On Mon, Mar 17, 2014 at 6:44 AM, Richard Biener <rguent...@suse.de> wrote: > 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?
Yes, it is a special case. But it is in this special case that those warnings are thrown out. Also, I think declaring an array with VF*N as length is not unusual. thanks, Cong > > 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
