Resurrect data moves in QList

Use the data moves to readjust the free space in the QList,
which ultimately fixes the out-of-memory issues caused by
cases like:
forever {
  list.prepend(list.back());
  list.removeLast();
}

Task-number: QTBUG-91801
Task-number: QTBUG-91360
Task-number: QTBUG-93019
Change-Id: Iacff69cbf36b8b5b176bb2663df635ec972c875c
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
(cherry picked from commit a0253f5f0249024580050e4ec22d50cb139ef8d9)

1 files changed, 10 insertions, 11 deletions

diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index 6aafb86c01..ddce07bbb7 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -676,9 +676,10 @@ inline void QList<T>::resize_internal(qsizetype newSize)
     Q_ASSERT(newSize >= 0);
 
     if (d->needsDetach() || newSize > capacity() - d.freeSpaceAtBegin()) {
-        d.reallocateAndGrow(QArrayData::GrowsAtEnd, newSize - d.size);
-    } else if (newSize < size())
+        d.detachAndGrow(QArrayData::GrowsAtEnd, newSize - d.size, nullptr, nullptr);
+    } else if (newSize < size()) {
         d->truncate(newSize);
+    }
 }
 
 template <typename T>
@@ -761,12 +762,7 @@ inline T QList<T>::value(qsizetype i, parameter_type defaultValue) const
 template <typename T>
 inline void QList<T>::append(const_iterator i1, const_iterator i2)
 {
-    if (i1 == i2)
-        return;
-    const auto distance = std::distance(i1, i2);
-    DataPointer oldData;
-    d.detachAndGrow(QArrayData::GrowsAtEnd, distance, &oldData);
-    d->copyAppend(i1, i2);
+    d->growAppend(i1, i2);
 }
 
 template <typename T>
@@ -778,7 +774,9 @@ inline void QList<T>::append(QList<T> &&other)
     if (other.d->needsDetach() || !std::is_nothrow_move_constructible_v<T>)
         return append(other);
 
-    d.detachAndGrow(QArrayData::GrowsAtEnd, other.size());
+    // due to precondition &other != this, we can unconditionally modify 'this'
+    d.detachAndGrow(QArrayData::GrowsAtEnd, other.size(), nullptr, nullptr);
+    Q_ASSERT(d.freeSpaceAtEnd() >= other.size());
     d->moveAppend(other.begin(), other.end());
 }
 
@@ -796,8 +794,9 @@ inline typename QList<T>::iterator
 QList<T>::insert(qsizetype i, qsizetype n, parameter_type t)
 {
     Q_ASSERT_X(size_t(i) <= size_t(d->size), "QList<T>::insert", "index out of range");
-
-    d->insert(i, n, t);
+    Q_ASSERT_X(n >= 0, "QList::insert", "invalid count");
+    if (Q_LIKELY(n))
+        d->insert(i, n, t);
     return d.begin() + i;
 }