Am Dienstag, dem 04.06.2024 um 08:33 +0200 schrieb Jakub Jelinek:
> Hi!
>
> 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.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk and
> release branches?
>From my (irrelevant) side this patch looks good.
Martin
>
> 2024-06-04 Jakub Jelinek <ja...@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.
>
> --- gcc/c/c-decl.cc.jj 2024-05-07 08:47:35.974836903 +0200
> +++ gcc/c/c-decl.cc 2024-06-03 19:55:53.819586291 +0200
> @@ -9446,6 +9446,17 @@ verify_counted_by_attribute (tree struct
> return;
> }
>
> +/* 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.
> @@ -9791,6 +9802,10 @@ finish_struct (location_t loc, tree t, t
>
> 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 && !C_TYPE_VARIABLE_SIZE (t))
> {
> --- gcc/testsuite/gcc.dg/pr114493-1.c.jj 2024-06-03 19:59:58.774336785
> +0200
> +++ gcc/testsuite/gcc.dg/pr114493-1.c 2024-06-03 19:59:12.931944923 +0200
> @@ -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) {};
> +}
> --- gcc/testsuite/gcc.dg/pr114493-2.c.jj 2024-06-03 19:59:58.774336785
> +0200
> +++ gcc/testsuite/gcc.dg/pr114493-2.c 2024-06-03 20:01:00.886512830 +0200
> @@ -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) {};
> +}
>
> Jakub
>
