Re: Bug 20375 - ia64 varadic regression

[Jeffrey A Law <law at redhat dot com>]

On Tue, 2005-03-08 at 09:06 -0800, Mark Mitchell wrote:
> Nathan Sidwell wrote:
> 
> > Notice that the last specified argument 'union U' has no name.  when
> > compiled for ia64-hp-hpux11.23 with -mlp64 this ICEs because of this
> > bit of code in assign_parm_find_data_types
> > 
> >   /* Set LAST_NAMED if this is last named arg before last anonymous 
> > args.  */
> >   if (current_function_stdarg)
> >     {
> >       tree tem;
> >       for (tem = TREE_CHAIN (parm); tem; tem = TREE_CHAIN (tem))
> >     if (DECL_NAME (tem))
> >       break;
> >       if (tem == 0)
> >     data->last_named = true;
> >     }
> > 
> > That triggers on the float argument, not union.  Naming the union
> > makes it trigger on the union, and compilation succeeds.  This is
> > clearly wrong.
> > 
> > The comment doesn't make sense, arguments with and without names can
> > be freely intermixed (in C++), and should not affect the ABI.  As this
> > is to do with varadic parameters, is this really talking about the
> > last typed argument before the varadic ones? 
> 
> Yes, it must be.  As you say, the current code is just plain bogus; the 
> idea that the ABI would change for a C++ function depending on whether 
> or not the argument is named is wrong, as, for example, function 
> pointers would cease to work.  I suspect this is a relic of our old 
> implementation of varargs, and depended on the fact that C functions do 
> not have unnamed arguments.
FWIW, there is actually a system which varies its ABI based on whether
or not an argument is named -- my old favorite, the 32bit PA SOM ABI
behaves in this manner.  In fact, I believe it is the only port which
gives a hoot about this kind of thing.

Is it lame, absolutely.  It was one of the many annoying discoveries
in my decade of PA hacking.

Jeff