Speedup is_weak_scc() if all transitions in the SCC are accepting.

* src/tgbaalgos/isweakscc.cc, src/tgbaalgos/isweakscc.hh: Speedup when
all transitions are accepting.

src/tgbaalgos/isweakscc.cc

@@ -71,6 +71,10 @@ namespace spot
     // If no cycle is accepting, the SCC is weak.
     if (!map.accepting(scc))
       return true;
+    // If all transitions use all acceptance conditions, the SCC is weak.
+    if (map.useful_acc_of(scc) ==
+	bdd_support(map.get_aut()->neg_acceptance_conditions()))
+      return true;
     // If the SCC is accepting, but one cycle is not, the SCC is not
     // weak.
     weak_checker w(map);

src/tgbaalgos/isweakscc.hh

@@ -35,9 +35,11 @@ namespace spot
   ///
   /// The scc_map \a map should have been built already.  The absence
   /// of accepting cycle is easy to check (the scc_map can tell
-  /// whether the SCC is non-accepting already).  For the accepting
-  /// SCCs, this function enumerates all cycles in the given SCC (it
-  /// stops if it find a non-accepting cycle).
+  /// whether the SCC is non-accepting already).  Similarly, an SCC in
+  /// which all transitions belong to all acceptance sets is
+  /// necessarily weak.
+  /// For other accepting SCCs, this function enumerates all cycles in
+  /// the given SCC (it stops if it find a non-accepting cycle).
   bool is_weak_scc(scc_map& map, unsigned scc);
 
   /// @}