lib/CodeGen/SjLjEHPrepare.cpp

   1 //===- SjLjEHPass.cpp - Eliminate Invoke & Unwind instructions -----------===//
   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 // This transformation is designed for use by code generators which use SjLj
  11 // based exception handling.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #define DEBUG_TYPE "sjljehprepare"
  16 #include "llvm/Transforms/Scalar.h"
  17 #include "llvm/Constants.h"
  18 #include "llvm/DerivedTypes.h"
  19 #include "llvm/Instructions.h"
  20 #include "llvm/Intrinsics.h"
  21 #include "llvm/LLVMContext.h"
  22 #include "llvm/Module.h"
  23 #include "llvm/Pass.h"
  24 #include "llvm/CodeGen/Passes.h"
  25 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  26 #include "llvm/Transforms/Utils/Local.h"
  27 #include "llvm/ADT/Statistic.h"
  28 #include "llvm/ADT/SmallVector.h"
  29 #include "llvm/Support/CommandLine.h"
  30 #include "llvm/Support/Compiler.h"
  31 #include "llvm/Support/Debug.h"
  32 #include "llvm/Support/raw_ostream.h"
  33 #include "llvm/Target/TargetLowering.h"
  34 using namespace llvm;
  35
  36 STATISTIC(NumInvokes, "Number of invokes replaced");
  37 STATISTIC(NumUnwinds, "Number of unwinds replaced");
  38 STATISTIC(NumSpilled, "Number of registers live across unwind edges");
  39
  40 namespace {
  41   class VISIBILITY_HIDDEN SjLjEHPass : public FunctionPass {
  42
  43     const TargetLowering *TLI;
  44
  45     const Type *FunctionContextTy;
  46     Constant *RegisterFn;
  47     Constant *UnregisterFn;
  48     Constant *ResumeFn;
  49     Constant *BuiltinSetjmpFn;
  50     Constant *FrameAddrFn;
  51     Constant *LSDAAddrFn;
  52     Value *PersonalityFn;
  53     Constant *Selector32Fn;
  54     Constant *Selector64Fn;
  55     Constant *ExceptionFn;
  56
  57     Value *CallSite;
  58   public:
  59     static char ID; // Pass identification, replacement for typeid
  60     explicit SjLjEHPass(const TargetLowering *tli = NULL)
  61       : FunctionPass(&ID), TLI(tli) { }
  62     bool doInitialization(Module &M);
  63     bool runOnFunction(Function &F);
  64
  65     virtual void getAnalysisUsage(AnalysisUsage &AU) const { }
  66     const char *getPassName() const {
  67       return "SJLJ Exception Handling preparation";
  68     }
  69
  70   private:
  71     void markInvokeCallSite(InvokeInst *II, unsigned InvokeNo,
  72                             Value *CallSite,
  73                             SwitchInst *CatchSwitch);
  74     void splitLiveRangesLiveAcrossInvokes(SmallVector<InvokeInst*,16> &Invokes);
  75     bool insertSjLjEHSupport(Function &F);
  76   };
  77 } // end anonymous namespace
  78
  79 char SjLjEHPass::ID = 0;
  80
  81 // Public Interface To the SjLjEHPass pass.
  82 FunctionPass *llvm::createSjLjEHPass(const TargetLowering *TLI) {
  83   return new SjLjEHPass(TLI);
  84 }
  85 // doInitialization - Set up decalarations and types needed to process
  86 // exceptions.
  87 bool SjLjEHPass::doInitialization(Module &M) {
  88   // Build the function context structure.
  89   // builtin_setjmp uses a five word jbuf
  90   const Type *VoidPtrTy =
  91           PointerType::getUnqual(Type::getInt8Ty(M.getContext()));
  92   const Type *Int32Ty = Type::getInt32Ty(M.getContext());
  93   FunctionContextTy =
  94     StructType::get(M.getContext(),
  95                     VoidPtrTy,                        // __prev
  96                     Int32Ty,                          // call_site
  97                     ArrayType::get(Int32Ty, 4),       // __data
  98                     VoidPtrTy,                        // __personality
  99                     VoidPtrTy,                        // __lsda
 100                     ArrayType::get(VoidPtrTy, 5),     // __jbuf
 101                     NULL);
 102   RegisterFn = M.getOrInsertFunction("_Unwind_SjLj_Register",
 103                                      Type::getVoidTy(M.getContext()),
 104                                      PointerType::getUnqual(FunctionContextTy),
 105                                      (Type *)0);
 106   UnregisterFn =
 107     M.getOrInsertFunction("_Unwind_SjLj_Unregister",
 108                           Type::getVoidTy(M.getContext()),
 109                           PointerType::getUnqual(FunctionContextTy),
 110                           (Type *)0);
 111   ResumeFn =
 112     M.getOrInsertFunction("_Unwind_SjLj_Resume",
 113                           Type::getVoidTy(M.getContext()),
 114                           VoidPtrTy,
 115                           (Type *)0);
 116   FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress);
 117   BuiltinSetjmpFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setjmp);
 118   LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
 119   Selector32Fn = Intrinsic::getDeclaration(&M, Intrinsic::eh_selector_i32);
 120   Selector64Fn = Intrinsic::getDeclaration(&M, Intrinsic::eh_selector_i64);
 121   ExceptionFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_exception);
 122   PersonalityFn = 0;
 123
 124   return true;
 125 }
 126
 127 /// markInvokeCallSite - Insert code to mark the call_site for this invoke
 128 void SjLjEHPass::markInvokeCallSite(InvokeInst *II, unsigned InvokeNo,
 129                                     Value *CallSite,
 130                                     SwitchInst *CatchSwitch) {
 131   ConstantInt *CallSiteNoC= ConstantInt::get(Type::getInt32Ty(II->getContext()),
 132                                             InvokeNo);
 133   // The runtime comes back to the dispatcher with the call_site - 1 in
 134   // the context. Odd, but there it is.
 135   ConstantInt *SwitchValC = ConstantInt::get(Type::getInt32Ty(II->getContext()),
 136                                             InvokeNo - 1);
 137
 138   // If the unwind edge has phi nodes, split the edge.
 139   if (isa<PHINode>(II->getUnwindDest()->begin())) {
 140     SplitCriticalEdge(II, 1, this);
 141
 142     // If there are any phi nodes left, they must have a single predecessor.
 143     while (PHINode *PN = dyn_cast<PHINode>(II->getUnwindDest()->begin())) {
 144       PN->replaceAllUsesWith(PN->getIncomingValue(0));
 145       PN->eraseFromParent();
 146     }
 147   }
 148
 149   // Insert a store of the invoke num before the invoke and store zero into the
 150   // location afterward.
 151   new StoreInst(CallSiteNoC, CallSite, true, II);  // volatile
 152
 153   // Add a switch case to our unwind block.
 154   CatchSwitch->addCase(SwitchValC, II->getUnwindDest());
 155   // We still want this to look like an invoke so we emit the LSDA properly
 156   // FIXME: ??? Or will this cause strangeness with mis-matched IDs like
 157   //  when it was in the front end?
 158 }
 159
 160 /// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
 161 /// we reach blocks we've already seen.
 162 static void MarkBlocksLiveIn(BasicBlock *BB, std::set<BasicBlock*> &LiveBBs) {
 163   if (!LiveBBs.insert(BB).second) return; // already been here.
 164
 165   for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
 166     MarkBlocksLiveIn(*PI, LiveBBs);
 167 }
 168
 169 /// splitLiveRangesAcrossInvokes - Each value that is live across an unwind edge
 170 /// we spill into a stack location, guaranteeing that there is nothing live
 171 /// across the unwind edge.  This process also splits all critical edges
 172 /// coming out of invoke's.
 173 void SjLjEHPass::
 174 splitLiveRangesLiveAcrossInvokes(SmallVector<InvokeInst*,16> &Invokes) {
 175   // First step, split all critical edges from invoke instructions.
 176   for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
 177     InvokeInst *II = Invokes[i];
 178     SplitCriticalEdge(II, 0, this);
 179     SplitCriticalEdge(II, 1, this);
 180     assert(!isa<PHINode>(II->getNormalDest()) &&
 181            !isa<PHINode>(II->getUnwindDest()) &&
 182            "critical edge splitting left single entry phi nodes?");
 183   }
 184
 185   Function *F = Invokes.back()->getParent()->getParent();
 186
 187   // To avoid having to handle incoming arguments specially, we lower each arg
 188   // to a copy instruction in the entry block.  This ensures that the argument
 189   // value itself cannot be live across the entry block.
 190   BasicBlock::iterator AfterAllocaInsertPt = F->begin()->begin();
 191   while (isa<AllocaInst>(AfterAllocaInsertPt) &&
 192         isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsertPt)->getArraySize()))
 193     ++AfterAllocaInsertPt;
 194   for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
 195        AI != E; ++AI) {
 196     // This is always a no-op cast because we're casting AI to AI->getType() so
 197     // src and destination types are identical. BitCast is the only possibility.
 198     CastInst *NC = new BitCastInst(
 199       AI, AI->getType(), AI->getName()+".tmp", AfterAllocaInsertPt);
 200     AI->replaceAllUsesWith(NC);
 201     // Normally its is forbidden to replace a CastInst's operand because it
 202     // could cause the opcode to reflect an illegal conversion. However, we're
 203     // replacing it here with the same value it was constructed with to simply
 204     // make NC its user.
 205     NC->setOperand(0, AI);
 206   }
 207
 208   // Finally, scan the code looking for instructions with bad live ranges.
 209   for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
 210     for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
 211       // Ignore obvious cases we don't have to handle.  In particular, most
 212       // instructions either have no uses or only have a single use inside the
 213       // current block.  Ignore them quickly.
 214       Instruction *Inst = II;
 215       if (Inst->use_empty()) continue;
 216       if (Inst->hasOneUse() &&
 217           cast<Instruction>(Inst->use_back())->getParent() == BB &&
 218           !isa<PHINode>(Inst->use_back())) continue;
 219
 220       // If this is an alloca in the entry block, it's not a real register
 221       // value.
 222       if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
 223         if (isa<ConstantInt>(AI->getArraySize()) && BB == F->begin())
 224           continue;
 225
 226       // Avoid iterator invalidation by copying users to a temporary vector.
 227       SmallVector<Instruction*,16> Users;
 228       for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end();
 229            UI != E; ++UI) {
 230         Instruction *User = cast<Instruction>(*UI);
 231         if (User->getParent() != BB || isa<PHINode>(User))
 232           Users.push_back(User);
 233       }
 234
 235       // Find all of the blocks that this value is live in.
 236       std::set<BasicBlock*> LiveBBs;
 237       LiveBBs.insert(Inst->getParent());
 238       while (!Users.empty()) {
 239         Instruction *U = Users.back();
 240         Users.pop_back();
 241
 242         if (!isa<PHINode>(U)) {
 243           MarkBlocksLiveIn(U->getParent(), LiveBBs);
 244         } else {
 245           // Uses for a PHI node occur in their predecessor block.
 246           PHINode *PN = cast<PHINode>(U);
 247           for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
 248             if (PN->getIncomingValue(i) == Inst)
 249               MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
 250         }
 251       }
 252
 253       // Now that we know all of the blocks that this thing is live in, see if
 254       // it includes any of the unwind locations.
 255       bool NeedsSpill = false;
 256       for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
 257         BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
 258         if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
 259           NeedsSpill = true;
 260         }
 261       }
 262
 263       // If we decided we need a spill, do it.
 264       if (NeedsSpill) {
 265         ++NumSpilled;
 266         DemoteRegToStack(*Inst, true);
 267       }
 268     }
 269 }
 270
 271 bool SjLjEHPass::insertSjLjEHSupport(Function &F) {
 272   SmallVector<ReturnInst*,16> Returns;
 273   SmallVector<UnwindInst*,16> Unwinds;
 274   SmallVector<InvokeInst*,16> Invokes;
 275
 276   // Look through the terminators of the basic blocks to find invokes, returns
 277   // and unwinds
 278   for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
 279     if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
 280       // Remember all return instructions in case we insert an invoke into this
 281       // function.
 282       Returns.push_back(RI);
 283     } else if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
 284       Invokes.push_back(II);
 285     } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
 286       Unwinds.push_back(UI);
 287     }
 288   // If we don't have any invokes or unwinds, there's nothing to do.
 289   if (Unwinds.empty() && Invokes.empty()) return false;
 290
 291   // Find the eh.selector.*  and eh.exception calls. We'll use the first
 292   // eh.selector to determine the right personality function to use. For
 293   // SJLJ, we always use the same personality for the whole function,
 294   // not on a per-selector basis.
 295   // FIXME: That's a bit ugly. Better way?
 296   SmallVector<CallInst*,16> EH_Selectors;
 297   SmallVector<CallInst*,16> EH_Exceptions;
 298   for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
 299     for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
 300       if (CallInst *CI = dyn_cast<CallInst>(I)) {
 301         if (CI->getCalledFunction() == Selector32Fn ||
 302             CI->getCalledFunction() == Selector64Fn) {
 303           if (!PersonalityFn) PersonalityFn = CI->getOperand(2);
 304           EH_Selectors.push_back(CI);
 305         } else if (CI->getCalledFunction() == ExceptionFn) {
 306           EH_Exceptions.push_back(CI);
 307         }
 308       }
 309     }
 310   }
 311   // If we don't have any eh.selector calls, we can't determine the personality
 312   // function. Without a personality function, we can't process exceptions.
 313   if (!PersonalityFn) return false;
 314
 315   NumInvokes += Invokes.size();
 316   NumUnwinds += Unwinds.size();
 317
 318   if (!Invokes.empty()) {
 319     // We have invokes, so we need to add register/unregister calls to get
 320     // this function onto the global unwind stack.
 321     //
 322     // First thing we need to do is scan the whole function for values that are
 323     // live across unwind edges.  Each value that is live across an unwind edge
 324     // we spill into a stack location, guaranteeing that there is nothing live
 325     // across the unwind edge.  This process also splits all critical edges
 326     // coming out of invoke's.
 327     splitLiveRangesLiveAcrossInvokes(Invokes);
 328
 329     BasicBlock *EntryBB = F.begin();
 330     // Create an alloca for the incoming jump buffer ptr and the new jump buffer
 331     // that needs to be restored on all exits from the function.  This is an
 332     // alloca because the value needs to be added to the global context list.
 333     unsigned Align = 4; // FIXME: Should be a TLI check?
 334     AllocaInst *FunctionContext =
 335       new AllocaInst(FunctionContextTy, 0, Align,
 336                      "fcn_context", F.begin()->begin());
 337
 338     Value *Idxs[2];
 339     const Type *Int32Ty = Type::getInt32Ty(F.getContext());
 340     Value *Zero = ConstantInt::get(Int32Ty, 0);
 341     // We need to also keep around a reference to the call_site field
 342     Idxs[0] = Zero;
 343     Idxs[1] = ConstantInt::get(Int32Ty, 1);
 344     CallSite = GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2,
 345                                          "call_site",
 346                                          EntryBB->getTerminator());
 347
 348     // The exception selector comes back in context->data[1]
 349     Idxs[1] = ConstantInt::get(Int32Ty, 2);
 350     Value *FCData = GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2,
 351                                               "fc_data",
 352                                               EntryBB->getTerminator());
 353     Idxs[1] = ConstantInt::get(Int32Ty, 1);
 354     Value *SelectorAddr = GetElementPtrInst::Create(FCData, Idxs, Idxs+2,
 355                                                     "exc_selector_gep",
 356                                                     EntryBB->getTerminator());
 357     // The exception value comes back in context->data[0]
 358     Idxs[1] = Zero;
 359     Value *ExceptionAddr = GetElementPtrInst::Create(FCData, Idxs, Idxs+2,
 360                                                      "exception_gep",
 361                                                      EntryBB->getTerminator());
 362
 363     // The result of the eh.selector call will be replaced with a
 364     // a reference to the selector value returned in the function
 365     // context. We leave the selector itself so the EH analysis later
 366     // can use it.
 367     for (int i = 0, e = EH_Selectors.size(); i < e; ++i) {
 368       CallInst *I = EH_Selectors[i];
 369       Value *SelectorVal = new LoadInst(SelectorAddr, "select_val", true, I);
 370       I->replaceAllUsesWith(SelectorVal);
 371     }
 372     // eh.exception calls are replaced with references to the proper
 373     // location in the context. Unlike eh.selector, the eh.exception
 374     // calls are removed entirely.
 375     for (int i = 0, e = EH_Exceptions.size(); i < e; ++i) {
 376       CallInst *I = EH_Exceptions[i];
 377       // Possible for there to be duplicates, so check to make sure
 378       // the instruction hasn't already been removed.
 379       if (!I->getParent()) continue;
 380       Value *Val = new LoadInst(ExceptionAddr, "exception", true, I);
 381       Type *Ty = PointerType::getUnqual(Type::getInt8Ty(F.getContext()));
 382       Val = CastInst::Create(Instruction::IntToPtr, Val, Ty, "", I);
 383
 384       I->replaceAllUsesWith(Val);
 385       I->eraseFromParent();
 386     }
 387
 388
 389
 390
 391     // The entry block changes to have the eh.sjlj.setjmp, with a conditional
 392     // branch to a dispatch block for non-zero returns. If we return normally,
 393     // we're not handling an exception and just register the function context
 394     // and continue.
 395
 396     // Create the dispatch block.  The dispatch block is basically a big switch
 397     // statement that goes to all of the invoke landing pads.
 398     BasicBlock *DispatchBlock =
 399             BasicBlock::Create(F.getContext(), "eh.sjlj.setjmp.catch", &F);
 400
 401     // Insert a load in the Catch block, and a switch on its value.  By default,
 402     // we go to a block that just does an unwind (which is the correct action
 403     // for a standard call).
 404     BasicBlock *UnwindBlock = BasicBlock::Create(F.getContext(), "unwindbb", &F);
 405     Unwinds.push_back(new UnwindInst(F.getContext(), UnwindBlock));
 406
 407     Value *DispatchLoad = new LoadInst(CallSite, "invoke.num", true,
 408                                        DispatchBlock);
 409     SwitchInst *DispatchSwitch =
 410       SwitchInst::Create(DispatchLoad, UnwindBlock, Invokes.size(), DispatchBlock);
 411     // Split the entry block to insert the conditional branch for the setjmp.
 412     BasicBlock *ContBlock = EntryBB->splitBasicBlock(EntryBB->getTerminator(),
 413                                                      "eh.sjlj.setjmp.cont");
 414
 415     // Populate the Function Context
 416     //   1. LSDA address
 417     //   2. Personality function address
 418     //   3. jmpbuf (save FP and call eh.sjlj.setjmp)
 419
 420     // LSDA address
 421     Idxs[0] = Zero;
 422     Idxs[1] = ConstantInt::get(Int32Ty, 4);
 423     Value *LSDAFieldPtr =
 424       GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2,
 425                                 "lsda_gep",
 426                                 EntryBB->getTerminator());
 427     Value *LSDA = CallInst::Create(LSDAAddrFn, "lsda_addr",
 428                                    EntryBB->getTerminator());
 429     new StoreInst(LSDA, LSDAFieldPtr, true, EntryBB->getTerminator());
 430
 431     Idxs[1] = ConstantInt::get(Int32Ty, 3);
 432     Value *PersonalityFieldPtr =
 433       GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2,
 434                                 "lsda_gep",
 435                                 EntryBB->getTerminator());
 436     new StoreInst(PersonalityFn, PersonalityFieldPtr, true,
 437                   EntryBB->getTerminator());
 438
 439     //   Save the frame pointer.
 440     Idxs[1] = ConstantInt::get(Int32Ty, 5);
 441     Value *FieldPtr
 442       = GetElementPtrInst::Create(FunctionContext, Idxs, Idxs+2,
 443                                   "jbuf_gep",
 444                                   EntryBB->getTerminator());
 445     Idxs[1] = ConstantInt::get(Int32Ty, 0);
 446     Value *ElemPtr =
 447       GetElementPtrInst::Create(FieldPtr, Idxs, Idxs+2, "jbuf_fp_gep",
 448                                 EntryBB->getTerminator());
 449
 450     Value *Val = CallInst::Create(FrameAddrFn,
 451                                   ConstantInt::get(Int32Ty, 0),
 452                                   "fp",
 453                                   EntryBB->getTerminator());
 454     new StoreInst(Val, ElemPtr, true, EntryBB->getTerminator());
 455     // Call the setjmp instrinsic. It fills in the rest of the jmpbuf
 456     Value *SetjmpArg =
 457       CastInst::Create(Instruction::BitCast, FieldPtr,
 458                         Type::getInt8Ty(F.getContext())->getPointerTo(), "",
 459                         EntryBB->getTerminator());
 460     Value *DispatchVal = CallInst::Create(BuiltinSetjmpFn, SetjmpArg,
 461                                           "dispatch",
 462                                           EntryBB->getTerminator());
 463     // check the return value of the setjmp. non-zero goes to dispatcher
 464     Value *IsNormal = new ICmpInst(EntryBB->getTerminator(),
 465                                    ICmpInst::ICMP_EQ, DispatchVal, Zero,
 466                                    "notunwind");
 467     // Nuke the uncond branch.
 468     EntryBB->getTerminator()->eraseFromParent();
 469
 470     // Put in a new condbranch in its place.
 471     BranchInst::Create(ContBlock, DispatchBlock, IsNormal, EntryBB);
 472
 473     // Register the function context and make sure it's known to not throw
 474     CallInst *Register =
 475       CallInst::Create(RegisterFn, FunctionContext, "",
 476                        ContBlock->getTerminator());
 477     Register->setDoesNotThrow();
 478
 479     // At this point, we are all set up, update the invoke instructions
 480     // to mark their call_site values, and fill in the dispatch switch
 481     // accordingly.
 482     for (unsigned i = 0, e = Invokes.size(); i != e; ++i)
 483       markInvokeCallSite(Invokes[i], i+1, CallSite, DispatchSwitch);
 484
 485     // The front end has likely added calls to _Unwind_Resume. We need
 486     // to find those calls and mark the call_site as -1 immediately prior.
 487     // resume is a noreturn function, so any block that has a call to it
 488     // should end in an 'unreachable' instruction with the call immediately
 489     // prior. That's how we'll search.
 490     // ??? There's got to be a better way. this is fugly.
 491     for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
 492       if ((dyn_cast<UnreachableInst>(BB->getTerminator()))) {
 493         BasicBlock::iterator I = BB->getTerminator();
 494         // Check the previous instruction and see if it's a resume call
 495         if (I == BB->begin()) continue;
 496         if (CallInst *CI = dyn_cast<CallInst>(--I)) {
 497           if (CI->getCalledFunction() == ResumeFn) {
 498             Value *NegativeOne = Constant::getAllOnesValue(Int32Ty);
 499             new StoreInst(NegativeOne, CallSite, true, I);  // volatile
 500           }
 501         }
 502       }
 503
 504     // Replace all unwinds with a branch to the unwind handler.
 505     // ??? Should this ever happen with sjlj exceptions?
 506     for (unsigned i = 0, e = Unwinds.size(); i != e; ++i) {
 507       BranchInst::Create(UnwindBlock, Unwinds[i]);
 508       Unwinds[i]->eraseFromParent();
 509     }
 510
 511     // Finally, for any returns from this function, if this function contains an
 512     // invoke, add a call to unregister the function context.
 513     for (unsigned i = 0, e = Returns.size(); i != e; ++i)
 514       CallInst::Create(UnregisterFn, FunctionContext, "", Returns[i]);
 515   }
 516
 517   return true;
 518 }
 519
 520 bool SjLjEHPass::runOnFunction(Function &F) {
 521   bool Res = insertSjLjEHSupport(F);
 522   return Res;
 523 }