#define DEBUG_TYPE "jump-threading"
#include "llvm/Transforms/Scalar.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/LLVMContext.h"
#include "llvm/Pass.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
STATISTIC(NumThreads, "Number of jumps threaded");
STATISTIC(NumFolds, "Number of terminators folded");
STATISTIC(NumDupes, "Number of branch blocks duplicated to eliminate phi");
static cl::opt<unsigned>
Threshold("jump-threading-threshold",
cl::desc("Max block size to duplicate for jump threading"),
cl::init(6), cl::Hidden);
namespace {
class JumpThreading : public FunctionPass {
TargetData *TD;
LazyValueInfo *LVI;
#ifdef NDEBUG
SmallPtrSet<BasicBlock*, 16> LoopHeaders;
#else
SmallSet<AssertingVH<BasicBlock>, 16> LoopHeaders;
#endif
DenseSet<std::pair<Value*, BasicBlock*> > RecursionSet;
struct RecursionSetRemover {
DenseSet<std::pair<Value*, BasicBlock*> > &TheSet;
std::pair<Value*, BasicBlock*> ThePair;
RecursionSetRemover(DenseSet<std::pair<Value*, BasicBlock*> > &S,
std::pair<Value*, BasicBlock*> P)
: TheSet(S), ThePair(P) { }
~RecursionSetRemover() {
TheSet.erase(ThePair);
}
};
public:
static char ID; JumpThreading() : FunctionPass(ID) {
initializeJumpThreadingPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LazyValueInfo>();
AU.addPreserved<LazyValueInfo>();
}
void FindLoopHeaders(Function &F);
bool ProcessBlock(BasicBlock *BB);
bool ThreadEdge(BasicBlock *BB, const SmallVectorImpl<BasicBlock*> &PredBBs,
BasicBlock *SuccBB);
bool DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
const SmallVectorImpl<BasicBlock *> &PredBBs);
typedef SmallVectorImpl<std::pair<ConstantInt*,
BasicBlock*> > PredValueInfo;
bool ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,
PredValueInfo &Result);
bool ProcessThreadableEdges(Value *Cond, BasicBlock *BB);
bool ProcessBranchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB);
bool ProcessSwitchOnDuplicateCond(BasicBlock *PredBB, BasicBlock *DestBB);
bool ProcessBranchOnPHI(PHINode *PN);
bool ProcessBranchOnXOR(BinaryOperator *BO);
bool SimplifyPartiallyRedundantLoad(LoadInst *LI);
};
}
char JumpThreading::ID = 0;
INITIALIZE_PASS_BEGIN(JumpThreading, "jump-threading",
"Jump Threading", false, false)
INITIALIZE_PASS_DEPENDENCY(LazyValueInfo)
INITIALIZE_PASS_END(JumpThreading, "jump-threading",
"Jump Threading", false, false)
FunctionPass *llvm::createJumpThreadingPass() { return new JumpThreading(); }
bool JumpThreading::runOnFunction(Function &F) {
DEBUG(dbgs() << "Jump threading on function '" << F.getName() << "'\n");
TD = getAnalysisIfAvailable<TargetData>();
LVI = &getAnalysis<LazyValueInfo>();
FindLoopHeaders(F);
bool Changed, EverChanged = false;
do {
Changed = false;
for (Function::iterator I = F.begin(), E = F.end(); I != E;) {
BasicBlock *BB = I;
while (ProcessBlock(BB))
Changed = true;
++I;
if (pred_begin(BB) == pred_end(BB) &&
BB != &BB->getParent()->getEntryBlock()) {
DEBUG(dbgs() << " JT: Deleting dead block '" << BB->getName()
<< "' with terminator: " << *BB->getTerminator() << '\n');
LoopHeaders.erase(BB);
LVI->eraseBlock(BB);
DeleteDeadBlock(BB);
Changed = true;
} else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
if (BI->isUnconditional() &&
BB != &BB->getParent()->getEntryBlock()) {
BasicBlock::iterator BBI = BB->getFirstNonPHI();
while (isa<DbgInfoIntrinsic>(BBI))
++BBI;
if (BBI->isTerminator()) {
bool ErasedFromLoopHeaders = LoopHeaders.erase(BB);
BasicBlock *Succ = BI->getSuccessor(0);
LVI->eraseBlock(BB);
if (TryToSimplifyUncondBranchFromEmptyBlock(BB)) {
Changed = true;
BB = Succ;
}
if (ErasedFromLoopHeaders)
LoopHeaders.insert(BB);
}
}
}
}
EverChanged |= Changed;
} while (Changed);
LoopHeaders.clear();
return EverChanged;
}
static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) {
BasicBlock::const_iterator I = BB->getFirstNonPHI();
unsigned Size = 0;
for (; !isa<TerminatorInst>(I); ++I) {
if (isa<DbgInfoIntrinsic>(I)) continue;
if (isa<BitCastInst>(I) && I->getType()->isPointerTy())
continue;
++Size;
if (const CallInst *CI = dyn_cast<CallInst>(I)) {
if (!isa<IntrinsicInst>(CI))
Size += 3;
else if (!CI->getType()->isVectorTy())
Size += 1;
}
}
if (isa<SwitchInst>(I))
Size = Size > 6 ? Size-6 : 0;
return Size;
}
void JumpThreading::FindLoopHeaders(Function &F) {
SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges;
FindFunctionBackedges(F, Edges);
for (unsigned i = 0, e = Edges.size(); i != e; ++i)
LoopHeaders.insert(const_cast<BasicBlock*>(Edges[i].second));
}
static void PushConstantIntOrUndef(SmallVectorImpl<std::pair<ConstantInt*,
BasicBlock*> > &Result,
Constant *Value, BasicBlock* BB){
if (ConstantInt *FoldedCInt = dyn_cast<ConstantInt>(Value))
Result.push_back(std::make_pair(FoldedCInt, BB));
else if (isa<UndefValue>(Value))
Result.push_back(std::make_pair((ConstantInt*)0, BB));
}
bool JumpThreading::
ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,PredValueInfo &Result){
if (!RecursionSet.insert(std::make_pair(V, BB)).second)
return false;
RecursionSetRemover remover(RecursionSet, std::make_pair(V, BB));
if (isa<ConstantInt>(V) || isa<UndefValue>(V)) {
ConstantInt *CI = dyn_cast<ConstantInt>(V);
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
Result.push_back(std::make_pair(CI, *PI));
return true;
}
Instruction *I = dyn_cast<Instruction>(V);
if (I == 0 || I->getParent() != BB) {
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
BasicBlock *P = *PI;
Constant *PredCst = LVI->getConstantOnEdge(V, P, BB);
if (PredCst == 0 ||
(!isa<ConstantInt>(PredCst) && !isa<UndefValue>(PredCst)))
continue;
Result.push_back(std::make_pair(dyn_cast<ConstantInt>(PredCst), P));
}
return !Result.empty();
}
if (PHINode *PN = dyn_cast<PHINode>(I)) {
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Value *InVal = PN->getIncomingValue(i);
if (isa<ConstantInt>(InVal) || isa<UndefValue>(InVal)) {
ConstantInt *CI = dyn_cast<ConstantInt>(InVal);
Result.push_back(std::make_pair(CI, PN->getIncomingBlock(i)));
} else {
Constant *CI = LVI->getConstantOnEdge(InVal,
PN->getIncomingBlock(i), BB);
if (!CI) continue;
PushConstantIntOrUndef(Result, CI, PN->getIncomingBlock(i));
}
}
return !Result.empty();
}
SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals, RHSVals;
if (I->getType()->getPrimitiveSizeInBits() == 1) {
if (I->getOpcode() == Instruction::Or ||
I->getOpcode() == Instruction::And) {
ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals);
ComputeValueKnownInPredecessors(I->getOperand(1), BB, RHSVals);
if (LHSVals.empty() && RHSVals.empty())
return false;
ConstantInt *InterestingVal;
if (I->getOpcode() == Instruction::Or)
InterestingVal = ConstantInt::getTrue(I->getContext());
else
InterestingVal = ConstantInt::getFalse(I->getContext());
SmallPtrSet<BasicBlock*, 4> LHSKnownBBs;
for (unsigned i = 0, e = LHSVals.size(); i != e; ++i)
if (LHSVals[i].first == InterestingVal || LHSVals[i].first == 0) {
Result.push_back(LHSVals[i]);
Result.back().first = InterestingVal;
LHSKnownBBs.insert(LHSVals[i].second);
}
for (unsigned i = 0, e = RHSVals.size(); i != e; ++i)
if (RHSVals[i].first == InterestingVal || RHSVals[i].first == 0) {
if (!LHSKnownBBs.count(RHSVals[i].second)) {
Result.push_back(RHSVals[i]);
Result.back().first = InterestingVal;
}
}
return !Result.empty();
}
if (I->getOpcode() == Instruction::Xor &&
isa<ConstantInt>(I->getOperand(1)) &&
cast<ConstantInt>(I->getOperand(1))->isOne()) {
ComputeValueKnownInPredecessors(I->getOperand(0), BB, Result);
if (Result.empty())
return false;
for (unsigned i = 0, e = Result.size(); i != e; ++i)
if (Result[i].first)
Result[i].first =
cast<ConstantInt>(ConstantExpr::getNot(Result[i].first));
return true;
}
} else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(I)) {
if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1))) {
SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals;
ComputeValueKnownInPredecessors(BO->getOperand(0), BB, LHSVals);
for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) {
Constant *V = LHSVals[i].first;
if (V == 0) V = UndefValue::get(BO->getType());
Constant *Folded = ConstantExpr::get(BO->getOpcode(), V, CI);
PushConstantIntOrUndef(Result, Folded, LHSVals[i].second);
}
}
return !Result.empty();
}
if (CmpInst *Cmp = dyn_cast<CmpInst>(I)) {
PHINode *PN = dyn_cast<PHINode>(Cmp->getOperand(0));
if (PN && PN->getParent() == BB) {
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *PredBB = PN->getIncomingBlock(i);
Value *LHS = PN->getIncomingValue(i);
Value *RHS = Cmp->getOperand(1)->DoPHITranslation(BB, PredBB);
Value *Res = SimplifyCmpInst(Cmp->getPredicate(), LHS, RHS, TD);
if (Res == 0) {
if (!isa<Constant>(RHS))
continue;
LazyValueInfo::Tristate
ResT = LVI->getPredicateOnEdge(Cmp->getPredicate(), LHS,
cast<Constant>(RHS), PredBB, BB);
if (ResT == LazyValueInfo::Unknown)
continue;
Res = ConstantInt::get(Type::getInt1Ty(LHS->getContext()), ResT);
}
if (Constant *ConstRes = dyn_cast<Constant>(Res))
PushConstantIntOrUndef(Result, ConstRes, PredBB);
}
return !Result.empty();
}
if (isa<Constant>(Cmp->getOperand(1)) && Cmp->getType()->isIntegerTy()) {
if (!isa<Instruction>(Cmp->getOperand(0)) ||
cast<Instruction>(Cmp->getOperand(0))->getParent() != BB) {
Constant *RHSCst = cast<Constant>(Cmp->getOperand(1));
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB);PI != E; ++PI){
BasicBlock *P = *PI;
LazyValueInfo::Tristate Res =
LVI->getPredicateOnEdge(Cmp->getPredicate(), Cmp->getOperand(0),
RHSCst, P, BB);
if (Res == LazyValueInfo::Unknown)
continue;
Constant *ResC = ConstantInt::get(Cmp->getType(), Res);
Result.push_back(std::make_pair(cast<ConstantInt>(ResC), P));
}
return !Result.empty();
}
if (Constant *CmpConst = dyn_cast<Constant>(Cmp->getOperand(1))) {
SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> LHSVals;
ComputeValueKnownInPredecessors(I->getOperand(0), BB, LHSVals);
for (unsigned i = 0, e = LHSVals.size(); i != e; ++i) {
Constant *V = LHSVals[i].first;
if (V == 0) V = UndefValue::get(CmpConst->getType());
Constant *Folded = ConstantExpr::getCompare(Cmp->getPredicate(),
V, CmpConst);
PushConstantIntOrUndef(Result, Folded, LHSVals[i].second);
}
return !Result.empty();
}
}
}
Constant *CI = LVI->getConstant(V, BB);
ConstantInt *CInt = dyn_cast_or_null<ConstantInt>(CI);
if (CInt) {
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
Result.push_back(std::make_pair(CInt, *PI));
}
return !Result.empty();
}
static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) {
TerminatorInst *BBTerm = BB->getTerminator();
unsigned MinSucc = 0;
BasicBlock *TestBB = BBTerm->getSuccessor(MinSucc);
unsigned MinNumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
for (unsigned i = 1, e = BBTerm->getNumSuccessors(); i != e; ++i) {
TestBB = BBTerm->getSuccessor(i);
unsigned NumPreds = std::distance(pred_begin(TestBB), pred_end(TestBB));
if (NumPreds < MinNumPreds)
MinSucc = i;
}
return MinSucc;
}
bool JumpThreading::ProcessBlock(BasicBlock *BB) {
if (pred_begin(BB) == pred_end(BB) &&
BB != &BB->getParent()->getEntryBlock())
return false;
if (BasicBlock *SinglePred = BB->getSinglePredecessor()) {
if (SinglePred->getTerminator()->getNumSuccessors() == 1 &&
SinglePred != BB) {
if (LoopHeaders.erase(SinglePred))
LoopHeaders.insert(BB);
bool isEntry = SinglePred == &SinglePred->getParent()->getEntryBlock();
LVI->eraseBlock(SinglePred);
MergeBasicBlockIntoOnlyPred(BB);
if (isEntry && BB != &BB->getParent()->getEntryBlock())
BB->moveBefore(&BB->getParent()->getEntryBlock());
return true;
}
}
Value *Condition;
if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
if (BI->isUnconditional()) return false;
Condition = BI->getCondition();
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator()))
Condition = SI->getCondition();
else
return false;
if (isa<ConstantInt>(Condition)) {
DEBUG(dbgs() << " In block '" << BB->getName()
<< "' folding terminator: " << *BB->getTerminator() << '\n');
++NumFolds;
ConstantFoldTerminator(BB);
return true;
}
if (isa<UndefValue>(Condition)) {
unsigned BestSucc = GetBestDestForJumpOnUndef(BB);
TerminatorInst *BBTerm = BB->getTerminator();
for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) {
if (i == BestSucc) continue;
BBTerm->getSuccessor(i)->removePredecessor(BB, true);
}
DEBUG(dbgs() << " In block '" << BB->getName()
<< "' folding undef terminator: " << *BBTerm << '\n');
BranchInst::Create(BBTerm->getSuccessor(BestSucc), BBTerm);
BBTerm->eraseFromParent();
return true;
}
Instruction *CondInst = dyn_cast<Instruction>(Condition);
if (CondInst == 0) {
if (ProcessThreadableEdges(Condition, BB))
return true;
return false;
}
if (CmpInst *CondCmp = dyn_cast<CmpInst>(CondInst)) {
BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
if (CondBr && CondConst && CondBr->isConditional() && PI != PE &&
(!isa<Instruction>(CondCmp->getOperand(0)) ||
cast<Instruction>(CondCmp->getOperand(0))->getParent() != BB)) {
LazyValueInfo::Tristate Baseline =
LVI->getPredicateOnEdge(CondCmp->getPredicate(), CondCmp->getOperand(0),
CondConst, *PI, BB);
if (Baseline != LazyValueInfo::Unknown) {
while (++PI != PE) {
LazyValueInfo::Tristate Ret =
LVI->getPredicateOnEdge(CondCmp->getPredicate(),
CondCmp->getOperand(0), CondConst, *PI, BB);
if (Ret != Baseline) break;
}
if (PI == PE) {
unsigned ToRemove = Baseline == LazyValueInfo::True ? 1 : 0;
unsigned ToKeep = Baseline == LazyValueInfo::True ? 0 : 1;
CondBr->getSuccessor(ToRemove)->removePredecessor(BB, true);
BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
CondBr->eraseFromParent();
return true;
}
}
}
}
Value *SimplifyValue = CondInst;
if (CmpInst *CondCmp = dyn_cast<CmpInst>(SimplifyValue))
if (isa<Constant>(CondCmp->getOperand(1)))
SimplifyValue = CondCmp->getOperand(0);
if (LoadInst *LI = dyn_cast<LoadInst>(SimplifyValue))
if (SimplifyPartiallyRedundantLoad(LI))
return true;
if (ProcessThreadableEdges(CondInst, BB))
return true;
if (PHINode *PN = dyn_cast<PHINode>(CondInst))
if (PN->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
return ProcessBranchOnPHI(PN);
if (CondInst->getOpcode() == Instruction::Xor &&
CondInst->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
return ProcessBranchOnXOR(cast<BinaryOperator>(CondInst));
return false;
}
bool JumpThreading::ProcessBranchOnDuplicateCond(BasicBlock *PredBB,
BasicBlock *BB) {
BranchInst *PredBI = cast<BranchInst>(PredBB->getTerminator());
bool BranchDir;
if (PredBI->getSuccessor(1) != BB)
BranchDir = true;
else if (PredBI->getSuccessor(0) != BB)
BranchDir = false;
else {
DEBUG(dbgs() << " In block '" << PredBB->getName()
<< "' folding terminator: " << *PredBB->getTerminator() << '\n');
++NumFolds;
ConstantFoldTerminator(PredBB);
return true;
}
BranchInst *DestBI = cast<BranchInst>(BB->getTerminator());
if (BB->getSinglePredecessor()) {
DEBUG(dbgs() << " In block '" << BB->getName()
<< "' folding condition to '" << BranchDir << "': "
<< *BB->getTerminator() << '\n');
++NumFolds;
Value *OldCond = DestBI->getCondition();
DestBI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
BranchDir));
RecursivelyDeleteTriviallyDeadInstructions(OldCond);
ConstantFoldTerminator(BB);
return true;
}
BasicBlock *SuccBB = DestBI->getSuccessor(!BranchDir);
SmallVector<BasicBlock*, 2> Preds;
Preds.push_back(PredBB);
return ThreadEdge(BB, Preds, SuccBB);
}
bool JumpThreading::ProcessSwitchOnDuplicateCond(BasicBlock *PredBB,
BasicBlock *DestBB) {
if (PredBB == DestBB)
return false;
SwitchInst *PredSI = cast<SwitchInst>(PredBB->getTerminator());
SwitchInst *DestSI = cast<SwitchInst>(DestBB->getTerminator());
BasicBlock::iterator BBI = DestBB->begin();
while (isa<DbgInfoIntrinsic>(BBI))
BBI++;
if (isa<SwitchInst>(BBI)) {
bool MadeChange = false;
for (unsigned i = 1, e = DestSI->getNumSuccessors(); i != e; ++i) {
ConstantInt *DestVal = DestSI->getCaseValue(i);
BasicBlock *DestSucc = DestSI->getSuccessor(i);
unsigned PredCase = PredSI->findCaseValue(DestVal);
if (PredCase == 0) continue;
if (PredSI->getSuccessor(PredCase) != DestBB &&
DestSI->getSuccessor(i) != DestBB)
continue;
if (PredSI->getSuccessor(PredCase) == DestSucc)
continue;
DEBUG(dbgs() << "FORWARDING EDGE " << *DestVal << " FROM: " << *PredSI);
DEBUG(dbgs() << "THROUGH: " << *DestSI);
if (isa<PHINode>(DestSucc->begin()) && !DestSucc->getSinglePredecessor()){
SplitCriticalEdge(DestSI, i, this);
DestSucc = DestSI->getSuccessor(i);
}
FoldSingleEntryPHINodes(DestSucc);
PredSI->setSuccessor(PredCase, DestSucc);
MadeChange = true;
}
if (MadeChange)
return true;
}
return false;
}
bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
if (LI->isVolatile()) return false;
BasicBlock *LoadBB = LI->getParent();
if (LoadBB->getSinglePredecessor())
return false;
Value *LoadedPtr = LI->getOperand(0);
if (Instruction *PtrOp = dyn_cast<Instruction>(LoadedPtr))
if (PtrOp->getParent() == LoadBB)
return false;
BasicBlock::iterator BBIt = LI;
if (Value *AvailableVal =
FindAvailableLoadedValue(LoadedPtr, LoadBB, BBIt, 6)) {
if (AvailableVal == LI) AvailableVal = UndefValue::get(LI->getType());
LI->replaceAllUsesWith(AvailableVal);
LI->eraseFromParent();
return true;
}
if (BBIt != LoadBB->begin())
return false;
SmallPtrSet<BasicBlock*, 8> PredsScanned;
typedef SmallVector<std::pair<BasicBlock*, Value*>, 8> AvailablePredsTy;
AvailablePredsTy AvailablePreds;
BasicBlock *OneUnavailablePred = 0;
for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
PI != PE; ++PI) {
BasicBlock *PredBB = *PI;
if (!PredsScanned.insert(PredBB))
continue;
BBIt = PredBB->end();
Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6);
if (!PredAvailable) {
OneUnavailablePred = PredBB;
continue;
}
AvailablePreds.push_back(std::make_pair(PredBB, PredAvailable));
}
if (AvailablePreds.empty()) return false;
BasicBlock *UnavailablePred = 0;
if (PredsScanned.size() == AvailablePreds.size()+1 &&
OneUnavailablePred->getTerminator()->getNumSuccessors() == 1) {
UnavailablePred = OneUnavailablePred;
} else if (PredsScanned.size() != AvailablePreds.size()) {
SmallVector<BasicBlock*, 8> PredsToSplit;
SmallPtrSet<BasicBlock*, 8> AvailablePredSet;
for (unsigned i = 0, e = AvailablePreds.size(); i != e; ++i)
AvailablePredSet.insert(AvailablePreds[i].first);
for (pred_iterator PI = pred_begin(LoadBB), PE = pred_end(LoadBB);
PI != PE; ++PI) {
BasicBlock *P = *PI;
if (isa<IndirectBrInst>(P->getTerminator()))
return false;
if (!AvailablePredSet.count(P))
PredsToSplit.push_back(P);
}
UnavailablePred =
SplitBlockPredecessors(LoadBB, &PredsToSplit[0], PredsToSplit.size(),
"thread-pre-split", this);
}
if (UnavailablePred) {
assert(UnavailablePred->getTerminator()->getNumSuccessors() == 1 &&
"Can't handle critical edge here!");
Value *NewVal = new LoadInst(LoadedPtr, LI->getName()+".pr", false,
LI->getAlignment(),
UnavailablePred->getTerminator());
AvailablePreds.push_back(std::make_pair(UnavailablePred, NewVal));
}
array_pod_sort(AvailablePreds.begin(), AvailablePreds.end());
PHINode *PN = PHINode::Create(LI->getType(), "", LoadBB->begin());
PN->takeName(LI);
for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); PI != E;
++PI) {
BasicBlock *P = *PI;
AvailablePredsTy::iterator I =
std::lower_bound(AvailablePreds.begin(), AvailablePreds.end(),
std::make_pair(P, (Value*)0));
assert(I != AvailablePreds.end() && I->first == P &&
"Didn't find entry for predecessor!");
PN->addIncoming(I->second, I->first);
}
LI->replaceAllUsesWith(PN);
LI->eraseFromParent();
return true;
}
static BasicBlock *
FindMostPopularDest(BasicBlock *BB,
const SmallVectorImpl<std::pair<BasicBlock*,
BasicBlock*> > &PredToDestList) {
assert(!PredToDestList.empty());
DenseMap<BasicBlock*, unsigned> DestPopularity;
for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
if (PredToDestList[i].second)
DestPopularity[PredToDestList[i].second]++;
DenseMap<BasicBlock*, unsigned>::iterator DPI = DestPopularity.begin();
BasicBlock *MostPopularDest = DPI->first;
unsigned Popularity = DPI->second;
SmallVector<BasicBlock*, 4> SamePopularity;
for (++DPI; DPI != DestPopularity.end(); ++DPI) {
if (DPI->second < Popularity)
; else if (DPI->second == Popularity) {
SamePopularity.push_back(DPI->first);
} else {
SamePopularity.clear();
MostPopularDest = DPI->first;
Popularity = DPI->second;
}
}
if (!SamePopularity.empty()) {
SamePopularity.push_back(MostPopularDest);
TerminatorInst *TI = BB->getTerminator();
for (unsigned i = 0; ; ++i) {
assert(i != TI->getNumSuccessors() && "Didn't find any successor!");
if (std::find(SamePopularity.begin(), SamePopularity.end(),
TI->getSuccessor(i)) == SamePopularity.end())
continue;
MostPopularDest = TI->getSuccessor(i);
break;
}
}
return MostPopularDest;
}
bool JumpThreading::ProcessThreadableEdges(Value *Cond, BasicBlock *BB) {
if (LoopHeaders.count(BB))
return false;
SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> PredValues;
if (!ComputeValueKnownInPredecessors(Cond, BB, PredValues))
return false;
assert(!PredValues.empty() &&
"ComputeValueKnownInPredecessors returned true with no values");
DEBUG(dbgs() << "IN BB: " << *BB;
for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
dbgs() << " BB '" << BB->getName() << "': FOUND condition = ";
if (PredValues[i].first)
dbgs() << *PredValues[i].first;
else
dbgs() << "UNDEF";
dbgs() << " for pred '" << PredValues[i].second->getName()
<< "'.\n";
});
SmallPtrSet<BasicBlock*, 16> SeenPreds;
SmallVector<std::pair<BasicBlock*, BasicBlock*>, 16> PredToDestList;
BasicBlock *OnlyDest = 0;
BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL;
for (unsigned i = 0, e = PredValues.size(); i != e; ++i) {
BasicBlock *Pred = PredValues[i].second;
if (!SeenPreds.insert(Pred))
continue;
if (isa<IndirectBrInst>(Pred->getTerminator()))
continue;
ConstantInt *Val = PredValues[i].first;
BasicBlock *DestBB;
if (Val == 0) DestBB = 0;
else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
DestBB = BI->getSuccessor(Val->isZero());
else {
SwitchInst *SI = cast<SwitchInst>(BB->getTerminator());
DestBB = SI->getSuccessor(SI->findCaseValue(Val));
}
if (i == 0)
OnlyDest = DestBB;
else if (OnlyDest != DestBB)
OnlyDest = MultipleDestSentinel;
PredToDestList.push_back(std::make_pair(Pred, DestBB));
}
if (PredToDestList.empty())
return false;
BasicBlock *MostPopularDest = OnlyDest;
if (MostPopularDest == MultipleDestSentinel)
MostPopularDest = FindMostPopularDest(BB, PredToDestList);
SmallVector<BasicBlock*, 16> PredsToFactor;
for (unsigned i = 0, e = PredToDestList.size(); i != e; ++i)
if (PredToDestList[i].second == MostPopularDest) {
BasicBlock *Pred = PredToDestList[i].first;
TerminatorInst *PredTI = Pred->getTerminator();
for (unsigned i = 0, e = PredTI->getNumSuccessors(); i != e; ++i)
if (PredTI->getSuccessor(i) == BB)
PredsToFactor.push_back(Pred);
}
if (MostPopularDest == 0)
MostPopularDest = BB->getTerminator()->
getSuccessor(GetBestDestForJumpOnUndef(BB));
return ThreadEdge(BB, PredsToFactor, MostPopularDest);
}
bool JumpThreading::ProcessBranchOnPHI(PHINode *PN) {
BasicBlock *BB = PN->getParent();
SmallVector<BasicBlock*, 1> PredBBs;
PredBBs.resize(1);
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *PredBB = PN->getIncomingBlock(i);
if (BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator()))
if (PredBr->isUnconditional()) {
PredBBs[0] = PredBB;
if (DuplicateCondBranchOnPHIIntoPred(BB, PredBBs))
return true;
}
}
return false;
}
bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) {
BasicBlock *BB = BO->getParent();
if (isa<ConstantInt>(BO->getOperand(0)) ||
isa<ConstantInt>(BO->getOperand(1)))
return false;
if (!isa<PHINode>(BB->front()))
return false;
SmallVector<std::pair<ConstantInt*, BasicBlock*>, 8> XorOpValues;
bool isLHS = true;
if (!ComputeValueKnownInPredecessors(BO->getOperand(0), BB, XorOpValues)) {
assert(XorOpValues.empty());
if (!ComputeValueKnownInPredecessors(BO->getOperand(1), BB, XorOpValues))
return false;
isLHS = false;
}
assert(!XorOpValues.empty() &&
"ComputeValueKnownInPredecessors returned true with no values");
unsigned NumTrue = 0, NumFalse = 0;
for (unsigned i = 0, e = XorOpValues.size(); i != e; ++i) {
if (!XorOpValues[i].first) continue; if (XorOpValues[i].first->isZero())
++NumFalse;
else
++NumTrue;
}
ConstantInt *SplitVal = 0;
if (NumTrue > NumFalse)
SplitVal = ConstantInt::getTrue(BB->getContext());
else if (NumTrue != 0 || NumFalse != 0)
SplitVal = ConstantInt::getFalse(BB->getContext());
SmallVector<BasicBlock*, 8> BlocksToFoldInto;
for (unsigned i = 0, e = XorOpValues.size(); i != e; ++i) {
if (XorOpValues[i].first != SplitVal && XorOpValues[i].first != 0) continue;
BlocksToFoldInto.push_back(XorOpValues[i].second);
}
if (BlocksToFoldInto.size() ==
cast<PHINode>(BB->front()).getNumIncomingValues()) {
if (SplitVal == 0) {
BO->replaceAllUsesWith(UndefValue::get(BO->getType()));
BO->eraseFromParent();
} else if (SplitVal->isZero()) {
BO->replaceAllUsesWith(BO->getOperand(isLHS));
BO->eraseFromParent();
} else {
BO->setOperand(!isLHS, SplitVal);
}
return true;
}
return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto);
}
static void AddPHINodeEntriesForMappedBlock(BasicBlock *PHIBB,
BasicBlock *OldPred,
BasicBlock *NewPred,
DenseMap<Instruction*, Value*> &ValueMap) {
for (BasicBlock::iterator PNI = PHIBB->begin();
PHINode *PN = dyn_cast<PHINode>(PNI); ++PNI) {
Value *IV = PN->getIncomingValueForBlock(OldPred);
if (Instruction *Inst = dyn_cast<Instruction>(IV)) {
DenseMap<Instruction*, Value*>::iterator I = ValueMap.find(Inst);
if (I != ValueMap.end())
IV = I->second;
}
PN->addIncoming(IV, NewPred);
}
}
bool JumpThreading::ThreadEdge(BasicBlock *BB,
const SmallVectorImpl<BasicBlock*> &PredBBs,
BasicBlock *SuccBB) {
if (SuccBB == BB) {
DEBUG(dbgs() << " Not threading across BB '" << BB->getName()
<< "' - would thread to self!\n");
return false;
}
if (LoopHeaders.count(BB)) {
DEBUG(dbgs() << " Not threading across loop header BB '" << BB->getName()
<< "' to dest BB '" << SuccBB->getName()
<< "' - it might create an irreducible loop!\n");
return false;
}
unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB);
if (JumpThreadCost > Threshold) {
DEBUG(dbgs() << " Not threading BB '" << BB->getName()
<< "' - Cost is too high: " << JumpThreadCost << "\n");
return false;
}
BasicBlock *PredBB;
if (PredBBs.size() == 1)
PredBB = PredBBs[0];
else {
DEBUG(dbgs() << " Factoring out " << PredBBs.size()
<< " common predecessors.\n");
PredBB = SplitBlockPredecessors(BB, &PredBBs[0], PredBBs.size(),
".thr_comm", this);
}
DEBUG(dbgs() << " Threading edge from '" << PredBB->getName() << "' to '"
<< SuccBB->getName() << "' with cost: " << JumpThreadCost
<< ", across block:\n "
<< *BB << "\n");
LVI->threadEdge(PredBB, BB, SuccBB);
DenseMap<Instruction*, Value*> ValueMapping;
BasicBlock *NewBB = BasicBlock::Create(BB->getContext(),
BB->getName()+".thread",
BB->getParent(), BB);
NewBB->moveAfter(PredBB);
BasicBlock::iterator BI = BB->begin();
for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
for (; !isa<TerminatorInst>(BI); ++BI) {
Instruction *New = BI->clone();
New->setName(BI->getName());
NewBB->getInstList().push_back(New);
ValueMapping[BI] = New;
for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
if (I != ValueMapping.end())
New->setOperand(i, I->second);
}
}
BranchInst::Create(SuccBB, NewBB);
AddPHINodeEntriesForMappedBlock(SuccBB, BB, NewBB, ValueMapping);
SSAUpdater SSAUpdate;
SmallVector<Use*, 16> UsesToRename;
for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
++UI) {
Instruction *User = cast<Instruction>(*UI);
if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
if (UserPN->getIncomingBlock(UI) == BB)
continue;
} else if (User->getParent() == BB)
continue;
UsesToRename.push_back(&UI.getUse());
}
if (UsesToRename.empty())
continue;
DEBUG(dbgs() << "JT: Renaming non-local uses of: " << *I << "\n");
SSAUpdate.Initialize(I->getType(), I->getName());
SSAUpdate.AddAvailableValue(BB, I);
SSAUpdate.AddAvailableValue(NewBB, ValueMapping[I]);
while (!UsesToRename.empty())
SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
DEBUG(dbgs() << "\n");
}
TerminatorInst *PredTerm = PredBB->getTerminator();
for (unsigned i = 0, e = PredTerm->getNumSuccessors(); i != e; ++i)
if (PredTerm->getSuccessor(i) == BB) {
BB->removePredecessor(PredBB, true);
PredTerm->setSuccessor(i, NewBB);
}
SimplifyInstructionsInBlock(NewBB, TD);
++NumThreads;
return true;
}
bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
const SmallVectorImpl<BasicBlock *> &PredBBs) {
assert(!PredBBs.empty() && "Can't handle an empty set");
if (LoopHeaders.count(BB)) {
DEBUG(dbgs() << " Not duplicating loop header '" << BB->getName()
<< "' into predecessor block '" << PredBBs[0]->getName()
<< "' - it might create an irreducible loop!\n");
return false;
}
unsigned DuplicationCost = getJumpThreadDuplicationCost(BB);
if (DuplicationCost > Threshold) {
DEBUG(dbgs() << " Not duplicating BB '" << BB->getName()
<< "' - Cost is too high: " << DuplicationCost << "\n");
return false;
}
BasicBlock *PredBB;
if (PredBBs.size() == 1)
PredBB = PredBBs[0];
else {
DEBUG(dbgs() << " Factoring out " << PredBBs.size()
<< " common predecessors.\n");
PredBB = SplitBlockPredecessors(BB, &PredBBs[0], PredBBs.size(),
".thr_comm", this);
}
DEBUG(dbgs() << " Duplicating block '" << BB->getName() << "' into end of '"
<< PredBB->getName() << "' to eliminate branch on phi. Cost: "
<< DuplicationCost << " block is:" << *BB << "\n");
BranchInst *OldPredBranch = dyn_cast<BranchInst>(PredBB->getTerminator());
if (OldPredBranch == 0 || !OldPredBranch->isUnconditional()) {
PredBB = SplitEdge(PredBB, BB, this);
OldPredBranch = cast<BranchInst>(PredBB->getTerminator());
}
DenseMap<Instruction*, Value*> ValueMapping;
BasicBlock::iterator BI = BB->begin();
for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
for (; BI != BB->end(); ++BI) {
Instruction *New = BI->clone();
for (unsigned i = 0, e = New->getNumOperands(); i != e; ++i)
if (Instruction *Inst = dyn_cast<Instruction>(New->getOperand(i))) {
DenseMap<Instruction*, Value*>::iterator I = ValueMapping.find(Inst);
if (I != ValueMapping.end())
New->setOperand(i, I->second);
}
if (Value *IV = SimplifyInstruction(New, TD)) {
delete New;
ValueMapping[BI] = IV;
} else {
New->setName(BI->getName());
PredBB->getInstList().insert(OldPredBranch, New);
ValueMapping[BI] = New;
}
}
BranchInst *BBBranch = cast<BranchInst>(BB->getTerminator());
AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(0), BB, PredBB,
ValueMapping);
AddPHINodeEntriesForMappedBlock(BBBranch->getSuccessor(1), BB, PredBB,
ValueMapping);
SSAUpdater SSAUpdate;
SmallVector<Use*, 16> UsesToRename;
for (BasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
++UI) {
Instruction *User = cast<Instruction>(*UI);
if (PHINode *UserPN = dyn_cast<PHINode>(User)) {
if (UserPN->getIncomingBlock(UI) == BB)
continue;
} else if (User->getParent() == BB)
continue;
UsesToRename.push_back(&UI.getUse());
}
if (UsesToRename.empty())
continue;
DEBUG(dbgs() << "JT: Renaming non-local uses of: " << *I << "\n");
SSAUpdate.Initialize(I->getType(), I->getName());
SSAUpdate.AddAvailableValue(BB, I);
SSAUpdate.AddAvailableValue(PredBB, ValueMapping[I]);
while (!UsesToRename.empty())
SSAUpdate.RewriteUse(*UsesToRename.pop_back_val());
DEBUG(dbgs() << "\n");
}
BB->removePredecessor(PredBB, true);
OldPredBranch->eraseFromParent();
++NumDupes;
return true;
}