Index: llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
===================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -990,8 +990,10 @@
   // Expand mask indices to byte indices and materialize them as operands
   for (size_t I = 0, Lanes = Mask.size(); I < Lanes; ++I) {
     for (size_t J = 0; J < LaneBytes; ++J) {
-      Ops[OpIdx++] =
-          DAG.getConstant((uint64_t)Mask[I] * LaneBytes + J, DL, MVT::i32);
+      // Lower undefs (represented by -1 in mask) to zero
+      uint64_t ByteIndex =
+          Mask[I] == -1 ? 0 : (uint64_t)Mask[I] * LaneBytes + J;
+      Ops[OpIdx++] = DAG.getConstant(ByteIndex, DL, MVT::i32);
     }
   }
 
Index: llvm/trunk/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td
===================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td
@@ -181,6 +181,28 @@
 def : Pat<(i32 (vector_extract (v8i16 V128:$vec), (i32 LaneIdx8:$idx))),
           (EXTRACT_LANE_v8i16_u V128:$vec, (i32 LaneIdx8:$idx))>;
 
+// Lower undef lane indices to zero
+def : Pat<(and (i32 (vector_extract (v16i8 V128:$vec), undef)), (i32 0xff)),
+          (EXTRACT_LANE_v16i8_u V128:$vec, 0)>;
+def : Pat<(and (i32 (vector_extract (v8i16 V128:$vec), undef)), (i32 0xffff)),
+          (EXTRACT_LANE_v8i16_u V128:$vec, 0)>;
+def : Pat<(i32 (vector_extract (v16i8 V128:$vec), undef)),
+          (EXTRACT_LANE_v16i8_u V128:$vec, 0)>;
+def : Pat<(i32 (vector_extract (v8i16 V128:$vec), undef)),
+          (EXTRACT_LANE_v8i16_u V128:$vec, 0)>;
+def : Pat<(sext_inreg (i32 (vector_extract (v16i8 V128:$vec), undef)), i8),
+          (EXTRACT_LANE_v16i8_s V128:$vec, 0)>;
+def : Pat<(sext_inreg (i32 (vector_extract (v8i16 V128:$vec), undef)), i16),
+          (EXTRACT_LANE_v8i16_s V128:$vec, 0)>;
+def : Pat<(vector_extract (v4i32 V128:$vec), undef),
+          (EXTRACT_LANE_v4i32 V128:$vec, 0)>;
+def : Pat<(vector_extract (v2i64 V128:$vec), undef),
+          (EXTRACT_LANE_v2i64 V128:$vec, 0)>;
+def : Pat<(vector_extract (v4f32 V128:$vec), undef),
+          (EXTRACT_LANE_v4f32 V128:$vec, 0)>;
+def : Pat<(vector_extract (v2f64 V128:$vec), undef),
+          (EXTRACT_LANE_v2f64 V128:$vec, 0)>;
+
 // Replace lane value: replace_lane
 multiclass ReplaceLane<ValueType vec_t, string vec, ImmLeaf imm_t,
                        WebAssemblyRegClass reg_t, ValueType lane_t,
@@ -201,6 +223,20 @@
 defm "" : ReplaceLane<v4f32, "f32x4", LaneIdx4, F32, f32, 21>;
 defm "" : ReplaceLane<v2f64, "f64x2", LaneIdx2, F64, f64, 22>;
 
+// Lower undef lane indices to zero
+def : Pat<(vector_insert (v16i8 V128:$vec), I32:$x, undef),
+          (REPLACE_LANE_v16i8 V128:$vec, 0, I32:$x)>;
+def : Pat<(vector_insert (v8i16 V128:$vec), I32:$x, undef),
+          (REPLACE_LANE_v8i16 V128:$vec, 0, I32:$x)>;
+def : Pat<(vector_insert (v4i32 V128:$vec), I32:$x, undef),
+          (REPLACE_LANE_v4i32 V128:$vec, 0, I32:$x)>;
+def : Pat<(vector_insert (v2i64 V128:$vec), I64:$x, undef),
+          (REPLACE_LANE_v2i64 V128:$vec, 0, I64:$x)>;
+def : Pat<(vector_insert (v4f32 V128:$vec), F32:$x, undef),
+          (REPLACE_LANE_v4f32 V128:$vec, 0, F32:$x)>;
+def : Pat<(vector_insert (v2f64 V128:$vec), F64:$x, undef),
+          (REPLACE_LANE_v2f64 V128:$vec, 0, F64:$x)>;
+
 // Arbitrary other BUILD_VECTOR patterns
 def : Pat<(v16i8 (build_vector
             (i32 I32:$x0), (i32 I32:$x1), (i32 I32:$x2), (i32 I32:$x3),
Index: llvm/trunk/test/CodeGen/WebAssembly/simd.ll
===================================================================
--- llvm/trunk/test/CodeGen/WebAssembly/simd.ll
+++ llvm/trunk/test/CodeGen/WebAssembly/simd.ll
@@ -54,6 +54,18 @@
   ret i32 %a
 }
 
+; CHECK-LABEL: extract_undef_v16i8_s:
+; NO-SIMD128-NOT: i8x16
+; SIMD128-NEXT: .param v128{{$}}
+; SIMD128-NEXT: .result i32{{$}}
+; SIMD128-NEXT: i8x16.extract_lane_s $push[[R:[0-9]+]]=, $0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define i32 @extract_undef_v16i8_s(<16 x i8> %v) {
+  %elem = extractelement <16 x i8> %v, i8 undef
+  %a = sext i8 %elem to i32
+  ret i32 %a
+}
+
 ; CHECK-LABEL: extract_v16i8_u:
 ; NO-SIMD128-NOT: i8x16
 ; SIMD128-NEXT: .param v128{{$}}
@@ -66,6 +78,18 @@
   ret i32 %a
 }
 
+; CHECK-LABEL: extract_undef_v16i8_u:
+; NO-SIMD128-NOT: i8x16
+; SIMD128-NEXT: .param v128{{$}}
+; SIMD128-NEXT: .result i32{{$}}
+; SIMD128-NEXT: i8x16.extract_lane_u $push[[R:[0-9]+]]=, $0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define i32 @extract_undef_v16i8_u(<16 x i8> %v) {
+  %elem = extractelement <16 x i8> %v, i8 undef
+  %a = zext i8 %elem to i32
+  ret i32 %a
+}
+
 ; CHECK-LABEL: extract_v16i8:
 ; NO-SIMD128-NOT: i8x16
 ; SIMD128-NEXT: .param v128{{$}}
@@ -77,6 +101,17 @@
   ret i8 %elem
 }
 
+; CHECK-LABEL: extract_undef_v16i8:
+; NO-SIMD128-NOT: i8x16
+; SIMD128-NEXT: .param v128{{$}}
+; SIMD128-NEXT: .result i32{{$}}
+; SIMD128-NEXT: i8x16.extract_lane_u $push[[R:[0-9]+]]=, $0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define i8 @extract_undef_v16i8(<16 x i8> %v) {
+  %elem = extractelement <16 x i8> %v, i8 undef
+  ret i8 %elem
+}
+
 ; CHECK-LABEL: replace_v16i8:
 ; NO-SIMD128-NOT: i8x16
 ; SIMD128-NEXT: .param v128, i32{{$}}
@@ -88,6 +123,17 @@
   ret <16 x i8> %res
 }
 
+; CHECK-LABEL: replace_undef_v16i8:
+; NO-SIMD128-NOT: i8x16
+; SIMD128-NEXT: .param v128, i32{{$}}
+; SIMD128-NEXT: .result v128{{$}}
+; SIMD128-NEXT: i8x16.replace_lane $push[[R:[0-9]+]]=, $0, 0, $1{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define <16 x i8> @replace_undef_v16i8(<16 x i8> %v, i8 %x) {
+  %res = insertelement <16 x i8> %v, i8 %x, i32 undef
+  ret <16 x i8> %res
+}
+
 ; CHECK-LABEL: shuffle_v16i8:
 ; NO-SIMD128-NOT: v8x16
 ; SIMD128-NEXT: .param v128, v128{{$}}
@@ -102,6 +148,22 @@
   ret <16 x i8> %res
 }
 
+; CHECK-LABEL: shuffle_undef_v16i8:
+; NO-SIMD128-NOT: v8x16
+; SIMD128-NEXT: .param v128, v128{{$}}
+; SIMD128-NEXT: .result v128{{$}}
+; SIMD128-NEXT: v8x16.shuffle $push[[R:[0-9]+]]=, $0, $0,
+; SIMD128-SAME: 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define <16 x i8> @shuffle_undef_v16i8(<16 x i8> %x, <16 x i8> %y) {
+  %res = shufflevector <16 x i8> %x, <16 x i8> %y,
+    <16 x i32> <i32 1, i32 undef, i32 undef, i32 undef,
+                i32 undef, i32 undef, i32 undef, i32 undef,
+                i32 undef, i32 undef, i32 undef, i32 undef,
+                i32 undef, i32 undef, i32 undef, i32 undef>
+  ret <16 x i8> %res
+}
+
 ; CHECK-LABEL: build_v16i8:
 ; NO-SIMD128-NOT: i8x16
 ; SIMD128-NEXT: .param i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32{{$}}
@@ -190,6 +252,18 @@
   ret i32 %a
 }
 
+; CHECK-LABEL: extract_undef_v8i16_s:
+; NO-SIMD128-NOT: i16x8
+; SIMD128-NEXT: .param v128{{$}}
+; SIMD128-NEXT: .result i32{{$}}
+; SIMD128-NEXT: i16x8.extract_lane_s $push[[R:[0-9]+]]=, $0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define i32 @extract_undef_v8i16_s(<8 x i16> %v) {
+  %elem = extractelement <8 x i16> %v, i16 undef
+  %a = sext i16 %elem to i32
+  ret i32 %a
+}
+
 ; CHECK-LABEL: extract_v8i16_u:
 ; NO-SIMD128-NOT: i16x8
 ; SIMD128-NEXT: .param v128{{$}}
@@ -202,6 +276,18 @@
   ret i32 %a
 }
 
+; CHECK-LABEL: extract_undef_v8i16_u:
+; NO-SIMD128-NOT: i16x8
+; SIMD128-NEXT: .param v128{{$}}
+; SIMD128-NEXT: .result i32{{$}}
+; SIMD128-NEXT: i16x8.extract_lane_u $push[[R:[0-9]+]]=, $0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define i32 @extract_undef_v8i16_u(<8 x i16> %v) {
+  %elem = extractelement <8 x i16> %v, i16 undef
+  %a = zext i16 %elem to i32
+  ret i32 %a
+}
+
 ; CHECK-LABEL: extract_v8i16:
 ; NO-SIMD128-NOT: i16x8
 ; SIMD128-NEXT: .param v128{{$}}
@@ -213,6 +299,17 @@
   ret i16 %elem
 }
 
+; CHECK-LABEL: extract_undef_v8i16:
+; NO-SIMD128-NOT: i16x8
+; SIMD128-NEXT: .param v128{{$}}
+; SIMD128-NEXT: .result i32{{$}}
+; SIMD128-NEXT: i16x8.extract_lane_u $push[[R:[0-9]+]]=, $0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define i16 @extract_undef_v8i16(<8 x i16> %v) {
+  %elem = extractelement <8 x i16> %v, i16 undef
+  ret i16 %elem
+}
+
 ; CHECK-LABEL: replace_v8i16:
 ; NO-SIMD128-NOT: i16x8
 ; SIMD128-NEXT: .param v128, i32{{$}}
@@ -224,6 +321,17 @@
   ret <8 x i16> %res
 }
 
+; CHECK-LABEL: replace_undef_v8i16:
+; NO-SIMD128-NOT: i16x8
+; SIMD128-NEXT: .param v128, i32{{$}}
+; SIMD128-NEXT: .result v128{{$}}
+; SIMD128-NEXT: i16x8.replace_lane $push[[R:[0-9]+]]=, $0, 0, $1{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define <8 x i16> @replace_undef_v8i16(<8 x i16> %v, i16 %x) {
+  %res = insertelement <8 x i16> %v, i16 %x, i32 undef
+  ret <8 x i16> %res
+}
+
 ; CHECK-LABEL: shuffle_v8i16:
 ; NO-SIMD128-NOT: v8x16
 ; SIMD128-NEXT: .param v128, v128{{$}}
@@ -237,6 +345,20 @@
   ret <8 x i16> %res
 }
 
+; CHECK-LABEL: shuffle_undef_v8i16:
+; NO-SIMD128-NOT: v8x16
+; SIMD128-NEXT: .param v128, v128{{$}}
+; SIMD128-NEXT: .result v128{{$}}
+; SIMD128-NEXT: v8x16.shuffle $push[[R:[0-9]+]]=, $0, $0,
+; SIMD128-SAME: 2, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define <8 x i16> @shuffle_undef_v8i16(<8 x i16> %x, <8 x i16> %y) {
+  %res = shufflevector <8 x i16> %x, <8 x i16> %y,
+    <8 x i32> <i32 1, i32 undef, i32 undef, i32 undef,
+               i32 undef, i32 undef, i32 undef, i32 undef>
+  ret <8 x i16> %res
+}
+
 ; CHECK-LABEL: build_v8i16:
 ; NO-SIMD128-NOT: i16x8
 ; SIMD128-NEXT: .param i32, i32, i32, i32, i32, i32, i32, i32{{$}}
@@ -305,6 +427,17 @@
   ret i32 %elem
 }
 
+; CHECK-LABEL: extract_undef_v4i32:
+; NO-SIMD128-NOT: i32x4
+; SIMD128-NEXT: .param v128{{$}}
+; SIMD128-NEXT: .result i32{{$}}
+; SIMD128-NEXT: i32x4.extract_lane $push[[R:[0-9]+]]=, $0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define i32 @extract_undef_v4i32(<4 x i32> %v) {
+  %elem = extractelement <4 x i32> %v, i32 undef
+  ret i32 %elem
+}
+
 ; CHECK-LABEL: replace_v4i32:
 ; NO-SIMD128-NOT: i32x4
 ; SIMD128-NEXT: .param v128, i32{{$}}
@@ -316,6 +449,17 @@
   ret <4 x i32> %res
 }
 
+; CHECK-LABEL: replace_undef_v4i32:
+; NO-SIMD128-NOT: i32x4
+; SIMD128-NEXT: .param v128, i32{{$}}
+; SIMD128-NEXT: .result v128{{$}}
+; SIMD128-NEXT: i32x4.replace_lane $push[[R:[0-9]+]]=, $0, 0, $1{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define <4 x i32> @replace_undef_v4i32(<4 x i32> %v, i32 %x) {
+  %res = insertelement <4 x i32> %v, i32 %x, i32 undef
+  ret <4 x i32> %res
+}
+
 ; CHECK-LABEL: shuffle_v4i32:
 ; NO-SIMD128-NOT: v8x16
 ; SIMD128-NEXT: .param v128, v128{{$}}
@@ -329,6 +473,19 @@
   ret <4 x i32> %res
 }
 
+; CHECK-LABEL: shuffle_undef_v4i32:
+; NO-SIMD128-NOT: v8x16
+; SIMD128-NEXT: .param v128, v128{{$}}
+; SIMD128-NEXT: .result v128{{$}}
+; SIMD128-NEXT: v8x16.shuffle $push[[R:[0-9]+]]=, $0, $0,
+; SIMD128-SAME: 4, 5, 6, 7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define <4 x i32> @shuffle_undef_v4i32(<4 x i32> %x, <4 x i32> %y) {
+  %res = shufflevector <4 x i32> %x, <4 x i32> %y,
+    <4 x i32> <i32 1, i32 undef, i32 undef, i32 undef>
+  ret <4 x i32> %res
+}
+
 ; CHECK-LABEL: build_v4i32:
 ; NO-SIMD128-NOT: i32x4
 ; SIMD128-NEXT: .param i32, i32, i32, i32{{$}}
@@ -390,6 +547,18 @@
   ret i64 %elem
 }
 
+; CHECK-LABEL: extract_undef_v2i64:
+; NO-SIMD128-NOT: i64x2
+; SIMD128-VM-NOT: i64x2
+; SIMD128-NEXT: .param v128{{$}}
+; SIMD128-NEXT: .result i64{{$}}
+; SIMD128-NEXT: i64x2.extract_lane $push[[R:[0-9]+]]=, $0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define i64 @extract_undef_v2i64(<2 x i64> %v) {
+  %elem = extractelement <2 x i64> %v, i64 undef
+  ret i64 %elem
+}
+
 ; CHECK-LABEL: replace_v2i64:
 ; NO-SIMD128-NOT: i64x2
 ; SIMD128-VM-NOT: i64x2
@@ -402,6 +571,18 @@
   ret <2 x i64> %res
 }
 
+; CHECK-LABEL: replace_undef_v2i64:
+; NO-SIMD128-NOT: i64x2
+; SIMD128-VM-NOT: i64x2
+; SIMD128-NEXT: .param v128, i64{{$}}
+; SIMD128-NEXT: .result v128{{$}}
+; SIMD128-NEXT: i64x2.replace_lane $push[[R:[0-9]+]]=, $0, 0, $1{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define <2 x i64> @replace_undef_v2i64(<2 x i64> %v, i64 %x) {
+  %res = insertelement <2 x i64> %v, i64 %x, i32 undef
+  ret <2 x i64> %res
+}
+
 ; CHECK-LABEL: shuffle_v2i64:
 ; NO-SIMD128-NOT: v8x16
 ; SIMD128-NEXT: .param v128, v128{{$}}
@@ -414,6 +595,19 @@
   ret <2 x i64> %res
 }
 
+; CHECK-LABEL: shuffle_undef_v2i64:
+; NO-SIMD128-NOT: v8x16
+; SIMD128-NEXT: .param v128, v128{{$}}
+; SIMD128-NEXT: .result v128{{$}}
+; SIMD128-NEXT: v8x16.shuffle $push[[R:[0-9]+]]=, $0, $0,
+; SIMD128-SAME: 8, 9, 10, 11, 12, 13, 14, 15, 0, 0, 0, 0, 0, 0, 0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define <2 x i64> @shuffle_undef_v2i64(<2 x i64> %x, <2 x i64> %y) {
+  %res = shufflevector <2 x i64> %x, <2 x i64> %y,
+    <2 x i32> <i32 1, i32 undef>
+  ret <2 x i64> %res
+}
+
 ; CHECK-LABEL: build_v2i64:
 ; NO-SIMD128-NOT: i64x2
 ; SIMD128-VM-NOT: i64x2
@@ -472,6 +666,17 @@
   ret float %elem
 }
 
+; CHECK-LABEL: extract_undef_v4f32:
+; NO-SIMD128-NOT: f32x4
+; SIMD128-NEXT: .param v128{{$}}
+; SIMD128-NEXT: .result f32{{$}}
+; SIMD128-NEXT: f32x4.extract_lane $push[[R:[0-9]+]]=, $0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define float @extract_undef_v4f32(<4 x float> %v) {
+  %elem = extractelement <4 x float> %v, i32 undef
+  ret float %elem
+}
+
 ; CHECK-LABEL: replace_v4f32:
 ; NO-SIMD128-NOT: f32x4
 ; SIMD128-NEXT: .param v128, f32{{$}}
@@ -483,6 +688,17 @@
   ret <4 x float> %res
 }
 
+; CHECK-LABEL: replace_undef_v4f32:
+; NO-SIMD128-NOT: f32x4
+; SIMD128-NEXT: .param v128, f32{{$}}
+; SIMD128-NEXT: .result v128{{$}}
+; SIMD128-NEXT: f32x4.replace_lane $push[[R:[0-9]+]]=, $0, 0, $1{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define <4 x float> @replace_undef_v4f32(<4 x float> %v, float %x) {
+  %res = insertelement <4 x float> %v, float %x, i32 undef
+  ret <4 x float> %res
+}
+
 ; CHECK-LABEL: shuffle_v4f32:
 ; NO-SIMD128-NOT: v8x16
 ; SIMD128-NEXT: .param v128, v128{{$}}
@@ -496,6 +712,19 @@
   ret <4 x float> %res
 }
 
+; CHECK-LABEL: shuffle_undef_v4f32:
+; NO-SIMD128-NOT: v8x16
+; SIMD128-NEXT: .param v128, v128{{$}}
+; SIMD128-NEXT: .result v128{{$}}
+; SIMD128-NEXT: v8x16.shuffle $push[[R:[0-9]+]]=, $0, $0,
+; SIMD128-SAME: 4, 5, 6, 7, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define <4 x float> @shuffle_undef_v4f32(<4 x float> %x, <4 x float> %y) {
+  %res = shufflevector <4 x float> %x, <4 x float> %y,
+    <4 x i32> <i32 1, i32 undef, i32 undef, i32 undef>
+  ret <4 x float> %res
+}
+
 ; CHECK-LABEL: build_v4f32:
 ; NO-SIMD128-NOT: f32x4
 ; SIMD128-NEXT: .param f32, f32, f32, f32{{$}}
@@ -556,6 +785,18 @@
   ret double %elem
 }
 
+; CHECK-LABEL: extract_undef_v2f64:
+; NO-SIMD128-NOT: f64x2
+; SIMD128-VM-NOT: f64x2
+; SIMD128-NEXT: .param v128{{$}}
+; SIMD128-NEXT: .result f64{{$}}
+; SIMD128-NEXT: f64x2.extract_lane $push[[R:[0-9]+]]=, $0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define double @extract_undef_v2f64(<2 x double> %v) {
+  %elem = extractelement <2 x double> %v, i32 undef
+  ret double %elem
+}
+
 ; CHECK-LABEL: replace_v2f64:
 ; NO-SIMD128-NOT: f64x2
 ; SIMD128-VM-NOT: f64x2
@@ -568,6 +809,18 @@
   ret <2 x double> %res
 }
 
+; CHECK-LABEL: replace_undef_v2f64:
+; NO-SIMD128-NOT: f64x2
+; SIMD128-VM-NOT: f64x2
+; SIMD128-NEXT: .param v128, f64{{$}}
+; SIMD128-NEXT: .result v128{{$}}
+; SIMD128-NEXT: f64x2.replace_lane $push[[R:[0-9]+]]=, $0, 0, $1{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define <2 x double> @replace_undef_v2f64(<2 x double> %v, double %x) {
+  %res = insertelement <2 x double> %v, double %x, i32 undef
+  ret <2 x double> %res
+}
+
 ; CHECK-LABEL: shuffle_v2f64:
 ; NO-SIMD128-NOT: v8x16
 ; SIMD128-NEXT: .param v128, v128{{$}}
@@ -581,6 +834,19 @@
   ret <2 x double> %res
 }
 
+; CHECK-LABEL: shuffle_undef_v2f64:
+; NO-SIMD128-NOT: v8x16
+; SIMD128-NEXT: .param v128, v128{{$}}
+; SIMD128-NEXT: .result v128{{$}}
+; SIMD128-NEXT: v8x16.shuffle $push[[R:[0-9]+]]=, $0, $0,
+; SIMD128-SAME: 8, 9, 10, 11, 12, 13, 14, 15, 0, 0, 0, 0, 0, 0, 0, 0{{$}}
+; SIMD128-NEXT: return $pop[[R]]{{$}}
+define <2 x double> @shuffle_undef_v2f64(<2 x double> %x, <2 x double> %y) {
+  %res = shufflevector <2 x double> %x, <2 x double> %y,
+    <2 x i32> <i32 1, i32 undef>
+  ret <2 x double> %res
+}
+
 ; CHECK-LABEL: build_v2f64:
 ; NO-SIMD128-NOT: f64x2
 ; SIMD128-VM-NOT: f64x2