[builtins] TurboFan version of Array.prototype.forEach including fast path for FAST_ELEMENTS

src/js/array.js

Index: src/js/array.js
diff --git a/src/js/array.js b/src/js/array.js
index fca75a3f65f85f32e3300f3669f056793fbf7973..c8b34e053dc5c209b40674781cb545597ee91160 100644
--- a/src/js/array.js
+++ b/src/js/array.js
@@ -1520,11 +1520,15 @@ utils.InstallFunctions(GlobalArray, DONT_ENUM, [
 ]);
 
 var specialFunctions = %SpecialArrayFunctions();
+var specialExperimentalArrayFunctions = null;
 
 function getFunction(name, jsBuiltin, len) {
   var f = jsBuiltin;
   if (specialFunctions.hasOwnProperty(name)) {
     f = specialFunctions[name];
+  } else if (specialExperimentalArrayFunctions != null &&
+             specialExperimentalArrayFunctions.hasOwnProperty(name)) {
+    f = specialExperimentalArrayFunctions[name];
   }
   if (!IS_UNDEFINED(len)) {
     %FunctionSetLength(f, len);
@@ -1551,7 +1555,6 @@ utils.InstallFunctions(GlobalArray.prototype, DONT_ENUM, [
   "splice", getFunction("splice", ArraySplice, 2),
   "sort", getFunction("sort", ArraySort),
   "filter", getFunction("filter", ArrayFilter, 1),
-  "forEach", getFunction("forEach", ArrayForEach, 1),
   "some", getFunction("some", ArraySome, 1),
   "every", getFunction("every", ArrayEvery, 1),
   "map", getFunction("map", ArrayMap, 1),
@@ -1569,6 +1572,17 @@ utils.InstallFunctions(GlobalArray.prototype, DONT_ENUM, [
   iteratorSymbol, ArrayValues
 ]);
 
+%FunctionRemovePrototype(ArrayForEach);
+
+var specialExperimentalArrayFunctions = null;
+
+function InstallExperimentalArrayFunctions() {
+  specialExperimentalArrayFunctions = %SpecialExperimentalArrayFunctions();

[Yang, 2017/02/02 10:04:58]

Can we have all of this in C++, in the bootstrapper?
See InitializeExperimentalGlobal. For an example, see
InitializeGlobal_harmony_sharedarraybuffer. That code is run after deserializing
the snapshot and can act on flags at runtime.

You would simply get the Array prototype from the global object, and install a
different built-in.

And please make sure the initial_array_prototype on the context is up-to-date
after you overwrite forEach.

[danno, 2017/02/02 17:15:48]

Done.

+  utils.InstallFunctions(global.Array.prototype, DONT_ENUM, [
+    "forEach", getFunction("forEach", ArrayForEach, 1),
+  ], false);
+}
+
 %FunctionSetName(ArrayValues, "values");
 
 %FinishArrayPrototypeSetup(GlobalArray.prototype);
@@ -1611,6 +1625,7 @@ utils.Export(function(to) {
   to.ArrayFrom = ArrayFrom;
   to.ArrayJoin = ArrayJoin;
   to.ArrayPush = ArrayPush;
+  to.InstallExperimentalArrayFunctions = InstallExperimentalArrayFunctions;
   to.ArrayToString = ArrayToString;
   to.ArrayValues = ArrayValues;
   to.InnerArrayCopyWithin = InnerArrayCopyWithin;