The fast paths follow the pattern that we established for fast ARC:
Framework base classes can opt in by implementing a `+_TrivialAllocInit`
method.
This opt-in behaviour is inherited and is removed implicitly in any
subclass that implements alloc or init methods (alloc and init are
treated independently).
Compilers can emit calls to `objc_alloc(cls)` instead of `[cls alloc]`,
`objc_allocWithZone(cls)` instead of `[cls allocWithZone: NULL]`, and
`objc_alloc_init` instead of `[[cls alloc] init]`.
Direct methods don't require very much support in the runtime. Apple
reuses their fast path for `-self` (which is supported only in the Apple
fork of clang, not the upstream version) for a fast init. Given that
the first few fields of the runtime's class structure have been stable
for around 30 years, I'm happy moving the flags word (and the
initialised bit, in particular) into the public ABI. This lets us do a
fast-path check for whether a class is initialised in class methods and
call `objc_send_initialize` if it isn't. This function is now exposed
as part of the public ABI, it was there already and does the relevant
checks without invoking any of the message-sending machinery.
Fixes#165#169
David Chisnall
David Chisnall
David Chisnall
David Chisnall
theraven