[llvm] [IR] Add `samesign` flag to icmp instruction (PR #111419)

[Yingwei Zheng via llvm-commits]

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

LGTM. Please wait for additional approval from other reviewers.

BTW, I believe we will encounter some miscompilation bugs as we don't drop poison-generating flags for `icmp` properly in some places. Please give me more time to do some testing before leveraging this flag to do more optimizations.


https://github.com/llvm/llvm-project/pull/111419