We know that 'this' is a QObject* since the metatypes stack frame
mandates it. Whenever you pass 'this' to anything it's loaded from the
special 'This' stack slot which then triggers a DTZ check. A DTZ check
is a noop if we can prove that the type is statically known, though.
In QmlCompiler, if we have a valid register content, then the register
has been set in all code paths that lead to the instruction in question.
Fixes: QTBUG-111439
Change-Id: I81d1cd140eea63f85628c3bef3a8f6db0a12096d
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>