Changeset 169316 in webkit for trunk/Source/JavaScriptCore/runtime/SmallStrings.cpp

Timestamp:

May 24, 2014, 8:50:43 PM (11 years ago)

Author:

[email protected]

Message:

Object.prototype.toString() should use cached strings for null/undefined.
<​https://webkit.org/b/133261>

Normally, when calling Object.prototype.toString() on a regular object,
we'd cache the result of the stringification on the object's structure,
making repeated calls fast.

For null and undefined, we were not as smart. We'd instead construct a
new string with either "[object Null]" or "[object Undefined]" each time.

This was exposed by Dromaeo's JS library tests, where some prototype.js
subtests generate millions of strings this way.

This patch adds two VM-permanent cached strings to the SmallStrings.
Looks like ~10% speed-up on Dromaeo/jslib-traverse-prototype.html

Reviewed by Darin Adler.

• runtime/ObjectPrototype.cpp:

(JSC::objectProtoFuncToString):

• runtime/SmallStrings.cpp:

(JSC::SmallStrings::SmallStrings):
(JSC::SmallStrings::initializeCommonStrings):
(JSC::SmallStrings::visitStrongReferences):

• runtime/SmallStrings.h:

(JSC::SmallStrings::nullObjectString):
(JSC::SmallStrings::undefinedObjectString):

File:

• trunk/Source/JavaScriptCore/runtime/SmallStrings.cpp (modified) (3 diffs)

trunk/Source/JavaScriptCore/runtime/SmallStrings.cpp

@@ -68 +68 @@
     JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE)
 #undef JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE
+    , m_nullObjectString(nullptr)
+    , m_undefinedObjectString(nullptr)
 {
     COMPILE_ASSERT(singleCharacterStringCount == sizeof(m_singleCharacterStrings) / sizeof(m_singleCharacterStrings[0]), IsNumCharactersConstInSyncWithClassUsage);
@@ -83 +85 @@
     JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE)
 #undef JSC_COMMON_STRINGS_ATTRIBUTE_INITIALIZE
+    initialize(&vm, m_nullObjectString, "[object Null]");
+    initialize(&vm, m_undefinedObjectString, "[object Undefined]");
 }
 
@@ -93 +97 @@
     JSC_COMMON_STRINGS_EACH_NAME(JSC_COMMON_STRINGS_ATTRIBUTE_VISIT)
 #undef JSC_COMMON_STRINGS_ATTRIBUTE_VISIT
+    visitor.appendUnbarrieredPointer(&m_nullObjectString);
+    visitor.appendUnbarrieredPointer(&m_undefinedObjectString);
 }