[llvm] [ValueTracking] Compute KnownFP state from recursive select/phi. (PR #113686)

[David Green via llvm-commits]

davemgreen wrote:

> As far as the regression on https://github.com/llvm/llvm-project/pull/83200 is concerned, I think it needs a local flag handling fix

Yeah there are probably a few ways to fix it, selects are often missing fmfs due to them coming from control flow.  This seemed generally useful.

> Needs a more targeted, dedicated test

I've tried to add some Attributor tests, which I see have been used to test similar patches in the past. Let me know if there is a better way.

https://github.com/llvm/llvm-project/pull/113686