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re PR middle-end/36369 (may_alias broken with previous uses of non attributed type in some cases)

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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.

	* gcc.dg/Wstrict-aliasing-bogus-ref-all.c: New testcase.

From-SVN: r137843
This commit is contained in:
Richard Guenther 2008-07-15 15:07:46 +00:00 • committed by Richard Biener
parent 96c72efecd
commit ac7ee6adbe
6 changed files with 87 additions and 10 deletions
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11
gcc/ChangeLog
View file

@ -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

13
gcc/c-common.c
View file

@ -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. */

14
gcc/doc/extend.texi
View file

@ -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:

5
gcc/testsuite/ChangeLog
View file

@ -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

41
gcc/testsuite/gcc.dg/Wstrict-aliasing-bogus-ref-all.c Normal file
View file

@ -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;
}

13
gcc/tree.c
View file

@ -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