[DAG] Add willNotOverflowAdd/willNotOverflowSub helper functions.

Matches similar instructions on InstCombine

Author: RKSimon

llvm/include/llvm/CodeGen/SelectionDAG.h

@@ -2041,6 +2041,11 @@ class SelectionDAG {
                     : computeOverflowForUnsignedAdd(N0, N1);
   }
 
+  /// Determine if the result of the addition of 2 nodes can never overflow.
+  bool willNotOverflowAdd(bool IsSigned, SDValue N0, SDValue N1) const {
+    return computeOverflowForAdd(IsSigned, N0, N1) == OFK_Never;
+  }
+
   /// Determine if the result of the signed sub of 2 nodes can overflow.
   OverflowKind computeOverflowForSignedSub(SDValue N0, SDValue N1) const;
 
@@ -2054,6 +2059,11 @@ class SelectionDAG {
                     : computeOverflowForUnsignedSub(N0, N1);
   }
 
+  /// Determine if the result of the sub of 2 nodes can never overflow.
+  bool willNotOverflowSub(bool IsSigned, SDValue N0, SDValue N1) const {
+    return computeOverflowForSub(IsSigned, N0, N1) == OFK_Never;
+  }
+
   /// Test if the given value is known to have exactly one bit set. This differs
   /// from computeKnownBits in that it doesn't necessarily determine which bit
   /// is set.

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -3040,7 +3040,7 @@ SDValue DAGCombiner::visitADDSAT(SDNode *N) {
     return N0;
 
   // If it cannot overflow, transform into an add.
-  if (DAG.computeOverflowForAdd(IsSigned, N0, N1) == SelectionDAG::OFK_Never)
+  if (DAG.willNotOverflowAdd(IsSigned, N0, N1))
     return DAG.getNode(ISD::ADD, DL, VT, N0, N1);
 
   return SDValue();
@@ -3310,7 +3310,7 @@ SDValue DAGCombiner::visitADDO(SDNode *N) {
     return CombineTo(N, N0, DAG.getConstant(0, DL, CarryVT));
 
   // If it cannot overflow, transform into an add.
-  if (DAG.computeOverflowForAdd(IsSigned, N0, N1) == SelectionDAG::OFK_Never)
+  if (DAG.willNotOverflowAdd(IsSigned, N0, N1))
     return CombineTo(N, DAG.getNode(ISD::ADD, DL, VT, N0, N1),
                      DAG.getConstant(0, DL, CarryVT));
 
@@ -4170,7 +4170,7 @@ SDValue DAGCombiner::visitSUBSAT(SDNode *N) {
     return N0;
 
   // If it cannot overflow, transform into an sub.
-  if (DAG.computeOverflowForSub(IsSigned, N0, N1) == SelectionDAG::OFK_Never)
+  if (DAG.willNotOverflowSub(IsSigned, N0, N1))
     return DAG.getNode(ISD::SUB, DL, VT, N0, N1);
 
   return SDValue();
@@ -4236,7 +4236,7 @@ SDValue DAGCombiner::visitSUBO(SDNode *N) {
     return CombineTo(N, N0, DAG.getConstant(0, DL, CarryVT));
 
   // If it cannot overflow, transform into an sub.
-  if (DAG.computeOverflowForSub(IsSigned, N0, N1) == SelectionDAG::OFK_Never)
+  if (DAG.willNotOverflowSub(IsSigned, N0, N1))
     return CombineTo(N, DAG.getNode(ISD::SUB, DL, VT, N0, N1),
                      DAG.getConstant(0, DL, CarryVT));
 

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -1040,13 +1040,10 @@ static SDValue combineShiftToAVG(SDValue Op, SelectionDAG &DAG,
     // larger type size to do the transform.
     if (!TLI.isOperationLegalOrCustom(AVGOpc, VT))
       return SDValue();
-
-    if (DAG.computeOverflowForAdd(IsSigned, Add.getOperand(0),
-                                  Add.getOperand(1)) ==
-            SelectionDAG::OFK_Never &&
-        (!Add2 || DAG.computeOverflowForAdd(IsSigned, Add2.getOperand(0),
-                                            Add2.getOperand(1)) ==
-                      SelectionDAG::OFK_Never))
+    if (DAG.willNotOverflowAdd(IsSigned, Add.getOperand(0),
+                               Add.getOperand(1)) &&
+        (!Add2 || DAG.willNotOverflowAdd(IsSigned, Add2.getOperand(0),
+                                         Add2.getOperand(1))))
       NVT = VT;
     else
       return SDValue();