1 /* Strict aliasing checks.
2 Copyright (C) 2007 Free Software Foundation, Inc.
3 Contributed by Silvius Rus <rus@google.com>.
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 2, or (at your option)
12 GCC is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING. If not, write to
19 the Free Software Foundation, 51 Franklin Street, Fifth Floor,
20 Boston, MA 02110-1301, USA. */
24 #include "coretypes.h"
26 #include "alloc-pool.h"
28 #include "tree-dump.h"
29 #include "tree-flow.h"
34 #include "diagnostic.h"
35 #include "tree-ssa-structalias.h"
36 #include "tree-ssa-propagate.h"
37 #include "langhooks.h"
39 /* Module to issue a warning when a program uses data through a type
40 different from the type through which the data were defined.
41 Implements -Wstrict-aliasing and -Wstrict-aliasing=n.
42 These checks only happen when -fstrict-aliasing is present.
44 The idea is to use the compiler to identify occurrences of nonstandard
45 aliasing, and report them to programmers. Programs free of such aliasing
46 are more portable, maintainable, and can usually be optimized better.
48 The current, as of April 2007, C and C++ language standards forbid
49 accessing data of type A through an lvalue of another type B,
50 with certain exceptions. See the C Standard ISO/IEC 9899:1999,
51 section 6.5, paragraph 7, and the C++ Standard ISO/IEC 14882:1998,
52 section 3.10, paragraph 15.
54 Example 1:*a is used as int but was defined as a float, *b.
56 float* b = reinterpret_cast<float*> (a);
60 Unfortunately, the problem is in general undecidable if we take into
61 account arithmetic expressions such as array indices or pointer arithmetic.
62 (It is at least as hard as Peano arithmetic decidability.)
63 Even ignoring arithmetic, the problem is still NP-hard, because it is
64 at least as hard as flow-insensitive may-alias analysis, which was proved
65 NP-hard by Horwitz et al, TOPLAS 1997.
67 It is clear that we need to choose some heuristics.
68 Unfortunately, various users have different goals which correspond to
69 different time budgets so a common approach will not suit all.
70 We present the user with three effort/accuracy levels. By accuracy, we mean
71 a common-sense mix of low count of false positives with a
72 reasonably low number of false negatives. We are heavily biased
73 towards a low count of false positives.
74 The effort (compilation time) is likely to increase with the level.
78 Most aggressive, least accurate. Possibly useful when higher levels
79 do not warn but -fstrict-aliasing still breaks the code, as
80 it has very few false negatives.
81 Warn for all bad pointer conversions, even if never dereferenced.
82 Implemented in the front end (c-common.c).
83 Uses alias_sets_might_conflict to compare types.
87 Aggressive, not too precise.
88 May still have many false positives (not as many as level 1 though),
89 and few false negatives (but possibly more than level 1).
90 Runs only in the front end. Uses alias_sets_might_conflict to
91 compare types. Does not check for pointer dereferences.
92 Only warns when an address is taken. Warns about incomplete type punning.
94 -Wstrict-aliasing=3 (default)
96 Should have very few false positives and few false negatives.
97 Takes care of the common punn+dereference pattern in the front end:
99 Takes care of multiple statement cases in the back end,
100 using flow-sensitive points-to information (-O required).
101 Uses alias_sets_conflict_p to compare types and only warns
102 when the converted pointer is dereferenced.
103 Does not warn about incomplete type punning.
105 Future improvements can be included by adding higher levels.
107 In summary, expression level analysis is performed in the front-end,
108 and multiple-statement analysis is performed in the backend.
109 The remainder of this discussion is only about the backend analysis.
111 This implementation uses flow-sensitive points-to information.
112 Flow-sensitivity refers to accesses to the pointer, and not the object
113 pointed. For instance, we do not warn about the following case.
116 int* a = (int*)malloc (...);
117 float* b = reinterpret_cast<float*> (a);
119 a = (int*)malloc (...);
122 In SSA, it becomes clear that the INT value *A_2 referenced in the
123 return statement is not aliased to the FLOAT defined through *B_1.
124 int* a_1 = (int*)malloc (...);
125 float* b_1 = reinterpret_cast<float*> (a_1);
127 a_2 = (int*)malloc (...);
134 ForEach (ptr, object) in the points-to table
135 If (incompatible_types (*ptr, object))
136 If (referenced (ptr, current function)
137 and referenced (object, current function))
138 Issue warning (ptr, object, reference locations)
141 O (sizeof (points-to table)
142 + sizeof (function body) * lookup_time (points-to table))
144 Pointer dereference locations are looked up on demand. The search is
145 a single scan of the function body, in which all references to pointers
146 and objects in the points-to table are recorded. However, this dominant
147 time factor occurs rarely, only when cross-type aliasing was detected.
150 Limitations of the Proposed Implementation
151 ==========================================
153 1. We do not catch the following case, because -fstrict-aliasing will
154 associate different tags with MEM while building points-to information,
155 thus before we get to analyze it.
156 XXX: this could be solved by either running with -fno-strict-aliasing
157 or by recording the points-to information before splitting the orignal
161 void* mem = malloc (...);
162 int* pi = reinterpret_cast<int*> (mem);
163 float* b = reinterpret_cast<float*> (mem);
167 2. We do not check whether the two conflicting (de)references can
168 reach each other in the control flow sense. If we fixed limitation
169 1, we would wrongly issue a warning in the following case.
172 void* raw = malloc (...);
174 float* b = reinterpret_cast<float*> (raw);
178 int* a = reinterpret_cast<int*> (raw);
182 3. Only simple types are compared, thus no structures, unions or classes
183 are analyzed. A first attempt to deal with structures introduced much
184 complication and has not showed much improvement in preliminary tests,
187 4. All analysis is intraprocedural. */
190 /* Local declarations. */
191 static void find_references_in_function (void);
195 /* Get main type of tree TYPE, stripping array dimensions and qualifiers. */
198 get_main_type (tree type)
200 while (TREE_CODE (type) == ARRAY_TYPE)
201 type = TREE_TYPE (type);
202 return TYPE_MAIN_VARIANT (type);
206 /* Get the type of the given object. If IS_PTR is true, get the type of the
207 object pointed to or referenced by OBJECT instead.
208 For arrays, return the element type. Ignore all qualifiers. */
211 get_otype (tree object, bool is_ptr)
213 tree otype = TREE_TYPE (object);
217 gcc_assert (POINTER_TYPE_P (otype));
218 otype = TREE_TYPE (otype);
220 return get_main_type (otype);
224 /* Return true if tree TYPE is struct, class or union. */
227 struct_class_union_p (tree type)
229 return (TREE_CODE (type) == RECORD_TYPE
230 || TREE_CODE (type) == UNION_TYPE
231 || TREE_CODE (type) == QUAL_UNION_TYPE);
236 /* Keep data during a search for an aliasing site.
237 RHS = object or pointer aliased. No LHS is specified because we are only
238 looking in the UseDef paths of a given variable, so LHS will always be
239 an SSA name of the same variable.
240 When IS_RHS_POINTER = true, we are looking for ... = RHS. Otherwise,
241 we are looking for ... = &RHS.
242 SITE is the output of a search, non-NULL if the search succeeded. */
252 /* Callback for find_alias_site. Return true if the right hand site
253 of STMT matches DATA. */
256 find_alias_site_helper (tree var ATTRIBUTE_UNUSED, tree stmt, void *data)
258 struct alias_match *match = (struct alias_match *) data;
259 tree rhs_pointer = get_rhs (stmt);
260 tree to_match = NULL_TREE;
262 while (TREE_CODE (rhs_pointer) == NOP_EXPR
263 || TREE_CODE (rhs_pointer) == CONVERT_EXPR
264 || TREE_CODE (rhs_pointer) == VIEW_CONVERT_EXPR)
265 rhs_pointer = TREE_OPERAND (rhs_pointer, 0);
268 /* Not a type conversion. */
271 if (TREE_CODE (rhs_pointer) == ADDR_EXPR && !match->is_rhs_pointer)
272 to_match = TREE_OPERAND (rhs_pointer, 0);
273 else if (POINTER_TYPE_P (rhs_pointer) && match->is_rhs_pointer)
274 to_match = rhs_pointer;
276 if (to_match != match->rhs)
277 /* Type conversion, but not a name match. */
286 /* Find the statement where OBJECT1 gets aliased to OBJECT2.
287 If IS_PTR2 is true, consider OBJECT2 to be the name of a pointer or
288 reference rather than the actual aliased object.
289 For now, just implement the case where OBJECT1 is an SSA name defined
290 by a PHI statement. */
293 find_alias_site (tree object1, bool is_ptr1 ATTRIBUTE_UNUSED,
294 tree object2, bool is_ptr2)
296 struct alias_match match;
299 match.is_rhs_pointer = is_ptr2;
300 match.site = NULL_TREE;
302 if (TREE_CODE (object1) != SSA_NAME)
305 walk_use_def_chains (object1, find_alias_site_helper, &match, false);
310 /* Structure to store temporary results when trying to figure out whether
311 an object is referenced. Just its presence in the text is not enough,
312 as we may just be taking its address. */
318 /* The difference between the number of references to OBJECT
319 and the number of occurences of &OBJECT. */
324 /* Return the base if EXPR is an SSA name. Return EXPR otherwise. */
327 get_ssa_base (tree expr)
329 if (TREE_CODE (expr) == SSA_NAME)
330 return SSA_NAME_VAR (expr);
336 /* Record references to objects and pointer dereferences across some piece of
337 code. The number of references is recorded for each item.
338 References to an object just to take its address are not counted.
339 For instance, if PTR is a pointer and OBJ is an object:
340 1. Expression &obj + *ptr will have the following reference match structure:
343 OBJ does not appear as referenced because we just take its address.
344 2. Expression ptr + *ptr will have the following reference match structure:
347 PTR shows up twice as an object, but is dereferenced only once.
349 The elements of the hash tables are tree_map objects. */
350 struct reference_matches
357 /* Return the match, if any. Otherwise, return NULL_TREE. It will
358 return NULL_TREE even when a match was found, if the value associated
359 to KEY is NULL_TREE. */
362 match (htab_t ref_map, tree key)
364 struct tree_map to_find;
365 struct tree_map *found;
369 to_find.hash = htab_hash_pointer (key);
370 slot = htab_find_slot (ref_map, &to_find, NO_INSERT);
375 found = (struct tree_map *) *slot;
380 /* Set the entry corresponding to KEY, but only if the entry
381 already exists and its value is NULL_TREE. Otherwise, do nothing. */
384 maybe_add_match (htab_t ref_map, struct tree_map *key)
386 struct tree_map *found = htab_find (ref_map, key);
388 if (found && !found->to)
393 /* Add an entry to HT, with key T and value NULL_TREE. */
396 add_key (htab_t ht, tree t, alloc_pool references_pool)
399 struct tree_map *tp = pool_alloc (references_pool);
403 tp->hash = htab_hash_pointer(tp->from);
405 slot = htab_find_slot (ht, tp, INSERT);
410 /* Some memory to keep the objects in the reference table. */
412 static alloc_pool ref_table_alloc_pool = NULL;
415 /* Get some memory to keep the objects in the reference table. */
417 static inline alloc_pool
418 reference_table_alloc_pool (bool build)
420 if (ref_table_alloc_pool || !build)
421 return ref_table_alloc_pool;
423 ref_table_alloc_pool =
424 create_alloc_pool ("ref_table_alloc_pool", sizeof (struct tree_map), 20);
426 return ref_table_alloc_pool;
430 /* Initialize the reference table by adding all pointers in the points-to
431 table as keys, and NULL_TREE as associated values. */
433 static struct reference_matches *
434 build_reference_table (void)
437 struct reference_matches *ref_table = NULL;
438 alloc_pool references_pool = reference_table_alloc_pool (true);
440 ref_table = XNEW (struct reference_matches);
441 ref_table->objs = htab_create (10, tree_map_hash, tree_map_eq, NULL);
442 ref_table->ptrs = htab_create (10, tree_map_hash, tree_map_eq, NULL);
444 for (i = 1; i < num_ssa_names; i++)
446 tree ptr = ssa_name (i);
447 struct ptr_info_def *pi;
449 if (ptr == NULL_TREE)
452 pi = SSA_NAME_PTR_INFO (ptr);
454 if (!SSA_NAME_IN_FREE_LIST (ptr) && pi && pi->name_mem_tag)
456 /* Add pointer to the interesting dereference list. */
457 add_key (ref_table->ptrs, ptr, references_pool);
459 /* Add all aliased names to the interesting reference list. */
465 EXECUTE_IF_SET_IN_BITMAP (pi->pt_vars, 0, ix, bi)
467 tree alias = referenced_var (ix);
468 add_key (ref_table->objs, alias, references_pool);
478 /* Reference table. */
480 static struct reference_matches *ref_table = NULL;
483 /* Clean up the reference table if allocated. */
486 maybe_free_reference_table (void)
490 htab_delete (ref_table->ptrs);
491 htab_delete (ref_table->objs);
496 if (ref_table_alloc_pool)
498 free_alloc_pool (ref_table_alloc_pool);
499 ref_table_alloc_pool = NULL;
504 /* Get the reference table. Initialize it if needed. */
506 static inline struct reference_matches *
507 reference_table (bool build)
509 if (ref_table || !build)
512 ref_table = build_reference_table ();
513 find_references_in_function ();
518 /* Callback for find_references_in_function.
519 Check whether *TP is an object reference or pointer dereference for the
520 variables given in ((struct match_info*)DATA)->OBJS or
521 ((struct match_info*)DATA)->PTRS. The total number of references
522 is stored in the same structures. */
525 find_references_in_tree_helper (tree *tp,
526 int *walk_subtrees ATTRIBUTE_UNUSED,
529 struct tree_map match;
530 static int parent_tree_code = ERROR_MARK;
532 /* Do not report references just for the purpose of taking an address.
533 XXX: we rely on the fact that the tree walk is in preorder
534 and that ADDR_EXPR is not a leaf, thus cannot be carried over across
536 if (parent_tree_code == ADDR_EXPR)
539 match.to = (tree) data;
541 if (TREE_CODE (*tp) == INDIRECT_REF)
543 match.from = TREE_OPERAND (*tp, 0);
544 match.hash = htab_hash_pointer (match.from);
545 maybe_add_match (reference_table (true)->ptrs, &match);
550 match.hash = htab_hash_pointer (match.from);
551 maybe_add_match (reference_table (true)->objs, &match);
555 parent_tree_code = TREE_CODE (*tp);
560 /* Find all the references to aliased variables in the current function. */
563 find_references_in_function (void)
566 block_stmt_iterator i;
569 for (i = bsi_start (bb); !bsi_end_p (i); bsi_next (&i))
570 walk_tree (bsi_stmt_ptr (i), find_references_in_tree_helper,
571 (void *) *bsi_stmt_ptr (i), NULL);
575 /* Find the reference site for OBJECT.
576 If IS_PTR is true, look for derferences of OBJECT instead.
577 XXX: only the first site is returned in the current
578 implementation. If there are no matching sites, return NULL_TREE. */
581 reference_site (tree object, bool is_ptr)
584 return match (reference_table (true)->ptrs, object);
586 return match (reference_table (true)->objs, object);
590 /* Try to get more location info when something is missing.
591 OBJECT1 and OBJECT2 are aliased names. If IS_PTR1 or IS_PTR2, the alias
592 is on the memory referenced or pointed to by OBJECT1 and OBJECT2.
593 ALIAS_SITE, DEREF_SITE1 and DEREF_SITE2 are the statements where the
594 alias takes place (some pointer assignment usually) and where the
595 alias is referenced through OBJECT1 and OBJECT2 respectively.
596 REF_TYPE1 and REF_TYPE2 will return the type of the reference at the
597 respective sites. Only the first matching reference is returned for
598 each name. If no statement is found, the function header is returned. */
601 maybe_find_missing_stmts (tree object1, bool is_ptr1,
602 tree object2, bool is_ptr2,
607 if (object1 && object2)
609 if (!*alias_site || !EXPR_HAS_LOCATION (*alias_site))
610 *alias_site = find_alias_site (object1, is_ptr1, object2, is_ptr2);
612 if (!*deref_site1 || !EXPR_HAS_LOCATION (*deref_site1))
613 *deref_site1 = reference_site (object1, is_ptr1);
615 if (!*deref_site2 || !EXPR_HAS_LOCATION (*deref_site2))
616 *deref_site2 = reference_site (object2, is_ptr2);
619 /* If we could not find the alias site, set it to one of the dereference
620 sites, if available. */
624 *alias_site = *deref_site1;
625 else if (*deref_site2)
626 *alias_site = *deref_site2;
629 /* If we could not find the dereference sites, set them to the alias site,
631 if (!*deref_site1 && *alias_site)
632 *deref_site1 = *alias_site;
633 if (!*deref_site2 && *alias_site)
634 *deref_site2 = *alias_site;
638 /* Callback for find_first_artificial_name.
639 Find out if there are no artificial names at tree node *T. */
642 ffan_walker (tree *t,
643 int *go_below ATTRIBUTE_UNUSED,
644 void *data ATTRIBUTE_UNUSED)
646 if (TREE_CODE (*t) == VAR_DECL || TREE_CODE (*t) == PARM_DECL)
647 if (DECL_ARTIFICIAL (*t))
653 /* Return the first artificial name within EXPR, or NULL_TREE if
657 find_first_artificial_name (tree expr)
659 return walk_tree_without_duplicates (&expr, ffan_walker, NULL);
663 /* Get a name from the original program for VAR. */
666 get_var_name (tree var)
668 if (TREE_CODE (var) == SSA_NAME)
669 return get_var_name (get_ssa_base (var));
671 if (find_first_artificial_name (var))
674 if (TREE_CODE (var) == VAR_DECL || TREE_CODE (var) == PARM_DECL)
676 return IDENTIFIER_POINTER (DECL_NAME (var));
682 /* Return true if VAR contains an artificial name. */
685 contains_artificial_name_p (tree var)
687 if (TREE_CODE (var) == SSA_NAME)
688 return contains_artificial_name_p (get_ssa_base (var));
690 return find_first_artificial_name (var) != NULL_TREE;
694 /* Return "*" if OBJECT is not the actual alias but a pointer to it, or
696 IS_PTR is true when OBJECT is not the actual alias.
697 In addition to checking IS_PTR, we also make sure that OBJECT is a pointer
698 since IS_PTR would also be true for C++ references, but we should only
699 print a * before a pointer and not before a reference. */
702 get_maybe_star_prefix (tree object, bool is_ptr)
706 && TREE_CODE (TREE_TYPE (object)) == POINTER_TYPE) ? "*" : "";
710 /* Callback for contains_node_type_p.
711 Returns true if *T has tree code *(int*)DATA. */
714 contains_node_type_p_callback (tree *t,
715 int *go_below ATTRIBUTE_UNUSED,
718 return ((int) TREE_CODE (*t) == *((int *) data)) ? *t : NULL_TREE;
722 /* Return true if T contains a node with tree code TYPE. */
725 contains_node_type_p (tree t, int type)
727 return (walk_tree_without_duplicates (&t, contains_node_type_p_callback,
733 /* Return true if a warning was issued in the front end at STMT. */
736 already_warned_in_frontend_p (tree stmt)
740 if (stmt == NULL_TREE)
743 rhs_pointer = get_rhs (stmt);
745 if ((TREE_CODE (rhs_pointer) == NOP_EXPR
746 || TREE_CODE (rhs_pointer) == CONVERT_EXPR
747 || TREE_CODE (rhs_pointer) == VIEW_CONVERT_EXPR)
748 && TREE_NO_WARNING (rhs_pointer))
755 /* Return true if and only if TYPE is a function or method pointer type,
756 or pointer to a pointer to ... to a function or method. */
759 is_method_pointer (tree type)
761 while (TREE_CODE (type) == POINTER_TYPE)
762 type = TREE_TYPE (type);
763 return TREE_CODE (type) == METHOD_TYPE || TREE_CODE (type) == FUNCTION_TYPE;
767 /* Issue a -Wstrict-aliasing warning.
768 OBJECT1 and OBJECT2 are aliased names.
769 If IS_PTR1 and/or IS_PTR2 is true, then the corresponding name
770 OBJECT1/OBJECT2 is a pointer or reference to the aliased memory,
771 rather than actual storage.
772 ALIAS_SITE is a statement where the alias took place. In the most common
773 case, that is where a pointer was assigned to the address of an object. */
776 strict_aliasing_warn (tree alias_site,
777 tree object1, bool is_ptr1,
778 tree object2, bool is_ptr2,
779 bool filter_artificials)
781 tree ref_site1 = NULL_TREE;
782 tree ref_site2 = NULL_TREE;
785 location_t alias_loc;
788 gcc_assert (object1);
789 gcc_assert (object2);
791 if (contains_artificial_name_p (object1)
792 || contains_artificial_name_p (object2))
795 name1 = get_var_name (object1);
796 name2 = get_var_name (object2);
798 if (is_method_pointer (get_main_type (TREE_TYPE (object2))))
801 maybe_find_missing_stmts (object1, is_ptr1, object2, is_ptr2, &alias_site,
802 &ref_site1, &ref_site2);
807 if (EXPR_HAS_LOCATION (alias_site))
808 alias_loc = EXPR_LOCATION (alias_site);
812 if (EXPR_HAS_LOCATION (ref_site1))
813 ref1_loc = EXPR_LOCATION (ref_site1);
815 ref1_loc = alias_loc;
817 if (EXPR_HAS_LOCATION (ref_site2))
818 ref2_loc = EXPR_LOCATION (ref_site2);
820 ref2_loc = alias_loc;
822 if (already_warned_in_frontend_p (alias_site))
825 /* If they are not SSA names, but contain SSA names, drop the warning
826 because it cannot be displayed well.
827 Also drop it if they both contain artificials.
828 XXX: this is a hack, must figure out a better way to display them. */
829 if (filter_artificials)
830 if ((find_first_artificial_name (get_ssa_base (object1))
831 && find_first_artificial_name (get_ssa_base (object2)))
832 || (TREE_CODE (object1) != SSA_NAME
833 && contains_node_type_p (object1, SSA_NAME))
834 || (TREE_CODE (object2) != SSA_NAME
835 && contains_node_type_p (object2, SSA_NAME)))
838 /* XXX: In the following format string, %s:%d should be replaced by %H.
839 However, in my tests only the first %H printed ok, while the
840 second and third were printed as blanks. */
841 warning (OPT_Wstrict_aliasing,
842 "%Hlikely type-punning may break strict-aliasing rules: "
843 "object %<%s%s%> of main type %qT is referenced at or around "
845 "aliased to object %<%s%s%> of main type %qT which is referenced "
846 "at or around %s:%d.",
848 get_maybe_star_prefix (object1, is_ptr1),
849 name1, get_otype (object1, is_ptr1),
850 LOCATION_FILE (ref1_loc), LOCATION_LINE (ref1_loc),
851 get_maybe_star_prefix (object2, is_ptr2),
852 name2, get_otype (object2, is_ptr2),
853 LOCATION_FILE (ref2_loc), LOCATION_LINE (ref2_loc));
860 /* Return true when any objects of TYPE1 and TYPE2 respectively
861 may not be aliased according to the language standard. */
864 nonstandard_alias_types_p (tree type1, tree type2)
869 if (VOID_TYPE_P (type1) || VOID_TYPE_P (type2))
872 set1 = get_alias_set (type1);
873 set2 = get_alias_set (type2);
874 return !alias_sets_conflict_p (set1, set2);
879 /* Returns true if the given name is a struct field tag (SFT). */
882 struct_field_tag_p (tree var)
884 return TREE_CODE (var) == STRUCT_FIELD_TAG;
888 /* Returns true when *PTR may not be aliased to ALIAS.
889 See C standard 6.5p7 and C++ standard 3.10p15.
890 If PTR_PTR is true, ALIAS represents a pointer or reference to the
891 aliased storage rather than its actual name. */
894 nonstandard_alias_p (tree ptr, tree alias, bool ptr_ptr)
896 /* Find the types to compare. */
897 tree ptr_type = get_otype (ptr, true);
898 tree alias_type = get_otype (alias, ptr_ptr);
900 /* XXX: for now, say it's OK if the alias escapes.
901 Not sure this is needed in general, but otherwise GCC will not
903 if (var_ann (get_ssa_base (alias))->escape_mask != NO_ESCAPE)
906 /* XXX: don't get into structures for now. It brings much complication
907 and little benefit. */
908 if (struct_class_union_p (ptr_type) || struct_class_union_p (alias_type))
911 /* XXX: In 4.2.1, field resolution in alias is not as good as in pre-4.3
912 This fixes problems found during the backport, where a pointer to the
913 first field of a struct appears to be aliased to the whole struct. */
914 if (struct_field_tag_p (alias))
917 /* If they are both SSA names of artificials, let it go, the warning
919 if (find_first_artificial_name (ptr) && find_first_artificial_name (alias))
922 /* Compare the types. */
923 return nonstandard_alias_types_p (ptr_type, alias_type);
927 /* Return true when we should skip analysis for pointer PTR based on the
928 fact that their alias information *PI is not considered relevant. */
931 skip_this_pointer (tree ptr ATTRIBUTE_UNUSED, struct ptr_info_def *pi)
933 /* If it is not dereferenced, it is not a problem (locally). */
934 if (!pi->is_dereferenced)
937 /* This would probably cause too many false positives. */
938 if (pi->value_escapes_p || pi->pt_anything)
945 /* Find aliasing to named objects for pointer PTR. */
948 dsa_named_for (tree ptr)
950 struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr);
954 if (skip_this_pointer (ptr, pi))
957 /* For all the variables it could be aliased to. */
963 EXECUTE_IF_SET_IN_BITMAP (pi->pt_vars, 0, ix, bi)
965 tree alias = referenced_var (ix);
967 if (is_global_var (alias))
970 if (nonstandard_alias_p (ptr, alias, false))
971 strict_aliasing_warn (SSA_NAME_DEF_STMT (ptr),
972 ptr, true, alias, false, true);
979 /* Detect and report strict aliasing violation of named objects. */
982 detect_strict_aliasing_named (void)
986 for (i = 1; i < num_ssa_names; i++)
988 tree ptr = ssa_name (i);
989 struct ptr_info_def *pi;
991 if (ptr == NULL_TREE)
994 pi = SSA_NAME_PTR_INFO (ptr);
996 if (!SSA_NAME_IN_FREE_LIST (ptr) && pi && pi->name_mem_tag)
1002 /* Return false only the first time I see each instance of FUNC. */
1005 processed_func_p (tree func)
1007 static htab_t seen = NULL;
1011 seen = htab_create (100, htab_hash_pointer, htab_eq_pointer, NULL);
1013 slot = htab_find_slot (seen, func, INSERT);
1024 /* Detect and warn about type-punning using points-to information. */
1027 strict_aliasing_warning_backend (void)
1029 if (!(flag_strict_aliasing
1030 && warn_strict_aliasing == 3
1031 && !processed_func_p (current_function_decl)))
1034 detect_strict_aliasing_named ();
1035 maybe_free_reference_table ();