llvm.org GIT mirror llvm / 667d4b8 lib / Transforms / IPO / LowerSetJmp.cpp
667d4b8

Tree @667d4b8 (Download .tar.gz)

LowerSetJmp.cpp @667d4b8raw · history · blame

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
//===- LowerSetJmp.cpp - Code pertaining to lowering set/long jumps -------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//  This file implements the lowering of setjmp and longjmp to use the
//  LLVM invoke and unwind instructions as necessary.
//
//  Lowering of longjmp is fairly trivial. We replace the call with a
//  call to the LLVM library function "__llvm_sjljeh_throw_longjmp()".
//  This unwinds the stack for us calling all of the destructors for
//  objects allocated on the stack.
//
//  At a setjmp call, the basic block is split and the setjmp removed.
//  The calls in a function that have a setjmp are converted to invoke
//  where the except part checks to see if it's a longjmp exception and,
//  if so, if it's handled in the function. If it is, then it gets the
//  value returned by the longjmp and goes to where the basic block was
//  split. Invoke instructions are handled in a similar fashion with the
//  original except block being executed if it isn't a longjmp except
//  that is handled by that function.
//
//===----------------------------------------------------------------------===//

//===----------------------------------------------------------------------===//
// FIXME: This pass doesn't deal with PHI statements just yet. That is,
// we expect this to occur before SSAification is done. This would seem
// to make sense, but in general, it might be a good idea to make this
// pass invokable via the "opt" command at will.
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "lowersetjmp"
#include "llvm/Transforms/IPO.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Intrinsics.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/InstVisitor.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/VectorExtras.h"
#include "llvm/ADT/SmallVector.h"
#include <map>
using namespace llvm;

STATISTIC(LongJmpsTransformed, "Number of longjmps transformed");
STATISTIC(SetJmpsTransformed , "Number of setjmps transformed");
STATISTIC(CallsTransformed   , "Number of calls invokified");
STATISTIC(InvokesTransformed , "Number of invokes modified");

namespace {
  //===--------------------------------------------------------------------===//
  // LowerSetJmp pass implementation.
  class VISIBILITY_HIDDEN LowerSetJmp : public ModulePass,
                      public InstVisitor<LowerSetJmp> {
    // LLVM library functions...
    Constant *InitSJMap;        // __llvm_sjljeh_init_setjmpmap
    Constant *DestroySJMap;     // __llvm_sjljeh_destroy_setjmpmap
    Constant *AddSJToMap;       // __llvm_sjljeh_add_setjmp_to_map
    Constant *ThrowLongJmp;     // __llvm_sjljeh_throw_longjmp
    Constant *TryCatchLJ;       // __llvm_sjljeh_try_catching_longjmp_exception
    Constant *IsLJException;    // __llvm_sjljeh_is_longjmp_exception
    Constant *GetLJValue;       // __llvm_sjljeh_get_longjmp_value

    typedef std::pair<SwitchInst*, CallInst*> SwitchValuePair;

    // Keep track of those basic blocks reachable via a depth-first search of
    // the CFG from a setjmp call. We only need to transform those "call" and
    // "invoke" instructions that are reachable from the setjmp call site.
    std::set<BasicBlock*> DFSBlocks;

    // The setjmp map is going to hold information about which setjmps
    // were called (each setjmp gets its own number) and with which
    // buffer it was called.
    std::map<Function*, AllocaInst*>            SJMap;

    // The rethrow basic block map holds the basic block to branch to if
    // the exception isn't handled in the current function and needs to
    // be rethrown.
    std::map<const Function*, BasicBlock*>      RethrowBBMap;

    // The preliminary basic block map holds a basic block that grabs the
    // exception and determines if it's handled by the current function.
    std::map<const Function*, BasicBlock*>      PrelimBBMap;

    // The switch/value map holds a switch inst/call inst pair. The
    // switch inst controls which handler (if any) gets called and the
    // value is the value returned to that handler by the call to
    // __llvm_sjljeh_get_longjmp_value.
    std::map<const Function*, SwitchValuePair>  SwitchValMap;

    // A map of which setjmps we've seen so far in a function.
    std::map<const Function*, unsigned>         SetJmpIDMap;

    AllocaInst*     GetSetJmpMap(Function* Func);
    BasicBlock*     GetRethrowBB(Function* Func);
    SwitchValuePair GetSJSwitch(Function* Func, BasicBlock* Rethrow);

    void TransformLongJmpCall(CallInst* Inst);
    void TransformSetJmpCall(CallInst* Inst);

    bool IsTransformableFunction(const std::string& Name);
  public:
    static char ID; // Pass identification, replacement for typeid
    LowerSetJmp() : ModulePass(&ID) {}

    void visitCallInst(CallInst& CI);
    void visitInvokeInst(InvokeInst& II);
    void visitReturnInst(ReturnInst& RI);
    void visitUnwindInst(UnwindInst& UI);

    bool runOnModule(Module& M);
    bool doInitialization(Module& M);
  };
} // end anonymous namespace

char LowerSetJmp::ID = 0;
static RegisterPass<LowerSetJmp> X("lowersetjmp", "Lower Set Jump");

// run - Run the transformation on the program. We grab the function
// prototypes for longjmp and setjmp. If they are used in the program,
// then we can go directly to the places they're at and transform them.
bool LowerSetJmp::runOnModule(Module& M) {
  bool Changed = false;

  // These are what the functions are called.
  Function* SetJmp = M.getFunction("llvm.setjmp");
  Function* LongJmp = M.getFunction("llvm.longjmp");

  // This program doesn't have longjmp and setjmp calls.
  if ((!LongJmp || LongJmp->use_empty()) &&
        (!SetJmp || SetJmp->use_empty())) return false;

  // Initialize some values and functions we'll need to transform the
  // setjmp/longjmp functions.
  doInitialization(M);

  if (SetJmp) {
    for (Value::use_iterator B = SetJmp->use_begin(), E = SetJmp->use_end();
         B != E; ++B) {
      BasicBlock* BB = cast<Instruction>(*B)->getParent();
      for (df_ext_iterator<BasicBlock*> I = df_ext_begin(BB, DFSBlocks),
             E = df_ext_end(BB, DFSBlocks); I != E; ++I)
        /* empty */;
    }

    while (!SetJmp->use_empty()) {
      assert(isa<CallInst>(SetJmp->use_back()) &&
             "User of setjmp intrinsic not a call?");
      TransformSetJmpCall(cast<CallInst>(SetJmp->use_back()));
      Changed = true;
    }
  }

  if (LongJmp)
    while (!LongJmp->use_empty()) {
      assert(isa<CallInst>(LongJmp->use_back()) &&
             "User of longjmp intrinsic not a call?");
      TransformLongJmpCall(cast<CallInst>(LongJmp->use_back()));
      Changed = true;
    }

  // Now go through the affected functions and convert calls and invokes
  // to new invokes...
  for (std::map<Function*, AllocaInst*>::iterator
      B = SJMap.begin(), E = SJMap.end(); B != E; ++B) {
    Function* F = B->first;
    for (Function::iterator BB = F->begin(), BE = F->end(); BB != BE; ++BB)
      for (BasicBlock::iterator IB = BB->begin(), IE = BB->end(); IB != IE; ) {
        visit(*IB++);
        if (IB != BB->end() && IB->getParent() != BB)
          break;  // The next instruction got moved to a different block!
      }
  }

  DFSBlocks.clear();
  SJMap.clear();
  RethrowBBMap.clear();
  PrelimBBMap.clear();
  SwitchValMap.clear();
  SetJmpIDMap.clear();

  return Changed;
}

// doInitialization - For the lower long/setjmp pass, this ensures that a
// module contains a declaration for the intrisic functions we are going
// to call to convert longjmp and setjmp calls.
//
// This function is always successful, unless it isn't.
bool LowerSetJmp::doInitialization(Module& M)
{
  const Type *SBPTy = PointerType::getUnqual(Type::Int8Ty);
  const Type *SBPPTy = PointerType::getUnqual(SBPTy);

  // N.B. See llvm/runtime/GCCLibraries/libexception/SJLJ-Exception.h for
  // a description of the following library functions.

  // void __llvm_sjljeh_init_setjmpmap(void**)
  InitSJMap = M.getOrInsertFunction("__llvm_sjljeh_init_setjmpmap",
                                    Type::VoidTy, SBPPTy, (Type *)0);
  // void __llvm_sjljeh_destroy_setjmpmap(void**)
  DestroySJMap = M.getOrInsertFunction("__llvm_sjljeh_destroy_setjmpmap",
                                       Type::VoidTy, SBPPTy, (Type *)0);

  // void __llvm_sjljeh_add_setjmp_to_map(void**, void*, unsigned)
  AddSJToMap = M.getOrInsertFunction("__llvm_sjljeh_add_setjmp_to_map",
                                     Type::VoidTy, SBPPTy, SBPTy,
                                     Type::Int32Ty, (Type *)0);

  // void __llvm_sjljeh_throw_longjmp(int*, int)
  ThrowLongJmp = M.getOrInsertFunction("__llvm_sjljeh_throw_longjmp",
                                       Type::VoidTy, SBPTy, Type::Int32Ty,
                                       (Type *)0);

  // unsigned __llvm_sjljeh_try_catching_longjmp_exception(void **)
  TryCatchLJ =
    M.getOrInsertFunction("__llvm_sjljeh_try_catching_longjmp_exception",
                          Type::Int32Ty, SBPPTy, (Type *)0);

  // bool __llvm_sjljeh_is_longjmp_exception()
  IsLJException = M.getOrInsertFunction("__llvm_sjljeh_is_longjmp_exception",
                                        Type::Int1Ty, (Type *)0);

  // int __llvm_sjljeh_get_longjmp_value()
  GetLJValue = M.getOrInsertFunction("__llvm_sjljeh_get_longjmp_value",
                                     Type::Int32Ty, (Type *)0);
  return true;
}

// IsTransformableFunction - Return true if the function name isn't one
// of the ones we don't want transformed. Currently, don't transform any
// "llvm.{setjmp,longjmp}" functions and none of the setjmp/longjmp error
// handling functions (beginning with __llvm_sjljeh_...they don't throw
// exceptions).
bool LowerSetJmp::IsTransformableFunction(const std::string& Name) {
  std::string SJLJEh("__llvm_sjljeh");

  if (Name.size() > SJLJEh.size())
    return std::string(Name.begin(), Name.begin() + SJLJEh.size()) != SJLJEh;

  return true;
}

// TransformLongJmpCall - Transform a longjmp call into a call to the
// internal __llvm_sjljeh_throw_longjmp function. It then takes care of
// throwing the exception for us.
void LowerSetJmp::TransformLongJmpCall(CallInst* Inst)
{
  const Type* SBPTy = PointerType::getUnqual(Type::Int8Ty);

  // Create the call to "__llvm_sjljeh_throw_longjmp". This takes the
  // same parameters as "longjmp", except that the buffer is cast to a
  // char*. It returns "void", so it doesn't need to replace any of
  // Inst's uses and doesn't get a name.
  CastInst* CI = 
    new BitCastInst(Inst->getOperand(1), SBPTy, "LJBuf", Inst);
  SmallVector<Value *, 2> Args;
  Args.push_back(CI);
  Args.push_back(Inst->getOperand(2));
  CallInst::Create(ThrowLongJmp, Args.begin(), Args.end(), "", Inst);

  SwitchValuePair& SVP = SwitchValMap[Inst->getParent()->getParent()];

  // If the function has a setjmp call in it (they are transformed first)
  // we should branch to the basic block that determines if this longjmp
  // is applicable here. Otherwise, issue an unwind.
  if (SVP.first)
    BranchInst::Create(SVP.first->getParent(), Inst);
  else
    new UnwindInst(Inst);

  // Remove all insts after the branch/unwind inst.  Go from back to front to
  // avoid replaceAllUsesWith if possible.
  BasicBlock *BB = Inst->getParent();
  Instruction *Removed;
  do {
    Removed = &BB->back();
    // If the removed instructions have any users, replace them now.
    if (!Removed->use_empty())
      Removed->replaceAllUsesWith(UndefValue::get(Removed->getType()));
    Removed->eraseFromParent();
  } while (Removed != Inst);

  ++LongJmpsTransformed;
}

// GetSetJmpMap - Retrieve (create and initialize, if necessary) the
// setjmp map. This map is going to hold information about which setjmps
// were called (each setjmp gets its own number) and with which buffer it
// was called. There can be only one!
AllocaInst* LowerSetJmp::GetSetJmpMap(Function* Func)
{
  if (SJMap[Func]) return SJMap[Func];

  // Insert the setjmp map initialization before the first instruction in
  // the function.
  Instruction* Inst = Func->getEntryBlock().begin();
  assert(Inst && "Couldn't find even ONE instruction in entry block!");

  // Fill in the alloca and call to initialize the SJ map.
  const Type *SBPTy = PointerType::getUnqual(Type::Int8Ty);
  AllocaInst* Map = new AllocaInst(SBPTy, 0, "SJMap", Inst);
  CallInst::Create(InitSJMap, Map, "", Inst);
  return SJMap[Func] = Map;
}

// GetRethrowBB - Only one rethrow basic block is needed per function.
// If this is a longjmp exception but not handled in this block, this BB
// performs the rethrow.
BasicBlock* LowerSetJmp::GetRethrowBB(Function* Func)
{
  if (RethrowBBMap[Func]) return RethrowBBMap[Func];

  // The basic block we're going to jump to if we need to rethrow the
  // exception.
  BasicBlock* Rethrow = BasicBlock::Create("RethrowExcept", Func);

  // Fill in the "Rethrow" BB with a call to rethrow the exception. This
  // is the last instruction in the BB since at this point the runtime
  // should exit this function and go to the next function.
  new UnwindInst(Rethrow);
  return RethrowBBMap[Func] = Rethrow;
}

// GetSJSwitch - Return the switch statement that controls which handler
// (if any) gets called and the value returned to that handler.
LowerSetJmp::SwitchValuePair LowerSetJmp::GetSJSwitch(Function* Func,
                                                      BasicBlock* Rethrow)
{
  if (SwitchValMap[Func].first) return SwitchValMap[Func];

  BasicBlock* LongJmpPre = BasicBlock::Create("LongJmpBlkPre", Func);

  // Keep track of the preliminary basic block for some of the other
  // transformations.
  PrelimBBMap[Func] = LongJmpPre;

  // Grab the exception.
  CallInst* Cond = CallInst::Create(IsLJException, "IsLJExcept", LongJmpPre);

  // The "decision basic block" gets the number associated with the
  // setjmp call returning to switch on and the value returned by
  // longjmp.
  BasicBlock* DecisionBB = BasicBlock::Create("LJDecisionBB", Func);

  BranchInst::Create(DecisionBB, Rethrow, Cond, LongJmpPre);

  // Fill in the "decision" basic block.
  CallInst* LJVal = CallInst::Create(GetLJValue, "LJVal", DecisionBB);
  CallInst* SJNum = CallInst::Create(TryCatchLJ, GetSetJmpMap(Func), "SJNum",
                                     DecisionBB);

  SwitchInst* SI = SwitchInst::Create(SJNum, Rethrow, 0, DecisionBB);
  return SwitchValMap[Func] = SwitchValuePair(SI, LJVal);
}

// TransformSetJmpCall - The setjmp call is a bit trickier to transform.
// We're going to convert all setjmp calls to nops. Then all "call" and
// "invoke" instructions in the function are converted to "invoke" where
// the "except" branch is used when returning from a longjmp call.
void LowerSetJmp::TransformSetJmpCall(CallInst* Inst)
{
  BasicBlock* ABlock = Inst->getParent();
  Function* Func = ABlock->getParent();

  // Add this setjmp to the setjmp map.
  const Type* SBPTy = PointerType::getUnqual(Type::Int8Ty);
  CastInst* BufPtr = 
    new BitCastInst(Inst->getOperand(1), SBPTy, "SBJmpBuf", Inst);
  std::vector<Value*> Args = 
    make_vector<Value*>(GetSetJmpMap(Func), BufPtr,
                        ConstantInt::get(Type::Int32Ty,
                                         SetJmpIDMap[Func]++), 0);
  CallInst::Create(AddSJToMap, Args.begin(), Args.end(), "", Inst);

  // We are guaranteed that there are no values live across basic blocks
  // (because we are "not in SSA form" yet), but there can still be values live
  // in basic blocks.  Because of this, splitting the setjmp block can cause
  // values above the setjmp to not dominate uses which are after the setjmp
  // call.  For all of these occasions, we must spill the value to the stack.
  //
  std::set<Instruction*> InstrsAfterCall;

  // The call is probably very close to the end of the basic block, for the
  // common usage pattern of: 'if (setjmp(...))', so keep track of the
  // instructions after the call.
  for (BasicBlock::iterator I = ++BasicBlock::iterator(Inst), E = ABlock->end();
       I != E; ++I)
    InstrsAfterCall.insert(I);

  for (BasicBlock::iterator II = ABlock->begin();
       II != BasicBlock::iterator(Inst); ++II)
    // Loop over all of the uses of instruction.  If any of them are after the
    // call, "spill" the value to the stack.
    for (Value::use_iterator UI = II->use_begin(), E = II->use_end();
         UI != E; ++UI)
      if (cast<Instruction>(*UI)->getParent() != ABlock ||
          InstrsAfterCall.count(cast<Instruction>(*UI))) {
        DemoteRegToStack(*II);
        break;
      }
  InstrsAfterCall.clear();

  // Change the setjmp call into a branch statement. We'll remove the
  // setjmp call in a little bit. No worries.
  BasicBlock* SetJmpContBlock = ABlock->splitBasicBlock(Inst);
  assert(SetJmpContBlock && "Couldn't split setjmp BB!!");

  SetJmpContBlock->setName(ABlock->getName()+"SetJmpCont");

  // Add the SetJmpContBlock to the set of blocks reachable from a setjmp.
  DFSBlocks.insert(SetJmpContBlock);

  // This PHI node will be in the new block created from the
  // splitBasicBlock call.
  PHINode* PHI = PHINode::Create(Type::Int32Ty, "SetJmpReturn", Inst);

  // Coming from a call to setjmp, the return is 0.
  PHI->addIncoming(ConstantInt::getNullValue(Type::Int32Ty), ABlock);

  // Add the case for this setjmp's number...
  SwitchValuePair SVP = GetSJSwitch(Func, GetRethrowBB(Func));
  SVP.first->addCase(ConstantInt::get(Type::Int32Ty, SetJmpIDMap[Func] - 1),
                     SetJmpContBlock);

  // Value coming from the handling of the exception.
  PHI->addIncoming(SVP.second, SVP.second->getParent());

  // Replace all uses of this instruction with the PHI node created by
  // the eradication of setjmp.
  Inst->replaceAllUsesWith(PHI);
  Inst->eraseFromParent();

  ++SetJmpsTransformed;
}

// visitCallInst - This converts all LLVM call instructions into invoke
// instructions. The except part of the invoke goes to the "LongJmpBlkPre"
// that grabs the exception and proceeds to determine if it's a longjmp
// exception or not.
void LowerSetJmp::visitCallInst(CallInst& CI)
{
  if (CI.getCalledFunction())
    if (!IsTransformableFunction(CI.getCalledFunction()->getName()) ||
        CI.getCalledFunction()->isIntrinsic()) return;

  BasicBlock* OldBB = CI.getParent();

  // If not reachable from a setjmp call, don't transform.
  if (!DFSBlocks.count(OldBB)) return;

  BasicBlock* NewBB = OldBB->splitBasicBlock(CI);
  assert(NewBB && "Couldn't split BB of \"call\" instruction!!");
  DFSBlocks.insert(NewBB);
  NewBB->setName("Call2Invoke");

  Function* Func = OldBB->getParent();

  // Construct the new "invoke" instruction.
  TerminatorInst* Term = OldBB->getTerminator();
  std::vector<Value*> Params(CI.op_begin() + 1, CI.op_end());
  InvokeInst* II =
    InvokeInst::Create(CI.getCalledValue(), NewBB, PrelimBBMap[Func],
                       Params.begin(), Params.end(), CI.getName(), Term);
  II->setCallingConv(CI.getCallingConv());
  II->setAttributes(CI.getAttributes());

  // Replace the old call inst with the invoke inst and remove the call.
  CI.replaceAllUsesWith(II);
  CI.eraseFromParent();

  // The old terminator is useless now that we have the invoke inst.
  Term->eraseFromParent();
  ++CallsTransformed;
}

// visitInvokeInst - Converting the "invoke" instruction is fairly
// straight-forward. The old exception part is replaced by a query asking
// if this is a longjmp exception. If it is, then it goes to the longjmp
// exception blocks. Otherwise, control is passed the old exception.
void LowerSetJmp::visitInvokeInst(InvokeInst& II)
{
  if (II.getCalledFunction())
    if (!IsTransformableFunction(II.getCalledFunction()->getName()) ||
        II.getCalledFunction()->isIntrinsic()) return;

  BasicBlock* BB = II.getParent();

  // If not reachable from a setjmp call, don't transform.
  if (!DFSBlocks.count(BB)) return;

  BasicBlock* ExceptBB = II.getUnwindDest();

  Function* Func = BB->getParent();
  BasicBlock* NewExceptBB = BasicBlock::Create("InvokeExcept", Func);

  // If this is a longjmp exception, then branch to the preliminary BB of
  // the longjmp exception handling. Otherwise, go to the old exception.
  CallInst* IsLJExcept = CallInst::Create(IsLJException, "IsLJExcept",
                                          NewExceptBB);

  BranchInst::Create(PrelimBBMap[Func], ExceptBB, IsLJExcept, NewExceptBB);

  II.setUnwindDest(NewExceptBB);
  ++InvokesTransformed;
}

// visitReturnInst - We want to destroy the setjmp map upon exit from the
// function.
void LowerSetJmp::visitReturnInst(ReturnInst &RI) {
  Function* Func = RI.getParent()->getParent();
  CallInst::Create(DestroySJMap, GetSetJmpMap(Func), "", &RI);
}

// visitUnwindInst - We want to destroy the setjmp map upon exit from the
// function.
void LowerSetJmp::visitUnwindInst(UnwindInst &UI) {
  Function* Func = UI.getParent()->getParent();
  CallInst::Create(DestroySJMap, GetSetJmpMap(Func), "", &UI);
}

ModulePass *llvm::createLowerSetJmpPass() {
  return new LowerSetJmp();
}