Pass merge_location to newly merged object

Extend region-contextt to pick this up if it needs to use it. Ever other
object just ignores it.

Author: jezhiggins

regression/goto-analyzer/region-tracking/main.c

@@ -0,0 +1,10 @@
+int main()
+{
+  int non_det;
+  int x = 0;
+
+  if(non_det)
+    x = 2;
+  else
+    x = 3;
+}

regression/goto-analyzer/region-tracking/test-region-tracking.desc

@@ -0,0 +1,7 @@
+CORE
+main.c
+--variable-sensitivity --vsd-values set-of-constants --vsd-region-tracking --show
+^EXIT=0$
+^SIGNAL=0$
+^main::1::x .* value-set-begin: 2, 3 :value-set-end @ \[7\]
+--

regression/goto-analyzer/region-tracking/test-write-location.desc

@@ -0,0 +1,7 @@
+CORE
+main.c
+--variable-sensitivity --vsd-values set-of-constants --show
+^EXIT=0$
+^SIGNAL=0$
+^main::1::x .* value-set-begin: 2, 3 :value-set-end @ \[4, 6\]
+--

src/analyses/variable-sensitivity/abstract_environment.cpp

@@ -364,8 +364,9 @@ bool abstract_environmentt::merge(
   bool modified = false;
   for(const auto &entry : env.map.get_delta_view(map))
   {
-    auto merge_result =
-      abstract_objectt::merge(entry.get_other_map_value(), entry.m, widen_mode);
+    auto merge_result = abstract_objectt::merge(
+      entry.get_other_map_value(), entry.m, merge_location, widen_mode);
+
     modified |= merge_result.modified;
     map.replace(entry.k, merge_result.object);
   }

src/analyses/variable-sensitivity/abstract_object.cpp

@@ -206,6 +206,19 @@ void abstract_objectt::output(
   }
 }
 
+abstract_objectt::combine_result abstract_objectt::merge(
+  const abstract_object_pointert &op1,
+  const abstract_object_pointert &op2,
+  const locationt &merge_location,
+  const widen_modet &widen_mode)
+{
+  abstract_object_pointert result = merge(op1, op2, widen_mode).object;
+  result = result->merge_location_context(merge_location);
+
+  // If no modifications, we will return the original pointer
+  return {result, result != op1};
+}
+
 abstract_objectt::combine_result abstract_objectt::merge(
   const abstract_object_pointert &op1,
   const abstract_object_pointert &op2,
@@ -214,6 +227,7 @@ abstract_objectt::combine_result abstract_objectt::merge(
   abstract_object_pointert result = op1->should_use_base_merge(op2)
                                       ? op1->abstract_object_merge(op2)
                                       : op1->merge(op2, widen_mode);
+
   // If no modifications, we will return the original pointer
   return {result, result != op1};
 }
@@ -247,6 +261,12 @@ abstract_objectt::write_location_context(const locationt &location) const
   return shared_from_this();
 }
 
+abstract_object_pointert
+abstract_objectt::merge_location_context(const locationt &location) const
+{
+  return shared_from_this();
+}
+
 void abstract_objectt::dump_map(
   std::ostream out,
   const abstract_objectt::shared_mapt &m)

src/analyses/variable-sensitivity/abstract_object.h

@@ -264,6 +264,11 @@ class abstract_objectt : public std::enable_shared_from_this<abstract_objectt>
     abstract_object_pointert object;
     bool modified;
   };
+  static combine_result merge(
+    const abstract_object_pointert &op1,
+    const abstract_object_pointert &op2,
+    const locationt &merge_location,
+    const widen_modet &widen_mode);
   static combine_result merge(
     const abstract_object_pointert &op1,
     const abstract_object_pointert &op2,
@@ -289,7 +294,7 @@ class abstract_objectt : public std::enable_shared_from_this<abstract_objectt>
   meet(const abstract_object_pointert &other) const;
 
   /**
-   * Update the location context for an abstract object.
+   * Update the write location context for an abstract object.
    *
    * \param location the location to be updated
    *
@@ -299,6 +304,17 @@ class abstract_objectt : public std::enable_shared_from_this<abstract_objectt>
   virtual abstract_object_pointert
   write_location_context(const locationt &location) const;
 
+  /**
+   * Update the merge location context for an abstract object.
+   *
+   * \param location the location to be updated
+   *
+   * \return a clone of this abstract object with its location context
+   * updated
+   */
+  virtual abstract_object_pointert
+  merge_location_context(const locationt &location) const;
+
   // Const versions must perform copy-on-write
   abstract_object_pointert make_top() const
   {

src/analyses/variable-sensitivity/region_context.cpp

@@ -202,3 +202,14 @@ bool region_contextt::has_been_modified(
   // in the other, since a set can assume at most one match
   return before_context->get_location() != get_location();
 }
+
+abstract_object_pointert
+region_contextt::merge_location_context(const locationt &location) const
+{
+  if(assign_location.has_value())
+    return shared_from_this();
+
+  auto update = std::dynamic_pointer_cast<region_contextt>(mutable_clone());
+  update->assign_location = location;
+  return update;
+}

src/analyses/variable-sensitivity/region_context.h

@@ -64,6 +64,9 @@ class region_contextt : public context_abstract_objectt
 
   bool has_been_modified(const abstract_object_pointert &before) const override;
 
+  abstract_object_pointert
+  merge_location_context(const locationt &location) const override;
+
   void output(std::ostream &out, const class ai_baset &ai, const namespacet &ns)
     const override;