1 /* Miscellaneous SSA utility functions.
2 Copyright (C) 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
11 GCC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING. If not, write to
18 the Free Software Foundation, 59 Temple Place - Suite 330,
19 Boston, MA 02111-1307, USA. */
23 #include "coretypes.h"
30 #include "langhooks.h"
31 #include "hard-reg-set.h"
32 #include "basic-block.h"
37 #include "diagnostic.h"
39 #include "tree-flow.h"
40 #include "tree-gimple.h"
41 #include "tree-inline.h"
44 #include "tree-alias-common.h"
46 #include "tree-dump.h"
47 #include "tree-pass.h"
50 /* Remove edge E and remove the corresponding arguments from the PHI nodes
51 in E's destination block. */
54 ssa_remove_edge (edge e
)
58 /* Remove the appropriate PHI arguments in E's destination block. */
59 for (phi
= phi_nodes (e
->dest
); phi
; phi
= next
)
61 next
= PHI_CHAIN (phi
);
62 remove_phi_arg (phi
, e
->src
);
68 /* Remove remove the corresponding arguments from the PHI nodes
69 in E's destination block and redirect it to DEST. Return redirected edge.
70 The list of removed arguments is stored in PENDING_STMT (e). */
73 ssa_redirect_edge (edge e
, basic_block dest
)
76 tree list
= NULL
, *last
= &list
;
80 /* Remove the appropriate PHI arguments in E's destination block. */
81 for (phi
= phi_nodes (e
->dest
); phi
; phi
= next
)
83 next
= PHI_CHAIN (phi
);
85 i
= phi_arg_from_edge (phi
, e
);
89 src
= PHI_ARG_DEF (phi
, i
);
90 dst
= PHI_RESULT (phi
);
91 node
= build_tree_list (dst
, src
);
93 last
= &TREE_CHAIN (node
);
95 remove_phi_arg_num (phi
, i
);
98 e
= redirect_edge_succ_nodup (e
, dest
);
99 PENDING_STMT (e
) = list
;
105 /* Return true if the definition of SSA_NAME at block BB is malformed.
107 STMT is the statement where SSA_NAME is created.
109 DEFINITION_BLOCK is an array of basic blocks indexed by SSA_NAME version
110 numbers. If DEFINITION_BLOCK[SSA_NAME_VERSION] is set, it means that the
111 block in that array slot contains the definition of SSA_NAME. */
114 verify_def (basic_block bb
, basic_block
*definition_block
, tree ssa_name
,
119 if (TREE_CODE (ssa_name
) != SSA_NAME
)
121 error ("Expected an SSA_NAME object");
122 debug_generic_stmt (ssa_name
);
123 debug_generic_stmt (stmt
);
126 if (definition_block
[SSA_NAME_VERSION (ssa_name
)])
128 error ("SSA_NAME created in two different blocks %i and %i",
129 definition_block
[SSA_NAME_VERSION (ssa_name
)]->index
, bb
->index
);
130 fprintf (stderr
, "SSA_NAME: ");
131 debug_generic_stmt (ssa_name
);
132 debug_generic_stmt (stmt
);
136 definition_block
[SSA_NAME_VERSION (ssa_name
)] = bb
;
138 if (SSA_NAME_DEF_STMT (ssa_name
) != stmt
)
140 error ("SSA_NAME_DEF_STMT is wrong");
141 fprintf (stderr
, "SSA_NAME: ");
142 debug_generic_stmt (ssa_name
);
143 fprintf (stderr
, "Expected definition statement:\n");
144 debug_generic_stmt (SSA_NAME_DEF_STMT (ssa_name
));
145 fprintf (stderr
, "\nActual definition statement:\n");
146 debug_generic_stmt (stmt
);
154 /* Return true if the use of SSA_NAME at statement STMT in block BB is
157 DEF_BB is the block where SSA_NAME was found to be created.
159 IDOM contains immediate dominator information for the flowgraph.
161 CHECK_ABNORMAL is true if the caller wants to check whether this use
162 is flowing through an abnormal edge (only used when checking PHI
166 verify_use (basic_block bb
, basic_block def_bb
, tree ssa_name
,
167 tree stmt
, bool check_abnormal
)
171 if (IS_EMPTY_STMT (SSA_NAME_DEF_STMT (ssa_name
)))
172 ; /* Nothing to do. */
175 error ("Missing definition");
178 else if (bb
!= def_bb
179 && !dominated_by_p (CDI_DOMINATORS
, bb
, def_bb
))
181 error ("Definition in block %i does not dominate use in block %i",
182 def_bb
->index
, bb
->index
);
187 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (ssa_name
))
189 error ("SSA_NAME_OCCURS_IN_ABNORMAL_PHI should be set");
195 fprintf (stderr
, "for SSA_NAME: ");
196 debug_generic_stmt (ssa_name
);
197 fprintf (stderr
, "in statement:\n");
198 debug_generic_stmt (stmt
);
205 /* Return true if any of the arguments for PHI node PHI at block BB is
208 IDOM contains immediate dominator information for the flowgraph.
210 DEFINITION_BLOCK is an array of basic blocks indexed by SSA_NAME version
211 numbers. If DEFINITION_BLOCK[SSA_NAME_VERSION] is set, it means that the
212 block in that array slot contains the definition of SSA_NAME. */
215 verify_phi_args (tree phi
, basic_block bb
, basic_block
*definition_block
)
219 int i
, phi_num_args
= PHI_NUM_ARGS (phi
);
221 /* Mark all the incoming edges. */
222 for (e
= bb
->pred
; e
; e
= e
->pred_next
)
225 for (i
= 0; i
< phi_num_args
; i
++)
227 tree op
= PHI_ARG_DEF (phi
, i
);
229 e
= PHI_ARG_EDGE (phi
, i
);
231 if (TREE_CODE (op
) == SSA_NAME
)
232 err
|= verify_use (e
->src
, definition_block
[SSA_NAME_VERSION (op
)], op
,
233 phi
, e
->flags
& EDGE_ABNORMAL
);
237 error ("Wrong edge %d->%d for PHI argument\n",
238 e
->src
->index
, e
->dest
->index
, bb
->index
);
242 if (e
->aux
== (void *) 0)
244 error ("PHI argument flowing through dead edge %d->%d\n",
245 e
->src
->index
, e
->dest
->index
);
249 if (e
->aux
== (void *) 2)
251 error ("PHI argument duplicated for edge %d->%d\n", e
->src
->index
,
258 fprintf (stderr
, "PHI argument\n");
259 debug_generic_stmt (op
);
265 for (e
= bb
->pred
; e
; e
= e
->pred_next
)
267 if (e
->aux
!= (void *) 2)
269 error ("No argument flowing through edge %d->%d\n", e
->src
->index
,
278 fprintf (stderr
, "for PHI node\n");
279 debug_generic_stmt (phi
);
287 /* Verify common invariants in the SSA web.
288 TODO: verify the variable annotations. */
295 basic_block
*definition_block
= xcalloc (num_ssa_names
, sizeof (basic_block
));
297 timevar_push (TV_TREE_SSA_VERIFY
);
299 calculate_dominance_info (CDI_DOMINATORS
);
301 /* Verify and register all the SSA_NAME definitions found in the
306 block_stmt_iterator bsi
;
308 for (phi
= phi_nodes (bb
); phi
; phi
= PHI_CHAIN (phi
))
309 err
|= verify_def (bb
, definition_block
, PHI_RESULT (phi
), phi
);
311 for (bsi
= bsi_start (bb
); !bsi_end_p (bsi
); bsi_next (&bsi
))
316 v_may_def_optype v_may_defs
;
317 v_must_def_optype v_must_defs
;
320 stmt
= bsi_stmt (bsi
);
321 ann
= stmt_ann (stmt
);
322 get_stmt_operands (stmt
);
324 v_may_defs
= V_MAY_DEF_OPS (ann
);
325 if (ann
->makes_aliased_stores
&& NUM_V_MAY_DEFS (v_may_defs
) == 0)
326 error ("Makes aliased stores, but no V_MAY_DEFS");
328 for (j
= 0; j
< NUM_V_MAY_DEFS (v_may_defs
); j
++)
330 tree op
= V_MAY_DEF_RESULT (v_may_defs
, j
);
331 if (is_gimple_reg (op
))
333 error ("Found a virtual definition for a GIMPLE register");
334 debug_generic_stmt (op
);
335 debug_generic_stmt (stmt
);
338 err
|= verify_def (bb
, definition_block
, op
, stmt
);
341 v_must_defs
= STMT_V_MUST_DEF_OPS (stmt
);
342 for (j
= 0; j
< NUM_V_MUST_DEFS (v_must_defs
); j
++)
344 tree op
= V_MUST_DEF_OP (v_must_defs
, j
);
345 if (is_gimple_reg (op
))
347 error ("Found a virtual must-def for a GIMPLE register");
348 debug_generic_stmt (op
);
349 debug_generic_stmt (stmt
);
352 err
|= verify_def (bb
, definition_block
, op
, stmt
);
355 defs
= DEF_OPS (ann
);
356 for (j
= 0; j
< NUM_DEFS (defs
); j
++)
358 tree op
= DEF_OP (defs
, j
);
359 if (TREE_CODE (op
) == SSA_NAME
&& !is_gimple_reg (op
))
361 error ("Found a real definition for a non-GIMPLE register");
362 debug_generic_stmt (op
);
363 debug_generic_stmt (stmt
);
366 err
|= verify_def (bb
, definition_block
, op
, stmt
);
372 /* Now verify all the uses and make sure they agree with the definitions
373 found in the previous pass. */
378 block_stmt_iterator bsi
;
380 /* Make sure that all edges have a clear 'aux' field. */
381 for (e
= bb
->pred
; e
; e
= e
->pred_next
)
385 error ("AUX pointer initialized for edge %d->%d\n", e
->src
->index
,
391 /* Verify the arguments for every PHI node in the block. */
392 for (phi
= phi_nodes (bb
); phi
; phi
= PHI_CHAIN (phi
))
393 err
|= verify_phi_args (phi
, bb
, definition_block
);
395 /* Now verify all the uses and vuses in every statement of the block.
397 Remember, the RHS of a V_MAY_DEF is a use as well. */
398 for (bsi
= bsi_start (bb
); !bsi_end_p (bsi
); bsi_next (&bsi
))
400 tree stmt
= bsi_stmt (bsi
);
401 stmt_ann_t ann
= stmt_ann (stmt
);
404 v_may_def_optype v_may_defs
;
407 vuses
= VUSE_OPS (ann
);
408 for (j
= 0; j
< NUM_VUSES (vuses
); j
++)
410 tree op
= VUSE_OP (vuses
, j
);
412 if (is_gimple_reg (op
))
414 error ("Found a virtual use for a GIMPLE register");
415 debug_generic_stmt (op
);
416 debug_generic_stmt (stmt
);
419 err
|= verify_use (bb
, definition_block
[SSA_NAME_VERSION (op
)],
423 v_may_defs
= V_MAY_DEF_OPS (ann
);
424 for (j
= 0; j
< NUM_V_MAY_DEFS (v_may_defs
); j
++)
426 tree op
= V_MAY_DEF_OP (v_may_defs
, j
);
428 if (is_gimple_reg (op
))
430 error ("Found a virtual use for a GIMPLE register");
431 debug_generic_stmt (op
);
432 debug_generic_stmt (stmt
);
435 err
|= verify_use (bb
, definition_block
[SSA_NAME_VERSION (op
)],
439 uses
= USE_OPS (ann
);
440 for (j
= 0; j
< NUM_USES (uses
); j
++)
442 tree op
= USE_OP (uses
, j
);
444 if (TREE_CODE (op
) == SSA_NAME
&& !is_gimple_reg (op
))
446 error ("Found a real use of a non-GIMPLE register");
447 debug_generic_stmt (op
);
448 debug_generic_stmt (stmt
);
451 err
|= verify_use (bb
, definition_block
[SSA_NAME_VERSION (op
)],
457 free (definition_block
);
459 timevar_pop (TV_TREE_SSA_VERIFY
);
462 internal_error ("verify_ssa failed.");
466 /* Set the USED bit in the annotation for T. */
476 switch (TREE_CODE (t
))
484 t
= TREE_OPERAND (t
, 0);
492 if (TREE_CODE (t
) == SSA_NAME
)
493 t
= SSA_NAME_VAR (t
);
495 var_ann (t
)->used
= 1;
499 /* Initialize global DFA and SSA structures. */
504 VARRAY_TREE_INIT (referenced_vars
, 20, "referenced_vars");
505 call_clobbered_vars
= BITMAP_XMALLOC ();
506 init_ssa_operands ();
509 global_var
= NULL_TREE
;
510 aliases_computed_p
= false;
514 /* Deallocate memory associated with SSA data structures for FNDECL. */
517 delete_tree_ssa (void)
521 block_stmt_iterator bsi
;
523 /* Remove annotations from every tree in the function. */
525 for (bsi
= bsi_start (bb
); !bsi_end_p (bsi
); bsi_next (&bsi
))
526 bsi_stmt (bsi
)->common
.ann
= NULL
;
528 /* Remove annotations from every referenced variable. */
531 for (i
= 0; i
< num_referenced_vars
; i
++)
532 referenced_var (i
)->common
.ann
= NULL
;
533 referenced_vars
= NULL
;
538 fini_ssa_operands ();
540 global_var
= NULL_TREE
;
541 BITMAP_XFREE (call_clobbered_vars
);
542 call_clobbered_vars
= NULL
;
543 aliases_computed_p
= false;
547 /* Return true if EXPR is a useless type conversion, otherwise return
551 tree_ssa_useless_type_conversion_1 (tree outer_type
, tree inner_type
)
553 /* If the inner and outer types are effectively the same, then
554 strip the type conversion and enter the equivalence into
556 if (inner_type
== outer_type
557 || (lang_hooks
.types_compatible_p (inner_type
, outer_type
)))
560 /* If both types are pointers and the outer type is a (void *), then
561 the conversion is not necessary. The opposite is not true since
562 that conversion would result in a loss of information if the
563 equivalence was used. Consider an indirect function call where
564 we need to know the exact type of the function to correctly
565 implement the ABI. */
566 else if (POINTER_TYPE_P (inner_type
)
567 && POINTER_TYPE_P (outer_type
)
568 && TREE_CODE (TREE_TYPE (outer_type
)) == VOID_TYPE
)
571 /* Pointers and references are equivalent once we get to GENERIC,
572 so strip conversions that just switch between them. */
573 else if (POINTER_TYPE_P (inner_type
)
574 && POINTER_TYPE_P (outer_type
)
575 && lang_hooks
.types_compatible_p (TREE_TYPE (inner_type
),
576 TREE_TYPE (outer_type
)))
579 /* If both the inner and outer types are integral types, then the
580 conversion is not necessary if they have the same mode and
581 signedness and precision. Note that type _Bool can have size of
582 4 (only happens on powerpc-darwin right now but can happen on any
583 target that defines BOOL_TYPE_SIZE to be INT_TYPE_SIZE) and a
584 precision of 1 while unsigned int is the same expect for a
585 precision of 4 so testing of precision is necessary. */
586 else if (INTEGRAL_TYPE_P (inner_type
)
587 && INTEGRAL_TYPE_P (outer_type
)
588 && TYPE_MODE (inner_type
) == TYPE_MODE (outer_type
)
589 && TYPE_UNSIGNED (inner_type
) == TYPE_UNSIGNED (outer_type
)
590 && TYPE_PRECISION (inner_type
) == TYPE_PRECISION (outer_type
))
593 /* Recurse for complex types. */
594 else if (TREE_CODE (inner_type
) == COMPLEX_TYPE
595 && TREE_CODE (outer_type
) == COMPLEX_TYPE
596 && tree_ssa_useless_type_conversion_1 (TREE_TYPE (outer_type
),
597 TREE_TYPE (inner_type
)))
603 /* Return true if EXPR is a useless type conversion, otherwise return
607 tree_ssa_useless_type_conversion (tree expr
)
609 /* If we have an assignment that merely uses a NOP_EXPR to change
610 the top of the RHS to the type of the LHS and the type conversion
611 is "safe", then strip away the type conversion so that we can
612 enter LHS = RHS into the const_and_copies table. */
613 if (TREE_CODE (expr
) == NOP_EXPR
|| TREE_CODE (expr
) == CONVERT_EXPR
)
614 return tree_ssa_useless_type_conversion_1 (TREE_TYPE (expr
),
615 TREE_TYPE (TREE_OPERAND (expr
,
623 /* Internal helper for walk_use_def_chains. VAR, FN and DATA are as
624 described in walk_use_def_chains. VISITED is a bitmap used to mark
625 visited SSA_NAMEs to avoid infinite loops. */
628 walk_use_def_chains_1 (tree var
, walk_use_def_chains_fn fn
, void *data
,
633 if (bitmap_bit_p (visited
, SSA_NAME_VERSION (var
)))
636 bitmap_set_bit (visited
, SSA_NAME_VERSION (var
));
638 def_stmt
= SSA_NAME_DEF_STMT (var
);
640 if (TREE_CODE (def_stmt
) != PHI_NODE
)
642 /* If we reached the end of the use-def chain, call FN. */
643 return (*fn
) (var
, def_stmt
, data
);
649 /* Otherwise, follow use-def links out of each PHI argument and call
650 FN after visiting each one. */
651 for (i
= 0; i
< PHI_NUM_ARGS (def_stmt
); i
++)
653 tree arg
= PHI_ARG_DEF (def_stmt
, i
);
654 if (TREE_CODE (arg
) == SSA_NAME
655 && walk_use_def_chains_1 (arg
, fn
, data
, visited
))
658 if ((*fn
) (arg
, def_stmt
, data
))
667 /* Walk use-def chains starting at the SSA variable VAR. Call function FN
668 at each reaching definition found. FN takes three arguments: VAR, its
669 defining statement (DEF_STMT) and a generic pointer to whatever state
670 information that FN may want to maintain (DATA). FN is able to stop the
671 walk by returning true, otherwise in order to continue the walk, FN
674 Note, that if DEF_STMT is a PHI node, the semantics are slightly
675 different. For each argument ARG of the PHI node, this function will:
677 1- Walk the use-def chains for ARG.
678 2- Call (*FN) (ARG, PHI, DATA).
680 Note how the first argument to FN is no longer the original variable
681 VAR, but the PHI argument currently being examined. If FN wants to get
682 at VAR, it should call PHI_RESULT (PHI). */
685 walk_use_def_chains (tree var
, walk_use_def_chains_fn fn
, void *data
)
689 #if defined ENABLE_CHECKING
690 if (TREE_CODE (var
) != SSA_NAME
)
694 def_stmt
= SSA_NAME_DEF_STMT (var
);
696 /* We only need to recurse if the reaching definition comes from a PHI
698 if (TREE_CODE (def_stmt
) != PHI_NODE
)
699 (*fn
) (var
, def_stmt
, data
);
702 bitmap visited
= BITMAP_XMALLOC ();
703 walk_use_def_chains_1 (var
, fn
, data
, visited
);
704 BITMAP_XFREE (visited
);
708 /* Replaces VAR with REPL in memory reference expression *X in
712 propagate_into_addr (tree stmt
, tree var
, tree
*x
, tree repl
)
714 tree new_var
, ass_stmt
, addr_var
;
716 block_stmt_iterator bsi
;
718 /* There is nothing special to handle in the other cases. */
719 if (TREE_CODE (repl
) != ADDR_EXPR
)
721 addr_var
= TREE_OPERAND (repl
, 0);
723 while (TREE_CODE (*x
) == ARRAY_REF
724 || TREE_CODE (*x
) == COMPONENT_REF
725 || TREE_CODE (*x
) == BIT_FIELD_REF
)
726 x
= &TREE_OPERAND (*x
, 0);
728 if (TREE_CODE (*x
) != INDIRECT_REF
729 || TREE_OPERAND (*x
, 0) != var
)
733 if (TREE_TYPE (*x
) == TREE_TYPE (addr_var
))
736 mark_new_vars_to_rename (stmt
, vars_to_rename
);
740 /* Frontends sometimes produce expressions like *&a instead of a[0].
741 Create a temporary variable to handle this case. */
742 ass_stmt
= build2 (MODIFY_EXPR
, void_type_node
, NULL_TREE
, repl
);
743 new_var
= duplicate_ssa_name (var
, ass_stmt
);
744 TREE_OPERAND (*x
, 0) = new_var
;
745 TREE_OPERAND (ass_stmt
, 0) = new_var
;
747 bb
= bb_for_stmt (stmt
);
748 tree_block_label (bb
);
749 bsi
= bsi_after_labels (bb
);
750 bsi_insert_after (&bsi
, ass_stmt
, BSI_NEW_STMT
);
752 mark_new_vars_to_rename (stmt
, vars_to_rename
);
755 /* Replaces immediate uses of VAR by REPL. */
758 replace_immediate_uses (tree var
, tree repl
)
762 v_may_def_optype v_may_defs
;
769 df
= get_immediate_uses (SSA_NAME_DEF_STMT (var
));
770 n
= num_immediate_uses (df
);
772 for (i
= 0; i
< n
; i
++)
774 stmt
= immediate_use (df
, i
);
775 ann
= stmt_ann (stmt
);
777 if (TREE_CODE (stmt
) == PHI_NODE
)
779 for (j
= 0; j
< PHI_NUM_ARGS (stmt
); j
++)
780 if (PHI_ARG_DEF (stmt
, j
) == var
)
782 SET_PHI_ARG_DEF (stmt
, j
, repl
);
783 if (TREE_CODE (repl
) == SSA_NAME
784 && PHI_ARG_EDGE (stmt
, j
)->flags
& EDGE_ABNORMAL
)
785 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (repl
) = 1;
791 get_stmt_operands (stmt
);
792 mark_new_vars
= false;
793 if (is_gimple_reg (SSA_NAME_VAR (var
)))
795 if (TREE_CODE (stmt
) == MODIFY_EXPR
)
797 propagate_into_addr (stmt
, var
, &TREE_OPERAND (stmt
, 0), repl
);
798 propagate_into_addr (stmt
, var
, &TREE_OPERAND (stmt
, 1), repl
);
801 uses
= USE_OPS (ann
);
802 for (j
= 0; j
< (int) NUM_USES (uses
); j
++)
803 if (USE_OP (uses
, j
) == var
)
805 propagate_value (USE_OP_PTR (uses
, j
), repl
);
806 mark_new_vars
= POINTER_TYPE_P (TREE_TYPE (repl
));
811 vuses
= VUSE_OPS (ann
);
812 for (j
= 0; j
< (int) NUM_VUSES (vuses
); j
++)
813 if (VUSE_OP (vuses
, j
) == var
)
814 propagate_value (VUSE_OP_PTR (vuses
, j
), repl
);
816 v_may_defs
= V_MAY_DEF_OPS (ann
);
817 for (j
= 0; j
< (int) NUM_V_MAY_DEFS (v_may_defs
); j
++)
818 if (V_MAY_DEF_OP (v_may_defs
, j
) == var
)
819 propagate_value (V_MAY_DEF_OP_PTR (v_may_defs
, j
), repl
);
822 /* If REPL is a pointer, it may have different memory tags associated
823 with it. For instance, VAR may have had a name tag while REPL
824 only had a type tag. In these cases, the virtual operands (if
825 any) in the statement will refer to different symbols which need
828 mark_new_vars_to_rename (stmt
, vars_to_rename
);
834 /* Raises value of phi node PHI by joining it with VAL. Processes immediate
835 uses of PHI recursively. */
838 raise_value (tree phi
, tree val
, tree
*eq_to
)
841 tree var
= PHI_RESULT (phi
), stmt
;
842 int ver
= SSA_NAME_VERSION (var
);
845 if (eq_to
[ver
] == var
)
850 if (operand_equal_p (eq_to
[ver
], val
, 0))
858 df
= get_immediate_uses (SSA_NAME_DEF_STMT (var
));
859 n
= num_immediate_uses (df
);
861 for (i
= 0; i
< n
; i
++)
863 stmt
= immediate_use (df
, i
);
865 if (TREE_CODE (stmt
) != PHI_NODE
)
868 raise_value (stmt
, eq_to
[ver
], eq_to
);
872 /* Removes redundant phi nodes.
874 A redundant PHI node is a PHI node where all of its PHI arguments
875 are the same value, excluding any PHI arguments which are the same
878 A redundant PHI node is effectively a copy, so we forward copy propagate
879 which removes all uses of the destination of the PHI node then
880 finally we delete the redundant PHI node.
882 Note that if we can not copy propagate the PHI node, then the PHI
883 will not be removed. Thus we do not have to worry about dependencies
884 between PHIs and the problems serializing PHIs into copies creates.
886 The most important effect of this pass is to remove degenerate PHI
887 nodes created by removing unreachable code. */
890 kill_redundant_phi_nodes (void)
895 tree phi
, t
, stmt
, var
;
897 /* The EQ_TO array holds the current value of the ssa name in the
906 Bottom is represented by NULL and top by the variable itself.
908 Once the dataflow stabilizes, we know that the phi nodes we need to keep
909 are exactly those with top as their result.
911 The remaining phi nodes have their uses replaced with their value
912 in the lattice and the phi node itself is removed. */
913 eq_to
= xcalloc (num_ssa_names
, sizeof (tree
));
915 /* We have had cases where computing immediate uses takes a
916 significant amount of compile time. If we run into such
917 problems here, we may want to only compute immediate uses for
918 a subset of all the SSA_NAMEs instead of computing it for
919 all of the SSA_NAMEs. */
920 compute_immediate_uses (TDFA_USE_OPS
| TDFA_USE_VOPS
, NULL
);
924 for (phi
= phi_nodes (bb
); phi
; phi
= PHI_CHAIN (phi
))
926 var
= PHI_RESULT (phi
);
928 /* If the destination of the PHI is associated with an
929 abnormal edge, then we can not propagate this PHI away. */
930 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (var
))
932 raise_value (phi
, var
, eq_to
);
936 for (i
= 0; i
< (unsigned) PHI_NUM_ARGS (phi
); i
++)
938 t
= PHI_ARG_DEF (phi
, i
);
940 if (TREE_CODE (t
) != SSA_NAME
)
942 raise_value (phi
, t
, eq_to
);
946 stmt
= SSA_NAME_DEF_STMT (t
);
948 /* If any particular PHI argument is associated with
949 an abnormal edge, then we know that we should not
950 be propagating away this PHI. Go ahead and raise
951 the result of this PHI to the top of the lattice. */
952 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (t
))
954 raise_value (phi
, var
, eq_to
);
958 /* If the defining statement for this argument is not a
959 phi node then we need to recursively start the forward
960 dataflow starting with PHI. */
961 if (TREE_CODE (stmt
) != PHI_NODE
)
963 eq_to
[SSA_NAME_VERSION (t
)] = t
;
964 raise_value (phi
, t
, eq_to
);
970 /* Now propagate the values. */
971 for (i
= 0; i
< num_ssa_names
; i
++)
973 && eq_to
[i
] != ssa_name (i
))
974 replace_immediate_uses (ssa_name (i
), eq_to
[i
]);
976 /* And remove the dead phis. */
977 for (i
= 0; i
< num_ssa_names
; i
++)
979 && eq_to
[i
] != ssa_name (i
))
981 stmt
= SSA_NAME_DEF_STMT (ssa_name (i
));
982 remove_phi_node (stmt
, 0, bb_for_stmt (stmt
));
989 struct tree_opt_pass pass_redundant_phi
=
993 kill_redundant_phi_nodes
, /* execute */
996 0, /* static_pass_number */
998 PROP_cfg
| PROP_ssa
, /* properties_required */
999 0, /* properties_provided */
1000 0, /* properties_destroyed */
1001 0, /* todo_flags_start */
1002 TODO_dump_func
| TODO_rename_vars
1003 | TODO_ggc_collect
| TODO_verify_ssa
/* todo_flags_finish */
1006 /* Emit warnings for uninitialized variables. This is done in two passes.
1008 The first pass notices real uses of SSA names with default definitions.
1009 Such uses are unconditionally uninitialized, and we can be certain that
1010 such a use is a mistake. This pass is run before most optimizations,
1011 so that we catch as many as we can.
1013 The second pass follows PHI nodes to find uses that are potentially
1014 uninitialized. In this case we can't necessarily prove that the use
1015 is really uninitialized. This pass is run after most optimizations,
1016 so that we thread as many jumps and possible, and delete as much dead
1017 code as possible, in order to reduce false positives. We also look
1018 again for plain uninitialized variables, since optimization may have
1019 changed conditionally uninitialized to unconditionally uninitialized. */
1021 /* Emit a warning for T, an SSA_NAME, being uninitialized. The exact
1022 warning text is in MSGID and LOCUS may contain a location or be null. */
1025 warn_uninit (tree t
, const char *msgid
, location_t
*locus
)
1027 tree var
= SSA_NAME_VAR (t
);
1028 tree def
= SSA_NAME_DEF_STMT (t
);
1030 /* Default uses (indicated by an empty definition statement),
1031 are uninitialized. */
1032 if (!IS_EMPTY_STMT (def
))
1035 /* Except for PARMs of course, which are always initialized. */
1036 if (TREE_CODE (var
) == PARM_DECL
)
1039 /* Hard register variables get their initial value from the ether. */
1040 if (DECL_HARD_REGISTER (var
))
1043 /* TREE_NO_WARNING either means we already warned, or the front end
1044 wishes to suppress the warning. */
1045 if (TREE_NO_WARNING (var
))
1049 locus
= &DECL_SOURCE_LOCATION (var
);
1050 warning (msgid
, locus
, var
);
1051 TREE_NO_WARNING (var
) = 1;
1054 /* Called via walk_tree, look for SSA_NAMEs that have empty definitions
1055 and warn about them. */
1058 warn_uninitialized_var (tree
*tp
, int *walk_subtrees
, void *data
)
1060 location_t
*locus
= data
;
1063 /* We only do data flow with SSA_NAMEs, so that's all we can warn about. */
1064 if (TREE_CODE (t
) == SSA_NAME
)
1066 warn_uninit (t
, "%H'%D' is used uninitialized in this function", locus
);
1069 else if (DECL_P (t
) || TYPE_P (t
))
1075 /* Look for inputs to PHI that are SSA_NAMEs that have empty definitions
1076 and warn about them. */
1079 warn_uninitialized_phi (tree phi
)
1081 int i
, n
= PHI_NUM_ARGS (phi
);
1083 /* Don't look at memory tags. */
1084 if (!is_gimple_reg (PHI_RESULT (phi
)))
1087 for (i
= 0; i
< n
; ++i
)
1089 tree op
= PHI_ARG_DEF (phi
, i
);
1090 if (TREE_CODE (op
) == SSA_NAME
)
1091 warn_uninit (op
, "%H'%D' may be used uninitialized in this function",
1097 execute_early_warn_uninitialized (void)
1099 block_stmt_iterator bsi
;
1103 for (bsi
= bsi_start (bb
); !bsi_end_p (bsi
); bsi_next (&bsi
))
1104 walk_tree (bsi_stmt_ptr (bsi
), warn_uninitialized_var
,
1105 EXPR_LOCUS (bsi_stmt (bsi
)), NULL
);
1109 execute_late_warn_uninitialized (void)
1114 /* Re-do the plain uninitialized variable check, as optimization may have
1115 straightened control flow. Do this first so that we don't accidentally
1116 get a "may be" warning when we'd have seen an "is" warning later. */
1117 execute_early_warn_uninitialized ();
1120 for (phi
= phi_nodes (bb
); phi
; phi
= PHI_CHAIN (phi
))
1121 warn_uninitialized_phi (phi
);
1125 gate_warn_uninitialized (void)
1127 return warn_uninitialized
!= 0;
1130 struct tree_opt_pass pass_early_warn_uninitialized
=
1133 gate_warn_uninitialized
, /* gate */
1134 execute_early_warn_uninitialized
, /* execute */
1137 0, /* static_pass_number */
1139 PROP_ssa
, /* properties_required */
1140 0, /* properties_provided */
1141 0, /* properties_destroyed */
1142 0, /* todo_flags_start */
1143 0 /* todo_flags_finish */
1146 struct tree_opt_pass pass_late_warn_uninitialized
=
1149 gate_warn_uninitialized
, /* gate */
1150 execute_late_warn_uninitialized
, /* execute */
1153 0, /* static_pass_number */
1155 PROP_ssa
, /* properties_required */
1156 0, /* properties_provided */
1157 0, /* properties_destroyed */
1158 0, /* todo_flags_start */
1159 0 /* todo_flags_finish */