[Bug tree-optimization/69980] New: [6 regression] Supposedly wrong SLP code emitted

[kyukhin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69980

            Bug ID: 69980
           Summary: [6 regression] Supposedly wrong SLP code emitted
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kyukhin at gcc dot gnu.org
  Target Milestone: ---

Created attachment 37806
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=37806&action=edit
Reproducer

Hello,
Attached test runfails when compiled is following:
$ gfortran -m64 -Ofast repro.f90 -msse

When compiled w/ -O2  - it works fine.

Second loop nest is just for verification.

Issue lives here:
  mumax = 0;
  do k=1,26
     do i=1,3
        mumax(i) = max(mumax(i), mu(i,k)+mu(i,k))
     end do
  end do

Looks like SLP emits some wrong permutations here.