[Bug target/100049] loop counter double increment with longjmp inside

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100049

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The testcase would be
#include <stdio.h>
#include <setjmp.h>

struct ctx { int cnt; struct S { jmp_buf env; } jmp_buf[4]; } ctx;

__attribute__((noipa)) void
do_jump (void)
{
  --ctx.cnt;
  longjmp (ctx.jmp_buf[ctx.cnt].env, 1);
}

static void
test (void)
{
  for (unsigned i = 0; i < 19; i++)
    {
      printf ("Message %d\n", i);
      if (setjmp ((&ctx.jmp_buf[ctx.cnt])->env) == 0)
        {
          ++ctx.cnt;
          do_jump ();
          --ctx.cnt;
        }
    }
}

int
main ()
{
  test ();
  return 0;
}

And gcc clearly warns about that with -O2 -W -Wall:
pr100049.c: In function ‘test’:
pr100049.c:16:17: warning: variable ‘i’ might be clobbered by ‘longjmp’ or
‘vfork’ [-Wclobbered]
   16 |   for (unsigned i = 0; i < 19; i++)
      |                 ^