🚀 go-pugleaf

I'm trying to determine whether a particular usage of setjmp is
sanctioned by the standard and I'm finding a compiler bug or whether my
usage is non-conforming.  My code boils down to this:

jmp_buf env[10];
int env_index;

void func(int *error_code)
{
  env_index = 0;

  if (*error_code = setjmp(env[env_index++])) {
    /* can env_index == 1 here? */
    return;
  }
  env_index--;
  longjmp(env[env_index], 1);
}

Should this code work correctly?  In particular, can a compiler
increment env_index after longjmp is called?

[Additional question because I'm curious:  what happens to
post-increments that are in parameters of the longjmp call?  Are they
ever executed?  I suppose the general question is where are the sequence
points when you're using setjmp and lonjmp?]

Thanks for any help,
michael j zehr