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llvm-project/llvm/lib/Transforms/Utils/LowerInvoke.cpp

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//===- 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/Visibility.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;
public:
LowerInvoke(unsigned Size = 200, unsigned Align = 0) : JumpBufSize(Size),
JumpBufAlign(Align) {}
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);
unsigned JumpBufSize;
unsigned JumpBufAlign;
};
RegisterOpt<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(unsigned JumpBufSize,
unsigned JumpBufAlign) {
return new LowerInvoke(JumpBufSize, JumpBufAlign);
}
// 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.
const Type *JmpBufTy = ArrayType::get(VoidPtrTy, JumpBufSize);
{ // 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) {
ConstantUInt *InvokeNoC = ConstantUInt::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.
AllocaInst *SpillLoc = 0;
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.
AllocaInst *JmpBuf =
new AllocaInst(JBLinkTy, 0, JumpBufAlign, "jblink", F.begin()->begin());
std::vector<Value*> Idx;
Idx.push_back(Constant::getNullValue(Type::IntTy));
Idx.push_back(ConstantUInt::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] = ConstantUInt::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(ConstantUInt::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);
}
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