Index: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -2526,7 +2526,7 @@
     }
   }
 
-  if (VectorType *DestVTy = dyn_cast<VectorType>(DestTy)) {
+  if (FixedVectorType *DestVTy = dyn_cast<FixedVectorType>(DestTy)) {
     // Beware: messing with this target-specific oddity may cause trouble.
     if (DestVTy->getNumElements() == 1 && SrcTy->isX86_MMXTy()) {
       Value *Elem = Builder.CreateBitCast(Src, DestVTy->getElementType());
@@ -2555,7 +2555,7 @@
     }
   }
 
-  if (VectorType *SrcVTy = dyn_cast<VectorType>(SrcTy)) {
+  if (FixedVectorType *SrcVTy = dyn_cast<FixedVectorType>(SrcTy)) {
     if (SrcVTy->getNumElements() == 1) {
       // If our destination is not a vector, then make this a straight
       // scalar-scalar cast.
Index: llvm/test/Transforms/InstCombine/AArch64/sve-bitcast.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstCombine/AArch64/sve-bitcast.ll
@@ -0,0 +1,13 @@
+; RUN: opt -instcombine -mtriple=aarch64-linux-gnu -mattr=+sve -S < %s | FileCheck %s
+
+; We shouldn't fold bitcast(insert <vscale x 1 x iX> .., iX %val, i32 0)
+; into bitcast(iX %val) for scalable vectors.
+define <vscale x 2 x i8> @bitcast_of_insert_i8_i16(i16 %val) #0 {
+; CHECK-LABEL: @bitcast_of_insert_i8_i16(
+; CHECK-NOT:   bitcast i16 %val to <vscale x 2 x i8>
+; CHECK:       bitcast <vscale x 1 x i16> %op2 to <vscale x 2 x i8>
+entry:
+  %op2 = insertelement <vscale x 1 x i16> undef, i16 %val, i32 0
+  %0 = bitcast <vscale x 1 x i16> %op2 to <vscale x 2 x i8>
+  ret <vscale x 2 x i8> %0
+}