[llvm] [clang] [InstCombine] Infer zext nneg flag (PR #71534)

[Nikita Popov via cfe-commits]

nikic wrote:

It looks like simplifyAssocCastAssoc() is the problematic transform. It modifies a zext in-place without clearing poison flags.

https://github.com/llvm/llvm-project/pull/71534