I want to think about this case for a bit. I'm wondering if the restriction here should be considered an ABI break. We do want to encourage the compiler to use even numbered register pairs as it can generate better code for both Arm state (using LDRD/STRD) and MVE; but I'm not sure we should require this for user assembly code.
-- https://forge.sourceware.org/gcc/gcc/pulls/217#issuecomment-7189
