[llvm] [X86] Combine LRINT/LLRINT and TRUNC when nuw/nsw (PR #126217)

[Andy Kaylor via llvm-commits]

andykaylor wrote:

> Do you have examples where we are able to infer an nuw/nsw flag for a truncate after lrint?

I was wondering that too. It doesn't look like clang ever sets these flags on trunc, though I suppose some other frontend might.

I was also wondering if it would be reasonable to apply this transformation in InstCombine -- for instance, convert `llvm.lrint.i64.f64+(nsw/nuw)trunc` to `llvm.rint.i32`? That's assuming we have reason to believe that this is useful.

https://github.com/llvm/llvm-project/pull/126217