[Libclc-dev] [PATCH] configure: Allow targets to override generic cl implementations with LLVM IR

[Peter Collingbourne]

On Tue, Oct 09, 2012 at 03:14:35PM -0400, Tom Stellard wrote:
> On Mon, Oct 08, 2012 at 04:31:19AM +0100, Peter Collingbourne wrote:
> > On Tue, Oct 02, 2012 at 09:01:43PM +0000, Tom Stellard wrote:
> > > From: Tom Stellard <thomas.stellard at amd.com>
> > > 
> > > ---
> > >  configure.py | 8 ++++++--
> > >  1 file changed, 6 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/configure.py b/configure.py
> > > index 66c6410..0449a0e 100755
> > > --- a/configure.py
> > > +++ b/configure.py
> > > @@ -112,8 +112,12 @@ for target in targets:
> > >      manifest_deps.add(subdir_list_file)
> > >      for src in open(subdir_list_file).readlines():
> > >        src = src.rstrip()
> > > -      if src not in sources_seen:
> > > -        sources_seen.add(src)
> > > +      # Only add the base filename (e.g. Add get_global_id instead of
> > > +      # get_global_id.cl) to sources_seen.
> > > +      # This allows targets to overide generic .cl sources with .ll sources.
> > > +      src_base = os.path.splitext(src)[0]
> > > +      if src_base not in sources_seen:
> > > +        sources_seen.add(src_base)
> > >          obj = os.path.join(target, 'lib', src + '.bc')
> > >          objects.append(obj)
> > >          src_file = os.path.join(libdir, src)
> > 
> > Hi Tom,
> > 
> > I am happy with the idea of allowing targets to override .cl's with
> > .ll's (or vice versa).
> > 
> > However, I don't think this would correctly handle the file
> > layout we currently have for add_sat (and sub_sat), which is
> > currently implemented using three files: add_sat.cl, add_sat.ll
> > and add_sat_impl.ll.  (I don't like the fact that this family of
> > functions has to be implemented using three files, but it turns out
> > to be necessary for PTX, which only supports two non-default calling
> > conventions).
> >
> 
> I took a look at the add_sat implementation, and I'm not quite sure how
> the code is using an alternate calling convention.  Would mind
> explaining a little more what is happening here?

Currently all OpenCL C functions when compiled to NVPTX use the
ptx_device calling convention for function calls.  This means that
we cannot simply write the add_sat functions in IR in a generic way,
as the caller will expect the callee to use ptx_device on PTX and
the default calling convention on all other architectures.  To solve
this, the functions are implemented in the default calling convention
in add_sat_impl.ll and add_sat.ll acts as a shim between the default
and the OpenCL C calling convention by calling the respective functions
in add_sat_impl.ll.

I'd love for there to be a better way to handle this.  Perhaps if you are
at the LLVM developers meeting tomorrow we can discuss it then.

> Would it be possible to move some of this code into the NVPTX
> implementation?

Unfortunately this scheme could not be implemented without either
touching the generic part of the code or duplicating code for every
architecture.

Thanks,
-- 
Peter