Optimize QSharedPointer::getAndRef with the three-operand testAndSet

Originally QAtomicPointer didn't have the three-operand version,
resulting in code like:
  if (!atomic.testAndSetXxx(expected, newvalue))
       expected = atomic.load();

The three-operand version gives us the current value of the atomic in
case the test failed and it's free in all architectures, unlike the
extra load.

I have to use testAndSetOrdered here because I need the failing load to
use the Acquire memory order, even though that has an extra Acquire for
the successful case we don't need. QAtomicPointer does not have
testAndSetReleaseAcquire.

Change-Id: I1bd327aeaf73421a8ec5fffd1560fe30d3bfd9b8
Reviewed-by: Romain Pokrzywka <romain.pokrzywka@gmail.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@qt.io>

0 files changed, 0 insertions, 0 deletions