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Re: [PATCH] TRACING: Fix a copmile warning
- From: Ian Lance Taylor <iant at google dot com>
- To: Steven Rostedt <rostedt at goodmis dot org>
- Cc: Arnaud Lacombe <lacombar at gmail dot com>, gcc-help at gcc dot gnu dot org, stufever at gmail dot com, linux-kernel at vger dot kernel dot org, Wang Shaoyan <wangshaoyan dot pt at taobao dot com>, Frederic Weisbecker <fweisbec at gmail dot com>, Ingo Molnar <mingo at redhat dot com>
- Date: Mon, 25 Jul 2011 17:44:25 -0700
- Subject: Re: [PATCH] TRACING: Fix a copmile warning
- References: <1310982010-13849-1-git-send-email-wangshaoyan.pt@taobao.com> <1311618747.3526.32.camel@gandalf.stny.rr.com> <CACqU3MVJ9Oj4pXH9O_2jnqDVBqKA+AgoWHwP-n2HGD4LU0pMHQ@mail.gmail.com> <1311625197.3526.35.camel@gandalf.stny.rr.com> <CACqU3MUKU_0FbOQT+TKLnnaoFVS_QOgzzx-tvunQy94v-eykTw@mail.gmail.com> <CACqU3MXO_oR+8Ac2Z7wSji0sUeu-2FwskmxZxtY9NV+XpJXuwA@mail.gmail.com> <1311640534.3526.50.camel@gandalf.stny.rr.com>
Steven Rostedt <rostedt@goodmis.org> writes:
>> It seems gcc transforms the conditional from:
>>
>> if (a != NULL && b != NULL) ...
>>
>> to
>>
>> if (b != NULL && a != NULL) ...
>>
>> In which case the warning is fully valid. I'm not sure what's the C
>> standard guarantee in term of conditional test order. gcc 4.7.0 has
>> the same behavior.
>
> Yes it seems to be doing this :-/
>
> This is a real bug!
To be clear, gcc is not doing that, and this is not a code generation
bug. It is a warning generation bug; the generated code is correct.
Ian