1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002-2018 Free Software Foundation, Inc.
3 Contributed by Ben Elliston <bje@redhat.com>
4 and Andrew MacLeod <amacleod@redhat.com>
5 Adapted to use control dependence by Steven Bosscher, SUSE Labs.
7 This file is part of GCC.
9 GCC is free software; you can redistribute it and/or modify it
10 under the terms of the GNU General Public License as published by the
11 Free Software Foundation; either version 3, or (at your option) any
14 GCC is distributed in the hope that it will be useful, but WITHOUT
15 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
16 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
19 You should have received a copy of the GNU General Public License
20 along with GCC; see the file COPYING3. If not see
21 <http://www.gnu.org/licenses/>. */
23 /* Dead code elimination.
27 Building an Optimizing Compiler,
28 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9.
30 Advanced Compiler Design and Implementation,
31 Steven Muchnick, Morgan Kaufmann, 1997, Section 18.10.
33 Dead-code elimination is the removal of statements which have no
34 impact on the program's output. "Dead statements" have no impact
35 on the program's output, while "necessary statements" may have
38 The algorithm consists of three phases:
39 1. Marking as necessary all statements known to be necessary,
40 e.g. most function calls, writing a value to memory, etc;
41 2. Propagating necessary statements, e.g., the statements
42 giving values to operands in necessary statements; and
43 3. Removing dead statements. */
47 #include "coretypes.h"
53 #include "tree-pass.h"
55 #include "gimple-pretty-print.h"
56 #include "fold-const.h"
61 #include "gimple-iterator.h"
63 #include "tree-ssa-loop-niter.h"
64 #include "tree-into-ssa.h"
67 #include "tree-scalar-evolution.h"
68 #include "tree-ssa-propagate.h"
69 #include "gimple-fold.h"
71 static struct stmt_stats
79 #define STMT_NECESSARY GF_PLF_1
81 static vec
<gimple
*> worklist
;
83 /* Vector indicating an SSA name has already been processed and marked
85 static sbitmap processed
;
87 /* Vector indicating that the last statement of a basic block has already
88 been marked as necessary. */
89 static sbitmap last_stmt_necessary
;
91 /* Vector indicating that BB contains statements that are live. */
92 static sbitmap bb_contains_live_stmts
;
94 /* Before we can determine whether a control branch is dead, we need to
95 compute which blocks are control dependent on which edges.
97 We expect each block to be control dependent on very few edges so we
98 use a bitmap for each block recording its edges. An array holds the
99 bitmap. The Ith bit in the bitmap is set if that block is dependent
101 static control_dependences
*cd
;
103 /* Vector indicating that a basic block has already had all the edges
104 processed that it is control dependent on. */
105 static sbitmap visited_control_parents
;
107 /* TRUE if this pass alters the CFG (by removing control statements).
110 If this pass alters the CFG, then it will arrange for the dominators
112 static bool cfg_altered
;
114 /* When non-NULL holds map from basic block index into the postorder. */
115 static int *bb_postorder
;
118 /* If STMT is not already marked necessary, mark it, and add it to the
119 worklist if ADD_TO_WORKLIST is true. */
122 mark_stmt_necessary (gimple
*stmt
, bool add_to_worklist
)
126 if (gimple_plf (stmt
, STMT_NECESSARY
))
129 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
131 fprintf (dump_file
, "Marking useful stmt: ");
132 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
133 fprintf (dump_file
, "\n");
136 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
138 worklist
.safe_push (stmt
);
139 if (add_to_worklist
&& bb_contains_live_stmts
&& !is_gimple_debug (stmt
))
140 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
144 /* Mark the statement defining operand OP as necessary. */
147 mark_operand_necessary (tree op
)
154 ver
= SSA_NAME_VERSION (op
);
155 if (bitmap_bit_p (processed
, ver
))
157 stmt
= SSA_NAME_DEF_STMT (op
);
158 gcc_assert (gimple_nop_p (stmt
)
159 || gimple_plf (stmt
, STMT_NECESSARY
));
162 bitmap_set_bit (processed
, ver
);
164 stmt
= SSA_NAME_DEF_STMT (op
);
167 if (gimple_plf (stmt
, STMT_NECESSARY
) || gimple_nop_p (stmt
))
170 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
172 fprintf (dump_file
, "marking necessary through ");
173 print_generic_expr (dump_file
, op
);
174 fprintf (dump_file
, " stmt ");
175 print_gimple_stmt (dump_file
, stmt
, 0);
178 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
179 if (bb_contains_live_stmts
)
180 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
181 worklist
.safe_push (stmt
);
185 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
186 it can make other statements necessary.
188 If AGGRESSIVE is false, control statements are conservatively marked as
192 mark_stmt_if_obviously_necessary (gimple
*stmt
, bool aggressive
)
194 /* With non-call exceptions, we have to assume that all statements could
195 throw. If a statement could throw, it can be deemed necessary. */
196 if (cfun
->can_throw_non_call_exceptions
197 && !cfun
->can_delete_dead_exceptions
198 && stmt_could_throw_p (cfun
, stmt
))
200 mark_stmt_necessary (stmt
, true);
204 /* Statements that are implicitly live. Most function calls, asm
205 and return statements are required. Labels and GIMPLE_BIND nodes
206 are kept because they are control flow, and we have no way of
207 knowing whether they can be removed. DCE can eliminate all the
208 other statements in a block, and CFG can then remove the block
210 switch (gimple_code (stmt
))
214 mark_stmt_necessary (stmt
, false);
220 mark_stmt_necessary (stmt
, true);
225 tree callee
= gimple_call_fndecl (stmt
);
226 if (callee
!= NULL_TREE
227 && fndecl_built_in_p (callee
, BUILT_IN_NORMAL
))
228 switch (DECL_FUNCTION_CODE (callee
))
230 case BUILT_IN_MALLOC
:
231 case BUILT_IN_ALIGNED_ALLOC
:
232 case BUILT_IN_CALLOC
:
233 CASE_BUILT_IN_ALLOCA
:
234 case BUILT_IN_STRDUP
:
235 case BUILT_IN_STRNDUP
:
240 /* Most, but not all function calls are required. Function calls that
241 produce no result and have no side effects (i.e. const pure
242 functions) are unnecessary. */
243 if (gimple_has_side_effects (stmt
))
245 mark_stmt_necessary (stmt
, true);
248 if (!gimple_call_lhs (stmt
))
254 /* Debug temps without a value are not useful. ??? If we could
255 easily locate the debug temp bind stmt for a use thereof,
256 would could refrain from marking all debug temps here, and
257 mark them only if they're used. */
258 if (gimple_debug_nonbind_marker_p (stmt
)
259 || !gimple_debug_bind_p (stmt
)
260 || gimple_debug_bind_has_value_p (stmt
)
261 || TREE_CODE (gimple_debug_bind_get_var (stmt
)) != DEBUG_EXPR_DECL
)
262 mark_stmt_necessary (stmt
, false);
266 gcc_assert (!simple_goto_p (stmt
));
267 mark_stmt_necessary (stmt
, true);
271 gcc_assert (EDGE_COUNT (gimple_bb (stmt
)->succs
) == 2);
276 mark_stmt_necessary (stmt
, true);
280 if (gimple_clobber_p (stmt
))
288 /* If the statement has volatile operands, it needs to be preserved.
289 Same for statements that can alter control flow in unpredictable
291 if (gimple_has_volatile_ops (stmt
) || is_ctrl_altering_stmt (stmt
))
293 mark_stmt_necessary (stmt
, true);
297 if (stmt_may_clobber_global_p (stmt
))
299 mark_stmt_necessary (stmt
, true);
307 /* Mark the last statement of BB as necessary. */
310 mark_last_stmt_necessary (basic_block bb
)
312 gimple
*stmt
= last_stmt (bb
);
314 bitmap_set_bit (last_stmt_necessary
, bb
->index
);
315 bitmap_set_bit (bb_contains_live_stmts
, bb
->index
);
317 /* We actually mark the statement only if it is a control statement. */
318 if (stmt
&& is_ctrl_stmt (stmt
))
319 mark_stmt_necessary (stmt
, true);
323 /* Mark control dependent edges of BB as necessary. We have to do this only
324 once for each basic block so we set the appropriate bit after we're done.
326 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
329 mark_control_dependent_edges_necessary (basic_block bb
, bool ignore_self
)
332 unsigned edge_number
;
333 bool skipped
= false;
335 gcc_assert (bb
!= EXIT_BLOCK_PTR_FOR_FN (cfun
));
337 if (bb
== ENTRY_BLOCK_PTR_FOR_FN (cfun
))
340 EXECUTE_IF_SET_IN_BITMAP (cd
->get_edges_dependent_on (bb
->index
),
343 basic_block cd_bb
= cd
->get_edge_src (edge_number
);
345 if (ignore_self
&& cd_bb
== bb
)
351 if (!bitmap_bit_p (last_stmt_necessary
, cd_bb
->index
))
352 mark_last_stmt_necessary (cd_bb
);
356 bitmap_set_bit (visited_control_parents
, bb
->index
);
360 /* Find obviously necessary statements. These are things like most function
361 calls, and stores to file level variables.
363 If EL is NULL, control statements are conservatively marked as
364 necessary. Otherwise it contains the list of edges used by control
365 dependence analysis. */
368 find_obviously_necessary_stmts (bool aggressive
)
371 gimple_stmt_iterator gsi
;
376 FOR_EACH_BB_FN (bb
, cfun
)
378 /* PHI nodes are never inherently necessary. */
379 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
381 phi
= gsi_stmt (gsi
);
382 gimple_set_plf (phi
, STMT_NECESSARY
, false);
385 /* Check all statements in the block. */
386 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
388 stmt
= gsi_stmt (gsi
);
389 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
390 mark_stmt_if_obviously_necessary (stmt
, aggressive
);
394 /* Pure and const functions are finite and thus have no infinite loops in
396 flags
= flags_from_decl_or_type (current_function_decl
);
397 if ((flags
& (ECF_CONST
|ECF_PURE
)) && !(flags
& ECF_LOOPING_CONST_OR_PURE
))
400 /* Prevent the empty possibly infinite loops from being removed. */
404 if (mark_irreducible_loops ())
405 FOR_EACH_BB_FN (bb
, cfun
)
408 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
409 if ((e
->flags
& EDGE_DFS_BACK
)
410 && (e
->flags
& EDGE_IRREDUCIBLE_LOOP
))
413 fprintf (dump_file
, "Marking back edge of irreducible loop %i->%i\n",
414 e
->src
->index
, e
->dest
->index
);
415 mark_control_dependent_edges_necessary (e
->dest
, false);
419 FOR_EACH_LOOP (loop
, 0)
420 if (!finite_loop_p (loop
))
423 fprintf (dump_file
, "can not prove finiteness of loop %i\n", loop
->num
);
424 mark_control_dependent_edges_necessary (loop
->latch
, false);
430 /* Return true if REF is based on an aliased base, otherwise false. */
433 ref_may_be_aliased (tree ref
)
435 gcc_assert (TREE_CODE (ref
) != WITH_SIZE_EXPR
);
436 while (handled_component_p (ref
))
437 ref
= TREE_OPERAND (ref
, 0);
438 if (TREE_CODE (ref
) == MEM_REF
439 && TREE_CODE (TREE_OPERAND (ref
, 0)) == ADDR_EXPR
)
440 ref
= TREE_OPERAND (TREE_OPERAND (ref
, 0), 0);
441 return !(DECL_P (ref
)
442 && !may_be_aliased (ref
));
445 static bitmap visited
= NULL
;
446 static unsigned int longest_chain
= 0;
447 static unsigned int total_chain
= 0;
448 static unsigned int nr_walks
= 0;
449 static bool chain_ovfl
= false;
451 /* Worker for the walker that marks reaching definitions of REF,
452 which is based on a non-aliased decl, necessary. It returns
453 true whenever the defining statement of the current VDEF is
454 a kill for REF, as no dominating may-defs are necessary for REF
455 anymore. DATA points to the basic-block that contains the
456 stmt that refers to REF. */
459 mark_aliased_reaching_defs_necessary_1 (ao_ref
*ref
, tree vdef
, void *data
)
461 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
463 /* All stmts we visit are necessary. */
464 if (! gimple_clobber_p (def_stmt
))
465 mark_operand_necessary (vdef
);
467 /* If the stmt lhs kills ref, then we can stop walking. */
468 if (gimple_has_lhs (def_stmt
)
469 && TREE_CODE (gimple_get_lhs (def_stmt
)) != SSA_NAME
470 /* The assignment is not necessarily carried out if it can throw
471 and we can catch it in the current function where we could inspect
473 ??? We only need to care about the RHS throwing. For aggregate
474 assignments or similar calls and non-call exceptions the LHS
475 might throw as well. */
476 && !stmt_can_throw_internal (cfun
, def_stmt
))
478 tree base
, lhs
= gimple_get_lhs (def_stmt
);
479 poly_int64 size
, offset
, max_size
;
483 = get_ref_base_and_extent (lhs
, &offset
, &size
, &max_size
, &reverse
);
484 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
485 so base == refd->base does not always hold. */
486 if (base
== ref
->base
)
488 /* For a must-alias check we need to be able to constrain
489 the accesses properly. */
490 if (known_eq (size
, max_size
)
491 && known_subrange_p (ref
->offset
, ref
->max_size
, offset
, size
))
493 /* Or they need to be exactly the same. */
495 /* Make sure there is no induction variable involved
496 in the references (gcc.c-torture/execute/pr42142.c).
497 The simplest way is to check if the kill dominates
499 /* But when both are in the same block we cannot
500 easily tell whether we came from a backedge
501 unless we decide to compute stmt UIDs
503 && (basic_block
) data
!= gimple_bb (def_stmt
)
504 && dominated_by_p (CDI_DOMINATORS
, (basic_block
) data
,
505 gimple_bb (def_stmt
))
506 && operand_equal_p (ref
->ref
, lhs
, 0))
511 /* Otherwise keep walking. */
516 mark_aliased_reaching_defs_necessary (gimple
*stmt
, tree ref
)
520 gcc_assert (!chain_ovfl
);
521 ao_ref_init (&refd
, ref
);
522 chain
= walk_aliased_vdefs (&refd
, gimple_vuse (stmt
),
523 mark_aliased_reaching_defs_necessary_1
,
524 gimple_bb (stmt
), NULL
);
525 if (chain
> longest_chain
)
526 longest_chain
= chain
;
527 total_chain
+= chain
;
531 /* Worker for the walker that marks reaching definitions of REF, which
532 is not based on a non-aliased decl. For simplicity we need to end
533 up marking all may-defs necessary that are not based on a non-aliased
534 decl. The only job of this walker is to skip may-defs based on
535 a non-aliased decl. */
538 mark_all_reaching_defs_necessary_1 (ao_ref
*ref ATTRIBUTE_UNUSED
,
539 tree vdef
, void *data ATTRIBUTE_UNUSED
)
541 gimple
*def_stmt
= SSA_NAME_DEF_STMT (vdef
);
543 /* We have to skip already visited (and thus necessary) statements
544 to make the chaining work after we dropped back to simple mode. */
546 && bitmap_bit_p (processed
, SSA_NAME_VERSION (vdef
)))
548 gcc_assert (gimple_nop_p (def_stmt
)
549 || gimple_plf (def_stmt
, STMT_NECESSARY
));
553 /* We want to skip stores to non-aliased variables. */
555 && gimple_assign_single_p (def_stmt
))
557 tree lhs
= gimple_assign_lhs (def_stmt
);
558 if (!ref_may_be_aliased (lhs
))
562 /* We want to skip statments that do not constitute stores but have
563 a virtual definition. */
564 if (is_gimple_call (def_stmt
))
566 tree callee
= gimple_call_fndecl (def_stmt
);
567 if (callee
!= NULL_TREE
568 && fndecl_built_in_p (callee
, BUILT_IN_NORMAL
))
569 switch (DECL_FUNCTION_CODE (callee
))
571 case BUILT_IN_MALLOC
:
572 case BUILT_IN_ALIGNED_ALLOC
:
573 case BUILT_IN_CALLOC
:
574 CASE_BUILT_IN_ALLOCA
:
582 if (! gimple_clobber_p (def_stmt
))
583 mark_operand_necessary (vdef
);
589 mark_all_reaching_defs_necessary (gimple
*stmt
)
591 walk_aliased_vdefs (NULL
, gimple_vuse (stmt
),
592 mark_all_reaching_defs_necessary_1
, NULL
, &visited
);
595 /* Return true for PHI nodes with one or identical arguments
598 degenerate_phi_p (gimple
*phi
)
601 tree op
= gimple_phi_arg_def (phi
, 0);
602 for (i
= 1; i
< gimple_phi_num_args (phi
); i
++)
603 if (gimple_phi_arg_def (phi
, i
) != op
)
608 /* Propagate necessity using the operands of necessary statements.
609 Process the uses on each statement in the worklist, and add all
610 feeding statements which contribute to the calculation of this
611 value to the worklist.
613 In conservative mode, EL is NULL. */
616 propagate_necessity (bool aggressive
)
620 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
621 fprintf (dump_file
, "\nProcessing worklist:\n");
623 while (worklist
.length () > 0)
625 /* Take STMT from worklist. */
626 stmt
= worklist
.pop ();
628 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
630 fprintf (dump_file
, "processing: ");
631 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
632 fprintf (dump_file
, "\n");
637 /* Mark the last statement of the basic blocks on which the block
638 containing STMT is control dependent, but only if we haven't
640 basic_block bb
= gimple_bb (stmt
);
641 if (bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
642 && !bitmap_bit_p (visited_control_parents
, bb
->index
))
643 mark_control_dependent_edges_necessary (bb
, false);
646 if (gimple_code (stmt
) == GIMPLE_PHI
647 /* We do not process virtual PHI nodes nor do we track their
649 && !virtual_operand_p (gimple_phi_result (stmt
)))
651 /* PHI nodes are somewhat special in that each PHI alternative has
652 data and control dependencies. All the statements feeding the
653 PHI node's arguments are always necessary. In aggressive mode,
654 we also consider the control dependent edges leading to the
655 predecessor block associated with each PHI alternative as
657 gphi
*phi
= as_a
<gphi
*> (stmt
);
660 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
662 tree arg
= PHI_ARG_DEF (stmt
, k
);
663 if (TREE_CODE (arg
) == SSA_NAME
)
664 mark_operand_necessary (arg
);
667 /* For PHI operands it matters from where the control flow arrives
668 to the BB. Consider the following example:
678 We need to mark control dependence of the empty basic blocks, since they
679 contains computation of PHI operands.
681 Doing so is too restrictive in the case the predecestor block is in
687 for (i = 0; i<1000; ++i)
693 There is PHI for J in the BB containing return statement.
694 In this case the control dependence of predecestor block (that is
695 within the empty loop) also contains the block determining number
696 of iterations of the block that would prevent removing of empty
699 This scenario can be avoided by splitting critical edges.
700 To save the critical edge splitting pass we identify how the control
701 dependence would look like if the edge was split.
703 Consider the modified CFG created from current CFG by splitting
704 edge B->C. In the postdominance tree of modified CFG, C' is
705 always child of C. There are two cases how chlids of C' can look
710 In this case the only basic block C' is control dependent on is B.
712 2) C' has single child that is B
714 In this case control dependence of C' is same as control
715 dependence of B in original CFG except for block B itself.
716 (since C' postdominate B in modified CFG)
718 Now how to decide what case happens? There are two basic options:
720 a) C postdominate B. Then C immediately postdominate B and
721 case 2 happens iff there is no other way from B to C except
724 There is other way from B to C iff there is succesor of B that
725 is not postdominated by B. Testing this condition is somewhat
726 expensive, because we need to iterate all succesors of B.
727 We are safe to assume that this does not happen: we will mark B
728 as needed when processing the other path from B to C that is
729 conrol dependent on B and marking control dependencies of B
730 itself is harmless because they will be processed anyway after
731 processing control statement in B.
733 b) C does not postdominate B. Always case 1 happens since there is
734 path from C to exit that does not go through B and thus also C'. */
736 if (aggressive
&& !degenerate_phi_p (stmt
))
738 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
740 basic_block arg_bb
= gimple_phi_arg_edge (phi
, k
)->src
;
743 != get_immediate_dominator (CDI_POST_DOMINATORS
, arg_bb
))
745 if (!bitmap_bit_p (last_stmt_necessary
, arg_bb
->index
))
746 mark_last_stmt_necessary (arg_bb
);
748 else if (arg_bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
749 && !bitmap_bit_p (visited_control_parents
,
751 mark_control_dependent_edges_necessary (arg_bb
, true);
757 /* Propagate through the operands. Examine all the USE, VUSE and
758 VDEF operands in this statement. Mark all the statements
759 which feed this statement's uses as necessary. */
763 /* If this is a call to free which is directly fed by an
764 allocation function do not mark that necessary through
765 processing the argument. */
766 if (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
))
768 tree ptr
= gimple_call_arg (stmt
, 0);
771 /* If the pointer we free is defined by an allocation
772 function do not add the call to the worklist. */
773 if (TREE_CODE (ptr
) == SSA_NAME
774 && is_gimple_call (def_stmt
= SSA_NAME_DEF_STMT (ptr
))
775 && (def_callee
= gimple_call_fndecl (def_stmt
))
776 && DECL_BUILT_IN_CLASS (def_callee
) == BUILT_IN_NORMAL
777 && (DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_ALIGNED_ALLOC
778 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_MALLOC
779 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_CALLOC
))
783 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
784 mark_operand_necessary (use
);
786 use
= gimple_vuse (stmt
);
790 /* If we dropped to simple mode make all immediately
791 reachable definitions necessary. */
794 mark_all_reaching_defs_necessary (stmt
);
798 /* For statements that may load from memory (have a VUSE) we
799 have to mark all reaching (may-)definitions as necessary.
800 We partition this task into two cases:
801 1) explicit loads based on decls that are not aliased
802 2) implicit loads (like calls) and explicit loads not
803 based on decls that are not aliased (like indirect
804 references or loads from globals)
805 For 1) we mark all reaching may-defs as necessary, stopping
806 at dominating kills. For 2) we want to mark all dominating
807 references necessary, but non-aliased ones which we handle
808 in 1). By keeping a global visited bitmap for references
809 we walk for 2) we avoid quadratic behavior for those. */
811 if (is_gimple_call (stmt
))
813 tree callee
= gimple_call_fndecl (stmt
);
816 /* Calls to functions that are merely acting as barriers
817 or that only store to memory do not make any previous
819 if (callee
!= NULL_TREE
820 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
821 && (DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET
822 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET_CHK
823 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MALLOC
824 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALIGNED_ALLOC
825 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_CALLOC
826 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_FREE
827 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_VA_END
828 || ALLOCA_FUNCTION_CODE_P (DECL_FUNCTION_CODE (callee
))
829 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_SAVE
830 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_RESTORE
831 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ASSUME_ALIGNED
))
834 /* Calls implicitly load from memory, their arguments
835 in addition may explicitly perform memory loads. */
836 mark_all_reaching_defs_necessary (stmt
);
837 for (i
= 0; i
< gimple_call_num_args (stmt
); ++i
)
839 tree arg
= gimple_call_arg (stmt
, i
);
840 if (TREE_CODE (arg
) == SSA_NAME
841 || is_gimple_min_invariant (arg
))
843 if (TREE_CODE (arg
) == WITH_SIZE_EXPR
)
844 arg
= TREE_OPERAND (arg
, 0);
845 if (!ref_may_be_aliased (arg
))
846 mark_aliased_reaching_defs_necessary (stmt
, arg
);
849 else if (gimple_assign_single_p (stmt
))
852 /* If this is a load mark things necessary. */
853 rhs
= gimple_assign_rhs1 (stmt
);
854 if (TREE_CODE (rhs
) != SSA_NAME
855 && !is_gimple_min_invariant (rhs
)
856 && TREE_CODE (rhs
) != CONSTRUCTOR
)
858 if (!ref_may_be_aliased (rhs
))
859 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
861 mark_all_reaching_defs_necessary (stmt
);
864 else if (greturn
*return_stmt
= dyn_cast
<greturn
*> (stmt
))
866 tree rhs
= gimple_return_retval (return_stmt
);
867 /* A return statement may perform a load. */
869 && TREE_CODE (rhs
) != SSA_NAME
870 && !is_gimple_min_invariant (rhs
)
871 && TREE_CODE (rhs
) != CONSTRUCTOR
)
873 if (!ref_may_be_aliased (rhs
))
874 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
876 mark_all_reaching_defs_necessary (stmt
);
879 else if (gasm
*asm_stmt
= dyn_cast
<gasm
*> (stmt
))
882 mark_all_reaching_defs_necessary (stmt
);
883 /* Inputs may perform loads. */
884 for (i
= 0; i
< gimple_asm_ninputs (asm_stmt
); ++i
)
886 tree op
= TREE_VALUE (gimple_asm_input_op (asm_stmt
, i
));
887 if (TREE_CODE (op
) != SSA_NAME
888 && !is_gimple_min_invariant (op
)
889 && TREE_CODE (op
) != CONSTRUCTOR
890 && !ref_may_be_aliased (op
))
891 mark_aliased_reaching_defs_necessary (stmt
, op
);
894 else if (gimple_code (stmt
) == GIMPLE_TRANSACTION
)
896 /* The beginning of a transaction is a memory barrier. */
897 /* ??? If we were really cool, we'd only be a barrier
898 for the memories touched within the transaction. */
899 mark_all_reaching_defs_necessary (stmt
);
904 /* If we over-used our alias oracle budget drop to simple
905 mode. The cost metric allows quadratic behavior
906 (number of uses times number of may-defs queries) up to
907 a constant maximal number of queries and after that falls back to
908 super-linear complexity. */
909 if (/* Constant but quadratic for small functions. */
910 total_chain
> 128 * 128
911 /* Linear in the number of may-defs. */
912 && total_chain
> 32 * longest_chain
913 /* Linear in the number of uses. */
914 && total_chain
> nr_walks
* 32)
918 bitmap_clear (visited
);
924 /* Remove dead PHI nodes from block BB. */
927 remove_dead_phis (basic_block bb
)
929 bool something_changed
= false;
933 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);)
938 /* We do not track necessity of virtual PHI nodes. Instead do
939 very simple dead PHI removal here. */
940 if (virtual_operand_p (gimple_phi_result (phi
)))
942 /* Virtual PHI nodes with one or identical arguments
944 if (degenerate_phi_p (phi
))
946 tree vdef
= gimple_phi_result (phi
);
947 tree vuse
= gimple_phi_arg_def (phi
, 0);
950 imm_use_iterator iter
;
952 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, vdef
)
953 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
954 SET_USE (use_p
, vuse
);
955 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef
)
956 && TREE_CODE (vuse
) == SSA_NAME
)
957 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse
) = 1;
960 gimple_set_plf (phi
, STMT_NECESSARY
, true);
963 if (!gimple_plf (phi
, STMT_NECESSARY
))
965 something_changed
= true;
966 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
968 fprintf (dump_file
, "Deleting : ");
969 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
970 fprintf (dump_file
, "\n");
973 remove_phi_node (&gsi
, true);
974 stats
.removed_phis
++;
980 return something_changed
;
984 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
985 containing I so that we don't have to look it up. */
988 remove_dead_stmt (gimple_stmt_iterator
*i
, basic_block bb
)
990 gimple
*stmt
= gsi_stmt (*i
);
992 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
994 fprintf (dump_file
, "Deleting : ");
995 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
996 fprintf (dump_file
, "\n");
1001 /* If we have determined that a conditional branch statement contributes
1002 nothing to the program, then we not only remove it, but we need to update
1003 the CFG. We can chose any of edges out of BB as long as we are sure to not
1004 close infinite loops. This is done by always choosing the edge closer to
1005 exit in inverted_post_order_compute order. */
1006 if (is_ctrl_stmt (stmt
))
1011 /* See if there is only one non-abnormal edge. */
1012 if (single_succ_p (bb
))
1013 e
= single_succ_edge (bb
);
1014 /* Otherwise chose one that is closer to bb with live statement in it.
1015 To be able to chose one, we compute inverted post order starting from
1016 all BBs with live statements. */
1021 auto_vec
<int, 20> postorder
;
1022 inverted_post_order_compute (&postorder
,
1023 &bb_contains_live_stmts
);
1024 bb_postorder
= XNEWVEC (int, last_basic_block_for_fn (cfun
));
1025 for (unsigned int i
= 0; i
< postorder
.length (); ++i
)
1026 bb_postorder
[postorder
[i
]] = i
;
1028 FOR_EACH_EDGE (e2
, ei
, bb
->succs
)
1029 if (!e
|| e2
->dest
== EXIT_BLOCK_PTR_FOR_FN (cfun
)
1030 || bb_postorder
[e
->dest
->index
]
1031 < bb_postorder
[e2
->dest
->index
])
1035 e
->probability
= profile_probability::always ();
1037 /* The edge is no longer associated with a conditional, so it does
1038 not have TRUE/FALSE flags.
1039 We are also safe to drop EH/ABNORMAL flags and turn them into
1040 normal control flow, because we know that all the destinations (including
1041 those odd edges) are equivalent for program execution. */
1042 e
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
| EDGE_EH
| EDGE_ABNORMAL
);
1044 /* The lone outgoing edge from BB will be a fallthru edge. */
1045 e
->flags
|= EDGE_FALLTHRU
;
1047 /* Remove the remaining outgoing edges. */
1048 for (ei
= ei_start (bb
->succs
); (e2
= ei_safe_edge (ei
)); )
1052 /* If we made a BB unconditionally exit a loop or removed
1053 an entry into an irreducible region, then this transform
1054 alters the set of BBs in the loop. Schedule a fixup. */
1055 if (loop_exit_edge_p (bb
->loop_father
, e
)
1056 || (e2
->dest
->flags
& BB_IRREDUCIBLE_LOOP
))
1057 loops_state_set (LOOPS_NEED_FIXUP
);
1064 /* If this is a store into a variable that is being optimized away,
1065 add a debug bind stmt if possible. */
1066 if (MAY_HAVE_DEBUG_BIND_STMTS
1067 && gimple_assign_single_p (stmt
)
1068 && is_gimple_val (gimple_assign_rhs1 (stmt
)))
1070 tree lhs
= gimple_assign_lhs (stmt
);
1071 if ((VAR_P (lhs
) || TREE_CODE (lhs
) == PARM_DECL
)
1072 && !DECL_IGNORED_P (lhs
)
1073 && is_gimple_reg_type (TREE_TYPE (lhs
))
1074 && !is_global_var (lhs
)
1075 && !DECL_HAS_VALUE_EXPR_P (lhs
))
1077 tree rhs
= gimple_assign_rhs1 (stmt
);
1079 = gimple_build_debug_bind (lhs
, unshare_expr (rhs
), stmt
);
1080 gsi_insert_after (i
, note
, GSI_SAME_STMT
);
1084 unlink_stmt_vdef (stmt
);
1085 gsi_remove (i
, true);
1086 release_defs (stmt
);
1089 /* Helper for maybe_optimize_arith_overflow. Find in *TP if there are any
1090 uses of data (SSA_NAME) other than REALPART_EXPR referencing it. */
1093 find_non_realpart_uses (tree
*tp
, int *walk_subtrees
, void *data
)
1095 if (TYPE_P (*tp
) || TREE_CODE (*tp
) == REALPART_EXPR
)
1097 if (*tp
== (tree
) data
)
1102 /* If the IMAGPART_EXPR of the {ADD,SUB,MUL}_OVERFLOW result is never used,
1103 but REALPART_EXPR is, optimize the {ADD,SUB,MUL}_OVERFLOW internal calls
1104 into plain unsigned {PLUS,MINUS,MULT}_EXPR, and if needed reset debug
1108 maybe_optimize_arith_overflow (gimple_stmt_iterator
*gsi
,
1109 enum tree_code subcode
)
1111 gimple
*stmt
= gsi_stmt (*gsi
);
1112 tree lhs
= gimple_call_lhs (stmt
);
1114 if (lhs
== NULL
|| TREE_CODE (lhs
) != SSA_NAME
)
1117 imm_use_iterator imm_iter
;
1118 use_operand_p use_p
;
1119 bool has_debug_uses
= false;
1120 bool has_realpart_uses
= false;
1121 bool has_other_uses
= false;
1122 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, lhs
)
1124 gimple
*use_stmt
= USE_STMT (use_p
);
1125 if (is_gimple_debug (use_stmt
))
1126 has_debug_uses
= true;
1127 else if (is_gimple_assign (use_stmt
)
1128 && gimple_assign_rhs_code (use_stmt
) == REALPART_EXPR
1129 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt
), 0) == lhs
)
1130 has_realpart_uses
= true;
1133 has_other_uses
= true;
1138 if (!has_realpart_uses
|| has_other_uses
)
1141 tree arg0
= gimple_call_arg (stmt
, 0);
1142 tree arg1
= gimple_call_arg (stmt
, 1);
1143 location_t loc
= gimple_location (stmt
);
1144 tree type
= TREE_TYPE (TREE_TYPE (lhs
));
1146 if (!TYPE_UNSIGNED (type
))
1147 utype
= build_nonstandard_integer_type (TYPE_PRECISION (type
), 1);
1148 tree result
= fold_build2_loc (loc
, subcode
, utype
,
1149 fold_convert_loc (loc
, utype
, arg0
),
1150 fold_convert_loc (loc
, utype
, arg1
));
1151 result
= fold_convert_loc (loc
, type
, result
);
1156 FOR_EACH_IMM_USE_STMT (use_stmt
, imm_iter
, lhs
)
1158 if (!gimple_debug_bind_p (use_stmt
))
1160 tree v
= gimple_debug_bind_get_value (use_stmt
);
1161 if (walk_tree (&v
, find_non_realpart_uses
, lhs
, NULL
))
1163 gimple_debug_bind_reset_value (use_stmt
);
1164 update_stmt (use_stmt
);
1169 if (TREE_CODE (result
) == INTEGER_CST
&& TREE_OVERFLOW (result
))
1170 result
= drop_tree_overflow (result
);
1171 tree overflow
= build_zero_cst (type
);
1172 tree ctype
= build_complex_type (type
);
1173 if (TREE_CODE (result
) == INTEGER_CST
)
1174 result
= build_complex (ctype
, result
, overflow
);
1176 result
= build2_loc (gimple_location (stmt
), COMPLEX_EXPR
,
1177 ctype
, result
, overflow
);
1179 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1181 fprintf (dump_file
, "Transforming call: ");
1182 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1183 fprintf (dump_file
, "because the overflow result is never used into: ");
1184 print_generic_stmt (dump_file
, result
, TDF_SLIM
);
1185 fprintf (dump_file
, "\n");
1188 if (!update_call_from_tree (gsi
, result
))
1189 gimplify_and_update_call_from_tree (gsi
, result
);
1192 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1193 contributes nothing to the program, and can be deleted. */
1196 eliminate_unnecessary_stmts (void)
1198 bool something_changed
= false;
1200 gimple_stmt_iterator gsi
, psi
;
1205 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1206 fprintf (dump_file
, "\nEliminating unnecessary statements:\n");
1208 clear_special_calls ();
1210 /* Walking basic blocks and statements in reverse order avoids
1211 releasing SSA names before any other DEFs that refer to them are
1212 released. This helps avoid loss of debug information, as we get
1213 a chance to propagate all RHSs of removed SSAs into debug uses,
1214 rather than only the latest ones. E.g., consider:
1220 If we were to release x_3 before a_5, when we reached a_5 and
1221 tried to substitute it into the debug stmt, we'd see x_3 there,
1222 but x_3's DEF, type, etc would have already been disconnected.
1223 By going backwards, the debug stmt first changes to:
1225 # DEBUG a => x_3 - b_4
1229 # DEBUG a => y_1 + z_2 - b_4
1232 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
1233 h
= get_all_dominated_blocks (CDI_DOMINATORS
,
1234 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun
)));
1240 /* Remove dead statements. */
1241 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi
= psi
)
1243 stmt
= gsi_stmt (gsi
);
1250 /* We can mark a call to free as not necessary if the
1251 defining statement of its argument is not necessary
1252 (and thus is getting removed). */
1253 if (gimple_plf (stmt
, STMT_NECESSARY
)
1254 && gimple_call_builtin_p (stmt
, BUILT_IN_FREE
))
1256 tree ptr
= gimple_call_arg (stmt
, 0);
1257 if (TREE_CODE (ptr
) == SSA_NAME
)
1259 gimple
*def_stmt
= SSA_NAME_DEF_STMT (ptr
);
1260 if (!gimple_nop_p (def_stmt
)
1261 && !gimple_plf (def_stmt
, STMT_NECESSARY
))
1262 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
1266 /* If GSI is not necessary then remove it. */
1267 if (!gimple_plf (stmt
, STMT_NECESSARY
))
1269 /* Keep clobbers that we can keep live live. */
1270 if (gimple_clobber_p (stmt
))
1273 use_operand_p use_p
;
1275 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_USE
)
1277 tree name
= USE_FROM_PTR (use_p
);
1278 if (!SSA_NAME_IS_DEFAULT_DEF (name
)
1279 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
)))
1288 if (!is_gimple_debug (stmt
))
1289 something_changed
= true;
1290 remove_dead_stmt (&gsi
, bb
);
1292 else if (is_gimple_call (stmt
))
1294 tree name
= gimple_call_lhs (stmt
);
1296 notice_special_calls (as_a
<gcall
*> (stmt
));
1298 /* When LHS of var = call (); is dead, simplify it into
1299 call (); saving one operand. */
1301 && TREE_CODE (name
) == SSA_NAME
1302 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
))
1303 /* Avoid doing so for allocation calls which we
1304 did not mark as necessary, it will confuse the
1305 special logic we apply to malloc/free pair removal. */
1306 && (!(call
= gimple_call_fndecl (stmt
))
1307 || DECL_BUILT_IN_CLASS (call
) != BUILT_IN_NORMAL
1308 || (DECL_FUNCTION_CODE (call
) != BUILT_IN_ALIGNED_ALLOC
1309 && DECL_FUNCTION_CODE (call
) != BUILT_IN_MALLOC
1310 && DECL_FUNCTION_CODE (call
) != BUILT_IN_CALLOC
1311 && !ALLOCA_FUNCTION_CODE_P
1312 (DECL_FUNCTION_CODE (call
)))))
1314 something_changed
= true;
1315 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1317 fprintf (dump_file
, "Deleting LHS of call: ");
1318 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1319 fprintf (dump_file
, "\n");
1322 gimple_call_set_lhs (stmt
, NULL_TREE
);
1323 maybe_clean_or_replace_eh_stmt (stmt
, stmt
);
1325 release_ssa_name (name
);
1327 /* GOMP_SIMD_LANE or ASAN_POISON without lhs is not
1329 if (gimple_call_internal_p (stmt
))
1330 switch (gimple_call_internal_fn (stmt
))
1332 case IFN_GOMP_SIMD_LANE
:
1333 case IFN_ASAN_POISON
:
1334 remove_dead_stmt (&gsi
, bb
);
1340 else if (gimple_call_internal_p (stmt
))
1341 switch (gimple_call_internal_fn (stmt
))
1343 case IFN_ADD_OVERFLOW
:
1344 maybe_optimize_arith_overflow (&gsi
, PLUS_EXPR
);
1346 case IFN_SUB_OVERFLOW
:
1347 maybe_optimize_arith_overflow (&gsi
, MINUS_EXPR
);
1349 case IFN_MUL_OVERFLOW
:
1350 maybe_optimize_arith_overflow (&gsi
, MULT_EXPR
);
1361 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1362 rendered some PHI nodes unreachable while they are still in use.
1363 Mark them for renaming. */
1366 basic_block prev_bb
;
1368 find_unreachable_blocks ();
1370 /* Delete all unreachable basic blocks in reverse dominator order. */
1371 for (bb
= EXIT_BLOCK_PTR_FOR_FN (cfun
)->prev_bb
;
1372 bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
); bb
= prev_bb
)
1374 prev_bb
= bb
->prev_bb
;
1376 if (!bitmap_bit_p (bb_contains_live_stmts
, bb
->index
)
1377 || !(bb
->flags
& BB_REACHABLE
))
1379 for (gphi_iterator gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
1381 if (virtual_operand_p (gimple_phi_result (gsi
.phi ())))
1384 imm_use_iterator iter
;
1386 FOR_EACH_IMM_USE_STMT (stmt
, iter
,
1387 gimple_phi_result (gsi
.phi ()))
1389 if (!(gimple_bb (stmt
)->flags
& BB_REACHABLE
))
1391 if (gimple_code (stmt
) == GIMPLE_PHI
1392 || gimple_plf (stmt
, STMT_NECESSARY
))
1395 BREAK_FROM_IMM_USE_STMT (iter
);
1399 mark_virtual_phi_result_for_renaming (gsi
.phi ());
1402 if (!(bb
->flags
& BB_REACHABLE
))
1404 /* Speed up the removal of blocks that don't
1405 dominate others. Walking backwards, this should
1406 be the common case. ??? Do we need to recompute
1407 dominators because of cfg_altered? */
1408 if (!first_dom_son (CDI_DOMINATORS
, bb
))
1409 delete_basic_block (bb
);
1412 h
= get_all_dominated_blocks (CDI_DOMINATORS
, bb
);
1417 prev_bb
= bb
->prev_bb
;
1418 /* Rearrangements to the CFG may have failed
1419 to update the dominators tree, so that
1420 formerly-dominated blocks are now
1421 otherwise reachable. */
1422 if (!!(bb
->flags
& BB_REACHABLE
))
1424 delete_basic_block (bb
);
1433 FOR_EACH_BB_FN (bb
, cfun
)
1435 /* Remove dead PHI nodes. */
1436 something_changed
|= remove_dead_phis (bb
);
1440 free (bb_postorder
);
1441 bb_postorder
= NULL
;
1443 return something_changed
;
1447 /* Print out removed statement statistics. */
1454 percg
= ((float) stats
.removed
/ (float) stats
.total
) * 100;
1455 fprintf (dump_file
, "Removed %d of %d statements (%d%%)\n",
1456 stats
.removed
, stats
.total
, (int) percg
);
1458 if (stats
.total_phis
== 0)
1461 percg
= ((float) stats
.removed_phis
/ (float) stats
.total_phis
) * 100;
1463 fprintf (dump_file
, "Removed %d of %d PHI nodes (%d%%)\n",
1464 stats
.removed_phis
, stats
.total_phis
, (int) percg
);
1467 /* Initialization for this pass. Set up the used data structures. */
1470 tree_dce_init (bool aggressive
)
1472 memset ((void *) &stats
, 0, sizeof (stats
));
1476 last_stmt_necessary
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1477 bitmap_clear (last_stmt_necessary
);
1478 bb_contains_live_stmts
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1479 bitmap_clear (bb_contains_live_stmts
);
1482 processed
= sbitmap_alloc (num_ssa_names
+ 1);
1483 bitmap_clear (processed
);
1485 worklist
.create (64);
1486 cfg_altered
= false;
1489 /* Cleanup after this pass. */
1492 tree_dce_done (bool aggressive
)
1497 sbitmap_free (visited_control_parents
);
1498 sbitmap_free (last_stmt_necessary
);
1499 sbitmap_free (bb_contains_live_stmts
);
1500 bb_contains_live_stmts
= NULL
;
1503 sbitmap_free (processed
);
1505 worklist
.release ();
1508 /* Main routine to eliminate dead code.
1510 AGGRESSIVE controls the aggressiveness of the algorithm.
1511 In conservative mode, we ignore control dependence and simply declare
1512 all but the most trivially dead branches necessary. This mode is fast.
1513 In aggressive mode, control dependences are taken into account, which
1514 results in more dead code elimination, but at the cost of some time.
1516 FIXME: Aggressive mode before PRE doesn't work currently because
1517 the dominance info is not invalidated after DCE1. This is
1518 not an issue right now because we only run aggressive DCE
1519 as the last tree SSA pass, but keep this in mind when you
1520 start experimenting with pass ordering. */
1523 perform_tree_ssa_dce (bool aggressive
)
1525 bool something_changed
= 0;
1527 calculate_dominance_info (CDI_DOMINATORS
);
1529 /* Preheaders are needed for SCEV to work.
1530 Simple lateches and recorded exits improve chances that loop will
1531 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1532 bool in_loop_pipeline
= scev_initialized_p ();
1533 if (aggressive
&& ! in_loop_pipeline
)
1536 loop_optimizer_init (LOOPS_NORMAL
1537 | LOOPS_HAVE_RECORDED_EXITS
);
1540 tree_dce_init (aggressive
);
1544 /* Compute control dependence. */
1545 calculate_dominance_info (CDI_POST_DOMINATORS
);
1546 cd
= new control_dependences ();
1548 visited_control_parents
=
1549 sbitmap_alloc (last_basic_block_for_fn (cfun
));
1550 bitmap_clear (visited_control_parents
);
1552 mark_dfs_back_edges ();
1555 find_obviously_necessary_stmts (aggressive
);
1557 if (aggressive
&& ! in_loop_pipeline
)
1559 loop_optimizer_finalize ();
1567 visited
= BITMAP_ALLOC (NULL
);
1568 propagate_necessity (aggressive
);
1569 BITMAP_FREE (visited
);
1571 something_changed
|= eliminate_unnecessary_stmts ();
1572 something_changed
|= cfg_altered
;
1574 /* We do not update postdominators, so free them unconditionally. */
1575 free_dominance_info (CDI_POST_DOMINATORS
);
1577 /* If we removed paths in the CFG, then we need to update
1578 dominators as well. I haven't investigated the possibility
1579 of incrementally updating dominators. */
1581 free_dominance_info (CDI_DOMINATORS
);
1583 statistics_counter_event (cfun
, "Statements deleted", stats
.removed
);
1584 statistics_counter_event (cfun
, "PHI nodes deleted", stats
.removed_phis
);
1586 /* Debugging dumps. */
1587 if (dump_file
&& (dump_flags
& (TDF_STATS
|TDF_DETAILS
)))
1590 tree_dce_done (aggressive
);
1592 if (something_changed
)
1594 free_numbers_of_iterations_estimates (cfun
);
1595 if (in_loop_pipeline
)
1597 return TODO_update_ssa
| TODO_cleanup_cfg
;
1602 /* Pass entry points. */
1606 return perform_tree_ssa_dce (/*aggressive=*/false);
1610 tree_ssa_cd_dce (void)
1612 return perform_tree_ssa_dce (/*aggressive=*/optimize
>= 2);
1617 const pass_data pass_data_dce
=
1619 GIMPLE_PASS
, /* type */
1621 OPTGROUP_NONE
, /* optinfo_flags */
1622 TV_TREE_DCE
, /* tv_id */
1623 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1624 0, /* properties_provided */
1625 0, /* properties_destroyed */
1626 0, /* todo_flags_start */
1627 0, /* todo_flags_finish */
1630 class pass_dce
: public gimple_opt_pass
1633 pass_dce (gcc::context
*ctxt
)
1634 : gimple_opt_pass (pass_data_dce
, ctxt
)
1637 /* opt_pass methods: */
1638 opt_pass
* clone () { return new pass_dce (m_ctxt
); }
1639 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1640 virtual unsigned int execute (function
*) { return tree_ssa_dce (); }
1642 }; // class pass_dce
1647 make_pass_dce (gcc::context
*ctxt
)
1649 return new pass_dce (ctxt
);
1654 const pass_data pass_data_cd_dce
=
1656 GIMPLE_PASS
, /* type */
1658 OPTGROUP_NONE
, /* optinfo_flags */
1659 TV_TREE_CD_DCE
, /* tv_id */
1660 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1661 0, /* properties_provided */
1662 0, /* properties_destroyed */
1663 0, /* todo_flags_start */
1664 0, /* todo_flags_finish */
1667 class pass_cd_dce
: public gimple_opt_pass
1670 pass_cd_dce (gcc::context
*ctxt
)
1671 : gimple_opt_pass (pass_data_cd_dce
, ctxt
)
1674 /* opt_pass methods: */
1675 opt_pass
* clone () { return new pass_cd_dce (m_ctxt
); }
1676 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1677 virtual unsigned int execute (function
*) { return tree_ssa_cd_dce (); }
1679 }; // class pass_cd_dce
1684 make_pass_cd_dce (gcc::context
*ctxt
)
1686 return new pass_cd_dce (ctxt
);
1690 /* A cheap DCE interface. WORKLIST is a list of possibly dead stmts and
1691 is consumed by this function. The function has linear complexity in
1692 the number of dead stmts with a constant factor like the average SSA
1693 use operands number. */
1696 simple_dce_from_worklist (bitmap worklist
)
1698 while (! bitmap_empty_p (worklist
))
1701 unsigned i
= bitmap_first_set_bit (worklist
);
1702 bitmap_clear_bit (worklist
, i
);
1704 tree def
= ssa_name (i
);
1705 /* Removed by somebody else or still in use. */
1706 if (! def
|| ! has_zero_uses (def
))
1709 gimple
*t
= SSA_NAME_DEF_STMT (def
);
1710 if (gimple_has_side_effects (t
))
1713 /* Add uses to the worklist. */
1715 use_operand_p use_p
;
1716 FOR_EACH_PHI_OR_STMT_USE (use_p
, t
, iter
, SSA_OP_USE
)
1718 tree use
= USE_FROM_PTR (use_p
);
1719 if (TREE_CODE (use
) == SSA_NAME
1720 && ! SSA_NAME_IS_DEFAULT_DEF (use
))
1721 bitmap_set_bit (worklist
, SSA_NAME_VERSION (use
));
1725 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1727 fprintf (dump_file
, "Removing dead stmt:");
1728 print_gimple_stmt (dump_file
, t
, 0);
1730 gimple_stmt_iterator gsi
= gsi_for_stmt (t
);
1731 if (gimple_code (t
) == GIMPLE_PHI
)
1732 remove_phi_node (&gsi
, true);
1735 gsi_remove (&gsi
, true);