1 //===-- X86WinEHState - Insert EH state updates for win32 exceptions ------===//
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 // All functions using an MSVC EH personality use an explicitly updated state
11 // number stored in an exception registration stack object. The registration
12 // object is linked into a thread-local chain of registrations stored at fs:00.
13 // This pass adds the registration object and EH state updates.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #include "X86.h"
18 #include "llvm/Analysis/LibCallSemantics.h"
19 #include "llvm/CodeGen/MachineModuleInfo.h"
20 #include "llvm/CodeGen/Passes.h"
21 #include "llvm/CodeGen/WinEHFuncInfo.h"
22 #include "llvm/IR/Dominators.h"
23 #include "llvm/IR/Function.h"
24 #include "llvm/IR/IRBuilder.h"
25 #include "llvm/IR/Instructions.h"
26 #include "llvm/IR/IntrinsicInst.h"
27 #include "llvm/IR/Module.h"
28 #include "llvm/IR/PatternMatch.h"
29 #include "llvm/Pass.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/Support/raw_ostream.h"
32 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
33 #include "llvm/Transforms/Utils/Cloning.h"
34 #include "llvm/Transforms/Utils/Local.h"
35 
36 using namespace llvm;
37 using namespace llvm::PatternMatch;
38 
39 #define DEBUG_TYPE "winehstate"
40 
41 namespace {
42 class WinEHStatePass : public FunctionPass {
43 public:
44   static char ID; // Pass identification, replacement for typeid.
45 
46   WinEHStatePass() : FunctionPass(ID) {}
47 
48   bool runOnFunction(Function &Fn) override;
49 
50   bool doInitialization(Module &M) override;
51 
52   bool doFinalization(Module &M) override;
53 
54   void getAnalysisUsage(AnalysisUsage &AU) const override;
55 
56   const char *getPassName() const override {
57     return "Windows 32-bit x86 EH state insertion";
58   }
59 
60 private:
61   void emitExceptionRegistrationRecord(Function *F);
62 
63   void linkExceptionRegistration(IRBuilder<> &Builder, Function *Handler);
64   void unlinkExceptionRegistration(IRBuilder<> &Builder);
65   void addCXXStateStores(Function &F, MachineModuleInfo &MMI);
66   void addSEHStateStores(Function &F, MachineModuleInfo &MMI);
67   void addCXXStateStoresToFunclet(Value *ParentRegNode, WinEHFuncInfo &FuncInfo,
68                                   Function &F, int BaseState);
69   void insertStateNumberStore(Value *ParentRegNode, Instruction *IP, int State);
70 
71   Value *emitEHLSDA(IRBuilder<> &Builder, Function *F);
72 
73   Function *generateLSDAInEAXThunk(Function *ParentFunc);
74 
75   int escapeRegNode(Function &F);
76 
77   // Module-level type getters.
78   Type *getEHLinkRegistrationType();
79   Type *getSEHRegistrationType();
80   Type *getCXXEHRegistrationType();
81 
82   // Per-module data.
83   Module *TheModule = nullptr;
84   StructType *EHLinkRegistrationTy = nullptr;
85   StructType *CXXEHRegistrationTy = nullptr;
86   StructType *SEHRegistrationTy = nullptr;
87   Function *FrameRecover = nullptr;
88   Function *FrameAddress = nullptr;
89   Function *FrameEscape = nullptr;
90 
91   // Per-function state
92   EHPersonality Personality = EHPersonality::Unknown;
93   Function *PersonalityFn = nullptr;
94 
95   /// The stack allocation containing all EH data, including the link in the
96   /// fs:00 chain and the current state.
97   AllocaInst *RegNode = nullptr;
98 
99   /// Struct type of RegNode. Used for GEPing.
100   Type *RegNodeTy = nullptr;
101 
102   /// The index of the state field of RegNode.
103   int StateFieldIndex = ~0U;
104 
105   /// The linked list node subobject inside of RegNode.
106   Value *Link = nullptr;
107 };
108 }
109 
110 FunctionPass *llvm::createX86WinEHStatePass() { return new WinEHStatePass(); }
111 
112 char WinEHStatePass::ID = 0;
113 
114 bool WinEHStatePass::doInitialization(Module &M) {
115   TheModule = &M;
116   FrameEscape = Intrinsic::getDeclaration(TheModule, Intrinsic::localescape);
117   FrameRecover = Intrinsic::getDeclaration(TheModule, Intrinsic::localrecover);
118   FrameAddress = Intrinsic::getDeclaration(TheModule, Intrinsic::frameaddress);
119   return false;
120 }
121 
122 bool WinEHStatePass::doFinalization(Module &M) {
123   assert(TheModule == &M);
124   TheModule = nullptr;
125   EHLinkRegistrationTy = nullptr;
126   CXXEHRegistrationTy = nullptr;
127   SEHRegistrationTy = nullptr;
128   FrameEscape = nullptr;
129   FrameRecover = nullptr;
130   FrameAddress = nullptr;
131   return false;
132 }
133 
134 void WinEHStatePass::getAnalysisUsage(AnalysisUsage &AU) const {
135   // This pass should only insert a stack allocation, memory accesses, and
136   // localrecovers.
137   AU.setPreservesCFG();
138 }
139 
140 bool WinEHStatePass::runOnFunction(Function &F) {
141   // If this is an outlined handler, don't do anything. We'll do state insertion
142   // for it in the parent.
143   StringRef WinEHParentName =
144       F.getFnAttribute("wineh-parent").getValueAsString();
145   if (WinEHParentName != F.getName() && !WinEHParentName.empty())
146     return false;
147 
148   // Check the personality. Do nothing if this is not an MSVC personality.
149   if (!F.hasPersonalityFn())
150     return false;
151   PersonalityFn =
152       dyn_cast<Function>(F.getPersonalityFn()->stripPointerCasts());
153   if (!PersonalityFn)
154     return false;
155   Personality = classifyEHPersonality(PersonalityFn);
156   if (!isMSVCEHPersonality(Personality))
157     return false;
158 
159   // Disable frame pointer elimination in this function.
160   // FIXME: Do the nested handlers need to keep the parent ebp in ebp, or can we
161   // use an arbitrary register?
162   F.addFnAttr("no-frame-pointer-elim", "true");
163 
164   emitExceptionRegistrationRecord(&F);
165 
166   auto *MMIPtr = getAnalysisIfAvailable<MachineModuleInfo>();
167   assert(MMIPtr && "MachineModuleInfo should always be available");
168   MachineModuleInfo &MMI = *MMIPtr;
169   switch (Personality) {
170   default: llvm_unreachable("unexpected personality function");
171   case EHPersonality::MSVC_CXX:    addCXXStateStores(F, MMI); break;
172   case EHPersonality::MSVC_X86SEH: addSEHStateStores(F, MMI); break;
173   }
174 
175   // Reset per-function state.
176   PersonalityFn = nullptr;
177   Personality = EHPersonality::Unknown;
178   return true;
179 }
180 
181 /// Get the common EH registration subobject:
182 ///   typedef _EXCEPTION_DISPOSITION (*PEXCEPTION_ROUTINE)(
183 ///       _EXCEPTION_RECORD *, void *, _CONTEXT *, void *);
184 ///   struct EHRegistrationNode {
185 ///     EHRegistrationNode *Next;
186 ///     PEXCEPTION_ROUTINE Handler;
187 ///   };
188 Type *WinEHStatePass::getEHLinkRegistrationType() {
189   if (EHLinkRegistrationTy)
190     return EHLinkRegistrationTy;
191   LLVMContext &Context = TheModule->getContext();
192   EHLinkRegistrationTy = StructType::create(Context, "EHRegistrationNode");
193   Type *FieldTys[] = {
194       EHLinkRegistrationTy->getPointerTo(0), // EHRegistrationNode *Next
195       Type::getInt8PtrTy(Context) // EXCEPTION_DISPOSITION (*Handler)(...)
196   };
197   EHLinkRegistrationTy->setBody(FieldTys, false);
198   return EHLinkRegistrationTy;
199 }
200 
201 /// The __CxxFrameHandler3 registration node:
202 ///   struct CXXExceptionRegistration {
203 ///     void *SavedESP;
204 ///     EHRegistrationNode SubRecord;
205 ///     int32_t TryLevel;
206 ///   };
207 Type *WinEHStatePass::getCXXEHRegistrationType() {
208   if (CXXEHRegistrationTy)
209     return CXXEHRegistrationTy;
210   LLVMContext &Context = TheModule->getContext();
211   Type *FieldTys[] = {
212       Type::getInt8PtrTy(Context), // void *SavedESP
213       getEHLinkRegistrationType(), // EHRegistrationNode SubRecord
214       Type::getInt32Ty(Context)    // int32_t TryLevel
215   };
216   CXXEHRegistrationTy =
217       StructType::create(FieldTys, "CXXExceptionRegistration");
218   return CXXEHRegistrationTy;
219 }
220 
221 /// The _except_handler3/4 registration node:
222 ///   struct EH4ExceptionRegistration {
223 ///     void *SavedESP;
224 ///     _EXCEPTION_POINTERS *ExceptionPointers;
225 ///     EHRegistrationNode SubRecord;
226 ///     int32_t EncodedScopeTable;
227 ///     int32_t TryLevel;
228 ///   };
229 Type *WinEHStatePass::getSEHRegistrationType() {
230   if (SEHRegistrationTy)
231     return SEHRegistrationTy;
232   LLVMContext &Context = TheModule->getContext();
233   Type *FieldTys[] = {
234       Type::getInt8PtrTy(Context), // void *SavedESP
235       Type::getInt8PtrTy(Context), // void *ExceptionPointers
236       getEHLinkRegistrationType(), // EHRegistrationNode SubRecord
237       Type::getInt32Ty(Context),   // int32_t EncodedScopeTable
238       Type::getInt32Ty(Context)    // int32_t TryLevel
239   };
240   SEHRegistrationTy = StructType::create(FieldTys, "SEHExceptionRegistration");
241   return SEHRegistrationTy;
242 }
243 
244 // Emit an exception registration record. These are stack allocations with the
245 // common subobject of two pointers: the previous registration record (the old
246 // fs:00) and the personality function for the current frame. The data before
247 // and after that is personality function specific.
248 void WinEHStatePass::emitExceptionRegistrationRecord(Function *F) {
249   assert(Personality == EHPersonality::MSVC_CXX ||
250          Personality == EHPersonality::MSVC_X86SEH);
251 
252   StringRef PersonalityName = PersonalityFn->getName();
253   IRBuilder<> Builder(&F->getEntryBlock(), F->getEntryBlock().begin());
254   Type *Int8PtrType = Builder.getInt8PtrTy();
255   if (Personality == EHPersonality::MSVC_CXX) {
256     RegNodeTy = getCXXEHRegistrationType();
257     RegNode = Builder.CreateAlloca(RegNodeTy);
258     // SavedESP = llvm.stacksave()
259     Value *SP = Builder.CreateCall(
260         Intrinsic::getDeclaration(TheModule, Intrinsic::stacksave), {});
261     Builder.CreateStore(SP, Builder.CreateStructGEP(RegNodeTy, RegNode, 0));
262     // TryLevel = -1
263     StateFieldIndex = 2;
264     insertStateNumberStore(RegNode, Builder.GetInsertPoint(), -1);
265     // Handler = __ehhandler$F
266     Function *Trampoline = generateLSDAInEAXThunk(F);
267     Link = Builder.CreateStructGEP(RegNodeTy, RegNode, 1);
268     linkExceptionRegistration(Builder, Trampoline);
269   } else if (Personality == EHPersonality::MSVC_X86SEH) {
270     // If _except_handler4 is in use, some additional guard checks and prologue
271     // stuff is required.
272     bool UseStackGuard = (PersonalityName == "_except_handler4");
273     RegNodeTy = getSEHRegistrationType();
274     RegNode = Builder.CreateAlloca(RegNodeTy);
275     // SavedESP = llvm.stacksave()
276     Value *SP = Builder.CreateCall(
277         Intrinsic::getDeclaration(TheModule, Intrinsic::stacksave), {});
278     Builder.CreateStore(SP, Builder.CreateStructGEP(RegNodeTy, RegNode, 0));
279     // TryLevel = -2 / -1
280     StateFieldIndex = 4;
281     insertStateNumberStore(RegNode, Builder.GetInsertPoint(),
282                            UseStackGuard ? -2 : -1);
283     // ScopeTable = llvm.x86.seh.lsda(F)
284     Value *FI8 = Builder.CreateBitCast(F, Int8PtrType);
285     Value *LSDA = Builder.CreateCall(
286         Intrinsic::getDeclaration(TheModule, Intrinsic::x86_seh_lsda), FI8);
287     Type *Int32Ty = Type::getInt32Ty(TheModule->getContext());
288     LSDA = Builder.CreatePtrToInt(LSDA, Int32Ty);
289     // If using _except_handler4, xor the address of the table with
290     // __security_cookie.
291     if (UseStackGuard) {
292       Value *Cookie =
293           TheModule->getOrInsertGlobal("__security_cookie", Int32Ty);
294       Value *Val = Builder.CreateLoad(Int32Ty, Cookie);
295       LSDA = Builder.CreateXor(LSDA, Val);
296     }
297     Builder.CreateStore(LSDA, Builder.CreateStructGEP(RegNodeTy, RegNode, 3));
298     Link = Builder.CreateStructGEP(RegNodeTy, RegNode, 2);
299     linkExceptionRegistration(Builder, PersonalityFn);
300   } else {
301     llvm_unreachable("unexpected personality function");
302   }
303 
304   // Insert an unlink before all returns.
305   for (BasicBlock &BB : *F) {
306     TerminatorInst *T = BB.getTerminator();
307     if (!isa<ReturnInst>(T))
308       continue;
309     Builder.SetInsertPoint(T);
310     unlinkExceptionRegistration(Builder);
311   }
312 }
313 
314 Value *WinEHStatePass::emitEHLSDA(IRBuilder<> &Builder, Function *F) {
315   Value *FI8 = Builder.CreateBitCast(F, Type::getInt8PtrTy(F->getContext()));
316   return Builder.CreateCall(
317       Intrinsic::getDeclaration(TheModule, Intrinsic::x86_seh_lsda), FI8);
318 }
319 
320 /// Generate a thunk that puts the LSDA of ParentFunc in EAX and then calls
321 /// PersonalityFn, forwarding the parameters passed to PEXCEPTION_ROUTINE:
322 ///   typedef _EXCEPTION_DISPOSITION (*PEXCEPTION_ROUTINE)(
323 ///       _EXCEPTION_RECORD *, void *, _CONTEXT *, void *);
324 /// We essentially want this code:
325 ///   movl $lsda, %eax
326 ///   jmpl ___CxxFrameHandler3
327 Function *WinEHStatePass::generateLSDAInEAXThunk(Function *ParentFunc) {
328   LLVMContext &Context = ParentFunc->getContext();
329   Type *Int32Ty = Type::getInt32Ty(Context);
330   Type *Int8PtrType = Type::getInt8PtrTy(Context);
331   Type *ArgTys[5] = {Int8PtrType, Int8PtrType, Int8PtrType, Int8PtrType,
332                      Int8PtrType};
333   FunctionType *TrampolineTy =
334       FunctionType::get(Int32Ty, makeArrayRef(&ArgTys[0], 4),
335                         /*isVarArg=*/false);
336   FunctionType *TargetFuncTy =
337       FunctionType::get(Int32Ty, makeArrayRef(&ArgTys[0], 5),
338                         /*isVarArg=*/false);
339   Function *Trampoline = Function::Create(
340       TrampolineTy, GlobalValue::InternalLinkage,
341       Twine("__ehhandler$") + ParentFunc->getName(), TheModule);
342   BasicBlock *EntryBB = BasicBlock::Create(Context, "entry", Trampoline);
343   IRBuilder<> Builder(EntryBB);
344   Value *LSDA = emitEHLSDA(Builder, ParentFunc);
345   Value *CastPersonality =
346       Builder.CreateBitCast(PersonalityFn, TargetFuncTy->getPointerTo());
347   auto AI = Trampoline->arg_begin();
348   Value *Args[5] = {LSDA, AI++, AI++, AI++, AI++};
349   CallInst *Call = Builder.CreateCall(CastPersonality, Args);
350   // Can't use musttail due to prototype mismatch, but we can use tail.
351   Call->setTailCall(true);
352   // Set inreg so we pass it in EAX.
353   Call->addAttribute(1, Attribute::InReg);
354   Builder.CreateRet(Call);
355   return Trampoline;
356 }
357 
358 void WinEHStatePass::linkExceptionRegistration(IRBuilder<> &Builder,
359                                                Function *Handler) {
360   // Emit the .safeseh directive for this function.
361   Handler->addFnAttr("safeseh");
362 
363   Type *LinkTy = getEHLinkRegistrationType();
364   // Handler = Handler
365   Value *HandlerI8 = Builder.CreateBitCast(Handler, Builder.getInt8PtrTy());
366   Builder.CreateStore(HandlerI8, Builder.CreateStructGEP(LinkTy, Link, 1));
367   // Next = [fs:00]
368   Constant *FSZero =
369       Constant::getNullValue(LinkTy->getPointerTo()->getPointerTo(257));
370   Value *Next = Builder.CreateLoad(FSZero);
371   Builder.CreateStore(Next, Builder.CreateStructGEP(LinkTy, Link, 0));
372   // [fs:00] = Link
373   Builder.CreateStore(Link, FSZero);
374 }
375 
376 void WinEHStatePass::unlinkExceptionRegistration(IRBuilder<> &Builder) {
377   // Clone Link into the current BB for better address mode folding.
378   if (auto *GEP = dyn_cast<GetElementPtrInst>(Link)) {
379     GEP = cast<GetElementPtrInst>(GEP->clone());
380     Builder.Insert(GEP);
381     Link = GEP;
382   }
383   Type *LinkTy = getEHLinkRegistrationType();
384   // [fs:00] = Link->Next
385   Value *Next =
386       Builder.CreateLoad(Builder.CreateStructGEP(LinkTy, Link, 0));
387   Constant *FSZero =
388       Constant::getNullValue(LinkTy->getPointerTo()->getPointerTo(257));
389   Builder.CreateStore(Next, FSZero);
390 }
391 
392 void WinEHStatePass::addCXXStateStores(Function &F, MachineModuleInfo &MMI) {
393   WinEHFuncInfo &FuncInfo = MMI.getWinEHFuncInfo(&F);
394   calculateWinCXXEHStateNumbers(&F, FuncInfo);
395 
396   // The base state for the parent is -1.
397   addCXXStateStoresToFunclet(RegNode, FuncInfo, F, -1);
398 
399   // Set up RegNodeEscapeIndex
400   int RegNodeEscapeIndex = escapeRegNode(F);
401   FuncInfo.EHRegNodeEscapeIndex = RegNodeEscapeIndex;
402 
403   // Only insert stores in catch handlers.
404   Constant *FI8 =
405       ConstantExpr::getBitCast(&F, Type::getInt8PtrTy(TheModule->getContext()));
406   for (auto P : FuncInfo.HandlerBaseState) {
407     Function *Handler = const_cast<Function *>(P.first);
408     int BaseState = P.second;
409     IRBuilder<> Builder(&Handler->getEntryBlock(),
410                         Handler->getEntryBlock().begin());
411     // FIXME: Find and reuse such a call if present.
412     Value *ParentFP = Builder.CreateCall(FrameAddress, {Builder.getInt32(1)});
413     Value *RecoveredRegNode = Builder.CreateCall(
414         FrameRecover, {FI8, ParentFP, Builder.getInt32(RegNodeEscapeIndex)});
415     RecoveredRegNode =
416         Builder.CreateBitCast(RecoveredRegNode, RegNodeTy->getPointerTo(0));
417     addCXXStateStoresToFunclet(RecoveredRegNode, FuncInfo, *Handler, BaseState);
418   }
419 }
420 
421 /// Escape RegNode so that we can access it from child handlers. Find the call
422 /// to localescape, if any, in the entry block and append RegNode to the list
423 /// of arguments.
424 int WinEHStatePass::escapeRegNode(Function &F) {
425   // Find the call to localescape and extract its arguments.
426   IntrinsicInst *EscapeCall = nullptr;
427   for (Instruction &I : F.getEntryBlock()) {
428     IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I);
429     if (II && II->getIntrinsicID() == Intrinsic::localescape) {
430       EscapeCall = II;
431       break;
432     }
433   }
434   SmallVector<Value *, 8> Args;
435   if (EscapeCall) {
436     auto Ops = EscapeCall->arg_operands();
437     Args.append(Ops.begin(), Ops.end());
438   }
439   Args.push_back(RegNode);
440 
441   // Replace the call (if it exists) with new one. Otherwise, insert at the end
442   // of the entry block.
443   Instruction *InsertPt = EscapeCall;
444   if (!EscapeCall)
445     InsertPt = F.getEntryBlock().getTerminator();
446   IRBuilder<> Builder(&F.getEntryBlock(), InsertPt);
447   Builder.CreateCall(FrameEscape, Args);
448   if (EscapeCall)
449     EscapeCall->eraseFromParent();
450   return Args.size() - 1;
451 }
452 
453 void WinEHStatePass::addCXXStateStoresToFunclet(Value *ParentRegNode,
454                                                 WinEHFuncInfo &FuncInfo,
455                                                 Function &F, int BaseState) {
456   // Iterate all the instructions and emit state number stores.
457   for (BasicBlock &BB : F) {
458     for (Instruction &I : BB) {
459       if (auto *CI = dyn_cast<CallInst>(&I)) {
460         // Possibly throwing call instructions have no actions to take after
461         // an unwind. Ensure they are in the -1 state.
462         if (CI->doesNotThrow())
463           continue;
464         insertStateNumberStore(ParentRegNode, CI, BaseState);
465       } else if (auto *II = dyn_cast<InvokeInst>(&I)) {
466         // Look up the state number of the landingpad this unwinds to.
467         LandingPadInst *LPI = II->getUnwindDest()->getLandingPadInst();
468         // FIXME: Why does this assertion fail?
469         //assert(FuncInfo.LandingPadStateMap.count(LPI) && "LP has no state!");
470         int State = FuncInfo.LandingPadStateMap[LPI];
471         insertStateNumberStore(ParentRegNode, II, State);
472       }
473     }
474   }
475 }
476 
477 /// Assign every distinct landingpad a unique state number for SEH. Unlike C++
478 /// EH, we can use this very simple algorithm while C++ EH cannot because catch
479 /// handlers aren't outlined and the runtime doesn't have to figure out which
480 /// catch handler frame to unwind to.
481 /// FIXME: __finally blocks are outlined, so this approach may break down there.
482 void WinEHStatePass::addSEHStateStores(Function &F, MachineModuleInfo &MMI) {
483   WinEHFuncInfo &FuncInfo = MMI.getWinEHFuncInfo(&F);
484 
485   // Remember and return the index that we used. We save it in WinEHFuncInfo so
486   // that we can lower llvm.x86.seh.recoverfp later in filter functions without
487   // too much trouble.
488   int RegNodeEscapeIndex = escapeRegNode(F);
489   FuncInfo.EHRegNodeEscapeIndex = RegNodeEscapeIndex;
490 
491   // Iterate all the instructions and emit state number stores.
492   int CurState = 0;
493   SmallPtrSet<BasicBlock *, 4> ExceptBlocks;
494   for (BasicBlock &BB : F) {
495     for (auto I = BB.begin(), E = BB.end(); I != E; ++I) {
496       if (auto *CI = dyn_cast<CallInst>(I)) {
497         auto *Intrin = dyn_cast<IntrinsicInst>(CI);
498         if (Intrin) {
499           // Calls that "don't throw" are considered to be able to throw asynch
500           // exceptions, but intrinsics cannot.
501           continue;
502         }
503         insertStateNumberStore(RegNode, CI, -1);
504       } else if (auto *II = dyn_cast<InvokeInst>(I)) {
505         // Look up the state number of the landingpad this unwinds to.
506         LandingPadInst *LPI = II->getUnwindDest()->getLandingPadInst();
507         auto InsertionPair =
508             FuncInfo.LandingPadStateMap.insert(std::make_pair(LPI, CurState));
509         auto Iter = InsertionPair.first;
510         int &State = Iter->second;
511         bool Inserted = InsertionPair.second;
512         if (Inserted) {
513           // Each action consumes a state number.
514           auto *EHActions = cast<IntrinsicInst>(LPI->getNextNode());
515           SmallVector<std::unique_ptr<ActionHandler>, 4> ActionList;
516           parseEHActions(EHActions, ActionList);
517           assert(!ActionList.empty());
518           CurState += ActionList.size();
519           State += ActionList.size() - 1;
520 
521           // Remember all the __except block targets.
522           for (auto &Handler : ActionList) {
523             if (auto *CH = dyn_cast<CatchHandler>(Handler.get())) {
524               auto *BA = cast<BlockAddress>(CH->getHandlerBlockOrFunc());
525 #ifndef NDEBUG
526               for (BasicBlock *Pred : predecessors(BA->getBasicBlock()))
527                 assert(Pred->isLandingPad() &&
528                        "WinEHPrepare failed to split block");
529 #endif
530               ExceptBlocks.insert(BA->getBasicBlock());
531             }
532           }
533         }
534         insertStateNumberStore(RegNode, II, State);
535       }
536     }
537   }
538 
539   // Insert llvm.x86.seh.restoreframe() into each __except block.
540   Function *RestoreFrame =
541       Intrinsic::getDeclaration(TheModule, Intrinsic::x86_seh_restoreframe);
542   for (BasicBlock *ExceptBB : ExceptBlocks) {
543     IRBuilder<> Builder(ExceptBB->begin());
544     Builder.CreateCall(RestoreFrame, {});
545   }
546 }
547 
548 void WinEHStatePass::insertStateNumberStore(Value *ParentRegNode,
549                                             Instruction *IP, int State) {
550   IRBuilder<> Builder(IP);
551   Value *StateField =
552       Builder.CreateStructGEP(RegNodeTy, ParentRegNode, StateFieldIndex);
553   Builder.CreateStore(Builder.getInt32(State), StateField);
554 }
555