On Fri, Jul 21, 2017 at 8:12 AM, Richard Biener <rguent...@suse.de> wrote: > > The following is sth I noticed when looking at a way to fix PR81303. > We happily compute a runtime cost model threshold that executes the > vectorized variant even though no vector iteration takes place due > to the number of prologue/epilogue iterations. The following fixes > that -- note that if we do not know the prologue/epilogue counts > statically they are estimated at vf/2 which means there's still the > chance the vector iteration won't execute. To fix that we'd have to > estimate those as vf-1 instead, sth we might consider doing anyway > given that we regularly completely peel the epilogues vf-1 times > in that case. Maybe as followup. Hi, Do we consider disabling epilogue peeling if # of iters is unknown at compilation time? When loop is versioned, could we share epilogue with versioned loop? Epilogue was shared before?
Thanks, bin > > Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk. > > Richard. > > 2016-07-21 Richard Biener <rguent...@suse.de> > > PR tree-optimization/81303 > * tree-vect-loop.c (vect_estimate_min_profitable_iters): Take > into account prologue and epilogue iterations when raising > min_profitable_iters to sth at least covering one vector iteration. > > Index: gcc/tree-vect-loop.c > =================================================================== > --- gcc/tree-vect-loop.c (revision 250384) > +++ gcc/tree-vect-loop.c (working copy) > @@ -3702,8 +3702,9 @@ vect_estimate_min_profitable_iters (loop > " Calculated minimum iters for profitability: %d\n", > min_profitable_iters); > > - min_profitable_iters = > - min_profitable_iters < vf ? vf : min_profitable_iters; > + /* We want the vectorized loop to execute at least once. */ > + if (min_profitable_iters < (vf + peel_iters_prologue + > peel_iters_epilogue)) > + min_profitable_iters = vf + peel_iters_prologue + peel_iters_epilogue; > > if (dump_enabled_p ()) > dump_printf_loc (MSG_NOTE, vect_location,
