https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128215
Bug ID: 128215
Summary: Incorrect mangling of inactive union elemental
subobjects
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: jakub at gcc dot gnu.org
Target Milestone: ---
union U { int a[4]; };
constexpr U bar (int n) {
U u;
__builtin_start_lifetime (&u.a);
u.a[0] = 42;
for (int i = 1; i < n; ++i)
u.a[i] = 0;
return u;
}
template <auto V, int N>
int foo () { return N; }
int a = foo <bar (1), 42> ();
int b = foo <bar (3), 43> ();
int main () {}
We mangle both calls as
_Z3fooITnDaXtl1Udi1atlA4_iLi42EEEELi42EEiv
_Z3fooITnDaXtl1Udi1atlA4_iLi42EEEELi43EEiv
so the mangling doesn't differentiate between trailing zeros and inactive
elemental subobjects.
Given that changing the mangling of trailing zeros would be an ABI change, I
think we want instead to mangle inactive elemental subobjects somehow
specially.
