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?
2024-06-04 Jakub Jelinek <[email protected]>
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
