[Libclc-dev] [PATCH 2/3] amdgcn-amdhsa: Add get_num_groups implementation

[Jan Vesely via Libclc-dev]

On Wed, 2016-09-14 at 10:58 -0400, Matt Arsenault via Libclc-dev wrote:
> > 
> > On Sep 14, 2016, at 07:22, Tom Stellard via Libclc-dev <libclc-dev@
> > lists.llvm.org> wrote:
> > 
> > +_CLC_DEF size_t get_num_groups(uint dim) {
> > +  size_t global_size = get_global_size(dim);
> > +  size_t local_size = get_local_size(dim);
> > +  size_t num_groups = global_size / local_size;
> > +  if (global_size % local_size != 0) {
> > +    num_groups++;
> > +  }
> > +  return num_groups;
> LGTM. I hope the % does get optimized out?

AMDGPU implements DIVREM for 64bit integers, so / and % are computed at
the same time. It's still rather expensive (~400 instructions).

(global_size + local_size -1) / local_size

allows elimination of REM only parts of DIVREM (although the savings
are negligible).

Jan

> _______________________________________________
> Libclc-dev mailing list
> Libclc-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/libclc-dev
-- 
Jan Vesely <jv356 at scarletmail.rutgers.edu>