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c: Fix up pointer types to may_alias structures [PR114493]

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The following testcase ICEs in ipa-free-lang, because the
fld_incomplete_type_of
          gcc_assert (TYPE_CANONICAL (t2) != t2
                      && TYPE_CANONICAL (t2) == TYPE_CANONICAL (TREE_TYPE (t)));
assertion doesn't hold.
This is because t is a struct S * type which was created while struct S
was still incomplete and without the may_alias attribute (and TYPE_CANONICAL
of a pointer type is a type created with can_alias_all = false argument),
while later on on the struct definition may_alias attribute was used.
fld_incomplete_type_of then creates an incomplete distinct copy of the
structure (but with the original attributes) but pointers created for it
are because of the "may_alias" attribute TYPE_REF_CAN_ALIAS_ALL, including
their TYPE_CANONICAL, because while that is created with !can_alias_all
argument, we later set it because of the "may_alias" attribute on the
to_type.

This doesn't ICE with C++ since PR70512 fix because the C++ FE sets
TYPE_REF_CAN_ALIAS_ALL on all pointer types to the class type (and its
variants) when the may_alias is added.

The following patch does that in the C FE as well.

2024-06-06  Jakub Jelinek  <jakub@redhat.com>

	PR c/114493
	* c-decl.cc (c_fixup_may_alias): New function.
	(finish_struct): Call it if "may_alias" attribute is
	specified.

	* gcc.dg/pr114493-1.c: New test.
	* gcc.dg/pr114493-2.c: New test.

(cherry picked from commit d5a3c6d43acb8b2211d9fb59d59482d74c010f01)
This commit is contained in:
Jakub Jelinek 2024-06-06 22:12:11 +02:00
parent 35ed54f136
commit 56c73729c3
3 changed files with 60 additions and 0 deletions
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15
gcc/c/c-decl.cc
View file

@ -9393,6 +9393,17 @@ c_update_type_canonical (tree t)
}
}
/* TYPE is a struct or union that we're applying may_alias to after the body is
parsed. Fixup any POINTER_TO types. */
static void
c_fixup_may_alias (tree type)
{
for (tree t = TYPE_POINTER_TO (type); t; t = TYPE_NEXT_PTR_TO (t))
for (tree v = TYPE_MAIN_VARIANT (t); v; v = TYPE_NEXT_VARIANT (v))
TYPE_REF_CAN_ALIAS_ALL (v) = true;
}
/* Fill in the fields of a RECORD_TYPE or UNION_TYPE node, T.
LOC is the location of the RECORD_TYPE or UNION_TYPE's definition.
FIELDLIST is a chain of FIELD_DECL nodes for the fields.
@ -9737,6 +9748,10 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
C_TYPE_BEING_DEFINED (t) = 0;
if (lookup_attribute ("may_alias", TYPE_ATTRIBUTES (t)))
for (x = TYPE_MAIN_VARIANT (t); x; x = TYPE_NEXT_VARIANT (x))
c_fixup_may_alias (x);
/* Set type canonical based on equivalence class. */
if (flag_isoc23)
{

19
gcc/testsuite/gcc.dg/pr114493-1.c Normal file
View file

@ -0,0 +1,19 @@
/* PR c/114493 */
/* { dg-do compile { target lto } } */
/* { dg-options "-O2 -flto" } */
void foo (void);
struct S;
struct S bar (struct S **);
struct S qux (const struct S **);
struct __attribute__((__may_alias__)) S {
int s;
};
struct S
baz (void)
{
foo ();
return (struct S) {};
}

26
gcc/testsuite/gcc.dg/pr114493-2.c Normal file
View file

@ -0,0 +1,26 @@
/* PR c/114493 */
/* { dg-do compile { target lto } } */
/* { dg-options "-O2 -flto -std=c23" } */
void foo (void);
struct S;
struct S bar (struct S **);
struct S qux (const struct S **);
void
corge (void)
{
struct S { int s; } s;
s.s = 0;
}
struct __attribute__((__may_alias__)) S {
int s;
};
struct S
baz (void)
{
foo ();
return (struct S) {};
}