[cfe-dev] Strict overflow warning

[Dmitri Gribenko]

On Friday, September 21, 2012, Richtarsky, Martin wrote:

> Hi all,
>
> a few days ago I ran across code that relied on signed overflow being
> defined. With gcc this worked fine, clang optimized and the program broke.
>
> With gcc it is possible to specify -Wstrict-overflow=x to get a warning in
> cases where the compiler relies on undefined behaviour (which will usually
> happen only with -O2 or above).
>
> I tried this with clang, but got no warning (but clang seems to know the
> option). Am I  doing something wrong?
>

Hi Martin,

I don't think there is such warning in clang, but you could use the -fwrapv
option to define signed integer arithmetic to wrap around on overflow --
this is the easy option.  You could also use the -fcatch-undefined-behavior
option to catch signed overflow at runtime and turn it into a crash so that
you can debug and fix it.

Dmitri



-- 
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/
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