[SelectionDAG] Expand UADDO/USUBO into ADD/SUBCARRY if legal for target

Additionally, implement handling of ADD/SUBCARRY on Hexagon, utilizing
the UADDO/USUBO expansion.

Differential Revision: https://reviews.llvm.org/D47559

llvm-svn: 333751

2 files changed, 25 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 93d9cfd73bd..3db05a56c5b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2283,8 +2283,11 @@ SDValue DAGCombiner::visitADDCARRY(SDNode *N) {
     return DAG.getNode(ISD::ADDCARRY, DL, N->getVTList(), N1, N0, CarryIn);
 
   // fold (addcarry x, y, false) -> (uaddo x, y)
-  if (isNullConstant(CarryIn))
-    return DAG.getNode(ISD::UADDO, DL, N->getVTList(), N0, N1);
+  if (isNullConstant(CarryIn)) {
+    if (!LegalOperations ||
+        TLI.isOperationLegalOrCustom(ISD::UADDO, N->getValueType(0)))
+      return DAG.getNode(ISD::UADDO, DL, N->getVTList(), N0, N1);
+  }
 
   // fold (addcarry 0, 0, X) -> (and (ext/trunc X), 1) and no carry.
   if (isNullConstant(N0) && isNullConstant(N1)) {
@@ -2592,8 +2595,11 @@ SDValue DAGCombiner::visitSUBCARRY(SDNode *N) {
   SDValue CarryIn = N->getOperand(2);
 
   // fold (subcarry x, y, false) -> (usubo x, y)
-  if (isNullConstant(CarryIn))
-    return DAG.getNode(ISD::USUBO, SDLoc(N), N->getVTList(), N0, N1);
+  if (isNullConstant(CarryIn)) {
+    if (!LegalOperations ||
+        TLI.isOperationLegalOrCustom(ISD::USUBO, N->getValueType(0)))
+      return DAG.getNode(ISD::USUBO, SDLoc(N), N->getVTList(), N0, N1);
+  }
 
   return SDValue();
 }
diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 7c9c06b6250..feb67819201 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -3499,15 +3499,25 @@ bool SelectionDAGLegalize::ExpandNode(SDNode *Node) {
   case ISD::USUBO: {
     SDValue LHS = Node->getOperand(0);
     SDValue RHS = Node->getOperand(1);
-    SDValue Sum = DAG.getNode(Node->getOpcode() == ISD::UADDO ?
-                              ISD::ADD : ISD::SUB, dl, LHS.getValueType(),
-                              LHS, RHS);
+    bool IsAdd = Node->getOpcode() == ISD::UADDO;
+    // If ADD/SUBCARRY is legal, use that instead.
+    unsigned OpcCarry = IsAdd ? ISD::ADDCARRY : ISD::SUBCARRY;
+    if (TLI.isOperationLegalOrCustom(OpcCarry, Node->getValueType(0))) {
+      SDValue CarryIn = DAG.getConstant(0, dl, Node->getValueType(1));
+      SDValue NodeCarry = DAG.getNode(OpcCarry, dl, Node->getVTList(),
+                                      { LHS, RHS, CarryIn });
+      Results.push_back(SDValue(NodeCarry.getNode(), 0));
+      Results.push_back(SDValue(NodeCarry.getNode(), 1));
+      break;
+    }
+
+    SDValue Sum = DAG.getNode(IsAdd ? ISD::ADD : ISD::SUB, dl,
+                              LHS.getValueType(), LHS, RHS);
     Results.push_back(Sum);
 
     EVT ResultType = Node->getValueType(1);
     EVT SetCCType = getSetCCResultType(Node->getValueType(0));
-    ISD::CondCode CC
-      = Node->getOpcode() == ISD::UADDO ? ISD::SETULT : ISD::SETUGT;
+    ISD::CondCode CC = IsAdd ? ISD::SETULT : ISD::SETUGT;
     SDValue SetCC = DAG.getSetCC(dl, SetCCType, Sum, LHS, CC);
 
     Results.push_back(DAG.getBoolExtOrTrunc(SetCC, dl, ResultType, ResultType));