In `rescheduleKillAboveMI`, current implementation uses `SmallSet` to track reg's defs and uses. When comparing, use `SmallSet.count` to find out if it's clobbered or used. It's not correct if involving subregisters. This patch uses `regOverlapsSet` already used by `rescheduleMIBelowKill` to fix the issue.
Fixed https://bugs.llvm.org/show_bug.cgi?id=47707.
Reviewed By: #powerpc, nemanjai
Differential Revision: https://reviews.llvm.org/D88716
Kai Luo