diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -2268,12 +2268,8 @@
   SmallVector<int, 16> Mask;
   Shuf.getShuffleMask(Mask);
 
-  // The shuffle must not change vector sizes.
-  // TODO: This restriction could be removed if the insert has only one use
-  //       (because the transform would require a new length-changing shuffle).
   int NumElts = Mask.size();
-  if (NumElts != (int)(cast<FixedVectorType>(V0->getType())->getNumElements()))
-    return nullptr;
+  int InpNumElts = cast<FixedVectorType>(V0->getType())->getNumElements();
 
   // This is a specialization of a fold in SimplifyDemandedVectorElts. We may
   // not be able to handle it there if the insertelement has >1 use.
@@ -2290,11 +2286,16 @@
   if (match(V1, m_InsertElt(m_Value(X), m_Value(), m_ConstantInt(IdxC)))) {
     // Offset the index constant by the vector width because we are checking for
     // accesses to the 2nd vector input of the shuffle.
-    IdxC += NumElts;
+    IdxC += InpNumElts;
     // shuf ?, (inselt X, ?, IdxC), Mask --> shuf ?, X, Mask
     if (!is_contained(Mask, (int)IdxC))
       return IC.replaceOperand(Shuf, 1, X);
   }
+  // For the rest of the transform, the shuffle must not change vector sizes.
+  // TODO: This restriction could be removed if the insert has only one use
+  //       (because the transform would require a new length-changing shuffle).
+  if (NumElts != InpNumElts)
+    return nullptr;
 
   // shuffle (insert ?, Scalar, IndexC), V1, Mask --> insert V1, Scalar, IndexC'
   auto isShufflingScalarIntoOp1 = [&](Value *&Scalar, ConstantInt *&IndexC) {
diff --git a/llvm/test/Transforms/InstCombine/insert-extract-shuffle.ll b/llvm/test/Transforms/InstCombine/insert-extract-shuffle.ll
--- a/llvm/test/Transforms/InstCombine/insert-extract-shuffle.ll
+++ b/llvm/test/Transforms/InstCombine/insert-extract-shuffle.ll
@@ -696,7 +696,7 @@
 ; CHECK-LABEL: @insert_undemanded_element_unequal_length_op0(
 ; CHECK-NEXT:    [[INS:%.*]] = insertelement <4 x float> [[X:%.*]], float 4.200000e+01, i32 3
 ; CHECK-NEXT:    call void @use(<4 x float> [[INS]])
-; CHECK-NEXT:    [[S:%.*]] = shufflevector <4 x float> [[INS]], <4 x float> [[Y:%.*]], <5 x i32> <i32 undef, i32 0, i32 7, i32 1, i32 4>
+; CHECK-NEXT:    [[S:%.*]] = shufflevector <4 x float> [[X]], <4 x float> [[Y:%.*]], <5 x i32> <i32 undef, i32 0, i32 7, i32 1, i32 4>
 ; CHECK-NEXT:    ret <5 x float> [[S]]
 ;
   %ins = insertelement <4 x float> %x, float 42.0, i32 3
@@ -709,7 +709,7 @@
 ; CHECK-LABEL: @insert_undemanded_element_unequal_length_op1(
 ; CHECK-NEXT:    [[INS:%.*]] = insertelement <4 x float> [[X:%.*]], float 4.200000e+01, i32 3
 ; CHECK-NEXT:    call void @use(<4 x float> [[INS]])
-; CHECK-NEXT:    [[S:%.*]] = shufflevector <4 x float> [[Y:%.*]], <4 x float> [[INS]], <5 x i32> <i32 undef, i32 3, i32 2, i32 1, i32 4>
+; CHECK-NEXT:    [[S:%.*]] = shufflevector <4 x float> [[Y:%.*]], <4 x float> [[X]], <5 x i32> <i32 undef, i32 3, i32 2, i32 1, i32 4>
 ; CHECK-NEXT:    ret <5 x float> [[S]]
 ;
   %ins = insertelement <4 x float> %x, float 42.0, i32 3