NagyDonat wrote:
> With the current version I have the following observations:
>
> * There is a warning for `(&x + 1) - &x` and `(&x - 1) - &x`. Should this
> be fixed?
The expression `(&x + 1) - &x` is valid and should not produce a warning. It
could appear e.g. in code that's structured like
```
void log_observations(double *begin, double *end, /*...*/) {
log_observation_count(end - begin);
// also log the actual observations
}
void do_observations(/*...*/) {
double array[1024], *p = array;
//...
while (can_observe()) {
*p++ = /* ... */
}
log_observations(array, p);
}
void do_single_observation(/*...*/) {
if (!can_observe())
return;
double result = /* ... */
// ...
log_observations(&result, &result + 1);
}
```
On the other hand `(&x - 1) - &x` is not standard-compliant, because the
standard guarantees an "after-the-end" pointer (which is valid in calculations
but must not be dereferenced) but it doesn't accept a "before-the-begin"
pointer.
> * The code `(int *)((char *)(&a[4]) + sizeof(int)) - &a[4]` produces no
> warning but `(int *)((char *)(&a[4]) + 1) - &a[4]` produces warning.
That's very nice, even a slightly less accurate solution would be acceptable.
> For 2-dimensional arrays there is warning for all of these cases (lines 44-47
> in the test file). Is this possible to fix (to get warning in all cases), or
> no warning is needed here?
I'd say that the current behavior (warning on all of 44-47) is OK here -- this
is very unusual trickery and deserves a highlight. However I could also accept
a situation where there was no warning for these complex multidimensional cases.
https://github.com/llvm/llvm-project/pull/93676
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