forked from OSchip/llvm-project
394 lines
15 KiB
C++
394 lines
15 KiB
C++
//===- MachineSSAUpdater.cpp - Unstructured SSA Update Tool ---------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the MachineSSAUpdater class. It's based on SSAUpdater
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// class in lib/Transforms/Utils.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/MachineSSAUpdater.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Target/TargetRegisterInfo.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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typedef DenseMap<MachineBasicBlock*, unsigned> AvailableValsTy;
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typedef std::vector<std::pair<MachineBasicBlock*, unsigned> >
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IncomingPredInfoTy;
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static AvailableValsTy &getAvailableVals(void *AV) {
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return *static_cast<AvailableValsTy*>(AV);
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}
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static IncomingPredInfoTy &getIncomingPredInfo(void *IPI) {
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return *static_cast<IncomingPredInfoTy*>(IPI);
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}
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MachineSSAUpdater::MachineSSAUpdater(MachineFunction &MF,
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SmallVectorImpl<MachineInstr*> *NewPHI)
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: AV(0), IPI(0), InsertedPHIs(NewPHI) {
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TII = MF.getTarget().getInstrInfo();
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MRI = &MF.getRegInfo();
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}
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MachineSSAUpdater::~MachineSSAUpdater() {
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delete &getAvailableVals(AV);
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delete &getIncomingPredInfo(IPI);
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}
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/// Initialize - Reset this object to get ready for a new set of SSA
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/// updates. ProtoValue is the value used to name PHI nodes.
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void MachineSSAUpdater::Initialize(unsigned V) {
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if (AV == 0)
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AV = new AvailableValsTy();
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else
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getAvailableVals(AV).clear();
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if (IPI == 0)
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IPI = new IncomingPredInfoTy();
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else
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getIncomingPredInfo(IPI).clear();
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VR = V;
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VRC = MRI->getRegClass(VR);
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}
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/// HasValueForBlock - Return true if the MachineSSAUpdater already has a value for
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/// the specified block.
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bool MachineSSAUpdater::HasValueForBlock(MachineBasicBlock *BB) const {
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return getAvailableVals(AV).count(BB);
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}
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/// AddAvailableValue - Indicate that a rewritten value is available in the
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/// specified block with the specified value.
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void MachineSSAUpdater::AddAvailableValue(MachineBasicBlock *BB, unsigned V) {
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getAvailableVals(AV)[BB] = V;
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}
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/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
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/// live at the end of the specified block.
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unsigned MachineSSAUpdater::GetValueAtEndOfBlock(MachineBasicBlock *BB) {
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return GetValueAtEndOfBlockInternal(BB);
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}
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static
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unsigned LookForIdenticalPHI(MachineBasicBlock *BB,
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SmallVector<std::pair<MachineBasicBlock*, unsigned>, 8> &PredValues) {
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if (BB->empty())
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return 0;
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MachineBasicBlock::iterator I = BB->front();
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if (I->getOpcode() != TargetInstrInfo::PHI)
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return 0;
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AvailableValsTy AVals;
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for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
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AVals[PredValues[i].first] = PredValues[i].second;
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while (I != BB->end() && I->getOpcode() == TargetInstrInfo::PHI) {
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bool Same = true;
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for (unsigned i = 1, e = I->getNumOperands(); i != e; i += 2) {
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unsigned SrcReg = I->getOperand(i).getReg();
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MachineBasicBlock *SrcBB = I->getOperand(i+1).getMBB();
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if (AVals[SrcBB] != SrcReg) {
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Same = false;
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break;
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}
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}
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if (Same)
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return I->getOperand(0).getReg();
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++I;
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}
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return 0;
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}
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/// InsertNewDef - Insert an empty PHI or IMPLICIT_DEF instruction which define
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/// a value of the given register class at the start of the specified basic
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/// block. It returns the virtual register defined by the instruction.
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static
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MachineInstr *InsertNewDef(unsigned Opcode,
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MachineBasicBlock *BB, MachineBasicBlock::iterator I,
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const TargetRegisterClass *RC,
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MachineRegisterInfo *MRI, const TargetInstrInfo *TII) {
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unsigned NewVR = MRI->createVirtualRegister(RC);
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return BuildMI(*BB, I, DebugLoc::getUnknownLoc(), TII->get(Opcode), NewVR);
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}
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/// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
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/// is live in the middle of the specified block.
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///
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/// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
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/// important case: if there is a definition of the rewritten value after the
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/// 'use' in BB. Consider code like this:
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///
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/// X1 = ...
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/// SomeBB:
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/// use(X)
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/// X2 = ...
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/// br Cond, SomeBB, OutBB
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///
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/// In this case, there are two values (X1 and X2) added to the AvailableVals
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/// set by the client of the rewriter, and those values are both live out of
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/// their respective blocks. However, the use of X happens in the *middle* of
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/// a block. Because of this, we need to insert a new PHI node in SomeBB to
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/// merge the appropriate values, and this value isn't live out of the block.
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///
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unsigned MachineSSAUpdater::GetValueInMiddleOfBlock(MachineBasicBlock *BB) {
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// If there is no definition of the renamed variable in this block, just use
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// GetValueAtEndOfBlock to do our work.
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if (!getAvailableVals(AV).count(BB))
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return GetValueAtEndOfBlockInternal(BB);
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// If there are no predecessors, just return undef.
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if (BB->pred_empty()) {
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// Insert an implicit_def to represent an undef value.
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MachineInstr *NewDef = InsertNewDef(TargetInstrInfo::IMPLICIT_DEF,
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BB, BB->getFirstTerminator(),
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VRC, MRI, TII);
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return NewDef->getOperand(0).getReg();
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}
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// Otherwise, we have the hard case. Get the live-in values for each
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// predecessor.
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SmallVector<std::pair<MachineBasicBlock*, unsigned>, 8> PredValues;
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unsigned SingularValue = 0;
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bool isFirstPred = true;
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for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
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E = BB->pred_end(); PI != E; ++PI) {
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MachineBasicBlock *PredBB = *PI;
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unsigned PredVal = GetValueAtEndOfBlockInternal(PredBB);
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PredValues.push_back(std::make_pair(PredBB, PredVal));
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// Compute SingularValue.
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if (isFirstPred) {
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SingularValue = PredVal;
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isFirstPred = false;
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} else if (PredVal != SingularValue)
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SingularValue = 0;
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}
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// Otherwise, if all the merged values are the same, just use it.
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if (SingularValue != 0)
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return SingularValue;
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// If an identical PHI is already in BB, just reuse it.
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unsigned DupPHI = LookForIdenticalPHI(BB, PredValues);
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if (DupPHI)
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return DupPHI;
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// Otherwise, we do need a PHI: insert one now.
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MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->front();
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MachineInstr *InsertedPHI = InsertNewDef(TargetInstrInfo::PHI, BB,
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Loc, VRC, MRI, TII);
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// Fill in all the predecessors of the PHI.
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MachineInstrBuilder MIB(InsertedPHI);
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for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
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MIB.addReg(PredValues[i].second).addMBB(PredValues[i].first);
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// See if the PHI node can be merged to a single value. This can happen in
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// loop cases when we get a PHI of itself and one other value.
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if (unsigned ConstVal = InsertedPHI->isConstantValuePHI()) {
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InsertedPHI->eraseFromParent();
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return ConstVal;
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}
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// If the client wants to know about all new instructions, tell it.
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if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
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DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
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return InsertedPHI->getOperand(0).getReg();
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}
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static
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MachineBasicBlock *findCorrespondingPred(const MachineInstr *MI,
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MachineOperand *U) {
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for (unsigned i = 1, e = MI->getNumOperands(); i != e; i += 2) {
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if (&MI->getOperand(i) == U)
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return MI->getOperand(i+1).getMBB();
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}
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llvm_unreachable("MachineOperand::getParent() failure?");
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return 0;
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}
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/// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
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/// which use their value in the corresponding predecessor.
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void MachineSSAUpdater::RewriteUse(MachineOperand &U) {
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MachineInstr *UseMI = U.getParent();
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unsigned NewVR = 0;
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if (UseMI->getOpcode() == TargetInstrInfo::PHI) {
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MachineBasicBlock *SourceBB = findCorrespondingPred(UseMI, &U);
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NewVR = GetValueAtEndOfBlockInternal(SourceBB);
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} else {
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NewVR = GetValueInMiddleOfBlock(UseMI->getParent());
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}
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U.setReg(NewVR);
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}
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void MachineSSAUpdater::ReplaceRegWith(unsigned OldReg, unsigned NewReg) {
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MRI->replaceRegWith(OldReg, NewReg);
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AvailableValsTy &AvailableVals = getAvailableVals(AV);
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for (DenseMap<MachineBasicBlock*, unsigned>::iterator
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I = AvailableVals.begin(), E = AvailableVals.end(); I != E; ++I)
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if (I->second == OldReg)
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I->second = NewReg;
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}
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/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
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/// for the specified BB and if so, return it. If not, construct SSA form by
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/// walking predecessors inserting PHI nodes as needed until we get to a block
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/// where the value is available.
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///
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unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
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AvailableValsTy &AvailableVals = getAvailableVals(AV);
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// Query AvailableVals by doing an insertion of null.
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std::pair<AvailableValsTy::iterator, bool> InsertRes =
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AvailableVals.insert(std::make_pair(BB, 0));
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// Handle the case when the insertion fails because we have already seen BB.
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if (!InsertRes.second) {
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// If the insertion failed, there are two cases. The first case is that the
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// value is already available for the specified block. If we get this, just
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// return the value.
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if (InsertRes.first->second != 0)
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return InsertRes.first->second;
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// Otherwise, if the value we find is null, then this is the value is not
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// known but it is being computed elsewhere in our recursion. This means
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// that we have a cycle. Handle this by inserting a PHI node and returning
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// it. When we get back to the first instance of the recursion we will fill
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// in the PHI node.
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MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->front();
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MachineInstr *NewPHI = InsertNewDef(TargetInstrInfo::PHI, BB, Loc,
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VRC, MRI,TII);
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unsigned NewVR = NewPHI->getOperand(0).getReg();
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InsertRes.first->second = NewVR;
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return NewVR;
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}
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// If there are no predecessors, then we must have found an unreachable block
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// just return 'undef'. Since there are no predecessors, InsertRes must not
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// be invalidated.
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if (BB->pred_empty()) {
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// Insert an implicit_def to represent an undef value.
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MachineInstr *NewDef = InsertNewDef(TargetInstrInfo::IMPLICIT_DEF,
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BB, BB->getFirstTerminator(),
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VRC, MRI, TII);
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return InsertRes.first->second = NewDef->getOperand(0).getReg();
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}
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// Okay, the value isn't in the map and we just inserted a null in the entry
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// to indicate that we're processing the block. Since we have no idea what
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// value is in this block, we have to recurse through our predecessors.
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//
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// While we're walking our predecessors, we keep track of them in a vector,
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// then insert a PHI node in the end if we actually need one. We could use a
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// smallvector here, but that would take a lot of stack space for every level
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// of the recursion, just use IncomingPredInfo as an explicit stack.
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IncomingPredInfoTy &IncomingPredInfo = getIncomingPredInfo(IPI);
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unsigned FirstPredInfoEntry = IncomingPredInfo.size();
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// As we're walking the predecessors, keep track of whether they are all
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// producing the same value. If so, this value will capture it, if not, it
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// will get reset to null. We distinguish the no-predecessor case explicitly
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// below.
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unsigned SingularValue = 0;
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bool isFirstPred = true;
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for (MachineBasicBlock::pred_iterator PI = BB->pred_begin(),
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E = BB->pred_end(); PI != E; ++PI) {
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MachineBasicBlock *PredBB = *PI;
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unsigned PredVal = GetValueAtEndOfBlockInternal(PredBB);
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IncomingPredInfo.push_back(std::make_pair(PredBB, PredVal));
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// Compute SingularValue.
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if (isFirstPred) {
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SingularValue = PredVal;
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isFirstPred = false;
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} else if (PredVal != SingularValue)
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SingularValue = 0;
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}
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/// Look up BB's entry in AvailableVals. 'InsertRes' may be invalidated. If
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/// this block is involved in a loop, a no-entry PHI node will have been
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/// inserted as InsertedVal. Otherwise, we'll still have the null we inserted
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/// above.
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unsigned &InsertedVal = AvailableVals[BB];
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// If all the predecessor values are the same then we don't need to insert a
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// PHI. This is the simple and common case.
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if (SingularValue) {
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// If a PHI node got inserted, replace it with the singlar value and delete
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// it.
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if (InsertedVal) {
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MachineInstr *OldVal = MRI->getVRegDef(InsertedVal);
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// Be careful about dead loops. These RAUW's also update InsertedVal.
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assert(InsertedVal != SingularValue && "Dead loop?");
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ReplaceRegWith(InsertedVal, SingularValue);
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OldVal->eraseFromParent();
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}
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InsertedVal = SingularValue;
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// Drop the entries we added in IncomingPredInfo to restore the stack.
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IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
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IncomingPredInfo.end());
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return InsertedVal;
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}
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// Otherwise, we do need a PHI: insert one now if we don't already have one.
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MachineInstr *InsertedPHI;
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if (InsertedVal == 0) {
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MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->front();
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InsertedPHI = InsertNewDef(TargetInstrInfo::PHI, BB, Loc,
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VRC, MRI, TII);
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InsertedVal = InsertedPHI->getOperand(0).getReg();
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} else {
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InsertedPHI = MRI->getVRegDef(InsertedVal);
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}
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// Fill in all the predecessors of the PHI.
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MachineInstrBuilder MIB(InsertedPHI);
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for (IncomingPredInfoTy::iterator I =
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IncomingPredInfo.begin()+FirstPredInfoEntry,
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E = IncomingPredInfo.end(); I != E; ++I)
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MIB.addReg(I->second).addMBB(I->first);
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// Drop the entries we added in IncomingPredInfo to restore the stack.
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IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
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IncomingPredInfo.end());
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// See if the PHI node can be merged to a single value. This can happen in
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// loop cases when we get a PHI of itself and one other value.
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if (unsigned ConstVal = InsertedPHI->isConstantValuePHI()) {
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MRI->replaceRegWith(InsertedVal, ConstVal);
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InsertedPHI->eraseFromParent();
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InsertedVal = ConstVal;
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} else {
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DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
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// If the client wants to know about all new instructions, tell it.
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if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
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}
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return InsertedVal;
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}
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