Reorganize Lookup data structure to make marking faster

Do this by always using odd numbers for protoId's, and
putting those into the same place as the InternalClass
pointers. That makes it possible to quickly check whether
the lookup contains a pointer to a valid heap object.

Change-Id: I330017b26c090b4dcbbcce1a127dca7ba7e148d1
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/qml/jsruntime/qv4engine_p.h b/src/qml/jsruntime/qv4engine_p.h
index 737f377730..4316967484 100644
--- a/src/qml/jsruntime/qv4engine_p.h
+++ b/src/qml/jsruntime/qv4engine_p.h
@@ -374,7 +374,7 @@ public:
     const bool m_canAllocateExecutableMemory;
 #endif
 
-    int internalClassIdCount = 0;
+    quintptr protoIdCount = 1;
 
     ExecutionEngine(QJSEngine *jsEngine = nullptr);
     ~ExecutionEngine();
@@ -398,7 +398,8 @@ public:
         return static_cast<ExecutionContext *>(&currentStackFrame->jsFrame->context);
     }
 
-    int newInternalClassId() { return ++internalClassIdCount; }
+    // ensure we always get odd prototype IDs. This helps make marking in QV4::Lookup fast
+    quintptr newProtoId() { return (protoIdCount += 2); }
 
     Heap::InternalClass *newInternalClass(const VTable *vtable, Object *prototype);