[Bug tree-optimization/51492] vectorizer does not support saturated arithmetic patterns

["tnfchris at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51492

--- Comment #17 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
(In reply to Li Pan from comment #16)
> I have a try like below and finally have the Standard Name "SAT_ADD". Could
> you please help to double-check if my understanding is correct?
> 
> Given below example code below:
> 
> typedef unsigned int uint32_t;
> 
> uint32_t
> sat_add (uint32_t x, uint32_t y)
> {
>   return (x + y) | - ((x + y) < x);
> }
> 
> And then add one simpify to match.pd and define new DEF_INTERNAL_OPTAB_FN
> for it. Then we have the SAT_ADD representation after expand.
> 
> uint32_t sat_add (uint32_t x, uint32_t y)
> {
>   uint32_t _6;
> 
> ;;   basic block 2, loop depth 0
> ;;    pred:       ENTRY
>   _6 = .SAT_ADD (x_4(D), y_5(D)); [tail call]
>   return _6;
> ;;    succ:       EXIT
> 
> }
> 
> If everything goes well, I will prepare the patch for it later. Thanks.

Yeah that's looks right, I assume above you mean before expand?

I believe saturating add is commutative but not associative, so you'd want to
add it to commutative_binary_fn_p in internal-fn.cc.

You may also want to provide some basic optimizations for it in match.pd such
as  .SAT_ADD (a, 0) = a. etc.