1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002-2022 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 tree callee
= gimple_call_fndecl (stmt
);
225 if (callee
!= NULL_TREE
226 && fndecl_built_in_p (callee
, BUILT_IN_NORMAL
))
227 switch (DECL_FUNCTION_CODE (callee
))
229 case BUILT_IN_MALLOC
:
230 case BUILT_IN_ALIGNED_ALLOC
:
231 case BUILT_IN_CALLOC
:
232 CASE_BUILT_IN_ALLOCA
:
233 case BUILT_IN_STRDUP
:
234 case BUILT_IN_STRNDUP
:
235 case BUILT_IN_GOMP_ALLOC
:
241 if (callee
!= NULL_TREE
242 && flag_allocation_dce
243 && DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
))
246 /* IFN_GOACC_LOOP calls are necessary in that they are used to
247 represent parameter (i.e. step, bound) of a lowered OpenACC
248 partitioned loop. But this kind of partitioned loop might not
249 survive from aggressive loop removal for it has loop exit and
250 is assumed to be finite. Therefore, we need to explicitly mark
251 these calls. (An example is libgomp.oacc-c-c++-common/pr84955.c) */
252 if (gimple_call_internal_p (stmt
, IFN_GOACC_LOOP
))
254 mark_stmt_necessary (stmt
, true);
261 /* Debug temps without a value are not useful. ??? If we could
262 easily locate the debug temp bind stmt for a use thereof,
263 would could refrain from marking all debug temps here, and
264 mark them only if they're used. */
265 if (gimple_debug_nonbind_marker_p (stmt
)
266 || !gimple_debug_bind_p (stmt
)
267 || gimple_debug_bind_has_value_p (stmt
)
268 || TREE_CODE (gimple_debug_bind_get_var (stmt
)) != DEBUG_EXPR_DECL
)
269 mark_stmt_necessary (stmt
, false);
273 gcc_assert (!simple_goto_p (stmt
));
274 mark_stmt_necessary (stmt
, true);
278 gcc_assert (EDGE_COUNT (gimple_bb (stmt
)->succs
) == 2);
283 mark_stmt_necessary (stmt
, true);
287 /* Mark indirect CLOBBERs to be lazily removed if their SSA operands
288 do not prevail. That also makes control flow leading to them
289 not necessary in aggressive mode. */
290 if (gimple_clobber_p (stmt
) && !zero_ssa_operands (stmt
, SSA_OP_USE
))
298 /* If the statement has volatile operands, it needs to be preserved.
299 Same for statements that can alter control flow in unpredictable
301 if (gimple_has_side_effects (stmt
) || is_ctrl_altering_stmt (stmt
))
303 mark_stmt_necessary (stmt
, true);
307 /* If a statement could throw, it can be deemed necessary unless we
308 are allowed to remove dead EH. Test this after checking for
309 new/delete operators since we always elide their EH. */
310 if (!cfun
->can_delete_dead_exceptions
311 && stmt_could_throw_p (cfun
, stmt
))
313 mark_stmt_necessary (stmt
, true);
317 if ((gimple_vdef (stmt
) && keep_all_vdefs_p ())
318 || stmt_may_clobber_global_p (stmt
, false))
320 mark_stmt_necessary (stmt
, true);
328 /* Mark the last statement of BB as necessary. */
331 mark_last_stmt_necessary (basic_block bb
)
333 gimple
*stmt
= last_stmt (bb
);
335 bitmap_set_bit (last_stmt_necessary
, bb
->index
);
336 bitmap_set_bit (bb_contains_live_stmts
, bb
->index
);
338 /* We actually mark the statement only if it is a control statement. */
339 if (stmt
&& is_ctrl_stmt (stmt
))
340 mark_stmt_necessary (stmt
, true);
344 /* Mark control dependent edges of BB as necessary. We have to do this only
345 once for each basic block so we set the appropriate bit after we're done.
347 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
350 mark_control_dependent_edges_necessary (basic_block bb
, bool ignore_self
)
353 unsigned edge_number
;
354 bool skipped
= false;
356 gcc_assert (bb
!= EXIT_BLOCK_PTR_FOR_FN (cfun
));
358 if (bb
== ENTRY_BLOCK_PTR_FOR_FN (cfun
))
361 EXECUTE_IF_SET_IN_BITMAP (cd
->get_edges_dependent_on (bb
->index
),
364 basic_block cd_bb
= cd
->get_edge_src (edge_number
);
366 if (ignore_self
&& cd_bb
== bb
)
372 if (!bitmap_bit_p (last_stmt_necessary
, cd_bb
->index
))
373 mark_last_stmt_necessary (cd_bb
);
377 bitmap_set_bit (visited_control_parents
, bb
->index
);
381 /* Find obviously necessary statements. These are things like most function
382 calls, and stores to file level variables.
384 If EL is NULL, control statements are conservatively marked as
385 necessary. Otherwise it contains the list of edges used by control
386 dependence analysis. */
389 find_obviously_necessary_stmts (bool aggressive
)
392 gimple_stmt_iterator gsi
;
397 FOR_EACH_BB_FN (bb
, cfun
)
399 /* PHI nodes are never inherently necessary. */
400 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
402 phi
= gsi_stmt (gsi
);
403 gimple_set_plf (phi
, STMT_NECESSARY
, false);
406 /* Check all statements in the block. */
407 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
409 stmt
= gsi_stmt (gsi
);
410 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
411 mark_stmt_if_obviously_necessary (stmt
, aggressive
);
415 /* Pure and const functions are finite and thus have no infinite loops in
417 flags
= flags_from_decl_or_type (current_function_decl
);
418 if ((flags
& (ECF_CONST
|ECF_PURE
)) && !(flags
& ECF_LOOPING_CONST_OR_PURE
))
421 /* Prevent the empty possibly infinite loops from being removed. This is
422 needed to make the logic in remove_dead_stmt work to identify the
423 correct edge to keep when removing a controlling condition. */
426 if (mark_irreducible_loops ())
427 FOR_EACH_BB_FN (bb
, cfun
)
430 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
431 if ((e
->flags
& EDGE_DFS_BACK
)
432 && (e
->flags
& EDGE_IRREDUCIBLE_LOOP
))
435 fprintf (dump_file
, "Marking back edge of irreducible "
436 "loop %i->%i\n", e
->src
->index
, e
->dest
->index
);
437 mark_control_dependent_edges_necessary (e
->dest
, false);
441 for (auto loop
: loops_list (cfun
, 0))
442 /* For loops without an exit do not mark any condition. */
443 if (loop
->exits
->next
->e
&& !finite_loop_p (loop
))
446 fprintf (dump_file
, "cannot prove finiteness of loop %i\n",
448 mark_control_dependent_edges_necessary (loop
->latch
, false);
454 /* Return true if REF is based on an aliased base, otherwise false. */
457 ref_may_be_aliased (tree ref
)
459 gcc_assert (TREE_CODE (ref
) != WITH_SIZE_EXPR
);
460 while (handled_component_p (ref
))
461 ref
= TREE_OPERAND (ref
, 0);
462 if ((TREE_CODE (ref
) == MEM_REF
|| TREE_CODE (ref
) == TARGET_MEM_REF
)
463 && TREE_CODE (TREE_OPERAND (ref
, 0)) == ADDR_EXPR
)
464 ref
= TREE_OPERAND (TREE_OPERAND (ref
, 0), 0);
465 return !(DECL_P (ref
)
466 && !may_be_aliased (ref
));
469 static bitmap visited
= NULL
;
470 static unsigned int longest_chain
= 0;
471 static unsigned int total_chain
= 0;
472 static unsigned int nr_walks
= 0;
473 static bool chain_ovfl
= false;
475 /* Worker for the walker that marks reaching definitions of REF,
476 which is based on a non-aliased decl, necessary. It returns
477 true whenever the defining statement of the current VDEF is
478 a kill for REF, as no dominating may-defs are necessary for REF
479 anymore. DATA points to the basic-block that contains the
480 stmt that refers to REF. */
483 mark_aliased_reaching_defs_necessary_1 (ao_ref
*ref
, tree vdef
, void *data
)
485 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
487 /* All stmts we visit are necessary. */
488 if (! gimple_clobber_p (def_stmt
))
489 mark_operand_necessary (vdef
);
491 /* If the stmt lhs kills ref, then we can stop walking. */
492 if (gimple_has_lhs (def_stmt
)
493 && TREE_CODE (gimple_get_lhs (def_stmt
)) != SSA_NAME
494 /* The assignment is not necessarily carried out if it can throw
495 and we can catch it in the current function where we could inspect
497 ??? We only need to care about the RHS throwing. For aggregate
498 assignments or similar calls and non-call exceptions the LHS
499 might throw as well. */
500 && !stmt_can_throw_internal (cfun
, def_stmt
))
502 tree base
, lhs
= gimple_get_lhs (def_stmt
);
503 poly_int64 size
, offset
, max_size
;
507 = get_ref_base_and_extent (lhs
, &offset
, &size
, &max_size
, &reverse
);
508 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
509 so base == refd->base does not always hold. */
510 if (base
== ref
->base
)
512 /* For a must-alias check we need to be able to constrain
513 the accesses properly. */
514 if (known_eq (size
, max_size
)
515 && known_subrange_p (ref
->offset
, ref
->max_size
, offset
, size
))
517 /* Or they need to be exactly the same. */
519 /* Make sure there is no induction variable involved
520 in the references (gcc.c-torture/execute/pr42142.c).
521 The simplest way is to check if the kill dominates
523 /* But when both are in the same block we cannot
524 easily tell whether we came from a backedge
525 unless we decide to compute stmt UIDs
527 && (basic_block
) data
!= gimple_bb (def_stmt
)
528 && dominated_by_p (CDI_DOMINATORS
, (basic_block
) data
,
529 gimple_bb (def_stmt
))
530 && operand_equal_p (ref
->ref
, lhs
, 0))
535 /* Otherwise keep walking. */
540 mark_aliased_reaching_defs_necessary (gimple
*stmt
, tree ref
)
542 /* Should have been caught before calling this function. */
543 gcc_checking_assert (!keep_all_vdefs_p ());
547 gcc_assert (!chain_ovfl
);
548 ao_ref_init (&refd
, ref
);
549 chain
= walk_aliased_vdefs (&refd
, gimple_vuse (stmt
),
550 mark_aliased_reaching_defs_necessary_1
,
551 gimple_bb (stmt
), NULL
);
552 if (chain
> longest_chain
)
553 longest_chain
= chain
;
554 total_chain
+= chain
;
558 /* Worker for the walker that marks reaching definitions of REF, which
559 is not based on a non-aliased decl. For simplicity we need to end
560 up marking all may-defs necessary that are not based on a non-aliased
561 decl. The only job of this walker is to skip may-defs based on
562 a non-aliased decl. */
565 mark_all_reaching_defs_necessary_1 (ao_ref
*ref ATTRIBUTE_UNUSED
,
566 tree vdef
, void *data ATTRIBUTE_UNUSED
)
568 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
570 /* We have to skip already visited (and thus necessary) statements
571 to make the chaining work after we dropped back to simple mode. */
573 && bitmap_bit_p (processed
, SSA_NAME_VERSION (vdef
)))
575 gcc_assert (gimple_nop_p (def_stmt
)
576 || gimple_plf (def_stmt
, STMT_NECESSARY
));
580 /* We want to skip stores to non-aliased variables. */
582 && gimple_assign_single_p (def_stmt
))
584 tree lhs
= gimple_assign_lhs (def_stmt
);
585 if (!ref_may_be_aliased (lhs
))
589 /* We want to skip statments that do not constitute stores but have
590 a virtual definition. */
591 if (gcall
*call
= dyn_cast
<gcall
*> (def_stmt
))
593 tree callee
= gimple_call_fndecl (call
);
594 if (callee
!= NULL_TREE
595 && fndecl_built_in_p (callee
, BUILT_IN_NORMAL
))
596 switch (DECL_FUNCTION_CODE (callee
))
598 case BUILT_IN_MALLOC
:
599 case BUILT_IN_ALIGNED_ALLOC
:
600 case BUILT_IN_CALLOC
:
601 CASE_BUILT_IN_ALLOCA
:
603 case BUILT_IN_GOMP_ALLOC
:
604 case BUILT_IN_GOMP_FREE
:
610 if (callee
!= NULL_TREE
611 && (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
)
612 || DECL_IS_OPERATOR_DELETE_P (callee
))
613 && gimple_call_from_new_or_delete (call
))
617 if (! gimple_clobber_p (def_stmt
))
618 mark_operand_necessary (vdef
);
624 mark_all_reaching_defs_necessary (gimple
*stmt
)
626 /* Should have been caught before calling this function. */
627 gcc_checking_assert (!keep_all_vdefs_p ());
628 walk_aliased_vdefs (NULL
, gimple_vuse (stmt
),
629 mark_all_reaching_defs_necessary_1
, NULL
, &visited
);
632 /* Return true for PHI nodes with one or identical arguments
635 degenerate_phi_p (gimple
*phi
)
638 tree op
= gimple_phi_arg_def (phi
, 0);
639 for (i
= 1; i
< gimple_phi_num_args (phi
); i
++)
640 if (gimple_phi_arg_def (phi
, i
) != op
)
645 /* Return that NEW_CALL and DELETE_CALL are a valid pair of new
646 and delete operators. */
649 valid_new_delete_pair_p (gimple
*new_call
, gimple
*delete_call
)
651 tree new_asm
= DECL_ASSEMBLER_NAME (gimple_call_fndecl (new_call
));
652 tree delete_asm
= DECL_ASSEMBLER_NAME (gimple_call_fndecl (delete_call
));
653 return valid_new_delete_pair_p (new_asm
, delete_asm
);
656 /* Propagate necessity using the operands of necessary statements.
657 Process the uses on each statement in the worklist, and add all
658 feeding statements which contribute to the calculation of this
659 value to the worklist.
661 In conservative mode, EL is NULL. */
664 propagate_necessity (bool aggressive
)
668 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
669 fprintf (dump_file
, "\nProcessing worklist:\n");
671 while (worklist
.length () > 0)
673 /* Take STMT from worklist. */
674 stmt
= worklist
.pop ();
676 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
678 fprintf (dump_file
, "processing: ");
679 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
680 fprintf (dump_file
, "\n");
685 /* Mark the last statement of the basic blocks on which the block
686 containing STMT is control dependent, but only if we haven't
688 basic_block bb
= gimple_bb (stmt
);
689 if (bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
690 && !bitmap_bit_p (visited_control_parents
, bb
->index
))
691 mark_control_dependent_edges_necessary (bb
, false);
694 if (gimple_code (stmt
) == GIMPLE_PHI
695 /* We do not process virtual PHI nodes nor do we track their
697 && !virtual_operand_p (gimple_phi_result (stmt
)))
699 /* PHI nodes are somewhat special in that each PHI alternative has
700 data and control dependencies. All the statements feeding the
701 PHI node's arguments are always necessary. In aggressive mode,
702 we also consider the control dependent edges leading to the
703 predecessor block associated with each PHI alternative as
705 gphi
*phi
= as_a
<gphi
*> (stmt
);
708 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
710 tree arg
= PHI_ARG_DEF (stmt
, k
);
711 if (TREE_CODE (arg
) == SSA_NAME
)
712 mark_operand_necessary (arg
);
715 /* For PHI operands it matters from where the control flow arrives
716 to the BB. Consider the following example:
726 We need to mark control dependence of the empty basic blocks, since they
727 contains computation of PHI operands.
729 Doing so is too restrictive in the case the predecestor block is in
735 for (i = 0; i<1000; ++i)
741 There is PHI for J in the BB containing return statement.
742 In this case the control dependence of predecestor block (that is
743 within the empty loop) also contains the block determining number
744 of iterations of the block that would prevent removing of empty
747 This scenario can be avoided by splitting critical edges.
748 To save the critical edge splitting pass we identify how the control
749 dependence would look like if the edge was split.
751 Consider the modified CFG created from current CFG by splitting
752 edge B->C. In the postdominance tree of modified CFG, C' is
753 always child of C. There are two cases how chlids of C' can look
758 In this case the only basic block C' is control dependent on is B.
760 2) C' has single child that is B
762 In this case control dependence of C' is same as control
763 dependence of B in original CFG except for block B itself.
764 (since C' postdominate B in modified CFG)
766 Now how to decide what case happens? There are two basic options:
768 a) C postdominate B. Then C immediately postdominate B and
769 case 2 happens iff there is no other way from B to C except
772 There is other way from B to C iff there is succesor of B that
773 is not postdominated by B. Testing this condition is somewhat
774 expensive, because we need to iterate all succesors of B.
775 We are safe to assume that this does not happen: we will mark B
776 as needed when processing the other path from B to C that is
777 conrol dependent on B and marking control dependencies of B
778 itself is harmless because they will be processed anyway after
779 processing control statement in B.
781 b) C does not postdominate B. Always case 1 happens since there is
782 path from C to exit that does not go through B and thus also C'. */
784 if (aggressive
&& !degenerate_phi_p (stmt
))
786 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
788 basic_block arg_bb
= gimple_phi_arg_edge (phi
, k
)->src
;
791 != get_immediate_dominator (CDI_POST_DOMINATORS
, arg_bb
))
793 if (!bitmap_bit_p (last_stmt_necessary
, arg_bb
->index
))
794 mark_last_stmt_necessary (arg_bb
);
796 else if (arg_bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
797 && !bitmap_bit_p (visited_control_parents
,
799 mark_control_dependent_edges_necessary (arg_bb
, true);
805 /* Propagate through the operands. Examine all the USE, VUSE and
806 VDEF operands in this statement. Mark all the statements
807 which feed this statement's uses as necessary. */
811 /* If this is a call to free which is directly fed by an
812 allocation function do not mark that necessary through
813 processing the argument. */
814 bool is_delete_operator
815 = (is_gimple_call (stmt
)
816 && gimple_call_from_new_or_delete (as_a
<gcall
*> (stmt
))
817 && gimple_call_operator_delete_p (as_a
<gcall
*> (stmt
)));
818 if (is_delete_operator
819 || gimple_call_builtin_p (stmt
, BUILT_IN_FREE
)
820 || gimple_call_builtin_p (stmt
, BUILT_IN_GOMP_FREE
))
822 tree ptr
= gimple_call_arg (stmt
, 0);
825 /* If the pointer we free is defined by an allocation
826 function do not add the call to the worklist. */
827 if (TREE_CODE (ptr
) == SSA_NAME
828 && (def_stmt
= dyn_cast
<gcall
*> (SSA_NAME_DEF_STMT (ptr
)))
829 && (def_callee
= gimple_call_fndecl (def_stmt
))
830 && ((DECL_BUILT_IN_CLASS (def_callee
) == BUILT_IN_NORMAL
831 && (DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_ALIGNED_ALLOC
832 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_MALLOC
833 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_CALLOC
834 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_GOMP_ALLOC
))
835 || (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (def_callee
)
836 && gimple_call_from_new_or_delete (def_stmt
))))
838 if (is_delete_operator
839 && !valid_new_delete_pair_p (def_stmt
, stmt
))
840 mark_operand_necessary (gimple_call_arg (stmt
, 0));
842 /* Delete operators can have alignment and (or) size
843 as next arguments. When being a SSA_NAME, they
844 must be marked as necessary. Similarly GOMP_free. */
845 if (gimple_call_num_args (stmt
) >= 2)
846 for (unsigned i
= 1; i
< gimple_call_num_args (stmt
);
849 tree arg
= gimple_call_arg (stmt
, i
);
850 if (TREE_CODE (arg
) == SSA_NAME
)
851 mark_operand_necessary (arg
);
858 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
859 mark_operand_necessary (use
);
861 use
= gimple_vuse (stmt
);
865 /* No need to search for vdefs if we intrinsicly keep them all. */
866 if (keep_all_vdefs_p ())
869 /* If we dropped to simple mode make all immediately
870 reachable definitions necessary. */
873 mark_all_reaching_defs_necessary (stmt
);
877 /* For statements that may load from memory (have a VUSE) we
878 have to mark all reaching (may-)definitions as necessary.
879 We partition this task into two cases:
880 1) explicit loads based on decls that are not aliased
881 2) implicit loads (like calls) and explicit loads not
882 based on decls that are not aliased (like indirect
883 references or loads from globals)
884 For 1) we mark all reaching may-defs as necessary, stopping
885 at dominating kills. For 2) we want to mark all dominating
886 references necessary, but non-aliased ones which we handle
887 in 1). By keeping a global visited bitmap for references
888 we walk for 2) we avoid quadratic behavior for those. */
890 if (gcall
*call
= dyn_cast
<gcall
*> (stmt
))
892 tree callee
= gimple_call_fndecl (call
);
895 /* Calls to functions that are merely acting as barriers
896 or that only store to memory do not make any previous
898 if (callee
!= NULL_TREE
899 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
900 && (DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET
901 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET_CHK
902 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MALLOC
903 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALIGNED_ALLOC
904 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_CALLOC
905 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_FREE
906 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_VA_END
907 || ALLOCA_FUNCTION_CODE_P (DECL_FUNCTION_CODE (callee
))
908 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_SAVE
909 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_RESTORE
910 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ASSUME_ALIGNED
))
913 if (callee
!= NULL_TREE
914 && (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
)
915 || DECL_IS_OPERATOR_DELETE_P (callee
))
916 && gimple_call_from_new_or_delete (call
))
919 /* Calls implicitly load from memory, their arguments
920 in addition may explicitly perform memory loads. */
921 mark_all_reaching_defs_necessary (call
);
922 for (i
= 0; i
< gimple_call_num_args (call
); ++i
)
924 tree arg
= gimple_call_arg (call
, i
);
925 if (TREE_CODE (arg
) == SSA_NAME
926 || is_gimple_min_invariant (arg
))
928 if (TREE_CODE (arg
) == WITH_SIZE_EXPR
)
929 arg
= TREE_OPERAND (arg
, 0);
930 if (!ref_may_be_aliased (arg
))
931 mark_aliased_reaching_defs_necessary (call
, arg
);
934 else if (gimple_assign_single_p (stmt
))
937 /* If this is a load mark things necessary. */
938 rhs
= gimple_assign_rhs1 (stmt
);
939 if (TREE_CODE (rhs
) != SSA_NAME
940 && !is_gimple_min_invariant (rhs
)
941 && TREE_CODE (rhs
) != CONSTRUCTOR
)
943 if (!ref_may_be_aliased (rhs
))
944 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
946 mark_all_reaching_defs_necessary (stmt
);
949 else if (greturn
*return_stmt
= dyn_cast
<greturn
*> (stmt
))
951 tree rhs
= gimple_return_retval (return_stmt
);
952 /* A return statement may perform a load. */
954 && TREE_CODE (rhs
) != SSA_NAME
955 && !is_gimple_min_invariant (rhs
)
956 && TREE_CODE (rhs
) != CONSTRUCTOR
)
958 if (!ref_may_be_aliased (rhs
))
959 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
961 mark_all_reaching_defs_necessary (stmt
);
964 else if (gasm
*asm_stmt
= dyn_cast
<gasm
*> (stmt
))
967 mark_all_reaching_defs_necessary (stmt
);
968 /* Inputs may perform loads. */
969 for (i
= 0; i
< gimple_asm_ninputs (asm_stmt
); ++i
)
971 tree op
= TREE_VALUE (gimple_asm_input_op (asm_stmt
, i
));
972 if (TREE_CODE (op
) != SSA_NAME
973 && !is_gimple_min_invariant (op
)
974 && TREE_CODE (op
) != CONSTRUCTOR
975 && !ref_may_be_aliased (op
))
976 mark_aliased_reaching_defs_necessary (stmt
, op
);
979 else if (gimple_code (stmt
) == GIMPLE_TRANSACTION
)
981 /* The beginning of a transaction is a memory barrier. */
982 /* ??? If we were really cool, we'd only be a barrier
983 for the memories touched within the transaction. */
984 mark_all_reaching_defs_necessary (stmt
);
989 /* If we over-used our alias oracle budget drop to simple
990 mode. The cost metric allows quadratic behavior
991 (number of uses times number of may-defs queries) up to
992 a constant maximal number of queries and after that falls back to
993 super-linear complexity. */
994 if (/* Constant but quadratic for small functions. */
995 total_chain
> 128 * 128
996 /* Linear in the number of may-defs. */
997 && total_chain
> 32 * longest_chain
998 /* Linear in the number of uses. */
999 && total_chain
> nr_walks
* 32)
1003 bitmap_clear (visited
);
1009 /* Remove dead PHI nodes from block BB. */
1012 remove_dead_phis (basic_block bb
)
1014 bool something_changed
= false;
1018 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);)
1023 /* We do not track necessity of virtual PHI nodes. Instead do
1024 very simple dead PHI removal here. */
1025 if (virtual_operand_p (gimple_phi_result (phi
)))
1027 /* Virtual PHI nodes with one or identical arguments
1029 if (!loops_state_satisfies_p (LOOP_CLOSED_SSA
)
1030 && degenerate_phi_p (phi
))
1032 tree vdef
= gimple_phi_result (phi
);
1033 tree vuse
= gimple_phi_arg_def (phi
, 0);
1035 use_operand_p use_p
;
1036 imm_use_iterator iter
;
1038 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, vdef
)
1039 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
1040 SET_USE (use_p
, vuse
);
1041 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef
)
1042 && TREE_CODE (vuse
) == SSA_NAME
)
1043 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse
) = 1;
1046 gimple_set_plf (phi
, STMT_NECESSARY
, true);
1049 if (!gimple_plf (phi
, STMT_NECESSARY
))
1051 something_changed
= true;
1052 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1054 fprintf (dump_file
, "Deleting : ");
1055 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
1056 fprintf (dump_file
, "\n");
1059 remove_phi_node (&gsi
, true);
1060 stats
.removed_phis
++;
1066 return something_changed
;
1070 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1071 containing I so that we don't have to look it up. */
1074 remove_dead_stmt (gimple_stmt_iterator
*i
, basic_block bb
,
1075 vec
<edge
> &to_remove_edges
)
1077 gimple
*stmt
= gsi_stmt (*i
);
1079 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1081 fprintf (dump_file
, "Deleting : ");
1082 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1083 fprintf (dump_file
, "\n");
1088 /* If we have determined that a conditional branch statement contributes
1089 nothing to the program, then we not only remove it, but we need to update
1090 the CFG. We can chose any of edges out of BB as long as we are sure to not
1091 close infinite loops. This is done by always choosing the edge closer to
1092 exit in inverted_post_order_compute order. */
1093 if (is_ctrl_stmt (stmt
))
1098 /* See if there is only one non-abnormal edge. */
1099 if (single_succ_p (bb
))
1100 e
= single_succ_edge (bb
);
1101 /* Otherwise chose one that is closer to bb with live statement in it.
1102 To be able to chose one, we compute inverted post order starting from
1103 all BBs with live statements. */
1108 auto_vec
<int, 20> postorder
;
1109 inverted_post_order_compute (&postorder
,
1110 &bb_contains_live_stmts
);
1111 bb_postorder
= XNEWVEC (int, last_basic_block_for_fn (cfun
));
1112 for (unsigned int i
= 0; i
< postorder
.length (); ++i
)
1113 bb_postorder
[postorder
[i
]] = i
;
1115 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1116 if (!e
|| e2
->dest
== EXIT_BLOCK_PTR_FOR_FN (cfun
)
1117 || bb_postorder
[e
->dest
->index
]
1118 < bb_postorder
[e2
->dest
->index
])
1122 e
->probability
= profile_probability::always ();
1124 /* The edge is no longer associated with a conditional, so it does
1125 not have TRUE/FALSE flags.
1126 We are also safe to drop EH/ABNORMAL flags and turn them into
1127 normal control flow, because we know that all the destinations (including
1128 those odd edges) are equivalent for program execution. */
1129 e
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
| EDGE_EH
| EDGE_ABNORMAL
);
1131 /* The lone outgoing edge from BB will be a fallthru edge. */
1132 e
->flags
|= EDGE_FALLTHRU
;
1134 /* Remove the remaining outgoing edges. */
1135 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1138 /* If we made a BB unconditionally exit a loop or removed
1139 an entry into an irreducible region, then this transform
1140 alters the set of BBs in the loop. Schedule a fixup. */
1141 if (loop_exit_edge_p (bb
->loop_father
, e
)
1142 || (e2
->dest
->flags
& BB_IRREDUCIBLE_LOOP
))
1143 loops_state_set (LOOPS_NEED_FIXUP
);
1144 to_remove_edges
.safe_push (e2
);
1148 /* If this is a store into a variable that is being optimized away,
1149 add a debug bind stmt if possible. */
1150 if (MAY_HAVE_DEBUG_BIND_STMTS
1151 && gimple_assign_single_p (stmt
)
1152 && is_gimple_val (gimple_assign_rhs1 (stmt
)))
1154 tree lhs
= gimple_assign_lhs (stmt
);
1155 if ((VAR_P (lhs
) || TREE_CODE (lhs
) == PARM_DECL
)
1156 && !DECL_IGNORED_P (lhs
)
1157 && is_gimple_reg_type (TREE_TYPE (lhs
))
1158 && !is_global_var (lhs
)
1159 && !DECL_HAS_VALUE_EXPR_P (lhs
))
1161 tree rhs
= gimple_assign_rhs1 (stmt
);
1163 = gimple_build_debug_bind (lhs
, unshare_expr (rhs
), stmt
);
1164 gsi_insert_after (i
, note
, GSI_SAME_STMT
);
1168 unlink_stmt_vdef (stmt
);
1169 gsi_remove (i
, true);
1170 release_defs (stmt
);
1173 /* Helper for maybe_optimize_arith_overflow. Find in *TP if there are any
1174 uses of data (SSA_NAME) other than REALPART_EXPR referencing it. */
1177 find_non_realpart_uses (tree
*tp
, int *walk_subtrees
, void *data
)
1179 if (TYPE_P (*tp
) || TREE_CODE (*tp
) == REALPART_EXPR
)
1181 if (*tp
== (tree
) data
)
1186 /* If the IMAGPART_EXPR of the {ADD,SUB,MUL}_OVERFLOW result is never used,
1187 but REALPART_EXPR is, optimize the {ADD,SUB,MUL}_OVERFLOW internal calls
1188 into plain unsigned {PLUS,MINUS,MULT}_EXPR, and if needed reset debug
1192 maybe_optimize_arith_overflow (gimple_stmt_iterator
*gsi
,
1193 enum tree_code subcode
)
1195 gimple
*stmt
= gsi_stmt (*gsi
);
1196 tree lhs
= gimple_call_lhs (stmt
);
1198 if (lhs
== NULL
|| TREE_CODE (lhs
) != SSA_NAME
)
1201 imm_use_iterator imm_iter
;
1202 use_operand_p use_p
;
1203 bool has_debug_uses
= false;
1204 bool has_realpart_uses
= false;
1205 bool has_other_uses
= false;
1206 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, lhs
)
1208 gimple
*use_stmt
= USE_STMT (use_p
);
1209 if (is_gimple_debug (use_stmt
))
1210 has_debug_uses
= true;
1211 else if (is_gimple_assign (use_stmt
)
1212 && gimple_assign_rhs_code (use_stmt
) == REALPART_EXPR
1213 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt
), 0) == lhs
)
1214 has_realpart_uses
= true;
1217 has_other_uses
= true;
1222 if (!has_realpart_uses
|| has_other_uses
)
1225 tree arg0
= gimple_call_arg (stmt
, 0);
1226 tree arg1
= gimple_call_arg (stmt
, 1);
1227 location_t loc
= gimple_location (stmt
);
1228 tree type
= TREE_TYPE (TREE_TYPE (lhs
));
1230 if (!TYPE_UNSIGNED (type
))
1231 utype
= build_nonstandard_integer_type (TYPE_PRECISION (type
), 1);
1232 tree result
= fold_build2_loc (loc
, subcode
, utype
,
1233 fold_convert_loc (loc
, utype
, arg0
),
1234 fold_convert_loc (loc
, utype
, arg1
));
1235 result
= fold_convert_loc (loc
, type
, result
);
1240 FOR_EACH_IMM_USE_STMT (use_stmt
, imm_iter
, lhs
)
1242 if (!gimple_debug_bind_p (use_stmt
))
1244 tree v
= gimple_debug_bind_get_value (use_stmt
);
1245 if (walk_tree (&v
, find_non_realpart_uses
, lhs
, NULL
))
1247 gimple_debug_bind_reset_value (use_stmt
);
1248 update_stmt (use_stmt
);
1253 if (TREE_CODE (result
) == INTEGER_CST
&& TREE_OVERFLOW (result
))
1254 result
= drop_tree_overflow (result
);
1255 tree overflow
= build_zero_cst (type
);
1256 tree ctype
= build_complex_type (type
);
1257 if (TREE_CODE (result
) == INTEGER_CST
)
1258 result
= build_complex (ctype
, result
, overflow
);
1260 result
= build2_loc (gimple_location (stmt
), COMPLEX_EXPR
,
1261 ctype
, result
, overflow
);
1263 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1265 fprintf (dump_file
, "Transforming call: ");
1266 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1267 fprintf (dump_file
, "because the overflow result is never used into: ");
1268 print_generic_stmt (dump_file
, result
, TDF_SLIM
);
1269 fprintf (dump_file
, "\n");
1272 gimplify_and_update_call_from_tree (gsi
, result
);
1275 /* Returns whether the control parents of BB are preserved. */
1278 control_parents_preserved_p (basic_block bb
)
1280 /* If we marked the control parents from BB they are preserved. */
1281 if (bitmap_bit_p (visited_control_parents
, bb
->index
))
1284 /* But they can also end up being marked from elsewhere. */
1286 unsigned edge_number
;
1287 EXECUTE_IF_SET_IN_BITMAP (cd
->get_edges_dependent_on (bb
->index
),
1290 basic_block cd_bb
= cd
->get_edge_src (edge_number
);
1292 && !bitmap_bit_p (last_stmt_necessary
, cd_bb
->index
))
1295 /* And cache the result. */
1296 bitmap_set_bit (visited_control_parents
, bb
->index
);
1300 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1301 contributes nothing to the program, and can be deleted. */
1304 eliminate_unnecessary_stmts (bool aggressive
)
1306 bool something_changed
= false;
1308 gimple_stmt_iterator gsi
, psi
;
1311 auto_vec
<edge
> to_remove_edges
;
1313 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1314 fprintf (dump_file
, "\nEliminating unnecessary statements:\n");
1316 clear_special_calls ();
1318 /* Walking basic blocks and statements in reverse order avoids
1319 releasing SSA names before any other DEFs that refer to them are
1320 released. This helps avoid loss of debug information, as we get
1321 a chance to propagate all RHSs of removed SSAs into debug uses,
1322 rather than only the latest ones. E.g., consider:
1328 If we were to release x_3 before a_5, when we reached a_5 and
1329 tried to substitute it into the debug stmt, we'd see x_3 there,
1330 but x_3's DEF, type, etc would have already been disconnected.
1331 By going backwards, the debug stmt first changes to:
1333 # DEBUG a => x_3 - b_4
1337 # DEBUG a => y_1 + z_2 - b_4
1340 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
1341 auto_vec
<basic_block
> h
;
1342 h
= get_all_dominated_blocks (CDI_DOMINATORS
,
1343 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun
)));
1349 /* Remove dead statements. */
1350 auto_bitmap debug_seen
;
1351 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi
= psi
)
1353 stmt
= gsi_stmt (gsi
);
1360 /* We can mark a call to free as not necessary if the
1361 defining statement of its argument is not necessary
1362 (and thus is getting removed). */
1363 if (gimple_plf (stmt
, STMT_NECESSARY
)
1364 && (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
)
1365 || (is_gimple_call (stmt
)
1366 && gimple_call_from_new_or_delete (as_a
<gcall
*> (stmt
))
1367 && gimple_call_operator_delete_p (as_a
<gcall
*> (stmt
)))))
1369 tree ptr
= gimple_call_arg (stmt
, 0);
1370 if (TREE_CODE (ptr
) == SSA_NAME
)
1372 gimple
*def_stmt
= SSA_NAME_DEF_STMT (ptr
);
1373 if (!gimple_nop_p (def_stmt
)
1374 && !gimple_plf (def_stmt
, STMT_NECESSARY
))
1375 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
1379 /* If GSI is not necessary then remove it. */
1380 if (!gimple_plf (stmt
, STMT_NECESSARY
))
1382 /* Keep clobbers that we can keep live live. */
1383 if (gimple_clobber_p (stmt
))
1386 use_operand_p use_p
;
1388 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_USE
)
1390 tree name
= USE_FROM_PTR (use_p
);
1391 if (!SSA_NAME_IS_DEFAULT_DEF (name
)
1392 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
)))
1399 /* When doing CD-DCE we have to ensure all controls
1400 of the stmt are still live. */
1401 && (!aggressive
|| control_parents_preserved_p (bb
)))
1403 bitmap_clear (debug_seen
);
1407 if (!is_gimple_debug (stmt
))
1408 something_changed
= true;
1409 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1412 else if (is_gimple_call (stmt
))
1414 tree name
= gimple_call_lhs (stmt
);
1416 notice_special_calls (as_a
<gcall
*> (stmt
));
1418 /* When LHS of var = call (); is dead, simplify it into
1419 call (); saving one operand. */
1421 && TREE_CODE (name
) == SSA_NAME
1422 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
))
1423 /* Avoid doing so for allocation calls which we
1424 did not mark as necessary, it will confuse the
1425 special logic we apply to malloc/free pair removal. */
1426 && (!(call
= gimple_call_fndecl (stmt
))
1427 || ((DECL_BUILT_IN_CLASS (call
) != BUILT_IN_NORMAL
1428 || (DECL_FUNCTION_CODE (call
) != BUILT_IN_ALIGNED_ALLOC
1429 && DECL_FUNCTION_CODE (call
) != BUILT_IN_MALLOC
1430 && DECL_FUNCTION_CODE (call
) != BUILT_IN_CALLOC
1431 && !ALLOCA_FUNCTION_CODE_P
1432 (DECL_FUNCTION_CODE (call
))))
1433 && !DECL_IS_REPLACEABLE_OPERATOR_NEW_P (call
))))
1435 something_changed
= true;
1436 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1438 fprintf (dump_file
, "Deleting LHS of call: ");
1439 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1440 fprintf (dump_file
, "\n");
1443 gimple_call_set_lhs (stmt
, NULL_TREE
);
1444 maybe_clean_or_replace_eh_stmt (stmt
, stmt
);
1446 release_ssa_name (name
);
1448 /* GOMP_SIMD_LANE (unless three argument) or ASAN_POISON
1449 without lhs is not needed. */
1450 if (gimple_call_internal_p (stmt
))
1451 switch (gimple_call_internal_fn (stmt
))
1453 case IFN_GOMP_SIMD_LANE
:
1454 if (gimple_call_num_args (stmt
) >= 3
1455 && !integer_nonzerop (gimple_call_arg (stmt
, 2)))
1458 case IFN_ASAN_POISON
:
1459 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1465 else if (gimple_call_internal_p (stmt
))
1466 switch (gimple_call_internal_fn (stmt
))
1468 case IFN_ADD_OVERFLOW
:
1469 maybe_optimize_arith_overflow (&gsi
, PLUS_EXPR
);
1471 case IFN_SUB_OVERFLOW
:
1472 maybe_optimize_arith_overflow (&gsi
, MINUS_EXPR
);
1474 case IFN_MUL_OVERFLOW
:
1475 maybe_optimize_arith_overflow (&gsi
, MULT_EXPR
);
1481 else if (gimple_debug_bind_p (stmt
))
1483 /* We are only keeping the last debug-bind of a
1484 non-DEBUG_EXPR_DECL variable in a series of
1485 debug-bind stmts. */
1486 tree var
= gimple_debug_bind_get_var (stmt
);
1487 if (TREE_CODE (var
) != DEBUG_EXPR_DECL
1488 && !bitmap_set_bit (debug_seen
, DECL_UID (var
)))
1489 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1492 bitmap_clear (debug_seen
);
1495 /* Remove dead PHI nodes. */
1496 something_changed
|= remove_dead_phis (bb
);
1500 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1501 rendered some PHI nodes unreachable while they are still in use.
1502 Mark them for renaming. */
1503 if (!to_remove_edges
.is_empty ())
1505 basic_block prev_bb
;
1507 /* Remove edges. We've delayed this to not get bogus debug stmts
1508 during PHI node removal. */
1509 for (unsigned i
= 0; i
< to_remove_edges
.length (); ++i
)
1510 remove_edge (to_remove_edges
[i
]);
1513 find_unreachable_blocks ();
1515 /* Delete all unreachable basic blocks in reverse dominator order. */
1516 for (bb
= EXIT_BLOCK_PTR_FOR_FN (cfun
)->prev_bb
;
1517 bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
); bb
= prev_bb
)
1519 prev_bb
= bb
->prev_bb
;
1521 if (!bitmap_bit_p (bb_contains_live_stmts
, bb
->index
)
1522 || !(bb
->flags
& BB_REACHABLE
))
1524 for (gphi_iterator gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
1526 if (virtual_operand_p (gimple_phi_result (gsi
.phi ())))
1529 imm_use_iterator iter
;
1531 FOR_EACH_IMM_USE_STMT (stmt
, iter
,
1532 gimple_phi_result (gsi
.phi ()))
1534 if (!(gimple_bb (stmt
)->flags
& BB_REACHABLE
))
1536 if (gimple_code (stmt
) == GIMPLE_PHI
1537 || gimple_plf (stmt
, STMT_NECESSARY
))
1544 mark_virtual_phi_result_for_renaming (gsi
.phi ());
1547 if (!(bb
->flags
& BB_REACHABLE
))
1549 /* Speed up the removal of blocks that don't
1550 dominate others. Walking backwards, this should
1551 be the common case. ??? Do we need to recompute
1552 dominators because of cfg_altered? */
1553 if (!first_dom_son (CDI_DOMINATORS
, bb
))
1554 delete_basic_block (bb
);
1557 h
= get_all_dominated_blocks (CDI_DOMINATORS
, bb
);
1562 prev_bb
= bb
->prev_bb
;
1563 /* Rearrangements to the CFG may have failed
1564 to update the dominators tree, so that
1565 formerly-dominated blocks are now
1566 otherwise reachable. */
1567 if (!!(bb
->flags
& BB_REACHABLE
))
1569 delete_basic_block (bb
);
1580 free (bb_postorder
);
1581 bb_postorder
= NULL
;
1583 return something_changed
;
1587 /* Print out removed statement statistics. */
1594 percg
= ((float) stats
.removed
/ (float) stats
.total
) * 100;
1595 fprintf (dump_file
, "Removed %d of %d statements (%d%%)\n",
1596 stats
.removed
, stats
.total
, (int) percg
);
1598 if (stats
.total_phis
== 0)
1601 percg
= ((float) stats
.removed_phis
/ (float) stats
.total_phis
) * 100;
1603 fprintf (dump_file
, "Removed %d of %d PHI nodes (%d%%)\n",
1604 stats
.removed_phis
, stats
.total_phis
, (int) percg
);
1607 /* Initialization for this pass. Set up the used data structures. */
1610 tree_dce_init (bool aggressive
)
1612 memset ((void *) &stats
, 0, sizeof (stats
));
1616 last_stmt_necessary
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1617 bitmap_clear (last_stmt_necessary
);
1618 bb_contains_live_stmts
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1619 bitmap_clear (bb_contains_live_stmts
);
1622 processed
= sbitmap_alloc (num_ssa_names
+ 1);
1623 bitmap_clear (processed
);
1625 worklist
.create (64);
1626 cfg_altered
= false;
1629 /* Cleanup after this pass. */
1632 tree_dce_done (bool aggressive
)
1637 sbitmap_free (visited_control_parents
);
1638 sbitmap_free (last_stmt_necessary
);
1639 sbitmap_free (bb_contains_live_stmts
);
1640 bb_contains_live_stmts
= NULL
;
1643 sbitmap_free (processed
);
1645 worklist
.release ();
1648 /* Sort PHI argument values for make_forwarders_with_degenerate_phis. */
1651 sort_phi_args (const void *a_
, const void *b_
)
1653 auto *a
= (const std::pair
<edge
, hashval_t
> *) a_
;
1654 auto *b
= (const std::pair
<edge
, hashval_t
> *) b_
;
1655 hashval_t ha
= a
->second
;
1656 hashval_t hb
= b
->second
;
1661 else if (a
->first
->dest_idx
< b
->first
->dest_idx
)
1663 else if (a
->first
->dest_idx
> b
->first
->dest_idx
)
1669 /* Look for a non-virtual PHIs and make a forwarder block when all PHIs
1670 have the same argument on a set of edges. This is to not consider
1671 control dependences of individual edges for same values but only for
1675 make_forwarders_with_degenerate_phis (function
*fn
)
1680 FOR_EACH_BB_FN (bb
, fn
)
1682 /* Only PHIs with three or more arguments have opportunities. */
1683 if (EDGE_COUNT (bb
->preds
) < 3)
1685 /* Do not touch loop headers or blocks with abnormal predecessors.
1686 ??? This is to avoid creating valid loops here, see PR103458.
1687 We might want to improve things to either explicitely add those
1688 loops or at least consider blocks with no backedges. */
1689 if (bb
->loop_father
->header
== bb
1690 || bb_has_abnormal_pred (bb
))
1693 /* Take one PHI node as template to look for identical
1694 arguments. Build a vector of candidates forming sets
1695 of argument edges with equal values. Note optimality
1696 depends on the particular choice of the template PHI
1697 since equal arguments are unordered leaving other PHIs
1698 with more than one set of equal arguments within this
1699 argument range unsorted. We'd have to break ties by
1700 looking at other PHI nodes. */
1701 gphi_iterator gsi
= gsi_start_nonvirtual_phis (bb
);
1702 if (gsi_end_p (gsi
))
1704 gphi
*phi
= gsi
.phi ();
1705 auto_vec
<std::pair
<edge
, hashval_t
>, 8> args
;
1706 bool need_resort
= false;
1707 for (unsigned i
= 0; i
< gimple_phi_num_args (phi
); ++i
)
1709 edge e
= gimple_phi_arg_edge (phi
, i
);
1710 /* Skip abnormal edges since we cannot redirect them. */
1711 if (e
->flags
& EDGE_ABNORMAL
)
1713 /* Skip loop exit edges when we are in loop-closed SSA form
1714 since the forwarder we'd create does not have a PHI node. */
1715 if (loops_state_satisfies_p (LOOP_CLOSED_SSA
)
1716 && loop_exit_edge_p (e
->src
->loop_father
, e
))
1719 tree arg
= gimple_phi_arg_def (phi
, i
);
1720 if (!CONSTANT_CLASS_P (arg
) && TREE_CODE (arg
) != SSA_NAME
)
1722 args
.safe_push (std::make_pair (e
, iterative_hash_expr (arg
, 0)));
1724 if (args
.length () < 2)
1726 args
.qsort (sort_phi_args
);
1727 /* The above sorting can be different between -g and -g0, as e.g. decls
1728 can have different uids (-g could have bigger gaps in between them).
1729 So, only use that to determine which args are equal, then change
1730 second from hash value to smallest dest_idx of the edges which have
1731 equal argument and sort again. If all the phi arguments are
1732 constants or SSA_NAME, there is no need for the second sort, the hash
1733 values are stable in that case. */
1734 hashval_t hash
= args
[0].second
;
1735 args
[0].second
= args
[0].first
->dest_idx
;
1736 bool any_equal
= false;
1737 for (unsigned i
= 1; i
< args
.length (); ++i
)
1738 if (hash
== args
[i
].second
1739 && operand_equal_p (PHI_ARG_DEF_FROM_EDGE (phi
, args
[i
- 1].first
),
1740 PHI_ARG_DEF_FROM_EDGE (phi
, args
[i
].first
)))
1742 args
[i
].second
= args
[i
- 1].second
;
1747 hash
= args
[i
].second
;
1748 args
[i
].second
= args
[i
].first
->dest_idx
;
1753 args
.qsort (sort_phi_args
);
1755 /* From the candidates vector now verify true candidates for
1756 forwarders and create them. */
1757 gphi
*vphi
= get_virtual_phi (bb
);
1759 while (start
< args
.length () - 1)
1762 for (i
= start
+ 1; i
< args
.length (); ++i
)
1763 if (args
[start
].second
!= args
[i
].second
)
1765 /* args[start]..args[i-1] are equal. */
1768 /* Check all PHI nodes for argument equality. */
1770 gphi_iterator gsi2
= gsi
;
1772 for (; !gsi_end_p (gsi2
); gsi_next (&gsi2
))
1774 gphi
*phi2
= gsi2
.phi ();
1775 if (virtual_operand_p (gimple_phi_result (phi2
)))
1778 = PHI_ARG_DEF_FROM_EDGE (phi2
, args
[start
].first
);
1779 for (unsigned j
= start
+ 1; j
< i
; ++j
)
1781 if (!operand_equal_p (start_arg
,
1782 PHI_ARG_DEF_FROM_EDGE
1783 (phi2
, args
[j
].first
)))
1785 /* Another PHI might have a shorter set of
1786 equivalent args. Go for that. */
1798 /* If we are asked to forward all edges the block
1799 has all degenerate PHIs. Do nothing in that case. */
1801 && i
== args
.length ()
1802 && args
.length () == gimple_phi_num_args (phi
))
1804 /* Instead of using make_forwarder_block we are
1805 rolling our own variant knowing that the forwarder
1806 does not need PHI nodes apart from eventually
1808 auto_vec
<tree
, 8> vphi_args
;
1811 vphi_args
.reserve_exact (i
- start
);
1812 for (unsigned j
= start
; j
< i
; ++j
)
1813 vphi_args
.quick_push
1814 (PHI_ARG_DEF_FROM_EDGE (vphi
, args
[j
].first
));
1816 free_dominance_info (fn
, CDI_DOMINATORS
);
1817 basic_block forwarder
= split_edge (args
[start
].first
);
1818 for (unsigned j
= start
+ 1; j
< i
; ++j
)
1820 edge e
= args
[j
].first
;
1821 redirect_edge_and_branch_force (e
, forwarder
);
1822 redirect_edge_var_map_clear (e
);
1826 tree def
= copy_ssa_name (vphi_args
[0]);
1827 gphi
*vphi_copy
= create_phi_node (def
, forwarder
);
1828 for (unsigned j
= start
; j
< i
; ++j
)
1829 add_phi_arg (vphi_copy
, vphi_args
[j
- start
],
1830 args
[j
].first
, UNKNOWN_LOCATION
);
1832 (vphi
, single_succ_edge (forwarder
)->dest_idx
, def
);
1834 todo
|= TODO_cleanup_cfg
;
1837 /* Continue searching for more opportunities. */
1844 /* Main routine to eliminate dead code.
1846 AGGRESSIVE controls the aggressiveness of the algorithm.
1847 In conservative mode, we ignore control dependence and simply declare
1848 all but the most trivially dead branches necessary. This mode is fast.
1849 In aggressive mode, control dependences are taken into account, which
1850 results in more dead code elimination, but at the cost of some time.
1852 FIXME: Aggressive mode before PRE doesn't work currently because
1853 the dominance info is not invalidated after DCE1. This is
1854 not an issue right now because we only run aggressive DCE
1855 as the last tree SSA pass, but keep this in mind when you
1856 start experimenting with pass ordering. */
1859 perform_tree_ssa_dce (bool aggressive
)
1861 bool something_changed
= 0;
1864 /* Preheaders are needed for SCEV to work.
1865 Simple lateches and recorded exits improve chances that loop will
1866 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1867 bool in_loop_pipeline
= scev_initialized_p ();
1868 if (aggressive
&& ! in_loop_pipeline
)
1870 loop_optimizer_init (LOOPS_NORMAL
1871 | LOOPS_HAVE_RECORDED_EXITS
);
1876 todo
|= make_forwarders_with_degenerate_phis (cfun
);
1878 calculate_dominance_info (CDI_DOMINATORS
);
1880 tree_dce_init (aggressive
);
1884 /* Compute control dependence. */
1885 calculate_dominance_info (CDI_POST_DOMINATORS
);
1886 cd
= new control_dependences ();
1888 visited_control_parents
=
1889 sbitmap_alloc (last_basic_block_for_fn (cfun
));
1890 bitmap_clear (visited_control_parents
);
1892 mark_dfs_back_edges ();
1895 find_obviously_necessary_stmts (aggressive
);
1897 if (aggressive
&& ! in_loop_pipeline
)
1900 loop_optimizer_finalize ();
1907 visited
= BITMAP_ALLOC (NULL
);
1908 propagate_necessity (aggressive
);
1909 BITMAP_FREE (visited
);
1911 something_changed
|= eliminate_unnecessary_stmts (aggressive
);
1912 something_changed
|= cfg_altered
;
1914 /* We do not update postdominators, so free them unconditionally. */
1915 free_dominance_info (CDI_POST_DOMINATORS
);
1917 /* If we removed paths in the CFG, then we need to update
1918 dominators as well. I haven't investigated the possibility
1919 of incrementally updating dominators. */
1921 free_dominance_info (CDI_DOMINATORS
);
1923 statistics_counter_event (cfun
, "Statements deleted", stats
.removed
);
1924 statistics_counter_event (cfun
, "PHI nodes deleted", stats
.removed_phis
);
1926 /* Debugging dumps. */
1927 if (dump_file
&& (dump_flags
& (TDF_STATS
|TDF_DETAILS
)))
1930 tree_dce_done (aggressive
);
1932 if (something_changed
)
1934 free_numbers_of_iterations_estimates (cfun
);
1935 if (in_loop_pipeline
)
1937 todo
|= TODO_update_ssa
| TODO_cleanup_cfg
;
1942 /* Pass entry points. */
1946 return perform_tree_ssa_dce (/*aggressive=*/false);
1950 tree_ssa_cd_dce (void)
1952 return perform_tree_ssa_dce (/*aggressive=*/optimize
>= 2);
1957 const pass_data pass_data_dce
=
1959 GIMPLE_PASS
, /* type */
1961 OPTGROUP_NONE
, /* optinfo_flags */
1962 TV_TREE_DCE
, /* tv_id */
1963 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1964 0, /* properties_provided */
1965 0, /* properties_destroyed */
1966 0, /* todo_flags_start */
1967 0, /* todo_flags_finish */
1970 class pass_dce
: public gimple_opt_pass
1973 pass_dce (gcc::context
*ctxt
)
1974 : gimple_opt_pass (pass_data_dce
, ctxt
)
1977 /* opt_pass methods: */
1978 opt_pass
* clone () final override
{ return new pass_dce (m_ctxt
); }
1979 bool gate (function
*) final override
{ return flag_tree_dce
!= 0; }
1980 unsigned int execute (function
*) final override
{ return tree_ssa_dce (); }
1982 }; // class pass_dce
1987 make_pass_dce (gcc::context
*ctxt
)
1989 return new pass_dce (ctxt
);
1994 const pass_data pass_data_cd_dce
=
1996 GIMPLE_PASS
, /* type */
1998 OPTGROUP_NONE
, /* optinfo_flags */
1999 TV_TREE_CD_DCE
, /* tv_id */
2000 ( PROP_cfg
| PROP_ssa
), /* properties_required */
2001 0, /* properties_provided */
2002 0, /* properties_destroyed */
2003 0, /* todo_flags_start */
2004 0, /* todo_flags_finish */
2007 class pass_cd_dce
: public gimple_opt_pass
2010 pass_cd_dce (gcc::context
*ctxt
)
2011 : gimple_opt_pass (pass_data_cd_dce
, ctxt
), update_address_taken_p (false)
2014 /* opt_pass methods: */
2015 opt_pass
* clone () final override
{ return new pass_cd_dce (m_ctxt
); }
2016 void set_pass_param (unsigned n
, bool param
) final override
2018 gcc_assert (n
== 0);
2019 update_address_taken_p
= param
;
2021 bool gate (function
*) final override
{ return flag_tree_dce
!= 0; }
2022 unsigned int execute (function
*) final override
2024 return (tree_ssa_cd_dce ()
2025 | (update_address_taken_p
? TODO_update_address_taken
: 0));
2029 bool update_address_taken_p
;
2030 }; // class pass_cd_dce
2035 make_pass_cd_dce (gcc::context
*ctxt
)
2037 return new pass_cd_dce (ctxt
);
2041 /* A cheap DCE interface. WORKLIST is a list of possibly dead stmts and
2042 is consumed by this function. The function has linear complexity in
2043 the number of dead stmts with a constant factor like the average SSA
2044 use operands number. */
2047 simple_dce_from_worklist (bitmap worklist
)
2049 while (! bitmap_empty_p (worklist
))
2052 unsigned i
= bitmap_first_set_bit (worklist
);
2053 bitmap_clear_bit (worklist
, i
);
2055 tree def
= ssa_name (i
);
2056 /* Removed by somebody else or still in use. */
2057 if (! def
|| ! has_zero_uses (def
))
2060 gimple
*t
= SSA_NAME_DEF_STMT (def
);
2061 if (gimple_has_side_effects (t
))
2064 /* The defining statement needs to be defining only this name.
2065 ASM is the only statement that can define more than one
2066 (non-virtual) name. */
2068 && !single_ssa_def_operand (t
, SSA_OP_DEF
))
2071 /* Don't remove statements that are needed for non-call
2073 if (stmt_unremovable_because_of_non_call_eh_p (cfun
, t
))
2076 /* Add uses to the worklist. */
2078 use_operand_p use_p
;
2079 FOR_EACH_PHI_OR_STMT_USE (use_p
, t
, iter
, SSA_OP_USE
)
2081 tree use
= USE_FROM_PTR (use_p
);
2082 if (TREE_CODE (use
) == SSA_NAME
2083 && ! SSA_NAME_IS_DEFAULT_DEF (use
))
2084 bitmap_set_bit (worklist
, SSA_NAME_VERSION (use
));
2088 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
2090 fprintf (dump_file
, "Removing dead stmt:");
2091 print_gimple_stmt (dump_file
, t
, 0);
2093 gimple_stmt_iterator gsi
= gsi_for_stmt (t
);
2094 if (gimple_code (t
) == GIMPLE_PHI
)
2095 remove_phi_node (&gsi
, true);
2098 gsi_remove (&gsi
, true);