https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98122
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jason at gcc dot gnu.org
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
--- gcc/cp/constexpr.c.jj 2020-12-03 15:43:00.491620290 +0100
+++ gcc/cp/constexpr.c 2020-12-04 13:02:06.874418746 +0100
@@ -4679,7 +4679,8 @@ cxx_fold_indirect_ref_1 (location_t loc,
}
}
/* ((foo *)&struct_with_foo_field)[x] => COMPONENT_REF */
- else if (TREE_CODE (optype) == RECORD_TYPE)
+ else if (TREE_CODE (optype) == RECORD_TYPE
+ || TREE_CODE (optype) == UNION_TYPE)
{
for (tree field = TYPE_FIELDS (optype);
field; field = DECL_CHAIN (field))
would fix this, but wonder if for unions we don't need to take into account the
currently active member.
In:
union U { int a; char b; };
constexpr bool
foo ()
{
U f { .b = 42 };
constexpr auto m = &U::a;
return (f.*m) == 42;
}
static_assert (foo (), "");
we even with the patch properly reject it:
pr98122-2.C:11:20: error: non-constant condition for static assertion
11 | static_assert (foo (), "");
| ~~~~^~
pr98122-2.C:11:20: in ‘constexpr’ expansion of ‘foo()’
pr98122-2.C:11:20: error: accessing ‘U::a’ member instead of initialized ‘U::b’
member in constant expression
But:
union U { int a; int b; };
constexpr bool
foo ()
{
U f { .b = 42 };
constexpr auto m = &U::b;
return (f.*m) == 42;
}
static_assert (foo (), "");
is rejected too and I think it should be accepted.
So I guess for UNION_TYPEs we need to first try the active member and only then
fall back to what the code would do after the above patch.
