QString::toLatin1_helper_inplace: simplify the code

Hot function, so help the compiler out. In particular, this removes any
touch to the ref count, so there are no atomic operations or dead code
leading to memory allocations and deallocations.

Change-Id: I0e5f6bec596a4a78bd3bfffd16c9a0fbd8dd2c12
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

1 files changed, 22 insertions, 0 deletions

diff --git a/src/corelib/tools/qarraydatapointer.h b/src/corelib/tools/qarraydatapointer.h
index 4d83b890cc..dda3cf13eb 100644
--- a/src/corelib/tools/qarraydatapointer.h
+++ b/src/corelib/tools/qarraydatapointer.h
@@ -168,6 +168,28 @@ public:
 
     /*! \internal
 
+        Reinterprets the data of this QArrayDataPointer to type X. It's the
+        caller's responsibility to ensure that the data contents are valid and
+        properly aligned, particularly if T and X are not trivial types (i.e,
+        don't do that). The current size is kept and the allocated capacity is
+        updated to account for the difference in the element type's size.
+
+        This is used in QString::fromLatin1 to perform in-place conversion of
+        QString to QByteArray.
+    */
+    template <typename X> QArrayDataPointer<X> reinterpreted() &&
+    {
+        if (sizeof(T) != sizeof(X)) {
+            Q_ASSERT(!d->isShared());
+            d->alloc = d->alloc * sizeof(T) / sizeof(X);
+        }
+        auto od = reinterpret_cast<QTypedArrayData<X> *>(std::exchange(d, nullptr));
+        auto optr = reinterpret_cast<X *>(std::exchange(ptr, nullptr));
+        return { od, optr, std::exchange(size, 0) };
+    }
+
+    /*! \internal
+
         Detaches this (optionally) and grows to accommodate the free space for
         \a n elements at the required side. The side is determined from \a pos.