Add move constructor to QDateTime

The move constructor is slightly more interesting than the copy
constructor because we can reset other to a short data state on 64-bit
systems. The assembly of that function is simply:

       mov    (%rsi),%rax
       mov    %rax,(%rdi)
       movq   $0x1,(%rsi)
       retq

The move-assignment operator for QDateTime was already there. There's no
need for one for QDateTime::Data since it's never called.

Change-Id: I06bae9392f534e45b3f1ffff144dffdd7f23b170
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

2 files changed, 26 insertions, 2 deletions

diff --git a/src/corelib/tools/qdatetime.cpp b/src/corelib/tools/qdatetime.cpp
index 4c19034bb1..02afacb861 100644
--- a/src/corelib/tools/qdatetime.cpp
+++ b/src/corelib/tools/qdatetime.cpp
@@ -2763,6 +2763,20 @@ inline QDateTime::Data::Data(const Data &other)
     }
 }
 
+inline QDateTime::Data::Data(Data &&other)
+    : d(other.d)
+{
+    // reset the other to a short state, if we can
+    if (CanBeSmall) {
+        Data dummy(Qt::LocalTime);
+        Q_ASSERT(dummy.isShort());
+        other.d = dummy.d;
+    } else if (!isShort()) {
+        // can't be small, so do implicit sharing
+        d->ref.ref();
+    }
+}
+
 inline QDateTime::Data &QDateTime::Data::operator=(const Data &other)
 {
     if (d == other.d)
@@ -3095,13 +3109,22 @@ QDateTime::QDateTime(const QDate &date, const QTime &time, const QTimeZone &time
 /*!
     Constructs a copy of the \a other datetime.
 */
-
 QDateTime::QDateTime(const QDateTime &other) Q_DECL_NOTHROW
     : d(other.d)
 {
 }
 
 /*!
+    \since 5.8
+    Moves the content of the temporary \a other datetime to this object and
+    leaves \a other in an unspecified (but proper) state.
+*/
+QDateTime::QDateTime(QDateTime &&other) Q_DECL_NOTHROW
+    : d(std::move(other.d))
+{
+}
+
+/*!
     Destroys the datetime.
 */
 QDateTime::~QDateTime()
diff --git a/src/corelib/tools/qdatetime.h b/src/corelib/tools/qdatetime.h
index 33dd20953a..0af13dd45f 100644
--- a/src/corelib/tools/qdatetime.h
+++ b/src/corelib/tools/qdatetime.h
@@ -232,8 +232,8 @@ class Q_CORE_EXPORT QDateTime
 
         Data(Qt::TimeSpec);
         Data(const Data &other);
+        Data(Data &&other);
         Data &operator=(const Data &other);
-        // no move semantics (would be the same as copy)
         ~Data();
 
         bool isShort() const;
@@ -256,6 +256,7 @@ public:
     QDateTime(const QDate &date, const QTime &time, const QTimeZone &timeZone);
 #endif // QT_BOOTSTRAPPED
     QDateTime(const QDateTime &other) Q_DECL_NOTHROW;
+    QDateTime(QDateTime &&other) Q_DECL_NOTHROW;
     ~QDateTime();
 
 #ifdef Q_COMPILER_RVALUE_REFS