[CIR][Codegen] VTT support for virtual class inheritance (#252)

This patch brings up the basic support for C++ virtual inheritance. VTT
(virtual table table) now can be laid out as expected for simple program
with single virtual inheritance. RTTI support is on the way.

This patch does not include LLVM lowering support.

clang/lib/CIR/CodeGen/CIRGenCXXABI.h

@@ -188,6 +188,11 @@ class CIRGenCXXABI {
   /// Emits the VTable definitions required for the given record type.
   virtual void emitVTableDefinitions(CIRGenVTables &CGVT,
                                      const CXXRecordDecl *RD) = 0;
+
+  /// Emit any tables needed to implement virtual inheritance.  For Itanium,
+  /// this emits virtual table tables.
+  virtual void emitVirtualInheritanceTables(const CXXRecordDecl *RD) = 0;
+
   virtual mlir::Attribute getAddrOfRTTIDescriptor(mlir::Location loc,
                                                   QualType Ty) = 0;
   virtual CatchTypeInfo
@@ -280,6 +285,12 @@ class CIRGenCXXABI {
   // directly or require access through a thread wrapper function.
   virtual bool usesThreadWrapperFunction(const VarDecl *VD) const = 0;
 
+  /// Emit the code to initialize hidden members required to handle virtual
+  /// inheritance, if needed by the ABI.
+  virtual void
+  initializeHiddenVirtualInheritanceMembers(CIRGenFunction &CGF,
+                                            const CXXRecordDecl *RD) {}
+
   /// Emit a single constructor/destructor with the gien type from a C++
   /// constructor Decl.
   virtual void buildCXXStructor(clang::GlobalDecl GD) = 0;

clang/lib/CIR/CodeGen/CIRGenClass.cpp

@@ -40,9 +40,8 @@ bool CIRGenFunction::IsConstructorDelegationValid(
   //   };
   // ...although even this example could in principle be emitted as a delegation
   // since the address of the parameter doesn't escape.
-  if (Ctor->getParent()->getNumVBases()) {
-    llvm_unreachable("NYI");
-  }
+  if (Ctor->getParent()->getNumVBases())
+    return false;
 
   // We also disable the optimization for variadic functions because it's
   // impossible to "re-pass" varargs.
@@ -236,7 +235,7 @@ static void buildMemberInitializer(CIRGenFunction &CGF,
   if (CGF.CurGD.getCtorType() == Ctor_Base)
     LHS = CGF.MakeNaturalAlignPointeeAddrLValue(ThisPtr, RecordTy);
   else
-    llvm_unreachable("NYI");
+    LHS = CGF.MakeNaturalAlignAddrLValue(ThisPtr, RecordTy);
 
   buildLValueForAnyFieldInitialization(CGF, MemberInit, LHS);
 
@@ -524,9 +523,10 @@ Address CIRGenFunction::getAddressOfDirectBaseInCompleteClass(
   // TODO: for complete types, this should be possible with a GEP.
   Address V = This;
   if (!Offset.isZero()) {
-    // TODO(cir): probably create a new operation to account for
-    // down casting when the offset isn't zero.
-    llvm_unreachable("NYI");
+    mlir::Value OffsetVal = builder.getSInt32(Offset.getQuantity(), loc);
+    mlir::Value VBaseThisPtr = builder.create<mlir::cir::PtrStrideOp>(
+        loc, This.getPointer().getType(), This.getPointer(), OffsetVal);
+    V = Address(VBaseThisPtr, CXXABIThisAlignment);
   }
   V = builder.createElementBitCast(loc, V, ConvertType(Base));
   return V;
@@ -605,7 +605,11 @@ void CIRGenFunction::buildCtorPrologue(const CXXConstructorDecl *CD,
   for (; B != E && (*B)->isBaseInitializer() && (*B)->isBaseVirtual(); B++) {
     if (!ConstructVBases)
       continue;
-    llvm_unreachable("NYI");
+    if (CGM.getCodeGenOpts().StrictVTablePointers &&
+        CGM.getCodeGenOpts().OptimizationLevel > 0 &&
+        isInitializerOfDynamicClass(*B))
+      llvm_unreachable("NYI");
+    buildBaseInitializer(getLoc(CD->getBeginLoc()), *this, ClassDecl, *B);
   }
 
   if (BaseCtorContinueBB) {
@@ -699,7 +703,7 @@ void CIRGenFunction::initializeVTablePointers(mlir::Location loc,
       initializeVTablePointer(loc, Vptr);
 
   if (RD->getNumVBases())
-    llvm_unreachable("NYI");
+    CGM.getCXXABI().initializeHiddenVirtualInheritanceMembers(*this, RD);
 }
 
 CIRGenFunction::VPtrsVector

clang/lib/CIR/CodeGen/CIRGenExprCXX.cpp

@@ -356,8 +356,10 @@ void CIRGenFunction::buildCXXConstructExpr(const CXXConstructExpr *E,
     break;
   case CXXConstructionKind::Delegating:
     llvm_unreachable("NYI");
+    break;
   case CXXConstructionKind::VirtualBase:
-    llvm_unreachable("NYI");
+    ForVirtualBase = true;
+    [[fallthrough]];
   case CXXConstructionKind::NonVirtualBase:
     Type = Ctor_Base;
     break;

clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp

@@ -197,6 +197,7 @@ class CIRGenItaniumCXXABI : public cir::CIRGenCXXABI {
       const CXXRecordDecl *NearestVBase) override;
   void emitVTableDefinitions(CIRGenVTables &CGVT,
                              const CXXRecordDecl *RD) override;
+  void emitVirtualInheritanceTables(const CXXRecordDecl *RD) override;
   mlir::Attribute getAddrOfRTTIDescriptor(mlir::Location loc,
                                           QualType Ty) override;
   bool useThunkForDtorVariant(const CXXDestructorDecl *Dtor,
@@ -821,10 +822,10 @@ class CIRGenItaniumRTTIBuilder {
   /// to the Itanium C++ ABI, 2.9.5p6b.
   void BuildSIClassTypeInfo(mlir::Location loc, const CXXRecordDecl *RD);
 
-  // /// Build an abi::__vmi_class_type_info, used for
-  // /// classes with bases that do not satisfy the abi::__si_class_type_info
-  // /// constraints, according ti the Itanium C++ ABI, 2.9.5p5c.
-  // void BuildVMIClassTypeInfo(const CXXRecordDecl *RD);
+  /// Build an abi::__vmi_class_type_info, used for
+  /// classes with bases that do not satisfy the abi::__si_class_type_info
+  /// constraints, according ti the Itanium C++ ABI, 2.9.5p5c.
+  void BuildVMIClassTypeInfo(const CXXRecordDecl *RD);
 
   // /// Build an abi::__pointer_type_info struct, used
   // /// for pointer types.
@@ -1436,6 +1437,10 @@ void CIRGenItaniumRTTIBuilder::BuildSIClassTypeInfo(mlir::Location loc,
   Fields.push_back(BaseTypeInfo);
 }
 
+void CIRGenItaniumRTTIBuilder::BuildVMIClassTypeInfo(const CXXRecordDecl *RD) {
+  // TODO: Implement this function.
+}
+
 mlir::Attribute
 CIRGenItaniumRTTIBuilder::GetAddrOfExternalRTTIDescriptor(mlir::Location loc,
                                                           QualType Ty) {
@@ -1560,8 +1565,7 @@ mlir::Attribute CIRGenItaniumRTTIBuilder::BuildTypeInfo(
     if (CanUseSingleInheritance(RD)) {
       BuildSIClassTypeInfo(loc, RD);
     } else {
-      llvm_unreachable("NYI");
-      // BuildVMIClassTypeInfo(RD);
+      BuildVMIClassTypeInfo(RD);
     }
 
     break;
@@ -1730,6 +1734,13 @@ void CIRGenItaniumCXXABI::emitVTableDefinitions(CIRGenVTables &CGVT,
     llvm_unreachable("NYI");
 }
 
+void CIRGenItaniumCXXABI::emitVirtualInheritanceTables(
+    const CXXRecordDecl *RD) {
+  CIRGenVTables &VTables = CGM.getVTables();
+  auto VTT = VTables.getAddrOfVTT(RD);
+  VTables.buildVTTDefinition(VTT, CGM.getVTableLinkage(RD), RD);
+}
+
 /// What sort of uniqueness rules should we use for the RTTI for the
 /// given type?
 CIRGenItaniumCXXABI::RTTIUniquenessKind
@@ -1842,4 +1853,4 @@ void CIRGenItaniumCXXABI::buildThrow(CIRGenFunction &CGF,
   // Now throw the exception.
   builder.create<mlir::cir::ThrowOp>(CGF.getLoc(E->getSourceRange()),
                                      exceptionPtr, typeInfo.getSymbol(), dtor);
-}
+}

clang/lib/CIR/CodeGen/CIRGenVTables.cpp

@@ -13,14 +13,17 @@
 #include "CIRGenCXXABI.h"
 #include "CIRGenFunction.h"
 #include "CIRGenModule.h"
+#include "mlir/IR/Attributes.h"
 #include "clang/AST/Attr.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/RecordLayout.h"
+#include "clang/AST/VTTBuilder.h"
 #include "clang/Basic/CodeGenOptions.h"
 #include "clang/CIR/Dialect/IR/CIRAttrs.h"
 #include "clang/CIR/Dialect/IR/CIRTypes.h"
 #include "clang/CodeGen/CGFunctionInfo.h"
 #include "clang/CodeGen/ConstantInitBuilder.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Transforms/Utils/Cloning.h"
 #include <algorithm>
@@ -151,17 +154,17 @@ void CIRGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
   assert(!UnimplementedFeature::generateDebugInfo());
 
   if (RD->getNumVBases())
-    llvm_unreachable("NYI");
+    CGM.getCXXABI().emitVirtualInheritanceTables(RD);
 
   CGM.getCXXABI().emitVTableDefinitions(*this, RD);
 }
 
 static void AddPointerLayoutOffset(CIRGenModule &CGM,
                                    ConstantArrayBuilder &builder,
                                    CharUnits offset) {
-  assert(offset.getQuantity() == 0 && "NYI");
-  builder.add(mlir::cir::ConstPtrAttr::get(
-      CGM.getBuilder().getContext(), CGM.getBuilder().getUInt8PtrTy(), 0));
+  builder.add(mlir::cir::ConstPtrAttr::get(CGM.getBuilder().getContext(),
+                                           CGM.getBuilder().getUInt8PtrTy(),
+                                           offset.getQuantity()));
 }
 
 static void AddRelativeLayoutOffset(CIRGenModule &CGM,
@@ -415,6 +418,118 @@ CIRGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
   llvm_unreachable("Invalid TemplateSpecializationKind!");
 }
 
+mlir::cir::GlobalOp
+getAddrOfVTTVTable(CIRGenVTables &CGVT, CIRGenModule &CGM,
+                   const CXXRecordDecl *MostDerivedClass,
+                   const VTTVTable &vtable,
+                   mlir::cir::GlobalLinkageKind linkage,
+                   VTableLayout::AddressPointsMapTy &addressPoints) {
+  if (vtable.getBase() == MostDerivedClass) {
+    assert(vtable.getBaseOffset().isZero() &&
+           "Most derived class vtable must have a zero offset!");
+    // This is a regular vtable.
+    return CGM.getCXXABI().getAddrOfVTable(MostDerivedClass, CharUnits());
+  }
+
+  llvm_unreachable("generateConstructionVTable NYI");
+}
+
+mlir::cir::GlobalOp CIRGenVTables::getAddrOfVTT(const CXXRecordDecl *RD)
+{
+  assert(RD->getNumVBases() && "Only classes with virtual bases need a VTT");
+
+  SmallString<256> OutName;
+  llvm::raw_svector_ostream Out(OutName);
+  cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
+      .mangleCXXVTT(RD, Out);
+  StringRef Name = OutName.str();
+
+  // This will also defer the definition of the VTT.
+  (void)CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
+
+  VTTBuilder Builder(CGM.getASTContext(), RD, /*GenerateDefinition=*/false);
+
+  auto ArrayType = mlir::cir::ArrayType::get(CGM.getBuilder().getContext(),
+                                             CGM.getBuilder().getUInt8PtrTy(),
+                                             Builder.getVTTComponents().size());
+  auto Align =
+      CGM.getDataLayout().getABITypeAlign(CGM.getBuilder().getUInt8PtrTy());
+  auto VTT = CGM.createOrReplaceCXXRuntimeVariable(
+      CGM.getLoc(RD->getSourceRange()), Name, ArrayType,
+      mlir::cir::GlobalLinkageKind::ExternalLinkage,
+      CharUnits::fromQuantity(Align));
+  CGM.setGVProperties(VTT, RD);
+  return VTT;
+}
+
+/// Emit the definition of the given vtable.
+void CIRGenVTables::buildVTTDefinition(mlir::cir::GlobalOp VTT,
+                                       mlir::cir::GlobalLinkageKind Linkage,
+                                       const CXXRecordDecl *RD) {
+  VTTBuilder Builder(CGM.getASTContext(), RD, /*GenerateDefinition=*/true);
+
+  auto ArrayType = mlir::cir::ArrayType::get(CGM.getBuilder().getContext(),
+                                             CGM.getBuilder().getUInt8PtrTy(),
+                                             Builder.getVTTComponents().size());
+
+  SmallVector<mlir::cir::GlobalOp, 8> VTables;
+  SmallVector<VTableAddressPointsMapTy, 8> VTableAddressPoints;
+  for (const VTTVTable *i = Builder.getVTTVTables().begin(),
+                       *e = Builder.getVTTVTables().end();
+       i != e; ++i) {
+    VTableAddressPoints.push_back(VTableAddressPointsMapTy());
+    VTables.push_back(getAddrOfVTTVTable(*this, CGM, RD, *i, Linkage,
+                                         VTableAddressPoints.back()));
+  }
+
+  SmallVector<mlir::Attribute, 8> VTTComponents;
+  for (const VTTComponent *i = Builder.getVTTComponents().begin(),
+                          *e = Builder.getVTTComponents().end();
+       i != e; ++i) {
+    const VTTVTable &VTTVT = Builder.getVTTVTables()[i->VTableIndex];
+    mlir::cir::GlobalOp VTable = VTables[i->VTableIndex];
+    VTableLayout::AddressPointLocation AddressPoint;
+    if (VTTVT.getBase() == RD) {
+      // Just get the address point for the regular vtable.
+      AddressPoint =
+          getItaniumVTableContext().getVTableLayout(RD).getAddressPoint(
+              i->VTableBase);
+    } else {
+      AddressPoint = VTableAddressPoints[i->VTableIndex].lookup(i->VTableBase);
+      assert(AddressPoint.AddressPointIndex != 0 &&
+             "Did not find ctor vtable address point!");
+    }
+
+    mlir::Attribute Idxs[3] = {
+        CGM.getBuilder().getI32IntegerAttr(0),
+        CGM.getBuilder().getI32IntegerAttr(AddressPoint.VTableIndex),
+        CGM.getBuilder().getI32IntegerAttr(AddressPoint.AddressPointIndex),
+    };
+
+    auto Init = mlir::cir::GlobalViewAttr::get(
+        CGM.getBuilder().getUInt8PtrTy(),
+        mlir::FlatSymbolRefAttr::get(VTable.getSymNameAttr()),
+        mlir::ArrayAttr::get(CGM.getBuilder().getContext(), Idxs));
+
+    VTTComponents.push_back(Init);
+  }
+
+  auto Init = CGM.getBuilder().getConstArray(
+      mlir::ArrayAttr::get(CGM.getBuilder().getContext(), VTTComponents),
+      ArrayType);
+
+  VTT.setInitialValueAttr(Init);
+
+  // Set the correct linkage.
+  VTT.setLinkage(Linkage);
+  mlir::SymbolTable::setSymbolVisibility(VTT,
+                                         CIRGenModule::getMLIRVisibility(VTT));
+
+  if (CGM.supportsCOMDAT() && VTT.isWeakForLinker()) {
+    assert(!UnimplementedFeature::setComdat());
+  }
+}
+
 void CIRGenVTables::buildThunks(GlobalDecl GD) {
   const CXXMethodDecl *MD =
       cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();

clang/lib/CIR/CodeGen/CIRGenVTables.h

@@ -138,13 +138,13 @@ class CIRGenVTables {
   //                              llvm::GlobalVariable::LinkageTypes Linkage,
   //                              VTableAddressPointsMapTy &AddressPoints);
 
-  //   /// GetAddrOfVTT - Get the address of the VTT for the given record decl.
-  //   llvm::GlobalVariable *GetAddrOfVTT(const CXXRecordDecl *RD);
+  /// Get the address of the VTT for the given record decl.
+  mlir::cir::GlobalOp getAddrOfVTT(const CXXRecordDecl *RD);
 
-  //   /// EmitVTTDefinition - Emit the definition of the given vtable.
-  //   void EmitVTTDefinition(llvm::GlobalVariable *VTT,
-  //                          llvm::GlobalVariable::LinkageTypes Linkage,
-  //                          const CXXRecordDecl *RD);
+  /// Emit the definition of the given vtable.
+  void buildVTTDefinition(mlir::cir::GlobalOp VTT,
+                          mlir::cir::GlobalLinkageKind Linkage,
+                          const CXXRecordDecl *RD);
 
   /// Emit the associated thunks for the given global decl.
   void buildThunks(GlobalDecl GD);

clang/lib/CIR/CodeGen/CIRRecordLayoutBuilder.cpp

@@ -410,15 +410,37 @@ void CIRRecordLowering::accumulateVBases() {
       const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
       if (BaseDecl->isEmpty())
         continue;
-      llvm_unreachable("NYI");
+      // If the vbase is a primary virtual base of some base, then it doesn't
+      // get its own storage location but instead lives inside of that base.
+      if (astContext.isNearlyEmpty(BaseDecl) &&
+          !hasOwnStorage(cxxRecordDecl, BaseDecl))
+        continue;
+      ScissorOffset = std::min(ScissorOffset,
+                               astRecordLayout.getVBaseClassOffset(BaseDecl));
     }
   members.push_back(MemberInfo(ScissorOffset, MemberInfo::InfoKind::Scissor,
                                mlir::Type{}, cxxRecordDecl));
   for (const auto &Base : cxxRecordDecl->vbases()) {
     const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
     if (BaseDecl->isEmpty())
       continue;
-    llvm_unreachable("NYI");
+    CharUnits Offset = astRecordLayout.getVBaseClassOffset(BaseDecl);
+    // If the vbase is a primary virtual base of some base, then it doesn't
+    // get its own storage location but instead lives inside of that base.
+    if (isOverlappingVBaseABI() && astContext.isNearlyEmpty(BaseDecl) &&
+        !hasOwnStorage(cxxRecordDecl, BaseDecl)) {
+      members.push_back(
+          MemberInfo(Offset, MemberInfo::InfoKind::VBase, nullptr, BaseDecl));
+      continue;
+    }
+    // If we've got a vtordisp, add it as a storage type.
+    if (astRecordLayout.getVBaseOffsetsMap()
+            .find(BaseDecl)
+            ->second.hasVtorDisp())
+      members.push_back(
+          StorageInfo(Offset - CharUnits::fromQuantity(4), getUIntNType(32)));
+    members.push_back(MemberInfo(Offset, MemberInfo::InfoKind::VBase,
+                                 getStorageType(BaseDecl), BaseDecl));
   }
 }
 
@@ -449,8 +471,7 @@ void CIRRecordLowering::fillOutputFields() {
     } else if (member.kind == MemberInfo::InfoKind::Base) {
       nonVirtualBases[member.cxxRecordDecl] = fieldTypes.size() - 1;
     } else if (member.kind == MemberInfo::InfoKind::VBase) {
-      llvm_unreachable("NYI");
-      // virtualBases[member.cxxRecordDecl] = fieldTypes.size() - 1;
+      virtualBases[member.cxxRecordDecl] = fieldTypes.size() - 1;
     }
   }
 }
@@ -657,4 +678,4 @@ CIRDataLayout::CIRDataLayout(mlir::ModuleOp modOp) : layout{modOp} {
         llvm_unreachable("unknown endianess");
     }
   }
-}
+}