CGDeclCXX.cpp revision 235633 
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
20using namespace clang;
21using namespace CodeGen;
22
23static 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.
57static 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.
106static 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
124void 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/// Register a global destructor using __cxa_atexit.
149static void emitGlobalDtorWithCXAAtExit(CodeGenFunction &CGF,
150                                        llvm::Constant *dtor,
151                                        llvm::Constant *addr) {
152  // We're assuming that the destructor function is something we can
153  // reasonably call with the default CC.  Go ahead and cast it to the
154  // right prototype.
155  llvm::Type *dtorTy =
156    llvm::FunctionType::get(CGF.VoidTy, CGF.Int8PtrTy, false)->getPointerTo();
157
158  // extern "C" int __cxa_atexit(void (*f)(void *), void *p, void *d);
159  llvm::Type *paramTys[] = { dtorTy, CGF.Int8PtrTy, CGF.Int8PtrTy };
160  llvm::FunctionType *atexitTy =
161    llvm::FunctionType::get(CGF.IntTy, paramTys, false);
162
163  // Fetch the actual function.
164  llvm::Constant *atexit =
165    CGF.CGM.CreateRuntimeFunction(atexitTy, "__cxa_atexit");
166  if (llvm::Function *fn = dyn_cast<llvm::Function>(atexit))
167    fn->setDoesNotThrow();
168
169  // Create a variable that binds the atexit to this shared object.
170  llvm::Constant *handle =
171    CGF.CGM.CreateRuntimeVariable(CGF.Int8Ty, "__dso_handle");
172
173  llvm::Value *args[] = {
174    llvm::ConstantExpr::getBitCast(dtor, dtorTy),
175    llvm::ConstantExpr::getBitCast(addr, CGF.Int8PtrTy),
176    handle
177  };
178  CGF.Builder.CreateCall(atexit, args);
179}
180
181static llvm::Function *
182CreateGlobalInitOrDestructFunction(CodeGenModule &CGM,
183                                   llvm::FunctionType *ty,
184                                   const Twine &name);
185
186/// Create a stub function, suitable for being passed to atexit,
187/// which passes the given address to the given destructor function.
188static llvm::Constant *createAtExitStub(CodeGenModule &CGM,
189                                        llvm::Constant *dtor,
190                                        llvm::Constant *addr) {
191  // Get the destructor function type, void(*)(void).
192  llvm::FunctionType *ty = llvm::FunctionType::get(CGM.VoidTy, false);
193  llvm::Function *fn =
194    CreateGlobalInitOrDestructFunction(CGM, ty,
195                                       Twine("__dtor_", addr->getName()));
196
197  CodeGenFunction CGF(CGM);
198
199  CGF.StartFunction(GlobalDecl(), CGM.getContext().VoidTy, fn,
200                    CGM.getTypes().arrangeNullaryFunction(),
201                    FunctionArgList(), SourceLocation());
202
203  llvm::CallInst *call = CGF.Builder.CreateCall(dtor, addr);
204
205 // Make sure the call and the callee agree on calling convention.
206  if (llvm::Function *dtorFn =
207        dyn_cast<llvm::Function>(dtor->stripPointerCasts()))
208    call->setCallingConv(dtorFn->getCallingConv());
209
210  CGF.FinishFunction();
211
212  return fn;
213}
214
215/// Register a global destructor using atexit.
216static void emitGlobalDtorWithAtExit(CodeGenFunction &CGF,
217                                     llvm::Constant *dtor,
218                                     llvm::Constant *addr) {
219  // Create a function which calls the destructor.
220  llvm::Constant *dtorStub = createAtExitStub(CGF.CGM, dtor, addr);
221
222  // extern "C" int atexit(void (*f)(void));
223  llvm::FunctionType *atexitTy =
224    llvm::FunctionType::get(CGF.IntTy, dtorStub->getType(), false);
225
226  llvm::Constant *atexit =
227    CGF.CGM.CreateRuntimeFunction(atexitTy, "atexit");
228  if (llvm::Function *atexitFn = dyn_cast<llvm::Function>(atexit))
229    atexitFn->setDoesNotThrow();
230
231  CGF.Builder.CreateCall(atexit, dtorStub);
232}
233
234void CodeGenFunction::EmitCXXGlobalDtorRegistration(llvm::Constant *dtor,
235                                                    llvm::Constant *addr) {
236  // Use __cxa_atexit if available.
237  if (CGM.getCodeGenOpts().CXAAtExit) {
238    emitGlobalDtorWithCXAAtExit(*this, dtor, addr);
239    return;
240  }
241
242  // In Apple kexts, we want to add a global destructor entry.
243  // FIXME: shouldn't this be guarded by some variable?
244  if (CGM.getContext().getLangOpts().AppleKext) {
245    // Generate a global destructor entry.
246    CGM.AddCXXDtorEntry(dtor, addr);
247    return;
248  }
249
250  // Otherwise, we just use atexit.
251  emitGlobalDtorWithAtExit(*this, dtor, addr);
252}
253
254void CodeGenFunction::EmitCXXGuardedInit(const VarDecl &D,
255                                         llvm::GlobalVariable *DeclPtr,
256                                         bool PerformInit) {
257  // If we've been asked to forbid guard variables, emit an error now.
258  // This diagnostic is hard-coded for Darwin's use case;  we can find
259  // better phrasing if someone else needs it.
260  if (CGM.getCodeGenOpts().ForbidGuardVariables)
261    CGM.Error(D.getLocation(),
262              "this initialization requires a guard variable, which "
263              "the kernel does not support");
264
265  CGM.getCXXABI().EmitGuardedInit(*this, D, DeclPtr, PerformInit);
266}
267
268static llvm::Function *
269CreateGlobalInitOrDestructFunction(CodeGenModule &CGM,
270                                   llvm::FunctionType *FTy,
271                                   const Twine &Name) {
272  llvm::Function *Fn =
273    llvm::Function::Create(FTy, llvm::GlobalValue::InternalLinkage,
274                           Name, &CGM.getModule());
275  if (!CGM.getContext().getLangOpts().AppleKext) {
276    // Set the section if needed.
277    if (const char *Section =
278          CGM.getContext().getTargetInfo().getStaticInitSectionSpecifier())
279      Fn->setSection(Section);
280  }
281
282  if (!CGM.getLangOpts().Exceptions)
283    Fn->setDoesNotThrow();
284
285  return Fn;
286}
287
288void
289CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl *D,
290                                            llvm::GlobalVariable *Addr,
291                                            bool PerformInit) {
292  llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
293
294  // Create a variable initialization function.
295  llvm::Function *Fn =
296    CreateGlobalInitOrDestructFunction(*this, FTy, "__cxx_global_var_init");
297
298  CodeGenFunction(*this).GenerateCXXGlobalVarDeclInitFunc(Fn, D, Addr,
299                                                          PerformInit);
300
301  if (D->hasAttr<InitPriorityAttr>()) {
302    unsigned int order = D->getAttr<InitPriorityAttr>()->getPriority();
303    OrderGlobalInits Key(order, PrioritizedCXXGlobalInits.size());
304    PrioritizedCXXGlobalInits.push_back(std::make_pair(Key, Fn));
305    DelayedCXXInitPosition.erase(D);
306  }
307  else {
308    llvm::DenseMap<const Decl *, unsigned>::iterator I =
309      DelayedCXXInitPosition.find(D);
310    if (I == DelayedCXXInitPosition.end()) {
311      CXXGlobalInits.push_back(Fn);
312    } else {
313      assert(CXXGlobalInits[I->second] == 0);
314      CXXGlobalInits[I->second] = Fn;
315      DelayedCXXInitPosition.erase(I);
316    }
317  }
318}
319
320void
321CodeGenModule::EmitCXXGlobalInitFunc() {
322  while (!CXXGlobalInits.empty() && !CXXGlobalInits.back())
323    CXXGlobalInits.pop_back();
324
325  if (CXXGlobalInits.empty() && PrioritizedCXXGlobalInits.empty())
326    return;
327
328  llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
329
330  // Create our global initialization function.
331  llvm::Function *Fn =
332    CreateGlobalInitOrDestructFunction(*this, FTy, "_GLOBAL__I_a");
333
334  if (!PrioritizedCXXGlobalInits.empty()) {
335    SmallVector<llvm::Constant*, 8> LocalCXXGlobalInits;
336    llvm::array_pod_sort(PrioritizedCXXGlobalInits.begin(),
337                         PrioritizedCXXGlobalInits.end());
338    for (unsigned i = 0; i < PrioritizedCXXGlobalInits.size(); i++) {
339      llvm::Function *Fn = PrioritizedCXXGlobalInits[i].second;
340      LocalCXXGlobalInits.push_back(Fn);
341    }
342    LocalCXXGlobalInits.append(CXXGlobalInits.begin(), CXXGlobalInits.end());
343    CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn,
344                                                    &LocalCXXGlobalInits[0],
345                                                    LocalCXXGlobalInits.size());
346  }
347  else
348    CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn,
349                                                     &CXXGlobalInits[0],
350                                                     CXXGlobalInits.size());
351  AddGlobalCtor(Fn);
352  CXXGlobalInits.clear();
353  PrioritizedCXXGlobalInits.clear();
354}
355
356void CodeGenModule::EmitCXXGlobalDtorFunc() {
357  if (CXXGlobalDtors.empty())
358    return;
359
360  llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
361
362  // Create our global destructor function.
363  llvm::Function *Fn =
364    CreateGlobalInitOrDestructFunction(*this, FTy, "_GLOBAL__D_a");
365
366  CodeGenFunction(*this).GenerateCXXGlobalDtorsFunc(Fn, CXXGlobalDtors);
367  AddGlobalDtor(Fn);
368}
369
370/// Emit the code necessary to initialize the given global variable.
371void CodeGenFunction::GenerateCXXGlobalVarDeclInitFunc(llvm::Function *Fn,
372                                                       const VarDecl *D,
373                                                 llvm::GlobalVariable *Addr,
374                                                       bool PerformInit) {
375  StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
376                getTypes().arrangeNullaryFunction(),
377                FunctionArgList(), SourceLocation());
378
379  // Use guarded initialization if the global variable is weak. This
380  // occurs for, e.g., instantiated static data members and
381  // definitions explicitly marked weak.
382  if (Addr->getLinkage() == llvm::GlobalValue::WeakODRLinkage ||
383      Addr->getLinkage() == llvm::GlobalValue::WeakAnyLinkage) {
384    EmitCXXGuardedInit(*D, Addr, PerformInit);
385  } else {
386    EmitCXXGlobalVarDeclInit(*D, Addr, PerformInit);
387  }
388
389  FinishFunction();
390}
391
392void CodeGenFunction::GenerateCXXGlobalInitFunc(llvm::Function *Fn,
393                                                llvm::Constant **Decls,
394                                                unsigned NumDecls) {
395  StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
396                getTypes().arrangeNullaryFunction(),
397                FunctionArgList(), SourceLocation());
398
399  RunCleanupsScope Scope(*this);
400
401  // When building in Objective-C++ ARC mode, create an autorelease pool
402  // around the global initializers.
403  if (getLangOpts().ObjCAutoRefCount && getLangOpts().CPlusPlus) {
404    llvm::Value *token = EmitObjCAutoreleasePoolPush();
405    EmitObjCAutoreleasePoolCleanup(token);
406  }
407
408  for (unsigned i = 0; i != NumDecls; ++i)
409    if (Decls[i])
410      Builder.CreateCall(Decls[i]);
411
412  Scope.ForceCleanup();
413
414  FinishFunction();
415}
416
417void CodeGenFunction::GenerateCXXGlobalDtorsFunc(llvm::Function *Fn,
418                  const std::vector<std::pair<llvm::WeakVH, llvm::Constant*> >
419                                                &DtorsAndObjects) {
420  StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
421                getTypes().arrangeNullaryFunction(),
422                FunctionArgList(), SourceLocation());
423
424  // Emit the dtors, in reverse order from construction.
425  for (unsigned i = 0, e = DtorsAndObjects.size(); i != e; ++i) {
426    llvm::Value *Callee = DtorsAndObjects[e - i - 1].first;
427    llvm::CallInst *CI = Builder.CreateCall(Callee,
428                                            DtorsAndObjects[e - i - 1].second);
429    // Make sure the call and the callee agree on calling convention.
430    if (llvm::Function *F = dyn_cast<llvm::Function>(Callee))
431      CI->setCallingConv(F->getCallingConv());
432  }
433
434  FinishFunction();
435}
436
437/// generateDestroyHelper - Generates a helper function which, when
438/// invoked, destroys the given object.
439llvm::Function *
440CodeGenFunction::generateDestroyHelper(llvm::Constant *addr,
441                                       QualType type,
442                                       Destroyer *destroyer,
443                                       bool useEHCleanupForArray) {
444  FunctionArgList args;
445  ImplicitParamDecl dst(0, SourceLocation(), 0, getContext().VoidPtrTy);
446  args.push_back(&dst);
447
448  const CGFunctionInfo &FI =
449    CGM.getTypes().arrangeFunctionDeclaration(getContext().VoidTy, args,
450                                              FunctionType::ExtInfo(),
451                                              /*variadic*/ false);
452  llvm::FunctionType *FTy = CGM.getTypes().GetFunctionType(FI);
453  llvm::Function *fn =
454    CreateGlobalInitOrDestructFunction(CGM, FTy, "__cxx_global_array_dtor");
455
456  StartFunction(GlobalDecl(), getContext().VoidTy, fn, FI, args,
457                SourceLocation());
458
459  emitDestroy(addr, type, destroyer, useEHCleanupForArray);
460
461  FinishFunction();
462
463  return fn;
464}
465