------- Comment #7 from john dot carter at tait dot co dot nz 2009-02-23 23:53
-------
R Guenther said...
> (int)u1 == (int)(u8_t)(~(int)u2)
>
> that we do not warn for the first case is because it is optimized to
> u1 == ~u2 before.
>
> Why do you think the warning is incorrect?
-----------------------------------------------
I would expect
u2 to be promoted to a 4 byte int
~ to do the ones complement on a 4 byte int
(unsigned char)~u2 to truncate to one byte discarding the most significant 3
bytes
and then the result get promoted to an int to evaluate the ==
ie. The cast cannot get optimized away, it's not a null op, it discards the
most significant bytes.
ie. (int)(unsigned char)~(int)u2 is not equivalent to
~(int)u2
ie. This is a bug
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38341
