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TLS initializers, for example constructors of thread-local variables, don't
necessarily get called. If for example a thread was created before a module is
loaded, the module's TLS initializers are not executed for this particular
thread.
This is why Microsoft added support for dynamic TLS initialization. Before
every use of thread-local variables, a check is added that runs the module's
TLS initializers on-demand.
To do this, the method `__dyn_tls_on_demand_init` gets called. Internally, it
simply calls `__dyn_tls_init`.
To prevent calling initializers again, a guard variable called `__tls_guard` is
checked and set before executing the call.
No additional TLS initializer that sets the guard needs to be emitted, as the
guard always gets set by `__dyn_tls_init`.
The guard is also checked again within `__dyn_tls_init`. This makes our check
redundant, however, as Microsoft's compiler also emits this check, the
behaviour is adopted here.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D115456
Files:
clang/lib/CodeGen/MicrosoftCXXABI.cpp
clang/test/CodeGenCXX/ms-thread_local.cpp
Index: clang/test/CodeGenCXX/ms-thread_local.cpp
===================================================================
--- clang/test/CodeGenCXX/ms-thread_local.cpp
+++ clang/test/CodeGenCXX/ms-thread_local.cpp
@@ -17,10 +17,20 @@
// CHECK-DAG: @"?b@@3UA@@A" = dso_local thread_local global %struct.A zeroinitializer, align 1
// CHECK-DAG: @"__tls_init$initializer$" = internal constant void ()* @__tls_init, section ".CRT$XDU"
+// CHECK-DAG: @__tls_guard = external dso_local thread_local global i8
// CHECK-LD-DAG: @"?b@@3UA@@A" = dso_local thread_local(localdynamic) global %struct.A zeroinitializer, align 1
// CHECK-LD-DAG: @"__tls_init$initializer$" = internal constant void ()* @__tls_init, section ".CRT$XDU"
+// CHECK-LD-DAG: @__tls_guard = external dso_local thread_local global i8
thread_local A b;
+// CHECK-LABEL: declare dso_local void @__dyn_tls_on_demand_init()
+// CHECK-LD-LABEL: declare dso_local void @__dyn_tls_on_demand_init()
+
+// CHECK-LABEL: define dso_local void @"?f@@YA?AUA@@XZ"(%struct.A* noalias sret(%struct.A) align 1 %agg.result)
+// CHECK: call void @__dyn_tls_on_demand_init()
+// CHECK-LD-LABEL: define dso_local void @"?f@@YA?AUA@@XZ"(%struct.A* noalias sret(%struct.A) align 1 %agg.result)
+// CHECK-LD: call void @__dyn_tls_on_demand_init()
+
// CHECK-LABEL: define internal void @__tls_init()
// CHECK: call void @"??__Eb@@YAXXZ"
// CHECK-LD-LABEL: define internal void @__tls_init()
Index: clang/lib/CodeGen/MicrosoftCXXABI.cpp
===================================================================
--- clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -401,7 +401,7 @@
ArrayRef<const VarDecl *> CXXThreadLocalInitVars) override;
bool usesThreadWrapperFunction(const VarDecl *VD) const override {
- return false;
+ return true;
}
LValue EmitThreadLocalVarDeclLValue(CodeGenFunction &CGF, const VarDecl *VD,
QualType LValType) override;
@@ -2397,11 +2397,87 @@
}
}
+static llvm::GlobalValue *getTlsGuardVar(CodeGenModule &CGM) {
+ llvm::Type *VTy = llvm::Type::getInt8Ty(CGM.getLLVMContext());
+ llvm::Constant *TlsGuardConstant =
+ CGM.CreateRuntimeVariable(VTy, "__tls_guard");
+ llvm::GlobalValue *TlsGuard = cast<llvm::GlobalValue>(TlsGuardConstant);
+
+ TlsGuard->setThreadLocal(true);
+
+ return TlsGuard;
+}
+
+static llvm::FunctionCallee getDynTlsOnDemandInitFn(CodeGenModule &CGM) {
+ llvm::FunctionType *FTy =
+ llvm::FunctionType::get(llvm::Type::getVoidTy(CGM.getLLVMContext()), {},
+ /*isVarArg=*/false);
+ return CGM.CreateRuntimeFunction(
+ FTy, "__dyn_tls_on_demand_init",
+ llvm::AttributeList::get(CGM.getLLVMContext(),
+ llvm::AttributeList::FunctionIndex,
+ llvm::Attribute::NoUnwind),
+ /*Local=*/true);
+}
+
+static void emitTlsGuardCheck(CodeGenFunction &CGF, llvm::GlobalValue *TlsGuard,
+ llvm::BasicBlock *DynInitBB,
+ llvm::BasicBlock *ContinueBB) {
+ llvm::LoadInst *TlsGuardValue =
+ CGF.Builder.CreateLoad(Address(TlsGuard, CharUnits::One()));
+ llvm::Value *CmpResult =
+ CGF.Builder.CreateICmpEQ(TlsGuardValue, CGF.Builder.getInt8(0));
+ CGF.Builder.CreateCondBr(CmpResult, DynInitBB, ContinueBB);
+}
+
+static void emitDynamicTlsInitialization(CodeGenFunction &CGF,
+ llvm::GlobalValue *TlsGuard,
+ llvm::BasicBlock *ContinueBB) {
+ CGF.Builder.CreateStore(CGF.Builder.getInt8(1),
+ Address(TlsGuard, CharUnits::One()));
+
+ llvm::FunctionCallee Initializer = getDynTlsOnDemandInitFn(CGF.CGM);
+ llvm::Function *InitializerFunction =
+ cast<llvm::Function>(Initializer.getCallee());
+ llvm::CallInst *CallVal = CGF.Builder.CreateCall(InitializerFunction);
+ CallVal->setCallingConv(InitializerFunction->getCallingConv());
+
+ CGF.Builder.CreateBr(ContinueBB);
+}
+
+static void emitDynamicTlsInitializationSequence(CodeGenFunction &CGF) {
+ llvm::BasicBlock *DynInitBB =
+ CGF.createBasicBlock("dyntls.dyn_init", CGF.CurFn);
+ llvm::BasicBlock *ContinueBB =
+ CGF.createBasicBlock("dyntls.continue", CGF.CurFn);
+
+ llvm::GlobalValue *TlsGuard = getTlsGuardVar(CGF.CGM);
+
+ emitTlsGuardCheck(CGF, TlsGuard, DynInitBB, ContinueBB);
+ CGF.Builder.SetInsertPoint(DynInitBB);
+ emitDynamicTlsInitialization(CGF, TlsGuard, ContinueBB);
+ CGF.Builder.SetInsertPoint(ContinueBB);
+}
+
LValue MicrosoftCXXABI::EmitThreadLocalVarDeclLValue(CodeGenFunction &CGF,
const VarDecl *VD,
QualType LValType) {
- CGF.CGM.ErrorUnsupported(VD, "thread wrappers");
- return LValue();
+ emitDynamicTlsInitializationSequence(CGF);
+
+ llvm::Value *V = CGF.CGM.GetAddrOfGlobalVar(VD);
+ llvm::Type *RealVarTy = CGF.getTypes().ConvertTypeForMem(VD->getType());
+
+ unsigned AS = cast<llvm::PointerType>(V->getType())->getAddressSpace();
+ V = CGF.Builder.CreateBitCast(V, RealVarTy->getPointerTo(AS));
+
+ CharUnits Alignment = CGF.getContext().getDeclAlign(VD);
+ Address Addr(V, Alignment);
+
+ LValue LV = VD->getType()->isReferenceType()
+ ? CGF.EmitLoadOfReferenceLValue(Addr, VD->getType(),
+ AlignmentSource::Decl)
+ : CGF.MakeAddrLValue(Addr, LValType, AlignmentSource::Decl);
+ return LV;
}
static ConstantAddress getInitThreadEpochPtr(CodeGenModule &CGM) {
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