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llvm-project/clang/lib/CodeGen/CGDeclCXX.cpp
Reid Kleckner d8110b6558 [ms-cxxabi] Implement guard variables for static initialization 
Static locals requiring initialization are not thread safe on Windows.
Unfortunately, it's possible to create static locals that are actually
externally visible with inline functions and templates.  As a result, we
have to implement an initialization guard scheme that is compatible with
TUs built by MSVC, which makes thread safety prohibitively difficult.

MSVC's scheme is that every function that requires a guard gets an i32
bitfield.  Each static local is assigned a bit that indicates if it has
been initialized, up to 32 bits, at which point a new bitfield is
created.  MSVC rejects inline functions with more than 32 static locals,
and the externally visible mangling (?_B) only allows for one guard
variable per function.

On Eli's recommendation, I used MangleNumberingContext to track which
bit each static corresponds to.

Implements PR16888.

Reviewers: rjmccall, eli.friedman

Differential Revision: http://llvm-reviews.chandlerc.com/D1416

llvm-svn: 190427
2013-09-10 20:14:30 +00:00

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//===--- CGDeclCXX.cpp - Emit LLVM Code for C++ declarations --------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This contains code dealing with code generation of C++ declarations
//
//===----------------------------------------------------------------------===//
#include "CodeGenFunction.h"
#include "CGCXXABI.h"
#include "CGObjCRuntime.h"
#include "clang/Frontend/CodeGenOptions.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/IR/Intrinsics.h"
using namespace clang;
using namespace CodeGen;
static void EmitDeclInit(CodeGenFunction &CGF, const VarDecl &D,
llvm::Constant *DeclPtr) {
assert(D.hasGlobalStorage() && "VarDecl must have global storage!");
assert(!D.getType()->isReferenceType() &&
"Should not call EmitDeclInit on a reference!");
ASTContext &Context = CGF.getContext();
CharUnits alignment = Context.getDeclAlign(&D);
QualType type = D.getType();
LValue lv = CGF.MakeAddrLValue(DeclPtr, type, alignment);
const Expr *Init = D.getInit();
switch (CGF.getEvaluationKind(type)) {
case TEK_Scalar: {
CodeGenModule &CGM = CGF.CGM;
if (lv.isObjCStrong())
CGM.getObjCRuntime().EmitObjCGlobalAssign(CGF, CGF.EmitScalarExpr(Init),
DeclPtr, D.getTLSKind());
else if (lv.isObjCWeak())
CGM.getObjCRuntime().EmitObjCWeakAssign(CGF, CGF.EmitScalarExpr(Init),
DeclPtr);
else
CGF.EmitScalarInit(Init, &D, lv, false);
return;
}
case TEK_Complex:
CGF.EmitComplexExprIntoLValue(Init, lv, /*isInit*/ true);
return;
case TEK_Aggregate:
CGF.EmitAggExpr(Init, AggValueSlot::forLValue(lv,AggValueSlot::IsDestructed,
AggValueSlot::DoesNotNeedGCBarriers,
AggValueSlot::IsNotAliased));
return;
}
llvm_unreachable("bad evaluation kind");
}
/// Emit code to cause the destruction of the given variable with
/// static storage duration.
static void EmitDeclDestroy(CodeGenFunction &CGF, const VarDecl &D,
llvm::Constant *addr) {
CodeGenModule &CGM = CGF.CGM;
// FIXME: __attribute__((cleanup)) ?
QualType type = D.getType();
QualType::DestructionKind dtorKind = type.isDestructedType();
switch (dtorKind) {
case QualType::DK_none:
return;
case QualType::DK_cxx_destructor:
break;
case QualType::DK_objc_strong_lifetime:
case QualType::DK_objc_weak_lifetime:
// We don't care about releasing objects during process teardown.
assert(!D.getTLSKind() && "should have rejected this");
return;
}
llvm::Constant *function;
llvm::Constant *argument;
// Special-case non-array C++ destructors, where there's a function
// with the right signature that we can just call.
const CXXRecordDecl *record = 0;
if (dtorKind == QualType::DK_cxx_destructor &&
(record = type->getAsCXXRecordDecl())) {
assert(!record->hasTrivialDestructor());
CXXDestructorDecl *dtor = record->getDestructor();
function = CGM.GetAddrOfCXXDestructor(dtor, Dtor_Complete);
argument = addr;
// Otherwise, the standard logic requires a helper function.
} else {
function = CodeGenFunction(CGM)
.generateDestroyHelper(addr, type, CGF.getDestroyer(dtorKind),
CGF.needsEHCleanup(dtorKind), &D);
argument = llvm::Constant::getNullValue(CGF.Int8PtrTy);
}
CGM.getCXXABI().registerGlobalDtor(CGF, D, function, argument);
}
/// Emit code to cause the variable at the given address to be considered as
/// constant from this point onwards.
static void EmitDeclInvariant(CodeGenFunction &CGF, const VarDecl &D,
llvm::Constant *Addr) {
// Don't emit the intrinsic if we're not optimizing.
if (!CGF.CGM.getCodeGenOpts().OptimizationLevel)
return;
// Grab the llvm.invariant.start intrinsic.
llvm::Intrinsic::ID InvStartID = llvm::Intrinsic::invariant_start;
llvm::Constant *InvariantStart = CGF.CGM.getIntrinsic(InvStartID);
// Emit a call with the size in bytes of the object.
CharUnits WidthChars = CGF.getContext().getTypeSizeInChars(D.getType());
uint64_t Width = WidthChars.getQuantity();
llvm::Value *Args[2] = { llvm::ConstantInt::getSigned(CGF.Int64Ty, Width),
llvm::ConstantExpr::getBitCast(Addr, CGF.Int8PtrTy)};
CGF.Builder.CreateCall(InvariantStart, Args);
}
void CodeGenFunction::EmitCXXGlobalVarDeclInit(const VarDecl &D,
llvm::Constant *DeclPtr,
bool PerformInit) {
const Expr *Init = D.getInit();
QualType T = D.getType();
if (!T->isReferenceType()) {
if (PerformInit)
EmitDeclInit(*this, D, DeclPtr);
if (CGM.isTypeConstant(D.getType(), true))
EmitDeclInvariant(*this, D, DeclPtr);
else
EmitDeclDestroy(*this, D, DeclPtr);
return;
}
assert(PerformInit && "cannot have constant initializer which needs "
"destruction for reference");
unsigned Alignment = getContext().getDeclAlign(&D).getQuantity();
RValue RV = EmitReferenceBindingToExpr(Init);
EmitStoreOfScalar(RV.getScalarVal(), DeclPtr, false, Alignment, T);
}
static llvm::Function *
CreateGlobalInitOrDestructFunction(CodeGenModule &CGM,
llvm::FunctionType *ty,
const Twine &name,
bool TLS = false);
/// Create a stub function, suitable for being passed to atexit,
/// which passes the given address to the given destructor function.
static llvm::Constant *createAtExitStub(CodeGenModule &CGM, const VarDecl &VD,
llvm::Constant *dtor,
llvm::Constant *addr) {
// Get the destructor function type, void(*)(void).
llvm::FunctionType *ty = llvm::FunctionType::get(CGM.VoidTy, false);
SmallString<256> FnName;
{
llvm::raw_svector_ostream Out(FnName);
CGM.getCXXABI().getMangleContext().mangleDynamicAtExitDestructor(&VD, Out);
}
llvm::Function *fn =
CreateGlobalInitOrDestructFunction(CGM, ty, FnName.str());
CodeGenFunction CGF(CGM);
CGF.StartFunction(&VD, CGM.getContext().VoidTy, fn,
CGM.getTypes().arrangeNullaryFunction(), FunctionArgList(),
SourceLocation());
llvm::CallInst *call = CGF.Builder.CreateCall(dtor, addr);
// Make sure the call and the callee agree on calling convention.
if (llvm::Function *dtorFn =
dyn_cast<llvm::Function>(dtor->stripPointerCasts()))
call->setCallingConv(dtorFn->getCallingConv());
CGF.FinishFunction();
return fn;
}
/// Register a global destructor using the C atexit runtime function.
void CodeGenFunction::registerGlobalDtorWithAtExit(const VarDecl &VD,
llvm::Constant *dtor,
llvm::Constant *addr) {
// Create a function which calls the destructor.
llvm::Constant *dtorStub = createAtExitStub(CGM, VD, dtor, addr);
// extern "C" int atexit(void (*f)(void));
llvm::FunctionType *atexitTy =
llvm::FunctionType::get(IntTy, dtorStub->getType(), false);
llvm::Constant *atexit =
CGM.CreateRuntimeFunction(atexitTy, "atexit");
if (llvm::Function *atexitFn = dyn_cast<llvm::Function>(atexit))
atexitFn->setDoesNotThrow();
EmitNounwindRuntimeCall(atexit, dtorStub);
}
void CodeGenFunction::EmitCXXGuardedInit(const VarDecl &D,
llvm::GlobalVariable *DeclPtr,
bool PerformInit) {
// If we've been asked to forbid guard variables, emit an error now.
// This diagnostic is hard-coded for Darwin's use case; we can find
// better phrasing if someone else needs it.
if (CGM.getCodeGenOpts().ForbidGuardVariables)
CGM.Error(D.getLocation(),
"this initialization requires a guard variable, which "
"the kernel does not support");
CGM.getCXXABI().EmitGuardedInit(*this, D, DeclPtr, PerformInit);
}
static llvm::Function *
CreateGlobalInitOrDestructFunction(CodeGenModule &CGM,
llvm::FunctionType *FTy,
const Twine &Name, bool TLS) {
llvm::Function *Fn =
llvm::Function::Create(FTy, llvm::GlobalValue::InternalLinkage,
Name, &CGM.getModule());
if (!CGM.getLangOpts().AppleKext && !TLS) {
// Set the section if needed.
if (const char *Section =
CGM.getTarget().getStaticInitSectionSpecifier())
Fn->setSection(Section);
}
Fn->setCallingConv(CGM.getRuntimeCC());
if (!CGM.getLangOpts().Exceptions)
Fn->setDoesNotThrow();
if (CGM.getSanOpts().Address)
Fn->addFnAttr(llvm::Attribute::SanitizeAddress);
if (CGM.getSanOpts().Thread)
Fn->addFnAttr(llvm::Attribute::SanitizeThread);
if (CGM.getSanOpts().Memory)
Fn->addFnAttr(llvm::Attribute::SanitizeMemory);
return Fn;
}
void
CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl *D,
llvm::GlobalVariable *Addr,
bool PerformInit) {
llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
// Create a variable initialization function.
llvm::Function *Fn =
CreateGlobalInitOrDestructFunction(*this, FTy, "__cxx_global_var_init");
CodeGenFunction(*this).GenerateCXXGlobalVarDeclInitFunc(Fn, D, Addr,
PerformInit);
if (D->getTLSKind()) {
// FIXME: Should we support init_priority for thread_local?
// FIXME: Ideally, initialization of instantiated thread_local static data
// members of class templates should not trigger initialization of other
// entities in the TU.
// FIXME: We only need to register one __cxa_thread_atexit function for the
// entire TU.
CXXThreadLocalInits.push_back(Fn);
} else if (D->hasAttr<InitPriorityAttr>()) {
unsigned int order = D->getAttr<InitPriorityAttr>()->getPriority();
OrderGlobalInits Key(order, PrioritizedCXXGlobalInits.size());
PrioritizedCXXGlobalInits.push_back(std::make_pair(Key, Fn));
DelayedCXXInitPosition.erase(D);
} else if (D->getTemplateSpecializationKind() != TSK_ExplicitSpecialization &&
D->getTemplateSpecializationKind() != TSK_Undeclared) {
// C++ [basic.start.init]p2:
// Definitions of explicitly specialized class template static data
// members have ordered initialization. Other class template static data
// members (i.e., implicitly or explicitly instantiated specializations)
// have unordered initialization.
//
// As a consequence, we can put them into their own llvm.global_ctors entry.
// This should allow GlobalOpt to fire more often, and allow us to implement
// the Microsoft C++ ABI, which uses COMDAT elimination to avoid double
// initializaiton.
AddGlobalCtor(Fn);
DelayedCXXInitPosition.erase(D);
} else {
llvm::DenseMap<const Decl *, unsigned>::iterator I =
DelayedCXXInitPosition.find(D);
if (I == DelayedCXXInitPosition.end()) {
CXXGlobalInits.push_back(Fn);
} else {
assert(CXXGlobalInits[I->second] == 0);
CXXGlobalInits[I->second] = Fn;
DelayedCXXInitPosition.erase(I);
}
}
}
void CodeGenModule::EmitCXXThreadLocalInitFunc() {
llvm::Function *InitFn = 0;
if (!CXXThreadLocalInits.empty()) {
// Generate a guarded initialization function.
llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
InitFn = CreateGlobalInitOrDestructFunction(*this, FTy, "__tls_init",
/*TLS*/ true);
llvm::GlobalVariable *Guard = new llvm::GlobalVariable(
getModule(), Int8Ty, false, llvm::GlobalVariable::InternalLinkage,
llvm::ConstantInt::get(Int8Ty, 0), "__tls_guard");
Guard->setThreadLocal(true);
CodeGenFunction(*this)
.GenerateCXXGlobalInitFunc(InitFn, CXXThreadLocalInits, Guard);
}
getCXXABI().EmitThreadLocalInitFuncs(CXXThreadLocals, InitFn);
CXXThreadLocalInits.clear();
CXXThreadLocals.clear();
}
void
CodeGenModule::EmitCXXGlobalInitFunc() {
while (!CXXGlobalInits.empty() && !CXXGlobalInits.back())
CXXGlobalInits.pop_back();
if (CXXGlobalInits.empty() && PrioritizedCXXGlobalInits.empty())
return;
llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
// Create our global initialization function.
if (!PrioritizedCXXGlobalInits.empty()) {
SmallVector<llvm::Constant*, 8> LocalCXXGlobalInits;
llvm::array_pod_sort(PrioritizedCXXGlobalInits.begin(),
PrioritizedCXXGlobalInits.end());
// Iterate over "chunks" of ctors with same priority and emit each chunk
// into separate function. Note - everything is sorted first by priority,
// second - by lex order, so we emit ctor functions in proper order.
for (SmallVectorImpl<GlobalInitData >::iterator
I = PrioritizedCXXGlobalInits.begin(),
E = PrioritizedCXXGlobalInits.end(); I != E; ) {
SmallVectorImpl<GlobalInitData >::iterator
PrioE = std::upper_bound(I + 1, E, *I, GlobalInitPriorityCmp());
LocalCXXGlobalInits.clear();
unsigned Priority = I->first.priority;
// Compute the function suffix from priority. Prepend with zeroes to make
// sure the function names are also ordered as priorities.
std::string PrioritySuffix = llvm::utostr(Priority);
// Priority is always <= 65535 (enforced by sema)..
PrioritySuffix = std::string(6-PrioritySuffix.size(), '0')+PrioritySuffix;
llvm::Function *Fn =
CreateGlobalInitOrDestructFunction(*this, FTy,
"_GLOBAL__I_" + PrioritySuffix);
for (; I < PrioE; ++I)
LocalCXXGlobalInits.push_back(I->second);
CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn, LocalCXXGlobalInits);
AddGlobalCtor(Fn, Priority);
}
}
llvm::Function *Fn =
CreateGlobalInitOrDestructFunction(*this, FTy, "_GLOBAL__I_a");
CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn, CXXGlobalInits);
AddGlobalCtor(Fn);
CXXGlobalInits.clear();
PrioritizedCXXGlobalInits.clear();
}
void CodeGenModule::EmitCXXGlobalDtorFunc() {
if (CXXGlobalDtors.empty())
return;
llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
// Create our global destructor function.
llvm::Function *Fn =
CreateGlobalInitOrDestructFunction(*this, FTy, "_GLOBAL__D_a");
CodeGenFunction(*this).GenerateCXXGlobalDtorsFunc(Fn, CXXGlobalDtors);
AddGlobalDtor(Fn);
}
/// Emit the code necessary to initialize the given global variable.
void CodeGenFunction::GenerateCXXGlobalVarDeclInitFunc(llvm::Function *Fn,
const VarDecl *D,
llvm::GlobalVariable *Addr,
bool PerformInit) {
// Check if we need to emit debug info for variable initializer.
if (D->hasAttr<NoDebugAttr>())
DebugInfo = NULL; // disable debug info indefinitely for this function
StartFunction(GlobalDecl(D), getContext().VoidTy, Fn,
getTypes().arrangeNullaryFunction(),
FunctionArgList(), D->getInit()->getExprLoc());
// Use guarded initialization if the global variable is weak. This
// occurs for, e.g., instantiated static data members and
// definitions explicitly marked weak.
if (Addr->getLinkage() == llvm::GlobalValue::WeakODRLinkage ||
Addr->getLinkage() == llvm::GlobalValue::WeakAnyLinkage) {
EmitCXXGuardedInit(*D, Addr, PerformInit);
} else {
EmitCXXGlobalVarDeclInit(*D, Addr, PerformInit);
}
FinishFunction();
}
void
CodeGenFunction::GenerateCXXGlobalInitFunc(llvm::Function *Fn,
ArrayRef<llvm::Constant *> Decls,
llvm::GlobalVariable *Guard) {
StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
getTypes().arrangeNullaryFunction(),
FunctionArgList(), SourceLocation());
llvm::BasicBlock *ExitBlock = 0;
if (Guard) {
// If we have a guard variable, check whether we've already performed these
// initializations. This happens for TLS initialization functions.
llvm::Value *GuardVal = Builder.CreateLoad(Guard);
llvm::Value *Uninit = Builder.CreateIsNull(GuardVal, "guard.uninitialized");
// Mark as initialized before initializing anything else. If the
// initializers use previously-initialized thread_local vars, that's
// probably supposed to be OK, but the standard doesn't say.
Builder.CreateStore(llvm::ConstantInt::get(GuardVal->getType(), 1), Guard);
llvm::BasicBlock *InitBlock = createBasicBlock("init");
ExitBlock = createBasicBlock("exit");
Builder.CreateCondBr(Uninit, InitBlock, ExitBlock);
EmitBlock(InitBlock);
}
RunCleanupsScope Scope(*this);
// When building in Objective-C++ ARC mode, create an autorelease pool
// around the global initializers.
if (getLangOpts().ObjCAutoRefCount && getLangOpts().CPlusPlus) {
llvm::Value *token = EmitObjCAutoreleasePoolPush();
EmitObjCAutoreleasePoolCleanup(token);
}
for (unsigned i = 0, e = Decls.size(); i != e; ++i)
if (Decls[i])
EmitRuntimeCall(Decls[i]);
Scope.ForceCleanup();
if (ExitBlock) {
Builder.CreateBr(ExitBlock);
EmitBlock(ExitBlock);
}
FinishFunction();
}
void CodeGenFunction::GenerateCXXGlobalDtorsFunc(llvm::Function *Fn,
const std::vector<std::pair<llvm::WeakVH, llvm::Constant*> >
&DtorsAndObjects) {
StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
getTypes().arrangeNullaryFunction(),
FunctionArgList(), SourceLocation());
// Emit the dtors, in reverse order from construction.
for (unsigned i = 0, e = DtorsAndObjects.size(); i != e; ++i) {
llvm::Value *Callee = DtorsAndObjects[e - i - 1].first;
llvm::CallInst *CI = Builder.CreateCall(Callee,
DtorsAndObjects[e - i - 1].second);
// Make sure the call and the callee agree on calling convention.
if (llvm::Function *F = dyn_cast<llvm::Function>(Callee))
CI->setCallingConv(F->getCallingConv());
}
FinishFunction();
}
/// generateDestroyHelper - Generates a helper function which, when
/// invoked, destroys the given object.
llvm::Function *CodeGenFunction::generateDestroyHelper(
llvm::Constant *addr, QualType type, Destroyer *destroyer,
bool useEHCleanupForArray, const VarDecl *VD) {
FunctionArgList args;
ImplicitParamDecl dst(0, SourceLocation(), 0, getContext().VoidPtrTy);
args.push_back(&dst);
const CGFunctionInfo &FI =
CGM.getTypes().arrangeFunctionDeclaration(getContext().VoidTy, args,
FunctionType::ExtInfo(),
/*variadic*/ false);
llvm::FunctionType *FTy = CGM.getTypes().GetFunctionType(FI);
llvm::Function *fn =
CreateGlobalInitOrDestructFunction(CGM, FTy, "__cxx_global_array_dtor");
StartFunction(VD, getContext().VoidTy, fn, FI, args, SourceLocation());
emitDestroy(addr, type, destroyer, useEHCleanupForArray);
FinishFunction();
return fn;
}
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