* c.opt (Wdouble-promotion): New.

	* doc/invoke.texi: Document -Wdouble-promotion.
	* c-typeck.c (convert_arguments): Check for implicit conversions
	from float to double.
	(do_warn_double_promotion): New function.
	(build_conditional_expr): Use it.
	(build_binary_op): Likewise.

	* gcc.dg/Wdouble-promotion.c: New.

From-SVN: r163884