[Bug tree-optimization/68773] New: fpta-ipa with GOACC_parallel does not work due to node->force_output

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68773

            Bug ID: 68773
           Summary: fpta-ipa with GOACC_parallel does not work due to
                    node->force_output
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

As reported here ( https://gcc.gnu.org/ml/gcc-patches/2015-12/msg00330.html ),
some c-c++-common/goacc/kernels-alias-ipa-pta-{,2}.c scan tests fail. The tests
pass for a compiler configured without accelerator, and fail for a compiler
configure with accelerator.

For the configuration with accelerator, the test fails because the force_output
flag is set for the offloaded function, which causes the thread function to be
handled as a non-local function in fipa-pta.

The force_output flag is set by this bit here in expand_omp_target (which
explains why we don't see the problem in the configuration without accelerator,
which doesn't have ENABLE_OFFLOADING set):
...
12682         /* Prevent IPA from removing child_fn as unreachable,
                 since there are no
12683            refs from the parent function to child_fn in offload
                 LTO mode.  */
12684         if (ENABLE_OFFLOADING)
12685           cgraph_node::get (child_fn)->mark_force_output ();
...