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
))
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 (degenerate_phi_p (phi
))
1031 tree vdef
= gimple_phi_result (phi
);
1032 tree vuse
= gimple_phi_arg_def (phi
, 0);
1034 use_operand_p use_p
;
1035 imm_use_iterator iter
;
1037 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, vdef
)
1038 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
1039 SET_USE (use_p
, vuse
);
1040 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef
)
1041 && TREE_CODE (vuse
) == SSA_NAME
)
1042 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse
) = 1;
1045 gimple_set_plf (phi
, STMT_NECESSARY
, true);
1048 if (!gimple_plf (phi
, STMT_NECESSARY
))
1050 something_changed
= true;
1051 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1053 fprintf (dump_file
, "Deleting : ");
1054 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
1055 fprintf (dump_file
, "\n");
1058 remove_phi_node (&gsi
, true);
1059 stats
.removed_phis
++;
1065 return something_changed
;
1069 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1070 containing I so that we don't have to look it up. */
1073 remove_dead_stmt (gimple_stmt_iterator
*i
, basic_block bb
,
1074 vec
<edge
> &to_remove_edges
)
1076 gimple
*stmt
= gsi_stmt (*i
);
1078 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1080 fprintf (dump_file
, "Deleting : ");
1081 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1082 fprintf (dump_file
, "\n");
1087 /* If we have determined that a conditional branch statement contributes
1088 nothing to the program, then we not only remove it, but we need to update
1089 the CFG. We can chose any of edges out of BB as long as we are sure to not
1090 close infinite loops. This is done by always choosing the edge closer to
1091 exit in inverted_post_order_compute order. */
1092 if (is_ctrl_stmt (stmt
))
1097 /* See if there is only one non-abnormal edge. */
1098 if (single_succ_p (bb
))
1099 e
= single_succ_edge (bb
);
1100 /* Otherwise chose one that is closer to bb with live statement in it.
1101 To be able to chose one, we compute inverted post order starting from
1102 all BBs with live statements. */
1107 auto_vec
<int, 20> postorder
;
1108 inverted_post_order_compute (&postorder
,
1109 &bb_contains_live_stmts
);
1110 bb_postorder
= XNEWVEC (int, last_basic_block_for_fn (cfun
));
1111 for (unsigned int i
= 0; i
< postorder
.length (); ++i
)
1112 bb_postorder
[postorder
[i
]] = i
;
1114 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1115 if (!e
|| e2
->dest
== EXIT_BLOCK_PTR_FOR_FN (cfun
)
1116 || bb_postorder
[e
->dest
->index
]
1117 < bb_postorder
[e2
->dest
->index
])
1121 e
->probability
= profile_probability::always ();
1123 /* The edge is no longer associated with a conditional, so it does
1124 not have TRUE/FALSE flags.
1125 We are also safe to drop EH/ABNORMAL flags and turn them into
1126 normal control flow, because we know that all the destinations (including
1127 those odd edges) are equivalent for program execution. */
1128 e
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
| EDGE_EH
| EDGE_ABNORMAL
);
1130 /* The lone outgoing edge from BB will be a fallthru edge. */
1131 e
->flags
|= EDGE_FALLTHRU
;
1133 /* Remove the remaining outgoing edges. */
1134 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1137 /* If we made a BB unconditionally exit a loop or removed
1138 an entry into an irreducible region, then this transform
1139 alters the set of BBs in the loop. Schedule a fixup. */
1140 if (loop_exit_edge_p (bb
->loop_father
, e
)
1141 || (e2
->dest
->flags
& BB_IRREDUCIBLE_LOOP
))
1142 loops_state_set (LOOPS_NEED_FIXUP
);
1143 to_remove_edges
.safe_push (e2
);
1147 /* If this is a store into a variable that is being optimized away,
1148 add a debug bind stmt if possible. */
1149 if (MAY_HAVE_DEBUG_BIND_STMTS
1150 && gimple_assign_single_p (stmt
)
1151 && is_gimple_val (gimple_assign_rhs1 (stmt
)))
1153 tree lhs
= gimple_assign_lhs (stmt
);
1154 if ((VAR_P (lhs
) || TREE_CODE (lhs
) == PARM_DECL
)
1155 && !DECL_IGNORED_P (lhs
)
1156 && is_gimple_reg_type (TREE_TYPE (lhs
))
1157 && !is_global_var (lhs
)
1158 && !DECL_HAS_VALUE_EXPR_P (lhs
))
1160 tree rhs
= gimple_assign_rhs1 (stmt
);
1162 = gimple_build_debug_bind (lhs
, unshare_expr (rhs
), stmt
);
1163 gsi_insert_after (i
, note
, GSI_SAME_STMT
);
1167 unlink_stmt_vdef (stmt
);
1168 gsi_remove (i
, true);
1169 release_defs (stmt
);
1172 /* Helper for maybe_optimize_arith_overflow. Find in *TP if there are any
1173 uses of data (SSA_NAME) other than REALPART_EXPR referencing it. */
1176 find_non_realpart_uses (tree
*tp
, int *walk_subtrees
, void *data
)
1178 if (TYPE_P (*tp
) || TREE_CODE (*tp
) == REALPART_EXPR
)
1180 if (*tp
== (tree
) data
)
1185 /* If the IMAGPART_EXPR of the {ADD,SUB,MUL}_OVERFLOW result is never used,
1186 but REALPART_EXPR is, optimize the {ADD,SUB,MUL}_OVERFLOW internal calls
1187 into plain unsigned {PLUS,MINUS,MULT}_EXPR, and if needed reset debug
1191 maybe_optimize_arith_overflow (gimple_stmt_iterator
*gsi
,
1192 enum tree_code subcode
)
1194 gimple
*stmt
= gsi_stmt (*gsi
);
1195 tree lhs
= gimple_call_lhs (stmt
);
1197 if (lhs
== NULL
|| TREE_CODE (lhs
) != SSA_NAME
)
1200 imm_use_iterator imm_iter
;
1201 use_operand_p use_p
;
1202 bool has_debug_uses
= false;
1203 bool has_realpart_uses
= false;
1204 bool has_other_uses
= false;
1205 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, lhs
)
1207 gimple
*use_stmt
= USE_STMT (use_p
);
1208 if (is_gimple_debug (use_stmt
))
1209 has_debug_uses
= true;
1210 else if (is_gimple_assign (use_stmt
)
1211 && gimple_assign_rhs_code (use_stmt
) == REALPART_EXPR
1212 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt
), 0) == lhs
)
1213 has_realpart_uses
= true;
1216 has_other_uses
= true;
1221 if (!has_realpart_uses
|| has_other_uses
)
1224 tree arg0
= gimple_call_arg (stmt
, 0);
1225 tree arg1
= gimple_call_arg (stmt
, 1);
1226 location_t loc
= gimple_location (stmt
);
1227 tree type
= TREE_TYPE (TREE_TYPE (lhs
));
1229 if (!TYPE_UNSIGNED (type
))
1230 utype
= build_nonstandard_integer_type (TYPE_PRECISION (type
), 1);
1231 tree result
= fold_build2_loc (loc
, subcode
, utype
,
1232 fold_convert_loc (loc
, utype
, arg0
),
1233 fold_convert_loc (loc
, utype
, arg1
));
1234 result
= fold_convert_loc (loc
, type
, result
);
1239 FOR_EACH_IMM_USE_STMT (use_stmt
, imm_iter
, lhs
)
1241 if (!gimple_debug_bind_p (use_stmt
))
1243 tree v
= gimple_debug_bind_get_value (use_stmt
);
1244 if (walk_tree (&v
, find_non_realpart_uses
, lhs
, NULL
))
1246 gimple_debug_bind_reset_value (use_stmt
);
1247 update_stmt (use_stmt
);
1252 if (TREE_CODE (result
) == INTEGER_CST
&& TREE_OVERFLOW (result
))
1253 result
= drop_tree_overflow (result
);
1254 tree overflow
= build_zero_cst (type
);
1255 tree ctype
= build_complex_type (type
);
1256 if (TREE_CODE (result
) == INTEGER_CST
)
1257 result
= build_complex (ctype
, result
, overflow
);
1259 result
= build2_loc (gimple_location (stmt
), COMPLEX_EXPR
,
1260 ctype
, result
, overflow
);
1262 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1264 fprintf (dump_file
, "Transforming call: ");
1265 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1266 fprintf (dump_file
, "because the overflow result is never used into: ");
1267 print_generic_stmt (dump_file
, result
, TDF_SLIM
);
1268 fprintf (dump_file
, "\n");
1271 gimplify_and_update_call_from_tree (gsi
, result
);
1274 /* Returns whether the control parents of BB are preserved. */
1277 control_parents_preserved_p (basic_block bb
)
1279 /* If we marked the control parents from BB they are preserved. */
1280 if (bitmap_bit_p (visited_control_parents
, bb
->index
))
1283 /* But they can also end up being marked from elsewhere. */
1285 unsigned edge_number
;
1286 EXECUTE_IF_SET_IN_BITMAP (cd
->get_edges_dependent_on (bb
->index
),
1289 basic_block cd_bb
= cd
->get_edge_src (edge_number
);
1291 && !bitmap_bit_p (last_stmt_necessary
, cd_bb
->index
))
1294 /* And cache the result. */
1295 bitmap_set_bit (visited_control_parents
, bb
->index
);
1299 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1300 contributes nothing to the program, and can be deleted. */
1303 eliminate_unnecessary_stmts (bool aggressive
)
1305 bool something_changed
= false;
1307 gimple_stmt_iterator gsi
, psi
;
1310 auto_vec
<edge
> to_remove_edges
;
1312 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1313 fprintf (dump_file
, "\nEliminating unnecessary statements:\n");
1315 clear_special_calls ();
1317 /* Walking basic blocks and statements in reverse order avoids
1318 releasing SSA names before any other DEFs that refer to them are
1319 released. This helps avoid loss of debug information, as we get
1320 a chance to propagate all RHSs of removed SSAs into debug uses,
1321 rather than only the latest ones. E.g., consider:
1327 If we were to release x_3 before a_5, when we reached a_5 and
1328 tried to substitute it into the debug stmt, we'd see x_3 there,
1329 but x_3's DEF, type, etc would have already been disconnected.
1330 By going backwards, the debug stmt first changes to:
1332 # DEBUG a => x_3 - b_4
1336 # DEBUG a => y_1 + z_2 - b_4
1339 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
1340 auto_vec
<basic_block
> h
;
1341 h
= get_all_dominated_blocks (CDI_DOMINATORS
,
1342 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun
)));
1348 /* Remove dead statements. */
1349 auto_bitmap debug_seen
;
1350 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi
= psi
)
1352 stmt
= gsi_stmt (gsi
);
1359 /* We can mark a call to free as not necessary if the
1360 defining statement of its argument is not necessary
1361 (and thus is getting removed). */
1362 if (gimple_plf (stmt
, STMT_NECESSARY
)
1363 && (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
)
1364 || (is_gimple_call (stmt
)
1365 && gimple_call_from_new_or_delete (as_a
<gcall
*> (stmt
))
1366 && gimple_call_operator_delete_p (as_a
<gcall
*> (stmt
)))))
1368 tree ptr
= gimple_call_arg (stmt
, 0);
1369 if (TREE_CODE (ptr
) == SSA_NAME
)
1371 gimple
*def_stmt
= SSA_NAME_DEF_STMT (ptr
);
1372 if (!gimple_nop_p (def_stmt
)
1373 && !gimple_plf (def_stmt
, STMT_NECESSARY
))
1374 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
1378 /* If GSI is not necessary then remove it. */
1379 if (!gimple_plf (stmt
, STMT_NECESSARY
))
1381 /* Keep clobbers that we can keep live live. */
1382 if (gimple_clobber_p (stmt
))
1385 use_operand_p use_p
;
1387 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_USE
)
1389 tree name
= USE_FROM_PTR (use_p
);
1390 if (!SSA_NAME_IS_DEFAULT_DEF (name
)
1391 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
)))
1398 /* When doing CD-DCE we have to ensure all controls
1399 of the stmt are still live. */
1400 && (!aggressive
|| control_parents_preserved_p (bb
)))
1402 bitmap_clear (debug_seen
);
1406 if (!is_gimple_debug (stmt
))
1407 something_changed
= true;
1408 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1411 else if (is_gimple_call (stmt
))
1413 tree name
= gimple_call_lhs (stmt
);
1415 notice_special_calls (as_a
<gcall
*> (stmt
));
1417 /* When LHS of var = call (); is dead, simplify it into
1418 call (); saving one operand. */
1420 && TREE_CODE (name
) == SSA_NAME
1421 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
))
1422 /* Avoid doing so for allocation calls which we
1423 did not mark as necessary, it will confuse the
1424 special logic we apply to malloc/free pair removal. */
1425 && (!(call
= gimple_call_fndecl (stmt
))
1426 || ((DECL_BUILT_IN_CLASS (call
) != BUILT_IN_NORMAL
1427 || (DECL_FUNCTION_CODE (call
) != BUILT_IN_ALIGNED_ALLOC
1428 && DECL_FUNCTION_CODE (call
) != BUILT_IN_MALLOC
1429 && DECL_FUNCTION_CODE (call
) != BUILT_IN_CALLOC
1430 && !ALLOCA_FUNCTION_CODE_P
1431 (DECL_FUNCTION_CODE (call
))))
1432 && !DECL_IS_REPLACEABLE_OPERATOR_NEW_P (call
))))
1434 something_changed
= true;
1435 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1437 fprintf (dump_file
, "Deleting LHS of call: ");
1438 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1439 fprintf (dump_file
, "\n");
1442 gimple_call_set_lhs (stmt
, NULL_TREE
);
1443 maybe_clean_or_replace_eh_stmt (stmt
, stmt
);
1445 release_ssa_name (name
);
1447 /* GOMP_SIMD_LANE (unless three argument) or ASAN_POISON
1448 without lhs is not needed. */
1449 if (gimple_call_internal_p (stmt
))
1450 switch (gimple_call_internal_fn (stmt
))
1452 case IFN_GOMP_SIMD_LANE
:
1453 if (gimple_call_num_args (stmt
) >= 3
1454 && !integer_nonzerop (gimple_call_arg (stmt
, 2)))
1457 case IFN_ASAN_POISON
:
1458 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1464 else if (gimple_call_internal_p (stmt
))
1465 switch (gimple_call_internal_fn (stmt
))
1467 case IFN_ADD_OVERFLOW
:
1468 maybe_optimize_arith_overflow (&gsi
, PLUS_EXPR
);
1470 case IFN_SUB_OVERFLOW
:
1471 maybe_optimize_arith_overflow (&gsi
, MINUS_EXPR
);
1473 case IFN_MUL_OVERFLOW
:
1474 maybe_optimize_arith_overflow (&gsi
, MULT_EXPR
);
1480 else if (gimple_debug_bind_p (stmt
))
1482 /* We are only keeping the last debug-bind of a
1483 non-DEBUG_EXPR_DECL variable in a series of
1484 debug-bind stmts. */
1485 tree var
= gimple_debug_bind_get_var (stmt
);
1486 if (TREE_CODE (var
) != DEBUG_EXPR_DECL
1487 && !bitmap_set_bit (debug_seen
, DECL_UID (var
)))
1488 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1491 bitmap_clear (debug_seen
);
1494 /* Remove dead PHI nodes. */
1495 something_changed
|= remove_dead_phis (bb
);
1499 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1500 rendered some PHI nodes unreachable while they are still in use.
1501 Mark them for renaming. */
1502 if (!to_remove_edges
.is_empty ())
1504 basic_block prev_bb
;
1506 /* Remove edges. We've delayed this to not get bogus debug stmts
1507 during PHI node removal. */
1508 for (unsigned i
= 0; i
< to_remove_edges
.length (); ++i
)
1509 remove_edge (to_remove_edges
[i
]);
1512 find_unreachable_blocks ();
1514 /* Delete all unreachable basic blocks in reverse dominator order. */
1515 for (bb
= EXIT_BLOCK_PTR_FOR_FN (cfun
)->prev_bb
;
1516 bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
); bb
= prev_bb
)
1518 prev_bb
= bb
->prev_bb
;
1520 if (!bitmap_bit_p (bb_contains_live_stmts
, bb
->index
)
1521 || !(bb
->flags
& BB_REACHABLE
))
1523 for (gphi_iterator gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
1525 if (virtual_operand_p (gimple_phi_result (gsi
.phi ())))
1528 imm_use_iterator iter
;
1530 FOR_EACH_IMM_USE_STMT (stmt
, iter
,
1531 gimple_phi_result (gsi
.phi ()))
1533 if (!(gimple_bb (stmt
)->flags
& BB_REACHABLE
))
1535 if (gimple_code (stmt
) == GIMPLE_PHI
1536 || gimple_plf (stmt
, STMT_NECESSARY
))
1543 mark_virtual_phi_result_for_renaming (gsi
.phi ());
1546 if (!(bb
->flags
& BB_REACHABLE
))
1548 /* Speed up the removal of blocks that don't
1549 dominate others. Walking backwards, this should
1550 be the common case. ??? Do we need to recompute
1551 dominators because of cfg_altered? */
1552 if (!first_dom_son (CDI_DOMINATORS
, bb
))
1553 delete_basic_block (bb
);
1556 h
= get_all_dominated_blocks (CDI_DOMINATORS
, bb
);
1561 prev_bb
= bb
->prev_bb
;
1562 /* Rearrangements to the CFG may have failed
1563 to update the dominators tree, so that
1564 formerly-dominated blocks are now
1565 otherwise reachable. */
1566 if (!!(bb
->flags
& BB_REACHABLE
))
1568 delete_basic_block (bb
);
1579 free (bb_postorder
);
1580 bb_postorder
= NULL
;
1582 return something_changed
;
1586 /* Print out removed statement statistics. */
1593 percg
= ((float) stats
.removed
/ (float) stats
.total
) * 100;
1594 fprintf (dump_file
, "Removed %d of %d statements (%d%%)\n",
1595 stats
.removed
, stats
.total
, (int) percg
);
1597 if (stats
.total_phis
== 0)
1600 percg
= ((float) stats
.removed_phis
/ (float) stats
.total_phis
) * 100;
1602 fprintf (dump_file
, "Removed %d of %d PHI nodes (%d%%)\n",
1603 stats
.removed_phis
, stats
.total_phis
, (int) percg
);
1606 /* Initialization for this pass. Set up the used data structures. */
1609 tree_dce_init (bool aggressive
)
1611 memset ((void *) &stats
, 0, sizeof (stats
));
1615 last_stmt_necessary
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1616 bitmap_clear (last_stmt_necessary
);
1617 bb_contains_live_stmts
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1618 bitmap_clear (bb_contains_live_stmts
);
1621 processed
= sbitmap_alloc (num_ssa_names
+ 1);
1622 bitmap_clear (processed
);
1624 worklist
.create (64);
1625 cfg_altered
= false;
1628 /* Cleanup after this pass. */
1631 tree_dce_done (bool aggressive
)
1636 sbitmap_free (visited_control_parents
);
1637 sbitmap_free (last_stmt_necessary
);
1638 sbitmap_free (bb_contains_live_stmts
);
1639 bb_contains_live_stmts
= NULL
;
1642 sbitmap_free (processed
);
1644 worklist
.release ();
1647 /* Sort PHI argument values for make_forwarders_with_degenerate_phis. */
1650 sort_phi_args (const void *a_
, const void *b_
)
1652 auto *a
= (const std::pair
<edge
, hashval_t
> *) a_
;
1653 auto *b
= (const std::pair
<edge
, hashval_t
> *) b_
;
1654 hashval_t ha
= a
->second
;
1655 hashval_t hb
= b
->second
;
1660 else if (a
->first
->dest_idx
< b
->first
->dest_idx
)
1662 else if (a
->first
->dest_idx
> b
->first
->dest_idx
)
1668 /* Look for a non-virtual PHIs and make a forwarder block when all PHIs
1669 have the same argument on a set of edges. This is to not consider
1670 control dependences of individual edges for same values but only for
1674 make_forwarders_with_degenerate_phis (function
*fn
)
1679 FOR_EACH_BB_FN (bb
, fn
)
1681 /* Only PHIs with three or more arguments have opportunities. */
1682 if (EDGE_COUNT (bb
->preds
) < 3)
1684 /* Do not touch loop headers or blocks with abnormal predecessors.
1685 ??? This is to avoid creating valid loops here, see PR103458.
1686 We might want to improve things to either explicitely add those
1687 loops or at least consider blocks with no backedges. */
1688 if (bb
->loop_father
->header
== bb
1689 || bb_has_abnormal_pred (bb
))
1692 /* Take one PHI node as template to look for identical
1693 arguments. Build a vector of candidates forming sets
1694 of argument edges with equal values. Note optimality
1695 depends on the particular choice of the template PHI
1696 since equal arguments are unordered leaving other PHIs
1697 with more than one set of equal arguments within this
1698 argument range unsorted. We'd have to break ties by
1699 looking at other PHI nodes. */
1700 gphi_iterator gsi
= gsi_start_nonvirtual_phis (bb
);
1701 if (gsi_end_p (gsi
))
1703 gphi
*phi
= gsi
.phi ();
1704 auto_vec
<std::pair
<edge
, hashval_t
>, 8> args
;
1705 bool need_resort
= false;
1706 for (unsigned i
= 0; i
< gimple_phi_num_args (phi
); ++i
)
1708 edge e
= gimple_phi_arg_edge (phi
, i
);
1709 /* Skip abnormal edges since we cannot redirect them. */
1710 if (e
->flags
& EDGE_ABNORMAL
)
1712 /* Skip loop exit edges when we are in loop-closed SSA form
1713 since the forwarder we'd create does not have a PHI node. */
1714 if (loops_state_satisfies_p (LOOP_CLOSED_SSA
)
1715 && loop_exit_edge_p (e
->src
->loop_father
, e
))
1718 tree arg
= gimple_phi_arg_def (phi
, i
);
1719 if (!CONSTANT_CLASS_P (arg
) && TREE_CODE (arg
) != SSA_NAME
)
1721 args
.safe_push (std::make_pair (e
, iterative_hash_expr (arg
, 0)));
1723 if (args
.length () < 2)
1725 args
.qsort (sort_phi_args
);
1726 /* The above sorting can be different between -g and -g0, as e.g. decls
1727 can have different uids (-g could have bigger gaps in between them).
1728 So, only use that to determine which args are equal, then change
1729 second from hash value to smallest dest_idx of the edges which have
1730 equal argument and sort again. If all the phi arguments are
1731 constants or SSA_NAME, there is no need for the second sort, the hash
1732 values are stable in that case. */
1733 hashval_t hash
= args
[0].second
;
1734 args
[0].second
= args
[0].first
->dest_idx
;
1735 bool any_equal
= false;
1736 for (unsigned i
= 1; i
< args
.length (); ++i
)
1737 if (hash
== args
[i
].second
1738 && operand_equal_p (PHI_ARG_DEF_FROM_EDGE (phi
, args
[i
- 1].first
),
1739 PHI_ARG_DEF_FROM_EDGE (phi
, args
[i
].first
)))
1741 args
[i
].second
= args
[i
- 1].second
;
1746 hash
= args
[i
].second
;
1747 args
[i
].second
= args
[i
].first
->dest_idx
;
1752 args
.qsort (sort_phi_args
);
1754 /* From the candidates vector now verify true candidates for
1755 forwarders and create them. */
1756 gphi
*vphi
= get_virtual_phi (bb
);
1758 while (start
< args
.length () - 1)
1761 for (i
= start
+ 1; i
< args
.length (); ++i
)
1762 if (args
[start
].second
!= args
[i
].second
)
1764 /* args[start]..args[i-1] are equal. */
1767 /* Check all PHI nodes for argument equality. */
1769 gphi_iterator gsi2
= gsi
;
1771 for (; !gsi_end_p (gsi2
); gsi_next (&gsi2
))
1773 gphi
*phi2
= gsi2
.phi ();
1774 if (virtual_operand_p (gimple_phi_result (phi2
)))
1777 = PHI_ARG_DEF_FROM_EDGE (phi2
, args
[start
].first
);
1778 for (unsigned j
= start
+ 1; j
< i
; ++j
)
1780 if (!operand_equal_p (start_arg
,
1781 PHI_ARG_DEF_FROM_EDGE
1782 (phi2
, args
[j
].first
)))
1784 /* Another PHI might have a shorter set of
1785 equivalent args. Go for that. */
1797 /* If we are asked to forward all edges the block
1798 has all degenerate PHIs. Do nothing in that case. */
1800 && i
== args
.length ()
1801 && args
.length () == gimple_phi_num_args (phi
))
1803 /* Instead of using make_forwarder_block we are
1804 rolling our own variant knowing that the forwarder
1805 does not need PHI nodes apart from eventually
1807 auto_vec
<tree
, 8> vphi_args
;
1810 vphi_args
.reserve_exact (i
- start
);
1811 for (unsigned j
= start
; j
< i
; ++j
)
1812 vphi_args
.quick_push
1813 (PHI_ARG_DEF_FROM_EDGE (vphi
, args
[j
].first
));
1815 free_dominance_info (fn
, CDI_DOMINATORS
);
1816 basic_block forwarder
= split_edge (args
[start
].first
);
1817 for (unsigned j
= start
+ 1; j
< i
; ++j
)
1819 edge e
= args
[j
].first
;
1820 redirect_edge_and_branch_force (e
, forwarder
);
1821 redirect_edge_var_map_clear (e
);
1825 tree def
= copy_ssa_name (vphi_args
[0]);
1826 gphi
*vphi_copy
= create_phi_node (def
, forwarder
);
1827 for (unsigned j
= start
; j
< i
; ++j
)
1828 add_phi_arg (vphi_copy
, vphi_args
[j
- start
],
1829 args
[j
].first
, UNKNOWN_LOCATION
);
1831 (vphi
, single_succ_edge (forwarder
)->dest_idx
, def
);
1833 todo
|= TODO_cleanup_cfg
;
1836 /* Continue searching for more opportunities. */
1843 /* Main routine to eliminate dead code.
1845 AGGRESSIVE controls the aggressiveness of the algorithm.
1846 In conservative mode, we ignore control dependence and simply declare
1847 all but the most trivially dead branches necessary. This mode is fast.
1848 In aggressive mode, control dependences are taken into account, which
1849 results in more dead code elimination, but at the cost of some time.
1851 FIXME: Aggressive mode before PRE doesn't work currently because
1852 the dominance info is not invalidated after DCE1. This is
1853 not an issue right now because we only run aggressive DCE
1854 as the last tree SSA pass, but keep this in mind when you
1855 start experimenting with pass ordering. */
1858 perform_tree_ssa_dce (bool aggressive
)
1860 bool something_changed
= 0;
1863 /* Preheaders are needed for SCEV to work.
1864 Simple lateches and recorded exits improve chances that loop will
1865 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1866 bool in_loop_pipeline
= scev_initialized_p ();
1867 if (aggressive
&& ! in_loop_pipeline
)
1870 loop_optimizer_init (LOOPS_NORMAL
1871 | LOOPS_HAVE_RECORDED_EXITS
);
1875 todo
|= make_forwarders_with_degenerate_phis (cfun
);
1877 calculate_dominance_info (CDI_DOMINATORS
);
1879 tree_dce_init (aggressive
);
1883 /* Compute control dependence. */
1884 calculate_dominance_info (CDI_POST_DOMINATORS
);
1885 cd
= new control_dependences ();
1887 visited_control_parents
=
1888 sbitmap_alloc (last_basic_block_for_fn (cfun
));
1889 bitmap_clear (visited_control_parents
);
1891 mark_dfs_back_edges ();
1894 find_obviously_necessary_stmts (aggressive
);
1896 if (aggressive
&& ! in_loop_pipeline
)
1898 loop_optimizer_finalize ();
1906 visited
= BITMAP_ALLOC (NULL
);
1907 propagate_necessity (aggressive
);
1908 BITMAP_FREE (visited
);
1910 something_changed
|= eliminate_unnecessary_stmts (aggressive
);
1911 something_changed
|= cfg_altered
;
1913 /* We do not update postdominators, so free them unconditionally. */
1914 free_dominance_info (CDI_POST_DOMINATORS
);
1916 /* If we removed paths in the CFG, then we need to update
1917 dominators as well. I haven't investigated the possibility
1918 of incrementally updating dominators. */
1920 free_dominance_info (CDI_DOMINATORS
);
1922 statistics_counter_event (cfun
, "Statements deleted", stats
.removed
);
1923 statistics_counter_event (cfun
, "PHI nodes deleted", stats
.removed_phis
);
1925 /* Debugging dumps. */
1926 if (dump_file
&& (dump_flags
& (TDF_STATS
|TDF_DETAILS
)))
1929 tree_dce_done (aggressive
);
1931 if (something_changed
)
1933 free_numbers_of_iterations_estimates (cfun
);
1934 if (in_loop_pipeline
)
1936 todo
|= TODO_update_ssa
| TODO_cleanup_cfg
;
1941 /* Pass entry points. */
1945 return perform_tree_ssa_dce (/*aggressive=*/false);
1949 tree_ssa_cd_dce (void)
1951 return perform_tree_ssa_dce (/*aggressive=*/optimize
>= 2);
1956 const pass_data pass_data_dce
=
1958 GIMPLE_PASS
, /* type */
1960 OPTGROUP_NONE
, /* optinfo_flags */
1961 TV_TREE_DCE
, /* tv_id */
1962 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1963 0, /* properties_provided */
1964 0, /* properties_destroyed */
1965 0, /* todo_flags_start */
1966 0, /* todo_flags_finish */
1969 class pass_dce
: public gimple_opt_pass
1972 pass_dce (gcc::context
*ctxt
)
1973 : gimple_opt_pass (pass_data_dce
, ctxt
)
1976 /* opt_pass methods: */
1977 opt_pass
* clone () { return new pass_dce (m_ctxt
); }
1978 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1979 virtual unsigned int execute (function
*) { return tree_ssa_dce (); }
1981 }; // class pass_dce
1986 make_pass_dce (gcc::context
*ctxt
)
1988 return new pass_dce (ctxt
);
1993 const pass_data pass_data_cd_dce
=
1995 GIMPLE_PASS
, /* type */
1997 OPTGROUP_NONE
, /* optinfo_flags */
1998 TV_TREE_CD_DCE
, /* tv_id */
1999 ( PROP_cfg
| PROP_ssa
), /* properties_required */
2000 0, /* properties_provided */
2001 0, /* properties_destroyed */
2002 0, /* todo_flags_start */
2003 0, /* todo_flags_finish */
2006 class pass_cd_dce
: public gimple_opt_pass
2009 pass_cd_dce (gcc::context
*ctxt
)
2010 : gimple_opt_pass (pass_data_cd_dce
, ctxt
), update_address_taken_p (false)
2013 /* opt_pass methods: */
2014 opt_pass
* clone () { return new pass_cd_dce (m_ctxt
); }
2015 void set_pass_param (unsigned n
, bool param
)
2017 gcc_assert (n
== 0);
2018 update_address_taken_p
= param
;
2020 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
2021 virtual unsigned int execute (function
*)
2023 return (tree_ssa_cd_dce ()
2024 | (update_address_taken_p
? TODO_update_address_taken
: 0));
2028 bool update_address_taken_p
;
2029 }; // class pass_cd_dce
2034 make_pass_cd_dce (gcc::context
*ctxt
)
2036 return new pass_cd_dce (ctxt
);
2040 /* A cheap DCE interface. WORKLIST is a list of possibly dead stmts and
2041 is consumed by this function. The function has linear complexity in
2042 the number of dead stmts with a constant factor like the average SSA
2043 use operands number. */
2046 simple_dce_from_worklist (bitmap worklist
)
2048 while (! bitmap_empty_p (worklist
))
2051 unsigned i
= bitmap_first_set_bit (worklist
);
2052 bitmap_clear_bit (worklist
, i
);
2054 tree def
= ssa_name (i
);
2055 /* Removed by somebody else or still in use. */
2056 if (! def
|| ! has_zero_uses (def
))
2059 gimple
*t
= SSA_NAME_DEF_STMT (def
);
2060 if (gimple_has_side_effects (t
))
2063 /* Don't remove statements that are needed for non-call
2065 if (stmt_unremovable_because_of_non_call_eh_p (cfun
, t
))
2068 /* Add uses to the worklist. */
2070 use_operand_p use_p
;
2071 FOR_EACH_PHI_OR_STMT_USE (use_p
, t
, iter
, SSA_OP_USE
)
2073 tree use
= USE_FROM_PTR (use_p
);
2074 if (TREE_CODE (use
) == SSA_NAME
2075 && ! SSA_NAME_IS_DEFAULT_DEF (use
))
2076 bitmap_set_bit (worklist
, SSA_NAME_VERSION (use
));
2080 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
2082 fprintf (dump_file
, "Removing dead stmt:");
2083 print_gimple_stmt (dump_file
, t
, 0);
2085 gimple_stmt_iterator gsi
= gsi_for_stmt (t
);
2086 if (gimple_code (t
) == GIMPLE_PHI
)
2087 remove_phi_node (&gsi
, true);
2090 gsi_remove (&gsi
, true);