C1X: implement generic selections

As an extension, generic selection support has been added for all
supported languages.  The syntax is the same as for C1X.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@129554 91177308-0d34-0410-b5e6-96231b3b80d8

40 files changed, 845 insertions, 57 deletions

diff --git a/docs/LanguageExtensions.html b/docs/LanguageExtensions.html
index b16c38c768..70c0ff2834 100644
--- a/docs/LanguageExtensions.html
+++ b/docs/LanguageExtensions.html
@@ -52,6 +52,7 @@ td {
 <li><a href="#checking_type_traits">Checks for Type Traits</a></li>
 <li><a href="#blocks">Blocks</a></li>
 <li><a href="#overloading-in-c">Function Overloading in C</a></li>
+<li><a href="#generic-selections">Generic Selections</a></li>
 <li><a href="#builtins">Builtin Functions</a>
   <ul>
   <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
@@ -604,6 +605,20 @@ caveats to this use of name mangling:</p>
 
 
 <!-- ======================================================================= -->
+<h2 id="generic-selections">Generic Selections</h2>
+<!-- ======================================================================= -->
+
+<p>The C1X generic selection expression is available in all languages
+supported by Clang.  The syntax is the same as that given in the C1X draft
+standard.</p>
+
+<p>In C, type compatibility is decided according to the rules given in the
+appropriate standard, but in C++, which lacks the type compatibility rules
+used in C, types are considered compatible only if they are equivalent.</p>
+
+<p>Query for this feature with __has_feature(generic_selections).</p>
+
+<!-- ======================================================================= -->
 <h2 id="builtins">Builtin Functions</h2>
 <!-- ======================================================================= -->
 
diff --git a/include/clang/AST/Expr.h b/include/clang/AST/Expr.h
index ef677610e6..9de01af64f 100644
--- a/include/clang/AST/Expr.h
+++ b/include/clang/AST/Expr.h
@@ -3679,6 +3679,118 @@ public:
 };
 
 
+/// \brief Represents a C1X generic selection.
+///
+/// A generic selection (C1X 6.5.1.1) contains an unevaluated controlling
+/// expression, followed by one or more generic associations.  Each generic
+/// association specifies a type name and an expression, or "default" and an
+/// expression (in which case it is known as a default generic association).
+/// The type and value of the generic selection are identical to those of its
+/// result expression, which is defined as the expression in the generic
+/// association with a type name that is compatible with the type of the
+/// controlling expression, or the expression in the default generic association
+/// if no types are compatible.  For example:
+///
+/// @code
+/// _Generic(X, double: 1, float: 2, default: 3)
+/// @endcode
+///
+/// The above expression evaluates to 1 if 1.0 is substituted for X, 2 if 1.0f
+/// or 3 if "hello".
+///
+/// As an extension, generic selections are allowed in C++, where the following
+/// additional semantics apply:
+///
+/// Any generic selection whose controlling expression is type-dependent or
+/// which names a dependent type in its association list is result-dependent,
+/// which means that the choice of result expression is dependent.
+/// Result-dependent generic associations are both type- and value-dependent.
+class GenericSelectionExpr : public Expr {
+  enum { CONTROLLING, END_EXPR };
+  TypeSourceInfo **AssocTypes;
+  Stmt **SubExprs;
+  unsigned NumAssocs, ResultIndex;
+  SourceLocation GenericLoc, DefaultLoc, RParenLoc;
+
+public:
+  GenericSelectionExpr(ASTContext &Context,
+                       SourceLocation GenericLoc, Expr *ControllingExpr,
+                       TypeSourceInfo **AssocTypes, Expr **AssocExprs,
+                       unsigned NumAssocs, SourceLocation DefaultLoc,
+                       SourceLocation RParenLoc,
+                       bool ContainsUnexpandedParameterPack,
+                       unsigned ResultIndex);
+
+  /// This constructor is used in the result-dependent case.
+  GenericSelectionExpr(ASTContext &Context,
+                       SourceLocation GenericLoc, Expr *ControllingExpr,
+                       TypeSourceInfo **AssocTypes, Expr **AssocExprs,
+                       unsigned NumAssocs, SourceLocation DefaultLoc,
+                       SourceLocation RParenLoc,
+                       bool ContainsUnexpandedParameterPack);
+
+  explicit GenericSelectionExpr(EmptyShell Empty)
+    : Expr(GenericSelectionExprClass, Empty) { }
+
+  unsigned getNumAssocs() const { return NumAssocs; }
+
+  SourceLocation getGenericLoc() const { return GenericLoc; }
+  SourceLocation getDefaultLoc() const { return DefaultLoc; }
+  SourceLocation getRParenLoc() const { return RParenLoc; }
+
+  const Expr *getAssocExpr(unsigned i) const {
+    return cast<Expr>(SubExprs[END_EXPR+i]);
+  }
+  Expr *getAssocExpr(unsigned i) { return cast<Expr>(SubExprs[END_EXPR+i]); }
+
+  const TypeSourceInfo *getAssocTypeSourceInfo(unsigned i) const {
+    return AssocTypes[i];
+  }
+  TypeSourceInfo *getAssocTypeSourceInfo(unsigned i) { return AssocTypes[i]; }
+
+  QualType getAssocType(unsigned i) const {
+    if (const TypeSourceInfo *TS = getAssocTypeSourceInfo(i))
+      return TS->getType();
+    else
+      return QualType();
+  }
+
+  const Expr *getControllingExpr() const {
+    return cast<Expr>(SubExprs[CONTROLLING]);
+  }
+  Expr *getControllingExpr() { return cast<Expr>(SubExprs[CONTROLLING]); }
+
+  /// Whether this generic selection is result-dependent.
+  bool isResultDependent() const { return ResultIndex == -1U; }
+
+  /// The zero-based index of the result expression's generic association in
+  /// the generic selection's association list.  Defined only if the
+  /// generic selection is not result-dependent.
+  unsigned getResultIndex() const {
+    assert(!isResultDependent() && "Generic selection is result-dependent");
+    return ResultIndex;
+  }
+
+  /// The generic selection's result expression.  Defined only if the
+  /// generic selection is not result-dependent.
+  const Expr *getResultExpr() const { return getAssocExpr(getResultIndex()); }
+  Expr *getResultExpr() { return getAssocExpr(getResultIndex()); }
+
+  SourceRange getSourceRange() const {
+    return SourceRange(GenericLoc, RParenLoc);
+  }
+  static bool classof(const Stmt *T) {
+    return T->getStmtClass() == GenericSelectionExprClass;
+  }
+  static bool classof(const GenericSelectionExpr *) { return true; }
+
+  child_range children() {
+    return child_range(SubExprs, SubExprs+END_EXPR+NumAssocs);
+  }
+
+  friend class ASTStmtReader;
+};
+
 //===----------------------------------------------------------------------===//
 // Clang Extensions
 //===----------------------------------------------------------------------===//
diff --git a/include/clang/AST/RecursiveASTVisitor.h b/include/clang/AST/RecursiveASTVisitor.h
index 2a4348feac..d4a90fbefd 100644
--- a/include/clang/AST/RecursiveASTVisitor.h
+++ b/include/clang/AST/RecursiveASTVisitor.h
@@ -1777,6 +1777,22 @@ bool RecursiveASTVisitor<Derived>::TraverseInitListExpr(InitListExpr *S) {
   return true;
 }
 
+// GenericSelectionExpr is a special case because the types and expressions
+// are interleaved.  We also need to watch out for null types (default
+// generic associations).
+template<typename Derived>
+bool RecursiveASTVisitor<Derived>::
+TraverseGenericSelectionExpr(GenericSelectionExpr *S) {
+  TRY_TO(WalkUpFromGenericSelectionExpr(S));
+  TRY_TO(TraverseStmt(S->getControllingExpr()));
+  for (unsigned i = 0; i != S->getNumAssocs(); ++i) {
+    if (TypeSourceInfo *TS = S->getAssocTypeSourceInfo(i))
+      TRY_TO(TraverseTypeLoc(TS->getTypeLoc()));
+    TRY_TO(TraverseStmt(S->getAssocExpr(i)));
+  }
+  return true;
+}
+
 DEF_TRAVERSE_STMT(CXXScalarValueInitExpr, {
     // This is called for code like 'return T()' where T is a built-in
     // (i.e. non-class) type.
diff --git a/include/clang/Basic/DiagnosticParseKinds.td b/include/clang/Basic/DiagnosticParseKinds.td
index 7baceb50bd..03067e845c 100644
--- a/include/clang/Basic/DiagnosticParseKinds.td
+++ b/include/clang/Basic/DiagnosticParseKinds.td
@@ -67,6 +67,13 @@ def ext_ms_enum_fixed_underlying_type : Extension<
   "enumeration types with a fixed underlying type are a Microsoft extension">, 
   InGroup<Microsoft>;
 
+def ext_c1x_generic_selection : Extension<
+  "generic selections are a C1X-specific feature">;
+def err_duplicate_default_assoc : Error<
+  "duplicate default generic association">;
+def note_previous_default_assoc : Note<
+  "previous default generic association is here">;
+
 def ext_gnu_indirect_goto : Extension<
   "use of GNU indirect-goto extension">, InGroup<GNU>;
 def ext_gnu_address_of_label : Extension<
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index b96c461c6c..bddfff2f6e 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3646,6 +3646,21 @@ def warn_stringcompare : Warning<
   "result of comparison against %select{a string literal|@encode}0 is "
   "unspecified (use strncmp instead)">;
 
+// Generic selections.
+def err_assoc_type_incomplete : Error<
+  "type %0 in generic association incomplete">;
+def err_assoc_type_nonobject : Error<
+  "type %0 in generic association not an object type">;
+def err_assoc_type_variably_modified : Error<
+  "type %0 in generic association is a variably modified type">;
+def err_assoc_compatible_types : Error<
+  "type %0 in generic association compatible with previously specified type %1">;
+def note_compat_assoc : Note<
+  "compatible type %0 specified here">;
+def err_generic_sel_no_match : Error<
+  "controlling expression type %0 not compatible with any generic association type">;
+def err_generic_sel_multi_match : Error<
+  "controlling expression type %0 compatible with %1 generic association types">;
 
 
 // Blocks
diff --git a/include/clang/Basic/StmtNodes.td b/include/clang/Basic/StmtNodes.td
index a25af44790..eaf4b85984 100644
--- a/include/clang/Basic/StmtNodes.td
+++ b/include/clang/Basic/StmtNodes.td
@@ -75,6 +75,7 @@ def DesignatedInitExpr : DStmt<Expr>;
 def ImplicitValueInitExpr : DStmt<Expr>;
 def ParenListExpr : DStmt<Expr>;
 def VAArgExpr : DStmt<Expr>;
+def GenericSelectionExpr : DStmt<Expr>;
 
 // GNU Extensions.
 def AddrLabelExpr : DStmt<Expr>;
diff --git a/include/clang/Basic/TokenKinds.def b/include/clang/Basic/TokenKinds.def
index d7d436c92c..e36803e959 100644
--- a/include/clang/Basic/TokenKinds.def
+++ b/include/clang/Basic/TokenKinds.def
@@ -238,6 +238,7 @@ KEYWORD(volatile                    , KEYALL)
 KEYWORD(while                       , KEYALL)
 KEYWORD(_Bool                       , KEYNOCXX)
 KEYWORD(_Complex                    , KEYALL)
+KEYWORD(_Generic                    , KEYALL)
 KEYWORD(_Imaginary                  , KEYALL)
 KEYWORD(__func__                    , KEYALL)
 
diff --git a/include/clang/Parse/Parser.h b/include/clang/Parse/Parser.h
index f10003fcd2..13972e6764 100644
--- a/include/clang/Parse/Parser.h
+++ b/include/clang/Parse/Parser.h
@@ -1101,6 +1101,8 @@ private:
 
   ExprResult ParseStringLiteralExpression();
 
+  ExprResult ParseGenericSelectionExpression();
+
   //===--------------------------------------------------------------------===//
   // C++ Expressions
   ExprResult ParseCXXIdExpression(bool isAddressOfOperand = false);
diff --git a/include/clang/Sema/Ownership.h b/include/clang/Sema/Ownership.h
index 5f2f0eba71..cef93fe583 100644
--- a/include/clang/Sema/Ownership.h
+++ b/include/clang/Sema/Ownership.h
@@ -383,11 +383,18 @@ namespace clang {
     template<typename T> T **takeAs() { return reinterpret_cast<T**>(take()); }
   };
 
+  /// An opaque type for threading parsed type information through the
+  /// parser.
+  typedef OpaquePtr<QualType> ParsedType;
+  typedef UnionOpaquePtr<QualType> UnionParsedType;
+
   /// A SmallVector of statements, with stack size 32 (as that is the only one
   /// used.)
   typedef ASTOwningVector<Stmt*, 32> StmtVector;
   /// A SmallVector of expressions, with stack size 12 (the maximum used.)
   typedef ASTOwningVector<Expr*, 12> ExprVector;
+  /// A SmallVector of types.
+  typedef ASTOwningVector<ParsedType, 12> TypeVector;
 
   template <class T, unsigned N> inline
   ASTMultiPtr<T> move_arg(ASTOwningVector<T, N> &vec) {
@@ -421,11 +428,6 @@ namespace clang {
     static const bool value = true;
   };
 
-  /// An opaque type for threading parsed type information through the
-  /// parser.
-  typedef OpaquePtr<QualType> ParsedType;
-  typedef UnionOpaquePtr<QualType> UnionParsedType;
-
   typedef ActionResult<Expr*> ExprResult;
   typedef ActionResult<Stmt*> StmtResult;
   typedef ActionResult<ParsedType> TypeResult;
@@ -440,6 +442,7 @@ namespace clang {
 
   typedef ASTMultiPtr<Expr*> MultiExprArg;
   typedef ASTMultiPtr<Stmt*> MultiStmtArg;
+  typedef ASTMultiPtr<ParsedType> MultiTypeArg;
   typedef ASTMultiPtr<TemplateParameterList*> MultiTemplateParamsArg;
 
   inline ExprResult ExprError() { return ExprResult(true); }
diff --git a/include/clang/Sema/Sema.h b/include/clang/Sema/Sema.h
index f03bfe49b4..1879ed9129 100644
--- a/include/clang/Sema/Sema.h
+++ b/include/clang/Sema/Sema.h
@@ -2009,6 +2009,20 @@ public:
   /// fragments (e.g. "foo" "bar" L"baz").
   ExprResult ActOnStringLiteral(const Token *Toks, unsigned NumToks);
 
+  ExprResult ActOnGenericSelectionExpr(SourceLocation KeyLoc,
+                                       SourceLocation DefaultLoc,
+                                       SourceLocation RParenLoc,
+                                       Expr *ControllingExpr,
+                                       MultiTypeArg Types,
+                                       MultiExprArg Exprs);
+  ExprResult CreateGenericSelectionExpr(SourceLocation KeyLoc,
+                                        SourceLocation DefaultLoc,
+                                        SourceLocation RParenLoc,
+                                        Expr *ControllingExpr,
+                                        TypeSourceInfo **Types,
+                                        Expr **Exprs,
+                                        unsigned NumAssocs);
+
   // Binary/Unary Operators.  'Tok' is the token for the operator.
   ExprResult CreateBuiltinUnaryOp(SourceLocation OpLoc, UnaryOperatorKind Opc,
                                   Expr *InputArg);
diff --git a/include/clang/Serialization/ASTBitCodes.h b/include/clang/Serialization/ASTBitCodes.h
index 35d6fe7f3b..e00fb3ae8b 100644
--- a/include/clang/Serialization/ASTBitCodes.h
+++ b/include/clang/Serialization/ASTBitCodes.h
@@ -878,6 +878,8 @@ namespace clang {
       EXPR_BLOCK,
       /// \brief A BlockDeclRef record.
       EXPR_BLOCK_DECL_REF,
+      /// \brief A GenericSelectionExpr record.
+      EXPR_GENERIC_SELECTION,
       
       // Objective-C
 
diff --git a/lib/AST/Expr.cpp b/lib/AST/Expr.cpp
index 259c39c7d8..1f6c2fab1b 100644
--- a/lib/AST/Expr.cpp
+++ b/lib/AST/Expr.cpp
@@ -35,18 +35,16 @@ using namespace clang;
 /// but also int expressions which are produced by things like comparisons in
 /// C.
 bool Expr::isKnownToHaveBooleanValue() const {
+  const Expr *E = IgnoreParens();
+
   // If this value has _Bool type, it is obvious 0/1.
-  if (getType()->isBooleanType()) return true;
+  if (E->getType()->isBooleanType()) return true;
   // If this is a non-scalar-integer type, we don't care enough to try. 
-  if (!getType()->isIntegralOrEnumerationType()) return false;
-  
-  if (const ParenExpr *PE = dyn_cast<ParenExpr>(this))
-    return PE->getSubExpr()->isKnownToHaveBooleanValue();
+  if (!E->getType()->isIntegralOrEnumerationType()) return false;
   
-  if (const UnaryOperator *UO = dyn_cast<UnaryOperator>(this)) {
+  if (const UnaryOperator *UO = dyn_cast<UnaryOperator>(E)) {
     switch (UO->getOpcode()) {
     case UO_Plus:
-    case UO_Extension:
       return UO->getSubExpr()->isKnownToHaveBooleanValue();
     default:
       return false;
@@ -55,10 +53,10 @@ bool Expr::isKnownToHaveBooleanValue() const {
   
   // Only look through implicit casts.  If the user writes
   // '(int) (a && b)' treat it as an arbitrary int.
-  if (const ImplicitCastExpr *CE = dyn_cast<ImplicitCastExpr>(this))
+  if (const ImplicitCastExpr *CE = dyn_cast<ImplicitCastExpr>(E))
     return CE->getSubExpr()->isKnownToHaveBooleanValue();
   
-  if (const BinaryOperator *BO = dyn_cast<BinaryOperator>(this)) {
+  if (const BinaryOperator *BO = dyn_cast<BinaryOperator>(E)) {
     switch (BO->getOpcode()) {
     default: return false;
     case BO_LT:   // Relational operators.
@@ -84,7 +82,7 @@ bool Expr::isKnownToHaveBooleanValue() const {
     }
   }
   
-  if (const ConditionalOperator *CO = dyn_cast<ConditionalOperator>(this))
+  if (const ConditionalOperator *CO = dyn_cast<ConditionalOperator>(E))
     return CO->getTrueExpr()->isKnownToHaveBooleanValue() &&
            CO->getFalseExpr()->isKnownToHaveBooleanValue();
   
@@ -1363,6 +1361,9 @@ bool Expr::isUnusedResultAWarning(SourceLocation &Loc, SourceRange &R1,
   case ParenExprClass:
     return cast<ParenExpr>(this)->getSubExpr()->
       isUnusedResultAWarning(Loc, R1, R2, Ctx);
+  case GenericSelectionExprClass:
+    return cast<GenericSelectionExpr>(this)->getResultExpr()->
+      isUnusedResultAWarning(Loc, R1, R2, Ctx);
   case UnaryOperatorClass: {
     const UnaryOperator *UO = cast<UnaryOperator>(this);
 
@@ -1573,21 +1574,20 @@ bool Expr::isUnusedResultAWarning(SourceLocation &Loc, SourceRange &R1,
 /// isOBJCGCCandidate - Check if an expression is objc gc'able.
 /// returns true, if it is; false otherwise.
 bool Expr::isOBJCGCCandidate(ASTContext &Ctx) const {
-  switch (getStmtClass()) {
+  const Expr *E = IgnoreParens();
+  switch (E->getStmtClass()) {
   default:
     return false;
   case ObjCIvarRefExprClass:
     return true;
   case Expr::UnaryOperatorClass:
-    return cast<UnaryOperator>(this)->getSubExpr()->isOBJCGCCandidate(Ctx);
-  case ParenExprClass:
-    return cast<ParenExpr>(this)->getSubExpr()->isOBJCGCCandidate(Ctx);
+    return cast<UnaryOperator>(E)->getSubExpr()->isOBJCGCCandidate(Ctx);
   case ImplicitCastExprClass:
-    return cast<ImplicitCastExpr>(this)->getSubExpr()->isOBJCGCCandidate(Ctx);
+    return cast<ImplicitCastExpr>(E)->getSubExpr()->isOBJCGCCandidate(Ctx);
   case CStyleCastExprClass:
-    return cast<CStyleCastExpr>(this)->getSubExpr()->isOBJCGCCandidate(Ctx);
+    return cast<CStyleCastExpr>(E)->getSubExpr()->isOBJCGCCandidate(Ctx);
   case DeclRefExprClass: {
-    const Decl *D = cast<DeclRefExpr>(this)->getDecl();
+    const Decl *D = cast<DeclRefExpr>(E)->getDecl();
     if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
       if (VD->hasGlobalStorage())
         return true;
@@ -1600,11 +1600,11 @@ bool Expr::isOBJCGCCandidate(ASTContext &Ctx) const {
     return false;
   }
   case MemberExprClass: {
-    const MemberExpr *M = cast<MemberExpr>(this);
+    const MemberExpr *M = cast<MemberExpr>(E);
     return M->getBase()->isOBJCGCCandidate(Ctx);
   }
   case ArraySubscriptExprClass:
-    return cast<ArraySubscriptExpr>(this)->getBase()->isOBJCGCCandidate(Ctx);
+    return cast<ArraySubscriptExpr>(E)->getBase()->isOBJCGCCandidate(Ctx);
   }
 }
 
@@ -1827,6 +1827,11 @@ Expr::CanThrowResult Expr::CanThrow(ASTContext &C) const {
       return CT_Dependent;
     return cast<ChooseExpr>(this)->getChosenSubExpr(C)->CanThrow(C);
 
+  case GenericSelectionExprClass:
+    if (cast<GenericSelectionExpr>(this)->isResultDependent())
+      return CT_Dependent;
+    return cast<GenericSelectionExpr>(this)->getResultExpr()->CanThrow(C);
+
     // Some expressions are always dependent.
   case DependentScopeDeclRefExprClass:
   case CXXUnresolvedConstructExprClass:
@@ -1853,6 +1858,12 @@ Expr* Expr::IgnoreParens() {
         continue;
       }
     }
+    if (GenericSelectionExpr* P = dyn_cast<GenericSelectionExpr>(E)) {
+      if (!P->isResultDependent()) {
+        E = P->getResultExpr();
+        continue;
+      }
+    }
     return E;
   }
 }
@@ -1876,6 +1887,12 @@ Expr *Expr::IgnoreParenCasts() {
         continue;
       }
     }
+    if (GenericSelectionExpr* P = dyn_cast<GenericSelectionExpr>(E)) {
+      if (!P->isResultDependent()) {
+        E = P->getResultExpr();
+        continue;
+      }
+    }
     return E;
   }
 }
@@ -1900,6 +1917,11 @@ Expr *Expr::IgnoreParenLValueCasts() {
         E = P->getSubExpr();
         continue;
       }
+    } else if (GenericSelectionExpr* P = dyn_cast<GenericSelectionExpr>(E)) {
+      if (!P->isResultDependent()) {
+        E = P->getResultExpr();
+        continue;
+      }
     }
     break;
   }
@@ -1923,6 +1945,12 @@ Expr *Expr::IgnoreParenImpCasts() {
         continue;
       }
     }
+    if (GenericSelectionExpr* P = dyn_cast<GenericSelectionExpr>(E)) {
+      if (!P->isResultDependent()) {
+        E = P->getResultExpr();
+        continue;
+      }
+    }
     return E;
   }
 }
@@ -1965,6 +1993,13 @@ Expr *Expr::IgnoreParenNoopCasts(ASTContext &Ctx) {
       }
     }
 
+    if (GenericSelectionExpr* P = dyn_cast<GenericSelectionExpr>(E)) {
+      if (!P->isResultDependent()) {
+        E = P->getResultExpr();
+        continue;
+      }
+    }
+
     return E;
   }
 }
@@ -2156,6 +2191,11 @@ bool Expr::isConstantInitializer(ASTContext &Ctx, bool IsForRef) const {
   case ParenExprClass:
     return cast<ParenExpr>(this)->getSubExpr()
       ->isConstantInitializer(Ctx, IsForRef);
+  case GenericSelectionExprClass:
+    if (cast<GenericSelectionExpr>(this)->isResultDependent())
+      return false;
+    return cast<GenericSelectionExpr>(this)->getResultExpr()
+      ->isConstantInitializer(Ctx, IsForRef);
   case ChooseExprClass:
     return cast<ChooseExpr>(this)->getChosenSubExpr(Ctx)
       ->isConstantInitializer(Ctx, IsForRef);
@@ -2242,6 +2282,9 @@ Expr::isNullPointerConstant(ASTContext &Ctx,
     // Accept ((void*)0) as a null pointer constant, as many other
     // implementations do.
     return PE->getSubExpr()->isNullPointerConstant(Ctx, NPC);
+  } else if (const GenericSelectionExpr *GE =
+               dyn_cast<GenericSelectionExpr>(this)) {
+    return GE->getResultExpr()->isNullPointerConstant(Ctx, NPC);
   } else if (const CXXDefaultArgExpr *DefaultArg
                = dyn_cast<CXXDefaultArgExpr>(this)) {
     // See through default argument expressions
@@ -2640,6 +2683,51 @@ void ShuffleVectorExpr::setExprs(ASTContext &C, Expr ** Exprs,
   memcpy(SubExprs, Exprs, sizeof(Expr *) * NumExprs);
 }
 
+GenericSelectionExpr::GenericSelectionExpr(ASTContext &Context,
+                               SourceLocation GenericLoc, Expr *ControllingExpr,
+                               TypeSourceInfo **AssocTypes, Expr **AssocExprs,
+                               unsigned NumAssocs, SourceLocation DefaultLoc,
+                               SourceLocation RParenLoc,
+                               bool ContainsUnexpandedParameterPack,
+                               unsigned ResultIndex)
+  : Expr(GenericSelectionExprClass,
+         AssocExprs[ResultIndex]->getType(),
+         AssocExprs[ResultIndex]->getValueKind(),
+         AssocExprs[ResultIndex]->getObjectKind(),
+         AssocExprs[ResultIndex]->isTypeDependent(),
+         AssocExprs[ResultIndex]->isValueDependent(),
+         ContainsUnexpandedParameterPack),
+    AssocTypes(new (Context) TypeSourceInfo*[NumAssocs]),
+    SubExprs(new (Context) Stmt*[END_EXPR+NumAssocs]), NumAssocs(NumAssocs),
+    ResultIndex(ResultIndex), GenericLoc(GenericLoc), DefaultLoc(DefaultLoc),
+    RParenLoc(RParenLoc) {
+  SubExprs[CONTROLLING] = ControllingExpr;
+  std::copy(AssocTypes, AssocTypes+NumAssocs, this->AssocTypes);
+  std::copy(AssocExprs, AssocExprs+NumAssocs, SubExprs+END_EXPR);
+}
+
+GenericSelectionExpr::GenericSelectionExpr(ASTContext &Context,
+                               SourceLocation GenericLoc, Expr *ControllingExpr,
+                               TypeSourceInfo **AssocTypes, Expr **AssocExprs,
+                               unsigned NumAssocs, SourceLocation DefaultLoc,
+                               SourceLocation RParenLoc,
+                               bool ContainsUnexpandedParameterPack)
+  : Expr(GenericSelectionExprClass,
+         Context.DependentTy,
+         VK_RValue,
+         OK_Ordinary,
+         /*isTypeDependent=*/  true,
+         /*isValueDependent=*/ true,
+         ContainsUnexpandedParameterPack),
+    AssocTypes(new (Context) TypeSourceInfo*[NumAssocs]),
+    SubExprs(new (Context) Stmt*[END_EXPR+NumAssocs]), NumAssocs(NumAssocs),
+    ResultIndex(-1U), GenericLoc(GenericLoc), DefaultLoc(DefaultLoc),
+    RParenLoc(RParenLoc) {
+  SubExprs[CONTROLLING] = ControllingExpr;
+  std::copy(AssocTypes, AssocTypes+NumAssocs, this->AssocTypes);
+  std::copy(AssocExprs, AssocExprs+NumAssocs, SubExprs+END_EXPR);
+}
+
 //===----------------------------------------------------------------------===//
 //  DesignatedInitExpr
 //===----------------------------------------------------------------------===//
diff --git a/lib/AST/ExprClassification.cpp b/lib/AST/ExprClassification.cpp
index e94ae82786..803bc561ba 100644
--- a/lib/AST/ExprClassification.cpp
+++ b/lib/AST/ExprClassification.cpp
@@ -233,6 +233,14 @@ static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
   case Expr::ParenExprClass:
     return ClassifyInternal(Ctx, cast<ParenExpr>(E)->getSubExpr());
 
+    // C1X 6.5.1.1p4: [A generic selection] is an lvalue, a function designator,
+    // or a void expression if its result expression is, respectively, an
+    // lvalue, a function designator, or a void expression.<