[llvm] [Instcombine] Write Instcombine pass to strength reduce lock xadd to lock sub (PR #184715)

[Nikita Popov via llvm-commits]

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

LGTM

I guess to use the negator we need to use it only for the sub case...

https://github.com/llvm/llvm-project/pull/184715