[Bug tree-optimization/126592] [13/14/15/16/17 Regression] Wrong code with compex mul vectorisation and is_linear_load_p

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D126592

--- Comment #2 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
(In reply to Tamar Christina from comment #1)
> (In reply to ktkachov from comment #0)
> > /* PR: candidate tree-vect-slp-patterns.cc:158 - wrong code.
> >=20
> >    is_linear_load_p decides PERM_EVENEVEN from the parity of each load
> >    permutation entry alone, so {0,2,2,2} is accepted exactly like the
> >    intended {0,0,2,2}.
>=20
> {0,0,2,2} is invalid too as the for linearity there can't be gaps.
>=20
> Testing a patch.

hmm actually no `{0,0,2,2}` is correct, the function is misnamed.
The fix cleans up the code a bit too.=