[llvm] InstCombine: Fix a crash in `PointerReplacer` when constructing a new PHI (PR #130256)

[Changpeng Fang via llvm-commits]

changpeng wrote:

> Why do we RAUW the load but not the store here? This might need to be done for the memcpy too, which looks dead by the time we insert it into the map.

My understanding is that it does not matter for memcpy and store because they are not used. We may possibly just do not insert them into the map. But need to additional research which is beyond this work.

https://github.com/llvm/llvm-project/pull/130256