PR debug/43177
	* var-tracking.c (loc_cmp): Don't assert VALUEs have the same mode.
	(VAL_EXPR_HAS_REVERSE): Define.
	(reverse_op): New function.
	(add_stores): For reversible operations add an extra MO_VAL_USE.

	* gcc.dg/guality/pr43177.c: New test.

From-SVN: r157188