This intrinsic only accepted proper machine vector lengths.
Fixed by this change. With unit tests.
One minor addition, this change is now tested for X86, but I thought it wouldn't do any harm to test this for ARM too. If you can and want to touch the ARM backend test, I wouldn't mind if you e.g. add test @create_mask7 to llvm/test/CodeGen/Thumb2/active_lane_mask.ll, otherwise I will just add that once this lands.
Thanks. No problem, I will add the Thumb test in a follow up CL right after this submits (just to spread the risk of breakage).
It will be a good exercise for me to branch out of X86 :-)