diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -4240,6 +4240,8 @@
                                 SelectionDAG &DAG) {
   int NumOps = Ops.size();
   assert(NumOps != 0 && "Can't build an empty vector!");
+  assert(!VT.isScalableVector() &&
+         "BUILD_VECTOR cannot be used with scalable types");
   assert(VT.getVectorNumElements() == (unsigned)NumOps &&
          "Incorrect element count in BUILD_VECTOR!");
 
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1552,16 +1552,17 @@
       return DAG.getBlockAddress(BA, VT);
 
     VectorType *VecTy = cast<VectorType>(V->getType());
-    unsigned NumElements = VecTy->getNumElements();
 
     // Now that we know the number and type of the elements, get that number of
     // elements into the Ops array based on what kind of constant it is.
-    SmallVector<SDValue, 16> Ops;
     if (const ConstantVector *CV = dyn_cast<ConstantVector>(C)) {
+      SmallVector<SDValue, 16> Ops;
+      unsigned NumElements = cast<FixedVectorType>(VecTy)->getNumElements();
       for (unsigned i = 0; i != NumElements; ++i)
         Ops.push_back(getValue(CV->getOperand(i)));
-    } else {
-      assert(isa<ConstantAggregateZero>(C) && "Unknown vector constant!");
+
+      return NodeMap[V] = DAG.getBuildVector(VT, getCurSDLoc(), Ops);
+    } else if (isa<ConstantAggregateZero>(C)) {
       EVT EltVT =
           TLI.getValueType(DAG.getDataLayout(), VecTy->getElementType());
 
@@ -1570,11 +1571,16 @@
         Op = DAG.getConstantFP(0, getCurSDLoc(), EltVT);
       else
         Op = DAG.getConstant(0, getCurSDLoc(), EltVT);
-      Ops.assign(NumElements, Op);
-    }
 
-    // Create a BUILD_VECTOR node.
-    return NodeMap[V] = DAG.getBuildVector(VT, getCurSDLoc(), Ops);
+      if (isa<ScalableVectorType>(VecTy))
+        return NodeMap[V] = DAG.getSplatVector(VT, getCurSDLoc(), Op);
+      else {
+        SmallVector<SDValue, 16> Ops;
+        Ops.assign(cast<FixedVectorType>(VecTy)->getNumElements(), Op);
+        return NodeMap[V] = DAG.getBuildVector(VT, getCurSDLoc(), Ops);
+      }
+    }
+    llvm_unreachable("Unknown vector constant");
   }
 
   // If this is a static alloca, generate it as the frameindex instead of