Add the `pass_object_size` attribute to clang.

`pass_object_size` is our way of enabling `__builtin_object_size` to
produce high quality results without requiring inlining to happen
everywhere.

A link to the design doc for this attribute is available at the
Differential review link below.

Differential Revision: http://reviews.llvm.org/D13263


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@254554 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/AST/Expr.h

@@ -628,6 +628,16 @@ public:
                                 const FunctionDecl *Callee,
                                 ArrayRef<const Expr*> Args) const;
 
+  /// \brief If the current Expr is a pointer, this will try to statically
+  /// determine the number of bytes available where the pointer is pointing.
+  /// Returns true if all of the above holds and we were able to figure out the
+  /// size, false otherwise.
+  ///
+  /// \param Type - How to evaluate the size of the Expr, as defined by the
+  /// "type" parameter of __builtin_object_size
+  bool tryEvaluateObjectSize(uint64_t &Result, ASTContext &Ctx,
+                             unsigned Type) const;
+
   /// \brief Enumeration used to describe the kind of Null pointer constant
   /// returned from \c isNullPointerConstant().
   enum NullPointerConstantKind {

include/clang/Basic/Attr.td

@@ -1012,6 +1012,15 @@ def ReturnsNonNull : InheritableAttr {
   let Documentation = [ReturnsNonNullDocs];
 }
 
+// pass_object_size(N) indicates that the parameter should have
+// __builtin_object_size with Type=N evaluated on the parameter at the callsite.
+def PassObjectSize : InheritableParamAttr {
+  let Spellings = [GNU<"pass_object_size">];
+  let Args = [IntArgument<"Type">];
+  let Subjects = SubjectList<[ParmVar]>;
+  let Documentation = [PassObjectSizeDocs];
+}
+
 // Nullability type attributes.
 def TypeNonNull : TypeAttr {
   let Spellings = [Keyword<"_Nonnull">];

include/clang/Basic/AttrDocs.td

@@ -263,6 +263,103 @@ Query for this feature with ``__has_attribute(enable_if)``.
   }];
 }
 
+def PassObjectSizeDocs : Documentation {
+  let Category = DocCatVariable; // Technically it's a parameter doc, but eh.
+  let Content = [{
+.. Note:: The mangling of functions with parameters that are annotated with
+  ``pass_object_size`` is subject to change. You can get around this by
+  using ``__asm__("foo")`` to explicitly name your functions, thus preserving
+  your ABI; also, non-overloadable C functions with ``pass_object_size`` are
+  not mangled.
+
+The ``pass_object_size(Type)`` attribute can be placed on function parameters to
+instruct clang to call ``__builtin_object_size(param, Type)`` at each callsite
+of said function, and implicitly pass the result of this call in as an invisible
+argument of type ``size_t`` directly after the parameter annotated with
+``pass_object_size``. Clang will also replace any calls to
+``__builtin_object_size(param, Type)`` in the function by said implicit
+parameter.
+
+Example usage:
+
+.. code-block:: c
+
+  int bzero1(char *const p __attribute__((pass_object_size(0))))
+      __attribute__((noinline)) {
+    int i = 0;
+    for (/**/; i < (int)__builtin_object_size(p, 0); ++i) {
+      p[i] = 0;
+    }
+    return i;
+  }
+
+  int main() {
+    char chars[100];
+    int n = bzero1(&chars[0]);
+    assert(n == sizeof(chars));
+    return 0;
+  }
+
+If successfully evaluating ``__builtin_object_size(param, Type)`` at the
+callsite is not possible, then the "failed" value is passed in. So, using the
+definition of ``bzero1`` from above, the following code would exit cleanly:
+
+.. code-block:: c
+
+  int main2(int argc, char *argv[]) {
+    int n = bzero1(argv);
+    assert(n == -1);
+    return 0;
+  }
+
+``pass_object_size`` plays a part in overload resolution. If two overload
+candidates are otherwise equally good, then the overload with one or more
+parameters with ``pass_object_size`` is preferred. This implies that the choice
+between two identical overloads both with ``pass_object_size`` on one or more
+parameters will always be ambiguous; for this reason, having two such overloads
+is illegal. For example:
+
+.. code-block:: c++
+
+  #define PS(N) __attribute__((pass_object_size(N)))
+  // OK
+  void Foo(char *a, char *b); // Overload A
+  // OK -- overload A has no parameters with pass_object_size.
+  void Foo(char *a PS(0), char *b PS(0)); // Overload B
+  // Error -- Same signature (sans pass_object_size) as overload B, and both
+  // overloads have one or more parameters with the pass_object_size attribute.
+  void Foo(void *a PS(0), void *b);
+
+  // OK
+  void Bar(void *a PS(0)); // Overload C
+  // OK
+  void Bar(char *c PS(1)); // Overload D
+
+  void main() {
+    char known[10], *unknown;
+    Foo(unknown, unknown); // Calls overload B
+    Foo(known, unknown); // Calls overload B
+    Foo(unknown, known); // Calls overload B
+    Foo(known, known); // Calls overload B
+
+    Bar(known); // Calls overload D
+    Bar(unknown); // Calls overload D
+  }
+
+Currently, ``pass_object_size`` is a bit restricted in terms of its usage:
+
+* Only one use of ``pass_object_size`` is allowed per parameter.
+
+* It is an error to take the address of a function with ``pass_object_size`` on
+  any of its parameters. If you wish to do this, you can create an overload
+  without ``pass_object_size`` on any parameters.
+
+* It is an error to apply the ``pass_object_size`` attribute to parameters that
+  are not pointers. Additionally, any parameter that ``pass_object_size`` is
+  applied to must be marked ``const`` at its function's definition.
+  }];
+}
+
 def OverloadableDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{

include/clang/Basic/DiagnosticSemaKinds.td

@@ -1567,8 +1567,7 @@ def err_init_conversion_failed : Error<
   "%select{none|const|restrict|const and restrict|volatile|const and volatile|"
   "volatile and restrict|const, volatile, and restrict}5 vs "
   "%select{none|const|restrict|const and restrict|volatile|const and volatile|"
-  "volatile and restrict|const, volatile, and restrict}6)"
-  "|: cannot take the address of a potentially disabled function}4">;
+  "volatile and restrict|const, volatile, and restrict}6)}4">;
 
 def err_lvalue_to_rvalue_ref : Error<"rvalue reference %diff{to type $ cannot "
   "bind to lvalue of type $|cannot bind to incompatible lvalue}0,1">;
@@ -2126,8 +2125,7 @@ def err_attribute_argument_type : Error<
   "%0 attribute requires %select{int or bool|an integer "
   "constant|a string|an identifier}1">;
 def err_attribute_argument_outof_range : Error<
-  "init_priority attribute requires integer constant between "
-  "101 and 65535 inclusive">;
+  "%0 attribute requires integer constant between %1 and %2 inclusive">;
 def err_init_priority_object_attr : Error<
   "can only use 'init_priority' attribute on file-scope definitions "
   "of objects of class type">;
@@ -2135,10 +2133,12 @@ def err_attribute_argument_vec_type_hint : Error<
   "invalid attribute argument %0 - expecting a vector or vectorizable scalar type">;
 def err_attribute_argument_out_of_bounds : Error<
   "%0 attribute parameter %1 is out of bounds">;
+def err_attribute_only_once_per_parameter : Error<
+  "%0 attribute can only be applied once per parameter">;
 def err_attribute_uuid_malformed_guid : Error<
   "uuid attribute contains a malformed GUID">;
 def warn_attribute_pointers_only : Warning<
-  "%0 attribute only applies to pointer arguments">,
+  "%0 attribute only applies to%select{| constant}1 pointer arguments">,
   InGroup<IgnoredAttributes>;
 def err_attribute_pointers_only : Error<warn_attribute_pointers_only.Text>;
 def warn_attribute_return_pointers_only : Warning<
@@ -3063,8 +3063,7 @@ def note_ovl_candidate : Note<"candidate "
     "%select{none|const|restrict|const and restrict|volatile|const and volatile"
     "|volatile and restrict|const, volatile, and restrict}3 but found "
     "%select{none|const|restrict|const and restrict|volatile|const and volatile"
-    "|volatile and restrict|const, volatile, and restrict}4)"
-    "| made ineligible by enable_if}2">;
+    "|volatile and restrict|const, volatile, and restrict}4)}2">;
 
 def note_ovl_candidate_inherited_constructor : Note<"inherited from here">;
 def note_ovl_candidate_illegal_constructor : Note<
@@ -3093,8 +3092,16 @@ def note_ovl_candidate_substitution_failure : Note<
     "candidate template ignored: substitution failure%0%1">;
 def note_ovl_candidate_disabled_by_enable_if : Note<
     "candidate template ignored: disabled by %0%1">;
+def note_ovl_candidate_has_pass_object_size_params: Note<
+    "candidate address cannot be taken because parameter %0 has "
+    "pass_object_size attribute">;
 def note_ovl_candidate_disabled_by_enable_if_attr : Note<
     "candidate disabled: %0">;
+def err_addrof_function_disabled_by_enable_if_attr : Error<
+    "cannot take address of function %0 becuase it has one or more "
+    "non-tautological enable_if conditions">;
+def note_addrof_ovl_candidate_disabled_by_enable_if_attr : Note<
+    "candidate function made ineligible by enable_if">;
 def note_ovl_candidate_failed_overload_resolution : Note<
     "candidate template ignored: couldn't resolve reference to overloaded "
     "function %0">;
@@ -3105,7 +3112,7 @@ def note_ovl_candidate_non_deduced_mismatch : Note<
 // can handle that case properly.
 def note_ovl_candidate_non_deduced_mismatch_qualified : Note<
     "candidate template ignored: could not match %q0 against %q1">;
-    
+
 // Note that we don't treat templates differently for this diagnostic.
 def note_ovl_candidate_arity : Note<"candidate "
     "%select{function|function|constructor|function|function|constructor|"
@@ -4245,6 +4252,8 @@ def err_dependent_tag_decl : Error<
 def err_tag_definition_of_typedef : Error<
   "definition of type %0 conflicts with %select{typedef|type alias}1 of the same name">;
 def err_conflicting_types : Error<"conflicting types for %0">;
+def err_different_pass_object_size_params : Error<
+  "conflicting pass_object_size attributes on parameters">;
 def err_nested_redefinition : Error<"nested redefinition of %0">;
 def err_use_with_wrong_tag : Error<
   "use of %0 with tag type that does not match previous declaration">;
@@ -5209,6 +5218,9 @@ def err_unqualified_pointer_member_function : Error<
   "must explicitly qualify name of member function when taking its address">;
 def err_invalid_form_pointer_member_function : Error<
   "cannot create a non-constant pointer to member function">;
+def err_address_of_function_with_pass_object_size_params: Error<
+  "cannot take address of function %0 because parameter %1 has "
+  "pass_object_size attribute">;
 def err_parens_pointer_member_function : Error<
   "cannot parenthesize the name of a method when forming a member pointer">;
 def err_typecheck_invalid_lvalue_addrof_addrof_function : Error<
@@ -5793,8 +5805,7 @@ def note_hidden_overloaded_virtual_declared_here : Note<
   "%select{none|const|restrict|const and restrict|volatile|const and volatile|"
   "volatile and restrict|const, volatile, and restrict}2 vs "
   "%select{none|const|restrict|const and restrict|volatile|const and volatile|"
-  "volatile and restrict|const, volatile, and restrict}3)"
-  "|: mismatch in enable_if attributes}1">;
+  "volatile and restrict|const, volatile, and restrict}3)}1">;
 def warn_using_directive_in_header : Warning<
   "using namespace directive in global context in header">,
   InGroup<HeaderHygiene>, DefaultIgnore;
@@ -6031,8 +6042,7 @@ def err_typecheck_convert_incompatible : Error<
   "%select{none|const|restrict|const and restrict|volatile|const and volatile|"
   "volatile and restrict|const, volatile, and restrict}5 vs "
   "%select{none|const|restrict|const and restrict|volatile|const and volatile|"
-  "volatile and restrict|const, volatile, and restrict}6)"
-  "|: cannot take the address of a potentially disabled function}4">;
+  "volatile and restrict|const, volatile, and restrict}6)}4">;
 def err_typecheck_missing_return_type_incompatible : Error<
   "%diff{return type $ must match previous return type $|"
   "return type must match previous return type}0,1 when %select{block "

include/clang/CodeGen/CodeGenABITypes.h

@@ -36,6 +36,7 @@ namespace llvm {
 namespace clang {
 class ASTContext;
 class CXXRecordDecl;
+class CXXMethodDecl;
 class CodeGenOptions;
 class CoverageSourceInfo;
 class DiagnosticsEngine;
@@ -60,12 +61,13 @@ public:
   const CGFunctionInfo &arrangeObjCMessageSendSignature(
                                                      const ObjCMethodDecl *MD,
                                                      QualType receiverType);
-  const CGFunctionInfo &arrangeFreeFunctionType(
-                                               CanQual<FunctionProtoType> Ty);
+  const CGFunctionInfo &arrangeFreeFunctionType(CanQual<FunctionProtoType> Ty,
+                                                const FunctionDecl *FD);
   const CGFunctionInfo &arrangeFreeFunctionType(
                                              CanQual<FunctionNoProtoType> Ty);
   const CGFunctionInfo &arrangeCXXMethodType(const CXXRecordDecl *RD,
-                                             const FunctionProtoType *FTP);
+                                             const FunctionProtoType *FTP,
+                                             const CXXMethodDecl *MD);
   const CGFunctionInfo &arrangeFreeFunctionCall(CanQualType returnType,
                                                 ArrayRef<CanQualType> argTypes,
                                                 FunctionType::ExtInfo info,

include/clang/Sema/Initialization.h

@@ -828,6 +828,9 @@ public:
     /// \brief Initializer has a placeholder type which cannot be
     /// resolved by initialization.
     FK_PlaceholderType,
+    /// \brief Trying to take the address of a function that doesn't support
+    /// having its address taken.
+    FK_AddressOfUnaddressableFunction,
     /// \brief List-copy-initialization chose an explicit constructor.
     FK_ExplicitConstructor
   };

include/clang/Sema/Sema.h

@@ -145,6 +145,7 @@ namespace clang {
   class ObjCProtocolDecl;
   class OMPThreadPrivateDecl;
   class OMPClause;
+  struct OverloadCandidate;
   class OverloadCandidateSet;
   class OverloadExpr;
   class ParenListExpr;
@@ -2475,6 +2476,14 @@ public:
   EnableIfAttr *CheckEnableIf(FunctionDecl *Function, ArrayRef<Expr *> Args,
                               bool MissingImplicitThis = false);
 
+  /// Returns whether the given function's address can be taken or not,
+  /// optionally emitting a diagnostic if the address can't be taken.
+  ///
+  /// Returns false if taking the address of the function is illegal.
+  bool checkAddressOfFunctionIsAvailable(const FunctionDecl *Function,
+                                         bool Complain = false,
+                                         SourceLocation Loc = SourceLocation());
+
   // [PossiblyAFunctionType]  -->   [Return]
   // NonFunctionType --> NonFunctionType
   // R (A) --> R(A)
@@ -8187,12 +8196,13 @@ public:
 
   // DefaultFunctionArrayConversion - converts functions and arrays
   // to their respective pointers (C99 6.3.2.1).
-  ExprResult DefaultFunctionArrayConversion(Expr *E);
+  ExprResult DefaultFunctionArrayConversion(Expr *E, bool Diagnose = true);
 
   // DefaultFunctionArrayLvalueConversion - converts functions and
   // arrays to their respective pointers and performs the
   // lvalue-to-rvalue conversion.
-  ExprResult DefaultFunctionArrayLvalueConversion(Expr *E);
+  ExprResult DefaultFunctionArrayLvalueConversion(Expr *E,
+                                                  bool Diagnose = true);
 
   // DefaultLvalueConversion - performs lvalue-to-rvalue conversion on
   // the operand.  This is DefaultFunctionArrayLvalueConversion,

include/clang/Sema/TemplateDeduction.h

@@ -236,7 +236,7 @@ struct TemplateSpecCandidate {
   }
 
   /// Diagnose a template argument deduction failure.
-  void NoteDeductionFailure(Sema &S);
+  void NoteDeductionFailure(Sema &S, bool ForTakingAddress);
 };
 
 /// TemplateSpecCandidateSet - A set of generalized overload candidates,
@@ -246,6 +246,10 @@ struct TemplateSpecCandidate {
 class TemplateSpecCandidateSet {
   SmallVector<TemplateSpecCandidate, 16> Candidates;
   SourceLocation Loc;
+  // Stores whether we're taking the address of these candidates. This helps us
+  // produce better error messages when dealing with the pass_object_size
+  // attribute on parameters.
+  bool ForTakingAddress;
 
   TemplateSpecCandidateSet(
       const TemplateSpecCandidateSet &) = delete;
@@ -254,7 +258,8 @@ class TemplateSpecCandidateSet {
   void destroyCandidates();
 
 public:
-  TemplateSpecCandidateSet(SourceLocation Loc) : Loc(Loc) {}
+  TemplateSpecCandidateSet(SourceLocation Loc, bool ForTakingAddress = false)
+      : Loc(Loc), ForTakingAddress(ForTakingAddress) {}
   ~TemplateSpecCandidateSet() { destroyCandidates(); }
 
   SourceLocation getLocation() const { return Loc; }

lib/AST/ExprConstant.cpp

@@ -1156,6 +1156,7 @@ static bool EvaluateIntegerOrLValue(const Expr *E, APValue &Result,
 static bool EvaluateFloat(const Expr *E, APFloat &Result, EvalInfo &Info);
 static bool EvaluateComplex(const Expr *E, ComplexValue &Res, EvalInfo &Info);
 static bool EvaluateAtomic(const Expr *E, APValue &Result, EvalInfo &Info);
+static bool EvaluateAsRValue(EvalInfo &Info, const Expr *E, APValue &Result);
 
 //===----------------------------------------------------------------------===//
 // Misc utilities
@@ -6377,8 +6378,28 @@ static bool refersToCompleteObject(const LValue &LVal) {
   return false;
 }
 
-bool IntExprEvaluator::TryEvaluateBuiltinObjectSize(const CallExpr *E,
-                                                    unsigned Type) {
+/// Tries to evaluate the __builtin_object_size for @p E. If successful, returns
+/// true and stores the result in @p Size.
+///
+/// If @p WasError is non-null, this will report whether the failure to evaluate
+/// is to be treated as an Error in IntExprEvaluator.
+static bool tryEvaluateBuiltinObjectSize(const Expr *E, unsigned Type,
+                                         EvalInfo &Info, uint64_t &Size,
+                                         bool *WasError = nullptr) {
+  if (WasError != nullptr)
+    *WasError = false;
+
+  auto Error = [&](const Expr *E) {
+    if (WasError != nullptr)
+      *WasError = true;
+    return false;
+  };
+
+  auto Success = [&](uint64_t S, const Expr *E) {
+    Size = S;
+    return true;
+  };
+
   // Determine the denoted object.
   LValue Base;
   {
@@ -6387,8 +6408,15 @@ bool IntExprEvaluator::TryEvaluateBuiltinObjectSize(const CallExpr *E,
     // ignore the side-effects.
     SpeculativeEvaluationRAII SpeculativeEval(Info);
     FoldOffsetRAII Fold(Info, Type & 1);
-    const Expr *Ptr = ignorePointerCastsAndParens(E->getArg(0));
-    if (!EvaluatePointer(Ptr, Base, Info))
+
+    if (E->isGLValue()) {
+      // It's possible for us to be given GLValues if we're called via
+      // Expr::tryEvaluateObjectSize.
+      APValue RVal;
+      if (!EvaluateAsRValue(Info, E, RVal))
+        return false;
+      Base.setFrom(Info.Ctx, RVal);
+    } else if (!EvaluatePointer(ignorePointerCastsAndParens(E), Base, Info))
       return false;
   }
 
@@ -6447,7 +6475,7 @@ bool IntExprEvaluator::TryEvaluateBuiltinObjectSize(const CallExpr *E,
       End.Designator.Entries.size() == End.Designator.MostDerivedPathLength) {
     // We got a pointer to an array. Step to its end.
     AmountToAdd = End.Designator.MostDerivedArraySize -
-      End.Designator.Entries.back().ArrayIndex;
+                  End.Designator.Entries.back().ArrayIndex;
   } else if (End.Designator.isOnePastTheEnd()) {
     // We're already pointing at the end of the object.
     AmountToAdd = 0;
@@ -6484,7 +6512,18 @@ bool IntExprEvaluator::TryEvaluateBuiltinObjectSize(const CallExpr *E,
   if (BaseOffset > EndOffset)
     return Success(0, E);
 
-  return Success(EndOffset - BaseOffset, E);
+  return Success((EndOffset - BaseOffset).getQuantity(), E);
+}
+
+bool IntExprEvaluator::TryEvaluateBuiltinObjectSize(const CallExpr *E,
+                                                    unsigned Type) {
+  uint64_t Size;
+  bool WasError;
+  if (::tryEvaluateBuiltinObjectSize(E->getArg(0), Type, Info, Size, &WasError))
+    return Success(Size, E);
+  if (WasError)
+    return Error(E);
+  return false;
 }
 
 bool IntExprEvaluator::VisitCallExpr(const CallExpr *E) {
@@ -6501,12 +6540,7 @@ bool IntExprEvaluator::VisitCallExpr(const CallExpr *E) {
     if (TryEvaluateBuiltinObjectSize(E, Type))
       return true;
 
-    // If evaluating the argument has side-effects, we can't determine the size
-    // of the object, and so we lower it to unknown now. CodeGen relies on us to
-    // handle all cases where the expression has side-effects.
-    // Likewise, if Type is 3, we must handle this because CodeGen cannot give a
-    // conservatively correct answer in that case.
-    if (E->getArg(0)->HasSideEffects(Info.Ctx) || Type == 3)
+    if (E->getArg(0)->HasSideEffects(Info.Ctx))
       return Success((Type & 2) ? 0 : -1, E);
 
     // Expression had no side effects, but we couldn't statically determine the
@@ -9483,3 +9517,13 @@ bool Expr::isPotentialConstantExprUnevaluated(Expr *E,
   Evaluate(ResultScratch, Info, E);
   return Diags.empty();
 }
+
+bool Expr::tryEvaluateObjectSize(uint64_t &Result, ASTContext &Ctx,
+                                 unsigned Type) const {
+  if (!getType()->isPointerType())
+    return false;
+
+  Expr::EvalStatus Status;
+  EvalInfo Info(Ctx, Status, EvalInfo::EM_ConstantFold);
+  return ::tryEvaluateBuiltinObjectSize(this, Type, Info, Result);
+}

lib/AST/ItaniumMangle.cpp

@@ -377,8 +377,8 @@ private:
 
   void mangleType(const TagType*);
   void mangleType(TemplateName);
-  void mangleBareFunctionType(const FunctionType *T,
-                              bool MangleReturnType);
+  void mangleBareFunctionType(const FunctionType *T, bool MangleReturnType,
+                              const FunctionDecl *FD = nullptr);
   void mangleNeonVectorType(const VectorType *T);
   void mangleAArch64NeonVectorType(const VectorType *T);
 
@@ -523,7 +523,7 @@ void CXXNameMangler::mangleFunctionEncoding(const FunctionDecl *FD) {
   }
 
   mangleBareFunctionType(FD->getType()->getAs<FunctionType>(), 
-                         MangleReturnType);
+                         MangleReturnType, FD);
 }
 
 static const DeclContext *IgnoreLinkageSpecDecls(const DeclContext *DC) {
@@ -1282,7 +1282,8 @@ void CXXNameMangler::mangleLambda(const CXXRecordDecl *Lambda) {
   Out << "Ul";
   const FunctionProtoType *Proto = Lambda->getLambdaTypeInfo()->getType()->
                                    getAs<FunctionProtoType>();
-  mangleBareFunctionType(Proto, /*MangleReturnType=*/false);        
+  mangleBareFunctionType(Proto, /*MangleReturnType=*/false,
+                         Lambda->getLambdaStaticInvoker());
   Out << "E";
   
   // The number is omitted for the first closure type with a given 
@@ -2171,7 +2172,8 @@ void CXXNameMangler::mangleType(const FunctionNoProtoType *T) {
 }
 
 void CXXNameMangler::mangleBareFunctionType(const FunctionType *T,
-                                            bool MangleReturnType) {
+                                            bool MangleReturnType,
+                                            const FunctionDecl *FD) {
   // We should never be mangling something without a prototype.
   const FunctionProtoType *Proto = cast<FunctionProtoType>(T);
 
@@ -2194,8 +2196,19 @@ void CXXNameMangler::mangleBareFunctionType(const FunctionType *T,
     return;
   }
 
-  for (const auto &Arg : Proto->param_types())
-    mangleType(Context.getASTContext().getSignatureParameterType(Arg));
+  assert(!FD || FD->getNumParams() == Proto->getNumParams());
+  for (unsigned I = 0, E = Proto->getNumParams(); I != E; ++I) {
+    const auto &ParamTy = Proto->getParamType(I);
+    mangleType(Context.getASTContext().getSignatureParameterType(ParamTy));
+
+    if (FD) {
+      if (auto *Attr = FD->getParamDecl(I)->getAttr<PassObjectSizeAttr>()) {
+        // Attr can only take 1 character, so we can hardcode the length below.
+        assert(Attr->getType() <= 9 && Attr->getType() >= 0);
+        Out << "U17pass_object_size" << Attr->getType();
+      }
+    }
+  }
 
   FunctionTypeDepth.pop(saved);
 
@@ -4228,4 +4241,3 @@ ItaniumMangleContext *
 ItaniumMangleContext::create(ASTContext &Context, DiagnosticsEngine &Diags) {
   return new ItaniumMangleContextImpl(Context, Diags);
 }
-

lib/AST/MicrosoftMangle.cpp

@@ -1841,8 +1841,20 @@ void MicrosoftCXXNameMangler::mangleFunctionType(const FunctionType *T,
     Out << 'X';
   } else {
     // Happens for function pointer type arguments for example.
-    for (const QualType &Arg : Proto->param_types())
-      mangleArgumentType(Arg, Range);
+    for (unsigned I = 0, E = Proto->getNumParams(); I != E; ++I) {
+      mangleArgumentType(Proto->getParamType(I), Range);
+      // Mangle each pass_object_size parameter as if it's a paramater of enum
+      // type passed directly after the parameter with the pass_object_size
+      // attribute. The aforementioned enum's name is __pass_object_size, and we
+      // pretend it resides in a top-level namespace called __clang.
+      //
+      // FIXME: Is there a defined extension notation for the MS ABI, or is it
+      // necessary to just cross our fingers and hope this type+namespace
+      // combination doesn't conflict with anything?
+      if (D)
+        if (auto *P = D->getParamDecl(I)->getAttr<PassObjectSizeAttr>())
+          Out << "W4__pass_object_size" << P->getType() << "@__clang@@";
+    }
     // <builtin-type>      ::= Z  # ellipsis
     if (Proto->isVariadic())
       Out << 'Z';

lib/CodeGen/CGBuiltin.cpp

@@ -342,6 +342,71 @@ Value *CodeGenFunction::EmitVAStartEnd(Value *ArgValue, bool IsStart) {
   return Builder.CreateCall(CGM.getIntrinsic(inst), ArgValue);
 }
 
+/// Checks if using the result of __builtin_object_size(p, @p From) in place of
+/// __builtin_object_size(p, @p To) is correct
+static bool areBOSTypesCompatible(int From, int To) {
+  // Note: Our __builtin_object_size implementation currently treats Type=0 and
+  // Type=2 identically. Encoding this implementation detail here may make
+  // improving __builtin_object_size difficult in the future, so it's omitted.
+  return From == To || (From == 0 && To == 1) || (From == 3 && To == 2);
+}
+
+static llvm::Value *
+getDefaultBuiltinObjectSizeResult(unsigned Type, llvm::IntegerType *ResType) {
+  return ConstantInt::get(ResType, (Type & 2) ? 0 : -1, /*isSigned=*/true);
+}
+
+llvm::Value *
+CodeGenFunction::evaluateOrEmitBuiltinObjectSize(const Expr *E, unsigned Type,
+                                                 llvm::IntegerType *ResType) {
+  uint64_t ObjectSize;
+  if (!E->tryEvaluateObjectSize(ObjectSize, getContext(), Type))
+    return emitBuiltinObjectSize(E, Type, ResType);
+  return ConstantInt::get(ResType, ObjectSize, /*isSigned=*/true);
+}
+
+/// Returns a Value corresponding to the size of the given expression.
+/// This Value may be either of the following:
+///   - A llvm::Argument (if E is a param with the pass_object_size attribute on
+///     it)
+///   - A call to the @llvm.objectsize intrinsic
+llvm::Value *
+CodeGenFunction::emitBuiltinObjectSize(const Expr *E, unsigned Type,
+                                       llvm::IntegerType *ResType) {
+  // We need to reference an argument if the pointer is a parameter with the
+  // pass_object_size attribute.
+  if (auto *D = dyn_cast<DeclRefExpr>(E->IgnoreParenImpCasts())) {
+    auto *Param = dyn_cast<ParmVarDecl>(D->getDecl());
+    auto *PS = D->getDecl()->getAttr<PassObjectSizeAttr>();
+    if (Param != nullptr && PS != nullptr &&
+        areBOSTypesCompatible(PS->getType(), Type)) {
+      auto Iter = SizeArguments.find(Param);
+      assert(Iter != SizeArguments.end());
+
+      const ImplicitParamDecl *D = Iter->second;
+      auto DIter = LocalDeclMap.find(D);
+      assert(DIter != LocalDeclMap.end());
+
+      return EmitLoadOfScalar(DIter->second, /*volatile=*/false,
+                              getContext().getSizeType(), E->getLocStart());
+    }
+  }
+
+  // LLVM can't handle Type=3 appropriately, and __builtin_object_size shouldn't
+  // evaluate E for side-effects. In either case, we shouldn't lower to
+  // @llvm.objectsize.
+  if (Type == 3 || E->HasSideEffects(getContext()))
+    return getDefaultBuiltinObjectSizeResult(Type, ResType);
+
+  // LLVM only supports 0 and 2, make sure that we pass along that
+  // as a boolean.
+  auto *CI = ConstantInt::get(Builder.getInt1Ty(), (Type & 2) >> 1);
+  // FIXME: Get right address space.
+  llvm::Type *Tys[] = {ResType, Builder.getInt8PtrTy(0)};
+  Value *F = CGM.getIntrinsic(Intrinsic::objectsize, Tys);
+  return Builder.CreateCall(F, {EmitScalarExpr(E), CI});
+}
+
 RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
                                         unsigned BuiltinID, const CallExpr *E,
                                         ReturnValueSlot ReturnValue) {
@@ -586,26 +651,13 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
     return RValue::get(Builder.CreateCall(F, ArgValue));
   }
   case Builtin::BI__builtin_object_size: {
-    // We rely on constant folding to deal with expressions with side effects.
-    assert(!E->getArg(0)->HasSideEffects(getContext()) &&
-           "should have been constant folded");
-
-    // We pass this builtin onto the optimizer so that it can
-    // figure out the object size in more complex cases.
-    llvm::Type *ResType = ConvertType(E->getType());
-
-    // LLVM only supports 0 and 2, make sure that we pass along that
-    // as a boolean.
-    Value *Ty = EmitScalarExpr(E->getArg(1));
-    ConstantInt *CI = dyn_cast<ConstantInt>(Ty);
-    assert(CI);
-    uint64_t val = CI->getZExtValue();
-    CI = ConstantInt::get(Builder.getInt1Ty(), (val & 0x2) >> 1);
-    // FIXME: Get right address space.
-    llvm::Type *Tys[] = { ResType, Builder.getInt8PtrTy(0) };
-    Value *F = CGM.getIntrinsic(Intrinsic::objectsize, Tys);
-    return RValue::get(
-        Builder.CreateCall(F, {EmitScalarExpr(E->getArg(0)), CI}));
+    unsigned Type =
+        E->getArg(1)->EvaluateKnownConstInt(getContext()).getZExtValue();
+    auto *ResType = cast<llvm::IntegerType>(ConvertType(E->getType()));
+
+    // We pass this builtin onto the optimizer so that it can figure out the
+    // object size in more complex cases.
+    return RValue::get(emitBuiltinObjectSize(E->getArg(0), Type, ResType));
   }
   case Builtin::BI__builtin_prefetch: {
     Value *Locality, *RW, *Address = EmitScalarExpr(E->getArg(0));

lib/CodeGen/CGCXXABI.cpp

@@ -85,7 +85,7 @@ llvm::Value *CGCXXABI::EmitLoadOfMemberFunctionPointer(
   const CXXRecordDecl *RD = 
     cast<CXXRecordDecl>(MPT->getClass()->getAs<RecordType>()->getDecl());
   llvm::FunctionType *FTy = CGM.getTypes().GetFunctionType(
-                              CGM.getTypes().arrangeCXXMethodType(RD, FPT));
+      CGM.getTypes().arrangeCXXMethodType(RD, FPT, /*FD=*/nullptr));
   return llvm::Constant::getNullValue(FTy->getPointerTo());
 }
 

lib/CodeGen/CGCall.cpp

@@ -92,15 +92,41 @@ CodeGenTypes::arrangeFreeFunctionType(CanQual<FunctionNoProtoType> FTNP) {
                                  FTNP->getExtInfo(), RequiredArgs(0));
 }
 
+/// Adds the formal paramaters in FPT to the given prefix. If any parameter in
+/// FPT has pass_object_size attrs, then we'll add parameters for those, too.
+static void appendParameterTypes(const CodeGenTypes &CGT,
+                                 SmallVectorImpl<CanQualType> &prefix,
+                                 const CanQual<FunctionProtoType> &FPT,
+                                 const FunctionDecl *FD) {
+  // Fast path: unknown target.
+  if (FD == nullptr) {
+    prefix.append(FPT->param_type_begin(), FPT->param_type_end());
+    return;
+  }
+
+  // In the vast majority cases, we'll have precisely FPT->getNumParams()
+  // parameters; the only thing that can change this is the presence of
+  // pass_object_size. So, we preallocate for the common case.
+  prefix.reserve(prefix.size() + FPT->getNumParams());
+
+  assert(FD->getNumParams() == FPT->getNumParams());
+  for (unsigned I = 0, E = FPT->getNumParams(); I != E; ++I) {
+    prefix.push_back(FPT->getParamType(I));
+    if (FD->getParamDecl(I)->hasAttr<PassObjectSizeAttr>())
+      prefix.push_back(CGT.getContext().getSizeType());
+  }
+}
+
 /// Arrange the LLVM function layout for a value of the given function
 /// type, on top of any implicit parameters already stored.
 static const CGFunctionInfo &
 arrangeLLVMFunctionInfo(CodeGenTypes &CGT, bool instanceMethod,
                         SmallVectorImpl<CanQualType> &prefix,
-                        CanQual<FunctionProtoType> FTP) {
+                        CanQual<FunctionProtoType> FTP,
+                        const FunctionDecl *FD) {
   RequiredArgs required = RequiredArgs::forPrototypePlus(FTP, prefix.size());
   // FIXME: Kill copy.
-  prefix.append(FTP->param_type_begin(), FTP->param_type_end());
+  appendParameterTypes(CGT, prefix, FTP, FD);
   CanQualType resultType = FTP->getReturnType().getUnqualifiedType();
   return CGT.arrangeLLVMFunctionInfo(resultType, instanceMethod,
                                      /*chainCall=*/false, prefix,
@@ -110,10 +136,11 @@ arrangeLLVMFunctionInfo(CodeGenTypes &CGT, bool instanceMethod,
 /// Arrange the argument and result information for a value of the
 /// given freestanding function type.
 const CGFunctionInfo &
-CodeGenTypes::arrangeFreeFunctionType(CanQual<FunctionProtoType> FTP) {
+CodeGenTypes::arrangeFreeFunctionType(CanQual<FunctionProtoType> FTP,
+                                      const FunctionDecl *FD) {
   SmallVector<CanQualType, 16> argTypes;
   return ::arrangeLLVMFunctionInfo(*this, /*instanceMethod=*/false, argTypes,
-                                   FTP);
+                                   FTP, FD);
 }
 
 static CallingConv getCallingConventionForDecl(const Decl *D, bool IsWindows) {
@@ -156,7 +183,8 @@ static CallingConv getCallingConventionForDecl(const Decl *D, bool IsWindows) {
 /// constructor or destructor.
 const CGFunctionInfo &
 CodeGenTypes::arrangeCXXMethodType(const CXXRecordDecl *RD,
-                                   const FunctionProtoType *FTP) {
+                                   const FunctionProtoType *FTP,
+                                   const CXXMethodDecl *MD) {
   SmallVector<CanQualType, 16> argTypes;
 
   // Add the 'this' pointer.
@@ -167,7 +195,7 @@ CodeGenTypes::arrangeCXXMethodType(const CXXRecordDecl *RD,
 
   return ::arrangeLLVMFunctionInfo(
       *this, true, argTypes,
-      FTP->getCanonicalTypeUnqualified().getAs<FunctionProtoType>());
+      FTP->getCanonicalTypeUnqualified().getAs<FunctionProtoType>(), MD);
 }
 
 /// Arrange the argument and result information for a declaration or
@@ -184,10 +212,10 @@ CodeGenTypes::arrangeCXXMethodDeclaration(const CXXMethodDecl *MD) {
   if (MD->isInstance()) {
     // The abstract case is perfectly fine.
     const CXXRecordDecl *ThisType = TheCXXABI.getThisArgumentTypeForMethod(MD);
-    return arrangeCXXMethodType(ThisType, prototype.getTypePtr());
+    return arrangeCXXMethodType(ThisType, prototype.getTypePtr(), MD);
   }
 
-  return arrangeFreeFunctionType(prototype);
+  return arrangeFreeFunctionType(prototype, MD);
 }
 
 const CGFunctionInfo &
@@ -208,7 +236,7 @@ CodeGenTypes::arrangeCXXStructorDeclaration(const CXXMethodDecl *MD,
   CanQual<FunctionProtoType> FTP = GetFormalType(MD);
 
   // Add the formal parameters.
-  argTypes.append(FTP->param_type_begin(), FTP->param_type_end());
+  appendParameterTypes(*this, argTypes, FTP, MD);
 
   TheCXXABI.buildStructorSignature(MD, Type, argTypes);
 
@@ -274,7 +302,7 @@ CodeGenTypes::arrangeFunctionDeclaration(const FunctionDecl *FD) {
   }
 
   assert(isa<FunctionProtoType>(FTy));
-  return arrangeFreeFunctionType(FTy.getAs<FunctionProtoType>());
+  return arrangeFreeFunctionType(FTy.getAs<FunctionProtoType>(), FD);
 }
 
 /// Arrange the argument and result information for the declaration or
@@ -2803,6 +2831,21 @@ void CodeGenFunction::EmitCallArgs(
     llvm::iterator_range<CallExpr::const_arg_iterator> ArgRange,
     const FunctionDecl *CalleeDecl, unsigned ParamsToSkip) {
   assert((int)ArgTypes.size() == (ArgRange.end() - ArgRange.begin()));
+
+  auto MaybeEmitImplicitObjectSize = [&](unsigned I, const Expr *Arg) {
+    if (CalleeDecl == nullptr || I >= CalleeDecl->getNumParams())
+      return;
+    auto *PS = CalleeDecl->getParamDecl(I)->getAttr<PassObjectSizeAttr>();
+    if (PS == nullptr)
+      return;
+
+    const auto &Context = getContext();
+    auto SizeTy = Context.getSizeType();
+    auto T = Builder.getIntNTy(Context.getTypeSize(SizeTy));
+    llvm::Value *V = evaluateOrEmitBuiltinObjectSize(Arg, PS->getType(), T);
+    Args.add(RValue::get(V), SizeTy);
+  };
+
   // We *have* to evaluate arguments from right to left in the MS C++ ABI,
   // because arguments are destroyed left to right in the callee.
   if (CGM.getTarget().getCXXABI().areArgsDestroyedLeftToRightInCallee()) {
@@ -2823,6 +2866,7 @@ void CodeGenFunction::EmitCallArgs(
       EmitCallArg(Args, *Arg, ArgTypes[I]);
       EmitNonNullArgCheck(Args.back().RV, ArgTypes[I], (*Arg)->getExprLoc(),
                           CalleeDecl, ParamsToSkip + I);
+      MaybeEmitImplicitObjectSize(I, *Arg);
     }
 
     // Un-reverse the arguments we just evaluated so they match up with the LLVM
@@ -2837,6 +2881,7 @@ void CodeGenFunction::EmitCallArgs(
     EmitCallArg(Args, *Arg, ArgTypes[I]);
     EmitNonNullArgCheck(Args.back().RV, ArgTypes[I], (*Arg)->getExprLoc(),
                         CalleeDecl, ParamsToSkip + I);
+    MaybeEmitImplicitObjectSize(I, *Arg);
   }
 }
 

lib/CodeGen/CodeGenABITypes.cpp

@@ -44,8 +44,9 @@ CodeGenABITypes::arrangeObjCMessageSendSignature(const ObjCMethodDecl *MD,
 }
 
 const CGFunctionInfo &
-CodeGenABITypes::arrangeFreeFunctionType(CanQual<FunctionProtoType> Ty) {
-  return CGM->getTypes().arrangeFreeFunctionType(Ty);
+CodeGenABITypes::arrangeFreeFunctionType(CanQual<FunctionProtoType> Ty,
+                                         const FunctionDecl *FD) {
+  return CGM->getTypes().arrangeFreeFunctionType(Ty, FD);
 }
 
 const CGFunctionInfo &
@@ -55,8 +56,9 @@ CodeGenABITypes::arrangeFreeFunctionType(CanQual<FunctionNoProtoType> Ty) {
 
 const CGFunctionInfo &
 CodeGenABITypes::arrangeCXXMethodType(const CXXRecordDecl *RD,
-                                      const FunctionProtoType *FTP) {
-  return CGM->getTypes().arrangeCXXMethodType(RD, FTP);
+                                      const FunctionProtoType *FTP,
+                                      const CXXMethodDecl *MD) {
+  return CGM->getTypes().arrangeCXXMethodType(RD, FTP, MD);
 }
 
 const CGFunctionInfo &CodeGenABITypes::arrangeFreeFunctionCall(

lib/CodeGen/CodeGenFunction.cpp

@@ -920,7 +920,18 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
     CGM.getCXXABI().buildThisParam(*this, Args);
   }
 
-  Args.append(FD->param_begin(), FD->param_end());
+  for (auto *Param : FD->params()) {
+    Args.push_back(Param);
+    if (!Param->hasAttr<PassObjectSizeAttr>())
+      continue;
+
+    IdentifierInfo *NoID = nullptr;
+    auto *Implicit = ImplicitParamDecl::Create(
+        getContext(), Param->getDeclContext(), Param->getLocation(), NoID,
+        getContext().getSizeType());
+    SizeArguments[Param] = Implicit;
+    Args.push_back(Implicit);
+  }
 
   if (MD && (isa<CXXConstructorDecl>(MD) || isa<CXXDestructorDecl>(MD)))
     CGM.getCXXABI().addImplicitStructorParams(*this, ResTy, Args);

lib/CodeGen/CodeGenFunction.h

@@ -914,6 +914,12 @@ private:
   /// decls.
   DeclMapTy LocalDeclMap;
 
+  /// SizeArguments - If a ParmVarDecl had the pass_object_size attribute, this
+  /// will contain a mapping from said ParmVarDecl to its implicit "object_size"
+  /// parameter.
+  llvm::SmallDenseMap<const ParmVarDecl *, const ImplicitParamDecl *, 2>
+      SizeArguments;
+
   /// Track escaped local variables with auto storage. Used during SEH
   /// outlining to produce a call to llvm.localescape.
   llvm::DenseMap<llvm::AllocaInst *, int> EscapedLocals;
@@ -3062,6 +3068,18 @@ private:
                                   std::string &ConstraintStr,
                                   SourceLocation Loc);
 
+  /// \brief Attempts to statically evaluate the object size of E. If that
+  /// fails, emits code to figure the size of E out for us. This is
+  /// pass_object_size aware.
+  llvm::Value *evaluateOrEmitBuiltinObjectSize(const Expr *E, unsigned Type,
+                                               llvm::IntegerType *ResType);
+
+  /// \brief Emits the size of E, as required by __builtin_object_size. This
+  /// function is aware of pass_object_size parameters, and will act accordingly
+  /// if E is a parameter with the pass_object_size attribute.
+  llvm::Value *emitBuiltinObjectSize(const Expr *E, unsigned Type,
+                                     llvm::IntegerType *ResType);
+
 public:
 #ifndef NDEBUG
   // Determine whether the given argument is an Objective-C method

lib/CodeGen/CodeGenModule.cpp

@@ -1830,8 +1830,11 @@ llvm::Constant *CodeGenModule::GetAddrOfFunction(GlobalDecl GD,
                                                  bool DontDefer,
                                                  bool IsForDefinition) {
   // If there was no specific requested type, just convert it now.
-  if (!Ty)
-    Ty = getTypes().ConvertType(cast<ValueDecl>(GD.getDecl())->getType());
+  if (!Ty) {
+    const auto *FD = cast<FunctionDecl>(GD.getDecl());
+    auto CanonTy = Context.getCanonicalType(FD->getType());
+    Ty = getTypes().ConvertFunctionType(CanonTy, FD);
+  }
 
   StringRef MangledName = getMangledName(GD);
   return GetOrCreateLLVMFunction(MangledName, Ty, GD, ForVTable, DontDefer,

lib/CodeGen/CodeGenTypes.cpp

@@ -294,6 +294,76 @@ static llvm::Type *getTypeForFormat(llvm::LLVMContext &VMContext,
   llvm_unreachable("Unknown float format!");
 }
 
+llvm::Type *CodeGenTypes::ConvertFunctionType(QualType QFT,
+                                              const FunctionDecl *FD) {
+  assert(QFT.isCanonical());
+  const Type *Ty = QFT.getTypePtr();
+  const FunctionType *FT = cast<FunctionType>(QFT.getTypePtr());
+  // First, check whether we can build the full function type.  If the
+  // function type depends on an incomplete type (e.g. a struct or enum), we
+  // cannot lower the function type.
+  if (!isFuncTypeConvertible(FT)) {
+    // This function's type depends on an incomplete tag type.
+
+    // Force conversion of all the relevant record types, to make sure
+    // we re-convert the FunctionType when appropriate.
+    if (const RecordType *RT = FT->getReturnType()->getAs<RecordType>())
+      ConvertRecordDeclType(RT->getDecl());
+    if (const FunctionProtoType *FPT = dyn_cast<FunctionProtoType>(FT))
+      for (unsigned i = 0, e = FPT->getNumParams(); i != e; i++)
+        if (const RecordType *RT = FPT->getParamType(i)->getAs<RecordType>())
+          ConvertRecordDeclType(RT->getDecl());
+
+    SkippedLayout = true;
+
+    // Return a placeholder type.
+    return llvm::StructType::get(getLLVMContext());
+  }
+
+  // While we're converting the parameter types for a function, we don't want
+  // to recursively convert any pointed-to structs.  Converting directly-used
+  // structs is ok though.
+  if (!RecordsBeingLaidOut.insert(Ty).second) {
+    SkippedLayout = true;
+    return llvm::StructType::get(getLLVMContext());
+  }
+
+  // The function type can be built; call the appropriate routines to
+  // build it.
+  const CGFunctionInfo *FI;
+  if (const FunctionProtoType *FPT = dyn_cast<FunctionProtoType>(FT)) {
+    FI = &arrangeFreeFunctionType(
+        CanQual<FunctionProtoType>::CreateUnsafe(QualType(FPT, 0)), FD);
+  } else {
+    const FunctionNoProtoType *FNPT = cast<FunctionNoProtoType>(FT);
+    FI = &arrangeFreeFunctionType(
+        CanQual<FunctionNoProtoType>::CreateUnsafe(QualType(FNPT, 0)));
+  }
+
+  llvm::Type *ResultType = nullptr;
+  // If there is something higher level prodding our CGFunctionInfo, then
+  // don't recurse into it again.
+  if (FunctionsBeingProcessed.count(FI)) {
+
+    ResultType = llvm::StructType::get(getLLVMContext());
+    SkippedLayout = true;
+  } else {
+
+    // Otherwise, we're good to go, go ahead and convert it.
+    ResultType = GetFunctionType(*FI);
+  }
+
+  RecordsBeingLaidOut.erase(Ty);
+
+  if (SkippedLayout)
+    TypeCache.clear();
+
+  if (RecordsBeingLaidOut.empty())
+    while (!DeferredRecords.empty())
+      ConvertRecordDeclType(DeferredRecords.pop_back_val());
+  return ResultType;
+}
+
 /// ConvertType - Convert the specified type to its LLVM form.
 llvm::Type *CodeGenTypes::ConvertType(QualType T) {
   T = Context.getCanonicalType(T);
@@ -485,75 +555,9 @@ llvm::Type *CodeGenTypes::ConvertType(QualType T) {
     break;
   }
   case Type::FunctionNoProto:
-  case Type::FunctionProto: {
-    const FunctionType *FT = cast<FunctionType>(Ty);
-    // First, check whether we can build the full function type.  If the
-    // function type depends on an incomplete type (e.g. a struct or enum), we
-    // cannot lower the function type.
-    if (!isFuncTypeConvertible(FT)) {
-      // This function's type depends on an incomplete tag type.
-
-      // Force conversion of all the relevant record types, to make sure
-      // we re-convert the FunctionType when appropriate.
-      if (const RecordType *RT = FT->getReturnType()->getAs<RecordType>())
-        ConvertRecordDeclType(RT->getDecl());
-      if (const FunctionProtoType *FPT = dyn_cast<FunctionProtoType>(FT))
-        for (unsigned i = 0, e = FPT->getNumParams(); i != e; i++)
-          if (const RecordType *RT = FPT->getParamType(i)->getAs<RecordType>())
-            ConvertRecordDeclType(RT->getDecl());
-
-      // Return a placeholder type.
-      ResultType = llvm::StructType::get(getLLVMContext());
-
-      SkippedLayout = true;
-      break;
-    }
-
-    // While we're converting the parameter types for a function, we don't want
-    // to recursively convert any pointed-to structs.  Converting directly-used
-    // structs is ok though.
-    if (!RecordsBeingLaidOut.insert(Ty).second) {
-      ResultType = llvm::StructType::get(getLLVMContext());
-      
-      SkippedLayout = true;
-      break;
-    }
-    
-    // The function type can be built; call the appropriate routines to
-    // build it.
-    const CGFunctionInfo *FI;
-    if (const FunctionProtoType *FPT = dyn_cast<FunctionProtoType>(FT)) {
-      FI = &arrangeFreeFunctionType(
-                   CanQual<FunctionProtoType>::CreateUnsafe(QualType(FPT, 0)));
-    } else {
-      const FunctionNoProtoType *FNPT = cast<FunctionNoProtoType>(FT);
-      FI = &arrangeFreeFunctionType(
-                CanQual<FunctionNoProtoType>::CreateUnsafe(QualType(FNPT, 0)));
-    }
-    
-    // If there is something higher level prodding our CGFunctionInfo, then
-    // don't recurse into it again.
-    if (FunctionsBeingProcessed.count(FI)) {
-
-      ResultType = llvm::StructType::get(getLLVMContext());
-      SkippedLayout = true;
-    } else {
-
-      // Otherwise, we're good to go, go ahead and convert it.
-      ResultType = GetFunctionType(*FI);
-    }
-
-    RecordsBeingLaidOut.erase(Ty);
-
-    if (SkippedLayout)
-      TypeCache.clear();
-    
-    if (RecordsBeingLaidOut.empty())
-      while (!DeferredRecords.empty())
-        ConvertRecordDeclType(DeferredRecords.pop_back_val());
+  case Type::FunctionProto:
+    ResultType = ConvertFunctionType(T);
     break;
-  }
-
   case Type::ObjCObject:
     ResultType = ConvertType(cast<ObjCObjectType>(Ty)->getBaseType());
     break;

lib/CodeGen/CodeGenTypes.h

@@ -178,6 +178,14 @@ public:
   /// ConvertType - Convert type T into a llvm::Type.
   llvm::Type *ConvertType(QualType T);
 
+  /// \brief Converts the GlobalDecl into an llvm::Type. This should be used
+  /// when we know the target of the function we want to convert.  This is
+  /// because some functions (explicitly, those with pass_object_size
+  /// parameters) may not have the same signature as their type portrays, and
+  /// can only be called directly.
+  llvm::Type *ConvertFunctionType(QualType FT,
+                                  const FunctionDecl *FD = nullptr);
+
   /// ConvertTypeForMem - Convert type T into a llvm::Type.  This differs from
   /// ConvertType in that it is used to convert to the memory representation for
   /// a type.  For example, the scalar representation for _Bool is i1, but the
@@ -264,11 +272,12 @@ public:
   const CGFunctionInfo &arrangeMSMemberPointerThunk(const CXXMethodDecl *MD);
   const CGFunctionInfo &arrangeMSCtorClosure(const CXXConstructorDecl *CD,
                                                  CXXCtorType CT);
-
-  const CGFunctionInfo &arrangeFreeFunctionType(CanQual<FunctionProtoType> Ty);
+  const CGFunctionInfo &arrangeFreeFunctionType(CanQual<FunctionProtoType> Ty,
+                                                const FunctionDecl *FD);
   const CGFunctionInfo &arrangeFreeFunctionType(CanQual<FunctionNoProtoType> Ty);
   const CGFunctionInfo &arrangeCXXMethodType(const CXXRecordDecl *RD,
-                                             const FunctionProtoType *FTP);
+                                             const FunctionProtoType *FTP,
+                                             const CXXMethodDecl *MD);
 
   /// "Arrange" the LLVM information for a call or type with the given
   /// signature.  This is largely an internal method; other clients

lib/CodeGen/ItaniumCXXABI.cpp

@@ -534,9 +534,8 @@ llvm::Value *ItaniumCXXABI::EmitLoadOfMemberFunctionPointer(
   const CXXRecordDecl *RD = 
     cast<CXXRecordDecl>(MPT->getClass()->getAs<RecordType>()->getDecl());
 
-  llvm::FunctionType *FTy = 
-    CGM.getTypes().GetFunctionType(
-      CGM.getTypes().arrangeCXXMethodType(RD, FPT));
+  llvm::FunctionType *FTy = CGM.getTypes().GetFunctionType(
+      CGM.getTypes().arrangeCXXMethodType(RD, FPT, /*FD=*/nullptr));
 
   llvm::Constant *ptrdiff_1 = llvm::ConstantInt::get(CGM.PtrDiffTy, 1);
 

lib/CodeGen/MicrosoftCXXABI.cpp

@@ -3225,9 +3225,8 @@ llvm::Value *MicrosoftCXXABI::EmitLoadOfMemberFunctionPointer(
   const FunctionProtoType *FPT =
     MPT->getPointeeType()->castAs<FunctionProtoType>();
   const CXXRecordDecl *RD = MPT->getMostRecentCXXRecordDecl();
-  llvm::FunctionType *FTy =
-    CGM.getTypes().GetFunctionType(
-      CGM.getTypes().arrangeCXXMethodType(RD, FPT));
+  llvm::FunctionType *FTy = CGM.getTypes().GetFunctionType(
+      CGM.getTypes().arrangeCXXMethodType(RD, FPT, /*FD=*/nullptr));
   CGBuilderTy &Builder = CGF.Builder;
 
   MSInheritanceAttr::Spelling Inheritance = RD->getMSInheritanceModel();

lib/Sema/SemaChecking.cpp

@@ -8419,6 +8419,15 @@ bool Sema::CheckParmsForFunctionDef(ParmVarDecl *const *P,
         }
       }
     }
+
+    // Parameters with the pass_object_size attribute only need to be marked
+    // constant at function definitions. Because we lack information about
+    // whether we're on a declaration or definition when we're instantiating the
+    // attribute, we need to check for constness here.
+    if (const auto *Attr = Param->getAttr<PassObjectSizeAttr>())
+      if (!Param->getType().isConstQualified())
+        Diag(Param->getLocation(), diag::err_attribute_pointers_only)
+            << Attr->getSpelling() << 1;
   }
 
   return HasInvalidParm;
@@ -9869,4 +9878,3 @@ void Sema::CheckArgumentWithTypeTag(const ArgumentWithTypeTagAttr *Attr,
         << ArgumentExpr->getSourceRange()
         << TypeTagExpr->getSourceRange();
 }
-

lib/Sema/SemaDecl.cpp

@@ -2621,6 +2621,21 @@ static bool checkUsingShadowRedecl(Sema &S, UsingShadowDecl *OldS,
   return false;
 }
 
+static bool hasIdenticalPassObjectSizeAttrs(const FunctionDecl *A,
+                                            const FunctionDecl *B) {
+  assert(A->getNumParams() == B->getNumParams());
+
+  auto AttrEq = [](const ParmVarDecl *A, const ParmVarDecl *B) {
+    const auto *AttrA = A->getAttr<PassObjectSizeAttr>();
+    const auto *AttrB = B->getAttr<PassObjectSizeAttr>();
+    if (AttrA == AttrB)
+      return true;
+    return AttrA && AttrB && AttrA->getType() == AttrB->getType();
+  };
+
+  return std::equal(A->param_begin(), A->param_end(), B->param_begin(), AttrEq);
+}
+
 /// MergeFunctionDecl - We just parsed a function 'New' from
 /// declarator D which has the same name and scope as a previous
 /// declaration 'Old'.  Figure out how to resolve this situation,
@@ -2799,7 +2814,17 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, NamedDecl *&OldD,
       Old->isInlined() && !Old->hasAttr<GNUInlineAttr>()) {
     UndefinedButUsed.erase(Old->getCanonicalDecl());
   }
-  
+
+  // If pass_object_size params don't match up perfectly, this isn't a valid
+  // redeclaration.
+  if (Old->getNumParams() > 0 && Old->getNumParams() == New->getNumParams() &&
+      !hasIdenticalPassObjectSizeAttrs(Old, New)) {
+    Diag(New->getLocation(), diag::err_different_pass_object_size_params)
+        << New->getDeclName();
+    Diag(OldLocation, PrevDiag) << Old << Old->getType();
+    return true;
+  }
+
   if (getLangOpts().CPlusPlus) {
     // (C++98 13.1p2):
     //   Certain function declarations cannot be overloaded:

lib/Sema/SemaDeclAttr.cpp

@@ -809,6 +809,43 @@ static void handleEnableIfAttr(Sema &S, Decl *D, const AttributeList &Attr) {
                           Attr.getAttributeSpellingListIndex()));
 }
 
+static void handlePassObjectSizeAttr(Sema &S, Decl *D,
+                                     const AttributeList &Attr) {
+  if (D->hasAttr<PassObjectSizeAttr>()) {
+    S.Diag(D->getLocStart(), diag::err_attribute_only_once_per_parameter)
+        << Attr.getName();
+    return;
+  }
+
+  Expr *E = Attr.getArgAsExpr(0);
+  uint32_t Type;
+  if (!checkUInt32Argument(S, Attr, E, Type, /*Idx=*/1))
+    return;
+
+  // pass_object_size's argument is passed in as the second argument of
+  // __builtin_object_size. So, it has the same constraints as that second
+  // argument; namely, it must be in the range [0, 3].
+  if (Type > 3) {
+    S.Diag(E->getLocStart(), diag::err_attribute_argument_outof_range)
+        << Attr.getName() << 0 << 3 << E->getSourceRange();
+    return;
+  }
+
+  // pass_object_size is only supported on constant pointer parameters; as a
+  // kindness to users, we allow the parameter to be non-const for declarations.
+  // At this point, we have no clue if `D` belongs to a function declaration or
+  // definition, so we defer the constness check until later.
+  if (!cast<ParmVarDecl>(D)->getType()->isPointerType()) {
+    S.Diag(D->getLocStart(), diag::err_attribute_pointers_only)
+        << Attr.getName() << 1;
+    return;
+  }
+
+  D->addAttr(::new (S.Context)
+                 PassObjectSizeAttr(Attr.getRange(), S.Context, (int)Type,
+                                    Attr.getAttributeSpellingListIndex()));
+}
+
 static void handleConsumableAttr(Sema &S, Decl *D, const AttributeList &Attr) {
   ConsumableAttr::ConsumedState DefaultState;
 
@@ -1162,10 +1199,12 @@ static bool attrNonNullArgCheck(Sema &S, QualType T, const AttributeList &Attr,
                                 SourceRange TypeRange,
                                 bool isReturnValue = false) {
   if (!S.isValidPointerAttrType(T)) {
-    S.Diag(Attr.getLoc(), isReturnValue
-                              ? diag::warn_attribute_return_pointers_only
-                              : diag::warn_attribute_pointers_only)
-        << Attr.getName() << AttrParmRange << TypeRange;
+    if (isReturnValue)
+      S.Diag(Attr.getLoc(), diag::warn_attribute_return_pointers_only)
+          << Attr.getName() << AttrParmRange << TypeRange;
+    else
+      S.Diag(Attr.getLoc(), diag::warn_attribute_pointers_only)
+          << Attr.getName() << AttrParmRange << TypeRange << 0;
     return false;
   }
   return true;
@@ -2724,7 +2763,7 @@ static void handleInitPriorityAttr(Sema &S, Decl *D,
 
   if (prioritynum < 101 || prioritynum > 65535) {
     S.Diag(Attr.getLoc(), diag::err_attribute_argument_outof_range)
-      << E->getSourceRange();
+      << E->getSourceRange() << Attr.getName() << 101 << 65535;
     Attr.setInvalid();
     return;
   }
@@ -3862,7 +3901,7 @@ static void handleArgumentWithTypeTagAttr(Sema &S, Decl *D,
     QualType BufferTy = getFunctionOrMethodParamType(D, ArgumentIdx);
     if (!BufferTy->isPointerType()) {
       S.Diag(Attr.getLoc(), diag::err_attribute_pointers_only)
-        << Attr.getName();
+        << Attr.getName() << 0;
     }
   }
 
@@ -4972,6 +5011,9 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_CUDAConstant:
     handleSimpleAttribute<CUDAConstantAttr>(S, D, Attr);
     break;
+  case AttributeList::AT_PassObjectSize:
+    handlePassObjectSizeAttr(S, D, Attr);
+    break;
   case AttributeList::AT_Constructor:
     handleConstructorAttr(S, D, Attr);
     break;

lib/Sema/SemaExpr.cpp

@@ -496,7 +496,7 @@ SourceRange Sema::getExprRange(Expr *E) const {
 //===----------------------------------------------------------------------===//
 
 /// DefaultFunctionArrayConversion (C99 6.3.2.1p3, C99 6.3.2.1p4).
-ExprResult Sema::DefaultFunctionArrayConversion(Expr *E) {
+ExprResult Sema::DefaultFunctionArrayConversion(Expr *E, bool Diagnose) {
   // Handle any placeholder expressions which made it here.
   if (E->getType()->isPlaceholderType()) {
     ExprResult result = CheckPlaceholderExpr(E);
@@ -511,9 +511,16 @@ ExprResult Sema::DefaultFunctionArrayConversion(Expr *E) {
     // If we are here, we are not calling a function but taking
     // its address (which is not allowed in OpenCL v1.0 s6.8.a.3).
     if (getLangOpts().OpenCL) {
-      Diag(E->getExprLoc(), diag::err_opencl_taking_function_address);
+      if (Diagnose)
+        Diag(E->getExprLoc(), diag::err_opencl_taking_function_address);
       return ExprError();
     }
+
+    if (auto *DRE = dyn_cast<DeclRefExpr>(E->IgnoreParenCasts()))
+      if (auto *FD = dyn_cast<FunctionDecl>(DRE->getDecl()))
+        if (!checkAddressOfFunctionIsAvailable(FD, Diagnose, E->getExprLoc()))
+          return ExprError();
+
     E = ImpCastExprToType(E, Context.getPointerType(Ty),
                           CK_FunctionToPointerDecay).get();
   } else if (Ty->isArrayType()) {
@@ -706,8 +713,8 @@ ExprResult Sema::DefaultLvalueConversion(Expr *E) {
   return Res;
 }
 
-ExprResult Sema::DefaultFunctionArrayLvalueConversion(Expr *E) {
-  ExprResult Res = DefaultFunctionArrayConversion(E);
+ExprResult Sema::DefaultFunctionArrayLvalueConversion(Expr *E, bool Diagnose) {
+  ExprResult Res = DefaultFunctionArrayConversion(E, Diagnose);
   if (Res.isInvalid())
     return ExprError();
   Res = DefaultLvalueConversion(Res.get());
@@ -7338,7 +7345,7 @@ Sema::CheckSingleAssignmentConstraints(QualType LHSType, ExprResult &CallerRHS,
   // Suppress this for references: C++ 8.5.3p5.
   if (!LHSType->isReferenceType()) {
     // FIXME: We potentially allocate here even if ConvertRHS is false.
-    RHS = DefaultFunctionArrayLvalueConversion(RHS.get());
+    RHS = DefaultFunctionArrayLvalueConversion(RHS.get(), Diagnose);
     if (RHS.isInvalid())
       return Incompatible;
   }
@@ -9882,6 +9889,12 @@ QualType Sema::CheckAddressOfOperand(ExprResult &OrigOp, SourceLocation OpLoc) {
     // expressions here, but the result of one is always an lvalue anyway.
   }
   ValueDecl *dcl = getPrimaryDecl(op);
+
+  if (auto *FD = dyn_cast_or_null<FunctionDecl>(dcl))
+    if (!checkAddressOfFunctionIsAvailable(FD, /*Complain=*/true,
+                                           op->getLocStart()))
+      return QualType();
+
   Expr::LValueClassification lval = op->ClassifyLValue(Context);
   unsigned AddressOfError = AO_No_Error;
 
@@ -11831,6 +11844,25 @@ Sema::ConversionToObjCStringLiteralCheck(QualType DstType, Expr *&Exp) {
   return true;
 }
 
+static bool maybeDiagnoseAssignmentToFunction(Sema &S, QualType DstType,
+                                              const Expr *SrcExpr) {
+  if (!DstType->isFunctionPointerType() ||
+      !SrcExpr->getType()->isFunctionType())
+    return false;
+
+  auto *DRE = dyn_cast<DeclRefExpr>(SrcExpr->IgnoreParenImpCasts());
+  if (!DRE)
+    return false;
+
+  auto *FD = dyn_cast<FunctionDecl>(DRE->getDecl());
+  if (!FD)
+    return false;
+
+  return !S.checkAddressOfFunctionIsAvailable(FD,
+                                              /*Complain=*/true,
+                                              SrcExpr->getLocStart());
+}
+
 bool Sema::DiagnoseAssignmentResult(AssignConvertType ConvTy,
                                     SourceLocation Loc,
                                     QualType DstType, QualType SrcType,
@@ -11963,6 +11995,12 @@ bool Sema::DiagnoseAssignmentResult(AssignConvertType ConvTy,
     DiagKind = diag::err_arc_weak_unavailable_assign;
     break;
   case Incompatible:
+    if (maybeDiagnoseAssignmentToFunction(*this, DstType, SrcExpr)) {
+      if (Complained)
+        *Complained = true;
+      return true;
+    }
+
     DiagKind = diag::err_typecheck_convert_incompatible;
     ConvHints.tryToFixConversion(SrcExpr, SrcType, DstType, *this);
     MayHaveConvFixit = true;

lib/Sema/SemaInit.cpp

@@ -3011,6 +3011,7 @@ bool InitializationSequence::isAmbiguous() const {
   case FK_VariableLengthArrayHasInitializer:
   case FK_PlaceholderType:
   case FK_ExplicitConstructor:
+  case FK_AddressOfUnaddressableFunction:
     return false;
 
   case FK_ReferenceInitOverloadFailed:
@@ -4801,6 +4802,17 @@ InitializationSequence::InitializationSequence(Sema &S,
   InitializeFrom(S, Entity, Kind, Args, TopLevelOfInitList);
 }
 
+/// Tries to get a FunctionDecl out of `E`. If it succeeds and we can take the
+/// address of that function, this returns true. Otherwise, it returns false.
+static bool isExprAnUnaddressableFunction(Sema &S, const Expr *E) {
+  auto *DRE = dyn_cast<DeclRefExpr>(E);
+  if (!DRE || !isa<FunctionDecl>(DRE->getDecl()))
+    return false;
+
+  return !S.checkAddressOfFunctionIsAvailable(
+      cast<FunctionDecl>(DRE->getDecl()));
+}
+
 void InitializationSequence::InitializeFrom(Sema &S,
                                             const InitializedEntity &Entity,
                                             const InitializationKind &Kind,
@@ -4982,7 +4994,7 @@ void InitializationSequence::InitializeFrom(Sema &S,
   }
 
   assert(S.getLangOpts().CPlusPlus);
-      
+
   //     - If the destination type is a (possibly cv-qualified) class type:
   if (DestType->isRecordType()) {
     //     - If the initialization is direct-initialization, or if it is
@@ -5079,6 +5091,9 @@ void InitializationSequence::InitializeFrom(Sema &S,
                !S.ResolveAddressOfOverloadedFunction(Initializer, DestType,
                                                      false, dap))
       SetFailed(InitializationSequence::FK_AddressOfOverloadFailed);
+    else if (Initializer->getType()->isFunctionType() &&
+             isExprAnUnaddressableFunction(S, Initializer))
+      SetFailed(InitializationSequence::FK_AddressOfUnaddressableFunction);
     else
       SetFailed(InitializationSequence::FK_ConversionFailed);
   } else {
@@ -6926,6 +6941,13 @@ bool InitializationSequence::Diagnose(Sema &S,
     break;
   }
 
+  case FK_AddressOfUnaddressableFunction: {
+    auto *FD = cast<FunctionDecl>(cast<DeclRefExpr>(Args[0])->getDecl());
+    S.checkAddressOfFunctionIsAvailable(FD, /*Complain=*/true,
+                                        Args[0]->getLocStart());
+    break;
+  }
+
   case FK_ReferenceInitOverloadFailed:
   case FK_UserConversionOverloadFailed:
     switch (FailedOverloadResult) {
@@ -7248,6 +7270,10 @@ void InitializationSequence::dump(raw_ostream &OS) const {
       OS << "array requires initializer list";
       break;
 
+    case FK_AddressOfUnaddressableFunction:
+      OS << "address of unaddressable function was taken";
+      break;
+
     case FK_ArrayNeedsInitListOrStringLiteral:
       OS << "array requires initializer list or string literal";
       break;

lib/Sema/SemaLambda.cpp

@@ -1141,6 +1141,12 @@ static void addFunctionPointerConversion(Sema &S,
                                          SourceRange IntroducerRange,
                                          CXXRecordDecl *Class,
                                          CXXMethodDecl *CallOperator) {
+  // This conversion is explicitly disabled if the lambda's function has
+  // pass_object_size attributes on any of its parameters.
+  if (std::any_of(CallOperator->param_begin(), CallOperator->param_end(),
+                  std::mem_fn(&ParmVarDecl::hasAttr<PassObjectSizeAttr>)))
+    return;
+
   // Add the conversion to function pointer.
   const FunctionProtoType *CallOpProto = 
       CallOperator->getType()->getAs<FunctionProtoType>();

lib/Sema/SemaOverload.cpp

@@ -38,6 +38,11 @@
 using namespace clang;
 using namespace sema;
 
+static bool functionHasPassObjectSizeParams(const FunctionDecl *FD) {
+  return std::any_of(FD->param_begin(), FD->param_end(),
+                     std::mem_fn(&ParmVarDecl::hasAttr<PassObjectSizeAttr>));
+}
+
 /// A convenience routine for creating a decayed reference to a function.
 static ExprResult
 CreateFunctionRefExpr(Sema &S, FunctionDecl *Fn, NamedDecl *FoundDecl,
@@ -60,12 +65,8 @@ CreateFunctionRefExpr(Sema &S, FunctionDecl *Fn, NamedDecl *FoundDecl,
     DRE->setHadMultipleCandidates(true);
 
   S.MarkDeclRefReferenced(DRE);
-
-  ExprResult E = DRE;
-  E = S.DefaultFunctionArrayConversion(E.get());
-  if (E.isInvalid())
-    return ExprError();
-  return E;
+  return S.ImpCastExprToType(DRE, S.Context.getPointerType(DRE->getType()),
+                             CK_FunctionToPointerDecay);
 }
 
 static bool IsStandardConversion(Sema &S, Expr* From, QualType ToType,
@@ -1062,6 +1063,14 @@ bool Sema::IsOverload(FunctionDecl *New, FunctionDecl *Old,
       return true;
   }
 
+  // Though pass_object_size is placed on parameters and takes an argument, we
+  // consider it to be a function-level modifier for the sake of function
+  // identity. Either the function has one or more parameters with
+  // pass_object_size or it doesn't.
+  if (functionHasPassObjectSizeParams(New) !=
+      functionHasPassObjectSizeParams(Old))
+    return true;
+
   // enable_if attributes are an order-sensitive part of the signature.
   for (specific_attr_iterator<EnableIfAttr>
          NewI = New->specific_attr_begin<EnableIfAttr>(),
@@ -1548,6 +1557,11 @@ static bool IsStandardConversion(Sema &S, Expr* From, QualType ToType,
     // Function-to-pointer conversion (C++ 4.3).
     SCS.First = ICK_Function_To_Pointer;
 
+    if (auto *DRE = dyn_cast<DeclRefExpr>(From->IgnoreParenCasts()))
+      if (auto *FD = dyn_cast<FunctionDecl>(DRE->getDecl()))
+        if (!S.checkAddressOfFunctionIsAvailable(FD))
+          return false;
+
     // An lvalue of function type T can be converted to an rvalue of
     // type "pointer to T." The result is a pointer to the
     // function. (C++ 4.3p1).
@@ -2508,10 +2522,21 @@ enum {
   ft_parameter_arity,
   ft_parameter_mismatch,
   ft_return_type,
-  ft_qualifer_mismatch,
-  ft_addr_enable_if
+  ft_qualifer_mismatch
 };
 
+/// Attempts to get the FunctionProtoType from a Type. Handles
+/// MemberFunctionPointers properly.
+static const FunctionProtoType *tryGetFunctionProtoType(QualType FromType) {
+  if (auto *FPT = FromType->getAs<FunctionProtoType>())
+    return FPT;
+
+  if (auto *MPT = FromType->getAs<MemberPointerType>())
+    return MPT->getPointeeType()->getAs<FunctionProtoType>();
+
+  return nullptr;
+}
+
 /// HandleFunctionTypeMismatch - Gives diagnostic information for differeing
 /// function types.  Catches different number of parameter, mismatch in
 /// parameter types, and different return types.
@@ -2558,8 +2583,8 @@ void Sema::HandleFunctionTypeMismatch(PartialDiagnostic &PDiag,
     return;
   }
 
-  const FunctionProtoType *FromFunction = FromType->getAs<FunctionProtoType>(),
-                          *ToFunction = ToType->getAs<FunctionProtoType>();
+  const FunctionProtoType *FromFunction = tryGetFunctionProtoType(FromType),
+                          *ToFunction = tryGetFunctionProtoType(ToType);
 
   // Both types need to be function types.
   if (!FromFunction || !ToFunction) {
@@ -8572,7 +8597,11 @@ bool clang::isBetterOverloadCandidate(Sema &S, const OverloadCandidate &Cand1,
            S.IdentifyCUDAPreference(Caller, Cand2.Function);
   }
 
-  return false;
+  bool HasPS1 = Cand1.Function != nullptr &&
+                functionHasPassObjectSizeParams(Cand1.Function);
+  bool HasPS2 = Cand2.Function != nullptr &&
+                functionHasPassObjectSizeParams(Cand2.Function);
+  return HasPS1 != HasPS2 && HasPS1;
 }
 
 /// Determine whether two declarations are "equivalent" for the purposes of
@@ -8642,9 +8671,6 @@ void Sema::diagnoseEquivalentInternalLinkageDeclarations(
   }
 }
 
-static void NoteFunctionCandidate(Sema &S, OverloadCandidate *Cand,
-                                  unsigned NumArgs);
-
 /// \brief Computes the best viable function (C++ 13.3.3)
 /// within an overload candidate set.
 ///
@@ -8794,17 +8820,75 @@ static bool isFunctionAlwaysEnabled(const ASTContext &Ctx,
   return true;
 }
 
+/// \brief Returns true if we can take the address of the function.
+///
+/// \param Complain - If true, we'll emit a diagnostic
+/// \param InOverloadResolution - For the purposes of emitting a diagnostic, are
+///   we in overload resolution?
+/// \param Loc - The location of the statement we're complaining about. Ignored
+///   if we're not complaining, or if we're in overload resolution.
+static bool checkAddressOfFunctionIsAvailable(Sema &S, const FunctionDecl *FD,
+                                              bool Complain,
+                                              bool InOverloadResolution,
+                                              SourceLocation Loc) {
+  if (!isFunctionAlwaysEnabled(S.Context, FD)) {
+    if (Complain) {
+      // FIXME(gbiv): Both diagnostics below lack tests. We should add tests.
+      if (InOverloadResolution)
+        S.Diag(FD->getLocStart(),
+               diag::note_addrof_ovl_candidate_disabled_by_enable_if_attr);
+      else
+        S.Diag(Loc, diag::err_addrof_function_disabled_by_enable_if_attr) << FD;
+    }
+    return false;
+  }
+
+  auto I = std::find_if(FD->param_begin(), FD->param_end(),
+                        std::mem_fn(&ParmVarDecl::hasAttr<PassObjectSizeAttr>));
+  if (I == FD->param_end())
+    return true;
+
+  if (Complain) {
+    // Add one to ParamNo because it's user-facing
+    unsigned ParamNo = std::distance(FD->param_begin(), I) + 1;
+    if (InOverloadResolution)
+      S.Diag(FD->getLocation(),
+             diag::note_ovl_candidate_has_pass_object_size_params)
+          << ParamNo;
+    else
+      S.Diag(Loc, diag::err_address_of_function_with_pass_object_size_params)
+          << FD << ParamNo;
+  }
+  return false;
+}
+
+static bool checkAddressOfCandidateIsAvailable(Sema &S,
+                                               const FunctionDecl *FD) {
+  return checkAddressOfFunctionIsAvailable(S, FD, /*Complain=*/true,
+                                           /*InOverloadResolution=*/true,
+                                           /*Loc=*/SourceLocation());
+}
+
+bool Sema::checkAddressOfFunctionIsAvailable(const FunctionDecl *Function,
+                                             bool Complain,
+                                             SourceLocation Loc) {
+  return ::checkAddressOfFunctionIsAvailable(*this, Function, Complain,
+                                             /*InOverloadResolution=*/false,
+                                             Loc);
+}
+
 // Notes the location of an overload candidate.
 void Sema::NoteOverloadCandidate(FunctionDecl *Fn, QualType DestType,
                                  bool TakingAddress) {
+  if (TakingAddress && !checkAddressOfCandidateIsAvailable(*this, Fn))
+    return;
+
   std::string FnDesc;
   OverloadCandidateKind K = ClassifyOverloadCandidate(*this, Fn, FnDesc);
   PartialDiagnostic PD = PDiag(diag::note_ovl_candidate)
                              << (unsigned) K << FnDesc;
-  if (TakingAddress && !isFunctionAlwaysEnabled(Context, Fn))
-    PD << ft_addr_enable_if;
-  else
-    HandleFunctionTypeMismatch(PD, Fn->getType(), DestType);
+
+  HandleFunctionTypeMismatch(PD, Fn->getType(), DestType);
   Diag(Fn->getLocation(), PD);
   MaybeEmitInheritedConstructorNote(*this, Fn);
 }
@@ -8858,7 +8942,7 @@ void ImplicitConversionSequence::DiagnoseAmbiguousConversion(
 }
 
 static void DiagnoseBadConversion(Sema &S, OverloadCandidate *Cand,
-                                  unsigned I) {
+                                  unsigned I, bool TakingCandidateAddress) {
   const ImplicitConversionSequence &Conv = Cand->Conversions[I];
   assert(Conv.isBad());
   assert(Cand->Function && "for now, candidate must be a function");
@@ -9056,7 +9140,11 @@ static void DiagnoseBadConversion(Sema &S, OverloadCandidate *Cand,
         return;
       }
   }
-  
+
+  if (TakingCandidateAddress &&
+      !checkAddressOfCandidateIsAvailable(S, Cand->Function))
+    return;
+
   // Emit the generic diagnostic and, optionally, add the hints to it.
   PartialDiagnostic FDiag = S.PDiag(diag::note_ovl_candidate_bad_conv);
   FDiag << (unsigned) FnKind << FnDesc
@@ -9167,7 +9255,8 @@ static TemplateDecl *getDescribedTemplate(Decl *Templated) {
 /// Diagnose a failed template-argument deduction.
 static void DiagnoseBadDeduction(Sema &S, Decl *Templated,
                                  DeductionFailureInfo &DeductionFailure,
-                                 unsigned NumArgs) {
+                                 unsigned NumArgs,
+                                 bool TakingCandidateAddress) {
   TemplateParameter Param = DeductionFailure.getTemplateParameter();
   NamedDecl *ParamD;
   (ParamD = Param.dyn_cast<TemplateTypeParmDecl*>()) ||
@@ -9335,6 +9424,11 @@ static void DiagnoseBadDeduction(Sema &S, Decl *Templated,
         }
       }
     }
+
+    if (TakingCandidateAddress && isa<FunctionDecl>(Templated) &&
+        !checkAddressOfCandidateIsAvailable(S, cast<FunctionDecl>(Templated)))
+      return;
+
     // FIXME: For generic lambda parameters, check if the function is a lambda
     // call operator, and if so, emit a prettier and more informative 
     // diagnostic that mentions 'auto' and lambda in addition to 
@@ -9355,14 +9449,15 @@ static void DiagnoseBadDeduction(Sema &S, Decl *Templated,
 
 /// Diagnose a failed template-argument deduction, for function calls.
 static void DiagnoseBadDeduction(Sema &S, OverloadCandidate *Cand,
-                                 unsigned NumArgs) {
+                                 unsigned NumArgs,
+                                 bool TakingCandidateAddress) {
   unsigned TDK = Cand->DeductionFailure.Result;
   if (TDK == Sema::TDK_TooFewArguments || TDK == Sema::TDK_TooManyArguments) {
     if (CheckArityMismatch(S, Cand, NumArgs))
       return;
   }
   DiagnoseBadDeduction(S, Cand->Function, // pattern
-                       Cand->DeductionFailure, NumArgs);
+                       Cand->DeductionFailure, NumArgs, TakingCandidateAddress);
 }
 
 /// CUDA: diagnose an invalid call across targets.
@@ -9443,7 +9538,8 @@ static void DiagnoseFailedEnableIfAttr(Sema &S, OverloadCandidate *Cand) {
 /// more richly for those diagnostic clients that cared, but we'd
 /// still have to be just as careful with the default diagnostics.
 static void NoteFunctionCandidate(Sema &S, OverloadCandidate *Cand,
-                                  unsigned NumArgs) {
+                                  unsigned NumArgs,
+                                  bool TakingCandidateAddress) {
   FunctionDecl *Fn = Cand->Function;
 
   // Note deleted candidates, but only if they're viable.
@@ -9471,7 +9567,7 @@ static void NoteFunctionCandidate(Sema &S, OverloadCandidate *Cand,
     return DiagnoseArityMismatch(S, Cand, NumArgs);
 
   case ovl_fail_bad_deduction:
-    return DiagnoseBadDeduction(S, Cand, NumArgs);
+    return DiagnoseBadDeduction(S, Cand, NumArgs, TakingCandidateAddress);
 
   case ovl_fail_illegal_constructor: {
     S.Diag(Fn->getLocation(), diag::note_ovl_candidate_illegal_constructor)
@@ -9489,7 +9585,7 @@ static void NoteFunctionCandidate(Sema &S, OverloadCandidate *Cand,
     unsigned I = (Cand->IgnoreObjectArgument ? 1 : 0);
     for (unsigned N = Cand->NumConversions; I != N; ++I)
       if (Cand->Conversions[I].isBad())
-        return DiagnoseBadConversion(S, Cand, I);
+        return DiagnoseBadConversion(S, Cand, I, TakingCandidateAddress);
 
     // FIXME: this currently happens when we're called from SemaInit
     // when user-conversion overload fails.  Figure out how to handle
@@ -9860,7 +9956,8 @@ void OverloadCandidateSet::NoteCandidates(Sema &S,
     ++CandsShown;
 
     if (Cand->Function)
-      NoteFunctionCandidate(S, Cand, Args.size());
+      NoteFunctionCandidate(S, Cand, Args.size(),
+                            /*TakingCandidateAddress=*/false);
     else if (Cand->IsSurrogate)
       NoteSurrogateCandidate(S, Cand);
     else {
@@ -9928,9 +10025,10 @@ struct CompareTemplateSpecCandidatesForDisplay {
 /// Diagnose a template argument deduction failure.
 /// We are treating these failures as overload failures due to bad
 /// deductions.
-void TemplateSpecCandidate::NoteDeductionFailure(Sema &S) {
+void TemplateSpecCandidate::NoteDeductionFailure(Sema &S,
+                                                 bool ForTakingAddress) {
   DiagnoseBadDeduction(S, Specialization, // pattern
-                       DeductionFailure, /*NumArgs=*/0);
+                       DeductionFailure, /*NumArgs=*/0, ForTakingAddress);
 }
 
 void TemplateSpecCandidateSet::destroyCandidates() {
@@ -9983,7 +10081,7 @@ void TemplateSpecCandidateSet::NoteCandidates(Sema &S, SourceLocation Loc) {
 
     assert(Cand->Specialization &&
            "Non-matching built-in candidates are not added to Cands.");
-    Cand->NoteDeductionFailure(S);
+    Cand->NoteDeductionFailure(S, ForTakingAddress);
   }
 
   if (I != E)
@@ -10048,7 +10146,7 @@ public:
         HasComplained(false),
         OvlExprInfo(OverloadExpr::find(SourceExpr)),
         OvlExpr(OvlExprInfo.Expression),
-        FailedCandidates(OvlExpr->getNameLoc()) {
+        FailedCandidates(OvlExpr->getNameLoc(), /*ForTakingAddress=*/true) {
     ExtractUnqualifiedFunctionTypeFromTargetType();
 
     if (TargetFunctionType->isFunctionType()) {
@@ -10182,10 +10280,9 @@ private:
     Specialization = cast<FunctionDecl>(Specialization->getCanonicalDecl());
     assert(S.isSameOrCompatibleFunctionType(
               Context.getCanonicalType(Specialization->getType()),
-              Context.getCanonicalType(TargetFunctionType)) ||
-           (!S.getLangOpts().CPlusPlus && TargetType->isVoidPointerType()));
+              Context.getCanonicalType(TargetFunctionType)));
 
-    if (!isFunctionAlwaysEnabled(S.Context, Specialization))
+    if (!S.checkAddressOfFunctionIsAvailable(Specialization))
       return false;
 
     Matches.push_back(std::make_pair(CurAccessFunPair, Specialization));
@@ -10218,7 +10315,7 @@ private:
         return false;
       }
 
-      if (!isFunctionAlwaysEnabled(S.Context, FunDecl))
+      if (!S.checkAddressOfFunctionIsAvailable(FunDecl))
         return false;
 
       QualType ResultTy;
@@ -10341,8 +10438,9 @@ public:
            I != IEnd; ++I)
         if (FunctionDecl *Fun =
                 dyn_cast<FunctionDecl>((*I)->getUnderlyingDecl()))
-          S.NoteOverloadCandidate(Fun, TargetFunctionType,
-                                  /*TakingAddress=*/true);
+          if (!functionHasPassObjectSizeParams(Fun))
+            S.NoteOverloadCandidate(Fun, TargetFunctionType,
+                                    /*TakingAddress=*/true);
       FailedCandidates.NoteCandidates(S, OvlExpr->getLocStart());
     }
   }
@@ -11052,9 +11150,23 @@ static ExprResult FinishOverloadedCallExpr(Sema &SemaRef, Scope *S, Expr *Fn,
     if (!Recovery.isInvalid())
       return Recovery;
 
-    SemaRef.Diag(Fn->getLocStart(),
-         diag::err_ovl_no_viable_function_in_call)
-      << ULE->getName() << Fn->getSourceRange();
+    // If the user passes in a function that we can't take the address of, we
+    // generally end up emitting really bad error messages. Here, we attempt to
+    // emit better ones.
+    for (const Expr *Arg : Args) {
+      if (!Arg->getType()->isFunctionType())
+        continue;
+      if (auto *DRE = dyn_cast<DeclRefExpr>(Arg->IgnoreParenImpCasts())) {
+        auto *FD = dyn_cast<FunctionDecl>(DRE->getDecl());
+        if (FD &&
+            !SemaRef.checkAddressOfFunctionIsAvailable(FD, /*Complain=*/true,
+                                                       Arg->getExprLoc()))
+          return ExprError();
+      }
+    }
+
+    SemaRef.Diag(Fn->getLocStart(), diag::err_ovl_no_viable_function_in_call)
+        << ULE->getName() << Fn->getSourceRange();
     CandidateSet->NoteCandidates(SemaRef, OCD_AllCandidates, Args);
     break;
   }

lib/Sema/SemaTemplate.cpp

@@ -2748,7 +2748,8 @@ Sema::CheckVarTemplateId(VarTemplateDecl *Template, SourceLocation TemplateLoc,
   typedef PartialSpecMatchResult MatchResult;
   SmallVector<MatchResult, 4> Matched;
   SourceLocation PointOfInstantiation = TemplateNameLoc;
-  TemplateSpecCandidateSet FailedCandidates(PointOfInstantiation);
+  TemplateSpecCandidateSet FailedCandidates(PointOfInstantiation,
+                                            /*ForTakingAddress=*/false);
 
   // 1. Attempt to find the closest partial specialization that this
   // specializes, if any.
@@ -6822,7 +6823,8 @@ bool Sema::CheckFunctionTemplateSpecialization(
   // The set of function template specializations that could match this
   // explicit function template specialization.
   UnresolvedSet<8> Candidates;
-  TemplateSpecCandidateSet FailedCandidates(FD->getLocation());
+  TemplateSpecCandidateSet FailedCandidates(FD->getLocation(),
+                                            /*ForTakingAddress=*/false);
 
   llvm::SmallDenseMap<FunctionDecl *, TemplateArgumentListInfo, 8>
       ConvertedTemplateArgs;

lib/Sema/SemaType.cpp

@@ -5483,9 +5483,12 @@ static bool handleMSPointerTypeQualifierAttr(TypeProcessingState &State,
   // Pointer type qualifiers can only operate on pointer types, but not
   // pointer-to-member types.
   if (!isa<PointerType>(Desugared)) {
-    S.Diag(Attr.getLoc(), Type->isMemberPointerType() ?
-                          diag::err_attribute_no_member_pointers :
-                          diag::err_attribute_pointers_only) << Attr.getName();
+    if (Type->isMemberPointerType())
+      S.Diag(Attr.getLoc(), diag::err_attribute_no_member_pointers)
+          << Attr.getName();
+    else
+      S.Diag(Attr.getLoc(), diag::err_attribute_pointers_only)
+          << Attr.getName() << 0;
     return true;
   }
 

test/CodeGenCXX/mangle-ms.cpp

@@ -418,3 +418,22 @@ void f(S::T6) {}
 // X64-DAG: @"\01?f@UnnamedType@@YAXUT5@S@1@@Z"
 // X64-DAG: @"\01?f@UnnamedType@@YAXPEAU<unnamed-type-T6>@S@1@@Z"
 }
+
+namespace PassObjectSize {
+// NOTE: This mangling is subject to change.
+// Reiterating from the comment in MicrosoftMangle, the scheme is pretend a
+// parameter of type __clang::__pass_object_sizeN exists after each pass object
+// size param P, where N is the Type of the pass_object_size attribute on P.
+//
+// e.g. we want to mangle:
+//   void foo(void *const __attribute__((pass_object_size(0))));
+// as if it were
+//   namespace __clang { enum __pass_object_size0 : size_t {}; }
+//   void foo(void *const, __clang::__pass_object_size0);
+// where __clang is a top-level namespace.
+
+// CHECK-DAG: define i32 @"\01?foo@PassObjectSize@@YAHQAHW4__pass_object_size0@__clang@@@Z"
+int foo(int *const i __attribute__((pass_object_size(0)))) { return 0; }
+// CHECK-DAG: define i32 @"\01?bar@PassObjectSize@@YAHQAHW4__pass_object_size1@__clang@@@Z"
+int bar(int *const i __attribute__((pass_object_size(1)))) { return 0; }
+}

test/SemaCXX/init-priority-attr.cpp

@@ -21,7 +21,7 @@ Two foo __attribute__((init_priority(101))) ( 5, 6 );
 
 Two goo __attribute__((init_priority(2,3))) ( 5, 6 ); // expected-error {{'init_priority' attribute takes one argument}}
 
-Two coo[2]  __attribute__((init_priority(3)));	// expected-error {{init_priority attribute requires integer constant between 101 and 65535 inclusive}}
+Two coo[2]  __attribute__((init_priority(3)));	// expected-error {{'init_priority' attribute requires integer constant between 101 and 65535 inclusive}}
 
 Two koo[4]  __attribute__((init_priority(1.13))); // expected-error {{'init_priority' attribute requires an integer constant}}