diff --git a/.gitignore b/.gitignore
index 79f88211..7e041025 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,4 @@ docs/
 node_modules/
 out/
 raw/
+.history
diff --git a/src/builtins.ts b/src/builtins.ts
index 3b4ecf25..b193ab16 100644
--- a/src/builtins.ts
+++ b/src/builtins.ts
@@ -40,7 +40,8 @@ import {
   getExpressionType,
   getConstValueI64High,
   getConstValueI64Low,
-  getConstValueI32
+  getConstValueI32,
+  AtomicRMWOp
 } from "./module";
 
 import {
@@ -51,7 +52,8 @@ import {
   OperatorKind,
   FlowFlags,
   Global,
-  DecoratorFlags
+  DecoratorFlags,
+  Element
 } from "./program";
 
 import {
@@ -1676,6 +1678,416 @@ export function compileCall(
       compiler.currentType = Type.void;
       return module.createStore(typeArguments[0].byteSize, arg0, arg1, type.toNativeType(), offset);
     }
+    case "Atomic.load": { // Atomic.load<T!>(offset: usize, constantOffset?: usize) -> *
+      if (operands.length < 1 || operands.length > 2) {
+        if (!(typeArguments && typeArguments.length == 1)) {
+          compiler.error(
+            DiagnosticCode.Expected_0_type_arguments_but_got_1,
+            reportNode.range, "1", typeArguments ? typeArguments.length.toString(10) : "0"
+          );
+        }
+        if (operands.length < 1) {
+          compiler.error(
+            DiagnosticCode.Expected_at_least_0_arguments_but_got_1,
+            reportNode.range, "1", operands.length.toString(10)
+          );
+        } else {
+          compiler.error(
+            DiagnosticCode.Expected_0_arguments_but_got_1,
+            reportNode.range, "2", operands.length.toString(10)
+          );
+        }
+        return module.createUnreachable();
+      }
+      if (!(typeArguments && typeArguments.length == 1)) {
+        if (typeArguments && typeArguments.length) compiler.currentType = typeArguments[0];
+        compiler.error(
+          DiagnosticCode.Expected_0_type_arguments_but_got_1,
+          reportNode.range, "1", typeArguments ? typeArguments.length.toString(10) : "0"
+        );
+        return module.createUnreachable();
+      }
+      arg0 = compiler.compileExpression(
+        operands[0],
+        compiler.options.usizeType,
+        ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+      let offset = operands.length == 2 ? evaluateConstantOffset(compiler, operands[1]) : 0; // reports
+      if (offset < 0) { // reported in evaluateConstantOffset
+        return module.createUnreachable();
+      }
+      compiler.currentType = typeArguments[0];
+      return module.createAtomicLoad(
+        typeArguments[0].byteSize,
+        arg0,
+        typeArguments[0].is(TypeFlags.INTEGER) &&
+        contextualType.is(TypeFlags.INTEGER) &&
+        contextualType.size > typeArguments[0].size
+          ? (compiler.currentType = contextualType).toNativeType()
+          : (compiler.currentType = typeArguments[0]).toNativeType(),
+        offset
+      );
+    }
+    case "Atomic.store": { // Atomic.store<T!>(offset: usize, value: *, constantOffset?: usize) -> void
+      compiler.currentType = Type.void;
+      if (operands.length < 2 || operands.length > 3) {
+        if (!(typeArguments && typeArguments.length == 1)) {
+          compiler.error(
+            DiagnosticCode.Expected_0_type_arguments_but_got_1,
+            reportNode.range, "1", typeArguments ? typeArguments.length.toString(10) : "0"
+          );
+        }
+        if (operands.length < 2) {
+          compiler.error(
+            DiagnosticCode.Expected_at_least_0_arguments_but_got_1,
+            reportNode.range, "2", operands.length.toString(10)
+          );
+        } else {
+          compiler.error(
+            DiagnosticCode.Expected_0_arguments_but_got_1,
+            reportNode.range, "3", operands.length.toString(10)
+          );
+        }
+        return module.createUnreachable();
+      }
+      if (!(typeArguments && typeArguments.length == 1)) {
+        compiler.error(
+          DiagnosticCode.Expected_0_type_arguments_but_got_1,
+          reportNode.range, "1", typeArguments ? typeArguments.length.toString(10) : "0"
+        );
+        return module.createUnreachable();
+      }
+      arg0 = compiler.compileExpression(
+        operands[0],
+        compiler.options.usizeType,
+        ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+      arg1 = compiler.compileExpression(
+        operands[1],
+        typeArguments[0],
+        typeArguments[0].is(TypeFlags.INTEGER)
+          ? ConversionKind.NONE // no need to convert to small int (but now might result in a float)
+          : ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+      let type: Type;
+      if (
+        typeArguments[0].is(TypeFlags.INTEGER) &&
+        (
+          !compiler.currentType.is(TypeFlags.INTEGER) ||    // float to int
+          compiler.currentType.size < typeArguments[0].size // int to larger int (clear garbage bits)
+        )
+      ) {
+        arg1 = compiler.convertExpression(
+          arg1,
+          compiler.currentType, typeArguments[0],
+          ConversionKind.IMPLICIT,
+          WrapMode.NONE, // still clears garbage bits
+          operands[1]
+        );
+        type = typeArguments[0];
+      } else {
+        type = compiler.currentType;
+      }
+      let offset = operands.length == 3 ? evaluateConstantOffset(compiler, operands[2]) : 0; // reports
+      if (offset < 0) { // reported in evaluateConstantOffset
+        return module.createUnreachable();
+      }
+      compiler.currentType = Type.void;
+      return module.createAtomicStore(typeArguments[0].byteSize, arg0, arg1, type.toNativeType(), offset);
+    }
+    case "Atomic.add":  // add<T!>(ptr: usize, value: T, constantOffset?: usize): T;
+    case "Atomic.sub":  // sub<T!>(ptr: usize, value: T, constantOffset?: usize): T;
+    case "Atomic.and":  // and<T!>(ptr: usize, value: T, constantOffset?: usize): T;
+    case "Atomic.or":   // or<T!>(ptr: usize, value: T, constantOffset?: usize): T;
+    case "Atomic.xor":  // xor<T!>(ptr: usize, value: T, constantOffset?: usize): T;
+    case "Atomic.xchg": // xchg<T!>(ptr: usize, value: T, constantOffset?: usize): T;
+    {
+      if (operands.length < 2 || operands.length > 3) {
+        if (!(typeArguments && typeArguments.length == 1)) {
+          compiler.error(
+            DiagnosticCode.Expected_0_type_arguments_but_got_1,
+            reportNode.range, "1", typeArguments ? typeArguments.length.toString(10) : "0"
+          );
+        }
+        if (operands.length < 2) {
+          compiler.error(
+            DiagnosticCode.Expected_at_least_0_arguments_but_got_1,
+            reportNode.range, "2", operands.length.toString(10)
+          );
+        } else {
+          compiler.error(
+            DiagnosticCode.Expected_0_arguments_but_got_1,
+            reportNode.range, "3", operands.length.toString(10)
+          );
+        }
+        return module.createUnreachable();
+      }
+      if (!(typeArguments && typeArguments.length == 1)) {
+        compiler.error(
+          DiagnosticCode.Expected_0_type_arguments_but_got_1,
+          reportNode.range, "1", typeArguments ? typeArguments.length.toString(10) : "0"
+        );
+        return module.createUnreachable();
+      }
+      arg0 = compiler.compileExpression(
+        operands[0],
+        compiler.options.usizeType,
+        ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+      arg1 = compiler.compileExpression(
+        operands[1],
+        typeArguments[0],
+        typeArguments[0].is(TypeFlags.INTEGER)
+          ? ConversionKind.NONE // no need to convert to small int (but now might result in a float)
+          : ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+
+      let type: Type;
+      if (
+        typeArguments[0].is(TypeFlags.INTEGER) &&
+        (
+          !compiler.currentType.is(TypeFlags.INTEGER) ||    // float to int
+          compiler.currentType.size < typeArguments[0].size // int to larger int (clear garbage bits)
+        )
+      ) {
+        arg1 = compiler.convertExpression(
+          arg1,
+          compiler.currentType, typeArguments[0],
+          ConversionKind.IMPLICIT,
+          WrapMode.NONE, // still clears garbage bits
+          operands[1]
+        );
+        type = typeArguments[0];
+      } else {
+        type = compiler.currentType;
+      }
+
+      let offset = operands.length == 3 ? evaluateConstantOffset(compiler, operands[2]) : 0; // reports
+      if (offset < 0) { // reported in evaluateConstantOffset
+        return module.createUnreachable();
+      }
+      let RMWOp: AtomicRMWOp | null = null;
+      switch (prototype.internalName) {
+        case "Atomic.add": { RMWOp = AtomicRMWOp.Add; break; }
+        case "Atomic.sub": { RMWOp = AtomicRMWOp.Sub; break; }
+        case "Atomic.and": { RMWOp = AtomicRMWOp.And; break; }
+        case "Atomic.or": { RMWOp = AtomicRMWOp.Or; break; }
+        case "Atomic.xor": { RMWOp = AtomicRMWOp.Xor; break; }
+        case "Atomic.xchg": { RMWOp = AtomicRMWOp.Xchg; break; }
+      }
+      compiler.currentType = typeArguments[0];
+      if (RMWOp !== null) {
+        return module.createAtomicRMW(
+          RMWOp, typeArguments[0].byteSize, offset, arg0, arg1, type.toNativeType()
+        );
+      } else {
+        compiler.error(
+          DiagnosticCode.Operation_not_supported,
+          reportNode.range, "1", typeArguments ? typeArguments.length.toString(10) : "0"
+        );
+        return module.createUnreachable();
+      }
+    }
+    case "Atomic.cmpxchg": { // cmpxchg<T!>(ptr: usize, expected:T, replacement: T, constantOffset?: usize): T;
+      if (operands.length < 3 || operands.length > 4) {
+        if (!(typeArguments && typeArguments.length == 1)) {
+          compiler.error(
+            DiagnosticCode.Expected_0_type_arguments_but_got_1,
+            reportNode.range, "1", typeArguments ? typeArguments.length.toString(10) : "0"
+          );
+        }
+        if (operands.length < 3) {
+          compiler.error(
+            DiagnosticCode.Expected_at_least_0_arguments_but_got_1,
+            reportNode.range, "2", operands.length.toString(10)
+          );
+        } else {
+          compiler.error(
+            DiagnosticCode.Expected_0_arguments_but_got_1,
+            reportNode.range, "3", operands.length.toString(10)
+          );
+        }
+        return module.createUnreachable();
+      }
+      if (!(typeArguments && typeArguments.length == 1)) {
+        compiler.error(
+          DiagnosticCode.Expected_0_type_arguments_but_got_1,
+          reportNode.range, "1", typeArguments ? typeArguments.length.toString(10) : "0"
+        );
+        return module.createUnreachable();
+      }
+      arg0 = compiler.compileExpression(
+        operands[0],
+        compiler.options.usizeType,
+        ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+      arg1 = compiler.compileExpression(
+        operands[1],
+        typeArguments[0],
+        typeArguments[0].is(TypeFlags.INTEGER)
+          ? ConversionKind.NONE // no need to convert to small int (but now might result in a float)
+          : ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+      arg2 = compiler.compileExpression(
+        operands[2],
+        typeArguments[0],
+        typeArguments[0].is(TypeFlags.INTEGER)
+          ? ConversionKind.NONE // no need to convert to small int (but now might result in a float)
+          : ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+
+      let type: Type;
+      if (
+        typeArguments[0].is(TypeFlags.INTEGER) &&
+        (
+          !compiler.currentType.is(TypeFlags.INTEGER) ||    // float to int
+          compiler.currentType.size < typeArguments[0].size // int to larger int (clear garbage bits)
+        )
+      ) {
+        arg1 = compiler.convertExpression(
+          arg1,
+          compiler.currentType, typeArguments[0],
+          ConversionKind.IMPLICIT,
+          WrapMode.NONE, // still clears garbage bits
+          operands[1]
+        );
+        arg2 = compiler.convertExpression(
+          arg2,
+          compiler.currentType, typeArguments[0],
+          ConversionKind.IMPLICIT,
+          WrapMode.NONE, // still clears garbage bits
+          operands[2]
+        );
+        type = typeArguments[0];
+      } else {
+        type = compiler.currentType;
+      }
+
+      let offset = operands.length == 4 ? evaluateConstantOffset(compiler, operands[3]) : 0; // reports
+      if (offset < 0) { // reported in evaluateConstantOffset
+        return module.createUnreachable();
+      }
+      compiler.currentType = typeArguments[0];
+      return module.createAtomicCmpxchg(
+        typeArguments[0].byteSize, offset, arg0, arg1, arg2, type.toNativeType()
+      );
+    }
+    case "Atomic.wait": { // wait<T!>(ptr: usize, expected:T, timeout: i64): i32;
+      let hasError = typeArguments == null;
+      if (operands.length != 3) {
+        compiler.error(
+          DiagnosticCode.Expected_0_arguments_but_got_1,
+          reportNode.range, "3", operands.length.toString(10)
+        );
+        hasError = true;
+      }
+      if (!(typeArguments && typeArguments.length == 1)) {
+        compiler.error(
+          DiagnosticCode.Expected_0_type_arguments_but_got_1,
+          reportNode.range, "1", typeArguments ? typeArguments.length.toString(10) : "0"
+        );
+        hasError = true;
+      }
+
+      if (!typeArguments || hasError) {
+        return module.createUnreachable();
+      }
+
+      arg0 = compiler.compileExpression(
+        operands[0],
+        compiler.options.usizeType,
+        ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+      arg1 = compiler.compileExpression(
+        operands[1],
+        typeArguments[0],
+        typeArguments[0].is(TypeFlags.INTEGER)
+          ? ConversionKind.NONE // no need to convert to small int (but now might result in a float)
+          : ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+      arg2 = compiler.compileExpression(
+        operands[2],
+        Type.i64,
+        ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+
+      let type: Type = typeArguments[0];
+      if (
+        typeArguments[0].is(TypeFlags.INTEGER) &&
+        (
+          !compiler.currentType.is(TypeFlags.INTEGER) ||    // float to int
+          compiler.currentType.size < typeArguments[0].size // int to larger int (clear garbage bits)
+        )
+      ) {
+        arg1 = compiler.convertExpression(
+          arg1,
+          compiler.currentType, typeArguments[0],
+          ConversionKind.IMPLICIT,
+          WrapMode.NONE, // still clears garbage bits
+          operands[1]
+        );
+        arg2 = compiler.convertExpression(
+          arg2,
+          compiler.currentType, typeArguments[0],
+          ConversionKind.IMPLICIT,
+          WrapMode.NONE, // still clears garbage bits
+          operands[2]
+        );
+      }
+
+      return module.createAtomicWait(
+        arg0, arg1, arg2, type.toNativeType()
+      );
+    }
+    case "Atomic.notify": { // notify<T!>(ptr: usize, count: u32): u32;
+      let hasError = typeArguments == null;
+      if (operands.length != 2) {
+        compiler.error(
+          DiagnosticCode.Expected_0_arguments_but_got_1,
+          reportNode.range, "2", operands.length.toString(10)
+        );
+        hasError = true;
+      }
+      if (!(typeArguments && typeArguments.length == 1)) {
+        compiler.error(
+          DiagnosticCode.Expected_0_type_arguments_but_got_1,
+          reportNode.range, "1", typeArguments ? typeArguments.length.toString(10) : "0"
+        );
+        hasError = true;
+      }
+
+      if (!typeArguments || hasError) {
+        return module.createUnreachable();
+      }
+
+      arg0 = compiler.compileExpression(
+        operands[0],
+        compiler.options.usizeType,
+        ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+      arg1 = compiler.compileExpression(
+        operands[1],
+        Type.i32,
+        ConversionKind.IMPLICIT,
+        WrapMode.NONE
+      );
+
+      return module.createAtomicWake(
+        arg0, arg1
+      );
+    }
     case "sizeof": { // sizeof<T!>() -> usize
       compiler.currentType = compiler.options.usizeType;
       if (operands.length != 0) {
@@ -2851,6 +3263,83 @@ function deferASMCall(
     case "i64.store": return deferASM("store", compiler, Type.i64, operands, Type.i64, reportNode);
     case "f32.store": return deferASM("store", compiler, Type.f32, operands, Type.f32, reportNode);
     case "f64.store": return deferASM("store", compiler, Type.f64, operands, Type.f64, reportNode);
+
+    case "i32.atomic.load8_u": return deferASM("Atomic.load", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i32.atomic.load16_u": return deferASM("Atomic.load", compiler, Type.u16, operands, Type.u32, reportNode);
+    case "i32.atomic.load": return deferASM("Atomic.load", compiler, Type.i32, operands, Type.i32, reportNode);
+    case "i64.atomic.load8_u": return deferASM("Atomic.load", compiler, Type.u8, operands, Type.u64, reportNode);
+    case "i64.atomic.load16_u": return deferASM("Atomic.load", compiler, Type.u16, operands, Type.u64, reportNode);
+    case "i64.atomic.load32_u": return deferASM("Atomic.load", compiler, Type.u32, operands, Type.u64, reportNode);
+    case "i64.atomic.load": return deferASM("Atomic.load", compiler, Type.i64, operands, Type.i64, reportNode);
+
+    case "i32.atomic.store8": return deferASM("Atomic.store", compiler, Type.i8, operands, Type.i32, reportNode);
+    case "i32.atomic.store16": return deferASM("Atomic.store", compiler, Type.i16, operands, Type.i32, reportNode);
+    case "i32.atomic.store": return deferASM("Atomic.store", compiler, Type.i32, operands, Type.i32, reportNode);
+    case "i64.atomic.store8": return deferASM("Atomic.store", compiler, Type.i8, operands, Type.i64, reportNode);
+    case "i64.atomic.store16": return deferASM("Atomic.store", compiler, Type.i16, operands, Type.i64, reportNode);
+    case "i64.atomic.store32": return deferASM("Atomic.store", compiler, Type.i32, operands, Type.i64, reportNode);
+    case "i64.atomic.store": return deferASM("Atomic.store", compiler, Type.i64, operands, Type.i64, reportNode);
+
+    case "i32.atomic.rmw8_u.add": return deferASM("Atomic.add", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw16_u.add": return deferASM("Atomic.add", compiler, Type.u16, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw.add": return deferASM("Atomic.add", compiler, Type.u32, operands, Type.u32, reportNode);
+    case "i64.atomic.rmw8_u.add": return deferASM("Atomic.add", compiler, Type.u8, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw16_u.add": return deferASM("Atomic.add", compiler, Type.u16, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw32_u.add": return deferASM("Atomic.add", compiler, Type.u32, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw.add": return deferASM("Atomic.add", compiler, Type.u64, operands, Type.u64, reportNode);
+
+    case "i32.atomic.rmw8_u.sub": return deferASM("Atomic.sub", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw16_u.sub": return deferASM("Atomic.sub", compiler, Type.u16, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw.sub": return deferASM("Atomic.sub", compiler, Type.u32, operands, Type.u32, reportNode);
+    case "i64.atomic.rmw8_u.sub": return deferASM("Atomic.sub", compiler, Type.u8, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw16_u.sub": return deferASM("Atomic.sub", compiler, Type.u16, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw32_u.sub": return deferASM("Atomic.sub", compiler, Type.u32, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw.sub": return deferASM("Atomic.sub", compiler, Type.u64, operands, Type.u64, reportNode);
+
+    case "i32.atomic.rmw8_u.and": return deferASM("Atomic.and", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw16_u.and": return deferASM("Atomic.and", compiler, Type.u16, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw.and": return deferASM("Atomic.and", compiler, Type.u32, operands, Type.u32, reportNode);
+    case "i64.atomic.rmw8_u.and": return deferASM("Atomic.and", compiler, Type.u8, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw16_u.and": return deferASM("Atomic.and", compiler, Type.u16, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw32_u.and": return deferASM("Atomic.and", compiler, Type.u32, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw.and": return deferASM("Atomic.and", compiler, Type.u64, operands, Type.u64, reportNode);
+
+    case "i32.atomic.rmw8_u.or": return deferASM("Atomic.or", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw16_u.or": return deferASM("Atomic.or", compiler, Type.u16, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw.or": return deferASM("Atomic.or", compiler, Type.u32, operands, Type.u32, reportNode);
+    case "i64.atomic.rmw8_u.or": return deferASM("Atomic.or", compiler, Type.u8, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw16_u.or": return deferASM("Atomic.or", compiler, Type.u16, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw32_u.or": return deferASM("Atomic.or", compiler, Type.u32, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw.or": return deferASM("Atomic.or", compiler, Type.u64, operands, Type.u64, reportNode);
+
+    case "i32.atomic.rmw8_u.xor": return deferASM("Atomic.xor", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw16_u.xor": return deferASM("Atomic.xor", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw.xor": return deferASM("Atomic.xor", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i64.atomic.rmw8_u.xor": return deferASM("Atomic.xor", compiler, Type.u8, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw16_u.xor": return deferASM("Atomic.xor", compiler, Type.u16, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw32_u.xor": return deferASM("Atomic.xor", compiler, Type.u32, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw.xor": return deferASM("Atomic.xor", compiler, Type.u64, operands, Type.u64, reportNode);
+
+    case "i32.atomic.rmw8_u.xchg": return deferASM("Atomic.xchg", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw16_u.xchg": return deferASM("Atomic.xchg", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw.xchg": return deferASM("Atomic.xchg", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i64.atomic.rmw8_u.xchg": return deferASM("Atomic.xchg", compiler, Type.u8, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw16_u.xchg": return deferASM("Atomic.xchg", compiler, Type.u16, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw32_u.xchg": return deferASM("Atomic.xchg", compiler, Type.u32, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw.xchg": return deferASM("Atomic.xchg", compiler, Type.u64, operands, Type.u64, reportNode);
+
+    case "i32.atomic.rmw8_u.cmpxchg": return deferASM("Atomic.cmpxchg", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw16_u.cmpxchg": return deferASM("Atomic.cmpxchg", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i32.atomic.rmw.cmpxchg": return deferASM("Atomic.cmpxchg", compiler, Type.u8, operands, Type.u32, reportNode);
+    case "i64.atomic.rmw8_u.cmpxchg": return deferASM("Atomic.cmpxchg", compiler, Type.u8, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw16_u.cmpxchg": return deferASM("Atomic.cmpxchg", compiler, Type.u16, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw32_u.cmpxchg": return deferASM("Atomic.cmpxchg", compiler, Type.u32, operands, Type.u64, reportNode);
+    case "i64.atomic.rmw.cmpxchg": return deferASM("Atomic.cmpxchg", compiler, Type.u64, operands, Type.u64, reportNode);
+
+    case "i32.wait": return deferASM("Atomic.wait", compiler, Type.i32, operands, Type.u32, reportNode);
+    case "i64.wait": return deferASM("Atomic.wait", compiler, Type.i64, operands, Type.i64, reportNode);
+    case "i32.notify": return deferASM("Atomic.notify", compiler, Type.i32, operands, Type.u32, reportNode);
+    case "i64.notify": return deferASM("Atomic.notify", compiler, Type.i64, operands, Type.i64, reportNode);
   }
   return 0;
 }
@@ -2864,7 +3353,18 @@ function deferASM(
   valueType: Type,
   reportNode: Node
 ): ExpressionRef {
-  var prototype = assert(compiler.program.elementsLookup.get(name));
+  // Built-in wasm functions can be namespaced like Atomic.{OPERATION}
+  // Split name by '.' to find member function prototype
+  var names = name.split(".");
+  var prototype: Element = assert(compiler.program.elementsLookup.get(names[0]));
+  if (names.length > 1) {
+    for (let i = 1; i < names.length; i++) {
+      const subName = names[i];
+      if (prototype && prototype.members) {
+        prototype = assert(prototype.members.get(subName));
+      }
+    }
+  }
   assert(prototype.kind == ElementKind.FUNCTION_PROTOTYPE);
   return compileCall(compiler, <FunctionPrototype>prototype, [ typeArgument ], operands, valueType, reportNode);
 }
diff --git a/std/assembly/builtins.ts b/std/assembly/builtins.ts
index ea3fe937..a40b5be9 100644
--- a/std/assembly/builtins.ts
+++ b/std/assembly/builtins.ts
@@ -43,6 +43,20 @@
 @builtin export declare function call_indirect<T>(target: void, ...args: void[]): T;
 @builtin export declare function instantiate<T>(...args: void[]): T;
 
+export namespace Atomic {
+  @builtin export declare function load<T>(offset: usize, constantOffset?: usize): T;
+  @builtin export declare function store<T>(offset: usize, value: void, constantOffset?: usize): void;
+  @builtin export declare function add<T>(ptr: usize, value: T, constantOffset?: usize): T;
+  @builtin export declare function sub<T>(ptr: usize, value: T, constantOffset?: usize): T;
+  @builtin export declare function and<T>(ptr: usize, value: T, constantOffset?: usize): T;
+  @builtin export declare function or<T>(ptr: usize, value: T, constantOffset?: usize): T;
+  @builtin export declare function xor<T>(ptr: usize, value: T, constantOffset?: usize): T;
+  @builtin export declare function xchg<T>(ptr: usize, value: T, constantOffset?: usize): T;
+  @builtin export declare function cmpxchg<T>(ptr: usize, expected:T, replacement: T, constantOffset?: usize): T;
+  @builtin export declare function wait<T>(ptr: usize, expected:T, timeout:i64): i32;
+  @builtin export declare function notify<T>(ptr: usize, count: u32): u32;
+}
+
 @builtin export declare function i8(value: void): i8;
 export namespace i8 {
   export const MIN_VALUE: i8 = -128;
@@ -73,6 +87,49 @@ export namespace i32 {
   @builtin export declare function store8(offset: usize, value: i32, constantOffset?: usize): void;
   @builtin export declare function store16(offset: usize, value: i32, constantOffset?: usize): void;
   @builtin export declare function store(offset: usize, value: i32, constantOffset?: usize): void;
+  
+  namespace atomic {
+    @builtin export declare function load8_s(offset: usize, constantOffset?: usize): i32;
+    @builtin export declare function load8_u(offset: usize, constantOffset?: usize): i32;
+    @builtin export declare function load16_s(offset: usize, constantOffset?: usize): i32;
+    @builtin export declare function load16_u(offset: usize, constantOffset?: usize): i32;
+    @builtin export declare function load(offset: usize, constantOffset?: usize): i32;
+    @builtin export declare function store8(offset: usize, value: i32, constantOffset?: usize): void;
+    @builtin export declare function store16(offset: usize, value: i32, constantOffset?: usize): void;
+    @builtin export declare function store(offset: usize, value: i32, constantOffset?: usize): void;
+    @builtin export declare function wait(ptr: usize, expected:i32, timeout:i64): i32;
+    @builtin export declare function notify(ptr: usize, count:u32): u32;
+
+    namespace rmw8_u {
+      @builtin export declare function add(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function sub(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function and(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function or(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function xor(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function xchg(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function cmpxchg(offset: usize, expected:i32, replacement: i32, constantOffset?: usize): i32;
+    }
+
+    namespace rmw16_u {
+      @builtin export declare function add(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function sub(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function and(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function or(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function xor(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function xchg(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function cmpxchg(offset: usize, expected:i32, replacement: i32, constantOffset?: usize): i32;
+    }
+
+    namespace rmw {
+      @builtin export declare function add(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function sub(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function and(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function or(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function xor(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function xchg(offset: usize, value: i32, constantOffset?: usize): i32
+      @builtin export declare function cmpxchg(offset: usize, expected:i32, replacement: i32, constantOffset?: usize): i32;
+    }
+  }
 }
 
 @builtin export declare function i64(value: void): i64;
@@ -96,6 +153,59 @@ export namespace i64 {
   @builtin export declare function store16(offset: usize, value: i64, constantOffset?: usize): void;
   @builtin export declare function store32(offset: usize, value: i64, constantOffset?: usize): void;
   @builtin export declare function store(offset: usize, value: i64, constantOffset?: usize): void;
+
+  namespace atomic {
+    @builtin export declare function load8_s(offset: usize, constantOffset?: usize): i64;
+    @builtin export declare function load8_u(offset: usize, constantOffset?: usize): i64;
+    @builtin export declare function load16_s(offset: usize, constantOffset?: usize): i64;
+    @builtin export declare function load16_u(offset: usize, constantOffset?: usize): i64;
+    @builtin export declare function load(offset: usize, constantOffset?: usize): i64;
+    @builtin export declare function store8(offset: usize, value: i64, constantOffset?: usize): void;
+    @builtin export declare function store16(offset: usize, value: i64, constantOffset?: usize): void;
+    @builtin export declare function store(offset: usize, value: i64, constantOffset?: usize): void;
+    @builtin export declare function wait(ptr: usize, expected:i64, timeout:i64): i32;
+    @builtin export declare function notify(ptr: usize, count:u32): u32;
+
+    namespace rmw8_u {
+      @builtin export declare function add(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function sub(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function and(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function or(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function xor(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function xchg(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function cmpxchg(offset: usize, expected:i64, replacement: i64, constantOffset?: usize): i64;
+    }
+
+    namespace rmw16_u {
+      @builtin export declare function add(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function sub(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function and(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function or(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function xor(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function xchg(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function cmpxchg(offset: usize, expected:i64, replacement: i64, constantOffset?: usize): i64;
+    }
+
+    namespace rmw32_u {
+      @builtin export declare function add(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function sub(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function and(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function or(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function xor(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function xchg(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function cmpxchg(offset: usize, expected:i64, replacement: i64, constantOffset?: usize): i64;
+    }
+
+    namespace rmw {
+      @builtin export declare function add(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function sub(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function and(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function or(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function xor(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function xchg(offset: usize, value: i64, constantOffset?: usize): i64
+      @builtin export declare function cmpxchg(offset: usize, expected:i64, replacement: i64, constantOffset?: usize): i64;
+    }
+  } 
 }
 
 @builtin export declare function isize(value: void): isize;