[wasm] Update WebAssembly.Global constructor

The new spec has two arguments, the first is the global descriptor, and
the second is the initial value:

    new WebAssembly.Global({type: i32}, 42);

If the initial value argument is omitted, the value is set to 0.

Bug: v8:7625
Change-Id: I679d4b7c49c69ec7ffcdfeb8ae506fa7ab9bba95
Reviewed-on: https://chromium-review.googlesource.com/1028847Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Ben Smith <binji@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52822}

src/wasm/wasm-js.cc

@@ -686,10 +686,6 @@ void WebAssemblyGlobal(const v8::FunctionCallbackInfo<v8::Value>& args) {
   Local<Context> context = isolate->GetCurrentContext();
   Local<v8::Object> descriptor = Local<Object>::Cast(args[0]);
 
-  // The descriptor's 'value'.
-  v8::MaybeLocal<v8::Value> maybe_value =
-      descriptor->Get(context, v8_str(isolate, "value"));
-
   // The descriptor's 'mutable'.
   bool is_mutable = false;
   {
@@ -738,38 +734,43 @@ void WebAssemblyGlobal(const v8::FunctionCallbackInfo<v8::Value>& args) {
     return;
   }
 
-  // Convert value to a WebAssembly value.
-  v8::Local<v8::Value> value;
-  if (maybe_value.ToLocal(&value)) {
-    switch (type) {
-      case i::wasm::kWasmI32: {
-        int32_t i32_value = 0;
+  // Convert value to a WebAssembly value, the default value is 0.
+  Local<v8::Value> value = Local<Value>::Cast(args[1]);
+  switch (type) {
+    case i::wasm::kWasmI32: {
+      int32_t i32_value = 0;
+      if (!value->IsUndefined()) {
         v8::Local<v8::Int32> int32_value;
         if (!value->ToInt32(context).ToLocal(&int32_value)) return;
         if (!int32_value->Int32Value(context).To(&i32_value)) return;
-        global_obj->SetI32(i32_value);
-        break;
       }
-      case i::wasm::kWasmF32: {
+      global_obj->SetI32(i32_value);
+      break;
+    }
+    case i::wasm::kWasmF32: {
+      float f32_value = 0;
+      if (!value->IsUndefined()) {
         double f64_value = 0;
         v8::Local<v8::Number> number_value;
         if (!value->ToNumber(context).ToLocal(&number_value)) return;
         if (!number_value->NumberValue(context).To(&f64_value)) return;
-        float f32_value = static_cast<float>(f64_value);
-        global_obj->SetF32(f32_value);
-        break;
+        f32_value = static_cast<float>(f64_value);
       }
-      case i::wasm::kWasmF64: {
-        double f64_value = 0;
+      global_obj->SetF32(f32_value);
+      break;
+    }
+    case i::wasm::kWasmF64: {
+      double f64_value = 0;
+      if (!value->IsUndefined()) {
         v8::Local<v8::Number> number_value;
         if (!value->ToNumber(context).ToLocal(&number_value)) return;
         if (!number_value->NumberValue(context).To(&f64_value)) return;
-        global_obj->SetF64(f64_value);
-        break;
       }
-      default:
-        UNREACHABLE();
+      global_obj->SetF64(f64_value);
+      break;
     }
+    default:
+      UNREACHABLE();
   }
 
   i::Handle<i::JSObject> global_js_object(global_obj);

test/mjsunit/wasm/import-mutable-global.js

@@ -8,7 +8,7 @@ load("test/mjsunit/wasm/wasm-constants.js");
 load("test/mjsunit/wasm/wasm-module-builder.js");
 
 (function TestBasic() {
-  let global = new WebAssembly.Global({type: 'i32', value: 1});
+  let global = new WebAssembly.Global({type: 'i32'}, 1);
   let builder = new WasmModuleBuilder();
   builder.addImportedGlobal("mod", "g", kWasmI32);
   builder.addFunction("main", kSig_i_v)
@@ -20,7 +20,7 @@ load("test/mjsunit/wasm/wasm-module-builder.js");
 })();
 
 (function TestTypeMismatch() {
-  let global = new WebAssembly.Global({type: 'f32', value: 1});
+  let global = new WebAssembly.Global({type: 'f32'}, 1);
   let builder = new WasmModuleBuilder();
   builder.addImportedGlobal("mod", "g", kWasmI32);
   builder.addFunction("main", kSig_i_v)

test/mjsunit/wasm/mutable-globals.js

@@ -215,24 +215,21 @@ const f64_values = [
 ];
 
 function GlobalI32(value) {
-  return new WebAssembly.Global({type: 'i32', value});
+  return new WebAssembly.Global({type: 'i32'}, value);
 }
 
 function GlobalF32(value) {
-  return new WebAssembly.Global({type: 'f32', value});
+  return new WebAssembly.Global({type: 'f32'}, value);
 }
 
 function GlobalF64(value) {
-  return new WebAssembly.Global({type: 'f64', value});
+  return new WebAssembly.Global({type: 'f64'}, value);
 }
 
 (function TestDefaultValue() {
   assertSame(0, GlobalI32().value);
-  // TODO(binji): The spec currently requires the default value to be NaN, but
-  // I think we should change this to 0. See
-  // https://github.com/WebAssembly/mutable-global/issues/6
-  assertSame(NaN, GlobalF32().value);
-  assertSame(NaN, GlobalF64().value);
+  assertSame(0, GlobalF32().value);
+  assertSame(0, GlobalF64().value);
 })();
 
 (function TestValueOf() {