llvm-6502/lib/Transforms/Utils/LowerInvoke.cpp
Reid Spencer 3ed469ccd7 For PR786:
Turn on -Wunused and -Wno-unused-parameter. Clean up most of the resulting
fall out by removing unused variables. Remaining warnings have to do with
unused functions (I didn't want to delete code without review) and unused
variables in generated code. Maintainers should clean up the remaining
issues when they see them. All changes pass DejaGnu tests and Olden.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31380 91177308-0d34-0410-b5e6-96231b3b80d8
2006-11-02 20:25:50 +00:00

596 lines
25 KiB
C++

//===- LowerInvoke.cpp - Eliminate Invoke & Unwind instructions -----------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This transformation is designed for use by code generators which do not yet
// support stack unwinding. This pass supports two models of exception handling
// lowering, the 'cheap' support and the 'expensive' support.
//
// 'Cheap' exception handling support gives the program the ability to execute
// any program which does not "throw an exception", by turning 'invoke'
// instructions into calls and by turning 'unwind' instructions into calls to
// abort(). If the program does dynamically use the unwind instruction, the
// program will print a message then abort.
//
// 'Expensive' exception handling support gives the full exception handling
// support to the program at the cost of making the 'invoke' instruction
// really expensive. It basically inserts setjmp/longjmp calls to emulate the
// exception handling as necessary.
//
// Because the 'expensive' support slows down programs a lot, and EH is only
// used for a subset of the programs, it must be specifically enabled by an
// option.
//
// Note that after this pass runs the CFG is not entirely accurate (exceptional
// control flow edges are not correct anymore) so only very simple things should
// be done after the lowerinvoke pass has run (like generation of native code).
// This should not be used as a general purpose "my LLVM-to-LLVM pass doesn't
// support the invoke instruction yet" lowering pass.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Instructions.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Target/TargetLowering.h"
#include <csetjmp>
using namespace llvm;
namespace {
Statistic<> NumInvokes("lowerinvoke", "Number of invokes replaced");
Statistic<> NumUnwinds("lowerinvoke", "Number of unwinds replaced");
Statistic<> NumSpilled("lowerinvoke",
"Number of registers live across unwind edges");
cl::opt<bool> ExpensiveEHSupport("enable-correct-eh-support",
cl::desc("Make the -lowerinvoke pass insert expensive, but correct, EH code"));
class VISIBILITY_HIDDEN LowerInvoke : public FunctionPass {
// Used for both models.
Function *WriteFn;
Function *AbortFn;
Value *AbortMessage;
unsigned AbortMessageLength;
// Used for expensive EH support.
const Type *JBLinkTy;
GlobalVariable *JBListHead;
Function *SetJmpFn, *LongJmpFn;
// We peek in TLI to grab the target's jmp_buf size and alignment
const TargetLowering *TLI;
public:
LowerInvoke(const TargetLowering *tli = NULL) : TLI(tli) { }
bool doInitialization(Module &M);
bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
// This is a cluster of orthogonal Transforms
AU.addPreservedID(PromoteMemoryToRegisterID);
AU.addPreservedID(LowerSelectID);
AU.addPreservedID(LowerSwitchID);
AU.addPreservedID(LowerAllocationsID);
}
private:
void createAbortMessage();
void writeAbortMessage(Instruction *IB);
bool insertCheapEHSupport(Function &F);
void splitLiveRangesLiveAcrossInvokes(std::vector<InvokeInst*> &Invokes);
void rewriteExpensiveInvoke(InvokeInst *II, unsigned InvokeNo,
AllocaInst *InvokeNum, SwitchInst *CatchSwitch);
bool insertExpensiveEHSupport(Function &F);
};
RegisterPass<LowerInvoke>
X("lowerinvoke", "Lower invoke and unwind, for unwindless code generators");
}
const PassInfo *llvm::LowerInvokePassID = X.getPassInfo();
// Public Interface To the LowerInvoke pass.
FunctionPass *llvm::createLowerInvokePass(const TargetLowering *TLI) {
return new LowerInvoke(TLI);
}
// doInitialization - Make sure that there is a prototype for abort in the
// current module.
bool LowerInvoke::doInitialization(Module &M) {
const Type *VoidPtrTy = PointerType::get(Type::SByteTy);
AbortMessage = 0;
if (ExpensiveEHSupport) {
// Insert a type for the linked list of jump buffers.
unsigned JBSize = TLI ? TLI->getJumpBufSize() : 0;
JBSize = JBSize ? JBSize : 200;
const Type *JmpBufTy = ArrayType::get(VoidPtrTy, JBSize);
{ // The type is recursive, so use a type holder.
std::vector<const Type*> Elements;
Elements.push_back(JmpBufTy);
OpaqueType *OT = OpaqueType::get();
Elements.push_back(PointerType::get(OT));
PATypeHolder JBLType(StructType::get(Elements));
OT->refineAbstractTypeTo(JBLType.get()); // Complete the cycle.
JBLinkTy = JBLType.get();
M.addTypeName("llvm.sjljeh.jmpbufty", JBLinkTy);
}
const Type *PtrJBList = PointerType::get(JBLinkTy);
// Now that we've done that, insert the jmpbuf list head global, unless it
// already exists.
if (!(JBListHead = M.getGlobalVariable("llvm.sjljeh.jblist", PtrJBList))) {
JBListHead = new GlobalVariable(PtrJBList, false,
GlobalValue::LinkOnceLinkage,
Constant::getNullValue(PtrJBList),
"llvm.sjljeh.jblist", &M);
}
SetJmpFn = M.getOrInsertFunction("llvm.setjmp", Type::IntTy,
PointerType::get(JmpBufTy), (Type *)0);
LongJmpFn = M.getOrInsertFunction("llvm.longjmp", Type::VoidTy,
PointerType::get(JmpBufTy),
Type::IntTy, (Type *)0);
}
// We need the 'write' and 'abort' functions for both models.
AbortFn = M.getOrInsertFunction("abort", Type::VoidTy, (Type *)0);
// Unfortunately, 'write' can end up being prototyped in several different
// ways. If the user defines a three (or more) operand function named 'write'
// we will use their prototype. We _do not_ want to insert another instance
// of a write prototype, because we don't know that the funcresolve pass will
// run after us. If there is a definition of a write function, but it's not
// suitable for our uses, we just don't emit write calls. If there is no
// write prototype at all, we just add one.
if (Function *WF = M.getNamedFunction("write")) {
if (WF->getFunctionType()->getNumParams() > 3 ||
WF->getFunctionType()->isVarArg())
WriteFn = WF;
else
WriteFn = 0;
} else {
WriteFn = M.getOrInsertFunction("write", Type::VoidTy, Type::IntTy,
VoidPtrTy, Type::IntTy, (Type *)0);
}
return true;
}
void LowerInvoke::createAbortMessage() {
Module &M = *WriteFn->getParent();
if (ExpensiveEHSupport) {
// The abort message for expensive EH support tells the user that the
// program 'unwound' without an 'invoke' instruction.
Constant *Msg =
ConstantArray::get("ERROR: Exception thrown, but not caught!\n");
AbortMessageLength = Msg->getNumOperands()-1; // don't include \0
GlobalVariable *MsgGV = new GlobalVariable(Msg->getType(), true,
GlobalValue::InternalLinkage,
Msg, "abortmsg", &M);
std::vector<Constant*> GEPIdx(2, Constant::getNullValue(Type::IntTy));
AbortMessage = ConstantExpr::getGetElementPtr(MsgGV, GEPIdx);
} else {
// The abort message for cheap EH support tells the user that EH is not
// enabled.
Constant *Msg =
ConstantArray::get("Exception handler needed, but not enabled. Recompile"
" program with -enable-correct-eh-support.\n");
AbortMessageLength = Msg->getNumOperands()-1; // don't include \0
GlobalVariable *MsgGV = new GlobalVariable(Msg->getType(), true,
GlobalValue::InternalLinkage,
Msg, "abortmsg", &M);
std::vector<Constant*> GEPIdx(2, Constant::getNullValue(Type::IntTy));
AbortMessage = ConstantExpr::getGetElementPtr(MsgGV, GEPIdx);
}
}
void LowerInvoke::writeAbortMessage(Instruction *IB) {
if (WriteFn) {
if (AbortMessage == 0) createAbortMessage();
// These are the arguments we WANT...
std::vector<Value*> Args;
Args.push_back(ConstantInt::get(Type::IntTy, 2));
Args.push_back(AbortMessage);
Args.push_back(ConstantInt::get(Type::IntTy, AbortMessageLength));
// If the actual declaration of write disagrees, insert casts as
// appropriate.
const FunctionType *FT = WriteFn->getFunctionType();
unsigned NumArgs = FT->getNumParams();
for (unsigned i = 0; i != 3; ++i)
if (i < NumArgs && FT->getParamType(i) != Args[i]->getType())
Args[i] = ConstantExpr::getCast(cast<Constant>(Args[i]),
FT->getParamType(i));
(new CallInst(WriteFn, Args, "", IB))->setTailCall();
}
}
bool LowerInvoke::insertCheapEHSupport(Function &F) {
bool Changed = false;
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
// Insert a normal call instruction...
std::string Name = II->getName(); II->setName("");
CallInst *NewCall = new CallInst(II->getCalledValue(),
std::vector<Value*>(II->op_begin()+3,
II->op_end()), Name, II);
NewCall->setCallingConv(II->getCallingConv());
II->replaceAllUsesWith(NewCall);
// Insert an unconditional branch to the normal destination.
new BranchInst(II->getNormalDest(), II);
// Remove any PHI node entries from the exception destination.
II->getUnwindDest()->removePredecessor(BB);
// Remove the invoke instruction now.
BB->getInstList().erase(II);
++NumInvokes; Changed = true;
} else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
// Insert a new call to write(2, AbortMessage, AbortMessageLength);
writeAbortMessage(UI);
// Insert a call to abort()
(new CallInst(AbortFn, std::vector<Value*>(), "", UI))->setTailCall();
// Insert a return instruction. This really should be a "barrier", as it
// is unreachable.
new ReturnInst(F.getReturnType() == Type::VoidTy ? 0 :
Constant::getNullValue(F.getReturnType()), UI);
// Remove the unwind instruction now.
BB->getInstList().erase(UI);
++NumUnwinds; Changed = true;
}
return Changed;
}
/// rewriteExpensiveInvoke - Insert code and hack the function to replace the
/// specified invoke instruction with a call.
void LowerInvoke::rewriteExpensiveInvoke(InvokeInst *II, unsigned InvokeNo,
AllocaInst *InvokeNum,
SwitchInst *CatchSwitch) {
ConstantInt *InvokeNoC = ConstantInt::get(Type::UIntTy, InvokeNo);
// Insert a store of the invoke num before the invoke and store zero into the
// location afterward.
new StoreInst(InvokeNoC, InvokeNum, true, II); // volatile
BasicBlock::iterator NI = II->getNormalDest()->begin();
while (isa<PHINode>(NI)) ++NI;
// nonvolatile.
new StoreInst(Constant::getNullValue(Type::UIntTy), InvokeNum, false, NI);
// Add a switch case to our unwind block.
CatchSwitch->addCase(InvokeNoC, II->getUnwindDest());
// Insert a normal call instruction.
std::string Name = II->getName(); II->setName("");
CallInst *NewCall = new CallInst(II->getCalledValue(),
std::vector<Value*>(II->op_begin()+3,
II->op_end()), Name,
II);
NewCall->setCallingConv(II->getCallingConv());
II->replaceAllUsesWith(NewCall);
// Replace the invoke with an uncond branch.
new BranchInst(II->getNormalDest(), NewCall->getParent());
II->eraseFromParent();
}
/// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
/// we reach blocks we've already seen.
static void MarkBlocksLiveIn(BasicBlock *BB, std::set<BasicBlock*> &LiveBBs) {
if (!LiveBBs.insert(BB).second) return; // already been here.
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
MarkBlocksLiveIn(*PI, LiveBBs);
}
// First thing we need to do is scan the whole function for values that are
// live across unwind edges. Each value that is live across an unwind edge
// we spill into a stack location, guaranteeing that there is nothing live
// across the unwind edge. This process also splits all critical edges
// coming out of invoke's.
void LowerInvoke::
splitLiveRangesLiveAcrossInvokes(std::vector<InvokeInst*> &Invokes) {
// First step, split all critical edges from invoke instructions.
for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
InvokeInst *II = Invokes[i];
SplitCriticalEdge(II, 0, this);
SplitCriticalEdge(II, 1, this);
assert(!isa<PHINode>(II->getNormalDest()) &&
!isa<PHINode>(II->getUnwindDest()) &&
"critical edge splitting left single entry phi nodes?");
}
Function *F = Invokes.back()->getParent()->getParent();
// To avoid having to handle incoming arguments specially, we lower each arg
// to a copy instruction in the entry block. This ensure that the argument
// value itself cannot be live across the entry block.
BasicBlock::iterator AfterAllocaInsertPt = F->begin()->begin();
while (isa<AllocaInst>(AfterAllocaInsertPt) &&
isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsertPt)->getArraySize()))
++AfterAllocaInsertPt;
for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end();
AI != E; ++AI) {
CastInst *NC = new CastInst(AI, AI->getType(), AI->getName()+".tmp",
AfterAllocaInsertPt);
AI->replaceAllUsesWith(NC);
NC->setOperand(0, AI);
}
// Finally, scan the code looking for instructions with bad live ranges.
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
// Ignore obvious cases we don't have to handle. In particular, most
// instructions either have no uses or only have a single use inside the
// current block. Ignore them quickly.
Instruction *Inst = II;
if (Inst->use_empty()) continue;
if (Inst->hasOneUse() &&
cast<Instruction>(Inst->use_back())->getParent() == BB &&
!isa<PHINode>(Inst->use_back())) continue;
// If this is an alloca in the entry block, it's not a real register
// value.
if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
if (isa<ConstantInt>(AI->getArraySize()) && BB == F->begin())
continue;
// Avoid iterator invalidation by copying users to a temporary vector.
std::vector<Instruction*> Users;
for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end();
UI != E; ++UI) {
Instruction *User = cast<Instruction>(*UI);
if (User->getParent() != BB || isa<PHINode>(User))
Users.push_back(User);
}
// Scan all of the uses and see if the live range is live across an unwind
// edge. If we find a use live across an invoke edge, create an alloca
// and spill the value.
std::set<InvokeInst*> InvokesWithStoreInserted;
// Find all of the blocks that this value is live in.
std::set<BasicBlock*> LiveBBs;
LiveBBs.insert(Inst->getParent());
while (!Users.empty()) {
Instruction *U = Users.back();
Users.pop_back();
if (!isa<PHINode>(U)) {
MarkBlocksLiveIn(U->getParent(), LiveBBs);
} else {
// Uses for a PHI node occur in their predecessor block.
PHINode *PN = cast<PHINode>(U);
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) == Inst)
MarkBlocksLiveIn(PN->getIncomingBlock(i), LiveBBs);
}
}
// Now that we know all of the blocks that this thing is live in, see if
// it includes any of the unwind locations.
bool NeedsSpill = false;
for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
BasicBlock *UnwindBlock = Invokes[i]->getUnwindDest();
if (UnwindBlock != BB && LiveBBs.count(UnwindBlock)) {
NeedsSpill = true;
}
}
// If we decided we need a spill, do it.
if (NeedsSpill) {
++NumSpilled;
DemoteRegToStack(*Inst, true);
}
}
}
bool LowerInvoke::insertExpensiveEHSupport(Function &F) {
std::vector<ReturnInst*> Returns;
std::vector<UnwindInst*> Unwinds;
std::vector<InvokeInst*> Invokes;
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
// Remember all return instructions in case we insert an invoke into this
// function.
Returns.push_back(RI);
} else if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
Invokes.push_back(II);
} else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
Unwinds.push_back(UI);
}
if (Unwinds.empty() && Invokes.empty()) return false;
NumInvokes += Invokes.size();
NumUnwinds += Unwinds.size();
// TODO: This is not an optimal way to do this. In particular, this always
// inserts setjmp calls into the entries of functions with invoke instructions
// even though there are possibly paths through the function that do not
// execute any invokes. In particular, for functions with early exits, e.g.
// the 'addMove' method in hexxagon, it would be nice to not have to do the
// setjmp stuff on the early exit path. This requires a bit of dataflow, but
// would not be too hard to do.
// If we have an invoke instruction, insert a setjmp that dominates all
// invokes. After the setjmp, use a cond branch that goes to the original
// code path on zero, and to a designated 'catch' block of nonzero.
Value *OldJmpBufPtr = 0;
if (!Invokes.empty()) {
// First thing we need to do is scan the whole function for values that are
// live across unwind edges. Each value that is live across an unwind edge
// we spill into a stack location, guaranteeing that there is nothing live
// across the unwind edge. This process also splits all critical edges
// coming out of invoke's.
splitLiveRangesLiveAcrossInvokes(Invokes);
BasicBlock *EntryBB = F.begin();
// Create an alloca for the incoming jump buffer ptr and the new jump buffer
// that needs to be restored on all exits from the function. This is an
// alloca because the value needs to be live across invokes.
unsigned Align = TLI ? TLI->getJumpBufAlignment() : 0;
AllocaInst *JmpBuf =
new AllocaInst(JBLinkTy, 0, Align, "jblink", F.begin()->begin());
std::vector<Value*> Idx;
Idx.push_back(Constant::getNullValue(Type::IntTy));
Idx.push_back(ConstantInt::get(Type::UIntTy, 1));
OldJmpBufPtr = new GetElementPtrInst(JmpBuf, Idx, "OldBuf",
EntryBB->getTerminator());
// Copy the JBListHead to the alloca.
Value *OldBuf = new LoadInst(JBListHead, "oldjmpbufptr", true,
EntryBB->getTerminator());
new StoreInst(OldBuf, OldJmpBufPtr, true, EntryBB->getTerminator());
// Add the new jumpbuf to the list.
new StoreInst(JmpBuf, JBListHead, true, EntryBB->getTerminator());
// Create the catch block. The catch block is basically a big switch
// statement that goes to all of the invoke catch blocks.
BasicBlock *CatchBB = new BasicBlock("setjmp.catch", &F);
// Create an alloca which keeps track of which invoke is currently
// executing. For normal calls it contains zero.
AllocaInst *InvokeNum = new AllocaInst(Type::UIntTy, 0, "invokenum",
EntryBB->begin());
new StoreInst(ConstantInt::get(Type::UIntTy, 0), InvokeNum, true,
EntryBB->getTerminator());
// Insert a load in the Catch block, and a switch on its value. By default,
// we go to a block that just does an unwind (which is the correct action
// for a standard call).
BasicBlock *UnwindBB = new BasicBlock("unwindbb", &F);
Unwinds.push_back(new UnwindInst(UnwindBB));
Value *CatchLoad = new LoadInst(InvokeNum, "invoke.num", true, CatchBB);
SwitchInst *CatchSwitch =
new SwitchInst(CatchLoad, UnwindBB, Invokes.size(), CatchBB);
// Now that things are set up, insert the setjmp call itself.
// Split the entry block to insert the conditional branch for the setjmp.
BasicBlock *ContBlock = EntryBB->splitBasicBlock(EntryBB->getTerminator(),
"setjmp.cont");
Idx[1] = ConstantInt::get(Type::UIntTy, 0);
Value *JmpBufPtr = new GetElementPtrInst(JmpBuf, Idx, "TheJmpBuf",
EntryBB->getTerminator());
Value *SJRet = new CallInst(SetJmpFn, JmpBufPtr, "sjret",
EntryBB->getTerminator());
// Compare the return value to zero.
Value *IsNormal = BinaryOperator::createSetEQ(SJRet,
Constant::getNullValue(SJRet->getType()),
"notunwind", EntryBB->getTerminator());
// Nuke the uncond branch.
EntryBB->getTerminator()->eraseFromParent();
// Put in a new condbranch in its place.
new BranchInst(ContBlock, CatchBB, IsNormal, EntryBB);
// At this point, we are all set up, rewrite each invoke instruction.
for (unsigned i = 0, e = Invokes.size(); i != e; ++i)
rewriteExpensiveInvoke(Invokes[i], i+1, InvokeNum, CatchSwitch);
}
// We know that there is at least one unwind.
// Create three new blocks, the block to load the jmpbuf ptr and compare
// against null, the block to do the longjmp, and the error block for if it
// is null. Add them at the end of the function because they are not hot.
BasicBlock *UnwindHandler = new BasicBlock("dounwind", &F);
BasicBlock *UnwindBlock = new BasicBlock("unwind", &F);
BasicBlock *TermBlock = new BasicBlock("unwinderror", &F);
// If this function contains an invoke, restore the old jumpbuf ptr.
Value *BufPtr;
if (OldJmpBufPtr) {
// Before the return, insert a copy from the saved value to the new value.
BufPtr = new LoadInst(OldJmpBufPtr, "oldjmpbufptr", UnwindHandler);
new StoreInst(BufPtr, JBListHead, UnwindHandler);
} else {
BufPtr = new LoadInst(JBListHead, "ehlist", UnwindHandler);
}
// Load the JBList, if it's null, then there was no catch!
Value *NotNull = BinaryOperator::createSetNE(BufPtr,
Constant::getNullValue(BufPtr->getType()),
"notnull", UnwindHandler);
new BranchInst(UnwindBlock, TermBlock, NotNull, UnwindHandler);
// Create the block to do the longjmp.
// Get a pointer to the jmpbuf and longjmp.
std::vector<Value*> Idx;
Idx.push_back(Constant::getNullValue(Type::IntTy));
Idx.push_back(ConstantInt::get(Type::UIntTy, 0));
Idx[0] = new GetElementPtrInst(BufPtr, Idx, "JmpBuf", UnwindBlock);
Idx[1] = ConstantInt::get(Type::IntTy, 1);
new CallInst(LongJmpFn, Idx, "", UnwindBlock);
new UnreachableInst(UnwindBlock);
// Set up the term block ("throw without a catch").
new UnreachableInst(TermBlock);
// Insert a new call to write(2, AbortMessage, AbortMessageLength);
writeAbortMessage(TermBlock->getTerminator());
// Insert a call to abort()
(new CallInst(AbortFn, std::vector<Value*>(), "",
TermBlock->getTerminator()))->setTailCall();
// Replace all unwinds with a branch to the unwind handler.
for (unsigned i = 0, e = Unwinds.size(); i != e; ++i) {
new BranchInst(UnwindHandler, Unwinds[i]);
Unwinds[i]->eraseFromParent();
}
// Finally, for any returns from this function, if this function contains an
// invoke, restore the old jmpbuf pointer to its input value.
if (OldJmpBufPtr) {
for (unsigned i = 0, e = Returns.size(); i != e; ++i) {
ReturnInst *R = Returns[i];
// Before the return, insert a copy from the saved value to the new value.
Value *OldBuf = new LoadInst(OldJmpBufPtr, "oldjmpbufptr", true, R);
new StoreInst(OldBuf, JBListHead, true, R);
}
}
return true;
}
bool LowerInvoke::runOnFunction(Function &F) {
if (ExpensiveEHSupport)
return insertExpensiveEHSupport(F);
else
return insertCheapEHSupport(F);
}