//===- SSAUpdater.cpp - Unstructured SSA Update Tool ----------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the SSAUpdater class.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/TinyPtrVector.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
using namespace llvm;
#define DEBUG_TYPE "ssaupdater"
typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
static AvailableValsTy &getAvailableVals(void *AV) {
return *static_cast<AvailableValsTy*>(AV);
}
SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
: AV(nullptr), ProtoType(nullptr), ProtoName(), InsertedPHIs(NewPHI) {}
SSAUpdater::~SSAUpdater() {
delete static_cast<AvailableValsTy*>(AV);
}
void SSAUpdater::Initialize(Type *Ty, StringRef Name) {
if (!AV)
AV = new AvailableValsTy();
else
getAvailableVals(AV).clear();
ProtoType = Ty;
ProtoName = Name;
}
bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
return getAvailableVals(AV).count(BB);
}
void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
assert(ProtoType && "Need to initialize SSAUpdater");
assert(ProtoType == V->getType() &&
"All rewritten values must have the same type");
getAvailableVals(AV)[BB] = V;
}
static bool IsEquivalentPHI(PHINode *PHI,
SmallDenseMap<BasicBlock*, Value*, 8> &ValueMapping) {
unsigned PHINumValues = PHI->getNumIncomingValues();
if (PHINumValues != ValueMapping.size())
return false;
// Scan the phi to see if it matches.
for (unsigned i = 0, e = PHINumValues; i != e; ++i)
if (ValueMapping[PHI->getIncomingBlock(i)] !=
PHI->getIncomingValue(i)) {
return false;
}
return true;
}
Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
Value *Res = GetValueAtEndOfBlockInternal(BB);
return Res;
}
Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
// If there is no definition of the renamed variable in this block, just use
// GetValueAtEndOfBlock to do our work.
if (!HasValueForBlock(BB))
return GetValueAtEndOfBlock(BB);
// Otherwise, we have the hard case. Get the live-in values for each
// predecessor.
SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
Value *SingularValue = nullptr;
// We can get our predecessor info by walking the pred_iterator list, but it
// is relatively slow. If we already have PHI nodes in this block, walk one
// of them to get the predecessor list instead.
if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
Value *PredVal = GetValueAtEndOfBlock(PredBB);
PredValues.push_back(std::make_pair(PredBB, PredVal));
// Compute SingularValue.
if (i == 0)
SingularValue = PredVal;
else if (PredVal != SingularValue)
SingularValue = nullptr;
}
} else {
bool isFirstPred = true;
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
BasicBlock *PredBB = *PI;
Value *PredVal = GetValueAtEndOfBlock(PredBB);
PredValues.push_back(std::make_pair(PredBB, PredVal));
// Compute SingularValue.
if (isFirstPred) {
SingularValue = PredVal;
isFirstPred = false;
} else if (PredVal != SingularValue)
SingularValue = nullptr;
}
}
// If there are no predecessors, just return undef.
if (PredValues.empty())
return UndefValue::get(ProtoType);
// Otherwise, if all the merged values are the same, just use it.
if (SingularValue)
return SingularValue;
// Otherwise, we do need a PHI: check to see if we already have one available
// in this block that produces the right value.
if (isa<PHINode>(BB->begin())) {
SmallDenseMap<BasicBlock*, Value*, 8> ValueMapping(PredValues.begin(),
PredValues.end());
PHINode *SomePHI;
for (BasicBlock::iterator It = BB->begin();
(SomePHI = dyn_cast<PHINode>(It)); ++It) {
if (IsEquivalentPHI(SomePHI, ValueMapping))
return SomePHI;
}
}
// Ok, we have no way out, insert a new one now.
PHINode *InsertedPHI = PHINode::Create(ProtoType, PredValues.size(),
ProtoName, &BB->front());
// Fill in all the predecessors of the PHI.
for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
InsertedPHI->addIncoming(PredValues[i].second, PredValues[i].first);
// See if the PHI node can be merged to a single value. This can happen in
// loop cases when we get a PHI of itself and one other value.
if (Value *V = SimplifyInstruction(InsertedPHI)) {
InsertedPHI->eraseFromParent();
return V;
}
// Set the DebugLoc of the inserted PHI, if available.
DebugLoc DL;
if (const Instruction *I = BB->getFirstNonPHI())
DL = I->getDebugLoc();
InsertedPHI->setDebugLoc(DL);
// If the client wants to know about all new instructions, tell it.
if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
return InsertedPHI;
}
void SSAUpdater::RewriteUse(Use &U) {
Instruction *User = cast<Instruction>(U.getUser());
Value *V;
if (PHINode *UserPN = dyn_cast<PHINode>(User))
V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
else
V = GetValueInMiddleOfBlock(User->getParent());
// Notify that users of the existing value that it is being replaced.
Value *OldVal = U.get();
if (OldVal != V && OldVal->hasValueHandle())
ValueHandleBase::ValueIsRAUWd(OldVal, V);
U.set(V);
}
void SSAUpdater::RewriteUseAfterInsertions(Use &U) {
Instruction *User = cast<Instruction>(U.getUser());
Value *V;
if (PHINode *UserPN = dyn_cast<PHINode>(User))
V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
else
V = GetValueAtEndOfBlock(User->getParent());
U.set(V);
}
namespace llvm {
template<>
class SSAUpdaterTraits<SSAUpdater> {
public:
typedef BasicBlock BlkT;
typedef Value *ValT;
typedef PHINode PhiT;
typedef succ_iterator BlkSucc_iterator;
static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
class PHI_iterator {
private:
PHINode *PHI;
unsigned idx;
public:
explicit PHI_iterator(PHINode *P) // begin iterator
: PHI(P), idx(0) {}
PHI_iterator(PHINode *P, bool) // end iterator
: PHI(P), idx(PHI->getNumIncomingValues()) {}
PHI_iterator &operator++() { ++idx; return *this; }
bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
bool operator!=(const PHI_iterator& x) const { return !operator==(x); }
Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
};
static PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
static PHI_iterator PHI_end(PhiT *PHI) {
return PHI_iterator(PHI, true);
}
/// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
/// vector, set Info->NumPreds, and allocate space in Info->Preds.
static void FindPredecessorBlocks(BasicBlock *BB,
SmallVectorImpl<BasicBlock*> *Preds) {
// We can get our predecessor info by walking the pred_iterator list,
// but it is relatively slow. If we already have PHI nodes in this
// block, walk one of them to get the predecessor list instead.
if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
Preds->push_back(SomePhi->getIncomingBlock(PI));
} else {
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
Preds->push_back(*PI);
}
}
/// GetUndefVal - Get an undefined value of the same type as the value
/// being handled.
static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
return UndefValue::get(Updater->ProtoType);
}
/// CreateEmptyPHI - Create a new PHI instruction in the specified block.
/// Reserve space for the operands but do not fill them in yet.
static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
SSAUpdater *Updater) {
PHINode *PHI = PHINode::Create(Updater->ProtoType, NumPreds,
Updater->ProtoName, &BB->front());
return PHI;
}
/// AddPHIOperand - Add the specified value as an operand of the PHI for
/// the specified predecessor block.
static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
PHI->addIncoming(Val, Pred);
}
/// InstrIsPHI - Check if an instruction is a PHI.
///
static PHINode *InstrIsPHI(Instruction *I) {
return dyn_cast<PHINode>(I);
}
/// ValueIsPHI - Check if a value is a PHI.
///
static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
return dyn_cast<PHINode>(Val);
}
/// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
/// operands, i.e., it was just added.
static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
PHINode *PHI = ValueIsPHI(Val, Updater);
if (PHI && PHI->getNumIncomingValues() == 0)
return PHI;
return nullptr;
}
/// GetPHIValue - For the specified PHI instruction, return the value
/// that it defines.
static Value *GetPHIValue(PHINode *PHI) {
return PHI;
}
};
} // End llvm namespace
/// Check to see if AvailableVals has an entry for the specified BB and if so,
/// return it. If not, construct SSA form by first calculating the required
/// placement of PHIs and then inserting new PHIs where needed.
Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
AvailableValsTy &AvailableVals = getAvailableVals(AV);
if (Value *V = AvailableVals[BB])
return V;
SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
return Impl.GetValue(BB);
}
//===----------------------------------------------------------------------===//
// LoadAndStorePromoter Implementation
//===----------------------------------------------------------------------===//
LoadAndStorePromoter::
LoadAndStorePromoter(const SmallVectorImpl<Instruction*> &Insts,
SSAUpdater &S, StringRef BaseName) : SSA(S) {
if (Insts.empty()) return;
Value *SomeVal;
if (LoadInst *LI = dyn_cast<LoadInst>(Insts[0]))
SomeVal = LI;
else
SomeVal = cast<StoreInst>(Insts[0])->getOperand(0);
if (BaseName.empty())
BaseName = SomeVal->getName();
SSA.Initialize(SomeVal->getType(), BaseName);
}
void LoadAndStorePromoter::
run(const SmallVectorImpl<Instruction*> &Insts) const {
// First step: bucket up uses of the alloca by the block they occur in.
// This is important because we have to handle multiple defs/uses in a block
// ourselves: SSAUpdater is purely for cross-block references.
DenseMap<BasicBlock*, TinyPtrVector<Instruction*> > UsesByBlock;
for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
Instruction *User = Insts[i];
UsesByBlock[User->getParent()].push_back(User);
}
// Okay, now we can iterate over all the blocks in the function with uses,
// processing them. Keep track of which loads are loading a live-in value.
// Walk the uses in the use-list order to be determinstic.
SmallVector<LoadInst*, 32> LiveInLoads;
DenseMap<Value*, Value*> ReplacedLoads;
for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
Instruction *User = Insts[i];
BasicBlock *BB = User->getParent();
TinyPtrVector<Instruction*> &BlockUses = UsesByBlock[BB];
// If this block has already been processed, ignore this repeat use.
if (BlockUses.empty()) continue;
// Okay, this is the first use in the block. If this block just has a
// single user in it, we can rewrite it trivially.
if (BlockUses.size() == 1) {
// If it is a store, it is a trivial def of the value in the block.
if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
updateDebugInfo(SI);
SSA.AddAvailableValue(BB, SI->getOperand(0));
} else
// Otherwise it is a load, queue it to rewrite as a live-in load.
LiveInLoads.push_back(cast<LoadInst>(User));
BlockUses.clear();
continue;
}
// Otherwise, check to see if this block is all loads.
bool HasStore = false;
for (unsigned i = 0, e = BlockUses.size(); i != e; ++i) {
if (isa<StoreInst>(BlockUses[i])) {
HasStore = true;
break;
}
}
// If so, we can queue them all as live in loads. We don't have an
// efficient way to tell which on is first in the block and don't want to
// scan large blocks, so just add all loads as live ins.
if (!HasStore) {
for (unsigned i = 0, e = BlockUses.size(); i != e; ++i)
LiveInLoads.push_back(cast<LoadInst>(BlockUses[i]));
BlockUses.clear();
continue;
}
// Otherwise, we have mixed loads and stores (or just a bunch of stores).
// Since SSAUpdater is purely for cross-block values, we need to determine
// the order of these instructions in the block. If the first use in the
// block is a load, then it uses the live in value. The last store defines
// the live out value. We handle this by doing a linear scan of the block.
Value *StoredValue = nullptr;
for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
if (LoadInst *L = dyn_cast<LoadInst>(II)) {
// If this is a load from an unrelated pointer, ignore it.
if (!isInstInList(L, Insts)) continue;
// If we haven't seen a store yet, this is a live in use, otherwise
// use the stored value.
if (StoredValue) {
replaceLoadWithValue(L, StoredValue);
L->replaceAllUsesWith(StoredValue);
ReplacedLoads[L] = StoredValue;
} else {
LiveInLoads.push_back(L);
}
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(II)) {
// If this is a store to an unrelated pointer, ignore it.
if (!isInstInList(SI, Insts)) continue;
updateDebugInfo(SI);
// Remember that this is the active value in the block.
StoredValue = SI->getOperand(0);
}
}
// The last stored value that happened is the live-out for the block.
assert(StoredValue && "Already checked that there is a store in block");
SSA.AddAvailableValue(BB, StoredValue);
BlockUses.clear();
}
// Okay, now we rewrite all loads that use live-in values in the loop,
// inserting PHI nodes as necessary.
for (unsigned i = 0, e = LiveInLoads.size(); i != e; ++i) {
LoadInst *ALoad = LiveInLoads[i];
Value *NewVal = SSA.GetValueInMiddleOfBlock(ALoad->getParent());
replaceLoadWithValue(ALoad, NewVal);
// Avoid assertions in unreachable code.
if (NewVal == ALoad) NewVal = UndefValue::get(NewVal->getType());
ALoad->replaceAllUsesWith(NewVal);
ReplacedLoads[ALoad] = NewVal;
}
// Allow the client to do stuff before we start nuking things.
doExtraRewritesBeforeFinalDeletion();
// Now that everything is rewritten, delete the old instructions from the
// function. They should all be dead now.
for (unsigned i = 0, e = Insts.size(); i != e; ++i) {
Instruction *User = Insts[i];
// If this is a load that still has uses, then the load must have been added
// as a live value in the SSAUpdate data structure for a block (e.g. because
// the loaded value was stored later). In this case, we need to recursively
// propagate the updates until we get to the real value.
if (!User->use_empty()) {
Value *NewVal = ReplacedLoads[User];
assert(NewVal && "not a replaced load?");
// Propagate down to the ultimate replacee. The intermediately loads
// could theoretically already have been deleted, so we don't want to
// dereference the Value*'s.
DenseMap<Value*, Value*>::iterator RLI = ReplacedLoads.find(NewVal);
while (RLI != ReplacedLoads.end()) {
NewVal = RLI->second;
RLI = ReplacedLoads.find(NewVal);
}
replaceLoadWithValue(cast<LoadInst>(User), NewVal);
User->replaceAllUsesWith(NewVal);
}
instructionDeleted(User);
User->eraseFromParent();
}
}
bool
LoadAndStorePromoter::isInstInList(Instruction *I,
const SmallVectorImpl<Instruction*> &Insts)
const {
return std::find(Insts.begin(), Insts.end(), I) != Insts.end();
}