[llvm] [InstCombine] Avoid rewriting multi-use post-inc latch icmps (preserve nsw/nuw for later passes) (PR #215960)

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yasmincs wrote:

> This also contains Instcombine and SCEV changes; they should be submitted separately for review

Thank you for the feedback! I have opened separate PRs #215990 and #215989 for the SCEV and InstCombine changes respectively. The SCEV changes are mainly motivated by the InstCombine changes so if it is decided that the InstCombine change is not the best way to fix the dropping of wrap flags, it may not make sense to proceed with the SCEV changes, even though they strengthen SCEV analysis. I will close this PR since the other two contain all of the changes.

https://github.com/llvm/llvm-project/pull/215960