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shorter/easier and have the DAG use that to do the same lookup. This can be used in the future for TargetMachine based caching lookups from the MachineFunction easily. Update the MIPS subtarget switching machinery to update this pointer at the same time it runs. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214838 91177308-0d34-0410-b5e6-96231b3b80d8
358 lines
13 KiB
C++
358 lines
13 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/ADT/DenseMap.h"
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#include "llvm/ADT/SmallVector.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/Support/AlignOf.h"
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#include "llvm/Support/Allocator.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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#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/Target/TargetSubtargetInfo.h"
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#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
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using namespace llvm;
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#define DEBUG_TYPE "machine-ssaupdater"
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typedef DenseMap<MachineBasicBlock*, unsigned> AvailableValsTy;
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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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MachineSSAUpdater::MachineSSAUpdater(MachineFunction &MF,
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SmallVectorImpl<MachineInstr*> *NewPHI)
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: AV(nullptr), InsertedPHIs(NewPHI) {
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TII = MF.getSubtarget().getInstrInfo();
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MRI = &MF.getRegInfo();
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}
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MachineSSAUpdater::~MachineSSAUpdater() {
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delete static_cast<AvailableValsTy*>(AV);
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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)
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AV = new AvailableValsTy();
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else
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getAvailableVals(AV).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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SmallVectorImpl<std::pair<MachineBasicBlock*, unsigned> > &PredValues) {
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if (BB->empty())
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return 0;
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MachineBasicBlock::iterator I = BB->begin();
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if (!I->isPHI())
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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->isPHI()) {
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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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MachineInstrBuilder 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,
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const TargetInstrInfo *TII) {
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unsigned NewVR = MRI->createVirtualRegister(RC);
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return BuildMI(*BB, I, DebugLoc(), 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 (!HasValueForBlock(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(TargetOpcode::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->begin();
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MachineInstrBuilder InsertedPHI = InsertNewDef(TargetOpcode::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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for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
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InsertedPHI.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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}
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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->isPHI()) {
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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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/// SSAUpdaterTraits<MachineSSAUpdater> - Traits for the SSAUpdaterImpl
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/// template, specialized for MachineSSAUpdater.
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namespace llvm {
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template<>
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class SSAUpdaterTraits<MachineSSAUpdater> {
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public:
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typedef MachineBasicBlock BlkT;
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typedef unsigned ValT;
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typedef MachineInstr PhiT;
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typedef MachineBasicBlock::succ_iterator BlkSucc_iterator;
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static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return BB->succ_begin(); }
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static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return BB->succ_end(); }
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/// Iterator for PHI operands.
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class PHI_iterator {
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private:
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MachineInstr *PHI;
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unsigned idx;
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public:
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explicit PHI_iterator(MachineInstr *P) // begin iterator
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: PHI(P), idx(1) {}
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PHI_iterator(MachineInstr *P, bool) // end iterator
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: PHI(P), idx(PHI->getNumOperands()) {}
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PHI_iterator &operator++() { idx += 2; return *this; }
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bool operator==(const PHI_iterator& x) const { return idx == x.idx; }
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bool operator!=(const PHI_iterator& x) const { return !operator==(x); }
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unsigned getIncomingValue() { return PHI->getOperand(idx).getReg(); }
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MachineBasicBlock *getIncomingBlock() {
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return PHI->getOperand(idx+1).getMBB();
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}
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};
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static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
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static inline PHI_iterator PHI_end(PhiT *PHI) {
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return PHI_iterator(PHI, true);
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}
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/// FindPredecessorBlocks - Put the predecessors of BB into the Preds
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/// vector.
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static void FindPredecessorBlocks(MachineBasicBlock *BB,
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SmallVectorImpl<MachineBasicBlock*> *Preds){
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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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Preds->push_back(*PI);
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}
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/// GetUndefVal - Create an IMPLICIT_DEF instruction with a new register.
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/// Add it into the specified block and return the register.
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static unsigned GetUndefVal(MachineBasicBlock *BB,
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MachineSSAUpdater *Updater) {
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// Insert an implicit_def to represent an undef value.
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MachineInstr *NewDef = InsertNewDef(TargetOpcode::IMPLICIT_DEF,
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BB, BB->getFirstTerminator(),
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Updater->VRC, Updater->MRI,
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Updater->TII);
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return NewDef->getOperand(0).getReg();
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}
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/// CreateEmptyPHI - Create a PHI instruction that defines a new register.
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/// Add it into the specified block and return the register.
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static unsigned CreateEmptyPHI(MachineBasicBlock *BB, unsigned NumPreds,
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MachineSSAUpdater *Updater) {
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MachineBasicBlock::iterator Loc = BB->empty() ? BB->end() : BB->begin();
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MachineInstr *PHI = InsertNewDef(TargetOpcode::PHI, BB, Loc,
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Updater->VRC, Updater->MRI,
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Updater->TII);
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return PHI->getOperand(0).getReg();
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}
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/// AddPHIOperand - Add the specified value as an operand of the PHI for
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/// the specified predecessor block.
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static void AddPHIOperand(MachineInstr *PHI, unsigned Val,
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MachineBasicBlock *Pred) {
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MachineInstrBuilder(*Pred->getParent(), PHI).addReg(Val).addMBB(Pred);
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}
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/// InstrIsPHI - Check if an instruction is a PHI.
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///
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static MachineInstr *InstrIsPHI(MachineInstr *I) {
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if (I && I->isPHI())
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return I;
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return nullptr;
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}
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/// ValueIsPHI - Check if the instruction that defines the specified register
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/// is a PHI instruction.
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static MachineInstr *ValueIsPHI(unsigned Val, MachineSSAUpdater *Updater) {
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return InstrIsPHI(Updater->MRI->getVRegDef(Val));
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}
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/// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
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/// operands, i.e., it was just added.
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static MachineInstr *ValueIsNewPHI(unsigned Val, MachineSSAUpdater *Updater) {
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MachineInstr *PHI = ValueIsPHI(Val, Updater);
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if (PHI && PHI->getNumOperands() <= 1)
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return PHI;
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return nullptr;
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}
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/// GetPHIValue - For the specified PHI instruction, return the register
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/// that it defines.
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static unsigned GetPHIValue(MachineInstr *PHI) {
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return PHI->getOperand(0).getReg();
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}
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};
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} // End llvm namespace
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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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/// first calculating the required placement of PHIs and then inserting new
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/// PHIs where needed.
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unsigned MachineSSAUpdater::GetValueAtEndOfBlockInternal(MachineBasicBlock *BB){
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AvailableValsTy &AvailableVals = getAvailableVals(AV);
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if (unsigned V = AvailableVals[BB])
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return V;
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SSAUpdaterImpl<MachineSSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
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return Impl.GetValue(BB);
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}
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