[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

1 files changed, 10 insertions, 4 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();
 }