Re: [objc-improvements] Just remembered something about multiple method signatures...

[David Ayers]

Ziemowit Laski wrote:

> On Monday, Sep 8, 2003, at 03:44 US/Pacific, David Ayers wrote:
>
> > Ziemowit Laski wrote:
> >
> > > On Saturday, Sep 6, 2003, at 00:54 US/Pacific, David Ayers wrote:
> So now we need compiler logic to distinguish "conflicting" prototypes 
> from "incompatible" ones.  Are you offering to write it (and explain 
> it to end-users)? :-)

Yes, see my upcomming mail...

> > > >  But the new IMP promotion for id typed receivers will promote them 
> > > > to doubles and clobber not only of the float but all following 
> > > > arguments as well
> > >
> > > I absolutely agree with you in that using the IMP prototype can also 
> > > result in "bad" (i.e., unintended) codegen.
> >
> >
> > The 'IMP' assumption *will* result in "bad" code generation as soon 
> > as either return type or arguments contain floats.  There is 
> > absolutly no ambiguity in that.
>
>
> Don't follow you here.  Why?

In the case of vardic function (...), the callers argument will be 
promoted to different types according to certain promotion rules.  
Arguments of the 'float' type will get promoted to the 'double' type.  
So the implementation must expect a 'double'.  Hardly any (if any at 
all) of the OpenStep methods expect 'doubles'.  What happens in this 
case is that the caller will put the value as a 'double' value on the 
stack, but the method will only retrieve the first half of that value 
and interpret it as a 'float'.  If there are further arguments (like in 
my example the integer) the called method will interpret the second half 
of the 'double' as the 'int' argument and ignore the actual 'int'.

Also the -compare: example is a real example that will break on 
architectures where 'id' is not the same size of small enums.  The IMP 
assumption is unacceptable.

Cheers,
David