1 //===--- CGDeclCXX.cpp - Emit LLVM Code for C++ declarations --------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This contains code dealing with code generation of C++ declarations
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "CodeGenFunction.h"
15 #include "CGObjCRuntime.h"
16 #include "CGCXXABI.h"
17 #include "clang/Frontend/CodeGenOptions.h"
18 #include "llvm/Intrinsics.h"
19 
20 using namespace clang;
21 using namespace CodeGen;
22 
23 static void EmitDeclInit(CodeGenFunction &CGF, const VarDecl &D,
24                          llvm::Constant *DeclPtr) {
25   assert(D.hasGlobalStorage() && "VarDecl must have global storage!");
26   assert(!D.getType()->isReferenceType() &&
27          "Should not call EmitDeclInit on a reference!");
28 
29   ASTContext &Context = CGF.getContext();
30 
31   CharUnits alignment = Context.getDeclAlign(&D);
32   QualType type = D.getType();
33   LValue lv = CGF.MakeAddrLValue(DeclPtr, type, alignment);
34 
35   const Expr *Init = D.getInit();
36   if (!CGF.hasAggregateLLVMType(type)) {
37     CodeGenModule &CGM = CGF.CGM;
38     if (lv.isObjCStrong())
39       CGM.getObjCRuntime().EmitObjCGlobalAssign(CGF, CGF.EmitScalarExpr(Init),
40                                                 DeclPtr, D.isThreadSpecified());
41     else if (lv.isObjCWeak())
42       CGM.getObjCRuntime().EmitObjCWeakAssign(CGF, CGF.EmitScalarExpr(Init),
43                                               DeclPtr);
44     else
45       CGF.EmitScalarInit(Init, &D, lv, false);
46   } else if (type->isAnyComplexType()) {
47     CGF.EmitComplexExprIntoAddr(Init, DeclPtr, lv.isVolatile());
48   } else {
49     CGF.EmitAggExpr(Init, AggValueSlot::forLValue(lv,AggValueSlot::IsDestructed,
50                                           AggValueSlot::DoesNotNeedGCBarriers,
51                                                   AggValueSlot::IsNotAliased));
52   }
53 }
54 
55 /// Emit code to cause the destruction of the given variable with
56 /// static storage duration.
57 static void EmitDeclDestroy(CodeGenFunction &CGF, const VarDecl &D,
58                             llvm::Constant *addr) {
59   CodeGenModule &CGM = CGF.CGM;
60 
61   // FIXME:  __attribute__((cleanup)) ?
62 
63   QualType type = D.getType();
64   QualType::DestructionKind dtorKind = type.isDestructedType();
65 
66   switch (dtorKind) {
67   case QualType::DK_none:
68     return;
69 
70   case QualType::DK_cxx_destructor:
71     break;
72 
73   case QualType::DK_objc_strong_lifetime:
74   case QualType::DK_objc_weak_lifetime:
75     // We don't care about releasing objects during process teardown.
76     return;
77   }
78 
79   llvm::Constant *function;
80   llvm::Constant *argument;
81 
82   // Special-case non-array C++ destructors, where there's a function
83   // with the right signature that we can just call.
84   const CXXRecordDecl *record = 0;
85   if (dtorKind == QualType::DK_cxx_destructor &&
86       (record = type->getAsCXXRecordDecl())) {
87     assert(!record->hasTrivialDestructor());
88     CXXDestructorDecl *dtor = record->getDestructor();
89 
90     function = CGM.GetAddrOfCXXDestructor(dtor, Dtor_Complete);
91     argument = addr;
92 
93   // Otherwise, the standard logic requires a helper function.
94   } else {
95     function = CodeGenFunction(CGM).generateDestroyHelper(addr, type,
96                                                   CGF.getDestroyer(dtorKind),
97                                                   CGF.needsEHCleanup(dtorKind));
98     argument = llvm::Constant::getNullValue(CGF.Int8PtrTy);
99   }
100 
101   CGF.EmitCXXGlobalDtorRegistration(function, argument);
102 }
103 
104 /// Emit code to cause the variable at the given address to be considered as
105 /// constant from this point onwards.
106 static void EmitDeclInvariant(CodeGenFunction &CGF, const VarDecl &D,
107                               llvm::Constant *Addr) {
108   // Don't emit the intrinsic if we're not optimizing.
109   if (!CGF.CGM.getCodeGenOpts().OptimizationLevel)
110     return;
111 
112   // Grab the llvm.invariant.start intrinsic.
113   llvm::Intrinsic::ID InvStartID = llvm::Intrinsic::invariant_start;
114   llvm::Constant *InvariantStart = CGF.CGM.getIntrinsic(InvStartID);
115 
116   // Emit a call with the size in bytes of the object.
117   CharUnits WidthChars = CGF.getContext().getTypeSizeInChars(D.getType());
118   uint64_t Width = WidthChars.getQuantity();
119   llvm::Value *Args[2] = { llvm::ConstantInt::getSigned(CGF.Int64Ty, Width),
120                            llvm::ConstantExpr::getBitCast(Addr, CGF.Int8PtrTy)};
121   CGF.Builder.CreateCall(InvariantStart, Args);
122 }
123 
124 void CodeGenFunction::EmitCXXGlobalVarDeclInit(const VarDecl &D,
125                                                llvm::Constant *DeclPtr,
126                                                bool PerformInit) {
127 
128   const Expr *Init = D.getInit();
129   QualType T = D.getType();
130 
131   if (!T->isReferenceType()) {
132     if (PerformInit)
133       EmitDeclInit(*this, D, DeclPtr);
134     if (CGM.isTypeConstant(D.getType(), true))
135       EmitDeclInvariant(*this, D, DeclPtr);
136     else
137       EmitDeclDestroy(*this, D, DeclPtr);
138     return;
139   }
140 
141   assert(PerformInit && "cannot have constant initializer which needs "
142          "destruction for reference");
143   unsigned Alignment = getContext().getDeclAlign(&D).getQuantity();
144   RValue RV = EmitReferenceBindingToExpr(Init, &D);
145   EmitStoreOfScalar(RV.getScalarVal(), DeclPtr, false, Alignment, T);
146 }
147 
148 void
149 CodeGenFunction::EmitCXXGlobalDtorRegistration(llvm::Constant *DtorFn,
150                                                llvm::Constant *DeclPtr) {
151   // Generate a global destructor entry if not using __cxa_atexit.
152   if (!CGM.getCodeGenOpts().CXAAtExit) {
153     CGM.AddCXXDtorEntry(DtorFn, DeclPtr);
154     return;
155   }
156 
157   // Get the destructor function type
158   llvm::Type *DtorFnTy = llvm::FunctionType::get(VoidTy, Int8PtrTy, false);
159   DtorFnTy = llvm::PointerType::getUnqual(DtorFnTy);
160 
161   llvm::Type *Params[] = { DtorFnTy, Int8PtrTy, Int8PtrTy };
162 
163   // Get the __cxa_atexit function type
164   // extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
165   llvm::FunctionType *AtExitFnTy =
166     llvm::FunctionType::get(ConvertType(getContext().IntTy), Params, false);
167 
168   llvm::Constant *AtExitFn = CGM.CreateRuntimeFunction(AtExitFnTy,
169                                                        "__cxa_atexit");
170   if (llvm::Function *Fn = dyn_cast<llvm::Function>(AtExitFn))
171     Fn->setDoesNotThrow();
172 
173   llvm::Constant *Handle = CGM.CreateRuntimeVariable(Int8PtrTy,
174                                                      "__dso_handle");
175   llvm::Value *Args[3] = { llvm::ConstantExpr::getBitCast(DtorFn, DtorFnTy),
176                            llvm::ConstantExpr::getBitCast(DeclPtr, Int8PtrTy),
177                            llvm::ConstantExpr::getBitCast(Handle, Int8PtrTy) };
178   Builder.CreateCall(AtExitFn, Args);
179 }
180 
181 void CodeGenFunction::EmitCXXGuardedInit(const VarDecl &D,
182                                          llvm::GlobalVariable *DeclPtr,
183                                          bool PerformInit) {
184   // If we've been asked to forbid guard variables, emit an error now.
185   // This diagnostic is hard-coded for Darwin's use case;  we can find
186   // better phrasing if someone else needs it.
187   if (CGM.getCodeGenOpts().ForbidGuardVariables)
188     CGM.Error(D.getLocation(),
189               "this initialization requires a guard variable, which "
190               "the kernel does not support");
191 
192   CGM.getCXXABI().EmitGuardedInit(*this, D, DeclPtr, PerformInit);
193 }
194 
195 static llvm::Function *
196 CreateGlobalInitOrDestructFunction(CodeGenModule &CGM,
197                                    llvm::FunctionType *FTy,
198                                    StringRef Name) {
199   llvm::Function *Fn =
200     llvm::Function::Create(FTy, llvm::GlobalValue::InternalLinkage,
201                            Name, &CGM.getModule());
202   if (!CGM.getContext().getLangOptions().AppleKext) {
203     // Set the section if needed.
204     if (const char *Section =
205           CGM.getContext().getTargetInfo().getStaticInitSectionSpecifier())
206       Fn->setSection(Section);
207   }
208 
209   if (!CGM.getLangOptions().Exceptions)
210     Fn->setDoesNotThrow();
211 
212   return Fn;
213 }
214 
215 void
216 CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl *D,
217                                             llvm::GlobalVariable *Addr,
218                                             bool PerformInit) {
219   llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
220 
221   // Create a variable initialization function.
222   llvm::Function *Fn =
223     CreateGlobalInitOrDestructFunction(*this, FTy, "__cxx_global_var_init");
224 
225   CodeGenFunction(*this).GenerateCXXGlobalVarDeclInitFunc(Fn, D, Addr,
226                                                           PerformInit);
227 
228   if (D->hasAttr<InitPriorityAttr>()) {
229     unsigned int order = D->getAttr<InitPriorityAttr>()->getPriority();
230     OrderGlobalInits Key(order, PrioritizedCXXGlobalInits.size());
231     PrioritizedCXXGlobalInits.push_back(std::make_pair(Key, Fn));
232     DelayedCXXInitPosition.erase(D);
233   }
234   else {
235     llvm::DenseMap<const Decl *, unsigned>::iterator I =
236       DelayedCXXInitPosition.find(D);
237     if (I == DelayedCXXInitPosition.end()) {
238       CXXGlobalInits.push_back(Fn);
239     } else {
240       assert(CXXGlobalInits[I->second] == 0);
241       CXXGlobalInits[I->second] = Fn;
242       DelayedCXXInitPosition.erase(I);
243     }
244   }
245 }
246 
247 void
248 CodeGenModule::EmitCXXGlobalInitFunc() {
249   while (!CXXGlobalInits.empty() && !CXXGlobalInits.back())
250     CXXGlobalInits.pop_back();
251 
252   if (CXXGlobalInits.empty() && PrioritizedCXXGlobalInits.empty())
253     return;
254 
255   llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
256 
257   // Create our global initialization function.
258   llvm::Function *Fn =
259     CreateGlobalInitOrDestructFunction(*this, FTy, "_GLOBAL__I_a");
260 
261   if (!PrioritizedCXXGlobalInits.empty()) {
262     SmallVector<llvm::Constant*, 8> LocalCXXGlobalInits;
263     llvm::array_pod_sort(PrioritizedCXXGlobalInits.begin(),
264                          PrioritizedCXXGlobalInits.end());
265     for (unsigned i = 0; i < PrioritizedCXXGlobalInits.size(); i++) {
266       llvm::Function *Fn = PrioritizedCXXGlobalInits[i].second;
267       LocalCXXGlobalInits.push_back(Fn);
268     }
269     LocalCXXGlobalInits.append(CXXGlobalInits.begin(), CXXGlobalInits.end());
270     CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn,
271                                                     &LocalCXXGlobalInits[0],
272                                                     LocalCXXGlobalInits.size());
273   }
274   else
275     CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn,
276                                                      &CXXGlobalInits[0],
277                                                      CXXGlobalInits.size());
278   AddGlobalCtor(Fn);
279   CXXGlobalInits.clear();
280   PrioritizedCXXGlobalInits.clear();
281 }
282 
283 void CodeGenModule::EmitCXXGlobalDtorFunc() {
284   if (CXXGlobalDtors.empty())
285     return;
286 
287   llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
288 
289   // Create our global destructor function.
290   llvm::Function *Fn =
291     CreateGlobalInitOrDestructFunction(*this, FTy, "_GLOBAL__D_a");
292 
293   CodeGenFunction(*this).GenerateCXXGlobalDtorFunc(Fn, CXXGlobalDtors);
294   AddGlobalDtor(Fn);
295 }
296 
297 /// Emit the code necessary to initialize the given global variable.
298 void CodeGenFunction::GenerateCXXGlobalVarDeclInitFunc(llvm::Function *Fn,
299                                                        const VarDecl *D,
300                                                  llvm::GlobalVariable *Addr,
301                                                        bool PerformInit) {
302   StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
303                 getTypes().arrangeNullaryFunction(),
304                 FunctionArgList(), SourceLocation());
305 
306   // Use guarded initialization if the global variable is weak. This
307   // occurs for, e.g., instantiated static data members and
308   // definitions explicitly marked weak.
309   if (Addr->getLinkage() == llvm::GlobalValue::WeakODRLinkage ||
310       Addr->getLinkage() == llvm::GlobalValue::WeakAnyLinkage) {
311     EmitCXXGuardedInit(*D, Addr, PerformInit);
312   } else {
313     EmitCXXGlobalVarDeclInit(*D, Addr, PerformInit);
314   }
315 
316   FinishFunction();
317 }
318 
319 void CodeGenFunction::GenerateCXXGlobalInitFunc(llvm::Function *Fn,
320                                                 llvm::Constant **Decls,
321                                                 unsigned NumDecls) {
322   StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
323                 getTypes().arrangeNullaryFunction(),
324                 FunctionArgList(), SourceLocation());
325 
326   RunCleanupsScope Scope(*this);
327 
328   // When building in Objective-C++ ARC mode, create an autorelease pool
329   // around the global initializers.
330   if (getLangOptions().ObjCAutoRefCount && getLangOptions().CPlusPlus) {
331     llvm::Value *token = EmitObjCAutoreleasePoolPush();
332     EmitObjCAutoreleasePoolCleanup(token);
333   }
334 
335   for (unsigned i = 0; i != NumDecls; ++i)
336     if (Decls[i])
337       Builder.CreateCall(Decls[i]);
338 
339   Scope.ForceCleanup();
340 
341   FinishFunction();
342 }
343 
344 void CodeGenFunction::GenerateCXXGlobalDtorFunc(llvm::Function *Fn,
345                   const std::vector<std::pair<llvm::WeakVH, llvm::Constant*> >
346                                                 &DtorsAndObjects) {
347   StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
348                 getTypes().arrangeNullaryFunction(),
349                 FunctionArgList(), SourceLocation());
350 
351   // Emit the dtors, in reverse order from construction.
352   for (unsigned i = 0, e = DtorsAndObjects.size(); i != e; ++i) {
353     llvm::Value *Callee = DtorsAndObjects[e - i - 1].first;
354     llvm::CallInst *CI = Builder.CreateCall(Callee,
355                                             DtorsAndObjects[e - i - 1].second);
356     // Make sure the call and the callee agree on calling convention.
357     if (llvm::Function *F = dyn_cast<llvm::Function>(Callee))
358       CI->setCallingConv(F->getCallingConv());
359   }
360 
361   FinishFunction();
362 }
363 
364 /// generateDestroyHelper - Generates a helper function which, when
365 /// invoked, destroys the given object.
366 llvm::Function *
367 CodeGenFunction::generateDestroyHelper(llvm::Constant *addr,
368                                        QualType type,
369                                        Destroyer *destroyer,
370                                        bool useEHCleanupForArray) {
371   FunctionArgList args;
372   ImplicitParamDecl dst(0, SourceLocation(), 0, getContext().VoidPtrTy);
373   args.push_back(&dst);
374 
375   const CGFunctionInfo &FI =
376     CGM.getTypes().arrangeFunctionDeclaration(getContext().VoidTy, args,
377                                               FunctionType::ExtInfo(),
378                                               /*variadic*/ false);
379   llvm::FunctionType *FTy = CGM.getTypes().GetFunctionType(FI);
380   llvm::Function *fn =
381     CreateGlobalInitOrDestructFunction(CGM, FTy, "__cxx_global_array_dtor");
382 
383   StartFunction(GlobalDecl(), getContext().VoidTy, fn, FI, args,
384                 SourceLocation());
385 
386   emitDestroy(addr, type, destroyer, useEHCleanupForArray);
387 
388   FinishFunction();
389 
390   return fn;
391 }
392