On Mon, Nov 4, 2019 at 4:29 PM Richard Sandiford <richard.sandif...@arm.com> wrote: > > The number of iterations of an epilogue loop is always smaller than the > VF of the main loop. vect_analyze_loop_costing was taking this into > account when deciding whether the loop is cheap enough to vectorise, > but that has no effect with the unlimited cost model. We need to use > a separate check for correctness as well. > > This can happen if the sizes returned by autovectorize_vector_sizes > happen to be out of order, e.g. because the target prefers smaller > vectors. It can also happen with later patches if two vectorisation > attempts happen to end up with the same VF.
OK. > > 2019-11-04 Richard Sandiford <richard.sandif...@arm.com> > > gcc/ > * tree-vect-loop.c (vect_analyze_loop_2): When vectorizing an > epilogue loop, make sure that the VF is small enough or that > the epilogue loop can be fully-masked. > > Index: gcc/tree-vect-loop.c > =================================================================== > --- gcc/tree-vect-loop.c 2019-11-04 15:17:35.924940111 +0000 > +++ gcc/tree-vect-loop.c 2019-11-04 15:17:50.736838681 +0000 > @@ -2142,6 +2142,16 @@ vect_analyze_loop_2 (loop_vec_info loop_ > " support peeling for gaps.\n"); > } > > + /* If we're vectorizing an epilogue loop, we either need a fully-masked > + loop or a loop that has a lower VF than the main loop. */ > + if (LOOP_VINFO_EPILOGUE_P (loop_vinfo) > + && !LOOP_VINFO_FULLY_MASKED_P (loop_vinfo) > + && maybe_ge (LOOP_VINFO_VECT_FACTOR (loop_vinfo), > + LOOP_VINFO_VECT_FACTOR (orig_loop_vinfo))) > + return opt_result::failure_at (vect_location, > + "Vectorization factor too high for" > + " epilogue loop.\n"); > + > /* Check the costings of the loop make vectorizing worthwhile. */ > res = vect_analyze_loop_costing (loop_vinfo); > if (res < 0)
