Compute dependency graph in string_refinement

This is only activated with the debug option.
This can be useful to detect problem in the solver or in the dependency
graph computation.

Author: romainbrenguier

src/solvers/refinement/string_refinement.cpp

@@ -679,6 +679,15 @@ decision_proceduret::resultt string_refinementt::dec_solve()
 
 #ifdef DEBUG
   output_equations(debug(), equations, ns);
+
+  dependency_grapht dependencies;
+  for(const equal_exprt &eq : equations)
+    add_node(dependencies, eq, generator.array_pool);
+
+  debug() << "dec_solve: dependency graph:" << eom;
+  dependencies.output_dot(debug(), [&](const exprt &e) { // NOLINT
+    return from_expr(ns, "", e);
+  });
 #endif
 
   debug() << "dec_solve: Replace function applications" << eom;