Add an actual write barrier and centralize it in one place

All stores into the Heap from C++ and Moth should now go through
the write barrier.

Change-Id: Iae9347754b90d68c10fade9f345842e86ec460cd
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/plugins/qmltooling/qmldbg_debugger/qv4datacollector.cpp

@@ -366,8 +366,8 @@ QV4DataCollector::Ref QV4DataCollector::addRef(QV4::Value value, bool deduplicat
 {
     class ExceptionStateSaver
     {
-        quint32 *hasExceptionLoc;
-        quint32 hadException;
+        quint8 *hasExceptionLoc;
+        quint8 hadException;
 
     public:
         ExceptionStateSaver(QV4::ExecutionEngine *engine)

src/qml/jit/qv4assembler_p.h

@@ -1249,7 +1249,7 @@ public:
                                  const RegisterInformation &fpRegistersToSave);
 
     void checkException() {
-        load32(Address(EngineRegister, qOffsetOf(QV4::ExecutionEngine, hasException)), ScratchRegister);
+        this->load8(Address(EngineRegister, qOffsetOf(QV4::ExecutionEngine, hasException)), ScratchRegister);
         Jump exceptionThrown = branch32(RelationalCondition::NotEqual, ScratchRegister, TrustedImm32(0));
         if (catchBlock)
             addPatch(catchBlock, exceptionThrown);

src/qml/jsruntime/qv4engine_p.h

@@ -100,7 +100,9 @@ public:
     Heap::ExecutionContext *current;
 
     Value *jsStackTop;
-    quint32 hasException;
+    quint8 hasException;
+    quint8 writeBarrierActive = false;
+    quint16 unused = 0;
     qint32 callDepth;
 
     MemoryManager *memoryManager;

src/qml/jsruntime/qv4managed_p.h

@@ -53,6 +53,7 @@
 #include "qv4global_p.h"
 #include "qv4value_p.h"
 #include <private/qv4heap_p.h>
+#include <private/qv4writebarrier_p.h>
 
 QT_BEGIN_NAMESPACE
 

src/qml/jsruntime/qv4value_p.h

@@ -708,52 +708,6 @@ inline unsigned int Value::toUInt32() const
     return (unsigned int)toInt32();
 }
 
-template <size_t offset>
-struct HeapValue : Value {
-    void set(ExecutionEngine *e, const Value &newVal) {
-        Q_UNUSED(e);
-        setRawValue(newVal.rawValue());
-    }
-};
-
-template <size_t offset>
-struct ValueArray {
-    uint size;
-    uint alloc;
-    Value values[1];
-
-    void set(ExecutionEngine *e, uint index, Value v) {
-        Q_UNUSED(e);
-        Q_ASSERT(index < alloc);
-        values[index] = v;
-    }
-    void set(ExecutionEngine *e, uint index, Heap::Base *b) {
-        Q_UNUSED(e);
-        Q_ASSERT(index < alloc);
-        values[index] = b;
-    }
-    inline const Value &operator[] (uint index) const {
-        Q_ASSERT(index < alloc);
-        return values[index];
-    }
-    inline const Value *data() const {
-        return values;
-    }
-
-    void insertData(ExecutionEngine *e, uint index, Value v) {
-        for (uint i = size - 1; i > index; --i) {
-            values[i] = values[i - 1];
-        }
-        set(e, index, v);
-    }
-    void removeData(ExecutionEngine *e, uint index, int n = 1) {
-        Q_UNUSED(e);
-        for (uint i = index; i < size - n; ++i) {
-            values[i] = values[i + n];
-        }
-    }
-};
-
 }
 
 QT_END_NAMESPACE

src/qml/jsruntime/qv4vme_moth.cpp

@@ -344,8 +344,13 @@ Param traceParam(const Param &param)
     QV4::ReturnedValue tmp = (value); \
     if (engine->hasException) \
         goto catchException; \
-    VALUE(param) = tmp; \
-    }
+    if (Q_LIKELY(!engine->writeBarrierActive || !scopes[param.scope].base)) { \
+        VALUE(param) = tmp; \
+    } else { \
+        QV4::WriteBarrier::write(engine, scopes[param.scope].base, VALUEPTR(param), QV4::Value::fromReturnedValue(tmp)); \
+    } \
+}
+
 // qv4scopedvalue_p.h also defines a CHECK_EXCEPTION macro
 #ifdef CHECK_EXCEPTION
 #undef CHECK_EXCEPTION

src/qml/memory/memory.pri

@@ -7,7 +7,8 @@ SOURCES += \
 
 HEADERS += \
     $$PWD/qv4mm_p.h \
-    $$PWD/qv4mmdefs_p.h
+    $$PWD/qv4mmdefs_p.h \
+    $$PWD/qv4writebarrier_p.h
 }
 
 HEADERS += \

src/qml/memory/qv4heap_p.h

@@ -164,26 +164,6 @@ struct Q_QML_EXPORT Base {
 };
 V4_ASSERT_IS_TRIVIAL(Base)
 
-template <typename T, size_t o>
-struct Pointer {
-    static Q_CONSTEXPR size_t offset = o;
-    T operator->() const { return ptr; }
-    operator T () const { return ptr; }
-
-    void set(ExecutionEngine *e, T newVal) {
-        Q_UNUSED(e);
-        ptr = newVal;
-    }
-
-    template <typename Type>
-    Type *cast() { return static_cast<Type *>(ptr); }
-
-private:
-    T ptr;
-};
-typedef Pointer<char *, 0> V4PointerCheck;
-V4_ASSERT_IS_TRIVIAL(V4PointerCheck)
-
 }
 
 #ifdef QT_NO_QOBJECT

src/qml/memory/qv4writebarrier_p.h

@@ -0,0 +1,152 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQml module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+#ifndef QV4WRITEBARRIER_P_H
+#define QV4WRITEBARRIER_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <private/qv4global_p.h>
+#include <private/qv4value_p.h>
+
+QT_BEGIN_NAMESPACE
+
+namespace QV4 {
+
+namespace WriteBarrier {
+
+inline void write(QV4::ExecutionEngine *engine, QV4::Heap::Base *base, QV4::Value *slot, QV4::Value value)
+{
+    Q_UNUSED(engine);
+    Q_UNUSED(base);
+    *slot = value;
+}
+
+inline void write(QV4::ExecutionEngine *engine, QV4::Heap::Base *base, QV4::Heap::Base **slot, QV4::Heap::Base *value)
+{
+    Q_UNUSED(engine);
+    Q_UNUSED(base);
+    *slot = value;
+}
+
+}
+
+namespace Heap {
+
+template <typename T, size_t o>
+struct Pointer {
+    static Q_CONSTEXPR size_t offset = o;
+    T operator->() const { return ptr; }
+    operator T () const { return ptr; }
+
+    void set(ExecutionEngine *e, T newVal) {
+        Q_UNUSED(e);
+        ptr = newVal;
+    }
+
+    template <typename Type>
+    Type *cast() { return static_cast<Type *>(ptr); }
+
+private:
+    T ptr;
+};
+typedef Pointer<char *, 0> V4PointerCheck;
+V4_ASSERT_IS_TRIVIAL(V4PointerCheck)
+
+}
+
+template <size_t offset>
+struct HeapValue : Value {
+    void set(ExecutionEngine *e, const Value &newVal) {
+        Q_UNUSED(e);
+        setRawValue(newVal.rawValue());
+    }
+};
+
+template <size_t offset>
+struct ValueArray {
+    uint size;
+    uint alloc;
+    Value values[1];
+
+    void set(ExecutionEngine *e, uint index, Value v) {
+        Q_UNUSED(e);
+        Q_ASSERT(index < alloc);
+        values[index] = v;
+    }
+    void set(ExecutionEngine *e, uint index, Heap::Base *b) {
+        Q_UNUSED(e);
+        Q_ASSERT(index < alloc);
+        values[index] = b;
+    }
+    inline const Value &operator[] (uint index) const {
+        Q_ASSERT(index < alloc);
+        return values[index];
+    }
+    inline const Value *data() const {
+        return values;
+    }
+
+    void insertData(ExecutionEngine *e, uint index, Value v) {
+        for (uint i = size - 1; i > index; --i) {
+            values[i] = values[i - 1];
+        }
+        set(e, index, v);
+    }
+    void removeData(ExecutionEngine *e, uint index, int n = 1) {
+        Q_UNUSED(e);
+        for (uint i = index; i < size - n; ++i) {
+            values[i] = values[i + n];
+        }
+    }
+};
+
+}
+
+QT_END_NAMESPACE
+
+#endif