[llvm] [DSE] Refactor DSE (PR #100956)

[Haopeng Liu via llvm-commits]

haopliu wrote:

> I mean in this PR `DefinedLocation` shouldn't be a `SmallVector`, just a `MemoryLocationWrapper`. The PR that introduces multiple MemoryLocations per MemoryDef should make that change instead.

Changed the `DefinedLocations (SmallVector)` field to `DefinedLocation (optional)`.

> I thought the code was originally in DSEState?

The major code was originally in `static bool eliminateDeadStores(...)`, this loop:
https://github.com/llvm/llvm-project/blob/main/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp#L2145

https://github.com/llvm/llvm-project/pull/100956