[cfe-commits] PATCH: Enhance array bounds checking

[Eli Friedman]

On Wed, Jul 20, 2011 at 11:39 AM, Kaelyn Uhrain <rikka at google.com> wrote:
> I've attached an updated version of my patch that better handles cases where
> pointer arithmetic is done after casting a constant-size array to a pointer
> for a smaller base type (e.g. casting an int array to char*). Of the pointer
> arithmetic warnings, about 24% could be considered false positives; however,
> the actual number of false positives is quite small and 2/3 of them stem
> from the use of a single macro--if you count those as a single warning &
> false positive, the rate drops to 17%. Of the false positives most are from
> semi-questionable pointer arithmetic where a constant greater than the
> length of the array/pointer is being added to the pointer and some int > 1
> being subtracted from it, e.g.:
>
> void foo(int n) {
>   char x[5];
>   if (n > 0) bar(x + 6 - n);
> }

Strictly speaking, that isn't a false positive... I can't think of how
we would actually produce anything other than the expected result, but
it has undefined behavior, and the IR we generate for it has undefined
behavior.

-Eli