swift234

stdlib: Add a _isClassOrObjCExistentialAndSizeofAnyObject function

The function _isClassOrObjCExistentialAndSizeofAnyObject encapsulates the
"sizeof(x) == sizeof(AnyObject)" check and the call to
swift_isClassOrObjCExistential. The sizeof(x) check cannot be eliminated at the
SIL level and creates extra control flow such that the call to
swift_isClassOrObjCExistential does not dominate. Encapsulating both checks
results in one function call that does dominate allowing us to CSE calls when we
add the attributes inline(late) and effects(readnone).

benchmark``````````````,``baserun0``,``optrun2``,``delta,``speedup
ClassArrayGetter```````,``977.00````,``571.00```,``409.00``,````````72.0%
DeltaBlue``````````````,``2594.00```,``2086.00``,``311.00``,````````14.9%
Rectangles`````````````,``921.00````,``605.00```,``314.00``,````````52.0%

rdar://17961249

Swift SVN r21287