diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -16179,6 +16179,33 @@
   SDValue Op1 = N->getOperand(1);
   EVT ResVT = N->getValueType(0);
 
+  // uzp1(x, undef) -> concat(truncate(x), undef)
+  if (Op1.getOpcode() == ISD::UNDEF) {
+    EVT BCVT = MVT::Other, HalfVT = MVT::Other;
+    switch (ResVT.getSimpleVT().SimpleTy) {
+    default:
+      break;
+    case MVT::v16i8:
+      BCVT = MVT::v8i16;
+      HalfVT = MVT::v8i8;
+      break;
+    case MVT::v8i16:
+      BCVT = MVT::v4i32;
+      HalfVT = MVT::v4i16;
+      break;
+    case MVT::v4i32:
+      BCVT = MVT::v2i64;
+      HalfVT = MVT::v2i32;
+      break;
+    }
+    if (BCVT != MVT::Other) {
+      SDValue BC = DAG.getBitcast(BCVT, Op0);
+      SDValue Trunc = DAG.getNode(ISD::TRUNCATE, DL, HalfVT, BC);
+      return DAG.getNode(ISD::CONCAT_VECTORS, DL, ResVT, Trunc,
+                         DAG.getUNDEF(HalfVT));
+    }
+  }
+
   // uzp1(unpklo(uzp1(x, y)), z) => uzp1(x, z)
   if (Op0.getOpcode() == AArch64ISD::UUNPKLO) {
     if (Op0.getOperand(0).getOpcode() == AArch64ISD::UZP1) {
diff --git a/llvm/test/CodeGen/AArch64/insert-subvector.ll b/llvm/test/CodeGen/AArch64/insert-subvector.ll
--- a/llvm/test/CodeGen/AArch64/insert-subvector.ll
+++ b/llvm/test/CodeGen/AArch64/insert-subvector.ll
@@ -260,11 +260,9 @@
 define <16 x i8> @load_v16i8_4_1(float %tmp, <16 x i8> %b, <4 x i8> *%a) {
 ; CHECK-LABEL: load_v16i8_4_1:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    ldr s0, [x0]
-; CHECK-NEXT:    ushll v0.8h, v0.8b, #0
-; CHECK-NEXT:    uzp1 v2.16b, v0.16b, v0.16b
 ; CHECK-NEXT:    mov v0.16b, v1.16b
-; CHECK-NEXT:    mov v0.s[0], v2.s[0]
+; CHECK-NEXT:    ldr s1, [x0]
+; CHECK-NEXT:    mov v0.s[0], v1.s[0]
 ; CHECK-NEXT:    ret
   %l = load <4 x i8>, <4 x i8> *%a
   %s1 = shufflevector <4 x i8> %l, <4 x i8> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
@@ -275,11 +273,9 @@
 define <16 x i8> @load_v16i8_4_15(float %tmp, <16 x i8> %b, <4 x i8> *%a) {
 ; CHECK-LABEL: load_v16i8_4_15:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    ldr s0, [x0]
 ; CHECK-NEXT:    adrp x8, .LCPI24_0
-; CHECK-NEXT:    ushll v2.8h, v0.8b, #0
 ; CHECK-NEXT:    // kill: def $q1 killed $q1 def $q0_q1
-; CHECK-NEXT:    uzp1 v0.16b, v2.16b, v0.16b
+; CHECK-NEXT:    ldr s0, [x0]
 ; CHECK-NEXT:    ldr q2, [x8, :lo12:.LCPI24_0]
 ; CHECK-NEXT:    tbl v0.16b, { v0.16b, v1.16b }, v2.16b
 ; CHECK-NEXT:    ret
@@ -292,11 +288,9 @@
 define <16 x i8> @load_v16i8_4_2(float %tmp, <16 x i8> %b, <4 x i8> *%a) {
 ; CHECK-LABEL: load_v16i8_4_2:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    ldr s0, [x0]
-; CHECK-NEXT:    ushll v0.8h, v0.8b, #0
-; CHECK-NEXT:    uzp1 v2.16b, v0.16b, v0.16b
 ; CHECK-NEXT:    mov v0.16b, v1.16b
-; CHECK-NEXT:    mov v0.s[1], v2.s[0]
+; CHECK-NEXT:    ldr s1, [x0]
+; CHECK-NEXT:    mov v0.s[1], v1.s[0]
 ; CHECK-NEXT:    ret
   %l = load <4 x i8>, <4 x i8> *%a
   %s1 = shufflevector <4 x i8> %l, <4 x i8> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
@@ -307,11 +301,9 @@
 define <16 x i8> @load_v16i8_4_3(float %tmp, <16 x i8> %b, <4 x i8> *%a) {
 ; CHECK-LABEL: load_v16i8_4_3:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    ldr s0, [x0]
-; CHECK-NEXT:    ushll v0.8h, v0.8b, #0
-; CHECK-NEXT:    uzp1 v2.16b, v0.16b, v0.16b
 ; CHECK-NEXT:    mov v0.16b, v1.16b
-; CHECK-NEXT:    mov v0.s[2], v2.s[0]
+; CHECK-NEXT:    ldr s1, [x0]
+; CHECK-NEXT:    mov v0.s[2], v1.s[0]
 ; CHECK-NEXT:    ret
   %l = load <4 x i8>, <4 x i8> *%a
   %s1 = shufflevector <4 x i8> %l, <4 x i8> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
@@ -322,11 +314,9 @@
 define <16 x i8> @load_v16i8_4_4(float %tmp, <16 x i8> %b, <4 x i8> *%a) {
 ; CHECK-LABEL: load_v16i8_4_4:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    ldr s0, [x0]
-; CHECK-NEXT:    ushll v0.8h, v0.8b, #0
-; CHECK-NEXT:    uzp1 v2.16b, v0.16b, v0.16b
 ; CHECK-NEXT:    mov v0.16b, v1.16b
-; CHECK-NEXT:    mov v0.s[3], v2.s[0]
+; CHECK-NEXT:    ldr s1, [x0]
+; CHECK-NEXT:    mov v0.s[3], v1.s[0]
 ; CHECK-NEXT:    ret
   %l = load <4 x i8>, <4 x i8> *%a
   %s1 = shufflevector <4 x i8> %l, <4 x i8> poison, <16 x i32> <i32 0, i32 1, i32 2, i32 3, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
@@ -399,11 +389,11 @@
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    ldrh w9, [x0]
 ; CHECK-NEXT:    add x8, x0, #2
-; CHECK-NEXT:    fmov s0, w9
-; CHECK-NEXT:    ld1 { v0.h }[2], [x8]
-; CHECK-NEXT:    uzp1 v2.8h, v0.8h, v0.8h
 ; CHECK-NEXT:    mov v0.16b, v1.16b
-; CHECK-NEXT:    mov v0.s[0], v2.s[0]
+; CHECK-NEXT:    fmov s2, w9
+; CHECK-NEXT:    ld1 { v2.h }[2], [x8]
+; CHECK-NEXT:    xtn v1.4h, v2.4s
+; CHECK-NEXT:    mov v0.s[0], v1.s[0]
 ; CHECK-NEXT:    ret
   %l = load <2 x i16>, <2 x i16> *%a
   %s1 = shufflevector <2 x i16> %l, <2 x i16> poison, <8 x i32> <i32 0, i32 1, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
@@ -420,9 +410,9 @@
 ; CHECK-NEXT:    fmov s2, w9
 ; CHECK-NEXT:    ld1 { v2.h }[2], [x8]
 ; CHECK-NEXT:    adrp x8, .LCPI33_0
-; CHECK-NEXT:    uzp1 v0.8h, v2.8h, v0.8h
-; CHECK-NEXT:    ldr q2, [x8, :lo12:.LCPI33_0]
-; CHECK-NEXT:    tbl v0.16b, { v0.16b, v1.16b }, v2.16b
+; CHECK-NEXT:    ldr q3, [x8, :lo12:.LCPI33_0]
+; CHECK-NEXT:    xtn v0.4h, v2.4s
+; CHECK-NEXT:    tbl v0.16b, { v0.16b, v1.16b }, v3.16b
 ; CHECK-NEXT:    ret
   %l = load <2 x i16>, <2 x i16> *%a
   %s1 = shufflevector <2 x i16> %l, <2 x i16> poison, <8 x i32> <i32 0, i32 1, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
@@ -435,11 +425,11 @@
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    ldrh w9, [x0]
 ; CHECK-NEXT:    add x8, x0, #2
-; CHECK-NEXT:    fmov s0, w9
-; CHECK-NEXT:    ld1 { v0.h }[2], [x8]
-; CHECK-NEXT:    uzp1 v2.8h, v0.8h, v0.8h
 ; CHECK-NEXT:    mov v0.16b, v1.16b
-; CHECK-NEXT:    mov v0.s[1], v2.s[0]
+; CHECK-NEXT:    fmov s2, w9
+; CHECK-NEXT:    ld1 { v2.h }[2], [x8]
+; CHECK-NEXT:    xtn v1.4h, v2.4s
+; CHECK-NEXT:    mov v0.s[1], v1.s[0]
 ; CHECK-NEXT:    ret
   %l = load <2 x i16>, <2 x i16> *%a
   %s1 = shufflevector <2 x i16> %l, <2 x i16> poison, <8 x i32> <i32 0, i32 1, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
@@ -452,11 +442,11 @@
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    ldrh w9, [x0]
 ; CHECK-NEXT:    add x8, x0, #2
-; CHECK-NEXT:    fmov s0, w9
-; CHECK-NEXT:    ld1 { v0.h }[2], [x8]
-; CHECK-NEXT:    uzp1 v2.8h, v0.8h, v0.8h
 ; CHECK-NEXT:    mov v0.16b, v1.16b
-; CHECK-NEXT:    mov v0.s[2], v2.s[0]
+; CHECK-NEXT:    fmov s2, w9
+; CHECK-NEXT:    ld1 { v2.h }[2], [x8]
+; CHECK-NEXT:    xtn v1.4h, v2.4s
+; CHECK-NEXT:    mov v0.s[2], v1.s[0]
 ; CHECK-NEXT:    ret
   %l = load <2 x i16>, <2 x i16> *%a
   %s1 = shufflevector <2 x i16> %l, <2 x i16> poison, <8 x i32> <i32 0, i32 1, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
@@ -469,11 +459,11 @@
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    ldrh w9, [x0]
 ; CHECK-NEXT:    add x8, x0, #2
-; CHECK-NEXT:    fmov s0, w9
-; CHECK-NEXT:    ld1 { v0.h }[2], [x8]
-; CHECK-NEXT:    uzp1 v2.8h, v0.8h, v0.8h
 ; CHECK-NEXT:    mov v0.16b, v1.16b
-; CHECK-NEXT:    mov v0.s[3], v2.s[0]
+; CHECK-NEXT:    fmov s2, w9
+; CHECK-NEXT:    ld1 { v2.h }[2], [x8]
+; CHECK-NEXT:    xtn v1.4h, v2.4s
+; CHECK-NEXT:    mov v0.s[3], v1.s[0]
 ; CHECK-NEXT:    ret
   %l = load <2 x i16>, <2 x i16> *%a
   %s1 = shufflevector <2 x i16> %l, <2 x i16> poison, <8 x i32> <i32 0, i32 1, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef>
diff --git a/llvm/test/CodeGen/AArch64/neon-perm.ll b/llvm/test/CodeGen/AArch64/neon-perm.ll
--- a/llvm/test/CodeGen/AArch64/neon-perm.ll
+++ b/llvm/test/CodeGen/AArch64/neon-perm.ll
@@ -2203,7 +2203,7 @@
 define <16 x i8> @test_undef_vuzp1q_s8(<16 x i8> %a) {
 ; CHECK-LABEL: test_undef_vuzp1q_s8:
 ; CHECK:       // %bb.0: // %entry
-; CHECK-NEXT:    uzp1 v0.16b, v0.16b, v0.16b
+; CHECK-NEXT:    xtn v0.8b, v0.8h
 ; CHECK-NEXT:    ret
 entry:
   %shuffle.i = shufflevector <16 x i8> %a, <16 x i8> undef, <16 x i32> <i32 0, i32 2, i32 4, i32 6, i32 8, i32 10, i32 12, i32 14, i32 16, i32 18, i32 20, i32 22, i32 24, i32 26, i32 28, i32 30>
@@ -2223,7 +2223,7 @@
 define <8 x i16> @test_undef_vuzp1q_s16(<8 x i16> %a) {
 ; CHECK-LABEL: test_undef_vuzp1q_s16:
 ; CHECK:       // %bb.0: // %entry
-; CHECK-NEXT:    uzp1 v0.8h, v0.8h, v0.8h
+; CHECK-NEXT:    xtn v0.4h, v0.4s
 ; CHECK-NEXT:    ret
 entry:
   %shuffle.i = shufflevector <8 x i16> %a, <8 x i16> undef, <8 x i32> <i32 0, i32 2, i32 4, i32 6, i32 8, i32 10, i32 12, i32 14>
@@ -2233,7 +2233,7 @@
 define <4 x i32> @test_undef_vuzp1q_s32(<4 x i32> %a) {
 ; CHECK-LABEL: test_undef_vuzp1q_s32:
 ; CHECK:       // %bb.0: // %entry
-; CHECK-NEXT:    uzp1 v0.4s, v0.4s, v0.4s
+; CHECK-NEXT:    xtn v0.2s, v0.2d
 ; CHECK-NEXT:    ret
 entry:
   %shuffle.i = shufflevector <4 x i32> %a, <4 x i32> undef, <4 x i32> <i32 0, i32 2, i32 4, i32 6>
@@ -2253,7 +2253,7 @@
 define <16 x i8> @test_undef_vuzp1q_u8(<16 x i8> %a) {
 ; CHECK-LABEL: test_undef_vuzp1q_u8:
 ; CHECK:       // %bb.0: // %entry
-; CHECK-NEXT:    uzp1 v0.16b, v0.16b, v0.16b
+; CHECK-NEXT:    xtn v0.8b, v0.8h
 ; CHECK-NEXT:    ret
 entry:
   %shuffle.i = shufflevector <16 x i8> %a, <16 x i8> undef, <16 x i32> <i32 0, i32 2, i32 4, i32 6, i32 8, i32 10, i32 12, i32 14, i32 16, i32 18, i32 20, i32 22, i32 24, i32 26, i32 28, i32 30>
@@ -2273,7 +2273,7 @@
 define <8 x i16> @test_undef_vuzp1q_u16(<8 x i16> %a) {
 ; CHECK-LABEL: test_undef_vuzp1q_u16:
 ; CHECK:       // %bb.0: // %entry
-; CHECK-NEXT:    uzp1 v0.8h, v0.8h, v0.8h
+; CHECK-NEXT:    xtn v0.4h, v0.4s
 ; CHECK-NEXT:    ret
 entry:
   %shuffle.i = shufflevector <8 x i16> %a, <8 x i16> undef, <8 x i32> <i32 0, i32 2, i32 4, i32 6, i32 8, i32 10, i32 12, i32 14>
@@ -2283,7 +2283,7 @@
 define <4 x i32> @test_undef_vuzp1q_u32(<4 x i32> %a) {
 ; CHECK-LABEL: test_undef_vuzp1q_u32:
 ; CHECK:       // %bb.0: // %entry
-; CHECK-NEXT:    uzp1 v0.4s, v0.4s, v0.4s
+; CHECK-NEXT:    xtn v0.2s, v0.2d
 ; CHECK-NEXT:    ret
 entry:
   %shuffle.i = shufflevector <4 x i32> %a, <4 x i32> undef, <4 x i32> <i32 0, i32 2, i32 4, i32 6>
@@ -2313,7 +2313,7 @@
 define <16 x i8> @test_undef_vuzp1q_p8(<16 x i8> %a) {
 ; CHECK-LABEL: test_undef_vuzp1q_p8:
 ; CHECK:       // %bb.0: // %entry
-; CHECK-NEXT:    uzp1 v0.16b, v0.16b, v0.16b
+; CHECK-NEXT:    xtn v0.8b, v0.8h
 ; CHECK-NEXT:    ret
 entry:
   %shuffle.i = shufflevector <16 x i8> %a, <16 x i8> undef, <16 x i32> <i32 0, i32 2, i32 4, i32 6, i32 8, i32 10, i32 12, i32 14, i32 16, i32 18, i32 20, i32 22, i32 24, i32 26, i32 28, i32 30>
@@ -2333,7 +2333,7 @@
 define <8 x i16> @test_undef_vuzp1q_p16(<8 x i16> %a) {
 ; CHECK-LABEL: test_undef_vuzp1q_p16:
 ; CHECK:       // %bb.0: // %entry
-; CHECK-NEXT:    uzp1 v0.8h, v0.8h, v0.8h
+; CHECK-NEXT:    xtn v0.4h, v0.4s
 ; CHECK-NEXT:    ret
 entry:
   %shuffle.i = shufflevector <8 x i16> %a, <8 x i16> undef, <8 x i32> <i32 0, i32 2, i32 4, i32 6, i32 8, i32 10, i32 12, i32 14>