Index: llvm/trunk/lib/Target/WebAssembly/WebAssemblyISD.def
===================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblyISD.def
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblyISD.def
@@ -26,5 +26,6 @@
 HANDLE_NODETYPE(VEC_SHR_U)
 HANDLE_NODETYPE(THROW)
 HANDLE_NODETYPE(MEMORY_COPY)
+HANDLE_NODETYPE(MEMORY_FILL)
 
 // add memory opcodes starting at ISD::FIRST_TARGET_MEMORY_OPCODE here...
Index: llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
===================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp
@@ -245,11 +245,13 @@
   setMaxAtomicSizeInBitsSupported(64);
 
   if (Subtarget->hasBulkMemory()) {
-    // Using memory.copy is always better than using multiple loads and stores
+    // Use memory.copy and friends over multiple loads and stores
     MaxStoresPerMemcpy = 1;
     MaxStoresPerMemcpyOptSize = 1;
     MaxStoresPerMemmove = 1;
     MaxStoresPerMemmoveOptSize = 1;
+    MaxStoresPerMemset = 1;
+    MaxStoresPerMemsetOptSize = 1;
   }
 }
 
Index: llvm/trunk/lib/Target/WebAssembly/WebAssemblyInstrBulkMemory.td
===================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblyInstrBulkMemory.td
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblyInstrBulkMemory.td
@@ -27,11 +27,13 @@
 def wasm_memcpy : SDNode<"WebAssemblyISD::MEMORY_COPY", wasm_memcpy_t,
                          [SDNPHasChain, SDNPMayLoad, SDNPMayStore]>;
 
-//===----------------------------------------------------------------------===//
-// memory.init
-//===----------------------------------------------------------------------===//
+def wasm_memset_t : SDTypeProfile<0, 4,
+  [SDTCisInt<0>, SDTCisPtrTy<1>, SDTCisInt<2>, SDTCisInt<3>]
+>;
+def wasm_memset : SDNode<"WebAssemblyISD::MEMORY_FILL", wasm_memset_t,
+                         [SDNPHasChain, SDNPMayStore]>;
 
-let mayStore = 1 in
+let mayStore = 1, hasSideEffects = 1 in
 defm MEMORY_INIT :
   BULK_I<(outs),
          (ins i32imm_op:$seg, i32imm_op:$idx, I32:$dest,
@@ -43,19 +45,12 @@
          "memory.init\t$seg, $idx, $dest, $offset, $size",
          "memory.init\t$seg, $idx", 0x08>;
 
-//===----------------------------------------------------------------------===//
-// data.drop
-//===----------------------------------------------------------------------===//
-
+let hasSideEffects = 1 in
 defm DATA_DROP :
   BULK_I<(outs), (ins i32imm_op:$seg), (outs), (ins i32imm_op:$seg),
          [(int_wasm_data_drop (i32 imm:$seg))],
          "data.drop\t$seg", "data.drop\t$seg", 0x09>;
 
-//===----------------------------------------------------------------------===//
-// memory.copy
-//===----------------------------------------------------------------------===//
-
 let mayLoad = 1, mayStore = 1 in
 defm MEMORY_COPY :
   BULK_I<(outs), (ins i32imm_op:$src_idx, i32imm_op:$dst_idx,
@@ -66,3 +61,11 @@
          )],
          "memory.copy\t$src_idx, $dst_idx, $dst, $src, $len",
          "memory.copy\t$src_idx, $dst_idx", 0x0a>;
+
+let mayStore = 1 in
+defm MEMORY_FILL :
+  BULK_I<(outs), (ins i32imm_op:$idx, I32:$dst, I32:$value, I32:$size),
+         (outs), (ins i32imm_op:$idx),
+         [(wasm_memset (i32 imm:$idx), I32:$dst, I32:$value, I32:$size)],
+         "memory.fill\t$idx, $dst, $value, $size",
+         "memory.fill\t$idx", 0x0b>;
Index: llvm/trunk/lib/Target/WebAssembly/WebAssemblySelectionDAGInfo.h
===================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblySelectionDAGInfo.h
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblySelectionDAGInfo.h
@@ -33,6 +33,10 @@
                                    SDValue Op3, unsigned Align, bool isVolatile,
                                    MachinePointerInfo DstPtrInfo,
                                    MachinePointerInfo SrcPtrInfo) const override;
+  SDValue EmitTargetCodeForMemset(SelectionDAG &DAG, const SDLoc &DL,
+                                  SDValue Chain, SDValue Op1, SDValue Op2,
+                                  SDValue Op3, unsigned Align, bool IsVolatile,
+                                  MachinePointerInfo DstPtrInfo) const override;
 };
 
 } // end namespace llvm
Index: llvm/trunk/lib/Target/WebAssembly/WebAssemblySelectionDAGInfo.cpp
===================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblySelectionDAGInfo.cpp
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblySelectionDAGInfo.cpp
@@ -41,3 +41,19 @@
                                  IsVolatile, false, DstPtrInfo,
                                  SrcPtrInfo);
 }
+
+SDValue WebAssemblySelectionDAGInfo::EmitTargetCodeForMemset(
+    SelectionDAG &DAG, const SDLoc &DL, SDValue Chain, SDValue Dst, SDValue Val,
+    SDValue Size, unsigned Align, bool IsVolatile,
+    MachinePointerInfo DstPtrInfo) const {
+  if (!DAG.getMachineFunction()
+           .getSubtarget<WebAssemblySubtarget>()
+           .hasBulkMemory())
+    return SDValue();
+
+  SDValue MemIdx = DAG.getConstant(0, DL, MVT::i32);
+  // Only low byte matters for val argument, so anyext the i8
+  return DAG.getNode(WebAssemblyISD::MEMORY_FILL, DL, MVT::Other, Chain, MemIdx,
+                     Dst, DAG.getAnyExtOrTrunc(Val, DL, MVT::i32),
+                     DAG.getZExtOrTrunc(Size, DL, MVT::i32));
+}
Index: llvm/trunk/test/CodeGen/WebAssembly/bulk-memory.ll
===================================================================
--- llvm/trunk/test/CodeGen/WebAssembly/bulk-memory.ll
+++ llvm/trunk/test/CodeGen/WebAssembly/bulk-memory.ll
@@ -14,6 +14,10 @@
 declare void @llvm.memmove.p0i8.p0i8.i32(i8*, i8*, i32, i1)
 declare void @llvm.memmove.p0i32.p0i32.i32(i32*, i32*, i32, i1)
 
+declare void @llvm.memset.p0i8.i8(i8*, i8, i8, i1)
+declare void @llvm.memset.p0i8.i32(i8*, i8, i32, i1)
+declare void @llvm.memset.p0i32.i32(i32*, i8, i32, i1)
+
 ; CHECK-LABEL: memcpy_i8:
 ; NO-BULK-MEM-NOT: memory.copy
 ; BULK-MEM-NEXT: .functype memcpy_i8 (i32, i32, i32) -> ()
@@ -34,6 +38,16 @@
   ret void
 }
 
+; CHECK-LABEL: memset_i8:
+; NO-BULK-MEM-NOT: memory.fill
+; BULK-MEM-NEXT: .functype memset_i8 (i32, i32, i32) -> ()
+; BULK-MEM-NEXT: memory.fill 0, $0, $1, $2
+; BULK-MEM-NEXT: return
+define void @memset_i8(i8* %dest, i8 %val, i8 zeroext %len) {
+  call void @llvm.memset.p0i8.i8(i8* %dest, i8 %val, i8 %len, i1 0)
+  ret void
+}
+
 ; CHECK-LABEL: memcpy_i32:
 ; NO-BULK-MEM-NOT: memory.copy
 ; BULK-MEM-NEXT: .functype memcpy_i32 (i32, i32, i32) -> ()
@@ -54,6 +68,16 @@
   ret void
 }
 
+; CHECK-LABEL: memset_i32:
+; NO-BULK-MEM-NOT: memory.fill
+; BULK-MEM-NEXT: .functype memset_i32 (i32, i32, i32) -> ()
+; BULK-MEM-NEXT: memory.fill 0, $0, $1, $2
+; BULK-MEM-NEXT: return
+define void @memset_i32(i32* %dest, i8 %val, i32 %len) {
+  call void @llvm.memset.p0i32.i32(i32* %dest, i8 %val, i32 %len, i1 0)
+  ret void
+}
+
 ; CHECK-LABEL: memcpy_1:
 ; CHECK-NEXT: .functype memcpy_1 (i32, i32) -> ()
 ; CHECK-NEXT: i32.load8_u $push[[L0:[0-9]+]]=, 0($1)
@@ -74,6 +98,16 @@
   ret void
 }
 
+; CHECK-LABEL: memset_1:
+; NO-BULK-MEM-NOT: memory.fill
+; BULK-MEM-NEXT: .functype memset_1 (i32, i32) -> ()
+; BULK-MEM-NEXT: i32.store8 0($0), $1
+; BULK-MEM-NEXT: return
+define void @memset_1(i8* %dest, i8 %val) {
+  call void @llvm.memset.p0i8.i32(i8* %dest, i8 %val, i32 1, i1 0)
+  ret void
+}
+
 ; CHECK-LABEL: memcpy_1024:
 ; NO-BULK-MEM-NOT: memory.copy
 ; BULK-MEM-NEXT: .functype memcpy_1024 (i32, i32) -> ()
@@ -95,3 +129,14 @@
   call void @llvm.memmove.p0i8.p0i8.i32(i8* %dest, i8* %src, i32 1024, i1 0)
   ret void
 }
+
+; CHECK-LABEL: memset_1024:
+; NO-BULK-MEM-NOT: memory.fill
+; BULK-MEM-NEXT: .functype memset_1024 (i32, i32) -> ()
+; BULK-MEM-NEXT: i32.const $push[[L0:[0-9]+]]=, 1024
+; BULK-MEM-NEXT: memory.fill 0, $0, $1, $pop[[L0]]
+; BULK-MEM-NEXT: return
+define void @memset_1024(i8* %dest, i8 %val) {
+  call void @llvm.memset.p0i8.i32(i8* %dest, i8 %val, i32 1024, i1 0)
+  ret void
+}
Index: llvm/trunk/test/MC/WebAssembly/bulk-memory-encodings.s
===================================================================
--- llvm/trunk/test/MC/WebAssembly/bulk-memory-encodings.s
+++ llvm/trunk/test/MC/WebAssembly/bulk-memory-encodings.s
@@ -0,0 +1,18 @@
+# RUN: llvm-mc -show-encoding -triple=wasm32-unkown-unknown -mattr=+bulk-memory < %s | FileCheck %s
+
+main:
+    .functype main () -> ()
+
+    # CHECK: memory.init 3, 0 # encoding: [0xfc,0x08,0x03,0x00]
+    memory.init 3, 0
+
+    # CHECK: data.drop 3 # encoding: [0xfc,0x09,0x03]
+    data.drop 3
+
+    # CHECK: memory.copy 0, 0 # encoding: [0xfc,0x0a,0x00,0x00]
+    memory.copy 0, 0
+
+    # CHECK: memory.fill 0 # encoding: [0xfc,0x0b,0x00]
+    memory.fill 0
+
+    end_function