[DAG] visitABD - rewrite "(abs x, 0)" folds to use SDPatternMatch

No need for this to be vector specific, and its more likely that scalar cases will appear after #92576

Author: RKSimon

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -5253,24 +5253,25 @@ SDValue DAGCombiner::visitABD(SDNode *N) {
       !DAG.isConstantIntBuildVectorOrConstantInt(N1))
     return DAG.getNode(Opcode, DL, N->getVTList(), N1, N0);
 
-  if (VT.isVector()) {
+  if (VT.isVector())
     if (SDValue FoldedVOp = SimplifyVBinOp(N, DL))
       return FoldedVOp;
 
-    // fold (abds x, 0) -> abs x
-    // fold (abdu x, 0) -> x
-    if (ISD::isConstantSplatVectorAllZeros(N1.getNode())) {
-      if (Opcode == ISD::ABDS)
-        return DAG.getNode(ISD::ABS, DL, VT, N0);
-      if (Opcode == ISD::ABDU)
-        return N0;
-    }
-  }
-
   // fold (abd x, undef) -> 0
   if (N0.isUndef() || N1.isUndef())
     return DAG.getConstant(0, DL, VT);
 
+  SDValue X;
+
+  // fold (abds x, 0) -> abs x
+  if (sd_match(N, m_c_BinOp(ISD::ABDS, m_Value(X), m_Zero())) &&
+      (!LegalOperations || hasOperation(ISD::ABS, VT)))
+    return DAG.getNode(ISD::ABS, DL, VT, X);
+
+  // fold (abdu x, 0) -> x
+  if (sd_match(N, m_c_BinOp(ISD::ABDU, m_Value(X), m_Zero())))
+    return X;
+
   // fold (abds x, y) -> (abdu x, y) iff both args are known positive
   if (Opcode == ISD::ABDS && hasOperation(ISD::ABDU, VT) &&
       DAG.SignBitIsZero(N0) && DAG.SignBitIsZero(N1))