[Bug tree-optimization/64081] New: [5 Regression] r217827 prevents RTL loop unroll

[izamyatin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64081

            Bug ID: 64081
           Summary: [5 Regression] r217827 prevents RTL loop unroll
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: izamyatin at gmail dot com
            Target: x86

Created attachment 34123
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34123&action=edit
reproducer

Noticed that for the attached test no RTL loop unroll started to happen.
It is because of changes in dom - namely, I see in dumps that dom2 complicates
loop structure. (probably because of changes in lookup_avail_expr?)
Looks like r217827 doesn't mean this :)

Options that should be used - just "-O2  -funroll-loops"