Add abstraction for temporarily setting StaticData when saving

The StaticData flag needs to be saved to disk, but removed again
afterwards so that we can free() the malloc'd data. This also allows us
to avoid copying all the data into a byte array before saving.

Change-Id: I96513f8d98acf0ea0b4514d96376b487e8444917
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

3 files changed, 46 insertions, 19 deletions

diff --git a/src/qml/compiler/qqmlirbuilder.cpp b/src/qml/compiler/qqmlirbuilder.cpp
index e63aa3b66d..6f46648572 100644
--- a/src/qml/compiler/qqmlirbuilder.cpp
+++ b/src/qml/compiler/qqmlirbuilder.cpp
@@ -1565,9 +1565,6 @@ void QmlUnitGenerator::generate(Document &output, const QV4::CompiledData::Depen
                 break;
             }
         }
-        // This unit's memory was allocated with malloc on the heap, so it's
-        // definitely not suitable for StaticData access.
-        createdUnit->flags &= ~QV4::CompiledData::Unit::StaticData;
 
         if (dependencyHasher) {
             const QByteArray checksum = dependencyHasher();
diff --git a/src/qml/compiler/qv4compileddata.cpp b/src/qml/compiler/qv4compileddata.cpp
index 091c29c8c7..71015107ad 100644
--- a/src/qml/compiler/qv4compileddata.cpp
+++ b/src/qml/compiler/qv4compileddata.cpp
@@ -82,14 +82,8 @@ CompilationUnit::~CompilationUnit()
             free(const_cast<QmlUnit *>(qmlData));
         qmlData = nullptr;
 
-#ifndef V4_BOOTSTRAP
         if (!(data->flags & QV4::CompiledData::Unit::StaticData))
             free(const_cast<Unit *>(data));
-#else
-        // Unconditionally free the memory. In the dev tools we create units that have
-        // the flag set and will be saved to disk, so intended to persist later.
-        free(const_cast<Unit *>(data));
-#endif
     }
     data = nullptr;
 #if Q_BYTE_ORDER == Q_BIG_ENDIAN
@@ -113,16 +107,9 @@ bool CompilationUnit::saveToDisk(const QString &outputFileName, QString *errorSt
         return false;
     }
 
-    QByteArray modifiedUnit;
-    modifiedUnit.resize(data->unitSize);
-    memcpy(modifiedUnit.data(), data, data->unitSize);
-    const char *dataPtr = modifiedUnit.data();
-    Unit *unitPtr;
-    memcpy(&unitPtr, &dataPtr, sizeof(unitPtr));
-    unitPtr->flags |= Unit::StaticData;
-
-    qint64 headerWritten = cacheFile.write(modifiedUnit);
-    if (headerWritten != modifiedUnit.size()) {
+    SaveableUnitPointer saveable(this);
+    qint64 headerWritten = cacheFile.write(saveable.data<char>(), saveable.size());
+    if (headerWritten != saveable.size()) {
         *errorString = cacheFile.errorString();
         return false;
     }
diff --git a/src/qml/compiler/qv4compileddata_p.h b/src/qml/compiler/qv4compileddata_p.h
index 9301939bff..629adf8231 100644
--- a/src/qml/compiler/qv4compileddata_p.h
+++ b/src/qml/compiler/qv4compileddata_p.h
@@ -1158,6 +1158,49 @@ public:
     bool saveToDisk(const QString &outputFileName, QString *errorString) const;
 };
 
+class SaveableUnitPointer
+{
+    Q_DISABLE_COPY_MOVE(SaveableUnitPointer)
+public:
+    SaveableUnitPointer(const CompilationUnit *unit, quint32 temporaryFlags = Unit::StaticData) :
+          unit(unit)
+    {
+        quint32_le &unitFlags = mutableFlags();
+        quint32 origFlags = unitFlags;
+        unitFlags |= temporaryFlags;
+        changedFlags = origFlags ^ unitFlags;
+    }
+
+    ~SaveableUnitPointer()
+    {
+        mutableFlags() ^= changedFlags;
+    }
+
+    const CompilationUnit *operator->() const { return unit; }
+    const CompilationUnit &operator*() const { return *unit; }
+    operator const CompilationUnit *() { return unit; }
+
+    template<typename Char>
+    const Char *data() const
+    {
+        Q_STATIC_ASSERT(sizeof(Char) == 1);
+        const Char *dataPtr;
+        memcpy(&dataPtr, &unit->data, sizeof(dataPtr));
+        return dataPtr;
+    }
+
+    quint32 size() const
+    {
+        return unit->data->unitSize;
+    }
+
+private:
+    quint32_le &mutableFlags() { return const_cast<Unit *>(unit->unitData())->flags; };
+    const CompilationUnit *unit;
+    quint32 changedFlags;
+};
+
+
 } // CompiledData namespace
 } // QV4 namespace