[llvm] InstSimplify: support floating-point equivalences (PR #115152)

[Nikita Popov via llvm-commits]

nikic wrote:

I was wondering why this gets folded at all, given that this is the AllowRefinement case. I think the reason is this code: https://github.com/llvm/llvm-project/blob/76f258920d3baf32be297f60bee5b8520f195c25/llvm/lib/Analysis/InstructionSimplify.cpp#L4347-L4352

We assume that folding `x op id` to `x` is non-refining, which is not strictly true for FP.

https://github.com/llvm/llvm-project/pull/115152