308 lines
12 KiB
C++
308 lines
12 KiB
C++
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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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// 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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// Derive the type for the alias.
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llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);
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llvm::PointerType *AliasType = AliasValueType->getPointerTo();
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// Find the referent. Some aliases might require a bitcast, in
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// which case the caller is responsible for ensuring the soundness
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// of these semantics.
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auto *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
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llvm::Constant *Aliasee = Ref;
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if (Ref->getType() != AliasType)
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Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);
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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 (Ref->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->getType() == AliasType &&
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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 = Ty->getPointerTo()->getPointerTo();
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VTable = CGF.Builder.CreateBitCast(VTable, Ty);
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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(VTable, VTableIndex, "vfnkxt");
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llvm::Value *VFunc = CGF.Builder.CreateAlignedLoad(
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VFuncPtr, llvm::Align(CGF.PointerAlignInBytes));
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CGCallee Callee(GD, VFunc);
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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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