1 //===- LowerInvoke.cpp - Eliminate Invoke & Unwind instructions -----------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This transformation is designed for use by code generators which do not yet
11 // support stack unwinding. This pass supports two models of exception handling
12 // lowering, the 'cheap' support and the 'expensive' support.
14 // 'Cheap' exception handling support gives the program the ability to execute
15 // any program which does not "throw an exception", by turning 'invoke'
16 // instructions into calls and by turning 'unwind' instructions into calls to
17 // abort(). If the program does dynamically use the unwind instruction, the
18 // program will print a message then abort.
20 // 'Expensive' exception handling support gives the full exception handling
21 // support to the program at the cost of making the 'invoke' instruction
22 // really expensive. It basically inserts setjmp/longjmp calls to emulate the
23 // exception handling as necessary.
25 // Because the 'expensive' support slows down programs a lot, and EH is only
26 // used for a subset of the programs, it must be specifically enabled by an
29 // Note that after this pass runs the CFG is not entirely accurate (exceptional
30 // control flow edges are not correct anymore) so only very simple things should
31 // be done after the lowerinvoke pass has run (like generation of native code).
32 // This should not be used as a general purpose "my LLVM-to-LLVM pass doesn't
33 // support the invoke instruction yet" lowering pass.
35 //===----------------------------------------------------------------------===//
37 #include "llvm/Transforms/Scalar.h"
38 #include "llvm/Constants.h"
39 #include "llvm/DerivedTypes.h"
40 #include "llvm/Instructions.h"
41 #include "llvm/Module.h"
42 #include "llvm/Pass.h"
43 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
44 #include "llvm/Transforms/Utils/Local.h"
45 #include "llvm/ADT/Statistic.h"
46 #include "llvm/Support/CommandLine.h"
51 Statistic<> NumInvokes("lowerinvoke", "Number of invokes replaced");
52 Statistic<> NumUnwinds("lowerinvoke", "Number of unwinds replaced");
53 Statistic<> NumSpilled("lowerinvoke",
54 "Number of registers live across unwind edges");
55 cl::opt<bool> ExpensiveEHSupport("enable-correct-eh-support",
56 cl::desc("Make the -lowerinvoke pass insert expensive, but correct, EH code"));
58 class LowerInvoke : public FunctionPass {
59 // Used for both models.
63 unsigned AbortMessageLength;
65 // Used for expensive EH support.
67 GlobalVariable *JBListHead;
68 Function *SetJmpFn, *LongJmpFn;
70 LowerInvoke(unsigned Size = 200, unsigned Align = 0) : JumpBufSize(Size),
71 JumpBufAlign(Align) {}
72 bool doInitialization(Module &M);
73 bool runOnFunction(Function &F);
75 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
76 // This is a cluster of orthogonal Transforms
77 AU.addPreservedID(PromoteMemoryToRegisterID);
78 AU.addPreservedID(LowerSelectID);
79 AU.addPreservedID(LowerSwitchID);
80 AU.addPreservedID(LowerAllocationsID);
84 void createAbortMessage();
85 void writeAbortMessage(Instruction *IB);
86 bool insertCheapEHSupport(Function &F);
87 void splitLiveRangesLiveAcrossInvokes(std::vector<InvokeInst*> &Invokes);
88 void rewriteExpensiveInvoke(InvokeInst *II, unsigned InvokeNo,
89 AllocaInst *InvokeNum, SwitchInst *CatchSwitch);
90 bool insertExpensiveEHSupport(Function &F);
93 unsigned JumpBufAlign;
96 RegisterOpt<LowerInvoke>
97 X("lowerinvoke", "Lower invoke and unwind, for unwindless code generators");
100 const PassInfo *llvm::LowerInvokePassID = X.getPassInfo();
102 // Public Interface To the LowerInvoke pass.
103 FunctionPass *llvm::createLowerInvokePass(unsigned JumpBufSize,
104 unsigned JumpBufAlign) {
105 return new LowerInvoke(JumpBufSize, JumpBufAlign);
108 // doInitialization - Make sure that there is a prototype for abort in the
110 bool LowerInvoke::doInitialization(Module &M) {
111 const Type *VoidPtrTy = PointerType::get(Type::SByteTy);
113 if (ExpensiveEHSupport) {
114 // Insert a type for the linked list of jump buffers.
115 const Type *JmpBufTy = ArrayType::get(VoidPtrTy, JumpBufSize);
117 { // The type is recursive, so use a type holder.
118 std::vector<const Type*> Elements;
119 Elements.push_back(JmpBufTy);
120 OpaqueType *OT = OpaqueType::get();
121 Elements.push_back(PointerType::get(OT));
122 PATypeHolder JBLType(StructType::get(Elements));
123 OT->refineAbstractTypeTo(JBLType.get()); // Complete the cycle.
124 JBLinkTy = JBLType.get();
125 M.addTypeName("llvm.sjljeh.jmpbufty", JBLinkTy);
128 const Type *PtrJBList = PointerType::get(JBLinkTy);
130 // Now that we've done that, insert the jmpbuf list head global, unless it
132 if (!(JBListHead = M.getGlobalVariable("llvm.sjljeh.jblist", PtrJBList)))
133 JBListHead = new GlobalVariable(PtrJBList, false,
134 GlobalValue::LinkOnceLinkage,
135 Constant::getNullValue(PtrJBList),
136 "llvm.sjljeh.jblist", &M);
137 SetJmpFn = M.getOrInsertFunction("llvm.setjmp", Type::IntTy,
138 PointerType::get(JmpBufTy), (Type *)0);
139 LongJmpFn = M.getOrInsertFunction("llvm.longjmp", Type::VoidTy,
140 PointerType::get(JmpBufTy),
141 Type::IntTy, (Type *)0);
144 // We need the 'write' and 'abort' functions for both models.
145 AbortFn = M.getOrInsertFunction("abort", Type::VoidTy, (Type *)0);
147 // Unfortunately, 'write' can end up being prototyped in several different
148 // ways. If the user defines a three (or more) operand function named 'write'
149 // we will use their prototype. We _do not_ want to insert another instance
150 // of a write prototype, because we don't know that the funcresolve pass will
151 // run after us. If there is a definition of a write function, but it's not
152 // suitable for our uses, we just don't emit write calls. If there is no
153 // write prototype at all, we just add one.
154 if (Function *WF = M.getNamedFunction("write")) {
155 if (WF->getFunctionType()->getNumParams() > 3 ||
156 WF->getFunctionType()->isVarArg())
161 WriteFn = M.getOrInsertFunction("write", Type::VoidTy, Type::IntTy,
162 VoidPtrTy, Type::IntTy, (Type *)0);
167 void LowerInvoke::createAbortMessage() {
168 Module &M = *WriteFn->getParent();
169 if (ExpensiveEHSupport) {
170 // The abort message for expensive EH support tells the user that the
171 // program 'unwound' without an 'invoke' instruction.
173 ConstantArray::get("ERROR: Exception thrown, but not caught!\n");
174 AbortMessageLength = Msg->getNumOperands()-1; // don't include \0
176 GlobalVariable *MsgGV = new GlobalVariable(Msg->getType(), true,
177 GlobalValue::InternalLinkage,
178 Msg, "abortmsg", &M);
179 std::vector<Constant*> GEPIdx(2, Constant::getNullValue(Type::IntTy));
180 AbortMessage = ConstantExpr::getGetElementPtr(MsgGV, GEPIdx);
182 // The abort message for cheap EH support tells the user that EH is not
185 ConstantArray::get("Exception handler needed, but not enabled. Recompile"
186 " program with -enable-correct-eh-support.\n");
187 AbortMessageLength = Msg->getNumOperands()-1; // don't include \0
189 GlobalVariable *MsgGV = new GlobalVariable(Msg->getType(), true,
190 GlobalValue::InternalLinkage,
191 Msg, "abortmsg", &M);
192 std::vector<Constant*> GEPIdx(2, Constant::getNullValue(Type::IntTy));
193 AbortMessage = ConstantExpr::getGetElementPtr(MsgGV, GEPIdx);
198 void LowerInvoke::writeAbortMessage(Instruction *IB) {
200 if (AbortMessage == 0) createAbortMessage();
202 // These are the arguments we WANT...
203 std::vector<Value*> Args;
204 Args.push_back(ConstantInt::get(Type::IntTy, 2));
205 Args.push_back(AbortMessage);
206 Args.push_back(ConstantInt::get(Type::IntTy, AbortMessageLength));
208 // If the actual declaration of write disagrees, insert casts as
210 const FunctionType *FT = WriteFn->getFunctionType();
211 unsigned NumArgs = FT->getNumParams();
212 for (unsigned i = 0; i != 3; ++i)
213 if (i < NumArgs && FT->getParamType(i) != Args[i]->getType())
214 Args[i] = ConstantExpr::getCast(cast<Constant>(Args[i]),
215 FT->getParamType(i));
217 (new CallInst(WriteFn, Args, "", IB))->setTailCall();
221 bool LowerInvoke::insertCheapEHSupport(Function &F) {
222 bool Changed = false;
223 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
224 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
225 // Insert a normal call instruction...
226 std::string Name = II->getName(); II->setName("");
227 CallInst *NewCall = new CallInst(II->getCalledValue(),
228 std::vector<Value*>(II->op_begin()+3,
229 II->op_end()), Name, II);
230 NewCall->setCallingConv(II->getCallingConv());
231 II->replaceAllUsesWith(NewCall);
233 // Insert an unconditional branch to the normal destination.
234 new BranchInst(II->getNormalDest(), II);
236 // Remove any PHI node entries from the exception destination.
237 II->getUnwindDest()->removePredecessor(BB);
239 // Remove the invoke instruction now.
240 BB->getInstList().erase(II);
242 ++NumInvokes; Changed = true;
243 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
244 // Insert a new call to write(2, AbortMessage, AbortMessageLength);
245 writeAbortMessage(UI);
247 // Insert a call to abort()
248 (new CallInst(AbortFn, std::vector<Value*>(), "", UI))->setTailCall();
250 // Insert a return instruction. This really should be a "barrier", as it
252 new ReturnInst(F.getReturnType() == Type::VoidTy ? 0 :
253 Constant::getNullValue(F.getReturnType()), UI);
255 // Remove the unwind instruction now.
256 BB->getInstList().erase(UI);
258 ++NumUnwinds; Changed = true;
263 /// rewriteExpensiveInvoke - Insert code and hack the function to replace the
264 /// specified invoke instruction with a call.
265 void LowerInvoke::rewriteExpensiveInvoke(InvokeInst *II, unsigned InvokeNo,
266 AllocaInst *InvokeNum,
267 SwitchInst *CatchSwitch) {
268 ConstantUInt *InvokeNoC = ConstantUInt::get(Type::UIntTy, InvokeNo);
270 // Insert a store of the invoke num before the invoke and store zero into the
271 // location afterward.
272 new StoreInst(InvokeNoC, InvokeNum, true, II); // volatile
274 BasicBlock::iterator NI = II->getNormalDest()->begin();
275 while (isa<PHINode>(NI)) ++NI;
277 new StoreInst(Constant::getNullValue(Type::UIntTy), InvokeNum, false, NI);
279 // Add a switch case to our unwind block.
280 CatchSwitch->addCase(InvokeNoC, II->getUnwindDest());
282 // Insert a normal call instruction.
283 std::string Name = II->getName(); II->setName("");
284 CallInst *NewCall = new CallInst(II->getCalledValue(),
285 std::vector<Value*>(II->op_begin()+3,
288 NewCall->setCallingConv(II->getCallingConv());
289 II->replaceAllUsesWith(NewCall);
291 // Replace the invoke with an uncond branch.
292 new BranchInst(II->getNormalDest(), NewCall->getParent());
293 II->eraseFromParent();
296 /// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
297 /// we reach blocks we've already seen.
298 static void MarkBlocksLiveIn(BasicBlock *BB, std::set<BasicBlock*> &LiveBBs) {
299 if (!LiveBBs.insert(BB).second) return; // already been here.
301 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
302 MarkBlocksLiveIn(*PI, LiveBBs);
305 // First thing we need to do is scan the whole function for values that are
306 // live across unwind edges. Each value that is live across an unwind edge
307 // we spill into a stack location, guaranteeing that there is nothing live
308 // across the unwind edge. This process also splits all critical edges
309 // coming out of invoke's.
311 splitLiveRangesLiveAcrossInvokes(std::vector<InvokeInst*> &Invokes) {
312 // First step, split all critical edges from invoke instructions.
313 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
314 InvokeInst *II = Invokes[i];
315 SplitCriticalEdge(II, 0, this);
316 SplitCriticalEdge(II, 1, this);
317 assert(!isa<PHINode>(II->getNormalDest()) &&
318 !isa<PHINode>(II->getUnwindDest()) &&
319 "critical edge splitting left single entry phi nodes?");
322 Function *F = Invokes.back()->getParent()->getParent();
324 // To avoid having to handle incoming arguments specially, we lower each arg
325 // to a copy instruction in the entry block. This ensure that the argument
326 // value itself cannot be live across the entry block.
327 BasicBlock::iterator AfterAllocaInsertPt = F->begin()->begin();
328 while (isa<AllocaInst>(AfterAllocaInsertPt) &&
329 isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsertPt)->getArraySize()))
330 ++AfterAllocaInsertPt;
331 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
333 CastInst *NC = new CastInst(AI, AI->getType(), AI->getName()+".tmp",
334 AfterAllocaInsertPt);
335 AI->replaceAllUsesWith(NC);
336 NC->setOperand(0, AI);
339 // Finally, scan the code looking for instructions with bad live ranges.
340 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
341 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
342 // Ignore obvious cases we don't have to handle. In particular, most
343 // instructions either have no uses or only have a single use inside the
344 // current block. Ignore them quickly.
345 Instruction *Inst = II;
346 if (Inst->use_empty()) continue;
347 if (Inst->hasOneUse() &&
348 cast<Instruction>(Inst->use_back())->getParent() == BB &&
349 !isa<PHINode>(Inst->use_back())) continue;
351 // If this is an alloca in the entry block, it's not a real register
353 if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
354 if (isa<ConstantInt>(AI->getArraySize()) && BB == F->begin())
357 // Avoid iterator invalidation by copying users to a temporary vector.
358 std::vector<Instruction*> Users;
359 for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end();
361 Instruction *User = cast<Instruction>(*UI);
362 if (User->getParent() != BB || isa<PHINode>(User))
363 Users.push_back(User);
366 // Scan all of the uses and see if the live range is live across an unwind
367 // edge. If we find a use live across an invoke edge, create an alloca
368 // and spill the value.
369 AllocaInst *SpillLoc = 0;
370 std::set<InvokeInst*> InvokesWithStoreInserted;
372 // Find all of the blocks that this value is live in.
373 std::set<BasicBlock*> LiveBBs;
374 LiveBBs.insert(Inst->getParent());
375 while (!Users.empty()) {
376 Instruction *U = Users.back();
379 if (!isa<PHINode>(U)) {
380 MarkBlocksLiveIn(U->getParent(), LiveBBs);
382 // Uses for a PHI node occur in their predecessor block.
383 PHINode *PN = cast<PHINode>(U);
384 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
385 if (PN->getIncomingValue(i) == Inst)
386 MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
390 // Now that we know all of the blocks that this thing is live in, see if
391 // it includes any of the unwind locations.
392 bool NeedsSpill = false;
393 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
394 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
395 if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
400 // If we decided we need a spill, do it.
403 DemoteRegToStack(*Inst, true);
408 bool LowerInvoke::insertExpensiveEHSupport(Function &F) {
409 std::vector<ReturnInst*> Returns;
410 std::vector<UnwindInst*> Unwinds;
411 std::vector<InvokeInst*> Invokes;
413 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
414 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
415 // Remember all return instructions in case we insert an invoke into this
417 Returns.push_back(RI);
418 } else if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
419 Invokes.push_back(II);
420 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
421 Unwinds.push_back(UI);
424 if (Unwinds.empty() && Invokes.empty()) return false;
426 NumInvokes += Invokes.size();
427 NumUnwinds += Unwinds.size();
429 // TODO: This is not an optimal way to do this. In particular, this always
430 // inserts setjmp calls into the entries of functions with invoke instructions
431 // even though there are possibly paths through the function that do not
432 // execute any invokes. In particular, for functions with early exits, e.g.
433 // the 'addMove' method in hexxagon, it would be nice to not have to do the
434 // setjmp stuff on the early exit path. This requires a bit of dataflow, but
435 // would not be too hard to do.
437 // If we have an invoke instruction, insert a setjmp that dominates all
438 // invokes. After the setjmp, use a cond branch that goes to the original
439 // code path on zero, and to a designated 'catch' block of nonzero.
440 Value *OldJmpBufPtr = 0;
441 if (!Invokes.empty()) {
442 // First thing we need to do is scan the whole function for values that are
443 // live across unwind edges. Each value that is live across an unwind edge
444 // we spill into a stack location, guaranteeing that there is nothing live
445 // across the unwind edge. This process also splits all critical edges
446 // coming out of invoke's.
447 splitLiveRangesLiveAcrossInvokes(Invokes);
449 BasicBlock *EntryBB = F.begin();
451 // Create an alloca for the incoming jump buffer ptr and the new jump buffer
452 // that needs to be restored on all exits from the function. This is an
453 // alloca because the value needs to be live across invokes.
455 new AllocaInst(JBLinkTy, 0, JumpBufAlign, "jblink", F.begin()->begin());
457 std::vector<Value*> Idx;
458 Idx.push_back(Constant::getNullValue(Type::IntTy));
459 Idx.push_back(ConstantUInt::get(Type::UIntTy, 1));
460 OldJmpBufPtr = new GetElementPtrInst(JmpBuf, Idx, "OldBuf",
461 EntryBB->getTerminator());
463 // Copy the JBListHead to the alloca.
464 Value *OldBuf = new LoadInst(JBListHead, "oldjmpbufptr", true,
465 EntryBB->getTerminator());
466 new StoreInst(OldBuf, OldJmpBufPtr, true, EntryBB->getTerminator());
468 // Add the new jumpbuf to the list.
469 new StoreInst(JmpBuf, JBListHead, true, EntryBB->getTerminator());
471 // Create the catch block. The catch block is basically a big switch
472 // statement that goes to all of the invoke catch blocks.
473 BasicBlock *CatchBB = new BasicBlock("setjmp.catch", &F);
475 // Create an alloca which keeps track of which invoke is currently
476 // executing. For normal calls it contains zero.
477 AllocaInst *InvokeNum = new AllocaInst(Type::UIntTy, 0, "invokenum",
479 new StoreInst(ConstantInt::get(Type::UIntTy, 0), InvokeNum, true,
480 EntryBB->getTerminator());
482 // Insert a load in the Catch block, and a switch on its value. By default,
483 // we go to a block that just does an unwind (which is the correct action
484 // for a standard call).
485 BasicBlock *UnwindBB = new BasicBlock("unwindbb", &F);
486 Unwinds.push_back(new UnwindInst(UnwindBB));
488 Value *CatchLoad = new LoadInst(InvokeNum, "invoke.num", true, CatchBB);
489 SwitchInst *CatchSwitch =
490 new SwitchInst(CatchLoad, UnwindBB, Invokes.size(), CatchBB);
492 // Now that things are set up, insert the setjmp call itself.
494 // Split the entry block to insert the conditional branch for the setjmp.
495 BasicBlock *ContBlock = EntryBB->splitBasicBlock(EntryBB->getTerminator(),
498 Idx[1] = ConstantUInt::get(Type::UIntTy, 0);
499 Value *JmpBufPtr = new GetElementPtrInst(JmpBuf, Idx, "TheJmpBuf",
500 EntryBB->getTerminator());
501 Value *SJRet = new CallInst(SetJmpFn, JmpBufPtr, "sjret",
502 EntryBB->getTerminator());
504 // Compare the return value to zero.
505 Value *IsNormal = BinaryOperator::createSetEQ(SJRet,
506 Constant::getNullValue(SJRet->getType()),
507 "notunwind", EntryBB->getTerminator());
508 // Nuke the uncond branch.
509 EntryBB->getTerminator()->eraseFromParent();
511 // Put in a new condbranch in its place.
512 new BranchInst(ContBlock, CatchBB, IsNormal, EntryBB);
514 // At this point, we are all set up, rewrite each invoke instruction.
515 for (unsigned i = 0, e = Invokes.size(); i != e; ++i)
516 rewriteExpensiveInvoke(Invokes[i], i+1, InvokeNum, CatchSwitch);
519 // We know that there is at least one unwind.
521 // Create three new blocks, the block to load the jmpbuf ptr and compare
522 // against null, the block to do the longjmp, and the error block for if it
523 // is null. Add them at the end of the function because they are not hot.
524 BasicBlock *UnwindHandler = new BasicBlock("dounwind", &F);
525 BasicBlock *UnwindBlock = new BasicBlock("unwind", &F);
526 BasicBlock *TermBlock = new BasicBlock("unwinderror", &F);
528 // If this function contains an invoke, restore the old jumpbuf ptr.
531 // Before the return, insert a copy from the saved value to the new value.
532 BufPtr = new LoadInst(OldJmpBufPtr, "oldjmpbufptr", UnwindHandler);
533 new StoreInst(BufPtr, JBListHead, UnwindHandler);
535 BufPtr = new LoadInst(JBListHead, "ehlist", UnwindHandler);
538 // Load the JBList, if it's null, then there was no catch!
539 Value *NotNull = BinaryOperator::createSetNE(BufPtr,
540 Constant::getNullValue(BufPtr->getType()),
541 "notnull", UnwindHandler);
542 new BranchInst(UnwindBlock, TermBlock, NotNull, UnwindHandler);
544 // Create the block to do the longjmp.
545 // Get a pointer to the jmpbuf and longjmp.
546 std::vector<Value*> Idx;
547 Idx.push_back(Constant::getNullValue(Type::IntTy));
548 Idx.push_back(ConstantUInt::get(Type::UIntTy, 0));
549 Idx[0] = new GetElementPtrInst(BufPtr, Idx, "JmpBuf", UnwindBlock);
550 Idx[1] = ConstantInt::get(Type::IntTy, 1);
551 new CallInst(LongJmpFn, Idx, "", UnwindBlock);
552 new UnreachableInst(UnwindBlock);
554 // Set up the term block ("throw without a catch").
555 new UnreachableInst(TermBlock);
557 // Insert a new call to write(2, AbortMessage, AbortMessageLength);
558 writeAbortMessage(TermBlock->getTerminator());
560 // Insert a call to abort()
561 (new CallInst(AbortFn, std::vector<Value*>(), "",
562 TermBlock->getTerminator()))->setTailCall();
565 // Replace all unwinds with a branch to the unwind handler.
566 for (unsigned i = 0, e = Unwinds.size(); i != e; ++i) {
567 new BranchInst(UnwindHandler, Unwinds[i]);
568 Unwinds[i]->eraseFromParent();
571 // Finally, for any returns from this function, if this function contains an
572 // invoke, restore the old jmpbuf pointer to its input value.
574 for (unsigned i = 0, e = Returns.size(); i != e; ++i) {
575 ReturnInst *R = Returns[i];
577 // Before the return, insert a copy from the saved value to the new value.
578 Value *OldBuf = new LoadInst(OldJmpBufPtr, "oldjmpbufptr", true, R);
579 new StoreInst(OldBuf, JBListHead, true, R);
586 bool LowerInvoke::runOnFunction(Function &F) {
587 if (ExpensiveEHSupport)
588 return insertExpensiveEHSupport(F);
590 return insertCheapEHSupport(F);