LLVM API Documentation

LowerInvoke.cpp

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00001 //===- LowerInvoke.cpp - Eliminate Invoke & Unwind instructions -----------===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by the LLVM research group and is distributed under
00006 // the University of Illinois Open Source License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This transformation is designed for use by code generators which do not yet
00011 // support stack unwinding.  This pass supports two models of exception handling
00012 // lowering, the 'cheap' support and the 'expensive' support.
00013 //
00014 // 'Cheap' exception handling support gives the program the ability to execute
00015 // any program which does not "throw an exception", by turning 'invoke'
00016 // instructions into calls and by turning 'unwind' instructions into calls to
00017 // abort().  If the program does dynamically use the unwind instruction, the
00018 // program will print a message then abort.
00019 //
00020 // 'Expensive' exception handling support gives the full exception handling
00021 // support to the program at the cost of making the 'invoke' instruction
00022 // really expensive.  It basically inserts setjmp/longjmp calls to emulate the
00023 // exception handling as necessary.
00024 //
00025 // Because the 'expensive' support slows down programs a lot, and EH is only
00026 // used for a subset of the programs, it must be specifically enabled by an
00027 // option.
00028 //
00029 // Note that after this pass runs the CFG is not entirely accurate (exceptional
00030 // control flow edges are not correct anymore) so only very simple things should
00031 // be done after the lowerinvoke pass has run (like generation of native code).
00032 // This should not be used as a general purpose "my LLVM-to-LLVM pass doesn't
00033 // support the invoke instruction yet" lowering pass.
00034 //
00035 //===----------------------------------------------------------------------===//
00036 
00037 #include "llvm/Transforms/Scalar.h"
00038 #include "llvm/Constants.h"
00039 #include "llvm/DerivedTypes.h"
00040 #include "llvm/Instructions.h"
00041 #include "llvm/Module.h"
00042 #include "llvm/Pass.h"
00043 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
00044 #include "llvm/Transforms/Utils/Local.h"
00045 #include "llvm/ADT/Statistic.h"
00046 #include "llvm/Support/CommandLine.h"
00047 #include "llvm/Support/Visibility.h"
00048 #include <csetjmp>
00049 using namespace llvm;
00050 
00051 namespace {
00052   Statistic<> NumInvokes("lowerinvoke", "Number of invokes replaced");
00053   Statistic<> NumUnwinds("lowerinvoke", "Number of unwinds replaced");
00054   Statistic<> NumSpilled("lowerinvoke",
00055                          "Number of registers live across unwind edges");
00056   cl::opt<bool> ExpensiveEHSupport("enable-correct-eh-support",
00057  cl::desc("Make the -lowerinvoke pass insert expensive, but correct, EH code"));
00058 
00059   class VISIBILITY_HIDDEN LowerInvoke : public FunctionPass {
00060     // Used for both models.
00061     Function *WriteFn;
00062     Function *AbortFn;
00063     Value *AbortMessage;
00064     unsigned AbortMessageLength;
00065 
00066     // Used for expensive EH support.
00067     const Type *JBLinkTy;
00068     GlobalVariable *JBListHead;
00069     Function *SetJmpFn, *LongJmpFn;
00070   public:
00071     LowerInvoke(unsigned Size = 200, unsigned Align = 0) : JumpBufSize(Size),
00072       JumpBufAlign(Align) {}
00073     bool doInitialization(Module &M);
00074     bool runOnFunction(Function &F);
00075  
00076     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
00077       // This is a cluster of orthogonal Transforms 
00078       AU.addPreservedID(PromoteMemoryToRegisterID);
00079       AU.addPreservedID(LowerSelectID);
00080       AU.addPreservedID(LowerSwitchID);
00081       AU.addPreservedID(LowerAllocationsID);
00082     }
00083        
00084   private:
00085     void createAbortMessage();
00086     void writeAbortMessage(Instruction *IB);
00087     bool insertCheapEHSupport(Function &F);
00088     void splitLiveRangesLiveAcrossInvokes(std::vector<InvokeInst*> &Invokes);
00089     void rewriteExpensiveInvoke(InvokeInst *II, unsigned InvokeNo,
00090                                 AllocaInst *InvokeNum, SwitchInst *CatchSwitch);
00091     bool insertExpensiveEHSupport(Function &F);
00092     
00093     unsigned JumpBufSize;
00094     unsigned JumpBufAlign;
00095   };
00096 
00097   RegisterOpt<LowerInvoke>
00098   X("lowerinvoke", "Lower invoke and unwind, for unwindless code generators");
00099 }
00100 
00101 const PassInfo *llvm::LowerInvokePassID = X.getPassInfo();
00102 
00103 // Public Interface To the LowerInvoke pass.
00104 FunctionPass *llvm::createLowerInvokePass(unsigned JumpBufSize, 
00105                                           unsigned JumpBufAlign) { 
00106   return new LowerInvoke(JumpBufSize, JumpBufAlign); 
00107 }
00108 
00109 // doInitialization - Make sure that there is a prototype for abort in the
00110 // current module.
00111 bool LowerInvoke::doInitialization(Module &M) {
00112   const Type *VoidPtrTy = PointerType::get(Type::SByteTy);
00113   AbortMessage = 0;
00114   if (ExpensiveEHSupport) {
00115     // Insert a type for the linked list of jump buffers.
00116     const Type *JmpBufTy = ArrayType::get(VoidPtrTy, JumpBufSize);
00117 
00118     { // The type is recursive, so use a type holder.
00119       std::vector<const Type*> Elements;
00120       Elements.push_back(JmpBufTy);
00121       OpaqueType *OT = OpaqueType::get();
00122       Elements.push_back(PointerType::get(OT));
00123       PATypeHolder JBLType(StructType::get(Elements));
00124       OT->refineAbstractTypeTo(JBLType.get());  // Complete the cycle.
00125       JBLinkTy = JBLType.get();
00126       M.addTypeName("llvm.sjljeh.jmpbufty", JBLinkTy);
00127     }
00128 
00129     const Type *PtrJBList = PointerType::get(JBLinkTy);
00130 
00131     // Now that we've done that, insert the jmpbuf list head global, unless it
00132     // already exists.
00133     if (!(JBListHead = M.getGlobalVariable("llvm.sjljeh.jblist", PtrJBList)))
00134       JBListHead = new GlobalVariable(PtrJBList, false,
00135                                       GlobalValue::LinkOnceLinkage,
00136                                       Constant::getNullValue(PtrJBList),
00137                                       "llvm.sjljeh.jblist", &M);
00138     SetJmpFn = M.getOrInsertFunction("llvm.setjmp", Type::IntTy,
00139                                      PointerType::get(JmpBufTy), (Type *)0);
00140     LongJmpFn = M.getOrInsertFunction("llvm.longjmp", Type::VoidTy,
00141                                       PointerType::get(JmpBufTy),
00142                                       Type::IntTy, (Type *)0);
00143   }
00144 
00145   // We need the 'write' and 'abort' functions for both models.
00146   AbortFn = M.getOrInsertFunction("abort", Type::VoidTy, (Type *)0);
00147 
00148   // Unfortunately, 'write' can end up being prototyped in several different
00149   // ways.  If the user defines a three (or more) operand function named 'write'
00150   // we will use their prototype.  We _do not_ want to insert another instance
00151   // of a write prototype, because we don't know that the funcresolve pass will
00152   // run after us.  If there is a definition of a write function, but it's not
00153   // suitable for our uses, we just don't emit write calls.  If there is no
00154   // write prototype at all, we just add one.
00155   if (Function *WF = M.getNamedFunction("write")) {
00156     if (WF->getFunctionType()->getNumParams() > 3 ||
00157         WF->getFunctionType()->isVarArg())
00158       WriteFn = WF;
00159     else
00160       WriteFn = 0;
00161   } else {
00162     WriteFn = M.getOrInsertFunction("write", Type::VoidTy, Type::IntTy,
00163                                     VoidPtrTy, Type::IntTy, (Type *)0);
00164   }
00165   return true;
00166 }
00167 
00168 void LowerInvoke::createAbortMessage() {
00169   Module &M = *WriteFn->getParent();
00170   if (ExpensiveEHSupport) {
00171     // The abort message for expensive EH support tells the user that the
00172     // program 'unwound' without an 'invoke' instruction.
00173     Constant *Msg =
00174       ConstantArray::get("ERROR: Exception thrown, but not caught!\n");
00175     AbortMessageLength = Msg->getNumOperands()-1;  // don't include \0
00176 
00177     GlobalVariable *MsgGV = new GlobalVariable(Msg->getType(), true,
00178                                                GlobalValue::InternalLinkage,
00179                                                Msg, "abortmsg", &M);
00180     std::vector<Constant*> GEPIdx(2, Constant::getNullValue(Type::IntTy));
00181     AbortMessage = ConstantExpr::getGetElementPtr(MsgGV, GEPIdx);
00182   } else {
00183     // The abort message for cheap EH support tells the user that EH is not
00184     // enabled.
00185     Constant *Msg =
00186       ConstantArray::get("Exception handler needed, but not enabled.  Recompile"
00187                          " program with -enable-correct-eh-support.\n");
00188     AbortMessageLength = Msg->getNumOperands()-1;  // don't include \0
00189 
00190     GlobalVariable *MsgGV = new GlobalVariable(Msg->getType(), true,
00191                                                GlobalValue::InternalLinkage,
00192                                                Msg, "abortmsg", &M);
00193     std::vector<Constant*> GEPIdx(2, Constant::getNullValue(Type::IntTy));
00194     AbortMessage = ConstantExpr::getGetElementPtr(MsgGV, GEPIdx);
00195   }
00196 }
00197 
00198 
00199 void LowerInvoke::writeAbortMessage(Instruction *IB) {
00200   if (WriteFn) {
00201     if (AbortMessage == 0) createAbortMessage();
00202 
00203     // These are the arguments we WANT...
00204     std::vector<Value*> Args;
00205     Args.push_back(ConstantInt::get(Type::IntTy, 2));
00206     Args.push_back(AbortMessage);
00207     Args.push_back(ConstantInt::get(Type::IntTy, AbortMessageLength));
00208 
00209     // If the actual declaration of write disagrees, insert casts as
00210     // appropriate.
00211     const FunctionType *FT = WriteFn->getFunctionType();
00212     unsigned NumArgs = FT->getNumParams();
00213     for (unsigned i = 0; i != 3; ++i)
00214       if (i < NumArgs && FT->getParamType(i) != Args[i]->getType())
00215         Args[i] = ConstantExpr::getCast(cast<Constant>(Args[i]),
00216                                         FT->getParamType(i));
00217 
00218     (new CallInst(WriteFn, Args, "", IB))->setTailCall();
00219   }
00220 }
00221 
00222 bool LowerInvoke::insertCheapEHSupport(Function &F) {
00223   bool Changed = false;
00224   for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
00225     if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
00226       // Insert a normal call instruction...
00227       std::string Name = II->getName(); II->setName("");
00228       CallInst *NewCall = new CallInst(II->getCalledValue(),
00229                                        std::vector<Value*>(II->op_begin()+3,
00230                                                        II->op_end()), Name, II);
00231       NewCall->setCallingConv(II->getCallingConv());
00232       II->replaceAllUsesWith(NewCall);
00233 
00234       // Insert an unconditional branch to the normal destination.
00235       new BranchInst(II->getNormalDest(), II);
00236 
00237       // Remove any PHI node entries from the exception destination.
00238       II->getUnwindDest()->removePredecessor(BB);
00239 
00240       // Remove the invoke instruction now.
00241       BB->getInstList().erase(II);
00242 
00243       ++NumInvokes; Changed = true;
00244     } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
00245       // Insert a new call to write(2, AbortMessage, AbortMessageLength);
00246       writeAbortMessage(UI);
00247 
00248       // Insert a call to abort()
00249       (new CallInst(AbortFn, std::vector<Value*>(), "", UI))->setTailCall();
00250 
00251       // Insert a return instruction.  This really should be a "barrier", as it
00252       // is unreachable.
00253       new ReturnInst(F.getReturnType() == Type::VoidTy ? 0 :
00254                             Constant::getNullValue(F.getReturnType()), UI);
00255 
00256       // Remove the unwind instruction now.
00257       BB->getInstList().erase(UI);
00258 
00259       ++NumUnwinds; Changed = true;
00260     }
00261   return Changed;
00262 }
00263 
00264 /// rewriteExpensiveInvoke - Insert code and hack the function to replace the
00265 /// specified invoke instruction with a call.
00266 void LowerInvoke::rewriteExpensiveInvoke(InvokeInst *II, unsigned InvokeNo,
00267                                          AllocaInst *InvokeNum,
00268                                          SwitchInst *CatchSwitch) {
00269   ConstantUInt *InvokeNoC = ConstantUInt::get(Type::UIntTy, InvokeNo);
00270 
00271   // Insert a store of the invoke num before the invoke and store zero into the
00272   // location afterward.
00273   new StoreInst(InvokeNoC, InvokeNum, true, II);  // volatile
00274   
00275   BasicBlock::iterator NI = II->getNormalDest()->begin();
00276   while (isa<PHINode>(NI)) ++NI;
00277   // nonvolatile.
00278   new StoreInst(Constant::getNullValue(Type::UIntTy), InvokeNum, false, NI);
00279   
00280   // Add a switch case to our unwind block.
00281   CatchSwitch->addCase(InvokeNoC, II->getUnwindDest());
00282   
00283   // Insert a normal call instruction.
00284   std::string Name = II->getName(); II->setName("");
00285   CallInst *NewCall = new CallInst(II->getCalledValue(),
00286                                    std::vector<Value*>(II->op_begin()+3,
00287                                                        II->op_end()), Name,
00288                                    II);
00289   NewCall->setCallingConv(II->getCallingConv());
00290   II->replaceAllUsesWith(NewCall);
00291   
00292   // Replace the invoke with an uncond branch.
00293   new BranchInst(II->getNormalDest(), NewCall->getParent());
00294   II->eraseFromParent();
00295 }
00296 
00297 /// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
00298 /// we reach blocks we've already seen.
00299 static void MarkBlocksLiveIn(BasicBlock *BB, std::set<BasicBlock*> &LiveBBs) {
00300   if (!LiveBBs.insert(BB).second) return; // already been here.
00301   
00302   for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
00303     MarkBlocksLiveIn(*PI, LiveBBs);  
00304 }
00305 
00306 // First thing we need to do is scan the whole function for values that are
00307 // live across unwind edges.  Each value that is live across an unwind edge
00308 // we spill into a stack location, guaranteeing that there is nothing live
00309 // across the unwind edge.  This process also splits all critical edges
00310 // coming out of invoke's.
00311 void LowerInvoke::
00312 splitLiveRangesLiveAcrossInvokes(std::vector<InvokeInst*> &Invokes) {
00313   // First step, split all critical edges from invoke instructions.
00314   for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
00315     InvokeInst *II = Invokes[i];
00316     SplitCriticalEdge(II, 0, this);
00317     SplitCriticalEdge(II, 1, this);
00318     assert(!isa<PHINode>(II->getNormalDest()) &&
00319            !isa<PHINode>(II->getUnwindDest()) &&
00320            "critical edge splitting left single entry phi nodes?");
00321   }
00322 
00323   Function *F = Invokes.back()->getParent()->getParent();
00324   
00325   // To avoid having to handle incoming arguments specially, we lower each arg
00326   // to a copy instruction in the entry block.  This ensure that the argument
00327   // value itself cannot be live across the entry block.
00328   BasicBlock::iterator AfterAllocaInsertPt = F->begin()->begin();
00329   while (isa<AllocaInst>(AfterAllocaInsertPt) &&
00330         isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsertPt)->getArraySize()))
00331     ++AfterAllocaInsertPt;
00332   for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
00333        AI != E; ++AI) {
00334     CastInst *NC = new CastInst(AI, AI->getType(), AI->getName()+".tmp",
00335                                 AfterAllocaInsertPt);
00336     AI->replaceAllUsesWith(NC);
00337     NC->setOperand(0, AI);
00338   }
00339   
00340   // Finally, scan the code looking for instructions with bad live ranges.
00341   for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
00342     for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
00343       // Ignore obvious cases we don't have to handle.  In particular, most
00344       // instructions either have no uses or only have a single use inside the
00345       // current block.  Ignore them quickly.
00346       Instruction *Inst = II;
00347       if (Inst->use_empty()) continue;
00348       if (Inst->hasOneUse() &&
00349           cast<Instruction>(Inst->use_back())->getParent() == BB &&
00350           !isa<PHINode>(Inst->use_back())) continue;
00351       
00352       // If this is an alloca in the entry block, it's not a real register
00353       // value.
00354       if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
00355         if (isa<ConstantInt>(AI->getArraySize()) && BB == F->begin())
00356           continue;
00357       
00358       // Avoid iterator invalidation by copying users to a temporary vector.
00359       std::vector<Instruction*> Users;
00360       for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end();
00361            UI != E; ++UI) {
00362         Instruction *User = cast<Instruction>(*UI);
00363         if (User->getParent() != BB || isa<PHINode>(User))
00364           Users.push_back(User);
00365       }
00366 
00367       // Scan all of the uses and see if the live range is live across an unwind
00368       // edge.  If we find a use live across an invoke edge, create an alloca
00369       // and spill the value.
00370       AllocaInst *SpillLoc = 0;
00371       std::set<InvokeInst*> InvokesWithStoreInserted;
00372 
00373       // Find all of the blocks that this value is live in.
00374       std::set<BasicBlock*> LiveBBs;
00375       LiveBBs.insert(Inst->getParent());
00376       while (!Users.empty()) {
00377         Instruction *U = Users.back();
00378         Users.pop_back();
00379         
00380         if (!isa<PHINode>(U)) {
00381           MarkBlocksLiveIn(U->getParent(), LiveBBs);
00382         } else {
00383           // Uses for a PHI node occur in their predecessor block.
00384           PHINode *PN = cast<PHINode>(U);
00385           for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
00386             if (PN->getIncomingValue(i) == Inst)
00387               MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
00388         }
00389       }
00390       
00391       // Now that we know all of the blocks that this thing is live in, see if
00392       // it includes any of the unwind locations.
00393       bool NeedsSpill = false;
00394       for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
00395         BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
00396         if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
00397           NeedsSpill = true;
00398         }
00399       }
00400 
00401       // If we decided we need a spill, do it.
00402       if (NeedsSpill) {
00403         ++NumSpilled;
00404         DemoteRegToStack(*Inst, true);
00405       }
00406     }
00407 }
00408 
00409 bool LowerInvoke::insertExpensiveEHSupport(Function &F) {
00410   std::vector<ReturnInst*> Returns;
00411   std::vector<UnwindInst*> Unwinds;
00412   std::vector<InvokeInst*> Invokes;
00413 
00414   for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
00415     if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
00416       // Remember all return instructions in case we insert an invoke into this
00417       // function.
00418       Returns.push_back(RI);
00419     } else if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
00420       Invokes.push_back(II);
00421     } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
00422       Unwinds.push_back(UI);
00423     }
00424 
00425   if (Unwinds.empty() && Invokes.empty()) return false;
00426 
00427   NumInvokes += Invokes.size();
00428   NumUnwinds += Unwinds.size();
00429   
00430   // TODO: This is not an optimal way to do this.  In particular, this always
00431   // inserts setjmp calls into the entries of functions with invoke instructions
00432   // even though there are possibly paths through the function that do not
00433   // execute any invokes.  In particular, for functions with early exits, e.g.
00434   // the 'addMove' method in hexxagon, it would be nice to not have to do the
00435   // setjmp stuff on the early exit path.  This requires a bit of dataflow, but
00436   // would not be too hard to do.
00437 
00438   // If we have an invoke instruction, insert a setjmp that dominates all
00439   // invokes.  After the setjmp, use a cond branch that goes to the original
00440   // code path on zero, and to a designated 'catch' block of nonzero.
00441   Value *OldJmpBufPtr = 0;
00442   if (!Invokes.empty()) {
00443     // First thing we need to do is scan the whole function for values that are
00444     // live across unwind edges.  Each value that is live across an unwind edge
00445     // we spill into a stack location, guaranteeing that there is nothing live
00446     // across the unwind edge.  This process also splits all critical edges
00447     // coming out of invoke's.
00448     splitLiveRangesLiveAcrossInvokes(Invokes);    
00449     
00450     BasicBlock *EntryBB = F.begin();
00451     
00452     // Create an alloca for the incoming jump buffer ptr and the new jump buffer
00453     // that needs to be restored on all exits from the function.  This is an
00454     // alloca because the value needs to be live across invokes.
00455     AllocaInst *JmpBuf = 
00456       new AllocaInst(JBLinkTy, 0, JumpBufAlign, "jblink", F.begin()->begin());
00457     
00458     std::vector<Value*> Idx;
00459     Idx.push_back(Constant::getNullValue(Type::IntTy));
00460     Idx.push_back(ConstantUInt::get(Type::UIntTy, 1));
00461     OldJmpBufPtr = new GetElementPtrInst(JmpBuf, Idx, "OldBuf",
00462                                          EntryBB->getTerminator());
00463 
00464     // Copy the JBListHead to the alloca.
00465     Value *OldBuf = new LoadInst(JBListHead, "oldjmpbufptr", true,
00466                                  EntryBB->getTerminator());
00467     new StoreInst(OldBuf, OldJmpBufPtr, true, EntryBB->getTerminator());
00468     
00469     // Add the new jumpbuf to the list.
00470     new StoreInst(JmpBuf, JBListHead, true, EntryBB->getTerminator());
00471 
00472     // Create the catch block.  The catch block is basically a big switch
00473     // statement that goes to all of the invoke catch blocks.
00474     BasicBlock *CatchBB = new BasicBlock("setjmp.catch", &F);
00475     
00476     // Create an alloca which keeps track of which invoke is currently
00477     // executing.  For normal calls it contains zero.
00478     AllocaInst *InvokeNum = new AllocaInst(Type::UIntTy, 0, "invokenum",
00479                                            EntryBB->begin());
00480     new StoreInst(ConstantInt::get(Type::UIntTy, 0), InvokeNum, true,
00481                   EntryBB->getTerminator());
00482     
00483     // Insert a load in the Catch block, and a switch on its value.  By default,
00484     // we go to a block that just does an unwind (which is the correct action
00485     // for a standard call).
00486     BasicBlock *UnwindBB = new BasicBlock("unwindbb", &F);
00487     Unwinds.push_back(new UnwindInst(UnwindBB));
00488     
00489     Value *CatchLoad = new LoadInst(InvokeNum, "invoke.num", true, CatchBB);
00490     SwitchInst *CatchSwitch = 
00491       new SwitchInst(CatchLoad, UnwindBB, Invokes.size(), CatchBB);
00492 
00493     // Now that things are set up, insert the setjmp call itself.
00494     
00495     // Split the entry block to insert the conditional branch for the setjmp.
00496     BasicBlock *ContBlock = EntryBB->splitBasicBlock(EntryBB->getTerminator(),
00497                                                      "setjmp.cont");
00498 
00499     Idx[1] = ConstantUInt::get(Type::UIntTy, 0);
00500     Value *JmpBufPtr = new GetElementPtrInst(JmpBuf, Idx, "TheJmpBuf",
00501                                              EntryBB->getTerminator());
00502     Value *SJRet = new CallInst(SetJmpFn, JmpBufPtr, "sjret",
00503                                 EntryBB->getTerminator());
00504     
00505     // Compare the return value to zero.
00506     Value *IsNormal = BinaryOperator::createSetEQ(SJRet,
00507                                      Constant::getNullValue(SJRet->getType()),
00508                                         "notunwind", EntryBB->getTerminator());
00509     // Nuke the uncond branch.
00510     EntryBB->getTerminator()->eraseFromParent();
00511     
00512     // Put in a new condbranch in its place.
00513     new BranchInst(ContBlock, CatchBB, IsNormal, EntryBB);
00514 
00515     // At this point, we are all set up, rewrite each invoke instruction.
00516     for (unsigned i = 0, e = Invokes.size(); i != e; ++i)
00517       rewriteExpensiveInvoke(Invokes[i], i+1, InvokeNum, CatchSwitch);
00518   }
00519 
00520   // We know that there is at least one unwind.
00521   
00522   // Create three new blocks, the block to load the jmpbuf ptr and compare
00523   // against null, the block to do the longjmp, and the error block for if it
00524   // is null.  Add them at the end of the function because they are not hot.
00525   BasicBlock *UnwindHandler = new BasicBlock("dounwind", &F);
00526   BasicBlock *UnwindBlock = new BasicBlock("unwind", &F);
00527   BasicBlock *TermBlock = new BasicBlock("unwinderror", &F);
00528 
00529   // If this function contains an invoke, restore the old jumpbuf ptr.
00530   Value *BufPtr;
00531   if (OldJmpBufPtr) {
00532     // Before the return, insert a copy from the saved value to the new value.
00533     BufPtr = new LoadInst(OldJmpBufPtr, "oldjmpbufptr", UnwindHandler);
00534     new StoreInst(BufPtr, JBListHead, UnwindHandler);
00535   } else {
00536     BufPtr = new LoadInst(JBListHead, "ehlist", UnwindHandler);
00537   }
00538   
00539   // Load the JBList, if it's null, then there was no catch!
00540   Value *NotNull = BinaryOperator::createSetNE(BufPtr,
00541                                       Constant::getNullValue(BufPtr->getType()),
00542                                           "notnull", UnwindHandler);
00543   new BranchInst(UnwindBlock, TermBlock, NotNull, UnwindHandler);
00544   
00545   // Create the block to do the longjmp.
00546   // Get a pointer to the jmpbuf and longjmp.
00547   std::vector<Value*> Idx;
00548   Idx.push_back(Constant::getNullValue(Type::IntTy));
00549   Idx.push_back(ConstantUInt::get(Type::UIntTy, 0));
00550   Idx[0] = new GetElementPtrInst(BufPtr, Idx, "JmpBuf", UnwindBlock);
00551   Idx[1] = ConstantInt::get(Type::IntTy, 1);
00552   new CallInst(LongJmpFn, Idx, "", UnwindBlock);
00553   new UnreachableInst(UnwindBlock);
00554   
00555   // Set up the term block ("throw without a catch").
00556   new UnreachableInst(TermBlock);
00557 
00558   // Insert a new call to write(2, AbortMessage, AbortMessageLength);
00559   writeAbortMessage(TermBlock->getTerminator());
00560   
00561   // Insert a call to abort()
00562   (new CallInst(AbortFn, std::vector<Value*>(), "",
00563                 TermBlock->getTerminator()))->setTailCall();
00564     
00565   
00566   // Replace all unwinds with a branch to the unwind handler.
00567   for (unsigned i = 0, e = Unwinds.size(); i != e; ++i) {
00568     new BranchInst(UnwindHandler, Unwinds[i]);
00569     Unwinds[i]->eraseFromParent();    
00570   } 
00571   
00572   // Finally, for any returns from this function, if this function contains an
00573   // invoke, restore the old jmpbuf pointer to its input value.
00574   if (OldJmpBufPtr) {
00575     for (unsigned i = 0, e = Returns.size(); i != e; ++i) {
00576       ReturnInst *R = Returns[i];
00577       
00578       // Before the return, insert a copy from the saved value to the new value.
00579       Value *OldBuf = new LoadInst(OldJmpBufPtr, "oldjmpbufptr", true, R);
00580       new StoreInst(OldBuf, JBListHead, true, R);
00581     }
00582   }
00583   
00584   return true;
00585 }
00586 
00587 bool LowerInvoke::runOnFunction(Function &F) {
00588   if (ExpensiveEHSupport)
00589     return insertExpensiveEHSupport(F);
00590   else
00591     return insertCheapEHSupport(F);
00592 }