On Jul 14, 2011, at 10:28 AM, Ted Kremenek wrote:
> I was reviewing this patch (which I think is a great step), and I had a
> high-level comment about the following test case:
>
> +void swallow (const char *x) { (void)x; }
> +void test_pointer_arithmetic() {
> + const char hello[] = "Hello world!"; // expected-note 2 {{declared here}}
> + const char *helloptr = hello;
> +
> + swallow("Hello world!" + 6); // no-warning
> + swallow("Hello world!" - 6); // expected-warning {{refers before the
> beginning of the array}}
> + swallow("Hello world!" + 14); // expected-warning {{refers past the end of
> the array}}
>
> Do we really want this to be a warning? There are plenty of examples where
> an out-of-bounds pointer is computed for legit reasons. As long as that
> address is not dereferenced, there isn't necessarily a problem. I'm fearful
> this may generate a fair amount of noise on codebases that do elaborate
> tricks with pointer offsets. Indeed this very example doesn't actually
> exhibit a "bug".
Note that it's undefined behavior to try to construct a pointer to before the
beginning or after the end of an array (except *immediately* past the end);
it's not tied to dereferencing that pointer. LLVM does do some optimizations
here; see in 'inbounds' modifier on getelementptr.
John.
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