[llvm] Intrinsic: introduce minimumnum and maximumnum for IR and SelectionDAG (PR #96649)

[Matt Arsenault via llvm-commits]

================
@@ -8531,6 +8531,94 @@ SDValue TargetLowering::expandFMINIMUM_FMAXIMUM(SDNode *N,
   return MinMax;
 }
 
+SDValue TargetLowering::expandFMINIMUMNUM_FMAXIMUMNUM(SDNode *Node,
+                                                      SelectionDAG &DAG) const {
+  SDLoc DL(Node);
+  SDValue LHS = Node->getOperand(0);
+  SDValue RHS = Node->getOperand(1);
+  unsigned Opc = Node->getOpcode();
+  EVT VT = Node->getValueType(0);
+  EVT CCVT = getSetCCResultType(DAG.getDataLayout(), *DAG.getContext(), VT);
+  bool IsMax = Opc == ISD::FMAXIMUMNUM;
+  SDNodeFlags Flags = Node->getFlags();
+
+  unsigned NewOp =
+      Opc == ISD::FMINIMUMNUM ? ISD::FMINNUM_IEEE : ISD::FMAXNUM_IEEE;
+
+  if (isOperationLegalOrCustom(NewOp, VT)) {
+    if (!Flags.hasNoNaNs()) {
+      // Insert canonicalizes if it's possible we need to quiet to get correct
+      // sNaN behavior.
+      if (!DAG.isKnownNeverSNaN(LHS)) {
+        LHS = DAG.getNode(ISD::FCANONICALIZE, DL, VT, LHS, Node->getFlags());
+      }
+      if (!DAG.isKnownNeverSNaN(RHS)) {
+        RHS = DAG.getNode(ISD::FCANONICALIZE, DL, VT, RHS, Node->getFlags());
+      }
+    }
+
+    return DAG.getNode(NewOp, DL, VT, LHS, RHS, Flags);
+  }
+
+  // FMINIMUM/FMAXIMUM always return NaN if either operand is NaN.
+  // It has same behavior about +0.0 vs -0.0.
+  if (Flags.hasNoNaNs() ||
+      (DAG.isKnownNeverNaN(LHS) && DAG.isKnownNeverNaN(RHS))) {
+    unsigned IEEE2019Op =
+        Opc == ISD::FMINIMUMNUM ? ISD::FMINIMUM : ISD::FMAXIMUM;
+    if (isOperationLegalOrCustom(IEEE2019Op, VT))
+      return DAG.getNode(IEEE2019Op, DL, VT, LHS, RHS, Flags);
+  }
+
+  // FMINNUM/FMAXMUM returns qNaN if either operand is sNaN, and it may return
+  // either one for +0.0 vs -0.0.
+  // FIXME: maybe we need hasNoSNaNs().
+  if ((Flags.hasNoNaNs() ||
+       (DAG.isKnownNeverSNaN(LHS) && DAG.isKnownNeverSNaN(RHS))) &&
+      (Flags.hasNoSignedZeros() || DAG.isKnownNeverZeroFloat(LHS) ||
+       DAG.isKnownNeverZeroFloat(RHS))) {
+    unsigned IEEE2008Op = Opc == ISD::FMINIMUMNUM ? ISD::FMINNUM : ISD::FMAXNUM;
+    if (isOperationLegalOrCustom(IEEE2008Op, VT))
+      return DAG.getNode(IEEE2008Op, DL, VT, LHS, RHS, Flags);
+  }
+
+  SDValue MinMax;
+  // If one operand is NaN, let's move another value to it.
+  // So that if only one operand is NaN, we can have both two operands are
+  // non-NaN now.
+  SDValue LHSCompareLHS = DAG.getSetCC(DL, CCVT, LHS, LHS, ISD::SETEQ);
+  LHS = DAG.getSelect(DL, VT, LHSCompareLHS, LHS, RHS, Flags);
+  SDValue RHSCompareRHS = DAG.getSetCC(DL, CCVT, RHS, RHS, ISD::SETEQ);
+  RHS = DAG.getSelect(DL, VT, RHSCompareRHS, RHS, LHS, Flags);
+
+  SDValue Compare =
+      DAG.getSetCC(DL, CCVT, LHS, RHS, IsMax ? ISD::SETGT : ISD::SETLT);
+  MinMax = DAG.getSelect(DL, VT, Compare, LHS, RHS, Flags);
+
+  // If MinMax is NaN, let's quiet it with MinMax = MinMax + 0.
+  SDValue MinMaxCompareMinMax =
+      DAG.getSetCC(DL, CCVT, MinMax, MinMax, ISD::SETEQ);
+  SDValue MinMaxQuiet = DAG.getNode(ISD::FADD, DL, VT, MinMax,
+                                    DAG.getConstantFP(0.0, DL, VT), Flags);
+  MinMax =
+      DAG.getSelect(DL, VT, MinMaxCompareMinMax, MinMax, MinMaxQuiet, Flags);
+
+  // Let's process +0.0 vs -0.0.
----------------
arsenm wrote:

```suggestion
  // Fixup signed zero behavior
```

https://github.com/llvm/llvm-project/pull/96649