[llvm] CodeGen: Strengthen definition of F{MIN|MAX}NUM_IEEE nodes (PR #85195)

[Serge Pavlov via llvm-commits]

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@@ -521,16 +521,18 @@ The return value of (FMAXNUM 0.0, -0.0) could be either 0.0 or -0.0.
 G_FMINNUM_IEEE
 ^^^^^^^^^^^^^^
 
-Perform floating-point minimum on two values, following the IEEE-754 2008
-definition. This differs from FMINNUM in the handling of signaling NaNs. If one
-input is a signaling NaN, returns a quiet NaN.
+Perform floating-point minimum on two values, following the IEEE-754
+2019 definition. This differs from FMINNUM in the handling of
+signaling NaNs. If one input is a signaling NaN, returns a quiet
+NaN. This treats -0 as ordered less than +0.
----------------
spavloff wrote:

IEEE-754 2019 defines two functions for minimum: `minimum` and `minimumNumber`. So it worth mentioning that this node represents just `minimumNumber`. The described treatment of SNaN is also slightly different from IEEE-754:
```
minimumNumber(x, y) is x if x < y, y if y < x, and the number if one operand is a number and the
other is a NaN. For this operation, −0 compares less than +0. If x = y and signs are the same it is
either x or y. If both operands are NaNs, a quiet NaN is returned, according to 6.2. If either
operand is a signaling NaN, an invalid operation exception is signaled, but unless both operands
are NaNs, the signaling NaN is otherwise ignored and not converted to a quiet NaN as stated in
6.2 for other operations.
```
Is this difference intentional?

https://github.com/llvm/llvm-project/pull/85195