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Do not turn source array elements into writable if doing Array.slice.

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Array.slice doesn't mutate original array, so it's fine with read only data.
Plus nuke unnecessary cast.

Review URL: http://codereview.chromium.org/5972004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6113 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
antonm@chromium.org 2010-12-22 15:45:48 +00:00
parent c5916f552f
commit 0071bf92f6
1 changed files with 32 additions and 36 deletions
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68
src/builtins.cc
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@ -380,7 +380,7 @@ static inline MaybeObject* EnsureJSArrayWithWritableFastElements(
Object* receiver) {
if (!receiver->IsJSArray()) return NULL;
JSArray* array = JSArray::cast(receiver);
HeapObject* elms = HeapObject::cast(array->elements());
HeapObject* elms = array->elements();
if (elms->map() == Heap::fixed_array_map()) return elms;
if (elms->map() == Heap::fixed_cow_array_map()) {
return array->EnsureWritableFastElements();
@ -613,42 +613,38 @@ BUILTIN(ArraySlice) {
Object* receiver = *args.receiver();
FixedArray* elms;
int len = -1;
{ MaybeObject* maybe_elms_obj =
EnsureJSArrayWithWritableFastElements(receiver);
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
if (receiver->IsJSArray()) {
JSArray* array = JSArray::cast(receiver);
if (!array->HasFastElements() ||
!IsJSArrayFastElementMovingAllowed(array)) {
return CallJsBuiltin("ArraySlice", args);
}
elms = FixedArray::cast(array->elements());
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;