QSlotObjectBase: re-enable tail-call optimisation in impl()

Two of the three operations in impl() return void, among them the
most common one, call(). Having impl() return bool prevents tail-
call optimisations for these.

Fix by passing the bool return value for Compare as an out-parameter.

Results in a nice decrease in text size
(GCC 4.8-pre -O2 -std=c++11, stripped):

   text    data     bss     dec     hex filename
 507343   13984      48  521375   7f49f tst_qobject (old)
 505551   13984      48  519583   7ed9f tst_qobject (new)

Reported-by: Thiago Macieira <thiago.macieira@intel.com>

Change-Id: I7538c5b3f0992970c089e44f07244e6b62794a1d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

0 files changed, 0 insertions, 0 deletions