Re: Linking Program with Lib That Uses -fwrapv or '-fno-strict-overflow'

[Ian Lance Taylor <iant at google dot com>]

Jeffrey Walton <noloader@gmail.com> writes:

> A simplified example (I know you gave a previous work around) assuming
> 32 bit ints:
>
> // liboverflow, compiled with -fwrapv
> int my_abs(int x, int* r)
> {
>     int y = abs(x);
>     if (y < 0)
>         return 0;
>
>     *r = y;
>     return 1;
> }
>
> // myprogram, compiled with -O2 and linked against liboverflow
> int x = 0x80000000, r = 0;
> if(my_abs(x, &r))
>     printf(...)
>
> Will the resulting program enjoy O2 and/or produce incorrect results?

If you are asking whether this program has signed overflow problems, the
answer is no.  Compiling liboverflow with -fwrapv does not affect
myprogram.  Similarly, compiling myprogram without -fwrapv does not
affect liboverflow.

Ian