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Do a backing store sparseness check on fast element delete.

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R=vegorov@chromium.org

Review URL: http://codereview.chromium.org/7298004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8516 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
vitalyr@chromium.org 2011-07-01 13:18:42 +00:00
parent fe7bdf1fe8
commit 8448d09d3b
1 changed files with 25 additions and 3 deletions
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28
src/objects.cc
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@ -3031,11 +3031,33 @@ MaybeObject* JSObject::DeleteFastElement(uint32_t index) {
if (!maybe->ToObject(&writable)) return maybe;
backing_store = FixedArray::cast(writable);
}
int length = IsJSArray()
uint32_t length = static_cast<uint32_t>(
IsJSArray()
? Smi::cast(JSArray::cast(this)->length())->value()
: backing_store->length();
if (index < static_cast<uint32_t>(length)) {
: backing_store->length());
if (index < length) {
backing_store->set_the_hole(index);
// If an old space backing store is larger than a certain size and
// has too few used values, normalize it.
// To avoid doing the check on every delete we require at least
// one adjacent hole to the value being deleted.
Object* hole = heap->the_hole_value();
const int kMinLengthForSparsenessCheck = 64;
if (backing_store->length() >= kMinLengthForSparsenessCheck &&
!heap->InNewSpace(backing_store) &&
((index > 0 && backing_store->get(index - 1) == hole) ||
(index + 1 < length && backing_store->get(index + 1) == hole))) {
int num_used = 0;
for (int i = 0; i < backing_store->length(); ++i) {
if (backing_store->get(i) != hole) ++num_used;
// Bail out early if more than 1/4 is used.
if (4 * num_used > backing_store->length()) break;
}
if (4 * num_used <= backing_store->length()) {
MaybeObject* result = NormalizeElements();
if (result->IsFailure()) return result;
}
}
}
return heap->true_value();
}