diff --git a/assembly.d.ts b/assembly.d.ts
index d20654f6..3003ff33 100644
--- a/assembly.d.ts
+++ b/assembly.d.ts
@@ -30,36 +30,36 @@ declare type f64 = number;
 // builtins
 
 /** Performs the sign-agnostic count leading zero bits operation on a 32-bit or 64-bit integer. All zero bits are considered leading if the value is zero. */
-declare function clz<T extends number>(value: T): T;
+declare function clz<T = i32 | i64>(value: T): T;
 /** Performs the sign-agnostic count tailing zero bits operation on a 32-bit or 64-bit integer. All zero bits are considered trailing if the value is zero. */
-declare function ctz<T>(value: T): T;
+declare function ctz<T = i32 | i64>(value: T): T;
 /** Performs the sign-agnostic count number of one bits operation on a 32-bit or 64-bit integer. */
-declare function popcnt<T>(value: T): T;
+declare function popcnt<T = i32 | i64>(value: T): T;
 /** Performs the sign-agnostic rotate left operation on a 32-bit or 64-bit integer. */
-declare function rotl<T>(value: T, shift: T): T;
+declare function rotl<T = i32 | i64>(value: T, shift: T): T;
 /** Performs the sign-agnostic rotate right operation on a 32-bit or 64-bit integer. */
-declare function rotr<T>(value: T, shift: T): T;
+declare function rotr<T = i32 | i64>(value: T, shift: T): T;
 
 /** Computes the absolute value of a 32-bit or 64-bit float. */
-declare function abs<T>(value: T): T;
+declare function abs<T = f32 | f64>(value: T): T;
 /** Performs the ceiling operation on a 32-bit or 64-bit float. */
-declare function ceil<T>(value: T): T;
+declare function ceil<T = f32 | f64>(value: T): T;
 /** Composes a 32-bit or 64-bit float from the magnitude of `x` and the sign of `y`. */
-declare function copysign<T>(x: T, y: T): T;
+declare function copysign<T = f32 | f64>(x: T, y: T): T;
 /** Performs the floor operation on a 32-bit or 64-bit float. */
-declare function floor<T>(value: T): T;
+declare function floor<T = f32 | f64>(value: T): T;
 /** Determines the maximum of two 32-bit or 64-bit floats. If either operand is `NaN`, returns `NaN`. */
-declare function max<T>(left: T, right: T): T;
+declare function max<T = f32 | f64>(left: T, right: T): T;
 /** Determines the minimum of two 32-bit or 64-bit floats. If either operand is `NaN`, returns `NaN`. */
-declare function min<T>(left: T, right: T): T;
+declare function min<T = f32 | f64>(left: T, right: T): T;
 /** Rounds to the nearest integer tied to even of a 32-bit or 64-bit float. */
-declare function nearest<T>(value: T): T;
+declare function nearest<T = f32 | f64>(value: T): T;
 /** Reinterprets the bits of a value of type `T1` as type `T2`. Valid reinterpretations are i32 to/from f32 and i64 to/from f64. */
-declare function reinterpret<T1,T2>(value: T1): T2;
+declare function reinterpret<T1 = i32 | i64 | f32 | f64, T2 = i32 | i64 | f32 | f64>(value: T1): T2;
 /** Calculates the square root of a 32-bit or 64-bit float. */
-declare function sqrt<T>(value: T): T;
+declare function sqrt<T = f32 | f64>(value: T): T;
 /** Rounds to the nearest integer towards zero of a 32-bit or 64-bit float. */
-declare function trunc<T>(value: T): T;
+declare function trunc<T = f32 | f64>(value: T): T;
 
 /** Returns the current memory size in units of pages. One page is 64kb. */
 declare function current_memory(): i32;
@@ -76,14 +76,14 @@ declare function store<T>(offset: usize, value: T): void;
 declare function sizeof<T>(): usize;
 
 /** NaN (not a number) as a 32-bit or 64-bit float depending on context. */
-declare const NaN: number;
+declare const NaN: f32 | f64;
 /** Positive infinity as a 32-bit or 64-bit float depending on context. */
-declare const Infinity: number;
+declare const Infinity: f32 | f64;
 
 /** Tests if a 32-bit or 64-bit float is NaN. */
-declare function isNaN<T>(value: T): bool;
+declare function isNaN<T = f32 | f64>(value: T): bool;
 /** Tests if a 32-bit or 64-bit float is finite, that is not NaN or +/-Infinity. */
-declare function isFinite<T>(value: T): bool;
+declare function isFinite<T = f32 | f64>(value: T): bool;
 /** Traps if the specified value is `false`. */
 declare function assert(isTrue: bool): void;
 
diff --git a/src/compiler.ts b/src/compiler.ts
index 49794986..bbb8f7b9 100644
--- a/src/compiler.ts
+++ b/src/compiler.ts
@@ -88,6 +88,8 @@ export class Options {
   noEmit: bool = false;
   /** If true, compiles everything instead of just reachable code. */
   noTreeShaking: bool = false;
+  /** If true, replaces assertions with nops. */
+  noDebug: bool = false;
 }
 
 const enum ConversionKind {
@@ -1398,16 +1400,73 @@ export class Compiler extends DiagnosticEmitter {
       const functionPrototype: FunctionPrototype = <FunctionPrototype>element;
       let functionInstance: Function | null = null;
       if (functionPrototype.isBuiltin) {
+        const k: i32 = expression.typeArguments.length;
+        const resolvedTypeArguments: Type[] = new Array(k);
         sb.length = 0;
-        for (let i: i32 = 0, k: i32 = expression.typeArguments.length; i < k; ++i) {
-          let type: Type | null = this.program.resolveType(expression.typeArguments[i], this.currentFunction.contextualTypeArguments, true); // reports
-          if (!type)
+        for (let i: i32 = 0; i < k; ++i) {
+          let resolvedType: Type | null = this.program.resolveType(expression.typeArguments[i], this.currentFunction.contextualTypeArguments, true); // reports
+          if (!resolvedType)
             return this.module.createUnreachable();
-          sb.push(type.toString());
+          resolvedTypeArguments[i] = resolvedType;
+          sb.push(resolvedType.toString());
         }
+
         functionInstance = <Function | null>functionPrototype.instances.get(sb.join(","));
         if (!functionInstance) {
-          // TODO: sizeof, load, store, see program.ts/initializeBuiltins
+          let arg0: ExpressionRef, arg1: ExpressionRef;
+
+          if (functionPrototype.internalName == "sizeof") { // no parameters
+            this.currentType = this.options.target == Target.WASM64 ? Type.usize64 : Type.usize32;
+            if (k != 1) {
+              this.error(DiagnosticCode.Expected_0_type_arguments_but_got_1, expression.range, "1", k.toString());
+              return this.module.createUnreachable();
+            }
+            if (expression.arguments.length != 0) {
+              this.error(DiagnosticCode.Expected_0_arguments_but_got_1, expression.range, "0", expression.arguments.length.toString());
+              return this.module.createUnreachable();
+            }
+            return this.options.target == Target.WASM64
+              ? this.module.createI64(resolvedTypeArguments[0].byteSize, 0)
+              : this.module.createI32(resolvedTypeArguments[0].byteSize);
+
+          } else if (functionPrototype.internalName == "load") {
+            this.currentType = resolvedTypeArguments[0];
+            if (k != 1) {
+              this.error(DiagnosticCode.Expected_0_type_arguments_but_got_1, expression.range, "1", k.toString());
+              return this.module.createUnreachable();
+            }
+            if (expression.arguments.length != 1) {
+              this.error(DiagnosticCode.Expected_0_arguments_but_got_1, expression.range, "1", expression.arguments.length.toString());
+              return this.module.createUnreachable();
+            }
+            arg0 = this.compileExpression(expression.arguments[0], Type.usize32, ConversionKind.IMPLICIT); // reports
+            this.currentType = resolvedTypeArguments[0];
+            if (!arg0)
+              return this.module.createUnreachable();
+            return this.module.createLoad(resolvedTypeArguments[0].byteSize, resolvedTypeArguments[0].isSignedInteger, arg0, typeToNativeType(resolvedTypeArguments[0]));
+
+          } else if (functionPrototype.internalName == "store") {
+            this.currentType = Type.void;
+            if (k != 1) {
+              this.error(DiagnosticCode.Expected_0_type_arguments_but_got_1, expression.range, "1", k.toString());
+              return this.module.createUnreachable();
+            }
+            if (expression.arguments.length != 2) {
+              this.error(DiagnosticCode.Expected_0_arguments_but_got_1, expression.range, "2", expression.arguments.length.toString());
+              return this.module.createUnreachable();
+            }
+            arg0 = this.compileExpression(expression.arguments[0], Type.usize32, ConversionKind.IMPLICIT); // reports
+            this.currentType = Type.void;
+            if (!arg0)
+              return this.module.createUnreachable();
+            arg1 = this.compileExpression(expression.arguments[1], resolvedTypeArguments[0], ConversionKind.IMPLICIT);
+            this.currentType = Type.void;
+            if (!arg1)
+              return this.module.createUnreachable();
+            return this.module.createStore(resolvedTypeArguments[0].byteSize, arg0, arg1, typeToNativeType(resolvedTypeArguments[0]));
+          }
+          this.error(DiagnosticCode.Operation_not_supported, expression.range);
+          return this.module.createUnreachable();
         }
       } else {
         // TODO: infer type arguments from parameter types if omitted
@@ -1458,8 +1517,8 @@ export class Compiler extends DiagnosticEmitter {
 
     this.currentType = functionInstance.returnType;
 
-    let tempLocal: Local;
     if (functionInstance.isBuiltin) {
+      let tempLocal: Local;
       switch (functionInstance.template.internalName) {
 
         case "clz": // i32/i64.clz
@@ -1570,11 +1629,6 @@ export class Compiler extends DiagnosticEmitter {
         case "unreachable":
           return this.module.createUnreachable();
 
-        case "sizeof": // T.size
-          if (this.options.target == Target.WASM64)
-            return this.module.createI64(Math.ceil(functionInstance.typeArguments[0].size / 8), 0);
-          return this.module.createI32(Math.ceil(functionInstance.typeArguments[0].size / 8));
-
         case "isNaN": // value != value
           if (functionInstance.typeArguments[0] == Type.f64) {
             tempLocal = this.currentFunction.addLocal(Type.f64);
@@ -1626,10 +1680,12 @@ export class Compiler extends DiagnosticEmitter {
           break;
 
         case "assert":
-          return this.module.createIf(
-            this.module.createUnary(UnaryOp.EqzI32, operands[0]),
-            this.module.createUnreachable()
-          );
+          return this.options.noDebug
+            ? this.module.createNop()
+            : this.module.createIf(
+              this.module.createUnary(UnaryOp.EqzI32, operands[0]),
+              this.module.createUnreachable()
+            );
       }
       this.error(DiagnosticCode.Operation_not_supported, reportNode.range);
       return this.module.createUnreachable();
diff --git a/src/glue/js.d.ts b/src/glue/js.d.ts
index 8badbc75..27af38aa 100644
--- a/src/glue/js.d.ts
+++ b/src/glue/js.d.ts
@@ -11,6 +11,6 @@ declare type f32 = number;
 declare type f64 = number;
 declare type bool = boolean;
 
-// Raw memory access (here: Binaryen memory, T=u8)
-declare function store<T>(ptr: usize, val: u8): void;
-declare function load<T>(ptr: usize): u8;
+// Raw memory access (here: Binaryen memory)
+declare function store<T = u8>(ptr: usize, val: T): void;
+declare function load<T = u8>(ptr: usize): T;
diff --git a/src/program.ts b/src/program.ts
index 820a20da..c2bf4c7f 100644
--- a/src/program.ts
+++ b/src/program.ts
@@ -1149,19 +1149,21 @@ function initializeBuiltins(program: Program): void {
   addGenericUnaryBuiltin(program, "sqrt", genericFloat);
   addGenericUnaryBuiltin(program, "trunc", genericFloat);
 
-  addBuiltin(program, "current_memory", [], usize);
-  addBuiltin(program, "grow_memory", [ usize ], usize);
-  addBuiltin(program, "unreachable", [], Type.void);
+  addSimpleBuiltin(program, "current_memory", [], usize);
+  addSimpleBuiltin(program, "grow_memory", [ usize ], usize);
+  addSimpleBuiltin(program, "unreachable", [], Type.void);
 
   addGenericUnaryTestBuiltin(program, "isNaN", genericFloat);
   addGenericUnaryTestBuiltin(program, "isFinite", genericFloat);
-  addBuiltin(program, "assert", [ Type.bool ], Type.void);
+  addSimpleBuiltin(program, "assert", [ Type.bool ], Type.void);
 
-  // TODO: load, store, sizeof
-  // sizeof, for example, has varying Ts but really shouldn't provide an instance for each class
+  addGenericAnyBuiltin(program, "sizeof");
+  addGenericAnyBuiltin(program, "load");
+  addGenericAnyBuiltin(program, "store");
 }
 
-function addBuiltin(program: Program, name: string, parameterTypes: Type[], returnType: Type) {
+/** Adds a simple (non-generic) builtin. */
+function addSimpleBuiltin(program: Program, name: string, parameterTypes: Type[], returnType: Type) {
   let prototype: FunctionPrototype = new FunctionPrototype(program, name, null, null);
   prototype.isGeneric = false;
   prototype.isBuiltin = true;
@@ -1173,6 +1175,7 @@ function addBuiltin(program: Program, name: string, parameterTypes: Type[], retu
   program.elements.set(name, prototype);
 }
 
+/** Adds a generic unary builtin that takes and returns a value of its generic type. */
 function addGenericUnaryBuiltin(program: Program, name: string, types: Type[]): void {
   let prototype: FunctionPrototype = new FunctionPrototype(program, name, null, null);
   prototype.isGeneric = true;
@@ -1184,6 +1187,7 @@ function addGenericUnaryBuiltin(program: Program, name: string, types: Type[]):
   program.elements.set(name, prototype);
 }
 
+/** Adds a generic binary builtin that takes two and returns a value of its generic type. */
 function addGenericBinaryBuiltin(program: Program, name: string, types: Type[]): void {
   let prototype: FunctionPrototype = new FunctionPrototype(program, name, null, null);
   prototype.isGeneric = true;
@@ -1195,6 +1199,7 @@ function addGenericBinaryBuiltin(program: Program, name: string, types: Type[]):
   program.elements.set(name, prototype);
 }
 
+/** Adds a generic unary builtin that alwways returns `bool`. */
 function addGenericUnaryTestBuiltin(program: Program, name: string, types: Type[]): void {
   let prototype: FunctionPrototype = new FunctionPrototype(program, name, null, null);
   prototype.isGeneric = true;
@@ -1205,3 +1210,12 @@ function addGenericUnaryTestBuiltin(program: Program, name: string, types: Type[
   }
   program.elements.set(name, prototype);
 }
+
+/** Adds a special generic builtin that takes any type argument. */
+function addGenericAnyBuiltin(program: Program, name: string): void {
+  let prototype: FunctionPrototype = new FunctionPrototype(program, name, null, null);
+  prototype.isGeneric = true;
+  prototype.isBuiltin = true;
+  program.elements.set(name, prototype);
+  // instances are hard coded in compiler.ts
+}
diff --git a/src/types.ts b/src/types.ts
index fea29639..b28aa58e 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -29,6 +29,7 @@ export class Type {
 
   kind: TypeKind;
   size: i32;
+  byteSize: i32;
   classType: Class | null;
   nullable: bool = false;
   nullableType: Type | null = null; // cached, of this type
@@ -36,6 +37,7 @@ export class Type {
   constructor(kind: TypeKind, size: i32) {
     this.kind = kind;
     this.size = size;
+    this.byteSize = Math.ceil(<f64>size / 8);
     this.classType = null;
   }
 
diff --git a/tests/compiler/binary.wast b/tests/compiler/binary.wast
index 2f275ada..9a26e7e6 100644
--- a/tests/compiler/binary.wast
+++ b/tests/compiler/binary.wast
@@ -838,6 +838,9 @@
   isNaN
   isFinite
   assert
+  sizeof
+  load
+  store
   binary/b
   binary/i
   binary/I
diff --git a/tests/compiler/builtins.ts b/tests/compiler/builtins.ts
index 71816910..ccf5a35b 100644
--- a/tests/compiler/builtins.ts
+++ b/tests/compiler/builtins.ts
@@ -104,3 +104,20 @@ s = grow_memory(1);
 if (0) unreachable();
 
 assert(true);
+
+sizeof<u8>();
+sizeof<u16>();
+sizeof<u32>();
+sizeof<u64>();
+sizeof<usize>();
+sizeof<bool>();
+sizeof<i8>();
+sizeof<i16>();
+sizeof<i32>();
+sizeof<i64>();
+sizeof<isize>();
+sizeof<f32>();
+sizeof<f64>();
+
+i = load<i32>(4);
+store<i32>(4, i);
diff --git a/tests/compiler/builtins.wast b/tests/compiler/builtins.wast
index 68aa2d5a..c7a188c1 100644
--- a/tests/compiler/builtins.wast
+++ b/tests/compiler/builtins.wast
@@ -475,6 +475,54 @@
    )
    (unreachable)
   )
+  (drop
+   (i32.const 1)
+  )
+  (drop
+   (i32.const 2)
+  )
+  (drop
+   (i32.const 4)
+  )
+  (drop
+   (i32.const 8)
+  )
+  (drop
+   (i32.const 4)
+  )
+  (drop
+   (i32.const 1)
+  )
+  (drop
+   (i32.const 1)
+  )
+  (drop
+   (i32.const 2)
+  )
+  (drop
+   (i32.const 4)
+  )
+  (drop
+   (i32.const 8)
+  )
+  (drop
+   (i32.const 4)
+  )
+  (drop
+   (i32.const 4)
+  )
+  (drop
+   (i32.const 8)
+  )
+  (set_global $builtins/i
+   (i32.load
+    (i32.const 4)
+   )
+  )
+  (i32.store
+   (i32.const 4)
+   (get_global $builtins/i)
+  )
  )
 )
 (;
@@ -499,6 +547,9 @@
   isNaN
   isFinite
   assert
+  sizeof
+  load
+  store
   builtins/b
   builtins/i
   builtins/I
diff --git a/tests/compiler/do.wast b/tests/compiler/do.wast
index 4dbdd366..e3a41b6c 100644
--- a/tests/compiler/do.wast
+++ b/tests/compiler/do.wast
@@ -77,6 +77,9 @@
   isNaN
   isFinite
   assert
+  sizeof
+  load
+  store
   do/loopDo
   do/loopDoInDo
 [program.exports]
diff --git a/tests/compiler/export.wast b/tests/compiler/export.wast
index 219bc5cf..546bd965 100644
--- a/tests/compiler/export.wast
+++ b/tests/compiler/export.wast
@@ -46,6 +46,9 @@
   isNaN
   isFinite
   assert
+  sizeof
+  load
+  store
   export/add
   export/sub
   export/a
diff --git a/tests/compiler/if.wast b/tests/compiler/if.wast
index 00437e2a..cccbdc97 100644
--- a/tests/compiler/if.wast
+++ b/tests/compiler/if.wast
@@ -68,6 +68,9 @@
   isNaN
   isFinite
   assert
+  sizeof
+  load
+  store
   if/ifThenElse
   if/ifThen
   if/ifThenElseBlock
diff --git a/tests/compiler/import.wast b/tests/compiler/import.wast
index 168866b4..1481eccc 100644
--- a/tests/compiler/import.wast
+++ b/tests/compiler/import.wast
@@ -60,6 +60,9 @@
   isNaN
   isFinite
   assert
+  sizeof
+  load
+  store
   export/add
   export/sub
   export/a
diff --git a/tests/compiler/literals.wast b/tests/compiler/literals.wast
index 845292be..776d19ad 100644
--- a/tests/compiler/literals.wast
+++ b/tests/compiler/literals.wast
@@ -161,6 +161,9 @@
   isNaN
   isFinite
   assert
+  sizeof
+  load
+  store
 [program.exports]
   
 ;)
diff --git a/tests/compiler/reexport.wast b/tests/compiler/reexport.wast
index 79bd0241..3ac882ef 100644
--- a/tests/compiler/reexport.wast
+++ b/tests/compiler/reexport.wast
@@ -62,6 +62,9 @@
   isNaN
   isFinite
   assert
+  sizeof
+  load
+  store
   export/add
   export/sub
   export/a
diff --git a/tests/compiler/switch.wast b/tests/compiler/switch.wast
index e292a04b..7704c19e 100644
--- a/tests/compiler/switch.wast
+++ b/tests/compiler/switch.wast
@@ -167,6 +167,9 @@
   isNaN
   isFinite
   assert
+  sizeof
+  load
+  store
   switch/doSwitch
   switch/doSwitchDefaultFirst
   switch/doSwitchDefaultOmitted
diff --git a/tests/compiler/unary.wast b/tests/compiler/unary.wast
index c2a61148..f79cbe41 100644
--- a/tests/compiler/unary.wast
+++ b/tests/compiler/unary.wast
@@ -655,6 +655,9 @@
   isNaN
   isFinite
   assert
+  sizeof
+  load
+  store
   unary/i
   unary/I
   unary/f
diff --git a/tests/compiler/while.wast b/tests/compiler/while.wast
index a5af328e..daa4a241 100644
--- a/tests/compiler/while.wast
+++ b/tests/compiler/while.wast
@@ -86,6 +86,9 @@
   isNaN
   isFinite
   assert
+  sizeof
+  load
+  store
   while/loopWhile
   while/loopWhileInWhile
 [program.exports]