PR debug/50299
	* calls.c (load_register_parameters): Use use_reg_mode instead
	of use_reg when adding a single register CALL_INSN_FUNCTION_USAGE
	entry.
	(expand_call): Set EXPR_LIST mode to TYPE_MODE of the argument
	for stack CALL_INSN_FUNCTION_USAGE uses.
	* expr.h (use_reg_mode): New prototype.
	(use_reg): Changed into inline around use_reg_mode.
	* expr.c (use_reg): Renamed to...
	(use_reg_mode): ... this.  Added MODE argument, set EXPR_LIST
	mode to that mode instead of VOIDmode.
	* var-tracking.c (prepare_call_arguments): Don't track parameters
	whose EXPR_LIST mode is VOIDmode, BLKmode or X mode isn't convertible
	to it using lowpart_subreg.  Convert VALUE and REG/MEM to the
	EXPR_LIST mode.

From-SVN: r178784