[C2x] implement typeof and typeof_unqual

[aaron.ballman]

Summary

This implements WG14 N2927 and WG14 N2930, which together define the feature for typeof and typeof_unqual, which get the type of their argument as either fully qualified or fully unqualified. The argument to either operator is either a type name or an expression. If given a type name, the type information is pulled directly from the given name. If given an expression, the type information is pulled from the expression. Recursive use of these operators is allowed and has the expected behavior (the innermost operator is resolved to a type, and that's used to resolve the next layer of typeof specifier, until a fully resolved type is determined.

Note, we already supported typeof in GNU mode as a non-conforming extension and we are *not* exposing typeof_unqual as a non-conforming extension in that mode, nor are we exposing typeof or typeof_unqual as a nonconforming extension in other language modes. The GNU variant of typeof supports a form where the parentheses are elided from the operator when given an expression (e.g., typeof 0 i = 12;). When in C2x mode, we do not support this extension.

[aaron.ballman]

Updated the C status page accordingly.

[erichkeane]

I'm on the fence about re-using the same nodes for typeof and typeof_unqual. However, I have a preference to stop shuffling a bool around everywhere as parameters, and would like an enum (even if we store it as a bitfield : 1). Something like:

enum class TypeofKind {
       Typeof, TypeofUnqual };

I think improves readability in a bunch of places, AND gives us less work to do if we need to extend this node in the future.

clang/include/clang/AST/ASTContext.h

1718

Mild preference for an enum, instead of a bool here.

Alternatively, depending on your design below that I haven't seen yet, perhaps unqual versions of these functions?

clang/include/clang/AST/Type.h

4542

This constructor is smelly.... Am I to guess this does something like, "if E, type is the type of this, else it is the type passed in Can?"

4592

Are TypedefType's EVER canonical? Should you just be asserting 'Can' is canonical?

clang/lib/AST/ASTContext.cpp

12910

I'm unfamiliar with this function, but I would expect you MIGHT need to? If only because they are the same AST node. Should 'unqual' version be its own node? I'm on the fence, as it is a LOT of code to do so, but also ends up being simpler in many places.

clang/lib/AST/Type.cpp

3502

In what situation is getTypePtrOrNull required here? I would imagine that the 'isNull' check above should make sure we aren't in a situation where 'Ret' could be 'null' here? Same with the 'if_present'.

clang/lib/Lex/Preprocessor.cpp

61

Oh?

clang/lib/Parse/ParseDecl.cpp

7463

Should it be an error to !HasParens if IsUnqual.

clang/lib/Sema/SemaType.cpp

9137

(IsUnqual + 2) maybe? Or perhaps too cute.

[shafik]

clang/include/clang/AST/ASTContext.h

1717

I guess these are not purely extensions anymore?

clang/include/clang/AST/Type.h

1071

I think your trying to say this is more than the unqualified type but maybe just be more explicit like it returns the ununqualified type including atomic type qualification and type attributes which behave like a qualifier, such as an address space attribute

4601

It is interesting that you do getTypeofUnqualType in the constructor and then you have to do it again when desuguring. Is this tested in the tests?

[mizvekov]

clang/include/clang/AST/Type.h

4537

You can use the Type Bitfields in order to avoid bumping the size of the node.

clang/lib/AST/ASTContext.cpp

12910–12916

A qualified and an unqualified typeof could have the same underlying type, so this assert can trip.

I think what makes most sense is to unify them to a qualified typeof in case they differ, as that holds the underlying type unchanged:

return Ctx.getTypeOfType(Ctx.getQualifiedType(Underlying),
                         cast<TypeOfType>(X)->isUnqual() && cast<TypeOfType>(Y)->isUnqual());

[mizvekov]

clang/include/clang/AST/Type.h

4601

The constructor takes the canonical type, while this preserves the unmodified type (which can be accessed through getUnderlyingType).

[mizvekov]

clang/include/clang/AST/Type.h

4592

They can't, the original assert didn't make much sense.

Though asserting on CanonicalType being canonical is a job better left to the Type constructor, just so we don't have to repeat it everywhere.

[mizvekov]

clang/lib/AST/ASTContext.cpp

12910–12916

By the way, one thing to notice is the confusion regarding what is the underlying type of this node, the result of desugar() or the result of getUnderlyingType()?

On my previous post, I meant the former.

Maybe this is a good reason to rename getUnderlyingType() to getUnmodifiedType() or something similar?

[aaron.ballman]

In D134286#3803077, @erichkeane wrote:

I'm on the fence about re-using the same nodes for typeof and typeof_unqual. However, I have a preference to stop shuffling a bool around everywhere as parameters, and would like an enum (even if we store it as a bitfield : 1). Something like:

enum class TypeofKind {
       Typeof, TypeofUnqual };

I think improves readability in a bunch of places, AND gives us less work to do if we need to extend this node in the future.

I'm happy to switch to an enum for this. I don't think it makes a whole lot of sense to add additional types for typeof_unqual support though. Using inheritance would be a bit risky (someone may accidentally use a typeof_unqual type as a typeof), and there's only one bit of difference between the two types.

clang/include/clang/AST/ASTContext.h

1717

Good catch!

clang/include/clang/AST/Type.h

4537

Good call!

4542

No, it's more that E holds the type and Can holds the canonical type, which can sometimes be different than the type of E in the case of dependent typeof expressions. See ASTContext::getTypeOfExprType() for the interesting use.

4601

Yup, this is covered in the tests. desugar() gets called as part of type merging, and the canonical type is used when printing aka information.

clang/lib/AST/Type.cpp

3502

This was a hold over from before I had the isNull() check above, so I've fixed this up.

clang/lib/Lex/Preprocessor.cpp

61

Wth? No idea how that got here, but it's gone now.

clang/lib/Parse/ParseDecl.cpp

7463

I don't think we can get here in C2x mode, and typeof_unqual is not exposed outside of that mode. We've got test coverage for this (in C2x):

typeof 0 int i = 12;         // expected-error {{expected '(' after 'typeof'}} expected-error {{expected identifier or '('}}
typeof 0 j = 12;             // expected-error {{expected '(' after 'typeof'}} expected-error {{expected identifier or '('}}
typeof_unqual 0 k = 12;      // expected-error {{expected '(' after 'typeof_unqual'}} expected-error {{expected identifier or '('}}
typeof_unqual 0 int l = 12;  // expected-error {{expected '(' after 'typeof_unqual'}} expected-error {{expected identifier or '('}}

clang/lib/Sema/SemaType.cpp

9137

LoL far too cute, but this will change now that I'm using an enum more.

[aaron.ballman]

Addressing review feedback.

[aaron.ballman]

Really update, don't just kinda sorta update.

clang/lib/AST/ASTContext.cpp

12910–12916

FWIW: I still have to address these comments in the patch, but I'll do that tomorrow.

[erichkeane]

clang/include/clang/AST/Type.h

1902

So the downside to doing the bitfields is that EVERY 'Type' pays for them, or at least, pays for the largest one. As this is a rarely used and 'leaf' AST node, I would say using the bitfields for this is at minimum 'unnecessary'.

That said, I doubt it is the 'biggest one', so I could go either way.

clang/lib/AST/Type.cpp

3474

Does this have to be defensive about Can being the 'default' value of an empty qual-type?

[aaron.ballman]

clang/include/clang/AST/Type.h

1902

This is a union of objects, I'm certain all of them are at least one bit wide, so we're not adding to any extra overhead, we're taking advantage of the overhead we're already paying for.

clang/lib/AST/ASTContext.cpp

12910–12916

Thanks @mizvekov -- that makes sense to me. I've changed the implementation here, and I've also renamed getUnderlyingType() to getUnmodifiedType(). I was hesitant to do the rename before (but I was thinking about it!) because all of the "this type represents another type" types use getUnderlyingType() (such as DecltypeType, UnaryTransformType, etc). But in this case, the "underlying type" is less clear because of the unqual variant, so I think renaming is a good idea here.

clang/lib/AST/Type.cpp

3474

getTypeofUnqualType() looks for a null type and handles it appropriately already. If Can isn't valid, then we pass along the invalid type in either branch.

[aaron.ballman]

Updating based on review feedback; I believe this handles all of the comments.

[mizvekov]

clang/lib/AST/Type.cpp

3501–3504

I think this block of code is not actually needed.

So the AttributedType node is just sugar right, the address space are real qualifiers applied to the type, just like const and such.

So the getAtomicUnqualifiedType() alone should do that, as it uses getUnqualifiedType() on the final result.

When unqualifying a type, this will already strip all top level sugar nodes necessary to get rid of the qualifiers.

[erichkeane]

clang/include/clang/AST/Type.h

1902

Yep, this was a 'general lament'. Sorry for not being more clear.

[aaron.ballman]

clang/lib/AST/Type.cpp

3501–3504

The situation I had in mind for this was something like:

typedef __attribute__((address_space(1))) int foo;
_Atomic foo i;
typeof_unqual(i) j; // Should be int

but I didn't realize we distribute the qualifiers from the inner type to the atomic type: https://godbolt.org/z/bbafvTKsj

So I think you're correct -- we don't seem to need this function at all. (Function type attributes like calling conventions, etc aren't handled via an AttributedType either, but are on the ExtInfo object for the function type.)

Good catch!

[aaron.ballman]

Simplifying based on review feedback.

[aaron.ballman]

Ping

[erichkeane]

LGTM.

[mizvekov]

clang/include/clang/AST/Type.h

4564

I only noticed this after rebasing some of my patches, I missed this on the original review (same for TypeOfType)

[aaron.ballman]

clang/include/clang/AST/Type.h

4564

Sure, on the whole I think this makes the code cleaner. I've updated in 42ad305bdbb87d567d4d365ec5ede8be4d2a4210, thank you for the suggestion!

[mizvekov]

clang/include/clang/AST/Type.h

4564

Thanks!

clang/docs/ReleaseNotes.rst

 
 C2x Feature Support
 -------------------
 - Implemented `WG14 N2662 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2662.pdf>`_,
   so the [[maybe_unused]] attribute may be applied to a label to silence an
   ``-Wunused-label`` warning.
 - Implemented `WG14 N2508 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2508.pdf>`_,
   so labels can placed everywhere inside a compound statement.
+- Implemented `WG14 N2927 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2927.htm>`_,
+  the Not-so-magic ``typeof`` operator. Also implemented
+  `WG14 N2930 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2930.pdf>`_,
+  renaming ``remove_quals``, so the ``typeof_unqual`` operator is also
+  supported. Both of these operators are supported only in C2x mode. The
+  ``typeof`` operator specifies the type of the given parenthesized expression
+  operand or type name, including all qualifiers. The ``typeof_unqual``
+  operator is similar to ``typeof`` except that all qualifiers are removed,
+  including atomic type qualification and type attributes which behave like a
+  qualifier, such as an address space attribute.
+
+  .. code-block:: c
+
+    __attribute__((address_space(1))) const _Atomic int Val;
+    typeof(Val) OtherVal; // type is '__attribute__((address_space(1))) const _Atomic int'
+    typeof_unqual(Val) OtherValUnqual; // type is 'int'
 
 C++ Language Changes in Clang
 -----------------------------
 - Implemented DR692, DR1395 and DR1432. Use the ``-fclang-abi-compat=15`` option
   to get the old partial ordering behavior regarding packs.
 - Clang's default C++/ObjC++ standard is now ``gnu++17`` instead of ``gnu++14``.
   This means Clang will by default accept code using features from C++17 and
   conforming GNU extensions. Projects incompatible with C++17 can add

clang/include/clang/AST/ASTContext.h

   /// QT's qualified-id protocol list adopt all protocols in IDecl's list
   /// of protocols.
   bool QIdProtocolsAdoptObjCObjectProtocols(QualType QT,
                                             ObjCInterfaceDecl *IDecl);
 
   /// Return a ObjCObjectPointerType type for the given ObjCObjectType.
   QualType getObjCObjectPointerType(QualType OIT) const;
 
   /// GCC extension.
-  QualType getTypeOfExprType(Expr *e) const;
-  QualType getTypeOfType(QualType t) const;
+  QualType getTypeOfExprType(Expr *E, bool IsUnqual) const;
+  QualType getTypeOfType(QualType QT, bool IsUnqual) const;
 
   QualType getReferenceQualifiedType(const Expr *e) const;
 
   /// C++11 decltype.
   QualType getDecltypeType(Expr *e, QualType UnderlyingType) const;
 
   /// Unary type transforms
   QualType getUnaryTransformType(QualType BaseType, QualType UnderlyingType,

clang/include/clang/AST/Type.h

   /// Returns the specified type after dropping any
   /// outer-level parentheses.
   QualType IgnoreParens() const {
     if (isa<ParenType>(*this))
       return QualType::IgnoreParens(*this);
     return *this;
   }
 
+  /// Returns the typeof_unqual-unqualified version of the type.
+  QualType getTypeofUnqualType() const;
+
   /// Indicate whether the specified types and qualifiers are identical.
   friend bool operator==(const QualType &LHS, const QualType &RHS) {
     return LHS.Value == RHS.Value;
   }
   friend bool operator!=(const QualType &LHS, const QualType &RHS) {
     return LHS.Value != RHS.Value;
   }
   friend bool operator<(const QualType &LHS, const QualType &RHS) {

     SubstTemplateTypeParmPackTypeBitfields SubstTemplateTypeParmPackTypeBits;
     TemplateSpecializationTypeBitfields TemplateSpecializationTypeBits;
     DependentTemplateSpecializationTypeBitfields
       DependentTemplateSpecializationTypeBits;
     PackExpansionTypeBitfields PackExpansionTypeBits;
   };
 
 private:
   template <class T> friend class TypePropertyCache;
 
   /// Set whether this type comes from an AST file.
   void setFromAST(bool V = true) const {
     TypeBits.FromAST = V;
   }
 
 protected:
   friend class ASTContext;

   bool isSugared() const { return true; }
   QualType desugar() const;
 
   static bool classof(const Type *T) {
     return T->getTypeClass() == MacroQualified;
   }
 };
 
-/// Represents a `typeof` (or __typeof__) expression (a GCC extension).
+/// Represents a `typeof` (or __typeof__) expression (a C2x feature and GCC
+/// extension) or a `typeof_unqual` expression (a C2x feature).
 class TypeOfExprType : public Type {
   Expr *TOExpr;
+  bool IsUnqual;
 
 protected:
   friend class ASTContext; // ASTContext creates these.
 
-  TypeOfExprType(Expr *E, QualType can = QualType());
+  TypeOfExprType(Expr *E, bool IsUnqual, QualType Can = QualType());
 
 public:
   Expr *getUnderlyingExpr() const { return TOExpr; }
 
+  /// Returns true if this is a typeof_unqual type.
+  bool isUnqual() const { return IsUnqual; }
+
   /// Remove a single level of sugar.
   QualType desugar() const;
 
   /// Returns whether this type directly provides sugar.
   bool isSugared() const;
 
   static bool classof(const Type *T) { return T->getTypeClass() == TypeOfExpr; }
 };
 
 /// Internal representation of canonical, dependent
 /// `typeof(expr)` types.
 ///
 /// This class is used internally by the ASTContext to manage
 /// canonical, dependent types, only. Clients will only see instances
 /// of this class via TypeOfExprType nodes.
 class DependentTypeOfExprType
   : public TypeOfExprType, public llvm::FoldingSetNode {
   const ASTContext &Context;
 
 public:
-  DependentTypeOfExprType(const ASTContext &Context, Expr *E)
-      : TypeOfExprType(E), Context(Context) {}
+  DependentTypeOfExprType(const ASTContext &Context, Expr *E, bool IsUnqual)
+      : TypeOfExprType(E, IsUnqual), Context(Context) {}
 
   void Profile(llvm::FoldingSetNodeID &ID) {
-    Profile(ID, Context, getUnderlyingExpr());
+    Profile(ID, Context, getUnderlyingExpr(), isUnqual());
   }
 
   static void Profile(llvm::FoldingSetNodeID &ID, const ASTContext &Context,
-                      Expr *E);
+                      Expr *E, bool IsUnqual);
 };
 
-/// Represents `typeof(type)`, a GCC extension.
+/// Represents `typeof(type)`, a C2x feature and GCC extension, or
+/// `typeof_unqual(type), a C2x feature.
 class TypeOfType : public Type {
   friend class ASTContext; // ASTContext creates these.
 
   QualType TOType;
+  bool IsUnqual; // typeof_unqual(type-name)
 
-  TypeOfType(QualType T, QualType can)
-      : Type(TypeOf, can, T->getDependence()), TOType(T) {
-    assert(!isa<TypedefType>(can) && "Invalid canonical type");
+  TypeOfType(QualType T, QualType Can, bool IsUnqual)
+      : Type(TypeOf, IsUnqual ? Can.getTypeofUnqualType() : Can,
+          T->getDependence()), TOType(T), IsUnqual(IsUnqual) {
+    assert(!isa<TypedefType>(Can) && "Invalid canonical type");
   }
 
 public:
   QualType getUnderlyingType() const { return TOType; }
 
   /// Remove a single level of sugar.
-  QualType desugar() const { return getUnderlyingType(); }
+  QualType desugar() const {
+    QualType QT = getUnderlyingType();
+    return IsUnqual ? QT.getTypeofUnqualType() : QT;
+  }
 
   /// Returns whether this type directly provides sugar.
   bool isSugared() const { return true; }
 
+  /// Returns true if this is a typeof_unqual type.
+  bool isUnqual() const { return IsUnqual; }
+
   static bool classof(const Type *T) { return T->getTypeClass() == TypeOf; }
 };
 
 /// Represents the type `decltype(expr)` (C++11).
 class DecltypeType : public Type {
   Expr *E;
   QualType UnderlyingType;
 

clang/include/clang/AST/TypeProperties.td

let Class = TypedefType in {
   }]>;
 }
 
 let Class = TypeOfExprType in {
   def : Property<"expression", ExprRef> {
     let Read = [{ node->getUnderlyingExpr() }];
   }
 
+  def : Property<"isUnqual", Bool> {
+    let Read = [{ node->isUnqual() }];
+  }
+
   def : Creator<[{
-    return ctx.getTypeOfExprType(expression);
+    return ctx.getTypeOfExprType(expression, isUnqual);
   }]>;
 }
 
 let Class = TypeOfType in {
   def : Property<"underlyingType", QualType> {
     let Read = [{ node->getUnderlyingType() }];
   }
 
+  def : Property<"isUnqual", Bool> {
+    let Read = [{ node->isUnqual() }];
+  }
+
   def : Creator<[{
-    return ctx.getTypeOfType(underlyingType);
+    return ctx.getTypeOfType(underlyingType, isUnqual);
   }]>;
 }
 
 let Class = DecltypeType in {
   def : Property<"underlyingType", QualType> {
     let Read = [{ node->getUnderlyingType() }];
   }
   def : Property<"expression", ExprRef> {

clang/include/clang/Basic/DiagnosticParseKinds.td

 def ext_decltype_auto_type_specifier : ExtWarn<
   "'decltype(auto)' type specifier is a C++14 extension">, InGroup<CXX14>;
 def warn_cxx11_compat_decltype_auto_type_specifier : Warning<
   "'decltype(auto)' type specifier is incompatible with C++ standards before "
   "C++14">, InGroup<CXXPre14Compat>, DefaultIgnore;
 def ext_auto_type : Extension<
   "'__auto_type' is a GNU extension">,
   InGroup<GNUAutoType>;
+def warn_c2x_compat_typeof_type_specifier : Warning<
+  "'%select{typeof|typeof_unqual}0' is incompatible with C standards before "
+  "C2x">, InGroup<CPre2xCompat>, DefaultIgnore;
 def ext_for_range : ExtWarn<
   "range-based for loop is a C++11 extension">, InGroup<CXX11>;
 def warn_cxx98_compat_for_range : Warning<
   "range-based for loop is incompatible with C++98">,
   InGroup<CXX98Compat>, DefaultIgnore;
 def err_for_range_identifier : Error<
   "range-based for loop requires type for loop variable">;
 def err_for_range_expected_decl : Error<

clang/include/clang/Basic/DiagnosticSemaKinds.td

   "invalid application of '%0' to a void type">;
 def err_sizeof_alignof_incomplete_or_sizeless_type : Error<
   "invalid application of '%0' to %select{an incomplete|sizeless}1 type %2">;
 def err_sizeof_alignof_function_type : Error<
   "invalid application of '%0' to a function type">;
 def err_openmp_default_simd_align_expr : Error<
   "invalid application of '__builtin_omp_required_simd_align' to an expression, only type is allowed">;
 def err_sizeof_alignof_typeof_bitfield : Error<
-  "invalid application of '%select{sizeof|alignof|typeof}0' to bit-field">;
+  "invalid application of '%select{sizeof|alignof|typeof|typeof_unqual}0' to "
+  "bit-field">;
 def err_alignof_member_of_incomplete_type : Error<
   "invalid application of 'alignof' to a field of a class still being defined">;
 def err_vecstep_non_scalar_vector_type : Error<
   "'vec_step' requires built-in scalar or vector type, %0 invalid">;
 def err_offsetof_incomplete_type : Error<
   "offsetof of incomplete type %0">;
 def err_offsetof_record_type : Error<
   "offsetof requires struct, union, or class type, %0 invalid">;

clang/include/clang/Basic/Specifiers.h

enum TypeSpecifierType {
     TST_decimal64,  // _Decimal64
     TST_decimal128, // _Decimal128
     TST_enum,
     TST_union,
     TST_struct,
     TST_class,     // C++ class type
     TST_interface, // C++ (Microsoft-specific) __interface type
     TST_typename,  // Typedef, C++ class-name or enum name, etc.
-    TST_typeofType,
-    TST_typeofExpr,
+    TST_typeofType,        // C2x (and GNU extension) typeof(type-name)
+    TST_typeofExpr,        // C2x (and GNU extension) typeof(expression)
+    TST_typeof_unqualType, // C2x typeof_unqual(type-name)
+    TST_typeof_unqualExpr, // C2x typeof_unqual(expression)
     TST_decltype, // C++11 decltype
 #define TRANSFORM_TYPE_TRAIT_DEF(_, Trait) TST_##Trait,
 #include "clang/Basic/TransformTypeTraits.def"
     TST_auto,            // C++11 auto
     TST_decltype_auto,   // C++1y decltype(auto)
     TST_auto_type,       // __auto_type extension
     TST_unknown_anytype, // __unknown_anytype extension
     TST_atomic,          // C11 _Atomic

clang/include/clang/Basic/TokenKinds.def

 #define CXX11_KEYWORD(X,Y) KEYWORD(X,KEYCXX11|(Y))
 #endif
 #ifndef CXX20_KEYWORD
 #define CXX20_KEYWORD(X,Y) KEYWORD(X,KEYCXX20|(Y))
 #endif
 #ifndef C99_KEYWORD
 #define C99_KEYWORD(X,Y) KEYWORD(X,KEYC99|(Y))
 #endif
+#ifndef C2X_KEYWORD
+#define C2X_KEYWORD(X,Y) KEYWORD(X,KEYC2X|(Y))
+#endif
 #ifndef COROUTINES_KEYWORD
 #define COROUTINES_KEYWORD(X) CXX20_KEYWORD(X,KEYCOROUTINES)
 #endif
 #ifndef MODULES_KEYWORD
 #define MODULES_KEYWORD(X) KEYWORD(X,KEYMODULES)
 #endif
 #ifndef TYPE_TRAIT
 #define TYPE_TRAIT(N,I,K) KEYWORD(I,K)

 CXX20_KEYWORD(requires              , 0)
 
 // Not a CXX20_KEYWORD because it is disabled by -fno-char8_t.
 KEYWORD(char8_t                     , CHAR8SUPPORT)
 
 // C11 Extension
 KEYWORD(_Float16                    , KEYALL)
 
+// C2x keywords
+C2X_KEYWORD(typeof                  , KEYGNU)
+C2X_KEYWORD(typeof_unqual           , 0)
+
 // ISO/IEC JTC1 SC22 WG14 N1169 Extension
 KEYWORD(_Accum                      , KEYNOCXX)
 KEYWORD(_Fract                      , KEYNOCXX)
 KEYWORD(_Sat                        , KEYNOCXX)
 
 // GNU Extensions (in impl-reserved namespace)
 KEYWORD(_Decimal32                  , KEYALL)
 KEYWORD(_Decimal64                  , KEYALL)

 KEYWORD(__int128                    , KEYALL)
 KEYWORD(__label__                   , KEYALL)
 KEYWORD(__real                      , KEYALL)
 KEYWORD(__thread                    , KEYALL)
 KEYWORD(__FUNCTION__                , KEYALL)
 KEYWORD(__PRETTY_FUNCTION__         , KEYALL)
 KEYWORD(__auto_type                 , KEYALL)
 
-// GNU Extensions (outside impl-reserved namespace)
-KEYWORD(typeof                      , KEYGNU|KEYC2X)
-
 // MS Extensions
 KEYWORD(__FUNCDNAME__               , KEYMS)
 KEYWORD(__FUNCSIG__                 , KEYMS)
 KEYWORD(L__FUNCTION__               , KEYMS)
 KEYWORD(L__FUNCSIG__                , KEYMS)
 TYPE_TRAIT_1(__is_interface_class, IsInterfaceClass, KEYMS)
 TYPE_TRAIT_1(__is_sealed, IsSealed, KEYMS)
 

 #undef TYPE_TRAIT_1
 #undef TYPE_TRAIT
 #undef CXX20_KEYWORD
 #undef CXX11_KEYWORD
 #undef KEYWORD
 #undef PUNCTUATOR
 #undef TOK
 #undef C99_KEYWORD
+#undef C2X_KEYWORD

clang/include/clang/Sema/DeclSpec.h

public:
   static const TST TST_enum = clang::TST_enum;
   static const TST TST_union = clang::TST_union;
   static const TST TST_struct = clang::TST_struct;
   static const TST TST_interface = clang::TST_interface;
   static const TST TST_class = clang::TST_class;
   static const TST TST_typename = clang::TST_typename;
   static const TST TST_typeofType = clang::TST_typeofType;
   static const TST TST_typeofExpr = clang::TST_typeofExpr;
+  static const TST TST_typeof_unqualType = clang::TST_typeof_unqualType;
+  static const TST TST_typeof_unqualExpr = clang::TST_typeof_unqualExpr;
   static const TST TST_decltype = clang::TST_decltype;
   static const TST TST_decltype_auto = clang::TST_decltype_auto;
 #define TRANSFORM_TYPE_TRAIT_DEF(_, Trait)                                     \
   static const TST TST_##Trait = clang::TST_##Trait;
 #include "clang/Basic/TransformTypeTraits.def"
   static const TST TST_auto = clang::TST_auto;
   static const TST TST_auto_type = clang::TST_auto_type;
   static const TST TST_unknown_anytype = clang::TST_unknown_anytype;
private:
 
   WrittenBuiltinSpecs writtenBS;
   void SaveWrittenBuiltinSpecs();
 
   ObjCDeclSpec *ObjCQualifiers;
 
   static bool isTypeRep(TST T) {
     return T == TST_atomic || T == TST_typename || T == TST_typeofType ||
-           isTransformTypeTrait(T);
+           T == TST_typeof_unqualType || isTransformTypeTrait(T);
   }
   static bool isExprRep(TST T) {
-    return (T == TST_typeofExpr || T == TST_decltype || T == TST_bitint);
+    return T == TST_typeofExpr || T == TST_typeof_unqualExpr ||
+           T == TST_decltype || T == TST_bitint;
   }
   static bool isTemplateIdRep(TST T) {
     return (T == TST_auto || T == TST_decltype_auto);
   }
 
   DeclSpec(const DeclSpec &) = delete;
   void operator=(const DeclSpec &) = delete;
 public:

clang/include/clang/Sema/Sema.h

 
   QualType getElaboratedType(ElaboratedTypeKeyword Keyword,
                              const CXXScopeSpec &SS, QualType T,
                              TagDecl *OwnedTagDecl = nullptr);
 
   // Returns the underlying type of a decltype with the given expression.
   QualType getDecltypeForExpr(Expr *E);
 
-  QualType BuildTypeofExprType(Expr *E);
+  QualType BuildTypeofExprType(Expr *E, bool IsUnqual);
   /// If AsUnevaluated is false, E is treated as though it were an evaluated
   /// context, such as when building a type for decltype(auto).
   QualType BuildDecltypeType(Expr *E, bool AsUnevaluated = true);
 
   using UTTKind = UnaryTransformType::UTTKind;
   QualType BuildUnaryTransformType(QualType BaseType, UTTKind UKind,
                                    SourceLocation Loc);
   QualType BuiltinEnumUnderlyingType(QualType BaseType, SourceLocation Loc);

clang/lib/AST/ASTContext.cpp

   return QualType(T, 0);
 }
 
 /// getTypeOfExprType - Unlike many "get<Type>" functions, we can't unique
 /// TypeOfExprType AST's (since expression's are never shared). For example,
 /// multiple declarations that refer to "typeof(x)" all contain different
 /// DeclRefExpr's. This doesn't effect the type checker, since it operates
 /// on canonical type's (which are always unique).
-QualType ASTContext::getTypeOfExprType(Expr *tofExpr) const {
+QualType ASTContext::getTypeOfExprType(Expr *tofExpr, bool IsUnqual) const {
   TypeOfExprType *toe;
   if (tofExpr->isTypeDependent()) {
     llvm::FoldingSetNodeID ID;
-    DependentTypeOfExprType::Profile(ID, *this, tofExpr);
+    DependentTypeOfExprType::Profile(ID, *this, tofExpr, IsUnqual);
 
     void *InsertPos = nullptr;
     DependentTypeOfExprType *Canon
       = DependentTypeOfExprTypes.FindNodeOrInsertPos(ID, InsertPos);
     if (Canon) {
       // We already have a "canonical" version of an identical, dependent
       // typeof(expr) type. Use that as our canonical type.
-      toe = new (*this, TypeAlignment) TypeOfExprType(tofExpr,
+      toe = new (*this, TypeAlignment) TypeOfExprType(tofExpr, IsUnqual,
                                           QualType((TypeOfExprType*)Canon, 0));
     } else {
       // Build a new, canonical typeof(expr) type.
-      Canon
-        = new (*this, TypeAlignment) DependentTypeOfExprType(*this, tofExpr);
+      Canon = new (*this, TypeAlignment)
+          DependentTypeOfExprType(*this, tofExpr, IsUnqual);
       DependentTypeOfExprTypes.InsertNode(Canon, InsertPos);
       toe = Canon;
     }
   } else {
     QualType Canonical = getCanonicalType(tofExpr->getType());
-    toe = new (*this, TypeAlignment) TypeOfExprType(tofExpr, Canonical);
+    toe =
+        new (*this, TypeAlignment) TypeOfExprType(tofExpr, IsUnqual, Canonical);
   }
   Types.push_back(toe);
   return QualType(toe, 0);
 }
 
 /// getTypeOfType -  Unlike many "get<Type>" functions, we don't unique
 /// TypeOfType nodes. The only motivation to unique these nodes would be
 /// memory savings. Since typeof(t) is fairly uncommon, space shouldn't be
 /// an issue. This doesn't affect the type checker, since it operates
 /// on canonical types (which are always unique).
-QualType ASTContext::getTypeOfType(QualType tofType) const {
+QualType ASTContext::getTypeOfType(QualType tofType, bool IsUnqual) const {
   QualType Canonical = getCanonicalType(tofType);
-  auto *tot = new (*this, TypeAlignment) TypeOfType(tofType, Canonical);
+  auto *tot =
+      new (*this, TypeAlignment) TypeOfType(tofType, Canonical, IsUnqual);
   Types.push_back(tot);
   return QualType(tot, 0);
 }
 
 /// getReferenceQualifiedType - Given an expr, will return the type for
 /// that expression, as in [dcl.type.simple]p4 but without taking id-expressions
 /// and class member access into account.
 QualType ASTContext::getReferenceQualifiedType(const Expr *E) const {

   case Type::Typedef: {
     const auto *TX = cast<TypedefType>(X), *TY = cast<TypedefType>(Y);
     const TypedefNameDecl *CD = ::getCommonDecl(TX->getDecl(), TY->getDecl());
     if (!CD)
       return QualType();
     return Ctx.getTypedefType(CD, Ctx.getQualifiedType(Underlying));
   }
   case Type::TypeOf:
-    return Ctx.getTypeOfType(Ctx.getQualifiedType(Underlying));
+    // FIXME:: is this assumption correct or do we need to do work here to find
+    // the common type sugar regarding the stripped qualifiers if only one side
+    // is unqual?
+    assert(cast<TypeOfType>(X)->isUnqual() == cast<TypeOfType>(Y)->isUnqual() &&
+           "typeof vs typeof_unqual mismatch?");
+    return Ctx.getTypeOfType(Ctx.getQualifiedType(Underlying),
+                             cast<TypeOfType>(X)->isUnqual());
   case Type::TypeOfExpr:
     return QualType();
 
   case Type::UnaryTransform: {
     const auto *UX = cast<UnaryTransformType>(X),
                *UY = cast<UnaryTransformType>(Y);
     UnaryTransformType::UTTKind KX = UX->getUTTKind();
     if (KX != UY->getUTTKind())

clang/lib/AST/ASTImporter.cpp

 
   return Importer.getToContext().getTypeDeclType(*ToDeclOrErr);
 }
 
 ExpectedType ASTNodeImporter::VisitTypeOfExprType(const TypeOfExprType *T) {
   ExpectedExpr ToExprOrErr = import(T->getUnderlyingExpr());
   if (!ToExprOrErr)
     return ToExprOrErr.takeError();
-
-  return Importer.getToContext().getTypeOfExprType(*ToExprOrErr);
+  return Importer.getToContext().getTypeOfExprType(*ToExprOrErr, T->isUnqual());
 }
 
 ExpectedType ASTNodeImporter::VisitTypeOfType(const TypeOfType *T) {
   ExpectedType ToUnderlyingTypeOrErr = import(T->getUnderlyingType());
   if (!ToUnderlyingTypeOrErr)
     return ToUnderlyingTypeOrErr.takeError();
-
-  return Importer.getToContext().getTypeOfType(*ToUnderlyingTypeOrErr);
+  return Importer.getToContext().getTypeOfType(*ToUnderlyingTypeOrErr,
+                                               T->isUnqual());
 }
 
 ExpectedType ASTNodeImporter::VisitUsingType(const UsingType *T) {
   Expected<UsingShadowDecl *> FoundOrErr = import(T->getFoundDecl());
   if (!FoundOrErr)
     return FoundOrErr.takeError();
   Expected<QualType> UnderlyingOrErr = import(T->getUnderlyingType());
   if (!UnderlyingOrErr)

clang/lib/AST/Type.cpp

   while (auto *InnerMQT = dyn_cast<MacroQualifiedType>(Inner)) {
     if (InnerMQT->getMacroIdentifier() != getMacroIdentifier())
       break;
     Inner = InnerMQT->getModifiedType();
   }
   return Inner;
 }
 
-TypeOfExprType::TypeOfExprType(Expr *E, QualType can)
-    : Type(TypeOfExpr, can,
+TypeOfExprType::TypeOfExprType(Expr *E, bool IsUnqual, QualType Can)
+    : Type(TypeOfExpr, IsUnqual ? Can.getTypeofUnqualType() : Can,
            toTypeDependence(E->getDependence()) |
                (E->getType()->getDependence() &
                 TypeDependence::VariablyModified)),
-      TOExpr(E) {}
+      TOExpr(E), IsUnqual(IsUnqual) {}
 
 bool TypeOfExprType::isSugared() const {
   return !TOExpr->isTypeDependent();
 }
 
 QualType TypeOfExprType::desugar() const {
-  if (isSugared())
-    return getUnderlyingExpr()->getType();
-
+  if (isSugared()) {
+    QualType QT = getUnderlyingExpr()->getType();
+    return IsUnqual ? QT.getTypeofUnqualType() : QT;
+  }
   return QualType(this, 0);
 }
 
+QualType QualType::getTypeofUnqualType() const {
+  if (isNull())
+    return *this;
+
+  // C2x 6.7.2.5p5:
+  // The result of the typeof_unqual operation is the non-atomic unqualified
+  // version of the type name that would result from the typeof operation.
+  // The typeof operator preserves all qualifiers.
+  QualType Ret = getAtomicUnqualifiedType();
+
+  // We strip all qualifier-like attributes as well.
+  if (const auto *AT =
+          dyn_cast_if_present<AttributedType>(Ret.getTypePtrOrNull());
+      AT && AT->isQualifier())
+    Ret = AT->getModifiedType();
+
+  return Ret;
+}
+
 void DependentTypeOfExprType::Profile(llvm::FoldingSetNodeID &ID,
-                                      const ASTContext &Context, Expr *E) {
+                                      const ASTContext &Context, Expr *E,
+                                      bool IsUnqual) {
   E->Profile(ID, Context, true);
+  ID.AddBoolean(IsUnqual);
 }
 
 DecltypeType::DecltypeType(Expr *E, QualType underlyingType, QualType can)
     // C++11 [temp.type]p2: "If an expression e involves a template parameter,
     // decltype(e) denotes a unique dependent type." Hence a decltype type is
     // type-dependent even if its expression is only instantiation-dependent.
     : Type(Decltype, can,
            toTypeDependence(E->getDependence()) |

clang/lib/AST/TypePrinter.cpp

                                            raw_ostream &OS) {
   printAfter(T->getModifiedType(), OS);
 }
 
 void TypePrinter::printTypedefAfter(const TypedefType *T, raw_ostream &OS) {}
 
 void TypePrinter::printTypeOfExprBefore(const TypeOfExprType *T,
                                         raw_ostream &OS) {
-  OS << "typeof ";
+  OS << (T->isUnqual() ? "typeof_unqual " : "typeof ");
   if (T->getUnderlyingExpr())
     T->getUnderlyingExpr()->printPretty(OS, nullptr, Policy);
   spaceBeforePlaceHolder(OS);
 }
 
 void TypePrinter::printTypeOfExprAfter(const TypeOfExprType *T,
                                        raw_ostream &OS) {}
 
 void TypePrinter::printTypeOfBefore(const TypeOfType *T, raw_ostream &OS) {
-  OS << "typeof(";
+  OS << (T->isUnqual() ? "typeof_unqual(" : "typeof(");
   print(T->getUnderlyingType(), OS, StringRef());
   OS << ')';
   spaceBeforePlaceHolder(OS);
 }
 
 void TypePrinter::printTypeOfAfter(const TypeOfType *T, raw_ostream &OS) {}
 
 void TypePrinter::printDecltypeBefore(const DecltypeType *T, raw_ostream &OS) {

clang/lib/Lex/Preprocessor.cpp

 #include "clang/Lex/TokenLexer.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/Capacity.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cassert>
 #include <memory>
 #include <string>

clang/lib/Parse/ParseDecl.cpp

       if (TryAnnotateTypeOrScopeToken()) {
         DS.SetTypeSpecError();
         goto DoneWithDeclSpec;
       }
       if (!Tok.is(tok::kw_typename))
         continue;
       break;
 
-    // GNU typeof support.
+    // C2x/GNU typeof support.
     case tok::kw_typeof:
+    case tok::kw_typeof_unqual:
       ParseTypeofSpecifier(DS);
       continue;
 
     case tok::annot_decltype:
       ParseDecltypeSpecifier(DS);
       continue;
 
     case tok::annot_pragma_pack:

       return false;
 
     if (TryAnnotateTypeOrScopeToken())
       return true;
     return isTypeSpecifierQualifier();
 
     // GNU attributes support.
   case tok::kw___attribute:
-    // GNU typeof support.
+    // C2x/GNU typeof support.
   case tok::kw_typeof:
+  case tok::kw_typeof_unqual:
 
     // type-specifiers
   case tok::kw_short:
   case tok::kw_long:
   case tok::kw___int64:
   case tok::kw___int128:
   case tok::kw_signed:
   case tok::kw_unsigned:

 
     // friend keyword.
   case tok::kw_friend:
 
     // static_assert-declaration
   case tok::kw_static_assert:
   case tok::kw__Static_assert:
 
-    // GNU typeof support.
+    // C2x/GNU typeof support.
   case tok::kw_typeof:
+  case tok::kw_typeof_unqual:
 
     // GNU attributes.
   case tok::kw___attribute:
 
     // C++11 decltype and constexpr.
   case tok::annot_decltype:
   case tok::kw_constexpr:
 

         << FixItHint::CreateRemoval(BracketRange);
   }
 }
 
 /// [GNU]   typeof-specifier:
 ///           typeof ( expressions )
 ///           typeof ( type-name )
 /// [GNU/C++] typeof unary-expression
+/// [C2x]   typeof-specifier:
+///           typeof '(' typeof-specifier-argument ')'
+///           typeof_unqual '(' typeof-specifier-argument ')'
+///
+///         typeof-specifier-argument:
+///           expression
+///           type-name
 ///
 void Parser::ParseTypeofSpecifier(DeclSpec &DS) {
-  assert(Tok.is(tok::kw_typeof) && "Not a typeof specifier");
+  assert(Tok.isOneOf(tok::kw_typeof, tok::kw_typeof_unqual) &&
+         "Not a typeof specifier");
+
+  bool IsUnqual = Tok.is(tok::kw_typeof_unqual);
+  const IdentifierInfo *II = Tok.getIdentifierInfo();
+  if (getLangOpts().C2x && !II->getName().startswith("__"))
+    Diag(Tok.getLocation(), diag::warn_c2x_compat_typeof_type_specifier)
+        << IsUnqual;
+
   Token OpTok = Tok;
   SourceLocation StartLoc = ConsumeToken();
-
-  const bool hasParens = Tok.is(tok::l_paren);
+  bool HasParens = Tok.is(tok::l_paren);
 
   EnterExpressionEvaluationContext Unevaluated(
       Actions, Sema::ExpressionEvaluationContext::Unevaluated,
       Sema::ReuseLambdaContextDecl);
 
   bool isCastExpr;
   ParsedType CastTy;
   SourceRange CastRange;
   ExprResult Operand = Actions.CorrectDelayedTyposInExpr(
       ParseExprAfterUnaryExprOrTypeTrait(OpTok, isCastExpr, CastTy, CastRange));
-  if (hasParens)
+  if (HasParens)
     DS.setTypeArgumentRange(CastRange);
 
   if (CastRange.getEnd().isInvalid())
     // FIXME: Not accurate, the range gets one token more than it should.
     DS.SetRangeEnd(Tok.getLocation());
   else
     DS.SetRangeEnd(CastRange.getEnd());
 
   if (isCastExpr) {
     if (!CastTy) {
       DS.SetTypeSpecError();
       return;
     }
 
     const char *PrevSpec = nullptr;
     unsigned DiagID;
     // Check for duplicate type specifiers (e.g. "int typeof(int)").
-    if (DS.SetTypeSpecType(DeclSpec::TST_typeofType, StartLoc, PrevSpec,
+    if (DS.SetTypeSpecType(IsUnqual ? DeclSpec::TST_typeof_unqualType
+                                    : DeclSpec::TST_typeofType,
+                           StartLoc, PrevSpec,
                            DiagID, CastTy,
                            Actions.getASTContext().getPrintingPolicy()))
       Diag(StartLoc, DiagID) << PrevSpec;
     return;
   }
 
   // If we get here, the operand to the typeof was an expression.
   if (Operand.isInvalid()) {
     DS.SetTypeSpecError();
     return;
   }
 
   // We might need to transform the operand if it is potentially evaluated.
   Operand = Actions.HandleExprEvaluationContextForTypeof(Operand.get());
   if (Operand.isInvalid()) {
     DS.SetTypeSpecError();
     return;
   }
 
   const char *PrevSpec = nullptr;
   unsigned DiagID;
   // Check for duplicate type specifiers (e.g. "int typeof(int)").
-  if (DS.SetTypeSpecType(DeclSpec::TST_typeofExpr, StartLoc, PrevSpec,
+  if (DS.SetTypeSpecType(IsUnqual ? DeclSpec::TST_typeof_unqualExpr
+                                  : DeclSpec::TST_typeofExpr,
+                         StartLoc, PrevSpec,
                          DiagID, Operand.get(),
                          Actions.getASTContext().getPrintingPolicy()))
     Diag(StartLoc, DiagID) << PrevSpec;
 }
 
 /// [C11]   atomic-specifier:
 ///           _Atomic ( type-name )
 ///

clang/lib/Parse/ParseExpr.cpp

 /// [GNU]   '__alignof' '(' type-name ')'
 /// [C11]   '_Alignof' '(' type-name ')'
 /// [C++0x] 'alignof' '(' type-id ')'
 ///
 /// [GNU]   typeof-specifier:
 ///           typeof ( expressions )
 ///           typeof ( type-name )
 /// [GNU/C++] typeof unary-expression
+/// [C2x]   typeof-specifier:
+///           typeof '(' typeof-specifier-argument ')'
+///           typeof_unqual '(' typeof-specifier-argument ')'
+///
+///         typeof-specifier-argument:
+///           expression
+///           type-name
 ///
 /// [OpenCL 1.1 6.11.12] vec_step built-in function:
 ///           vec_step ( expressions )
 ///           vec_step ( type-name )
 /// \endverbatim
 ExprResult
 Parser::ParseExprAfterUnaryExprOrTypeTrait(const Token &OpTok,
                                            bool &isCastExpr,
                                            ParsedType &CastTy,
                                            SourceRange &CastRange) {
 
-  assert(OpTok.isOneOf(tok::kw_typeof, tok::kw_sizeof, tok::kw___alignof,
-                       tok::kw_alignof, tok::kw__Alignof, tok::kw_vec_step,
+  assert(OpTok.isOneOf(tok::kw_typeof, tok::kw_typeof_unqual, tok::kw_sizeof,
+                       tok::kw___alignof, tok::kw_alignof, tok::kw__Alignof,
+                       tok::kw_vec_step,
                        tok::kw___builtin_omp_required_simd_align) &&
          "Not a typeof/sizeof/alignof/vec_step expression!");
 
   ExprResult Operand;
 
   // If the operand doesn't start with an '(', it must be an expression.
   if (Tok.isNot(tok::l_paren)) {
     // If construct allows a form without parenthesis, user may forget to put

               << FixItHint::CreateInsertion(RParenLoc, ")");
         }
         isCastExpr = true;
         return ExprEmpty();
       }
     }
 
     isCastExpr = false;
-    if (OpTok.is(tok::kw_typeof) && !getLangOpts().CPlusPlus) {
+    if (OpTok.isOneOf(tok::kw_typeof, tok::kw_typeof_unqual) &&
+        !getLangOpts().CPlusPlus) {
       Diag(Tok, diag::err_expected_after) << OpTok.getIdentifierInfo()
                                           << tok::l_paren;
       return ExprError();
     }
 
     Operand = ParseCastExpression(UnaryExprOnly);
   } else {
     // If it starts with a '(', we know that it is either a parenthesized

 
     // If ParseParenExpression parsed a '(typename)' sequence only, then this is
     // a type.
     if (ExprType == CastExpr) {
       isCastExpr = true;
       return ExprEmpty();
     }
 
-    if (getLangOpts().CPlusPlus || OpTok.isNot(tok::kw_typeof)) {
+    if (getLangOpts().CPlusPlus ||
+        !OpTok.isOneOf(tok::kw_typeof, tok::kw_typeof_unqual)) {
       // GNU typeof in C requires the expression to be parenthesized. Not so for
       // sizeof/alignof or in C++. Therefore, the parenthesized expression is
       // the start of a unary-expression, but doesn't include any postfix
       // pieces. Parse these now if present.
       if (!Operand.isInvalid())
         Operand = ParsePostfixExpressionSuffix(Operand.get());
     }
   }

clang/lib/Sema/DeclSpec.cpp

#include "clang/Basic/OpenCLImageTypes.def"
       return false;
 
     case TST_decltype_auto:
       // This must have an initializer, so can't be a function declaration,
       // even if the initializer has function type.
       return false;
 
     case TST_decltype:
+    case TST_typeof_unqualExpr:
     case TST_typeofExpr:
       if (Expr *E = DS.getRepAsExpr())
         return E->getType()->isFunctionType();
       return false;
 
 #define TRANSFORM_TYPE_TRAIT_DEF(_, Trait) case TST_##Trait:
 #include "clang/Basic/TransformTypeTraits.def"
     case TST_typename:
+    case TST_typeof_unqualType:
     case TST_typeofType: {
       QualType QT = DS.getRepAsType().get();
       if (QT.isNull())
         return false;
 
       if (const LocInfoType *LIT = dyn_cast<LocInfoType>(QT))
         QT = LIT->getType();
 
const char *DeclSpec::getSpecifierName(DeclSpec::TST T,
   case DeclSpec::TST_enum:        return "enum";
   case DeclSpec::TST_class:       return "class";
   case DeclSpec::TST_union:       return "union";
   case DeclSpec::TST_struct:      return "struct";
   case DeclSpec::TST_interface:   return "__interface";
   case DeclSpec::TST_typename:    return "type-name";
   case DeclSpec::TST_typeofType:
   case DeclSpec::TST_typeofExpr:  return "typeof";
+  case DeclSpec::TST_typeof_unqualType:
+  case DeclSpec::TST_typeof_unqualExpr: return "typeof_unqual";
   case DeclSpec::TST_auto:        return "auto";
   case DeclSpec::TST_auto_type:   return "__auto_type";
   case DeclSpec::TST_decltype:    return "(decltype)";
   case DeclSpec::TST_decltype_auto: return "decltype(auto)";
 #define TRANSFORM_TYPE_TRAIT_DEF(_, Trait)                                     \
   case DeclSpec::TST_##Trait:                                                  \
     return "__" #Trait;
 #include "clang/Basic/TransformTypeTraits.def"

clang/lib/Sema/SemaDecl.cpp

   // Of course, we also need to rebuild any type referencing such a
   // type.  It's safest to just say "dependent", but we call out a
   // few cases here.
 
   DeclSpec &DS = D.getMutableDeclSpec();
   switch (DS.getTypeSpecType()) {
   case DeclSpec::TST_typename:
   case DeclSpec::TST_typeofType:
+  case DeclSpec::TST_typeof_unqualType:
 #define TRANSFORM_TYPE_TRAIT_DEF(_, Trait) case DeclSpec::TST_##Trait:
 #include "clang/Basic/TransformTypeTraits.def"
   case DeclSpec::TST_atomic: {
     // Grab the type from the parser.
     TypeSourceInfo *TSI = nullptr;
     QualType T = S.GetTypeFromParser(DS.getRepAsType(), &TSI);
     if (T.isNull() || !T->isInstantiationDependentType()) break;
 

 
     // Store the new type back in the decl spec.
     ParsedType LocType = S.CreateParsedType(TSI->getType(), TSI);
     DS.UpdateTypeRep(LocType);
     break;
   }
 
   case DeclSpec::TST_decltype:
+  case DeclSpec::TST_typeof_unqualExpr:
   case DeclSpec::TST_typeofExpr: {
     Expr *E = DS.getRepAsExpr();
     ExprResult Result = S.RebuildExprInCurrentInstantiation(E);
     if (Result.isInvalid()) return true;
     DS.UpdateExprRep(Result.get());
     break;
   }
 

clang/lib/Sema/SemaTemplateVariadic.cpp

Optional<unsigned> Sema::getNumArgumentsInExpansion(QualType T,
 
   return Result;
 }
 
 bool Sema::containsUnexpandedParameterPacks(Declarator &D) {
   const DeclSpec &DS = D.getDeclSpec();
   switch (DS.getTypeSpecType()) {
   case TST_typename:
+  case TST_typeof_unqualType:
   case TST_typeofType:
 #define TRANSFORM_TYPE_TRAIT_DEF(_, Trait) case TST_##Trait:
 #include "clang/Basic/TransformTypeTraits.def"
   case TST_atomic: {
     QualType T = DS.getRepAsType().get();
     if (!T.isNull() && T->containsUnexpandedParameterPack())
       return true;
     break;
   }
 
+  case TST_typeof_unqualExpr:
   case TST_typeofExpr:
   case TST_decltype:
   case TST_bitint:
     if (DS.getRepAsExpr() &&
         DS.getRepAsExpr()->containsUnexpandedParameterPack())
       return true;
     break;
 

clang/lib/Sema/SemaType.cpp

     Result = S.GetTypeFromParser(DS.getRepAsType());
     if (Result.isNull()) {
       declarator.setInvalidType(true);
     }
 
     // TypeQuals handled by caller.
     break;
   }
+  case DeclSpec::TST_typeof_unqualType:
   case DeclSpec::TST_typeofType:
     // FIXME: Preserve type source info.
     Result = S.GetTypeFromParser(DS.getRepAsType());
     assert(!Result.isNull() && "Didn't get a type for typeof?");
     if (!Result->isDependentType())
       if (const TagType *TT = Result->getAs<TagType>())
         S.DiagnoseUseOfDecl(TT->getDecl(), DS.getTypeSpecTypeLoc());
     // TypeQuals handled by caller.
-    Result = Context.getTypeOfType(Result);
+    Result = Context.getTypeOfType(Result, DS.getTypeSpecType() ==
+                                               DeclSpec::TST_typeof_unqualType);
     break;
+  case DeclSpec::TST_typeof_unqualExpr:
   case DeclSpec::TST_typeofExpr: {
     Expr *E = DS.getRepAsExpr();
     assert(E && "Didn't get an expression for typeof?");
     // TypeQuals handled by caller.
-    Result = S.BuildTypeofExprType(E);
+    Result = S.BuildTypeofExprType(E, DS.getTypeSpecType() ==
+                                          DeclSpec::TST_typeof_unqualExpr);
     if (Result.isNull()) {
       Result = Context.IntTy;
       declarator.setInvalidType(true);
     }
     break;
   }
   case DeclSpec::TST_decltype: {
     Expr *E = DS.getRepAsExpr();

         TL.copy(NamedTL);
       } else {
         TL.copy(OldTL.castAs<TemplateSpecializationTypeLoc>());
         assert(TL.getRAngleLoc() == OldTL.castAs<TemplateSpecializationTypeLoc>().getRAngleLoc());
       }
 
     }
     void VisitTypeOfExprTypeLoc(TypeOfExprTypeLoc TL) {
-      assert(DS.getTypeSpecType() == DeclSpec::TST_typeofExpr);
+      assert(DS.getTypeSpecType() == DeclSpec::TST_typeofExpr ||
+             DS.getTypeSpecType() == DeclSpec::TST_typeof_unqualExpr);
       TL.setTypeofLoc(DS.getTypeSpecTypeLoc());
       TL.setParensRange(DS.getTypeofParensRange());
     }
     void VisitTypeOfTypeLoc(TypeOfTypeLoc TL) {
-      assert(DS.getTypeSpecType() == DeclSpec::TST_typeofType);
+      assert(DS.getTypeSpecType() == DeclSpec::TST_typeofType ||
+             DS.getTypeSpecType() == DeclSpec::TST_typeof_unqualType);
       TL.setTypeofLoc(DS.getTypeSpecTypeLoc());
       TL.setParensRange(DS.getTypeofParensRange());
       assert(DS.getRepAsType());
       TypeSourceInfo *TInfo = nullptr;
       Sema::GetTypeFromParser(DS.getRepAsType(), &TInfo);
       TL.setUnderlyingTInfo(TInfo);
     }
     void VisitDecltypeTypeLoc(DecltypeTypeLoc TL) {

                                  const CXXScopeSpec &SS, QualType T,
                                  TagDecl *OwnedTagDecl) {
   if (T.isNull())
     return T;
   return Context.getElaboratedType(
       Keyword, SS.isValid() ? SS.getScopeRep() : nullptr, T, OwnedTagDecl);
 }
 
-QualType Sema::BuildTypeofExprType(Expr *E) {
+QualType Sema::BuildTypeofExprType(Expr *E, bool IsUnqual) {
   assert(!E->hasPlaceholderType() && "unexpected placeholder");
 
   if (!getLangOpts().CPlusPlus && E->refersToBitField())
-    Diag(E->getExprLoc(), diag::err_sizeof_alignof_typeof_bitfield) << 2;
+    Diag(E->getExprLoc(), diag::err_sizeof_alignof_typeof_bitfield)
+        << (IsUnqual ? 3 : 2);
 
   if (!E->isTypeDependent()) {
     QualType T = E->getType();
     if (const TagType *TT = T->getAs<TagType>())
       DiagnoseUseOfDecl(TT->getDecl(), E->getExprLoc());
   }
-  return Context.getTypeOfExprType(E);
+  return Context.getTypeOfExprType(E, IsUnqual);
 }
 
 /// getDecltypeForExpr - Given an expr, will return the decltype for
 /// that expression, according to the rules in C++11
 /// [dcl.type.simple]p4 and C++11 [expr.lambda.prim]p18.
 QualType Sema::getDecltypeForExpr(Expr *E) {
   if (E->isTypeDependent())
     return Context.DependentTy;

clang/lib/Sema/TreeTransform.h

   QualType RebuildEnumType(EnumDecl *Enum) {
     return SemaRef.Context.getTypeDeclType(Enum);
   }
 
   /// Build a new typeof(expr) type.
   ///
   /// By default, performs semantic analysis when building the typeof type.
   /// Subclasses may override this routine to provide different behavior.
-  QualType RebuildTypeOfExprType(Expr *Underlying, SourceLocation Loc);
+  QualType RebuildTypeOfExprType(Expr *Underlying, SourceLocation Loc,
+                                 bool IsUnqual);
 
   /// Build a new typeof(type) type.
   ///
   /// By default, builds a new TypeOfType with the given underlying type.
-  QualType RebuildTypeOfType(QualType Underlying);
+  QualType RebuildTypeOfType(QualType Underlying, bool IsUnqual);
 
   /// Build a new unary transform type.
   QualType RebuildUnaryTransformType(QualType BaseType,
                                      UnaryTransformType::UTTKind UKind,
                                      SourceLocation Loc);
 
   /// Build a new C++11 decltype type.
   ///

   if (E.isInvalid())
     return QualType();
 
   E = SemaRef.HandleExprEvaluationContextForTypeof(E.get());
   if (E.isInvalid())
     return QualType();
 
   QualType Result = TL.getType();
+  bool IsUnqual = Result->getAs<TypeOfExprType>()->isUnqual();
   if (getDerived().AlwaysRebuild() ||
       E.get() != TL.getUnderlyingExpr()) {
-    Result = getDerived().RebuildTypeOfExprType(E.get(), TL.getTypeofLoc());
+    Result = getDerived().RebuildTypeOfExprType(E.get(), TL.getTypeofLoc(),
+                                                IsUnqual);
     if (Result.isNull())
       return QualType();
   }
-  else E.get();
 
   TypeOfExprTypeLoc NewTL = TLB.push<TypeOfExprTypeLoc>(Result);
   NewTL.setTypeofLoc(TL.getTypeofLoc());
   NewTL.setLParenLoc(TL.getLParenLoc());
   NewTL.setRParenLoc(TL.getRParenLoc());
 
   return Result;
 }
 
 template<typename Derived>
 QualType TreeTransform<Derived>::TransformTypeOfType(TypeLocBuilder &TLB,
                                                      TypeOfTypeLoc TL) {
   TypeSourceInfo* Old_Under_TI = TL.getUnderlyingTInfo();
   TypeSourceInfo* New_Under_TI = getDerived().TransformType(Old_Under_TI);
   if (!New_Under_TI)
     return QualType();
 
   QualType Result = TL.getType();
+  bool IsUnqual = Result->getAs<TypeOfType>()->isUnqual();
   if (getDerived().AlwaysRebuild() || New_Under_TI != Old_Under_TI) {
-    Result = getDerived().RebuildTypeOfType(New_Under_TI->getType());
+    Result = getDerived().RebuildTypeOfType(New_Under_TI->getType(), IsUnqual);
     if (Result.isNull())
       return QualType();
   }
 
   TypeOfTypeLoc NewTL = TLB.push<TypeOfTypeLoc>(Result);
   NewTL.setTypeofLoc(TL.getTypeofLoc());
   NewTL.setLParenLoc(TL.getLParenLoc());
   NewTL.setRParenLoc(TL.getRParenLoc());

     assert(isa<UnresolvedUsingTypenameDecl>(D) &&
            "UnresolvedUsingTypenameDecl transformed to non-using decl");
     return SemaRef.Context.getTypeDeclType(
         cast<UnresolvedUsingTypenameDecl>(D));
   }
 }
 
 template <typename Derived>
-QualType TreeTransform<Derived>::RebuildTypeOfExprType(Expr *E,
-                                                       SourceLocation) {
-  return SemaRef.BuildTypeofExprType(E);
+QualType TreeTransform<Derived>::RebuildTypeOfExprType(Expr *E, SourceLocation,
+                                                       bool IsUnqual) {
+  return SemaRef.BuildTypeofExprType(E, IsUnqual);
 }
 
 template<typename Derived>
-QualType TreeTransform<Derived>::RebuildTypeOfType(QualType Underlying) {
-  return SemaRef.Context.getTypeOfType(Underlying);
+QualType TreeTransform<Derived>::RebuildTypeOfType(QualType Underlying,
+                                                   bool IsUnqual) {
+  return SemaRef.Context.getTypeOfType(Underlying, IsUnqual);
 }
 
 template <typename Derived>
 QualType TreeTransform<Derived>::RebuildDecltypeType(Expr *E, SourceLocation) {
   return SemaRef.BuildDecltypeType(E);
 }
 
 template<typename Derived>

clang/test/C/C2x/n2927.c

+// RUN: %clang_cc1 -verify -std=c2x %s
+
+/* WG14 N2927: yes
+ * Not-so-magic: typeof
+ */
+
+// These examples originated in WG14 N2927 but were modified to test particular
+// compiler behaviors. Each of these examples come from C2x 6.7.2.5.
+
+// EXAMPLE 1
+typeof(1 + 1) func();
+int func();
+
+// EXAMPLE 2
+const _Atomic int purr = 0;
+const int meow = 1;
+const char *const mew[] = {
+  "aardvark",
+  "bluejay",
+  "catte",
+};
+
+extern typeof_unqual(purr) plain_purr;
+extern int plain_purr;
+
+extern typeof(_Atomic typeof(meow)) atomic_meow;
+extern const _Atomic int atomic_meow;
+
+extern typeof(mew) mew_array;
+extern const char *const mew_array[3];
+
+extern typeof_unqual(mew) mew2_array;
+extern const char *mew2_array[3];
+
+// EXAMPLE 3
+void foo(int argc, char *argv[]) { // expected-note 2 {{declared here}}
+  _Static_assert(sizeof(typeof('p')) == sizeof(int));
+  _Static_assert(sizeof(typeof('p')) == sizeof('p'));
+  _Static_assert(sizeof(typeof((char)'p')) == sizeof(char));
+  _Static_assert(sizeof(typeof((char)'p')) == sizeof((char)'p'));
+  _Static_assert(sizeof(typeof("meow")) == sizeof(char[5]));
+  _Static_assert(sizeof(typeof("meow")) == sizeof("meow"));
+  _Static_assert(sizeof(typeof(argc)) == sizeof(int));
+  _Static_assert(sizeof(typeof(argc)) == sizeof(argc));
+  _Static_assert(sizeof(typeof(argv)) == sizeof(char**));
+  _Static_assert(sizeof(typeof(argv)) == sizeof(argv)); // expected-warning {{sizeof on array function parameter will return size of 'char **' instead of 'char *[]'}}
+
+  _Static_assert(sizeof(typeof_unqual('p')) == sizeof(int));
+  _Static_assert(sizeof(typeof_unqual('p')) == sizeof('p'));
+  _Static_assert(sizeof(typeof_unqual((char)'p')) == sizeof(char));
+  _Static_assert(sizeof(typeof_unqual((char)'p')) == sizeof((char)'p'));
+  _Static_assert(sizeof(typeof_unqual("meow")) == sizeof(char[5]));
+  _Static_assert(sizeof(typeof_unqual("meow")) == sizeof("meow"));
+  _Static_assert(sizeof(typeof_unqual(argc)) == sizeof(int));
+  _Static_assert(sizeof(typeof_unqual(argc)) == sizeof(argc));
+  _Static_assert(sizeof(typeof_unqual(argv)) == sizeof(char**));
+  _Static_assert(sizeof(typeof_unqual(argv)) == sizeof(argv)); // expected-warning {{sizeof on array function parameter will return size of 'char **' instead of 'char *[]'}}
+}
+
+// EXAMPLE 4
+void bar(int argc) {
+  extern int val;
+  extern typeof(typeof_unqual(typeof(argc)))val;
+}
+
+// EXAMPLE 5 is tested by n2927_2.c because it is a codegen test.
+
+// EXAMPLE 6
+extern const char *y[4];
+extern typeof(typeof(const char*)[4]) y;
+
+// EXAMPLE 7
+void f(int);
+
+void g(double);
+typeof(f(5)) g(double x);          // g has type "void(double)"
+
+extern void (*h)(double);
+extern typeof(g)* h;               // h has type "void(*)(double)"
+extern typeof(true ? g : 0) h;  // h has type "void(*)(double)"
+
+void j(double *, double **);
+void j(double A[5], typeof(A)* B); // j has type "void(double*, double**)"
+
+extern typeof(double[]) D;         // D has an incomplete type
+
+extern double C[2];
+extern typeof(D) C;                // C has type "double[2]"
+
+typeof(D) D = { 5, 8.9, 0.1, 99 }; // D is now completed to "double[4]"
+extern double E[4];
+extern typeof(D) E;                // E has type "double[4]" from D痴 completed type

clang/test/C/C2x/n2927_2.c

+// RUN: %clang_cc1 -emit-llvm -o - -std=c2x %s | FileCheck %s
+
+// C2x 6.7.2.5 EXAMPLE 5
+unsigned long long vla_size(int n) {
+// CHECK: vla_size
+
+  return sizeof(
+    typeof_unqual(char[n + 3])
+  ); // execution-time sizeof, translation-time typeof operation
+// CHECK: [[N_ADDR:%.*]] = alloca i32
+// CHECK: store i32 {{%.*}} ptr [[N_ADDR]]
+// CHECK: [[N:%.*]] = load i32, ptr [[N_ADDR]]
+// CHECK: [[TEMP:%.*]] = add nsw i32 [[N]], 3
+// CHECK: [[RET:%.*]] = zext i32 [[TEMP]] to i64
+// CHECK: ret i64 [[RET]]
+}
+
+int main() {
+  return (int)vla_size(10); // vla_size returns 13
+}
+

clang/test/C/C2x/n2930.c

+// RUN: %clang_cc1 -verify -std=c2x %s
+
+/* WG14 N2930: yes
+ * Consider renaming remove_quals
+ */
+
+int remove_quals;
+int typeof_unqual; // expected-error {{expected '(' after 'typeof_unqual'}}
+typeof_unqual(remove_quals) val;

clang/test/Lexer/keywords_test.c

 C99_KEYWORD(inline);
 
 // C2x Keywords.
 C2x_KEYWORD(bool);
 C2x_KEYWORD(true);
 C2x_KEYWORD(false);
 C2x_KEYWORD(static_assert);
 C2x_KEYWORD(typeof);
+C2x_KEYWORD(typeof_unqual);
 C2x_KEYWORD(thread_local);
 C2x_KEYWORD(alignas);
 C2x_KEYWORD(alignof);
 
 void f() {
 // CHECK-NONE: int asm
 // CHECK-GNU-KEYWORDS: asm ("ret" : :)
 #if __is_identifier(asm)
#ifdef FutureKeyword
   int restrict; // c89-warning {{'restrict' is a keyword in C99}}
   int inline;  // c89-warning {{'inline' is a keyword in C99}}
 
   int bool; // c89-warning {{'bool' is a keyword in C2x}}
   char true; // c89-warning {{'true' is a keyword in C2x}}
   char false; // c89-warning {{'false' is a keyword in C2x}}
   float alignof; // c89-warning {{'alignof' is a keyword in C2x}}
   int typeof; // c89-warning {{'typeof' is a keyword in C2x}}
+  int typeof_unqual; // c89-warning {{'typeof_unqual' is a keyword in C2x}}
   int alignas; // c89-warning {{'alignas' is a keyword in C2x}}
   int static_assert; // c89-warning {{'static_assert' is a keyword in C2x}}
 
 #endif

clang/test/Parser/c2x-typeof-ext-warns.c

+// RUN: %clang_cc1 -verify=c2x -std=c2x %s
+// RUN: %clang_cc1 -verify=c11 -std=c11 %s
+// RUN: %clang_cc1 -verify=gnu11 -std=gnu11 %s
+// RUN: %clang_cc1 -verify=pedantic -pedantic -std=gnu11 -Wno-comment %s
+// RUN: %clang_cc1 -verify=compat -std=c2x -Wpre-c2x-compat %s
+
+// c2x-no-diagnostics
+
+// Exercise the various circumstances under which we will diagnose use of
+// typeof and typeof_unqual as either an extension or as a compatability
+// warning. Note that GCC exposes 'typeof' as a non-conforming extension in
+// standards before C2x, and Clang has followed suit. Neither compiler exposes
+// 'typeof_unqual' as a non-conforming extension.
+
+// Show what happens with the underscored version of the keyword, which is a
+// conforming extension.
+__typeof__(int) i = 12;
+
+// Show what happens with a regular 'typeof' use.
+typeof(i) j = 12; // c11-error {{expected function body after function declarator}} \
+                     pedantic-warning {{extension used}} \
+                     compat-warning {{'typeof' is incompatible with C standards before C2x}}
+
+// Same for 'typeof_unqual'.
+typeof_unqual(j) k = 12; // c11-error {{expected function body after function declarator}} \
+                            gnu11-error {{expected function body after function declarator}} \
+                            pedantic-error {{expected function body after function declarator}} \
+                            compat-warning {{'typeof_unqual' is incompatible with C standards before C2x}}
+

clang/test/Parser/c2x-typeof.c

+// RUN: %clang_cc1 -verify -std=c2x %s
+
+// Demonstrate that we don't support the expression form without parentheses in
+// C2x mode.
+typeof 0 int i = 12;         // expected-error {{expected '(' after 'typeof'}} expected-error {{expected identifier or '('}}
+typeof 0 j = 12;             // expected-error {{expected '(' after 'typeof'}} expected-error {{expected identifier or '('}}
+typeof_unqual 0 k = 12;      // expected-error {{expected '(' after 'typeof_unqual'}} expected-error {{expected identifier or '('}}
+typeof_unqual 0 int l = 12;  // expected-error {{expected '(' after 'typeof_unqual'}} expected-error {{expected identifier or '('}}
+
+// Show that combining typeof with another type specifier fails, but otherwise
+// the expression and type forms are both parsed properly.
+typeof(0) int a = 12;        // expected-error {{cannot combine with previous 'typeof' declaration specifier}}
+typeof(0) b = 12;
+typeof_unqual(0) int c = 12; // expected-error {{cannot combine with previous 'typeof_unqual' declaration specifier}}
+typeof_unqual(0) d = 12;
+typeof(int) e = 12;
+typeof_unqual(int) f = 12;
+
+// Show that we can parse nested constructs of both forms.
+typeof(typeof(0)) w;
+typeof_unqual(typeof(0)) x;
+typeof(typeof_unqual(0)) y;
+typeof_unqual(typeof_unqual(0)) z;
+
+// Show that you can spell the type in functions, structures, or as the base
+// type of an enumeration.
+typeof(b) func1(typeof(b) c);
+typeof_unqual(b) func2(typeof_unqual(b) c);
+
+struct S {
+  typeof(b) i;
+  typeof_unqual(b) j;
+} s;
+
+enum E1 : typeof(b) { FirstZero };
+enum E2 : typeof_unqual(b) { SecondZero };
+
+// Show that you can use this type in place of another type and everything
+// works as expected.
+_Static_assert(__builtin_offsetof(typeof(struct S), i) == 0);
+_Static_assert(__builtin_offsetof(typeof(s), i) == 0);
+_Static_assert(__builtin_offsetof(typeof_unqual(struct S), i) == 0);
+_Static_assert(__builtin_offsetof(typeof_unqual(s), i) == 0);
+

clang/test/Sema/c2x-typeof.c

+// RUN: %clang_cc1 -verify -std=c2x %s
+
+// Demonstrate that we get the correct type information. Do this by leaning
+// heavily on redeclarations needing to use the same type for both decls.
+extern int i;
+extern typeof(i) i;
+extern typeof_unqual(i) i;
+
+extern const int j;
+extern typeof(j) j;
+
+extern const int n;         // expected-note 2 {{previous declaration is here}}
+extern typeof(i) n;         // expected-error {{redeclaration of 'n' with a different type: 'typeof (i)' (aka 'int') vs 'const int'}}
+extern typeof_unqual(n) n;  // expected-error {{redeclaration of 'n' with a different type: 'typeof_unqual (n)' (aka 'int') vs 'const int'}}
+
+// Ensure we get a redeclaration error here for the types not matching.
+extern typeof(j) k;        // expected-note {{previous declaration is here}}
+extern typeof_unqual(j) k; // expected-error {{redeclaration of 'k' with a different type: 'typeof_unqual (j)' (aka 'int') vs 'typeof (j)' (aka 'const int')}}
+
+// Make sure the type-form of the operator also works.
+extern typeof(int) l;
+extern typeof_unqual(const int) l;
+
+extern typeof(const int) m;        // expected-note {{previous declaration is here}}
+extern typeof_unqual(const int) m; // expected-error {{redeclaration of 'm' with a different type: 'typeof_unqual(const int)' (aka 'int') vs 'typeof(const int)' (aka 'const int')}}
+
+// Show that we can use an incomplete type which is then completed later.
+extern typeof(struct T) *o;
+struct T { int a; } t;
+extern typeof(struct T) *o;
+extern typeof(t) *o;
+extern typeof(&t) o;
+extern typeof_unqual(volatile struct T) *o;
+extern typeof_unqual(t) *o;
+extern typeof_unqual(&t) o;
+
+// Show that we properly strip the _Atomic qualifier.
+extern _Atomic int i2;
+extern _Atomic(int) i2;
+extern typeof(i2) i2;        // expected-note {{previous declaration is here}}
+extern typeof_unqual(i2) i2; // expected-error {{redeclaration of 'i2' with a different type: 'typeof_unqual (i2)' (aka 'int') vs 'typeof (i2)' (aka '_Atomic(int)')}}
+
+// We cannot take the type of a bit-field.
+struct S {
+  int bit : 4;
+} s;
+
+typeof(s.bit) nope1; // expected-error {{invalid application of 'typeof' to bit-field}}
+typeof_unqual(s.bit) nope2; // expected-error {{invalid application of 'typeof_unqual' to bit-field}}
+
+// Show that we properly resolve nested typeof specifiers.
+extern typeof(typeof(0)) i3;
+extern typeof(typeof(int)) i3;
+extern typeof(typeof_unqual(0)) i3;
+extern typeof(typeof_unqual(int)) i3;
+extern typeof_unqual(typeof(0)) i3;
+extern typeof_unqual(typeof(int)) i3;
+extern typeof_unqual(typeof_unqual(0)) i3;
+extern typeof_unqual(typeof_unqual(int)) i3;
+extern typeof(typeof_unqual(j)) i3;
+extern typeof(typeof_unqual(const int)) i3;
+extern typeof_unqual(typeof(j)) i3;
+extern typeof_unqual(typeof(const int)) i3;
+extern typeof_unqual(typeof_unqual(j)) i3;
+extern typeof_unqual(typeof_unqual(const int)) i3;
+
+// Both of these result in a const int rather than an int.
+extern typeof(typeof(j)) i4;
+extern typeof(typeof(const int)) i4;
+
+// Ensure that redundant qualifiers are allowed, same as with typedefs.
+typedef const int CInt;
+extern CInt i4;
+extern const CInt i4;
+extern const typeof(j) i4;
+extern const typeof(const int) i4;
+extern const typeof(CInt) i4;
+
+// Qualifiers are not redundant here, but validating that the qualifiers are
+// still honored.
+extern const typeof_unqual(j) i4;
+extern const typeof_unqual(const int) i4;
+extern const typeof_unqual(CInt) i4;
+
+// Show that type attributes are stripped from the unqualified version.
+extern __attribute__((address_space(0))) int type_attr_test_2_obj;
+extern int type_attr_test_2;
+extern typeof_unqual(type_attr_test_2_obj) type_attr_test_2;            // expected-note {{previous declaration is here}}
+extern __attribute__((address_space(0))) int type_attr_test_2;          // expected-error {{redeclaration of 'type_attr_test_2' with a different type: '__attribute__((address_space(0))) int' vs 'typeof_unqual (type_attr_test_2_obj)' (aka 'int')}}
+
+// Ensure that an invalid type doesn't cause crashes.
+void invalid_param_fn(__attribute__((address_space(1))) int i); // expected-error {{parameter may not be qualified with an address space}}
+typeof(invalid_param_fn) invalid_param_1;
+typeof_unqual(invalid_param_fn) invalid_param_2;

clang/www/c_status.html

         <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3011.htm">N3011</a></td>
         <td class="unknown" align="center">Unknown</td>
       </tr>
     <tr id="typeof">
       <td rowspan="3">Not-so-magic: typeof</td>
     </tr>
       <tr> <!-- Feb 2022 -->
         <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2927.htm">N2927</a></td>
-        <td class="partial" align="center">
-          <details><summary>Partial</summary>
-            Clang supports <code>typeof</code> in GNU standards mode, but its
-            compatibility with this proposal is unknown. Also, Clang does not yet
-            support remove_quals.
-          </details>
-        </td>
+        <td class="unreleased" align="center">Clang 16</td>
       </tr>
       <tr> <!-- Jul 2022 -->
         <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2930.pdf">N2930</a></td>
-        <td class="none" align="center">No</td>
+        <td class="unreleased" align="center">Clang 16</td>
       </tr>
     <tr>
       <td>Type annex tgmath narrowing macros with integer args v2</td>
       <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2931.pdf">N2931</a></td>
       <td class="unknown" align="center">Unknown</td>
     </tr>
     <tr>
       <td>Revise spelling of keywords v7</td>