[DAG] Add foldSelectToABD helper. NFC.

Pull out of visitVSELECT to allow reuse in the future.

Author: RKSimon

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -598,6 +598,8 @@ namespace {
                               const SDLoc &DL);
     SDValue foldSubToUSubSat(EVT DstVT, SDNode *N, const SDLoc &DL);
     SDValue foldABSToABD(SDNode *N, const SDLoc &DL);
+    SDValue foldSelectToABD(SDValue LHS, SDValue RHS, SDValue True,
+                            SDValue False, ISD::CondCode CC, const SDLoc &DL);
     SDValue unfoldMaskedMerge(SDNode *N);
     SDValue unfoldExtremeBitClearingToShifts(SDNode *N);
     SDValue SimplifySetCC(EVT VT, SDValue N0, SDValue N1, ISD::CondCode Cond,
@@ -11568,6 +11570,45 @@ static SDValue foldVSelectToSignBitSplatMask(SDNode *N, SelectionDAG &DAG) {
   return SDValue();
 }
 
+// Match SELECTs with absolute difference patterns.
+// (select (setcc a, b, set?gt), (sub a, b), (sub b, a)) --> (abd? a, b)
+// (select (setcc a, b, set?ge), (sub a, b), (sub b, a)) --> (abd? a, b)
+// (select (setcc a, b, set?lt), (sub b, a), (sub a, b)) --> (abd? a, b)
+// (select (setcc a, b, set?le), (sub b, a), (sub a, b)) --> (abd? a, b)
+SDValue DAGCombiner::foldSelectToABD(SDValue LHS, SDValue RHS, SDValue True,
+                                     SDValue False, ISD::CondCode CC,
+                                     const SDLoc &DL) {
+  bool IsSigned = isSignedIntSetCC(CC);
+  unsigned ABDOpc = IsSigned ? ISD::ABDS : ISD::ABDU;
+  EVT VT = LHS.getValueType();
+
+  if (LegalOperations && !hasOperation(ABDOpc, VT))
+    return SDValue();
+
+  switch (CC) {
+  case ISD::SETGT:
+  case ISD::SETGE:
+  case ISD::SETUGT:
+  case ISD::SETUGE:
+    if (sd_match(True, m_Sub(m_Specific(LHS), m_Specific(RHS))) &&
+        sd_match(False, m_Sub(m_Specific(RHS), m_Specific(LHS))))
+      return DAG.getNode(ABDOpc, DL, VT, LHS, RHS);
+    break;
+  case ISD::SETLT:
+  case ISD::SETLE:
+  case ISD::SETULT:
+  case ISD::SETULE:
+    if (sd_match(True, m_Sub(m_Specific(RHS), m_Specific(LHS))) &&
+        sd_match(False, m_Sub(m_Specific(LHS), m_Specific(RHS))))
+      return DAG.getNode(ABDOpc, DL, VT, LHS, RHS);
+    break;
+  default:
+    break;
+  }
+
+  return SDValue();
+}
+
 SDValue DAGCombiner::visitSELECT(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
@@ -12368,37 +12409,8 @@ SDValue DAGCombiner::visitVSELECT(SDNode *N) {
       }
     }
 
-    // Match VSELECTs with absolute difference patterns.
-    // (vselect (setcc a, b, set?gt), (sub a, b), (sub b, a)) --> (abd? a, b)
-    // (vselect (setcc a, b, set?ge), (sub a, b), (sub b, a)) --> (abd? a, b)
-    // (vselect (setcc a, b, set?lt), (sub b, a), (sub a, b)) --> (abd? a, b)
-    // (vselect (setcc a, b, set?le), (sub b, a), (sub a, b)) --> (abd? a, b)
-    if (N1.getOpcode() == ISD::SUB && N2.getOpcode() == ISD::SUB &&
-        N1.getOperand(0) == N2.getOperand(1) &&
-        N1.getOperand(1) == N2.getOperand(0)) {
-      bool IsSigned = isSignedIntSetCC(CC);
-      unsigned ABDOpc = IsSigned ? ISD::ABDS : ISD::ABDU;
-      if (!LegalOperations || hasOperation(ABDOpc, VT)) {
-        switch (CC) {
-        case ISD::SETGT:
-        case ISD::SETGE:
-        case ISD::SETUGT:
-        case ISD::SETUGE:
-          if (LHS == N1.getOperand(0) && RHS == N1.getOperand(1))
-            return DAG.getNode(ABDOpc, DL, VT, LHS, RHS);
-          break;
-        case ISD::SETLT:
-        case ISD::SETLE:
-        case ISD::SETULT:
-        case ISD::SETULE:
-          if (RHS == N1.getOperand(0) && LHS == N1.getOperand(1) )
-            return DAG.getNode(ABDOpc, DL, VT, LHS, RHS);
-          break;
-        default:
-          break;
-        }
-      }
-    }
+    if (SDValue ABD = foldSelectToABD(LHS, RHS, N1, N2, CC, DL))
+      return ABD;
 
     // Match VSELECTs into add with unsigned saturation.
     if (hasOperation(ISD::UADDSAT, VT)) {