Richard Biener <richard.guent...@gmail.com> writes: > On Thu, Dec 20, 2018 at 2:43 PM Joern Wolfgang Rennecke <g...@amylaar.uk> > wrote: >> >> eSi-RISC has vector permute functionality, but no unaligned loads. We >> see execution failures on gcc.dg/vect/slp-perm-12.c because loop >> versioning is used to make the tptr aligned for the first loop >> iteration, and then with a step of originally 11, 22 after >> vectorization, and a vector alignment of 8 bytes, the second iteration >> causes an AlignmentError exception. >> The attached patch to tree-vect-data-refs.c suppresses attempts to align >> data accesses where the >> step alignment times the vectorization factor is insufficient to sustain >> the alignment during the loop. >> Bootstrapped and regression tested on x86_64-pc-linux-gnu . >> >> I have also attached a matching testsuite patch to not expect SLP >> vectorization for slp-perm-12 when >> no unaligned loads are available, although in terms of testing, I can >> only say that it works for us. > > vect_compute_data_ref_alignment uses DR_TARGET_ALIGNMENT > and DR_STEP_ALIGNMENT () % dr_target-alignment == 0 as check. > > I think it's preferable to use the same or similar values for the desired > alignment.
Yeah, I agree testing for a multiple is better than maybe_lt, and that we should be using DR_TARGET_ALIGNMENT rather than TYPE_ALIGN_UNIT. (TYPE_ALIGN_UNIT is the ABI alignment, which might be higher or lower than the alignment the vectoriser is aiming for. And I think the reasons for bailing out apply whenever the vectoriser can't reach the alignment it's aiming for, even if the alignment isn't needed for correctness.) Thanks, Richard
