1//===--- CGVTables.cpp - Emit LLVM Code for C++ vtables -------------------===//
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 of virtual tables.
10//
11//===----------------------------------------------------------------------===//
12
13#include "CGCXXABI.h"
14#include "CodeGenFunction.h"
15#include "CodeGenModule.h"
16#include "clang/AST/Attr.h"
17#include "clang/AST/CXXInheritance.h"
18#include "clang/AST/RecordLayout.h"
19#include "clang/Basic/CodeGenOptions.h"
20#include "clang/CodeGen/CGFunctionInfo.h"
21#include "clang/CodeGen/ConstantInitBuilder.h"
22#include "llvm/IR/IntrinsicInst.h"
23#include "llvm/Support/Format.h"
24#include "llvm/Transforms/Utils/Cloning.h"
25#include <algorithm>
26#include <cstdio>
27
28using namespace clang;
29using namespace CodeGen;
30
31CodeGenVTables::CodeGenVTables(CodeGenModule &CGM)
32 : CGM(CGM), VTContext(CGM.getContext().getVTableContext()) {}
33
34llvm::Constant *CodeGenModule::GetAddrOfThunk(StringRef Name, llvm::Type *FnTy,
35 GlobalDecl GD) {
36 return GetOrCreateLLVMFunction(Name, FnTy, GD, /*ForVTable=*/true,
37 /*DontDefer=*/true, /*IsThunk=*/true);
38}
39
40static void setThunkProperties(CodeGenModule &CGM, const ThunkInfo &Thunk,
41 llvm::Function *ThunkFn, bool ForVTable,
42 GlobalDecl GD) {
43 CGM.setFunctionLinkage(GD, ThunkFn);
44 CGM.getCXXABI().setThunkLinkage(ThunkFn, ForVTable, GD,
45 !Thunk.Return.isEmpty());
46
47 // Set the right visibility.
48 CGM.setGVProperties(ThunkFn, GD);
49
50 if (!CGM.getCXXABI().exportThunk()) {
51 ThunkFn->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
52 ThunkFn->setDSOLocal(true);
53 }
54
55 if (CGM.supportsCOMDAT() && ThunkFn->isWeakForLinker())
56 ThunkFn->setComdat(CGM.getModule().getOrInsertComdat(ThunkFn->getName()));
57}
58
59#ifndef NDEBUG
60static bool similar(const ABIArgInfo &infoL, CanQualType typeL,
61 const ABIArgInfo &infoR, CanQualType typeR) {
62 return (infoL.getKind() == infoR.getKind() &&
63 (typeL == typeR ||
64 (isa<PointerType>(typeL) && isa<PointerType>(typeR)) ||
65 (isa<ReferenceType>(typeL) && isa<ReferenceType>(typeR))));
66}
67#endif
68
69static RValue PerformReturnAdjustment(CodeGenFunction &CGF,
70 QualType ResultType, RValue RV,
71 const ThunkInfo &Thunk) {
72 // Emit the return adjustment.
73 bool NullCheckValue = !ResultType->isReferenceType();
74
75 llvm::BasicBlock *AdjustNull = nullptr;
76 llvm::BasicBlock *AdjustNotNull = nullptr;
77 llvm::BasicBlock *AdjustEnd = nullptr;
78
79 llvm::Value *ReturnValue = RV.getScalarVal();
80
81 if (NullCheckValue) {
82 AdjustNull = CGF.createBasicBlock("adjust.null");
83 AdjustNotNull = CGF.createBasicBlock("adjust.notnull");
84 AdjustEnd = CGF.createBasicBlock("adjust.end");
85
86 llvm::Value *IsNull = CGF.Builder.CreateIsNull(ReturnValue);
87 CGF.Builder.CreateCondBr(IsNull, AdjustNull, AdjustNotNull);
88 CGF.EmitBlock(AdjustNotNull);
89 }
90
91 auto ClassDecl = ResultType->getPointeeType()->getAsCXXRecordDecl();
92 auto ClassAlign = CGF.CGM.getClassPointerAlignment(ClassDecl);
93 ReturnValue = CGF.CGM.getCXXABI().performReturnAdjustment(CGF,
94 Address(ReturnValue, ClassAlign),
95 Thunk.Return);
96
97 if (NullCheckValue) {
98 CGF.Builder.CreateBr(AdjustEnd);
99 CGF.EmitBlock(AdjustNull);
100 CGF.Builder.CreateBr(AdjustEnd);
101 CGF.EmitBlock(AdjustEnd);
102
103 llvm::PHINode *PHI = CGF.Builder.CreatePHI(ReturnValue->getType(), 2);
104 PHI->addIncoming(ReturnValue, AdjustNotNull);
105 PHI->addIncoming(llvm::Constant::getNullValue(ReturnValue->getType()),
106 AdjustNull);
107 ReturnValue = PHI;
108 }
109
110 return RValue::get(ReturnValue);
111}
112
113/// This function clones a function's DISubprogram node and enters it into
114/// a value map with the intent that the map can be utilized by the cloner
115/// to short-circuit Metadata node mapping.
116/// Furthermore, the function resolves any DILocalVariable nodes referenced
117/// by dbg.value intrinsics so they can be properly mapped during cloning.
118static void resolveTopLevelMetadata(llvm::Function *Fn,
119 llvm::ValueToValueMapTy &VMap) {
120 // Clone the DISubprogram node and put it into the Value map.
121 auto *DIS = Fn->getSubprogram();
122 if (!DIS)
123 return;
124 auto *NewDIS = DIS->replaceWithDistinct(DIS->clone());
125 VMap.MD()[DIS].reset(NewDIS);
126
127 // Find all llvm.dbg.declare intrinsics and resolve the DILocalVariable nodes
128 // they are referencing.
129 for (auto &BB : Fn->getBasicBlockList()) {
130 for (auto &I : BB) {
131 if (auto *DII = dyn_cast<llvm::DbgVariableIntrinsic>(&I)) {
132 auto *DILocal = DII->getVariable();
133 if (!DILocal->isResolved())
134 DILocal->resolve();
135 }
136 }
137 }
138}
139
140// This function does roughly the same thing as GenerateThunk, but in a
141// very different way, so that va_start and va_end work correctly.
142// FIXME: This function assumes "this" is the first non-sret LLVM argument of
143// a function, and that there is an alloca built in the entry block
144// for all accesses to "this".
145// FIXME: This function assumes there is only one "ret" statement per function.
146// FIXME: Cloning isn't correct in the presence of indirect goto!
147// FIXME: This implementation of thunks bloats codesize by duplicating the
148// function definition. There are alternatives:
149// 1. Add some sort of stub support to LLVM for cases where we can
150// do a this adjustment, then a sibcall.
151// 2. We could transform the definition to take a va_list instead of an
152// actual variable argument list, then have the thunks (including a
153// no-op thunk for the regular definition) call va_start/va_end.
154// There's a bit of per-call overhead for this solution, but it's
155// better for codesize if the definition is long.
156llvm::Function *
157CodeGenFunction::GenerateVarArgsThunk(llvm::Function *Fn,
158 const CGFunctionInfo &FnInfo,
159 GlobalDecl GD, const ThunkInfo &Thunk) {
160 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
161 const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
162 QualType ResultType = FPT->getReturnType();
163
164 // Get the original function
165 assert(FnInfo.isVariadic());
166 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FnInfo);
167 llvm::Value *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
168 llvm::Function *BaseFn = cast<llvm::Function>(Callee);
169
170 // Cloning can't work if we don't have a definition. The Microsoft ABI may
171 // require thunks when a definition is not available. Emit an error in these
172 // cases.
173 if (!MD->isDefined()) {
174 CGM.ErrorUnsupported(MD, "return-adjusting thunk with variadic arguments");
175 return Fn;
176 }
177 assert(!BaseFn->isDeclaration() && "cannot clone undefined variadic method");
178
179 // Clone to thunk.
180 llvm::ValueToValueMapTy VMap;
181
182 // We are cloning a function while some Metadata nodes are still unresolved.
183 // Ensure that the value mapper does not encounter any of them.
184 resolveTopLevelMetadata(BaseFn, VMap);
185 llvm::Function *NewFn = llvm::CloneFunction(BaseFn, VMap);
186 Fn->replaceAllUsesWith(NewFn);
187 NewFn->takeName(Fn);
188 Fn->eraseFromParent();
189 Fn = NewFn;
190
191 // "Initialize" CGF (minimally).
192 CurFn = Fn;
193
194 // Get the "this" value
195 llvm::Function::arg_iterator AI = Fn->arg_begin();
196 if (CGM.ReturnTypeUsesSRet(FnInfo))
197 ++AI;
198
199 // Find the first store of "this", which will be to the alloca associated
200 // with "this".
201 Address ThisPtr(&*AI, CGM.getClassPointerAlignment(MD->getParent()));
202 llvm::BasicBlock *EntryBB = &Fn->front();
203 llvm::BasicBlock::iterator ThisStore =
204 std::find_if(EntryBB->begin(), EntryBB->end(), [&](llvm::Instruction &I) {
205 return isa<llvm::StoreInst>(I) &&
206 I.getOperand(0) == ThisPtr.getPointer();
207 });
208 assert(ThisStore != EntryBB->end() &&
209 "Store of this should be in entry block?");
210 // Adjust "this", if necessary.
211 Builder.SetInsertPoint(&*ThisStore);
212 llvm::Value *AdjustedThisPtr =
213 CGM.getCXXABI().performThisAdjustment(*this, ThisPtr, Thunk.This);
214 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr,
215 ThisStore->getOperand(0)->getType());
216 ThisStore->setOperand(0, AdjustedThisPtr);
217
218 if (!Thunk.Return.isEmpty()) {
219 // Fix up the returned value, if necessary.
220 for (llvm::BasicBlock &BB : *Fn) {
221 llvm::Instruction *T = BB.getTerminator();
222 if (isa<llvm::ReturnInst>(T)) {
223 RValue RV = RValue::get(T->getOperand(0));
224 T->eraseFromParent();
225 Builder.SetInsertPoint(&BB);
226 RV = PerformReturnAdjustment(*this, ResultType, RV, Thunk);
227 Builder.CreateRet(RV.getScalarVal());
228 break;
229 }
230 }
231 }
232
233 return Fn;
234}
235
236void CodeGenFunction::StartThunk(llvm::Function *Fn, GlobalDecl GD,
237 const CGFunctionInfo &FnInfo,
238 bool IsUnprototyped) {
239 assert(!CurGD.getDecl() && "CurGD was already set!");
240 CurGD = GD;
241 CurFuncIsThunk = true;
242
243 // Build FunctionArgs.
244 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
245 QualType ThisType = MD->getThisType();
246 QualType ResultType;
247 if (IsUnprototyped)
248 ResultType = CGM.getContext().VoidTy;
249 else if (CGM.getCXXABI().HasThisReturn(GD))
250 ResultType = ThisType;
251 else if (CGM.getCXXABI().hasMostDerivedReturn(GD))
252 ResultType = CGM.getContext().VoidPtrTy;
253 else
254 ResultType = MD->getType()->castAs<FunctionProtoType>()->getReturnType();
255 FunctionArgList FunctionArgs;
256
257 // Create the implicit 'this' parameter declaration.
258 CGM.getCXXABI().buildThisParam(*this, FunctionArgs);
259
260 // Add the rest of the parameters, if we have a prototype to work with.
261 if (!IsUnprototyped) {
262 FunctionArgs.append(MD->param_begin(), MD->param_end());
263
264 if (isa<CXXDestructorDecl>(MD))
265 CGM.getCXXABI().addImplicitStructorParams(*this, ResultType,
266 FunctionArgs);
267 }
268
269 // Start defining the function.
270 auto NL = ApplyDebugLocation::CreateEmpty(*this);
271 StartFunction(GlobalDecl(), ResultType, Fn, FnInfo, FunctionArgs,
272 MD->getLocation());
273 // Create a scope with an artificial location for the body of this function.
274 auto AL = ApplyDebugLocation::CreateArtificial(*this);
275
276 // Since we didn't pass a GlobalDecl to StartFunction, do this ourselves.
277 CGM.getCXXABI().EmitInstanceFunctionProlog(*this);
278 CXXThisValue = CXXABIThisValue;
279 CurCodeDecl = MD;
280 CurFuncDecl = MD;
281}
282
283void CodeGenFunction::FinishThunk() {
284 // Clear these to restore the invariants expected by
285 // StartFunction/FinishFunction.
286 CurCodeDecl = nullptr;
287 CurFuncDecl = nullptr;
288
289 FinishFunction();
290}
291
292void CodeGenFunction::EmitCallAndReturnForThunk(llvm::FunctionCallee Callee,
293 const ThunkInfo *Thunk,
294 bool IsUnprototyped) {
295 assert(isa<CXXMethodDecl>(CurGD.getDecl()) &&
296 "Please use a new CGF for this thunk");
297 const CXXMethodDecl *MD = cast<CXXMethodDecl>(CurGD.getDecl());
298
299 // Adjust the 'this' pointer if necessary
300 llvm::Value *AdjustedThisPtr =
301 Thunk ? CGM.getCXXABI().performThisAdjustment(
302 *this, LoadCXXThisAddress(), Thunk->This)
303 : LoadCXXThis();
304
305 // If perfect forwarding is required a variadic method, a method using
306 // inalloca, or an unprototyped thunk, use musttail. Emit an error if this
307 // thunk requires a return adjustment, since that is impossible with musttail.
308 if (CurFnInfo->usesInAlloca() || CurFnInfo->isVariadic() || IsUnprototyped) {
309 if (Thunk && !Thunk->Return.isEmpty()) {
310 if (IsUnprototyped)
311 CGM.ErrorUnsupported(
312 MD, "return-adjusting thunk with incomplete parameter type");
313 else if (CurFnInfo->isVariadic())
314 llvm_unreachable("shouldn't try to emit musttail return-adjusting "
315 "thunks for variadic functions");
316 else
317 CGM.ErrorUnsupported(
318 MD, "non-trivial argument copy for return-adjusting thunk");
319 }
320 EmitMustTailThunk(CurGD, AdjustedThisPtr, Callee);
321 return;
322 }
323
324 // Start building CallArgs.
325 CallArgList CallArgs;
326 QualType ThisType = MD->getThisType();
327 CallArgs.add(RValue::get(AdjustedThisPtr), ThisType);
328
329 if (isa<CXXDestructorDecl>(MD))
330 CGM.getCXXABI().adjustCallArgsForDestructorThunk(*this, CurGD, CallArgs);
331
332#ifndef NDEBUG
333 unsigned PrefixArgs = CallArgs.size() - 1;
334#endif
335 // Add the rest of the arguments.
336 for (const ParmVarDecl *PD : MD->parameters())
337 EmitDelegateCallArg(CallArgs, PD, SourceLocation());
338
339 const FunctionProtoType *FPT = MD->getType()->castAs<FunctionProtoType>();
340
341#ifndef NDEBUG
342 const CGFunctionInfo &CallFnInfo = CGM.getTypes().arrangeCXXMethodCall(
343 CallArgs, FPT, RequiredArgs::forPrototypePlus(FPT, 1), PrefixArgs);
344 assert(CallFnInfo.getRegParm() == CurFnInfo->getRegParm() &&
345 CallFnInfo.isNoReturn() == CurFnInfo->isNoReturn() &&
346 CallFnInfo.getCallingConvention() == CurFnInfo->getCallingConvention());
347 assert(isa<CXXDestructorDecl>(MD) || // ignore dtor return types
348 similar(CallFnInfo.getReturnInfo(), CallFnInfo.getReturnType(),
349 CurFnInfo->getReturnInfo(), CurFnInfo->getReturnType()));
350 assert(CallFnInfo.arg_size() == CurFnInfo->arg_size());
351 for (unsigned i = 0, e = CurFnInfo->arg_size(); i != e; ++i)
352 assert(similar(CallFnInfo.arg_begin()[i].info,
353 CallFnInfo.arg_begin()[i].type,
354 CurFnInfo->arg_begin()[i].info,
355 CurFnInfo->arg_begin()[i].type));
356#endif
357
358 // Determine whether we have a return value slot to use.
359 QualType ResultType = CGM.getCXXABI().HasThisReturn(CurGD)
360 ? ThisType
361 : CGM.getCXXABI().hasMostDerivedReturn(CurGD)
362 ? CGM.getContext().VoidPtrTy
363 : FPT->getReturnType();
364 ReturnValueSlot Slot;
365 if (!ResultType->isVoidType() &&
366 (CurFnInfo->getReturnInfo().getKind() == ABIArgInfo::Indirect ||
367 hasAggregateEvaluationKind(ResultType)))
368 Slot = ReturnValueSlot(ReturnValue, ResultType.isVolatileQualified(),
369 /*IsUnused=*/false, /*IsExternallyDestructed=*/true);
370
371 // Now emit our call.
372 llvm::CallBase *CallOrInvoke;
373 RValue RV = EmitCall(*CurFnInfo, CGCallee::forDirect(Callee, CurGD), Slot,
374 CallArgs, &CallOrInvoke);
375
376 // Consider return adjustment if we have ThunkInfo.
377 if (Thunk && !Thunk->Return.isEmpty())
378 RV = PerformReturnAdjustment(*this, ResultType, RV, *Thunk);
379 else if (llvm::CallInst* Call = dyn_cast<llvm::CallInst>(CallOrInvoke))
380 Call->setTailCallKind(llvm::CallInst::TCK_Tail);
381
382 // Emit return.
383 if (!ResultType->isVoidType() && Slot.isNull())
384 CGM.getCXXABI().EmitReturnFromThunk(*this, RV, ResultType);
385
386 // Disable the final ARC autorelease.
387 AutoreleaseResult = false;
388
389 FinishThunk();
390}
391
392void CodeGenFunction::EmitMustTailThunk(GlobalDecl GD,
393 llvm::Value *AdjustedThisPtr,
394 llvm::FunctionCallee Callee) {
395 // Emitting a musttail call thunk doesn't use any of the CGCall.cpp machinery
396 // to translate AST arguments into LLVM IR arguments. For thunks, we know
397 // that the caller prototype more or less matches the callee prototype with
398 // the exception of 'this'.
399 SmallVector<llvm::Value *, 8> Args;
400 for (llvm::Argument &A : CurFn->args())
401 Args.push_back(&A);
402
403 // Set the adjusted 'this' pointer.
404 const ABIArgInfo &ThisAI = CurFnInfo->arg_begin()->info;
405 if (ThisAI.isDirect()) {
406 const ABIArgInfo &RetAI = CurFnInfo->getReturnInfo();
407 int ThisArgNo = RetAI.isIndirect() && !RetAI.isSRetAfterThis() ? 1 : 0;
408 llvm::Type *ThisType = Args[ThisArgNo]->getType();
409 if (ThisType != AdjustedThisPtr->getType())
410 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
411 Args[ThisArgNo] = AdjustedThisPtr;
412 } else {
413 assert(ThisAI.isInAlloca() && "this is passed directly or inalloca");
414 Address ThisAddr = GetAddrOfLocalVar(CXXABIThisDecl);
415 llvm::Type *ThisType = ThisAddr.getElementType();
416 if (ThisType != AdjustedThisPtr->getType())
417 AdjustedThisPtr = Builder.CreateBitCast(AdjustedThisPtr, ThisType);
418 Builder.CreateStore(AdjustedThisPtr, ThisAddr);
419 }
420
421 // Emit the musttail call manually. Even if the prologue pushed cleanups, we
422 // don't actually want to run them.
423 llvm::CallInst *Call = Builder.CreateCall(Callee, Args);
424 Call->setTailCallKind(llvm::CallInst::TCK_MustTail);
425
426 // Apply the standard set of call attributes.
427 unsigned CallingConv;
428 llvm::AttributeList Attrs;
429 CGM.ConstructAttributeList(Callee.getCallee()->getName(), *CurFnInfo, GD,
430 Attrs, CallingConv, /*AttrOnCallSite=*/true);
431 Call->setAttributes(Attrs);
432 Call->setCallingConv(static_cast<llvm::CallingConv::ID>(CallingConv));
433
434 if (Call->getType()->isVoidTy())
435 Builder.CreateRetVoid();
436 else
437 Builder.CreateRet(Call);
438
439 // Finish the function to maintain CodeGenFunction invariants.
440 // FIXME: Don't emit unreachable code.
441 EmitBlock(createBasicBlock());
442
443 FinishThunk();
444}
445
446void CodeGenFunction::generateThunk(llvm::Function *Fn,
447 const CGFunctionInfo &FnInfo, GlobalDecl GD,
448 const ThunkInfo &Thunk,
449 bool IsUnprototyped) {
450 StartThunk(Fn, GD, FnInfo, IsUnprototyped);
451 // Create a scope with an artificial location for the body of this function.
452 auto AL = ApplyDebugLocation::CreateArtificial(*this);
453
454 // Get our callee. Use a placeholder type if this method is unprototyped so
455 // that CodeGenModule doesn't try to set attributes.
456 llvm::Type *Ty;
457 if (IsUnprototyped)
458 Ty = llvm::StructType::get(getLLVMContext());
459 else
460 Ty = CGM.getTypes().GetFunctionType(FnInfo);
461
462 llvm::Constant *Callee = CGM.GetAddrOfFunction(GD, Ty, /*ForVTable=*/true);
463
464 // Fix up the function type for an unprototyped musttail call.
465 if (IsUnprototyped)
466 Callee = llvm::ConstantExpr::getBitCast(Callee, Fn->getType());
467
468 // Make the call and return the result.
469 EmitCallAndReturnForThunk(llvm::FunctionCallee(Fn->getFunctionType(), Callee),
470 &Thunk, IsUnprototyped);
471}
472
473static bool shouldEmitVTableThunk(CodeGenModule &CGM, const CXXMethodDecl *MD,
474 bool IsUnprototyped, bool ForVTable) {
475 // Always emit thunks in the MS C++ ABI. We cannot rely on other TUs to
476 // provide thunks for us.
477 if (CGM.getTarget().getCXXABI().isMicrosoft())
478 return true;
479
480 // In the Itanium C++ ABI, vtable thunks are provided by TUs that provide
481 // definitions of the main method. Therefore, emitting thunks with the vtable
482 // is purely an optimization. Emit the thunk if optimizations are enabled and
483 // all of the parameter types are complete.
484 if (ForVTable)
485 return CGM.getCodeGenOpts().OptimizationLevel && !IsUnprototyped;
486
487 // Always emit thunks along with the method definition.
488 return true;
489}
490
491llvm::Constant *CodeGenVTables::maybeEmitThunk(GlobalDecl GD,
492 const ThunkInfo &TI,
493 bool ForVTable) {
494 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
495
496 // First, get a declaration. Compute the mangled name. Don't worry about
497 // getting the function prototype right, since we may only need this
498 // declaration to fill in a vtable slot.
499 SmallString<256> Name;
500 MangleContext &MCtx = CGM.getCXXABI().getMangleContext();
501 llvm::raw_svector_ostream Out(Name);
502 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD))
503 MCtx.mangleCXXDtorThunk(DD, GD.getDtorType(), TI.This, Out);
504 else
505 MCtx.mangleThunk(MD, TI, Out);
506 llvm::Type *ThunkVTableTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
507 llvm::Constant *Thunk = CGM.GetAddrOfThunk(Name, ThunkVTableTy, GD);
508
509 // If we don't need to emit a definition, return this declaration as is.
510 bool IsUnprototyped = !CGM.getTypes().isFuncTypeConvertible(
511 MD->getType()->castAs<FunctionType>());
512 if (!shouldEmitVTableThunk(CGM, MD, IsUnprototyped, ForVTable))
513 return Thunk;
514
515 // Arrange a function prototype appropriate for a function definition. In some
516 // cases in the MS ABI, we may need to build an unprototyped musttail thunk.
517 const CGFunctionInfo &FnInfo =
518 IsUnprototyped ? CGM.getTypes().arrangeUnprototypedMustTailThunk(MD)
519 : CGM.getTypes().arrangeGlobalDeclaration(GD);
520 llvm::FunctionType *ThunkFnTy = CGM.getTypes().GetFunctionType(FnInfo);
521
522 // If the type of the underlying GlobalValue is wrong, we'll have to replace
523 // it. It should be a declaration.
524 llvm::Function *ThunkFn = cast<llvm::Function>(Thunk->stripPointerCasts());
525 if (ThunkFn->getFunctionType() != ThunkFnTy) {
526 llvm::GlobalValue *OldThunkFn = ThunkFn;
527
528 assert(OldThunkFn->isDeclaration() && "Shouldn't replace non-declaration");
529
530 // Remove the name from the old thunk function and get a new thunk.
531 OldThunkFn->setName(StringRef());
532 ThunkFn = llvm::Function::Create(ThunkFnTy, llvm::Function::ExternalLinkage,
533 Name.str(), &CGM.getModule());
534 CGM.SetLLVMFunctionAttributes(MD, FnInfo, ThunkFn);
535
536 // If needed, replace the old thunk with a bitcast.
537 if (!OldThunkFn->use_empty()) {
538 llvm::Constant *NewPtrForOldDecl =
539 llvm::ConstantExpr::getBitCast(ThunkFn, OldThunkFn->getType());
540 OldThunkFn->replaceAllUsesWith(NewPtrForOldDecl);
541 }
542
543 // Remove the old thunk.
544 OldThunkFn->eraseFromParent();
545 }
546
547 bool ABIHasKeyFunctions = CGM.getTarget().getCXXABI().hasKeyFunctions();
548 bool UseAvailableExternallyLinkage = ForVTable && ABIHasKeyFunctions;
549
550 if (!ThunkFn->isDeclaration()) {
551 if (!ABIHasKeyFunctions || UseAvailableExternallyLinkage) {
552 // There is already a thunk emitted for this function, do nothing.
553 return ThunkFn;
554 }
555
556 setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
557 return ThunkFn;
558 }
559
560 // If this will be unprototyped, add the "thunk" attribute so that LLVM knows
561 // that the return type is meaningless. These thunks can be used to call
562 // functions with differing return types, and the caller is required to cast
563 // the prototype appropriately to extract the correct value.
564 if (IsUnprototyped)
565 ThunkFn->addFnAttr("thunk");
566
567 CGM.SetLLVMFunctionAttributesForDefinition(GD.getDecl(), ThunkFn);
568
569 // Thunks for variadic methods are special because in general variadic
570 // arguments cannot be perfectly forwarded. In the general case, clang
571 // implements such thunks by cloning the original function body. However, for
572 // thunks with no return adjustment on targets that support musttail, we can
573 // use musttail to perfectly forward the variadic arguments.
574 bool ShouldCloneVarArgs = false;
575 if (!IsUnprototyped && ThunkFn->isVarArg()) {
576 ShouldCloneVarArgs = true;
577 if (TI.Return.isEmpty()) {
578 switch (CGM.getTriple().getArch()) {
579 case llvm::Triple::x86_64:
580 case llvm::Triple::x86:
581 case llvm::Triple::aarch64:
582 ShouldCloneVarArgs = false;
583 break;
584 default:
585 break;
586 }
587 }
588 }
589
590 if (ShouldCloneVarArgs) {
591 if (UseAvailableExternallyLinkage)
592 return ThunkFn;
593 ThunkFn =
594 CodeGenFunction(CGM).GenerateVarArgsThunk(ThunkFn, FnInfo, GD, TI);
595 } else {
596 // Normal thunk body generation.
597 CodeGenFunction(CGM).generateThunk(ThunkFn, FnInfo, GD, TI, IsUnprototyped);
598 }
599
600 setThunkProperties(CGM, TI, ThunkFn, ForVTable, GD);
601 return ThunkFn;
602}
603
604void CodeGenVTables::EmitThunks(GlobalDecl GD) {
605 const CXXMethodDecl *MD =
606 cast<CXXMethodDecl>(GD.getDecl())->getCanonicalDecl();
607
608 // We don't need to generate thunks for the base destructor.
609 if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() == Dtor_Base)
610 return;
611
612 const VTableContextBase::ThunkInfoVectorTy *ThunkInfoVector =
613 VTContext->getThunkInfo(GD);
614
615 if (!ThunkInfoVector)
616 return;
617
618 for (const ThunkInfo& Thunk : *ThunkInfoVector)
619 maybeEmitThunk(GD, Thunk, /*ForVTable=*/false);
620}
621
622void CodeGenVTables::addRelativeComponent(ConstantArrayBuilder &builder,
623 llvm::Constant *component,
624 unsigned vtableAddressPoint,
625 bool vtableHasLocalLinkage,
626 bool isCompleteDtor) const {
627 // No need to get the offset of a nullptr.
628 if (component->isNullValue())
629 return builder.add(llvm::ConstantInt::get(CGM.Int32Ty, 0));
630
631 auto *globalVal =
632 cast<llvm::GlobalValue>(component->stripPointerCastsAndAliases());
633 llvm::Module &module = CGM.getModule();
634
635 // We don't want to copy the linkage of the vtable exactly because we still
636 // want the stub/proxy to be emitted for properly calculating the offset.
637 // Examples where there would be no symbol emitted are available_externally
638 // and private linkages.
639 auto stubLinkage = vtableHasLocalLinkage ? llvm::GlobalValue::InternalLinkage
640 : llvm::GlobalValue::ExternalLinkage;
641
642 llvm::Constant *target;
643 if (auto *func = dyn_cast<llvm::Function>(globalVal)) {
644 target = llvm::DSOLocalEquivalent::get(func);
645 } else {
646 llvm::SmallString<16> rttiProxyName(globalVal->getName());
647 rttiProxyName.append(".rtti_proxy");
648
649 // The RTTI component may not always be emitted in the same linkage unit as
650 // the vtable. As a general case, we can make a dso_local proxy to the RTTI
651 // that points to the actual RTTI struct somewhere. This will result in a
652 // GOTPCREL relocation when taking the relative offset to the proxy.
653 llvm::GlobalVariable *proxy = module.getNamedGlobal(rttiProxyName);
654 if (!proxy) {
655 proxy = new llvm::GlobalVariable(module, globalVal->getType(),
656 /*isConstant=*/true, stubLinkage,
657 globalVal, rttiProxyName);
658 proxy->setDSOLocal(true);
659 proxy->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
660 if (!proxy->hasLocalLinkage()) {
661 proxy->setVisibility(llvm::GlobalValue::HiddenVisibility);
662 proxy->setComdat(module.getOrInsertComdat(rttiProxyName));
663 }
664 }
665 target = proxy;
666 }
667
668 builder.addRelativeOffsetToPosition(CGM.Int32Ty, target,
669 /*position=*/vtableAddressPoint);
670}
671
672bool CodeGenVTables::useRelativeLayout() const {
673 return CGM.getTarget().getCXXABI().isItaniumFamily() &&
674 CGM.getItaniumVTableContext().isRelativeLayout();
675}
676
677llvm::Type *CodeGenVTables::getVTableComponentType() const {
678 if (useRelativeLayout())
679 return CGM.Int32Ty;
680 return CGM.Int8PtrTy;
681}
682
683static void AddPointerLayoutOffset(const CodeGenModule &CGM,
684 ConstantArrayBuilder &builder,
685 CharUnits offset) {
686 builder.add(llvm::ConstantExpr::getIntToPtr(
687 llvm::ConstantInt::get(CGM.PtrDiffTy, offset.getQuantity()),
688 CGM.Int8PtrTy));
689}
690
691static void AddRelativeLayoutOffset(const CodeGenModule &CGM,
692 ConstantArrayBuilder &builder,
693 CharUnits offset) {
694 builder.add(llvm::ConstantInt::get(CGM.Int32Ty, offset.getQuantity()));
695}
696
697void CodeGenVTables::addVTableComponent(ConstantArrayBuilder &builder,
698 const VTableLayout &layout,
699 unsigned componentIndex,
700 llvm::Constant *rtti,
701 unsigned &nextVTableThunkIndex,
702 unsigned vtableAddressPoint,
703 bool vtableHasLocalLinkage) {
704 auto &component = layout.vtable_components()[componentIndex];
705
706 auto addOffsetConstant =
707 useRelativeLayout() ? AddRelativeLayoutOffset : AddPointerLayoutOffset;
708
709 switch (component.getKind()) {
710 case VTableComponent::CK_VCallOffset:
711 return addOffsetConstant(CGM, builder, component.getVCallOffset());
712
713 case VTableComponent::CK_VBaseOffset:
714 return addOffsetConstant(CGM, builder, component.getVBaseOffset());
715
716 case VTableComponent::CK_OffsetToTop:
717 return addOffsetConstant(CGM, builder, component.getOffsetToTop());
718
719 case VTableComponent::CK_RTTI:
720 if (useRelativeLayout())
721 return addRelativeComponent(builder, rtti, vtableAddressPoint,
722 vtableHasLocalLinkage,
723 /*isCompleteDtor=*/false);
724 else
725 return builder.add(llvm::ConstantExpr::getBitCast(rtti, CGM.Int8PtrTy));
726
727 case VTableComponent::CK_FunctionPointer:
728 case VTableComponent::CK_CompleteDtorPointer:
729 case VTableComponent::CK_DeletingDtorPointer: {
730 GlobalDecl GD;
731
732 // Get the right global decl.
733 switch (component.getKind()) {
734 default:
735 llvm_unreachable("Unexpected vtable component kind");
736 case VTableComponent::CK_FunctionPointer:
737 GD = component.getFunctionDecl();
738 break;
739 case VTableComponent::CK_CompleteDtorPointer:
740 GD = GlobalDecl(component.getDestructorDecl(), Dtor_Complete);
741 break;
742 case VTableComponent::CK_DeletingDtorPointer:
743 GD = GlobalDecl(component.getDestructorDecl(), Dtor_Deleting);
744 break;
745 }
746
747 if (CGM.getLangOpts().CUDA) {
748 // Emit NULL for methods we can't codegen on this
749 // side. Otherwise we'd end up with vtable with unresolved
750 // references.
751 const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
752 // OK on device side: functions w/ __device__ attribute
753 // OK on host side: anything except __device__-only functions.
754 bool CanEmitMethod =
755 CGM.getLangOpts().CUDAIsDevice
756 ? MD->hasAttr<CUDADeviceAttr>()
757 : (MD->hasAttr<CUDAHostAttr>() || !MD->hasAttr<CUDADeviceAttr>());
758 if (!CanEmitMethod)
759 return builder.add(llvm::ConstantExpr::getNullValue(CGM.Int8PtrTy));
760 // Method is acceptable, continue processing as usual.
761 }
762
763 auto getSpecialVirtualFn = [&](StringRef name) -> llvm::Constant * {
764 // FIXME(PR43094): When merging comdat groups, lld can select a local
765 // symbol as the signature symbol even though it cannot be accessed
766 // outside that symbol's TU. The relative vtables ABI would make
767 // __cxa_pure_virtual and __cxa_deleted_virtual local symbols, and
768 // depending on link order, the comdat groups could resolve to the one
769 // with the local symbol. As a temporary solution, fill these components
770 // with zero. We shouldn't be calling these in the first place anyway.
771 if (useRelativeLayout())
772 return llvm::ConstantPointerNull::get(CGM.Int8PtrTy);
773
774 // For NVPTX devices in OpenMP emit special functon as null pointers,
775 // otherwise linking ends up with unresolved references.
776 if (CGM.getLangOpts().OpenMP && CGM.getLangOpts().OpenMPIsDevice &&
777 CGM.getTriple().isNVPTX())
778 return llvm::ConstantPointerNull::get(CGM.Int8PtrTy);
779 llvm::FunctionType *fnTy =
780 llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
781 llvm::Constant *fn = cast<llvm::Constant>(
782 CGM.CreateRuntimeFunction(fnTy, name).getCallee());
783 if (auto f = dyn_cast<llvm::Function>(fn))
784 f->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
785 return llvm::ConstantExpr::getBitCast(fn, CGM.Int8PtrTy);
786 };
787
788 llvm::Constant *fnPtr;
789
790 // Pure virtual member functions.
791 if (cast<CXXMethodDecl>(GD.getDecl())->isPure()) {
792 if (!PureVirtualFn)
793 PureVirtualFn =
794 getSpecialVirtualFn(CGM.getCXXABI().GetPureVirtualCallName());
795 fnPtr = PureVirtualFn;
796
797 // Deleted virtual member functions.
798 } else if (cast<CXXMethodDecl>(GD.getDecl())->isDeleted()) {
799 if (!DeletedVirtualFn)
800 DeletedVirtualFn =
801 getSpecialVirtualFn(CGM.getCXXABI().GetDeletedVirtualCallName());
802 fnPtr = DeletedVirtualFn;
803
804 // Thunks.
805 } else if (nextVTableThunkIndex < layout.vtable_thunks().size() &&
806 layout.vtable_thunks()[nextVTableThunkIndex].first ==
807 componentIndex) {
808 auto &thunkInfo = layout.vtable_thunks()[nextVTableThunkIndex].second;
809
810 nextVTableThunkIndex++;
811 fnPtr = maybeEmitThunk(GD, thunkInfo, /*ForVTable=*/true);
812
813 // Otherwise we can use the method definition directly.
814 } else {
815 llvm::Type *fnTy = CGM.getTypes().GetFunctionTypeForVTable(GD);
816 fnPtr = CGM.GetAddrOfFunction(GD, fnTy, /*ForVTable=*/true);
817 }
818
819 if (useRelativeLayout()) {
820 return addRelativeComponent(
821 builder, fnPtr, vtableAddressPoint, vtableHasLocalLinkage,
822 component.getKind() == VTableComponent::CK_CompleteDtorPointer);
823 } else
824 return builder.add(llvm::ConstantExpr::getBitCast(fnPtr, CGM.Int8PtrTy));
825 }
826
827 case VTableComponent::CK_UnusedFunctionPointer:
828 if (useRelativeLayout())
829 return builder.add(llvm::ConstantExpr::getNullValue(CGM.Int32Ty));
830 else
831 return builder.addNullPointer(CGM.Int8PtrTy);
832 }
833
834 llvm_unreachable("Unexpected vtable component kind");
835}
836
837llvm::Type *CodeGenVTables::getVTableType(const VTableLayout &layout) {
838 SmallVector<llvm::Type *, 4> tys;
839 llvm::Type *componentType = getVTableComponentType();
840 for (unsigned i = 0, e = layout.getNumVTables(); i != e; ++i)
841 tys.push_back(llvm::ArrayType::get(componentType, layout.getVTableSize(i)));
842
843 return llvm::StructType::get(CGM.getLLVMContext(), tys);
844}
845
846void CodeGenVTables::createVTableInitializer(ConstantStructBuilder &builder,
847 const VTableLayout &layout,
848 llvm::Constant *rtti,
849 bool vtableHasLocalLinkage) {
850 llvm::Type *componentType = getVTableComponentType();
851
852 const auto &addressPoints = layout.getAddressPointIndices();
853 unsigned nextVTableThunkIndex = 0;
854 for (unsigned vtableIndex = 0, endIndex = layout.getNumVTables();
855 vtableIndex != endIndex; ++vtableIndex) {
856 auto vtableElem = builder.beginArray(componentType);
857
858 size_t vtableStart = layout.getVTableOffset(vtableIndex);
859 size_t vtableEnd = vtableStart + layout.getVTableSize(vtableIndex);
860 for (size_t componentIndex = vtableStart; componentIndex < vtableEnd;
861 ++componentIndex) {
862 addVTableComponent(vtableElem, layout, componentIndex, rtti,
863 nextVTableThunkIndex, addressPoints[vtableIndex],
864 vtableHasLocalLinkage);
865 }
866 vtableElem.finishAndAddTo(builder);
867 }
868}
869
870llvm::GlobalVariable *CodeGenVTables::GenerateConstructionVTable(
871 const CXXRecordDecl *RD, const BaseSubobject &Base, bool BaseIsVirtual,
872 llvm::GlobalVariable::LinkageTypes Linkage,
873 VTableAddressPointsMapTy &AddressPoints) {
874 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
875 DI->completeClassData(Base.getBase());
876
877 std::unique_ptr<VTableLayout> VTLayout(
878 getItaniumVTableContext().createConstructionVTableLayout(
879 Base.getBase(), Base.getBaseOffset(), BaseIsVirtual, RD));
880
881 // Add the address points.
882 AddressPoints = VTLayout->getAddressPoints();
883
884 // Get the mangled construction vtable name.
885 SmallString<256> OutName;
886 llvm::raw_svector_ostream Out(OutName);
887 cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
888 .mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),
889 Base.getBase(), Out);
890 SmallString<256> Name(OutName);
891
892 bool UsingRelativeLayout = getItaniumVTableContext().isRelativeLayout();
893 bool VTableAliasExists =
894 UsingRelativeLayout && CGM.getModule().getNamedAlias(Name);
895 if (VTableAliasExists) {
896 // We previously made the vtable hidden and changed its name.
897 Name.append(".local");
898 }
899
900 llvm::Type *VTType = getVTableType(*VTLayout);
901
902 // Construction vtable symbols are not part of the Itanium ABI, so we cannot
903 // guarantee that they actually will be available externally. Instead, when
904 // emitting an available_externally VTT, we provide references to an internal
905 // linkage construction vtable. The ABI only requires complete-object vtables
906 // to be the same for all instances of a type, not construction vtables.
907 if (Linkage == llvm::GlobalVariable::AvailableExternallyLinkage)
908 Linkage = llvm::GlobalVariable::InternalLinkage;
909
910 unsigned Align = CGM.getDataLayout().getABITypeAlignment(VTType);
911
912 // Create the variable that will hold the construction vtable.
913 llvm::GlobalVariable *VTable =
914 CGM.CreateOrReplaceCXXRuntimeVariable(Name, VTType, Linkage, Align);
915
916 // V-tables are always unnamed_addr.
917 VTable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
918
919 llvm::Constant *RTTI = CGM.GetAddrOfRTTIDescriptor(
920 CGM.getContext().getTagDeclType(Base.getBase()));
921
922 // Create and set the initializer.
923 ConstantInitBuilder builder(CGM);
924 auto components = builder.beginStruct();
925 createVTableInitializer(components, *VTLayout, RTTI,
926 VTable->hasLocalLinkage());
927 components.finishAndSetAsInitializer(VTable);
928
929 // Set properties only after the initializer has been set to ensure that the
930 // GV is treated as definition and not declaration.
931 assert(!VTable->isDeclaration() && "Shouldn't set properties on declaration");
932 CGM.setGVProperties(VTable, RD);
933
934 CGM.EmitVTableTypeMetadata(RD, VTable, *VTLayout.get());
935
936 if (UsingRelativeLayout && !VTable->isDSOLocal())
937 GenerateRelativeVTableAlias(VTable, OutName);
938
939 return VTable;
940}
941
942// If the VTable is not dso_local, then we will not be able to indicate that
943// the VTable does not need a relocation and move into rodata. A frequent
944// time this can occur is for classes that should be made public from a DSO
945// (like in libc++). For cases like these, we can make the vtable hidden or
946// private and create a public alias with the same visibility and linkage as
947// the original vtable type.
948void CodeGenVTables::GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
949 llvm::StringRef AliasNameRef) {
950 assert(getItaniumVTableContext().isRelativeLayout() &&
951 "Can only use this if the relative vtable ABI is used");
952 assert(!VTable->isDSOLocal() && "This should be called only if the vtable is "
953 "not guaranteed to be dso_local");
954
955 // If the vtable is available_externally, we shouldn't (or need to) generate
956 // an alias for it in the first place since the vtable won't actually by
957 // emitted in this compilation unit.
958 if (VTable->hasAvailableExternallyLinkage())
959 return;
960
961 // Create a new string in the event the alias is already the name of the
962 // vtable. Using the reference directly could lead to use of an inititialized
963 // value in the module's StringMap.
964 llvm::SmallString<256> AliasName(AliasNameRef);
965 VTable->setName(AliasName + ".local");
966
967 auto Linkage = VTable->getLinkage();
968 assert(llvm::GlobalAlias::isValidLinkage(Linkage) &&
969 "Invalid vtable alias linkage");
970
971 llvm::GlobalAlias *VTableAlias = CGM.getModule().getNamedAlias(AliasName);
972 if (!VTableAlias) {
973 VTableAlias = llvm::GlobalAlias::create(VTable->getValueType(),
974 VTable->getAddressSpace(), Linkage,
975 AliasName, &CGM.getModule());
976 } else {
977 assert(VTableAlias->getValueType() == VTable->getValueType());
978 assert(VTableAlias->getLinkage() == Linkage);
979 }
980 VTableAlias->setVisibility(VTable->getVisibility());
981 VTableAlias->setUnnamedAddr(VTable->getUnnamedAddr());
982
983 // Both of these imply dso_local for the vtable.
984 if (!VTable->hasComdat()) {
985 // If this is in a comdat, then we shouldn't make the linkage private due to
986 // an issue in lld where private symbols can be used as the key symbol when
987 // choosing the prevelant group. This leads to "relocation refers to a
988 // symbol in a discarded section".
989 VTable->setLinkage(llvm::GlobalValue::PrivateLinkage);
990 } else {
991 // We should at least make this hidden since we don't want to expose it.
992 VTable->setVisibility(llvm::GlobalValue::HiddenVisibility);
993 }
994
995 VTableAlias->setAliasee(VTable);
996}
997
998static bool shouldEmitAvailableExternallyVTable(const CodeGenModule &CGM,
999 const CXXRecordDecl *RD) {
1000 return CGM.getCodeGenOpts().OptimizationLevel > 0 &&
1001 CGM.getCXXABI().canSpeculativelyEmitVTable(RD);
1002}
1003
1004/// Compute the required linkage of the vtable for the given class.
1005///
1006/// Note that we only call this at the end of the translation unit.
1007llvm::GlobalVariable::LinkageTypes
1008CodeGenModule::getVTableLinkage(const CXXRecordDecl *RD) {
1009 if (!RD->isExternallyVisible())
1010 return llvm::GlobalVariable::InternalLinkage;
1011
1012 // We're at the end of the translation unit, so the current key
1013 // function is fully correct.
1014 const CXXMethodDecl *keyFunction = Context.getCurrentKeyFunction(RD);
1015 if (keyFunction && !RD->hasAttr<DLLImportAttr>()) {
1016 // If this class has a key function, use that to determine the
1017 // linkage of the vtable.
1018 const FunctionDecl *def = nullptr;
1019 if (keyFunction->hasBody(def))
1020 keyFunction = cast<CXXMethodDecl>(def);
1021
1022 switch (keyFunction->getTemplateSpecializationKind()) {
1023 case TSK_Undeclared:
1024 case TSK_ExplicitSpecialization:
1025 assert((def || CodeGenOpts.OptimizationLevel > 0 ||
1026 CodeGenOpts.getDebugInfo() != codegenoptions::NoDebugInfo) &&
1027 "Shouldn't query vtable linkage without key function, "
1028 "optimizations, or debug info");
1029 if (!def && CodeGenOpts.OptimizationLevel > 0)
1030 return llvm::GlobalVariable::AvailableExternallyLinkage;
1031
1032 if (keyFunction->isInlined())
1033 return !Context.getLangOpts().AppleKext ?
1034 llvm::GlobalVariable::LinkOnceODRLinkage :
1035 llvm::Function::InternalLinkage;
1036
1037 return llvm::GlobalVariable::ExternalLinkage;
1038
1039 case TSK_ImplicitInstantiation:
1040 return !Context.getLangOpts().AppleKext ?
1041 llvm::GlobalVariable::LinkOnceODRLinkage :
1042 llvm::Function::InternalLinkage;
1043
1044 case TSK_ExplicitInstantiationDefinition:
1045 return !Context.getLangOpts().AppleKext ?
1046 llvm::GlobalVariable::WeakODRLinkage :
1047 llvm::Function::InternalLinkage;
1048
1049 case TSK_ExplicitInstantiationDeclaration:
1050 llvm_unreachable("Should not have been asked to emit this");
1051 }
1052 }
1053
1054 // -fapple-kext mode does not support weak linkage, so we must use
1055 // internal linkage.
1056 if (Context.getLangOpts().AppleKext)
1057 return llvm::Function::InternalLinkage;
1058
1059 llvm::GlobalVariable::LinkageTypes DiscardableODRLinkage =
1060 llvm::GlobalValue::LinkOnceODRLinkage;
1061 llvm::GlobalVariable::LinkageTypes NonDiscardableODRLinkage =
1062 llvm::GlobalValue::WeakODRLinkage;
1063 if (RD->hasAttr<DLLExportAttr>()) {
1064 // Cannot discard exported vtables.
1065 DiscardableODRLinkage = NonDiscardableODRLinkage;
1066 } else if (RD->hasAttr<DLLImportAttr>()) {
1067 // Imported vtables are available externally.
1068 DiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
1069 NonDiscardableODRLinkage = llvm::GlobalVariable::AvailableExternallyLinkage;
1070 }
1071
1072 switch (RD->getTemplateSpecializationKind()) {
1073 case TSK_Undeclared:
1074 case TSK_ExplicitSpecialization:
1075 case TSK_ImplicitInstantiation:
1076 return DiscardableODRLinkage;
1077
1078 case TSK_ExplicitInstantiationDeclaration:
1079 // Explicit instantiations in MSVC do not provide vtables, so we must emit
1080 // our own.
1081 if (getTarget().getCXXABI().isMicrosoft())
1082 return DiscardableODRLinkage;
1083 return shouldEmitAvailableExternallyVTable(*this, RD)
1084 ? llvm::GlobalVariable::AvailableExternallyLinkage
1085 : llvm::GlobalVariable::ExternalLinkage;
1086
1087 case TSK_ExplicitInstantiationDefinition:
1088 return NonDiscardableODRLinkage;
1089 }
1090
1091 llvm_unreachable("Invalid TemplateSpecializationKind!");
1092}
1093
1094/// This is a callback from Sema to tell us that a particular vtable is
1095/// required to be emitted in this translation unit.
1096///
1097/// This is only called for vtables that _must_ be emitted (mainly due to key
1098/// functions). For weak vtables, CodeGen tracks when they are needed and
1099/// emits them as-needed.
1100void CodeGenModule::EmitVTable(CXXRecordDecl *theClass) {
1101 VTables.GenerateClassData(theClass);
1102}
1103
1104void
1105CodeGenVTables::GenerateClassData(const CXXRecordDecl *RD) {
1106 if (CGDebugInfo *DI = CGM.getModuleDebugInfo())
1107 DI->completeClassData(RD);
1108
1109 if (RD->getNumVBases())
1110 CGM.getCXXABI().emitVirtualInheritanceTables(RD);
1111
1112 CGM.getCXXABI().emitVTableDefinitions(*this, RD);
1113}
1114
1115/// At this point in the translation unit, does it appear that can we
1116/// rely on the vtable being defined elsewhere in the program?
1117///
1118/// The response is really only definitive when called at the end of
1119/// the translation unit.
1120///
1121/// The only semantic restriction here is that the object file should
1122/// not contain a vtable definition when that vtable is defined
1123/// strongly elsewhere. Otherwise, we'd just like to avoid emitting
1124/// vtables when unnecessary.
1125bool CodeGenVTables::isVTableExternal(const CXXRecordDecl *RD) {
1126 assert(RD->isDynamicClass() && "Non-dynamic classes have no VTable.");
1127
1128 // We always synthesize vtables if they are needed in the MS ABI. MSVC doesn't
1129 // emit them even if there is an explicit template instantiation.
1130 if (CGM.getTarget().getCXXABI().isMicrosoft())
1131 return false;
1132
1133 // If we have an explicit instantiation declaration (and not a
1134 // definition), the vtable is defined elsewhere.
1135 TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
1136 if (TSK == TSK_ExplicitInstantiationDeclaration)
1137 return true;
1138
1139 // Otherwise, if the class is an instantiated template, the
1140 // vtable must be defined here.
1141 if (TSK == TSK_ImplicitInstantiation ||
1142 TSK == TSK_ExplicitInstantiationDefinition)
1143 return false;
1144
1145 // Otherwise, if the class doesn't have a key function (possibly
1146 // anymore), the vtable must be defined here.
1147 const CXXMethodDecl *keyFunction = CGM.getContext().getCurrentKeyFunction(RD);
1148 if (!keyFunction)
1149 return false;
1150
1151 // Otherwise, if we don't have a definition of the key function, the
1152 // vtable must be defined somewhere else.
1153 return !keyFunction->hasBody();
1154}
1155
1156/// Given that we're currently at the end of the translation unit, and
1157/// we've emitted a reference to the vtable for this class, should
1158/// we define that vtable?
1159static bool shouldEmitVTableAtEndOfTranslationUnit(CodeGenModule &CGM,
1160 const CXXRecordDecl *RD) {
1161 // If vtable is internal then it has to be done.
1162 if (!CGM.getVTables().isVTableExternal(RD))
1163 return true;
1164
1165 // If it's external then maybe we will need it as available_externally.
1166 return shouldEmitAvailableExternallyVTable(CGM, RD);
1167}
1168
1169/// Given that at some point we emitted a reference to one or more
1170/// vtables, and that we are now at the end of the translation unit,
1171/// decide whether we should emit them.
1172void CodeGenModule::EmitDeferredVTables() {
1173#ifndef NDEBUG
1174 // Remember the size of DeferredVTables, because we're going to assume
1175 // that this entire operation doesn't modify it.
1176 size_t savedSize = DeferredVTables.size();
1177#endif
1178
1179 for (const CXXRecordDecl *RD : DeferredVTables)
1180 if (shouldEmitVTableAtEndOfTranslationUnit(*this, RD))
1181 VTables.GenerateClassData(RD);
1182 else if (shouldOpportunisticallyEmitVTables())
1183 OpportunisticVTables.push_back(RD);
1184
1185 assert(savedSize == DeferredVTables.size() &&
1186 "deferred extra vtables during vtable emission?");
1187 DeferredVTables.clear();
1188}
1189
1190bool CodeGenModule::HasLTOVisibilityPublicStd(const CXXRecordDecl *RD) {
1191 if (!getCodeGenOpts().LTOVisibilityPublicStd)
1192 return false;
1193
1194 const DeclContext *DC = RD;
1195 while (1) {
1196 auto *D = cast<Decl>(DC);
1197 DC = DC->getParent();
1198 if (isa<TranslationUnitDecl>(DC->getRedeclContext())) {
1199 if (auto *ND = dyn_cast<NamespaceDecl>(D))
1200 if (const IdentifierInfo *II = ND->getIdentifier())
1201 if (II->isStr("std") || II->isStr("stdext"))
1202 return true;
1203 break;
1204 }
1205 }
1206
1207 return false;
1208}
1209
1210bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
1211 LinkageInfo LV = RD->getLinkageAndVisibility();
1212 if (!isExternallyVisible(LV.getLinkage()))
1213 return true;
1214
1215 if (RD->hasAttr<LTOVisibilityPublicAttr>() || RD->hasAttr<UuidAttr>())
1216 return false;
1217
1218 if (getTriple().isOSBinFormatCOFF()) {
1219 if (RD->hasAttr<DLLExportAttr>() || RD->hasAttr<DLLImportAttr>())
1220 return false;
1221 } else {
1222 if (LV.getVisibility() != HiddenVisibility)
1223 return false;
1224 }
1225
1226 return !HasLTOVisibilityPublicStd(RD);
1227}
1228
1229llvm::GlobalObject::VCallVisibility CodeGenModule::GetVCallVisibilityLevel(
1230 const CXXRecordDecl *RD, llvm::DenseSet<const CXXRecordDecl *> &Visited) {
1231 // If we have already visited this RD (which means this is a recursive call
1232 // since the initial call should have an empty Visited set), return the max
1233 // visibility. The recursive calls below compute the min between the result
1234 // of the recursive call and the current TypeVis, so returning the max here
1235 // ensures that it will have no effect on the current TypeVis.
1236 if (!Visited.insert(RD).second)
1237 return llvm::GlobalObject::VCallVisibilityTranslationUnit;
1238
1239 LinkageInfo LV = RD->getLinkageAndVisibility();
1240 llvm::GlobalObject::VCallVisibility TypeVis;
1241 if (!isExternallyVisible(LV.getLinkage()))
1242 TypeVis = llvm::GlobalObject::VCallVisibilityTranslationUnit;
1243 else if (HasHiddenLTOVisibility(RD))
1244 TypeVis = llvm::GlobalObject::VCallVisibilityLinkageUnit;
1245 else
1246 TypeVis = llvm::GlobalObject::VCallVisibilityPublic;
1247
1248 for (auto B : RD->bases())
1249 if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1250 TypeVis = std::min(
1251 TypeVis,
1252 GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl(), Visited));
1253
1254 for (auto B : RD->vbases())
1255 if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
1256 TypeVis = std::min(
1257 TypeVis,
1258 GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl(), Visited));
1259
1260 return TypeVis;
1261}
1262
1263void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
1264 llvm::GlobalVariable *VTable,
1265 const VTableLayout &VTLayout) {
1266 if (!getCodeGenOpts().LTOUnit)
1267 return;
1268
1269 CharUnits PointerWidth =
1270 Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
1271
1272 typedef std::pair<const CXXRecordDecl *, unsigned> AddressPoint;
1273 std::vector<AddressPoint> AddressPoints;
1274 for (auto &&AP : VTLayout.getAddressPoints())
1275 AddressPoints.push_back(std::make_pair(
1276 AP.first.getBase(), VTLayout.getVTableOffset(AP.second.VTableIndex) +
1277 AP.second.AddressPointIndex));
1278
1279 // Sort the address points for determinism.
1280 llvm::sort(AddressPoints, [this](const AddressPoint &AP1,
1281 const AddressPoint &AP2) {
1282 if (&AP1 == &AP2)
1283 return false;
1284
1285 std::string S1;
1286 llvm::raw_string_ostream O1(S1);
1287 getCXXABI().getMangleContext().mangleTypeName(
1288 QualType(AP1.first->getTypeForDecl(), 0), O1);
1289 O1.flush();
1290
1291 std::string S2;
1292 llvm::raw_string_ostream O2(S2);
1293 getCXXABI().getMangleContext().mangleTypeName(
1294 QualType(AP2.first->getTypeForDecl(), 0), O2);
1295 O2.flush();
1296
1297 if (S1 < S2)
1298 return true;
1299 if (S1 != S2)
1300 return false;
1301
1302 return AP1.second < AP2.second;
1303 });
1304
1305 ArrayRef<VTableComponent> Comps = VTLayout.vtable_components();
1306 for (auto AP : AddressPoints) {
1307 // Create type metadata for the address point.
1308 AddVTableTypeMetadata(VTable, PointerWidth * AP.second, AP.first);
1309
1310 // The class associated with each address point could also potentially be
1311 // used for indirect calls via a member function pointer, so we need to
1312 // annotate the address of each function pointer with the appropriate member
1313 // function pointer type.
1314 for (unsigned I = 0; I != Comps.size(); ++I) {
1315 if (Comps[I].getKind() != VTableComponent::CK_FunctionPointer)
1316 continue;
1317 llvm::Metadata *MD = CreateMetadataIdentifierForVirtualMemPtrType(
1318 Context.getMemberPointerType(
1319 Comps[I].getFunctionDecl()->getType(),
1320 Context.getRecordType(AP.first).getTypePtr()));
1321 VTable->addTypeMetadata((PointerWidth * I).getQuantity(), MD);
1322 }
1323 }
1324
1325 if (getCodeGenOpts().VirtualFunctionElimination ||
1326 getCodeGenOpts().WholeProgramVTables) {
1327 llvm::DenseSet<const CXXRecordDecl *> Visited;
1328 llvm::GlobalObject::VCallVisibility TypeVis =
1329 GetVCallVisibilityLevel(RD, Visited);
1330 if (TypeVis != llvm::GlobalObject::VCallVisibilityPublic)
1331 VTable->setVCallVisibilityMetadata(TypeVis);
1332 }
1333}
1334