Re: [PATCH] data prefetch support and __builtin_prefetch (take 2)

[Jan Hubicka <jh at suse dot cz>]

> > > 1) The arm.md already has a "prefetch" expander that takes a different 
> > > number of arguments.  (I can fix this, but it should have been fixed in 
> > > the above check-in).
> > 
> > Sorry, I should have done more searching for possible conflicts.  Let's
> > get the next piece figured out and then you can let me know whether you
> > want me to fix this or do it yourself.
> 
> As much as anything, these problems should have been caught during the 
> review process; particularly as this defines a new generic builtin.  I've 
> been away for the last month, so out of touch.  How thoroughly was the 
> spec for this builtin examined?  It wouldn't be good if we found we needed 

Janis did quite in depth searching for possible alternatives and I believe
his sollution covers all cases, except for somewhat weird Altivec scheme
that can be (should be) covered by specialized builtin.

> a further argument a couple of releases from now.
> 
> With respect to the internal problems, I'll fix them -- I've probably got 
> more facilities for testing the ARM changes than you have ;-)
> 
> > 
> > > 2) ARM targets already have a __builtin_prefetch function that takes one 
> > > argument; as far as I can tell your new implementation will mean an API 
> > > change for users of gcc-3.0
> > 
> > I looked through all of the documentation to see if there was existing
> > prefetch support and all I found was __builtin_ia32_prefetch.  Now I'll
> > know to look through the target-dependent code, too, for undocumented
> > builtin functions.
> > 
> > I suppose it's too much to hope for that since it's not documented, no
> > one knows about it and it's not being used.
> 
> Possibly, I've no idea.  I think it was the Cygnus/Red Hat guys who added 
> this.  Nick, any idea if this feature is widely used by your customers?

They still can use #define if we provide __builtin_arm_prefetch

Honza