[Windows SEH]: HARDWARE EXCEPTION HANDLING (MSVC -EHa) - Part 1

This patch is the Part-1 (FE Clang) implementation of HW Exception handling.

This new feature adds the support of Hardware Exception for Microsoft Windows
SEH (Structured Exception Handling).
This is the first step of this project; only X86_64 target is enabled in this patch.

Compiler options:
For clang-cl.exe, the option is -EHa, the same as MSVC.
For clang.exe, the extra option is -fasync-exceptions,
plus -triple x86_64-windows -fexceptions and -fcxx-exceptions as usual.

NOTE:: Without the -EHa or -fasync-exceptions, this patch is a NO-DIFF change.

The rules for C code:
For C-code, one way (MSVC approach) to achieve SEH -EHa semantic is to follow
three rules:
* First, no exception can move in or out of _try region., i.e., no "potential
  faulty instruction can be moved across _try boundary.
* Second, the order of exceptions for instructions 'directly' under a _try
  must be preserved (not applied to those in callees).
* Finally, global states (local/global/heap variables) that can be read
  outside of _try region must be updated in memory (not just in register)
  before the subsequent exception occurs.

The impact to C++ code:
Although SEH is a feature for C code, -EHa does have a profound effect on C++
side. When a C++ function (in the same compilation unit with option -EHa ) is
called by a SEH C function, a hardware exception occurs in C++ code can also
be handled properly by an upstream SEH _try-handler or a C++ catch(...).
As such, when that happens in the middle of an object's life scope, the dtor
must be invoked the same way as C++ Synchronous Exception during unwinding
process.

Design:
A natural way to achieve the rules above in LLVM today is to allow an EH edge
added on memory/computation instruction (previous iload/istore idea) so that
exception path is modeled in Flow graph preciously. However, tracking every
single memory instruction and potential faulty instruction can create many
Invokes, complicate flow graph and possibly result in negative performance
impact for downstream optimization and code generation. Making all
optimizations be aware of the new semantic is also substantial.

This design does not intend to model exception path at instruction level.
Instead, the proposed design tracks and reports EH state at BLOCK-level to
reduce the complexity of flow graph and minimize the performance-impact on CPP
code under -EHa option.

One key element of this design is the ability to compute State number at
block-level. Our algorithm is based on the following rationales:

A _try scope is always a SEME (Single Entry Multiple Exits) region as jumping
into a _try is not allowed. The single entry must start with a seh_try_begin()
invoke with a correct State number that is the initial state of the SEME.
Through control-flow, state number is propagated into all blocks. Side exits
marked by seh_try_end() will unwind to parent state based on existing
SEHUnwindMap[].
Note side exits can ONLY jump into parent scopes (lower state number).
Thus, when a block succeeds various states from its predecessors, the lowest
State triumphs others.  If some exits flow to unreachable, propagation on those
paths terminate, not affecting remaining blocks.
For CPP code, object lifetime region is usually a SEME as SEH _try.
However there is one rare exception: jumping into a lifetime that has Dtor but
has no Ctor is warned, but allowed:

Warning: jump bypasses variable with a non-trivial destructor

In that case, the region is actually a MEME (multiple entry multiple exits).
Our solution is to inject a eha_scope_begin() invoke in the side entry block to
ensure a correct State.

Implementation:
Part-1: Clang implementation described below.

Two intrinsic are created to track CPP object scopes; eha_scope_begin() and eha_scope_end().
_scope_begin() is immediately added after ctor() is called and EHStack is pushed.
So it must be an invoke, not a call. With that it's also guaranteed an
EH-cleanup-pad is created regardless whether there exists a call in this scope.
_scope_end is added before dtor(). These two intrinsics make the computation of
Block-State possible in downstream code gen pass, even in the presence of
ctor/dtor inlining.

Two intrinsic, seh_try_begin() and seh_try_end(), are added for C-code to mark
_try boundary and to prevent from exceptions being moved across _try boundary.
All memory instructions inside a _try are considered as 'volatile' to assure
2nd and 3rd rules for C-code above. This is a little sub-optimized. But it's
acceptable as the amount of code directly under _try is very small.

Part-2 (will be in Part-2 patch): LLVM implementation described below.

For both C++ & C-code, the state of each block is computed at the same place in
BE (WinEHPreparing pass) where all other EH tables/maps are calculated.
In addition to _scope_begin & _scope_end, the computation of block state also
rely on the existing State tracking code (UnwindMap and InvokeStateMap).

For both C++ & C-code, the state of each block with potential trap instruction
is marked and reported in DAG Instruction Selection pass, the same place where
the state for -EHsc (synchronous exceptions) is done.
If the first instruction in a reported block scope can trap, a Nop is injected
before this instruction. This nop is needed to accommodate LLVM Windows EH
implementation, in which the address in IPToState table is offset by +1.
(note the purpose of that is to ensure the return address of a call is in the
same scope as the call address.

The handler for catch(...) for -EHa must handle HW exception. So it is
'adjective' flag is reset (it cannot be IsStdDotDot (0x40) that only catches
C++ exceptions).
Suppress push/popTerminate() scope (from noexcept/noTHrow) so that HW
exceptions can be passed through.

Original llvm-dev [RFC] discussions can be found in these two threads below:
https://lists.llvm.org/pipermail/llvm-dev/2020-March/140541.html
https://lists.llvm.org/pipermail/llvm-dev/2020-April/141338.html

Differential Revision: https://reviews.llvm.org/D80344/new/

Author: tentzen

clang/include/clang/AST/Stmt.h

@@ -1798,6 +1798,7 @@ class ValueStmt : public Stmt {
 class LabelStmt : public ValueStmt {
   LabelDecl *TheDecl;
   Stmt *SubStmt;
+  bool SideEntry = false;
 
 public:
   /// Build a label statement.
@@ -1833,6 +1834,8 @@ class LabelStmt : public ValueStmt {
   static bool classof(const Stmt *T) {
     return T->getStmtClass() == LabelStmtClass;
   }
+  bool isSideEntry() const { return SideEntry; }
+  void setSideEntry(bool SE) { SideEntry = SE; }
 };
 
 /// Represents an attribute applied to a statement.

clang/include/clang/Basic/LangOptions.def

@@ -132,6 +132,7 @@ LANGOPT(ZVector           , 1, 0, "System z vector extensions")
 LANGOPT(Exceptions        , 1, 0, "exception handling")
 LANGOPT(ObjCExceptions    , 1, 0, "Objective-C exceptions")
 LANGOPT(CXXExceptions     , 1, 0, "C++ exceptions")
+LANGOPT(EHAsynch          , 1, 0, "C/C++ EH Asynch exceptions")
 ENUM_LANGOPT(ExceptionHandling, ExceptionHandlingKind, 3,
              ExceptionHandlingKind::None, "exception handling")
 LANGOPT(IgnoreExceptions  , 1, 0, "ignore exceptions")

clang/include/clang/Driver/Options.td

@@ -1322,6 +1322,9 @@ def fcreate_profile : Flag<["-"], "fcreate-profile">, Group<f_Group>;
 defm cxx_exceptions: BoolFOption<"cxx-exceptions",
   LangOpts<"CXXExceptions">, DefaultFalse,
   PosFlag<SetTrue, [CC1Option], "Enable C++ exceptions">, NegFlag<SetFalse>>;
+defm async_exceptions: BoolFOption<"async-exceptions",
+  LangOpts<"EHAsynch">, DefaultFalse,
+  PosFlag<SetTrue, [CC1Option], "Enable EH Asynchronous exceptions">, NegFlag<SetFalse>>;
 def fcxx_modules : Flag <["-"], "fcxx-modules">, Group<f_Group>,
   Flags<[NoXarchOption]>;
 def fdebug_pass_arguments : Flag<["-"], "fdebug-pass-arguments">, Group<f_Group>;

clang/lib/AST/JSONNodeDumper.cpp

@@ -1451,6 +1451,7 @@ void JSONNodeDumper::VisitCaseStmt(const CaseStmt *CS) {
 void JSONNodeDumper::VisitLabelStmt(const LabelStmt *LS) {
   JOS.attribute("name", LS->getName());
   JOS.attribute("declId", createPointerRepresentation(LS->getDecl()));
+  attributeOnlyIfTrue("sideEntry", LS->isSideEntry());
 }
 void JSONNodeDumper::VisitGotoStmt(const GotoStmt *GS) {
   JOS.attribute("targetLabelDeclId",

clang/lib/AST/TextNodeDumper.cpp

@@ -923,6 +923,8 @@ void TextNodeDumper::VisitWhileStmt(const WhileStmt *Node) {
 
 void TextNodeDumper::VisitLabelStmt(const LabelStmt *Node) {
   OS << " '" << Node->getName() << "'";
+  if (Node->isSideEntry())
+    OS << " side_entry";
 }
 
 void TextNodeDumper::VisitGotoStmt(const GotoStmt *Node) {

clang/lib/CodeGen/CGCleanup.cpp

@@ -194,6 +194,11 @@ void *EHScopeStack::pushCleanup(CleanupKind Kind, size_t Size) {
   if (IsLifetimeMarker)
     Scope->setLifetimeMarker();
 
+  // With Windows -EHa, Invoke llvm.seh.scope.begin() for EHCleanup
+  if (CGF->getLangOpts().EHAsynch && IsEHCleanup &&
+      CGF->getTarget().getCXXABI().isMicrosoft())
+    CGF->EmitSehCppScopeBegin();
+
   return Scope->getCleanupBuffer();
 }
 
@@ -759,14 +764,31 @@ void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
   if (Scope.isEHCleanup())
     cleanupFlags.setIsEHCleanupKind();
 
+  // Under -EHa, invoke seh.scope.end() to mark scope end before dtor
+  bool IsEHa = getLangOpts().EHAsynch && !Scope.isLifetimeMarker();
+  const EHPersonality &Personality = EHPersonality::get(*this);
   if (!RequiresNormalCleanup) {
+    // Mark CPP scope end for passed-by-value Arg temp
+    //   per Windows ABI which is "normally" Cleanup in callee
+    if (IsEHa && getInvokeDest()) {
+      if (Personality.isMSVCXXPersonality())
+        EmitSehCppScopeEnd();
+    }
     destroyOptimisticNormalEntry(*this, Scope);
     EHStack.popCleanup();
   } else {
     // If we have a fallthrough and no other need for the cleanup,
     // emit it directly.
-    if (HasFallthrough && !HasPrebranchedFallthrough &&
-        !HasFixups && !HasExistingBranches) {
+    if (HasFallthrough && !HasPrebranchedFallthrough && !HasFixups &&
+        !HasExistingBranches) {
+
+      // mark SEH scope end for fall-through flow
+      if (IsEHa && getInvokeDest()) {
+        if (Personality.isMSVCXXPersonality())
+          EmitSehCppScopeEnd();
+        else
+          EmitSehTryScopeEnd();
+      }
 
       destroyOptimisticNormalEntry(*this, Scope);
       EHStack.popCleanup();
@@ -801,6 +823,14 @@ void CodeGenFunction::PopCleanupBlock(bool FallthroughIsBranchThrough) {
       // should already be branched to it.
       EmitBlock(NormalEntry);
 
+      // intercept normal cleanup to mark SEH scope end
+      if (IsEHa) {
+        if (Personality.isMSVCXXPersonality())
+          EmitSehCppScopeEnd();
+        else
+          EmitSehTryScopeEnd();
+      }
+
       // III.  Figure out where we're going and build the cleanup
       // epilogue.
 
@@ -1248,11 +1278,17 @@ void CodeGenFunction::DeactivateCleanupBlock(EHScopeStack::stable_iterator C,
   // to the current RunCleanupsScope.
   if (C == EHStack.stable_begin() &&
       CurrentCleanupScopeDepth.strictlyEncloses(C)) {
-    // If it's a normal cleanup, we need to pretend that the
-    // fallthrough is unreachable.
-    CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
-    PopCleanupBlock();
-    Builder.restoreIP(SavedIP);
+    // Per comment below, checking EHAsynch is not really necessary
+    // it's there to assure zero-impact w/o EHAsynch option
+    if (!Scope.isNormalCleanup() && getLangOpts().EHAsynch) {
+      PopCleanupBlock();
+    } else {
+      // If it's a normal cleanup, we need to pretend that the
+      // fallthrough is unreachable.
+      CGBuilderTy::InsertPoint SavedIP = Builder.saveAndClearIP();
+      PopCleanupBlock();
+      Builder.restoreIP(SavedIP);
+    }
     return;
   }
 
@@ -1276,3 +1312,60 @@ void CodeGenFunction::EmitCXXTemporary(const CXXTemporary *Temporary,
   pushDestroy(NormalAndEHCleanup, Ptr, TempType, destroyCXXObject,
               /*useEHCleanup*/ true);
 }
+
+// Need to set "funclet" in OperandBundle properly for noThrow
+//       intrinsic (see CGCall.cpp)
+static void EmitSehScope(CodeGenFunction &CGF,
+                         llvm::FunctionCallee &SehCppScope) {
+  llvm::BasicBlock *InvokeDest = CGF.getInvokeDest();
+  llvm::BasicBlock *BB = CGF.Builder.GetInsertBlock();
+  assert(BB && InvokeDest);
+  llvm::BasicBlock *Cont = CGF.createBasicBlock("invoke.cont");
+  SmallVector<llvm::OperandBundleDef, 1> BundleList =
+      CGF.getBundlesForFunclet(SehCppScope.getCallee());
+  if (CGF.CurrentFuncletPad)
+    BundleList.emplace_back("funclet", CGF.CurrentFuncletPad);
+  CGF.Builder.CreateInvoke(SehCppScope, Cont, InvokeDest, None, BundleList);
+  CGF.EmitBlock(Cont);
+}
+
+// Invoke a llvm.seh.scope.begin at the beginning of a CPP scope for -EHa
+void CodeGenFunction::EmitSehCppScopeBegin() {
+  assert(getLangOpts().EHAsynch);
+  llvm::FunctionType *FTy =
+      llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
+  llvm::FunctionCallee SehCppScope =
+      CGM.CreateRuntimeFunction(FTy, "llvm.seh.scope.begin");
+  EmitSehScope(*this, SehCppScope);
+}
+
+// Invoke a llvm.seh.scope.end at the end of a CPP scope for -EHa
+//   llvm.seh.scope.end is emitted before popCleanup, so it's "invoked"
+void CodeGenFunction::EmitSehCppScopeEnd() {
+  assert(getLangOpts().EHAsynch);
+  llvm::FunctionType *FTy =
+      llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
+  llvm::FunctionCallee SehCppScope =
+      CGM.CreateRuntimeFunction(FTy, "llvm.seh.scope.end");
+  EmitSehScope(*this, SehCppScope);
+}
+
+// Invoke a llvm.seh.try.begin at the beginning of a SEH scope for -EHa
+void CodeGenFunction::EmitSehTryScopeBegin() {
+  assert(getLangOpts().EHAsynch);
+  llvm::FunctionType *FTy =
+      llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
+  llvm::FunctionCallee SehCppScope =
+      CGM.CreateRuntimeFunction(FTy, "llvm.seh.try.begin");
+  EmitSehScope(*this, SehCppScope);
+}
+
+// Invoke a llvm.seh.try.end at the end of a SEH scope for -EHa
+void CodeGenFunction::EmitSehTryScopeEnd() {
+  assert(getLangOpts().EHAsynch);
+  llvm::FunctionType *FTy =
+      llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
+  llvm::FunctionCallee SehCppScope =
+      CGM.CreateRuntimeFunction(FTy, "llvm.seh.try.end");
+  EmitSehScope(*this, SehCppScope);
+}

clang/lib/CodeGen/CGException.cpp

@@ -39,6 +39,18 @@ static llvm::FunctionCallee getFreeExceptionFn(CodeGenModule &CGM) {
   return CGM.CreateRuntimeFunction(FTy, "__cxa_free_exception");
 }
 
+static llvm::FunctionCallee getSehTryBeginFn(CodeGenModule &CGM) {
+  llvm::FunctionType *FTy =
+      llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
+  return CGM.CreateRuntimeFunction(FTy, "llvm.seh.try.begin");
+}
+
+static llvm::FunctionCallee getSehTryEndFn(CodeGenModule &CGM) {
+  llvm::FunctionType *FTy =
+      llvm::FunctionType::get(CGM.VoidTy, /*isVarArg=*/false);
+  return CGM.CreateRuntimeFunction(FTy, "llvm.seh.try.end");
+}
+
 static llvm::FunctionCallee getUnexpectedFn(CodeGenModule &CGM) {
   // void __cxa_call_unexpected(void *thrown_exception);
 
@@ -467,7 +479,8 @@ void CodeGenFunction::EmitStartEHSpec(const Decl *D) {
   ExceptionSpecificationType EST = Proto->getExceptionSpecType();
   if (isNoexceptExceptionSpec(EST) && Proto->canThrow() == CT_Cannot) {
     // noexcept functions are simple terminate scopes.
-    EHStack.pushTerminate();
+    if (!getLangOpts().EHAsynch) // -EHa: HW exception still can occur
+      EHStack.pushTerminate();
   } else if (EST == EST_Dynamic || EST == EST_DynamicNone) {
     // TODO: Revisit exception specifications for the MS ABI.  There is a way to
     // encode these in an object file but MSVC doesn't do anything with it.
@@ -544,7 +557,7 @@ void CodeGenFunction::EmitEndEHSpec(const Decl *D) {
   if (!FD) {
     // Check if CapturedDecl is nothrow and pop terminate scope for it.
     if (const CapturedDecl* CD = dyn_cast_or_null<CapturedDecl>(D)) {
-      if (CD->isNothrow())
+      if (CD->isNothrow() && !EHStack.empty())
         EHStack.popTerminate();
     }
     return;
@@ -554,7 +567,8 @@ void CodeGenFunction::EmitEndEHSpec(const Decl *D) {
     return;
 
   ExceptionSpecificationType EST = Proto->getExceptionSpecType();
-  if (isNoexceptExceptionSpec(EST) && Proto->canThrow() == CT_Cannot) {
+  if (isNoexceptExceptionSpec(EST) && Proto->canThrow() == CT_Cannot &&
+      !EHStack.empty() /* possible empty when under async exceptions */) {
     EHStack.popTerminate();
   } else if (EST == EST_Dynamic || EST == EST_DynamicNone) {
     // TODO: Revisit exception specifications for the MS ABI.  There is a way to
@@ -610,6 +624,10 @@ void CodeGenFunction::EnterCXXTryStmt(const CXXTryStmt &S, bool IsFnTryBlock) {
     } else {
       // No exception decl indicates '...', a catch-all.
       CatchScope->setHandler(I, CGM.getCXXABI().getCatchAllTypeInfo(), Handler);
+      // Under async exceptions, catch(...) need to catch HW exception too
+      // Mark scope with SehTryBegin as a SEH __try scope
+      if (getLangOpts().EHAsynch)
+        EmitRuntimeCallOrInvoke(getSehTryBeginFn(CGM));
     }
   }
 }
@@ -724,7 +742,7 @@ llvm::BasicBlock *CodeGenFunction::getInvokeDestImpl() {
   // If exceptions are disabled/ignored and SEH is not in use, then there is no
   // invoke destination. SEH "works" even if exceptions are off. In practice,
   // this means that C++ destructors and other EH cleanups don't run, which is
-  // consistent with MSVC's behavior.
+  // consistent with MSVC's behavior, except in the presence of -EHa
   const LangOptions &LO = CGM.getLangOpts();
   if (!LO.Exceptions || LO.IgnoreExceptions) {
     if (!LO.Borland && !LO.MicrosoftExt)
@@ -1606,7 +1624,23 @@ void CodeGenFunction::EmitSEHTryStmt(const SEHTryStmt &S) {
     JumpDest TryExit = getJumpDestInCurrentScope("__try.__leave");
 
     SEHTryEpilogueStack.push_back(&TryExit);
+
+    llvm::BasicBlock *TryBB = nullptr;
+    // IsEHa: emit an invoke to _seh_try_begin() runtime for -EHa
+    if (getLangOpts().EHAsynch) {
+      EmitRuntimeCallOrInvoke(getSehTryBeginFn(CGM));
+      if (SEHTryEpilogueStack.size() == 1) // outermost only
+        TryBB = Builder.GetInsertBlock();
+    }
+
     EmitStmt(S.getTryBlock());
+
+    // Volatilize all blocks in Try, till current insert point
+    if (TryBB) {
+      llvm::SmallPtrSet<llvm::BasicBlock *, 10> Visited;
+      VolatilizeTryBlocks(TryBB, Visited);
+    }
+
     SEHTryEpilogueStack.pop_back();
 
     if (!TryExit.getBlock()->use_empty())
@@ -1617,6 +1651,35 @@ void CodeGenFunction::EmitSEHTryStmt(const SEHTryStmt &S) {
   ExitSEHTryStmt(S);
 }
 
+//  Recursively walk through blocks in a _try
+//      and make all memory instructions volatile
+void CodeGenFunction::VolatilizeTryBlocks(
+    llvm::BasicBlock *BB, llvm::SmallPtrSet<llvm::BasicBlock *, 10> &V) {
+  if (BB == SEHTryEpilogueStack.back()->getBlock() /* end of Try */ ||
+      !V.insert(BB).second /* already visited */ ||
+      !BB->getParent() /* not emitted */ || BB->empty())
+    return;
+
+  if (!BB->isEHPad()) {
+    for (llvm::BasicBlock::iterator J = BB->begin(), JE = BB->end(); J != JE;
+         ++J) {
+      if (auto LI = dyn_cast<llvm::LoadInst>(J)) {
+        LI->setVolatile(true);
+      } else if (auto SI = dyn_cast<llvm::StoreInst>(J)) {
+        SI->setVolatile(true);
+      } else if (auto* MCI = dyn_cast<llvm::MemIntrinsic>(J)) {
+        MCI->setVolatile(llvm::ConstantInt::get(Builder.getInt1Ty(), 1));
+      }
+    }
+  }
+  const llvm::Instruction *TI = BB->getTerminator();
+  if (TI) {
+    unsigned N = TI->getNumSuccessors();
+    for (unsigned I = 0; I < N; I++)
+      VolatilizeTryBlocks(TI->getSuccessor(I), V);
+  }
+}
+
 namespace {
 struct PerformSEHFinally final : EHScopeStack::Cleanup {
   llvm::Function *OutlinedFinally;
@@ -2118,6 +2181,12 @@ void CodeGenFunction::ExitSEHTryStmt(const SEHTryStmt &S) {
     return;
   }
 
+  // IsEHa: emit an invoke _seh_try_end() to mark end of FT flow
+  if (getLangOpts().EHAsynch && Builder.GetInsertBlock()) {
+    llvm::FunctionCallee SehTryEnd = getSehTryEndFn(CGM);
+    EmitRuntimeCallOrInvoke(SehTryEnd);
+  }
+
   // Otherwise, we must have an __except block.
   const SEHExceptStmt *Except = S.getExceptHandler();
   assert(Except && "__try must have __finally xor __except");

clang/lib/CodeGen/CGStmt.cpp

@@ -646,6 +646,11 @@ void CodeGenFunction::LexicalScope::rescopeLabels() {
 
 void CodeGenFunction::EmitLabelStmt(const LabelStmt &S) {
   EmitLabel(S.getDecl());
+
+  // IsEHa - emit eha.scope.begin if it's a side entry of a scope
+  if (getLangOpts().EHAsynch && S.isSideEntry())
+    EmitSehCppScopeBegin();
+
   EmitStmt(S.getSubStmt());
 }
 

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -75,6 +75,7 @@ CodeGenFunction::CodeGenFunction(CodeGenModule &cgm, bool suppressNewContext)
           shouldEmitLifetimeMarkers(CGM.getCodeGenOpts(), CGM.getLangOpts())) {
   if (!suppressNewContext)
     CGM.getCXXABI().getMangleContext().startNewFunction();
+  EHStack.setCGF(this);
 
   SetFastMathFlags(CurFPFeatures);
   SetFPModel();

clang/lib/CodeGen/CodeGenFunction.h

@@ -2867,6 +2867,11 @@ class CodeGenFunction : public CodeGenTypeCache {
   void EmitCXXTemporary(const CXXTemporary *Temporary, QualType TempType,
                         Address Ptr);
 
+  void EmitSehCppScopeBegin();
+  void EmitSehCppScopeEnd();
+  void EmitSehTryScopeBegin();
+  void EmitSehTryScopeEnd();
+
   llvm::Value *EmitLifetimeStart(uint64_t Size, llvm::Value *Addr);
   void EmitLifetimeEnd(llvm::Value *Size, llvm::Value *Addr);
 
@@ -3217,6 +3222,8 @@ class CodeGenFunction : public CodeGenTypeCache {
   void EmitSEHLeaveStmt(const SEHLeaveStmt &S);
   void EnterSEHTryStmt(const SEHTryStmt &S);
   void ExitSEHTryStmt(const SEHTryStmt &S);
+  void VolatilizeTryBlocks(llvm::BasicBlock *BB,
+                           llvm::SmallPtrSet<llvm::BasicBlock *, 10> &V);
 
   void pushSEHCleanup(CleanupKind kind,
                       llvm::Function *FinallyFunc);

clang/lib/CodeGen/CodeGenModule.cpp

@@ -697,6 +697,9 @@ void CodeGenModule::Release() {
                                   llvm::DenormalMode::IEEE);
   }
 
+  if (LangOpts.EHAsynch)
+    getModule().addModuleFlag(llvm::Module::Warning, "eh-asynch", 1);
+
   // Emit OpenCL specific module metadata: OpenCL/SPIR version.
   if (LangOpts.OpenCL) {
     EmitOpenCLMetadata();