Surprisingly, not all instructions are always simplified after unrolling and before MVE gather/scatter lowering. Notably dead gather operations can be left around which cause the gather/scatter lowering pass to crash after if there are multiple gathers, some of which are dead.
This can change some of the existing tests, including making them no-longer test what they originally tested. This uses a combination of disabling the gather/scatter lowering pass and adjusting the test to keep them as before.