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From: Jim Meyering <jim@meyering.net>
To: Jakub Jelinek <jakub@redhat.com>
Cc: Janne Blomqvist <blomqvist.janne@gmail.com>,  "Joseph S. Myers" <joseph@codesourcery.com>,  gcc-patches@gcc.gnu.org,  java-patches@gcc.gnu.org,  fortran@gcc.gnu.org
Subject: Re: [PATCH gcc/fortran] get rid of gfc_free
In-Reply-To: <20110315100826.GV30899@tyan-ft48-01.lab.bos.redhat.com> (Jakub	Jelinek's message of "Tue, 15 Mar 2011 11:08:26 +0100")
References: <87zkp9zmq0.fsf@rho.meyering.net>	<Pine.LNX.4.64.1103051908320.3878@digraph.polyomino.org.uk>	<877hc9r8w6.fsf_-_@rho.meyering.net>	<877hc9pkhp.fsf_-_@rho.meyering.net>	<AANLkTimAfkfmmfxrNp4w_wD2rGiQ7x07esgtVDT_-8Cj@mail.gmail.com>	<87zkow3dmp.fsf_-_@rho.meyering.net>	<20110315100826.GV30899@tyan-ft48-01.lab.bos.redhat.com>
Date: Tue, 15 Mar 2011 10:27:00 -0000
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Jakub Jelinek wrote:
> On Tue, Mar 15, 2011 at 11:02:38AM +0100, Jim Meyering wrote:
>> > Instead of "please let us know", maybe recommend using
>> > __builtin_expect instead? E.g. something like
>> >
>> > if (__builtin_expect (ptr != NULL, 0))
>> >     free (ptr);
>>
>> Good idea.  Thanks.
>> Though how about avoiding the double negative?
>>
>>    if (__builtin_expect (ptr == NULL, 1))
>>      free (ptr);
>
> What double negative?  if (__builtin_expect (ptr != NULL, 0)) free (ptr);
> is certainly correct, the latter is wrong, it will leak memory.
> It will call free only if ptr is NULL, i.e. do a useless free (NULL),
> if it is non-NULL, it will not do anything.
> You could do
>   if (!__builtin_expect (ptr == NULL, 1))
>     free (ptr);
> but that doesn't seem to be nicer or clearer than
>   if (__builtin_expect (ptr != NULL, 0))
>     free (ptr);

Thanks for the quick correction.
I've fixed it locally, too.