Reviewers: Toon Verwaest,
Description:
Force small array literals to have FAST_ELEMENTs
[email protected]
Please review this at https://codereview.chromium.org/11414139/
SVN Base: https://v8.googlecode.com/svn/branches/bleeding_edge
Affected files:
M src/parser.cc
Index: src/parser.cc
diff --git a/src/parser.cc b/src/parser.cc
index
a7bb4e7985f7a3ac75de531d41415a4d73f47b5a..75fd7b73667eb611dd1393f26c1dc559addeff67
100644
--- a/src/parser.cc
+++ b/src/parser.cc
@@ -3718,6 +3718,7 @@ Expression* Parser::ParseArrayLiteral(bool* ok) {
isolate()->factory()->NewFixedArray(values->length(), TENURED);
Handle<FixedDoubleArray> double_literals;
ElementsKind elements_kind = FAST_SMI_ELEMENTS;
+ bool has_only_undefined_values = true;
bool has_hole_values = false;
// Fill in the literals.
@@ -3749,6 +3750,7 @@ 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_ELEMENTS) {
// Smi only elements. Notice if a transition to
FAST_DOUBLE_ELEMENTS or
@@ -3787,6 +3789,13 @@ 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 &&
--
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