Optimize InputValidator to avoid unnecessary copy when retrieving the input directly before a reset, and to release memory when reset.

lib/MetaProcessor/InputValidator.cpp

@@ -213,8 +213,13 @@ namespace cling {
     return Res;
   }
 
-  void InputValidator::reset() {
-    m_Input = "";
-    m_ParenStack.clear();
+  void InputValidator::reset(std::string* input) {
+    if (input) {
+      assert(input->empty() && "InputValidator::reset got non empty argument");
+      input->swap(m_Input);
+    } else
+      std::string().swap(m_Input);
+
+    std::deque<int>().swap(m_ParenStack);
   }
 } // end namespace cling

lib/MetaProcessor/InputValidator.h

@@ -54,12 +54,6 @@ namespace cling {
     ///
     ValidationResult validate(llvm::StringRef line);
 
-    ///\returns Reference to the collected input.
-    ///
-    std::string& getInput() {
-      return m_Input;
-    }
-
     ///\brief Retrieves the number of spaces that the next input line should be
     /// indented.
     ///
@@ -67,7 +61,9 @@ namespace cling {
 
     ///\brief Resets the collected input and its corresponding brace stack.
     ///
-    void reset();
+    ///\param[in] input - Grab the collected input before reseting.
+    ///
+    void reset(std::string* input = nullptr);
 
     ///\brief Return whether we are inside a mult-line comment
     ///

lib/MetaProcessor/MetaProcessor.cpp

@@ -169,8 +169,8 @@ namespace cling {
     }
 
     //  We have a complete statement, compile and execute it.
-    std::string input = m_InputValidator->getInput();
-    m_InputValidator->reset();
+    std::string input;
+    m_InputValidator->reset(&input);
     // if (m_Options.RawInput)
     //   compResLocal = m_Interp.declare(input);
     // else