alpha regression on 920625-1

[Joern Rennecke]

>    typedef struct{double x,y;}point;
>    point pts[]={{1.0,2.0},{3.0,4.0},{5.0,6.0},{7.0,8.0}};
>    static int va1(int nargs,...)
>    {
>      va_list args;
>      int i;
>      point pi;
>      va_start(args,nargs);
>      for(i=0;i<nargs;i++){
>        pi=va_arg(args,point);
>        if(pts[i].x!=pi.x||pts[i].y!=pi.y)abort();
>      }
>      va_end(args);
>    }
> 
> `pi' is initially allocated to a TImode register, and when comes reload
> time, we find that we must drop the register to memory.  It so happens
> that the copy from varargs is done in DImode, while the comparison must
> of course be done in DFmode.
> 
> The problem arose with jfc's recent mode-dependant aliasing changes.  
> Because the memory block created for the TImode register is not marked
> as a structure, and we have two different modes manipulating the memory,
> the DFmode load gets scheduled before the DImode store.

Everything that gets read via varargs should be treated as part of a
structure; this is already necessary to treat the writing to the varargs
area properly.
You can archive this with a suitable definitions of va_arg.