Revision: 6085
Author: [email protected]
Date: Mon Dec 20 06:41:41 2010
Log: Teach C++ ArraySlice builtin to deal with arguments object.
Array.prototype.slice.call(arguments, ...) idiom is pretty common (up to
97% of invocations
in GMail), so we'd better handle it efficiently too.
Review URL: http://codereview.chromium.org/6034003
http://code.google.com/p/v8/source/detail?r=6085
Modified:
/branches/bleeding_edge/src/builtins.cc
/branches/bleeding_edge/test/mjsunit/array-slice.js
=======================================
--- /branches/bleeding_edge/src/builtins.cc Tue Dec 7 03:31:57 2010
+++ /branches/bleeding_edge/src/builtins.cc Mon Dec 20 06:41:41 2010
@@ -515,10 +515,10 @@
Object* elms_obj;
{ MaybeObject* maybe_elms_obj =
EnsureJSArrayWithWritableFastElements(receiver);
+ if (maybe_elms_obj == NULL) return CallJsBuiltin("ArrayShift", args);
if (!maybe_elms_obj->ToObject(&elms_obj)) return maybe_elms_obj;
}
- if (elms_obj == NULL ||
- !IsJSArrayFastElementMovingAllowed(JSArray::cast(receiver))) {
+ if (!IsJSArrayFastElementMovingAllowed(JSArray::cast(receiver))) {
return CallJsBuiltin("ArrayShift", args);
}
FixedArray* elms = FixedArray::cast(elms_obj);
@@ -557,10 +557,10 @@
Object* elms_obj;
{ MaybeObject* maybe_elms_obj =
EnsureJSArrayWithWritableFastElements(receiver);
+ if (maybe_elms_obj == NULL) return CallJsBuiltin("ArrayUnshift", args);
if (!maybe_elms_obj->ToObject(&elms_obj)) return maybe_elms_obj;
}
- if (elms_obj == NULL ||
- !IsJSArrayFastElementMovingAllowed(JSArray::cast(receiver))) {
+ if (!IsJSArrayFastElementMovingAllowed(JSArray::cast(receiver))) {
return CallJsBuiltin("ArrayUnshift", args);
}
FixedArray* elms = FixedArray::cast(elms_obj);
@@ -611,21 +611,46 @@
BUILTIN(ArraySlice) {
Object* receiver = *args.receiver();
- Object* elms_obj;
+ FixedArray* elms;
+ int len = -1;
{ MaybeObject* maybe_elms_obj =
EnsureJSArrayWithWritableFastElements(receiver);
- if (!maybe_elms_obj->ToObject(&elms_obj)) return maybe_elms_obj;
- }
- if (elms_obj == NULL ||
- !IsJSArrayFastElementMovingAllowed(JSArray::cast(receiver))) {
- return CallJsBuiltin("ArraySlice", args);
- }
- FixedArray* elms = FixedArray::cast(elms_obj);
- JSArray* array = JSArray::cast(receiver);
- ASSERT(array->HasFastElements());
-
- int len = Smi::cast(array->length())->value();
-
+ Object* elms_obj;
+ if (maybe_elms_obj != NULL && maybe_elms_obj->ToObject(&elms_obj)) {
+ if (!IsJSArrayFastElementMovingAllowed(JSArray::cast(receiver))) {
+ return CallJsBuiltin("ArraySlice", args);
+ }
+ elms = FixedArray::cast(elms_obj);
+ JSArray* array = JSArray::cast(receiver);
+ ASSERT(array->HasFastElements());
+
+ len = Smi::cast(array->length())->value();
+ } else {
+ // Array.slice(arguments, ...) is quite a common idiom (notably more
+ // than 50% of invocations in Web apps). Treat it in C++ as well.
+ Map* arguments_map =
+ Top::context()->global_context()->arguments_boilerplate()->map();
+
+ bool is_arguments_object_with_fast_elements =
+ receiver->IsJSObject()
+ && JSObject::cast(receiver)->map() == arguments_map
+ && JSObject::cast(receiver)->HasFastElements();
+ if (!is_arguments_object_with_fast_elements) {
+ return CallJsBuiltin("ArraySlice", args);
+ }
+ elms = FixedArray::cast(JSObject::cast(receiver)->elements());
+ len = elms->length();
+#ifdef DEBUG
+ // Arguments object by construction should have no holes, check it.
+ if (FLAG_enable_slow_asserts) {
+ for (int i = 0; i < len; i++) {
+ ASSERT(elms->get(i) != Heap::the_hole_value());
+ }
+ }
+#endif
+ }
+ }
+ ASSERT(len >= 0);
int n_arguments = args.length() - 1;
// Note carefully choosen defaults---if argument is missing,
@@ -693,10 +718,10 @@
Object* elms_obj;
{ MaybeObject* maybe_elms_obj =
EnsureJSArrayWithWritableFastElements(receiver);
+ if (maybe_elms_obj == NULL) return CallJsBuiltin("ArraySplice", args);
if (!maybe_elms_obj->ToObject(&elms_obj)) return maybe_elms_obj;
}
- if (elms_obj == NULL ||
- !IsJSArrayFastElementMovingAllowed(JSArray::cast(receiver))) {
+ if (!IsJSArrayFastElementMovingAllowed(JSArray::cast(receiver))) {
return CallJsBuiltin("ArraySplice", args);
}
FixedArray* elms = FixedArray::cast(elms_obj);
=======================================
--- /branches/bleeding_edge/test/mjsunit/array-slice.js Tue Dec 7 03:01:02
2010
+++ /branches/bleeding_edge/test/mjsunit/array-slice.js Mon Dec 20 06:41:41
2010
@@ -218,3 +218,16 @@
assertTrue(delete Array.prototype[5]);
}
})();
+
+// Check slicing on arguments object.
+(function() {
+ function func(expected, a0, a1, a2) {
+ assertEquals(expected, Array.prototype.slice.call(arguments, 1));
+ }
+
+ func([]);
+ func(['a'], 'a');
+ func(['a', 1], 'a', 1);
+ func(['a', 1, undefined], 'a', 1, undefined);
+ func(['a', 1, undefined, void(0)], 'a', 1, undefined, void(0));
+})();
--
v8-dev mailing list
[email protected]
http://groups.google.com/group/v8-dev
