http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51744
--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Mark Pizzolato from comment #7)
> Thanks for reducing this test case further. That illuminates something for
> me:
>
> Specifically:
>
> Notice in the following lines:
>
> if (__builtin_constant_p (__len) && __len == 0
> && (!__builtin_constant_p (__ch) || __ch != 0))
> {
>
> The part of the expression "|| __ch != 0)"
>
> What could possibly be the purpose of this check?
>
> That is exactly why the 3rd condition I previously mentioned:
>
> > 3) memset is called with a NON zero fill value argument.
>
> triggers this issue. The warning is about the length, but it is checking
> the value being set. How could that make sense? Clearly this check lets
> the vast majority of uses of memset pass without issue since all of those
> cases use 0 as the value to be set.
>
> From my point of view, if that check wasn't there (i.e. remove "|| __ch !=
> 0" from the expression), the problem would not exist.
When val == 0 then the case of len == 0 is ambiguous and you can't really
tell the user they swapped val and len (because they are equal).
