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 #define DEBUG_TYPE "lowerinvoke"
38 #include "llvm/Transforms/Scalar.h"
39 #include "llvm/Constants.h"
40 #include "llvm/DerivedTypes.h"
41 #include "llvm/Instructions.h"
42 #include "llvm/Module.h"
43 #include "llvm/Pass.h"
44 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
45 #include "llvm/Transforms/Utils/Local.h"
46 #include "llvm/ADT/Statistic.h"
47 #include "llvm/Support/CommandLine.h"
48 #include "llvm/Support/Compiler.h"
49 #include "llvm/Target/TargetLowering.h"
54 STATISTIC(NumInvokes, "Number of invokes replaced");
55 STATISTIC(NumUnwinds, "Number of unwinds replaced");
56 STATISTIC(NumSpilled, "Number of registers live across unwind edges");
58 static cl::opt<bool> ExpensiveEHSupport("enable-correct-eh-support",
59 cl::desc("Make the -lowerinvoke pass insert expensive, but correct, EH code"));
62 class VISIBILITY_HIDDEN LowerInvoke : public FunctionPass {
63 // Used for both models.
67 unsigned AbortMessageLength;
69 // Used for expensive EH support.
71 GlobalVariable *JBListHead;
72 Constant *SetJmpFn, *LongJmpFn;
74 // We peek in TLI to grab the target's jmp_buf size and alignment
75 const TargetLowering *TLI;
78 LowerInvoke(const TargetLowering *tli = NULL) : TLI(tli) { }
79 bool doInitialization(Module &M);
80 bool runOnFunction(Function &F);
82 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
83 // This is a cluster of orthogonal Transforms
84 AU.addPreservedID(PromoteMemoryToRegisterID);
85 AU.addPreservedID(LowerSelectID);
86 AU.addPreservedID(LowerSwitchID);
87 AU.addPreservedID(LowerAllocationsID);
91 void createAbortMessage(Module *M);
92 void writeAbortMessage(Instruction *IB);
93 bool insertCheapEHSupport(Function &F);
94 void splitLiveRangesLiveAcrossInvokes(std::vector<InvokeInst*> &Invokes);
95 void rewriteExpensiveInvoke(InvokeInst *II, unsigned InvokeNo,
96 AllocaInst *InvokeNum, SwitchInst *CatchSwitch);
97 bool insertExpensiveEHSupport(Function &F);
100 RegisterPass<LowerInvoke>
101 X("lowerinvoke", "Lower invoke and unwind, for unwindless code generators");
104 const PassInfo *llvm::LowerInvokePassID = X.getPassInfo();
106 // Public Interface To the LowerInvoke pass.
107 FunctionPass *llvm::createLowerInvokePass(const TargetLowering *TLI) {
108 return new LowerInvoke(TLI);
111 // doInitialization - Make sure that there is a prototype for abort in the
113 bool LowerInvoke::doInitialization(Module &M) {
114 const Type *VoidPtrTy = PointerType::get(Type::Int8Ty);
116 if (ExpensiveEHSupport) {
117 // Insert a type for the linked list of jump buffers.
118 unsigned JBSize = TLI ? TLI->getJumpBufSize() : 0;
119 JBSize = JBSize ? JBSize : 200;
120 const Type *JmpBufTy = ArrayType::get(VoidPtrTy, JBSize);
122 { // The type is recursive, so use a type holder.
123 std::vector<const Type*> Elements;
124 Elements.push_back(JmpBufTy);
125 OpaqueType *OT = OpaqueType::get();
126 Elements.push_back(PointerType::get(OT));
127 PATypeHolder JBLType(StructType::get(Elements));
128 OT->refineAbstractTypeTo(JBLType.get()); // Complete the cycle.
129 JBLinkTy = JBLType.get();
130 M.addTypeName("llvm.sjljeh.jmpbufty", JBLinkTy);
133 const Type *PtrJBList = PointerType::get(JBLinkTy);
135 // Now that we've done that, insert the jmpbuf list head global, unless it
137 if (!(JBListHead = M.getGlobalVariable("llvm.sjljeh.jblist", PtrJBList))) {
138 JBListHead = new GlobalVariable(PtrJBList, false,
139 GlobalValue::LinkOnceLinkage,
140 Constant::getNullValue(PtrJBList),
141 "llvm.sjljeh.jblist", &M);
143 SetJmpFn = M.getOrInsertFunction("llvm.setjmp", Type::Int32Ty,
144 PointerType::get(JmpBufTy), (Type *)0);
145 LongJmpFn = M.getOrInsertFunction("llvm.longjmp", Type::VoidTy,
146 PointerType::get(JmpBufTy),
147 Type::Int32Ty, (Type *)0);
150 // We need the 'write' and 'abort' functions for both models.
151 AbortFn = M.getOrInsertFunction("abort", Type::VoidTy, (Type *)0);
152 #if 0 // "write" is Unix-specific.. code is going away soon anyway.
153 WriteFn = M.getOrInsertFunction("write", Type::VoidTy, Type::Int32Ty,
154 VoidPtrTy, Type::Int32Ty, (Type *)0);
161 void LowerInvoke::createAbortMessage(Module *M) {
162 if (ExpensiveEHSupport) {
163 // The abort message for expensive EH support tells the user that the
164 // program 'unwound' without an 'invoke' instruction.
166 ConstantArray::get("ERROR: Exception thrown, but not caught!\n");
167 AbortMessageLength = Msg->getNumOperands()-1; // don't include \0
169 GlobalVariable *MsgGV = new GlobalVariable(Msg->getType(), true,
170 GlobalValue::InternalLinkage,
172 std::vector<Constant*> GEPIdx(2, Constant::getNullValue(Type::Int32Ty));
173 AbortMessage = ConstantExpr::getGetElementPtr(MsgGV, &GEPIdx[0], 2);
175 // The abort message for cheap EH support tells the user that EH is not
178 ConstantArray::get("Exception handler needed, but not enabled. Recompile"
179 " program with -enable-correct-eh-support.\n");
180 AbortMessageLength = Msg->getNumOperands()-1; // don't include \0
182 GlobalVariable *MsgGV = new GlobalVariable(Msg->getType(), true,
183 GlobalValue::InternalLinkage,
185 std::vector<Constant*> GEPIdx(2, Constant::getNullValue(Type::Int32Ty));
186 AbortMessage = ConstantExpr::getGetElementPtr(MsgGV, &GEPIdx[0], 2);
191 void LowerInvoke::writeAbortMessage(Instruction *IB) {
193 if (AbortMessage == 0)
194 createAbortMessage(IB->getParent()->getParent()->getParent());
196 // These are the arguments we WANT...
198 Args[0] = ConstantInt::get(Type::Int32Ty, 2);
199 Args[1] = AbortMessage;
200 Args[2] = ConstantInt::get(Type::Int32Ty, AbortMessageLength);
201 (new CallInst(WriteFn, Args, 3, "", IB))->setTailCall();
205 bool LowerInvoke::insertCheapEHSupport(Function &F) {
206 bool Changed = false;
207 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
208 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
209 std::vector<Value*> CallArgs(II->op_begin()+3, II->op_end());
210 // Insert a normal call instruction...
211 CallInst *NewCall = new CallInst(II->getCalledValue(),
212 &CallArgs[0], CallArgs.size(), "", II);
213 NewCall->takeName(II);
214 NewCall->setCallingConv(II->getCallingConv());
215 II->replaceAllUsesWith(NewCall);
217 // Insert an unconditional branch to the normal destination.
218 new BranchInst(II->getNormalDest(), II);
220 // Remove any PHI node entries from the exception destination.
221 II->getUnwindDest()->removePredecessor(BB);
223 // Remove the invoke instruction now.
224 BB->getInstList().erase(II);
226 ++NumInvokes; Changed = true;
227 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
228 // Insert a new call to write(2, AbortMessage, AbortMessageLength);
229 writeAbortMessage(UI);
231 // Insert a call to abort()
232 (new CallInst(AbortFn, "", UI))->setTailCall();
234 // Insert a return instruction. This really should be a "barrier", as it
236 new ReturnInst(F.getReturnType() == Type::VoidTy ? 0 :
237 Constant::getNullValue(F.getReturnType()), UI);
239 // Remove the unwind instruction now.
240 BB->getInstList().erase(UI);
242 ++NumUnwinds; Changed = true;
247 /// rewriteExpensiveInvoke - Insert code and hack the function to replace the
248 /// specified invoke instruction with a call.
249 void LowerInvoke::rewriteExpensiveInvoke(InvokeInst *II, unsigned InvokeNo,
250 AllocaInst *InvokeNum,
251 SwitchInst *CatchSwitch) {
252 ConstantInt *InvokeNoC = ConstantInt::get(Type::Int32Ty, InvokeNo);
254 // Insert a store of the invoke num before the invoke and store zero into the
255 // location afterward.
256 new StoreInst(InvokeNoC, InvokeNum, true, II); // volatile
258 BasicBlock::iterator NI = II->getNormalDest()->begin();
259 while (isa<PHINode>(NI)) ++NI;
261 new StoreInst(Constant::getNullValue(Type::Int32Ty), InvokeNum, false, NI);
263 // Add a switch case to our unwind block.
264 CatchSwitch->addCase(InvokeNoC, II->getUnwindDest());
266 // Insert a normal call instruction.
267 std::vector<Value*> CallArgs(II->op_begin()+3, II->op_end());
268 CallInst *NewCall = new CallInst(II->getCalledValue(),
269 &CallArgs[0], CallArgs.size(), "",
271 NewCall->takeName(II);
272 NewCall->setCallingConv(II->getCallingConv());
273 II->replaceAllUsesWith(NewCall);
275 // Replace the invoke with an uncond branch.
276 new BranchInst(II->getNormalDest(), NewCall->getParent());
277 II->eraseFromParent();
280 /// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
281 /// we reach blocks we've already seen.
282 static void MarkBlocksLiveIn(BasicBlock *BB, std::set<BasicBlock*> &LiveBBs) {
283 if (!LiveBBs.insert(BB).second) return; // already been here.
285 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
286 MarkBlocksLiveIn(*PI, LiveBBs);
289 // First thing we need to do is scan the whole function for values that are
290 // live across unwind edges. Each value that is live across an unwind edge
291 // we spill into a stack location, guaranteeing that there is nothing live
292 // across the unwind edge. This process also splits all critical edges
293 // coming out of invoke's.
295 splitLiveRangesLiveAcrossInvokes(std::vector<InvokeInst*> &Invokes) {
296 // First step, split all critical edges from invoke instructions.
297 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
298 InvokeInst *II = Invokes[i];
299 SplitCriticalEdge(II, 0, this);
300 SplitCriticalEdge(II, 1, this);
301 assert(!isa<PHINode>(II->getNormalDest()) &&
302 !isa<PHINode>(II->getUnwindDest()) &&
303 "critical edge splitting left single entry phi nodes?");
306 Function *F = Invokes.back()->getParent()->getParent();
308 // To avoid having to handle incoming arguments specially, we lower each arg
309 // to a copy instruction in the entry block. This ensures that the argument
310 // value itself cannot be live across the entry block.
311 BasicBlock::iterator AfterAllocaInsertPt = F->begin()->begin();
312 while (isa<AllocaInst>(AfterAllocaInsertPt) &&
313 isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsertPt)->getArraySize()))
314 ++AfterAllocaInsertPt;
315 for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
317 // This is always a no-op cast because we're casting AI to AI->getType() so
318 // src and destination types are identical. BitCast is the only possibility.
319 CastInst *NC = new BitCastInst(
320 AI, AI->getType(), AI->getName()+".tmp", AfterAllocaInsertPt);
321 AI->replaceAllUsesWith(NC);
322 // Normally its is forbidden to replace a CastInst's operand because it
323 // could cause the opcode to reflect an illegal conversion. However, we're
324 // replacing it here with the same value it was constructed with to simply
326 NC->setOperand(0, AI);
329 // Finally, scan the code looking for instructions with bad live ranges.
330 for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
331 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
332 // Ignore obvious cases we don't have to handle. In particular, most
333 // instructions either have no uses or only have a single use inside the
334 // current block. Ignore them quickly.
335 Instruction *Inst = II;
336 if (Inst->use_empty()) continue;
337 if (Inst->hasOneUse() &&
338 cast<Instruction>(Inst->use_back())->getParent() == BB &&
339 !isa<PHINode>(Inst->use_back())) continue;
341 // If this is an alloca in the entry block, it's not a real register
343 if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
344 if (isa<ConstantInt>(AI->getArraySize()) && BB == F->begin())
347 // Avoid iterator invalidation by copying users to a temporary vector.
348 std::vector<Instruction*> Users;
349 for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end();
351 Instruction *User = cast<Instruction>(*UI);
352 if (User->getParent() != BB || isa<PHINode>(User))
353 Users.push_back(User);
356 // Scan all of the uses and see if the live range is live across an unwind
357 // edge. If we find a use live across an invoke edge, create an alloca
358 // and spill the value.
359 std::set<InvokeInst*> InvokesWithStoreInserted;
361 // Find all of the blocks that this value is live in.
362 std::set<BasicBlock*> LiveBBs;
363 LiveBBs.insert(Inst->getParent());
364 while (!Users.empty()) {
365 Instruction *U = Users.back();
368 if (!isa<PHINode>(U)) {
369 MarkBlocksLiveIn(U->getParent(), LiveBBs);
371 // Uses for a PHI node occur in their predecessor block.
372 PHINode *PN = cast<PHINode>(U);
373 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
374 if (PN->getIncomingValue(i) == Inst)
375 MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
379 // Now that we know all of the blocks that this thing is live in, see if
380 // it includes any of the unwind locations.
381 bool NeedsSpill = false;
382 for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
383 BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
384 if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
389 // If we decided we need a spill, do it.
392 DemoteRegToStack(*Inst, true);
397 bool LowerInvoke::insertExpensiveEHSupport(Function &F) {
398 std::vector<ReturnInst*> Returns;
399 std::vector<UnwindInst*> Unwinds;
400 std::vector<InvokeInst*> Invokes;
402 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
403 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
404 // Remember all return instructions in case we insert an invoke into this
406 Returns.push_back(RI);
407 } else if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
408 Invokes.push_back(II);
409 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
410 Unwinds.push_back(UI);
413 if (Unwinds.empty() && Invokes.empty()) return false;
415 NumInvokes += Invokes.size();
416 NumUnwinds += Unwinds.size();
418 // TODO: This is not an optimal way to do this. In particular, this always
419 // inserts setjmp calls into the entries of functions with invoke instructions
420 // even though there are possibly paths through the function that do not
421 // execute any invokes. In particular, for functions with early exits, e.g.
422 // the 'addMove' method in hexxagon, it would be nice to not have to do the
423 // setjmp stuff on the early exit path. This requires a bit of dataflow, but
424 // would not be too hard to do.
426 // If we have an invoke instruction, insert a setjmp that dominates all
427 // invokes. After the setjmp, use a cond branch that goes to the original
428 // code path on zero, and to a designated 'catch' block of nonzero.
429 Value *OldJmpBufPtr = 0;
430 if (!Invokes.empty()) {
431 // First thing we need to do is scan the whole function for values that are
432 // live across unwind edges. Each value that is live across an unwind edge
433 // we spill into a stack location, guaranteeing that there is nothing live
434 // across the unwind edge. This process also splits all critical edges
435 // coming out of invoke's.
436 splitLiveRangesLiveAcrossInvokes(Invokes);
438 BasicBlock *EntryBB = F.begin();
440 // Create an alloca for the incoming jump buffer ptr and the new jump buffer
441 // that needs to be restored on all exits from the function. This is an
442 // alloca because the value needs to be live across invokes.
443 unsigned Align = TLI ? TLI->getJumpBufAlignment() : 0;
445 new AllocaInst(JBLinkTy, 0, Align, "jblink", F.begin()->begin());
447 std::vector<Value*> Idx;
448 Idx.push_back(Constant::getNullValue(Type::Int32Ty));
449 Idx.push_back(ConstantInt::get(Type::Int32Ty, 1));
450 OldJmpBufPtr = new GetElementPtrInst(JmpBuf, &Idx[0], 2, "OldBuf",
451 EntryBB->getTerminator());
453 // Copy the JBListHead to the alloca.
454 Value *OldBuf = new LoadInst(JBListHead, "oldjmpbufptr", true,
455 EntryBB->getTerminator());
456 new StoreInst(OldBuf, OldJmpBufPtr, true, EntryBB->getTerminator());
458 // Add the new jumpbuf to the list.
459 new StoreInst(JmpBuf, JBListHead, true, EntryBB->getTerminator());
461 // Create the catch block. The catch block is basically a big switch
462 // statement that goes to all of the invoke catch blocks.
463 BasicBlock *CatchBB = new BasicBlock("setjmp.catch", &F);
465 // Create an alloca which keeps track of which invoke is currently
466 // executing. For normal calls it contains zero.
467 AllocaInst *InvokeNum = new AllocaInst(Type::Int32Ty, 0, "invokenum",
469 new StoreInst(ConstantInt::get(Type::Int32Ty, 0), InvokeNum, true,
470 EntryBB->getTerminator());
472 // Insert a load in the Catch block, and a switch on its value. By default,
473 // we go to a block that just does an unwind (which is the correct action
474 // for a standard call).
475 BasicBlock *UnwindBB = new BasicBlock("unwindbb", &F);
476 Unwinds.push_back(new UnwindInst(UnwindBB));
478 Value *CatchLoad = new LoadInst(InvokeNum, "invoke.num", true, CatchBB);
479 SwitchInst *CatchSwitch =
480 new SwitchInst(CatchLoad, UnwindBB, Invokes.size(), CatchBB);
482 // Now that things are set up, insert the setjmp call itself.
484 // Split the entry block to insert the conditional branch for the setjmp.
485 BasicBlock *ContBlock = EntryBB->splitBasicBlock(EntryBB->getTerminator(),
488 Idx[1] = ConstantInt::get(Type::Int32Ty, 0);
489 Value *JmpBufPtr = new GetElementPtrInst(JmpBuf, &Idx[0], Idx.size(),
491 EntryBB->getTerminator());
492 Value *SJRet = new CallInst(SetJmpFn, JmpBufPtr, "sjret",
493 EntryBB->getTerminator());
495 // Compare the return value to zero.
496 Value *IsNormal = new ICmpInst(ICmpInst::ICMP_EQ, SJRet,
497 Constant::getNullValue(SJRet->getType()),
498 "notunwind", EntryBB->getTerminator());
499 // Nuke the uncond branch.
500 EntryBB->getTerminator()->eraseFromParent();
502 // Put in a new condbranch in its place.
503 new BranchInst(ContBlock, CatchBB, IsNormal, EntryBB);
505 // At this point, we are all set up, rewrite each invoke instruction.
506 for (unsigned i = 0, e = Invokes.size(); i != e; ++i)
507 rewriteExpensiveInvoke(Invokes[i], i+1, InvokeNum, CatchSwitch);
510 // We know that there is at least one unwind.
512 // Create three new blocks, the block to load the jmpbuf ptr and compare
513 // against null, the block to do the longjmp, and the error block for if it
514 // is null. Add them at the end of the function because they are not hot.
515 BasicBlock *UnwindHandler = new BasicBlock("dounwind", &F);
516 BasicBlock *UnwindBlock = new BasicBlock("unwind", &F);
517 BasicBlock *TermBlock = new BasicBlock("unwinderror", &F);
519 // If this function contains an invoke, restore the old jumpbuf ptr.
522 // Before the return, insert a copy from the saved value to the new value.
523 BufPtr = new LoadInst(OldJmpBufPtr, "oldjmpbufptr", UnwindHandler);
524 new StoreInst(BufPtr, JBListHead, UnwindHandler);
526 BufPtr = new LoadInst(JBListHead, "ehlist", UnwindHandler);
529 // Load the JBList, if it's null, then there was no catch!
530 Value *NotNull = new ICmpInst(ICmpInst::ICMP_NE, BufPtr,
531 Constant::getNullValue(BufPtr->getType()),
532 "notnull", UnwindHandler);
533 new BranchInst(UnwindBlock, TermBlock, NotNull, UnwindHandler);
535 // Create the block to do the longjmp.
536 // Get a pointer to the jmpbuf and longjmp.
537 std::vector<Value*> Idx;
538 Idx.push_back(Constant::getNullValue(Type::Int32Ty));
539 Idx.push_back(ConstantInt::get(Type::Int32Ty, 0));
540 Idx[0] = new GetElementPtrInst(BufPtr, &Idx[0], 2, "JmpBuf", UnwindBlock);
541 Idx[1] = ConstantInt::get(Type::Int32Ty, 1);
542 new CallInst(LongJmpFn, &Idx[0], Idx.size(), "", UnwindBlock);
543 new UnreachableInst(UnwindBlock);
545 // Set up the term block ("throw without a catch").
546 new UnreachableInst(TermBlock);
548 // Insert a new call to write(2, AbortMessage, AbortMessageLength);
549 writeAbortMessage(TermBlock->getTerminator());
551 // Insert a call to abort()
552 (new CallInst(AbortFn, "",
553 TermBlock->getTerminator()))->setTailCall();
556 // Replace all unwinds with a branch to the unwind handler.
557 for (unsigned i = 0, e = Unwinds.size(); i != e; ++i) {
558 new BranchInst(UnwindHandler, Unwinds[i]);
559 Unwinds[i]->eraseFromParent();
562 // Finally, for any returns from this function, if this function contains an
563 // invoke, restore the old jmpbuf pointer to its input value.
565 for (unsigned i = 0, e = Returns.size(); i != e; ++i) {
566 ReturnInst *R = Returns[i];
568 // Before the return, insert a copy from the saved value to the new value.
569 Value *OldBuf = new LoadInst(OldJmpBufPtr, "oldjmpbufptr", true, R);
570 new StoreInst(OldBuf, JBListHead, true, R);
577 bool LowerInvoke::runOnFunction(Function &F) {
578 if (ExpensiveEHSupport)
579 return insertExpensiveEHSupport(F);
581 return insertCheapEHSupport(F);