re PR middle-end/54315 (unnecessary copy of return value for union)

re PR middle-end/54315 (unnecessary copy of return value for union)

	PR rtl-optimization/54315
	* calls.c (expand_call): Don't deal specifically with BLKmode values
	returned in naked registers.
	* expr.h (copy_blkmode_from_reg): Adjust prototype.
	* expr.c (copy_blkmode_from_reg): Rename first parameter into TARGET and
	make it required.  Assert that SRCREG hasn't BLKmode.  Add a couple of
	short-circuits for common cases and be prepared for sub-word registers.
	(expand_assignment): Call copy_blkmode_from_reg for BLKmode values
	returned in naked registers.
	(store_expr): Likewise.
	(store_field): Likewise.

From-SVN: r192641