re PR c++/26943 ([gomp] firstprivate + lastprivate uses inefficient barrier)

re PR c++/26943 ([gomp] firstprivate + lastprivate uses inefficient barrier)

	PR c++/26943
	* omp-low.c (maybe_lookup_decl_in_outer_ctx): New function.
	(build_outer_var_ref): Use maybe_lookup_decl_in_outer_ctx
	to find if var will be a global variable even in the nested context.
	(omp_copy_decl): Only check for global variable at the end, it might
	be overridden in outer contexts.
	(scan_sharing_clauses): For global variables don't create a field.
	(lower_rec_input_clauses): Do nothing for global shared variables.
	Emit a barrier at the end of ILIST if there were any decls in both
	firstprivate and lastprivate clauses.
	(lower_send_clauses): Do nothing for global variables except for
	COPYIN.

	* testsuite/libgomp.c/pr26943-1.c: New test.
	* testsuite/libgomp.c/pr26943-2.c: New test.
	* testsuite/libgomp.c/pr26943-3.c: New test.
	* testsuite/libgomp.c/pr26943-4.c: New test.
	* testsuite/libgomp.c++/pr27337.C: Remove barrier.
	* testsuite/libgomp.c++/pr26943.C: New test.

From-SVN: r113483