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 the corresponding arguments from the PHI nodes in E's
69 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 if (TREE_CODE (t) == REALPART_EXPR || TREE_CODE (t) == IMAGPART_EXPR)
477 t = TREE_OPERAND (t, 0);
479 while (handled_component_p (t))
480 t = TREE_OPERAND (t, 0);
483 if (TREE_CODE (t) == SSA_NAME)
484 t = SSA_NAME_VAR (t);
486 var_ann (t)->used = 1;
490 /* Initialize global DFA and SSA structures. */
495 VARRAY_TREE_INIT (referenced_vars, 20, "referenced_vars");
496 call_clobbered_vars = BITMAP_XMALLOC ();
497 addressable_vars = BITMAP_XMALLOC ();
498 init_ssa_operands ();
501 global_var = NULL_TREE;
502 aliases_computed_p = false;
506 /* Deallocate memory associated with SSA data structures for FNDECL. */
509 delete_tree_ssa (void)
513 block_stmt_iterator bsi;
515 /* Remove annotations from every tree in the function. */
517 for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
518 bsi_stmt (bsi)->common.ann = NULL;
520 /* Remove annotations from every referenced variable. */
523 for (i = 0; i < num_referenced_vars; i++)
524 referenced_var (i)->common.ann = NULL;
525 referenced_vars = NULL;
530 fini_ssa_operands ();
532 global_var = NULL_TREE;
533 BITMAP_XFREE (call_clobbered_vars);
534 call_clobbered_vars = NULL;
535 aliases_computed_p = false;
536 BITMAP_XFREE (addressable_vars);
537 addressable_vars = NULL;
541 /* Return true if EXPR is a useless type conversion, otherwise return
545 tree_ssa_useless_type_conversion_1 (tree outer_type, tree inner_type)
547 /* If the inner and outer types are effectively the same, then
548 strip the type conversion and enter the equivalence into
550 if (inner_type == outer_type
551 || (lang_hooks.types_compatible_p (inner_type, outer_type)))
554 /* If both types are pointers and the outer type is a (void *), then
555 the conversion is not necessary. The opposite is not true since
556 that conversion would result in a loss of information if the
557 equivalence was used. Consider an indirect function call where
558 we need to know the exact type of the function to correctly
559 implement the ABI. */
560 else if (POINTER_TYPE_P (inner_type)
561 && POINTER_TYPE_P (outer_type)
562 && TREE_CODE (TREE_TYPE (outer_type)) == VOID_TYPE)
565 /* Pointers and references are equivalent once we get to GENERIC,
566 so strip conversions that just switch between them. */
567 else if (POINTER_TYPE_P (inner_type)
568 && POINTER_TYPE_P (outer_type)
569 && lang_hooks.types_compatible_p (TREE_TYPE (inner_type),
570 TREE_TYPE (outer_type)))
573 /* If both the inner and outer types are integral types, then the
574 conversion is not necessary if they have the same mode and
575 signedness and precision, and both or neither are boolean. Some
576 code assumes an invariant that boolean types stay boolean and do
577 not become 1-bit bit-field types. Note that types with precision
578 not using all bits of the mode (such as bit-field types in C)
579 mean that testing of precision is necessary. */
580 else if (INTEGRAL_TYPE_P (inner_type)
581 && INTEGRAL_TYPE_P (outer_type)
582 && TYPE_MODE (inner_type) == TYPE_MODE (outer_type)
583 && TYPE_UNSIGNED (inner_type) == TYPE_UNSIGNED (outer_type)
584 && TYPE_PRECISION (inner_type) == TYPE_PRECISION (outer_type))
586 bool first_boolean = (TREE_CODE (inner_type) == BOOLEAN_TYPE);
587 bool second_boolean = (TREE_CODE (outer_type) == BOOLEAN_TYPE);
588 if (first_boolean == second_boolean)
592 /* Recurse for complex types. */
593 else if (TREE_CODE (inner_type) == COMPLEX_TYPE
594 && TREE_CODE (outer_type) == COMPLEX_TYPE
595 && tree_ssa_useless_type_conversion_1 (TREE_TYPE (outer_type),
596 TREE_TYPE (inner_type)))
602 /* Return true if EXPR is a useless type conversion, otherwise return
606 tree_ssa_useless_type_conversion (tree expr)
608 /* If we have an assignment that merely uses a NOP_EXPR to change
609 the top of the RHS to the type of the LHS and the type conversion
610 is "safe", then strip away the type conversion so that we can
611 enter LHS = RHS into the const_and_copies table. */
612 if (TREE_CODE (expr) == NOP_EXPR || TREE_CODE (expr) == CONVERT_EXPR
613 || TREE_CODE (expr) == VIEW_CONVERT_EXPR
614 || TREE_CODE (expr) == NON_LVALUE_EXPR)
615 return tree_ssa_useless_type_conversion_1 (TREE_TYPE (expr),
616 TREE_TYPE (TREE_OPERAND (expr,
624 /* Internal helper for walk_use_def_chains. VAR, FN and DATA are as
625 described in walk_use_def_chains. VISITED is a bitmap used to mark
626 visited SSA_NAMEs to avoid infinite loops. */
629 walk_use_def_chains_1 (tree var, walk_use_def_chains_fn fn, void *data,
634 if (bitmap_bit_p (visited, SSA_NAME_VERSION (var)))
637 bitmap_set_bit (visited, SSA_NAME_VERSION (var));
639 def_stmt = SSA_NAME_DEF_STMT (var);
641 if (TREE_CODE (def_stmt) != PHI_NODE)
643 /* If we reached the end of the use-def chain, call FN. */
644 return (*fn) (var, def_stmt, data);
650 /* Otherwise, follow use-def links out of each PHI argument and call
651 FN after visiting each one. */
652 for (i = 0; i < PHI_NUM_ARGS (def_stmt); i++)
654 tree arg = PHI_ARG_DEF (def_stmt, i);
655 if (TREE_CODE (arg) == SSA_NAME
656 && walk_use_def_chains_1 (arg, fn, data, visited))
659 if ((*fn) (arg, def_stmt, data))
668 /* Walk use-def chains starting at the SSA variable VAR. Call function FN
669 at each reaching definition found. FN takes three arguments: VAR, its
670 defining statement (DEF_STMT) and a generic pointer to whatever state
671 information that FN may want to maintain (DATA). FN is able to stop the
672 walk by returning true, otherwise in order to continue the walk, FN
675 Note, that if DEF_STMT is a PHI node, the semantics are slightly
676 different. For each argument ARG of the PHI node, this function will:
678 1- Walk the use-def chains for ARG.
679 2- Call (*FN) (ARG, PHI, DATA).
681 Note how the first argument to FN is no longer the original variable
682 VAR, but the PHI argument currently being examined. If FN wants to get
683 at VAR, it should call PHI_RESULT (PHI). */
686 walk_use_def_chains (tree var, walk_use_def_chains_fn fn, void *data)
690 #if defined ENABLE_CHECKING
691 if (TREE_CODE (var) != SSA_NAME)
695 def_stmt = SSA_NAME_DEF_STMT (var);
697 /* We only need to recurse if the reaching definition comes from a PHI
699 if (TREE_CODE (def_stmt) != PHI_NODE)
700 (*fn) (var, def_stmt, data);
703 bitmap visited = BITMAP_XMALLOC ();
704 walk_use_def_chains_1 (var, fn, data, visited);
705 BITMAP_XFREE (visited);
709 /* Replaces VAR with REPL in memory reference expression *X in
713 propagate_into_addr (tree stmt, tree var, tree *x, tree repl)
715 tree new_var, ass_stmt, addr_var;
717 block_stmt_iterator bsi;
719 /* There is nothing special to handle in the other cases. */
720 if (TREE_CODE (repl) != ADDR_EXPR)
722 addr_var = TREE_OPERAND (repl, 0);
724 while (TREE_CODE (*x) == ARRAY_REF
725 || TREE_CODE (*x) == COMPONENT_REF
726 || TREE_CODE (*x) == BIT_FIELD_REF)
727 x = &TREE_OPERAND (*x, 0);
729 if (TREE_CODE (*x) != INDIRECT_REF
730 || TREE_OPERAND (*x, 0) != var)
734 if (TREE_TYPE (*x) == TREE_TYPE (addr_var))
737 mark_new_vars_to_rename (stmt, vars_to_rename);
741 /* Frontends sometimes produce expressions like *&a instead of a[0].
742 Create a temporary variable to handle this case. */
743 ass_stmt = build2 (MODIFY_EXPR, void_type_node, NULL_TREE, repl);
744 new_var = duplicate_ssa_name (var, ass_stmt);
745 TREE_OPERAND (*x, 0) = new_var;
746 TREE_OPERAND (ass_stmt, 0) = new_var;
748 bb = bb_for_stmt (stmt);
749 tree_block_label (bb);
750 bsi = bsi_after_labels (bb);
751 bsi_insert_after (&bsi, ass_stmt, BSI_NEW_STMT);
753 mark_new_vars_to_rename (stmt, vars_to_rename);
756 /* Replaces immediate uses of VAR by REPL. */
759 replace_immediate_uses (tree var, tree repl)
763 v_may_def_optype v_may_defs;
770 df = get_immediate_uses (SSA_NAME_DEF_STMT (var));
771 n = num_immediate_uses (df);
773 for (i = 0; i < n; i++)
775 stmt = immediate_use (df, i);
776 ann = stmt_ann (stmt);
778 if (TREE_CODE (stmt) == PHI_NODE)
780 for (j = 0; j < PHI_NUM_ARGS (stmt); j++)
781 if (PHI_ARG_DEF (stmt, j) == var)
783 SET_PHI_ARG_DEF (stmt, j, repl);
784 if (TREE_CODE (repl) == SSA_NAME
785 && PHI_ARG_EDGE (stmt, j)->flags & EDGE_ABNORMAL)
786 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (repl) = 1;
792 get_stmt_operands (stmt);
793 mark_new_vars = false;
794 if (is_gimple_reg (SSA_NAME_VAR (var)))
796 if (TREE_CODE (stmt) == MODIFY_EXPR)
798 propagate_into_addr (stmt, var, &TREE_OPERAND (stmt, 0), repl);
799 propagate_into_addr (stmt, var, &TREE_OPERAND (stmt, 1), repl);
802 uses = USE_OPS (ann);
803 for (j = 0; j < (int) NUM_USES (uses); j++)
804 if (USE_OP (uses, j) == var)
806 propagate_value (USE_OP_PTR (uses, j), repl);
807 mark_new_vars = POINTER_TYPE_P (TREE_TYPE (repl));
812 vuses = VUSE_OPS (ann);
813 for (j = 0; j < (int) NUM_VUSES (vuses); j++)
814 if (VUSE_OP (vuses, j) == var)
815 propagate_value (VUSE_OP_PTR (vuses, j), repl);
817 v_may_defs = V_MAY_DEF_OPS (ann);
818 for (j = 0; j < (int) NUM_V_MAY_DEFS (v_may_defs); j++)
819 if (V_MAY_DEF_OP (v_may_defs, j) == var)
820 propagate_value (V_MAY_DEF_OP_PTR (v_may_defs, j), repl);
823 /* If REPL is a pointer, it may have different memory tags associated
824 with it. For instance, VAR may have had a name tag while REPL
825 only had a type tag. In these cases, the virtual operands (if
826 any) in the statement will refer to different symbols which need
829 mark_new_vars_to_rename (stmt, vars_to_rename);
835 /* Gets the value VAR is equivalent to according to EQ_TO. */
838 get_eq_name (tree *eq_to, tree var)
843 while (TREE_CODE (val) == SSA_NAME)
845 ver = SSA_NAME_VERSION (val);
852 while (TREE_CODE (var) == SSA_NAME)
854 ver = SSA_NAME_VERSION (var);
865 /* Checks whether phi node PHI is redundant and if it is, records the ssa name
866 its result is redundant to to EQ_TO array. */
869 check_phi_redundancy (tree phi, tree *eq_to)
871 tree val = NULL_TREE, def, res = PHI_RESULT (phi), stmt;
872 unsigned i, ver = SSA_NAME_VERSION (res), n;
875 /* It is unlikely that such large phi node would be redundant. */
876 if (PHI_NUM_ARGS (phi) > 16)
879 for (i = 0; i < (unsigned) PHI_NUM_ARGS (phi); i++)
881 def = PHI_ARG_DEF (phi, i);
883 if (TREE_CODE (def) == SSA_NAME)
885 def = get_eq_name (eq_to, def);
891 && !operand_equal_p (val, def, 0))
897 /* At least one of the arguments should not be equal to the result, or
898 something strange is happening. */
902 if (get_eq_name (eq_to, res) == val)
905 if (!may_propagate_copy (res, val))
910 df = get_immediate_uses (SSA_NAME_DEF_STMT (res));
911 n = num_immediate_uses (df);
913 for (i = 0; i < n; i++)
915 stmt = immediate_use (df, i);
917 if (TREE_CODE (stmt) == PHI_NODE)
918 check_phi_redundancy (stmt, eq_to);
922 /* Removes redundant phi nodes.
924 A redundant PHI node is a PHI node where all of its PHI arguments
925 are the same value, excluding any PHI arguments which are the same
928 A redundant PHI node is effectively a copy, so we forward copy propagate
929 which removes all uses of the destination of the PHI node then
930 finally we delete the redundant PHI node.
932 Note that if we can not copy propagate the PHI node, then the PHI
933 will not be removed. Thus we do not have to worry about dependencies
934 between PHIs and the problems serializing PHIs into copies creates.
936 The most important effect of this pass is to remove degenerate PHI
937 nodes created by removing unreachable code. */
940 kill_redundant_phi_nodes (void)
943 unsigned i, old_num_ssa_names;
945 tree phi, var, repl, stmt;
947 /* The EQ_TO[VER] holds the value by that the ssa name VER should be
948 replaced. If EQ_TO[VER] is ssa name and it is decided to replace it by
949 other value, it may be necessary to follow the chain till the final value.
950 We perform path shortening (replacing the entries of the EQ_TO array with
951 heads of these chains) whenever we access the field to prevent quadratic
952 complexity (probably would not occur in practice anyway, but let us play
954 eq_to = xcalloc (num_ssa_names, sizeof (tree));
956 /* We have had cases where computing immediate uses takes a
957 significant amount of compile time. If we run into such
958 problems here, we may want to only compute immediate uses for
959 a subset of all the SSA_NAMEs instead of computing it for
960 all of the SSA_NAMEs. */
961 compute_immediate_uses (TDFA_USE_OPS | TDFA_USE_VOPS, NULL);
962 old_num_ssa_names = num_ssa_names;
966 for (phi = phi_nodes (bb); phi; phi = TREE_CHAIN (phi))
968 var = PHI_RESULT (phi);
969 check_phi_redundancy (phi, eq_to);
973 /* Now propagate the values. */
974 for (i = 0; i < old_num_ssa_names; i++)
979 repl = get_eq_name (eq_to, ssa_name (i));
980 if (repl != ssa_name (i))
981 replace_immediate_uses (ssa_name (i), repl);
984 /* And remove the dead phis. */
985 for (i = 0; i < old_num_ssa_names; i++)
990 repl = get_eq_name (eq_to, ssa_name (i));
991 if (repl != ssa_name (i))
993 stmt = SSA_NAME_DEF_STMT (ssa_name (i));
994 remove_phi_node (stmt, NULL_TREE, bb_for_stmt (stmt));
1002 struct tree_opt_pass pass_redundant_phi =
1004 "redphi", /* name */
1006 kill_redundant_phi_nodes, /* execute */
1009 0, /* static_pass_number */
1011 PROP_cfg | PROP_ssa, /* properties_required */
1012 0, /* properties_provided */
1013 0, /* properties_destroyed */
1014 0, /* todo_flags_start */
1015 TODO_dump_func | TODO_rename_vars
1016 | TODO_ggc_collect | TODO_verify_ssa /* todo_flags_finish */
1019 /* Emit warnings for uninitialized variables. This is done in two passes.
1021 The first pass notices real uses of SSA names with default definitions.
1022 Such uses are unconditionally uninitialized, and we can be certain that
1023 such a use is a mistake. This pass is run before most optimizations,
1024 so that we catch as many as we can.
1026 The second pass follows PHI nodes to find uses that are potentially
1027 uninitialized. In this case we can't necessarily prove that the use
1028 is really uninitialized. This pass is run after most optimizations,
1029 so that we thread as many jumps and possible, and delete as much dead
1030 code as possible, in order to reduce false positives. We also look
1031 again for plain uninitialized variables, since optimization may have
1032 changed conditionally uninitialized to unconditionally uninitialized. */
1034 /* Emit a warning for T, an SSA_NAME, being uninitialized. The exact
1035 warning text is in MSGID and LOCUS may contain a location or be null. */
1038 warn_uninit (tree t, const char *msgid, location_t *locus)
1040 tree var = SSA_NAME_VAR (t);
1041 tree def = SSA_NAME_DEF_STMT (t);
1043 /* Default uses (indicated by an empty definition statement),
1044 are uninitialized. */
1045 if (!IS_EMPTY_STMT (def))
1048 /* Except for PARMs of course, which are always initialized. */
1049 if (TREE_CODE (var) == PARM_DECL)
1052 /* Hard register variables get their initial value from the ether. */
1053 if (DECL_HARD_REGISTER (var))
1056 /* TREE_NO_WARNING either means we already warned, or the front end
1057 wishes to suppress the warning. */
1058 if (TREE_NO_WARNING (var))
1062 locus = &DECL_SOURCE_LOCATION (var);
1063 warning (msgid, locus, var);
1064 TREE_NO_WARNING (var) = 1;
1067 /* Called via walk_tree, look for SSA_NAMEs that have empty definitions
1068 and warn about them. */
1071 warn_uninitialized_var (tree *tp, int *walk_subtrees, void *data)
1073 location_t *locus = data;
1076 /* We only do data flow with SSA_NAMEs, so that's all we can warn about. */
1077 if (TREE_CODE (t) == SSA_NAME)
1079 warn_uninit (t, "%H'%D' is used uninitialized in this function", locus);
1082 else if (DECL_P (t) || TYPE_P (t))
1088 /* Look for inputs to PHI that are SSA_NAMEs that have empty definitions
1089 and warn about them. */
1092 warn_uninitialized_phi (tree phi)
1094 int i, n = PHI_NUM_ARGS (phi);
1096 /* Don't look at memory tags. */
1097 if (!is_gimple_reg (PHI_RESULT (phi)))
1100 for (i = 0; i < n; ++i)
1102 tree op = PHI_ARG_DEF (phi, i);
1103 if (TREE_CODE (op) == SSA_NAME)
1104 warn_uninit (op, "%H'%D' may be used uninitialized in this function",
1110 execute_early_warn_uninitialized (void)
1112 block_stmt_iterator bsi;
1116 for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
1117 walk_tree (bsi_stmt_ptr (bsi), warn_uninitialized_var,
1118 EXPR_LOCUS (bsi_stmt (bsi)), NULL);
1122 execute_late_warn_uninitialized (void)
1127 /* Re-do the plain uninitialized variable check, as optimization may have
1128 straightened control flow. Do this first so that we don't accidentally
1129 get a "may be" warning when we'd have seen an "is" warning later. */
1130 execute_early_warn_uninitialized ();
1133 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
1134 warn_uninitialized_phi (phi);
1138 gate_warn_uninitialized (void)
1140 return warn_uninitialized != 0;
1143 struct tree_opt_pass pass_early_warn_uninitialized =
1146 gate_warn_uninitialized, /* gate */
1147 execute_early_warn_uninitialized, /* execute */
1150 0, /* static_pass_number */
1152 PROP_ssa, /* properties_required */
1153 0, /* properties_provided */
1154 0, /* properties_destroyed */
1155 0, /* todo_flags_start */
1156 0 /* todo_flags_finish */
1159 struct tree_opt_pass pass_late_warn_uninitialized =
1162 gate_warn_uninitialized, /* gate */
1163 execute_late_warn_uninitialized, /* execute */
1166 0, /* static_pass_number */
1168 PROP_ssa, /* properties_required */
1169 0, /* properties_provided */
1170 0, /* properties_destroyed */
1171 0, /* todo_flags_start */
1172 0 /* todo_flags_finish */