Change QVector's in-memory data layout

The new layout matches that of QByteArrayData and QStringData, except
for offset which is measured from the beginning of QVectorData, whereas
in those classes it (still?) references the end of the header data.

The new layout uses an extra member for storing an offset into the data,
which will allow introducing QVector::fromRawData, similar to the same
functionality already existing in QString and QByteArray.

By not using an actual array to index array members, we also steer clear
of GCC bug #43247:

    http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43247

Change-Id: I408915aacadf616b4633bbbf5cae1fc19e415087
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/tests/benchmarks/corelib/tools/qvector/qrawvector.h b/tests/benchmarks/corelib/tools/qvector/qrawvector.h
index 1342513a7f..0fdfa86f1d 100644
--- a/tests/benchmarks/corelib/tools/qvector/qrawvector.h
+++ b/tests/benchmarks/corelib/tools/qvector/qrawvector.h
@@ -66,7 +66,7 @@ QT_BEGIN_NAMESPACE
 template <typename T>
 class QRawVector
 {
-    struct Data : QVectorData { T array[1]; };
+    typedef QVectorTypedData<T> Data;
 
     T *m_begin;
     int m_size;
@@ -265,15 +265,17 @@ private:
     void realloc(int size, int alloc, bool ref);
     void free(T *begin, int size);
 
+    class AlignmentDummy { QVectorData header; T array[1]; };
+
     static Q_DECL_CONSTEXPR int offsetOfTypedData()
     {
-        // (non-POD)-safe offsetof(Data, array)
+        // (non-POD)-safe offsetof(AlignmentDummy, array)
         return (sizeof(QVectorData) + (alignOfTypedData() - 1)) & ~(alignOfTypedData() - 1);
     }
     static Q_DECL_CONSTEXPR int alignOfTypedData()
     {
 #ifdef Q_ALIGNOF
-        return Q_ALIGNOF(Data);
+        return Q_ALIGNOF(AlignmentDummy);
 #else
         return sizeof(void *);
 #endif
@@ -286,7 +288,8 @@ public:
         d->ref.initializeOwned();
         d->alloc = m_alloc;
         d->size = m_size;
-        d->capacity = 0;
+        d->capacityReserved = 0;
+        d->offset = offsetOfTypedData();
 
         QVector<T> v;
         *reinterpret_cast<QVectorData **>(&v) = d;