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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/109230] [13 Regression] Maybe wrong code for
 opus package on aarch64 since r13-4122-g1bc7efa948f751
Date: Tue, 21 Mar 2023 16:20:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109230

--- Comment #14 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think series_p clearly documents that:
/* Return true if index OUT_BASE + I * OUT_STEP selects input
   element IN_BASE + I * IN_STEP.  For example, the call to test
   whether a permute reverses a vector of N elements would be:

     series_p (0, 1, N - 1, -1)

   which would return true for { N - 1, N - 2, N - 3, ... }.
   The calls to test for an interleaving of elements starting
   at N1 and N2 would be:

     series_p (0, 2, N1, 1) && series_p (1, 2, N2, 1).

   which would return true for { N1, N2, N1 + 1, N2 + 1, ... }.  */

bool
vec_perm_indices::series_p (unsigned int out_base, unsigned int out_step,
                            element_type in_base, element_type in_step) con=
st

So, if you want to catch permutation { 0, nelts, 2, nelts + 2, 4, nelts + 4,
... }
then I think you need sel.series_p (0, 2, 0, 2) && sel.series_p (1, 2, nelt=
s +
1, 2).=