[Bug c/110399] New: pointer substraction causes coredump with ftrapv on edge case

["baiwfg2 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110399

            Bug ID: 110399
           Summary: pointer substraction causes coredump with ftrapv on
                    edge case
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: baiwfg2 at gmail dot com
  Target Milestone: ---

The demo code is :

```c
#include <stdio.h>
#include <stdint.h>
#include <signal.h>
#include <assert.h>

int main() {
    {
        char *p = (char *)0x80000001;
        char *q = (char *)0x7fffffff;
        uint32_t w = p - q;
        printf("32 bit, w1=%u\n", w);
    }

    {
        char *p = (char *)0x7fffffffffffffff;
        char *q = (char *)0x7ffffffffffffffd;
        uint32_t w2 = p - q;
        printf("w2=%u\n", w2);
    }

    {
        char *p = (char *)0x8000000000000003;
        char *q = (char *)0x8000000000000001;
        uint32_t w3 = p - q;
        printf("w3=%u\n", w3);
    }

    {
        char *p = (char *)0x8000000000000001;
        char *q = (char *)0x0000000000000001;
        uint32_t w4 = p - q;
        printf("w4=%u\n", w4); // ans is 0, not crash under -ftrapv
    }

    {
        char *p = (char *)0x8000000000000001;
        char *q = (char *)0x7fffffffffffffff;
        uint32_t w5 = (uintptr_t)p - (uintptr_t)q;
        printf("w5=%u\n", w5);
    }

    {
        char *p = (char *)0x8000000000000001; // use uint8_t also crash
        char *q = (char *)0x7fffffffffffffff; // use smaller num
0x0000000000000011, also crash
        uint32_t w6 = p - q;
        printf("w6=%u\n", w6); // crash under gcc -ftrapv, not crash under
clang -ftrapv
    }

    return 0;
}
```

The statement w6 = p - q cause coredump. But what program actually means do
pointer unsigned arithmetic operation. How can I make it right(that is, output
2) with ftrapv option ? I find it's ok with clang -ftrapv .

This happens on many gcc versions.