https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84005
--- Comment #11 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> --- Author: rsandifo Date: Sat Mar 24 10:52:34 2018 New Revision: 258833 URL: https://gcc.gnu.org/viewcvs?rev=258833&root=gcc&view=rev Log: Use SCEV information when aligning for vectorisation (PR 84005) This PR is another regression caused by the removal of the simple_iv check in dr_analyze_innermost for BB analysis. Without splitting out the step, we weren't able to find an underlying object whose alignment could be increased. As with PR81635, I think the simple_iv was only handling one special case of something that ought to be more general. The more general thing here is that if the address can be analysed as a scalar evolution, and if all updates preserve alignment N, it's possible to align the address to N by increasing the alignment of the base object to N. That applies also to outer loops, and to both loop and BB analysis. I wasn't sure where the new functions ought to live, but tree-data-ref.c seemed OK since (a) that already does scev analysis on addresses and (b) you'd want to use dr_analyze_innermost first if you were analysing a reference. 2018-03-24 Richard Sandiford <richard.sandif...@linaro.org> gcc/ PR tree-optimization/84005 * tree-data-ref.h (get_base_for_alignment): Declare. * tree-data-ref.c (get_base_for_alignment_1): New function. (get_base_for_alignment): Likewise. * tree-vect-data-refs.c (vect_compute_data_ref_alignment): Use get_base_for_alignment to find a suitable base object, instead of always using drb->base_address. gcc/testsuite/ PR tree-optimization/84005 * gcc.dg/vect/bb-slp-1.c: Make sure there is no message about failing to force the alignment. Modified: trunk/gcc/ChangeLog trunk/gcc/testsuite/ChangeLog trunk/gcc/testsuite/gcc.dg/vect/bb-slp-1.c trunk/gcc/tree-data-ref.c trunk/gcc/tree-data-ref.h trunk/gcc/tree-vect-data-refs.c
