llvm/lib/CodeGen/SjLjEHPrepare.cpp - toolchain/llvm-project - Gitiles

 //===- SjLjEHPrepare.cpp - Eliminate Invoke & Unwind instructions ---------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This transformation is designed for use by code generators which use SjLj
 // based exception handling.
 //
 //===----------------------------------------------------------------------===//

 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/CodeGen/Passes.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;

 #define DEBUG_TYPE "sjljehprepare"

 STATISTIC(NumInvokes, "Number of invokes replaced");
 STATISTIC(NumSpilled, "Number of registers live across unwind edges");

 namespace {
 class SjLjEHPrepare : public FunctionPass {
   Type *doubleUnderDataTy;
   Type *doubleUnderJBufTy;
   Type *FunctionContextTy;
   Constant *RegisterFn;
   Constant *UnregisterFn;
   Constant *BuiltinSetupDispatchFn;
   Constant *FrameAddrFn;
   Constant *StackAddrFn;
   Constant *StackRestoreFn;
   Constant *LSDAAddrFn;
   Constant *CallSiteFn;
   Constant *FuncCtxFn;
   AllocaInst *FuncCtx;

 public:
   static char ID; // Pass identification, replacement for typeid
   explicit SjLjEHPrepare() : FunctionPass(ID) {}
   bool doInitialization(Module &M) override;
   bool runOnFunction(Function &F) override;

   void getAnalysisUsage(AnalysisUsage &AU) const override {}
   StringRef getPassName() const override {
     return "SJLJ Exception Handling preparation";
   }

 private:
   bool setupEntryBlockAndCallSites(Function &F);
   void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, Value *SelVal);
   Value *setupFunctionContext(Function &F, ArrayRef<LandingPadInst *> LPads);
   void lowerIncomingArguments(Function &F);
   void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst *> Invokes);
   void insertCallSiteStore(Instruction *I, int Number);
 };
 } // end anonymous namespace

 char SjLjEHPrepare::ID = 0;
 INITIALIZE_PASS(SjLjEHPrepare, DEBUG_TYPE, "Prepare SjLj exceptions",
                 false, false)

 // Public Interface To the SjLjEHPrepare pass.
 FunctionPass *llvm::createSjLjEHPreparePass() { return new SjLjEHPrepare(); }
 // doInitialization - Set up decalarations and types needed to process
 // exceptions.
 bool SjLjEHPrepare::doInitialization(Module &M) {
   // Build the function context structure.
   // builtin_setjmp uses a five word jbuf
   Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
   Type *Int32Ty = Type::getInt32Ty(M.getContext());
   doubleUnderDataTy = ArrayType::get(Int32Ty, 4);
   doubleUnderJBufTy = ArrayType::get(VoidPtrTy, 5);
   FunctionContextTy = StructType::get(VoidPtrTy,         // __prev
                                       Int32Ty,           // call_site
                                       doubleUnderDataTy, // __data
                                       VoidPtrTy,         // __personality
                                       VoidPtrTy,         // __lsda
                                       doubleUnderJBufTy  // __jbuf
                                       );

   return true;
 }

 /// insertCallSiteStore - Insert a store of the call-site value to the
 /// function context
 void SjLjEHPrepare::insertCallSiteStore(Instruction *I, int Number) {
   IRBuilder<> Builder(I);

   // Get a reference to the call_site field.
   Type *Int32Ty = Type::getInt32Ty(I->getContext());
   Value *Zero = ConstantInt::get(Int32Ty, 0);
   Value *One = ConstantInt::get(Int32Ty, 1);
   Value *Idxs[2] = { Zero, One };
   Value *CallSite =
       Builder.CreateGEP(FunctionContextTy, FuncCtx, Idxs, "call_site");

   // Insert a store of the call-site number
   ConstantInt *CallSiteNoC =
       ConstantInt::get(Type::getInt32Ty(I->getContext()), Number);
   Builder.CreateStore(CallSiteNoC, CallSite, true /*volatile*/);
 }

 /// MarkBlocksLiveIn - Insert BB and all of its predecessors into LiveBBs until
 /// we reach blocks we've already seen.
 static void MarkBlocksLiveIn(BasicBlock *BB,
                              SmallPtrSetImpl<BasicBlock *> &LiveBBs) {
   if (!LiveBBs.insert(BB).second)
     return; // already been here.

   df_iterator_default_set<BasicBlock*> Visited;

   for (BasicBlock *B : inverse_depth_first_ext(BB, Visited))
     LiveBBs.insert(B);

 }

 /// substituteLPadValues - Substitute the values returned by the landingpad
 /// instruction with those returned by the personality function.
 void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
                                          Value *SelVal) {
   SmallVector<Value *, 8> UseWorkList(LPI->user_begin(), LPI->user_end());
   while (!UseWorkList.empty()) {
     Value *Val = UseWorkList.pop_back_val();
     auto *EVI = dyn_cast<ExtractValueInst>(Val);
     if (!EVI)
       continue;
     if (EVI->getNumIndices() != 1)
       continue;
     if (*EVI->idx_begin() == 0)
       EVI->replaceAllUsesWith(ExnVal);
     else if (*EVI->idx_begin() == 1)
       EVI->replaceAllUsesWith(SelVal);
     if (EVI->use_empty())
       EVI->eraseFromParent();
   }

   if (LPI->use_empty())
     return;

   // There are still some uses of LPI. Construct an aggregate with the exception
   // values and replace the LPI with that aggregate.
   Type *LPadType = LPI->getType();
   Value *LPadVal = UndefValue::get(LPadType);
   auto *SelI = cast<Instruction>(SelVal);
   IRBuilder<> Builder(SelI->getParent(), std::next(SelI->getIterator()));
   LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
   LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");

   LPI->replaceAllUsesWith(LPadVal);
 }

 /// setupFunctionContext - Allocate the function context on the stack and fill
 /// it with all of the data that we know at this point.
 Value *SjLjEHPrepare::setupFunctionContext(Function &F,
                                            ArrayRef<LandingPadInst *> LPads) {
   BasicBlock *EntryBB = &F.front();

   // Create an alloca for the incoming jump buffer ptr and the new jump buffer
   // that needs to be restored on all exits from the function. This is an alloca
   // because the value needs to be added to the global context list.
   auto &DL = F.getParent()->getDataLayout();
   unsigned Align = DL.getPrefTypeAlignment(FunctionContextTy);
   FuncCtx = new AllocaInst(FunctionContextTy, DL.getAllocaAddrSpace(),
                            nullptr, Align, "fn_context", &EntryBB->front());

   // Fill in the function context structure.
   for (LandingPadInst *LPI : LPads) {
     IRBuilder<> Builder(LPI->getParent(),
                         LPI->getParent()->getFirstInsertionPt());

     // Reference the __data field.
     Value *FCData =
         Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 2, "__data");

     // The exception values come back in context->__data[0].
     Value *ExceptionAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
                                                       0, 0, "exception_gep");
     Value *ExnVal = Builder.CreateLoad(ExceptionAddr, true, "exn_val");
     ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());

     Value *SelectorAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
                                                      0, 1, "exn_selector_gep");
     Value *SelVal = Builder.CreateLoad(SelectorAddr, true, "exn_selector_val");

     substituteLPadValues(LPI, ExnVal, SelVal);
   }

   // Personality function
   IRBuilder<> Builder(EntryBB->getTerminator());
   Value *PersonalityFn = F.getPersonalityFn();
   Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32(
       FunctionContextTy, FuncCtx, 0, 3, "pers_fn_gep");
   Builder.CreateStore(
       Builder.CreateBitCast(PersonalityFn, Builder.getInt8PtrTy()),
       PersonalityFieldPtr, /*isVolatile=*/true);

   // LSDA address
   Value *LSDA = Builder.CreateCall(LSDAAddrFn, {}, "lsda_addr");
   Value *LSDAFieldPtr =
       Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 4, "lsda_gep");
   Builder.CreateStore(LSDA, LSDAFieldPtr, /*isVolatile=*/true);

   return FuncCtx;
 }

 /// lowerIncomingArguments - To avoid having to handle incoming arguments
 /// specially, we lower each arg to a copy instruction in the entry block. This
 /// ensures that the argument value itself cannot be live out of the entry
 /// block.
 void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
   BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin();
   while (isa<AllocaInst>(AfterAllocaInsPt) &&
          cast<AllocaInst>(AfterAllocaInsPt)->isStaticAlloca())
     ++AfterAllocaInsPt;
   assert(AfterAllocaInsPt != F.front().end());

   for (auto &AI : F.args()) {
     // Swift error really is a register that we model as memory -- instruction
     // selection will perform mem-to-reg for us and spill/reload appropriately
     // around calls that clobber it. There is no need to spill this
     // value to the stack and doing so would not be allowed.
     if (AI.isSwiftError())
       continue;

     Type *Ty = AI.getType();

     // Use 'select i8 true, %arg, undef' to simulate a 'no-op' instruction.
     Value *TrueValue = ConstantInt::getTrue(F.getContext());
     Value *UndefValue = UndefValue::get(Ty);
     Instruction *SI = SelectInst::Create(
         TrueValue, &AI, UndefValue, AI.getName() + ".tmp", &*AfterAllocaInsPt);
     AI.replaceAllUsesWith(SI);

     // Reset the operand, because it  was clobbered by the RAUW above.
     SI->setOperand(1, &AI);
   }
 }

 /// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
 /// edge and spill them.
 void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
                                            ArrayRef<InvokeInst *> Invokes) {
   // Finally, scan the code looking for instructions with bad live ranges.
   for (BasicBlock &BB : F) {
     for (Instruction &Inst : BB) {
       // Ignore obvious cases we don't have to handle. In particular, most
       // instructions either have no uses or only have a single use inside the
       // current block. Ignore them quickly.
       if (Inst.use_empty())
         continue;
       if (Inst.hasOneUse() &&
           cast<Instruction>(Inst.user_back())->getParent() == &BB &&
           !isa<PHINode>(Inst.user_back()))
         continue;

       // If this is an alloca in the entry block, it's not a real register
       // value.
       if (auto *AI = dyn_cast<AllocaInst>(&Inst))
         if (AI->isStaticAlloca())
           continue;

       // Avoid iterator invalidation by copying users to a temporary vector.
       SmallVector<Instruction *, 16> Users;
       for (User *U : Inst.users()) {
         Instruction *UI = cast<Instruction>(U);
         if (UI->getParent() != &BB || isa<PHINode>(UI))
           Users.push_back(UI);
       }

       // Find all of the blocks that this value is live in.
       SmallPtrSet<BasicBlock *, 32> LiveBBs;
       LiveBBs.insert(&BB);
       while (!Users.empty()) {
         Instruction *U = Users.pop_back_val();

         if (!isa<PHINode>(U)) {
           MarkBlocksLiveIn(U->getParent(), LiveBBs);
         } else {
           // Uses for a PHI node occur in their predecessor block.
           PHINode *PN = cast<PHINode>(U);
           for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
             if (PN->getIncomingValue(i) == &Inst)
               MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
         }
       }

       // Now that we know all of the blocks that this thing is live in, see if
       // it includes any of the unwind locations.
       bool NeedsSpill = false;
       for (InvokeInst *Invoke : Invokes) {
         BasicBlock *UnwindBlock = Invoke->getUnwindDest();
         if (UnwindBlock != &BB && LiveBBs.count(UnwindBlock)) {
           LLVM_DEBUG(dbgs() << "SJLJ Spill: " << Inst << " around "
                             << UnwindBlock->getName() << "\n");
           NeedsSpill = true;
           break;
         }
       }

       // If we decided we need a spill, do it.
       // FIXME: Spilling this way is overkill, as it forces all uses of
       // the value to be reloaded from the stack slot, even those that aren't
       // in the unwind blocks. We should be more selective.
       if (NeedsSpill) {
         DemoteRegToStack(Inst, true);
         ++NumSpilled;
       }
     }
   }

   // Go through the landing pads and remove any PHIs there.
   for (InvokeInst *Invoke : Invokes) {
     BasicBlock *UnwindBlock = Invoke->getUnwindDest();
     LandingPadInst *LPI = UnwindBlock->getLandingPadInst();

     // Place PHIs into a set to avoid invalidating the iterator.
     SmallPtrSet<PHINode *, 8> PHIsToDemote;
     for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
       PHIsToDemote.insert(cast<PHINode>(PN));
     if (PHIsToDemote.empty())
       continue;

     // Demote the PHIs to the stack.
     for (PHINode *PN : PHIsToDemote)
       DemotePHIToStack(PN);

     // Move the landingpad instruction back to the top of the landing pad block.
     LPI->moveBefore(&UnwindBlock->front());
   }
 }

 /// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
 /// the function context and marking the call sites with the appropriate
 /// values. These values are used by the DWARF EH emitter.
 bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
   SmallVector<ReturnInst *, 16> Returns;
   SmallVector<InvokeInst *, 16> Invokes;
   SmallSetVector<LandingPadInst *, 16> LPads;

   // Look through the terminators of the basic blocks to find invokes.
   for (BasicBlock &BB : F)
     if (auto *II = dyn_cast<InvokeInst>(BB.getTerminator())) {
       if (Function *Callee = II->getCalledFunction())
         if (Callee->getIntrinsicID() == Intrinsic::donothing) {
           // Remove the NOP invoke.
           BranchInst::Create(II->getNormalDest(), II);
           II->eraseFromParent();
           continue;
         }

       Invokes.push_back(II);
       LPads.insert(II->getUnwindDest()->getLandingPadInst());
     } else if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator())) {
       Returns.push_back(RI);
     }

   if (Invokes.empty())
     return false;

   NumInvokes += Invokes.size();

   lowerIncomingArguments(F);
   lowerAcrossUnwindEdges(F, Invokes);

   Value *FuncCtx =
       setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
   BasicBlock *EntryBB = &F.front();
   IRBuilder<> Builder(EntryBB->getTerminator());

   // Get a reference to the jump buffer.
   Value *JBufPtr =
       Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep");

   // Save the frame pointer.
   Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0,
                                                "jbuf_fp_gep");

   Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
   Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);

   // Save the stack pointer.
   Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2,
                                                "jbuf_sp_gep");

   Val = Builder.CreateCall(StackAddrFn, {}, "sp");
   Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);

   // Call the setup_dispatch instrinsic. It fills in the rest of the jmpbuf.
   Builder.CreateCall(BuiltinSetupDispatchFn, {});

   // Store a pointer to the function context so that the back-end will know
   // where to look for it.
   Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
   Builder.CreateCall(FuncCtxFn, FuncCtxArg);

   // At this point, we are all set up, update the invoke instructions to mark
   // their call_site values.
   for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
     insertCallSiteStore(Invokes[I], I + 1);

     ConstantInt *CallSiteNum =
         ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);

     // Record the call site value for the back end so it stays associated with
     // the invoke.
     CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
   }

   // Mark call instructions that aren't nounwind as no-action (call_site ==
   // -1). Skip the entry block, as prior to then, no function context has been
   // created for this function and any unexpected exceptions thrown will go
   // directly to the caller's context, which is what we want anyway, so no need
   // to do anything here.
   for (BasicBlock &BB : F) {
     if (&BB == &F.front())
       continue;
     for (Instruction &I : BB)
       if (I.mayThrow())
         insertCallSiteStore(&I, -1);
   }

   // Register the function context and make sure it's known to not throw
   CallInst *Register =
       CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
   Register->setDoesNotThrow();

   // Following any allocas not in the entry block, update the saved SP in the
   // jmpbuf to the new value.
   for (BasicBlock &BB : F) {
     if (&BB == &F.front())
       continue;
     for (Instruction &I : BB) {
       if (auto *CI = dyn_cast<CallInst>(&I)) {
         if (CI->getCalledFunction() != StackRestoreFn)
           continue;
       } else if (!isa<AllocaInst>(&I)) {
         continue;
       }
       Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
       StackAddr->insertAfter(&I);
       Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true);
       StoreStackAddr->insertAfter(StackAddr);
     }
   }

   // Finally, for any returns from this function, if this function contains an
   // invoke, add a call to unregister the function context.
   for (ReturnInst *Return : Returns)
     CallInst::Create(UnregisterFn, FuncCtx, "", Return);

   return true;
 }

 bool SjLjEHPrepare::runOnFunction(Function &F) {
   Module &M = *F.getParent();
   RegisterFn = M.getOrInsertFunction(
       "_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
       PointerType::getUnqual(FunctionContextTy));
   UnregisterFn = M.getOrInsertFunction(
       "_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
       PointerType::getUnqual(FunctionContextTy));
   FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress);
   StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
   StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
   BuiltinSetupDispatchFn =
     Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setup_dispatch);
   LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
   CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
   FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);

   bool Res = setupEntryBlockAndCallSites(F);
   return Res;
 }
	//===- SjLjEHPrepare.cpp - Eliminate Invoke & Unwind instructions ---------===//
	//
	// The LLVM Compiler Infrastructure
	//
	// This file is distributed under the University of Illinois Open Source
	// License. See LICENSE.TXT for details.
	//
	//===----------------------------------------------------------------------===//
	//
	// This transformation is designed for use by code generators which use SjLj
	// based exception handling.
	//
	//===----------------------------------------------------------------------===//

	#include "llvm/ADT/SetVector.h"
	#include "llvm/ADT/SmallPtrSet.h"
	#include "llvm/ADT/SmallVector.h"
	#include "llvm/ADT/Statistic.h"
	#include "llvm/Transforms/Utils/Local.h"
	#include "llvm/CodeGen/Passes.h"
	#include "llvm/IR/Constants.h"
	#include "llvm/IR/DataLayout.h"
	#include "llvm/IR/DerivedTypes.h"
	#include "llvm/IR/IRBuilder.h"
	#include "llvm/IR/Instructions.h"
	#include "llvm/IR/Intrinsics.h"
	#include "llvm/IR/Module.h"
	#include "llvm/Pass.h"
	#include "llvm/Support/Debug.h"
	#include "llvm/Support/raw_ostream.h"
	using namespace llvm;

	#define DEBUG_TYPE "sjljehprepare"

	STATISTIC(NumInvokes, "Number of invokes replaced");
	STATISTIC(NumSpilled, "Number of registers live across unwind edges");

	namespace {
	class SjLjEHPrepare : public FunctionPass {
	Type *doubleUnderDataTy;
	Type *doubleUnderJBufTy;
	Type *FunctionContextTy;
	Constant *RegisterFn;
	Constant *UnregisterFn;
	Constant *BuiltinSetupDispatchFn;
	Constant *FrameAddrFn;
	Constant *StackAddrFn;
	Constant *StackRestoreFn;
	Constant *LSDAAddrFn;
	Constant *CallSiteFn;
	Constant *FuncCtxFn;
	AllocaInst *FuncCtx;

	public:
	static char ID; // Pass identification, replacement for typeid
	explicit SjLjEHPrepare() : FunctionPass(ID) {}
	bool doInitialization(Module &M) override;
	bool runOnFunction(Function &F) override;

	void getAnalysisUsage(AnalysisUsage &AU) const override {}
	StringRef getPassName() const override {
	return "SJLJ Exception Handling preparation";
	}

	private:
	bool setupEntryBlockAndCallSites(Function &F);
	void substituteLPadValues(LandingPadInst LPI, Value ExnVal, Value *SelVal);
	Value setupFunctionContext(Function &F, ArrayRef<LandingPadInst > LPads);
	void lowerIncomingArguments(Function &F);
	void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst *> Invokes);
	void insertCallSiteStore(Instruction *I, int Number);
	};
	} // end anonymous namespace

	char SjLjEHPrepare::ID = 0;
	INITIALIZE_PASS(SjLjEHPrepare, DEBUG_TYPE, "Prepare SjLj exceptions",
	false, false)

	// Public Interface To the SjLjEHPrepare pass.
	FunctionPass *llvm::createSjLjEHPreparePass() { return new SjLjEHPrepare(); }
	// doInitialization - Set up decalarations and types needed to process
	// exceptions.
	bool SjLjEHPrepare::doInitialization(Module &M) {
	// Build the function context structure.
	// builtin_setjmp uses a five word jbuf
	Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
	Type *Int32Ty = Type::getInt32Ty(M.getContext());
	doubleUnderDataTy = ArrayType::get(Int32Ty, 4);
	doubleUnderJBufTy = ArrayType::get(VoidPtrTy, 5);
	FunctionContextTy = StructType::get(VoidPtrTy, // __prev
	Int32Ty, // call_site
	doubleUnderDataTy, // __data
	VoidPtrTy, // __personality
	VoidPtrTy, // __lsda
	doubleUnderJBufTy // __jbuf
	);

	return true;
	}

	/// insertCallSiteStore - Insert a store of the call-site value to the
	/// function context
	void SjLjEHPrepare::insertCallSiteStore(Instruction *I, int Number) {
	IRBuilder<> Builder(I);

	// Get a reference to the call_site field.
	Type *Int32Ty = Type::getInt32Ty(I->getContext());
	Value *Zero = ConstantInt::get(Int32Ty, 0);
	Value *One = ConstantInt::get(Int32Ty, 1);
	Value *Idxs[2] = { Zero, One };
	Value *CallSite =
	Builder.CreateGEP(FunctionContextTy, FuncCtx, Idxs, "call_site");

	// Insert a store of the call-site number
	ConstantInt *CallSiteNoC =
	ConstantInt::get(Type::getInt32Ty(I->getContext()), Number);
	Builder.CreateStore(CallSiteNoC, CallSite, true /volatile/);
	}

	/// MarkBlocksLiveIn - Insert BB and all of its predecessors into LiveBBs until
	/// we reach blocks we've already seen.
	static void MarkBlocksLiveIn(BasicBlock *BB,
	SmallPtrSetImpl<BasicBlock *> &LiveBBs) {
	if (!LiveBBs.insert(BB).second)
	return; // already been here.

	df_iterator_default_set<BasicBlock*> Visited;

	for (BasicBlock *B : inverse_depth_first_ext(BB, Visited))
	LiveBBs.insert(B);

	}

	/// substituteLPadValues - Substitute the values returned by the landingpad
	/// instruction with those returned by the personality function.
	void SjLjEHPrepare::substituteLPadValues(LandingPadInst LPI, Value ExnVal,
	Value *SelVal) {
	SmallVector<Value *, 8> UseWorkList(LPI->user_begin(), LPI->user_end());
	while (!UseWorkList.empty()) {
	Value *Val = UseWorkList.pop_back_val();
	auto *EVI = dyn_cast<ExtractValueInst>(Val);
	if (!EVI)
	continue;
	if (EVI->getNumIndices() != 1)
	continue;
	if (*EVI->idx_begin() == 0)
	EVI->replaceAllUsesWith(ExnVal);
	else if (*EVI->idx_begin() == 1)
	EVI->replaceAllUsesWith(SelVal);
	if (EVI->use_empty())
	EVI->eraseFromParent();
	}

	if (LPI->use_empty())
	return;

	// There are still some uses of LPI. Construct an aggregate with the exception
	// values and replace the LPI with that aggregate.
	Type *LPadType = LPI->getType();
	Value *LPadVal = UndefValue::get(LPadType);
	auto *SelI = cast<Instruction>(SelVal);
	IRBuilder<> Builder(SelI->getParent(), std::next(SelI->getIterator()));
	LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
	LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");

	LPI->replaceAllUsesWith(LPadVal);
	}

	/// setupFunctionContext - Allocate the function context on the stack and fill
	/// it with all of the data that we know at this point.
	Value *SjLjEHPrepare::setupFunctionContext(Function &F,
	ArrayRef<LandingPadInst *> LPads) {
	BasicBlock *EntryBB = &F.front();

	// Create an alloca for the incoming jump buffer ptr and the new jump buffer
	// that needs to be restored on all exits from the function. This is an alloca
	// because the value needs to be added to the global context list.
	auto &DL = F.getParent()->getDataLayout();
	unsigned Align = DL.getPrefTypeAlignment(FunctionContextTy);
	FuncCtx = new AllocaInst(FunctionContextTy, DL.getAllocaAddrSpace(),
	nullptr, Align, "fn_context", &EntryBB->front());

	// Fill in the function context structure.
	for (LandingPadInst *LPI : LPads) {
	IRBuilder<> Builder(LPI->getParent(),
	LPI->getParent()->getFirstInsertionPt());

	// Reference the __data field.
	Value *FCData =
	Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 2, "__data");

	// The exception values come back in context->__data[0].
	Value *ExceptionAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
	0, 0, "exception_gep");
	Value *ExnVal = Builder.CreateLoad(ExceptionAddr, true, "exn_val");
	ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());

	Value *SelectorAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
	0, 1, "exn_selector_gep");
	Value *SelVal = Builder.CreateLoad(SelectorAddr, true, "exn_selector_val");

	substituteLPadValues(LPI, ExnVal, SelVal);
	}

	// Personality function
	IRBuilder<> Builder(EntryBB->getTerminator());
	Value *PersonalityFn = F.getPersonalityFn();
	Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32(
	FunctionContextTy, FuncCtx, 0, 3, "pers_fn_gep");
	Builder.CreateStore(
	Builder.CreateBitCast(PersonalityFn, Builder.getInt8PtrTy()),
	PersonalityFieldPtr, /isVolatile=/true);

	// LSDA address
	Value *LSDA = Builder.CreateCall(LSDAAddrFn, {}, "lsda_addr");
	Value *LSDAFieldPtr =
	Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 4, "lsda_gep");
	Builder.CreateStore(LSDA, LSDAFieldPtr, /isVolatile=/true);

	return FuncCtx;
	}

	/// lowerIncomingArguments - To avoid having to handle incoming arguments
	/// specially, we lower each arg to a copy instruction in the entry block. This
	/// ensures that the argument value itself cannot be live out of the entry
	/// block.
	void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
	BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin();
	while (isa<AllocaInst>(AfterAllocaInsPt) &&
	cast<AllocaInst>(AfterAllocaInsPt)->isStaticAlloca())
	++AfterAllocaInsPt;
	assert(AfterAllocaInsPt != F.front().end());

	for (auto &AI : F.args()) {
	// Swift error really is a register that we model as memory -- instruction
	// selection will perform mem-to-reg for us and spill/reload appropriately
	// around calls that clobber it. There is no need to spill this
	// value to the stack and doing so would not be allowed.
	if (AI.isSwiftError())
	continue;

	Type *Ty = AI.getType();

	// Use 'select i8 true, %arg, undef' to simulate a 'no-op' instruction.
	Value *TrueValue = ConstantInt::getTrue(F.getContext());
	Value *UndefValue = UndefValue::get(Ty);
	Instruction *SI = SelectInst::Create(
	TrueValue, &AI, UndefValue, AI.getName() + ".tmp", &*AfterAllocaInsPt);
	AI.replaceAllUsesWith(SI);

	// Reset the operand, because it was clobbered by the RAUW above.
	SI->setOperand(1, &AI);
	}
	}

	/// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
	/// edge and spill them.
	void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
	ArrayRef<InvokeInst *> Invokes) {
	// Finally, scan the code looking for instructions with bad live ranges.
	for (BasicBlock &BB : F) {
	for (Instruction &Inst : BB) {
	// Ignore obvious cases we don't have to handle. In particular, most
	// instructions either have no uses or only have a single use inside the
	// current block. Ignore them quickly.
	if (Inst.use_empty())
	continue;
	if (Inst.hasOneUse() &&
	cast<Instruction>(Inst.user_back())->getParent() == &BB &&
	!isa<PHINode>(Inst.user_back()))
	continue;

	// If this is an alloca in the entry block, it's not a real register
	// value.
	if (auto *AI = dyn_cast<AllocaInst>(&Inst))
	if (AI->isStaticAlloca())
	continue;

	// Avoid iterator invalidation by copying users to a temporary vector.
	SmallVector<Instruction *, 16> Users;
	for (User *U : Inst.users()) {
	Instruction *UI = cast<Instruction>(U);
	if (UI->getParent() != &BB \|\| isa<PHINode>(UI))
	Users.push_back(UI);
	}

	// Find all of the blocks that this value is live in.
	SmallPtrSet<BasicBlock *, 32> LiveBBs;
	LiveBBs.insert(&BB);
	while (!Users.empty()) {
	Instruction *U = Users.pop_back_val();

	if (!isa<PHINode>(U)) {
	MarkBlocksLiveIn(U->getParent(), LiveBBs);
	} else {
	// Uses for a PHI node occur in their predecessor block.
	PHINode *PN = cast<PHINode>(U);
	for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
	if (PN->getIncomingValue(i) == &Inst)
	MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
	}
	}

	// Now that we know all of the blocks that this thing is live in, see if
	// it includes any of the unwind locations.
	bool NeedsSpill = false;
	for (InvokeInst *Invoke : Invokes) {
	BasicBlock *UnwindBlock = Invoke->getUnwindDest();
	if (UnwindBlock != &BB && LiveBBs.count(UnwindBlock)) {
	LLVM_DEBUG(dbgs() << "SJLJ Spill: " << Inst << " around "
	<< UnwindBlock->getName() << "\n");
	NeedsSpill = true;
	break;
	}
	}

	// If we decided we need a spill, do it.
	// FIXME: Spilling this way is overkill, as it forces all uses of
	// the value to be reloaded from the stack slot, even those that aren't
	// in the unwind blocks. We should be more selective.
	if (NeedsSpill) {
	DemoteRegToStack(Inst, true);
	++NumSpilled;
	}
	}
	}

	// Go through the landing pads and remove any PHIs there.
	for (InvokeInst *Invoke : Invokes) {
	BasicBlock *UnwindBlock = Invoke->getUnwindDest();
	LandingPadInst *LPI = UnwindBlock->getLandingPadInst();

	// Place PHIs into a set to avoid invalidating the iterator.
	SmallPtrSet<PHINode *, 8> PHIsToDemote;
	for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
	PHIsToDemote.insert(cast<PHINode>(PN));
	if (PHIsToDemote.empty())
	continue;

	// Demote the PHIs to the stack.
	for (PHINode *PN : PHIsToDemote)
	DemotePHIToStack(PN);

	// Move the landingpad instruction back to the top of the landing pad block.
	LPI->moveBefore(&UnwindBlock->front());
	}
	}

	/// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
	/// the function context and marking the call sites with the appropriate
	/// values. These values are used by the DWARF EH emitter.
	bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
	SmallVector<ReturnInst *, 16> Returns;
	SmallVector<InvokeInst *, 16> Invokes;
	SmallSetVector<LandingPadInst *, 16> LPads;

	// Look through the terminators of the basic blocks to find invokes.
	for (BasicBlock &BB : F)
	if (auto *II = dyn_cast<InvokeInst>(BB.getTerminator())) {
	if (Function *Callee = II->getCalledFunction())
	if (Callee->getIntrinsicID() == Intrinsic::donothing) {
	// Remove the NOP invoke.
	BranchInst::Create(II->getNormalDest(), II);
	II->eraseFromParent();
	continue;
	}

	Invokes.push_back(II);
	LPads.insert(II->getUnwindDest()->getLandingPadInst());
	} else if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator())) {
	Returns.push_back(RI);
	}

	if (Invokes.empty())
	return false;

	NumInvokes += Invokes.size();

	lowerIncomingArguments(F);
	lowerAcrossUnwindEdges(F, Invokes);

	Value *FuncCtx =
	setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
	BasicBlock *EntryBB = &F.front();
	IRBuilder<> Builder(EntryBB->getTerminator());

	// Get a reference to the jump buffer.
	Value *JBufPtr =
	Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep");

	// Save the frame pointer.
	Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0,
	"jbuf_fp_gep");

	Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
	Builder.CreateStore(Val, FramePtr, /isVolatile=/true);

	// Save the stack pointer.
	Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2,
	"jbuf_sp_gep");

	Val = Builder.CreateCall(StackAddrFn, {}, "sp");
	Builder.CreateStore(Val, StackPtr, /isVolatile=/true);

	// Call the setup_dispatch instrinsic. It fills in the rest of the jmpbuf.
	Builder.CreateCall(BuiltinSetupDispatchFn, {});

	// Store a pointer to the function context so that the back-end will know
	// where to look for it.
	Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
	Builder.CreateCall(FuncCtxFn, FuncCtxArg);

	// At this point, we are all set up, update the invoke instructions to mark
	// their call_site values.
	for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
	insertCallSiteStore(Invokes[I], I + 1);

	ConstantInt *CallSiteNum =
	ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);

	// Record the call site value for the back end so it stays associated with
	// the invoke.
	CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
	}

	// Mark call instructions that aren't nounwind as no-action (call_site ==
	// -1). Skip the entry block, as prior to then, no function context has been
	// created for this function and any unexpected exceptions thrown will go
	// directly to the caller's context, which is what we want anyway, so no need
	// to do anything here.
	for (BasicBlock &BB : F) {
	if (&BB == &F.front())
	continue;
	for (Instruction &I : BB)
	if (I.mayThrow())
	insertCallSiteStore(&I, -1);
	}

	// Register the function context and make sure it's known to not throw
	CallInst *Register =
	CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
	Register->setDoesNotThrow();

	// Following any allocas not in the entry block, update the saved SP in the
	// jmpbuf to the new value.
	for (BasicBlock &BB : F) {
	if (&BB == &F.front())
	continue;
	for (Instruction &I : BB) {
	if (auto *CI = dyn_cast<CallInst>(&I)) {
	if (CI->getCalledFunction() != StackRestoreFn)
	continue;
	} else if (!isa<AllocaInst>(&I)) {
	continue;
	}
	Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
	StackAddr->insertAfter(&I);
	Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true);
	StoreStackAddr->insertAfter(StackAddr);
	}
	}

	// Finally, for any returns from this function, if this function contains an
	// invoke, add a call to unregister the function context.
	for (ReturnInst *Return : Returns)
	CallInst::Create(UnregisterFn, FuncCtx, "", Return);

	return true;
	}

	bool SjLjEHPrepare::runOnFunction(Function &F) {
	Module &M = *F.getParent();
	RegisterFn = M.getOrInsertFunction(
	"_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
	PointerType::getUnqual(FunctionContextTy));
	UnregisterFn = M.getOrInsertFunction(
	"_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
	PointerType::getUnqual(FunctionContextTy));
	FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress);
	StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
	StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
	BuiltinSetupDispatchFn =
	Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setup_dispatch);
	LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
	CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
	FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);

	bool Res = setupEntryBlockAndCallSites(F);
	return Res;
	}