[DAGCombiner] Sub/SUBSAT - use general SelectionDAG::FoldConstantArithmetic

This handles all the constant splat / opaque testing for us.

Author: RKSimon

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -2976,11 +2976,10 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
   // FIXME: Refactor this and xor and other similar operations together.
   if (N0 == N1)
     return tryFoldToZero(DL, TLI, VT, DAG, LegalOperations);
-  if (DAG.isConstantIntBuildVectorOrConstantInt(N0) &&
-      DAG.isConstantIntBuildVectorOrConstantInt(N1)) {
-    // fold (sub c1, c2) -> c1-c2
-    return DAG.FoldConstantArithmetic(ISD::SUB, DL, VT, {N0, N1});
-  }
+
+  // fold (sub c1, c2) -> c3
+  if (SDValue C = DAG.FoldConstantArithmetic(ISD::SUB, DL, VT, {N0, N1}))
+    return C;
 
   if (SDValue NewSel = foldBinOpIntoSelect(N))
     return NewSel;
@@ -3300,11 +3299,9 @@ SDValue DAGCombiner::visitSUBSAT(SDNode *N) {
   if (N0 == N1)
     return DAG.getConstant(0, DL, VT);
 
-  if (DAG.isConstantIntBuildVectorOrConstantInt(N0) &&
-      DAG.isConstantIntBuildVectorOrConstantInt(N1)) {
-    // fold (sub_sat c1, c2) -> c3
-    return DAG.FoldConstantArithmetic(N->getOpcode(), DL, VT, {N0, N1});
-  }
+  // fold (sub_sat c1, c2) -> c3
+  if (SDValue C = DAG.FoldConstantArithmetic(N->getOpcode(), DL, VT, {N0, N1}))
+    return C;
 
   // fold (sub_sat x, 0) -> x
   if (isNullConstant(N1))