PR c++/66555
	PR c/54979
	* c-common.c (find_array_ref_with_const_idx_r): New function.
	(warn_tautological_cmp): New function.
	* c-common.h (warn_tautological_cmp): Declare.
	* c.opt (Wtautological-compare): New option.

	* c-typeck.c (parser_build_binary_op): Call warn_tautological_cmp.

	* call.c (build_new_op_1): Call warn_tautological_cmp.
	* pt.c (tsubst_copy_and_build): Use sentinel to suppress tautological
	compare warnings.

	* doc/invoke.texi: Document -Wtautological-compare.

	* c-c++-common/Wtautological-compare-1.c: New test.

From-SVN: r226242