QML: Make Heap::Object and all subclasses trivial

GCC6 might dead-store-eliminate out our secret write to Base::mmdata,
because it expects all memory content to be "undefined" before
constructor calls. Clang might take the same approach if the constructor
of Heap::Object is removed.

By making these structs trivial, it also makes them memcpy-able.

Change-Id: I055b2ad28311b997fbe059849ebda4d5894eaa9b
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 6 insertions, 4 deletions

diff --git a/src/qml/jsruntime/qv4stringobject.cpp b/src/qml/jsruntime/qv4stringobject.cpp
index 1c474fb18d..829ada0c1a 100644
--- a/src/qml/jsruntime/qv4stringobject.cpp
+++ b/src/qml/jsruntime/qv4stringobject.cpp
@@ -73,15 +73,17 @@ using namespace QV4;
 
 DEFINE_OBJECT_VTABLE(StringObject);
 
-Heap::StringObject::StringObject()
+void Heap::StringObject::init()
 {
+    Object::init();
     Q_ASSERT(vtable() == QV4::StringObject::staticVTable());
     string = internalClass->engine->id_empty()->d();
     *propertyData(LengthPropertyIndex) = Primitive::fromInt32(0);
 }
 
-Heap::StringObject::StringObject(const QV4::String *str)
+void Heap::StringObject::init(const QV4::String *str)
 {
+    Object::init();
     string = str->d();
     *propertyData(LengthPropertyIndex) = Primitive::fromInt32(length());
 }
@@ -152,9 +154,9 @@ void StringObject::markObjects(Heap::Base *that, ExecutionEngine *e)
 
 DEFINE_OBJECT_VTABLE(StringCtor);
 
-Heap::StringCtor::StringCtor(QV4::ExecutionContext *scope)
-    : Heap::FunctionObject(scope, QStringLiteral("String"))
+void Heap::StringCtor::init(QV4::ExecutionContext *scope)
 {
+    Heap::FunctionObject::init(scope, QStringLiteral("String"));
 }
 
 void StringCtor::construct(const Managed *m, Scope &scope, CallData *callData)