On 04/29/2014 10:13 AM, Evgeny Stupachenko wrote:
> + /* For a rotaion permutation with one operand like: {5 6 7 0 1 2 3 4}
> + PALIGNR is better than PSHUFB. Check for a rotation in permutation. */
> + for (i = 0; i < nelt; ++i)
> + if ((((d->perm[(i + 1) & (nelt - 1)] - d->perm[i])) & (nelt - 1)) != 1)
> + return false;
> +
> + min = d->perm[0];
Why are you running this loop NELT times instead of NELT-1 like I suggested?
Why is that test expression so complicated?
Obviously d->perm[0] is the anchor and everything else can be computed relative
to that. I'd expect no more than
min = d->perm[0];
for (i = 1; i < nelt; ++i)
if (d->perm[i] != ((min + i) & (nelt - 1)))
return false;
Now that I think of it,
> + /* PALIGNR of 2 128-bits registers takes only 1 instrucion.
> + Requires SSSE3. */
> + if (GET_MODE_SIZE (d->vmode) == 16)
> + {
> + if (!TARGET_SSSE3)
> + return false;
> + }
> + /* PALIGNR of 2 256-bits registers on AVX2 costs only 2 instructions:
> + PERM and PALIGNR. It is more profitable than 2 PSHUFB and PERM. */
> + else if (GET_MODE_SIZE (d->vmode) == 32)
> + {
> + if (!TARGET_AVX2)
> + return false;
> + }
> + else
> + return false;
> +
> + if (!d->one_operand_p)
> + return false;
The comments are wrong. Move the operand_p test to the top,
where it should be, and they're more obviously wrong:
"must have one operand"
"palignr of two operands..."
I think your comment
/* For a rotaion permutation with one operand like: {5 6 7 0 1 2 3 4}
we want to use PALIGNR. */
belongs up there instead of those two incorrect comments.
r~
