PR opt/3995
	* fold-const.c (sign_bit_p): New function.
	(fold) [EQ_EXPR]: Use this to convert (A & C) == 0 into A >= 0 and
        (A & C) != 0 into A < 0, when constant C is the sign bit of A's type.
	Reapply fold when converting (A & C) == C into (A & C) != 0.
	(fold_binary_op_with_conditional_arg): Fix typo in comment.

testsuite/
	* gcc.c-torture/execute/20020506-1.c: New test case.

From-SVN: r53241