Re: [PATCH] Fix an "variable might be used uninitialized" gcc warning

From: Miles Bader <miles@gnu.org>
Date: Feb 1, 2012, 07:16 UTC
Message-ID: <buo7h07rpl8.fsf@dhlpc061.dev.necel.com>
In-Reply-To: <20120131194302.GD12443@burratino>

Jonathan Nieder <jrnieder@gmail.com> writes:

Show 18 quoted lines

>> The versions which complain are 3.4.4 and 4.1.2, whereas 4.4.0 compiles
>> the code without complaint. So, gcc *may* be getting more sane, but I wouldn't
>> bet on it! :-P
>>
>> I've had examples of this kind of warning, which relies heavily on the
>> analysis performed primarily for the optimizer, come-and-go in gcc before
>
> Yep, judging from the commit message, Junio found the same warning
> in 4.6.2.
>
>> Having said that, unless you are going to decree that the project only
>> supports gcc (and presumably only some particular versions of gcc), then you
>> may well find similar warnings triggered when using other compilers anyway ...
>
> Sure, when the control flow grows too complicated, that's probably worth
> fixing anyway, for the sake of humans especially.
>
> Sometimes gcc is the only crazy one, though. ;-)

It's hard to see how any compiler could detect that "mode" always receives a value here .... it would have to realize that "stage" always becomes 2 before the loop is exited, and that seems to depend on non-trivial properties of external data structures...

-miles

-- 
Joy, n. An emotion variously excited, but in its highest degree arising from
the contemplation of grief in another.