This works around issue packing 32-bit scalar swizzles zero-extended to
64-bit, seen with the umul_high implementation. I tried for a while
figuring out the root cause (even rewrote a big chunk of disassembler)
but am still a bit lost. Nevertheless this is a safe workaround with no
performance impact (and avoids relying on NIR undefined behaviour to
implement GPU undefined behaviour), so let's do this for now to fix
umul_high.
Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17860>
7b78e05ba8