Add ScopedValue and ScopedValueArray classes

Use these classes to hold Values on the stack. They
are known by the GC and very fast to create and destroy.

Change-Id: Idacf639485295ff446f290c5b0e149465354720e
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>

3 files changed, 160 insertions, 6 deletions

diff --git a/src/qml/jsruntime/jsruntime.pri b/src/qml/jsruntime/jsruntime.pri
index 9a1325b58a..c504f750e9 100644
--- a/src/qml/jsruntime/jsruntime.pri
+++ b/src/qml/jsruntime/jsruntime.pri
@@ -90,6 +90,7 @@ HEADERS += \
     $$PWD/qv4unwindhelper_arm_p.h \
     $$PWD/qv4serialize_p.h \
     $$PWD/qv4script_p.h \
+    $$PWD/qv4scopedvalue_p.h \
     $$PWD/qv4util_p.h \
     $$PWD/qv4executableallocator_p.h \
     $$PWD/qv4sequenceobject_p.h \
diff --git a/src/qml/jsruntime/qv4runtime.cpp b/src/qml/jsruntime/qv4runtime.cpp
index 33521efb02..77b11a4fa8 100644
--- a/src/qml/jsruntime/qv4runtime.cpp
+++ b/src/qml/jsruntime/qv4runtime.cpp
@@ -51,6 +51,7 @@
 #include "qv4function_p.h"
 #include "qv4exception_p.h"
 #include "private/qlocale_tools_p.h"
+#include "qv4scopedvalue_p.h"
 
 #include <QtCore/qmath.h>
 #include <QtCore/qnumeric.h>
@@ -159,14 +160,16 @@ void __qmljs_delete_name(ExecutionContext *ctx, Value *result, String *name)
 
 void __qmljs_add_helper(ExecutionContext *ctx, Value *result, const Value &left, const Value &right)
 {
-    Value pleft = __qmljs_to_primitive(left, PREFERREDTYPE_HINT);
-    Value pright = __qmljs_to_primitive(right, PREFERREDTYPE_HINT);
-    if (pleft.isString() || pright.isString()) {
-        if (!pleft.isString())
+    ValueScope scope(ctx);
+
+    ScopedValue pleft(scope, __qmljs_to_primitive(left, PREFERREDTYPE_HINT));
+    ScopedValue pright(scope, __qmljs_to_primitive(right, PREFERREDTYPE_HINT));
+    if (pleft->isString() || pright->isString()) {
+        if (!pleft->isString())
             pleft = __qmljs_to_string(pleft, ctx);
-        if (!pright.isString())
+        if (!pright->isString())
             pright = __qmljs_to_string(pright, ctx);
-        String *string = __qmljs_string_concat(ctx, pleft.stringValue(), pright.stringValue());
+        String *string = __qmljs_string_concat(ctx, pleft->stringValue(), pright->stringValue());
         *result = Value::fromString(string);
         return;
     }
diff --git a/src/qml/jsruntime/qv4scopedvalue_p.h b/src/qml/jsruntime/qv4scopedvalue_p.h
new file mode 100644
index 0000000000..9d19025d83
--- /dev/null
+++ b/src/qml/jsruntime/qv4scopedvalue_p.h
@@ -0,0 +1,150 @@
+/****************************************************************************
+**
+** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** 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 Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/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 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+#ifndef QV4SCOPEDVALUE_P_H
+#define QV4SCOPEDVALUE_P_H
+
+#include "qv4engine_p.h"
+#include "qv4value_def_p.h"
+
+QT_BEGIN_NAMESPACE
+
+namespace QV4 {
+
+struct ScopedValueArray {
+    ScopedValueArray(ExecutionEngine *e, int size)
+        : engine(e)
+#ifndef QT_NO_DEBUG
+        , size(size)
+#endif
+    {
+        ptr = e->stackPush(size);
+    }
+
+    ~ScopedValueArray() {
+#ifndef QT_NO_DEBUG
+        engine->stackPop(size);
+        Q_ASSERT(engine->jsStackTop == ptr);
+#else
+        engine->jsStackTop = ptr;
+#endif
+    }
+
+    ExecutionEngine *engine;
+#ifndef QT_NO_DEBUG
+    int size;
+#endif
+    Value *ptr;
+};
+
+struct ScopedValue;
+
+struct ValueScope {
+    ValueScope(ExecutionContext *ctx)
+        : engine(ctx->engine)
+    {
+        mark = ctx->engine->jsStackTop;
+    }
+
+    ValueScope(ExecutionEngine *e)
+        : engine(e)
+    {
+        mark = e->jsStackTop;
+    }
+
+    ~ValueScope() {
+        Q_ASSERT(engine->jsStackTop >= mark);
+        engine->jsStackTop = mark;
+    }
+
+    ExecutionEngine *engine;
+    Value *mark;
+};
+
+struct ScopedValue
+{
+    ScopedValue(ExecutionEngine *engine)
+    {
+        ptr = engine->jsStackTop++;
+    }
+
+    ScopedValue(ExecutionEngine *engine, const Value &v)
+    {
+        ptr = engine->jsStackTop++;
+        *ptr = v;
+    }
+
+    ScopedValue(const ValueScope &scope)
+    {
+        ptr = scope.engine->jsStackTop++;
+    }
+
+    ScopedValue(const ValueScope &scope, const Value &v)
+    {
+        ptr = scope.engine->jsStackTop++;
+        *ptr = v;
+    }
+
+    ScopedValue &operator=(const Value &v) {
+        *ptr = v;
+        return *this;
+    }
+
+    ScopedValue &operator=(const ScopedValue &other) {
+        *ptr = *other.ptr;
+        return *this;
+    }
+
+    Value *operator->() {
+        return ptr;
+    }
+
+    operator const Value &() const {
+        return *ptr;
+    }
+
+    Value *ptr;
+};
+
+}
+
+QT_END_NAMESPACE
+
+#endif