When the destination of both instructions is NULL and the conditional
modifier matches, operands_match (by way of instructions_match) will
only test the first two operands. This can result in bad CSE
happening.
This is a very, very narrow edge case.
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29848>
