On Fri, 14 Mar 2014, Cong Hou wrote: > On Fri, Mar 14, 2014 at 12:58 AM, Richard Biener <rguent...@suse.de> wrote: > > On Fri, 14 Mar 2014, Jakub Jelinek wrote: > > > >> On Fri, Mar 14, 2014 at 08:52:07AM +0100, Richard Biener wrote: > >> > > Consider this fact and if there are alias checks, we can safely remove > >> > > the epilogue if the maximum trip count of the loop is less than or > >> > > equal to the calculated threshold. > >> > > >> > You have to consider n % vf != 0, so an argument on only maximum > >> > trip count or threshold cannot work. > >> > >> Well, if you only check if maximum trip count is <= vf and you know > >> that for n < vf the vectorized loop + it's epilogue path will not be taken, > >> then perhaps you could, but it is a very special case. > >> Now, the question is when we are guaranteed we enter the scalar versioned > >> loop instead for n < vf, is that in case of versioning for alias or > >> versioning for alignment? > > > > I think neither - I have plans to do the cost model check together > > with the versioning condition but didn't get around to implement that. > > That would allow stronger max bounds for the epilogue loop. > > In vect_transform_loop(), check_profitability will be set to true if > th >= VF-1 and the number of iteration is unknown (we only consider > unknown trip count here), where th is calculated based on the > parameter PARAM_MIN_VECT_LOOP_BOUND and cost model, with the minimum > value VF-1. If the loop needs to be versioned, then > check_profitability with true value will be passed to > vect_loop_versioning(), in which an enhanced loop bound check > (considering cost) will be built. So I think if the loop is versioned > and n < VF, then we must enter the scalar version, and in this case > removing epilogue should be safe when the maximum trip count <= th+1.
You mean exactly in the case where the profitability check ensures that n % vf == 0? Thus effectively if n == maximum trip count? That's quite a special case, no? Richard. -- Richard Biener <rguent...@suse.de> SUSE / SUSE Labs SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746 GF: Jeff Hawn, Jennifer Guild, Felix Imend"orffer
