[llvm] [MoveAutoInit] Fix for miscompilation for #150120 (PR #173961)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw commented:

<img width="1664" height="1800" alt="image" src="https://github.com/user-attachments/assets/2bb21658-8540-4a73-b6ee-6feb622975a2" />

`UsersDominator` for the store is `lbl_629`.
IIRC `lbl_629` was excluded during the LCA computation since it belongs to the cycle.
Then `DominatingPredecessor` was set to `if.then` and the miscompilation happens.


https://github.com/llvm/llvm-project/pull/173961