[Bug c++/105438] New: Incorrect array-bounds warning with array size carried over from a previous template instantiation

[bernie at codewiz dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105438

            Bug ID: 105438
           Summary: Incorrect array-bounds warning with array size carried
                    over from a previous template instantiation
           Product: gcc
           Version: 11.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bernie at codewiz dot org
  Target Milestone: ---

Minified testcase (almost every line is necessary to reproduce):

```
/* g++ -Warray-bounds -O2 repro.cc */

int longer[7] = {};
int shorter[2] = {};
int out[10] = {};

template <int N>
void configure(const int(&in)[N], const int nrows = N)
{
    if (nrows <= 10)
    {
        for (int i = 0; i < nrows; i++)
        {
            out[i] = in[i];
        }
    }
}

int main()
{
  configure(longer);
  configure(shorter);
}
```

Output:

```
$ g++ -Warray-bounds -O2 repro.cc
repro.cc: In function 'int main()':
repro.cc:13:24: warning: array subscript 'const int [7][0]' is partly outside
array bounds of 'int [2]' [-Warray-bounds]
   13 |             out[i] = in[i];
      |                      ~~^
repro.cc:3:5: note: while referencing 'shorter'
    3 | int shorter[2] = {};
      |     ^~~~~~~
repro.cc:13:24: warning: array subscript 'const int [7][0]' is partly outside
array bounds of 'int [2]' [-Warray-bounds]
   13 |             out[i] = in[i];
      |                      ~~^
repro.cc:3:5: note: while referencing 'shorter'
    3 | int shorter[2] = {};
      |     ^~~~~~~
```

Static analysis appears to be using the length of the longer array for the call
using the shorter array.

The warning disappears by:
 * commenting out the first call to configure() suppresses the warning
 * swapping the two calls to configure()
 * commenting out if statement also eliminates the warning
 * making longer and shorter the same size
 * using N as loop counter instead of nrows