diff --git a/llvm/include/llvm/IR/Instructions.h b/llvm/include/llvm/IR/Instructions.h
--- a/llvm/include/llvm/IR/Instructions.h
+++ b/llvm/include/llvm/IR/Instructions.h
@@ -1977,7 +1977,7 @@
   ///           shufflevector <4 x n> A, <4 x n> B, <1,2,3,4,5>
   bool changesLength() const {
     unsigned NumSourceElts =
-        cast<VectorType>(Op<0>()->getType())->getNumElements();
+        cast<VectorType>(Op<0>()->getType())->getElementCount().Min;
     unsigned NumMaskElts = ShuffleMask.size();
     return NumSourceElts != NumMaskElts;
   }
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -2205,8 +2205,14 @@
 bool ShuffleVectorInst::isIdentityWithExtract() const {
   if (isa<UndefValue>(Op<2>()))
     return false;
-  int NumOpElts = cast<VectorType>(Op<0>()->getType())->getNumElements();
-  int NumMaskElts = getType()->getNumElements();
+
+  // FIXME: Not currently possible to express a shuffle mask for a scalable
+  // vector for this case
+  if (isa<ScalableVectorType>(getType()))
+    return false;
+
+  int NumOpElts = cast<FixedVectorType>(Op<0>()->getType())->getNumElements();
+  int NumMaskElts = cast<FixedVectorType>(getType())->getNumElements();
   if (NumMaskElts >= NumOpElts)
     return false;