https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111820
--- Comment #8 from rguenther at suse dot de <rguenther at suse dot de> --- On Tue, 17 Oct 2023, crazylht at gmail dot com wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111820 > > --- Comment #7 from Hongtao.liu <crazylht at gmail dot com> --- > (In reply to rguent...@suse.de from comment #6) > > On Mon, 16 Oct 2023, crazylht at gmail dot com wrote: > > > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111820 > > > > > > --- Comment #5 from Hongtao.liu <crazylht at gmail dot com> --- > > > (In reply to Richard Biener from comment #3) > > > > for (unsigned i = 0; i != skipn - 1; i++) > > > > begin = wi::mul (begin, wi::to_wide (step_expr)); > > > > > > > > (gdb) p skipn > > > > $5 = 4294967292 > > > > > > > > niters is 4294967292 in vect_update_ivs_after_vectorizer. Maybe the > > > > loop > > > > should terminate when begin is zero. But I wonder why we pass in > > > > 'niters' > > > Here, it want to calculate begin * pow (step_expr, skipn), yes we can > > > just skip > > > the loop when begin is 0. > > > > I mean terminate it when the multiplication overflowed to zero. > for pow (3, skipn), it will never overflowed to zero. > To solve this problem once and for all, I'm leaning towards setting a > threshold > in vect_can_peel_nonlinear_iv_p for vect_step_op_mul,if step_expr is not > exact_log2() and niter > TYPE_PRECISION (step_expr) we give up on doing > vectorization. Hm, yeah - that's probably best. > > > > As for the MASK_ thing the skip is to be interpreted negative (we > > should either not use a 'tree' here or make it have the correct type > > maybe). Can we even handle this here? It would need to be > > a division, no? > > > > So I think we need to disable non-linear IV or masked peeling for > > niter/aligment? But I wonder how we run into this with plain -O3. > I think we already disabled negative niters_skip in > vect_can_peel_nonlinear_iv_p. > > 416 /* Also doens't support peel for neg when niter is variable. > 1417 ??? generate something like niter_expr & 1 ? init_expr : -init_expr? > */ > 1418 niters_skip = LOOP_VINFO_MASK_SKIP_NITERS (loop_vinfo); > 1419 if ((niters_skip != NULL_TREE > 1420 && TREE_CODE (niters_skip) != INTEGER_CST) But we end up here with niters_skip being INTEGER_CST and .. > 1421 || (!vect_use_loop_mask_for_alignment_p (loop_vinfo) possibly vect_use_loop_mask_for_alignment_p. Note LOOP_VINFO_PEELING_FOR_ALIGNMENT < 0 simply means the amount of peeling is unknown. But I wonder how we run into this on x86 without enabling loop masking ... > 1422 && LOOP_VINFO_PEELING_FOR_ALIGNMENT (loop_vinfo) < 0)) > 1423 { > 1424 if (dump_enabled_p ()) > 1425 dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location, > 1426 "Peeling for alignement is not supported" > 1427 " for nonlinear induction when niters_skip" > 1428 " is not constant.\n"); > 1429 return false; > 1430 }
