Function prune_impossible_nodes

compat/regex/regexec.c:939–1028

    match_ctx_free (&mctx);
  re_string_destruct (&mctx.input);
  return err;
}

static reg_errcode_t
prune_impossible_nodes (re_match_context_t *mctx)
{
  const re_dfa_t *const dfa = mctx->dfa;
  int halt_node, match_last;
  reg_errcode_t ret;
  re_dfastate_t **sifted_states;
  re_dfastate_t **lim_states = NULL;
  re_sift_context_t sctx;
#ifdef DEBUG
  assert (mctx->state_log != NULL);
#endif
  match_last = mctx->match_last;
  halt_node = mctx->last_node;

  /* Avoid overflow.  */
  if (BE (SIZE_MAX / sizeof (re_dfastate_t *) <= match_last, 0))
    return REG_ESPACE;

  sifted_states = re_malloc (re_dfastate_t *, match_last + 1);
  if (BE (sifted_states == NULL, 0))
    {
      ret = REG_ESPACE;
      goto free_return;
    }
  if (dfa->nbackref)
    {
      lim_states = re_malloc (re_dfastate_t *, match_last + 1);
      if (BE (lim_states == NULL, 0))
	{
	  ret = REG_ESPACE;
	  goto free_return;
	}
      while (1)
	{
	  memset (lim_states, '\0',
		  sizeof (re_dfastate_t *) * (match_last + 1));
	  sift_ctx_init (&sctx, sifted_states, lim_states, halt_node,
			 match_last);
	  ret = sift_states_backward (mctx, &sctx);
	  re_node_set_free (&sctx.limits);
	  if (BE (ret != REG_NOERROR, 0))
	      goto free_return;
	  if (sifted_states[0] != NULL || lim_states[0] != NULL)
	    break;
	  do
	    {
	      --match_last;
	      if (match_last < 0)
		{
		  ret = REG_NOMATCH;
		  goto free_return;
		}
	    } while (mctx->state_log[match_last] == NULL
		     || !mctx->state_log[match_last]->halt);