Hi Tom,
this patch provides a 'bool independent' field in struct loop, which
will be switched on by an "independent" clause in a #pragma acc loop directive.
I assume you'll be wiring it to the kernels parloops pass in a followup patch.

Note: there are already a few other similar fields in struct loop, namely
'safelen' and 'can_be_parallel', used by OMP simd safelen and GRAPHITE respectively.
The intention and/or setting of these fields are all a bit different, so I've
decided to add a new bool for OpenACC.

Tested and committed to gomp-4_0-branch.

Chung-Lin

2015-07-14  Chung-Lin Tang  <cltang@codesourcery.com>

        * cfgloop.h (struct loop): Add 'bool marked_independent' field.
        * gimplify.c (gimplify_scan_omp_clauses): Keep OMP_CLAUSE_INDEPENDENT.
        * omp-low.c (struct omp_region): Add 'int kind' and
        'bool independent' fields.
        (expand_omp_for): Set 'marked_independent' field for loop
        corresponding to region.
        (find_omp_for_region_data): New function.
        (find_omp_target_region_data): Set kind field.
        (build_omp_regions_1): Call find_omp_for_region_data() for
        GIMPLE_OMP_FOR statements.