[Bug middle-end/85586] [8/9 Regression] Optimizer produces different result on -O2 and -O3

[rsandifo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85586

--- Comment #4 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
Author: rsandifo
Date: Wed May  2 07:40:22 2018
New Revision: 259822

URL: https://gcc.gnu.org/viewcvs?rev=259822&root=gcc&view=rev
Log:
Tighten early exit in vect_analyze_data_ref_dependence (PR85586)

The problem in this PR was that we didn't consider aliases between
writes in the same strided group.  After tightening the early exit
we get the expected abs(step) >= 2 versioning check.

2018-05-02  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
        PR tree-optimization/85586
        * tree-vect-data-refs.c (vect_analyze_data_ref_dependence): Only
        exit early for statements in the same group if the accesses are
        not strided.

gcc/testsuite/
        PR tree-optimization/85586
        * gcc.dg/vect/pr85586.c: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/vect/pr85586.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-vect-data-refs.c