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//===- MachineSSAUpdater.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 MachineSSAUpdater class. It's based on SSAUpdater
// class in lib/Transforms/Utils.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/MachineSSAUpdater.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/AlignOf.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
using namespace llvm;
typedef DenseMap<MachineBasicBlock*, unsigned> AvailableValsTy;
static AvailableValsTy &getAvailableVals(void *AV) {
return *static_cast<AvailableValsTy*>(AV);
}
MachineSSAUpdater::MachineSSAUpdater(MachineFunction &MF,
SmallVectorImpl<MachineInstr*> *NewPHI)
: AV(0), InsertedPHIs(NewPHI) {
TII = MF.getTarget().getInstrInfo();
MRI = &MF.getRegInfo();
}
MachineSSAUpdater::~MachineSSAUpdater() {
delete static_cast<AvailableValsTy*>(AV);
}
/// Initialize - Reset this object to get ready for a new set of SSA
/// updates. ProtoValue is the value used to name PHI nodes.
void MachineSSAUpdater::Initialize(unsigned V) {
if (AV == 0)
AV = new AvailableValsTy();
else
getAvailableVals(AV).clear();
VR = V;
VRC = MRI->getRegClass(VR);
}
/// HasValueForBlock - Return true if the MachineSSAUpdater already has a value for
/// the specified block.
bool MachineSSAUpdater::HasValueForBlock(MachineBasicBlock *BB) const {
return getAvailableVals(AV).count(BB);
}
/// AddAvailableValue - Indicate that a rewritten value is available in the
/// specified block with the specified value.
void MachineSSAUpdater::AddAvailableValue(MachineBasicBlock *BB, unsigned V) {
getAvailableVals(AV)[BB] = V;
}
/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
/// live at the end of the specified block.
unsigned MachineSSAUpdater::GetValueAtEndOfBlock(MachineBasicBlock *BB) {
return GetValueAtEndOfBlockInternal(BB);
}
static
unsigned LookForIdenticalPHI(MachineBasicBlock *BB,
SmallVector<std::pair<MachineBasicBlock*, unsigned>, 8> &PredValues) {
if (BB->empty())
return 0;
MachineBasicBlock::iterator I = BB->front();
if (!I->isPHI())
return 0;
AvailableValsTy AVals;
for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
AVals[PredValues[i].first] = PredValues[i].second;
while (I != BB->end() && I->isPHI()) {
bool Same = true;
for (unsigned i = 1, e = I->getNumOperands(); i != e; i += 2) {
unsigned SrcReg = I->getOperand(i).getReg();
MachineBasicBlock *SrcBB = I->getOperand(i+1).getMBB();
if (AVals[SrcBB] != SrcReg) {
Same = false;
break;
}
}
if (Same)
return I->getOperand(0).getReg();
++I;
}
return 0;
}
/// InsertNewDef - Insert an empty PHI or IMPLICIT_DEF instruction which define
/// a value of the given register class at the start of the specified basic
/// block. It returns the virtual register defined by the instruction.
static
MachineInstr *InsertNewDef(unsigned Opcode,
MachineBasicBlock *BB, MachineBasicBlock::iterator I,
const TargetRegisterClass *RC,
MachineRegisterInfo *MRI,
const TargetInstrInfo *TII) {
unsigned NewVR = MRI->createVirtualRegister(RC);
return BuildMI(*BB, I, DebugLoc(), TII->get(Opcode), NewVR);
}
/// 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.
///
unsigned MachineSSAUpdater::GetValueInMiddleOfBlock(MachineBasicBlock *BB) {
// If there is no definition of the renamed variable in this block, just use
// GetValueAtEndOfBlock to do our work.
if (!HasValueForBlock(BB))
return GetValueAtEndOfBlockInternal(BB);
// If there are no predecessors, just return undef.
if (BB->pred_empty()) {
// Insert an implicit_def to represent an undef value.
MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
BB, BB->getFirstTerminator(),
VRC, MRI, TII);
return NewDef->getOperand(0).getReg();
}
// Otherwise, we have the hard case. Get the live-in values for each
// predecessor.
SmallVector<std::pair<MachineBasicBlock*, unsigned>, 8> PredValues;
unsigned SingularValue = 0;
bool isFirstPred = true;
for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
E = BB->pred_end(); PI != E; ++PI) {
MachineBasicBlock *PredBB = *PI;
unsigned PredVal = GetValueAtEndOfBlockInternal(PredBB);
PredValues.push_back(std::make_pair(PredBB, PredVal));
// Compute SingularValue.
if (isFirstPred) {
SingularValue = PredVal;
isFirstPred = false;
} else if (PredVal != SingularValue)
SingularValue = 0;
}
// Otherwise, if all the merged values are the same, just use it.
if (SingularValue != 0)
return SingularValue;
// If an identical PHI is already in BB, just reuse it.
unsigned DupPHI = LookForIdenticalPHI(BB, PredValues);
if (DupPHI)
return DupPHI;
// Otherwise, we do need a PHI: insert one now.
MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->front();
MachineInstr *InsertedPHI = InsertNewDef(TargetOpcode::PHI, BB,
Loc, VRC, MRI, TII);
// Fill in all the predecessors of the PHI.
MachineInstrBuilder MIB(InsertedPHI);
for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
MIB.addReg(PredValues[i].second).addMBB(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 (unsigned ConstVal = InsertedPHI->isConstantValuePHI()) {
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->getOperand(0).getReg();
}
static
MachineBasicBlock *findCorrespondingPred(const MachineInstr *MI,
MachineOperand *U) {
for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
if (&MI->getOperand(i) == U)
return MI->getOperand(i+1).getMBB();
}
llvm_unreachable("MachineOperand::getParent() failure?");
return 0;
}
/// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
/// which use their value in the corresponding predecessor.
void MachineSSAUpdater::RewriteUse(MachineOperand &U) {
MachineInstr *UseMI = U.getParent();
unsigned NewVR = 0;
if (UseMI->isPHI()) {
MachineBasicBlock *SourceBB = findCorrespondingPred(UseMI, &U);
NewVR = GetValueAtEndOfBlockInternal(SourceBB);
} else {
NewVR = GetValueInMiddleOfBlock(UseMI->getParent());
}
U.setReg(NewVR);
}
void MachineSSAUpdater::ReplaceRegWith(unsigned OldReg, unsigned NewReg) {
MRI->replaceRegWith(OldReg, NewReg);
AvailableValsTy &AvailableVals = getAvailableVals(AV);
for (DenseMap<MachineBasicBlock*, unsigned>::iterator
I = AvailableVals.begin(), E = AvailableVals.end(); I != E; ++I)
if (I->second == OldReg)
I->second = NewReg;
}
/// MachinePHIiter - Iterator for PHI operands. This is used for the
/// PHI_iterator in the SSAUpdaterImpl template.
namespace {
class MachinePHIiter {
private:
MachineInstr *PHI;
unsigned idx;
public:
explicit MachinePHIiter(MachineInstr *P) // begin iterator
: PHI(P), idx(1) {}
MachinePHIiter(MachineInstr *P, bool) // end iterator
: PHI(P), idx(PHI->getNumOperands()) {}
MachinePHIiter &operator++() { idx += 2; return *this; }
bool operator==(const MachinePHIiter& x) const { return idx == x.idx; }
bool operator!=(const MachinePHIiter& x) const { return !operator==(x); }
unsigned getIncomingValue() { return PHI->getOperand(idx).getReg(); }
MachineBasicBlock *getIncomingBlock() {
return PHI->getOperand(idx+1).getMBB();
}
};
}
/// SSAUpdaterTraits<MachineSSAUpdater> - Traits for the SSAUpdaterImpl
/// template, specialized for MachineSSAUpdater.
namespace llvm {
template<>
class SSAUpdaterTraits<MachineSSAUpdater> {
public:
typedef MachineBasicBlock BlkT;
typedef unsigned ValT;
typedef MachineInstr PhiT;
typedef MachineBasicBlock::succ_iterator BlkSucc_iterator;
static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return BB->succ_begin(); }
static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return BB->succ_end(); }
typedef MachinePHIiter 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 BB into the Preds
/// vector.
static void FindPredecessorBlocks(MachineBasicBlock *BB,
SmallVectorImpl<MachineBasicBlock*> *Preds){
for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
E = BB->pred_end(); PI != E; ++PI)
Preds->push_back(*PI);
}
/// GetUndefVal - Create an IMPLICIT_DEF instruction with a new register.
/// Add it into the specified block and return the register.
static unsigned GetUndefVal(MachineBasicBlock *BB,
MachineSSAUpdater *Updater) {
// Insert an implicit_def to represent an undef value.
MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
BB, BB->getFirstTerminator(),
Updater->VRC, Updater->MRI,
Updater->TII);
return NewDef->getOperand(0).getReg();
}
/// CreateEmptyPHI - Create a PHI instruction that defines a new register.
/// Add it into the specified block and return the register.
static unsigned CreateEmptyPHI(MachineBasicBlock *BB, unsigned NumPreds,
MachineSSAUpdater *Updater) {
MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->front();
MachineInstr *PHI = InsertNewDef(TargetOpcode::PHI, BB, Loc,
Updater->VRC, Updater->MRI,
Updater->TII);
return PHI->getOperand(0).getReg();
}
/// AddPHIOperand - Add the specified value as an operand of the PHI for
/// the specified predecessor block.
static void AddPHIOperand(MachineInstr *PHI, unsigned Val,
MachineBasicBlock *Pred) {
PHI->addOperand(MachineOperand::CreateReg(Val, false));
PHI->addOperand(MachineOperand::CreateMBB(Pred));
}
/// InstrIsPHI - Check if an instruction is a PHI.
///
static MachineInstr *InstrIsPHI(MachineInstr *I) {
if (I && I->isPHI())
return I;
return 0;
}
/// ValueIsPHI - Check if the instruction that defines the specified register
/// is a PHI instruction.
static MachineInstr *ValueIsPHI(unsigned Val, MachineSSAUpdater *Updater) {
return InstrIsPHI(Updater->MRI->getVRegDef(Val));
}
/// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
/// operands, i.e., it was just added.
static MachineInstr *ValueIsNewPHI(unsigned Val, MachineSSAUpdater *Updater) {
MachineInstr *PHI = ValueIsPHI(Val, Updater);
if (PHI && PHI->getNumOperands() <= 1)
return PHI;
return 0;
}
/// GetPHIValue - For the specified PHI instruction, return the register
/// that it defines.
static unsigned GetPHIValue(MachineInstr *PHI) {
return PHI->getOperand(0).getReg();
}
};
} // 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.
unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
AvailableValsTy &AvailableVals = getAvailableVals(AV);
if (unsigned V = AvailableVals[BB])
return V;
SSAUpdaterImpl<MachineSSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
return Impl.GetValue(BB);
}