text: //===- 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/CodeGen/Passes.h"
  #include "llvm/ADT/DenseMap.h"
  #include "llvm/ADT/SetVector.h"
  #include "llvm/ADT/SmallPtrSet.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/Statistic.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/LLVMContext.h"
  #include "llvm/IR/Module.h"
  #include "llvm/Pass.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/Debug.h"
  #include "llvm/Support/raw_ostream.h"
  #include "llvm/Target/TargetLowering.h"
  #include "llvm/Target/TargetSubtargetInfo.h"
  #include "llvm/Transforms/Scalar.h"
  #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  #include "llvm/Transforms/Utils/Local.h"
  #include <set>
  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 *BuiltinSetjmpFn;
    Constant *FrameAddrFn;
    Constant *StackAddrFn;
    Constant *StackRestoreFn;
    Constant *LSDAAddrFn;
    Value *PersonalityFn;
    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 {}
    const char *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, "sjljehprepare", "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
                                        nullptr);
    RegisterFn = M.getOrInsertFunction(
        "_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
        PointerType::getUnqual(FunctionContextTy), (Type *)nullptr);
    UnregisterFn = M.getOrInsertFunction(
        "_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
        PointerType::getUnqual(FunctionContextTy), (Type *)nullptr);
    FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress);
    StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
    StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
    BuiltinSetjmpFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setjmp);
    LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
    CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
    FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);
    PersonalityFn = nullptr;
  
    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 predescessors 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.
  
    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
      MarkBlocksLiveIn(*PI, LiveBBs);
  }
  
  /// 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();
      ExtractValueInst *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->getNumUses() == 0)
        EVI->eraseFromParent();
    }
  
    if (LPI->getNumUses() == 0)
      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);
    IRBuilder<> Builder(
        std::next(BasicBlock::iterator(cast<Instruction>(SelVal))));
    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.begin();
  
    // 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, nullptr, Align, "fn_context",
                             EntryBB->begin());
  
    // Fill in the function context structure.
    for (unsigned I = 0, E = LPads.size(); I != E; ++I) {
      LandingPadInst *LPI = LPads[I];
      IRBuilder<> Builder(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());
    if (!PersonalityFn)
      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) &&
           isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsPt)->getArraySize()))
      ++AfterAllocaInsPt;
  
    for (Function::arg_iterator AI = F.arg_begin(), AE = F.arg_end(); AI != AE;
         ++AI) {
      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 (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
      for (BasicBlock::iterator II = BB->begin(), IIE = BB->end(); II != IIE;
           ++II) {
        // 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.
        Instruction *Inst = II;
        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 (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
          if (isa<ConstantInt>(AI->getArraySize()) && BB == F.begin())
            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 *, 64> LiveBBs;
        LiveBBs.insert(Inst->getParent());
        while (!Users.empty()) {
          Instruction *U = Users.back();
          Users.pop_back();
  
          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 (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
          BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
          if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
            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 (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
      BasicBlock *UnwindBlock = Invokes[i]->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->begin());
    }
  }
  
  /// 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 (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
      if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
        if (Function *Callee = II->getCalledFunction())
          if (Callee->isIntrinsic() &&
              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 (ReturnInst *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.begin();
    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 setjmp instrinsic. It fills in the rest of the jmpbuf.
    Value *SetjmpArg = Builder.CreateBitCast(JBufPtr, Builder.getInt8PtrTy());
    Builder.CreateCall(BuiltinSetjmpFn, SetjmpArg);
  
    // 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 (Function::iterator BB = F.begin(), E = F.end(); ++BB != E;)
      for (BasicBlock::iterator I = BB->begin(), end = BB->end(); I != end; ++I)
        if (CallInst *CI = dyn_cast<CallInst>(I)) {
          if (!CI->doesNotThrow())
            insertCallSiteStore(CI, -1);
        } else if (ResumeInst *RI = dyn_cast<ResumeInst>(I)) {
          insertCallSiteStore(RI, -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 (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
      if (BB == F.begin())
        continue;
      for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
        if (CallInst *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 (unsigned I = 0, E = Returns.size(); I != E; ++I)
      CallInst::Create(UnregisterFn, FuncCtx, "", Returns[I]);
  
    return true;
  }
  
  bool SjLjEHPrepare::runOnFunction(Function &F) {
    bool Res = setupEntryBlockAndCallSites(F);
    return Res;
  }
  