[Bug sanitizer/78106] New: ASAN can't find heap-use-after-free with -O1

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78106

            Bug ID: 78106
           Summary: ASAN can't find heap-use-after-free with -O1
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: marxin at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org
  Target Milestone: ---

Running following code snippet:

int *variable;

void release()
{
  __builtin_free (variable);
}

int main2(int argc)
{
  *variable = 2;

  if (argc <= 5)
    asm volatile ("call release");

  *variable = 2;
  __builtin_abort ();

  return 0;
}

int main(int argc, char **argv)
{
  variable = __builtin_malloc (sizeof(int));
  return main2(argc);
}

$ gcc asm-test.c -fsanitize=address -O1 && ./a.out 
Aborted (core dumped)

$ gcc asm-test.c -fsanitize=address -O0 && ./a.out 
=================================================================
==7550==ERROR: AddressSanitizer: heap-use-after-free on address 0x60200000eff0
at pc 0x000000400885 bp 0x7fff26b46520 sp 0x7fff26b46518
WRITE of size 4 at 0x60200000eff0 thread T0
    #0 0x400884 in main2 (/tmp/a.out+0x400884)
    #1 0x4008be in main (/tmp/a.out+0x4008be)
    #2 0x7ff63783a290 in __libc_start_main (/lib64/libc.so.6+0x20290)
    #3 0x400719 in _start (/tmp/a.out+0x400719)
...

I'm having patch for that that I'll send shortly.