Re: aliasing problem with va_arg

[Andi Kleen <ak at muc dot de>]

In article <21508.909509785@hurl.cygnus.com>,
Jeffrey A Law <law@cygnus.com> writes:
> One possibility would be to have the va_arg macro expand in the normal fashion,
> but also emit something similar to __builtin_saveregs -- ie a marker to
> indicate that we're accessing stuff on a varargs list.

> When we see the marker we turn off type based alias analysis, or just generate
> alias set zero for all mems.

> We then have a different marker emitted by va_end which returns us to normal
> behavior.

> That's easier than fixing the varargs stuff to work strictly with builtins. 

> We could even have the builtins be named __builtin_va_arg (ap, type) and
> __builtin_va_end (ap) as a step towards actually implementing them as builtins.

A __norestrict pointer qualifier and an appropiate cast in the va_* macros 
looks a lot cleaner and more general purpose for me - I could imagine that 
it would be very useful to fix other macros where the maintainers don't
have the possibility to change the compiler @)

-Andi