) are equivalent for program execution. */
1143 e
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
| EDGE_EH
| EDGE_ABNORMAL
);
1145 /* The lone outgoing edge from BB will be a fallthru edge. */
1146 e
->flags
|= EDGE_FALLTHRU
;
1148 /* Remove the remaining outgoing edges. */
1149 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1152 /* If we made a BB unconditionally exit a loop or removed
1153 an entry into an irreducible region, then this transform
1154 alters the set of BBs in the loop. Schedule a fixup. */
1155 if (loop_exit_edge_p (bb
->loop_father
, e
)
1156 || (e2
->dest
->flags
& BB_IRREDUCIBLE_LOOP
))
1157 loops_state_set (LOOPS_NEED_FIXUP
);
1158 to_remove_edges
.safe_push (e2
);
1162 /* If this is a store into a variable that is being optimized away,
1163 add a debug bind stmt if possible. */
1164 if (MAY_HAVE_DEBUG_BIND_STMTS
1165 && gimple_assign_single_p (stmt
)
1166 && is_gimple_val (gimple_assign_rhs1 (stmt
)))
1168 tree lhs
= gimple_assign_lhs (stmt
);
1169 if ((VAR_P (lhs
) || TREE_CODE (lhs
) == PARM_DECL
)
1170 && !DECL_IGNORED_P (lhs
)
1171 && is_gimple_reg_type (TREE_TYPE (lhs
))
1172 && !is_global_var (lhs
)
1173 && !DECL_HAS_VALUE_EXPR_P (lhs
))
1175 tree rhs
= gimple_assign_rhs1 (stmt
);
1177 = gimple_build_debug_bind (lhs
, unshare_expr (rhs
), stmt
);
1178 gsi_insert_after (i
, note
, GSI_SAME_STMT
);
1182 unlink_stmt_vdef (stmt
);
1183 gsi_remove (i
, true);
1184 release_defs (stmt
);
1187 /* Helper for maybe_optimize_arith_overflow. Find in *TP if there are any
1188 uses of data (SSA_NAME) other than REALPART_EXPR referencing it. */
1191 find_non_realpart_uses (tree
*tp
, int *walk_subtrees
, void *data
)
1193 if (TYPE_P (*tp
) || TREE_CODE (*tp
) == REALPART_EXPR
)
1195 if (*tp
== (tree
) data
)
1200 /* If the IMAGPART_EXPR of the {ADD,SUB,MUL}_OVERFLOW result is never used,
1201 but REALPART_EXPR is, optimize the {ADD,SUB,MUL}_OVERFLOW internal calls
1202 into plain unsigned {PLUS,MINUS,MULT}_EXPR, and if needed reset debug
1206 maybe_optimize_arith_overflow (gimple_stmt_iterator
*gsi
,
1207 enum tree_code subcode
)
1209 gimple
*stmt
= gsi_stmt (*gsi
);
1210 tree lhs
= gimple_call_lhs (stmt
);
1212 if (lhs
== NULL
|| TREE_CODE (lhs
) != SSA_NAME
)
1215 imm_use_iterator imm_iter
;
1216 use_operand_p use_p
;
1217 bool has_debug_uses
= false;
1218 bool has_realpart_uses
= false;
1219 bool has_other_uses
= false;
1220 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, lhs
)
1222 gimple
*use_stmt
= USE_STMT (use_p
);
1223 if (is_gimple_debug (use_stmt
))
1224 has_debug_uses
= true;
1225 else if (is_gimple_assign (use_stmt
)
1226 && gimple_assign_rhs_code (use_stmt
) == REALPART_EXPR
1227 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt
), 0) == lhs
)
1228 has_realpart_uses
= true;
1231 has_other_uses
= true;
1236 if (!has_realpart_uses
|| has_other_uses
)
1239 tree arg0
= gimple_call_arg (stmt
, 0);
1240 tree arg1
= gimple_call_arg (stmt
, 1);
1241 location_t loc
= gimple_location (stmt
);
1242 tree type
= TREE_TYPE (TREE_TYPE (lhs
));
1244 if (!TYPE_UNSIGNED (type
))
1245 utype
= build_nonstandard_integer_type (TYPE_PRECISION (type
), 1);
1246 tree result
= fold_build2_loc (loc
, subcode
, utype
,
1247 fold_convert_loc (loc
, utype
, arg0
),
1248 fold_convert_loc (loc
, utype
, arg1
));
1249 result
= fold_convert_loc (loc
, type
, result
);
1254 FOR_EACH_IMM_USE_STMT (use_stmt
, imm_iter
, lhs
)
1256 if (!gimple_debug_bind_p (use_stmt
))
1258 tree v
= gimple_debug_bind_get_value (use_stmt
);
1259 if (walk_tree (&v
, find_non_realpart_uses
, lhs
, NULL
))
1261 gimple_debug_bind_reset_value (use_stmt
);
1262 update_stmt (use_stmt
);
1267 if (TREE_CODE (result
) == INTEGER_CST
&& TREE_OVERFLOW (result
))
1268 result
= drop_tree_overflow (result
);
1269 tree overflow
= build_zero_cst (type
);
1270 tree ctype
= build_complex_type (type
);
1271 if (TREE_CODE (result
) == INTEGER_CST
)
1272 result
= build_complex (ctype
, result
, overflow
);
1274 result
= build2_loc (gimple_location (stmt
), COMPLEX_EXPR
,
1275 ctype
, result
, overflow
);
1277 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1279 fprintf (dump_file
, "Transforming call: ");
1280 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1281 fprintf (dump_file
, "because the overflow result is never used into: ");
1282 print_generic_stmt (dump_file
, result
, TDF_SLIM
);
1283 fprintf (dump_file
, "\n");
1286 gimplify_and_update_call_from_tree (gsi
, result
);
1289 /* Returns whether the control parents of BB are preserved. */
1292 control_parents_preserved_p (basic_block bb
)
1294 /* If we marked the control parents from BB they are preserved. */
1295 if (bitmap_bit_p (visited_control_parents
, bb
->index
))
1298 /* But they can also end up being marked from elsewhere. */
1300 unsigned edge_number
;
1301 EXECUTE_IF_SET_IN_BITMAP (cd
->get_edges_dependent_on (bb
->index
),
1304 basic_block cd_bb
= cd
->get_edge_src (edge_number
);
1306 && !bitmap_bit_p (last_stmt_necessary
, cd_bb
->index
))
1309 /* And cache the result. */
1310 bitmap_set_bit (visited_control_parents
, bb
->index
);
1314 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1315 contributes nothing to the program, and can be deleted. */
1318 eliminate_unnecessary_stmts (bool aggressive
)
1320 bool something_changed
= false;
1322 gimple_stmt_iterator gsi
, psi
;
1325 auto_vec
<edge
> to_remove_edges
;
1327 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1328 fprintf (dump_file
, "\nEliminating unnecessary statements:\n");
1330 bool had_setjmp
= cfun
->calls_setjmp
;
1331 clear_special_calls ();
1333 /* Walking basic blocks and statements in reverse order avoids
1334 releasing SSA names before any other DEFs that refer to them are
1335 released. This helps avoid loss of debug information, as we get
1336 a chance to propagate all RHSs of removed SSAs into debug uses,
1337 rather than only the latest ones. E.g., consider:
1343 If we were to release x_3 before a_5, when we reached a_5 and
1344 tried to substitute it into the debug stmt, we'd see x_3 there,
1345 but x_3's DEF, type, etc would have already been disconnected.
1346 By going backwards, the debug stmt first changes to:
1348 # DEBUG a => x_3 - b_4
1352 # DEBUG a => y_1 + z_2 - b_4
1355 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
1356 auto_vec
<basic_block
> h
;
1357 h
= get_all_dominated_blocks (CDI_DOMINATORS
,
1358 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun
)));
1364 /* Remove dead statements. */
1365 auto_bitmap debug_seen
;
1366 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi
= psi
)
1368 stmt
= gsi_stmt (gsi
);
1375 /* We can mark a call to free as not necessary if the
1376 defining statement of its argument is not necessary
1377 (and thus is getting removed). */
1378 if (gimple_plf (stmt
, STMT_NECESSARY
)
1379 && (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
)
1380 || (is_gimple_call (stmt
)
1381 && gimple_call_from_new_or_delete (as_a
<gcall
*> (stmt
))
1382 && gimple_call_operator_delete_p (as_a
<gcall
*> (stmt
)))))
1384 tree ptr
= gimple_call_arg (stmt
, 0);
1385 if (TREE_CODE (ptr
) == SSA_NAME
)
1387 gimple
*def_stmt
= SSA_NAME_DEF_STMT (ptr
);
1388 if (!gimple_nop_p (def_stmt
)
1389 && !gimple_plf (def_stmt
, STMT_NECESSARY
))
1390 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
1394 /* If GSI is not necessary then remove it. */
1395 if (!gimple_plf (stmt
, STMT_NECESSARY
))
1397 /* Keep clobbers that we can keep live live. */
1398 if (gimple_clobber_p (stmt
))
1401 use_operand_p use_p
;
1403 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_USE
)
1405 tree name
= USE_FROM_PTR (use_p
);
1406 if (!SSA_NAME_IS_DEFAULT_DEF (name
)
1407 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
)))
1414 /* When doing CD-DCE we have to ensure all controls
1415 of the stmt are still live. */
1416 && (!aggressive
|| control_parents_preserved_p (bb
)))
1418 bitmap_clear (debug_seen
);
1422 if (!is_gimple_debug (stmt
))
1423 something_changed
= true;
1424 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1427 else if (is_gimple_call (stmt
))
1429 tree name
= gimple_call_lhs (stmt
);
1431 notice_special_calls (as_a
<gcall
*> (stmt
));
1433 /* When LHS of var = call (); is dead, simplify it into
1434 call (); saving one operand. */
1436 && TREE_CODE (name
) == SSA_NAME
1437 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
))
1438 /* Avoid doing so for allocation calls which we
1439 did not mark as necessary, it will confuse the
1440 special logic we apply to malloc/free pair removal. */
1441 && (!(call
= gimple_call_fndecl (stmt
))
1442 || ((DECL_BUILT_IN_CLASS (call
) != BUILT_IN_NORMAL
1443 || (DECL_FUNCTION_CODE (call
) != BUILT_IN_ALIGNED_ALLOC
1444 && DECL_FUNCTION_CODE (call
) != BUILT_IN_MALLOC
1445 && DECL_FUNCTION_CODE (call
) != BUILT_IN_CALLOC
1446 && !ALLOCA_FUNCTION_CODE_P
1447 (DECL_FUNCTION_CODE (call
))))
1448 && !DECL_IS_REPLACEABLE_OPERATOR_NEW_P (call
))))
1450 something_changed
= true;
1451 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1453 fprintf (dump_file
, "Deleting LHS of call: ");
1454 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1455 fprintf (dump_file
, "\n");
1458 gimple_call_set_lhs (stmt
, NULL_TREE
);
1459 maybe_clean_or_replace_eh_stmt (stmt
, stmt
);
1461 release_ssa_name (name
);
1463 /* GOMP_SIMD_LANE (unless three argument) or ASAN_POISON
1464 without lhs is not needed. */
1465 if (gimple_call_internal_p (stmt
))
1466 switch (gimple_call_internal_fn (stmt
))
1468 case IFN_GOMP_SIMD_LANE
:
1469 if (gimple_call_num_args (stmt
) >= 3
1470 && !integer_nonzerop (gimple_call_arg (stmt
, 2)))
1473 case IFN_ASAN_POISON
:
1474 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1480 else if (gimple_call_internal_p (stmt
))
1481 switch (gimple_call_internal_fn (stmt
))
1483 case IFN_ADD_OVERFLOW
:
1484 maybe_optimize_arith_overflow (&gsi
, PLUS_EXPR
);
1486 case IFN_SUB_OVERFLOW
:
1487 maybe_optimize_arith_overflow (&gsi
, MINUS_EXPR
);
1489 case IFN_MUL_OVERFLOW
:
1490 maybe_optimize_arith_overflow (&gsi
, MULT_EXPR
);
1493 if (integer_zerop (gimple_call_arg (stmt
, 2)))
1494 maybe_optimize_arith_overflow (&gsi
, PLUS_EXPR
);
1497 if (integer_zerop (gimple_call_arg (stmt
, 2)))
1498 maybe_optimize_arith_overflow (&gsi
, MINUS_EXPR
);
1504 else if (gimple_debug_bind_p (stmt
))
1506 /* We are only keeping the last debug-bind of a
1507 non-DEBUG_EXPR_DECL variable in a series of
1508 debug-bind stmts. */
1509 tree var
= gimple_debug_bind_get_var (stmt
);
1510 if (TREE_CODE (var
) != DEBUG_EXPR_DECL
1511 && !bitmap_set_bit (debug_seen
, DECL_UID (var
)))
1512 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1515 bitmap_clear (debug_seen
);
1518 /* Remove dead PHI nodes. */
1519 something_changed
|= remove_dead_phis (bb
);
1522 /* First remove queued edges. */
1523 if (!to_remove_edges
.is_empty ())
1525 /* Remove edges. We've delayed this to not get bogus debug stmts
1526 during PHI node removal. */
1527 for (unsigned i
= 0; i
< to_remove_edges
.length (); ++i
)
1528 remove_edge (to_remove_edges
[i
]);
1531 /* When we cleared calls_setjmp we can purge all abnormal edges. Do so.
1532 ??? We'd like to assert that setjmp calls do not pop out of nothing
1533 but we currently lack a per-stmt way of noting whether a call was
1534 recognized as returns-twice (or rather receives-control). */
1535 if (!cfun
->calls_setjmp
&& had_setjmp
)
1537 /* Make sure we only remove the edges, not dominated blocks. Using
1538 gimple_purge_dead_abnormal_call_edges would do that and we
1539 cannot free dominators yet. */
1540 FOR_EACH_BB_FN (bb
, cfun
)
1541 if (gcall
*stmt
= safe_dyn_cast
<gcall
*> (*gsi_last_bb (bb
)))
1542 if (!stmt_can_make_abnormal_goto (stmt
))
1546 for (ei
= ei_start (bb
->succs
); (e
= ei_safe_edge (ei
)); )
1548 if (e
->flags
& EDGE_ABNORMAL
)
1550 if (e
->flags
& EDGE_FALLTHRU
)
1551 e
->flags
&= ~EDGE_ABNORMAL
;
1562 /* Now remove the unreachable blocks. */
1565 basic_block prev_bb
;
1567 find_unreachable_blocks ();
1569 /* Delete all unreachable basic blocks in reverse dominator order. */
1570 for (bb
= EXIT_BLOCK_PTR_FOR_FN (cfun
)->prev_bb
;
1571 bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
); bb
= prev_bb
)
1573 prev_bb
= bb
->prev_bb
;
1575 if ((bb_contains_live_stmts
1576 && !bitmap_bit_p (bb_contains_live_stmts
, bb
->index
))
1577 || !(bb
->flags
& BB_REACHABLE
))
1579 /* Since we don't track liveness of virtual PHI nodes, it is
1580 possible that we rendered some PHI nodes unreachable while
1581 they are still in use. Mark them for renaming. */
1582 for (gphi_iterator gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
1584 if (virtual_operand_p (gimple_phi_result (gsi
.phi ())))
1587 imm_use_iterator iter
;
1589 FOR_EACH_IMM_USE_STMT (stmt
, iter
,
1590 gimple_phi_result (gsi
.phi ()))
1592 if (!(gimple_bb (stmt
)->flags
& BB_REACHABLE
))
1594 if (gimple_code (stmt
) == GIMPLE_PHI
1595 || gimple_plf (stmt
, STMT_NECESSARY
))
1602 mark_virtual_phi_result_for_renaming (gsi
.phi ());
1605 if (!(bb
->flags
& BB_REACHABLE
))
1607 /* Speed up the removal of blocks that don't
1608 dominate others. Walking backwards, this should
1609 be the common case. ??? Do we need to recompute
1610 dominators because of cfg_altered? */
1611 if (!first_dom_son (CDI_DOMINATORS
, bb
))
1612 delete_basic_block (bb
);
1615 h
= get_all_dominated_blocks (CDI_DOMINATORS
, bb
);
1620 prev_bb
= bb
->prev_bb
;
1621 /* Rearrangements to the CFG may have failed
1622 to update the dominators tree, so that
1623 formerly-dominated blocks are now
1624 otherwise reachable. */
1625 if (!!(bb
->flags
& BB_REACHABLE
))
1627 delete_basic_block (bb
);
1638 free (bb_postorder
);
1639 bb_postorder
= NULL
;
1641 return something_changed
;
1645 /* Print out removed statement statistics. */
1652 percg
= ((float) stats
.removed
/ (float) stats
.total
) * 100;
1653 fprintf (dump_file
, "Removed %d of %d statements (%d%%)\n",
1654 stats
.removed
, stats
.total
, (int) percg
);
1656 if (stats
.total_phis
== 0)
1659 percg
= ((float) stats
.removed_phis
/ (float) stats
.total_phis
) * 100;
1661 fprintf (dump_file
, "Removed %d of %d PHI nodes (%d%%)\n",
1662 stats
.removed_phis
, stats
.total_phis
, (int) percg
);
1665 /* Initialization for this pass. Set up the used data structures. */
1668 tree_dce_init (bool aggressive
)
1670 memset ((void *) &stats
, 0, sizeof (stats
));
1674 last_stmt_necessary
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1675 bitmap_clear (last_stmt_necessary
);
1676 bb_contains_live_stmts
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1677 bitmap_clear (bb_contains_live_stmts
);
1680 processed
= sbitmap_alloc (num_ssa_names
+ 1);
1681 bitmap_clear (processed
);
1683 worklist
.create (64);
1684 cfg_altered
= false;
1687 /* Cleanup after this pass. */
1690 tree_dce_done (bool aggressive
)
1695 sbitmap_free (visited_control_parents
);
1696 sbitmap_free (last_stmt_necessary
);
1697 sbitmap_free (bb_contains_live_stmts
);
1698 bb_contains_live_stmts
= NULL
;
1701 sbitmap_free (processed
);
1703 worklist
.release ();
1706 /* Sort PHI argument values for make_forwarders_with_degenerate_phis. */
1709 sort_phi_args (const void *a_
, const void *b_
)
1711 auto *a
= (const std::pair
<edge
, hashval_t
> *) a_
;
1712 auto *b
= (const std::pair
<edge
, hashval_t
> *) b_
;
1713 hashval_t ha
= a
->second
;
1714 hashval_t hb
= b
->second
;
1719 else if (a
->first
->dest_idx
< b
->first
->dest_idx
)
1721 else if (a
->first
->dest_idx
> b
->first
->dest_idx
)
1727 /* Look for a non-virtual PHIs and make a forwarder block when all PHIs
1728 have the same argument on a set of edges. This is to not consider
1729 control dependences of individual edges for same values but only for
1733 make_forwarders_with_degenerate_phis (function
*fn
)
1738 FOR_EACH_BB_FN (bb
, fn
)
1740 /* Only PHIs with three or more arguments have opportunities. */
1741 if (EDGE_COUNT (bb
->preds
) < 3)
1743 /* Do not touch loop headers or blocks with abnormal predecessors.
1744 ??? This is to avoid creating valid loops here, see PR103458.
1745 We might want to improve things to either explicitely add those
1746 loops or at least consider blocks with no backedges. */
1747 if (bb
->loop_father
->header
== bb
1748 || bb_has_abnormal_pred (bb
))
1751 /* Take one PHI node as template to look for identical
1752 arguments. Build a vector of candidates forming sets
1753 of argument edges with equal values. Note optimality
1754 depends on the particular choice of the template PHI
1755 since equal arguments are unordered leaving other PHIs
1756 with more than one set of equal arguments within this
1757 argument range unsorted. We'd have to break ties by
1758 looking at other PHI nodes. */
1759 gphi_iterator gsi
= gsi_start_nonvirtual_phis (bb
);
1760 if (gsi_end_p (gsi
))
1762 gphi
*phi
= gsi
.phi ();
1763 auto_vec
<std::pair
<edge
, hashval_t
>, 8> args
;
1764 bool need_resort
= false;
1765 for (unsigned i
= 0; i
< gimple_phi_num_args (phi
); ++i
)
1767 edge e
= gimple_phi_arg_edge (phi
, i
);
1768 /* Skip abnormal edges since we cannot redirect them. */
1769 if (e
->flags
& EDGE_ABNORMAL
)
1771 /* Skip loop exit edges when we are in loop-closed SSA form
1772 since the forwarder we'd create does not have a PHI node. */
1773 if (loops_state_satisfies_p (LOOP_CLOSED_SSA
)
1774 && loop_exit_edge_p (e
->src
->loop_father
, e
))
1777 tree arg
= gimple_phi_arg_def (phi
, i
);
1778 if (!CONSTANT_CLASS_P (arg
) && TREE_CODE (arg
) != SSA_NAME
)
1780 args
.safe_push (std::make_pair (e
, iterative_hash_expr (arg
, 0)));
1782 if (args
.length () < 2)
1784 args
.qsort (sort_phi_args
);
1785 /* The above sorting can be different between -g and -g0, as e.g. decls
1786 can have different uids (-g could have bigger gaps in between them).
1787 So, only use that to determine which args are equal, then change
1788 second from hash value to smallest dest_idx of the edges which have
1789 equal argument and sort again. If all the phi arguments are
1790 constants or SSA_NAME, there is no need for the second sort, the hash
1791 values are stable in that case. */
1792 hashval_t hash
= args
[0].second
;
1793 args
[0].second
= args
[0].first
->dest_idx
;
1794 bool any_equal
= false;
1795 for (unsigned i
= 1; i
< args
.length (); ++i
)
1796 if (hash
== args
[i
].second
1797 && operand_equal_p (PHI_ARG_DEF_FROM_EDGE (phi
, args
[i
- 1].first
),
1798 PHI_ARG_DEF_FROM_EDGE (phi
, args
[i
].first
)))
1800 args
[i
].second
= args
[i
- 1].second
;
1805 hash
= args
[i
].second
;
1806 args
[i
].second
= args
[i
].first
->dest_idx
;
1811 args
.qsort (sort_phi_args
);
1813 /* From the candidates vector now verify true candidates for
1814 forwarders and create them. */
1815 gphi
*vphi
= get_virtual_phi (bb
);
1817 while (start
< args
.length () - 1)
1820 for (i
= start
+ 1; i
< args
.length (); ++i
)
1821 if (args
[start
].second
!= args
[i
].second
)
1823 /* args[start]..args[i-1] are equal. */
1826 /* Check all PHI nodes for argument equality. */
1828 gphi_iterator gsi2
= gsi
;
1830 for (; !gsi_end_p (gsi2
); gsi_next (&gsi2
))
1832 gphi
*phi2
= gsi2
.phi ();
1833 if (virtual_operand_p (gimple_phi_result (phi2
)))
1836 = PHI_ARG_DEF_FROM_EDGE (phi2
, args
[start
].first
);
1837 for (unsigned j
= start
+ 1; j
< i
; ++j
)
1839 if (!operand_equal_p (start_arg
,
1840 PHI_ARG_DEF_FROM_EDGE
1841 (phi2
, args
[j
].first
)))
1843 /* Another PHI might have a shorter set of
1844 equivalent args. Go for that. */
1856 /* If we are asked to forward all edges the block
1857 has all degenerate PHIs. Do nothing in that case. */
1859 && i
== args
.length ()
1860 && args
.length () == gimple_phi_num_args (phi
))
1862 /* Instead of using make_forwarder_block we are
1863 rolling our own variant knowing that the forwarder
1864 does not need PHI nodes apart from eventually
1866 auto_vec
<tree
, 8> vphi_args
;
1869 vphi_args
.reserve_exact (i
- start
);
1870 for (unsigned j
= start
; j
< i
; ++j
)
1871 vphi_args
.quick_push
1872 (PHI_ARG_DEF_FROM_EDGE (vphi
, args
[j
].first
));
1874 free_dominance_info (fn
, CDI_DOMINATORS
);
1875 basic_block forwarder
= split_edge (args
[start
].first
);
1876 profile_count count
= profile_count::zero ();
1877 for (unsigned j
= start
+ 1; j
< i
; ++j
)
1879 edge e
= args
[j
].first
;
1880 redirect_edge_and_branch_force (e
, forwarder
);
1881 redirect_edge_var_map_clear (e
);
1882 count
+= e
->count ();
1884 forwarder
->count
= count
;
1887 tree def
= copy_ssa_name (vphi_args
[0]);
1888 gphi
*vphi_copy
= create_phi_node (def
, forwarder
);
1889 for (unsigned j
= start
; j
< i
; ++j
)
1890 add_phi_arg (vphi_copy
, vphi_args
[j
- start
],
1891 args
[j
].first
, UNKNOWN_LOCATION
);
1893 (vphi
, single_succ_edge (forwarder
)->dest_idx
, def
);
1895 todo
|= TODO_cleanup_cfg
;
1898 /* Continue searching for more opportunities. */
1905 /* Main routine to eliminate dead code.
1907 AGGRESSIVE controls the aggressiveness of the algorithm.
1908 In conservative mode, we ignore control dependence and simply declare
1909 all but the most trivially dead branches necessary. This mode is fast.
1910 In aggressive mode, control dependences are taken into account, which
1911 results in more dead code elimination, but at the cost of some time.
1913 FIXME: Aggressive mode before PRE doesn't work currently because
1914 the dominance info is not invalidated after DCE1. This is
1915 not an issue right now because we only run aggressive DCE
1916 as the last tree SSA pass, but keep this in mind when you
1917 start experimenting with pass ordering. */
1920 perform_tree_ssa_dce (bool aggressive
)
1922 bool something_changed
= 0;
1925 /* Preheaders are needed for SCEV to work.
1926 Simple lateches and recorded exits improve chances that loop will
1927 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1928 bool in_loop_pipeline
= scev_initialized_p ();
1929 if (aggressive
&& ! in_loop_pipeline
)
1931 loop_optimizer_init (LOOPS_NORMAL
1932 | LOOPS_HAVE_RECORDED_EXITS
);
1937 todo
|= make_forwarders_with_degenerate_phis (cfun
);
1939 calculate_dominance_info (CDI_DOMINATORS
);
1941 tree_dce_init (aggressive
);
1945 /* Compute control dependence. */
1946 calculate_dominance_info (CDI_POST_DOMINATORS
);
1947 cd
= new control_dependences ();
1949 visited_control_parents
=
1950 sbitmap_alloc (last_basic_block_for_fn (cfun
));
1951 bitmap_clear (visited_control_parents
);
1953 mark_dfs_back_edges ();
1956 find_obviously_necessary_stmts (aggressive
);
1958 if (aggressive
&& ! in_loop_pipeline
)
1961 loop_optimizer_finalize ();
1968 visited
= BITMAP_ALLOC (NULL
);
1969 propagate_necessity (aggressive
);
1970 BITMAP_FREE (visited
);
1972 something_changed
|= eliminate_unnecessary_stmts (aggressive
);
1973 something_changed
|= cfg_altered
;
1975 /* We do not update postdominators, so free them unconditionally. */
1976 free_dominance_info (CDI_POST_DOMINATORS
);
1978 /* If we removed paths in the CFG, then we need to update
1979 dominators as well. I haven't investigated the possibility
1980 of incrementally updating dominators. */
1982 free_dominance_info (CDI_DOMINATORS
);
1984 statistics_counter_event (cfun
, "Statements deleted", stats
.removed
);
1985 statistics_counter_event (cfun
, "PHI nodes deleted", stats
.removed_phis
);
1987 /* Debugging dumps. */
1988 if (dump_file
&& (dump_flags
& (TDF_STATS
|TDF_DETAILS
)))
1991 tree_dce_done (aggressive
);
1993 if (something_changed
)
1995 free_numbers_of_iterations_estimates (cfun
);
1996 if (in_loop_pipeline
)
1998 todo
|= TODO_update_ssa
| TODO_cleanup_cfg
;
2003 /* Pass entry points. */
2007 return perform_tree_ssa_dce (/*aggressive=*/false);
2011 tree_ssa_cd_dce (void)
2013 return perform_tree_ssa_dce (/*aggressive=*/optimize
>= 2);
2018 const pass_data pass_data_dce
=
2020 GIMPLE_PASS
, /* type */
2022 OPTGROUP_NONE
, /* optinfo_flags */
2023 TV_TREE_DCE
, /* tv_id */
2024 ( PROP_cfg
| PROP_ssa
), /* properties_required */
2025 0, /* properties_provided */
2026 0, /* properties_destroyed */
2027 0, /* todo_flags_start */
2028 0, /* todo_flags_finish */
2031 class pass_dce
: public gimple_opt_pass
2034 pass_dce (gcc::context
*ctxt
)
2035 : gimple_opt_pass (pass_data_dce
, ctxt
), update_address_taken_p (false)
2038 /* opt_pass methods: */
2039 opt_pass
* clone () final override
{ return new pass_dce (m_ctxt
); }
2040 void set_pass_param (unsigned n
, bool param
) final override
2042 gcc_assert (n
== 0);
2043 update_address_taken_p
= param
;
2045 bool gate (function
*) final override
{ return flag_tree_dce
!= 0; }
2046 unsigned int execute (function
*) final override
2048 return (tree_ssa_dce ()
2049 | (update_address_taken_p
? TODO_update_address_taken
: 0));
2053 bool update_address_taken_p
;
2054 }; // class pass_dce
2059 make_pass_dce (gcc::context
*ctxt
)
2061 return new pass_dce (ctxt
);
2066 const pass_data pass_data_cd_dce
=
2068 GIMPLE_PASS
, /* type */
2070 OPTGROUP_NONE
, /* optinfo_flags */
2071 TV_TREE_CD_DCE
, /* tv_id */
2072 ( PROP_cfg
| PROP_ssa
), /* properties_required */
2073 0, /* properties_provided */
2074 0, /* properties_destroyed */
2075 0, /* todo_flags_start */
2076 0, /* todo_flags_finish */
2079 class pass_cd_dce
: public gimple_opt_pass
2082 pass_cd_dce (gcc::context
*ctxt
)
2083 : gimple_opt_pass (pass_data_cd_dce
, ctxt
), update_address_taken_p (false)
2086 /* opt_pass methods: */
2087 opt_pass
* clone () final override
{ return new pass_cd_dce (m_ctxt
); }
2088 void set_pass_param (unsigned n
, bool param
) final override
2090 gcc_assert (n
== 0);
2091 update_address_taken_p
= param
;
2093 bool gate (function
*) final override
{ return flag_tree_dce
!= 0; }
2094 unsigned int execute (function
*) final override
2096 return (tree_ssa_cd_dce ()
2097 | (update_address_taken_p
? TODO_update_address_taken
: 0));
2101 bool update_address_taken_p
;
2102 }; // class pass_cd_dce
2107 make_pass_cd_dce (gcc::context
*ctxt
)
2109 return new pass_cd_dce (ctxt
);
2113 /* A cheap DCE interface. WORKLIST is a list of possibly dead stmts and
2114 is consumed by this function. The function has linear complexity in
2115 the number of dead stmts with a constant factor like the average SSA
2116 use operands number. */
2119 simple_dce_from_worklist (bitmap worklist
, bitmap need_eh_cleanup
)
2122 int stmtremoved
= 0;
2123 while (! bitmap_empty_p (worklist
))
2126 unsigned i
= bitmap_clear_first_set_bit (worklist
);
2128 tree def
= ssa_name (i
);
2129 /* Removed by somebody else or still in use.
2130 Note use in itself for a phi node is not counted as still in use. */
2133 if (!has_zero_uses (def
))
2135 gimple
*def_stmt
= SSA_NAME_DEF_STMT (def
);
2137 if (gimple_code (def_stmt
) != GIMPLE_PHI
)
2141 imm_use_iterator use_iter
;
2142 bool canremove
= true;
2144 FOR_EACH_IMM_USE_STMT (use_stmt
, use_iter
, def
)
2146 /* Ignore debug statements. */
2147 if (is_gimple_debug (use_stmt
))
2149 if (use_stmt
!= def_stmt
)
2159 gimple
*t
= SSA_NAME_DEF_STMT (def
);
2160 if (gimple_has_side_effects (t
))
2163 /* The defining statement needs to be defining only this name.
2164 ASM is the only statement that can define more than one
2167 && !single_ssa_def_operand (t
, SSA_OP_ALL_DEFS
))
2170 /* Don't remove statements that are needed for non-call
2172 if (stmt_unremovable_because_of_non_call_eh_p (cfun
, t
))
2175 /* Tell the caller that we removed a statement that might
2176 throw so it could cleanup the cfg for that block. */
2177 if (need_eh_cleanup
&& stmt_could_throw_p (cfun
, t
))
2178 bitmap_set_bit (need_eh_cleanup
, gimple_bb (t
)->index
);
2180 /* Add uses to the worklist. */
2182 use_operand_p use_p
;
2183 FOR_EACH_PHI_OR_STMT_USE (use_p
, t
, iter
, SSA_OP_USE
)
2185 tree use
= USE_FROM_PTR (use_p
);
2186 if (TREE_CODE (use
) == SSA_NAME
2187 && ! SSA_NAME_IS_DEFAULT_DEF (use
))
2188 bitmap_set_bit (worklist
, SSA_NAME_VERSION (use
));
2192 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
2194 fprintf (dump_file
, "Removing dead stmt:");
2195 print_gimple_stmt (dump_file
, t
, 0);
2197 gimple_stmt_iterator gsi
= gsi_for_stmt (t
);
2198 if (gimple_code (t
) == GIMPLE_PHI
)
2200 remove_phi_node (&gsi
, true);
2205 unlink_stmt_vdef (t
);
2206 gsi_remove (&gsi
, true);
2211 statistics_counter_event (cfun
, "PHIs removed",
2213 statistics_counter_event (cfun
, "Statements removed",