[llvm] [MergeICmps] Perform dereferenceability check with context (PR #202884)

[Antonio Frighetto via llvm-commits]

https://github.com/antoniofrighetto approved this pull request.

LGTM

> This is something we currently don't allow, but I think it's something we want to allow

Do we intend to refine the LangRef to allow allocation shrinking some time soon?

https://github.com/llvm/llvm-project/pull/202884