Reviewers: Mads Ager,
Description:
StringDictionary::FindEntry optimized for symbol strings.
Please review this at http://codereview.chromium.org/3020003/show
SVN Base: http://v8.googlecode.com/svn/branches/bleeding_edge/
Affected files:
M src/objects.h
M src/objects.cc
Index: src/objects.cc
===================================================================
--- src/objects.cc (revision 5077)
+++ src/objects.cc (working copy)
@@ -7338,6 +7338,46 @@
}
+// Find entry for key otherwise return kNotFound.
+int StringDictionary::FindEntry(String* key) {
+ if (!key->IsSymbol()) {
+ return HashTable<StringDictionaryShape, String*>::FindEntry(key);
+ }
+
+ // Optimized for symbol key. Knowledge of the key type allows:
+ // 1. Move the check if the key is a symbol out of the loop.
+ // 2. Avoid comparing hash codes in symbol to symbol comparision.
+ // 3. Detect a case when a dictionary key is not a symbol but the key is.
+ // In case of positive result the dictionary key may be replaced by
+ // the symbol with minimal performance penalty. It gives a chance to
+ // perform futher lookups in code stubs (and significant performance
boost
+ // a certain style of code).
+
+ // EnsureCapacity will guarantee the hash table is never full.
+ uint32_t capacity = Capacity();
+ uint32_t entry = FirstProbe(key->Hash(), capacity);
+ uint32_t count = 1;
+
+ while (true) {
+ int index = EntryToIndex(entry);
+ Object* element = get(index);
+ if (element->IsUndefined()) break; // Empty entry.
+ if (key == element) return entry;
+ if (!element->IsSymbol() &&
+ !element->IsNull() &&
+ String::cast(element)->Equals(key)) {
+ // Replace a non-symbol key by the equivalent symbol for faster
further
+ // lookups.
+ set(index, key);
+ return entry;
+ }
+ ASSERT(element->IsNull() || !String::cast(element)->Equals(key));
+ entry = NextProbe(entry, count++, capacity);
+ }
+ return kNotFound;
+}
+
+
template<typename Shape, typename Key>
Object* HashTable<Shape, Key>::EnsureCapacity(int n, Key key) {
int capacity = Capacity();
Index: src/objects.h
===================================================================
--- src/objects.h (revision 5077)
+++ src/objects.h (working copy)
@@ -2294,6 +2294,10 @@
// For transforming properties of a JSObject.
Object* TransformPropertiesToFastFor(JSObject* obj,
int unused_property_fields);
+
+ // Find entry for key otherwise return -1. Optimzed version of
+ // HashTable::FindEntry.
+ int FindEntry(String* key);
};
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