Re: objc_msgSendSuper implementation?

[Luboš Doležel]

On Tue, 9 Oct 2012 10:34:02 +0100, David Chisnall wrote:
> On 9 Oct 2012, at 10:29, Luboš Doležel wrote:
>
> > And what exactly is the fast path? objc_msg_lookup_super()?
>
> The fast path is the cached lookup, which involves no calls into the
> runtime at all and just checks that the cached lookup is valid before
> calling it.

Could you point me to how to do that in my code? Or at least tell me 
how to make Clang emit such code, since

clang objc_super.m -o objc_super -l:libobjc.so.4 -lgnustep-base

uses objc_msg_lookup_super(). With -fobjc-abi-version=2, it emits a 
objc_slot_lookup_super() call.

> > Because I wrote my own objc_msgSendSuper()/objc_msgSendSuper2() in 
> > assembly that passes the arguments on to objc_msg_lookup_super and 
> > then jumps to the return value of that.
>
> For what platform?  This is indeed possible, but it's going to be
> slower than the existing mechanism because it won't play as well with
> the CPU's branch predictor...

x86/x86-64 only, in other words the platforms for which OS X apps exist 
(not including iOS).

--
Luboš Doležel