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Don't track Smi->Double->Object element transitions for small undefined arrays.

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R=jkummerow@chromium.org
BUG=
TEST=

Review URL: http://codereview.chromium.org/8816009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10181 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
This commit is contained in:
danno@chromium.org 2011-12-06 17:21:48 +00:00
parent ff6f2fa9b3
commit c33dfd1154
1 changed files with 9 additions and 0 deletions
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9
src/parser.cc
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@ -3378,6 +3378,7 @@ Expression* Parser::ParseArrayLiteral(bool* ok) {
isolate()->factory()->NewFixedArray(values->length(), TENURED);
Handle<FixedDoubleArray> double_literals;
ElementsKind elements_kind = FAST_SMI_ONLY_ELEMENTS;
bool has_only_undefined_values = true;
// Fill in the literals.
bool is_simple = true;
@ -3401,6 +3402,7 @@ Expression* Parser::ParseArrayLiteral(bool* ok) {
// FAST_DOUBLE_ELEMENTS and FAST_ELEMENTS as necessary. Always remember
// the tagged value, no matter what the ElementsKind is in case we
// ultimately end up in FAST_ELEMENTS.
has_only_undefined_values = false;
object_literals->set(i, *boilerplate_value);
if (elements_kind == FAST_SMI_ONLY_ELEMENTS) {
// Smi only elements. Notice if a transition to FAST_DOUBLE_ELEMENTS or
@ -3439,6 +3441,13 @@ Expression* Parser::ParseArrayLiteral(bool* ok) {
}
}
// Very small array literals that don't have a concrete hint about their type
// from a constant value should default to the slow case to avoid lots of
// elements transitions on really small objects.
if (has_only_undefined_values && values->length() <= 2) {
elements_kind = FAST_ELEMENTS;
}
// Simple and shallow arrays can be lazily copied, we transform the
// elements array to a copy-on-write array.
if (is_simple && depth == 1 && values->length() > 0 &&