[Bug c/123600] New: && unary operator (Labels as Values) issue when using optimisation level 2 (and higher)

[colin.i.king at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123600

            Bug ID: 123600
           Summary: && unary operator (Labels as Values) issue when using
                    optimisation level 2 (and higher)
           Product: gcc
           Version: 15.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: colin.i.king at gmail dot com
  Target Milestone: ---

Optimisation level O2 and above on the following code returns the same address
for labels l1, l2 and l3, tested on gcc-10 to gcc 15.2, same issue occurs. 
Testing with other compilers (clang, pcc, tcc this works OK and returns the
correct addresses)

Tested on x86-64 only.

Reproducer:

$ cat bug.c
#include <stdio.h>
#include <unistd.h>
#include <inttypes.h>

const uintptr_t *labels(void)
{
        static const uintptr_t addrs[] = {
                (uintptr_t)&&l1,
                (uintptr_t)&&l2,
                (uintptr_t)&&l3
        };
l1:
        printf("%p\n", &&l1);
l2:
        printf("%p\n", &&l2);
l3:
        return addrs;
}

int main(void)
{
        const uintptr_t *ptr = labels();

        printf("ptr[0] %" PRIxPTR "\n", ptr[0]);
        printf("ptr[1] %" PRIxPTR "\n", ptr[1]);
        printf("ptr[2] %" PRIxPTR "\n", ptr[2]);

        return 0;
}

Tests:

$ gcc-15 -O0 bug.c
$ ./a.out 
0x55555555513d
0x55555555515b
ptr[0] 55555555513d
ptr[1] 55555555515b
ptr[2] 555555555179

$ gcc-15 -O1 bug.c
$ ./a.out 
0x55555555513a
0x555555555155
ptr[0] 55555555513a
ptr[1] 555555555155
ptr[2] 555555555169

$ gcc-15 -O2 bug.c
$ ./a.out 
0x555555555190
0x555555555190
ptr[0] 555555555190
ptr[1] 555555555190
ptr[2] 555555555190

$ gcc-15 -O3 bug.c
$ ./a.out 
0x555555555190
0x555555555190
ptr[0] 555555555190
ptr[1] 555555555190
ptr[2] 555555555190