diff --git a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
index 95e1f96c71b48..3e459f5ea4ce5 100644
--- a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
+++ b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -2282,6 +2282,17 @@ bool VectorCombine::foldShuffleOfShuffles(Instruction &I) {
   if (!Match0 && !Match1)
     return false;
 
+  // If the outer shuffle is a permute, then create a fake inner all-poison
+  // shuffle. This is easier than accounting for length-changing shuffles below.
+  SmallVector<int, 16> PoisonMask1;
+  if (!Match1 && isa<PoisonValue>(OuterV1)) {
+    X1 = X0;
+    Y1 = Y0;
+    PoisonMask1.append(InnerMask0.size(), PoisonMaskElem);
+    InnerMask1 = PoisonMask1;
+    Match1 = true; // fake match
+  }
+
   X0 = Match0 ? X0 : OuterV0;
   Y0 = Match0 ? Y0 : OuterV0;
   X1 = Match1 ? X1 : OuterV1;
@@ -2356,11 +2367,11 @@ bool VectorCombine::foldShuffleOfShuffles(Instruction &I) {
   // Try to merge the shuffles if the new shuffle is not costly.
   InstructionCost InnerCost0 = 0;
   if (Match0)
-    InnerCost0 = TTI.getInstructionCost(cast<Instruction>(OuterV0), CostKind);
+    InnerCost0 = TTI.getInstructionCost(cast<User>(OuterV0), CostKind);
 
   InstructionCost InnerCost1 = 0;
   if (Match1)
-    InnerCost1 = TTI.getInstructionCost(cast<Instruction>(OuterV1), CostKind);
+    InnerCost1 = TTI.getInstructionCost(cast<User>(OuterV1), CostKind);
 
   InstructionCost OuterCost = TTI.getInstructionCost(&I, CostKind);
 
diff --git a/llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity.ll b/llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity.ll
index 1c9bc77ac3bef..1c128c8f56a03 100644
--- a/llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity.ll
+++ b/llvm/test/Transforms/VectorCombine/AArch64/shuffletoidentity.ll
@@ -262,10 +262,8 @@ define <8 x half> @splatandidentity(<8 x half> %a, <8 x half> %b) {
 
 define <8 x half> @splattwice(<8 x half> %a, <8 x half> %b) {
 ; CHECK-LABEL: @splattwice(
-; CHECK-NEXT:    [[AS:%.*]] = shufflevector <8 x half> [[A:%.*]], <8 x half> poison, <4 x i32> zeroinitializer
-; CHECK-NEXT:    [[BS:%.*]] = shufflevector <8 x half> [[B:%.*]], <8 x half> poison, <4 x i32> zeroinitializer
-; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x half> [[AS]], <4 x half> poison, <8 x i32> <i32 3, i32 2, i32 1, i32 0, i32 3, i32 2, i32 1, i32 0>
-; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <4 x half> [[BS]], <4 x half> poison, <8 x i32> <i32 3, i32 2, i32 1, i32 0, i32 3, i32 2, i32 1, i32 0>
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <8 x half> [[A:%.*]], <8 x half> poison, <8 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP2:%.*]] = shufflevector <8 x half> [[B:%.*]], <8 x half> poison, <8 x i32> zeroinitializer
 ; CHECK-NEXT:    [[R:%.*]] = fadd <8 x half> [[TMP1]], [[TMP2]]
 ; CHECK-NEXT:    ret <8 x half> [[R]]
 ;
diff --git a/llvm/test/Transforms/VectorCombine/X86/extract-insert-poison.ll b/llvm/test/Transforms/VectorCombine/X86/extract-insert-poison.ll
index 642d07a8f3253..e85c092b1b213 100644
--- a/llvm/test/Transforms/VectorCombine/X86/extract-insert-poison.ll
+++ b/llvm/test/Transforms/VectorCombine/X86/extract-insert-poison.ll
@@ -32,8 +32,7 @@ define <4 x double> @src_ins2_v4f64_ext0_v2f64(<4 x double> %a, <2 x double> %b)
 ; SSE-NEXT:    ret <4 x double> [[INS]]
 ;
 ; AVX-LABEL: @src_ins2_v4f64_ext0_v2f64(
-; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <2 x double> [[B:%.*]], <2 x double> poison, <4 x i32> <i32 0, i32 poison, i32 poison, i32 poison>
-; AVX-NEXT:    [[INS:%.*]] = shufflevector <4 x double> [[TMP1]], <4 x double> poison, <4 x i32> <i32 poison, i32 poison, i32 0, i32 poison>
+; AVX-NEXT:    [[INS:%.*]] = shufflevector <2 x double> [[B:%.*]], <2 x double> poison, <4 x i32> <i32 poison, i32 poison, i32 0, i32 poison>
 ; AVX-NEXT:    ret <4 x double> [[INS]]
 ;
   %ext = extractelement <2 x double> %b, i32 0
@@ -48,8 +47,7 @@ define <4 x double> @src_ins3_v4f64_ext0_v2f64(<4 x double> %a, <2 x double> %b)
 ; SSE-NEXT:    ret <4 x double> [[INS]]
 ;
 ; AVX-LABEL: @src_ins3_v4f64_ext0_v2f64(
-; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <2 x double> [[B:%.*]], <2 x double> poison, <4 x i32> <i32 0, i32 poison, i32 poison, i32 poison>
-; AVX-NEXT:    [[INS:%.*]] = shufflevector <4 x double> [[TMP1]], <4 x double> poison, <4 x i32> <i32 poison, i32 poison, i32 poison, i32 0>
+; AVX-NEXT:    [[INS:%.*]] = shufflevector <2 x double> [[B:%.*]], <2 x double> poison, <4 x i32> <i32 poison, i32 poison, i32 poison, i32 0>
 ; AVX-NEXT:    ret <4 x double> [[INS]]
 ;
   %ext = extractelement <2 x double> %b, i32 0
@@ -86,8 +84,7 @@ define <4 x double> @src_ins2_v4f64_ext1_v2f64(<4 x double> %a, <2 x double> %b)
 ; SSE-NEXT:    ret <4 x double> [[INS]]
 ;
 ; AVX-LABEL: @src_ins2_v4f64_ext1_v2f64(
-; AVX-NEXT:    [[TMP1:%.*]] = shufflevector <2 x double> [[B:%.*]], <2 x double> poison, <4 x i32> <i32 poison, i32 1, i32 poison, i32 poison>
-; AVX-NEXT:    [[INS:%.*]] = shufflevector <4 x double> [[TMP1]], <4 x double> poison, <4 x i32> <i32 poison, i32 poison, i32 1, i32 poison>
+; AVX-NEXT:    [[INS:%.*]] = shufflevector <2 x double> [[B:%.*]], <2 x double> poison, <4 x i32> <i32 poison, i32 poison, i32 1, i32 poison>
 ; AVX-NEXT:    ret <4 x double> [[INS]]
 ;
   %ext = extractelement <2 x double> %b, i32 1
@@ -96,10 +93,14 @@ define <4 x double> @src_ins2_v4f64_ext1_v2f64(<4 x double> %a, <2 x double> %b)
 }
 
 define <4 x double> @src_ins3_v4f64_ext1_v2f64(<4 x double> %a, <2 x double> %b) #0 {
-; CHECK-LABEL: @src_ins3_v4f64_ext1_v2f64(
-; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <2 x double> [[B:%.*]], <2 x double> poison, <4 x i32> <i32 poison, i32 1, i32 poison, i32 poison>
-; CHECK-NEXT:    [[INS:%.*]] = shufflevector <4 x double> [[TMP1]], <4 x double> poison, <4 x i32> <i32 poison, i32 poison, i32 poison, i32 1>
-; CHECK-NEXT:    ret <4 x double> [[INS]]
+; SSE-LABEL: @src_ins3_v4f64_ext1_v2f64(
+; SSE-NEXT:    [[TMP1:%.*]] = shufflevector <2 x double> [[B:%.*]], <2 x double> poison, <4 x i32> <i32 poison, i32 1, i32 poison, i32 poison>
+; SSE-NEXT:    [[INS:%.*]] = shufflevector <4 x double> [[TMP1]], <4 x double> poison, <4 x i32> <i32 poison, i32 poison, i32 poison, i32 1>
+; SSE-NEXT:    ret <4 x double> [[INS]]
+;
+; AVX-LABEL: @src_ins3_v4f64_ext1_v2f64(
+; AVX-NEXT:    [[INS:%.*]] = shufflevector <2 x double> [[B:%.*]], <2 x double> poison, <4 x i32> <i32 poison, i32 poison, i32 poison, i32 1>
+; AVX-NEXT:    ret <4 x double> [[INS]]
 ;
   %ext = extractelement <2 x double> %b, i32 1
   %ins = insertelement <4 x double> poison, double %ext, i32 3
@@ -119,8 +120,7 @@ define <2 x double> @src_ins0_v2f64_ext0_v4f64(<2 x double> %a, <4 x double> %b)
 
 define <2 x double> @src_ins0_v2f64_ext1_v4f64(<2 x double> %a, <4 x double> %b) {
 ; CHECK-LABEL: @src_ins0_v2f64_ext1_v4f64(
-; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x double> [[B:%.*]], <4 x double> poison, <2 x i32> <i32 poison, i32 1>
-; CHECK-NEXT:    [[INS:%.*]] = shufflevector <2 x double> [[TMP1]], <2 x double> poison, <2 x i32> <i32 1, i32 poison>
+; CHECK-NEXT:    [[INS:%.*]] = shufflevector <4 x double> [[B:%.*]], <4 x double> poison, <2 x i32> <i32 1, i32 poison>
 ; CHECK-NEXT:    ret <2 x double> [[INS]]
 ;
   %ext = extractelement <4 x double> %b, i32 1
@@ -152,8 +152,7 @@ define <2 x double> @src_ins0_v2f64_ext3_v4f64(<2 x double> %a, <4 x double> %b)
 
 define <2 x double> @src_ins1_v2f64_ext0_v4f64(<2 x double> %a, <4 x double> %b) {
 ; CHECK-LABEL: @src_ins1_v2f64_ext0_v4f64(
-; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x double> [[B:%.*]], <4 x double> poison, <2 x i32> <i32 0, i32 poison>
-; CHECK-NEXT:    [[INS:%.*]] = shufflevector <2 x double> [[TMP1]], <2 x double> poison, <2 x i32> <i32 poison, i32 0>
+; CHECK-NEXT:    [[INS:%.*]] = shufflevector <4 x double> [[B:%.*]], <4 x double> poison, <2 x i32> <i32 poison, i32 0>
 ; CHECK-NEXT:    ret <2 x double> [[INS]]
 ;
   %ext = extractelement <4 x double> %b, i32 0
@@ -164,8 +163,7 @@ define <2 x double> @src_ins1_v2f64_ext0_v4f64(<2 x double> %a, <4 x double> %b)
 define <2 x double> @src_ins1_v2f64_ext1_v4f64(<2 x double> %a, <4 x double> %b) {
 ; CHECK-LABEL: @src_ins1_v2f64_ext1_v4f64(
 ; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x double> [[B:%.*]], <4 x double> poison, <2 x i32> <i32 poison, i32 1>
-; CHECK-NEXT:    [[INS:%.*]] = shufflevector <2 x double> [[TMP1]], <2 x double> poison, <2 x i32> <i32 poison, i32 1>
-; CHECK-NEXT:    ret <2 x double> [[INS]]
+; CHECK-NEXT:    ret <2 x double> [[TMP1]]
 ;
   %ext = extractelement <4 x double> %b, i32 1
   %ins = insertelement <2 x double> poison, double %ext, i32 1
@@ -174,8 +172,7 @@ define <2 x double> @src_ins1_v2f64_ext1_v4f64(<2 x double> %a, <4 x double> %b)
 
 define <2 x double> @src_ins1_v2f64_ext2_v4f64(<2 x double> %a, <4 x double> %b) {
 ; SSE-LABEL: @src_ins1_v2f64_ext2_v4f64(
-; SSE-NEXT:    [[TMP1:%.*]] = shufflevector <4 x double> [[B:%.*]], <4 x double> poison, <2 x i32> <i32 2, i32 poison>
-; SSE-NEXT:    [[INS:%.*]] = shufflevector <2 x double> [[TMP1]], <2 x double> poison, <2 x i32> <i32 poison, i32 0>
+; SSE-NEXT:    [[INS:%.*]] = shufflevector <4 x double> [[B:%.*]], <4 x double> poison, <2 x i32> <i32 poison, i32 2>
 ; SSE-NEXT:    ret <2 x double> [[INS]]
 ;
 ; AVX-LABEL: @src_ins1_v2f64_ext2_v4f64(
@@ -190,8 +187,7 @@ define <2 x double> @src_ins1_v2f64_ext2_v4f64(<2 x double> %a, <4 x double> %b)
 
 define <2 x double> @src_ins1_v2f64_ext3_v4f64(<2 x double> %a, <4 x double> %b) {
 ; CHECK-LABEL: @src_ins1_v2f64_ext3_v4f64(
-; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x double> [[B:%.*]], <4 x double> poison, <2 x i32> <i32 3, i32 poison>
-; CHECK-NEXT:    [[INS:%.*]] = shufflevector <2 x double> [[TMP1]], <2 x double> poison, <2 x i32> <i32 poison, i32 0>
+; CHECK-NEXT:    [[INS:%.*]] = shufflevector <4 x double> [[B:%.*]], <4 x double> poison, <2 x i32> <i32 poison, i32 3>
 ; CHECK-NEXT:    ret <2 x double> [[INS]]
 ;
   %ext = extractelement <4 x double> %b, i32 3
diff --git a/llvm/test/Transforms/VectorCombine/X86/load-inseltpoison.ll b/llvm/test/Transforms/VectorCombine/X86/load-inseltpoison.ll
index 73476308916fb..40437ca345224 100644
--- a/llvm/test/Transforms/VectorCombine/X86/load-inseltpoison.ll
+++ b/llvm/test/Transforms/VectorCombine/X86/load-inseltpoison.ll
@@ -578,8 +578,7 @@ define <8 x i32> @load_v1i32_extract_insert_v8i32_extra_use(ptr align 16 derefer
 ; CHECK-NEXT:    [[L:%.*]] = load <1 x i32>, ptr [[P:%.*]], align 4
 ; CHECK-NEXT:    store <1 x i32> [[L]], ptr [[STORE_PTR:%.*]], align 4
 ; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <1 x i32> [[L]], <1 x i32> poison, <8 x i32> <i32 0, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
-; CHECK-NEXT:    [[R:%.*]] = shufflevector <8 x i32> [[TMP1]], <8 x i32> poison, <8 x i32> <i32 0, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
-; CHECK-NEXT:    ret <8 x i32> [[R]]
+; CHECK-NEXT:    ret <8 x i32> [[TMP1]]
 ;
   %l = load <1 x i32>, ptr %p, align 4
   store <1 x i32> %l, ptr %store_ptr