clang/lib/CodeGen/CGCXXABI.cpp

   1 //===----- CGCXXABI.cpp - Interface to C++ ABIs ---------------------------===//
   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 provides an abstract class for C++ code generation. Concrete subclasses
  10 // of this implement code generation for specific C++ ABIs.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "CGCXXABI.h"
  15 #include "CGCleanup.h"
  16 #include "clang/AST/Attr.h"
  17
  18 using namespace clang;
  19 using namespace CodeGen;
  20
  21 CGCXXABI::~CGCXXABI() { }
  22
  23 void CGCXXABI::ErrorUnsupportedABI(CodeGenFunction &CGF, StringRef S) {
  24   DiagnosticsEngine &Diags = CGF.CGM.getDiags();
  25   unsigned DiagID = Diags.getCustomDiagID(DiagnosticsEngine::Error,
  26                                           "cannot yet compile %0 in this ABI");
  27   Diags.Report(CGF.getContext().getFullLoc(CGF.CurCodeDecl->getLocation()),
  28                DiagID)
  29     << S;
  30 }
  31
  32 llvm::Constant *CGCXXABI::GetBogusMemberPointer(QualType T) {
  33   return llvm::Constant::getNullValue(CGM.getTypes().ConvertType(T));
  34 }
  35
  36 llvm::Type *
  37 CGCXXABI::ConvertMemberPointerType(const MemberPointerType *MPT) {
  38   return CGM.getTypes().ConvertType(CGM.getContext().getPointerDiffType());
  39 }
  40
  41 CGCallee CGCXXABI::EmitLoadOfMemberFunctionPointer(
  42     CodeGenFunction &CGF, const Expr *E, Address This,
  43     llvm::Value *&ThisPtrForCall,
  44     llvm::Value *MemPtr, const MemberPointerType *MPT) {
  45   ErrorUnsupportedABI(CGF, "calls through member pointers");
  46
  47   ThisPtrForCall = This.getPointer();
  48   const auto *FPT = MPT->getPointeeType()->castAs<FunctionProtoType>();
  49   llvm::Constant *FnPtr = llvm::Constant::getNullValue(
  50       llvm::PointerType::getUnqual(CGM.getLLVMContext()));
  51   return CGCallee::forDirect(FnPtr, FPT);
  52 }
  53
  54 llvm::Value *
  55 CGCXXABI::EmitMemberDataPointerAddress(CodeGenFunction &CGF, const Expr *E,
  56                                        Address Base, llvm::Value *MemPtr,
  57                                        const MemberPointerType *MPT) {
  58   ErrorUnsupportedABI(CGF, "loads of member pointers");
  59   llvm::Type *Ty =
  60       llvm::PointerType::get(CGF.getLLVMContext(), Base.getAddressSpace());
  61   return llvm::Constant::getNullValue(Ty);
  62 }
  63
  64 llvm::Value *CGCXXABI::EmitMemberPointerConversion(CodeGenFunction &CGF,
  65                                                    const CastExpr *E,
  66                                                    llvm::Value *Src) {
  67   ErrorUnsupportedABI(CGF, "member function pointer conversions");
  68   return GetBogusMemberPointer(E->getType());
  69 }
  70
  71 llvm::Constant *CGCXXABI::EmitMemberPointerConversion(const CastExpr *E,
  72                                                       llvm::Constant *Src) {
  73   return GetBogusMemberPointer(E->getType());
  74 }
  75
  76 llvm::Value *
  77 CGCXXABI::EmitMemberPointerComparison(CodeGenFunction &CGF,
  78                                       llvm::Value *L,
  79                                       llvm::Value *R,
  80                                       const MemberPointerType *MPT,
  81                                       bool Inequality) {
  82   ErrorUnsupportedABI(CGF, "member function pointer comparison");
  83   return CGF.Builder.getFalse();
  84 }
  85
  86 llvm::Value *
  87 CGCXXABI::EmitMemberPointerIsNotNull(CodeGenFunction &CGF,
  88                                      llvm::Value *MemPtr,
  89                                      const MemberPointerType *MPT) {
  90   ErrorUnsupportedABI(CGF, "member function pointer null testing");
  91   return CGF.Builder.getFalse();
  92 }
  93
  94 llvm::Constant *
  95 CGCXXABI::EmitNullMemberPointer(const MemberPointerType *MPT) {
  96   return GetBogusMemberPointer(QualType(MPT, 0));
  97 }
  98
  99 llvm::Constant *CGCXXABI::EmitMemberFunctionPointer(const CXXMethodDecl *MD) {
 100   return GetBogusMemberPointer(CGM.getContext().getMemberPointerType(
 101       MD->getType(), MD->getParent()->getTypeForDecl()));
 102 }
 103
 104 llvm::Constant *CGCXXABI::EmitMemberDataPointer(const MemberPointerType *MPT,
 105                                                 CharUnits offset) {
 106   return GetBogusMemberPointer(QualType(MPT, 0));
 107 }
 108
 109 llvm::Constant *CGCXXABI::EmitMemberPointer(const APValue &MP, QualType MPT) {
 110   return GetBogusMemberPointer(MPT);
 111 }
 112
 113 bool CGCXXABI::isZeroInitializable(const MemberPointerType *MPT) {
 114   // Fake answer.
 115   return true;
 116 }
 117
 118 void CGCXXABI::buildThisParam(CodeGenFunction &CGF, FunctionArgList &params) {
 119   const CXXMethodDecl *MD = cast<CXXMethodDecl>(CGF.CurGD.getDecl());
 120
 121   // FIXME: I'm not entirely sure I like using a fake decl just for code
 122   // generation. Maybe we can come up with a better way?
 123   auto *ThisDecl = ImplicitParamDecl::Create(
 124       CGM.getContext(), nullptr, MD->getLocation(),
 125       &CGM.getContext().Idents.get("this"), MD->getThisType(),
 126       ImplicitParamDecl::CXXThis);
 127   params.push_back(ThisDecl);
 128   CGF.CXXABIThisDecl = ThisDecl;
 129
 130   // Compute the presumed alignment of 'this', which basically comes
 131   // down to whether we know it's a complete object or not.
 132   auto &Layout = CGF.getContext().getASTRecordLayout(MD->getParent());
 133   if (MD->getParent()->getNumVBases() == 0 || // avoid vcall in common case
 134       MD->getParent()->isEffectivelyFinal() ||
 135       isThisCompleteObject(CGF.CurGD)) {
 136     CGF.CXXABIThisAlignment = Layout.getAlignment();
 137   } else {
 138     CGF.CXXABIThisAlignment = Layout.getNonVirtualAlignment();
 139   }
 140 }
 141
 142 llvm::Value *CGCXXABI::loadIncomingCXXThis(CodeGenFunction &CGF) {
 143   return CGF.Builder.CreateLoad(CGF.GetAddrOfLocalVar(getThisDecl(CGF)),
 144                                 "this");
 145 }
 146
 147 void CGCXXABI::setCXXABIThisValue(CodeGenFunction &CGF, llvm::Value *ThisPtr) {
 148   /// Initialize the 'this' slot.
 149   assert(getThisDecl(CGF) && "no 'this' variable for function");
 150   CGF.CXXABIThisValue = ThisPtr;
 151 }
 152
 153 bool CGCXXABI::mayNeedDestruction(const VarDecl *VD) const {
 154   if (VD->needsDestruction(getContext()))
 155     return true;
 156
 157   // If the variable has an incomplete class type (or array thereof), it
 158   // might need destruction.
 159   const Type *T = VD->getType()->getBaseElementTypeUnsafe();
 160   if (T->getAs<RecordType>() && T->isIncompleteType())
 161     return true;
 162
 163   return false;
 164 }
 165
 166 bool CGCXXABI::isEmittedWithConstantInitializer(
 167     const VarDecl *VD, bool InspectInitForWeakDef) const {
 168   VD = VD->getMostRecentDecl();
 169   if (VD->hasAttr<ConstInitAttr>())
 170     return true;
 171
 172   // All later checks examine the initializer specified on the variable. If
 173   // the variable is weak, such examination would not be correct.
 174   if (!InspectInitForWeakDef && (VD->isWeak() || VD->hasAttr<SelectAnyAttr>()))
 175     return false;
 176
 177   const VarDecl *InitDecl = VD->getInitializingDeclaration();
 178   if (!InitDecl)
 179     return false;
 180
 181   // If there's no initializer to run, this is constant initialization.
 182   if (!InitDecl->hasInit())
 183     return true;
 184
 185   // If we have the only definition, we don't need a thread wrapper if we
 186   // will emit the value as a constant.
 187   if (isUniqueGVALinkage(getContext().GetGVALinkageForVariable(VD)))
 188     return !mayNeedDestruction(VD) && InitDecl->evaluateValue();
 189
 190   // Otherwise, we need a thread wrapper unless we know that every
 191   // translation unit will emit the value as a constant. We rely on the
 192   // variable being constant-initialized in every translation unit if it's
 193   // constant-initialized in any translation unit, which isn't actually
 194   // guaranteed by the standard but is necessary for sanity.
 195   return InitDecl->hasConstantInitialization();
 196 }
 197
 198 void CGCXXABI::EmitReturnFromThunk(CodeGenFunction &CGF,
 199                                    RValue RV, QualType ResultType) {
 200   assert(!CGF.hasAggregateEvaluationKind(ResultType) &&
 201          "cannot handle aggregates");
 202   CGF.EmitReturnOfRValue(RV, ResultType);
 203 }
 204
 205 CharUnits CGCXXABI::GetArrayCookieSize(const CXXNewExpr *expr) {
 206   if (!requiresArrayCookie(expr))
 207     return CharUnits::Zero();
 208   return getArrayCookieSizeImpl(expr->getAllocatedType());
 209 }
 210
 211 CharUnits CGCXXABI::getArrayCookieSizeImpl(QualType elementType) {
 212   // BOGUS
 213   return CharUnits::Zero();
 214 }
 215
 216 Address CGCXXABI::InitializeArrayCookie(CodeGenFunction &CGF,
 217                                         Address NewPtr,
 218                                         llvm::Value *NumElements,
 219                                         const CXXNewExpr *expr,
 220                                         QualType ElementType) {
 221   // Should never be called.
 222   ErrorUnsupportedABI(CGF, "array cookie initialization");
 223   return Address::invalid();
 224 }
 225
 226 bool CGCXXABI::requiresArrayCookie(const CXXDeleteExpr *expr,
 227                                    QualType elementType) {
 228   // If the class's usual deallocation function takes two arguments,
 229   // it needs a cookie.
 230   if (expr->doesUsualArrayDeleteWantSize())
 231     return true;
 232
 233   return elementType.isDestructedType();
 234 }
 235
 236 bool CGCXXABI::requiresArrayCookie(const CXXNewExpr *expr) {
 237   // If the class's usual deallocation function takes two arguments,
 238   // it needs a cookie.
 239   if (expr->doesUsualArrayDeleteWantSize())
 240     return true;
 241
 242   return expr->getAllocatedType().isDestructedType();
 243 }
 244
 245 void CGCXXABI::ReadArrayCookie(CodeGenFunction &CGF, Address ptr,
 246                                const CXXDeleteExpr *expr, QualType eltTy,
 247                                llvm::Value *&numElements,
 248                                llvm::Value *&allocPtr, CharUnits &cookieSize) {
 249   // Derive a char* in the same address space as the pointer.
 250   ptr = ptr.withElementType(CGF.Int8Ty);
 251
 252   // If we don't need an array cookie, bail out early.
 253   if (!requiresArrayCookie(expr, eltTy)) {
 254     allocPtr = ptr.getPointer();
 255     numElements = nullptr;
 256     cookieSize = CharUnits::Zero();
 257     return;
 258   }
 259
 260   cookieSize = getArrayCookieSizeImpl(eltTy);
 261   Address allocAddr =
 262     CGF.Builder.CreateConstInBoundsByteGEP(ptr, -cookieSize);
 263   allocPtr = allocAddr.getPointer();
 264   numElements = readArrayCookieImpl(CGF, allocAddr, cookieSize);
 265 }
 266
 267 llvm::Value *CGCXXABI::readArrayCookieImpl(CodeGenFunction &CGF,
 268                                            Address ptr,
 269                                            CharUnits cookieSize) {
 270   ErrorUnsupportedABI(CGF, "reading a new[] cookie");
 271   return llvm::ConstantInt::get(CGF.SizeTy, 0);
 272 }
 273
 274 /// Returns the adjustment, in bytes, required for the given
 275 /// member-pointer operation.  Returns null if no adjustment is
 276 /// required.
 277 llvm::Constant *CGCXXABI::getMemberPointerAdjustment(const CastExpr *E) {
 278   assert(E->getCastKind() == CK_DerivedToBaseMemberPointer ||
 279          E->getCastKind() == CK_BaseToDerivedMemberPointer);
 280
 281   QualType derivedType;
 282   if (E->getCastKind() == CK_DerivedToBaseMemberPointer)
 283     derivedType = E->getSubExpr()->getType();
 284   else
 285     derivedType = E->getType();
 286
 287   const CXXRecordDecl *derivedClass =
 288     derivedType->castAs<MemberPointerType>()->getClass()->getAsCXXRecordDecl();
 289
 290   return CGM.GetNonVirtualBaseClassOffset(derivedClass,
 291                                           E->path_begin(),
 292                                           E->path_end());
 293 }
 294
 295 llvm::BasicBlock *
 296 CGCXXABI::EmitCtorCompleteObjectHandler(CodeGenFunction &CGF,
 297                                         const CXXRecordDecl *RD) {
 298   if (CGM.getTarget().getCXXABI().hasConstructorVariants())
 299     llvm_unreachable("shouldn't be called in this ABI");
 300
 301   ErrorUnsupportedABI(CGF, "complete object detection in ctor");
 302   return nullptr;
 303 }
 304
 305 void CGCXXABI::setCXXDestructorDLLStorage(llvm::GlobalValue *GV,
 306                                           const CXXDestructorDecl *Dtor,
 307                                           CXXDtorType DT) const {
 308   // Assume the base C++ ABI has no special rules for destructor variants.
 309   CGM.setDLLImportDLLExport(GV, Dtor);
 310 }
 311
 312 llvm::GlobalValue::LinkageTypes CGCXXABI::getCXXDestructorLinkage(
 313     GVALinkage Linkage, const CXXDestructorDecl *Dtor, CXXDtorType DT) const {
 314   // Delegate back to CGM by default.
 315   return CGM.getLLVMLinkageForDeclarator(Dtor, Linkage);
 316 }
 317
 318 bool CGCXXABI::NeedsVTTParameter(GlobalDecl GD) {
 319   return false;
 320 }
 321
 322 llvm::CallInst *
 323 CGCXXABI::emitTerminateForUnexpectedException(CodeGenFunction &CGF,
 324                                               llvm::Value *Exn) {
 325   // Just call std::terminate and ignore the violating exception.
 326   return CGF.EmitNounwindRuntimeCall(CGF.CGM.getTerminateFn());
 327 }
 328
 329 CatchTypeInfo CGCXXABI::getCatchAllTypeInfo() {
 330   return CatchTypeInfo{nullptr, 0};
 331 }
 332
 333 std::vector<CharUnits> CGCXXABI::getVBPtrOffsets(const CXXRecordDecl *RD) {
 334   return std::vector<CharUnits>();
 335 }
 336
 337 CGCXXABI::AddedStructorArgCounts CGCXXABI::addImplicitConstructorArgs(
 338     CodeGenFunction &CGF, const CXXConstructorDecl *D, CXXCtorType Type,
 339     bool ForVirtualBase, bool Delegating, CallArgList &Args) {
 340   AddedStructorArgs AddedArgs =
 341       getImplicitConstructorArgs(CGF, D, Type, ForVirtualBase, Delegating);
 342   for (size_t i = 0; i < AddedArgs.Prefix.size(); ++i) {
 343     Args.insert(Args.begin() + 1 + i,
 344                 CallArg(RValue::get(AddedArgs.Prefix[i].Value),
 345                         AddedArgs.Prefix[i].Type));
 346   }
 347   for (const auto &arg : AddedArgs.Suffix) {
 348     Args.add(RValue::get(arg.Value), arg.Type);
 349   }
 350   return AddedStructorArgCounts(AddedArgs.Prefix.size(),
 351                                 AddedArgs.Suffix.size());
 352 }