1 /* Dead code elimination pass for the GNU compiler.
2 Copyright (C) 2002-2015 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"
56 #include "fold-const.h"
58 #include "gimple-pretty-print.h"
60 #include "hard-reg-set.h"
62 #include "dominance.h"
65 #include "basic-block.h"
66 #include "tree-ssa-alias.h"
67 #include "internal-fn.h"
69 #include "gimple-expr.h"
73 #include "gimple-iterator.h"
74 #include "gimple-ssa.h"
76 #include "tree-phinodes.h"
77 #include "ssa-iterators.h"
78 #include "stringpool.h"
79 #include "tree-ssanames.h"
80 #include "tree-ssa-loop-niter.h"
81 #include "tree-into-ssa.h"
85 #include "statistics.h"
86 #include "insn-config.h"
95 #include "tree-pass.h"
97 #include "tree-scalar-evolution.h"
98 #include "tree-chkp.h"
99 #include "tree-ssa-propagate.h"
100 #include "gimple-fold.h"
102 static struct stmt_stats
110 #define STMT_NECESSARY GF_PLF_1
112 static vec
<gimple
> worklist
;
114 /* Vector indicating an SSA name has already been processed and marked
116 static sbitmap processed
;
118 /* Vector indicating that the last statement of a basic block has already
119 been marked as necessary. */
120 static sbitmap last_stmt_necessary
;
122 /* Vector indicating that BB contains statements that are live. */
123 static sbitmap bb_contains_live_stmts
;
125 /* Before we can determine whether a control branch is dead, we need to
126 compute which blocks are control dependent on which edges.
128 We expect each block to be control dependent on very few edges so we
129 use a bitmap for each block recording its edges. An array holds the
130 bitmap. The Ith bit in the bitmap is set if that block is dependent
132 static control_dependences
*cd
;
134 /* Vector indicating that a basic block has already had all the edges
135 processed that it is control dependent on. */
136 static sbitmap visited_control_parents
;
138 /* TRUE if this pass alters the CFG (by removing control statements).
141 If this pass alters the CFG, then it will arrange for the dominators
143 static bool cfg_altered
;
146 /* If STMT is not already marked necessary, mark it, and add it to the
147 worklist if ADD_TO_WORKLIST is true. */
150 mark_stmt_necessary (gimple stmt
, bool add_to_worklist
)
154 if (gimple_plf (stmt
, STMT_NECESSARY
))
157 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
159 fprintf (dump_file
, "Marking useful stmt: ");
160 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
161 fprintf (dump_file
, "\n");
164 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
166 worklist
.safe_push (stmt
);
167 if (bb_contains_live_stmts
&& !is_gimple_debug (stmt
))
168 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
172 /* Mark the statement defining operand OP as necessary. */
175 mark_operand_necessary (tree op
)
182 ver
= SSA_NAME_VERSION (op
);
183 if (bitmap_bit_p (processed
, ver
))
185 stmt
= SSA_NAME_DEF_STMT (op
);
186 gcc_assert (gimple_nop_p (stmt
)
187 || gimple_plf (stmt
, STMT_NECESSARY
));
190 bitmap_set_bit (processed
, ver
);
192 stmt
= SSA_NAME_DEF_STMT (op
);
195 if (gimple_plf (stmt
, STMT_NECESSARY
) || gimple_nop_p (stmt
))
198 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
200 fprintf (dump_file
, "marking necessary through ");
201 print_generic_expr (dump_file
, op
, 0);
202 fprintf (dump_file
, " stmt ");
203 print_gimple_stmt (dump_file
, stmt
, 0, 0);
206 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
207 if (bb_contains_live_stmts
)
208 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
209 worklist
.safe_push (stmt
);
213 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
214 it can make other statements necessary.
216 If AGGRESSIVE is false, control statements are conservatively marked as
220 mark_stmt_if_obviously_necessary (gimple stmt
, bool aggressive
)
222 /* With non-call exceptions, we have to assume that all statements could
223 throw. If a statement could throw, it can be deemed necessary. */
224 if (cfun
->can_throw_non_call_exceptions
225 && !cfun
->can_delete_dead_exceptions
226 && stmt_could_throw_p (stmt
))
228 mark_stmt_necessary (stmt
, true);
232 /* Statements that are implicitly live. Most function calls, asm
233 and return statements are required. Labels and GIMPLE_BIND nodes
234 are kept because they are control flow, and we have no way of
235 knowing whether they can be removed. DCE can eliminate all the
236 other statements in a block, and CFG can then remove the block
238 switch (gimple_code (stmt
))
242 mark_stmt_necessary (stmt
, false);
248 mark_stmt_necessary (stmt
, true);
253 tree callee
= gimple_call_fndecl (stmt
);
254 if (callee
!= NULL_TREE
255 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
)
256 switch (DECL_FUNCTION_CODE (callee
))
258 case BUILT_IN_MALLOC
:
259 case BUILT_IN_ALIGNED_ALLOC
:
260 case BUILT_IN_CALLOC
:
261 case BUILT_IN_ALLOCA
:
262 case BUILT_IN_ALLOCA_WITH_ALIGN
:
267 /* Most, but not all function calls are required. Function calls that
268 produce no result and have no side effects (i.e. const pure
269 functions) are unnecessary. */
270 if (gimple_has_side_effects (stmt
))
272 mark_stmt_necessary (stmt
, true);
275 if (!gimple_call_lhs (stmt
))
281 /* Debug temps without a value are not useful. ??? If we could
282 easily locate the debug temp bind stmt for a use thereof,
283 would could refrain from marking all debug temps here, and
284 mark them only if they're used. */
285 if (!gimple_debug_bind_p (stmt
)
286 || gimple_debug_bind_has_value_p (stmt
)
287 || TREE_CODE (gimple_debug_bind_get_var (stmt
)) != DEBUG_EXPR_DECL
)
288 mark_stmt_necessary (stmt
, false);
292 gcc_assert (!simple_goto_p (stmt
));
293 mark_stmt_necessary (stmt
, true);
297 gcc_assert (EDGE_COUNT (gimple_bb (stmt
)->succs
) == 2);
302 mark_stmt_necessary (stmt
, true);
306 if (gimple_clobber_p (stmt
))
314 /* If the statement has volatile operands, it needs to be preserved.
315 Same for statements that can alter control flow in unpredictable
317 if (gimple_has_volatile_ops (stmt
) || is_ctrl_altering_stmt (stmt
))
319 mark_stmt_necessary (stmt
, true);
323 if (stmt_may_clobber_global_p (stmt
))
325 mark_stmt_necessary (stmt
, true);
333 /* Mark the last statement of BB as necessary. */
336 mark_last_stmt_necessary (basic_block bb
)
338 gimple stmt
= last_stmt (bb
);
340 bitmap_set_bit (last_stmt_necessary
, bb
->index
);
341 bitmap_set_bit (bb_contains_live_stmts
, bb
->index
);
343 /* We actually mark the statement only if it is a control statement. */
344 if (stmt
&& is_ctrl_stmt (stmt
))
345 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 (edge_number
)->src
;
371 if (ignore_self
&& cd_bb
== bb
)
377 if (!bitmap_bit_p (last_stmt_necessary
, cd_bb
->index
))
378 mark_last_stmt_necessary (cd_bb
);
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. */
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 loop %i->%i\n",
441 e
->src
->index
, e
->dest
->index
);
442 mark_control_dependent_edges_necessary (e
->dest
, false);
446 FOR_EACH_LOOP (loop
, 0)
447 if (!finite_loop_p (loop
))
450 fprintf (dump_file
, "can not prove finiteness of loop %i\n", loop
->num
);
451 mark_control_dependent_edges_necessary (loop
->latch
, false);
458 /* Return true if REF is based on an aliased base, otherwise false. */
461 ref_may_be_aliased (tree ref
)
463 gcc_assert (TREE_CODE (ref
) != WITH_SIZE_EXPR
);
464 while (handled_component_p (ref
))
465 ref
= TREE_OPERAND (ref
, 0);
466 if (TREE_CODE (ref
) == MEM_REF
467 && TREE_CODE (TREE_OPERAND (ref
, 0)) == ADDR_EXPR
)
468 ref
= TREE_OPERAND (TREE_OPERAND (ref
, 0), 0);
469 return !(DECL_P (ref
)
470 && !may_be_aliased (ref
));
473 static bitmap visited
= NULL
;
474 static unsigned int longest_chain
= 0;
475 static unsigned int total_chain
= 0;
476 static unsigned int nr_walks
= 0;
477 static bool chain_ovfl
= false;
479 /* Worker for the walker that marks reaching definitions of REF,
480 which is based on a non-aliased decl, necessary. It returns
481 true whenever the defining statement of the current VDEF is
482 a kill for REF, as no dominating may-defs are necessary for REF
483 anymore. DATA points to the basic-block that contains the
484 stmt that refers to REF. */
487 mark_aliased_reaching_defs_necessary_1 (ao_ref
*ref
, tree vdef
, void *data
)
489 gimple def_stmt
= SSA_NAME_DEF_STMT (vdef
);
491 /* All stmts we visit are necessary. */
492 mark_operand_necessary (vdef
);
494 /* If the stmt lhs kills ref, then we can stop walking. */
495 if (gimple_has_lhs (def_stmt
)
496 && TREE_CODE (gimple_get_lhs (def_stmt
)) != SSA_NAME
497 /* The assignment is not necessarily carried out if it can throw
498 and we can catch it in the current function where we could inspect
500 ??? We only need to care about the RHS throwing. For aggregate
501 assignments or similar calls and non-call exceptions the LHS
502 might throw as well. */
503 && !stmt_can_throw_internal (def_stmt
))
505 tree base
, lhs
= gimple_get_lhs (def_stmt
);
506 HOST_WIDE_INT size
, offset
, max_size
;
508 base
= get_ref_base_and_extent (lhs
, &offset
, &size
, &max_size
);
509 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
510 so base == refd->base does not always hold. */
511 if (base
== ref
->base
)
513 /* For a must-alias check we need to be able to constrain
514 the accesses properly. */
515 if (size
!= -1 && size
== max_size
516 && ref
->max_size
!= -1)
518 if (offset
<= ref
->offset
519 && offset
+ size
>= ref
->offset
+ ref
->max_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
)
549 gcc_assert (!chain_ovfl
);
550 ao_ref_init (&refd
, ref
);
551 chain
= walk_aliased_vdefs (&refd
, gimple_vuse (stmt
),
552 mark_aliased_reaching_defs_necessary_1
,
553 gimple_bb (stmt
), NULL
);
554 if (chain
> longest_chain
)
555 longest_chain
= chain
;
556 total_chain
+= chain
;
560 /* Worker for the walker that marks reaching definitions of REF, which
561 is not based on a non-aliased decl. For simplicity we need to end
562 up marking all may-defs necessary that are not based on a non-aliased
563 decl. The only job of this walker is to skip may-defs based on
564 a non-aliased decl. */
567 mark_all_reaching_defs_necessary_1 (ao_ref
*ref ATTRIBUTE_UNUSED
,
568 tree vdef
, void *data ATTRIBUTE_UNUSED
)
570 gimple def_stmt
= SSA_NAME_DEF_STMT (vdef
);
572 /* We have to skip already visited (and thus necessary) statements
573 to make the chaining work after we dropped back to simple mode. */
575 && bitmap_bit_p (processed
, SSA_NAME_VERSION (vdef
)))
577 gcc_assert (gimple_nop_p (def_stmt
)
578 || gimple_plf (def_stmt
, STMT_NECESSARY
));
582 /* We want to skip stores to non-aliased variables. */
584 && gimple_assign_single_p (def_stmt
))
586 tree lhs
= gimple_assign_lhs (def_stmt
);
587 if (!ref_may_be_aliased (lhs
))
591 /* We want to skip statments that do not constitute stores but have
592 a virtual definition. */
593 if (is_gimple_call (def_stmt
))
595 tree callee
= gimple_call_fndecl (def_stmt
);
596 if (callee
!= NULL_TREE
597 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
)
598 switch (DECL_FUNCTION_CODE (callee
))
600 case BUILT_IN_MALLOC
:
601 case BUILT_IN_ALIGNED_ALLOC
:
602 case BUILT_IN_CALLOC
:
603 case BUILT_IN_ALLOCA
:
604 case BUILT_IN_ALLOCA_WITH_ALIGN
:
612 mark_operand_necessary (vdef
);
618 mark_all_reaching_defs_necessary (gimple stmt
)
620 walk_aliased_vdefs (NULL
, gimple_vuse (stmt
),
621 mark_all_reaching_defs_necessary_1
, NULL
, &visited
);
624 /* Return true for PHI nodes with one or identical arguments
627 degenerate_phi_p (gimple phi
)
630 tree op
= gimple_phi_arg_def (phi
, 0);
631 for (i
= 1; i
< gimple_phi_num_args (phi
); i
++)
632 if (gimple_phi_arg_def (phi
, i
) != op
)
637 /* Propagate necessity using the operands of necessary statements.
638 Process the uses on each statement in the worklist, and add all
639 feeding statements which contribute to the calculation of this
640 value to the worklist.
642 In conservative mode, EL is NULL. */
645 propagate_necessity (bool aggressive
)
649 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
650 fprintf (dump_file
, "\nProcessing worklist:\n");
652 while (worklist
.length () > 0)
654 /* Take STMT from worklist. */
655 stmt
= worklist
.pop ();
657 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
659 fprintf (dump_file
, "processing: ");
660 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
661 fprintf (dump_file
, "\n");
666 /* Mark the last statement of the basic blocks on which the block
667 containing STMT is control dependent, but only if we haven't
669 basic_block bb
= gimple_bb (stmt
);
670 if (bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
671 && !bitmap_bit_p (visited_control_parents
, bb
->index
))
672 mark_control_dependent_edges_necessary (bb
, false);
675 if (gimple_code (stmt
) == GIMPLE_PHI
676 /* We do not process virtual PHI nodes nor do we track their
678 && !virtual_operand_p (gimple_phi_result (stmt
)))
680 /* PHI nodes are somewhat special in that each PHI alternative has
681 data and control dependencies. All the statements feeding the
682 PHI node's arguments are always necessary. In aggressive mode,
683 we also consider the control dependent edges leading to the
684 predecessor block associated with each PHI alternative as
686 gphi
*phi
= as_a
<gphi
*> (stmt
);
689 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
691 tree arg
= PHI_ARG_DEF (stmt
, k
);
692 if (TREE_CODE (arg
) == SSA_NAME
)
693 mark_operand_necessary (arg
);
696 /* For PHI operands it matters from where the control flow arrives
697 to the BB. Consider the following example:
707 We need to mark control dependence of the empty basic blocks, since they
708 contains computation of PHI operands.
710 Doing so is too restrictive in the case the predecestor block is in
716 for (i = 0; i<1000; ++i)
722 There is PHI for J in the BB containing return statement.
723 In this case the control dependence of predecestor block (that is
724 within the empty loop) also contains the block determining number
725 of iterations of the block that would prevent removing of empty
728 This scenario can be avoided by splitting critical edges.
729 To save the critical edge splitting pass we identify how the control
730 dependence would look like if the edge was split.
732 Consider the modified CFG created from current CFG by splitting
733 edge B->C. In the postdominance tree of modified CFG, C' is
734 always child of C. There are two cases how chlids of C' can look
739 In this case the only basic block C' is control dependent on is B.
741 2) C' has single child that is B
743 In this case control dependence of C' is same as control
744 dependence of B in original CFG except for block B itself.
745 (since C' postdominate B in modified CFG)
747 Now how to decide what case happens? There are two basic options:
749 a) C postdominate B. Then C immediately postdominate B and
750 case 2 happens iff there is no other way from B to C except
753 There is other way from B to C iff there is succesor of B that
754 is not postdominated by B. Testing this condition is somewhat
755 expensive, because we need to iterate all succesors of B.
756 We are safe to assume that this does not happen: we will mark B
757 as needed when processing the other path from B to C that is
758 conrol dependent on B and marking control dependencies of B
759 itself is harmless because they will be processed anyway after
760 processing control statement in B.
762 b) C does not postdominate B. Always case 1 happens since there is
763 path from C to exit that does not go through B and thus also C'. */
765 if (aggressive
&& !degenerate_phi_p (stmt
))
767 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
769 basic_block arg_bb
= gimple_phi_arg_edge (phi
, k
)->src
;
772 != get_immediate_dominator (CDI_POST_DOMINATORS
, arg_bb
))
774 if (!bitmap_bit_p (last_stmt_necessary
, arg_bb
->index
))
775 mark_last_stmt_necessary (arg_bb
);
777 else if (arg_bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
778 && !bitmap_bit_p (visited_control_parents
,
780 mark_control_dependent_edges_necessary (arg_bb
, true);
786 /* Propagate through the operands. Examine all the USE, VUSE and
787 VDEF operands in this statement. Mark all the statements
788 which feed this statement's uses as necessary. */
792 /* If this is a call to free which is directly fed by an
793 allocation function do not mark that necessary through
794 processing the argument. */
795 if (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
))
797 tree ptr
= gimple_call_arg (stmt
, 0);
800 /* If the pointer we free is defined by an allocation
801 function do not add the call to the worklist. */
802 if (TREE_CODE (ptr
) == SSA_NAME
803 && is_gimple_call (def_stmt
= SSA_NAME_DEF_STMT (ptr
))
804 && (def_callee
= gimple_call_fndecl (def_stmt
))
805 && DECL_BUILT_IN_CLASS (def_callee
) == BUILT_IN_NORMAL
806 && (DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_ALIGNED_ALLOC
807 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_MALLOC
808 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_CALLOC
))
810 gimple bounds_def_stmt
;
813 /* For instrumented calls we should also check used
814 bounds are returned by the same allocation call. */
815 if (!gimple_call_with_bounds_p (stmt
)
816 || ((bounds
= gimple_call_arg (stmt
, 1))
817 && TREE_CODE (bounds
) == SSA_NAME
818 && (bounds_def_stmt
= SSA_NAME_DEF_STMT (bounds
))
819 && chkp_gimple_call_builtin_p (bounds_def_stmt
,
820 BUILT_IN_CHKP_BNDRET
)
821 && gimple_call_arg (bounds_def_stmt
, 0) == ptr
))
826 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
827 mark_operand_necessary (use
);
829 use
= gimple_vuse (stmt
);
833 /* If we dropped to simple mode make all immediately
834 reachable definitions necessary. */
837 mark_all_reaching_defs_necessary (stmt
);
841 /* For statements that may load from memory (have a VUSE) we
842 have to mark all reaching (may-)definitions as necessary.
843 We partition this task into two cases:
844 1) explicit loads based on decls that are not aliased
845 2) implicit loads (like calls) and explicit loads not
846 based on decls that are not aliased (like indirect
847 references or loads from globals)
848 For 1) we mark all reaching may-defs as necessary, stopping
849 at dominating kills. For 2) we want to mark all dominating
850 references necessary, but non-aliased ones which we handle
851 in 1). By keeping a global visited bitmap for references
852 we walk for 2) we avoid quadratic behavior for those. */
854 if (is_gimple_call (stmt
))
856 tree callee
= gimple_call_fndecl (stmt
);
859 /* Calls to functions that are merely acting as barriers
860 or that only store to memory do not make any previous
862 if (callee
!= NULL_TREE
863 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
864 && (DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET
865 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET_CHK
866 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MALLOC
867 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALIGNED_ALLOC
868 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_CALLOC
869 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_FREE
870 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_VA_END
871 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALLOCA
872 || (DECL_FUNCTION_CODE (callee
)
873 == BUILT_IN_ALLOCA_WITH_ALIGN
)
874 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_SAVE
875 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_RESTORE
876 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ASSUME_ALIGNED
))
879 /* Calls implicitly load from memory, their arguments
880 in addition may explicitly perform memory loads. */
881 mark_all_reaching_defs_necessary (stmt
);
882 for (i
= 0; i
< gimple_call_num_args (stmt
); ++i
)
884 tree arg
= gimple_call_arg (stmt
, i
);
885 if (TREE_CODE (arg
) == SSA_NAME
886 || is_gimple_min_invariant (arg
))
888 if (TREE_CODE (arg
) == WITH_SIZE_EXPR
)
889 arg
= TREE_OPERAND (arg
, 0);
890 if (!ref_may_be_aliased (arg
))
891 mark_aliased_reaching_defs_necessary (stmt
, arg
);
894 else if (gimple_assign_single_p (stmt
))
897 /* If this is a load mark things necessary. */
898 rhs
= gimple_assign_rhs1 (stmt
);
899 if (TREE_CODE (rhs
) != SSA_NAME
900 && !is_gimple_min_invariant (rhs
)
901 && TREE_CODE (rhs
) != CONSTRUCTOR
)
903 if (!ref_may_be_aliased (rhs
))
904 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
906 mark_all_reaching_defs_necessary (stmt
);
909 else if (greturn
*return_stmt
= dyn_cast
<greturn
*> (stmt
))
911 tree rhs
= gimple_return_retval (return_stmt
);
912 /* A return statement may perform a load. */
914 && TREE_CODE (rhs
) != SSA_NAME
915 && !is_gimple_min_invariant (rhs
)
916 && TREE_CODE (rhs
) != CONSTRUCTOR
)
918 if (!ref_may_be_aliased (rhs
))
919 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
921 mark_all_reaching_defs_necessary (stmt
);
924 else if (gasm
*asm_stmt
= dyn_cast
<gasm
*> (stmt
))
927 mark_all_reaching_defs_necessary (stmt
);
928 /* Inputs may perform loads. */
929 for (i
= 0; i
< gimple_asm_ninputs (asm_stmt
); ++i
)
931 tree op
= TREE_VALUE (gimple_asm_input_op (asm_stmt
, i
));
932 if (TREE_CODE (op
) != SSA_NAME
933 && !is_gimple_min_invariant (op
)
934 && TREE_CODE (op
) != CONSTRUCTOR
935 && !ref_may_be_aliased (op
))
936 mark_aliased_reaching_defs_necessary (stmt
, op
);
939 else if (gimple_code (stmt
) == GIMPLE_TRANSACTION
)
941 /* The beginning of a transaction is a memory barrier. */
942 /* ??? If we were really cool, we'd only be a barrier
943 for the memories touched within the transaction. */
944 mark_all_reaching_defs_necessary (stmt
);
949 /* If we over-used our alias oracle budget drop to simple
950 mode. The cost metric allows quadratic behavior
951 (number of uses times number of may-defs queries) up to
952 a constant maximal number of queries and after that falls back to
953 super-linear complexity. */
954 if (/* Constant but quadratic for small functions. */
955 total_chain
> 128 * 128
956 /* Linear in the number of may-defs. */
957 && total_chain
> 32 * longest_chain
958 /* Linear in the number of uses. */
959 && total_chain
> nr_walks
* 32)
963 bitmap_clear (visited
);
969 /* Remove dead PHI nodes from block BB. */
972 remove_dead_phis (basic_block bb
)
974 bool something_changed
= false;
978 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);)
983 /* We do not track necessity of virtual PHI nodes. Instead do
984 very simple dead PHI removal here. */
985 if (virtual_operand_p (gimple_phi_result (phi
)))
987 /* Virtual PHI nodes with one or identical arguments
989 if (degenerate_phi_p (phi
))
991 tree vdef
= gimple_phi_result (phi
);
992 tree vuse
= gimple_phi_arg_def (phi
, 0);
995 imm_use_iterator iter
;
997 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, vdef
)
998 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
999 SET_USE (use_p
, vuse
);
1000 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef
)
1001 && TREE_CODE (vuse
) == SSA_NAME
)
1002 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse
) = 1;
1005 gimple_set_plf (phi
, STMT_NECESSARY
, true);
1008 if (!gimple_plf (phi
, STMT_NECESSARY
))
1010 something_changed
= true;
1011 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1013 fprintf (dump_file
, "Deleting : ");
1014 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
1015 fprintf (dump_file
, "\n");
1018 remove_phi_node (&gsi
, true);
1019 stats
.removed_phis
++;
1025 return something_changed
;
1028 /* Forward edge E to respective POST_DOM_BB and update PHIs. */
1031 forward_edge_to_pdom (edge e
, basic_block post_dom_bb
)
1037 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1038 fprintf (dump_file
, "Redirecting edge %i->%i to %i\n", e
->src
->index
,
1039 e
->dest
->index
, post_dom_bb
->index
);
1041 e2
= redirect_edge_and_branch (e
, post_dom_bb
);
1044 /* If edge was already around, no updating is necessary. */
1048 if (!gimple_seq_empty_p (phi_nodes (post_dom_bb
)))
1050 /* We are sure that for every live PHI we are seeing control dependent BB.
1051 This means that we can pick any edge to duplicate PHI args from. */
1052 FOR_EACH_EDGE (e2
, ei
, post_dom_bb
->preds
)
1055 for (gsi
= gsi_start_phis (post_dom_bb
); !gsi_end_p (gsi
);)
1057 gphi
*phi
= gsi
.phi ();
1059 source_location locus
;
1061 /* PHIs for virtuals have no control dependency relation on them.
1062 We are lost here and must force renaming of the symbol. */
1063 if (virtual_operand_p (gimple_phi_result (phi
)))
1065 mark_virtual_phi_result_for_renaming (phi
);
1066 remove_phi_node (&gsi
, true);
1070 /* Dead PHI do not imply control dependency. */
1071 if (!gimple_plf (phi
, STMT_NECESSARY
))
1077 op
= gimple_phi_arg_def (phi
, e2
->dest_idx
);
1078 locus
= gimple_phi_arg_location (phi
, e2
->dest_idx
);
1079 add_phi_arg (phi
, op
, e
, locus
);
1080 /* The resulting PHI if not dead can only be degenerate. */
1081 gcc_assert (degenerate_phi_p (phi
));
1088 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1089 containing I so that we don't have to look it up. */
1092 remove_dead_stmt (gimple_stmt_iterator
*i
, basic_block bb
)
1094 gimple stmt
= gsi_stmt (*i
);
1096 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1098 fprintf (dump_file
, "Deleting : ");
1099 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1100 fprintf (dump_file
, "\n");
1105 /* If we have determined that a conditional branch statement contributes
1106 nothing to the program, then we not only remove it, but we also change
1107 the flow graph so that the current block will simply fall-thru to its
1108 immediate post-dominator. The blocks we are circumventing will be
1109 removed by cleanup_tree_cfg if this change in the flow graph makes them
1111 if (is_ctrl_stmt (stmt
))
1113 basic_block post_dom_bb
;
1117 post_dom_bb
= get_immediate_dominator (CDI_POST_DOMINATORS
, bb
);
1119 e
= find_edge (bb
, post_dom_bb
);
1121 /* If edge is already there, try to use it. This avoids need to update
1122 PHI nodes. Also watch for cases where post dominator does not exists
1123 or is exit block. These can happen for infinite loops as we create
1124 fake edges in the dominator tree. */
1127 else if (! post_dom_bb
|| post_dom_bb
== EXIT_BLOCK_PTR_FOR_FN (cfun
))
1128 e
= EDGE_SUCC (bb
, 0);
1130 e
= forward_edge_to_pdom (EDGE_SUCC (bb
, 0), post_dom_bb
);
1132 e
->probability
= REG_BR_PROB_BASE
;
1133 e
->count
= bb
->count
;
1135 /* The edge is no longer associated with a conditional, so it does
1136 not have TRUE/FALSE flags. */
1137 e
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
);
1139 /* The lone outgoing edge from BB will be a fallthru edge. */
1140 e
->flags
|= EDGE_FALLTHRU
;
1142 /* Remove the remaining outgoing edges. */
1143 for (ei
= ei_start (bb
->succs
); (e2
= ei_safe_edge (ei
)); )
1147 /* If we made a BB unconditionally exit a loop then this
1148 transform alters the set of BBs in the loop. Schedule
1150 if (loop_exit_edge_p (bb
->loop_father
, e
))
1151 loops_state_set (LOOPS_NEED_FIXUP
);
1158 /* If this is a store into a variable that is being optimized away,
1159 add a debug bind stmt if possible. */
1160 if (MAY_HAVE_DEBUG_STMTS
1161 && gimple_assign_single_p (stmt
)
1162 && is_gimple_val (gimple_assign_rhs1 (stmt
)))
1164 tree lhs
= gimple_assign_lhs (stmt
);
1165 if ((TREE_CODE (lhs
) == VAR_DECL
|| TREE_CODE (lhs
) == PARM_DECL
)
1166 && !DECL_IGNORED_P (lhs
)
1167 && is_gimple_reg_type (TREE_TYPE (lhs
))
1168 && !is_global_var (lhs
)
1169 && !DECL_HAS_VALUE_EXPR_P (lhs
))
1171 tree rhs
= gimple_assign_rhs1 (stmt
);
1173 = gimple_build_debug_bind (lhs
, unshare_expr (rhs
), stmt
);
1174 gsi_insert_after (i
, note
, GSI_SAME_STMT
);
1178 unlink_stmt_vdef (stmt
);
1179 gsi_remove (i
, true);
1180 release_defs (stmt
);
1183 /* Helper for maybe_optimize_arith_overflow. Find in *TP if there are any
1184 uses of data (SSA_NAME) other than REALPART_EXPR referencing it. */
1187 find_non_realpart_uses (tree
*tp
, int *walk_subtrees
, void *data
)
1189 if (TYPE_P (*tp
) || TREE_CODE (*tp
) == REALPART_EXPR
)
1191 if (*tp
== (tree
) data
)
1196 /* If the IMAGPART_EXPR of the {ADD,SUB,MUL}_OVERFLOW result is never used,
1197 but REALPART_EXPR is, optimize the {ADD,SUB,MUL}_OVERFLOW internal calls
1198 into plain unsigned {PLUS,MINUS,MULT}_EXPR, and if needed reset debug
1202 maybe_optimize_arith_overflow (gimple_stmt_iterator
*gsi
,
1203 enum tree_code subcode
)
1205 gimple stmt
= gsi_stmt (*gsi
);
1206 tree lhs
= gimple_call_lhs (stmt
);
1208 if (lhs
== NULL
|| TREE_CODE (lhs
) != SSA_NAME
)
1211 imm_use_iterator imm_iter
;
1212 use_operand_p use_p
;
1213 bool has_debug_uses
= false;
1214 bool has_realpart_uses
= false;
1215 bool has_other_uses
= false;
1216 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, lhs
)
1218 gimple use_stmt
= USE_STMT (use_p
);
1219 if (is_gimple_debug (use_stmt
))
1220 has_debug_uses
= true;
1221 else if (is_gimple_assign (use_stmt
)
1222 && gimple_assign_rhs_code (use_stmt
) == REALPART_EXPR
1223 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt
), 0) == lhs
)
1224 has_realpart_uses
= true;
1227 has_other_uses
= true;
1232 if (!has_realpart_uses
|| has_other_uses
)
1235 tree arg0
= gimple_call_arg (stmt
, 0);
1236 tree arg1
= gimple_call_arg (stmt
, 1);
1237 location_t loc
= gimple_location (stmt
);
1238 tree type
= TREE_TYPE (TREE_TYPE (lhs
));
1240 if (!TYPE_UNSIGNED (type
))
1241 utype
= build_nonstandard_integer_type (TYPE_PRECISION (type
), 1);
1242 tree result
= fold_build2_loc (loc
, subcode
, utype
,
1243 fold_convert_loc (loc
, utype
, arg0
),
1244 fold_convert_loc (loc
, utype
, arg1
));
1245 result
= fold_convert_loc (loc
, type
, result
);
1250 FOR_EACH_IMM_USE_STMT (use_stmt
, imm_iter
, lhs
)
1252 if (!gimple_debug_bind_p (use_stmt
))
1254 tree v
= gimple_debug_bind_get_value (use_stmt
);
1255 if (walk_tree (&v
, find_non_realpart_uses
, lhs
, NULL
))
1257 gimple_debug_bind_reset_value (use_stmt
);
1258 update_stmt (use_stmt
);
1263 if (TREE_CODE (result
) == INTEGER_CST
&& TREE_OVERFLOW (result
))
1264 result
= drop_tree_overflow (result
);
1265 tree overflow
= build_zero_cst (type
);
1266 tree ctype
= build_complex_type (type
);
1267 if (TREE_CODE (result
) == INTEGER_CST
)
1268 result
= build_complex (ctype
, result
, overflow
);
1270 result
= build2_loc (gimple_location (stmt
), COMPLEX_EXPR
,
1271 ctype
, result
, overflow
);
1273 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1275 fprintf (dump_file
, "Transforming call: ");
1276 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1277 fprintf (dump_file
, "because the overflow result is never used into: ");
1278 print_generic_stmt (dump_file
, result
, TDF_SLIM
);
1279 fprintf (dump_file
, "\n");
1282 if (!update_call_from_tree (gsi
, result
))
1283 gimplify_and_update_call_from_tree (gsi
, result
);
1286 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1287 contributes nothing to the program, and can be deleted. */
1290 eliminate_unnecessary_stmts (void)
1292 bool something_changed
= false;
1294 gimple_stmt_iterator gsi
, psi
;
1299 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1300 fprintf (dump_file
, "\nEliminating unnecessary statements:\n");
1302 clear_special_calls ();
1304 /* Walking basic blocks and statements in reverse order avoids
1305 releasing SSA names before any other DEFs that refer to them are
1306 released. This helps avoid loss of debug information, as we get
1307 a chance to propagate all RHSs of removed SSAs into debug uses,
1308 rather than only the latest ones. E.g., consider:
1314 If we were to release x_3 before a_5, when we reached a_5 and
1315 tried to substitute it into the debug stmt, we'd see x_3 there,
1316 but x_3's DEF, type, etc would have already been disconnected.
1317 By going backwards, the debug stmt first changes to:
1319 # DEBUG a => x_3 - b_4
1323 # DEBUG a => y_1 + z_2 - b_4
1326 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
1327 h
= get_all_dominated_blocks (CDI_DOMINATORS
,
1328 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun
)));
1334 /* Remove dead statements. */
1335 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi
= psi
)
1337 stmt
= gsi_stmt (gsi
);
1344 /* We can mark a call to free as not necessary if the
1345 defining statement of its argument is not necessary
1346 (and thus is getting removed). */
1347 if (gimple_plf (stmt
, STMT_NECESSARY
)
1348 && gimple_call_builtin_p (stmt
, BUILT_IN_FREE
))
1350 tree ptr
= gimple_call_arg (stmt
, 0);
1351 if (TREE_CODE (ptr
) == SSA_NAME
)
1353 gimple def_stmt
= SSA_NAME_DEF_STMT (ptr
);
1354 if (!gimple_nop_p (def_stmt
)
1355 && !gimple_plf (def_stmt
, STMT_NECESSARY
))
1356 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
1358 /* We did not propagate necessity for free calls fed
1359 by allocation function to allow unnecessary
1360 alloc-free sequence elimination. For instrumented
1361 calls it also means we did not mark bounds producer
1362 as necessary and it is time to do it in case free
1363 call is not removed. */
1364 if (gimple_call_with_bounds_p (stmt
))
1366 gimple bounds_def_stmt
;
1367 tree bounds
= gimple_call_arg (stmt
, 1);
1368 gcc_assert (TREE_CODE (bounds
) == SSA_NAME
);
1369 bounds_def_stmt
= SSA_NAME_DEF_STMT (bounds
);
1371 && !gimple_plf (bounds_def_stmt
, STMT_NECESSARY
))
1372 gimple_set_plf (bounds_def_stmt
, STMT_NECESSARY
,
1373 gimple_plf (stmt
, STMT_NECESSARY
));
1377 /* If GSI is not necessary then remove it. */
1378 if (!gimple_plf (stmt
, STMT_NECESSARY
))
1380 /* Keep clobbers that we can keep live live. */
1381 if (gimple_clobber_p (stmt
))
1384 use_operand_p use_p
;
1386 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_USE
)
1388 tree name
= USE_FROM_PTR (use_p
);
1389 if (!SSA_NAME_IS_DEFAULT_DEF (name
)
1390 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
)))
1399 if (!is_gimple_debug (stmt
))
1400 something_changed
= true;
1401 remove_dead_stmt (&gsi
, bb
);
1403 else if (is_gimple_call (stmt
))
1405 tree name
= gimple_call_lhs (stmt
);
1407 notice_special_calls (as_a
<gcall
*> (stmt
));
1409 /* When LHS of var = call (); is dead, simplify it into
1410 call (); saving one operand. */
1412 && TREE_CODE (name
) == SSA_NAME
1413 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
))
1414 /* Avoid doing so for allocation calls which we
1415 did not mark as necessary, it will confuse the
1416 special logic we apply to malloc/free pair removal. */
1417 && (!(call
= gimple_call_fndecl (stmt
))
1418 || DECL_BUILT_IN_CLASS (call
) != BUILT_IN_NORMAL
1419 || (DECL_FUNCTION_CODE (call
) != BUILT_IN_ALIGNED_ALLOC
1420 && DECL_FUNCTION_CODE (call
) != BUILT_IN_MALLOC
1421 && DECL_FUNCTION_CODE (call
) != BUILT_IN_CALLOC
1422 && DECL_FUNCTION_CODE (call
) != BUILT_IN_ALLOCA
1423 && (DECL_FUNCTION_CODE (call
)
1424 != BUILT_IN_ALLOCA_WITH_ALIGN
)))
1425 /* Avoid doing so for bndret calls for the same reason. */
1426 && !chkp_gimple_call_builtin_p (stmt
, BUILT_IN_CHKP_BNDRET
))
1428 something_changed
= true;
1429 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1431 fprintf (dump_file
, "Deleting LHS of call: ");
1432 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1433 fprintf (dump_file
, "\n");
1436 gimple_call_set_lhs (stmt
, NULL_TREE
);
1437 maybe_clean_or_replace_eh_stmt (stmt
, stmt
);
1439 release_ssa_name (name
);
1441 /* GOMP_SIMD_LANE without lhs is not needed. */
1442 if (gimple_call_internal_p (stmt
)
1443 && gimple_call_internal_fn (stmt
) == IFN_GOMP_SIMD_LANE
)
1444 remove_dead_stmt (&gsi
, bb
);
1446 else if (gimple_call_internal_p (stmt
))
1447 switch (gimple_call_internal_fn (stmt
))
1449 case IFN_ADD_OVERFLOW
:
1450 maybe_optimize_arith_overflow (&gsi
, PLUS_EXPR
);
1452 case IFN_SUB_OVERFLOW
:
1453 maybe_optimize_arith_overflow (&gsi
, MINUS_EXPR
);
1455 case IFN_MUL_OVERFLOW
:
1456 maybe_optimize_arith_overflow (&gsi
, MULT_EXPR
);
1467 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1468 rendered some PHI nodes unreachable while they are still in use.
1469 Mark them for renaming. */
1472 basic_block prev_bb
;
1474 find_unreachable_blocks ();
1476 /* Delete all unreachable basic blocks in reverse dominator order. */
1477 for (bb
= EXIT_BLOCK_PTR_FOR_FN (cfun
)->prev_bb
;
1478 bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
); bb
= prev_bb
)
1480 prev_bb
= bb
->prev_bb
;
1482 if (!bitmap_bit_p (bb_contains_live_stmts
, bb
->index
)
1483 || !(bb
->flags
& BB_REACHABLE
))
1485 for (gphi_iterator gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
1487 if (virtual_operand_p (gimple_phi_result (gsi
.phi ())))
1490 imm_use_iterator iter
;
1492 FOR_EACH_IMM_USE_STMT (stmt
, iter
,
1493 gimple_phi_result (gsi
.phi ()))
1495 if (!(gimple_bb (stmt
)->flags
& BB_REACHABLE
))
1497 if (gimple_code (stmt
) == GIMPLE_PHI
1498 || gimple_plf (stmt
, STMT_NECESSARY
))
1501 BREAK_FROM_IMM_USE_STMT (iter
);
1505 mark_virtual_phi_result_for_renaming (gsi
.phi ());
1508 if (!(bb
->flags
& BB_REACHABLE
))
1510 /* Speed up the removal of blocks that don't
1511 dominate others. Walking backwards, this should
1512 be the common case. ??? Do we need to recompute
1513 dominators because of cfg_altered? */
1514 if (!MAY_HAVE_DEBUG_STMTS
1515 || !first_dom_son (CDI_DOMINATORS
, bb
))
1516 delete_basic_block (bb
);
1519 h
= get_all_dominated_blocks (CDI_DOMINATORS
, bb
);
1524 prev_bb
= bb
->prev_bb
;
1525 /* Rearrangements to the CFG may have failed
1526 to update the dominators tree, so that
1527 formerly-dominated blocks are now
1528 otherwise reachable. */
1529 if (!!(bb
->flags
& BB_REACHABLE
))
1531 delete_basic_block (bb
);
1540 FOR_EACH_BB_FN (bb
, cfun
)
1542 /* Remove dead PHI nodes. */
1543 something_changed
|= remove_dead_phis (bb
);
1546 return something_changed
;
1550 /* Print out removed statement statistics. */
1557 percg
= ((float) stats
.removed
/ (float) stats
.total
) * 100;
1558 fprintf (dump_file
, "Removed %d of %d statements (%d%%)\n",
1559 stats
.removed
, stats
.total
, (int) percg
);
1561 if (stats
.total_phis
== 0)
1564 percg
= ((float) stats
.removed_phis
/ (float) stats
.total_phis
) * 100;
1566 fprintf (dump_file
, "Removed %d of %d PHI nodes (%d%%)\n",
1567 stats
.removed_phis
, stats
.total_phis
, (int) percg
);
1570 /* Initialization for this pass. Set up the used data structures. */
1573 tree_dce_init (bool aggressive
)
1575 memset ((void *) &stats
, 0, sizeof (stats
));
1579 last_stmt_necessary
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1580 bitmap_clear (last_stmt_necessary
);
1581 bb_contains_live_stmts
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1582 bitmap_clear (bb_contains_live_stmts
);
1585 processed
= sbitmap_alloc (num_ssa_names
+ 1);
1586 bitmap_clear (processed
);
1588 worklist
.create (64);
1589 cfg_altered
= false;
1592 /* Cleanup after this pass. */
1595 tree_dce_done (bool aggressive
)
1600 sbitmap_free (visited_control_parents
);
1601 sbitmap_free (last_stmt_necessary
);
1602 sbitmap_free (bb_contains_live_stmts
);
1603 bb_contains_live_stmts
= NULL
;
1606 sbitmap_free (processed
);
1608 worklist
.release ();
1611 /* Main routine to eliminate dead code.
1613 AGGRESSIVE controls the aggressiveness of the algorithm.
1614 In conservative mode, we ignore control dependence and simply declare
1615 all but the most trivially dead branches necessary. This mode is fast.
1616 In aggressive mode, control dependences are taken into account, which
1617 results in more dead code elimination, but at the cost of some time.
1619 FIXME: Aggressive mode before PRE doesn't work currently because
1620 the dominance info is not invalidated after DCE1. This is
1621 not an issue right now because we only run aggressive DCE
1622 as the last tree SSA pass, but keep this in mind when you
1623 start experimenting with pass ordering. */
1626 perform_tree_ssa_dce (bool aggressive
)
1628 bool something_changed
= 0;
1630 calculate_dominance_info (CDI_DOMINATORS
);
1632 /* Preheaders are needed for SCEV to work.
1633 Simple lateches and recorded exits improve chances that loop will
1634 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1636 loop_optimizer_init (LOOPS_NORMAL
1637 | LOOPS_HAVE_RECORDED_EXITS
);
1639 tree_dce_init (aggressive
);
1643 /* Compute control dependence. */
1644 calculate_dominance_info (CDI_POST_DOMINATORS
);
1645 cd
= new control_dependences (create_edge_list ());
1647 visited_control_parents
=
1648 sbitmap_alloc (last_basic_block_for_fn (cfun
));
1649 bitmap_clear (visited_control_parents
);
1651 mark_dfs_back_edges ();
1654 find_obviously_necessary_stmts (aggressive
);
1657 loop_optimizer_finalize ();
1663 visited
= BITMAP_ALLOC (NULL
);
1664 propagate_necessity (aggressive
);
1665 BITMAP_FREE (visited
);
1667 something_changed
|= eliminate_unnecessary_stmts ();
1668 something_changed
|= cfg_altered
;
1670 /* We do not update postdominators, so free them unconditionally. */
1671 free_dominance_info (CDI_POST_DOMINATORS
);
1673 /* If we removed paths in the CFG, then we need to update
1674 dominators as well. I haven't investigated the possibility
1675 of incrementally updating dominators. */
1677 free_dominance_info (CDI_DOMINATORS
);
1679 statistics_counter_event (cfun
, "Statements deleted", stats
.removed
);
1680 statistics_counter_event (cfun
, "PHI nodes deleted", stats
.removed_phis
);
1682 /* Debugging dumps. */
1683 if (dump_file
&& (dump_flags
& (TDF_STATS
|TDF_DETAILS
)))
1686 tree_dce_done (aggressive
);
1688 if (something_changed
)
1690 free_numbers_of_iterations_estimates ();
1691 if (scev_initialized_p ())
1693 return TODO_update_ssa
| TODO_cleanup_cfg
;
1698 /* Pass entry points. */
1702 return perform_tree_ssa_dce (/*aggressive=*/false);
1706 tree_ssa_cd_dce (void)
1708 return perform_tree_ssa_dce (/*aggressive=*/optimize
>= 2);
1713 const pass_data pass_data_dce
=
1715 GIMPLE_PASS
, /* type */
1717 OPTGROUP_NONE
, /* optinfo_flags */
1718 TV_TREE_DCE
, /* tv_id */
1719 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1720 0, /* properties_provided */
1721 0, /* properties_destroyed */
1722 0, /* todo_flags_start */
1723 0, /* todo_flags_finish */
1726 class pass_dce
: public gimple_opt_pass
1729 pass_dce (gcc::context
*ctxt
)
1730 : gimple_opt_pass (pass_data_dce
, ctxt
)
1733 /* opt_pass methods: */
1734 opt_pass
* clone () { return new pass_dce (m_ctxt
); }
1735 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1736 virtual unsigned int execute (function
*) { return tree_ssa_dce (); }
1738 }; // class pass_dce
1743 make_pass_dce (gcc::context
*ctxt
)
1745 return new pass_dce (ctxt
);
1750 const pass_data pass_data_cd_dce
=
1752 GIMPLE_PASS
, /* type */
1754 OPTGROUP_NONE
, /* optinfo_flags */
1755 TV_TREE_CD_DCE
, /* tv_id */
1756 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1757 0, /* properties_provided */
1758 0, /* properties_destroyed */
1759 0, /* todo_flags_start */
1760 0, /* todo_flags_finish */
1763 class pass_cd_dce
: public gimple_opt_pass
1766 pass_cd_dce (gcc::context
*ctxt
)
1767 : gimple_opt_pass (pass_data_cd_dce
, ctxt
)
1770 /* opt_pass methods: */
1771 opt_pass
* clone () { return new pass_cd_dce (m_ctxt
); }
1772 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1773 virtual unsigned int execute (function
*) { return tree_ssa_cd_dce (); }
1775 }; // class pass_cd_dce
1780 make_pass_cd_dce (gcc::context
*ctxt
)
1782 return new pass_cd_dce (ctxt
);