Re: [Patch] 1/3 Add new builtin __builtin_flush_icache().

[David Daney <ddaney at avtrex dot com>]

Mark Mitchell wrote:
> Paolo Bonzini wrote:
>   
> > > 1) Rename the new builtin to __builtin_clear_cache (char *beg ,  char
> > > *end), and have it call the function in libgcc if there is not an
> > > inline expansion for it?
> > >       
> > (And use libgcc's prototype).  This would be the cleanest.
> >
> > This, plus, try to see how __clear_cache could use the definition of the
> > builtin.
> >     
>
> Paolo, I didn't quite follow your suggestion.  So, I'm not sure if I'm
> agreeing or disagreeing. :-)
>
> Anyhow, here's my suggestion.
>
> 1. The builtin should be:
>
>   __builtin___clear_cache (char *beg, char *end)
>
> following the standard convention that the builtin for X is __builtin_X.
>
> 2. The default implementation of the builtin should be to call
> __clear_cache.  That means that users can call __builtin_clear_cache
> from their code, on all platforms.
>
>   
I agree and had arrived at the same conclusion for your first two points.
> 3. Targets which can do something clever can implement the builtin as
> they please and can define CLEAR_INSN_CACHE(BEG, END) to expand to
> __builtin_clear_cache(BEG, END).  On such targets, then, __clear_cache
> in libgcc will call the builtin, which we can be assured will not
> recursively expand to __clear_cache.
>
>
>   
My current idea for this can, I think,,be best expressed by looking at 
the proposed code for libgcc:

void
__clear_cache (char *beg, char *end)
{
 if (__builtin_clear_cache_inline_p())
   __builtin___clear_cache (beg, end);
 else
   {
#ifdef CLEAR_INSN_CACHE
     CLEAR_INSN_CACHE (beg, end);
#endif /* CLEAR_INSN_CACHE */
   }
}

No changes to any existing  CLEAR_INSN_CACHE definitions are needed.  
There is a new target hook that determines the value of 
__builtin_clear_cache_inline_p().  I chose to do it this way because I 
think it would be impossible to reliably determine if the 
__builtin___clear_cache would expand in-line without such a predicate.

A revised patch is in the works.

Thanks,
David Daney