[Bug middle-end/68142] New: unsafe association of multiplication

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68142

            Bug ID: 68142
           Summary: unsafe association of multiplication
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

While working on PR66313 I noticed we fail for the following with 
-fsanitize=undefined

int __attribute__((noinline,noclone))
i(int a)
{
  return (2 * a) * (__INT_MAX__/2 + 1);
}
int main()
{
  volatile tem = i(-1);
  return 0;
}

this is because we simplify the above to

;; Function i (null)
;; enabled by -tree-original


{
  return a * -2147483648(OVF);
}

which is of course invalid.