llvm-project

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//===--- CGCXX.cpp - Emit LLVM Code for declarations ----------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This contains code dealing with C++ code generation.
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//
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//===----------------------------------------------------------------------===//
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// We might split this into multiple files if it gets too unwieldy
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#include "CGCXXABI.h"
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#include "CodeGenFunction.h"
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#include "CodeGenModule.h"
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#include "clang/AST/ASTContext.h"
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#include "clang/AST/Attr.h"
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#include "clang/AST/Decl.h"
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#include "clang/AST/DeclCXX.h"
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#include "clang/AST/DeclObjC.h"
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#include "clang/AST/Mangle.h"
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#include "clang/AST/RecordLayout.h"
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#include "clang/AST/StmtCXX.h"
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#include "clang/Basic/CodeGenOptions.h"
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#include "llvm/ADT/StringExtras.h"
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using namespace clang;
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using namespace CodeGen;
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/// Try to emit a base destructor as an alias to its primary
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/// base-class destructor.
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bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
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  if (!getCodeGenOpts().CXXCtorDtorAliases)
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    return true;
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  // Producing an alias to a base class ctor/dtor can degrade debug quality
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  // as the debugger cannot tell them apart.
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  if (getCodeGenOpts().OptimizationLevel == 0)
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    return true;
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  // Disable this optimization for ARM64EC.  FIXME: This probably should work,
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  // but getting the symbol table correct is complicated.
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  if (getTarget().getTriple().isWindowsArm64EC())
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    return true;
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  // If sanitizing memory to check for use-after-dtor, do not emit as
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  //  an alias, unless this class owns no members.
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  if (getCodeGenOpts().SanitizeMemoryUseAfterDtor &&
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      !D->getParent()->field_empty())
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    return true;
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  // If the destructor doesn't have a trivial body, we have to emit it
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  // separately.
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  if (!D->hasTrivialBody())
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    return true;
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  const CXXRecordDecl *Class = D->getParent();
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  // We are going to instrument this destructor, so give up even if it is
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  // currently empty.
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  if (Class->mayInsertExtraPadding())
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    return true;
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  // If we need to manipulate a VTT parameter, give up.
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  if (Class->getNumVBases()) {
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    // Extra Credit:  passing extra parameters is perfectly safe
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    // in many calling conventions, so only bail out if the ctor's
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    // calling convention is nonstandard.
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    return true;
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  }
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  // If any field has a non-trivial destructor, we have to emit the
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  // destructor separately.
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  for (const auto *I : Class->fields())
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    if (I->getType().isDestructedType())
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      return true;
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  // Try to find a unique base class with a non-trivial destructor.
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  const CXXRecordDecl *UniqueBase = nullptr;
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  for (const auto &I : Class->bases()) {
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    // We're in the base destructor, so skip virtual bases.
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    if (I.isVirtual()) continue;
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    // Skip base classes with trivial destructors.
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    const auto *Base =
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        cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
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    if (Base->hasTrivialDestructor()) continue;
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    // If we've already found a base class with a non-trivial
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    // destructor, give up.
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    if (UniqueBase) return true;
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    UniqueBase = Base;
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  }
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  // If we didn't find any bases with a non-trivial destructor, then
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  // the base destructor is actually effectively trivial, which can
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  // happen if it was needlessly user-defined or if there are virtual
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  // bases with non-trivial destructors.
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  if (!UniqueBase)
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    return true;
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  // If the base is at a non-zero offset, give up.
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  const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
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  if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())
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    return true;
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  // Give up if the calling conventions don't match. We could update the call,
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  // but it is probably not worth it.
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  const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
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  if (BaseD->getType()->castAs<FunctionType>()->getCallConv() !=
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      D->getType()->castAs<FunctionType>()->getCallConv())
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    return true;
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  GlobalDecl AliasDecl(D, Dtor_Base);
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  GlobalDecl TargetDecl(BaseD, Dtor_Base);
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  // The alias will use the linkage of the referent.  If we can't
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  // support aliases with that linkage, fail.
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  llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
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  // We can't use an alias if the linkage is not valid for one.
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  if (!llvm::GlobalAlias::isValidLinkage(Linkage))
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    return true;
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  llvm::GlobalValue::LinkageTypes TargetLinkage =
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      getFunctionLinkage(TargetDecl);
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  // Check if we have it already.
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  StringRef MangledName = getMangledName(AliasDecl);
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  llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
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  if (Entry && !Entry->isDeclaration())
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    return false;
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  if (Replacements.count(MangledName))
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    return false;
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  llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);
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  // Find the referent.
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  auto *Aliasee = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
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  // Instead of creating as alias to a linkonce_odr, replace all of the uses
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  // of the aliasee.
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  if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
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      !(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage &&
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        TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
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    // FIXME: An extern template instantiation will create functions with
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    // linkage "AvailableExternally". In libc++, some classes also define
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    // members with attribute "AlwaysInline" and expect no reference to
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    // be generated. It is desirable to reenable this optimisation after
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    // corresponding LLVM changes.
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    addReplacement(MangledName, Aliasee);
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    return false;
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  }
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  // If we have a weak, non-discardable alias (weak, weak_odr), like an extern
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  // template instantiation or a dllexported class, avoid forming it on COFF.
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  // A COFF weak external alias cannot satisfy a normal undefined symbol
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  // reference from another TU. The other TU must also mark the referenced
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  // symbol as weak, which we cannot rely on.
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  if (llvm::GlobalValue::isWeakForLinker(Linkage) &&
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      getTriple().isOSBinFormatCOFF()) {
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    return true;
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  }
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  // If we don't have a definition for the destructor yet or the definition is
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  // avaialable_externally, don't emit an alias.  We can't emit aliases to
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  // declarations; that's just not how aliases work.
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  if (Aliasee->isDeclarationForLinker())
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    return true;
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  // Don't create an alias to a linker weak symbol. This avoids producing
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  // different COMDATs in different TUs. Another option would be to
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  // output the alias both for weak_odr and linkonce_odr, but that
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  // requires explicit comdat support in the IL.
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  if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
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    return true;
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  // Create the alias with no name.
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  auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",
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                                          Aliasee, &getModule());
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  // Destructors are always unnamed_addr.
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  Alias->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
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  // Switch any previous uses to the alias.
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  if (Entry) {
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    assert(Entry->getValueType() == AliasValueType &&
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           Entry->getAddressSpace() == Alias->getAddressSpace() &&
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           "declaration exists with different type");
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    Alias->takeName(Entry);
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    Entry->replaceAllUsesWith(Alias);
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    Entry->eraseFromParent();
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  } else {
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    Alias->setName(MangledName);
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  }
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  // Finally, set up the alias with its proper name and attributes.
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  SetCommonAttributes(AliasDecl, Alias);
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  return false;
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}
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llvm::Function *CodeGenModule::codegenCXXStructor(GlobalDecl GD) {
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  const CGFunctionInfo &FnInfo = getTypes().arrangeCXXStructorDeclaration(GD);
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  auto *Fn = cast<llvm::Function>(
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      getAddrOfCXXStructor(GD, &FnInfo, /*FnType=*/nullptr,
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                           /*DontDefer=*/true, ForDefinition));
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  setFunctionLinkage(GD, Fn);
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  CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);
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  setNonAliasAttributes(GD, Fn);
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  SetLLVMFunctionAttributesForDefinition(cast<CXXMethodDecl>(GD.getDecl()), Fn);
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  return Fn;
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}
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llvm::FunctionCallee CodeGenModule::getAddrAndTypeOfCXXStructor(
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    GlobalDecl GD, const CGFunctionInfo *FnInfo, llvm::FunctionType *FnType,
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    bool DontDefer, ForDefinition_t IsForDefinition) {
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  auto *MD = cast<CXXMethodDecl>(GD.getDecl());
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  if (isa<CXXDestructorDecl>(MD)) {
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    // Always alias equivalent complete destructors to base destructors in the
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    // MS ABI.
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    if (getTarget().getCXXABI().isMicrosoft() &&
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        GD.getDtorType() == Dtor_Complete &&
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        MD->getParent()->getNumVBases() == 0)
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      GD = GD.getWithDtorType(Dtor_Base);
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  }
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  if (!FnType) {
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    if (!FnInfo)
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      FnInfo = &getTypes().arrangeCXXStructorDeclaration(GD);
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    FnType = getTypes().GetFunctionType(*FnInfo);
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  }
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  llvm::Constant *Ptr = GetOrCreateLLVMFunction(
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      getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer,
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      /*IsThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition);
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  return {FnType, Ptr};
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}
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static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF,
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                                          GlobalDecl GD,
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                                          llvm::Type *Ty,
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                                          const CXXRecordDecl *RD) {
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  assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
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         "No kext in Microsoft ABI");
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  CodeGenModule &CGM = CGF.CGM;
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  llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
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  Ty = llvm::PointerType::getUnqual(CGM.getLLVMContext());
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  assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
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  uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
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  const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD);
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  VTableLayout::AddressPointLocation AddressPoint =
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      VTLayout.getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));
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  VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) +
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                 AddressPoint.AddressPointIndex;
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  llvm::Value *VFuncPtr =
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    CGF.Builder.CreateConstInBoundsGEP1_64(Ty, VTable, VTableIndex, "vfnkxt");
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  llvm::Value *VFunc = CGF.Builder.CreateAlignedLoad(
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      Ty, VFuncPtr, llvm::Align(CGF.PointerAlignInBytes));
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  CGPointerAuthInfo PointerAuth;
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  if (auto &Schema =
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          CGM.getCodeGenOpts().PointerAuth.CXXVirtualFunctionPointers) {
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    GlobalDecl OrigMD =
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        CGM.getItaniumVTableContext().findOriginalMethod(GD.getCanonicalDecl());
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    PointerAuth = CGF.EmitPointerAuthInfo(Schema, VFuncPtr, OrigMD, QualType());
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  }
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  CGCallee Callee(GD, VFunc, PointerAuth);
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  return Callee;
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}
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/// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
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/// indirect call to virtual functions. It makes the call through indexing
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/// into the vtable.
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CGCallee
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CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
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                                           NestedNameSpecifier *Qual,
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                                           llvm::Type *Ty) {
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  assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
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         "BuildAppleKextVirtualCall - bad Qual kind");
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  const Type *QTy = Qual->getAsType();
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  QualType T = QualType(QTy, 0);
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  const RecordType *RT = T->getAs<RecordType>();
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  assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
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  const auto *RD = cast<CXXRecordDecl>(RT->getDecl());
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  if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))
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    return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
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  return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
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}
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/// BuildVirtualCall - This routine makes indirect vtable call for
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/// call to virtual destructors. It returns 0 if it could not do it.
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CGCallee
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CodeGenFunction::BuildAppleKextVirtualDestructorCall(
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                                            const CXXDestructorDecl *DD,
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                                            CXXDtorType Type,
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                                            const CXXRecordDecl *RD) {
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  assert(DD->isVirtual() && Type != Dtor_Base);
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  // Compute the function type we're calling.
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  const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(
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      GlobalDecl(DD, Dtor_Complete));
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  llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
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  return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);
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}
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