//===--- CGCXX.cpp - Emit LLVM Code for declarations ----------------------===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// This contains code dealing with C++ code generation.

//

//===----------------------------------------------------------------------===//

// We might split this into multiple files if it gets too unwieldy

#include "CGCXXABI.h"

#include "CodeGenFunction.h"

#include "CodeGenModule.h"

#include "clang/AST/ASTContext.h"

#include "clang/AST/Attr.h"

#include "clang/AST/Decl.h"

#include "clang/AST/DeclCXX.h"

#include "clang/AST/DeclObjC.h"

#include "clang/AST/Mangle.h"

#include "clang/AST/RecordLayout.h"

#include "clang/AST/StmtCXX.h"

#include "clang/Basic/CodeGenOptions.h"

#include "llvm/ADT/StringExtras.h"

using namespace clang;

using namespace CodeGen;

/// Try to emit a base destructor as an alias to its primary

/// base-class destructor.

bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {

  if (!getCodeGenOpts().CXXCtorDtorAliases)

    return true;

  // Producing an alias to a base class ctor/dtor can degrade debug quality

  // as the debugger cannot tell them apart.

  if (getCodeGenOpts().OptimizationLevel == 0)

    return true;

  // If sanitizing memory to check for use-after-dtor, do not emit as

  //  an alias, unless this class owns no members.

  if (getCodeGenOpts().SanitizeMemoryUseAfterDtor &&

      !D->getParent()->field_empty())

    return true;

  // If the destructor doesn't have a trivial body, we have to emit it

  // separately.

  if (!D->hasTrivialBody())

    return true;

  const CXXRecordDecl *Class = D->getParent();

  // We are going to instrument this destructor, so give up even if it is

  // currently empty.

  if (Class->mayInsertExtraPadding())

    return true;

  // If we need to manipulate a VTT parameter, give up.

  if (Class->getNumVBases()) {

    // Extra Credit:  passing extra parameters is perfectly safe

    // in many calling conventions, so only bail out if the ctor's

    // calling convention is nonstandard.

    return true;

  }

  // If any field has a non-trivial destructor, we have to emit the

  // destructor separately.

  for (const auto *I : Class->fields())

    if (I->getType().isDestructedType())

      return true;

  // Try to find a unique base class with a non-trivial destructor.

  const CXXRecordDecl *UniqueBase = nullptr;

  for (const auto &I : Class->bases()) {

    // We're in the base destructor, so skip virtual bases.

    if (I.isVirtual()) continue;

    // Skip base classes with trivial destructors.

    const auto *Base =

        cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());

    if (Base->hasTrivialDestructor()) continue;

    // If we've already found a base class with a non-trivial

    // destructor, give up.

    if (UniqueBase) return true;

    UniqueBase = Base;

  }

  // If we didn't find any bases with a non-trivial destructor, then

  // the base destructor is actually effectively trivial, which can

  // happen if it was needlessly user-defined or if there are virtual

  // bases with non-trivial destructors.

  if (!UniqueBase)

    return true;

  // If the base is at a non-zero offset, give up.

  const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);

  if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())

    return true;

  // Give up if the calling conventions don't match. We could update the call,

  // but it is probably not worth it.

  const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();

  if (BaseD->getType()->castAs<FunctionType>()->getCallConv() !=

      D->getType()->castAs<FunctionType>()->getCallConv())

    return true;

  GlobalDecl AliasDecl(D, Dtor_Base);

  GlobalDecl TargetDecl(BaseD, Dtor_Base);

  // The alias will use the linkage of the referent.  If we can't

  // support aliases with that linkage, fail.

  llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);

  // We can't use an alias if the linkage is not valid for one.

  if (!llvm::GlobalAlias::isValidLinkage(Linkage))

    return true;

  llvm::GlobalValue::LinkageTypes TargetLinkage =

      getFunctionLinkage(TargetDecl);

  // Check if we have it already.

  StringRef MangledName = getMangledName(AliasDecl);

  llvm::GlobalValue *Entry = GetGlobalValue(MangledName);

  if (Entry && !Entry->isDeclaration())

    return false;

  if (Replacements.count(MangledName))

    return false;

  llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);

  // Find the referent.

  auto *Aliasee = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));

  // Instead of creating as alias to a linkonce_odr, replace all of the uses

  // of the aliasee.

  if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&

      !(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage &&

        TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {

    // FIXME: An extern template instantiation will create functions with

    // linkage "AvailableExternally". In libc++, some classes also define

    // members with attribute "AlwaysInline" and expect no reference to

    // be generated. It is desirable to reenable this optimisation after

    // corresponding LLVM changes.

    addReplacement(MangledName, Aliasee);

    return false;

  }

  // If we have a weak, non-discardable alias (weak, weak_odr), like an extern

  // template instantiation or a dllexported class, avoid forming it on COFF.

  // A COFF weak external alias cannot satisfy a normal undefined symbol

  // reference from another TU. The other TU must also mark the referenced

  // symbol as weak, which we cannot rely on.

  if (llvm::GlobalValue::isWeakForLinker(Linkage) &&

      getTriple().isOSBinFormatCOFF()) {

    return true;

  }

  // If we don't have a definition for the destructor yet or the definition is

  // avaialable_externally, don't emit an alias.  We can't emit aliases to

  // declarations; that's just not how aliases work.

  if (Aliasee->isDeclarationForLinker())

    return true;

  // Don't create an alias to a linker weak symbol. This avoids producing

  // different COMDATs in different TUs. Another option would be to

  // output the alias both for weak_odr and linkonce_odr, but that

  // requires explicit comdat support in the IL.

  if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))

    return true;

  // Create the alias with no name.

  auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",

                                          Aliasee, &getModule());

  // Destructors are always unnamed_addr.

  Alias->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);

  // Switch any previous uses to the alias.

  if (Entry) {

    assert(Entry->getValueType() == AliasValueType &&

           Entry->getAddressSpace() == Alias->getAddressSpace() &&

           "declaration exists with different type");

    Alias->takeName(Entry);

    Entry->replaceAllUsesWith(Alias);

    Entry->eraseFromParent();

  } else {

    Alias->setName(MangledName);

  }

  // Finally, set up the alias with its proper name and attributes.

  SetCommonAttributes(AliasDecl, Alias);

  return false;

}

llvm::Function *CodeGenModule::codegenCXXStructor(GlobalDecl GD) {

  const CGFunctionInfo &FnInfo = getTypes().arrangeCXXStructorDeclaration(GD);

  auto *Fn = cast<llvm::Function>(

      getAddrOfCXXStructor(GD, &FnInfo, /*FnType=*/nullptr,

                           /*DontDefer=*/true, ForDefinition));

  setFunctionLinkage(GD, Fn);

  CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);

  setNonAliasAttributes(GD, Fn);

  SetLLVMFunctionAttributesForDefinition(cast<CXXMethodDecl>(GD.getDecl()), Fn);

  return Fn;

}

llvm::FunctionCallee CodeGenModule::getAddrAndTypeOfCXXStructor(

    GlobalDecl GD, const CGFunctionInfo *FnInfo, llvm::FunctionType *FnType,

    bool DontDefer, ForDefinition_t IsForDefinition) {

  auto *MD = cast<CXXMethodDecl>(GD.getDecl());

  if (isa<CXXDestructorDecl>(MD)) {

    // Always alias equivalent complete destructors to base destructors in the

    // MS ABI.

    if (getTarget().getCXXABI().isMicrosoft() &&

        GD.getDtorType() == Dtor_Complete &&

        MD->getParent()->getNumVBases() == 0)

      GD = GD.getWithDtorType(Dtor_Base);

  }

  if (!FnType) {

    if (!FnInfo)

      FnInfo = &getTypes().arrangeCXXStructorDeclaration(GD);

    FnType = getTypes().GetFunctionType(*FnInfo);

  }

  llvm::Constant *Ptr = GetOrCreateLLVMFunction(

      getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer,

      /*IsThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition);

  return {FnType, Ptr};

}

static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF,

                                          GlobalDecl GD,

                                          llvm::Type *Ty,

                                          const CXXRecordDecl *RD) {

  assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&

         "No kext in Microsoft ABI");

  CodeGenModule &CGM = CGF.CGM;

  llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());

  Ty = llvm::PointerType::getUnqual(CGM.getLLVMContext());

  assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");

  uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);

  const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD);

  VTableLayout::AddressPointLocation AddressPoint =

      VTLayout.getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));

  VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) +

                 AddressPoint.AddressPointIndex;

  llvm::Value *VFuncPtr =

    CGF.Builder.CreateConstInBoundsGEP1_64(Ty, VTable, VTableIndex, "vfnkxt");

  llvm::Value *VFunc = CGF.Builder.CreateAlignedLoad(

      Ty, VFuncPtr, llvm::Align(CGF.PointerAlignInBytes));

  CGCallee Callee(GD, VFunc);

  return Callee;

}

/// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making

/// indirect call to virtual functions. It makes the call through indexing

/// into the vtable.

CGCallee

CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,

                                           NestedNameSpecifier *Qual,

                                           llvm::Type *Ty) {

  assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&

         "BuildAppleKextVirtualCall - bad Qual kind");

  const Type *QTy = Qual->getAsType();

  QualType T = QualType(QTy, 0);

  const RecordType *RT = T->getAs<RecordType>();

  assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");

  const auto *RD = cast<CXXRecordDecl>(RT->getDecl());

  if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))

    return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);

  return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);

}

/// BuildVirtualCall - This routine makes indirect vtable call for

/// call to virtual destructors. It returns 0 if it could not do it.

CGCallee

CodeGenFunction::BuildAppleKextVirtualDestructorCall(

                                            const CXXDestructorDecl *DD,

                                            CXXDtorType Type,

                                            const CXXRecordDecl *RD) {

  assert(DD->isVirtual() && Type != Dtor_Base);

  // Compute the function type we're calling.

  const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(

      GlobalDecl(DD, Dtor_Complete));

  llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);

  return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);

}