degen: detect superfluous SCCs and remove them
Suggested by Maximilien Colange. * spot/twaalgos/degen.cc: If the output has more SCC than the input, detect useless SCCs and remove them. * spot/twaalgos/postproc.cc, spot/twaalgos/postproc.hh, spot/twaalgos/degen.hh: Add support for a degen-remscc option. * bin/spot-x.cc, NEWS: Document it. * tests/core/degenscc.test: New file. * tests/Makefile.am: Add it. * tests/core/det.test: Lower some expected size (yay!).
This commit is contained in:
Alexandre Duret-Lutz
parent
ce5e3b654f
commit
900b344c9a
9 changed files with 147 additions and 22 deletions
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@ -26,6 +26,7 @@
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#include <vector>
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#include <algorithm>
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#include <iterator>
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#include <memory>
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#include <spot/twaalgos/sccinfo.hh>
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#include <spot/twa/bddprint.hh>
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@ -240,7 +241,8 @@ namespace spot
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twa_graph_ptr
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degeneralize_aux(const const_twa_graph_ptr& a, bool use_z_lvl,
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bool use_cust_acc_orders, int use_lvl_cache,
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bool skip_levels, bool ignaccsl)
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bool skip_levels, bool ignaccsl,
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bool remove_extra_scc)
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{
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if (!a->acc().is_generalized_buchi())
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throw std::runtime_error
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@ -249,7 +251,10 @@ namespace spot
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throw std::runtime_error
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("degeneralize() does not support alternation");
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bool use_scc = use_lvl_cache || use_cust_acc_orders || use_z_lvl;
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bool use_scc = (use_lvl_cache
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|| use_cust_acc_orders
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|| use_z_lvl
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|| remove_extra_scc);
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bdd_dict_ptr dict = a->get_dict();
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@ -305,12 +310,11 @@ namespace spot
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std::vector<std::pair<unsigned, bool>> lvl_cache(a->num_states());
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// Compute SCCs in order to use any optimization.
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scc_info* m = nullptr;
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if (use_scc)
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m = new scc_info(a);
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std::unique_ptr<scc_info> m = use_scc ?
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std::make_unique<scc_info>(a) : nullptr;
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// Cache for common outgoing/incoming acceptances.
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inout_acc inout(a, m);
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inout_acc inout(a, m.get());
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queue_t todo;
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@ -337,7 +341,7 @@ namespace spot
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if (!skip_levels)
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break;
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}
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// There is not accepting level for TBA, let reuse level 0.
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// There is no accepting level for TBA, let reuse level 0.
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if (!want_sba && s.second == order.size())
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s.second = 0;
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}
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@ -373,9 +377,8 @@ namespace spot
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// Level cache stores one encountered level for each state
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// (the value of use_lvl_cache determinates which level
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// should be remembered).
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// When entering an SCC first the lvl_cache is checked.
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// If such state exists level from chache is used.
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// should be remembered). This cache is used when
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// re-entering the SCC.
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if (use_lvl_cache)
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{
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unsigned lvl = ds.second;
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@ -612,10 +615,49 @@ namespace spot
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std::cout << '\n';
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orders.print();
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#endif
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delete m;
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res->merge_edges();
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unsigned res_ns = res->num_states();
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if (!remove_extra_scc || res_ns <= a->num_states())
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return res;
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scc_info si_res(res);
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unsigned res_scc_count = si_res.scc_count();
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if (res_scc_count <= m->scc_count())
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return res;
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// If we reach this place, we have more SCCs in the output than
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// in the input. This means that we have created some redundant
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// SCCs. Often, these are trivial SCCs created in front of
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// their larger sisters, because we did not pick the correct
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// level when entering the SCC for the first time, and the level
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// we picked has not been seen again when exploring the SCC.
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// But it could also be the case that by entering the SCC in two
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// different ways, we create two clones of the SCC (I haven't
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// encountered any such case, but I do not want to rule it out
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// in the code below).
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//
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// Now we will iterate over the SCCs in topological order to
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// remember the "bottomost" SCCs that contain each original
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// state. If an original state is duplicated in a higher SCC,
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// it can be shunted away. Amen.
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std::vector<unsigned> bottomost_occurence(a->num_states());
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{
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unsigned n = res_scc_count;
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do
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for (unsigned s: si_res.states_of(--n))
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bottomost_occurence[(*orig_states)[s]] = s;
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while (n);
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}
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std::vector<unsigned> retarget(res_ns);
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for (unsigned n = 0; n < res_ns; ++n)
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{
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unsigned other = bottomost_occurence[(*orig_states)[n]];
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retarget[n] = (si_res.scc_of(n) != si_res.scc_of(other)) ? other : n;
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}
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for (auto& e: res->edges())
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e.dst = retarget[e.dst];
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res->purge_unreachable_states();
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return res;
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}
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}
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@ -623,7 +665,8 @@ namespace spot
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twa_graph_ptr
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degeneralize(const const_twa_graph_ptr& a,
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bool use_z_lvl, bool use_cust_acc_orders,
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int use_lvl_cache, bool skip_levels, bool ignaccsl)
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int use_lvl_cache, bool skip_levels, bool ignaccsl,
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bool remove_extra_scc)
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{
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// If this already a degeneralized digraph, there is nothing we
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// can improve.
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@ -631,13 +674,15 @@ namespace spot
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return std::const_pointer_cast<twa_graph>(a);
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return degeneralize_aux<true>(a, use_z_lvl, use_cust_acc_orders,
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use_lvl_cache, skip_levels, ignaccsl);
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use_lvl_cache, skip_levels, ignaccsl,
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remove_extra_scc);
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}
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twa_graph_ptr
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degeneralize_tba(const const_twa_graph_ptr& a,
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bool use_z_lvl, bool use_cust_acc_orders,
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int use_lvl_cache, bool skip_levels, bool ignaccsl)
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int use_lvl_cache, bool skip_levels, bool ignaccsl,
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bool remove_extra_scc)
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{
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// If this already a degeneralized digraph, there is nothing we
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// can improve.
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@ -645,6 +690,7 @@ namespace spot
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return std::const_pointer_cast<twa_graph>(a);
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return degeneralize_aux<false>(a, use_z_lvl, use_cust_acc_orders,
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use_lvl_cache, skip_levels, ignaccsl);
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use_lvl_cache, skip_levels, ignaccsl,
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remove_extra_scc);
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}
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}
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@ -41,7 +41,9 @@ namespace spot
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/// smallest number, 3 to keep the largest level, and 1 to keep the
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/// first level found). If \a ignaccsl is set, we do not directly
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/// jump to the accepting level if the entering state has an
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/// accepting self-loop.
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/// accepting self-loop. If \a remove_extra_scc is set (the default)
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/// we ensure that the output automaton has as many SCCs as the input
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/// by removing superfluous SCCs.
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///
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/// Any of these three options will cause the SCCs of the automaton
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/// \a a to be computed prior to its actual degeneralization.
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@ -65,13 +67,15 @@ namespace spot
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bool use_cust_acc_orders = false,
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int use_lvl_cache = 1,
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bool skip_levels = true,
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bool ignaccsl = false);
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bool ignaccsl = false,
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bool remove_extra_scc = true);
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SPOT_API twa_graph_ptr
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degeneralize_tba(const const_twa_graph_ptr& a, bool use_z_lvl = true,
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bool use_cust_acc_orders = false,
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int use_lvl_cache = 1,
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bool skip_levels = true,
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bool ignaccsl = false);
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bool ignaccsl = false,
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bool remove_extra_scc = true);
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/// \@}
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}
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@ -62,6 +62,7 @@ namespace spot
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degen_cache_ = opt->get("degen-lcache", 1);
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degen_lskip_ = opt->get("degen-lskip", 1);
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degen_lowinit_ = opt->get("degen-lowinit", 0);
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degen_remscc_ = opt->get("degen-remscc", 1);
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det_scc_ = opt->get("det-scc", 1);
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det_simul_ = opt->get("det-simul", 1);
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det_stutter_ = opt->get("det-stutter", 1);
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@ -142,7 +143,7 @@ namespace spot
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auto d = degeneralize(a,
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degen_reset_, degen_order_,
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degen_cache_, degen_lskip_,
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degen_lowinit_);
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degen_lowinit_, degen_remscc_);
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return do_sba_simul(d, ba_simul_);
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}
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@ -207,6 +207,7 @@ namespace spot
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int degen_cache_ = 1;
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bool degen_lskip_ = true;
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bool degen_lowinit_ = false;
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bool degen_remscc_ = true;
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bool det_scc_ = true;
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bool det_simul_ = true;
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bool det_stutter_ = true;
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