[llvm] [InstCombine] Fold fcmp ogt (x - y), 0 into fcmp ogt x, y #85245 (PR #85506)

[Matt Arsenault via llvm-commits]

arsenm wrote:

LGTM with some nits, also has some conflicts. Should be converted to a not-draft PR 

https://github.com/llvm/llvm-project/pull/85506