Optimize MakeRegionBranchOpSuccessorInputsDead patterns in
`ControlFlowInterfaces.cpp`:
- Add early exit to `computeReachableValuesFromSuccessorInput` when the
caller only needs to know if there is exactly one reachable value,
avoiding unnecessary traversal.
Assisted-by: Claude Code
Co-authored-by: Yang Bai <yangb@nvidia.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>