Make QDateTime's default constructor not allocate memory on 32-bit

Commit fb498a651990df5e04c75a9076da28e875c43f73 introduced the short
datetime optimization, but it accidentally removed the optimization from
Qt 5.7 that made QDateTime's default constructor not allocate memory.
Instead of bringing back the Q_GLOBAL_STATIC that was used, let's use
the short date time optimization on 32-bit too.

The CanBeSmall constant remains false on 32-bit systems, but judicious
non-use of that constant in a few functions allows 32-bit systems to use
the optimization. We still say that any date/time value is "unsmall", as
there's no sense in calculating whether the date is between 1970-01-01
and July 14 of the same year.

Change-Id: I413d458307aa46469b80fffd145a9db0325c08cc
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/corelib/tools/qdatetime.h b/src/corelib/tools/qdatetime.h
index 7111509bcc..ec0eaa1edf 100644
--- a/src/corelib/tools/qdatetime.h
+++ b/src/corelib/tools/qdatetime.h
@@ -230,6 +230,7 @@ class Q_CORE_EXPORT QDateTime
             CanBeSmall = sizeof(ShortData) * 8 > 50
         };
 
+        Data();
         Data(Qt::TimeSpec);
         Data(const Data &other);
         Data(Data &&other);