Replace InternalClass transitions hash with a sorted vector.

In a reasonable test application, there were some 1697 transition entries. Out
of these, 1663 of them had only a single item. The remainder, with the exception
of three, had <10 items. Only one of these had a count of >50 items (86).

As can be seen, most of the time, transitions is usually quite sparsely
populated, so using a hash is a large amount of overhead considering there's
just a few elements. For the times when it isn't, the vector being sorted
should help take care of that.

Since transitions are never removed, we can use a similar trick to
ba690fb73864915b4a35bbec5b7dc134ff1dafd0 and use a sorted vector to store them.

Compared to the hash approach, this saved ~412kb according to malloc_stats on a
reasonably comprehensive test application. Coincidentally, this also improved
v8bench for me by ~10%.

Note that this undoes 132cdfa69cae45d0c02ea715ce58722bbcd57e73, but the
expectation is that the fewer allocations done by using a vector will outweigh
the need to reserve any specific allocation initially.

Change-Id: Iec57a7db7e9a60347c9683b1cb1598f6d9c866f7
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/qml/jsruntime/qv4internalclass_p.h b/src/qml/jsruntime/qv4internalclass_p.h
index 4367f6576d..5973ca2c7c 100644
--- a/src/qml/jsruntime/qv4internalclass_p.h
+++ b/src/qml/jsruntime/qv4internalclass_p.h
@@ -193,6 +193,7 @@ struct InternalClassTransition
         Identifier *id;
         const ManagedVTable *vtable;
     };
+    InternalClass *lookup;
     int flags;
     enum {
         // range 0-0xff is reserved for attribute changes
@@ -201,8 +202,10 @@ struct InternalClassTransition
 
     bool operator==(const InternalClassTransition &other) const
     { return id == other.id && flags == other.flags; }
+
+    bool operator<(const InternalClassTransition &other) const
+    { return id < other.id; }
 };
-uint qHash(const QV4::InternalClassTransition &t, uint = 0);
 
 struct InternalClass : public QQmlJS::Managed {
     ExecutionEngine *engine;
@@ -213,7 +216,8 @@ struct InternalClass : public QQmlJS::Managed {
     SharedInternalClassData<PropertyAttributes> propertyData;
 
     typedef InternalClassTransition Transition;
-    QHash<Transition, InternalClass *> transitions; // id to next class, positive means add, negative delete
+    std::vector<Transition> transitions;
+    InternalClassTransition &lookupOrInsertTransition(const InternalClassTransition &t);
 
     InternalClass *m_sealed;
     InternalClass *m_frozen;