[PATCH] D117500: [clang] Mention MS on-demand TLS initialization in release notes

[Maurice Heumann via Phabricator via cfe-commits]

momo5502 added a comment.

Seems like this can be merged, right?


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[PATCH] D115456: Implement on-demand TLS initialization for Microsoft CXX ABI

[Maurice Heumann via Phabricator via cfe-commits]

momo5502 updated this revision to Diff 396783.
momo5502 marked 4 inline comments as done.
momo5502 added a comment.

Comments were addressed


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Files:
  clang/include/clang/Basic/LangOptions.h
  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
@@ -1,5 +1,6 @@
-// RUN: %clang_cc1 %s -std=c++1y -triple=i686-pc-win32 -emit-llvm -o - | FileCheck %s
-// RUN: %clang_cc1 %s  -std=c++1y -triple=i686-pc-win32 -ftls-model=local-dynamic -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-LD
+// RUN: %clang_cc1 %s -std=c++1y -triple=i686-pc-win32 -fms-compatibility-version=19.25 -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 %s -std=c++1y -triple=i686-pc-win32 -fms-compatibility-version=19.20 -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-LEGACY
+// RUN: %clang_cc1 %s -std=c++1y -triple=i686-pc-win32 -fms-compatibility-version=19.25 -ftls-model=local-dynamic -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-LD
 
 struct A {
   A();
@@ -17,10 +18,23 @@
 
 // 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
+// CHECK-LEGACY-NOT: @__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-LEGACY-NOT: 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-LEGACY-NOT: 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 +401,8 @@
   ArrayRef CXXThreadLocalInitVars) override;
 
   bool usesThreadWrapperFunction(const VarDecl *VD) const override {
-return false;
+return getContext().getLangOpts().isCompatibleWithMSVC(
+LangOptions::MSVC2019_5);
   }
   LValue EmitThreadLocalVarDeclLValue(CodeGenFunction &CGF, const VarDecl *VD,
   QualType LValType) override;
@@ -2397,11 +2398,97 @@
   }
 }
 
+static llvm::GlobalValue *getTlsGuardVar(CodeGenModule &CGM) {
+  // __tls_guard comes from the MSVC runtime and reflects
+  // whether TLS has been initialized for a particular thread.
+  // It is set from within __dyn_tls_init by the runtime.
+  // Every library and executable has its own variable.
+  llvm::Type *VTy = llvm::Type::getInt8Ty(CGM.getLLVMContext());
+  llvm::Constant *TlsGuardConstant =
+  CGM.CreateRuntimeVariable(VTy, "__tls_guard");
+  llvm::GlobalValue *TlsGuard = cast(TlsGuardConstant);
+
+  TlsGuard->setThreadLocal(true);
+
+  return TlsGuard;
+}
+
+static llvm::FunctionCallee getDynTlsOnDemandInitFn(CodeGenModule &CGM) {
+  // __dyn_tls_on_demand_init comes from the MSVC runtime and triggers
+  // dynamic TLS initialization by calling __dyn_tls_init internally.
+  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

[PATCH] D115456: Implement on-demand TLS initialization for Microsoft CXX ABI

[Maurice Heumann via Phabricator via cfe-commits]

momo5502 added a comment.

In D115456#3216811 , @majnemer wrote:

> This is looking great! Just a few more questions.
>
> What is the behavior with something like:
>
>   thread_local int x = 2;
>   int f() {
> return x;
>   }
>
> I'm wondering if we need to move this logic 
> 
>  into the generic C++ ABI implementation.

The MS compiler only emits the dynamic initializers for variables with 
constructors/destructors, just like it is currently done here for the Itanium 
ABI.
I also thought about adopting that behaviour, but I think threre are edge-cases 
when triggering dynamic TLS initialization even for constant variables is 
useful.
For example there might be custom TLS callbacks that can affect the value of 
this variable.

If desired, I can change it to match the behaviour of MS, but I thought it 
could be beneficial to diverge in this case.


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[PATCH] D115456: Implement on-demand TLS initialization for Microsoft CXX ABI

[Maurice Heumann via Phabricator via cfe-commits]

momo5502 updated this revision to Diff 397107.
momo5502 added a comment.

In D115456#3217857 , @majnemer wrote:

> In D115456#3217595 , @momo5502 
> wrote:
>
>> In D115456#3216811 , @majnemer 
>> wrote:
>>
>>> This is looking great! Just a few more questions.
>>>
>>> What is the behavior with something like:
>>>
>>>   thread_local int x = 2;
>>>   int f() {
>>> return x;
>>>   }
>>>
>>> I'm wondering if we need to move this logic 
>>> 
>>>  into the generic C++ ABI implementation.
>>
>> The MS compiler only emits the dynamic initializers for variables with 
>> constructors/destructors, just like it is currently done here for the 
>> Itanium ABI.
>> I also thought about adopting that behaviour, but I think threre are 
>> edge-cases when triggering dynamic TLS initialization even for constant 
>> variables is useful.
>> For example there might be custom TLS callbacks that can affect the value of 
>> this variable.
>>
>> If desired, I can change it to match the behaviour of MS, but I thought it 
>> could be beneficial to diverge in this case.
>
> IMO, it is probably best to match behavior here within reason (ignoring bugs 
> latent in MSVC) here. My thinking is that in the face of COMDATs, we cannot 
> ensure which copy of an inline function will make its way to the binary and 
> different link orders would provide different behavior.

Fair enough. Logic has now moved to the generic C++ ABI implementation and the 
test was adjusted.


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Files:
  clang/include/clang/Basic/LangOptions.h
  clang/lib/CodeGen/CGCXXABI.cpp
  clang/lib/CodeGen/CGCXXABI.h
  clang/lib/CodeGen/ItaniumCXXABI.cpp
  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
@@ -1,5 +1,6 @@
-// RUN: %clang_cc1 %s -std=c++1y -triple=i686-pc-win32 -emit-llvm -o - | FileCheck %s
-// RUN: %clang_cc1 %s  -std=c++1y -triple=i686-pc-win32 -ftls-model=local-dynamic -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-LD
+// RUN: %clang_cc1 %s -std=c++1y -triple=i686-pc-win32 -fms-compatibility-version=19.25 -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 %s -std=c++1y -triple=i686-pc-win32 -fms-compatibility-version=19.20 -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-LEGACY
+// RUN: %clang_cc1 %s -std=c++1y -triple=i686-pc-win32 -fms-compatibility-version=19.25 -ftls-model=local-dynamic -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-LD
 
 struct A {
   A();
@@ -17,14 +18,22 @@
 
 // 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
+// CHECK-LEGACY-NOT: @__tls_guard = external dso_local thread_local global i8
 thread_local A b;
 
-// CHECK-LABEL: define internal void @__tls_init()
-// CHECK: call void @"??__Eb@@YAXXZ"
-// CHECK-LD-LABEL: define internal void @__tls_init()
-// CHECK-LD: call void @"??__Eb@@YAXXZ"
+// CHECK-LABEL: declare dso_local void @__dyn_tls_on_demand_init()
+// CHECK-LD-LABEL: declare dso_local void @__dyn_tls_on_demand_init()
+// CHECK-LEGACY-NOT: 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-LEGACY-NOT: call void @__dyn_tls_on_demand_init()
 
 thread_local A &c = b;
 thread_local A &d = c;
@@ -35,6 +44,22 @@
   return c;
 }
 
+// CHECK-LABEL: define dso_local i32 @"?g@@YAHXZ"()
+// CHECK-NOT: call void @__dyn_tls_on_demand_init()
+// CHECK-LD-LABEL: define dso_local i32 @"?g@@YAHXZ"()
+// CHECK-LD-NOT: call void @__dyn_tls_on_demand_init()
+
+thread_local int e = 2;
+
+int g() {
+  return e;
+}
+
+// CHECK-LABEL: define internal void @__tls_init()
+// CHECK: call void @"??__Eb@@YAXXZ"
+// CHECK-LD-LABEL: define internal void @__tls_init()
+// CHECK-LD: call void @"??__Eb@@YAXXZ"
+
 // CHECK: 

[PATCH] D117500: [clang] Mention MS on-demand TLS initialization in release notes

[Maurice Heumann via Phabricator via cfe-commits]

momo5502 created this revision.
momo5502 added reviewers: majnemer, hans.
momo5502 added a project: clang.
momo5502 requested review of this revision.
Herald added a subscriber: cfe-commits.

In change https://reviews.llvm.org/D115456 on-demand TLS initialization for 
Microsoft CXX ABI was added.

This mentions the change in the release notes.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D117500

Files:
  clang/docs/ReleaseNotes.rst


Index: clang/docs/ReleaseNotes.rst
===
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -136,6 +136,8 @@
   or pass ``/permissive`` to disable C++ operator names altogether. See
   `PR42427 ` for more info.
 
+- Support for on-demand initialization of TLS variables was added.
+
 C Language Changes in Clang
 ---
 


Index: clang/docs/ReleaseNotes.rst
===
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -136,6 +136,8 @@
   or pass ``/permissive`` to disable C++ operator names altogether. See
   `PR42427 ` for more info.
 
+- Support for on-demand initialization of TLS variables was added.
+
 C Language Changes in Clang
 ---
 
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[PATCH] D115456: [MS] Implement on-demand TLS initialization for Microsoft CXX ABI

[Maurice Heumann via Phabricator via cfe-commits]

momo5502 added a comment.

In D115456#3248313 , @hans wrote:

> Looks great, thanks! Maurice, do you want to add a note about this to 
> docs/ReleaseNotes.rst?

Good point. I created a new change: https://reviews.llvm.org/D117500


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[PATCH] D115456: Implement on-demand TLS initialization for Microsoft CXX ABI

[Maurice Heumann via Phabricator via cfe-commits]

momo5502 created this revision.
momo5502 added reviewers: rnk, eugenis.
momo5502 added a project: clang.
momo5502 requested review of this revision.
Herald added a subscriber: cfe-commits.

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 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(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::Funct

[PATCH] D115456: Implement on-demand TLS initialization for Microsoft CXX ABI

[Maurice Heumann via Phabricator via cfe-commits]

momo5502 updated this revision to Diff 393247.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D115456/new/

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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 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 +2397,83 @@
   }
 }
 
+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(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(Initializer.getCallee());
+  llvm::CallInst *CallVal = CGF.Builder.CreateCall(InitializerFunction);
+  CallVal->setCallingConv(InitializerFunction->getCallingConv());
+
+  CGF.Builder.CreateBr(ContinueBB);
+}
+
 LValue MicrosoftCXXABI::EmitThreadLocalVarDeclLValue(CodeGenFunction &CGF,
  const VarDecl *VD,
  QualType LValType) {
-  CGF.CGM.ErrorUnsupported(VD, "thread wrappers");
-  return LValue();
+  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);
+
+  l

[PATCH] D115456: Implement on-demand TLS initialization for Microsoft CXX ABI

[Maurice Heumann via Phabricator via cfe-commits]

momo5502 updated this revision to Diff 395856.
momo5502 edited the summary of this revision.
momo5502 added a comment.
Herald added a subscriber: dexonsmith.

A call to `isCompatibleWithMSVC` was added with the proper version that 
introduced the change (1925) and comments describing the intention of the 
change were added.

Additionally, a bug was fixed. Setting the guard variable to true before doing 
the initialization breaks the feature, as the guard needs to be false for 
`__dyn_tls_init` to work.
Not emitting the store to the guard should be fine, as it will be set by 
`__dyn_tls_init` anyways. The behaviour is now identical to the way Microsoft's 
compiler does it.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D115456/new/

https://reviews.llvm.org/D115456

Files:
  clang/include/clang/Basic/LangOptions.h
  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
@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 %s -std=c++1y -triple=i686-pc-win32 -emit-llvm -o - | FileCheck %s
-// RUN: %clang_cc1 %s  -std=c++1y -triple=i686-pc-win32 -ftls-model=local-dynamic -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-LD
+// RUN: %clang_cc1 %s -std=c++1y -triple=i686-pc-win32 -fms-compatibility-version=1925 -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 %s -std=c++1y -triple=i686-pc-win32 -fms-compatibility-version=1925 -ftls-model=local-dynamic -emit-llvm -o - | FileCheck %s -check-prefix=CHECK-LD
 
 struct A {
   A();
@@ -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 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 +2397,99 @@
   }
 }
 
+static llvm::GlobalValue *getTlsGuardVar(CodeGenModule &CGM) {
+  // __tls_guard comes from the MSVC runtime and reflects
+  // whether TLS has been initialized for a particular thread.
+  // It is set from within __dyn_tls_init by the runtime.
+  // Every library and executable has its own variable.
+  llvm::Type *VTy = llvm::Type::getInt8Ty(CGM.getLLVMContext());
+  llvm::Constant *TlsGuardConstant =
+  CGM.CreateRuntimeVariable(VTy, "__tls_guard");
+  llvm::GlobalValue *TlsGuard = cast(TlsGuardConstant);
+
+  TlsGuard->setThreadLocal(true);
+
+  return TlsGuard;
+}
+
+static llvm::FunctionCallee getDynTlsOnDemandInitFn(CodeGenModule &CGM) {
+  // __dyn_tls_on_demand_init comes from the MSVC runtime and triggers
+  // dynamic TLS initialization by calling __dyn_tls_init internally.
+  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(TlsGuar