cmDefinitions: Don't store parent lookups

When looking up scopes, it is faster to not store the lookup locally to
keep the maps smaller and avoid extra allocations and rebalancing.

Source/cmDefinitions.cxx

@@ -28,7 +28,7 @@ void cmDefinitions::Reset(cmDefinitions* parent)
 
 //----------------------------------------------------------------------------
 cmDefinitions::Def const&
-cmDefinitions::GetInternal(const std::string& key)
+cmDefinitions::GetInternal(const std::string& key) const
 {
   MapType::const_iterator i = this->Map.find(key);
   if(i != this->Map.end())
@@ -37,9 +37,8 @@ cmDefinitions::GetInternal(const std::string& key)
     }
   else if(cmDefinitions* up = this->Up)
     {
-    // Query the parent scope and store the result locally.
-    Def def = up->GetInternal(key);
-    return this->Map.insert(MapType::value_type(key, def)).first->second;
+    // Query the parent scope.
+    return up->GetInternal(key);
     }
   return this->NoDef;
 }
@@ -71,12 +70,25 @@ cmDefinitions::SetInternal(const std::string& key, Def const& def)
 }
 
 //----------------------------------------------------------------------------
-const char* cmDefinitions::Get(const std::string& key)
+const char* cmDefinitions::Get(const std::string& key) const
 {
   Def const& def = this->GetInternal(key);
   return def.Exists? def.c_str() : 0;
 }
 
+//----------------------------------------------------------------------------
+void cmDefinitions::Pull(const std::string& key)
+{
+  if (this->Up)
+    {
+    Def const& def = this->Up->GetInternal(key);
+    if (def.Exists)
+      {
+      this->SetInternal(key, def);
+      }
+    }
+}
+
 //----------------------------------------------------------------------------
 const char* cmDefinitions::Set(const std::string& key, const char* value)
 {

Source/cmDefinitions.h

@@ -33,9 +33,11 @@ public:
   /** Returns the parent scope, if any.  */
   cmDefinitions* GetParent() const { return this->Up; }
 
-  /** Get the value associated with a key; null if none.
-      Store the result locally if it came from a parent.  */
-  const char* Get(const std::string& key);
+  /** Get the value associated with a key; null if none. */
+  const char* Get(const std::string& key) const;
+
+  /** Pull a variable from the parent. */
+  void Pull(const std::string& key);
 
   /** Set (or unset if null) a value associated with a key.  */
   const char* Set(const std::string& key, const char* value);
@@ -73,7 +75,7 @@ private:
   MapType Map;
 
   // Internal query and update methods.
-  Def const& GetInternal(const std::string& key);
+  Def const& GetInternal(const std::string& key) const;
   Def const& SetInternal(const std::string& key, Def const& def);
 
   // Implementation of Closure() method.

Source/cmMakefile.cxx

@@ -4422,7 +4422,7 @@ void cmMakefile::RaiseScope(const std::string& var, const char *varDef)
   if(cmDefinitions* up = cur.GetParent())
     {
     // First localize the definition in the current scope.
-    cur.Get(var);
+    cur.Pull(var);
 
     // Now update the definition in the parent scope.
     up->Set(var, varDef);