Use sharing_map instead of unordered_map for cache

Author: TGWDB

src/goto-symex/goto_state.cpp

@@ -16,21 +16,21 @@ optionalt<symbol_exprt>
 dereference_cachet::lookup(const exprt &dereference) const
 {
   auto it = cache.find(dereference);
-  if(it == cache.end())
+  if(it == nullopt)
   {
     return nullopt;
   }
   else
   {
-    return {it->second};
+    return {it->get()};
   }
 }
 
 void dereference_cachet::insert(
   exprt new_cached_expr,
   symbol_exprt new_cache_symbol)
 {
-  cache.emplace(std::move(new_cached_expr), std::move(new_cache_symbol));
+  cache.insert(std::move(new_cached_expr), std::move(new_cache_symbol));
 }
 
 /// Print the constant propagation map in a human-friendly format.

src/goto-symex/goto_state.h

@@ -31,7 +31,7 @@ class goto_symex_statet;
 struct dereference_cachet
 {
 private:
-  std::unordered_map<exprt, symbol_exprt, irep_hash> cache;
+  sharing_mapt<exprt, symbol_exprt, false, irep_hash> cache;
 
 public:
   optionalt<symbol_exprt> lookup(const exprt &pointer) const;