> I see. x86 doesn't have scalar saturating instructions, so the scalar
> version indeed can't be converted.
> I will amend x86 testcases after the vector part of your patch is committed.
Thanks for the confirmation. Just curious, the .SAT_SUB for scalar has sorts of
forms, like a branch version as below.
.SAT_SUB (x, y) = x > y ? x - y : 0. // or leverage __builtin_sub_overflow here
It is reasonable to implement the scalar .SAT_SUB for x86? Given somehow we can
eliminate the branch here.
Pan
-----Original Message-----
From: Uros Bizjak <ubiz...@gmail.com>
Sent: Wednesday, June 5, 2024 4:30 PM
To: Li, Pan2 <pan2...@intel.com>
Cc: Richard Biener <richard.guent...@gmail.com>; gcc-patches@gcc.gnu.org;
juzhe.zh...@rivai.ai; kito.ch...@gmail.com; tamar.christ...@arm.com
Subject: Re: [PATCH v1] Internal-fn: Support new IFN SAT_SUB for unsigned
scalar int
On Wed, Jun 5, 2024 at 10:22 AM Li, Pan2 <pan2...@intel.com> wrote:
>
> > Is the above testcase correct? You need "(x + y)" as the first term.
>
> Thanks for comments, should be copy issue here, you can take SAT_SUB (x, y)
> => (x - y) & (-(TYPE)(x >= y)) or below template for reference.
>
> +#define DEF_SAT_U_SUB_FMT_1(T) \
> +T __attribute__((noinline)) \
> +sat_u_sub_##T##_fmt_1 (T x, T y) \
> +{ \
> + return (x - y) & (-(T)(x >= y)); \
> +}
> +
> +#define DEF_SAT_U_SUB_FMT_2(T) \
> +T __attribute__((noinline)) \
> +sat_u_sub_##T##_fmt_2 (T x, T y) \
> +{ \
> + return (x - y) & (-(T)(x > y)); \
> +}
>
> > BTW: After applying your patch, I'm not able to produce .SAT_SUB with
> > x86_64 and the following testcase:
>
> You mean vectorize part? This patch is only for unsigned scalar int (see
> title) and the below is the vect part.
> Could you please help to double confirm if you cannot see .SAT_SUB after
> widen_mul pass in x86 for unsigned scalar int?
> Of course, I will have a try later as in the middle of sth.
>
> https://gcc.gnu.org/pipermail/gcc-patches/2024-May/653024.html
I see. x86 doesn't have scalar saturating instructions, so the scalar
version indeed can't be converted.
I will amend x86 testcases after the vector part of your patch is committed.
Thanks,
Uros.
