[vect] PR103997: Fix epilogue mode skipping

[Richard Biener]

On Tue, 18 Jan 2022, Andre Vieira (lists) wrote:

> 
> On 14/01/2022 09:57, Richard Biener wrote:
> >
> > The 'used_vector_modes' is also a heuristic by itself since it registers
> > every vector type we query, not only those that are used in the end ...
> >
> > So it's really all heuristics that can eventually go bad.
> >
> > IMHO remembering the VF that we ended up with (maybe w/o unrolling)
> > for each analyzed vector_mode[] might be really the easiest thing to do,
> > that should make it easy to skip those modes where the VF is larger
> > or equal as the VF of the main loop for the purpose of epilogue
> > vectorization.  Likewise those vector_mode[] that failed analysis can
> > be remembered (with -1U VF for example).
> >
> > Richard.
> 
> I liked the caching suggestion, so here it is. Sorry for the delay, wanted to
> post this after pushing the vect unroll which was waiting on some retesting
> for the rebase.

LGTM.

Thanks,
Richard.

> gcc/ChangeLog:
> 
>         PR 103997
>         * tree-vect-loop.c (vect_analyze_loop): Fix mode skipping for 
> epilogue
>         vectorization.
>