On Wed, Aug 15, 2012 at 02:36:54PM +0200, Richard Guenther wrote: > On Wed, Aug 15, 2012 at 2:29 PM, Jakub Jelinek <ja...@redhat.com> wrote: > > On Wed, Aug 15, 2012 at 02:15:03PM +0200, Richard Guenther wrote: > >> Ok. That would still leave us with the issue Ramana brought up - the > >> target hook returning true unconditionally if a generic permute is > >> implemented. > >> We just avoid generic expansion by tree-vect-generic.c that way. > > > > Yeah, if there is a generic permute, can_vec_perm_p will return true always > > for the modes for which it is available. Which is why I've been suggesting > > also the target hook which should return false if only generic permute is > > going to be used. > > Well. What about returning a cost instead? We don't want to transform > two insns to four either.
That could work, it would just be a lot of work to change it (and more costly). E.g. on i386 for 16-byte vectors with certain ISAs we return true right away, when returning cost we'd need to go the slow path always even when the caller is just interested in a boolean flag whether it is possible or not. CCing rth as the author of the hooks. Jakub