Index: llvm/trunk/utils/TableGen/CodeGenDAGPatterns.cpp
===================================================================
--- llvm/trunk/utils/TableGen/CodeGenDAGPatterns.cpp
+++ llvm/trunk/utils/TableGen/CodeGenDAGPatterns.cpp
@@ -603,6 +603,11 @@
   auto IsSubVec = [](MVT B, MVT P) -> bool {
     if (!B.isVector() || !P.isVector())
       return false;
+    // Logically a <4 x i32> is a valid subvector of <n x 4 x i32>
+    // but until there are obvious use-cases for this, keep the
+    // types separate.
+    if (B.isScalableVector() != P.isScalableVector())
+      return false;
     if (B.getVectorElementType() != P.getVectorElementType())
       return false;
     return B.getVectorNumElements() < P.getVectorNumElements();