Make every member of a Heap object aware of its offset inside the object

This will allow adding a write barrier to those fields with manageable
effort.

Change-Id: I7d06d7ffccbcefe66e2524c64c962353c91c2766
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

3 files changed, 45 insertions, 9 deletions

diff --git a/src/qml/memory/qv4heap_p.h b/src/qml/memory/qv4heap_p.h
index febe4e6446..b3dfa407f8 100644
--- a/src/qml/memory/qv4heap_p.h
+++ b/src/qml/memory/qv4heap_p.h
@@ -164,8 +164,10 @@ struct Q_QML_EXPORT Base {
 };
 V4_ASSERT_IS_TRIVIAL(Base)
 
-template <typename T, size_t>
+template <typename T, size_t o>
 struct Pointer {
+    static Q_CONSTEXPR size_t offset = o;
+    static Q_CONSTEXPR quint64 markBits = Mark_Pointer << (o >> 2);
     T operator->() const { return ptr; }
     operator T () const { return ptr; }
 
diff --git a/src/qml/memory/qv4mm.cpp b/src/qml/memory/qv4mm.cpp
index 89cf9caf9e..edd26cf982 100644
--- a/src/qml/memory/qv4mm.cpp
+++ b/src/qml/memory/qv4mm.cpp
@@ -762,7 +762,7 @@ void MemoryManager::drainMarkStack(Value *markBase)
                     break;
                 case Mark_Pointer: {
 //                    qDebug() << "marking pointer at " << mem;
-                    Heap::Base *p = reinterpret_cast<Heap::Base *>(mem);
+                    Heap::Base *p = *reinterpret_cast<Heap::Base **>(mem);
                     if (p)
                         p->mark(engine);
                     break;
diff --git a/src/qml/memory/qv4mmdefs_p.h b/src/qml/memory/qv4mmdefs_p.h
index e4d5ce9da2..63e51f9742 100644
--- a/src/qml/memory/qv4mmdefs_p.h
+++ b/src/qml/memory/qv4mmdefs_p.h
@@ -265,24 +265,58 @@ enum MarkFlags {
     Mark_ValueArray = 3
 };
 
+template <typename T>
+struct MarkFlagEvaluator {
+    static Q_CONSTEXPR quint64 value = 0;
+};
+template <typename T, size_t o>
+struct MarkFlagEvaluator<Heap::Pointer<T, o>> {
+    static Q_CONSTEXPR quint64 value = static_cast<quint64>(Mark_Pointer) << (2*o / sizeof(quintptr));
+};
+template <size_t o>
+struct MarkFlagEvaluator<ValueArray<o>> {
+    static Q_CONSTEXPR quint64 value = static_cast<quint64>(Mark_ValueArray) << (2*o / sizeof(quintptr));
+};
+template <size_t o>
+struct MarkFlagEvaluator<HeapValue<o>> {
+    static Q_CONSTEXPR quint64 value = static_cast<quint64>(Mark_Value) << (2 *o / sizeof(quintptr));
+};
+
+#define HEAP_OBJECT_OFFSET_MEMBER_EXPANSION(c, gcType, type, name) \
+    HEAP_OBJECT_OFFSET_MEMBER_EXPANSION_##gcType(c, type, name)
+
+#define HEAP_OBJECT_OFFSET_MEMBER_EXPANSION_Pointer(c, type, name) Pointer<type, 0> name;
+#define HEAP_OBJECT_OFFSET_MEMBER_EXPANSION_NoMark(c, type, name) type name;
+#define HEAP_OBJECT_OFFSET_MEMBER_EXPANSION_HeapValue(c, type, name) HeapValue<0> name;
+#define HEAP_OBJECT_OFFSET_MEMBER_EXPANSION_ValueArray(c, type, name) ValueArray<0> name;
+
 #define HEAP_OBJECT_MEMBER_EXPANSION(c, gcType, type, name) \
     HEAP_OBJECT_MEMBER_EXPANSION_##gcType(c, type, name)
 
-#define HEAP_OBJECT_MEMBER_EXPANSION_Pointer(c, type, name) Pointer<type, 0> name;
-#define HEAP_OBJECT_MEMBER_EXPANSION_NoMark(c, type, name) type name;
-#define HEAP_OBJECT_MEMBER_EXPANSION_Value(c, type, name) type name;
-#define HEAP_OBJECT_MEMBER_EXPANSION_ValueArray(c, type, name) ValueArray<0> name;
+#define HEAP_OBJECT_MEMBER_EXPANSION_Pointer(c, type, name) \
+    Pointer<type, offsetof(c##OffsetStruct, name) + baseOffset> name;
+#define HEAP_OBJECT_MEMBER_EXPANSION_NoMark(c, type, name) \
+    type name;
+#define HEAP_OBJECT_MEMBER_EXPANSION_HeapValue(c, type, name) \
+    HeapValue<offsetof(c##OffsetStruct, name) + baseOffset> name;
+#define HEAP_OBJECT_MEMBER_EXPANSION_ValueArray(c, type, name) \
+    ValueArray<offsetof(c##OffsetStruct, name) + baseOffset> name;
 
 #define HEAP_OBJECT_MARK_EXPANSION(class, gcType, type, name) \
-    (Mark_##gcType << (offsetof(class, name) >> 2)) |
+    MarkFlagEvaluator<decltype(class::name)>::value |
 
 #define DECLARE_HEAP_OBJECT(name, base) \
+struct name##OffsetStruct { \
+    name##Members(name, HEAP_OBJECT_OFFSET_MEMBER_EXPANSION) \
+}; \
+struct name##SizeStruct : base, name##OffsetStruct {}; \
 struct name##Data { \
+    static Q_CONSTEXPR size_t baseOffset = sizeof(name##SizeStruct) - sizeof(name##OffsetStruct); \
     name##Members(name, HEAP_OBJECT_MEMBER_EXPANSION) \
 }; \
-struct name##SizeStruct : base, name##Data {}; \
+Q_STATIC_ASSERT(sizeof(name##SizeStruct) == sizeof(name##Data) + name##Data::baseOffset); \
 static Q_CONSTEXPR quint64 name##_markTable = \
-    (name##Members(name##Data, HEAP_OBJECT_MARK_EXPANSION) 0) << (((sizeof(name##SizeStruct) - sizeof(name##Data)) >> 2) | QV4::Heap::base::markTable; \
+    (name##Members(name##Data, HEAP_OBJECT_MARK_EXPANSION) 0) | QV4::Heap::base::markTable; \
     \
 struct name : base, name##Data