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"
52 #include "double-int.h"
59 #include "fold-const.h"
61 #include "gimple-pretty-print.h"
63 #include "hard-reg-set.h"
66 #include "dominance.h"
69 #include "basic-block.h"
70 #include "tree-ssa-alias.h"
71 #include "internal-fn.h"
73 #include "gimple-expr.h"
77 #include "gimple-iterator.h"
78 #include "gimple-ssa.h"
80 #include "tree-phinodes.h"
81 #include "ssa-iterators.h"
82 #include "stringpool.h"
83 #include "tree-ssanames.h"
84 #include "tree-ssa-loop-niter.h"
85 #include "tree-into-ssa.h"
88 #include "tree-pass.h"
91 #include "tree-scalar-evolution.h"
92 #include "tree-chkp.h"
93 #include "tree-ssa-propagate.h"
94 #include "gimple-fold.h"
96 static struct stmt_stats
104 #define STMT_NECESSARY GF_PLF_1
106 static vec
<gimple
> worklist
;
108 /* Vector indicating an SSA name has already been processed and marked
110 static sbitmap processed
;
112 /* Vector indicating that the last statement of a basic block has already
113 been marked as necessary. */
114 static sbitmap last_stmt_necessary
;
116 /* Vector indicating that BB contains statements that are live. */
117 static sbitmap bb_contains_live_stmts
;
119 /* Before we can determine whether a control branch is dead, we need to
120 compute which blocks are control dependent on which edges.
122 We expect each block to be control dependent on very few edges so we
123 use a bitmap for each block recording its edges. An array holds the
124 bitmap. The Ith bit in the bitmap is set if that block is dependent
126 static control_dependences
*cd
;
128 /* Vector indicating that a basic block has already had all the edges
129 processed that it is control dependent on. */
130 static sbitmap visited_control_parents
;
132 /* TRUE if this pass alters the CFG (by removing control statements).
135 If this pass alters the CFG, then it will arrange for the dominators
137 static bool cfg_altered
;
140 /* If STMT is not already marked necessary, mark it, and add it to the
141 worklist if ADD_TO_WORKLIST is true. */
144 mark_stmt_necessary (gimple stmt
, bool add_to_worklist
)
148 if (gimple_plf (stmt
, STMT_NECESSARY
))
151 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
153 fprintf (dump_file
, "Marking useful stmt: ");
154 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
155 fprintf (dump_file
, "\n");
158 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
160 worklist
.safe_push (stmt
);
161 if (bb_contains_live_stmts
&& !is_gimple_debug (stmt
))
162 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
166 /* Mark the statement defining operand OP as necessary. */
169 mark_operand_necessary (tree op
)
176 ver
= SSA_NAME_VERSION (op
);
177 if (bitmap_bit_p (processed
, ver
))
179 stmt
= SSA_NAME_DEF_STMT (op
);
180 gcc_assert (gimple_nop_p (stmt
)
181 || gimple_plf (stmt
, STMT_NECESSARY
));
184 bitmap_set_bit (processed
, ver
);
186 stmt
= SSA_NAME_DEF_STMT (op
);
189 if (gimple_plf (stmt
, STMT_NECESSARY
) || gimple_nop_p (stmt
))
192 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
194 fprintf (dump_file
, "marking necessary through ");
195 print_generic_expr (dump_file
, op
, 0);
196 fprintf (dump_file
, " stmt ");
197 print_gimple_stmt (dump_file
, stmt
, 0, 0);
200 gimple_set_plf (stmt
, STMT_NECESSARY
, true);
201 if (bb_contains_live_stmts
)
202 bitmap_set_bit (bb_contains_live_stmts
, gimple_bb (stmt
)->index
);
203 worklist
.safe_push (stmt
);
207 /* Mark STMT as necessary if it obviously is. Add it to the worklist if
208 it can make other statements necessary.
210 If AGGRESSIVE is false, control statements are conservatively marked as
214 mark_stmt_if_obviously_necessary (gimple stmt
, bool aggressive
)
216 /* With non-call exceptions, we have to assume that all statements could
217 throw. If a statement could throw, it can be deemed necessary. */
218 if (cfun
->can_throw_non_call_exceptions
219 && !cfun
->can_delete_dead_exceptions
220 && stmt_could_throw_p (stmt
))
222 mark_stmt_necessary (stmt
, true);
226 /* Statements that are implicitly live. Most function calls, asm
227 and return statements are required. Labels and GIMPLE_BIND nodes
228 are kept because they are control flow, and we have no way of
229 knowing whether they can be removed. DCE can eliminate all the
230 other statements in a block, and CFG can then remove the block
232 switch (gimple_code (stmt
))
236 mark_stmt_necessary (stmt
, false);
242 mark_stmt_necessary (stmt
, true);
247 tree callee
= gimple_call_fndecl (stmt
);
248 if (callee
!= NULL_TREE
249 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
)
250 switch (DECL_FUNCTION_CODE (callee
))
252 case BUILT_IN_MALLOC
:
253 case BUILT_IN_ALIGNED_ALLOC
:
254 case BUILT_IN_CALLOC
:
255 case BUILT_IN_ALLOCA
:
256 case BUILT_IN_ALLOCA_WITH_ALIGN
:
261 /* Most, but not all function calls are required. Function calls that
262 produce no result and have no side effects (i.e. const pure
263 functions) are unnecessary. */
264 if (gimple_has_side_effects (stmt
))
266 mark_stmt_necessary (stmt
, true);
269 if (!gimple_call_lhs (stmt
))
275 /* Debug temps without a value are not useful. ??? If we could
276 easily locate the debug temp bind stmt for a use thereof,
277 would could refrain from marking all debug temps here, and
278 mark them only if they're used. */
279 if (!gimple_debug_bind_p (stmt
)
280 || gimple_debug_bind_has_value_p (stmt
)
281 || TREE_CODE (gimple_debug_bind_get_var (stmt
)) != DEBUG_EXPR_DECL
)
282 mark_stmt_necessary (stmt
, false);
286 gcc_assert (!simple_goto_p (stmt
));
287 mark_stmt_necessary (stmt
, true);
291 gcc_assert (EDGE_COUNT (gimple_bb (stmt
)->succs
) == 2);
296 mark_stmt_necessary (stmt
, true);
300 if (gimple_clobber_p (stmt
))
308 /* If the statement has volatile operands, it needs to be preserved.
309 Same for statements that can alter control flow in unpredictable
311 if (gimple_has_volatile_ops (stmt
) || is_ctrl_altering_stmt (stmt
))
313 mark_stmt_necessary (stmt
, true);
317 if (stmt_may_clobber_global_p (stmt
))
319 mark_stmt_necessary (stmt
, true);
327 /* Mark the last statement of BB as necessary. */
330 mark_last_stmt_necessary (basic_block bb
)
332 gimple stmt
= last_stmt (bb
);
334 bitmap_set_bit (last_stmt_necessary
, bb
->index
);
335 bitmap_set_bit (bb_contains_live_stmts
, bb
->index
);
337 /* We actually mark the statement only if it is a control statement. */
338 if (stmt
&& is_ctrl_stmt (stmt
))
339 mark_stmt_necessary (stmt
, true);
343 /* Mark control dependent edges of BB as necessary. We have to do this only
344 once for each basic block so we set the appropriate bit after we're done.
346 When IGNORE_SELF is true, ignore BB in the list of control dependences. */
349 mark_control_dependent_edges_necessary (basic_block bb
, bool ignore_self
)
352 unsigned edge_number
;
353 bool skipped
= false;
355 gcc_assert (bb
!= EXIT_BLOCK_PTR_FOR_FN (cfun
));
357 if (bb
== ENTRY_BLOCK_PTR_FOR_FN (cfun
))
360 EXECUTE_IF_SET_IN_BITMAP (cd
->get_edges_dependent_on (bb
->index
),
363 basic_block cd_bb
= cd
->get_edge (edge_number
)->src
;
365 if (ignore_self
&& cd_bb
== bb
)
371 if (!bitmap_bit_p (last_stmt_necessary
, cd_bb
->index
))
372 mark_last_stmt_necessary (cd_bb
);
376 bitmap_set_bit (visited_control_parents
, bb
->index
);
380 /* Find obviously necessary statements. These are things like most function
381 calls, and stores to file level variables.
383 If EL is NULL, control statements are conservatively marked as
384 necessary. Otherwise it contains the list of edges used by control
385 dependence analysis. */
388 find_obviously_necessary_stmts (bool aggressive
)
391 gimple_stmt_iterator gsi
;
396 FOR_EACH_BB_FN (bb
, cfun
)
398 /* PHI nodes are never inherently necessary. */
399 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
401 phi
= gsi_stmt (gsi
);
402 gimple_set_plf (phi
, STMT_NECESSARY
, false);
405 /* Check all statements in the block. */
406 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); gsi_next (&gsi
))
408 stmt
= gsi_stmt (gsi
);
409 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
410 mark_stmt_if_obviously_necessary (stmt
, aggressive
);
414 /* Pure and const functions are finite and thus have no infinite loops in
416 flags
= flags_from_decl_or_type (current_function_decl
);
417 if ((flags
& (ECF_CONST
|ECF_PURE
)) && !(flags
& ECF_LOOPING_CONST_OR_PURE
))
420 /* Prevent the empty possibly infinite loops from being removed. */
425 if (mark_irreducible_loops ())
426 FOR_EACH_BB_FN (bb
, cfun
)
429 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
430 if ((e
->flags
& EDGE_DFS_BACK
)
431 && (e
->flags
& EDGE_IRREDUCIBLE_LOOP
))
434 fprintf (dump_file
, "Marking back edge of irreducible loop %i->%i\n",
435 e
->src
->index
, e
->dest
->index
);
436 mark_control_dependent_edges_necessary (e
->dest
, false);
440 FOR_EACH_LOOP (loop
, 0)
441 if (!finite_loop_p (loop
))
444 fprintf (dump_file
, "can not prove finiteness of loop %i\n", loop
->num
);
445 mark_control_dependent_edges_necessary (loop
->latch
, false);
452 /* Return true if REF is based on an aliased base, otherwise false. */
455 ref_may_be_aliased (tree ref
)
457 gcc_assert (TREE_CODE (ref
) != WITH_SIZE_EXPR
);
458 while (handled_component_p (ref
))
459 ref
= TREE_OPERAND (ref
, 0);
460 if (TREE_CODE (ref
) == MEM_REF
461 && TREE_CODE (TREE_OPERAND (ref
, 0)) == ADDR_EXPR
)
462 ref
= TREE_OPERAND (TREE_OPERAND (ref
, 0), 0);
463 return !(DECL_P (ref
)
464 && !may_be_aliased (ref
));
467 static bitmap visited
= NULL
;
468 static unsigned int longest_chain
= 0;
469 static unsigned int total_chain
= 0;
470 static unsigned int nr_walks
= 0;
471 static bool chain_ovfl
= false;
473 /* Worker for the walker that marks reaching definitions of REF,
474 which is based on a non-aliased decl, necessary. It returns
475 true whenever the defining statement of the current VDEF is
476 a kill for REF, as no dominating may-defs are necessary for REF
477 anymore. DATA points to the basic-block that contains the
478 stmt that refers to REF. */
481 mark_aliased_reaching_defs_necessary_1 (ao_ref
*ref
, tree vdef
, void *data
)
483 gimple def_stmt
= SSA_NAME_DEF_STMT (vdef
);
485 /* All stmts we visit are necessary. */
486 mark_operand_necessary (vdef
);
488 /* If the stmt lhs kills ref, then we can stop walking. */
489 if (gimple_has_lhs (def_stmt
)
490 && TREE_CODE (gimple_get_lhs (def_stmt
)) != SSA_NAME
491 /* The assignment is not necessarily carried out if it can throw
492 and we can catch it in the current function where we could inspect
494 ??? We only need to care about the RHS throwing. For aggregate
495 assignments or similar calls and non-call exceptions the LHS
496 might throw as well. */
497 && !stmt_can_throw_internal (def_stmt
))
499 tree base
, lhs
= gimple_get_lhs (def_stmt
);
500 HOST_WIDE_INT size
, offset
, max_size
;
502 base
= get_ref_base_and_extent (lhs
, &offset
, &size
, &max_size
);
503 /* We can get MEM[symbol: sZ, index: D.8862_1] here,
504 so base == refd->base does not always hold. */
505 if (base
== ref
->base
)
507 /* For a must-alias check we need to be able to constrain
508 the accesses properly. */
509 if (size
!= -1 && size
== max_size
510 && ref
->max_size
!= -1)
512 if (offset
<= ref
->offset
513 && offset
+ size
>= ref
->offset
+ ref
->max_size
)
516 /* Or they need to be exactly the same. */
518 /* Make sure there is no induction variable involved
519 in the references (gcc.c-torture/execute/pr42142.c).
520 The simplest way is to check if the kill dominates
522 /* But when both are in the same block we cannot
523 easily tell whether we came from a backedge
524 unless we decide to compute stmt UIDs
526 && (basic_block
) data
!= gimple_bb (def_stmt
)
527 && dominated_by_p (CDI_DOMINATORS
, (basic_block
) data
,
528 gimple_bb (def_stmt
))
529 && operand_equal_p (ref
->ref
, lhs
, 0))
534 /* Otherwise keep walking. */
539 mark_aliased_reaching_defs_necessary (gimple stmt
, tree ref
)
543 gcc_assert (!chain_ovfl
);
544 ao_ref_init (&refd
, ref
);
545 chain
= walk_aliased_vdefs (&refd
, gimple_vuse (stmt
),
546 mark_aliased_reaching_defs_necessary_1
,
547 gimple_bb (stmt
), NULL
);
548 if (chain
> longest_chain
)
549 longest_chain
= chain
;
550 total_chain
+= chain
;
554 /* Worker for the walker that marks reaching definitions of REF, which
555 is not based on a non-aliased decl. For simplicity we need to end
556 up marking all may-defs necessary that are not based on a non-aliased
557 decl. The only job of this walker is to skip may-defs based on
558 a non-aliased decl. */
561 mark_all_reaching_defs_necessary_1 (ao_ref
*ref ATTRIBUTE_UNUSED
,
562 tree vdef
, void *data ATTRIBUTE_UNUSED
)
564 gimple def_stmt
= SSA_NAME_DEF_STMT (vdef
);
566 /* We have to skip already visited (and thus necessary) statements
567 to make the chaining work after we dropped back to simple mode. */
569 && bitmap_bit_p (processed
, SSA_NAME_VERSION (vdef
)))
571 gcc_assert (gimple_nop_p (def_stmt
)
572 || gimple_plf (def_stmt
, STMT_NECESSARY
));
576 /* We want to skip stores to non-aliased variables. */
578 && gimple_assign_single_p (def_stmt
))
580 tree lhs
= gimple_assign_lhs (def_stmt
);
581 if (!ref_may_be_aliased (lhs
))
585 /* We want to skip statments that do not constitute stores but have
586 a virtual definition. */
587 if (is_gimple_call (def_stmt
))
589 tree callee
= gimple_call_fndecl (def_stmt
);
590 if (callee
!= NULL_TREE
591 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
)
592 switch (DECL_FUNCTION_CODE (callee
))
594 case BUILT_IN_MALLOC
:
595 case BUILT_IN_ALIGNED_ALLOC
:
596 case BUILT_IN_CALLOC
:
597 case BUILT_IN_ALLOCA
:
598 case BUILT_IN_ALLOCA_WITH_ALIGN
:
606 mark_operand_necessary (vdef
);
612 mark_all_reaching_defs_necessary (gimple stmt
)
614 walk_aliased_vdefs (NULL
, gimple_vuse (stmt
),
615 mark_all_reaching_defs_necessary_1
, NULL
, &visited
);
618 /* Return true for PHI nodes with one or identical arguments
621 degenerate_phi_p (gimple phi
)
624 tree op
= gimple_phi_arg_def (phi
, 0);
625 for (i
= 1; i
< gimple_phi_num_args (phi
); i
++)
626 if (gimple_phi_arg_def (phi
, i
) != op
)
631 /* Propagate necessity using the operands of necessary statements.
632 Process the uses on each statement in the worklist, and add all
633 feeding statements which contribute to the calculation of this
634 value to the worklist.
636 In conservative mode, EL is NULL. */
639 propagate_necessity (bool aggressive
)
643 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
644 fprintf (dump_file
, "\nProcessing worklist:\n");
646 while (worklist
.length () > 0)
648 /* Take STMT from worklist. */
649 stmt
= worklist
.pop ();
651 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
653 fprintf (dump_file
, "processing: ");
654 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
655 fprintf (dump_file
, "\n");
660 /* Mark the last statement of the basic blocks on which the block
661 containing STMT is control dependent, but only if we haven't
663 basic_block bb
= gimple_bb (stmt
);
664 if (bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
665 && !bitmap_bit_p (visited_control_parents
, bb
->index
))
666 mark_control_dependent_edges_necessary (bb
, false);
669 if (gimple_code (stmt
) == GIMPLE_PHI
670 /* We do not process virtual PHI nodes nor do we track their
672 && !virtual_operand_p (gimple_phi_result (stmt
)))
674 /* PHI nodes are somewhat special in that each PHI alternative has
675 data and control dependencies. All the statements feeding the
676 PHI node's arguments are always necessary. In aggressive mode,
677 we also consider the control dependent edges leading to the
678 predecessor block associated with each PHI alternative as
680 gphi
*phi
= as_a
<gphi
*> (stmt
);
683 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
685 tree arg
= PHI_ARG_DEF (stmt
, k
);
686 if (TREE_CODE (arg
) == SSA_NAME
)
687 mark_operand_necessary (arg
);
690 /* For PHI operands it matters from where the control flow arrives
691 to the BB. Consider the following example:
701 We need to mark control dependence of the empty basic blocks, since they
702 contains computation of PHI operands.
704 Doing so is too restrictive in the case the predecestor block is in
710 for (i = 0; i<1000; ++i)
716 There is PHI for J in the BB containing return statement.
717 In this case the control dependence of predecestor block (that is
718 within the empty loop) also contains the block determining number
719 of iterations of the block that would prevent removing of empty
722 This scenario can be avoided by splitting critical edges.
723 To save the critical edge splitting pass we identify how the control
724 dependence would look like if the edge was split.
726 Consider the modified CFG created from current CFG by splitting
727 edge B->C. In the postdominance tree of modified CFG, C' is
728 always child of C. There are two cases how chlids of C' can look
733 In this case the only basic block C' is control dependent on is B.
735 2) C' has single child that is B
737 In this case control dependence of C' is same as control
738 dependence of B in original CFG except for block B itself.
739 (since C' postdominate B in modified CFG)
741 Now how to decide what case happens? There are two basic options:
743 a) C postdominate B. Then C immediately postdominate B and
744 case 2 happens iff there is no other way from B to C except
747 There is other way from B to C iff there is succesor of B that
748 is not postdominated by B. Testing this condition is somewhat
749 expensive, because we need to iterate all succesors of B.
750 We are safe to assume that this does not happen: we will mark B
751 as needed when processing the other path from B to C that is
752 conrol dependent on B and marking control dependencies of B
753 itself is harmless because they will be processed anyway after
754 processing control statement in B.
756 b) C does not postdominate B. Always case 1 happens since there is
757 path from C to exit that does not go through B and thus also C'. */
759 if (aggressive
&& !degenerate_phi_p (stmt
))
761 for (k
= 0; k
< gimple_phi_num_args (stmt
); k
++)
763 basic_block arg_bb
= gimple_phi_arg_edge (phi
, k
)->src
;
766 != get_immediate_dominator (CDI_POST_DOMINATORS
, arg_bb
))
768 if (!bitmap_bit_p (last_stmt_necessary
, arg_bb
->index
))
769 mark_last_stmt_necessary (arg_bb
);
771 else if (arg_bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
)
772 && !bitmap_bit_p (visited_control_parents
,
774 mark_control_dependent_edges_necessary (arg_bb
, true);
780 /* Propagate through the operands. Examine all the USE, VUSE and
781 VDEF operands in this statement. Mark all the statements
782 which feed this statement's uses as necessary. */
786 /* If this is a call to free which is directly fed by an
787 allocation function do not mark that necessary through
788 processing the argument. */
789 if (gimple_call_builtin_p (stmt
, BUILT_IN_FREE
))
791 tree ptr
= gimple_call_arg (stmt
, 0);
794 /* If the pointer we free is defined by an allocation
795 function do not add the call to the worklist. */
796 if (TREE_CODE (ptr
) == SSA_NAME
797 && is_gimple_call (def_stmt
= SSA_NAME_DEF_STMT (ptr
))
798 && (def_callee
= gimple_call_fndecl (def_stmt
))
799 && DECL_BUILT_IN_CLASS (def_callee
) == BUILT_IN_NORMAL
800 && (DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_ALIGNED_ALLOC
801 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_MALLOC
802 || DECL_FUNCTION_CODE (def_callee
) == BUILT_IN_CALLOC
))
804 gimple bounds_def_stmt
;
807 /* For instrumented calls we should also check used
808 bounds are returned by the same allocation call. */
809 if (!gimple_call_with_bounds_p (stmt
)
810 || ((bounds
= gimple_call_arg (stmt
, 1))
811 && TREE_CODE (bounds
) == SSA_NAME
812 && (bounds_def_stmt
= SSA_NAME_DEF_STMT (bounds
))
813 && chkp_gimple_call_builtin_p (bounds_def_stmt
,
814 BUILT_IN_CHKP_BNDRET
)
815 && gimple_call_arg (bounds_def_stmt
, 0) == ptr
))
820 FOR_EACH_SSA_TREE_OPERAND (use
, stmt
, iter
, SSA_OP_USE
)
821 mark_operand_necessary (use
);
823 use
= gimple_vuse (stmt
);
827 /* If we dropped to simple mode make all immediately
828 reachable definitions necessary. */
831 mark_all_reaching_defs_necessary (stmt
);
835 /* For statements that may load from memory (have a VUSE) we
836 have to mark all reaching (may-)definitions as necessary.
837 We partition this task into two cases:
838 1) explicit loads based on decls that are not aliased
839 2) implicit loads (like calls) and explicit loads not
840 based on decls that are not aliased (like indirect
841 references or loads from globals)
842 For 1) we mark all reaching may-defs as necessary, stopping
843 at dominating kills. For 2) we want to mark all dominating
844 references necessary, but non-aliased ones which we handle
845 in 1). By keeping a global visited bitmap for references
846 we walk for 2) we avoid quadratic behavior for those. */
848 if (is_gimple_call (stmt
))
850 tree callee
= gimple_call_fndecl (stmt
);
853 /* Calls to functions that are merely acting as barriers
854 or that only store to memory do not make any previous
856 if (callee
!= NULL_TREE
857 && DECL_BUILT_IN_CLASS (callee
) == BUILT_IN_NORMAL
858 && (DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET
859 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MEMSET_CHK
860 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_MALLOC
861 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALIGNED_ALLOC
862 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_CALLOC
863 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_FREE
864 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_VA_END
865 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ALLOCA
866 || (DECL_FUNCTION_CODE (callee
)
867 == BUILT_IN_ALLOCA_WITH_ALIGN
)
868 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_SAVE
869 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_STACK_RESTORE
870 || DECL_FUNCTION_CODE (callee
) == BUILT_IN_ASSUME_ALIGNED
))
873 /* Calls implicitly load from memory, their arguments
874 in addition may explicitly perform memory loads. */
875 mark_all_reaching_defs_necessary (stmt
);
876 for (i
= 0; i
< gimple_call_num_args (stmt
); ++i
)
878 tree arg
= gimple_call_arg (stmt
, i
);
879 if (TREE_CODE (arg
) == SSA_NAME
880 || is_gimple_min_invariant (arg
))
882 if (TREE_CODE (arg
) == WITH_SIZE_EXPR
)
883 arg
= TREE_OPERAND (arg
, 0);
884 if (!ref_may_be_aliased (arg
))
885 mark_aliased_reaching_defs_necessary (stmt
, arg
);
888 else if (gimple_assign_single_p (stmt
))
891 /* If this is a load mark things necessary. */
892 rhs
= gimple_assign_rhs1 (stmt
);
893 if (TREE_CODE (rhs
) != SSA_NAME
894 && !is_gimple_min_invariant (rhs
)
895 && TREE_CODE (rhs
) != CONSTRUCTOR
)
897 if (!ref_may_be_aliased (rhs
))
898 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
900 mark_all_reaching_defs_necessary (stmt
);
903 else if (greturn
*return_stmt
= dyn_cast
<greturn
*> (stmt
))
905 tree rhs
= gimple_return_retval (return_stmt
);
906 /* A return statement may perform a load. */
908 && TREE_CODE (rhs
) != SSA_NAME
909 && !is_gimple_min_invariant (rhs
)
910 && TREE_CODE (rhs
) != CONSTRUCTOR
)
912 if (!ref_may_be_aliased (rhs
))
913 mark_aliased_reaching_defs_necessary (stmt
, rhs
);
915 mark_all_reaching_defs_necessary (stmt
);
918 else if (gasm
*asm_stmt
= dyn_cast
<gasm
*> (stmt
))
921 mark_all_reaching_defs_necessary (stmt
);
922 /* Inputs may perform loads. */
923 for (i
= 0; i
< gimple_asm_ninputs (asm_stmt
); ++i
)
925 tree op
= TREE_VALUE (gimple_asm_input_op (asm_stmt
, i
));
926 if (TREE_CODE (op
) != SSA_NAME
927 && !is_gimple_min_invariant (op
)
928 && TREE_CODE (op
) != CONSTRUCTOR
929 && !ref_may_be_aliased (op
))
930 mark_aliased_reaching_defs_necessary (stmt
, op
);
933 else if (gimple_code (stmt
) == GIMPLE_TRANSACTION
)
935 /* The beginning of a transaction is a memory barrier. */
936 /* ??? If we were really cool, we'd only be a barrier
937 for the memories touched within the transaction. */
938 mark_all_reaching_defs_necessary (stmt
);
943 /* If we over-used our alias oracle budget drop to simple
944 mode. The cost metric allows quadratic behavior
945 (number of uses times number of may-defs queries) up to
946 a constant maximal number of queries and after that falls back to
947 super-linear complexity. */
948 if (/* Constant but quadratic for small functions. */
949 total_chain
> 128 * 128
950 /* Linear in the number of may-defs. */
951 && total_chain
> 32 * longest_chain
952 /* Linear in the number of uses. */
953 && total_chain
> nr_walks
* 32)
957 bitmap_clear (visited
);
963 /* Remove dead PHI nodes from block BB. */
966 remove_dead_phis (basic_block bb
)
968 bool something_changed
= false;
972 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);)
977 /* We do not track necessity of virtual PHI nodes. Instead do
978 very simple dead PHI removal here. */
979 if (virtual_operand_p (gimple_phi_result (phi
)))
981 /* Virtual PHI nodes with one or identical arguments
983 if (degenerate_phi_p (phi
))
985 tree vdef
= gimple_phi_result (phi
);
986 tree vuse
= gimple_phi_arg_def (phi
, 0);
989 imm_use_iterator iter
;
991 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, vdef
)
992 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
993 SET_USE (use_p
, vuse
);
994 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef
)
995 && TREE_CODE (vuse
) == SSA_NAME
)
996 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse
) = 1;
999 gimple_set_plf (phi
, STMT_NECESSARY
, true);
1002 if (!gimple_plf (phi
, STMT_NECESSARY
))
1004 something_changed
= true;
1005 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1007 fprintf (dump_file
, "Deleting : ");
1008 print_gimple_stmt (dump_file
, phi
, 0, TDF_SLIM
);
1009 fprintf (dump_file
, "\n");
1012 remove_phi_node (&gsi
, true);
1013 stats
.removed_phis
++;
1019 return something_changed
;
1022 /* Forward edge E to respective POST_DOM_BB and update PHIs. */
1025 forward_edge_to_pdom (edge e
, basic_block post_dom_bb
)
1031 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1032 fprintf (dump_file
, "Redirecting edge %i->%i to %i\n", e
->src
->index
,
1033 e
->dest
->index
, post_dom_bb
->index
);
1035 e2
= redirect_edge_and_branch (e
, post_dom_bb
);
1038 /* If edge was already around, no updating is necessary. */
1042 if (!gimple_seq_empty_p (phi_nodes (post_dom_bb
)))
1044 /* We are sure that for every live PHI we are seeing control dependent BB.
1045 This means that we can pick any edge to duplicate PHI args from. */
1046 FOR_EACH_EDGE (e2
, ei
, post_dom_bb
->preds
)
1049 for (gsi
= gsi_start_phis (post_dom_bb
); !gsi_end_p (gsi
);)
1051 gphi
*phi
= gsi
.phi ();
1053 source_location locus
;
1055 /* PHIs for virtuals have no control dependency relation on them.
1056 We are lost here and must force renaming of the symbol. */
1057 if (virtual_operand_p (gimple_phi_result (phi
)))
1059 mark_virtual_phi_result_for_renaming (phi
);
1060 remove_phi_node (&gsi
, true);
1064 /* Dead PHI do not imply control dependency. */
1065 if (!gimple_plf (phi
, STMT_NECESSARY
))
1071 op
= gimple_phi_arg_def (phi
, e2
->dest_idx
);
1072 locus
= gimple_phi_arg_location (phi
, e2
->dest_idx
);
1073 add_phi_arg (phi
, op
, e
, locus
);
1074 /* The resulting PHI if not dead can only be degenerate. */
1075 gcc_assert (degenerate_phi_p (phi
));
1082 /* Remove dead statement pointed to by iterator I. Receives the basic block BB
1083 containing I so that we don't have to look it up. */
1086 remove_dead_stmt (gimple_stmt_iterator
*i
, basic_block bb
)
1088 gimple stmt
= gsi_stmt (*i
);
1090 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1092 fprintf (dump_file
, "Deleting : ");
1093 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1094 fprintf (dump_file
, "\n");
1099 /* If we have determined that a conditional branch statement contributes
1100 nothing to the program, then we not only remove it, but we also change
1101 the flow graph so that the current block will simply fall-thru to its
1102 immediate post-dominator. The blocks we are circumventing will be
1103 removed by cleanup_tree_cfg if this change in the flow graph makes them
1105 if (is_ctrl_stmt (stmt
))
1107 basic_block post_dom_bb
;
1111 post_dom_bb
= get_immediate_dominator (CDI_POST_DOMINATORS
, bb
);
1113 e
= find_edge (bb
, post_dom_bb
);
1115 /* If edge is already there, try to use it. This avoids need to update
1116 PHI nodes. Also watch for cases where post dominator does not exists
1117 or is exit block. These can happen for infinite loops as we create
1118 fake edges in the dominator tree. */
1121 else if (! post_dom_bb
|| post_dom_bb
== EXIT_BLOCK_PTR_FOR_FN (cfun
))
1122 e
= EDGE_SUCC (bb
, 0);
1124 e
= forward_edge_to_pdom (EDGE_SUCC (bb
, 0), post_dom_bb
);
1126 e
->probability
= REG_BR_PROB_BASE
;
1127 e
->count
= bb
->count
;
1129 /* The edge is no longer associated with a conditional, so it does
1130 not have TRUE/FALSE flags. */
1131 e
->flags
&= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
);
1133 /* The lone outgoing edge from BB will be a fallthru edge. */
1134 e
->flags
|= EDGE_FALLTHRU
;
1136 /* Remove the remaining outgoing edges. */
1137 for (ei
= ei_start (bb
->succs
); (e2
= ei_safe_edge (ei
)); )
1147 /* If this is a store into a variable that is being optimized away,
1148 add a debug bind stmt if possible. */
1149 if (MAY_HAVE_DEBUG_STMTS
1150 && gimple_assign_single_p (stmt
)
1151 && is_gimple_val (gimple_assign_rhs1 (stmt
)))
1153 tree lhs
= gimple_assign_lhs (stmt
);
1154 if ((TREE_CODE (lhs
) == VAR_DECL
|| TREE_CODE (lhs
) == PARM_DECL
)
1155 && !DECL_IGNORED_P (lhs
)
1156 && is_gimple_reg_type (TREE_TYPE (lhs
))
1157 && !is_global_var (lhs
)
1158 && !DECL_HAS_VALUE_EXPR_P (lhs
))
1160 tree rhs
= gimple_assign_rhs1 (stmt
);
1162 = gimple_build_debug_bind (lhs
, unshare_expr (rhs
), stmt
);
1163 gsi_insert_after (i
, note
, GSI_SAME_STMT
);
1167 unlink_stmt_vdef (stmt
);
1168 gsi_remove (i
, true);
1169 release_defs (stmt
);
1172 /* Helper for maybe_optimize_arith_overflow. Find in *TP if there are any
1173 uses of data (SSA_NAME) other than REALPART_EXPR referencing it. */
1176 find_non_realpart_uses (tree
*tp
, int *walk_subtrees
, void *data
)
1178 if (TYPE_P (*tp
) || TREE_CODE (*tp
) == REALPART_EXPR
)
1180 if (*tp
== (tree
) data
)
1185 /* If the IMAGPART_EXPR of the {ADD,SUB,MUL}_OVERFLOW result is never used,
1186 but REALPART_EXPR is, optimize the {ADD,SUB,MUL}_OVERFLOW internal calls
1187 into plain unsigned {PLUS,MINUS,MULT}_EXPR, and if needed reset debug
1191 maybe_optimize_arith_overflow (gimple_stmt_iterator
*gsi
,
1192 enum tree_code subcode
)
1194 gimple stmt
= gsi_stmt (*gsi
);
1195 tree lhs
= gimple_call_lhs (stmt
);
1197 if (lhs
== NULL
|| TREE_CODE (lhs
) != SSA_NAME
)
1200 imm_use_iterator imm_iter
;
1201 use_operand_p use_p
;
1202 bool has_debug_uses
= false;
1203 bool has_realpart_uses
= false;
1204 bool has_other_uses
= false;
1205 FOR_EACH_IMM_USE_FAST (use_p
, imm_iter
, lhs
)
1207 gimple use_stmt
= USE_STMT (use_p
);
1208 if (is_gimple_debug (use_stmt
))
1209 has_debug_uses
= true;
1210 else if (is_gimple_assign (use_stmt
)
1211 && gimple_assign_rhs_code (use_stmt
) == REALPART_EXPR
1212 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt
), 0) == lhs
)
1213 has_realpart_uses
= true;
1216 has_other_uses
= true;
1221 if (!has_realpart_uses
|| has_other_uses
)
1224 tree arg0
= gimple_call_arg (stmt
, 0);
1225 tree arg1
= gimple_call_arg (stmt
, 1);
1226 location_t loc
= gimple_location (stmt
);
1227 tree type
= TREE_TYPE (TREE_TYPE (lhs
));
1229 if (!TYPE_UNSIGNED (type
))
1230 utype
= build_nonstandard_integer_type (TYPE_PRECISION (type
), 1);
1231 tree result
= fold_build2_loc (loc
, subcode
, utype
,
1232 fold_convert_loc (loc
, utype
, arg0
),
1233 fold_convert_loc (loc
, utype
, arg1
));
1234 result
= fold_convert_loc (loc
, type
, result
);
1239 FOR_EACH_IMM_USE_STMT (use_stmt
, imm_iter
, lhs
)
1241 if (!gimple_debug_bind_p (use_stmt
))
1243 tree v
= gimple_debug_bind_get_value (use_stmt
);
1244 if (walk_tree (&v
, find_non_realpart_uses
, lhs
, NULL
))
1246 gimple_debug_bind_reset_value (use_stmt
);
1247 update_stmt (use_stmt
);
1252 if (TREE_CODE (result
) == INTEGER_CST
&& TREE_OVERFLOW (result
))
1253 result
= drop_tree_overflow (result
);
1254 tree overflow
= build_zero_cst (type
);
1255 tree ctype
= build_complex_type (type
);
1256 if (TREE_CODE (result
) == INTEGER_CST
)
1257 result
= build_complex (ctype
, result
, overflow
);
1259 result
= build2_loc (gimple_location (stmt
), COMPLEX_EXPR
,
1260 ctype
, result
, overflow
);
1262 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1264 fprintf (dump_file
, "Transforming call: ");
1265 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1266 fprintf (dump_file
, "because the overflow result is never used into: ");
1267 print_generic_stmt (dump_file
, result
, TDF_SLIM
);
1268 fprintf (dump_file
, "\n");
1271 if (!update_call_from_tree (gsi
, result
))
1272 gimplify_and_update_call_from_tree (gsi
, result
);
1275 /* Eliminate unnecessary statements. Any instruction not marked as necessary
1276 contributes nothing to the program, and can be deleted. */
1279 eliminate_unnecessary_stmts (void)
1281 bool something_changed
= false;
1283 gimple_stmt_iterator gsi
, psi
;
1288 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1289 fprintf (dump_file
, "\nEliminating unnecessary statements:\n");
1291 clear_special_calls ();
1293 /* Walking basic blocks and statements in reverse order avoids
1294 releasing SSA names before any other DEFs that refer to them are
1295 released. This helps avoid loss of debug information, as we get
1296 a chance to propagate all RHSs of removed SSAs into debug uses,
1297 rather than only the latest ones. E.g., consider:
1303 If we were to release x_3 before a_5, when we reached a_5 and
1304 tried to substitute it into the debug stmt, we'd see x_3 there,
1305 but x_3's DEF, type, etc would have already been disconnected.
1306 By going backwards, the debug stmt first changes to:
1308 # DEBUG a => x_3 - b_4
1312 # DEBUG a => y_1 + z_2 - b_4
1315 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
1316 h
= get_all_dominated_blocks (CDI_DOMINATORS
,
1317 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun
)));
1323 /* Remove dead statements. */
1324 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi
= psi
)
1326 stmt
= gsi_stmt (gsi
);
1333 /* We can mark a call to free as not necessary if the
1334 defining statement of its argument is not necessary
1335 (and thus is getting removed). */
1336 if (gimple_plf (stmt
, STMT_NECESSARY
)
1337 && gimple_call_builtin_p (stmt
, BUILT_IN_FREE
))
1339 tree ptr
= gimple_call_arg (stmt
, 0);
1340 if (TREE_CODE (ptr
) == SSA_NAME
)
1342 gimple def_stmt
= SSA_NAME_DEF_STMT (ptr
);
1343 if (!gimple_nop_p (def_stmt
)
1344 && !gimple_plf (def_stmt
, STMT_NECESSARY
))
1345 gimple_set_plf (stmt
, STMT_NECESSARY
, false);
1347 /* We did not propagate necessity for free calls fed
1348 by allocation function to allow unnecessary
1349 alloc-free sequence elimination. For instrumented
1350 calls it also means we did not mark bounds producer
1351 as necessary and it is time to do it in case free
1352 call is not removed. */
1353 if (gimple_call_with_bounds_p (stmt
))
1355 gimple bounds_def_stmt
;
1356 tree bounds
= gimple_call_arg (stmt
, 1);
1357 gcc_assert (TREE_CODE (bounds
) == SSA_NAME
);
1358 bounds_def_stmt
= SSA_NAME_DEF_STMT (bounds
);
1360 && !gimple_plf (bounds_def_stmt
, STMT_NECESSARY
))
1361 gimple_set_plf (bounds_def_stmt
, STMT_NECESSARY
,
1362 gimple_plf (stmt
, STMT_NECESSARY
));
1366 /* If GSI is not necessary then remove it. */
1367 if (!gimple_plf (stmt
, STMT_NECESSARY
))
1369 /* Keep clobbers that we can keep live live. */
1370 if (gimple_clobber_p (stmt
))
1373 use_operand_p use_p
;
1375 FOR_EACH_SSA_USE_OPERAND (use_p
, stmt
, iter
, SSA_OP_USE
)
1377 tree name
= USE_FROM_PTR (use_p
);
1378 if (!SSA_NAME_IS_DEFAULT_DEF (name
)
1379 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
)))
1388 if (!is_gimple_debug (stmt
))
1389 something_changed
= true;
1390 remove_dead_stmt (&gsi
, bb
);
1392 else if (is_gimple_call (stmt
))
1394 tree name
= gimple_call_lhs (stmt
);
1396 notice_special_calls (as_a
<gcall
*> (stmt
));
1398 /* When LHS of var = call (); is dead, simplify it into
1399 call (); saving one operand. */
1401 && TREE_CODE (name
) == SSA_NAME
1402 && !bitmap_bit_p (processed
, SSA_NAME_VERSION (name
))
1403 /* Avoid doing so for allocation calls which we
1404 did not mark as necessary, it will confuse the
1405 special logic we apply to malloc/free pair removal. */
1406 && (!(call
= gimple_call_fndecl (stmt
))
1407 || DECL_BUILT_IN_CLASS (call
) != BUILT_IN_NORMAL
1408 || (DECL_FUNCTION_CODE (call
) != BUILT_IN_ALIGNED_ALLOC
1409 && DECL_FUNCTION_CODE (call
) != BUILT_IN_MALLOC
1410 && DECL_FUNCTION_CODE (call
) != BUILT_IN_CALLOC
1411 && DECL_FUNCTION_CODE (call
) != BUILT_IN_ALLOCA
1412 && (DECL_FUNCTION_CODE (call
)
1413 != BUILT_IN_ALLOCA_WITH_ALIGN
)))
1414 /* Avoid doing so for bndret calls for the same reason. */
1415 && !chkp_gimple_call_builtin_p (stmt
, BUILT_IN_CHKP_BNDRET
))
1417 something_changed
= true;
1418 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
1420 fprintf (dump_file
, "Deleting LHS of call: ");
1421 print_gimple_stmt (dump_file
, stmt
, 0, TDF_SLIM
);
1422 fprintf (dump_file
, "\n");
1425 gimple_call_set_lhs (stmt
, NULL_TREE
);
1426 maybe_clean_or_replace_eh_stmt (stmt
, stmt
);
1428 release_ssa_name (name
);
1430 /* GOMP_SIMD_LANE without lhs is not needed. */
1431 if (gimple_call_internal_p (stmt
)
1432 && gimple_call_internal_fn (stmt
) == IFN_GOMP_SIMD_LANE
)
1433 remove_dead_stmt (&gsi
, bb
);
1435 else if (gimple_call_internal_p (stmt
))
1436 switch (gimple_call_internal_fn (stmt
))
1438 case IFN_ADD_OVERFLOW
:
1439 maybe_optimize_arith_overflow (&gsi
, PLUS_EXPR
);
1441 case IFN_SUB_OVERFLOW
:
1442 maybe_optimize_arith_overflow (&gsi
, MINUS_EXPR
);
1444 case IFN_MUL_OVERFLOW
:
1445 maybe_optimize_arith_overflow (&gsi
, MULT_EXPR
);
1456 /* Since we don't track liveness of virtual PHI nodes, it is possible that we
1457 rendered some PHI nodes unreachable while they are still in use.
1458 Mark them for renaming. */
1461 basic_block prev_bb
;
1463 find_unreachable_blocks ();
1465 /* Delete all unreachable basic blocks in reverse dominator order. */
1466 for (bb
= EXIT_BLOCK_PTR_FOR_FN (cfun
)->prev_bb
;
1467 bb
!= ENTRY_BLOCK_PTR_FOR_FN (cfun
); bb
= prev_bb
)
1469 prev_bb
= bb
->prev_bb
;
1471 if (!bitmap_bit_p (bb_contains_live_stmts
, bb
->index
)
1472 || !(bb
->flags
& BB_REACHABLE
))
1474 for (gphi_iterator gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
1476 if (virtual_operand_p (gimple_phi_result (gsi
.phi ())))
1479 imm_use_iterator iter
;
1481 FOR_EACH_IMM_USE_STMT (stmt
, iter
,
1482 gimple_phi_result (gsi
.phi ()))
1484 if (!(gimple_bb (stmt
)->flags
& BB_REACHABLE
))
1486 if (gimple_code (stmt
) == GIMPLE_PHI
1487 || gimple_plf (stmt
, STMT_NECESSARY
))
1490 BREAK_FROM_IMM_USE_STMT (iter
);
1494 mark_virtual_phi_result_for_renaming (gsi
.phi ());
1497 if (!(bb
->flags
& BB_REACHABLE
))
1499 /* Speed up the removal of blocks that don't
1500 dominate others. Walking backwards, this should
1501 be the common case. ??? Do we need to recompute
1502 dominators because of cfg_altered? */
1503 if (!MAY_HAVE_DEBUG_STMTS
1504 || !first_dom_son (CDI_DOMINATORS
, bb
))
1505 delete_basic_block (bb
);
1508 h
= get_all_dominated_blocks (CDI_DOMINATORS
, bb
);
1513 prev_bb
= bb
->prev_bb
;
1514 /* Rearrangements to the CFG may have failed
1515 to update the dominators tree, so that
1516 formerly-dominated blocks are now
1517 otherwise reachable. */
1518 if (!!(bb
->flags
& BB_REACHABLE
))
1520 delete_basic_block (bb
);
1529 FOR_EACH_BB_FN (bb
, cfun
)
1531 /* Remove dead PHI nodes. */
1532 something_changed
|= remove_dead_phis (bb
);
1535 return something_changed
;
1539 /* Print out removed statement statistics. */
1546 percg
= ((float) stats
.removed
/ (float) stats
.total
) * 100;
1547 fprintf (dump_file
, "Removed %d of %d statements (%d%%)\n",
1548 stats
.removed
, stats
.total
, (int) percg
);
1550 if (stats
.total_phis
== 0)
1553 percg
= ((float) stats
.removed_phis
/ (float) stats
.total_phis
) * 100;
1555 fprintf (dump_file
, "Removed %d of %d PHI nodes (%d%%)\n",
1556 stats
.removed_phis
, stats
.total_phis
, (int) percg
);
1559 /* Initialization for this pass. Set up the used data structures. */
1562 tree_dce_init (bool aggressive
)
1564 memset ((void *) &stats
, 0, sizeof (stats
));
1568 last_stmt_necessary
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1569 bitmap_clear (last_stmt_necessary
);
1570 bb_contains_live_stmts
= sbitmap_alloc (last_basic_block_for_fn (cfun
));
1571 bitmap_clear (bb_contains_live_stmts
);
1574 processed
= sbitmap_alloc (num_ssa_names
+ 1);
1575 bitmap_clear (processed
);
1577 worklist
.create (64);
1578 cfg_altered
= false;
1581 /* Cleanup after this pass. */
1584 tree_dce_done (bool aggressive
)
1589 sbitmap_free (visited_control_parents
);
1590 sbitmap_free (last_stmt_necessary
);
1591 sbitmap_free (bb_contains_live_stmts
);
1592 bb_contains_live_stmts
= NULL
;
1595 sbitmap_free (processed
);
1597 worklist
.release ();
1600 /* Main routine to eliminate dead code.
1602 AGGRESSIVE controls the aggressiveness of the algorithm.
1603 In conservative mode, we ignore control dependence and simply declare
1604 all but the most trivially dead branches necessary. This mode is fast.
1605 In aggressive mode, control dependences are taken into account, which
1606 results in more dead code elimination, but at the cost of some time.
1608 FIXME: Aggressive mode before PRE doesn't work currently because
1609 the dominance info is not invalidated after DCE1. This is
1610 not an issue right now because we only run aggressive DCE
1611 as the last tree SSA pass, but keep this in mind when you
1612 start experimenting with pass ordering. */
1615 perform_tree_ssa_dce (bool aggressive
)
1617 bool something_changed
= 0;
1619 calculate_dominance_info (CDI_DOMINATORS
);
1621 /* Preheaders are needed for SCEV to work.
1622 Simple lateches and recorded exits improve chances that loop will
1623 proved to be finite in testcases such as in loop-15.c and loop-24.c */
1625 loop_optimizer_init (LOOPS_NORMAL
1626 | LOOPS_HAVE_RECORDED_EXITS
);
1628 tree_dce_init (aggressive
);
1632 /* Compute control dependence. */
1633 calculate_dominance_info (CDI_POST_DOMINATORS
);
1634 cd
= new control_dependences (create_edge_list ());
1636 visited_control_parents
=
1637 sbitmap_alloc (last_basic_block_for_fn (cfun
));
1638 bitmap_clear (visited_control_parents
);
1640 mark_dfs_back_edges ();
1643 find_obviously_necessary_stmts (aggressive
);
1646 loop_optimizer_finalize ();
1652 visited
= BITMAP_ALLOC (NULL
);
1653 propagate_necessity (aggressive
);
1654 BITMAP_FREE (visited
);
1656 something_changed
|= eliminate_unnecessary_stmts ();
1657 something_changed
|= cfg_altered
;
1659 /* We do not update postdominators, so free them unconditionally. */
1660 free_dominance_info (CDI_POST_DOMINATORS
);
1662 /* If we removed paths in the CFG, then we need to update
1663 dominators as well. I haven't investigated the possibility
1664 of incrementally updating dominators. */
1666 free_dominance_info (CDI_DOMINATORS
);
1668 statistics_counter_event (cfun
, "Statements deleted", stats
.removed
);
1669 statistics_counter_event (cfun
, "PHI nodes deleted", stats
.removed_phis
);
1671 /* Debugging dumps. */
1672 if (dump_file
&& (dump_flags
& (TDF_STATS
|TDF_DETAILS
)))
1675 tree_dce_done (aggressive
);
1677 if (something_changed
)
1679 free_numbers_of_iterations_estimates ();
1680 if (scev_initialized_p ())
1682 return TODO_update_ssa
| TODO_cleanup_cfg
;
1687 /* Pass entry points. */
1691 return perform_tree_ssa_dce (/*aggressive=*/false);
1695 tree_ssa_cd_dce (void)
1697 return perform_tree_ssa_dce (/*aggressive=*/optimize
>= 2);
1702 const pass_data pass_data_dce
=
1704 GIMPLE_PASS
, /* type */
1706 OPTGROUP_NONE
, /* optinfo_flags */
1707 TV_TREE_DCE
, /* tv_id */
1708 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1709 0, /* properties_provided */
1710 0, /* properties_destroyed */
1711 0, /* todo_flags_start */
1712 0, /* todo_flags_finish */
1715 class pass_dce
: public gimple_opt_pass
1718 pass_dce (gcc::context
*ctxt
)
1719 : gimple_opt_pass (pass_data_dce
, ctxt
)
1722 /* opt_pass methods: */
1723 opt_pass
* clone () { return new pass_dce (m_ctxt
); }
1724 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1725 virtual unsigned int execute (function
*) { return tree_ssa_dce (); }
1727 }; // class pass_dce
1732 make_pass_dce (gcc::context
*ctxt
)
1734 return new pass_dce (ctxt
);
1739 const pass_data pass_data_cd_dce
=
1741 GIMPLE_PASS
, /* type */
1743 OPTGROUP_NONE
, /* optinfo_flags */
1744 TV_TREE_CD_DCE
, /* tv_id */
1745 ( PROP_cfg
| PROP_ssa
), /* properties_required */
1746 0, /* properties_provided */
1747 0, /* properties_destroyed */
1748 0, /* todo_flags_start */
1749 0, /* todo_flags_finish */
1752 class pass_cd_dce
: public gimple_opt_pass
1755 pass_cd_dce (gcc::context
*ctxt
)
1756 : gimple_opt_pass (pass_data_cd_dce
, ctxt
)
1759 /* opt_pass methods: */
1760 opt_pass
* clone () { return new pass_cd_dce (m_ctxt
); }
1761 virtual bool gate (function
*) { return flag_tree_dce
!= 0; }
1762 virtual unsigned int execute (function
*) { return tree_ssa_cd_dce (); }
1764 }; // class pass_cd_dce
1769 make_pass_cd_dce (gcc::context
*ctxt
)
1771 return new pass_cd_dce (ctxt
);