call graph helper interface to "disconnect unreachable functions"

Author: polgreen

src/analyses/call_graph_helpers.cpp

@@ -102,6 +102,15 @@ std::set<irep_idt> get_functions_reachable_within_n_steps(
     graph, start_functions, n, forwards);
 }
 
+void disconnect_unreachable_functions(
+  call_grapht::directed_grapht &graph,
+  const irep_idt &function)
+{
+  std::size_t start_idx = *(graph.get_node_index(function));
+  if(start_idx != optionalt<std::size_t>())
+    graph.disconnect_unreachable(start_idx);
+}
+
 std::set<irep_idt> get_shortest_function_path(
   const call_grapht::directed_grapht &graph,
   const irep_idt &src,

src/analyses/call_graph_helpers.h

@@ -82,4 +82,15 @@ std::set<irep_idt> get_functions_reachable_within_n_steps(
   std::size_t &n,
   bool forwards);
 
+/// Disconnects all functions in the call graph that are unreachable from
+/// a given start function.
+/// Removing nodes requires re-indexing, so instead we disconnect them, removing
+/// all in and out edges from those nodes.
+/// This speeds up backwards reachability.
+/// \param graph: call graph
+/// \param function: start function
+void disconnect_unreachable_functions(
+  call_grapht::directed_grapht &graph,
+  const irep_idt &function);
+
 #endif