P0136R1, DR1573, DR1645, DR1715, DR1736, DR1903, DR1941, DR1959, DR1991:

Replace inheriting constructors implementation with new approach, voted into
C++ last year as a DR against C++11.

Instead of synthesizing a set of derived class constructors for each inherited
base class constructor, we make the constructors of the base class visible to
constructor lookup in the derived class, using the normal rules for
using-declarations.

For constructors, UsingShadowDecl now has a ConstructorUsingShadowDecl derived
class that tracks the requisite additional information. We create shadow
constructors (not found by name lookup) in the derived class to model the
actual initialization, and have a new expression node,
CXXInheritedCtorInitExpr, to model the initialization of a base class from such
a constructor. (This initialization is special because it performs real perfect
forwarding of arguments.)

In cases where argument forwarding is not possible (for inalloca calls,
variadic calls, and calls with callee parameter cleanup), the shadow inheriting
constructor is not emitted and instead we directly emit the initialization code
into the caller of the inherited constructor.

Note that this new model is not perfectly compatible with the old model in some
corner cases. In particular:
 * if B inherits a private constructor from A, and C uses that constructor to
   construct a B, then we previously required that A befriends B and B
   befriends C, but the new rules require A to befriend C directly, and
 * if a derived class has its own constructors (and so its implicit default
   constructor is suppressed), it may still inherit a default constructor from
   a base class

llvm-svn: 274049

8 files changed, 337 insertions, 69 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index c562602d96b..d683b899022 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -244,6 +244,15 @@ CodeGenTypes::arrangeCXXMethodDeclaration(const CXXMethodDecl *MD) {
   return arrangeFreeFunctionType(prototype, MD);
 }
 
+bool CodeGenTypes::inheritingCtorHasParams(
+    const InheritedConstructor &Inherited, CXXCtorType Type) {
+  // Parameters are unnecessary if we're constructing a base class subobject
+  // and the inherited constructor lives in a virtual base.
+  return Type == Ctor_Complete ||
+         !Inherited.getShadowDecl()->constructsVirtualBase() ||
+         !Target.getCXXABI().hasConstructorVariants();
+  }
+
 const CGFunctionInfo &
 CodeGenTypes::arrangeCXXStructorDeclaration(const CXXMethodDecl *MD,
                                             StructorType Type) {
@@ -252,9 +261,16 @@ CodeGenTypes::arrangeCXXStructorDeclaration(const CXXMethodDecl *MD,
   SmallVector<FunctionProtoType::ExtParameterInfo, 16> paramInfos;
   argTypes.push_back(GetThisType(Context, MD->getParent()));
 
+  bool PassParams = true;
+
   GlobalDecl GD;
   if (auto *CD = dyn_cast<CXXConstructorDecl>(MD)) {
     GD = GlobalDecl(CD, toCXXCtorType(Type));
+
+    // A base class inheriting constructor doesn't get forwarded arguments
+    // needed to construct a virtual base (or base class thereof).
+    if (auto Inherited = CD->getInheritedConstructor())
+      PassParams = inheritingCtorHasParams(Inherited, toCXXCtorType(Type));
   } else {
     auto *DD = dyn_cast<CXXDestructorDecl>(MD);
     GD = GlobalDecl(DD, toCXXDtorType(Type));
@@ -263,12 +279,14 @@ CodeGenTypes::arrangeCXXStructorDeclaration(const CXXMethodDecl *MD,
   CanQual<FunctionProtoType> FTP = GetFormalType(MD);
 
   // Add the formal parameters.
-  appendParameterTypes(*this, argTypes, paramInfos, FTP, MD);
+  if (PassParams)
+    appendParameterTypes(*this, argTypes, paramInfos, FTP, MD);
 
   TheCXXABI.buildStructorSignature(MD, Type, argTypes);
 
   RequiredArgs required =
-      (MD->isVariadic() ? RequiredArgs(argTypes.size()) : RequiredArgs::All);
+      (PassParams && MD->isVariadic() ? RequiredArgs(argTypes.size())
+                                      : RequiredArgs::All);
 
   FunctionType::ExtInfo extInfo = FTP->getExtInfo();
   CanQualType resultType = TheCXXABI.HasThisReturn(GD)
@@ -3186,10 +3204,10 @@ void CodeGenFunction::EmitCallArgs(
     size_t CallArgsStart = Args.size();
     for (int I = ArgTypes.size() - 1; I >= 0; --I) {
       CallExpr::const_arg_iterator Arg = ArgRange.begin() + I;
+      MaybeEmitImplicitObjectSize(I, *Arg);
       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
diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index 56e24840c82..7ed891f426a 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -2048,6 +2048,62 @@ void CodeGenFunction::EmitCXXConstructorCall(const CXXConstructorDecl *D,
                                              bool ForVirtualBase,
                                              bool Delegating, Address This,
                                              const CXXConstructExpr *E) {
+  CallArgList Args;
+
+  // Push the this ptr.
+  Args.add(RValue::get(This.getPointer()), D->getThisType(getContext()));
+
+  // If this is a trivial constructor, emit a memcpy now before we lose
+  // the alignment information on the argument.
+  // FIXME: It would be better to preserve alignment information into CallArg.
+  if (isMemcpyEquivalentSpecialMember(D)) {
+    assert(E->getNumArgs() == 1 && "unexpected argcount for trivial ctor");
+
+    const Expr *Arg = E->getArg(0);
+    QualType SrcTy = Arg->getType();
+    Address Src = EmitLValue(Arg).getAddress();
+    QualType DestTy = getContext().getTypeDeclType(D->getParent());
+    EmitAggregateCopyCtor(This, Src, DestTy, SrcTy);
+    return;
+  }
+
+  // Add the rest of the user-supplied arguments.
+  const FunctionProtoType *FPT = D->getType()->castAs<FunctionProtoType>();
+  EmitCallArgs(Args, FPT, E->arguments(), E->getConstructor());
+
+  EmitCXXConstructorCall(D, Type, ForVirtualBase, Delegating, This, Args);
+}
+
+static bool canEmitDelegateCallArgs(CodeGenFunction &CGF,
+                                    const CXXConstructorDecl *Ctor,
+                                    CXXCtorType Type, CallArgList &Args) {
+  // We can't forward a variadic call.
+  if (Ctor->isVariadic())
+    return false;
+
+  if (CGF.getTarget().getCXXABI().areArgsDestroyedLeftToRightInCallee()) {
+    // If the parameters are callee-cleanup, it's not safe to forward.
+    for (auto *P : Ctor->parameters())
+      if (P->getType().isDestructedType())
+        return false;
+
+    // Likewise if they're inalloca.
+    const CGFunctionInfo &Info =
+        CGF.CGM.getTypes().arrangeCXXConstructorCall(Args, Ctor, Type, 0);
+    if (Info.usesInAlloca())
+      return false;
+  }
+
+  // Anything else should be OK.
+  return true;
+}
+
+void CodeGenFunction::EmitCXXConstructorCall(const CXXConstructorDecl *D,
+                                             CXXCtorType Type,
+                                             bool ForVirtualBase,
+                                             bool Delegating,
+                                             Address This,
+                                             CallArgList &Args) {
   const CXXRecordDecl *ClassDecl = D->getParent();
 
   // C++11 [class.mfct.non-static]p2:
@@ -2058,7 +2114,7 @@ void CodeGenFunction::EmitCXXConstructorCall(const CXXConstructorDecl *D,
                 This.getPointer(), getContext().getRecordType(ClassDecl));
 
   if (D->isTrivial() && D->isDefaultConstructor()) {
-    assert(E->getNumArgs() == 0 && "trivial default ctor with args");
+    assert(Args.size() == 1 && "trivial default ctor with args");
     return;
   }
 
@@ -2066,24 +2122,24 @@ void CodeGenFunction::EmitCXXConstructorCall(const CXXConstructorDecl *D,
   // union copy constructor, we must emit a memcpy, because the AST does not
   // model that copy.
   if (isMemcpyEquivalentSpecialMember(D)) {
-    assert(E->getNumArgs() == 1 && "unexpected argcount for trivial ctor");
+    assert(Args.size() == 2 && "unexpected argcount for trivial ctor");
 
-    const Expr *Arg = E->getArg(0);
-    QualType SrcTy = Arg->getType();
-    Address Src = EmitLValue(Arg).getAddress();
+    QualType SrcTy = D->getParamDecl(0)->getType().getNonReferenceType();
+    Address Src(Args[1].RV.getScalarVal(), getNaturalTypeAlignment(SrcTy));
     QualType DestTy = getContext().getTypeDeclType(ClassDecl);
     EmitAggregateCopyCtor(This, Src, DestTy, SrcTy);
     return;
   }
 
-  CallArgList Args;
-
-  // Push the this ptr.
-  Args.add(RValue::get(This.getPointer()), D->getThisType(getContext()));
-
-  // Add the rest of the user-supplied arguments.
-  const FunctionProtoType *FPT = D->getType()->castAs<FunctionProtoType>();
-  EmitCallArgs(Args, FPT, E->arguments(), E->getConstructor());
+  // Check whether we can actually emit the constructor before trying to do so.
+  if (auto Inherited = D->getInheritedConstructor()) {
+    if (getTypes().inheritingCtorHasParams(Inherited, Type) &&
+        !canEmitDelegateCallArgs(*this, D, Type, Args)) {
+      EmitInlinedInheritingCXXConstructorCall(D, Type, ForVirtualBase,
+                                              Delegating, Args);
+      return;
+    }
+  }
 
   // Insert any ABI-specific implicit constructor arguments.
   unsigned ExtraArgs = CGM.getCXXABI().addImplicitConstructorArgs(
@@ -2113,6 +2169,95 @@ void CodeGenFunction::EmitCXXConstructorCall(const CXXConstructorDecl *D,
     EmitVTableAssumptionLoads(ClassDecl, This);
 }
 
+void CodeGenFunction::EmitInheritedCXXConstructorCall(
+    const CXXConstructorDecl *D, bool ForVirtualBase, Address This,
+    bool InheritedFromVBase, const CXXInheritedCtorInitExpr *E) {
+  CallArgList Args;
+  CallArg ThisArg(RValue::get(This.getPointer()), D->getThisType(getContext()),
+                  /*NeedsCopy=*/false);
+
+  // Forward the parameters.
+  if (InheritedFromVBase &&
+      CGM.getTarget().getCXXABI().hasConstructorVariants()) {
+    // Nothing to do; this construction is not responsible for constructing
+    // the base class containing the inherited constructor.
+    // FIXME: Can we just pass undef's for the remaining arguments if we don't
+    // have constructor variants?
+    Args.push_back(ThisArg);
+  } else if (!CXXInheritedCtorInitExprArgs.empty()) {
+    // The inheriting constructor was inlined; just inject its arguments.
+    assert(CXXInheritedCtorInitExprArgs.size() >= D->getNumParams() &&
+           "wrong number of parameters for inherited constructor call");
+    Args = CXXInheritedCtorInitExprArgs;
+    Args[0] = ThisArg;
+  } else {
+    // The inheriting constructor was not inlined. Emit delegating arguments.
+    Args.push_back(ThisArg);
+    const auto *OuterCtor = cast<CXXConstructorDecl>(CurCodeDecl);
+    assert(OuterCtor->getNumParams() == D->getNumParams());
+    assert(!OuterCtor->isVariadic() && "should have been inlined");
+
+    for (const auto *Param : OuterCtor->parameters()) {
+      assert(getContext().hasSameUnqualifiedType(
+          OuterCtor->getParamDecl(Param->getFunctionScopeIndex())->getType(),
+          Param->getType()));
+      EmitDelegateCallArg(Args, Param, E->getLocation());
+
+      // Forward __attribute__(pass_object_size).
+      if (Param->hasAttr<PassObjectSizeAttr>()) {
+        auto *POSParam = SizeArguments[Param];
+        assert(POSParam && "missing pass_object_size value for forwarding");
+        EmitDelegateCallArg(Args, POSParam, E->getLocation());
+      }
+    }
+  }
+
+  EmitCXXConstructorCall(D, Ctor_Base, ForVirtualBase, /*Delegating*/false,
+                         This, Args);
+}
+
+void CodeGenFunction::EmitInlinedInheritingCXXConstructorCall(
+    const CXXConstructorDecl *Ctor, CXXCtorType CtorType, bool ForVirtualBase,
+    bool Delegating, CallArgList &Args) {
+  InlinedInheritingConstructorScope Scope(*this, GlobalDecl(Ctor, CtorType));
+
+  // Save the arguments to be passed to the inherited constructor.
+  CXXInheritedCtorInitExprArgs = Args;
+
+  FunctionArgList Params;
+  QualType RetType = BuildFunctionArgList(CurGD, Params);
+  FnRetTy = RetType;
+
+  // Insert any ABI-specific implicit constructor arguments.
+  CGM.getCXXABI().addImplicitConstructorArgs(*this, Ctor, CtorType,
+                                             ForVirtualBase, Delegating, Args);
+
+  // Emit a simplified prolog. We only need to emit the implicit params.
+  assert(Args.size() >= Params.size() && "too few arguments for call");
+  for (unsigned I = 0, N = Args.size(); I != N; ++I) {
+    if (I < Params.size() && isa<ImplicitParamDecl>(Params[I])) {
+      const RValue &RV = Args[I].RV;
+      assert(!RV.isComplex() && "complex indirect params not supported");
+      ParamValue Val = RV.isScalar()
+                           ? ParamValue::forDirect(RV.getScalarVal())
+                           : ParamValue::forIndirect(RV.getAggregateAddress());
+      EmitParmDecl(*Params[I], Val, I + 1);
+    }
+  }
+
+  // Create a return value slot if the ABI implementation wants one.
+  // FIXME: This is dumb, we should ask the ABI not to try to set the return
+  // value instead.
+  if (!RetType->isVoidType())
+    ReturnValue = CreateIRTemp(RetType, "retval.inhctor");
+
+  CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
+  CXXThisValue = CXXABIThisValue;
+
+  // Directly emit the constructor initializers.
+  EmitCtorPrologue(Ctor, CtorType, Params);
+}
+
 void CodeGenFunction::EmitVTableAssumptionLoad(const VPtr &Vptr, Address This) {
   llvm::Value *VTableGlobal =
       CGM.getCXXABI().getVTableAddressPoint(Vptr.Base, Vptr.VTableClass);
@@ -2145,19 +2290,6 @@ void
 CodeGenFunction::EmitSynthesizedCXXCopyCtorCall(const CXXConstructorDecl *D,
                                                 Address This, Address Src,
                                                 const CXXConstructExpr *E) {
-  if (isMemcpyEquivalentSpecialMember(D)) {
-    assert(E->getNumArgs() == 1 && "unexpected argcount for trivial ctor");
-    assert(D->isCopyOrMoveConstructor() &&
-           "trivial 1-arg ctor not a copy/move ctor");
-    EmitAggregateCopyCtor(This, Src,
-                          getContext().getTypeDeclType(D->getParent()),
-                          (*E->arg_begin())->getType());
-    return;
-  }
-  llvm::Value *Callee = CGM.getAddrOfCXXStructor(D, StructorType::Complete);
-  assert(D->isInstance() &&
-         "Trying to emit a member call expr on a static method!");
-
   const FunctionProtoType *FPT = D->getType()->castAs<FunctionProtoType>();
 
   CallArgList Args;
@@ -2175,8 +2307,7 @@ CodeGenFunction::EmitSynthesizedCXXCopyCtorCall(const CXXConstructorDecl *D,
   EmitCallArgs(Args, FPT, drop_begin(E->arguments(), 1), E->getConstructor(),
                /*ParamsToSkip*/ 1);
 
-  EmitCall(CGM.getTypes().arrangeCXXMethodCall(Args, FPT, RequiredArgs::All),
-           Callee, ReturnValueSlot(), Args, D);
+  EmitCXXConstructorCall(D, Ctor_Complete, false, false, This, Args);
 }
 
 void
@@ -2190,21 +2321,17 @@ CodeGenFunction::EmitDelegateCXXConstructorCall(const CXXConstructorDecl *Ctor,
   assert(I != E && "no parameters to constructor");
 
   // this
-  DelegateArgs.add(RValue::get(LoadCXXThis()), (*I)->getType());
+  Address This = LoadCXXThisAddress();
+  DelegateArgs.add(RValue::get(This.getPointer()), (*I)->getType());
   ++I;
 
-  // vtt
-  if (llvm::Value *VTT = GetVTTParameter(GlobalDecl(Ctor, CtorType),
-                                         /*ForVirtualBase=*/false,
-                                         /*Delegating=*/true)) {
-    QualType VoidPP = getContext().getPointerType(getContext().VoidPtrTy);
-    DelegateArgs.add(RValue::get(VTT), VoidPP);
-
-    if (CGM.getCXXABI().NeedsVTTParameter(CurGD)) {
-      assert(I != E && "cannot skip vtt parameter, already done with args");
-      assert((*I)->getType() == VoidPP && "skipping parameter not of vtt type");
-      ++I;
-    }
+  // FIXME: The location of the VTT parameter in the parameter list is
+  // specific to the Itanium ABI and shouldn't be hardcoded here.
+  if (CGM.getCXXABI().NeedsVTTParameter(CurGD)) {
+    assert(I != E && "cannot skip vtt parameter, already done with args");
+    assert((*I)->getType()->isPointerType() &&
+           "skipping parameter not of vtt type");
+    ++I;
   }
 
   // Explicit arguments.
@@ -2214,11 +2341,8 @@ CodeGenFunction::EmitDelegateCXXConstructorCall(const CXXConstructorDecl *Ctor,
     EmitDelegateCallArg(DelegateArgs, param, Loc);
   }
 
-  llvm::Value *Callee =
-      CGM.getAddrOfCXXStructor(Ctor, getFromCtorType(CtorType));
-  EmitCall(CGM.getTypes()
-               .arrangeCXXStructorDeclaration(Ctor, getFromCtorType(CtorType)),
-           Callee, ReturnValueSlot(), DelegateArgs, Ctor);
+  EmitCXXConstructorCall(Ctor, CtorType, /*ForVirtualBase=*/false,
+                         /*Delegating=*/true, This, DelegateArgs);
 }
 
 namespace {
diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index 83730597939..508720f5b9a 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -85,6 +85,7 @@ void CodeGenFunction::EmitDecl(const Decl &D) {
   case Decl::Captured:
   case Decl::ClassScopeFunctionSpecialization:
   case Decl::UsingShadow:
+  case Decl::ConstructorUsingShadow:
   case Decl::ObjCTypeParam:
     llvm_unreachable("Declaration should not be in declstmts!");
   case Decl::Function:  // void X();
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 42aa94575a7..6d18843591f 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -175,6 +175,7 @@ public:
   }
   void VisitCXXBindTemporaryExpr(CXXBindTemporaryExpr *E);
   void VisitCXXConstructExpr(const CXXConstructExpr *E);
+  void VisitCXXInheritedCtorInitExpr(const CXXInheritedCtorInitExpr *E);
   void VisitLambdaExpr(LambdaExpr *E);
   void VisitCXXStdInitializerListExpr(CXXStdInitializerListExpr *E);
   void VisitExprWithCleanups(ExprWithCleanups *E);
@@ -998,6 +999,14 @@ AggExprEmitter::VisitCXXConstructExpr(const CXXConstructExpr *E) {
   CGF.EmitCXXConstructExpr(E, Slot);
 }
 
+void AggExprEmitter::VisitCXXInheritedCtorInitExpr(
+    const CXXInheritedCtorInitExpr *E) {
+  AggValueSlot Slot = EnsureSlot(E->getType());
+  CGF.EmitInheritedCXXConstructorCall(
+      E->getConstructor(), E->constructsVBase(), Slot.getAddress(),
+      E->inheritedFromVBase(), E);
+}
+
 void
 AggExprEmitter::VisitLambdaExpr(LambdaExpr *E) {
   AggValueSlot Slot = EnsureSlot(E->getType());
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index e914d793559..a0158d8b4b2 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -928,18 +928,11 @@ static void TryMarkNoThrow(llvm::Function *F) {
   F->setDoesNotThrow();
 }
 
-void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
-                                   const CGFunctionInfo &FnInfo) {
+QualType CodeGenFunction::BuildFunctionArgList(GlobalDecl GD,
+                                               FunctionArgList &Args) {
   const FunctionDecl *FD = cast<FunctionDecl>(GD.getDecl());
-
-  // Check if we should generate debug info for this function.
-  if (FD->hasAttr<NoDebugAttr>())
-    DebugInfo = nullptr; // disable debug info indefinitely for this function
-
-  FunctionArgList Args;
   QualType ResTy = FD->getReturnType();
 
-  CurGD = GD;
   const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD);
   if (MD && MD->isInstance()) {
     if (CGM.getCXXABI().HasThisReturn(GD))
@@ -949,22 +942,48 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
     CGM.getCXXABI().buildThisParam(*this, Args);
   }
 
-  for (auto *Param : FD->parameters()) {
-    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);
+  // The base version of an inheriting constructor whose constructed base is a
+  // virtual base is not passed any arguments (because it doesn't actually call
+  // the inherited constructor).
+  bool PassedParams = true;
+  if (const CXXConstructorDecl *CD = dyn_cast<CXXConstructorDecl>(FD))
+    if (auto Inherited = CD->getInheritedConstructor())
+      PassedParams =
+          getTypes().inheritingCtorHasParams(Inherited, GD.getCtorType());
+
+  if (PassedParams) {
+    for (auto *Param : FD->parameters()) {
+      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);
 
+  return ResTy;
+}
+
+void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
+                                   const CGFunctionInfo &FnInfo) {
+  const FunctionDecl *FD = cast<FunctionDecl>(GD.getDecl());
+  CurGD = GD;
+
+  FunctionArgList Args;
+  QualType ResTy = BuildFunctionArgList(GD, Args);
+
+  // Check if we should generate debug info for this function.
+  if (FD->hasAttr<NoDebugAttr>())
+    DebugInfo = nullptr; // disable debug info indefinitely for this function
+
   SourceRange BodyRange;
   if (Stmt *Body = FD->getBody()) BodyRange = Body->getSourceRange();
   CurEHLocation = BodyRange.getEnd();
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index 4748e6b47dc..441cee54fc1 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -1065,6 +1065,61 @@ public:
     CharUnits OldCXXThisAlignment;
   };
 
+  class InlinedInheritingConstructorScope {
+  public:
+    InlinedInheritingConstructorScope(CodeGenFunction &CGF, GlobalDecl GD)
+        : CGF(CGF), OldCurGD(CGF.CurGD), OldCurFuncDecl(CGF.CurFuncDecl),
+          OldCurCodeDecl(CGF.CurCodeDecl),
+          OldCXXABIThisDecl(CGF.CXXABIThisDecl),
+          OldCXXABIThisValue(CGF.CXXABIThisValue),
+          OldCXXThisValue(CGF.CXXThisValue),
+          OldCXXABIThisAlignment(CGF.CXXABIThisAlignment),
+          OldCXXThisAlignment(CGF.CXXThisAlignment),
+          OldReturnValue(CGF.ReturnValue), OldFnRetTy(CGF.FnRetTy),
+          OldCXXInheritedCtorInitExprArgs(
+              std::move(CGF.CXXInheritedCtorInitExprArgs)) {
+      CGF.CurGD = GD;
+      CGF.CurFuncDecl = CGF.CurCodeDecl =
+          cast<CXXConstructorDecl>(GD.getDecl());
+      CGF.CXXABIThisDecl = nullptr;
+      CGF.CXXABIThisValue = nullptr;
+      CGF.CXXThisValue = nullptr;
+      CGF.CXXABIThisAlignment = CharUnits();
+      CGF.CXXThisAlignment = CharUnits();
+      CGF.ReturnValue = Address::invalid();
+      CGF.FnRetTy = QualType();
+      CGF.CXXInheritedCtorInitExprArgs.clear();
+    }
+    ~InlinedInheritingConstructorScope() {
+      CGF.CurGD = OldCurGD;
+      CGF.CurFuncDecl = OldCurFuncDecl;
+      CGF.CurCodeDecl = OldCurCodeDecl;
+      CGF.CXXABIThisDecl = OldCXXABIThisDecl;
+      CGF.CXXABIThisValue = OldCXXABIThisValue;
+      CGF.CXXThisValue = OldCXXThisValue;
+      CGF.CXXABIThisAlignment = OldCXXABIThisAlignment;
+      CGF.CXXThisAlignment = OldCXXThisAlignment;
+      CGF.ReturnValue = OldReturnValue;
+      CGF.FnRetTy = OldFnRetTy;
+      CGF.CXXInheritedCtorInitExprArgs =
+          std::move(OldCXXInheritedCtorInitExprArgs);
+    }
+
+  private:
+    CodeGenFunction &CGF;
+    GlobalDecl OldCurGD;
+    const Decl *OldCurFuncDecl;
+    const Decl *OldCurCodeDecl;
+    ImplicitParamDecl *OldCXXABIThisDecl;
+    llvm::Value *OldCXXABIThisValue;
+    llvm::Value *OldCXXThisValue;
+    CharUnits OldCXXABIThisAlignment;
+    CharUnits OldCXXThisAlignment;
+    Address OldReturnValue;
+    QualType OldFnRetTy;
+    CallArgList OldCXXInheritedCtorInitExprArgs;
+  };
+
 private:
   /// CXXThisDecl - When generating code for a C++ member function,
   /// this will hold the implicit 'this' declaration.
@@ -1078,6 +1133,10 @@ private:
   /// this expression.
   Address CXXDefaultInitExprThis = Address::invalid();
 
+  /// The values of function arguments to use when evaluating
+  /// CXXInheritedCtorInitExprs within this context.
+  CallArgList CXXInheritedCtorInitExprArgs;
+
   /// CXXStructorImplicitParamDecl - When generating code for a constructor or
   /// destructor, this will hold the implicit argument (e.g. VTT).
   ImplicitParamDecl *CXXStructorImplicitParamDecl;
@@ -1301,6 +1360,8 @@ public:
 
   const BlockByrefInfo &getBlockByrefInfo(const VarDecl *var);
 
+  QualType BuildFunctionArgList(GlobalDecl GD, FunctionArgList &Args);
+
   void GenerateCode(GlobalDecl GD, llvm::Function *Fn,
                     const CGFunctionInfo &FnInfo);
   /// \brief Emit code for the start of a function.
@@ -1874,10 +1935,32 @@ public:
   void EmitDelegatingCXXConstructorCall(const CXXConstructorDecl *Ctor,
                                         const FunctionArgList &Args);
 
+  /// Emit a call to an inheriting constructor (that is, one that invokes a
+  /// constructor inherited from a base class) by inlining its definition. This
+  /// is necessary if the ABI does not support forwarding the arguments to the
+  /// base class constructor (because they're variadic or similar).
+  void EmitInlinedInheritingCXXConstructorCall(const CXXConstructorDecl *Ctor,
+                                               CXXCtorType CtorType,
+                                               bool ForVirtualBase,
+                                               bool Delegating,
+                                               CallArgList &Args);
+
+  /// Emit a call to a constructor inherited from a base class, passing the
+  /// current constructor's arguments along unmodified (without even making
+  /// a copy).
+  void EmitInheritedCXXConstructorCall(const CXXConstructorDecl *D,
+                                       bool ForVirtualBase, Address This,
+                                       bool InheritedFromVBase,
+                                       const CXXInheritedCtorInitExpr *E);
+
   void EmitCXXConstructorCall(const CXXConstructorDecl *D, CXXCtorType Type,
                               bool ForVirtualBase, bool Delegating,
                               Address This, const CXXConstructExpr *E);
 
+  void EmitCXXConstructorCall(const CXXConstructorDecl *D, CXXCtorType Type,
+                              bool ForVirtualBase, bool Delegating,
+                              Address This, CallArgList &Args);
+
   /// Emit assumption load for all bases. Requires to be be called only on
   /// most-derived class and not under construction of the object.
   void EmitVTableAssumptionLoads(const CXXRecordDecl *ClassDecl, Address This);
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index ac00bf85cd3..bbec03842cb 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -765,6 +765,15 @@ CodeGenModule::getFunctionLinkage(GlobalDecl GD) {
                                    : llvm::GlobalValue::LinkOnceODRLinkage;
   }
 
+  if (isa<CXXConstructorDecl>(D) &&
+      cast<CXXConstructorDecl>(D)->isInheritingConstructor() &&
+      Context.getTargetInfo().getCXXABI().isMicrosoft()) {
+    // Our approach to inheriting constructors is fundamentally different from
+    // that used by the MS ABI, so keep our inheriting constructor thunks
+    // internal rather than trying to pick an unambiguous mangling for them.
+    return llvm::GlobalValue::InternalLinkage;
+  }
+
   return getLLVMLinkageForDeclarator(D, Linkage, /*isConstantVariable=*/false);
 }
 
diff --git a/clang/lib/CodeGen/CodeGenTypes.h b/clang/lib/CodeGen/CodeGenTypes.h
index c77790100a8..affa3344103 100644
--- a/clang/lib/CodeGen/CodeGenTypes.h
+++ b/clang/lib/CodeGen/CodeGenTypes.h
@@ -205,6 +205,11 @@ public:
   bool isFuncTypeConvertible(const FunctionType *FT);
   bool isFuncParamTypeConvertible(QualType Ty);
 
+  /// Determine if a C++ inheriting constructor should have parameters matching
+  /// those of its inherited constructor.
+  bool inheritingCtorHasParams(const InheritedConstructor &Inherited,
+                               CXXCtorType Type);
+
   /// GetFunctionTypeForVTable - Get the LLVM function type for use in a vtable,
   /// given a CXXMethodDecl. If the method to has an incomplete return type,
   /// and/or incomplete argument types, this will return the opaque type.