[Bug tree-optimization/69949] New: Optimally handle case that outer phi res is not used in a phi in gather_scalar_reductions

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69949

            Bug ID: 69949
           Summary: Optimally handle case that outer phi res is not used
                    in a phi in gather_scalar_reductions
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

Here ( https://gcc.gnu.org/ml/gcc-patches/2016-01/msg00545.html ) we fix
PR69108: "Handle case that outer phi res is not used in a phi in
gather_scalar_reductions" conservatively.

We want to fix it optimally, by allowing parallelization for the test-case.