https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105075
Thomas Schwinge <tschwinge at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu.org,
| |tschwinge at gcc dot gnu.org
Last reconfirmed| |2022-03-28
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
--- Comment #4 from Thomas Schwinge <tschwinge at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #0)
> ptx has sad ((sum of absolute differences)) insn, which is currently not
> modeled in the .md file.
I also had noticed this, a while ago (but no opportunity to work on it
properly).
I had found GCC/RTL 'ssad', 'usad', and 'gcc/tree.def:SAD_EXPR', but not
verified their applicability.
(In reply to Tom de Vries from comment #2)
> AFAIU, at gimple level support is limited to vectors, so that doesn't help
> to generate the insn for the simple, scalar case.
>
> It would be nice if combine could generate it and we wouldn't have to use a
> peephole, but AFAIU the pattern is too complex for that.
>
> I wonder if reformulating using a conditional could help there (ptx isa
> describes semantics using "c + ((a<b) ? b-a : a-b)".
Would that not be a case for a proper TREE-level representation, and
'gcc/match.pd' patterns to catch and transform any appearances to that, and
then let each back end generate an ideal sequence of instructions (with a
default to the expression you gave above)?
> Also, I wonder if defining a stepping-stone intermediate pattern could help
> combine.
