[Bug tree-optimization/68707] [6 Regression] testcase gcc.dg/vect/O3-pr36098.c vectorized using VEC_PERM_EXPR rather than VEC_LOAD_LANES

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68707

--- Comment #15 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to alalaw01 from comment #13)
> Hmmm, I realize a "definite" codegen improvement was maybe a bad choice of
> wording. A "substantial" (albeit uncertain!) improvement, may have been more
> accurate...
> 
> However, yes it looks like we want that patch (indeed, it still helps even
> when we up the cost of permute operations and drop the -fno-vect-cost-model)
> - so thanks, Richard. We'll clean up the testisms in due course.
> 
> In the longer term, is the issue here, that we aren't comparing costs of SLP
> vs load-lanes, right? We merely compare the cost of whichever of those
> vectorization strategies we favour, permutes et al, vs leaving it in scalar
> code?

Yes, at the moment cost comparison would be apples to oranges :(

Note the  commit was a revert - I accidentially committed the patch.