Index: lib/Target/WebAssembly/WebAssemblyInstrSIMD.td
===================================================================
--- lib/Target/WebAssembly/WebAssemblyInstrSIMD.td
+++ lib/Target/WebAssembly/WebAssemblyInstrSIMD.td
@@ -74,6 +74,27 @@
 def : Pat<(i32 (vector_extract (v8i16 V128:$vec), (i32 LaneIdx8:$idx))),
           (EXTRACT_LANE_U_I16x8 V128:$vec, (i32 LaneIdx8:$idx))>;
 
+// lane replacement
+multiclass ReplaceLane<ValueType vec_t, string name, WebAssemblyRegClass reg_t,
+                       ValueType lane_t, ImmLeaf imm_t, bits<32> simdop> {
+  defm REPLACE_LANE_#vec_t : SIMD_I<(outs V128:$dst),
+                                    (ins V128:$vec, I32:$idx, reg_t:$x),
+                                    (outs), (ins I32:$idx),
+                                    [(set V128:$dst, (vector_insert
+                                      (vec_t V128:$vec),
+                                      (lane_t reg_t:$x),
+                                      (i32 imm_t:$idx)))],
+                                    name#".replace_lane\t$dst, $vec, $idx, $x",
+                                    "i8x16.replace_lane\t$idx", simdop>;
+}
+let Defs = [ARGUMENTS] in {
+defm "" : ReplaceLane<v16i8, "i8x16", I32, i32, LaneIdx16, 17>;
+defm "" : ReplaceLane<v8i16, "i16x8", I32, i32, LaneIdx8, 18>;
+defm "" : ReplaceLane<v4i32, "i32x4", I32, i32, LaneIdx4, 19>;
+defm "" : ReplaceLane<v2i64, "i64x2", I64, i64, LaneIdx2, 20>;
+defm "" : ReplaceLane<v4f32, "f32x4", F32, f32, LaneIdx4, 21>;
+defm "" : ReplaceLane<v2f64, "f64x2", F64, f64, LaneIdx2, 22>;
+} // Defs = [ARGUMENTS]
 
 // splats
 def splat2 : PatFrag<(ops node:$x), (build_vector node:$x, node:$x)>;
@@ -100,7 +121,7 @@
 defm "" : Splat<v2i64, "i64x2", I64, splat2, 6>;
 defm "" : Splat<v4f32, "f32x4", F32, splat4, 7>;
 defm "" : Splat<v2f64, "f64x2", F64, splat2, 8>;
-}
+} // Defs = [ARGUMENTS]
 
 // arithmetic
 let Defs = [ARGUMENTS] in {
Index: test/CodeGen/WebAssembly/simd.ll
===================================================================
--- test/CodeGen/WebAssembly/simd.ll
+++ test/CodeGen/WebAssembly/simd.ll
@@ -59,6 +59,17 @@
   ret i8 %elem
 }
 
+; CHECK-LABEL: replace_v16i8:
+; NO-SIMD128-NOT: i8x16
+; SIMD128: .param v128, i32{{$}}
+; SIMD128: .result v128{{$}}
+; SIMD128: i8x16.replace_lane $push0=, $0, 11, $1 # encoding: [0xfd,0x11,0x0b]{{$}}
+; SIMD128: return $pop0 # encoding: [0x0f]{{$}}
+define <16 x i8> @replace_v16i8(<16 x i8> %v, i8 %x) {
+  %res = insertelement <16 x i8> %v, i8 %x, i32 11
+  ret <16 x i8> %res
+}
+
 ; ==============================================================================
 ; 8 x i16
 ; ==============================================================================
@@ -110,6 +121,17 @@
   ret i16 %elem
 }
 
+; CHECK-LABEL: replace_v8i16:
+; NO-SIMD128-NOT: i16x8
+; SIMD128: .param v128, i32{{$}}
+; SIMD128: .result v128{{$}}
+; SIMD128: i16x8.replace_lane $push0=, $0, 7, $1 # encoding: [0xfd,0x12,0x07]{{$}}
+; SIMD128: return $pop0 # encoding: [0x0f]{{$}}
+define <8 x i16> @replace_v8i16(<8 x i16> %v, i16 %x) {
+  %res = insertelement <8 x i16> %v, i16 %x, i32 7
+  ret <8 x i16> %res
+}
+
 ; ==============================================================================
 ; 4 x i32
 ; ==============================================================================
@@ -137,6 +159,17 @@
   ret i32 %elem
 }
 
+; CHECK-LABEL: replace_v4i32:
+; NO-SIMD128-NOT: i32x4
+; SIMD128: .param v128, i32{{$}}
+; SIMD128: .result v128{{$}}
+; SIMD128: i32x4.replace_lane $push0=, $0, 2, $1 # encoding: [0xfd,0x13,0x02]{{$}}
+; SIMD128: return $pop0 # encoding: [0x0f]{{$}}
+define <4 x i32> @replace_v4i32(<4 x i32> %v, i32 %x) {
+  %res = insertelement <4 x i32> %v, i32 %x, i32 2
+  ret <4 x i32> %res
+}
+
 ; ==============================================================================
 ; 2 x i64
 ; ==============================================================================
@@ -165,6 +198,18 @@
   ret i64 %elem
 }
 
+; CHECK-LABEL: replace_v2i64:
+; NO-SIMD128-NOT: i64x2
+; SIMD128-VM-NOT: i64x2
+; SIMD128: .param v128, i64{{$}}
+; SIMD128: .result v128{{$}}
+; SIMD128: i64x2.replace_lane $push0=, $0, 0, $1 # encoding: [0xfd,0x14,0x00]{{$}}
+; SIMD128: return $pop0 # encoding: [0x0f]{{$}}
+define <2 x i64> @replace_v2i64(<2 x i64> %v, i64 %x) {
+  %res = insertelement <2 x i64> %v, i64 %x, i32 0
+  ret <2 x i64> %res
+}
+
 ; ==============================================================================
 ; 4 x f32
 ; ==============================================================================
@@ -192,6 +237,17 @@
   ret float %elem
 }
 
+; CHECK-LABEL: replace_v4f32:
+; NO-SIMD128-NOT: f32x4
+; SIMD128: .param v128, f32{{$}}
+; SIMD128: .result v128{{$}}
+; SIMD128: f32x4.replace_lane $push0=, $0, 2, $1 # encoding: [0xfd,0x15,0x02]{{$}}
+; SIMD128: return $pop0 # encoding: [0x0f]{{$}}
+define <4 x float> @replace_v4f32(<4 x float> %v, float %x) {
+  %res = insertelement <4 x float> %v, float %x, i32 2
+  ret <4 x float> %res
+}
+
 ; ==============================================================================
 ; 2 x f64
 ; ==============================================================================
@@ -219,3 +275,15 @@
   %elem = extractelement <2 x double> %v, i32 1
   ret double %elem
 }
+
+; CHECK-LABEL: replace_v2f64:
+; NO-SIMD128-NOT: f64x2
+; SIMD128-VM-NOT: f64x2
+; SIMD128: .param v128, f64{{$}}
+; SIMD128: .result v128{{$}}
+; SIMD128: f64x2.replace_lane $push0=, $0, 0, $1 # encoding: [0xfd,0x16,0x00]{{$}}
+; SIMD128: return $pop0 # encoding: [0x0f]{{$}}
+define <2 x double> @replace_v2f64(<2 x double> %v, double %x) {
+  %res = insertelement <2 x double> %v, double %x, i32 0
+  ret <2 x double> %res
+}