I am wondering what the semantics for fdiv is, if the denominator is
zero. For sdiv, the language reference specifies that this is undefined
behavior. For fdiv, the language reference says nothing (hence, I assume
that it is defined somehow).

So how is it defined? Does it follow IEEE-754 definition, i.e., +Inf if
nominator is > 0, -Inf if nominator is < 0, otherwise NaN?

Unfortunately, no flag in [1] mentions anything about devision by zero. So it still seems
that there is no place in the reference where anything is stated about the semantics of it.

I am wondering what the semantics for fdiv is, if the denominator is
zero. For sdiv, the language reference specifies that this is undefined
behavior. For fdiv, the language reference says nothing (hence, I assume
that it is defined somehow).

So how is it defined? Does it follow IEEE-754 definition, i.e., +Inf if
nominator is > 0, -Inf if nominator is < 0, otherwise NaN?

That's correct (it follows the semantics for the underlying type, which is generally IEEE with default rounding).