Introduce the Mutable flag and move QArrayDataPointer::needsDetach

The Mutable flag now contains the information on whether the data this
QArrayData points to is mutable. This decouples the mutability /
immutability setting from the allocation and from the type of data,
opening the way for mutable raw or foreign data.

There are still plenty of places in the source code that check the
size of the allocation when it actually wants d->isMutable(). Fixing
this will require reviewing all the code, so is left for later.

The needsDetach() function is moved to QArrayData and
de-constified. It returns true when a reallocation is necessary if the
data is to be modified.

Change-Id: I17e2bc5a3f6ef1f3eba8a205acd9852b95524f57
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

8 files changed, 48 insertions, 37 deletions

diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp
index d7fcfce90c..da91a93700 100644
--- a/src/corelib/text/qbytearray.cpp
+++ b/src/corelib/text/qbytearray.cpp
@@ -63,7 +63,7 @@
 #include <string.h>
 #include <stdlib.h>
 
-#define IS_RAW_DATA(d) (!(d)->isMutable())
+#define IS_RAW_DATA(d) ((d)->flags & QArrayData::RawDataType)
 
 QT_BEGIN_NAMESPACE
 
@@ -1208,7 +1208,7 @@ QByteArray &QByteArray::operator=(const char *str)
     } else {
         const int len = int(strlen(str));
         const int fullLen = len + 1;
-        if (d->ref.isShared() || fullLen > int(d->allocatedCapacity())
+        if (d->needsDetach() || fullLen > int(d->allocatedCapacity())
                 || (len < d->size && fullLen < int(d->allocatedCapacity() >> 1)))
             reallocData(fullLen, d->detachFlags());
         x = d;
@@ -1755,7 +1755,7 @@ void QByteArray::resize(int size)
     if (size < 0)
         size = 0;
 
-    if (IS_RAW_DATA(d) && !d->ref.isShared() && size < d->size) {
+    if (!d->ref.isShared() && !d->isMutable() && size < d->size) {
         d->size = size;
         return;
     }
@@ -1775,9 +1775,9 @@ void QByteArray::resize(int size)
         x->data()[size] = '\0';
         d = x;
     } else {
-        if (d->ref.isShared() || size > capacity())
+        if (d->needsDetach() || size > capacity())
             reallocData(uint(size) + 1u, d->detachFlags() | Data::GrowsForward);
-        if (d->allocatedCapacity()) {
+        if (d->isMutable()) {
             d->size = size;
             d->data()[size] = '\0';
         }
@@ -1805,7 +1805,7 @@ QByteArray &QByteArray::fill(char ch, int size)
 
 void QByteArray::reallocData(uint alloc, Data::ArrayOptions options)
 {
-    if (d->ref.isShared() || IS_RAW_DATA(d)) {
+    if (d->needsDetach()) {
         Data *x = Data::allocate(alloc, options);
         Q_CHECK_PTR(x);
         x->size = qMin(int(alloc) - 1, d->size);
@@ -1900,7 +1900,7 @@ QByteArray &QByteArray::prepend(const char *str)
 QByteArray &QByteArray::prepend(const char *str, int len)
 {
     if (str) {
-        if (d->ref.isShared() || d->size + len > capacity())
+        if (d->needsDetach() || d->size + len > capacity())
             reallocData(uint(d->size + len) + 1u, d->detachFlags() | Data::GrowsForward);
         memmove(d->data()+len, d->data(), d->size);
         memcpy(d->data(), str, len);
@@ -1926,7 +1926,7 @@ QByteArray &QByteArray::prepend(const char *str, int len)
 
 QByteArray &QByteArray::prepend(char ch)
 {
-    if (d->ref.isShared() || d->size + 1 > capacity())
+    if (d->needsDetach() || d->size + 1 > capacity())
         reallocData(uint(d->size) + 2u, d->detachFlags() | Data::GrowsForward);
     memmove(d->data()+1, d->data(), d->size);
     d->data()[0] = ch;
@@ -1964,7 +1964,7 @@ QByteArray &QByteArray::append(const QByteArray &ba)
     if (d->size == 0 && d->ref.isStatic() && !IS_RAW_DATA(ba.d)) {
         *this = ba;
     } else if (ba.d->size != 0) {
-        if (d->ref.isShared() || d->size + ba.d->size > capacity())
+        if (d->needsDetach() || d->size + ba.d->size > capacity())
             reallocData(uint(d->size + ba.d->size) + 1u, d->detachFlags() | Data::GrowsForward);
         memcpy(d->data() + d->size, ba.d->data(), ba.d->size);
         d->size += ba.d->size;
@@ -1996,7 +1996,7 @@ QByteArray& QByteArray::append(const char *str)
 {
     if (str) {
         const int len = int(strlen(str));
-        if (d->ref.isShared() || d->size + len > capacity())
+        if (d->needsDetach() || d->size + len > capacity())
             reallocData(uint(d->size + len) + 1u, d->detachFlags() | Data::GrowsForward);
         memcpy(d->data() + d->size, str, len + 1); // include null terminator
         d->size += len;
@@ -2021,7 +2021,7 @@ QByteArray &QByteArray::append(const char *str, int len)
     if (len < 0)
         len = qstrlen(str);
     if (str && len) {
-        if (d->ref.isShared() || d->size + len > capacity())
+        if (d->needsDetach() || d->size + len > capacity())
             reallocData(uint(d->size + len) + 1u, d->detachFlags() | Data::GrowsForward);
         memcpy(d->data() + d->size, str, len); // include null terminator
         d->size += len;
@@ -2049,7 +2049,7 @@ QByteArray &QByteArray::append(const char *str, int len)
 
 QByteArray& QByteArray::append(char ch)
 {
-    if (d->ref.isShared() || d->size + 1 > capacity())
+    if (d->needsDetach() || d->size + 1 > capacity())
         reallocData(uint(d->size) + 2u, d->detachFlags() | Data::GrowsForward);
     d->data()[d->size++] = ch;
     d->data()[d->size] = '\0';
diff --git a/src/corelib/text/qbytearray.h b/src/corelib/text/qbytearray.h
index 611cacc646..597bc8bcb3 100644
--- a/src/corelib/text/qbytearray.h
+++ b/src/corelib/text/qbytearray.h
@@ -495,7 +495,7 @@ inline const char *QByteArray::data() const
 inline const char *QByteArray::constData() const
 { return d->data(); }
 inline void QByteArray::detach()
-{ if (d->ref.isShared() || !d->isMutable()) reallocData(uint(d->size) + 1u, d->detachFlags()); }
+{ if (d->needsDetach()) reallocData(uint(d->size) + 1u, d->detachFlags()); }
 inline bool QByteArray::isDetached() const
 { return !d->ref.isShared(); }
 inline QByteArray::QByteArray(const QByteArray &a) noexcept : d(a.d)
@@ -506,7 +506,7 @@ inline int QByteArray::capacity() const
 
 inline void QByteArray::reserve(int asize)
 {
-    if (d->ref.isShared() || asize > capacity()) {
+    if (d->needsDetach() || asize > capacity()) {
         reallocData(qMax(uint(size()), uint(asize)) + 1u, d->detachFlags() | Data::CapacityReserved);
     } else {
         d->flags |= Data::CapacityReserved;
@@ -515,7 +515,9 @@ inline void QByteArray::reserve(int asize)
 
 inline void QByteArray::squeeze()
 {
-    if (d->ref.isShared() || d->size < capacity()) {
+    if ((d->flags & Data::CapacityReserved) == 0)
+        return;
+    if (d->needsDetach() || d->size < capacity()) {
         reallocData(uint(d->size) + 1u, d->detachFlags() & ~Data::CapacityReserved);
     } else {
         d->flags &= ~Data::CapacityReserved;
diff --git a/src/corelib/text/qstring.cpp b/src/corelib/text/qstring.cpp
index d0f141e079..ab08d497bd 100644
--- a/src/corelib/text/qstring.cpp
+++ b/src/corelib/text/qstring.cpp
@@ -100,7 +100,7 @@
 #define ULLONG_MAX quint64_C(18446744073709551615)
 #endif
 
-#define IS_RAW_DATA(d) (!(d)->isMutable())
+#define IS_RAW_DATA(d) ((d)->flags & QArrayData::RawDataType)
 
 QT_BEGIN_NAMESPACE
 
@@ -2265,14 +2265,14 @@ void QString::resize(int size)
     if (size < 0)
         size = 0;
 
-    if (IS_RAW_DATA(d) && !d->ref.isShared() && size < d->size) {
+    if (!d->ref.isShared() && !d->isMutable() && size < d->size) {
         d->size = size;
         return;
     }
 
-    if (d->ref.isShared() || uint(size) + 1u > d->allocatedCapacity())
+    if (d->needsDetach() || size > capacity())
         reallocData(uint(size) + 1u, true);
-    if (d->flags & Data::AllocatedDataType) {
+    if (d->isMutable()) {
         d->size = size;
         d->data()[size] = '\0';
     }
@@ -2353,7 +2353,7 @@ void QString::reallocData(uint alloc, bool grow)
     if (grow)
         allocOptions |= QArrayData::GrowsForward;
 
-    if (d->ref.isShared() || IS_RAW_DATA(d)) {
+    if (d->needsDetach()) {
         Data *x = Data::allocate(alloc, allocOptions);
         Q_CHECK_PTR(x);
         x->size = qMin(int(alloc) - 1, d->size);
@@ -2658,7 +2658,7 @@ QString &QString::append(const QString &str)
         if (d == Data::sharedNull()) {
             operator=(str);
         } else {
-            if (d->ref.isShared() || d->size + str.d->size > capacity())
+            if (d->needsDetach() || d->size + str.d->size > capacity())
                 reallocData(uint(d->size + str.d->size) + 1u, true);
             memcpy(d->data() + d->size, str.d->data(), str.d->size * sizeof(QChar));
             d->size += str.d->size;
@@ -2696,7 +2696,7 @@ QString &QString::append(QLatin1String str)
     const char *s = str.latin1();
     if (s) {
         int len = str.size();
-        if (d->ref.isShared() || d->size + len > capacity())
+        if (d->needsDetach() || d->size + len > capacity())
             reallocData(uint(d->size + len) + 1u, true);
         ushort *i = d->data() + d->size;
         qt_from_latin1(i, s, uint(len));
@@ -2743,7 +2743,7 @@ QString &QString::append(QLatin1String str)
 */
 QString &QString::append(QChar ch)
 {
-    if (d->ref.isShared() || d->size + 1 > capacity())
+    if (d->needsDetach() || d->size + 1 > capacity())
         reallocData(uint(d->size) + 2u, true);
     d->data()[d->size++] = ch.unicode();
     d->data()[d->size] = '\0';
@@ -6457,7 +6457,7 @@ int QString::localeAwareCompare_helper(const QChar *data1, int length1,
 
 const ushort *QString::utf16() const
 {
-    if (IS_RAW_DATA(d)) {
+    if (!d->isMutable()) {
         // ensure '\0'-termination for ::fromRawData strings
         const_cast<QString*>(this)->reallocData(uint(d->size) + 1u);
     }
diff --git a/src/corelib/text/qstring.h b/src/corelib/text/qstring.h
index 03d83eeab9..fd674284fe 100644
--- a/src/corelib/text/qstring.h
+++ b/src/corelib/text/qstring.h
@@ -542,7 +542,7 @@ public:
     inline QString &prepend(QLatin1String s) { return insert(0, s); }
 
     inline QString &operator+=(QChar c) {
-        if (d->ref.isShared() || d->size + 1 > capacity())
+        if (d->needsDetach() || d->size + 1 > capacity())
             reallocData(uint(d->size) + 2u, true);
         d->data()[d->size++] = c.unicode();
         d->data()[d->size] = '\0';
@@ -1041,7 +1041,7 @@ inline QChar *QString::data()
 inline const QChar *QString::constData() const
 { return reinterpret_cast<const QChar*>(d->data()); }
 inline void QString::detach()
-{ if (d->ref.isShared() || !d->isMutable()) reallocData(uint(d->size) + 1u); }
+{ if (d->needsDetach()) reallocData(uint(d->size) + 1u); }
 inline bool QString::isDetached() const
 { return !d->ref.isShared(); }
 inline void QString::clear()
@@ -1263,7 +1263,7 @@ inline QString::~QString() { if (!d->ref.deref()) Data::deallocate(d); }
 
 inline void QString::reserve(int asize)
 {
-    if (d->ref.isShared() || asize >= capacity())
+    if (d->needsDetach() || asize >= capacity())
         reallocData(qMax(asize, size()) + 1u);
 
     // we're not shared anymore, for sure
@@ -1272,7 +1272,9 @@ inline void QString::reserve(int asize)
 
 inline void QString::squeeze()
 {
-    if (d->ref.isShared() || d->size < capacity())
+    if ((d->flags & Data::CapacityReserved) == 0)
+        return;
+    if (d->needsDetach() || d->size < capacity())
         reallocData(uint(d->size) + 1u);
 
     // we're not shared anymore, for sure
diff --git a/src/corelib/tools/qarraydata.cpp b/src/corelib/tools/qarraydata.cpp
index bc48619349..3123d7467f 100644
--- a/src/corelib/tools/qarraydata.cpp
+++ b/src/corelib/tools/qarraydata.cpp
@@ -222,7 +222,7 @@ QArrayData *QArrayData::allocate(size_t objectSize, size_t alignment,
         return nullptr;
 
     size_t allocSize = calculateBlockSize(capacity, objectSize, headerSize, options);
-    options |= ArrayOption(AllocatedDataType);
+    options |= AllocatedDataType | Mutable;
     QArrayData *header = allocateData(allocSize, options);
     if (header) {
         quintptr data = (quintptr(header) + sizeof(QArrayData) + alignment - 1)
@@ -252,6 +252,7 @@ QArrayData *QArrayData::reallocateUnaligned(QArrayData *data, size_t objectSize,
     options |= ArrayOption(AllocatedDataType);
     size_t headerSize = sizeof(QArrayData);
     size_t allocSize = calculateBlockSize(capacity, objectSize, headerSize, options);
+    options |= AllocatedDataType | Mutable;
     QArrayData *header = reallocateData(data, allocSize, options);
     if (header)
         header->alloc = capacity;
diff --git a/src/corelib/tools/qarraydata.h b/src/corelib/tools/qarraydata.h
index babccc6017..8c21fd55c8 100644
--- a/src/corelib/tools/qarraydata.h
+++ b/src/corelib/tools/qarraydata.h
@@ -56,6 +56,7 @@ struct Q_CORE_EXPORT QArrayData
         CapacityReserved     = 0x0010,  //!< the capacity was reserved by the user, try to keep it
         GrowsForward         = 0x0020,  //!< allocate with eyes towards growing through append()
         GrowsBackwards       = 0x0040,  //!< allocate with eyes towards growing through prepend()
+        Mutable              = 0x0080,  //!< the data can be changed; doesn't say anything about the header
 
         /// this option is used by the Q_ARRAY_LITERAL and similar macros
         StaticDataFlags = RawDataType,
@@ -102,7 +103,16 @@ struct Q_CORE_EXPORT QArrayData
     // follow COW principles.
     bool isMutable() const
     {
-        return flags & AllocatedDataType;
+        return flags & Mutable;
+    }
+
+    // Returns true if a detach is necessary before modifying the data
+    // This method is intentionally not const: if you want to know whether
+    // detaching is necessary, you should be in a non-const function already
+    bool needsDetach()
+    {
+        // ### optimize me -- this currently requires 3 conditionals!
+        return !isMutable() || ref.isShared();
     }
 
     size_t detachCapacity(size_t newSize) const
diff --git a/src/corelib/tools/qarraydatapointer.h b/src/corelib/tools/qarraydatapointer.h
index ffeaff5862..b7236d485a 100644
--- a/src/corelib/tools/qarraydatapointer.h
+++ b/src/corelib/tools/qarraydatapointer.h
@@ -126,11 +126,6 @@ public:
         return d;
     }
 
-    bool needsDetach() const
-    {
-        return (!d->isMutable() || d->ref.isShared());
-    }
-
     void swap(QArrayDataPointer &other) noexcept
     {
         qSwap(d, other.d);
@@ -144,7 +139,7 @@ public:
 
     bool detach()
     {
-        if (needsDetach()) {
+        if (d->needsDetach()) {
             Data *copy = clone(d->detachFlags());
             QArrayDataPointer old(d);
             d = copy;
diff --git a/src/corelib/tools/qvector.h b/src/corelib/tools/qvector.h
index 9ef2ace471..a596beedcf 100644
--- a/src/corelib/tools/qvector.h
+++ b/src/corelib/tools/qvector.h
@@ -390,10 +390,11 @@ inline QVector<T>::QVector(const QVector<T> &v)
 template <typename T>
 void QVector<T>::detach()
 {
+    // ### check whether this is still required
     if (d->ref.isStatic())
         return;
 
-    if (!isDetached())
+    if (d->needsDetach())
         realloc(d->allocatedCapacity(), d->detachFlags());
     Q_ASSERT(isDetached());
 }