Get rid of QArrayData::sharedNull()

Remove the last places where those got used and avoid
allocations when we resize to 0.

Change-Id: Ib553f4e7ce7cc24c31da15a55a86d18bdf1cc5c3
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

8 files changed, 22 insertions, 123 deletions

diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp
index 350fa3be25..e0f720bc86 100644
--- a/src/corelib/text/qbytearray.cpp
+++ b/src/corelib/text/qbytearray.cpp
@@ -1732,7 +1732,7 @@ QByteArray QByteArray::nulTerminated() const
 
 QByteArray &QByteArray::prepend(const QByteArray &ba)
 {
-    if (size() == 0 && d->isStatic() && ba.d.isMutable()) {
+    if (size() == 0 && ba.d.isMutable()) {
         *this = ba;
     } else if (ba.size() != 0) {
         QByteArray tmp = *this;
@@ -1825,7 +1825,7 @@ QByteArray &QByteArray::prepend(char ch)
 
 QByteArray &QByteArray::append(const QByteArray &ba)
 {
-    if (size() == 0 && d->isStatic() && ba.d.isMutable()) {
+    if (size() == 0 && ba.d.isMutable()) {
         *this = ba;
     } else if (ba.size() != 0) {
         if (d->needsDetach() || size() + ba.size() > capacity())
diff --git a/src/corelib/tools/qarraydata.cpp b/src/corelib/tools/qarraydata.cpp
index 42599bbf2a..1a369a879a 100644
--- a/src/corelib/tools/qarraydata.cpp
+++ b/src/corelib/tools/qarraydata.cpp
@@ -147,25 +147,7 @@ qCalculateGrowingBlockSize(size_t elementCount, size_t elementSize, size_t heade
     return result;
 }
 
-// End of qtools_p.h implementation
-
-QT_WARNING_PUSH
-QT_WARNING_DISABLE_GCC("-Wmissing-field-initializers")
-
-const QArrayData QArrayData::shared_null[2] = {
-    { Q_BASIC_ATOMIC_INITIALIZER(-1), 0, 0 }, // shared null
-    /* zero initialized terminator */};
-
-static const QArrayData emptyNotNullShared[2] = {
-    { Q_BASIC_ATOMIC_INITIALIZER(-1), 0, 0 }, // shared empty
-    /* zero initialized terminator */};
-
-QT_WARNING_POP
-
-static const QArrayData &qt_array_empty = emptyNotNullShared[0];
-
-static inline size_t calculateBlockSize(size_t &capacity, size_t objectSize, size_t headerSize,
-                                        uint options)
+static inline size_t calculateBlockSize(size_t &capacity, size_t objectSize, size_t headerSize, uint options)
 {
     // Calculate the byte size
     // allocSize = objectSize * capacity + headerSize, but checked for overflow
@@ -199,9 +181,8 @@ void *QArrayData::allocate(QArrayData **dptr, size_t objectSize, size_t alignmen
             && !(alignment & (alignment - 1)));
 
     if (capacity == 0) {
-        // optimization for empty headers
-        *dptr = const_cast<QArrayData *>(&qt_array_empty);
-        return sharedNullData();
+        *dptr = nullptr;
+        return nullptr;
     }
 
     size_t headerSize = sizeof(QArrayData);
diff --git a/src/corelib/tools/qarraydata.h b/src/corelib/tools/qarraydata.h
index b3b559e222..fe8827afb8 100644
--- a/src/corelib/tools/qarraydata.h
+++ b/src/corelib/tools/qarraydata.h
@@ -77,24 +77,16 @@ struct Q_CORE_EXPORT QArrayData
     /// Returns true if sharing took place
     bool ref()
     {
-        if (!isStatic())
-            ref_.ref();
+        ref_.ref();
         return true;
     }
 
     /// Returns false if deallocation is necessary
     bool deref()
     {
-        if (isStatic())
-            return true;
         return ref_.deref();
     }
 
-    bool isStatic() const
-    {
-        return ref_.loadRelaxed() == -1;
-    }
-
     bool isShared() const
     {
         return ref_.loadRelaxed() != 1;
@@ -133,14 +125,6 @@ struct Q_CORE_EXPORT QArrayData
             size_t objectSize, size_t newCapacity, ArrayOptions newOptions = DefaultAllocationFlags) Q_DECL_NOTHROW;
     static void deallocate(QArrayData *data, size_t objectSize,
             size_t alignment) noexcept;
-
-    static const QArrayData shared_null[2];
-    static QArrayData *sharedNull() noexcept { return const_cast<QArrayData*>(shared_null); }
-    static void *sharedNullData()
-    {
-        QArrayData *const null = const_cast<QArrayData *>(&shared_null[1]);
-        return null;
-    }
 };
 
 Q_DECLARE_OPERATORS_FOR_FLAGS(QArrayData::ArrayOptions)
diff --git a/src/corelib/tools/qarraydatapointer.h b/src/corelib/tools/qarraydatapointer.h
index 8e30373211..1f9a9d840c 100644
--- a/src/corelib/tools/qarraydatapointer.h
+++ b/src/corelib/tools/qarraydatapointer.h
@@ -78,7 +78,6 @@ public:
     explicit QArrayDataPointer(QPair<QTypedArrayData<T> *, T *> adata, size_t n = 0)
         : d(adata.first), ptr(adata.second), size(int(n))
     {
-        Q_CHECK_PTR(d);
     }
 
     static QArrayDataPointer fromRawData(const T *rawData, size_t length)
@@ -183,7 +182,6 @@ public:
     void ref() noexcept { if (d) d->ref(); }
     bool deref() noexcept { return !d || d->deref(); }
     bool isMutable() const noexcept { return d; }
-    bool isStatic() const noexcept { return !d; }
     bool isShared() const noexcept { return !d || d->isShared(); }
     bool isSharedWith(const QArrayDataPointer &other) const noexcept { return d && d == other.d; }
     bool needsDetach() const noexcept { return !d || d->needsDetach(); }
@@ -199,7 +197,6 @@ private:
     Q_REQUIRED_RESULT QPair<Data *, T *> clone(QArrayData::ArrayOptions options) const
     {
         QPair<Data *, T *> pair = Data::allocate(detachCapacity(size), options);
-        Q_CHECK_PTR(pair.first);
         QArrayDataPointer copy(pair.first, pair.second, 0);
         if (size)
             copy->copyAppend(begin(), end());
diff --git a/tests/auto/corelib/text/qbytearray/tst_qbytearray.cpp b/tests/auto/corelib/text/qbytearray/tst_qbytearray.cpp
index e566cc21a2..80ad8e0515 100644
--- a/tests/auto/corelib/text/qbytearray/tst_qbytearray.cpp
+++ b/tests/auto/corelib/text/qbytearray/tst_qbytearray.cpp
@@ -167,8 +167,8 @@ QByteArray verifyZeroTermination(const QByteArray &ba)
 
     QByteArray::DataPointer baDataPtr = const_cast<QByteArray &>(ba).data_ptr();
 
-    // Skip if isStatic() as those offer no guarantees
-    if (baDataPtr->isStatic())
+    // Skip if !isMutable() as those offer no guarantees
+    if (!baDataPtr->isMutable())
         return ba;
 
     int baSize = ba.size();
diff --git a/tests/auto/corelib/text/qstring/tst_qstring.cpp b/tests/auto/corelib/text/qstring/tst_qstring.cpp
index 4d2e91a694..850def64ab 100644
--- a/tests/auto/corelib/text/qstring/tst_qstring.cpp
+++ b/tests/auto/corelib/text/qstring/tst_qstring.cpp
@@ -618,7 +618,7 @@ QString verifyZeroTermination(const QString &str)
     QString::DataPointer strDataPtr = const_cast<QString &>(str).data_ptr();
 
     // Skip if isStatic() or fromRawData(), as those offer no guarantees
-    if (strDataPtr->isStatic() || !strDataPtr->isMutable())
+    if (!strDataPtr->isMutable())
         return str;
 
     int strSize = str.size();
diff --git a/tests/auto/corelib/tools/qarraydata/simplevector.h b/tests/auto/corelib/tools/qarraydata/simplevector.h
index 8109c463a3..6be785a628 100644
--- a/tests/auto/corelib/tools/qarraydata/simplevector.h
+++ b/tests/auto/corelib/tools/qarraydata/simplevector.h
@@ -85,7 +85,7 @@ public:
     bool isNull() const { return d.isNull(); }
     bool isEmpty() const { return this->empty(); }
 
-    bool isStatic() const { return d->isStatic(); }
+    bool isStatic() const { return !d.isMutable(); }
     bool isShared() const { return d->isShared(); }
     bool isSharedWith(const SimpleVector &other) const { return d == other.d; }
 
diff --git a/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp b/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp
index 5c7484a49a..9ebcda4cef 100644
--- a/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp
+++ b/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp
@@ -33,29 +33,12 @@
 
 #include "simplevector.h"
 
-struct SharedNullVerifier
-{
-    SharedNullVerifier()
-    {
-        Q_ASSERT(QArrayData::shared_null[0].isStatic());
-        Q_ASSERT(QArrayData::shared_null[0].isShared());
-    }
-};
-
-// This is meant to verify/ensure that shared_null is not being dynamically
-// initialized and stays away from the order-of-static-initialization fiasco.
-//
-// Of course, if this was to fail, qmake and the build should have crashed and
-// burned before we ever got to this point :-)
-SharedNullVerifier globalInit;
-
 class tst_QArrayData : public QObject
 {
     Q_OBJECT
 
 private slots:
     void referenceCounting();
-    void sharedNullEmpty();
     void simpleVector();
     void simpleVectorReserve_data();
     void simpleVectorReserve();
@@ -87,8 +70,6 @@ void tst_QArrayData::referenceCounting()
 
         QCOMPARE(array.ref_.loadRelaxed(), 1);
 
-        QVERIFY(!array.isStatic());
-
         QVERIFY(array.ref());
         QCOMPARE(array.ref_.loadRelaxed(), 2);
 
@@ -108,37 +89,6 @@ void tst_QArrayData::referenceCounting()
     }
 }
 
-void tst_QArrayData::sharedNullEmpty()
-{
-    QArrayData *null = const_cast<QArrayData *>(QArrayData::shared_null);
-    QArrayData *empty;
-    QArrayData::allocate(&empty, 1, alignof(QArrayData), 0);
-
-    QVERIFY(null->isStatic());
-    QVERIFY(null->isShared());
-
-    QVERIFY(empty->isStatic());
-    QVERIFY(empty->isShared());
-
-    QCOMPARE(null->ref_.loadRelaxed(), -1);
-    QCOMPARE(empty->ref_.loadRelaxed(), -1);
-
-    QCOMPARE(null->ref_.loadRelaxed(), -1);
-    QCOMPARE(empty->ref_.loadRelaxed(), -1);
-
-    QVERIFY(null->deref());
-    QVERIFY(empty->deref());
-
-    QCOMPARE(null->ref_.loadRelaxed(), -1);
-    QCOMPARE(empty->ref_.loadRelaxed(), -1);
-
-    QVERIFY(null != empty);
-
-    QCOMPARE(null->allocatedCapacity(), size_t(0));
-
-    QCOMPARE(empty->allocatedCapacity(), size_t(0));
-}
-
 void tst_QArrayData::simpleVector()
 {
     int data[] = { 0, 1, 2, 3, 4, 5, 6 };
@@ -479,7 +429,6 @@ void tst_QArrayData::allocate_data()
     QTest::addColumn<size_t>("alignment");
     QTest::addColumn<QArrayData::ArrayOptions>("allocateOptions");
     QTest::addColumn<bool>("isCapacityReserved");
-    QTest::addColumn<const QArrayData *>("commonEmpty");
 
     struct {
         char const *typeName;
@@ -491,19 +440,14 @@ void tst_QArrayData::allocate_data()
         { "void *", sizeof(void *), alignof(void *) }
     };
 
-    QArrayData *shared_empty;
-    (void)QArrayData::allocate(&shared_empty, 1, alignof(QArrayData), 0);
-    QVERIFY(shared_empty);
-
     struct {
         char const *description;
         QArrayData::ArrayOptions allocateOptions;
         bool isCapacityReserved;
-        const QArrayData *commonEmpty;
     } options[] = {
-        { "Default", QArrayData::DefaultAllocationFlags, false, shared_empty },
-        { "Reserved", QArrayData::CapacityReserved, true, shared_empty },
-        { "Grow", QArrayData::GrowsForward, false, shared_empty }
+        { "Default", QArrayData::DefaultAllocationFlags, false },
+        { "Reserved", QArrayData::CapacityReserved, true },
+        { "Grow", QArrayData::GrowsForward, false }
     };
 
     for (size_t i = 0; i < sizeof(types)/sizeof(types[0]); ++i)
@@ -513,8 +457,7 @@ void tst_QArrayData::allocate_data()
                         + QLatin1String(": ")
                         + QLatin1String(options[j].description)))
                 << types[i].objectSize << types[i].alignment
-                << options[j].allocateOptions << options[j].isCapacityReserved
-                << options[j].commonEmpty;
+                << options[j].allocateOptions << options[j].isCapacityReserved;
 }
 
 void tst_QArrayData::allocate()
@@ -523,21 +466,15 @@ void tst_QArrayData::allocate()
     QFETCH(size_t, alignment);
     QFETCH(QArrayData::ArrayOptions, allocateOptions);
     QFETCH(bool, isCapacityReserved);
-    QFETCH(const QArrayData *, commonEmpty);
 
     // Minimum alignment that can be requested is that of QArrayData.
     // Typically, this alignment is sizeof(void *) and ensured by malloc.
     size_t minAlignment = qMax(alignment, alignof(QArrayData));
 
-    // Shared Empty
-    QArrayData *empty;
-    QCOMPARE((QArrayData::allocate(&empty, objectSize, minAlignment, 0,
-                QArrayData::ArrayOptions(allocateOptions)), empty), commonEmpty);
-
     Deallocator keeper(objectSize, minAlignment);
     keeper.headers.reserve(1024);
 
-    for (int capacity = 1; capacity <= 1024; capacity <<= 1) {
+    for (qsizetype capacity = 1; capacity <= 1024; capacity <<= 1) {
         QArrayData *data;
         void *dataPointer = QArrayData::allocate(&data, objectSize, minAlignment,
                 capacity, QArrayData::ArrayOptions(allocateOptions));
@@ -545,9 +482,9 @@ void tst_QArrayData::allocate()
         keeper.headers.append(data);
 
         if (allocateOptions & QArrayData::GrowsForward)
-            QVERIFY(data->allocatedCapacity() > uint(capacity));
+            QVERIFY(data->allocatedCapacity() > capacity);
         else
-            QCOMPARE(data->allocatedCapacity(), size_t(capacity));
+            QCOMPARE(data->allocatedCapacity(), capacity);
         QCOMPARE(bool(data->flags & QArrayData::CapacityReserved), isCapacityReserved);
 
         // Check that the allocated array can be used. Best tested with a
@@ -587,9 +524,9 @@ void tst_QArrayData::reallocate()
     keeper.headers.append(data);
 
     if (allocateOptions & QArrayData::GrowsForward)
-        QVERIFY(data->allocatedCapacity() > size_t(newCapacity));
+        QVERIFY(data->allocatedCapacity() > newCapacity);
     else
-        QCOMPARE(data->allocatedCapacity(), size_t(newCapacity));
+        QCOMPARE(data->allocatedCapacity(), newCapacity);
     QCOMPARE(!(data->flags & QArrayData::CapacityReserved), !isCapacityReserved);
 
     for (int i = 0; i < capacity; ++i)
@@ -658,7 +595,7 @@ void tst_QArrayData::typedData()
         keeper.headers.append(array);
 
         QVERIFY(array);
-        QCOMPARE(array->allocatedCapacity(), size_t(10));
+        QCOMPARE(array->allocatedCapacity(), qsizetype(10));
 
         // Check that the allocated array can be used. Best tested with a
         // memory checker, such as valgrind, running.
@@ -678,7 +615,7 @@ void tst_QArrayData::typedData()
         keeper.headers.append(array);
 
         QVERIFY(array);
-        QCOMPARE(array->allocatedCapacity(), size_t(10));
+        QCOMPARE(array->allocatedCapacity(), qsizetype(10));
 
         // Check that the allocated array can be used. Best tested with a
         // memory checker, such as valgrind, running.
@@ -698,7 +635,7 @@ void tst_QArrayData::typedData()
         keeper.headers.append(array);
 
         QVERIFY(array);
-        QCOMPARE(array->allocatedCapacity(), size_t(10));
+        QCOMPARE(array->allocatedCapacity(), qsizetype(10));
 
         // Check that the allocated array can be used. Best tested with a
         // memory checker, such as valgrind, running.