CodeGen: Strengthen definition of F{MIN|MAX}NUM_IEEE nodes

llvm/docs/GlobalISel/GenericOpcode.rst

@@ -521,16 +521,32 @@ 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 IEEE-754
+definitions. This differs from FMINNUM in the handling of signaling
+NaNs.
+
+If one input is a signaling NaN, returns a quiet NaN. This matches
+IEEE-754 2008's minnum/maxnum for signaling NaNs (which differs from
+2019).
+
+These treat -0 as ordered less than +0, matching the behavior of
+IEEE-754 2019's minimumNumber/maximumNumber (which was unspecified in
+2008).
 
 G_FMAXNUM_IEEE
 ^^^^^^^^^^^^^^
 
-Perform floating-point maximum on two values, following the IEEE-754 2008
-definition. This differs from FMAXNUM in the handling of signaling NaNs. If one
-input is a signaling NaN, returns a quiet NaN.
+Perform floating-point maximum on two values, following IEEE-754
+definitions. This differs from FMAXNUM in the handling of signaling
+NaNs.
+
+If one input is a signaling NaN, returns a quiet NaN. This matches
+IEEE-754 2008's minnum/maxnum for signaling NaNs (which differs from
+2019).
+
+These treat -0 as ordered less than +0, matching the behavior of
+IEEE-754 2019's minimumNumber/maximumNumber (which was unspecified in
+2008).
 
 G_FMINIMUM
 ^^^^^^^^^^

llvm/include/llvm/CodeGen/ISDOpcodes.h

@@ -971,10 +971,16 @@ enum NodeType {
   FMINNUM,
   FMAXNUM,
 
-  /// FMINNUM_IEEE/FMAXNUM_IEEE - Perform floating-point minimum or maximum on
-  /// two values, following the IEEE-754 2008 definition. This differs from
-  /// FMINNUM/FMAXNUM in the handling of signaling NaNs. If one input is a
-  /// signaling NaN, returns a quiet NaN.
+  /// FMINNUM_IEEE/FMAXNUM_IEEE - Perform floating-point minimumNumber or
+  /// maximumNumber on two values, following IEEE-754 definitions. This differs
+  /// from FMINNUM/FMAXNUM in the handling of signaling NaNs, and signed zero.
+  ///
+  /// If one input is a signaling NaN, returns a quiet NaN. This matches
+  /// IEEE-754 2008's minnum/maxnum behavior for signaling NaNs (which differs
+  /// from 2019).
+  ///
+  /// These treat -0 as ordered less than +0, matching the behavior of IEEE-754
+  /// 2019's minimumNumber/maximumNumber.
   FMINNUM_IEEE,
   FMAXNUM_IEEE,
 

llvm/include/llvm/Target/GenericOpcodes.td

@@ -795,10 +795,17 @@ def G_FMAXNUM : GenericInstruction {
   let isCommutable = true;
 }
 
-// FMINNUM_IEEE/FMAXNUM_IEEE - Perform floating-point minimum or maximum on
-// two values, following the IEEE-754 2008 definition. This differs from
-// FMINNUM/FMAXNUM in the handling of signaling NaNs. If one input is a
-// signaling NaN, returns a quiet NaN.
+// FMINNUM_IEEE/FMAXNUM_IEEE - Perform floating-point minimumNumber or
+// maximumNumber on two values, following IEEE-754 definitions. This
+// differs from FMINNUM/FMAXNUM in the handling of signaling NaNs, and
+// signed zero.
+//
+// If one input is a signaling NaN, returns a quiet NaN. This matches
+// IEEE-754 2008's minnum/maxnum behavior for signaling NaNs (which
+// differs from 2019).
+//
+// These treat -0 as ordered less than +0, matching the behavior of
+// IEEE-754 2019's minimumNumber/maximumNumber.
 def G_FMINNUM_IEEE : GenericInstruction {
   let OutOperandList = (outs type0:$dst);
   let InOperandList = (ins type0:$src1, type0:$src2);