[Bug c/106526] New: array-bounds warning on constant pointer dereferencing

[Bug c/106526] New: array-bounds warning on constant pointer dereferencing

[wrenger at sra dot uni-hannover.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106526

            Bug ID: 106526
           Summary: array-bounds warning on constant pointer dereferencing
           Product: gcc
           Version: 12.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wrenger at sra dot uni-hannover.de
  Target Milestone: ---

On optimization levels 2 and 3 the GCC frontend emits false array-bounds
warnings when dereferencing constant pointers.

# Example

CFLAGS: -O2 -Wall -Werror

```
int main(void) {
    int ebda = *((int*)(0x40e));
    return ebda;
}
```

The following error only occurs on GCC 12.1 and newer.
```
<source>: In function 'main':
<source>:2:16: error: array subscript 0 is outside array bounds of 'int[0]'
[-Werror=array-bounds]
    2 |     int ebda = *((int*)(0x40e));
      |                ^~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
```

> See: https://godbolt.org/z/Kff744P58

[Bug c/106526] array-bounds warning on constant pointer dereferencing

[wrenger at sra dot uni-hannover.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106526

--- Comment #1 from Lars Wrenger <wrenger at sra dot uni-hannover.de> ---
Same on C++: https://godbolt.org/z/7do3zhavf

[Bug c/106526] array-bounds warning on constant pointer dereferencing

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106526

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is a deliberate change, dup of bug 105762.

If the address is a valid address, you can also pass --param=min-pagesize=0 to
say that all addresses are valid (see PR 99578).

*** This bug has been marked as a duplicate of bug 105762 ***

[Bug c/106526] array-bounds warning on constant pointer dereferencing

[wrenger at sra dot uni-hannover.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106526

--- Comment #3 from Lars Wrenger <wrenger at sra dot uni-hannover.de> ---
The array-bounds warning itself is nice. In most cases, it is good if the
compiler can find invalid memory accesses.
However, the wording of the warning is confusing. Strictly speaking, we are not
accessing an array (even if *x == x[0]).