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|
//===- 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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "ssaupdater"
#include "llvm/Instructions.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/Support/AlignOf.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
using namespace llvm;
typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
static AvailableValsTy &getAvailableVals(void *AV) {
return *static_cast<AvailableValsTy*>(AV);
}
SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
: AV(0), ProtoType(0), ProtoName(), InsertedPHIs(NewPHI) {}
SSAUpdater::~SSAUpdater() {
delete &getAvailableVals(AV);
}
/// Initialize - Reset this object to get ready for a new set of SSA
/// updates with type 'Ty'. PHI nodes get a name based on 'Name'.
void SSAUpdater::Initialize(const Type *Ty, StringRef Name) {
if (AV == 0)
AV = new AvailableValsTy();
else
getAvailableVals(AV).clear();
ProtoType = Ty;
ProtoName = Name;
}
/// 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(ProtoType != 0 && "Need to initialize SSAUpdater");
assert(ProtoType == 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;
}
/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
/// live at the end of the specified block.
Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
Value *Res = GetValueAtEndOfBlockInternal(BB);
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 (!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 = 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(ProtoType);
// Otherwise, if all the merged values are the same, just use it.
if (SingularValue != 0)
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())) {
DenseMap<BasicBlock*, Value*> 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, ProtoName, &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);
}
/// RewriteUseAfterInsertions - Rewrite a use, just like RewriteUse. However,
/// this version of the method can rewrite uses in the same block as a
/// definition, because it assumes that all uses of a value are below any
/// inserted values.
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);
}
/// PHIiter - Iterator for PHI operands. This is used for the PHI_iterator
/// in the SSAUpdaterImpl template.
namespace {
class PHIiter {
private:
PHINode *PHI;
unsigned idx;
public:
explicit PHIiter(PHINode *P) // begin iterator
: PHI(P), idx(0) {}
PHIiter(PHINode *P, bool) // end iterator
: PHI(P), idx(PHI->getNumIncomingValues()) {}
PHIiter &operator++() { ++idx; return *this; }
bool operator==(const PHIiter& x) const { return idx == x.idx; }
bool operator!=(const PHIiter& x) const { return !operator==(x); }
Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
};
}
/// SSAUpdaterTraits<SSAUpdater> - Traits for the SSAUpdaterImpl template,
/// specialized for SSAUpdater.
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); }
typedef PHIiter PHI_iterator;
static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
static inline 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, Updater->ProtoName,
&BB->front());
PHI->reserveOperandSpace(NumPreds);
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 0;
}
/// GetPHIValue - For the specified PHI instruction, return the value
/// that it defines.
static Value *GetPHIValue(PHINode *PHI) {
return PHI;
}
};
} // End llvm namespace
/// GetValueAtEndOfBlockInternal - 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);
}
|