When we use the scalar ALU we will start inserting moves with different
API-level semantics from readInvocation() or readFirstInvocation(). We
need to distinguish between these moves and lowered readInvocation()
moves, to avoid unnecessarily keeping helper invocations alive when
inserting (eq).
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22075>