1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002-2023 Free Software Foundation, Inc.
3 Contributed by Ben Elliston <bje@redhat.com>
4 and Andrew MacLeod <amacleod@redhat.com>
5 Adapted to use control dependence by Steven Bosscher, SUSE Labs.
7 This file is part of GCC.
9 GCC is free software; you can redistribute it and/or modify it
10 under the terms of the GNU General Public License as published by the
11 Free Software Foundation; either version 3, or (at your option) any
14 GCC is distributed in the hope that it will be useful, but WITHOUT
15 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
16 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
19 You should have received a copy of the GNU General Public License
20 along with GCC; see the file COPYING3. If not see
21 <http://www.gnu.org/licenses/>. */
23 /* Dead code elimination.
27 Building an Optimizing Compiler,
28 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
30 Advanced Compiler Design and Implementation,
31 Steven Muchnick, Morgan Kaufmann, 1997, Section 18.10.
33 Dead-code elimination is the removal of statements which have no
34 impact on the program's output. "Dead statements" have no impact
35 on the program's output, while "necessary statements" may have
38 The algorithm consists of three phases:
39 1. Marking as necessary all statements known to be necessary,
40 e.g. most function calls, writing a value to memory, etc;
41 2. Propagating necessary statements, e.g., the statements
42 giving values to operands in necessary statements; and
43 3. Removing dead statements. */
47 #include "coretypes.h"
53 #include "tree-pass.h"
55 #include "gimple-pretty-print.h"
56 #include "fold-const.h"
61 #include "gimple-iterator.h"
63 #include "tree-ssa-loop-niter.h"
64 #include "tree-into-ssa.h"
67 #include "tree-scalar-evolution.h"
68 #include "tree-ssa-propagate.h"
69 #include "gimple-fold.h"
72 static struct stmt_stats
80 #define STMT_NECESSARY GF_PLF_1
82 static vec
<gimple
*> worklist
;
84 /* Vector indicating an SSA name has already been processed and marked
86 static sbitmap processed
;
88 /* Vector indicating that the last statement of a basic block has already
89 been marked as necessary. */
90 static sbitmap last_stmt_necessary
;
92 /* Vector indicating that BB contains statements that are live. */
93 static sbitmap bb_contains_live_stmts
;
95 /* Before we can determine whether a control branch is dead, we need to
96 compute which blocks are control dependent on which edges.
98 We expect each block to be control dependent on very few edges so we
99 use a bitmap for each block recording its edges. An array holds the
100 bitmap. The Ith bit in the bitmap is set if that block is dependent
102 static control_dependences
*cd
;
104 /* Vector indicating that a basic block has already had all the edges
105 processed that it is control dependent on. */
106 static sbitmap visited_control_parents
;
108 /* TRUE if this pass alters the CFG (by removing control statements).
111 If this pass alters the CFG, then it will arrange for the dominators
113 static bool cfg_altered
;
115 /* When non-NULL holds map from basic block index into the postorder. */
116 static int *bb_postorder
;
119 /* True if we should treat any stmt with a vdef as necessary. */
124 return optimize_debug
;
127 /* If STMT is not already marked necessary, mark it, and add it to the
128 worklist if ADD_TO_WORKLIST is true. */
131 mark_stmt_necessary (gimple
*stmt
, bool add_to_worklist
)
135 if (gimple_plf (stmt
, STMT_NECESSARY
))
138 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
140 fprintf (dump_file
, "Marking useful stmt: ");
141 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
142 fprintf (dump_file
, "\n");
145 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
147 worklist
.safe_push (stmt
);
148 if (add_to_worklist
&& bb_contains_live_stmts
&& !is_gimple_debug (stmt
))
149 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
153 /* Mark the statement defining operand OP as necessary. */
156 mark_operand_necessary (tree op
)
163 ver
= SSA_NAME_VERSION (op
);
164 if (bitmap_bit_p (processed
, ver
))
166 stmt
= SSA_NAME_DEF_STMT (op
);
167 gcc_assert (gimple_nop_p (stmt
)
168 || gimple_plf (stmt
, STMT_NECESSARY
));
171 bitmap_set_bit (processed
, ver
);
173 stmt
= SSA_NAME_DEF_STMT (op
);
176 if (gimple_plf (stmt
, STMT_NECESSARY
) || gimple_nop_p (stmt
))
179 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
181 fprintf (dump_file
, "marking necessary through ");
182 print_generic_expr (dump_file
, op
);
183 fprintf (dump_file
, " stmt ");
184 print_gimple_stmt (dump_file
, stmt
, 0);
187 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
188 if (bb_contains_live_stmts
)
189 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
190 worklist
.safe_push (stmt
);
194 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
195 it can make other statements necessary.
197 If AGGRESSIVE is false, control statements are conservatively marked as
201 mark_stmt_if_obviously_necessary (gimple
*stmt
, bool aggressive
)
203 /* Statements that are implicitly live. Most function calls, asm
204 and return statements are required. Labels and GIMPLE_BIND nodes
205 are kept because they are control flow, and we have no way of
206 knowing whether they can be removed. DCE can eliminate all the
207 other statements in a block, and CFG can then remove the block
209 switch (gimple_code (stmt
))
213 mark_stmt_necessary (stmt
, false);
219 mark_stmt_necessary (stmt
, true);
224 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 if (!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 gimple
*stmt
= *gsi_last_bb (bb
);
340 if (stmt
&& is_ctrl_stmt (stmt
))
342 mark_stmt_necessary (stmt
, true);
349 /* Mark control dependent edges of BB as necessary. We have to do this only
350 once for each basic block so we set the appropriate bit after we're done.
352 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
355 mark_control_dependent_edges_necessary (basic_block bb
, bool ignore_self
)
358 unsigned edge_number
;
359 bool skipped
= false;
361 gcc_assert (bb
!= EXIT_BLOCK_PTR_FOR_FN (cfun
));
363 if (bb
== ENTRY_BLOCK_PTR_FOR_FN (cfun
))
366 EXECUTE_IF_SET_IN_BITMAP (cd
->get_edges_dependent_on (bb
->index
),
369 basic_block cd_bb
= cd
->get_edge_src (edge_number
);
371 if (ignore_self
&& cd_bb
== bb
)
377 if (!mark_last_stmt_necessary (cd_bb
))
378 mark_control_dependent_edges_necessary (cd_bb
, false);
382 bitmap_set_bit (visited_control_parents
, bb
->index
);
386 /* Find obviously necessary statements. These are things like most function
387 calls, and stores to file level variables.
389 If EL is NULL, control statements are conservatively marked as
390 necessary. Otherwise it contains the list of edges used by control
391 dependence analysis. */
394 find_obviously_necessary_stmts (bool aggressive
)
397 gimple_stmt_iterator gsi
;
402 FOR_EACH_BB_FN (bb
, cfun
)
404 /* PHI nodes are never inherently necessary. */
405 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
407 phi
= gsi_stmt (gsi
);
408 gimple_set_plf (phi
, STMT_NECESSARY
, false);
411 /* Check all statements in the block. */
412 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
414 stmt
= gsi_stmt (gsi
);
415 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
416 mark_stmt_if_obviously_necessary (stmt
, aggressive
);
420 /* Pure and const functions are finite and thus have no infinite loops in
422 flags
= flags_from_decl_or_type (current_function_decl
);
423 if ((flags
& (ECF_CONST
|ECF_PURE
)) && !(flags
& ECF_LOOPING_CONST_OR_PURE
))
426 /* Prevent the empty possibly infinite loops from being removed. This is
427 needed to make the logic in remove_dead_stmt work to identify the
428 correct edge to keep when removing a controlling condition. */
431 if (mark_irreducible_loops ())
432 FOR_EACH_BB_FN (bb
, cfun
)
435 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
436 if ((e
->flags
& EDGE_DFS_BACK
)
437 && (e
->flags
& EDGE_IRREDUCIBLE_LOOP
))
440 fprintf (dump_file
, "Marking back edge of irreducible "
441 "loop %i->%i\n", e
->src
->index
, e
->dest
->index
);
442 mark_control_dependent_edges_necessary (e
->dest
, false);
446 for (auto loop
: loops_list (cfun
, 0))
447 /* For loops without an exit do not mark any condition. */
448 if (loop
->exits
->next
->e
&& !finite_loop_p (loop
))
451 fprintf (dump_file
, "cannot prove finiteness of loop %i\n",
453 mark_control_dependent_edges_necessary (loop
->latch
, false);
459 /* Return true if REF is based on an aliased base, otherwise false. */
462 ref_may_be_aliased (tree ref
)
464 gcc_assert (TREE_CODE (ref
) != WITH_SIZE_EXPR
);
465 while (handled_component_p (ref
))
466 ref
= TREE_OPERAND (ref
, 0);
467 if ((TREE_CODE (ref
) == MEM_REF
|| TREE_CODE (ref
) == TARGET_MEM_REF
)
468 && TREE_CODE (TREE_OPERAND (ref
, 0)) == ADDR_EXPR
)
469 ref
= TREE_OPERAND (TREE_OPERAND (ref
, 0), 0);
470 return !(DECL_P (ref
)
471 && !may_be_aliased (ref
));
474 static bitmap visited
= NULL
;
475 static unsigned int longest_chain
= 0;
476 static unsigned int total_chain
= 0;
477 static unsigned int nr_walks
= 0;
478 static bool chain_ovfl
= false;
480 /* Worker for the walker that marks reaching definitions of REF,
481 which is based on a non-aliased decl, necessary. It returns
482 true whenever the defining statement of the current VDEF is
483 a kill for REF, as no dominating may-defs are necessary for REF
484 anymore. DATA points to the basic-block that contains the
485 stmt that refers to REF. */
488 mark_aliased_reaching_defs_necessary_1 (ao_ref
*ref
, tree vdef
, void *data
)
490 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
492 /* All stmts we visit are necessary. */
493 if (! gimple_clobber_p (def_stmt
))
494 mark_operand_necessary (vdef
);
496 /* If the stmt lhs kills ref, then we can stop walking. */
497 if (gimple_has_lhs (def_stmt
)
498 && TREE_CODE (gimple_get_lhs (def_stmt
)) != SSA_NAME
499 /* The assignment is not necessarily carried out if it can throw
500 and we can catch it in the current function where we could inspect
502 ??? We only need to care about the RHS throwing. For aggregate
503 assignments or similar calls and non-call exceptions the LHS
504 might throw as well. */
505 && !stmt_can_throw_internal (cfun
, def_stmt
))
507 tree base
, lhs
= gimple_get_lhs (def_stmt
);
508 poly_int64 size
, offset
, max_size
;
512 = get_ref_base_and_extent (lhs
, &offset
, &size
, &max_size
, &reverse
);
513 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
514 so base == refd->base does not always hold. */
515 if (base
== ref
->base
)
517 /* For a must-alias check we need to be able to constrain
518 the accesses properly. */
519 if (known_eq (size
, max_size
)
520 && known_subrange_p (ref
->offset
, ref
->max_size
, offset
, size
))
522 /* Or they need to be exactly the same. */
524 /* Make sure there is no induction variable involved
525 in the references (gcc.c-torture/execute/pr42142.c).
526 The simplest way is to check if the kill dominates
528 /* But when both are in the same block we cannot
529 easily tell whether we came from a backedge
530 unless we decide to compute stmt UIDs
532 && (basic_block
) data
!= gimple_bb (def_stmt
)
533 && dominated_by_p (CDI_DOMINATORS
, (basic_block
) data
,
534 gimple_bb (def_stmt
))
535 && operand_equal_p (ref
->ref
, lhs
, 0))
540 /* Otherwise keep walking. */
545 mark_aliased_reaching_defs_necessary (gimple
*stmt
, tree ref
)
547 /* Should have been caught before calling this function. */
548 gcc_checking_assert (!keep_all_vdefs_p ());
552 gcc_assert (!chain_ovfl
);
553 ao_ref_init (&refd
, ref
);
554 chain
= walk_aliased_vdefs (&refd
, gimple_vuse (stmt
),
555 mark_aliased_reaching_defs_necessary_1
,
556 gimple_bb (stmt
), NULL
);
557 if (chain
> longest_chain
)
558 longest_chain
= chain
;
559 total_chain
+= chain
;
563 /* Worker for the walker that marks reaching definitions of REF, which
564 is not based on a non-aliased decl. For simplicity we need to end
565 up marking all may-defs necessary that are not based on a non-aliased
566 decl. The only job of this walker is to skip may-defs based on
567 a non-aliased decl. */
570 mark_all_reaching_defs_necessary_1 (ao_ref
*ref ATTRIBUTE_UNUSED
,
571 tree vdef
, void *data ATTRIBUTE_UNUSED
)
573 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
575 /* We have to skip already visited (and thus necessary) statements
576 to make the chaining work after we dropped back to simple mode. */
578 && bitmap_bit_p (processed
, SSA_NAME_VERSION (vdef
)))
580 gcc_assert (gimple_nop_p (def_stmt
)
581 || gimple_plf (def_stmt
, STMT_NECESSARY
));
585 /* We want to skip stores to non-aliased variables. */
587 && gimple_assign_single_p (def_stmt
))
589 tree lhs
= gimple_assign_lhs (def_stmt
);
590 if (!ref_may_be_aliased (lhs
))
594 /* We want to skip statments that do not constitute stores but have
595 a virtual definition. */
596 if (gcall
*call
= dyn_cast
<gcall
*> (def_stmt
))
598 tree callee
= gimple_call_fndecl (call
);
599 if (callee
!= NULL_TREE
600 && fndecl_built_in_p (callee
, BUILT_IN_NORMAL
))
601 switch (DECL_FUNCTION_CODE (callee
))
603 case BUILT_IN_MALLOC
:
604 case BUILT_IN_ALIGNED_ALLOC
:
605 case BUILT_IN_CALLOC
:
606 CASE_BUILT_IN_ALLOCA
:
608 case BUILT_IN_GOMP_ALLOC
:
609 case BUILT_IN_GOMP_FREE
:
615 if (callee
!= NULL_TREE
616 && (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
)
617 || DECL_IS_OPERATOR_DELETE_P (callee
))
618 && gimple_call_from_new_or_delete (call
))
622 if (! gimple_clobber_p (def_stmt
))
623 mark_operand_necessary (vdef
);
629 mark_all_reaching_defs_necessary (gimple
*stmt
)
631 /* Should have been caught before calling this function. */
632 gcc_checking_assert (!keep_all_vdefs_p ());
633 walk_aliased_vdefs (NULL
, gimple_vuse (stmt
),
634 mark_all_reaching_defs_necessary_1
, NULL
, &visited
);
637 /* Return true for PHI nodes with one or identical arguments
640 degenerate_phi_p (gimple
*phi
)
643 tree op
= gimple_phi_arg_def (phi
, 0);
644 for (i
= 1; i
< gimple_phi_num_args (phi
); i
++)
645 if (gimple_phi_arg_def (phi
, i
) != op
)
650 /* Return that NEW_CALL and DELETE_CALL are a valid pair of new
651 and delete operators. */
654 valid_new_delete_pair_p (gimple
*new_call
, gimple
*delete_call
)
656 tree new_asm
= DECL_ASSEMBLER_NAME (gimple_call_fndecl (new_call
));
657 tree delete_asm
= DECL_ASSEMBLER_NAME (gimple_call_fndecl (delete_call
));
658 return valid_new_delete_pair_p (new_asm
, delete_asm
);
661 /* Propagate necessity using the operands of necessary statements.
662 Process the uses on each statement in the worklist, and add all
663 feeding statements which contribute to the calculation of this
664 value to the worklist.
666 In conservative mode, EL is NULL. */
669 propagate_necessity (bool aggressive
)
673 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
674 fprintf (dump_file
, "\nProcessing worklist:\n");
676 while (worklist
.length () > 0)
678 /* Take STMT from worklist. */
679 stmt
= worklist
.pop ();
681 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
683 fprintf (dump_file
, "processing: ");
684 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
685 fprintf (dump_file
, "\n");
690 /* Mark the last statement of the basic blocks on which the block
691 containing STMT is control dependent, but only if we haven't
693 basic_block bb
= gimple_bb (stmt
);
694 if (bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
695 && !bitmap_bit_p (visited_control_parents
, bb
->index
))
696 mark_control_dependent_edges_necessary (bb
, false);
699 if (gimple_code (stmt
) == GIMPLE_PHI
700 /* We do not process virtual PHI nodes nor do we track their
702 && !virtual_operand_p (gimple_phi_result (stmt
)))
704 /* PHI nodes are somewhat special in that each PHI alternative has
705 data and control dependencies. All the statements feeding the
706 PHI node's arguments are always necessary. In aggressive mode,
707 we also consider the control dependent edges leading to the
708 predecessor block associated with each PHI alternative as
710 gphi
*phi
= as_a
<gphi
*> (stmt
);
713 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
715 tree arg
= PHI_ARG_DEF (stmt
, k
);
716 if (TREE_CODE (arg
) == SSA_NAME
)
717 mark_operand_necessary (arg
);
720 /* For PHI operands it matters from where the control flow arrives
721 to the BB. Consider the following example:
731 We need to mark control dependence of the empty basic blocks, since they
732 contains computation of PHI operands.
734 Doing so is too restrictive in the case the predecestor block is in
740 for (i = 0; i<1000; ++i)
746 There is PHI for J in the BB containing return statement.
747 In this case the control dependence of predecestor block (that is
748 within the empty loop) also contains the block determining number
749 of iterations of the block that would prevent removing of empty
752 This scenario can be avoided by splitting critical edges.
753 To save the critical edge splitting pass we identify how the control
754 dependence would look like if the edge was split.
756 Consider the modified CFG created from current CFG by splitting
757 edge B->C. In the postdominance tree of modified CFG, C' is
758 always child of C. There are two cases how chlids of C' can look
763 In this case the only basic block C' is control dependent on is B.
765 2) C' has single child that is B
767 In this case control dependence of C' is same as control
768 dependence of B in original CFG except for block B itself.
769 (since C' postdominate B in modified CFG)
771 Now how to decide what case happens? There are two basic options:
773 a) C postdominate B. Then C immediately postdominate B and
774 case 2 happens iff there is no other way from B to C except
777 There is other way from B to C iff there is succesor of B that
778 is not postdominated by B. Testing this condition is somewhat
779 expensive, because we need to iterate all succesors of B.
780 We are safe to assume that this does not happen: we will mark B
781 as needed when processing the other path from B to C that is
782 conrol dependent on B and marking control dependencies of B
783 itself is harmless because they will be processed anyway after
784 processing control statement in B.
786 b) C does not postdominate B. Always case 1 happens since there is
787 path from C to exit that does not go through B and thus also C'. */
789 if (aggressive
&& !degenerate_phi_p (stmt
))
791 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
793 basic_block arg_bb
= gimple_phi_arg_edge (phi
, k
)->src
;
796 != get_immediate_dominator (CDI_POST_DOMINATORS
, arg_bb
))
798 if (!mark_last_stmt_necessary (arg_bb
))
799 mark_control_dependent_edges_necessary (arg_bb
, false);
801 else if (arg_bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
802 && !bitmap_bit_p (visited_control_parents
,
804 mark_control_dependent_edges_necessary (arg_bb
, true);
810 /* Propagate through the operands. Examine all the USE, VUSE and
811 VDEF operands in this statement. Mark all the statements
812 which feed this statement's uses as necessary. */
816 /* If this is a call to free which is directly fed by an
817 allocation function do not mark that necessary through
818 processing the argument. */
819 bool is_delete_operator
820 = (is_gimple_call (stmt
)
821 && gimple_call_from_new_or_delete (as_a
<gcall
*> (stmt
))
822 && gimple_call_operator_delete_p (as_a
<gcall
*> (stmt
)));
823 if (is_delete_operator
824 || gimple_call_builtin_p (stmt
, BUILT_IN_FREE
)
825 || gimple_call_builtin_p (stmt
, BUILT_IN_GOMP_FREE
))
827 tree ptr
= gimple_call_arg (stmt
, 0);
830 /* If the pointer we free is defined by an allocation
831 function do not add the call to the worklist. */
832 if (TREE_CODE (ptr
) == SSA_NAME
833 && (def_stmt
= dyn_cast
<gcall
*> (SSA_NAME_DEF_STMT (ptr
)))
834 && (def_callee
= gimple_call_fndecl (def_stmt
))
835 && ((DECL_BUILT_IN_CLASS (def_callee
) == BUILT_IN_NORMAL
836 && (DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_ALIGNED_ALLOC
837 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_MALLOC
838 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_CALLOC
839 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_GOMP_ALLOC
))
840 || (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (def_callee
)
841 && gimple_call_from_new_or_delete (def_stmt
))))
843 if (is_delete_operator
844 && !valid_new_delete_pair_p (def_stmt
, stmt
))
845 mark_operand_necessary (gimple_call_arg (stmt
, 0));
847 /* Delete operators can have alignment and (or) size
848 as next arguments. When being a SSA_NAME, they
849 must be marked as necessary. Similarly GOMP_free. */
850 if (gimple_call_num_args (stmt
) >= 2)
851 for (unsigned i
= 1; i
< gimple_call_num_args (stmt
);
854 tree arg
= gimple_call_arg (stmt
, i
);
855 if (TREE_CODE (arg
) == SSA_NAME
)
856 mark_operand_necessary (arg
);
863 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
864 mark_operand_necessary (use
);
866 use
= gimple_vuse (stmt
);
870 /* No need to search for vdefs if we intrinsicly keep them all. */
871 if (keep_all_vdefs_p ())
874 /* If we dropped to simple mode make all immediately
875 reachable definitions necessary. */
878 mark_all_reaching_defs_necessary (stmt
);
882 /* For statements that may load from memory (have a VUSE) we
883 have to mark all reaching (may-)definitions as necessary.
884 We partition this task into two cases:
885 1) explicit loads based on decls that are not aliased
886 2) implicit loads (like calls) and explicit loads not
887 based on decls that are not aliased (like indirect
888 references or loads from globals)
889 For 1) we mark all reaching may-defs as necessary, stopping
890 at dominating kills. For 2) we want to mark all dominating
891 references necessary, but non-aliased ones which we handle
892 in 1). By keeping a global visited bitmap for references
893 we walk for 2) we avoid quadratic behavior for those. */
895 if (gcall
*call
= dyn_cast
<gcall
*> (stmt
))
897 tree callee
= gimple_call_fndecl (call
);
900 /* Calls to functions that are merely acting as barriers
901 or that only store to memory do not make any previous
903 if (callee
!= NULL_TREE
904 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
905 && (DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET
906 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET_CHK
907 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MALLOC
908 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALIGNED_ALLOC
909 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_CALLOC
910 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_FREE
911 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_VA_END
912 || ALLOCA_FUNCTION_CODE_P (DECL_FUNCTION_CODE (callee
))
913 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_SAVE
914 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_RESTORE
915 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ASSUME_ALIGNED
))
918 if (callee
!= NULL_TREE
919 && (DECL_IS_REPLACEABLE_OPERATOR_NEW_P (callee
)
920 || DECL_IS_OPERATOR_DELETE_P (callee
))
921 && gimple_call_from_new_or_delete (call
))
924 /* Calls implicitly load from memory, their arguments
925 in addition may explicitly perform memory loads. */
926 mark_all_reaching_defs_necessary (call
);
927 for (i
= 0; i
< gimple_call_num_args (call
); ++i
)
929 tree arg
= gimple_call_arg (call
, i
);
930 if (TREE_CODE (arg
) == SSA_NAME
931 || is_gimple_min_invariant (arg
))
933 if (TREE_CODE (arg
) == WITH_SIZE_EXPR
)
934 arg
= TREE_OPERAND (arg
, 0);
935 if (!ref_may_be_aliased (arg
))
936 mark_aliased_reaching_defs_necessary (call
, arg
);
939 else if (gimple_assign_single_p (stmt
))
942 /* If this is a load mark things necessary. */
943 rhs
= gimple_assign_rhs1 (stmt
);
944 if (TREE_CODE (rhs
) != SSA_NAME
945 && !is_gimple_min_invariant (rhs
)
946 && TREE_CODE (rhs
) != CONSTRUCTOR
)
948 if (!ref_may_be_aliased (rhs
))
949 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
951 mark_all_reaching_defs_necessary (stmt
);
954 else if (greturn
*return_stmt
= dyn_cast
<greturn
*> (stmt
))
956 tree rhs
= gimple_return_retval (return_stmt
);
957 /* A return statement may perform a load. */
959 && TREE_CODE (rhs
) != SSA_NAME
960 && !is_gimple_min_invariant (rhs
)
961 && TREE_CODE (rhs
) != CONSTRUCTOR
)
963 if (!ref_may_be_aliased (rhs
))
964 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
966 mark_all_reaching_defs_necessary (stmt
);
969 else if (gasm
*asm_stmt
= dyn_cast
<gasm
*> (stmt
))
972 mark_all_reaching_defs_necessary (stmt
);
973 /* Inputs may perform loads. */
974 for (i
= 0; i
< gimple_asm_ninputs (asm_stmt
); ++i
)
976 tree op
= TREE_VALUE (gimple_asm_input_op (asm_stmt
, i
));
977 if (TREE_CODE (op
) != SSA_NAME
978 && !is_gimple_min_invariant (op
)
979 && TREE_CODE (op
) != CONSTRUCTOR
980 && !ref_may_be_aliased (op
))
981 mark_aliased_reaching_defs_necessary (stmt
, op
);
984 else if (gimple_code (stmt
) == GIMPLE_TRANSACTION
)
986 /* The beginning of a transaction is a memory barrier. */
987 /* ??? If we were really cool, we'd only be a barrier
988 for the memories touched within the transaction. */
989 mark_all_reaching_defs_necessary (stmt
);
994 /* If we over-used our alias oracle budget drop to simple
995 mode. The cost metric allows quadratic behavior
996 (number of uses times number of may-defs queries) up to
997 a constant maximal number of queries and after that falls back to
998 super-linear complexity. */
999 if (/* Constant but quadratic for small functions. */
1000 total_chain
> 128 * 128
1001 /* Linear in the number of may-defs. */
1002 && total_chain
> 32 * longest_chain
1003 /* Linear in the number of uses. */
1004 && total_chain
> nr_walks
* 32)
1008 bitmap_clear (visited
);
1014 /* Remove dead PHI nodes from block BB. */
1017 remove_dead_phis (basic_block bb
)
1019 bool something_changed
= false;
1023 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);)
1028 /* We do not track necessity of virtual PHI nodes. Instead do
1029 very simple dead PHI removal here. */
1030 if (virtual_operand_p (gimple_phi_result (phi
)))
1032 /* Virtual PHI nodes with one or identical arguments
1034 if (!loops_state_satisfies_p (LOOP_CLOSED_SSA
)
1035 && degenerate_phi_p (phi
))
1037 tree vdef
= gimple_phi_result (phi
);
1038 tree vuse
= gimple_phi_arg_def (phi
, 0);
1040 use_operand_p use_p
;
1041 imm_use_iterator iter
;
1043 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, vdef
)
1044 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
1045 SET_USE (use_p
, vuse
);
1046 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef
)
1047 && TREE_CODE (vuse
) == SSA_NAME
)
1048 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse
) = 1;
1051 gimple_set_plf (phi
, STMT_NECESSARY
, true);
1054 if (!gimple_plf (phi
, STMT_NECESSARY
))
1056 something_changed
= true;
1057 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1059 fprintf (dump_file
, "Deleting : ");
1060 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
1061 fprintf (dump_file
, "\n");
1064 remove_phi_node (&gsi
, true);
1065 stats
.removed_phis
++;
1071 return something_changed
;
1075 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1076 containing I so that we don't have to look it up. */
1079 remove_dead_stmt (gimple_stmt_iterator
*i
, basic_block bb
,
1080 vec
<edge
> &to_remove_edges
)
1082 gimple
*stmt
= gsi_stmt (*i
);
1084 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1086 fprintf (dump_file
, "Deleting : ");
1087 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1088 fprintf (dump_file
, "\n");
1093 /* If we have determined that a conditional branch statement contributes
1094 nothing to the program, then we not only remove it, but we need to update
1095 the CFG. We can chose any of edges out of BB as long as we are sure to not
1096 close infinite loops. This is done by always choosing the edge closer to
1097 exit in inverted_rev_post_order_compute order. */
1098 if (is_ctrl_stmt (stmt
))
1103 /* See if there is only one non-abnormal edge. */
1104 if (single_succ_p (bb
))
1105 e
= single_succ_edge (bb
);
1106 /* Otherwise chose one that is closer to bb with live statement in it.
1107 To be able to chose one, we compute inverted post order starting from
1108 all BBs with live statements. */
1113 int *rpo
= XNEWVEC (int, n_basic_blocks_for_fn (cfun
));
1114 int n
= inverted_rev_post_order_compute (cfun
, rpo
,
1115 &bb_contains_live_stmts
);
1116 bb_postorder
= XNEWVEC (int, last_basic_block_for_fn (cfun
));
1117 for (int i
= 0; i
< n
; ++i
)
1118 bb_postorder
[rpo
[i
]] = i
;
1121 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1122 if (!e
|| e2
->dest
== EXIT_BLOCK_PTR_FOR_FN (cfun
)
1123 || bb_postorder
[e
->dest
->index
]
1124 >= bb_postorder
[e2
->dest
->index
])
1128 e
->probability
= profile_probability::always ();
1130 /* The edge is no longer associated with a conditional, so it does
1131 not have TRUE/FALSE flags.
1132 We are also safe to drop EH/ABNORMAL flags and turn them into
1133 normal control flow, because we know that all the destinations (including
1134 those odd edges) are equivalent for program execution. */
1135 e
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
| EDGE_EH
| EDGE_ABNORMAL
);
1137 /* The lone outgoing edge from BB will be a fallthru edge. */
1138 e
->flags
|= EDGE_FALLTHRU
;
1140 /* Remove the remaining outgoing edges. */
1141 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1144 /* If we made a BB unconditionally exit a loop or removed
1145 an entry into an irreducible region, then this transform
1146 alters the set of BBs in the loop. Schedule a fixup. */
1147 if (loop_exit_edge_p (bb
->loop_father
, e
)
1148 || (e2
->dest
->flags
& BB_IRREDUCIBLE_LOOP
))
1149 loops_state_set (LOOPS_NEED_FIXUP
);
1150 to_remove_edges
.safe_push (e2
);
1154 /* If this is a store into a variable that is being optimized away,
1155 add a debug bind stmt if possible. */
1156 if (MAY_HAVE_DEBUG_BIND_STMTS
1157 && gimple_assign_single_p (stmt
)
1158 && is_gimple_val (gimple_assign_rhs1 (stmt
)))
1160 tree lhs
= gimple_assign_lhs (stmt
);
1161 if ((VAR_P (lhs
) || TREE_CODE (lhs
) == PARM_DECL
)
1162 && !DECL_IGNORED_P (lhs
)
1163 && is_gimple_reg_type (TREE_TYPE (lhs
))
1164 && !is_global_var (lhs
)
1165 && !DECL_HAS_VALUE_EXPR_P (lhs
))
1167 tree rhs
= gimple_assign_rhs1 (stmt
);
1169 = gimple_build_debug_bind (lhs
, unshare_expr (rhs
), stmt
);
1170 gsi_insert_after (i
, note
, GSI_SAME_STMT
);
1174 unlink_stmt_vdef (stmt
);
1175 gsi_remove (i
, true);
1176 release_defs (stmt
);
1179 /* Helper for maybe_optimize_arith_overflow. Find in *TP if there are any
1180 uses of data (SSA_NAME) other than REALPART_EXPR referencing it. */
1183 find_non_realpart_uses (tree
*tp
, int *walk_subtrees
, void *data
)
1185 if (TYPE_P (*tp
) || TREE_CODE (*tp
) == REALPART_EXPR
)
1187 if (*tp
== (tree
) data
)
1192 /* If the IMAGPART_EXPR of the {ADD,SUB,MUL}_OVERFLOW result is never used,
1193 but REALPART_EXPR is, optimize the {ADD,SUB,MUL}_OVERFLOW internal calls
1194 into plain unsigned {PLUS,MINUS,MULT}_EXPR, and if needed reset debug
1198 maybe_optimize_arith_overflow (gimple_stmt_iterator
*gsi
,
1199 enum tree_code subcode
)
1201 gimple
*stmt
= gsi_stmt (*gsi
);
1202 tree lhs
= gimple_call_lhs (stmt
);
1204 if (lhs
== NULL
|| TREE_CODE (lhs
) != SSA_NAME
)
1207 imm_use_iterator imm_iter
;
1208 use_operand_p use_p
;
1209 bool has_debug_uses
= false;
1210 bool has_realpart_uses
= false;
1211 bool has_other_uses
= false;
1212 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, lhs
)
1214 gimple
*use_stmt
= USE_STMT (use_p
);
1215 if (is_gimple_debug (use_stmt
))
1216 has_debug_uses
= true;
1217 else if (is_gimple_assign (use_stmt
)
1218 && gimple_assign_rhs_code (use_stmt
) == REALPART_EXPR
1219 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt
), 0) == lhs
)
1220 has_realpart_uses
= true;
1223 has_other_uses
= true;
1228 if (!has_realpart_uses
|| has_other_uses
)
1231 tree arg0
= gimple_call_arg (stmt
, 0);
1232 tree arg1
= gimple_call_arg (stmt
, 1);
1233 location_t loc
= gimple_location (stmt
);
1234 tree type
= TREE_TYPE (TREE_TYPE (lhs
));
1236 if (!TYPE_UNSIGNED (type
))
1237 utype
= build_nonstandard_integer_type (TYPE_PRECISION (type
), 1);
1238 tree result
= fold_build2_loc (loc
, subcode
, utype
,
1239 fold_convert_loc (loc
, utype
, arg0
),
1240 fold_convert_loc (loc
, utype
, arg1
));
1241 result
= fold_convert_loc (loc
, type
, result
);
1246 FOR_EACH_IMM_USE_STMT (use_stmt
, imm_iter
, lhs
)
1248 if (!gimple_debug_bind_p (use_stmt
))
1250 tree v
= gimple_debug_bind_get_value (use_stmt
);
1251 if (walk_tree (&v
, find_non_realpart_uses
, lhs
, NULL
))
1253 gimple_debug_bind_reset_value (use_stmt
);
1254 update_stmt (use_stmt
);
1259 if (TREE_CODE (result
) == INTEGER_CST
&& TREE_OVERFLOW (result
))
1260 result
= drop_tree_overflow (result
);
1261 tree overflow
= build_zero_cst (type
);
1262 tree ctype
= build_complex_type (type
);
1263 if (TREE_CODE (result
) == INTEGER_CST
)
1264 result
= build_complex (ctype
, result
, overflow
);
1266 result
= build2_loc (gimple_location (stmt
), COMPLEX_EXPR
,
1267 ctype
, result
, overflow
);
1269 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1271 fprintf (dump_file
, "Transforming call: ");
1272 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1273 fprintf (dump_file
, "because the overflow result is never used into: ");
1274 print_generic_stmt (dump_file
, result
, TDF_SLIM
);
1275 fprintf (dump_file
, "\n");
1278 gimplify_and_update_call_from_tree (gsi
, result
);
1281 /* Returns whether the control parents of BB are preserved. */
1284 control_parents_preserved_p (basic_block bb
)
1286 /* If we marked the control parents from BB they are preserved. */
1287 if (bitmap_bit_p (visited_control_parents
, bb
->index
))
1290 /* But they can also end up being marked from elsewhere. */
1292 unsigned edge_number
;
1293 EXECUTE_IF_SET_IN_BITMAP (cd
->get_edges_dependent_on (bb
->index
),
1296 basic_block cd_bb
= cd
->get_edge_src (edge_number
);
1298 && !bitmap_bit_p (last_stmt_necessary
, cd_bb
->index
))
1301 /* And cache the result. */
1302 bitmap_set_bit (visited_control_parents
, bb
->index
);
1306 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1307 contributes nothing to the program, and can be deleted. */
1310 eliminate_unnecessary_stmts (bool aggressive
)
1312 bool something_changed
= false;
1314 gimple_stmt_iterator gsi
, psi
;
1317 auto_vec
<edge
> to_remove_edges
;
1319 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1320 fprintf (dump_file
, "\nEliminating unnecessary statements:\n");
1322 bool had_setjmp
= cfun
->calls_setjmp
;
1323 clear_special_calls ();
1325 /* Walking basic blocks and statements in reverse order avoids
1326 releasing SSA names before any other DEFs that refer to them are
1327 released. This helps avoid loss of debug information, as we get
1328 a chance to propagate all RHSs of removed SSAs into debug uses,
1329 rather than only the latest ones. E.g., consider:
1335 If we were to release x_3 before a_5, when we reached a_5 and
1336 tried to substitute it into the debug stmt, we'd see x_3 there,
1337 but x_3's DEF, type, etc would have already been disconnected.
1338 By going backwards, the debug stmt first changes to:
1340 # DEBUG a => x_3 - b_4
1344 # DEBUG a => y_1 + z_2 - b_4
1347 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
1348 auto_vec
<basic_block
> h
;
1349 h
= get_all_dominated_blocks (CDI_DOMINATORS
,
1350 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun
)));
1356 /* Remove dead statements. */
1357 auto_bitmap debug_seen
;
1358 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi
= psi
)
1360 stmt
= gsi_stmt (gsi
);
1367 /* We can mark a call to free as not necessary if the
1368 defining statement of its argument is not necessary
1369 (and thus is getting removed). */
1370 if (gimple_plf (stmt
, STMT_NECESSARY
)
1371 && (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
)
1372 || (is_gimple_call (stmt
)
1373 && gimple_call_from_new_or_delete (as_a
<gcall
*> (stmt
))
1374 && gimple_call_operator_delete_p (as_a
<gcall
*> (stmt
)))))
1376 tree ptr
= gimple_call_arg (stmt
, 0);
1377 if (TREE_CODE (ptr
) == SSA_NAME
)
1379 gimple
*def_stmt
= SSA_NAME_DEF_STMT (ptr
);
1380 if (!gimple_nop_p (def_stmt
)
1381 && !gimple_plf (def_stmt
, STMT_NECESSARY
))
1382 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
1386 /* If GSI is not necessary then remove it. */
1387 if (!gimple_plf (stmt
, STMT_NECESSARY
))
1389 /* Keep clobbers that we can keep live live. */
1390 if (gimple_clobber_p (stmt
))
1393 use_operand_p use_p
;
1395 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_USE
)
1397 tree name
= USE_FROM_PTR (use_p
);
1398 if (!SSA_NAME_IS_DEFAULT_DEF (name
)
1399 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
)))
1406 /* When doing CD-DCE we have to ensure all controls
1407 of the stmt are still live. */
1408 && (!aggressive
|| control_parents_preserved_p (bb
)))
1410 bitmap_clear (debug_seen
);
1414 if (!is_gimple_debug (stmt
))
1415 something_changed
= true;
1416 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1419 else if (is_gimple_call (stmt
))
1421 tree name
= gimple_call_lhs (stmt
);
1423 notice_special_calls (as_a
<gcall
*> (stmt
));
1425 /* When LHS of var = call (); is dead, simplify it into
1426 call (); saving one operand. */
1428 && TREE_CODE (name
) == SSA_NAME
1429 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
))
1430 /* Avoid doing so for allocation calls which we
1431 did not mark as necessary, it will confuse the
1432 special logic we apply to malloc/free pair removal. */
1433 && (!(call
= gimple_call_fndecl (stmt
))
1434 || ((DECL_BUILT_IN_CLASS (call
) != BUILT_IN_NORMAL
1435 || (DECL_FUNCTION_CODE (call
) != BUILT_IN_ALIGNED_ALLOC
1436 && DECL_FUNCTION_CODE (call
) != BUILT_IN_MALLOC
1437 && DECL_FUNCTION_CODE (call
) != BUILT_IN_CALLOC
1438 && !ALLOCA_FUNCTION_CODE_P
1439 (DECL_FUNCTION_CODE (call
))))
1440 && !DECL_IS_REPLACEABLE_OPERATOR_NEW_P (call
))))
1442 something_changed
= true;
1443 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1445 fprintf (dump_file
, "Deleting LHS of call: ");
1446 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1447 fprintf (dump_file
, "\n");
1450 gimple_call_set_lhs (stmt
, NULL_TREE
);
1451 maybe_clean_or_replace_eh_stmt (stmt
, stmt
);
1453 release_ssa_name (name
);
1455 /* GOMP_SIMD_LANE (unless three argument) or ASAN_POISON
1456 without lhs is not needed. */
1457 if (gimple_call_internal_p (stmt
))
1458 switch (gimple_call_internal_fn (stmt
))
1460 case IFN_GOMP_SIMD_LANE
:
1461 if (gimple_call_num_args (stmt
) >= 3
1462 && !integer_nonzerop (gimple_call_arg (stmt
, 2)))
1465 case IFN_ASAN_POISON
:
1466 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1472 else if (gimple_call_internal_p (stmt
))
1473 switch (gimple_call_internal_fn (stmt
))
1475 case IFN_ADD_OVERFLOW
:
1476 maybe_optimize_arith_overflow (&gsi
, PLUS_EXPR
);
1478 case IFN_SUB_OVERFLOW
:
1479 maybe_optimize_arith_overflow (&gsi
, MINUS_EXPR
);
1481 case IFN_MUL_OVERFLOW
:
1482 maybe_optimize_arith_overflow (&gsi
, MULT_EXPR
);
1485 if (integer_zerop (gimple_call_arg (stmt
, 2)))
1486 maybe_optimize_arith_overflow (&gsi
, PLUS_EXPR
);
1489 if (integer_zerop (gimple_call_arg (stmt
, 2)))
1490 maybe_optimize_arith_overflow (&gsi
, MINUS_EXPR
);
1496 else if (gimple_debug_bind_p (stmt
))
1498 /* We are only keeping the last debug-bind of a
1499 non-DEBUG_EXPR_DECL variable in a series of
1500 debug-bind stmts. */
1501 tree var
= gimple_debug_bind_get_var (stmt
);
1502 if (TREE_CODE (var
) != DEBUG_EXPR_DECL
1503 && !bitmap_set_bit (debug_seen
, DECL_UID (var
)))
1504 remove_dead_stmt (&gsi
, bb
, to_remove_edges
);
1507 bitmap_clear (debug_seen
);
1510 /* Remove dead PHI nodes. */
1511 something_changed
|= remove_dead_phis (bb
);
1514 /* First remove queued edges. */
1515 if (!to_remove_edges
.is_empty ())
1517 /* Remove edges. We've delayed this to not get bogus debug stmts
1518 during PHI node removal. */
1519 for (unsigned i
= 0; i
< to_remove_edges
.length (); ++i
)
1520 remove_edge (to_remove_edges
[i
]);
1523 /* When we cleared calls_setjmp we can purge all abnormal edges. Do so.
1524 ??? We'd like to assert that setjmp calls do not pop out of nothing
1525 but we currently lack a per-stmt way of noting whether a call was
1526 recognized as returns-twice (or rather receives-control). */
1527 if (!cfun
->calls_setjmp
&& had_setjmp
)
1529 /* Make sure we only remove the edges, not dominated blocks. Using
1530 gimple_purge_dead_abnormal_call_edges would do that and we
1531 cannot free dominators yet. */
1532 FOR_EACH_BB_FN (bb
, cfun
)
1533 if (gcall
*stmt
= safe_dyn_cast
<gcall
*> (*gsi_last_bb (bb
)))
1534 if (!stmt_can_make_abnormal_goto (stmt
))
1538 for (ei
= ei_start (bb
->succs
); (e
= ei_safe_edge (ei
)); )
1540 if (e
->flags
& EDGE_ABNORMAL
)
1542 if (e
->flags
& EDGE_FALLTHRU
)
1543 e
->flags
&= ~EDGE_ABNORMAL
;
1554 /* Now remove the unreachable blocks. */
1557 basic_block prev_bb
;
1559 find_unreachable_blocks ();
1561 /* Delete all unreachable basic blocks in reverse dominator order. */
1562 for (bb
= EXIT_BLOCK_PTR_FOR_FN (cfun
)->prev_bb
;
1563 bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
); bb
= prev_bb
)
1565 prev_bb
= bb
->prev_bb
;
1567 if ((bb_contains_live_stmts
1568 && !bitmap_bit_p (bb_contains_live_stmts
, bb
->index
))
1569 || !(bb
->flags
& BB_REACHABLE
))
1571 /* Since we don't track liveness of virtual PHI nodes, it is
1572 possible that we rendered some PHI nodes unreachable while
1573 they are still in use. Mark them for renaming. */
1574 for (gphi_iterator gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
1576 if (virtual_operand_p (gimple_phi_result (gsi
.phi ())))
1579 imm_use_iterator iter
;
1581 FOR_EACH_IMM_USE_STMT (stmt
, iter
,
1582 gimple_phi_result (gsi
.phi ()))
1584 if (!(gimple_bb (stmt
)->flags
& BB_REACHABLE
))
1586 if (gimple_code (stmt
) == GIMPLE_PHI
1587 || gimple_plf (stmt
, STMT_NECESSARY
))
1594 mark_virtual_phi_result_for_renaming (gsi
.phi ());
1597 if (!(bb
->flags
& BB_REACHABLE
))
1599 /* Speed up the removal of blocks that don't
1600 dominate others. Walking backwards, this should
1601 be the common case. ??? Do we need to recompute
1602 dominators because of cfg_altered? */
1603 if (!first_dom_son (CDI_DOMINATORS
, bb
))
1604 delete_basic_block (bb
);
1607 h
= get_all_dominated_blocks (CDI_DOMINATORS
, bb
);
1612 prev_bb
= bb
->prev_bb
;
1613 /* Rearrangements to the CFG may have failed
1614 to update the dominators tree, so that
1615 formerly-dominated blocks are now
1616 otherwise reachable. */
1617 if (!!(bb
->flags
& BB_REACHABLE
))
1619 delete_basic_block (bb
);
1630 free (bb_postorder
);
1631 bb_postorder
= NULL
;
1633 return something_changed
;
1637 /* Print out removed statement statistics. */
1644 percg
= ((float) stats
.removed
/ (float) stats
.total
) * 100;
1645 fprintf (dump_file
, "Removed %d of %d statements (%d%%)\n",
1646 stats
.removed
, stats
.total
, (int) percg
);
1648 if (stats
.total_phis
== 0)
1651 percg
= ((float) stats
.removed_phis
/ (float) stats
.total_phis
) * 100;
1653 fprintf (dump_file
, "Removed %d of %d PHI nodes (%d%%)\n",
1654 stats
.removed_phis
, stats
.total_phis
, (int) percg
);
1657 /* Initialization for this pass. Set up the used data structures. */
1660 tree_dce_init (bool aggressive
)
1662 memset ((void *) &stats
, 0, sizeof (stats
));
1666 last_stmt_necessary
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1667 bitmap_clear (last_stmt_necessary
);
1668 bb_contains_live_stmts
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1669 bitmap_clear (bb_contains_live_stmts
);
1672 processed
= sbitmap_alloc (num_ssa_names
+ 1);
1673 bitmap_clear (processed
);
1675 worklist
.create (64);
1676 cfg_altered
= false;
1679 /* Cleanup after this pass. */
1682 tree_dce_done (bool aggressive
)
1687 sbitmap_free (visited_control_parents
);
1688 sbitmap_free (last_stmt_necessary
);
1689 sbitmap_free (bb_contains_live_stmts
);
1690 bb_contains_live_stmts
= NULL
;
1693 sbitmap_free (processed
);
1695 worklist
.release ();
1698 /* Sort PHI argument values for make_forwarders_with_degenerate_phis. */
1701 sort_phi_args (const void *a_
, const void *b_
)
1703 auto *a
= (const std::pair
<edge
, hashval_t
> *) a_
;
1704 auto *b
= (const std::pair
<edge
, hashval_t
> *) b_
;
1705 hashval_t ha
= a
->second
;
1706 hashval_t hb
= b
->second
;
1711 else if (a
->first
->dest_idx
< b
->first
->dest_idx
)
1713 else if (a
->first
->dest_idx
> b
->first
->dest_idx
)
1719 /* Look for a non-virtual PHIs and make a forwarder block when all PHIs
1720 have the same argument on a set of edges. This is to not consider
1721 control dependences of individual edges for same values but only for
1725 make_forwarders_with_degenerate_phis (function
*fn
)
1730 FOR_EACH_BB_FN (bb
, fn
)
1732 /* Only PHIs with three or more arguments have opportunities. */
1733 if (EDGE_COUNT (bb
->preds
) < 3)
1735 /* Do not touch loop headers or blocks with abnormal predecessors.
1736 ??? This is to avoid creating valid loops here, see PR103458.
1737 We might want to improve things to either explicitely add those
1738 loops or at least consider blocks with no backedges. */
1739 if (bb
->loop_father
->header
== bb
1740 || bb_has_abnormal_pred (bb
))
1743 /* Take one PHI node as template to look for identical
1744 arguments. Build a vector of candidates forming sets
1745 of argument edges with equal values. Note optimality
1746 depends on the particular choice of the template PHI
1747 since equal arguments are unordered leaving other PHIs
1748 with more than one set of equal arguments within this
1749 argument range unsorted. We'd have to break ties by
1750 looking at other PHI nodes. */
1751 gphi_iterator gsi
= gsi_start_nonvirtual_phis (bb
);
1752 if (gsi_end_p (gsi
))
1754 gphi
*phi
= gsi
.phi ();
1755 auto_vec
<std::pair
<edge
, hashval_t
>, 8> args
;
1756 bool need_resort
= false;
1757 for (unsigned i
= 0; i
< gimple_phi_num_args (phi
); ++i
)
1759 edge e
= gimple_phi_arg_edge (phi
, i
);
1760 /* Skip abnormal edges since we cannot redirect them. */
1761 if (e
->flags
& EDGE_ABNORMAL
)
1763 /* Skip loop exit edges when we are in loop-closed SSA form
1764 since the forwarder we'd create does not have a PHI node. */
1765 if (loops_state_satisfies_p (LOOP_CLOSED_SSA
)
1766 && loop_exit_edge_p (e
->src
->loop_father
, e
))
1769 tree arg
= gimple_phi_arg_def (phi
, i
);
1770 if (!CONSTANT_CLASS_P (arg
) && TREE_CODE (arg
) != SSA_NAME
)
1772 args
.safe_push (std::make_pair (e
, iterative_hash_expr (arg
, 0)));
1774 if (args
.length () < 2)
1776 args
.qsort (sort_phi_args
);
1777 /* The above sorting can be different between -g and -g0, as e.g. decls
1778 can have different uids (-g could have bigger gaps in between them).
1779 So, only use that to determine which args are equal, then change
1780 second from hash value to smallest dest_idx of the edges which have
1781 equal argument and sort again. If all the phi arguments are
1782 constants or SSA_NAME, there is no need for the second sort, the hash
1783 values are stable in that case. */
1784 hashval_t hash
= args
[0].second
;
1785 args
[0].second
= args
[0].first
->dest_idx
;
1786 bool any_equal
= false;
1787 for (unsigned i
= 1; i
< args
.length (); ++i
)
1788 if (hash
== args
[i
].second
1789 && operand_equal_p (PHI_ARG_DEF_FROM_EDGE (phi
, args
[i
- 1].first
),
1790 PHI_ARG_DEF_FROM_EDGE (phi
, args
[i
].first
)))
1792 args
[i
].second
= args
[i
- 1].second
;
1797 hash
= args
[i
].second
;
1798 args
[i
].second
= args
[i
].first
->dest_idx
;
1803 args
.qsort (sort_phi_args
);
1805 /* From the candidates vector now verify true candidates for
1806 forwarders and create them. */
1807 gphi
*vphi
= get_virtual_phi (bb
);
1809 while (start
< args
.length () - 1)
1812 for (i
= start
+ 1; i
< args
.length (); ++i
)
1813 if (args
[start
].second
!= args
[i
].second
)
1815 /* args[start]..args[i-1] are equal. */
1818 /* Check all PHI nodes for argument equality. */
1820 gphi_iterator gsi2
= gsi
;
1822 for (; !gsi_end_p (gsi2
); gsi_next (&gsi2
))
1824 gphi
*phi2
= gsi2
.phi ();
1825 if (virtual_operand_p (gimple_phi_result (phi2
)))
1828 = PHI_ARG_DEF_FROM_EDGE (phi2
, args
[start
].first
);
1829 for (unsigned j
= start
+ 1; j
< i
; ++j
)
1831 if (!operand_equal_p (start_arg
,
1832 PHI_ARG_DEF_FROM_EDGE
1833 (phi2
, args
[j
].first
)))
1835 /* Another PHI might have a shorter set of
1836 equivalent args. Go for that. */
1848 /* If we are asked to forward all edges the block
1849 has all degenerate PHIs. Do nothing in that case. */
1851 && i
== args
.length ()
1852 && args
.length () == gimple_phi_num_args (phi
))
1854 /* Instead of using make_forwarder_block we are
1855 rolling our own variant knowing that the forwarder
1856 does not need PHI nodes apart from eventually
1858 auto_vec
<tree
, 8> vphi_args
;
1861 vphi_args
.reserve_exact (i
- start
);
1862 for (unsigned j
= start
; j
< i
; ++j
)
1863 vphi_args
.quick_push
1864 (PHI_ARG_DEF_FROM_EDGE (vphi
, args
[j
].first
));
1866 free_dominance_info (fn
, CDI_DOMINATORS
);
1867 basic_block forwarder
= split_edge (args
[start
].first
);
1868 profile_count count
= profile_count::zero ();
1869 for (unsigned j
= start
+ 1; j
< i
; ++j
)
1871 edge e
= args
[j
].first
;
1872 redirect_edge_and_branch_force (e
, forwarder
);
1873 redirect_edge_var_map_clear (e
);
1874 count
+= e
->count ();
1876 forwarder
->count
= count
;
1879 tree def
= copy_ssa_name (vphi_args
[0]);
1880 gphi
*vphi_copy
= create_phi_node (def
, forwarder
);
1881 for (unsigned j
= start
; j
< i
; ++j
)
1882 add_phi_arg (vphi_copy
, vphi_args
[j
- start
],
1883 args
[j
].first
, UNKNOWN_LOCATION
);
1885 (vphi
, single_succ_edge (forwarder
)->dest_idx
, def
);
1887 todo
|= TODO_cleanup_cfg
;
1890 /* Continue searching for more opportunities. */
1897 /* Main routine to eliminate dead code.
1899 AGGRESSIVE controls the aggressiveness of the algorithm.
1900 In conservative mode, we ignore control dependence and simply declare
1901 all but the most trivially dead branches necessary. This mode is fast.
1902 In aggressive mode, control dependences are taken into account, which
1903 results in more dead code elimination, but at the cost of some time.
1905 FIXME: Aggressive mode before PRE doesn't work currently because
1906 the dominance info is not invalidated after DCE1. This is
1907 not an issue right now because we only run aggressive DCE
1908 as the last tree SSA pass, but keep this in mind when you
1909 start experimenting with pass ordering. */
1912 perform_tree_ssa_dce (bool aggressive
)
1914 bool something_changed
= 0;
1917 /* Preheaders are needed for SCEV to work.
1918 Simple lateches and recorded exits improve chances that loop will
1919 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1920 bool in_loop_pipeline
= scev_initialized_p ();
1921 if (aggressive
&& ! in_loop_pipeline
)
1923 loop_optimizer_init (LOOPS_NORMAL
1924 | LOOPS_HAVE_RECORDED_EXITS
);
1929 todo
|= make_forwarders_with_degenerate_phis (cfun
);
1931 calculate_dominance_info (CDI_DOMINATORS
);
1933 tree_dce_init (aggressive
);
1937 /* Compute control dependence. */
1938 calculate_dominance_info (CDI_POST_DOMINATORS
);
1939 cd
= new control_dependences ();
1941 visited_control_parents
=
1942 sbitmap_alloc (last_basic_block_for_fn (cfun
));
1943 bitmap_clear (visited_control_parents
);
1945 mark_dfs_back_edges ();
1948 find_obviously_necessary_stmts (aggressive
);
1950 if (aggressive
&& ! in_loop_pipeline
)
1953 loop_optimizer_finalize ();
1960 visited
= BITMAP_ALLOC (NULL
);
1961 propagate_necessity (aggressive
);
1962 BITMAP_FREE (visited
);
1964 something_changed
|= eliminate_unnecessary_stmts (aggressive
);
1965 something_changed
|= cfg_altered
;
1967 /* We do not update postdominators, so free them unconditionally. */
1968 free_dominance_info (CDI_POST_DOMINATORS
);
1970 /* If we removed paths in the CFG, then we need to update
1971 dominators as well. I haven't investigated the possibility
1972 of incrementally updating dominators. */
1974 free_dominance_info (CDI_DOMINATORS
);
1976 statistics_counter_event (cfun
, "Statements deleted", stats
.removed
);
1977 statistics_counter_event (cfun
, "PHI nodes deleted", stats
.removed_phis
);
1979 /* Debugging dumps. */
1980 if (dump_file
&& (dump_flags
& (TDF_STATS
|TDF_DETAILS
)))
1983 tree_dce_done (aggressive
);
1985 if (something_changed
)
1987 free_numbers_of_iterations_estimates (cfun
);
1988 if (in_loop_pipeline
)
1990 todo
|= TODO_update_ssa
| TODO_cleanup_cfg
;
1995 /* Pass entry points. */
1999 return perform_tree_ssa_dce (/*aggressive=*/false);
2003 tree_ssa_cd_dce (void)
2005 return perform_tree_ssa_dce (/*aggressive=*/optimize
>= 2);
2010 const pass_data pass_data_dce
=
2012 GIMPLE_PASS
, /* type */
2014 OPTGROUP_NONE
, /* optinfo_flags */
2015 TV_TREE_DCE
, /* tv_id */
2016 ( PROP_cfg
| PROP_ssa
), /* properties_required */
2017 0, /* properties_provided */
2018 0, /* properties_destroyed */
2019 0, /* todo_flags_start */
2020 0, /* todo_flags_finish */
2023 class pass_dce
: public gimple_opt_pass
2026 pass_dce (gcc::context
*ctxt
)
2027 : gimple_opt_pass (pass_data_dce
, ctxt
), update_address_taken_p (false)
2030 /* opt_pass methods: */
2031 opt_pass
* clone () final override
{ return new pass_dce (m_ctxt
); }
2032 void set_pass_param (unsigned n
, bool param
) final override
2034 gcc_assert (n
== 0);
2035 update_address_taken_p
= param
;
2037 bool gate (function
*) final override
{ return flag_tree_dce
!= 0; }
2038 unsigned int execute (function
*) final override
2040 return (tree_ssa_dce ()
2041 | (update_address_taken_p
? TODO_update_address_taken
: 0));
2045 bool update_address_taken_p
;
2046 }; // class pass_dce
2051 make_pass_dce (gcc::context
*ctxt
)
2053 return new pass_dce (ctxt
);
2058 const pass_data pass_data_cd_dce
=
2060 GIMPLE_PASS
, /* type */
2062 OPTGROUP_NONE
, /* optinfo_flags */
2063 TV_TREE_CD_DCE
, /* tv_id */
2064 ( PROP_cfg
| PROP_ssa
), /* properties_required */
2065 0, /* properties_provided */
2066 0, /* properties_destroyed */
2067 0, /* todo_flags_start */
2068 0, /* todo_flags_finish */
2071 class pass_cd_dce
: public gimple_opt_pass
2074 pass_cd_dce (gcc::context
*ctxt
)
2075 : gimple_opt_pass (pass_data_cd_dce
, ctxt
), update_address_taken_p (false)
2078 /* opt_pass methods: */
2079 opt_pass
* clone () final override
{ return new pass_cd_dce (m_ctxt
); }
2080 void set_pass_param (unsigned n
, bool param
) final override
2082 gcc_assert (n
== 0);
2083 update_address_taken_p
= param
;
2085 bool gate (function
*) final override
{ return flag_tree_dce
!= 0; }
2086 unsigned int execute (function
*) final override
2088 return (tree_ssa_cd_dce ()
2089 | (update_address_taken_p
? TODO_update_address_taken
: 0));
2093 bool update_address_taken_p
;
2094 }; // class pass_cd_dce
2099 make_pass_cd_dce (gcc::context
*ctxt
)
2101 return new pass_cd_dce (ctxt
);
2105 /* A cheap DCE interface. WORKLIST is a list of possibly dead stmts and
2106 is consumed by this function. The function has linear complexity in
2107 the number of dead stmts with a constant factor like the average SSA
2108 use operands number. */
2111 simple_dce_from_worklist (bitmap worklist
, bitmap need_eh_cleanup
)
2114 int stmtremoved
= 0;
2115 while (! bitmap_empty_p (worklist
))
2118 unsigned i
= bitmap_clear_first_set_bit (worklist
);
2120 tree def
= ssa_name (i
);
2121 /* Removed by somebody else or still in use.
2122 Note use in itself for a phi node is not counted as still in use. */
2125 if (!has_zero_uses (def
))
2127 gimple
*def_stmt
= SSA_NAME_DEF_STMT (def
);
2129 if (gimple_code (def_stmt
) != GIMPLE_PHI
)
2133 imm_use_iterator use_iter
;
2134 bool canremove
= true;
2136 FOR_EACH_IMM_USE_STMT (use_stmt
, use_iter
, def
)
2138 /* Ignore debug statements. */
2139 if (is_gimple_debug (use_stmt
))
2141 if (use_stmt
!= def_stmt
)
2151 gimple
*t
= SSA_NAME_DEF_STMT (def
);
2152 if (gimple_has_side_effects (t
))
2155 /* The defining statement needs to be defining only this name.
2156 ASM is the only statement that can define more than one
2159 && !single_ssa_def_operand (t
, SSA_OP_ALL_DEFS
))
2162 /* Don't remove statements that are needed for non-call
2164 if (stmt_unremovable_because_of_non_call_eh_p (cfun
, t
))
2167 /* Tell the caller that we removed a statement that might
2168 throw so it could cleanup the cfg for that block. */
2169 if (need_eh_cleanup
&& stmt_could_throw_p (cfun
, t
))
2170 bitmap_set_bit (need_eh_cleanup
, gimple_bb (t
)->index
);
2172 /* Add uses to the worklist. */
2174 use_operand_p use_p
;
2175 FOR_EACH_PHI_OR_STMT_USE (use_p
, t
, iter
, SSA_OP_USE
)
2177 tree use
= USE_FROM_PTR (use_p
);
2178 if (TREE_CODE (use
) == SSA_NAME
2179 && ! SSA_NAME_IS_DEFAULT_DEF (use
))
2180 bitmap_set_bit (worklist
, SSA_NAME_VERSION (use
));
2184 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
2186 fprintf (dump_file
, "Removing dead stmt:");
2187 print_gimple_stmt (dump_file
, t
, 0);
2189 gimple_stmt_iterator gsi
= gsi_for_stmt (t
);
2190 if (gimple_code (t
) == GIMPLE_PHI
)
2192 remove_phi_node (&gsi
, true);
2197 unlink_stmt_vdef (t
);
2198 gsi_remove (&gsi
, true);
2203 statistics_counter_event (cfun
, "PHIs removed",
2205 statistics_counter_event (cfun
, "Statements removed",