diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1574,7 +1574,10 @@
 
   Type *MinType = nullptr;
 
-  unsigned NumElts = cast<FixedVectorType>(CVVTy)->getNumElements();
+  unsigned NumElts = (isa<FixedVectorType>(CVVTy))
+                         ? cast<FixedVectorType>(CVVTy)->getNumElements()
+                         : cast<ScalableVectorType>(CVVTy)->getMinNumElements();
+
   for (unsigned i = 0; i != NumElts; ++i) {
     auto *CFP = dyn_cast_or_null<ConstantFP>(CV->getAggregateElement(i));
     if (!CFP)
@@ -1591,7 +1594,7 @@
   }
 
   // Make a vector type from the minimal type.
-  return FixedVectorType::get(MinType, NumElts);
+  return VectorType::get(MinType, NumElts, isa<ScalableVectorType>(CVVTy));
 }
 
 /// Find the minimum FP type we can safely truncate to.
diff --git a/llvm/test/Transforms/InstCombine/instcombine-vectors.ll b/llvm/test/Transforms/InstCombine/instcombine-vectors.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/instcombine-vectors.ll
@@ -0,0 +1,8 @@
+; RUN: opt -instcombine -march=armv8.1-a+sve -S -o - < %s | FileCheck %s
+
+define <vscale x 2 x float> @foo(<vscale x 2 x double> %a) {
+  ; CHECK-LABEL: @foo
+  %1 = fadd <vscale x 2 x double> %a, shufflevector (<vscale x 2 x double> insertelement (<vscale x 2 x double> poison, double -1.000000e+00, i32 0), <vscale x 2 x double> poison, <vscale x 2 x i32> zeroinitializer)
+  %2 = fptrunc <vscale x 2 x double> %1 to <vscale x 2 x float>
+  ret <vscale x 2 x float> %2
+}