[Bug analyzer/115380] New: Missing MUL_OVERFLOW support in analayzer

[Bug analyzer/115380] New: Missing MUL_OVERFLOW support in analayzer

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115380

            Bug ID: 115380
           Summary: Missing MUL_OVERFLOW support in analayzer
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
            Blocks: 109896
  Target Milestone: ---

Take (which is a modified version of g++.dg/analyzer/placement-new-size.C):
```
/* { dg-additional-options "-Wno-placement-new
-Wno-analyzer-use-of-uninitialized-value" } */

#include <new>
#include <stdlib.h>
#include <stdint.h>

void static_buffer_too_short (int t)
{
  int n = t*4;
  int n1 = (t+1);
  if (__builtin_mul_overflow(n1, 4, &n1))
    __builtin_abort();
  char buf[n];
  char *p = new (buf) char[n1]; /* { dg-warning "stack-based buffer overflow" }
*/
}

void static_buffer_too_short1 (int t)
{
  int n = t*4;
  int n1 = (t+1);
  n1 = n1*4;
  char buf[n];
  char *p = new (buf) char[n1]; /* { dg-warning "stack-based buffer overflow" }
*/
}

```
static_buffer_too_short should warn the same way as static_buffer_too_short1
currently does.

Note this was found while looking into the regressions developing of the patch
for PR 109896.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109896
[Bug 109896] Missed optimisation: overflow detection in multiplication
instructions for operator new