[llvm] LangRef: Clarify behaviors of nsz in fast math flag (PR #137567)

[Serge Pavlov via llvm-commits]

spavloff wrote:

It is not clear why some particular cases should be mentioned in documentation, if they don't clarify meaning of the flag or its usage. If some specific transformation suffers from this flag, it can simply ignore `nsz`, a comment in code looks sufficient. Anyway, fast math flags allow some (unsafe) transformations, but not require to use them.

Also, `nsz` enables transformations that break FP semantics. Nothing surprizing if they produce the result that do not conform to the semantics of some functions.


https://github.com/llvm/llvm-project/pull/137567