Store the stack of executioncontext's on the JS stack

This saves one pointer per allocated execution context.
Now every execution context that is pushed, allocates two
Values on the js stack. One contains the context itself, the
other one the offset to the parent context.

Things are a bit tricky for with and catch scopes, as those
are called from the generated code, and can't open a Scope
anymore. In addition, all methods iterating over the js
stack frames need to work with ExecutionContext pointers,
not ScopedContext's.

Change-Id: I6f3013749d4e73d2fac37973b976ba6029686b82
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

1 files changed, 16 insertions, 20 deletions

diff --git a/src/qml/jsruntime/qv4engine_p.h b/src/qml/jsruntime/qv4engine_p.h
index 968c9d5df0..e9d505c858 100644
--- a/src/qml/jsruntime/qv4engine_p.h
+++ b/src/qml/jsruntime/qv4engine_p.h
@@ -88,6 +88,7 @@ public:
     ExecutableAllocator *regExpAllocator;
     QScopedPointer<EvalISelFactory> iselFactory;
 
+    ExecutionContext *currentExecutionContext;
 
     Value *jsStackLimit;
     quintptr cStackLimit;
@@ -128,6 +129,7 @@ public:
 
     enum JSObjects {
         RootContect,
+        IntegerNull, // Has to come after the RootContext to make the context stack safe
         ObjectProto,
         ArrayProto,
         StringProto,
@@ -351,6 +353,7 @@ public:
     void pushContext(Heap::ExecutionContext *context);
     void pushContext(CallContext *context);
     Heap::ExecutionContext *popContext();
+    ExecutionContext *parentContext(ExecutionContext *context) const;
 
     Heap::Object *newObject();
     Heap::Object *newObject(InternalClass *internalClass, Object *prototype);
@@ -444,9 +447,12 @@ public:
 
 inline void ExecutionEngine::pushContext(Heap::ExecutionContext *context)
 {
-    Q_ASSERT(current && context);
-    context->parent = current;
-    current = context;
+    Q_ASSERT(currentExecutionContext && context);
+    Value *v = jsAlloca(2);
+    v[0] = Encode(context);
+    v[1] = Encode((int)(v - static_cast<Value *>(currentExecutionContext)));
+    currentExecutionContext = static_cast<ExecutionContext *>(v);
+    current = currentExecutionContext->d();
 }
 
 inline void ExecutionEngine::pushContext(CallContext *context)
@@ -457,27 +463,17 @@ inline void ExecutionEngine::pushContext(CallContext *context)
 
 inline Heap::ExecutionContext *ExecutionEngine::popContext()
 {
-    Q_ASSERT(current->parent);
-    current = current->parent;
-    Q_ASSERT(current);
+    Q_ASSERT(jsStackTop > currentExecutionContext);
+    QV4::Value *offset = (currentExecutionContext + 1);
+    Q_ASSERT(offset->isInteger());
+    int o = offset->integerValue();
+    Q_ASSERT(o);
+    currentExecutionContext -= o;
+    current = currentExecutionContext->d();
     return current;
 }
 
 inline
-Heap::ExecutionContext::ExecutionContext(ExecutionEngine *engine, ContextType t)
-    : engine(engine)
-    , parent(engine->currentContext())
-    , outer(0)
-    , lookups(0)
-    , compilationUnit(0)
-    , type(t)
-    , strictMode(false)
-    , lineNumber(-1)
-{
-}
-
-
-inline
 void Heap::Base::mark(QV4::ExecutionEngine *engine)
 {
     Q_ASSERT(inUse());