SjLjEHPrepare.cpp revision a9203109f4ac95aa7e9624f2838e3d89623ec902 
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/ADT/SmallVector.h"
25#include "llvm/ADT/Statistic.h"
26#include "llvm/CodeGen/Passes.h"
27#include "llvm/Support/Debug.h"
28#include "llvm/Target/TargetLowering.h"
29#include "llvm/Transforms/Utils/BasicBlockUtils.h"
30#include "llvm/Transforms/Utils/Local.h"
31#include <set>
32using namespace llvm;
33
34STATISTIC(NumInvokes, "Number of invokes replaced");
35STATISTIC(NumUnwinds, "Number of unwinds replaced");
36STATISTIC(NumSpilled, "Number of registers live across unwind edges");
37
38namespace {
39  class SjLjEHPass : public FunctionPass {
40
41    const TargetLowering *TLI;
42
43    Type *FunctionContextTy;
44    Constant *RegisterFn;
45    Constant *UnregisterFn;
46    Constant *BuiltinSetjmpFn;
47    Constant *FrameAddrFn;
48    Constant *StackAddrFn;
49    Constant *StackRestoreFn;
50    Constant *LSDAAddrFn;
51    Value *PersonalityFn;
52    Constant *SelectorFn;
53    Constant *ExceptionFn;
54    Constant *CallSiteFn;
55    Constant *DispatchSetupFn;
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 insertCallSiteStore(Instruction *I, int Number, Value *CallSite);
72    void markInvokeCallSite(InvokeInst *II, int InvokeNo, Value *CallSite,
73                            SwitchInst *CatchSwitch);
74    void splitLiveRangesAcrossInvokes(SmallVector<InvokeInst*,16> &Invokes);
75    bool insertSjLjEHSupport(Function &F);
76  };
77} // end anonymous namespace
78
79char SjLjEHPass::ID = 0;
80
81// Public Interface To the SjLjEHPass pass.
82FunctionPass *llvm::createSjLjEHPass(const TargetLowering *TLI) {
83  return new SjLjEHPass(TLI);
84}
85// doInitialization - Set up decalarations and types needed to process
86// exceptions.
87bool SjLjEHPass::doInitialization(Module &M) {
88  // Build the function context structure.
89  // builtin_setjmp uses a five word jbuf
90  Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
91  Type *Int32Ty = Type::getInt32Ty(M.getContext());
92  FunctionContextTy =
93    StructType::get(VoidPtrTy,                        // __prev
94                    Int32Ty,                          // call_site
95                    ArrayType::get(Int32Ty, 4),       // __data
96                    VoidPtrTy,                        // __personality
97                    VoidPtrTy,                        // __lsda
98                    ArrayType::get(VoidPtrTy, 5),     // __jbuf
99                    NULL);
100  RegisterFn = M.getOrInsertFunction("_Unwind_SjLj_Register",
101                                     Type::getVoidTy(M.getContext()),
102                                     PointerType::getUnqual(FunctionContextTy),
103                                     (Type *)0);
104  UnregisterFn =
105    M.getOrInsertFunction("_Unwind_SjLj_Unregister",
106                          Type::getVoidTy(M.getContext()),
107                          PointerType::getUnqual(FunctionContextTy),
108                          (Type *)0);
109  FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress);
110  StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
111  StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
112  BuiltinSetjmpFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setjmp);
113  LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
114  SelectorFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_selector);
115  ExceptionFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_exception);
116  CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
117  DispatchSetupFn
118    = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_dispatch_setup);
119  PersonalityFn = 0;
120
121  return true;
122}
123
124/// insertCallSiteStore - Insert a store of the call-site value to the
125/// function context
126void SjLjEHPass::insertCallSiteStore(Instruction *I, int Number,
127                                     Value *CallSite) {
128  ConstantInt *CallSiteNoC = ConstantInt::get(Type::getInt32Ty(I->getContext()),
129                                              Number);
130  // Insert a store of the call-site number
131  new StoreInst(CallSiteNoC, CallSite, true, I);  // volatile
132}
133
134/// markInvokeCallSite - Insert code to mark the call_site for this invoke
135void SjLjEHPass::markInvokeCallSite(InvokeInst *II, int InvokeNo,
136                                    Value *CallSite,
137                                    SwitchInst *CatchSwitch) {
138  ConstantInt *CallSiteNoC= ConstantInt::get(Type::getInt32Ty(II->getContext()),
139                                              InvokeNo);
140  // The runtime comes back to the dispatcher with the call_site - 1 in
141  // the context. Odd, but there it is.
142  ConstantInt *SwitchValC = ConstantInt::get(Type::getInt32Ty(II->getContext()),
143                                            InvokeNo - 1);
144
145  // If the unwind edge has phi nodes, split the edge.
146  if (isa<PHINode>(II->getUnwindDest()->begin())) {
147    SplitCriticalEdge(II, 1, this);
148
149    // If there are any phi nodes left, they must have a single predecessor.
150    while (PHINode *PN = dyn_cast<PHINode>(II->getUnwindDest()->begin())) {
151      PN->replaceAllUsesWith(PN->getIncomingValue(0));
152      PN->eraseFromParent();
153    }
154  }
155
156  // Insert the store of the call site value
157  insertCallSiteStore(II, InvokeNo, CallSite);
158
159  // Record the call site value for the back end so it stays associated with
160  // the invoke.
161  CallInst::Create(CallSiteFn, CallSiteNoC, "", II);
162
163  // Add a switch case to our unwind block.
164  CatchSwitch->addCase(SwitchValC, II->getUnwindDest());
165  // We still want this to look like an invoke so we emit the LSDA properly,
166  // so we don't transform the invoke into a call here.
167}
168
169/// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
170/// we reach blocks we've already seen.
171static void MarkBlocksLiveIn(BasicBlock *BB, std::set<BasicBlock*> &LiveBBs) {
172  if (!LiveBBs.insert(BB).second) return; // already been here.
173
174  for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
175    MarkBlocksLiveIn(*PI, LiveBBs);
176}
177
178/// splitLiveRangesAcrossInvokes - Each value that is live across an unwind edge
179/// we spill into a stack location, guaranteeing that there is nothing live
180/// across the unwind edge.  This process also splits all critical edges
181/// coming out of invoke's.
182/// FIXME: Move this function to a common utility file (Local.cpp?) so
183/// both SjLj and LowerInvoke can use it.
184void SjLjEHPass::
185splitLiveRangesAcrossInvokes(SmallVector<InvokeInst*,16> &Invokes) {
186  // First step, split all critical edges from invoke instructions.
187  for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
188    InvokeInst *II = Invokes[i];
189    SplitCriticalEdge(II, 0, this);
190    SplitCriticalEdge(II, 1, this);
191    assert(!isa<PHINode>(II->getNormalDest()) &&
192           !isa<PHINode>(II->getUnwindDest()) &&
193           "critical edge splitting left single entry phi nodes?");
194  }
195
196  Function *F = Invokes.back()->getParent()->getParent();
197
198  // To avoid having to handle incoming arguments specially, we lower each arg
199  // to a copy instruction in the entry block.  This ensures that the argument
200  // value itself cannot be live across the entry block.
201  BasicBlock::iterator AfterAllocaInsertPt = F->begin()->begin();
202  while (isa<AllocaInst>(AfterAllocaInsertPt) &&
203        isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsertPt)->getArraySize()))
204    ++AfterAllocaInsertPt;
205  for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
206       AI != E; ++AI) {
207    Type *Ty = AI->getType();
208    // Aggregate types can't be cast, but are legal argument types, so we have
209    // to handle them differently. We use an extract/insert pair as a
210    // lightweight method to achieve the same goal.
211    if (isa<StructType>(Ty) || isa<ArrayType>(Ty) || isa<VectorType>(Ty)) {
212      Instruction *EI = ExtractValueInst::Create(AI, 0, "",AfterAllocaInsertPt);
213      Instruction *NI = InsertValueInst::Create(AI, EI, 0);
214      NI->insertAfter(EI);
215      AI->replaceAllUsesWith(NI);
216      // Set the operand of the instructions back to the AllocaInst.
217      EI->setOperand(0, AI);
218      NI->setOperand(0, AI);
219    } else {
220      // This is always a no-op cast because we're casting AI to AI->getType()
221      // so src and destination types are identical. BitCast is the only
222      // possibility.
223      CastInst *NC = new BitCastInst(
224        AI, AI->getType(), AI->getName()+".tmp", AfterAllocaInsertPt);
225      AI->replaceAllUsesWith(NC);
226      // Set the operand of the cast instruction back to the AllocaInst.
227      // Normally it's forbidden to replace a CastInst's operand because it
228      // could cause the opcode to reflect an illegal conversion. However,
229      // we're replacing it here with the same value it was constructed with.
230      // We do this because the above replaceAllUsesWith() clobbered the
231      // operand, but we want this one to remain.
232      NC->setOperand(0, AI);
233    }
234  }
235
236  // Finally, scan the code looking for instructions with bad live ranges.
237  for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
238    for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
239      // Ignore obvious cases we don't have to handle.  In particular, most
240      // instructions either have no uses or only have a single use inside the
241      // current block.  Ignore them quickly.
242      Instruction *Inst = II;
243      if (Inst->use_empty()) continue;
244      if (Inst->hasOneUse() &&
245          cast<Instruction>(Inst->use_back())->getParent() == BB &&
246          !isa<PHINode>(Inst->use_back())) continue;
247
248      // If this is an alloca in the entry block, it's not a real register
249      // value.
250      if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
251        if (isa<ConstantInt>(AI->getArraySize()) && BB == F->begin())
252          continue;
253
254      // Avoid iterator invalidation by copying users to a temporary vector.
255      SmallVector<Instruction*,16> Users;
256      for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end();
257           UI != E; ++UI) {
258        Instruction *User = cast<Instruction>(*UI);
259        if (User->getParent() != BB || isa<PHINode>(User))
260          Users.push_back(User);
261      }
262
263      // Find all of the blocks that this value is live in.
264      std::set<BasicBlock*> LiveBBs;
265      LiveBBs.insert(Inst->getParent());
266      while (!Users.empty()) {
267        Instruction *U = Users.back();
268        Users.pop_back();
269
270        if (!isa<PHINode>(U)) {
271          MarkBlocksLiveIn(U->getParent(), LiveBBs);
272        } else {
273          // Uses for a PHI node occur in their predecessor block.
274          PHINode *PN = cast<PHINode>(U);
275          for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
276            if (PN->getIncomingValue(i) == Inst)
277              MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
278        }
279      }
280
281      // Now that we know all of the blocks that this thing is live in, see if
282      // it includes any of the unwind locations.
283      bool NeedsSpill = false;
284      for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
285        BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
286        if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
287          NeedsSpill = true;
288        }
289      }
290
291      // If we decided we need a spill, do it.
292      // FIXME: Spilling this way is overkill, as it forces all uses of
293      // the value to be reloaded from the stack slot, even those that aren't
294      // in the unwind blocks. We should be more selective.
295      if (NeedsSpill) {
296        ++NumSpilled;
297        DemoteRegToStack(*Inst, true);
298      }
299    }
300}
301
302bool SjLjEHPass::insertSjLjEHSupport(Function &F) {
303  SmallVector<ReturnInst*,16> Returns;
304  SmallVector<UnwindInst*,16> Unwinds;
305  SmallVector<InvokeInst*,16> Invokes;
306
307  // Look through the terminators of the basic blocks to find invokes, returns
308  // and unwinds.
309  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
310    if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
311      // Remember all return instructions in case we insert an invoke into this
312      // function.
313      Returns.push_back(RI);
314    } else if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
315      Invokes.push_back(II);
316    } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
317      Unwinds.push_back(UI);
318    }
319  }
320
321  NumInvokes += Invokes.size();
322  NumUnwinds += Unwinds.size();
323
324  // If we don't have any invokes, there's nothing to do.
325  if (Invokes.empty()) return false;
326
327  // Find the eh.selector.*, eh.exception and alloca calls.
328  //
329  // Remember any allocas() that aren't in the entry block, as the
330  // jmpbuf saved SP will need to be updated for them.
331  //
332  // We'll use the first eh.selector to determine the right personality
333  // function to use. For SJLJ, we always use the same personality for the
334  // whole function, not on a per-selector basis.
335  // FIXME: That's a bit ugly. Better way?
336  SmallVector<CallInst*,16> EH_Selectors;
337  SmallVector<CallInst*,16> EH_Exceptions;
338  SmallVector<Instruction*,16> JmpbufUpdatePoints;
339
340  // Note: Skip the entry block since there's nothing there that interests
341  // us. eh.selector and eh.exception shouldn't ever be there, and we
342  // want to disregard any allocas that are there.
343  for (Function::iterator BB = F.begin(), E = F.end(); ++BB != E;) {
344    for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
345      if (CallInst *CI = dyn_cast<CallInst>(I)) {
346        if (CI->getCalledFunction() == SelectorFn) {
347          if (!PersonalityFn) PersonalityFn = CI->getArgOperand(1);
348          EH_Selectors.push_back(CI);
349        } else if (CI->getCalledFunction() == ExceptionFn) {
350          EH_Exceptions.push_back(CI);
351        } else if (CI->getCalledFunction() == StackRestoreFn) {
352          JmpbufUpdatePoints.push_back(CI);
353        }
354      } else if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
355        JmpbufUpdatePoints.push_back(AI);
356      }
357    }
358  }
359
360  // If we don't have any eh.selector calls, we can't determine the personality
361  // function. Without a personality function, we can't process exceptions.
362  if (!PersonalityFn) return false;
363
364  // We have invokes, so we need to add register/unregister calls to get this
365  // function onto the global unwind stack.
366  //
367  // First thing we need to do is scan the whole function for values that are
368  // live across unwind edges.  Each value that is live across an unwind edge we
369  // spill into a stack location, guaranteeing that there is nothing live across
370  // the unwind edge.  This process also splits all critical edges coming out of
371  // invoke's.
372  splitLiveRangesAcrossInvokes(Invokes);
373
374  BasicBlock *EntryBB = F.begin();
375  // Create an alloca for the incoming jump buffer ptr and the new jump buffer
376  // that needs to be restored on all exits from the function.  This is an
377  // alloca because the value needs to be added to the global context list.
378  unsigned Align = 4; // FIXME: Should be a TLI check?
379  AllocaInst *FunctionContext =
380    new AllocaInst(FunctionContextTy, 0, Align,
381                   "fcn_context", F.begin()->begin());
382
383  Value *Idxs[2];
384  Type *Int32Ty = Type::getInt32Ty(F.getContext());
385  Value *Zero = ConstantInt::get(Int32Ty, 0);
386  // We need to also keep around a reference to the call_site field
387  Idxs[0] = Zero;
388  Idxs[1] = ConstantInt::get(Int32Ty, 1);
389  CallSite = GetElementPtrInst::Create(FunctionContext, Idxs, "call_site",
390                                       EntryBB->getTerminator());
391
392  // The exception selector comes back in context->data[1]
393  Idxs[1] = ConstantInt::get(Int32Ty, 2);
394  Value *FCData = GetElementPtrInst::Create(FunctionContext, Idxs, "fc_data",
395                                            EntryBB->getTerminator());
396  Idxs[1] = ConstantInt::get(Int32Ty, 1);
397  Value *SelectorAddr = GetElementPtrInst::Create(FCData, Idxs,
398                                                  "exc_selector_gep",
399                                                  EntryBB->getTerminator());
400  // The exception value comes back in context->data[0]
401  Idxs[1] = Zero;
402  Value *ExceptionAddr = GetElementPtrInst::Create(FCData, Idxs,
403                                                   "exception_gep",
404                                                   EntryBB->getTerminator());
405
406  // The result of the eh.selector call will be replaced with a a reference to
407  // the selector value returned in the function context. We leave the selector
408  // itself so the EH analysis later can use it.
409  for (int i = 0, e = EH_Selectors.size(); i < e; ++i) {
410    CallInst *I = EH_Selectors[i];
411    Value *SelectorVal = new LoadInst(SelectorAddr, "select_val", true, I);
412    I->replaceAllUsesWith(SelectorVal);
413  }
414
415  // eh.exception calls are replaced with references to the proper location in
416  // the context. Unlike eh.selector, the eh.exception calls are removed
417  // entirely.
418  for (int i = 0, e = EH_Exceptions.size(); i < e; ++i) {
419    CallInst *I = EH_Exceptions[i];
420    // Possible for there to be duplicates, so check to make sure the
421    // instruction hasn't already been removed.
422    if (!I->getParent()) continue;
423    Value *Val = new LoadInst(ExceptionAddr, "exception", true, I);
424    Type *Ty = Type::getInt8PtrTy(F.getContext());
425    Val = CastInst::Create(Instruction::IntToPtr, Val, Ty, "", I);
426
427    I->replaceAllUsesWith(Val);
428    I->eraseFromParent();
429  }
430
431  // The entry block changes to have the eh.sjlj.setjmp, with a conditional
432  // branch to a dispatch block for non-zero returns. If we return normally,
433  // we're not handling an exception and just register the function context and
434  // continue.
435
436  // Create the dispatch block.  The dispatch block is basically a big switch
437  // statement that goes to all of the invoke landing pads.
438  BasicBlock *DispatchBlock =
439    BasicBlock::Create(F.getContext(), "eh.sjlj.setjmp.catch", &F);
440
441  // Insert a load of the callsite in the dispatch block, and a switch on its
442  // value. By default, we issue a trap statement.
443  BasicBlock *TrapBlock =
444    BasicBlock::Create(F.getContext(), "trapbb", &F);
445  CallInst::Create(Intrinsic::getDeclaration(F.getParent(), Intrinsic::trap),
446                   "", TrapBlock);
447  new UnreachableInst(F.getContext(), TrapBlock);
448
449  Value *DispatchLoad = new LoadInst(CallSite, "invoke.num", true,
450                                     DispatchBlock);
451  SwitchInst *DispatchSwitch =
452    SwitchInst::Create(DispatchLoad, TrapBlock, Invokes.size(),
453                       DispatchBlock);
454  // Split the entry block to insert the conditional branch for the setjmp.
455  BasicBlock *ContBlock = EntryBB->splitBasicBlock(EntryBB->getTerminator(),
456                                                   "eh.sjlj.setjmp.cont");
457
458  // Populate the Function Context
459  //   1. LSDA address
460  //   2. Personality function address
461  //   3. jmpbuf (save SP, FP and call eh.sjlj.setjmp)
462
463  // LSDA address
464  Idxs[0] = Zero;
465  Idxs[1] = ConstantInt::get(Int32Ty, 4);
466  Value *LSDAFieldPtr =
467    GetElementPtrInst::Create(FunctionContext, Idxs, "lsda_gep",
468                              EntryBB->getTerminator());
469  Value *LSDA = CallInst::Create(LSDAAddrFn, "lsda_addr",
470                                 EntryBB->getTerminator());
471  new StoreInst(LSDA, LSDAFieldPtr, true, EntryBB->getTerminator());
472
473  Idxs[1] = ConstantInt::get(Int32Ty, 3);
474  Value *PersonalityFieldPtr =
475    GetElementPtrInst::Create(FunctionContext, Idxs, "lsda_gep",
476                              EntryBB->getTerminator());
477  new StoreInst(PersonalityFn, PersonalityFieldPtr, true,
478                EntryBB->getTerminator());
479
480  // Save the frame pointer.
481  Idxs[1] = ConstantInt::get(Int32Ty, 5);
482  Value *JBufPtr
483    = GetElementPtrInst::Create(FunctionContext, Idxs, "jbuf_gep",
484                                EntryBB->getTerminator());
485  Idxs[1] = ConstantInt::get(Int32Ty, 0);
486  Value *FramePtr =
487    GetElementPtrInst::Create(JBufPtr, Idxs, "jbuf_fp_gep",
488                              EntryBB->getTerminator());
489
490  Value *Val = CallInst::Create(FrameAddrFn,
491                                ConstantInt::get(Int32Ty, 0),
492                                "fp",
493                                EntryBB->getTerminator());
494  new StoreInst(Val, FramePtr, true, EntryBB->getTerminator());
495
496  // Save the stack pointer.
497  Idxs[1] = ConstantInt::get(Int32Ty, 2);
498  Value *StackPtr =
499    GetElementPtrInst::Create(JBufPtr, Idxs, "jbuf_sp_gep",
500                              EntryBB->getTerminator());
501
502  Val = CallInst::Create(StackAddrFn, "sp", EntryBB->getTerminator());
503  new StoreInst(Val, StackPtr, true, EntryBB->getTerminator());
504
505  // Call the setjmp instrinsic. It fills in the rest of the jmpbuf.
506  Value *SetjmpArg =
507    CastInst::Create(Instruction::BitCast, JBufPtr,
508                     Type::getInt8PtrTy(F.getContext()), "",
509                     EntryBB->getTerminator());
510  Value *DispatchVal = CallInst::Create(BuiltinSetjmpFn, SetjmpArg,
511                                        "dispatch",
512                                        EntryBB->getTerminator());
513
514  // Add a call to dispatch_setup after the setjmp call. This is expanded to any
515  // target-specific setup that needs to be done.
516  CallInst::Create(DispatchSetupFn, DispatchVal, "", EntryBB->getTerminator());
517
518  // check the return value of the setjmp. non-zero goes to dispatcher.
519  Value *IsNormal = new ICmpInst(EntryBB->getTerminator(),
520                                 ICmpInst::ICMP_EQ, DispatchVal, Zero,
521                                 "notunwind");
522  // Nuke the uncond branch.
523  EntryBB->getTerminator()->eraseFromParent();
524
525  // Put in a new condbranch in its place.
526  BranchInst::Create(ContBlock, DispatchBlock, IsNormal, EntryBB);
527
528  // Register the function context and make sure it's known to not throw
529  CallInst *Register =
530    CallInst::Create(RegisterFn, FunctionContext, "",
531                     ContBlock->getTerminator());
532  Register->setDoesNotThrow();
533
534  // At this point, we are all set up, update the invoke instructions to mark
535  // their call_site values, and fill in the dispatch switch accordingly.
536  for (unsigned i = 0, e = Invokes.size(); i != e; ++i)
537    markInvokeCallSite(Invokes[i], i+1, CallSite, DispatchSwitch);
538
539  // Mark call instructions that aren't nounwind as no-action (call_site ==
540  // -1). Skip the entry block, as prior to then, no function context has been
541  // created for this function and any unexpected exceptions thrown will go
542  // directly to the caller's context, which is what we want anyway, so no need
543  // to do anything here.
544  for (Function::iterator BB = F.begin(), E = F.end(); ++BB != E;) {
545    for (BasicBlock::iterator I = BB->begin(), end = BB->end(); I != end; ++I)
546      if (CallInst *CI = dyn_cast<CallInst>(I)) {
547        // Ignore calls to the EH builtins (eh.selector, eh.exception)
548        Constant *Callee = CI->getCalledFunction();
549        if (Callee != SelectorFn && Callee != ExceptionFn
550            && !CI->doesNotThrow())
551          insertCallSiteStore(CI, -1, CallSite);
552      }
553  }
554
555  // Replace all unwinds with a branch to the unwind handler.
556  // ??? Should this ever happen with sjlj exceptions?
557  for (unsigned i = 0, e = Unwinds.size(); i != e; ++i) {
558    BranchInst::Create(TrapBlock, Unwinds[i]);
559    Unwinds[i]->eraseFromParent();
560  }
561
562  // Following any allocas not in the entry block, update the saved SP in the
563  // jmpbuf to the new value.
564  for (unsigned i = 0, e = JmpbufUpdatePoints.size(); i != e; ++i) {
565    Instruction *AI = JmpbufUpdatePoints[i];
566    Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
567    StackAddr->insertAfter(AI);
568    Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true);
569    StoreStackAddr->insertAfter(StackAddr);
570  }
571
572  // Finally, for any returns from this function, if this function contains an
573  // invoke, add a call to unregister the function context.
574  for (unsigned i = 0, e = Returns.size(); i != e; ++i)
575    CallInst::Create(UnregisterFn, FunctionContext, "", Returns[i]);
576
577  return true;
578}
579
580bool SjLjEHPass::runOnFunction(Function &F) {
581  bool Res = insertSjLjEHSupport(F);
582  return Res;
583}
584