Index: llvm/lib/IR/Instructions.cpp
===================================================================
--- llvm/lib/IR/Instructions.cpp
+++ llvm/lib/IR/Instructions.cpp
@@ -2274,6 +2274,11 @@
       isa<UndefValue>(Op<2>()))
     return false;
 
+  // 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 * 2)
Index: llvm/unittests/IR/InstructionsTest.cpp
===================================================================
--- llvm/unittests/IR/InstructionsTest.cpp
+++ llvm/unittests/IR/InstructionsTest.cpp
@@ -1096,6 +1096,17 @@
   EXPECT_TRUE(Id14->changesLength());
   EXPECT_TRUE(Id14->increasesLength());
   delete Id14;
+
+  // Not possible to express these masks for scalable vectors, make sure we
+  // don't crash.
+  ShuffleVectorInst *Id15 =
+      new ShuffleVectorInst(Constant::getAllOnesValue(VScaleV2Int32Ty),
+                            Constant::getNullValue(VScaleV2Int32Ty),
+                            Constant::getNullValue(VScaleV2Int32Ty));
+  EXPECT_FALSE(Id15->isIdentityWithPadding());
+  EXPECT_FALSE(Id15->isIdentityWithExtract());
+  EXPECT_FALSE(Id15->isConcat());
+  delete Id15;
 }
 
 TEST(InstructionsTest, GetSplat) {