Recommit r231221: "Devirtualize ~parser<T> by making it protected in base classes and making derived classes final"

Reverted in r231254 due to a self-hosting crash of Clang (see Clang
PR22793). Workaround the crash by using {} instead of = default to
define a dtor.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231274 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/CommandLine.h

@@ -714,7 +714,6 @@ class basic_parser_impl { // non-template implementation of basic_parser<t>
 public:
   basic_parser_impl(Option &O) {}
 
-  virtual ~basic_parser_impl() {}
 
   enum ValueExpected getValueExpectedFlagDefault() const {
     return ValueRequired;
@@ -743,6 +742,7 @@ public:
   virtual void anchor();
 
 protected:
+  ~basic_parser_impl() = default;
   // A helper for basic_parser::printOptionDiff.
   void printOptionName(const Option &O, size_t GlobalWidth) const;
 };
@@ -755,12 +755,16 @@ public:
   basic_parser(Option &O) : basic_parser_impl(O) {}
   typedef DataType parser_data_type;
   typedef OptionValue<DataType> OptVal;
+
+protected:
+  // Workaround Clang PR22793
+  ~basic_parser() {}
 };
 
 //--------------------------------------------------
 // parser<bool>
 //
-template <> class parser<bool> : public basic_parser<bool> {
+template <> class parser<bool> final : public basic_parser<bool> {
 public:
   parser(Option &O) : basic_parser(O) {}
 
@@ -787,7 +791,8 @@ EXTERN_TEMPLATE_INSTANTIATION(class basic_parser<bool>);
 
 //--------------------------------------------------
 // parser<boolOrDefault>
-template <> class parser<boolOrDefault> : public basic_parser<boolOrDefault> {
+template <>
+class parser<boolOrDefault> final : public basic_parser<boolOrDefault> {
 public:
   parser(Option &O) : basic_parser(O) {}
 
@@ -813,7 +818,7 @@ EXTERN_TEMPLATE_INSTANTIATION(class basic_parser<boolOrDefault>);
 //--------------------------------------------------
 // parser<int>
 //
-template <> class parser<int> : public basic_parser<int> {
+template <> class parser<int> final : public basic_parser<int> {
 public:
   parser(Option &O) : basic_parser(O) {}
 
@@ -835,7 +840,7 @@ EXTERN_TEMPLATE_INSTANTIATION(class basic_parser<int>);
 //--------------------------------------------------
 // parser<unsigned>
 //
-template <> class parser<unsigned> : public basic_parser<unsigned> {
+template <> class parser<unsigned> final : public basic_parser<unsigned> {
 public:
   parser(Option &O) : basic_parser(O) {}
 
@@ -858,7 +863,8 @@ EXTERN_TEMPLATE_INSTANTIATION(class basic_parser<unsigned>);
 // parser<unsigned long long>
 //
 template <>
-class parser<unsigned long long> : public basic_parser<unsigned long long> {
+class parser<unsigned long long> final
+    : public basic_parser<unsigned long long> {
 public:
   parser(Option &O) : basic_parser(O) {}
 
@@ -881,7 +887,7 @@ EXTERN_TEMPLATE_INSTANTIATION(class basic_parser<unsigned long long>);
 //--------------------------------------------------
 // parser<double>
 //
-template <> class parser<double> : public basic_parser<double> {
+template <> class parser<double> final : public basic_parser<double> {
 public:
   parser(Option &O) : basic_parser(O) {}
 
@@ -903,7 +909,7 @@ EXTERN_TEMPLATE_INSTANTIATION(class basic_parser<double>);
 //--------------------------------------------------
 // parser<float>
 //
-template <> class parser<float> : public basic_parser<float> {
+template <> class parser<float> final : public basic_parser<float> {
 public:
   parser(Option &O) : basic_parser(O) {}
 
@@ -925,7 +931,7 @@ EXTERN_TEMPLATE_INSTANTIATION(class basic_parser<float>);
 //--------------------------------------------------
 // parser<std::string>
 //
-template <> class parser<std::string> : public basic_parser<std::string> {
+template <> class parser<std::string> final : public basic_parser<std::string> {
 public:
   parser(Option &O) : basic_parser(O) {}
 
@@ -950,7 +956,7 @@ EXTERN_TEMPLATE_INSTANTIATION(class basic_parser<std::string>);
 //--------------------------------------------------
 // parser<char>
 //
-template <> class parser<char> : public basic_parser<char> {
+template <> class parser<char> final : public basic_parser<char> {
 public:
   parser(Option &O) : basic_parser(O) {}