[llvm] LangRef: Clarify llvm.minnum and llvm.maxnum about sNaN (PR #112852)

[YunQiang Su via llvm-commits]

wzssyqa wrote:

> Please add some mention of the interaction with FP arithmetic. (In particular, that arithmetic on an sNaN doesn't consistently produce a qNaN, so arithmetic feeding into a minnum/maxnum can produce inconsistent results.)

qNaN is always produced in the following cases: 
1. In IEEE754-2008, qNaN is required for maxNUM and minNUM operations.
2. On architectures that implement these operation with hardware, such as MIPSr6, ARMv8, qNaN is also produced.
3. With the current glibc(2.25+) implementation, qNaN is also.

Yes, for older libc implementations (2.24-) qNaN vs sNaN may produce sNaN.

https://github.com/llvm/llvm-project/pull/112852