[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