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//===- SjLjEHPrepare.cpp - Eliminate Invoke & Unwind instructions ---------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This transformation is designed for use by code generators which use SjLj
// based exception handling.
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
#define DEBUG_TYPE "sjljehprepare"
STATISTIC(NumInvokes, "Number of invokes replaced");
STATISTIC(NumSpilled, "Number of registers live across unwind edges");
namespace {
class SjLjEHPrepare : public FunctionPass {
IntegerType *DataTy;
Type *doubleUnderDataTy;
Type *doubleUnderJBufTy;
Type *FunctionContextTy;
FunctionCallee RegisterFn;
FunctionCallee UnregisterFn;
Function *BuiltinSetupDispatchFn;
Function *FrameAddrFn;
Function *StackAddrFn;
Function *StackRestoreFn;
Function *LSDAAddrFn;
Function *CallSiteFn;
Function *FuncCtxFn;
AllocaInst *FuncCtx;
const TargetMachine *TM;
static char ID; // Pass identification, replacement for typeid
explicit SjLjEHPrepare(const TargetMachine *TM = nullptr)
: FunctionPass(ID), TM(TM) {}
bool doInitialization(Module &M) override;
bool runOnFunction(Function &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {}
StringRef getPassName() const override {
return "SJLJ Exception Handling preparation";
bool setupEntryBlockAndCallSites(Function &F);
void substituteLPadValues(LandingPadInst *LPI, Value *ExnVal, Value *SelVal);
Value *setupFunctionContext(Function &F, ArrayRef<LandingPadInst *> LPads);
void lowerIncomingArguments(Function &F);
void lowerAcrossUnwindEdges(Function &F, ArrayRef<InvokeInst *> Invokes);
void insertCallSiteStore(Instruction *I, int Number);
} // end anonymous namespace
char SjLjEHPrepare::ID = 0;
INITIALIZE_PASS(SjLjEHPrepare, DEBUG_TYPE, "Prepare SjLj exceptions",
false, false)
// Public Interface To the SjLjEHPrepare pass.
FunctionPass *llvm::createSjLjEHPreparePass(const TargetMachine *TM) {
return new SjLjEHPrepare(TM);
// doInitialization - Set up decalarations and types needed to process
// exceptions.
bool SjLjEHPrepare::doInitialization(Module &M) {
// Build the function context structure.
// builtin_setjmp uses a five word jbuf
Type *VoidPtrTy = Type::getInt8PtrTy(M.getContext());
unsigned DataBits =
TM ? TM->getSjLjDataSize() : TargetMachine::DefaultSjLjDataSize;
DataTy = Type::getIntNTy(M.getContext(), DataBits);
doubleUnderDataTy = ArrayType::get(DataTy, 4);
doubleUnderJBufTy = ArrayType::get(VoidPtrTy, 5);
FunctionContextTy = StructType::get(VoidPtrTy, // __prev
DataTy, // call_site
doubleUnderDataTy, // __data
VoidPtrTy, // __personality
VoidPtrTy, // __lsda
doubleUnderJBufTy // __jbuf
return true;
/// insertCallSiteStore - Insert a store of the call-site value to the
/// function context
void SjLjEHPrepare::insertCallSiteStore(Instruction *I, int Number) {
IRBuilder<> Builder(I);
// Get a reference to the call_site field.
Type *Int32Ty = Type::getInt32Ty(I->getContext());
Value *Zero = ConstantInt::get(Int32Ty, 0);
Value *One = ConstantInt::get(Int32Ty, 1);
Value *Idxs[2] = { Zero, One };
Value *CallSite =
Builder.CreateGEP(FunctionContextTy, FuncCtx, Idxs, "call_site");
// Insert a store of the call-site number
ConstantInt *CallSiteNoC = ConstantInt::get(DataTy, Number);
Builder.CreateStore(CallSiteNoC, CallSite, true /*volatile*/);
/// MarkBlocksLiveIn - Insert BB and all of its predecessors into LiveBBs until
/// we reach blocks we've already seen.
static void MarkBlocksLiveIn(BasicBlock *BB,
SmallPtrSetImpl<BasicBlock *> &LiveBBs) {
if (!LiveBBs.insert(BB).second)
return; // already been here.
df_iterator_default_set<BasicBlock*> Visited;
for (BasicBlock *B : inverse_depth_first_ext(BB, Visited))
/// substituteLPadValues - Substitute the values returned by the landingpad
/// instruction with those returned by the personality function.
void SjLjEHPrepare::substituteLPadValues(LandingPadInst *LPI, Value *ExnVal,
Value *SelVal) {
SmallVector<Value *, 8> UseWorkList(LPI->users());
while (!UseWorkList.empty()) {
Value *Val = UseWorkList.pop_back_val();
auto *EVI = dyn_cast<ExtractValueInst>(Val);
if (!EVI)
if (EVI->getNumIndices() != 1)
if (*EVI->idx_begin() == 0)
else if (*EVI->idx_begin() == 1)
if (EVI->use_empty())
if (LPI->use_empty())
// There are still some uses of LPI. Construct an aggregate with the exception
// values and replace the LPI with that aggregate.
Type *LPadType = LPI->getType();
Value *LPadVal = UndefValue::get(LPadType);
auto *SelI = cast<Instruction>(SelVal);
IRBuilder<> Builder(SelI->getParent(), std::next(SelI->getIterator()));
LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");
/// setupFunctionContext - Allocate the function context on the stack and fill
/// it with all of the data that we know at this point.
Value *SjLjEHPrepare::setupFunctionContext(Function &F,
ArrayRef<LandingPadInst *> LPads) {
BasicBlock *EntryBB = &F.front();
// 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 added to the global context list.
auto &DL = F.getParent()->getDataLayout();
const Align Alignment(DL.getPrefTypeAlignment(FunctionContextTy));
FuncCtx = new AllocaInst(FunctionContextTy, DL.getAllocaAddrSpace(), nullptr,
Alignment, "fn_context", &EntryBB->front());
// Fill in the function context structure.
for (LandingPadInst *LPI : LPads) {
IRBuilder<> Builder(LPI->getParent(),
// Reference the __data field.
Value *FCData =
Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 2, "__data");
// The exception values come back in context->__data[0].
Value *ExceptionAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
0, 0, "exception_gep");
Value *ExnVal = Builder.CreateLoad(DataTy, ExceptionAddr, true, "exn_val");
ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());
Value *SelectorAddr = Builder.CreateConstGEP2_32(doubleUnderDataTy, FCData,
0, 1, "exn_selector_gep");
Value *SelVal =
Builder.CreateLoad(DataTy, SelectorAddr, true, "exn_selector_val");
// SelVal must be Int32Ty, so trunc it
SelVal = Builder.CreateTrunc(SelVal, Type::getInt32Ty(F.getContext()));
substituteLPadValues(LPI, ExnVal, SelVal);
// Personality function
IRBuilder<> Builder(EntryBB->getTerminator());
Value *PersonalityFn = F.getPersonalityFn();
Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32(
FunctionContextTy, FuncCtx, 0, 3, "pers_fn_gep");
Builder.CreateBitCast(PersonalityFn, Builder.getInt8PtrTy()),
PersonalityFieldPtr, /*isVolatile=*/true);
// LSDA address
Value *LSDA = Builder.CreateCall(LSDAAddrFn, {}, "lsda_addr");
Value *LSDAFieldPtr =
Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 4, "lsda_gep");
Builder.CreateStore(LSDA, LSDAFieldPtr, /*isVolatile=*/true);
return FuncCtx;
/// lowerIncomingArguments - To avoid having to handle incoming arguments
/// specially, we lower each arg to a copy instruction in the entry block. This
/// ensures that the argument value itself cannot be live out of the entry
/// block.
void SjLjEHPrepare::lowerIncomingArguments(Function &F) {
BasicBlock::iterator AfterAllocaInsPt = F.begin()->begin();
while (isa<AllocaInst>(AfterAllocaInsPt) &&
assert(AfterAllocaInsPt != F.front().end());
for (auto &AI : F.args()) {
// Swift error really is a register that we model as memory -- instruction
// selection will perform mem-to-reg for us and spill/reload appropriately
// around calls that clobber it. There is no need to spill this
// value to the stack and doing so would not be allowed.
if (AI.isSwiftError())
Type *Ty = AI.getType();
// Use 'select i8 true, %arg, undef' to simulate a 'no-op' instruction.
Value *TrueValue = ConstantInt::getTrue(F.getContext());
Value *UndefValue = UndefValue::get(Ty);
Instruction *SI = SelectInst::Create(
TrueValue, &AI, UndefValue, AI.getName() + ".tmp", &*AfterAllocaInsPt);
// Reset the operand, because it was clobbered by the RAUW above.
SI->setOperand(1, &AI);
/// lowerAcrossUnwindEdges - Find all variables which are alive across an unwind
/// edge and spill them.
void SjLjEHPrepare::lowerAcrossUnwindEdges(Function &F,
ArrayRef<InvokeInst *> Invokes) {
// Finally, scan the code looking for instructions with bad live ranges.
for (BasicBlock &BB : F) {
for (Instruction &Inst : BB) {
// 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.
if (Inst.use_empty())
if (Inst.hasOneUse() &&
cast<Instruction>(Inst.user_back())->getParent() == &BB &&
// If this is an alloca in the entry block, it's not a real register
// value.
if (auto *AI = dyn_cast<AllocaInst>(&Inst))
if (AI->isStaticAlloca())
// Avoid iterator invalidation by copying users to a temporary vector.
SmallVector<Instruction *, 16> Users;
for (User *U : Inst.users()) {
Instruction *UI = cast<Instruction>(U);
if (UI->getParent() != &BB || isa<PHINode>(UI))
// Find all of the blocks that this value is live in.
SmallPtrSet<BasicBlock *, 32> LiveBBs;
while (!Users.empty()) {
Instruction *U = Users.pop_back_val();
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 (InvokeInst *Invoke : Invokes) {
BasicBlock *UnwindBlock = Invoke->getUnwindDest();
if (UnwindBlock != &BB && LiveBBs.count(UnwindBlock)) {
LLVM_DEBUG(dbgs() << "SJLJ Spill: " << Inst << " around "
<< UnwindBlock->getName() << "\n");
NeedsSpill = true;
// If we decided we need a spill, do it.
// FIXME: Spilling this way is overkill, as it forces all uses of
// the value to be reloaded from the stack slot, even those that aren't
// in the unwind blocks. We should be more selective.
if (NeedsSpill) {
DemoteRegToStack(Inst, true);
// Go through the landing pads and remove any PHIs there.
for (InvokeInst *Invoke : Invokes) {
BasicBlock *UnwindBlock = Invoke->getUnwindDest();
LandingPadInst *LPI = UnwindBlock->getLandingPadInst();
// Place PHIs into a set to avoid invalidating the iterator.
SmallPtrSet<PHINode *, 8> PHIsToDemote;
for (BasicBlock::iterator PN = UnwindBlock->begin(); isa<PHINode>(PN); ++PN)
if (PHIsToDemote.empty())
// Demote the PHIs to the stack.
for (PHINode *PN : PHIsToDemote)
// Move the landingpad instruction back to the top of the landing pad block.
/// setupEntryBlockAndCallSites - Setup the entry block by creating and filling
/// the function context and marking the call sites with the appropriate
/// values. These values are used by the DWARF EH emitter.
bool SjLjEHPrepare::setupEntryBlockAndCallSites(Function &F) {
SmallVector<ReturnInst *, 16> Returns;
SmallVector<InvokeInst *, 16> Invokes;
SmallSetVector<LandingPadInst *, 16> LPads;
// Look through the terminators of the basic blocks to find invokes.
for (BasicBlock &BB : F)
if (auto *II = dyn_cast<InvokeInst>(BB.getTerminator())) {
if (Function *Callee = II->getCalledFunction())
if (Callee->getIntrinsicID() == Intrinsic::donothing) {
// Remove the NOP invoke.
BranchInst::Create(II->getNormalDest(), II);
} else if (auto *RI = dyn_cast<ReturnInst>(BB.getTerminator())) {
if (Invokes.empty())
return false;
NumInvokes += Invokes.size();
lowerAcrossUnwindEdges(F, Invokes);
Value *FuncCtx =
setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
BasicBlock *EntryBB = &F.front();
IRBuilder<> Builder(EntryBB->getTerminator());
// Get a reference to the jump buffer.
Value *JBufPtr =
Builder.CreateConstGEP2_32(FunctionContextTy, FuncCtx, 0, 5, "jbuf_gep");
// Save the frame pointer.
Value *FramePtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 0,
Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
// Save the stack pointer.
Value *StackPtr = Builder.CreateConstGEP2_32(doubleUnderJBufTy, JBufPtr, 0, 2,
Val = Builder.CreateCall(StackAddrFn, {}, "sp");
Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
// Call the setup_dispatch instrinsic. It fills in the rest of the jmpbuf.
Builder.CreateCall(BuiltinSetupDispatchFn, {});
// Store a pointer to the function context so that the back-end will know
// where to look for it.
Value *FuncCtxArg = Builder.CreateBitCast(FuncCtx, Builder.getInt8PtrTy());
Builder.CreateCall(FuncCtxFn, FuncCtxArg);
// At this point, we are all set up, update the invoke instructions to mark
// their call_site values.
for (unsigned I = 0, E = Invokes.size(); I != E; ++I) {
insertCallSiteStore(Invokes[I], I + 1);
ConstantInt *CallSiteNum =
ConstantInt::get(Type::getInt32Ty(F.getContext()), I + 1);
// Record the call site value for the back end so it stays associated with
// the invoke.
CallInst::Create(CallSiteFn, CallSiteNum, "", Invokes[I]);
// Mark call instructions that aren't nounwind as no-action (call_site ==
// -1). Skip the entry block, as prior to then, no function context has been
// created for this function and any unexpected exceptions thrown will go
// directly to the caller's context, which is what we want anyway, so no need
// to do anything here.
for (BasicBlock &BB : F) {
if (&BB == &F.front())
for (Instruction &I : BB)
if (I.mayThrow())
insertCallSiteStore(&I, -1);
// Register the function context and make sure it's known to not throw
CallInst *Register =
CallInst::Create(RegisterFn, FuncCtx, "", EntryBB->getTerminator());
// Following any allocas not in the entry block, update the saved SP in the
// jmpbuf to the new value.
for (BasicBlock &BB : F) {
if (&BB == &F.front())
for (Instruction &I : BB) {
if (auto *CI = dyn_cast<CallInst>(&I)) {
if (CI->getCalledFunction() != StackRestoreFn)
} else if (!isa<AllocaInst>(&I)) {
Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
new StoreInst(StackAddr, StackPtr, true, StackAddr->getNextNode());
// Finally, for any returns from this function, if this function contains an
// invoke, add a call to unregister the function context.
for (ReturnInst *Return : Returns)
CallInst::Create(UnregisterFn, FuncCtx, "", Return);
return true;
bool SjLjEHPrepare::runOnFunction(Function &F) {
Module &M = *F.getParent();
RegisterFn = M.getOrInsertFunction(
"_Unwind_SjLj_Register", Type::getVoidTy(M.getContext()),
UnregisterFn = M.getOrInsertFunction(
"_Unwind_SjLj_Unregister", Type::getVoidTy(M.getContext()),
FrameAddrFn = Intrinsic::getDeclaration(
&M, Intrinsic::frameaddress,
StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
BuiltinSetupDispatchFn =
Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setup_dispatch);
LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);
bool Res = setupEntryBlockAndCallSites(F);
return Res;