PR middle-end/57344
	* expmed.c (store_split_bit_field): If op0 is a REG or
	SUBREG of a REG, don't lower unit.  Handle unit not being
	always BITS_PER_WORD.

	* gcc.c-torture/execute/pr57344-1.c: New test.
	* gcc.c-torture/execute/pr57344-2.c: New test.
	* gcc.c-torture/execute/pr57344-3.c: New test.
	* gcc.c-torture/execute/pr57344-4.c: New test.

From-SVN: r199238