Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2279,12 +2279,15 @@
 /// across all DemandedElts.
 bool SelectionDAG::isSplatValue(SDValue V, const APInt &DemandedElts,
                                 APInt &UndefElts) {
-  if (!DemandedElts)
-    return false; // No demanded elts, better to assume we don't know anything.
-
   EVT VT = V.getValueType();
   assert(VT.isVector() && "Vector type expected");
 
+  if (V.getOpcode() == ISD::SPLAT_VECTOR)
+    return true;
+
+  if (!DemandedElts || VT.isScalableVector())
+    return false; // No demanded elts, better to assume we don't know anything.
+
   unsigned NumElts = VT.getVectorNumElements();
   assert(NumElts == DemandedElts.getBitWidth() && "Vector size mismatch");
   UndefElts = APInt::getNullValue(NumElts);
@@ -2363,7 +2366,8 @@
 bool SelectionDAG::isSplatValue(SDValue V, bool AllowUndefs) {
   EVT VT = V.getValueType();
   assert(VT.isVector() && "Vector type expected");
-  unsigned NumElts = VT.getVectorNumElements();
+  // For now we don't support this with scalable vectors.
+  unsigned NumElts = VT.isScalableVector() ? 0 : VT.getVectorNumElements();
 
   APInt UndefElts;
   APInt DemandedElts = APInt::getAllOnesValue(NumElts);
@@ -2378,6 +2382,9 @@
   unsigned Opcode = V.getOpcode();
   switch (Opcode) {
   default: {
+    if (VT.isScalableVector())
+      return SDValue();
+
     APInt UndefElts;
     APInt DemandedElts = APInt::getAllOnesValue(VT.getVectorNumElements());
     if (isSplatValue(V, DemandedElts, UndefElts)) {
@@ -2391,6 +2398,8 @@
     }
     break;
   }
+  case ISD::SPLAT_VECTOR:
+    return V;
   case ISD::VECTOR_SHUFFLE: {
     // Check if this is a shuffle node doing a splat.
     // TODO - remove this and rely purely on SelectionDAG::isSplatValue,