macro_rules! test_impl {
    ($fun:ident ($($v:ident : $ty:ty),*) -> $r:ty [$call:ident, $instr:ident]) => { ... };
    ($fun:ident ($($v:ident : $ty:ty),*) -> $r:ty [$call:ident, $instr_altivec:ident / $instr_vsx:ident]) => { ... };
}
🔬This is a nightly-only experimental API. (stdsimd #48556)
Available on PowerPC or PowerPC-64 only.