Re: [Patch] Move Objective-C runtime flags to modern options system.

[Iain Sandoe <developer at sandoe-acoustics dot co dot uk>]

Hi Mike,

just want to state my understanding to allow you to comment if I'm  
off....

On 10 Nov 2011, at 16:12, Mike Stump wrote:

> On Nov 10, 2011, at 1:35 AM, Richard Guenther <rguenther@suse.de>  
> wrote:
> > flag_exceptions also triggers middle-end behavior - without it no
> > statement can possibly throw
>
> Actually, one version of exception handling for objective c++  
> doesn't require flag_exceptions...  One can indeed @throw without  
> it, they just can't throw without it.


Thanks for catching that --- brainstorm on my part ... the code under  
discussion should have been #ifndef OBCPLUS

Unfortunately, that particular blunder wasn't caught by the test-suite  
(which passes with the code I posted).

-=-

Specifically:
NeXT m32 (ABI=0 or 1) uses SjLj exceptions for @throw etc. (and the  
@throw is done from a library routine).

Moreover, there is no personality routine in m32 NeXT libobjc, so if  
one tries to engage the zero-cost exceptions, one gets a link error  
(and generates a load of unused eh data).  I can work around that if  
there is still reason to have "-fexceptions" on.

When c++ exceptions are operated in parallel with the ObjC ones - the  
personality routine is pointed at the libstc++ one.

===

m64 NeXT is a different beast altogether and the @throw and throw   
exceptions work together using the same unwinder.

===

With Joseph's suggestion I don't have a problem with the early use of  
flag_next_runtime - which means I can split the patch up - as I know  
Mike would prefer.

... will try an post a new version later.

Iain