1//===--- CGCXX.cpp - Emit LLVM Code for declarations ----------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This contains code dealing with C++ code generation.
10//
11//===----------------------------------------------------------------------===//
12
13// We might split this into multiple files if it gets too unwieldy
14
15#include "CGCXXABI.h"
16#include "CodeGenFunction.h"
17#include "CodeGenModule.h"
18#include "clang/AST/ASTContext.h"
19#include "clang/AST/Attr.h"
20#include "clang/AST/Decl.h"
21#include "clang/AST/DeclCXX.h"
22#include "clang/AST/DeclObjC.h"
23#include "clang/AST/Mangle.h"
24#include "clang/AST/RecordLayout.h"
25#include "clang/AST/StmtCXX.h"
26#include "clang/Basic/CodeGenOptions.h"
27#include "llvm/ADT/StringExtras.h"
28using namespace clang;
29using namespace CodeGen;
30
31
32/// Try to emit a base destructor as an alias to its primary
33/// base-class destructor.
34bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
35  if (!getCodeGenOpts().CXXCtorDtorAliases)
36    return true;
37
38  // Producing an alias to a base class ctor/dtor can degrade debug quality
39  // as the debugger cannot tell them apart.
40  if (getCodeGenOpts().OptimizationLevel == 0)
41    return true;
42
43  // Disable this optimization for ARM64EC.  FIXME: This probably should work,
44  // but getting the symbol table correct is complicated.
45  if (getTarget().getTriple().isWindowsArm64EC())
46    return true;
47
48  // If sanitizing memory to check for use-after-dtor, do not emit as
49  //  an alias, unless this class owns no members.
50  if (getCodeGenOpts().SanitizeMemoryUseAfterDtor &&
51      !D->getParent()->field_empty())
52    return true;
53
54  // If the destructor doesn't have a trivial body, we have to emit it
55  // separately.
56  if (!D->hasTrivialBody())
57    return true;
58
59  const CXXRecordDecl *Class = D->getParent();
60
61  // We are going to instrument this destructor, so give up even if it is
62  // currently empty.
63  if (Class->mayInsertExtraPadding())
64    return true;
65
66  // If we need to manipulate a VTT parameter, give up.
67  if (Class->getNumVBases()) {
68    // Extra Credit:  passing extra parameters is perfectly safe
69    // in many calling conventions, so only bail out if the ctor's
70    // calling convention is nonstandard.
71    return true;
72  }
73
74  // If any field has a non-trivial destructor, we have to emit the
75  // destructor separately.
76  for (const auto *I : Class->fields())
77    if (I->getType().isDestructedType())
78      return true;
79
80  // Try to find a unique base class with a non-trivial destructor.
81  const CXXRecordDecl *UniqueBase = nullptr;
82  for (const auto &I : Class->bases()) {
83
84    // We're in the base destructor, so skip virtual bases.
85    if (I.isVirtual()) continue;
86
87    // Skip base classes with trivial destructors.
88    const auto *Base =
89        cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
90    if (Base->hasTrivialDestructor()) continue;
91
92    // If we've already found a base class with a non-trivial
93    // destructor, give up.
94    if (UniqueBase) return true;
95    UniqueBase = Base;
96  }
97
98  // If we didn't find any bases with a non-trivial destructor, then
99  // the base destructor is actually effectively trivial, which can
100  // happen if it was needlessly user-defined or if there are virtual
101  // bases with non-trivial destructors.
102  if (!UniqueBase)
103    return true;
104
105  // If the base is at a non-zero offset, give up.
106  const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
107  if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())
108    return true;
109
110  // Give up if the calling conventions don't match. We could update the call,
111  // but it is probably not worth it.
112  const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
113  if (BaseD->getType()->castAs<FunctionType>()->getCallConv() !=
114      D->getType()->castAs<FunctionType>()->getCallConv())
115    return true;
116
117  GlobalDecl AliasDecl(D, Dtor_Base);
118  GlobalDecl TargetDecl(BaseD, Dtor_Base);
119
120  // The alias will use the linkage of the referent.  If we can't
121  // support aliases with that linkage, fail.
122  llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
123
124  // We can't use an alias if the linkage is not valid for one.
125  if (!llvm::GlobalAlias::isValidLinkage(Linkage))
126    return true;
127
128  llvm::GlobalValue::LinkageTypes TargetLinkage =
129      getFunctionLinkage(TargetDecl);
130
131  // Check if we have it already.
132  StringRef MangledName = getMangledName(AliasDecl);
133  llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
134  if (Entry && !Entry->isDeclaration())
135    return false;
136  if (Replacements.count(MangledName))
137    return false;
138
139  llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);
140
141  // Find the referent.
142  auto *Aliasee = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
143
144  // Instead of creating as alias to a linkonce_odr, replace all of the uses
145  // of the aliasee.
146  if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) &&
147      !(TargetLinkage == llvm::GlobalValue::AvailableExternallyLinkage &&
148        TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) {
149    // FIXME: An extern template instantiation will create functions with
150    // linkage "AvailableExternally". In libc++, some classes also define
151    // members with attribute "AlwaysInline" and expect no reference to
152    // be generated. It is desirable to reenable this optimisation after
153    // corresponding LLVM changes.
154    addReplacement(MangledName, Aliasee);
155    return false;
156  }
157
158  // If we have a weak, non-discardable alias (weak, weak_odr), like an extern
159  // template instantiation or a dllexported class, avoid forming it on COFF.
160  // A COFF weak external alias cannot satisfy a normal undefined symbol
161  // reference from another TU. The other TU must also mark the referenced
162  // symbol as weak, which we cannot rely on.
163  if (llvm::GlobalValue::isWeakForLinker(Linkage) &&
164      getTriple().isOSBinFormatCOFF()) {
165    return true;
166  }
167
168  // If we don't have a definition for the destructor yet or the definition is
169  // avaialable_externally, don't emit an alias.  We can't emit aliases to
170  // declarations; that's just not how aliases work.
171  if (Aliasee->isDeclarationForLinker())
172    return true;
173
174  // Don't create an alias to a linker weak symbol. This avoids producing
175  // different COMDATs in different TUs. Another option would be to
176  // output the alias both for weak_odr and linkonce_odr, but that
177  // requires explicit comdat support in the IL.
178  if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
179    return true;
180
181  // Create the alias with no name.
182  auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",
183                                          Aliasee, &getModule());
184
185  // Destructors are always unnamed_addr.
186  Alias->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
187
188  // Switch any previous uses to the alias.
189  if (Entry) {
190    assert(Entry->getValueType() == AliasValueType &&
191           Entry->getAddressSpace() == Alias->getAddressSpace() &&
192           "declaration exists with different type");
193    Alias->takeName(Entry);
194    Entry->replaceAllUsesWith(Alias);
195    Entry->eraseFromParent();
196  } else {
197    Alias->setName(MangledName);
198  }
199
200  // Finally, set up the alias with its proper name and attributes.
201  SetCommonAttributes(AliasDecl, Alias);
202
203  return false;
204}
205
206llvm::Function *CodeGenModule::codegenCXXStructor(GlobalDecl GD) {
207  const CGFunctionInfo &FnInfo = getTypes().arrangeCXXStructorDeclaration(GD);
208  auto *Fn = cast<llvm::Function>(
209      getAddrOfCXXStructor(GD, &FnInfo, /*FnType=*/nullptr,
210                           /*DontDefer=*/true, ForDefinition));
211
212  setFunctionLinkage(GD, Fn);
213
214  CodeGenFunction(*this).GenerateCode(GD, Fn, FnInfo);
215  setNonAliasAttributes(GD, Fn);
216  SetLLVMFunctionAttributesForDefinition(cast<CXXMethodDecl>(GD.getDecl()), Fn);
217  return Fn;
218}
219
220llvm::FunctionCallee CodeGenModule::getAddrAndTypeOfCXXStructor(
221    GlobalDecl GD, const CGFunctionInfo *FnInfo, llvm::FunctionType *FnType,
222    bool DontDefer, ForDefinition_t IsForDefinition) {
223  auto *MD = cast<CXXMethodDecl>(GD.getDecl());
224
225  if (isa<CXXDestructorDecl>(MD)) {
226    // Always alias equivalent complete destructors to base destructors in the
227    // MS ABI.
228    if (getTarget().getCXXABI().isMicrosoft() &&
229        GD.getDtorType() == Dtor_Complete &&
230        MD->getParent()->getNumVBases() == 0)
231      GD = GD.getWithDtorType(Dtor_Base);
232  }
233
234  if (!FnType) {
235    if (!FnInfo)
236      FnInfo = &getTypes().arrangeCXXStructorDeclaration(GD);
237    FnType = getTypes().GetFunctionType(*FnInfo);
238  }
239
240  llvm::Constant *Ptr = GetOrCreateLLVMFunction(
241      getMangledName(GD), FnType, GD, /*ForVTable=*/false, DontDefer,
242      /*IsThunk=*/false, /*ExtraAttrs=*/llvm::AttributeList(), IsForDefinition);
243  return {FnType, Ptr};
244}
245
246static CGCallee BuildAppleKextVirtualCall(CodeGenFunction &CGF,
247                                          GlobalDecl GD,
248                                          llvm::Type *Ty,
249                                          const CXXRecordDecl *RD) {
250  assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() &&
251         "No kext in Microsoft ABI");
252  CodeGenModule &CGM = CGF.CGM;
253  llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
254  Ty = llvm::PointerType::getUnqual(CGM.getLLVMContext());
255  assert(VTable && "BuildVirtualCall = kext vtbl pointer is null");
256  uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD);
257  const VTableLayout &VTLayout = CGM.getItaniumVTableContext().getVTableLayout(RD);
258  VTableLayout::AddressPointLocation AddressPoint =
259      VTLayout.getAddressPoint(BaseSubobject(RD, CharUnits::Zero()));
260  VTableIndex += VTLayout.getVTableOffset(AddressPoint.VTableIndex) +
261                 AddressPoint.AddressPointIndex;
262  llvm::Value *VFuncPtr =
263    CGF.Builder.CreateConstInBoundsGEP1_64(Ty, VTable, VTableIndex, "vfnkxt");
264  llvm::Value *VFunc = CGF.Builder.CreateAlignedLoad(
265      Ty, VFuncPtr, llvm::Align(CGF.PointerAlignInBytes));
266  CGCallee Callee(GD, VFunc);
267  return Callee;
268}
269
270/// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making
271/// indirect call to virtual functions. It makes the call through indexing
272/// into the vtable.
273CGCallee
274CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD,
275                                           NestedNameSpecifier *Qual,
276                                           llvm::Type *Ty) {
277  assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) &&
278         "BuildAppleKextVirtualCall - bad Qual kind");
279
280  const Type *QTy = Qual->getAsType();
281  QualType T = QualType(QTy, 0);
282  const RecordType *RT = T->getAs<RecordType>();
283  assert(RT && "BuildAppleKextVirtualCall - Qual type must be record");
284  const auto *RD = cast<CXXRecordDecl>(RT->getDecl());
285
286  if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD))
287    return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD);
288
289  return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD);
290}
291
292/// BuildVirtualCall - This routine makes indirect vtable call for
293/// call to virtual destructors. It returns 0 if it could not do it.
294CGCallee
295CodeGenFunction::BuildAppleKextVirtualDestructorCall(
296                                            const CXXDestructorDecl *DD,
297                                            CXXDtorType Type,
298                                            const CXXRecordDecl *RD) {
299  assert(DD->isVirtual() && Type != Dtor_Base);
300  // Compute the function type we're calling.
301  const CGFunctionInfo &FInfo = CGM.getTypes().arrangeCXXStructorDeclaration(
302      GlobalDecl(DD, Dtor_Complete));
303  llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo);
304  return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD);
305}
306