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Diffstat (limited to 'lib/Transforms/Utils/SSAUpdater.cpp')
| -rw-r--r-- | lib/Transforms/Utils/SSAUpdater.cpp | 396 |
1 files changed, 396 insertions, 0 deletions
diff --git a/lib/Transforms/Utils/SSAUpdater.cpp b/lib/Transforms/Utils/SSAUpdater.cpp new file mode 100644 index 0000000..a31235a --- /dev/null +++ b/lib/Transforms/Utils/SSAUpdater.cpp @@ -0,0 +1,396 @@ +//===- 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/Instructions.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/Support/CFG.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ValueHandle.h" +#include "llvm/Support/raw_ostream.h" +using namespace llvm; + +typedef DenseMap<BasicBlock*, TrackingVH<Value> > AvailableValsTy; +typedef std::vector<std::pair<BasicBlock*, TrackingVH<Value> > > + IncomingPredInfoTy; + +static AvailableValsTy &getAvailableVals(void *AV) { + return *static_cast<AvailableValsTy*>(AV); +} + +static IncomingPredInfoTy &getIncomingPredInfo(void *IPI) { + return *static_cast<IncomingPredInfoTy*>(IPI); +} + + +SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI) + : AV(0), PrototypeValue(0), IPI(0), InsertedPHIs(NewPHI) {} + +SSAUpdater::~SSAUpdater() { + delete &getAvailableVals(AV); + delete &getIncomingPredInfo(IPI); +} + +/// Initialize - Reset this object to get ready for a new set of SSA +/// updates. ProtoValue is the value used to name PHI nodes. +void SSAUpdater::Initialize(Value *ProtoValue) { + if (AV == 0) + AV = new AvailableValsTy(); + else + getAvailableVals(AV).clear(); + + if (IPI == 0) + IPI = new IncomingPredInfoTy(); + else + getIncomingPredInfo(IPI).clear(); + PrototypeValue = ProtoValue; +} + +/// HasValueForBlock - Return true if the SSAUpdater already has a value for +/// the specified block. +bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const { + return getAvailableVals(AV).count(BB); +} + +/// AddAvailableValue - Indicate that a rewritten value is available in the +/// specified block with the specified value. +void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) { + assert(PrototypeValue != 0 && "Need to initialize SSAUpdater"); + assert(PrototypeValue->getType() == V->getType() && + "All rewritten values must have the same type"); + getAvailableVals(AV)[BB] = V; +} + +/// IsEquivalentPHI - Check if PHI has the same incoming value as specified +/// in ValueMapping for each predecessor block. +static bool IsEquivalentPHI(PHINode *PHI, + DenseMap<BasicBlock*, Value*> &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; +} + +/// GetExistingPHI - Check if BB already contains a phi node that is equivalent +/// to the specified mapping from predecessor blocks to incoming values. +static Value *GetExistingPHI(BasicBlock *BB, + DenseMap<BasicBlock*, Value*> &ValueMapping) { + PHINode *SomePHI; + for (BasicBlock::iterator It = BB->begin(); + (SomePHI = dyn_cast<PHINode>(It)); ++It) { + if (IsEquivalentPHI(SomePHI, ValueMapping)) + return SomePHI; + } + return 0; +} + +/// GetExistingPHI - Check if BB already contains an equivalent phi node. +/// The InputIt type must be an iterator over std::pair<BasicBlock*, Value*> +/// objects that specify the mapping from predecessor blocks to incoming values. +template<typename InputIt> +static Value *GetExistingPHI(BasicBlock *BB, const InputIt &I, + const InputIt &E) { + // Avoid create the mapping if BB has no phi nodes at all. + if (!isa<PHINode>(BB->begin())) + return 0; + DenseMap<BasicBlock*, Value*> ValueMapping(I, E); + return GetExistingPHI(BB, ValueMapping); +} + +/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is +/// live at the end of the specified block. +Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) { + assert(getIncomingPredInfo(IPI).empty() && "Unexpected Internal State"); + Value *Res = GetValueAtEndOfBlockInternal(BB); + assert(getIncomingPredInfo(IPI).empty() && "Unexpected Internal State"); + return Res; +} + +/// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that +/// is live in the middle of the specified block. +/// +/// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one +/// important case: if there is a definition of the rewritten value after the +/// 'use' in BB. Consider code like this: +/// +/// X1 = ... +/// SomeBB: +/// use(X) +/// X2 = ... +/// br Cond, SomeBB, OutBB +/// +/// In this case, there are two values (X1 and X2) added to the AvailableVals +/// set by the client of the rewriter, and those values are both live out of +/// their respective blocks. However, the use of X happens in the *middle* of +/// a block. Because of this, we need to insert a new PHI node in SomeBB to +/// merge the appropriate values, and this value isn't live out of the block. +/// +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 (!getAvailableVals(AV).count(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 = 0; + + // 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 = 0; + } + } 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 = 0; + } + } + + // If there are no predecessors, just return undef. + if (PredValues.empty()) + return UndefValue::get(PrototypeValue->getType()); + + // Otherwise, if all the merged values are the same, just use it. + if (SingularValue != 0) + return SingularValue; + + // Otherwise, we do need a PHI. + if (Value *ExistingPHI = GetExistingPHI(BB, PredValues.begin(), + PredValues.end())) + return ExistingPHI; + + // Ok, we have no way out, insert a new one now. + PHINode *InsertedPHI = PHINode::Create(PrototypeValue->getType(), + PrototypeValue->getName(), + &BB->front()); + InsertedPHI->reserveOperandSpace(PredValues.size()); + + // 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 *ConstVal = InsertedPHI->hasConstantValue()) { + InsertedPHI->eraseFromParent(); + return ConstVal; + } + + // 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; +} + +/// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes, +/// which use their value in the corresponding predecessor. +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()); + + U.set(V); +} + + +/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry +/// for the specified BB and if so, return it. If not, construct SSA form by +/// walking predecessors inserting PHI nodes as needed until we get to a block +/// where the value is available. +/// +Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) { + AvailableValsTy &AvailableVals = getAvailableVals(AV); + + // Query AvailableVals by doing an insertion of null. + std::pair<AvailableValsTy::iterator, bool> InsertRes = + AvailableVals.insert(std::make_pair(BB, TrackingVH<Value>())); + + // Handle the case when the insertion fails because we have already seen BB. + if (!InsertRes.second) { + // If the insertion failed, there are two cases. The first case is that the + // value is already available for the specified block. If we get this, just + // return the value. + if (InsertRes.first->second != 0) + return InsertRes.first->second; + + // Otherwise, if the value we find is null, then this is the value is not + // known but it is being computed elsewhere in our recursion. This means + // that we have a cycle. Handle this by inserting a PHI node and returning + // it. When we get back to the first instance of the recursion we will fill + // in the PHI node. + return InsertRes.first->second = + PHINode::Create(PrototypeValue->getType(), PrototypeValue->getName(), + &BB->front()); + } + + // Okay, the value isn't in the map and we just inserted a null in the entry + // to indicate that we're processing the block. Since we have no idea what + // value is in this block, we have to recurse through our predecessors. + // + // While we're walking our predecessors, we keep track of them in a vector, + // then insert a PHI node in the end if we actually need one. We could use a + // smallvector here, but that would take a lot of stack space for every level + // of the recursion, just use IncomingPredInfo as an explicit stack. + IncomingPredInfoTy &IncomingPredInfo = getIncomingPredInfo(IPI); + unsigned FirstPredInfoEntry = IncomingPredInfo.size(); + + // As we're walking the predecessors, keep track of whether they are all + // producing the same value. If so, this value will capture it, if not, it + // will get reset to null. We distinguish the no-predecessor case explicitly + // below. + TrackingVH<Value> ExistingValue; + + // 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 = GetValueAtEndOfBlockInternal(PredBB); + IncomingPredInfo.push_back(std::make_pair(PredBB, PredVal)); + + // Set ExistingValue to singular value from all predecessors so far. + if (i == 0) + ExistingValue = PredVal; + else if (PredVal != ExistingValue) + ExistingValue = 0; + } + } else { + bool isFirstPred = true; + for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { + BasicBlock *PredBB = *PI; + Value *PredVal = GetValueAtEndOfBlockInternal(PredBB); + IncomingPredInfo.push_back(std::make_pair(PredBB, PredVal)); + + // Set ExistingValue to singular value from all predecessors so far. + if (isFirstPred) { + ExistingValue = PredVal; + isFirstPred = false; + } else if (PredVal != ExistingValue) + ExistingValue = 0; + } + } + + // If there are no predecessors, then we must have found an unreachable block + // just return 'undef'. Since there are no predecessors, InsertRes must not + // be invalidated. + if (IncomingPredInfo.size() == FirstPredInfoEntry) + return InsertRes.first->second = UndefValue::get(PrototypeValue->getType()); + + /// Look up BB's entry in AvailableVals. 'InsertRes' may be invalidated. If + /// this block is involved in a loop, a no-entry PHI node will have been + /// inserted as InsertedVal. Otherwise, we'll still have the null we inserted + /// above. + TrackingVH<Value> &InsertedVal = AvailableVals[BB]; + + // If the predecessor values are not all the same, then check to see if there + // is an existing PHI that can be used. + if (!ExistingValue) + ExistingValue = GetExistingPHI(BB, + IncomingPredInfo.begin()+FirstPredInfoEntry, + IncomingPredInfo.end()); + + // If there is an existing value we can use, then we don't need to insert a + // PHI. This is the simple and common case. + if (ExistingValue) { + // If a PHI node got inserted, replace it with the existing value and delete + // it. + if (InsertedVal) { + PHINode *OldVal = cast<PHINode>(InsertedVal); + // Be careful about dead loops. These RAUW's also update InsertedVal. + if (InsertedVal != ExistingValue) + OldVal->replaceAllUsesWith(ExistingValue); + else + OldVal->replaceAllUsesWith(UndefValue::get(InsertedVal->getType())); + OldVal->eraseFromParent(); + } else { + InsertedVal = ExistingValue; + } + + // Either path through the 'if' should have set InsertedVal -> ExistingVal. + assert((InsertedVal == ExistingValue || isa<UndefValue>(InsertedVal)) && + "RAUW didn't change InsertedVal to be ExistingValue"); + + // Drop the entries we added in IncomingPredInfo to restore the stack. + IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry, + IncomingPredInfo.end()); + return ExistingValue; + } + + // Otherwise, we do need a PHI: insert one now if we don't already have one. + if (InsertedVal == 0) + InsertedVal = PHINode::Create(PrototypeValue->getType(), + PrototypeValue->getName(), &BB->front()); + + PHINode *InsertedPHI = cast<PHINode>(InsertedVal); + InsertedPHI->reserveOperandSpace(IncomingPredInfo.size()-FirstPredInfoEntry); + + // Fill in all the predecessors of the PHI. + for (IncomingPredInfoTy::iterator I = + IncomingPredInfo.begin()+FirstPredInfoEntry, + E = IncomingPredInfo.end(); I != E; ++I) + InsertedPHI->addIncoming(I->second, I->first); + + // Drop the entries we added in IncomingPredInfo to restore the stack. + IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry, + IncomingPredInfo.end()); + + // 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 *ConstVal = InsertedPHI->hasConstantValue()) { + InsertedPHI->replaceAllUsesWith(ConstVal); + InsertedPHI->eraseFromParent(); + InsertedVal = ConstVal; + } else { + DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n"); + + // If the client wants to know about all new instructions, tell it. + if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI); + } + + return InsertedVal; +} |