We were only checking for the previous insructions to write exactly
the register or a super register. We ignored writes to a subregister
and continued searching for the producing instruction. We need to
abort instead.
There's another check inside the if body to abort if the registers
don't match exactly. So we just need to check for overlap so we
enter the if body.
Reviewed By: fakepaper56
Differential Revision: https://reviews.llvm.org/D153490
b105b3266f