debug code because I can't reproduce the appveyor error on my machine

Author: polgreen

src/util/graph.h

@@ -479,6 +479,7 @@ void grapht<N>::disconnect_unreachable(node_indext src)
   disconnect_unreachable(source_nodes);
 }
 
+#include <iostream>
 /// Removes any edges between nodes in a graph that are unreachable
 /// from a vector of start nodes.
 /// \param src: vector of indices of start nodes
@@ -488,8 +489,10 @@ void grapht<N>::disconnect_unreachable(const std::vector<node_indext> &src)
   std::vector<node_indext> reachable = get_reachable(src, true);
   std::sort(reachable.begin(), reachable.end());
   std::size_t reachable_idx = 0;
+  std::cout<< "reachable size "<< reachable.size()<<std::endl;
   for(std::size_t i = 0; i < nodes.size(); i++)
   {
+    std::cout<<"reachable_idx "<< reachable_idx <<" reachable[reachable_idx] "<< reachable[reachable_idx]<<" i "<< i <<std::endl;
     if(reachable_idx >= reachable.size())
       return;
 
@@ -529,7 +532,6 @@ void get_reachable(
   while(!stack.empty())
   {
     auto n = stack.back();
-    stack.pop_back();
     for_each_successor(n, [&](const nodet &node) {
       if(set.insert(node).second)
         stack.push_back(node);

unit/analyses/disconnect_unreachable_nodes_in_graph.cpp

@@ -188,7 +188,11 @@ SCENARIO("graph", "[core][util][graph]")
       for(node_indext i = 0; i < exported.size(); ++i)
         nodes_by_name[exported[i].function] = i;
 
+      std::cout<<"original graph:\n";
+      exported.output_dot(std::cout);
       exported.disconnect_unreachable(nodes_by_name["A"]);
+      std::cout<<"new graph \n";
+      exported.output_dot(std::cout);
 
       THEN("We expect edges A -> { A, B }, B -> { C, D }")
       {
@@ -208,13 +212,17 @@ SCENARIO("graph", "[core][util][graph]")
       THEN("We expect {F} to be able to reach F")
       {
         std::set<irep_idt> predecessors = get_reaching_functions(exported, "F");
+        for(const auto &p: predecessors)
+          std::cout<<"predecessor of F: "<< nodes_by_name[p]<<std::endl;
         REQUIRE(predecessors.size() == 1);
         REQUIRE(predecessors.count("F"));
       }
 
       THEN("We expect {G} to be able to reach G")
       {
         std::set<irep_idt> predecessors = get_reaching_functions(exported, "G");
+        for(const auto &p: predecessors)
+          std::cout<<"predecessor of G: "<< nodes_by_name[p]<<std::endl;
         REQUIRE(predecessors.size() == 1);
         REQUIRE(predecessors.count("G"));
       }