* posix/regcomp.c (parse_expression): Set the bit since the back
reference is used in the regular expression.
* posix/regex_internal.c (re_node_set_init_1): Make it clean in case
of malloc failure.
(re_node_set_init_copy): Likewise.
* posix/regex_internal.h (state_array_t): New structure.
(re_sub_match_last_t): Likewise.
(re_sub_match_top_t): Likewise.
(re_match_context_t): Add new members.
(re_dfa_t): Likewise.
* posix/regexec.c (re_search_internal): Invoke prune_impossible_nodes
to check the matching is really correct, and retry if failed.
Move the routin pruning the impossible nodes from here, ...
(prune_impossible_nodes): To this function.
(check_matching): Invoke check_subexp_matching_top, and replace
redundant checking with transit_state_bkref invocation.
(proceed_next_node): Replace strncmp with memcmp. Reported by
Paolo Bonzini <bonzini@gnu.org>.
(update_cur_sifted_state): Remove search_subexp invocation.
(search_subexp): Remove this function.
(check_dst_limits_calc_pos): Use search_cur_bkref_entry for
optimization.
(sift_states_bkref): Use search_cur_bkref_entry for optimization.
Remove unused invocation of match_ctx_add_entry.
(transit_state): Invoke check_subexp_matching_top.
(check_subexp_matching_top): New function.
(transit_state_bkref): Remove unused array.
Merge transit_state_bkref_loop.
(transit_state_bkref_loop): Use get_subexp instead of
sift_states_backward. Use search_cur_bkref_entry for optimization.
Merge this function to transit_state_bkref.
(get_subexp): New function.
(get_subexp_sub): Likewise.
(find_subexp_node): Likewise.
(check_arrival): Likewise.
(check_arrival_expand_ecl): Likewise.
(check_arrival_expand_ecl_sub): Likewise.
(expand_bkref_cache): Likewise.
(match_ctx_init): Initialize new members.
(match_ctx_clean): New function.
(match_ctx_free): Release new members.
(match_ctx_free_subtops): New function.
(match_ctx_add_entry): Fix indent.
(search_cur_bkref_entry): New function.
(match_ctx_add_subtop): Likewise.
(match_ctx_add_sublast): Likewise.