Revert "[Clang] Add __builtin_common_reference (#121199)"

This reverts commit 3b9e203.
Causes not-yet-understood semantic differences, see commits
on #121199.

Author: nico

clang/docs/LanguageExtensions.rst

@@ -1833,23 +1833,6 @@ Builtin type aliases
 
 Clang provides a few builtin aliases to improve the throughput of certain metaprogramming facilities.
 
-__builtin_common_reference
---------------------------
-
-.. code-block:: c++
-
-  template <template <class, class, template <class> class, template <class> class> class BasicCommonReferenceT,
-            template <class... Args> CommonTypeT,
-            template <class> HasTypeMember,
-            class HasNoTypeMember,
-            class... Ts>
-  using __builtin_common_reference = ...;
-
-This alias is used for implementing ``std::common_reference``. If ``std::common_reference`` should contain a ``type``
-member, it is an alias to ``HasTypeMember<TheCommonReference>``. Otherwse it is an alias to ``HasNoTypeMember``. The
-``CommonTypeT`` is usually ``std::common_type_t``. ``BasicCommonReferenceT`` is usually an alias template to
-``basic_common_reference<T, U, TX, UX>::type``.
-
 __builtin_common_type
 ---------------------
 

clang/include/clang/Basic/BuiltinTemplates.td

@@ -10,11 +10,11 @@ class TemplateArg<string name> {
   string Name = name;
 }
 
-class Template<list<TemplateArg> args, string name = ""> : TemplateArg<name> {
+class Template<list<TemplateArg> args, string name> : TemplateArg<name> {
   list<TemplateArg> Args = args;
 }
 
-class Class<string name = "", bit is_variadic = 0> : TemplateArg<name> {
+class Class<string name, bit is_variadic = 0> : TemplateArg<name> {
   bit IsVariadic = is_variadic;
 }
 
@@ -56,32 +56,6 @@ def __builtin_common_type : CPlusPlusBuiltinTemplate<
    Class<"HasNoTypeMember">,
    Class<"Ts", /*is_variadic=*/1>]>;
 
-// template <template <class,"
-//                     class,"
-//                     template <class> class,"
-//                     template <class> class> class BasicCommonReferenceT,"
-//           template <class... Args> class CommonTypeT,"
-//           template <class> class HasTypeMember,"
-//           class HasNoTypeMember,"
-//           class... Ts>"
-def __builtin_common_reference : CPlusPlusBuiltinTemplate<
-            [Template<[Class<>,
-                       Class<>,
-                       Template<[Class<>]>,
-                       Template<[Class<>]>], "BasicCommonReferenceT">,
-             Template<[Class<"Args", /*is_variadic=*/1>], "CommonTypeT">,
-             Template<[Class<>], "HasTypeMember">,
-             Class<"HasNoTypeMember">,
-             Class<"Ts", /*is_variadic=*/1>]>;
-
-foreach Ref = ["", "lvalue", "rvalue"] in {
-  foreach Const = ["", "const"] in {
-    foreach Volatile = ["", "volatile"] in {
-      def __clang_internal_xref_#Ref#Const#Volatile : CPlusPlusBuiltinTemplate<[Class<>]>;
-    }
-  }
-}
-
 // template <uint32_t Opcode,
 //           uint32_t Size,
 //           uint32_t Alignment,

clang/include/clang/Sema/Sema.h

@@ -15322,17 +15322,6 @@ class Sema final : public SemaBase {
   QualType BuiltinDecay(QualType BaseType, SourceLocation Loc);
   QualType BuiltinAddReference(QualType BaseType, UTTKind UKind,
                                SourceLocation Loc);
-
-  QualType BuiltinAddRValueReference(QualType BaseType, SourceLocation Loc) {
-    return BuiltinAddReference(BaseType, UnaryTransformType::AddRvalueReference,
-                               Loc);
-  }
-
-  QualType BuiltinAddLValueReference(QualType BaseType, SourceLocation Loc) {
-    return BuiltinAddReference(BaseType, UnaryTransformType::AddLvalueReference,
-                               Loc);
-  }
-
   QualType BuiltinRemoveExtent(QualType BaseType, UTTKind UKind,
                                SourceLocation Loc);
   QualType BuiltinRemoveReference(QualType BaseType, UTTKind UKind,
@@ -15347,9 +15336,6 @@ class Sema final : public SemaBase {
   QualType BuiltinChangeSignedness(QualType BaseType, UTTKind UKind,
                                    SourceLocation Loc);
 
-  bool BuiltinIsConvertible(QualType From, QualType To, SourceLocation Loc,
-                            bool CheckNothrow = false);
-
   bool BuiltinIsBaseOf(SourceLocation RhsTLoc, QualType LhsT, QualType RhsT);
 
   /// Ensure that the type T is a literal type.