[cfe-dev] Possible clang bug with -O2, wrong if branch entered, in clang version 2.1 (tags/Apple/clang-163.7.1)

[Sean McBride]

On Tue, 21 Feb 2012 17:57:01 +0200, Dmitri Gribenko said:

>> Sorry, there was a problem with cut&paste of the gist URL, the correct
>one is:
>>
>> https://gist.github.com/1876875
>
>Hi Salvatore,
>
>If I understand this code correctly, there is a signed overflow.
>Signed overflow is undefined behavior.  Clang (or LLVM) apparently
>takes advantage of that by optimizing (incr < 0 && value > oldvalue)
>=> false.

And you can get clang to barf on such occurrences:
<http://blog.llvm.org/2011/05/what-every-c-programmer-should-know.html>

-- 
____________________________________________________________
Sean McBride, B. Eng                 sean at rogue-research.com
Rogue Research                        www.rogue-research.com 
Mac Software Developer              Montréal, Québec, Canada