[Bug c/126003] New: integer overflow during compile-time arithmetic is not always detected

[douglas.mcilroy at dartmouth dot edu via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126003

            Bug ID: 126003
           Summary: integer overflow during compile-time arithmetic is not
                    always detected
           Product: gcc
           Version: 13.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: douglas.mcilroy at dartmouth dot edu
  Target Milestone: ---

The program below contains two instances of integer overflow. Under option -O1,
both are evaluated at compile time, yet only the first one gives a warning.
This seems inconsistent. At best, an opportunity to get better warnngs as a
side-effect of optimization has been wasted.

#include <stdio.h>
#define TWOGIG 2000000000 // 2,000,000,000
int x = TWOGIG+TWOGIG;
int main() {
    int twogig = TWOGIG;
    printf("%d\n", twogig+twogig);
}