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


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@274049 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 170 insertions, 46 deletions

diff --git a/lib/CodeGen/CGClass.cpp b/lib/CodeGen/CGClass.cpp
index 56e24840c8..7ed891f426 100644
--- a/lib/CodeGen/CGClass.cpp
+++ b/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 {