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llvm/lib/CodeGen/SjLjEHPrepare.cpp
Bill Wendling e36b47e17b Revert r176154 in favor of a better approach. 
Code generation makes some basic assumptions about the IR it's been given. In
particular, if there is only one 'invoke' in the function, then that invoke
won't be going away. However, with the advent of the `llvm.donothing' intrinsic,
those invokes may go away. If all of them go away, the landing pad no longer has
any users. This confuses the back-end, which asserts.

This happens with SjLj exceptions, because that's the model that modifies the IR
based on there being invokes, etc. in the function.

Remove any invokes of `llvm.donothing' during SjLj EH preparation. This will
give us a CFG that the back-end won't be confused about. If all of the invokes
in a function are removed, then the SjLj EH prepare pass won't insert the bogus
code the relies upon the invokes being there.
<rdar://problem/13228754&13316637>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176677 91177308-0d34-0410-b5e6-96231b3b80d8
2013-03-08 02:21:08 +00:00

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//===- SjLjEHPrepare.cpp - Eliminate Invoke & Unwind instructions ---------===//
//
// The LLVM Compiler Infrastructure
//
// This file 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 use SjLj
// based exception handling.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "sjljehprepare"
#include "llvm/CodeGen/Passes.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.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/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include <set>
using namespace llvm;
STATISTIC(NumInvokes, "Number of invokes replaced");
STATISTIC(NumSpilled, "Number of registers live across unwind edges");
namespace {
class SjLjEHPrepare : public FunctionPass {
const TargetLoweringBase *TLI;
Type *FunctionContextTy;
Constant *RegisterFn;
Constant *UnregisterFn;
Constant *BuiltinSetjmpFn;
Constant *FrameAddrFn;
Constant *StackAddrFn;
Constant *StackRestoreFn;
Constant *LSDAAddrFn;
Value *PersonalityFn;
Constant *CallSiteFn;
Constant *FuncCtxFn;
AllocaInst *FuncCtx;
public:
static char ID; // Pass identification, replacement for typeid
explicit SjLjEHPrepare(const TargetLoweringBase *tli = NULL)
: FunctionPass(ID), TLI(tli) { }
bool doInitialization(Module &M);
bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {}
const char *getPassName() const {
return "SJLJ Exception Handling preparation";
}
private:
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;
// Public Interface To the SjLjEHPrepare pass.
FunctionPass *llvm::createSjLjEHPreparePass(const TargetLoweringBase *TLI) {
return new SjLjEHPrepare(TLI);
}
// 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());
Type *Int32Ty = Type::getInt32Ty(M.getContext());
FunctionContextTy =
StructType::get(VoidPtrTy, // __prev
Int32Ty, // call_site
ArrayType::get(Int32Ty, 4), // __data
VoidPtrTy, // __personality
VoidPtrTy, // __lsda
ArrayType::get(VoidPtrTy, 5), // __jbuf
NULL);
RegisterFn = M.getOrInsertFunction("_Unwind_SjLj_Register",
Type::getVoidTy(M.getContext()),
PointerType::getUnqual(FunctionContextTy),
(Type *)0);
UnregisterFn =
M.getOrInsertFunction("_Unwind_SjLj_Unregister",
Type::getVoidTy(M.getContext()),
PointerType::getUnqual(FunctionContextTy),
(Type *)0);
FrameAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::frameaddress);
StackAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::stacksave);
StackRestoreFn = Intrinsic::getDeclaration(&M, Intrinsic::stackrestore);
BuiltinSetjmpFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_setjmp);
LSDAAddrFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_lsda);
CallSiteFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_callsite);
FuncCtxFn = Intrinsic::getDeclaration(&M, Intrinsic::eh_sjlj_functioncontext);
PersonalityFn = 0;
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(FuncCtx, Idxs, "call_site");
// Insert a store of the call-site number
ConstantInt *CallSiteNoC = ConstantInt::get(Type::getInt32Ty(I->getContext()),
Number);
Builder.CreateStore(CallSiteNoC, CallSite, true/*volatile*/);
}
/// MarkBlocksLiveIn - Insert BB and all of its predescessors into LiveBBs until
/// we reach blocks we've already seen.
static void MarkBlocksLiveIn(BasicBlock *BB,
SmallPtrSet<BasicBlock*, 64> &LiveBBs) {
if (!LiveBBs.insert(BB)) return; // already been here.
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
MarkBlocksLiveIn(*PI, LiveBBs);
}
/// 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->use_begin(), LPI->use_end());
while (!UseWorkList.empty()) {
Value *Val = UseWorkList.pop_back_val();
ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(Val);
if (!EVI) continue;
if (EVI->getNumIndices() != 1) continue;
if (*EVI->idx_begin() == 0)
EVI->replaceAllUsesWith(ExnVal);
else if (*EVI->idx_begin() == 1)
EVI->replaceAllUsesWith(SelVal);
if (EVI->getNumUses() == 0)
EVI->eraseFromParent();
}
if (LPI->getNumUses() == 0) return;
// 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);
IRBuilder<>
Builder(llvm::next(BasicBlock::iterator(cast<Instruction>(SelVal))));
LPadVal = Builder.CreateInsertValue(LPadVal, ExnVal, 0, "lpad.val");
LPadVal = Builder.CreateInsertValue(LPadVal, SelVal, 1, "lpad.val");
LPI->replaceAllUsesWith(LPadVal);
}
/// 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.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 added to the global context list.
unsigned Align =
TLI->getDataLayout()->getPrefTypeAlignment(FunctionContextTy);
FuncCtx =
new AllocaInst(FunctionContextTy, 0, Align, "fn_context", EntryBB->begin());
// Fill in the function context structure.
for (unsigned I = 0, E = LPads.size(); I != E; ++I) {
LandingPadInst *LPI = LPads[I];
IRBuilder<> Builder(LPI->getParent()->getFirstInsertionPt());
// Reference the __data field.
Value *FCData = Builder.CreateConstGEP2_32(FuncCtx, 0, 2, "__data");
// The exception values come back in context->__data[0].
Value *ExceptionAddr = Builder.CreateConstGEP2_32(FCData, 0, 0,
"exception_gep");
Value *ExnVal = Builder.CreateLoad(ExceptionAddr, true, "exn_val");
ExnVal = Builder.CreateIntToPtr(ExnVal, Builder.getInt8PtrTy());
Value *SelectorAddr = Builder.CreateConstGEP2_32(FCData, 0, 1,
"exn_selector_gep");
Value *SelVal = Builder.CreateLoad(SelectorAddr, true, "exn_selector_val");
substituteLPadValues(LPI, ExnVal, SelVal);
}
// Personality function
IRBuilder<> Builder(EntryBB->getTerminator());
if (!PersonalityFn)
PersonalityFn = LPads[0]->getPersonalityFn();
Value *PersonalityFieldPtr = Builder.CreateConstGEP2_32(FuncCtx, 0, 3,
"pers_fn_gep");
Builder.CreateStore(PersonalityFn, PersonalityFieldPtr, /*isVolatile=*/true);
// LSDA address
Value *LSDA = Builder.CreateCall(LSDAAddrFn, "lsda_addr");
Value *LSDAFieldPtr = Builder.CreateConstGEP2_32(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) &&
isa<ConstantInt>(cast<AllocaInst>(AfterAllocaInsPt)->getArraySize()))
++AfterAllocaInsPt;
for (Function::arg_iterator
AI = F.arg_begin(), AE = F.arg_end(); AI != AE; ++AI) {
Type *Ty = AI->getType();
// Aggregate types can't be cast, but are legal argument types, so we have
// to handle them differently. We use an extract/insert pair as a
// lightweight method to achieve the same goal.
if (isa<StructType>(Ty) || isa<ArrayType>(Ty) || isa<VectorType>(Ty)) {
Instruction *EI = ExtractValueInst::Create(AI, 0, "", AfterAllocaInsPt);
Instruction *NI = InsertValueInst::Create(AI, EI, 0);
NI->insertAfter(EI);
AI->replaceAllUsesWith(NI);
// Set the operand of the instructions back to the AllocaInst.
EI->setOperand(0, AI);
NI->setOperand(0, AI);
} else {
// This is always a no-op cast because we're casting AI to AI->getType()
// so src and destination types are identical. BitCast is the only
// possibility.
CastInst *NC =
new BitCastInst(AI, AI->getType(), AI->getName() + ".tmp",
AfterAllocaInsPt);
AI->replaceAllUsesWith(NC);
// Set the operand of the cast instruction back to the AllocaInst.
// Normally it's forbidden to replace a CastInst's operand because it
// could cause the opcode to reflect an illegal conversion. However, we're
// replacing it here with the same value it was constructed with. We do
// this because the above replaceAllUsesWith() clobbered the operand, but
// we want this one to remain.
NC->setOperand(0, 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 (Function::iterator
BB = F.begin(), BBE = F.end(); BB != BBE; ++BB) {
for (BasicBlock::iterator
II = BB->begin(), IIE = BB->end(); II != IIE; ++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.
SmallVector<Instruction*, 16> 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);
}
// Find all of the blocks that this value is live in.
SmallPtrSet<BasicBlock*, 64> 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)) {
DEBUG(dbgs() << "SJLJ Spill: " << *Inst << " around "
<< UnwindBlock->getName() << "\n");
NeedsSpill = true;
break;
}
}
// 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);
++NumSpilled;
}
}
}
// Go through the landing pads and remove any PHIs there.
for (unsigned i = 0, e = Invokes.size(); i != e; ++i) {
BasicBlock *UnwindBlock = Invokes[i]->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)
PHIsToDemote.insert(cast<PHINode>(PN));
if (PHIsToDemote.empty()) continue;
// Demote the PHIs to the stack.
for (SmallPtrSet<PHINode*, 8>::iterator
I = PHIsToDemote.begin(), E = PHIsToDemote.end(); I != E; ++I)
DemotePHIToStack(*I);
// Move the landingpad instruction back to the top of the landing pad block.
LPI->moveBefore(UnwindBlock->begin());
}
}
/// 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 (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
if (Function *Callee = II->getCalledFunction())
if (Callee->isIntrinsic() &&
Callee->getIntrinsicID() == Intrinsic::donothing) {
// Remove the NOP invoke.
BranchInst::Create(II->getNormalDest(), II);
II->eraseFromParent();
continue;
}
Invokes.push_back(II);
LPads.insert(II->getUnwindDest()->getLandingPadInst());
} else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
Returns.push_back(RI);
}
if (Invokes.empty()) return false;
NumInvokes += Invokes.size();
lowerIncomingArguments(F);
lowerAcrossUnwindEdges(F, Invokes);
Value *FuncCtx =
setupFunctionContext(F, makeArrayRef(LPads.begin(), LPads.end()));
BasicBlock *EntryBB = F.begin();
IRBuilder<> Builder(EntryBB->getTerminator());
// Get a reference to the jump buffer.
Value *JBufPtr = Builder.CreateConstGEP2_32(FuncCtx, 0, 5, "jbuf_gep");
// Save the frame pointer.
Value *FramePtr = Builder.CreateConstGEP2_32(JBufPtr, 0, 0, "jbuf_fp_gep");
Value *Val = Builder.CreateCall(FrameAddrFn, Builder.getInt32(0), "fp");
Builder.CreateStore(Val, FramePtr, /*isVolatile=*/true);
// Save the stack pointer.
Value *StackPtr = Builder.CreateConstGEP2_32(JBufPtr, 0, 2, "jbuf_sp_gep");
Val = Builder.CreateCall(StackAddrFn, "sp");
Builder.CreateStore(Val, StackPtr, /*isVolatile=*/true);
// Call the setjmp instrinsic. It fills in the rest of the jmpbuf.
Value *SetjmpArg = Builder.CreateBitCast(JBufPtr, Builder.getInt8PtrTy());
Builder.CreateCall(BuiltinSetjmpFn, SetjmpArg);
// 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 (Function::iterator BB = F.begin(), E = F.end(); ++BB != E;)
for (BasicBlock::iterator I = BB->begin(), end = BB->end(); I != end; ++I)
if (CallInst *CI = dyn_cast<CallInst>(I)) {
if (!CI->doesNotThrow())
insertCallSiteStore(CI, -1);
} else if (ResumeInst *RI = dyn_cast<ResumeInst>(I)) {
insertCallSiteStore(RI, -1);
}
// Register the function context and make sure it's known to not throw
CallInst *Register = CallInst::Create(RegisterFn, FuncCtx, "",
EntryBB->getTerminator());
Register->setDoesNotThrow();
// Following any allocas not in the entry block, update the saved SP in the
// jmpbuf to the new value.
for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
if (BB == F.begin())
continue;
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
if (CallInst *CI = dyn_cast<CallInst>(I)) {
if (CI->getCalledFunction() != StackRestoreFn)
continue;
} else if (!isa<AllocaInst>(I)) {
continue;
}
Instruction *StackAddr = CallInst::Create(StackAddrFn, "sp");
StackAddr->insertAfter(I);
Instruction *StoreStackAddr = new StoreInst(StackAddr, StackPtr, true);
StoreStackAddr->insertAfter(StackAddr);
}
}
// Finally, for any returns from this function, if this function contains an
// invoke, add a call to unregister the function context.
for (unsigned I = 0, E = Returns.size(); I != E; ++I)
CallInst::Create(UnregisterFn, FuncCtx, "", Returns[I]);
return true;
}
bool SjLjEHPrepare::runOnFunction(Function &F) {
bool Res = setupEntryBlockAndCallSites(F);
return Res;
}
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