Originally from #4963 (comment):

Should this discuss subnormal and NaN behavior, the way the description of max does?

We could add some language. SPIR-V says:

From the set of Value(s) provided by active invocations within a subgroup, if for any two Values one of them is a NaN, the other is chosen. If all Value(s) that are used by the current invocation are NaN, then the result is an undefined value.