diff options
| -rw-r--r-- | gcc/ChangeLog | 11 | ||||
| -rw-r--r-- | gcc/c-common.c | 13 | ||||
| -rw-r--r-- | gcc/doc/extend.texi | 14 | ||||
| -rw-r--r-- | gcc/testsuite/ChangeLog | 5 | ||||
| -rw-r--r-- | gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-ref-all.c | 41 | ||||
| -rw-r--r-- | gcc/tree.c | 13 |
6 files changed, 87 insertions, 10 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog index b4df1d50e8c..7ea39a7e316 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,14 @@ +2008-07-15 Richard Guenther <rguenther@suse.de> + + PR middle-end/36369 + * c-common.c (strict_aliasing_warning): Do not warn for + TYPE_REF_CAN_ALIAS_ALL pointers. + (c_common_get_alias_set): may_alias types are not special. + * tree.c (build_pointer_type_for_mode): Look up the may_alias + attribute and set can_ref_all accordingly. + (build_reference_type_for_mode): Likewise. + * doc/extend.texi (may_alias): Clarify. + 2008-07-15 Kaz Kojima <kkojima@gcc.gnu.org> PR target/36780 diff --git a/gcc/c-common.c b/gcc/c-common.c index 1af2120f84b..e93d2fba6df 100644 --- a/gcc/c-common.c +++ b/gcc/c-common.c @@ -1242,8 +1242,13 @@ warn_logical_operator (enum tree_code code, tree arg1, tree bool strict_aliasing_warning (tree otype, tree type, tree expr) { - if (!(flag_strict_aliasing && POINTER_TYPE_P (type) - && POINTER_TYPE_P (otype) && !VOID_TYPE_P (TREE_TYPE (type)))) + if (!(flag_strict_aliasing + && POINTER_TYPE_P (type) + && POINTER_TYPE_P (otype) + && !VOID_TYPE_P (TREE_TYPE (type))) + /* If the type we are casting to is a ref-all pointer + dereferencing it is always valid. */ + || TYPE_REF_CAN_ALIAS_ALL (type)) return false; if ((warn_strict_aliasing > 1) && TREE_CODE (expr) == ADDR_EXPR @@ -3464,10 +3469,6 @@ c_common_get_alias_set (tree t) || t == unsigned_char_type_node) return 0; - /* If it has the may_alias attribute, it can alias anything. */ - if (lookup_attribute ("may_alias", TYPE_ATTRIBUTES (t))) - return 0; - /* The C standard specifically allows aliasing between signed and unsigned variants of the same type. We treat the signed variant as canonical. */ diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index eecb4ca5bf4..4a4c9a3a4a1 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -4240,10 +4240,16 @@ The @code{deprecated} attribute can also be used for functions and variables (@pxref{Function Attributes}, @pxref{Variable Attributes}.) @item may_alias -Accesses to objects with types with this attribute are not subjected to -type-based alias analysis, but are instead assumed to be able to alias -any other type of objects, just like the @code{char} type. See -@option{-fstrict-aliasing} for more information on aliasing issues. +Accesses through pointers to types with this attribute are not subject +to type-based alias analysis, but are instead assumed to be able to alias +any other type of objects. In the context of 6.5/7 an lvalue expression +dereferencing such a pointer is treated like having a character type. +See @option{-fstrict-aliasing} for more information on aliasing issues. +This extension exists to support some vector APIs, in which pointers to +one vector type are permitted to alias pointers to a different vector type. + +Note that an object of a type with this attribute does not have any +special semantics. Example of use: diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index 4526d9fcb83..33d94fceaec 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,8 @@ +2008-07-15 Richard Guenther <rguenther@suse.de> + + PR middle-end/36369 + * gcc.dg/Wstrict-aliasing-bogus-ref-all.c: New testcase. + 2008-07-15 Andrew Pinski <andrew_pinski@playstation.sony.com> PR target/31568 diff --git a/gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-ref-all.c b/gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-ref-all.c new file mode 100644 index 00000000000..7e8d1771568 --- /dev/null +++ b/gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-ref-all.c @@ -0,0 +1,41 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -Wall" } */ + +struct g { long a; }; +unsigned long f(struct g *a) { return *(unsigned long *)&a->a; } + +struct A +{ + void *a; +}; + +int g(const struct A *x, long *y) +{ + typedef long __attribute__ ((may_alias)) long_a; + *y = *(const long_a *) (&x->a); + return 1; +} + +void *a; + +int +f0 (long *y) +{ + *y = *(const long *) &a; /* { dg-warning "will break" } */ + return 1; +} + +int +f1 (long *y) +{ + typedef long __attribute__ ((may_alias)) long_a; + *y = *(const long_a *) &a; + return 1; +} + +int +f2 (long *y) +{ + *y = *(const long *) &a; /* { dg-warning "will break" } */ + return 1; +} diff --git a/gcc/tree.c b/gcc/tree.c index 0bb9fd9367f..6441ae6ef33 100644 --- a/gcc/tree.c +++ b/gcc/tree.c @@ -5499,6 +5499,11 @@ build_pointer_type_for_mode (tree to_type, enum machine_mode mode, if (to_type == error_mark_node) return error_mark_node; + /* If the pointed-to type has the may_alias attribute set, force + a TYPE_REF_CAN_ALIAS_ALL pointer to be generated. */ + if (lookup_attribute ("may_alias", TYPE_ATTRIBUTES (to_type))) + can_alias_all = true; + /* In some cases, languages will have things that aren't a POINTER_TYPE (such as a RECORD_TYPE for fat pointers in Ada) as TYPE_POINTER_TO. In that case, return that type without regard to the rest of our @@ -5555,6 +5560,14 @@ build_reference_type_for_mode (tree to_type, enum machine_mode mode, { tree t; + if (to_type == error_mark_node) + return error_mark_node; + + /* If the pointed-to type has the may_alias attribute set, force + a TYPE_REF_CAN_ALIAS_ALL pointer to be generated. */ + if (lookup_attribute ("may_alias", TYPE_ATTRIBUTES (to_type))) + can_alias_all = true; + /* In some cases, languages will have things that aren't a REFERENCE_TYPE (such as a RECORD_TYPE for fat pointers in Ada) as TYPE_REFERENCE_TO. In that case, return that type without regard to the rest of our |