* tree-vrp.c (get_single_symbol): New function.
	(build_symbolic_expr): Likewise.
	(symbolic_range_based_on_p): New predicate.
	(extract_range_from_binary_expr_1): Deal with single-symbolic ranges
	for PLUS and MINUS.  Do not drop symbolic ranges at the end.
	(extract_range_from_binary_expr): Try harder for PLUS and MINUS if
	operand is symbolic and based on the other operand.

From-SVN: r215697