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llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
Evan Cheng 9193514e2e Re-materialize all loads from fixed stack slots. 
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35660 91177308-0d34-0410-b5e6-96231b3b80d8
2007-04-04 07:40:01 +00:00

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//===-- LiveIntervalAnalysis.cpp - Live Interval Analysis -----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the LiveInterval analysis pass which is used
// by the Linear Scan Register allocator. This pass linearizes the
// basic blocks of the function in DFS order and uses the
// LiveVariables pass to conservatively compute live intervals for
// each virtual and physical register.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "liveintervals"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "VirtRegMap.h"
#include "llvm/Value.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/SSARegMap.h"
#include "llvm/Target/MRegisterInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include <algorithm>
#include <cmath>
using namespace llvm;
STATISTIC(numIntervals, "Number of original intervals");
STATISTIC(numIntervalsAfter, "Number of intervals after coalescing");
STATISTIC(numJoins , "Number of interval joins performed");
STATISTIC(numPeep , "Number of identity moves eliminated after coalescing");
STATISTIC(numFolded , "Number of loads/stores folded into instructions");
STATISTIC(numAborts , "Number of times interval joining aborted");
namespace {
RegisterPass<LiveIntervals> X("liveintervals", "Live Interval Analysis");
static cl::opt<bool>
EnableJoining("join-liveintervals",
cl::desc("Coallesce copies (default=true)"),
cl::init(true));
}
void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LiveVariables>();
AU.addPreservedID(PHIEliminationID);
AU.addRequiredID(PHIEliminationID);
AU.addRequiredID(TwoAddressInstructionPassID);
AU.addRequired<LoopInfo>();
MachineFunctionPass::getAnalysisUsage(AU);
}
void LiveIntervals::releaseMemory() {
mi2iMap_.clear();
i2miMap_.clear();
r2iMap_.clear();
r2rMap_.clear();
JoinedLIs.clear();
}
static bool isZeroLengthInterval(LiveInterval *li) {
for (LiveInterval::Ranges::const_iterator
i = li->ranges.begin(), e = li->ranges.end(); i != e; ++i)
if (i->end - i->start > LiveIntervals::InstrSlots::NUM)
return false;
return true;
}
/// runOnMachineFunction - Register allocate the whole function
///
bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
mf_ = &fn;
tm_ = &fn.getTarget();
mri_ = tm_->getRegisterInfo();
tii_ = tm_->getInstrInfo();
lv_ = &getAnalysis<LiveVariables>();
allocatableRegs_ = mri_->getAllocatableSet(fn);
r2rMap_.grow(mf_->getSSARegMap()->getLastVirtReg());
// Number MachineInstrs and MachineBasicBlocks.
// Initialize MBB indexes to a sentinal.
MBB2IdxMap.resize(mf_->getNumBlockIDs(), ~0U);
unsigned MIIndex = 0;
for (MachineFunction::iterator MBB = mf_->begin(), E = mf_->end();
MBB != E; ++MBB) {
// Set the MBB2IdxMap entry for this MBB.
MBB2IdxMap[MBB->getNumber()] = MIIndex;
for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end();
I != E; ++I) {
bool inserted = mi2iMap_.insert(std::make_pair(I, MIIndex)).second;
assert(inserted && "multiple MachineInstr -> index mappings");
i2miMap_.push_back(I);
MIIndex += InstrSlots::NUM;
}
}
computeIntervals();
numIntervals += getNumIntervals();
DOUT << "********** INTERVALS **********\n";
for (iterator I = begin(), E = end(); I != E; ++I) {
I->second.print(DOUT, mri_);
DOUT << "\n";
}
// Join (coallesce) intervals if requested.
if (EnableJoining) joinIntervals();
numIntervalsAfter += getNumIntervals();
// perform a final pass over the instructions and compute spill
// weights, coalesce virtual registers and remove identity moves.
const LoopInfo &loopInfo = getAnalysis<LoopInfo>();
for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
mbbi != mbbe; ++mbbi) {
MachineBasicBlock* mbb = mbbi;
unsigned loopDepth = loopInfo.getLoopDepth(mbb->getBasicBlock());
for (MachineBasicBlock::iterator mii = mbb->begin(), mie = mbb->end();
mii != mie; ) {
// if the move will be an identity move delete it
unsigned srcReg, dstReg, RegRep;
if (tii_->isMoveInstr(*mii, srcReg, dstReg) &&
(RegRep = rep(srcReg)) == rep(dstReg)) {
// remove from def list
LiveInterval &RegInt = getOrCreateInterval(RegRep);
MachineOperand *MO = mii->findRegisterDefOperand(dstReg);
// If def of this move instruction is dead, remove its live range from
// the dstination register's live interval.
if (MO->isDead()) {
unsigned MoveIdx = getDefIndex(getInstructionIndex(mii));
LiveInterval::iterator MLR = RegInt.FindLiveRangeContaining(MoveIdx);
RegInt.removeRange(MLR->start, MoveIdx+1);
if (RegInt.empty())
removeInterval(RegRep);
}
RemoveMachineInstrFromMaps(mii);
mii = mbbi->erase(mii);
++numPeep;
} else {
for (unsigned i = 0, e = mii->getNumOperands(); i != e; ++i) {
const MachineOperand &mop = mii->getOperand(i);
if (mop.isRegister() && mop.getReg() &&
MRegisterInfo::isVirtualRegister(mop.getReg())) {
// replace register with representative register
unsigned reg = rep(mop.getReg());
mii->getOperand(i).setReg(reg);
LiveInterval &RegInt = getInterval(reg);
float w = (mop.isUse()+mop.isDef()) * powf(10.0F, (float)loopDepth);
// If the definition instruction is re-materializable, its spill
// weight is half of what it would have been normally unless it's
// a load from fixed stack slot.
int Dummy;
if (RegInt.remat && !tii_->isLoadFromStackSlot(RegInt.remat, Dummy))
w /= 2;
RegInt.weight += w;
}
}
++mii;
}
}
}
for (iterator I = begin(), E = end(); I != E; ++I) {
LiveInterval &LI = I->second;
if (MRegisterInfo::isVirtualRegister(LI.reg)) {
// If the live interval length is essentially zero, i.e. in every live
// range the use follows def immediately, it doesn't make sense to spill
// it and hope it will be easier to allocate for this li.
if (isZeroLengthInterval(&LI))
LI.weight = HUGE_VALF;
// Divide the weight of the interval by its size. This encourages
// spilling of intervals that are large and have few uses, and
// discourages spilling of small intervals with many uses.
unsigned Size = 0;
for (LiveInterval::iterator II = LI.begin(), E = LI.end(); II != E;++II)
Size += II->end - II->start;
LI.weight /= Size;
}
}
DEBUG(dump());
return true;
}
/// print - Implement the dump method.
void LiveIntervals::print(std::ostream &O, const Module* ) const {
O << "********** INTERVALS **********\n";
for (const_iterator I = begin(), E = end(); I != E; ++I) {
I->second.print(DOUT, mri_);
DOUT << "\n";
}
O << "********** MACHINEINSTRS **********\n";
for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
mbbi != mbbe; ++mbbi) {
O << ((Value*)mbbi->getBasicBlock())->getName() << ":\n";
for (MachineBasicBlock::iterator mii = mbbi->begin(),
mie = mbbi->end(); mii != mie; ++mii) {
O << getInstructionIndex(mii) << '\t' << *mii;
}
}
}
/// CreateNewLiveInterval - Create a new live interval with the given live
/// ranges. The new live interval will have an infinite spill weight.
LiveInterval&
LiveIntervals::CreateNewLiveInterval(const LiveInterval *LI,
const std::vector<LiveRange> &LRs) {
const TargetRegisterClass *RC = mf_->getSSARegMap()->getRegClass(LI->reg);
// Create a new virtual register for the spill interval.
unsigned NewVReg = mf_->getSSARegMap()->createVirtualRegister(RC);
// Replace the old virtual registers in the machine operands with the shiny
// new one.
for (std::vector<LiveRange>::const_iterator
I = LRs.begin(), E = LRs.end(); I != E; ++I) {
unsigned Index = getBaseIndex(I->start);
unsigned End = getBaseIndex(I->end - 1) + InstrSlots::NUM;
for (; Index != End; Index += InstrSlots::NUM) {
// Skip deleted instructions
while (Index != End && !getInstructionFromIndex(Index))
Index += InstrSlots::NUM;
if (Index == End) break;
MachineInstr *MI = getInstructionFromIndex(Index);
for (unsigned J = 0, e = MI->getNumOperands(); J != e; ++J) {
MachineOperand &MOp = MI->getOperand(J);
if (MOp.isRegister() && rep(MOp.getReg()) == LI->reg)
MOp.setReg(NewVReg);
}
}
}
LiveInterval &NewLI = getOrCreateInterval(NewVReg);
// The spill weight is now infinity as it cannot be spilled again
NewLI.weight = float(HUGE_VAL);
for (std::vector<LiveRange>::const_iterator
I = LRs.begin(), E = LRs.end(); I != E; ++I) {
DOUT << " Adding live range " << *I << " to new interval\n";
NewLI.addRange(*I);
}
DOUT << "Created new live interval " << NewLI << "\n";
return NewLI;
}
std::vector<LiveInterval*> LiveIntervals::
addIntervalsForSpills(const LiveInterval &li, VirtRegMap &vrm, int slot) {
// since this is called after the analysis is done we don't know if
// LiveVariables is available
lv_ = getAnalysisToUpdate<LiveVariables>();
std::vector<LiveInterval*> added;
assert(li.weight != HUGE_VALF &&
"attempt to spill already spilled interval!");
DOUT << "\t\t\t\tadding intervals for spills for interval: ";
li.print(DOUT, mri_);
DOUT << '\n';
const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(li.reg);
for (LiveInterval::Ranges::const_iterator
i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
unsigned index = getBaseIndex(i->start);
unsigned end = getBaseIndex(i->end-1) + InstrSlots::NUM;
for (; index != end; index += InstrSlots::NUM) {
// skip deleted instructions
while (index != end && !getInstructionFromIndex(index))
index += InstrSlots::NUM;
if (index == end) break;
MachineInstr *MI = getInstructionFromIndex(index);
RestartInstruction:
for (unsigned i = 0; i != MI->getNumOperands(); ++i) {
MachineOperand& mop = MI->getOperand(i);
if (mop.isRegister() && mop.getReg() == li.reg) {
MachineInstr *fmi = li.remat ? NULL
: mri_->foldMemoryOperand(MI, i, slot);
if (fmi) {
// Attempt to fold the memory reference into the instruction. If we
// can do this, we don't need to insert spill code.
if (lv_)
lv_->instructionChanged(MI, fmi);
MachineBasicBlock &MBB = *MI->getParent();
vrm.virtFolded(li.reg, MI, i, fmi);
mi2iMap_.erase(MI);
i2miMap_[index/InstrSlots::NUM] = fmi;
mi2iMap_[fmi] = index;
MI = MBB.insert(MBB.erase(MI), fmi);
++numFolded;
// Folding the load/store can completely change the instruction in
// unpredictable ways, rescan it from the beginning.
goto RestartInstruction;
} else {
// Create a new virtual register for the spill interval.
unsigned NewVReg = mf_->getSSARegMap()->createVirtualRegister(rc);
// Scan all of the operands of this instruction rewriting operands
// to use NewVReg instead of li.reg as appropriate. We do this for
// two reasons:
//
// 1. If the instr reads the same spilled vreg multiple times, we
// want to reuse the NewVReg.
// 2. If the instr is a two-addr instruction, we are required to
// keep the src/dst regs pinned.
//
// Keep track of whether we replace a use and/or def so that we can
// create the spill interval with the appropriate range.
mop.setReg(NewVReg);
bool HasUse = mop.isUse();
bool HasDef = mop.isDef();
for (unsigned j = i+1, e = MI->getNumOperands(); j != e; ++j) {
if (MI->getOperand(j).isReg() &&
MI->getOperand(j).getReg() == li.reg) {
MI->getOperand(j).setReg(NewVReg);
HasUse |= MI->getOperand(j).isUse();
HasDef |= MI->getOperand(j).isDef();
}
}
// create a new register for this spill
vrm.grow();
if (li.remat)
vrm.setVirtIsReMaterialized(NewVReg, li.remat);
vrm.assignVirt2StackSlot(NewVReg, slot);
LiveInterval &nI = getOrCreateInterval(NewVReg);
nI.remat = li.remat;
assert(nI.empty());
// the spill weight is now infinity as it
// cannot be spilled again
nI.weight = HUGE_VALF;
if (HasUse) {
LiveRange LR(getLoadIndex(index), getUseIndex(index),
nI.getNextValue(~0U, 0));
DOUT << " +" << LR;
nI.addRange(LR);
}
if (HasDef) {
LiveRange LR(getDefIndex(index), getStoreIndex(index),
nI.getNextValue(~0U, 0));
DOUT << " +" << LR;
nI.addRange(LR);
}
added.push_back(&nI);
// update live variables if it is available
if (lv_)
lv_->addVirtualRegisterKilled(NewVReg, MI);
DOUT << "\t\t\t\tadded new interval: ";
nI.print(DOUT, mri_);
DOUT << '\n';
}
}
}
}
}
return added;
}
void LiveIntervals::printRegName(unsigned reg) const {
if (MRegisterInfo::isPhysicalRegister(reg))
cerr << mri_->getName(reg);
else
cerr << "%reg" << reg;
}
/// isReDefinedByTwoAddr - Returns true if the Reg re-definition is due to
/// two addr elimination.
static bool isReDefinedByTwoAddr(MachineInstr *MI, unsigned Reg,
const TargetInstrInfo *TII) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO1 = MI->getOperand(i);
if (MO1.isRegister() && MO1.isDef() && MO1.getReg() == Reg) {
for (unsigned j = i+1; j < e; ++j) {
MachineOperand &MO2 = MI->getOperand(j);
if (MO2.isRegister() && MO2.isUse() && MO2.getReg() == Reg &&
MI->getInstrDescriptor()->
getOperandConstraint(j, TOI::TIED_TO) == (int)i)
return true;
}
}
}
return false;
}
void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
MachineBasicBlock::iterator mi,
unsigned MIIdx,
LiveInterval &interval) {
DOUT << "\t\tregister: "; DEBUG(printRegName(interval.reg));
LiveVariables::VarInfo& vi = lv_->getVarInfo(interval.reg);
// Virtual registers may be defined multiple times (due to phi
// elimination and 2-addr elimination). Much of what we do only has to be
// done once for the vreg. We use an empty interval to detect the first
// time we see a vreg.
if (interval.empty()) {
// Remember if the definition can be rematerialized. All load's from fixed
// stack slots are re-materializable.
int FrameIdx = 0;
if (vi.DefInst &&
(tii_->isReMaterializable(vi.DefInst->getOpcode()) ||
(tii_->isLoadFromStackSlot(vi.DefInst, FrameIdx) &&
mf_->getFrameInfo()->isFixedObjectIndex(FrameIdx))))
interval.remat = vi.DefInst;
// Get the Idx of the defining instructions.
unsigned defIndex = getDefIndex(MIIdx);
unsigned ValNum;
unsigned SrcReg, DstReg;
if (!tii_->isMoveInstr(*mi, SrcReg, DstReg))
ValNum = interval.getNextValue(~0U, 0);
else
ValNum = interval.getNextValue(defIndex, SrcReg);
assert(ValNum == 0 && "First value in interval is not 0?");
ValNum = 0; // Clue in the optimizer.
// Loop over all of the blocks that the vreg is defined in. There are
// two cases we have to handle here. The most common case is a vreg
// whose lifetime is contained within a basic block. In this case there
// will be a single kill, in MBB, which comes after the definition.
if (vi.Kills.size() == 1 && vi.Kills[0]->getParent() == mbb) {
// FIXME: what about dead vars?
unsigned killIdx;
if (vi.Kills[0] != mi)
killIdx = getUseIndex(getInstructionIndex(vi.Kills[0]))+1;
else
killIdx = defIndex+1;
// If the kill happens after the definition, we have an intra-block
// live range.
if (killIdx > defIndex) {
assert(vi.AliveBlocks.none() &&
"Shouldn't be alive across any blocks!");
LiveRange LR(defIndex, killIdx, ValNum);
interval.addRange(LR);
DOUT << " +" << LR << "\n";
return;
}
}
// The other case we handle is when a virtual register lives to the end
// of the defining block, potentially live across some blocks, then is
// live into some number of blocks, but gets killed. Start by adding a
// range that goes from this definition to the end of the defining block.
LiveRange NewLR(defIndex,
getInstructionIndex(&mbb->back()) + InstrSlots::NUM,
ValNum);
DOUT << " +" << NewLR;
interval.addRange(NewLR);
// Iterate over all of the blocks that the variable is completely
// live in, adding [insrtIndex(begin), instrIndex(end)+4) to the
// live interval.
for (unsigned i = 0, e = vi.AliveBlocks.size(); i != e; ++i) {
if (vi.AliveBlocks[i]) {
MachineBasicBlock *MBB = mf_->getBlockNumbered(i);
if (!MBB->empty()) {
LiveRange LR(getMBBStartIdx(i),
getInstructionIndex(&MBB->back()) + InstrSlots::NUM,
ValNum);
interval.addRange(LR);
DOUT << " +" << LR;
}
}
}
// Finally, this virtual register is live from the start of any killing
// block to the 'use' slot of the killing instruction.
for (unsigned i = 0, e = vi.Kills.size(); i != e; ++i) {
MachineInstr *Kill = vi.Kills[i];
LiveRange LR(getMBBStartIdx(Kill->getParent()),
getUseIndex(getInstructionIndex(Kill))+1,
ValNum);
interval.addRange(LR);
DOUT << " +" << LR;
}
} else {
// Can no longer safely assume definition is rematerializable.
interval.remat = NULL;
// If this is the second time we see a virtual register definition, it
// must be due to phi elimination or two addr elimination. If this is
// the result of two address elimination, then the vreg is one of the
// def-and-use register operand.
if (isReDefinedByTwoAddr(mi, interval.reg, tii_)) {
// If this is a two-address definition, then we have already processed
// the live range. The only problem is that we didn't realize there
// are actually two values in the live interval. Because of this we
// need to take the LiveRegion that defines this register and split it
// into two values.
unsigned DefIndex = getDefIndex(getInstructionIndex(vi.DefInst));
unsigned RedefIndex = getDefIndex(MIIdx);
// Delete the initial value, which should be short and continuous,
// because the 2-addr copy must be in the same MBB as the redef.
interval.removeRange(DefIndex, RedefIndex);
// Two-address vregs should always only be redefined once. This means
// that at this point, there should be exactly one value number in it.
assert(interval.containsOneValue() && "Unexpected 2-addr liveint!");
// The new value number (#1) is defined by the instruction we claimed
// defined value #0.
unsigned ValNo = interval.getNextValue(0, 0);
interval.setValueNumberInfo(1, interval.getValNumInfo(0));
// Value#0 is now defined by the 2-addr instruction.
interval.setValueNumberInfo(0, std::make_pair(~0U, 0U));
// Add the new live interval which replaces the range for the input copy.
LiveRange LR(DefIndex, RedefIndex, ValNo);
DOUT << " replace range with " << LR;
interval.addRange(LR);
// If this redefinition is dead, we need to add a dummy unit live
// range covering the def slot.
if (lv_->RegisterDefIsDead(mi, interval.reg))
interval.addRange(LiveRange(RedefIndex, RedefIndex+1, 0));
DOUT << " RESULT: ";
interval.print(DOUT, mri_);
} else {
// Otherwise, this must be because of phi elimination. If this is the
// first redefinition of the vreg that we have seen, go back and change
// the live range in the PHI block to be a different value number.
if (interval.containsOneValue()) {
assert(vi.Kills.size() == 1 &&
"PHI elimination vreg should have one kill, the PHI itself!");
// Remove the old range that we now know has an incorrect number.
MachineInstr *Killer = vi.Kills[0];
unsigned Start = getMBBStartIdx(Killer->getParent());
unsigned End = getUseIndex(getInstructionIndex(Killer))+1;
DOUT << " Removing [" << Start << "," << End << "] from: ";
interval.print(DOUT, mri_); DOUT << "\n";
interval.removeRange(Start, End);
DOUT << " RESULT: "; interval.print(DOUT, mri_);
// Replace the interval with one of a NEW value number. Note that this
// value number isn't actually defined by an instruction, weird huh? :)
LiveRange LR(Start, End, interval.getNextValue(~0U, 0));
DOUT << " replace range with " << LR;
interval.addRange(LR);
DOUT << " RESULT: "; interval.print(DOUT, mri_);
}
// In the case of PHI elimination, each variable definition is only
// live until the end of the block. We've already taken care of the
// rest of the live range.
unsigned defIndex = getDefIndex(MIIdx);
unsigned ValNum;
unsigned SrcReg, DstReg;
if (!tii_->isMoveInstr(*mi, SrcReg, DstReg))
ValNum = interval.getNextValue(~0U, 0);
else
ValNum = interval.getNextValue(defIndex, SrcReg);
LiveRange LR(defIndex,
getInstructionIndex(&mbb->back()) + InstrSlots::NUM, ValNum);
interval.addRange(LR);
DOUT << " +" << LR;
}
}
DOUT << '\n';
}
void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock *MBB,
MachineBasicBlock::iterator mi,
unsigned MIIdx,
LiveInterval &interval,
unsigned SrcReg) {
// A physical register cannot be live across basic block, so its
// lifetime must end somewhere in its defining basic block.
DOUT << "\t\tregister: "; DEBUG(printRegName(interval.reg));
unsigned baseIndex = MIIdx;
unsigned start = getDefIndex(baseIndex);
unsigned end = start;
// If it is not used after definition, it is considered dead at
// the instruction defining it. Hence its interval is:
// [defSlot(def), defSlot(def)+1)
if (lv_->RegisterDefIsDead(mi, interval.reg)) {
DOUT << " dead";
end = getDefIndex(start) + 1;
goto exit;
}
// If it is not dead on definition, it must be killed by a
// subsequent instruction. Hence its interval is:
// [defSlot(def), useSlot(kill)+1)
while (++mi != MBB->end()) {
baseIndex += InstrSlots::NUM;
if (lv_->KillsRegister(mi, interval.reg)) {
DOUT << " killed";
end = getUseIndex(baseIndex) + 1;
goto exit;
} else if (lv_->ModifiesRegister(mi, interval.reg)) {
// Another instruction redefines the register before it is ever read.
// Then the register is essentially dead at the instruction that defines
// it. Hence its interval is:
// [defSlot(def), defSlot(def)+1)
DOUT << " dead";
end = getDefIndex(start) + 1;
goto exit;
}
}
// The only case we should have a dead physreg here without a killing or
// instruction where we know it's dead is if it is live-in to the function
// and never used.
assert(!SrcReg && "physreg was not killed in defining block!");
end = getDefIndex(start) + 1; // It's dead.
exit:
assert(start < end && "did not find end of interval?");
LiveRange LR(start, end, interval.getNextValue(SrcReg != 0 ? start : ~0U,
SrcReg));
interval.addRange(LR);
DOUT << " +" << LR << '\n';
}
void LiveIntervals::handleRegisterDef(MachineBasicBlock *MBB,
MachineBasicBlock::iterator MI,
unsigned MIIdx,
unsigned reg) {
if (MRegisterInfo::isVirtualRegister(reg))
handleVirtualRegisterDef(MBB, MI, MIIdx, getOrCreateInterval(reg));
else if (allocatableRegs_[reg]) {
unsigned SrcReg, DstReg;
if (!tii_->isMoveInstr(*MI, SrcReg, DstReg))
SrcReg = 0;
handlePhysicalRegisterDef(MBB, MI, MIIdx, getOrCreateInterval(reg), SrcReg);
for (const unsigned* AS = mri_->getAliasSet(reg); *AS; ++AS)
handlePhysicalRegisterDef(MBB, MI, MIIdx, getOrCreateInterval(*AS), 0);
}
}
void LiveIntervals::handleLiveInRegister(MachineBasicBlock *MBB,
unsigned MIIdx,
LiveInterval &interval) {
DOUT << "\t\tlivein register: "; DEBUG(printRegName(interval.reg));
// Look for kills, if it reaches a def before it's killed, then it shouldn't
// be considered a livein.
MachineBasicBlock::iterator mi = MBB->begin();
unsigned baseIndex = MIIdx;
unsigned start = baseIndex;
unsigned end = start;
while (mi != MBB->end()) {
if (lv_->KillsRegister(mi, interval.reg)) {
DOUT << " killed";
end = getUseIndex(baseIndex) + 1;
goto exit;
} else if (lv_->ModifiesRegister(mi, interval.reg)) {
// Another instruction redefines the register before it is ever read.
// Then the register is essentially dead at the instruction that defines
// it. Hence its interval is:
// [defSlot(def), defSlot(def)+1)
DOUT << " dead";
end = getDefIndex(start) + 1;
goto exit;
}
baseIndex += InstrSlots::NUM;
++mi;
}
exit:
assert(start < end && "did not find end of interval?");
LiveRange LR(start, end, interval.getNextValue(~0U, 0));
DOUT << " +" << LR << '\n';
interval.addRange(LR);
}
/// computeIntervals - computes the live intervals for virtual
/// registers. for some ordering of the machine instructions [1,N] a
/// live interval is an interval [i, j) where 1 <= i <= j < N for
/// which a variable is live
void LiveIntervals::computeIntervals() {
DOUT << "********** COMPUTING LIVE INTERVALS **********\n"
<< "********** Function: "
<< ((Value*)mf_->getFunction())->getName() << '\n';
// Track the index of the current machine instr.
unsigned MIIndex = 0;
for (MachineFunction::iterator MBBI = mf_->begin(), E = mf_->end();
MBBI != E; ++MBBI) {
MachineBasicBlock *MBB = MBBI;
DOUT << ((Value*)MBB->getBasicBlock())->getName() << ":\n";
MachineBasicBlock::iterator MI = MBB->begin(), miEnd = MBB->end();
if (MBB->livein_begin() != MBB->livein_end()) {
// Create intervals for live-ins to this BB first.
for (MachineBasicBlock::const_livein_iterator LI = MBB->livein_begin(),
LE = MBB->livein_end(); LI != LE; ++LI) {
handleLiveInRegister(MBB, MIIndex, getOrCreateInterval(*LI));
for (const unsigned* AS = mri_->getAliasSet(*LI); *AS; ++AS)
handleLiveInRegister(MBB, MIIndex, getOrCreateInterval(*AS));
}
}
for (; MI != miEnd; ++MI) {
DOUT << MIIndex << "\t" << *MI;
// Handle defs.
for (int i = MI->getNumOperands() - 1; i >= 0; --i) {
MachineOperand &MO = MI->getOperand(i);
// handle register defs - build intervals
if (MO.isRegister() && MO.getReg() && MO.isDef())
handleRegisterDef(MBB, MI, MIIndex, MO.getReg());
}
MIIndex += InstrSlots::NUM;
}
}
}
/// AdjustCopiesBackFrom - We found a non-trivially-coallescable copy with IntA
/// being the source and IntB being the dest, thus this defines a value number
/// in IntB. If the source value number (in IntA) is defined by a copy from B,
/// see if we can merge these two pieces of B into a single value number,
/// eliminating a copy. For example:
///
/// A3 = B0
/// ...
/// B1 = A3 <- this copy
///
/// In this case, B0 can be extended to where the B1 copy lives, allowing the B1
/// value number to be replaced with B0 (which simplifies the B liveinterval).
///
/// This returns true if an interval was modified.
///
bool LiveIntervals::AdjustCopiesBackFrom(LiveInterval &IntA, LiveInterval &IntB,
MachineInstr *CopyMI) {
unsigned CopyIdx = getDefIndex(getInstructionIndex(CopyMI));
// BValNo is a value number in B that is defined by a copy from A. 'B3' in
// the example above.
LiveInterval::iterator BLR = IntB.FindLiveRangeContaining(CopyIdx);
unsigned BValNo = BLR->ValId;
// Get the location that B is defined at. Two options: either this value has
// an unknown definition point or it is defined at CopyIdx. If unknown, we
// can't process it.
unsigned BValNoDefIdx = IntB.getInstForValNum(BValNo);
if (BValNoDefIdx == ~0U) return false;
assert(BValNoDefIdx == CopyIdx &&
"Copy doesn't define the value?");
// AValNo is the value number in A that defines the copy, A0 in the example.
LiveInterval::iterator AValLR = IntA.FindLiveRangeContaining(CopyIdx-1);
unsigned AValNo = AValLR->ValId;
// If AValNo is defined as a copy from IntB, we can potentially process this.
// Get the instruction that defines this value number.
unsigned SrcReg = IntA.getSrcRegForValNum(AValNo);
if (!SrcReg) return false; // Not defined by a copy.
// If the value number is not defined by a copy instruction, ignore it.
// If the source register comes from an interval other than IntB, we can't
// handle this.
if (rep(SrcReg) != IntB.reg) return false;
// Get the LiveRange in IntB that this value number starts with.
unsigned AValNoInstIdx = IntA.getInstForValNum(AValNo);
LiveInterval::iterator ValLR = IntB.FindLiveRangeContaining(AValNoInstIdx-1);
// Make sure that the end of the live range is inside the same block as
// CopyMI.
MachineInstr *ValLREndInst = getInstructionFromIndex(ValLR->end-1);
if (!ValLREndInst ||
ValLREndInst->getParent() != CopyMI->getParent()) return false;
// Okay, we now know that ValLR ends in the same block that the CopyMI
// live-range starts. If there are no intervening live ranges between them in
// IntB, we can merge them.
if (ValLR+1 != BLR) return false;
DOUT << "\nExtending: "; IntB.print(DOUT, mri_);
// We are about to delete CopyMI, so need to remove it as the 'instruction
// that defines this value #'.
IntB.setValueNumberInfo(BValNo, std::make_pair(~0U, 0));
// Okay, we can merge them. We need to insert a new liverange:
// [ValLR.end, BLR.begin) of either value number, then we merge the
// two value numbers.
unsigned FillerStart = ValLR->end, FillerEnd = BLR->start;
IntB.addRange(LiveRange(FillerStart, FillerEnd, BValNo));
// If the IntB live range is assigned to a physical register, and if that
// physreg has aliases,
if (MRegisterInfo::isPhysicalRegister(IntB.reg)) {
for (const unsigned *AS = mri_->getAliasSet(IntB.reg); *AS; ++AS) {
LiveInterval &AliasLI = getInterval(*AS);
AliasLI.addRange(LiveRange(FillerStart, FillerEnd,
AliasLI.getNextValue(~0U, 0)));
}
}
// Okay, merge "B1" into the same value number as "B0".
if (BValNo != ValLR->ValId)
IntB.MergeValueNumberInto(BValNo, ValLR->ValId);
DOUT << " result = "; IntB.print(DOUT, mri_);
DOUT << "\n";
// If the source instruction was killing the source register before the
// merge, unset the isKill marker given the live range has been extended.
int UIdx = ValLREndInst->findRegisterUseOperand(IntB.reg, true);
if (UIdx != -1)
ValLREndInst->getOperand(UIdx).unsetIsKill();
// Finally, delete the copy instruction.
RemoveMachineInstrFromMaps(CopyMI);
CopyMI->eraseFromParent();
++numPeep;
return true;
}
/// JoinCopy - Attempt to join intervals corresponding to SrcReg/DstReg,
/// which are the src/dst of the copy instruction CopyMI. This returns true
/// if the copy was successfully coallesced away, or if it is never possible
/// to coallesce these this copy, due to register constraints. It returns
/// false if it is not currently possible to coallesce this interval, but
/// it may be possible if other things get coallesced.
bool LiveIntervals::JoinCopy(MachineInstr *CopyMI,
unsigned SrcReg, unsigned DstReg) {
DOUT << getInstructionIndex(CopyMI) << '\t' << *CopyMI;
// Get representative registers.
unsigned repSrcReg = rep(SrcReg);
unsigned repDstReg = rep(DstReg);
// If they are already joined we continue.
if (repSrcReg == repDstReg) {
DOUT << "\tCopy already coallesced.\n";
return true; // Not coallescable.
}
// If they are both physical registers, we cannot join them.
if (MRegisterInfo::isPhysicalRegister(repSrcReg) &&
MRegisterInfo::isPhysicalRegister(repDstReg)) {
DOUT << "\tCan not coallesce physregs.\n";
return true; // Not coallescable.
}
// We only join virtual registers with allocatable physical registers.
if (MRegisterInfo::isPhysicalRegister(repSrcReg) &&
!allocatableRegs_[repSrcReg]) {
DOUT << "\tSrc reg is unallocatable physreg.\n";
return true; // Not coallescable.
}
if (MRegisterInfo::isPhysicalRegister(repDstReg) &&
!allocatableRegs_[repDstReg]) {
DOUT << "\tDst reg is unallocatable physreg.\n";
return true; // Not coallescable.
}
// If they are not of the same register class, we cannot join them.
if (differingRegisterClasses(repSrcReg, repDstReg)) {
DOUT << "\tSrc/Dest are different register classes.\n";
return true; // Not coallescable.
}
LiveInterval &SrcInt = getInterval(repSrcReg);
LiveInterval &DestInt = getInterval(repDstReg);
assert(SrcInt.reg == repSrcReg && DestInt.reg == repDstReg &&
"Register mapping is horribly broken!");
DOUT << "\t\tInspecting "; SrcInt.print(DOUT, mri_);
DOUT << " and "; DestInt.print(DOUT, mri_);
DOUT << ": ";
// Check if it is necessary to propagate "isDead" property before intervals
// are joined.
MachineBasicBlock *CopyBB = CopyMI->getParent();
MachineOperand *mopd = CopyMI->findRegisterDefOperand(DstReg);
bool isDead = mopd->isDead();
bool isShorten = false;
unsigned SrcStart = 0, RemoveStart = 0;
unsigned SrcEnd = 0, RemoveEnd = 0;
if (isDead) {
unsigned CopyIdx = getInstructionIndex(CopyMI);
LiveInterval::iterator SrcLR =
SrcInt.FindLiveRangeContaining(getUseIndex(CopyIdx));
RemoveStart = SrcStart = SrcLR->start;
RemoveEnd = SrcEnd = SrcLR->end;
// The instruction which defines the src is only truly dead if there are
// no intermediate uses and there isn't a use beyond the copy.
// FIXME: find the last use, mark is kill and shorten the live range.
if (SrcEnd > getDefIndex(CopyIdx)) {
isDead = false;
} else {
MachineOperand *MOU;
MachineInstr *LastUse= lastRegisterUse(repSrcReg, SrcStart, CopyIdx, MOU);
if (LastUse) {
// Shorten the liveinterval to the end of last use.
MOU->setIsKill();
isDead = false;
isShorten = true;
RemoveStart = getDefIndex(getInstructionIndex(LastUse));
RemoveEnd = SrcEnd;
} else {
MachineInstr *SrcMI = getInstructionFromIndex(SrcStart);
if (SrcMI) {
MachineOperand *mops = findDefOperand(SrcMI, repSrcReg);
if (mops)
// A dead def should have a single cycle interval.
++RemoveStart;
}
}
}
}
// We need to be careful about coalescing a source physical register with a
// virtual register. Once the coalescing is done, it cannot be broken and
// these are not spillable! If the destination interval uses are far away,
// think twice about coalescing them!
if (!mopd->isDead() && MRegisterInfo::isPhysicalRegister(repSrcReg)) {
// Small function. No need to worry!
unsigned Threshold = allocatableRegs_.count() * 2;
if (r2iMap_.size() <= Threshold)
goto TryJoin;
LiveVariables::VarInfo& dvi = lv_->getVarInfo(repDstReg);
// Is the value used in the current BB or any immediate successroe BB?
if (dvi.UsedBlocks[CopyBB->getNumber()])
goto TryJoin;
for (MachineBasicBlock::succ_iterator SI = CopyBB->succ_begin(),
SE = CopyBB->succ_end(); SI != SE; ++SI) {
MachineBasicBlock *SuccMBB = *SI;
if (dvi.UsedBlocks[SuccMBB->getNumber()])
goto TryJoin;
}
// Ok, no use in this BB and no use in immediate successor BB's. Be really
// careful now!
// It's only used in one BB, forget about it!
if (dvi.UsedBlocks.count() < 2) {
++numAborts;
return false;
}
// Determine whether to allow coalescing based on how far the closest
// use is.
unsigned CopyIdx = getInstructionIndex(CopyMI);
unsigned MinDist = i2miMap_.size() * InstrSlots::NUM;
int UseBBNum = dvi.UsedBlocks.find_first();
while (UseBBNum != -1) {
MachineBasicBlock *UseBB = mf_->getBlockNumbered(UseBBNum);
unsigned UseIdx = getMBBStartIdx(UseBB);
if (UseIdx > CopyIdx) {
MinDist = std::min(MinDist, UseIdx - CopyIdx);
if (MinDist <= Threshold)
break;
}
UseBBNum = dvi.UsedBlocks.find_next(UseBBNum);
}
if (MinDist > Threshold) {
// Don't do it!
++numAborts;
return false;
}
}
TryJoin:
// Okay, attempt to join these two intervals. On failure, this returns false.
// Otherwise, if one of the intervals being joined is a physreg, this method
// always canonicalizes DestInt to be it. The output "SrcInt" will not have
// been modified, so we can use this information below to update aliases.
if (JoinIntervals(DestInt, SrcInt)) {
if (isDead) {
// Result of the copy is dead. Propagate this property.
if (SrcStart == 0) {
assert(MRegisterInfo::isPhysicalRegister(repSrcReg) &&
"Live-in must be a physical register!");
// Live-in to the function but dead. Remove it from entry live-in set.
// JoinIntervals may end up swapping the two intervals.
mf_->begin()->removeLiveIn(repSrcReg);
} else {
MachineInstr *SrcMI = getInstructionFromIndex(SrcStart);
if (SrcMI) {
MachineOperand *mops = findDefOperand(SrcMI, repSrcReg);
if (mops)
mops->setIsDead();
}
}
}
if (isShorten || isDead) {
// Shorten the live interval.
LiveInterval &LiveInInt = (repSrcReg == DestInt.reg) ? DestInt : SrcInt;
LiveInInt.removeRange(RemoveStart, RemoveEnd);
}
} else {
// Coallescing failed.
// If we can eliminate the copy without merging the live ranges, do so now.
if (AdjustCopiesBackFrom(SrcInt, DestInt, CopyMI))
return true;
// Otherwise, we are unable to join the intervals.
DOUT << "Interference!\n";
return false;
}
bool Swapped = repSrcReg == DestInt.reg;
if (Swapped)
std::swap(repSrcReg, repDstReg);
assert(MRegisterInfo::isVirtualRegister(repSrcReg) &&
"LiveInterval::join didn't work right!");
// If we're about to merge live ranges into a physical register live range,
// we have to update any aliased register's live ranges to indicate that they
// have clobbered values for this range.
if (MRegisterInfo::isPhysicalRegister(repDstReg)) {
for (const unsigned *AS = mri_->getAliasSet(repDstReg); *AS; ++AS)
getInterval(*AS).MergeInClobberRanges(SrcInt);
} else {
// Merge UsedBlocks info if the destination is a virtual register.
LiveVariables::VarInfo& dVI = lv_->getVarInfo(repDstReg);
LiveVariables::VarInfo& sVI = lv_->getVarInfo(repSrcReg);
dVI.UsedBlocks |= sVI.UsedBlocks;
}
DOUT << "\n\t\tJoined. Result = "; DestInt.print(DOUT, mri_);
DOUT << "\n";
// Remember these liveintervals have been joined.
JoinedLIs.set(repSrcReg - MRegisterInfo::FirstVirtualRegister);
if (MRegisterInfo::isVirtualRegister(repDstReg))
JoinedLIs.set(repDstReg - MRegisterInfo::FirstVirtualRegister);
// If the intervals were swapped by Join, swap them back so that the register
// mapping (in the r2i map) is correct.
if (Swapped) SrcInt.swap(DestInt);
removeInterval(repSrcReg);
r2rMap_[repSrcReg] = repDstReg;
// Finally, delete the copy instruction.
RemoveMachineInstrFromMaps(CopyMI);
CopyMI->eraseFromParent();
++numPeep;
++numJoins;
return true;
}
/// ComputeUltimateVN - Assuming we are going to join two live intervals,
/// compute what the resultant value numbers for each value in the input two
/// ranges will be. This is complicated by copies between the two which can
/// and will commonly cause multiple value numbers to be merged into one.
///
/// VN is the value number that we're trying to resolve. InstDefiningValue
/// keeps track of the new InstDefiningValue assignment for the result
/// LiveInterval. ThisFromOther/OtherFromThis are sets that keep track of
/// whether a value in this or other is a copy from the opposite set.
/// ThisValNoAssignments/OtherValNoAssignments keep track of value #'s that have
/// already been assigned.
///
/// ThisFromOther[x] - If x is defined as a copy from the other interval, this
/// contains the value number the copy is from.
///
static unsigned ComputeUltimateVN(unsigned VN,
SmallVector<std::pair<unsigned,
unsigned>, 16> &ValueNumberInfo,
SmallVector<int, 16> &ThisFromOther,
SmallVector<int, 16> &OtherFromThis,
SmallVector<int, 16> &ThisValNoAssignments,
SmallVector<int, 16> &OtherValNoAssignments,
LiveInterval &ThisLI, LiveInterval &OtherLI) {
// If the VN has already been computed, just return it.
if (ThisValNoAssignments[VN] >= 0)
return ThisValNoAssignments[VN];
// assert(ThisValNoAssignments[VN] != -2 && "Cyclic case?");
// If this val is not a copy from the other val, then it must be a new value
// number in the destination.
int OtherValNo = ThisFromOther[VN];
if (OtherValNo == -1) {
ValueNumberInfo.push_back(ThisLI.getValNumInfo(VN));
return ThisValNoAssignments[VN] = ValueNumberInfo.size()-1;
}
// Otherwise, this *is* a copy from the RHS. If the other side has already
// been computed, return it.
if (OtherValNoAssignments[OtherValNo] >= 0)
return ThisValNoAssignments[VN] = OtherValNoAssignments[OtherValNo];
// Mark this value number as currently being computed, then ask what the
// ultimate value # of the other value is.
ThisValNoAssignments[VN] = -2;
unsigned UltimateVN =
ComputeUltimateVN(OtherValNo, ValueNumberInfo,
OtherFromThis, ThisFromOther,
OtherValNoAssignments, ThisValNoAssignments,
OtherLI, ThisLI);
return ThisValNoAssignments[VN] = UltimateVN;
}
static bool InVector(unsigned Val, const SmallVector<unsigned, 8> &V) {
return std::find(V.begin(), V.end(), Val) != V.end();
}
/// SimpleJoin - Attempt to joint the specified interval into this one. The
/// caller of this method must guarantee that the RHS only contains a single
/// value number and that the RHS is not defined by a copy from this
/// interval. This returns false if the intervals are not joinable, or it
/// joins them and returns true.
bool LiveIntervals::SimpleJoin(LiveInterval &LHS, LiveInterval &RHS) {
assert(RHS.containsOneValue());
// Some number (potentially more than one) value numbers in the current
// interval may be defined as copies from the RHS. Scan the overlapping
// portions of the LHS and RHS, keeping track of this and looking for
// overlapping live ranges that are NOT defined as copies. If these exist, we
// cannot coallesce.
LiveInterval::iterator LHSIt = LHS.begin(), LHSEnd = LHS.end();
LiveInterval::iterator RHSIt = RHS.begin(), RHSEnd = RHS.end();
if (LHSIt->start < RHSIt->start) {
LHSIt = std::upper_bound(LHSIt, LHSEnd, RHSIt->start);
if (LHSIt != LHS.begin()) --LHSIt;
} else if (RHSIt->start < LHSIt->start) {
RHSIt = std::upper_bound(RHSIt, RHSEnd, LHSIt->start);
if (RHSIt != RHS.begin()) --RHSIt;
}
SmallVector<unsigned, 8> EliminatedLHSVals;
while (1) {
// Determine if these live intervals overlap.
bool Overlaps = false;
if (LHSIt->start <= RHSIt->start)
Overlaps = LHSIt->end > RHSIt->start;
else
Overlaps = RHSIt->end > LHSIt->start;
// If the live intervals overlap, there are two interesting cases: if the
// LHS interval is defined by a copy from the RHS, it's ok and we record
// that the LHS value # is the same as the RHS. If it's not, then we cannot
// coallesce these live ranges and we bail out.
if (Overlaps) {
// If we haven't already recorded that this value # is safe, check it.
if (!InVector(LHSIt->ValId, EliminatedLHSVals)) {
// Copy from the RHS?
unsigned SrcReg = LHS.getSrcRegForValNum(LHSIt->ValId);
if (rep(SrcReg) != RHS.reg)
return false; // Nope, bail out.
EliminatedLHSVals.push_back(LHSIt->ValId);
}
// We know this entire LHS live range is okay, so skip it now.
if (++LHSIt == LHSEnd) break;
continue;
}
if (LHSIt->end < RHSIt->end) {
if (++LHSIt == LHSEnd) break;
} else {
// One interesting case to check here. It's possible that we have
// something like "X3 = Y" which defines a new value number in the LHS,
// and is the last use of this liverange of the RHS. In this case, we
// want to notice this copy (so that it gets coallesced away) even though
// the live ranges don't actually overlap.
if (LHSIt->start == RHSIt->end) {
if (InVector(LHSIt->ValId, EliminatedLHSVals)) {
// We already know that this value number is going to be merged in
// if coallescing succeeds. Just skip the liverange.
if (++LHSIt == LHSEnd) break;
} else {
// Otherwise, if this is a copy from the RHS, mark it as being merged
// in.
if (rep(LHS.getSrcRegForValNum(LHSIt->ValId)) == RHS.reg) {
EliminatedLHSVals.push_back(LHSIt->ValId);
// We know this entire LHS live range is okay, so skip it now.
if (++LHSIt == LHSEnd) break;
}
}
}
if (++RHSIt == RHSEnd) break;
}
}
// If we got here, we know that the coallescing will be successful and that
// the value numbers in EliminatedLHSVals will all be merged together. Since
// the most common case is that EliminatedLHSVals has a single number, we
// optimize for it: if there is more than one value, we merge them all into
// the lowest numbered one, then handle the interval as if we were merging
// with one value number.
unsigned LHSValNo;
if (EliminatedLHSVals.size() > 1) {
// Loop through all the equal value numbers merging them into the smallest
// one.
unsigned Smallest = EliminatedLHSVals[0];
for (unsigned i = 1, e = EliminatedLHSVals.size(); i != e; ++i) {
if (EliminatedLHSVals[i] < Smallest) {
// Merge the current notion of the smallest into the smaller one.
LHS.MergeValueNumberInto(Smallest, EliminatedLHSVals[i]);
Smallest = EliminatedLHSVals[i];
} else {
// Merge into the smallest.
LHS.MergeValueNumberInto(EliminatedLHSVals[i], Smallest);
}
}
LHSValNo = Smallest;
} else {
assert(!EliminatedLHSVals.empty() && "No copies from the RHS?");
LHSValNo = EliminatedLHSVals[0];
}
// Okay, now that there is a single LHS value number that we're merging the
// RHS into, update the value number info for the LHS to indicate that the
// value number is defined where the RHS value number was.
LHS.setValueNumberInfo(LHSValNo, RHS.getValNumInfo(0));
// Okay, the final step is to loop over the RHS live intervals, adding them to
// the LHS.
LHS.MergeRangesInAsValue(RHS, LHSValNo);
LHS.weight += RHS.weight;
return true;
}
/// JoinIntervals - Attempt to join these two intervals. On failure, this
/// returns false. Otherwise, if one of the intervals being joined is a
/// physreg, this method always canonicalizes LHS to be it. The output
/// "RHS" will not have been modified, so we can use this information
/// below to update aliases.
bool LiveIntervals::JoinIntervals(LiveInterval &LHS, LiveInterval &RHS) {
// Compute the final value assignment, assuming that the live ranges can be
// coallesced.
SmallVector<int, 16> LHSValNoAssignments;
SmallVector<int, 16> RHSValNoAssignments;
SmallVector<std::pair<unsigned,unsigned>, 16> ValueNumberInfo;
// Compute ultimate value numbers for the LHS and RHS values.
if (RHS.containsOneValue()) {
// Copies from a liveinterval with a single value are simple to handle and
// very common, handle the special case here. This is important, because
// often RHS is small and LHS is large (e.g. a physreg).
// Find out if the RHS is defined as a copy from some value in the LHS.
int RHSValID = -1;
std::pair<unsigned,unsigned> RHSValNoInfo;
unsigned RHSSrcReg = RHS.getSrcRegForValNum(0);
if ((RHSSrcReg == 0 || rep(RHSSrcReg) != LHS.reg)) {
// If RHS is not defined as a copy from the LHS, we can use simpler and
// faster checks to see if the live ranges are coallescable. This joiner
// can't swap the LHS/RHS intervals though.
if (!MRegisterInfo::isPhysicalRegister(RHS.reg)) {
return SimpleJoin(LHS, RHS);
} else {
RHSValNoInfo = RHS.getValNumInfo(0);
}
} else {
// It was defined as a copy from the LHS, find out what value # it is.
unsigned ValInst = RHS.getInstForValNum(0);
RHSValID = LHS.getLiveRangeContaining(ValInst-1)->ValId;
RHSValNoInfo = LHS.getValNumInfo(RHSValID);
}
LHSValNoAssignments.resize(LHS.getNumValNums(), -1);
RHSValNoAssignments.resize(RHS.getNumValNums(), -1);
ValueNumberInfo.resize(LHS.getNumValNums());
// Okay, *all* of the values in LHS that are defined as a copy from RHS
// should now get updated.
for (unsigned VN = 0, e = LHS.getNumValNums(); VN != e; ++VN) {
if (unsigned LHSSrcReg = LHS.getSrcRegForValNum(VN)) {
if (rep(LHSSrcReg) != RHS.reg) {
// If this is not a copy from the RHS, its value number will be
// unmodified by the coallescing.
ValueNumberInfo[VN] = LHS.getValNumInfo(VN);
LHSValNoAssignments[VN] = VN;
} else if (RHSValID == -1) {
// Otherwise, it is a copy from the RHS, and we don't already have a
// value# for it. Keep the current value number, but remember it.
LHSValNoAssignments[VN] = RHSValID = VN;
ValueNumberInfo[VN] = RHSValNoInfo;
} else {
// Otherwise, use the specified value #.
LHSValNoAssignments[VN] = RHSValID;
if (VN != (unsigned)RHSValID)
ValueNumberInfo[VN].first = ~1U;
else
ValueNumberInfo[VN] = RHSValNoInfo;
}
} else {
ValueNumberInfo[VN] = LHS.getValNumInfo(VN);
LHSValNoAssignments[VN] = VN;
}
}
assert(RHSValID != -1 && "Didn't find value #?");
RHSValNoAssignments[0] = RHSValID;
} else {
// Loop over the value numbers of the LHS, seeing if any are defined from
// the RHS.
SmallVector<int, 16> LHSValsDefinedFromRHS;
LHSValsDefinedFromRHS.resize(LHS.getNumValNums(), -1);
for (unsigned VN = 0, e = LHS.getNumValNums(); VN != e; ++VN) {
unsigned ValSrcReg = LHS.getSrcRegForValNum(VN);
if (ValSrcReg == 0) // Src not defined by a copy?
continue;
// DstReg is known to be a register in the LHS interval. If the src is
// from the RHS interval, we can use its value #.
if (rep(ValSrcReg) != RHS.reg)
continue;
// Figure out the value # from the RHS.
unsigned ValInst = LHS.getInstForValNum(VN);
LHSValsDefinedFromRHS[VN] = RHS.getLiveRangeContaining(ValInst-1)->ValId;
}
// Loop over the value numbers of the RHS, seeing if any are defined from
// the LHS.
SmallVector<int, 16> RHSValsDefinedFromLHS;
RHSValsDefinedFromLHS.resize(RHS.getNumValNums(), -1);
for (unsigned VN = 0, e = RHS.getNumValNums(); VN != e; ++VN) {
unsigned ValSrcReg = RHS.getSrcRegForValNum(VN);
if (ValSrcReg == 0) // Src not defined by a copy?
continue;
// DstReg is known to be a register in the RHS interval. If the src is
// from the LHS interval, we can use its value #.
if (rep(ValSrcReg) != LHS.reg)
continue;
// Figure out the value # from the LHS.
unsigned ValInst = RHS.getInstForValNum(VN);
RHSValsDefinedFromLHS[VN] = LHS.getLiveRangeContaining(ValInst-1)->ValId;
}
LHSValNoAssignments.resize(LHS.getNumValNums(), -1);
RHSValNoAssignments.resize(RHS.getNumValNums(), -1);
ValueNumberInfo.reserve(LHS.getNumValNums() + RHS.getNumValNums());
for (unsigned VN = 0, e = LHS.getNumValNums(); VN != e; ++VN) {
if (LHSValNoAssignments[VN] >= 0 || LHS.getInstForValNum(VN) == ~2U)
continue;
ComputeUltimateVN(VN, ValueNumberInfo,
LHSValsDefinedFromRHS, RHSValsDefinedFromLHS,
LHSValNoAssignments, RHSValNoAssignments, LHS, RHS);
}
for (unsigned VN = 0, e = RHS.getNumValNums(); VN != e; ++VN) {
if (RHSValNoAssignments[VN] >= 0 || RHS.getInstForValNum(VN) == ~2U)
continue;
// If this value number isn't a copy from the LHS, it's a new number.
if (RHSValsDefinedFromLHS[VN] == -1) {
ValueNumberInfo.push_back(RHS.getValNumInfo(VN));
RHSValNoAssignments[VN] = ValueNumberInfo.size()-1;
continue;
}
ComputeUltimateVN(VN, ValueNumberInfo,
RHSValsDefinedFromLHS, LHSValsDefinedFromRHS,
RHSValNoAssignments, LHSValNoAssignments, RHS, LHS);
}
}
// Armed with the mappings of LHS/RHS values to ultimate values, walk the
// interval lists to see if these intervals are coallescable.
LiveInterval::const_iterator I = LHS.begin();
LiveInterval::const_iterator IE = LHS.end();
LiveInterval::const_iterator J = RHS.begin();
LiveInterval::const_iterator JE = RHS.end();
// Skip ahead until the first place of potential sharing.
if (I->start < J->start) {
I = std::upper_bound(I, IE, J->start);
if (I != LHS.begin()) --I;
} else if (J->start < I->start) {
J = std::upper_bound(J, JE, I->start);
if (J != RHS.begin()) --J;
}
while (1) {
// Determine if these two live ranges overlap.
bool Overlaps;
if (I->start < J->start) {
Overlaps = I->end > J->start;
} else {
Overlaps = J->end > I->start;
}
// If so, check value # info to determine if they are really different.
if (Overlaps) {
// If the live range overlap will map to the same value number in the
// result liverange, we can still coallesce them. If not, we can't.
if (LHSValNoAssignments[I->ValId] != RHSValNoAssignments[J->ValId])
return false;
}
if (I->end < J->end) {
++I;
if (I == IE) break;
} else {
++J;
if (J == JE) break;
}
}
// If we get here, we know that we can coallesce the live ranges. Ask the
// intervals to coallesce themselves now.
LHS.join(RHS, &LHSValNoAssignments[0], &RHSValNoAssignments[0],
ValueNumberInfo);
return true;
}
namespace {
// DepthMBBCompare - Comparison predicate that sort first based on the loop
// depth of the basic block (the unsigned), and then on the MBB number.
struct DepthMBBCompare {
typedef std::pair<unsigned, MachineBasicBlock*> DepthMBBPair;
bool operator()(const DepthMBBPair &LHS, const DepthMBBPair &RHS) const {
if (LHS.first > RHS.first) return true; // Deeper loops first
return LHS.first == RHS.first &&
LHS.second->getNumber() < RHS.second->getNumber();
}
};
}
void LiveIntervals::CopyCoallesceInMBB(MachineBasicBlock *MBB,
std::vector<CopyRec> &TryAgain) {
DOUT << ((Value*)MBB->getBasicBlock())->getName() << ":\n";
for (MachineBasicBlock::iterator MII = MBB->begin(), E = MBB->end();
MII != E;) {
MachineInstr *Inst = MII++;
// If this isn't a copy, we can't join intervals.
unsigned SrcReg, DstReg;
if (!tii_->isMoveInstr(*Inst, SrcReg, DstReg)) continue;
if (!JoinCopy(Inst, SrcReg, DstReg))
TryAgain.push_back(getCopyRec(Inst, SrcReg, DstReg));
}
}
void LiveIntervals::joinIntervals() {
DOUT << "********** JOINING INTERVALS ***********\n";
JoinedLIs.resize(getNumIntervals());
JoinedLIs.reset();
std::vector<CopyRec> TryAgainList;
const LoopInfo &LI = getAnalysis<LoopInfo>();
if (LI.begin() == LI.end()) {
// If there are no loops in the function, join intervals in function order.
for (MachineFunction::iterator I = mf_->begin(), E = mf_->end();
I != E; ++I)
CopyCoallesceInMBB(I, TryAgainList);
} else {
// Otherwise, join intervals in inner loops before other intervals.
// Unfortunately we can't just iterate over loop hierarchy here because
// there may be more MBB's than BB's. Collect MBB's for sorting.
std::vector<std::pair<unsigned, MachineBasicBlock*> > MBBs;
for (MachineFunction::iterator I = mf_->begin(), E = mf_->end();
I != E; ++I)
MBBs.push_back(std::make_pair(LI.getLoopDepth(I->getBasicBlock()), I));
// Sort by loop depth.
std::sort(MBBs.begin(), MBBs.end(), DepthMBBCompare());
// Finally, join intervals in loop nest order.
for (unsigned i = 0, e = MBBs.size(); i != e; ++i)
CopyCoallesceInMBB(MBBs[i].second, TryAgainList);
}
// Joining intervals can allow other intervals to be joined. Iteratively join
// until we make no progress.
bool ProgressMade = true;
while (ProgressMade) {
ProgressMade = false;
for (unsigned i = 0, e = TryAgainList.size(); i != e; ++i) {
CopyRec &TheCopy = TryAgainList[i];
if (TheCopy.MI &&
JoinCopy(TheCopy.MI, TheCopy.SrcReg, TheCopy.DstReg)) {
TheCopy.MI = 0; // Mark this one as done.
ProgressMade = true;
}
}
}
// Some live range has been lengthened due to colaescing, eliminate the
// unnecessary kills.
int RegNum = JoinedLIs.find_first();
while (RegNum != -1) {
unsigned Reg = RegNum + MRegisterInfo::FirstVirtualRegister;
unsigned repReg = rep(Reg);
LiveInterval &LI = getInterval(repReg);
LiveVariables::VarInfo& svi = lv_->getVarInfo(Reg);
for (unsigned i = 0, e = svi.Kills.size(); i != e; ++i) {
MachineInstr *Kill = svi.Kills[i];
// Suppose vr1 = op vr2, x
// and vr1 and vr2 are coalesced. vr2 should still be marked kill
// unless it is a two-address operand.
if (isRemoved(Kill) || hasRegisterDef(Kill, repReg))
continue;
if (LI.liveAt(getInstructionIndex(Kill) + InstrSlots::NUM))
unsetRegisterKill(Kill, repReg);
}
RegNum = JoinedLIs.find_next(RegNum);
}
DOUT << "*** Register mapping ***\n";
for (int i = 0, e = r2rMap_.size(); i != e; ++i)
if (r2rMap_[i]) {
DOUT << " reg " << i << " -> ";
DEBUG(printRegName(r2rMap_[i]));
DOUT << "\n";
}
}
/// Return true if the two specified registers belong to different register
/// classes. The registers may be either phys or virt regs.
bool LiveIntervals::differingRegisterClasses(unsigned RegA,
unsigned RegB) const {
// Get the register classes for the first reg.
if (MRegisterInfo::isPhysicalRegister(RegA)) {
assert(MRegisterInfo::isVirtualRegister(RegB) &&
"Shouldn't consider two physregs!");
return !mf_->getSSARegMap()->getRegClass(RegB)->contains(RegA);
}
// Compare against the regclass for the second reg.
const TargetRegisterClass *RegClass = mf_->getSSARegMap()->getRegClass(RegA);
if (MRegisterInfo::isVirtualRegister(RegB))
return RegClass != mf_->getSSARegMap()->getRegClass(RegB);
else
return !RegClass->contains(RegB);
}
/// lastRegisterUse - Returns the last use of the specific register between
/// cycles Start and End. It also returns the use operand by reference. It
/// returns NULL if there are no uses.
MachineInstr *
LiveIntervals::lastRegisterUse(unsigned Reg, unsigned Start, unsigned End,
MachineOperand *&MOU) {
int e = (End-1) / InstrSlots::NUM * InstrSlots::NUM;
int s = Start;
while (e >= s) {
// Skip deleted instructions
MachineInstr *MI = getInstructionFromIndex(e);
while ((e - InstrSlots::NUM) >= s && !MI) {
e -= InstrSlots::NUM;
MI = getInstructionFromIndex(e);
}
if (e < s || MI == NULL)
return NULL;
for (unsigned i = 0, NumOps = MI->getNumOperands(); i != NumOps; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isUse() && MO.getReg() &&
mri_->regsOverlap(rep(MO.getReg()), Reg)) {
MOU = &MO;
return MI;
}
}
e -= InstrSlots::NUM;
}
return NULL;
}
/// findDefOperand - Returns the MachineOperand that is a def of the specific
/// register. It returns NULL if the def is not found.
MachineOperand *LiveIntervals::findDefOperand(MachineInstr *MI, unsigned Reg) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isDef() &&
mri_->regsOverlap(rep(MO.getReg()), Reg))
return &MO;
}
return NULL;
}
/// unsetRegisterKill - Unset IsKill property of all uses of specific register
/// of the specific instruction.
void LiveIntervals::unsetRegisterKill(MachineInstr *MI, unsigned Reg) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isUse() && MO.isKill() && MO.getReg() &&
mri_->regsOverlap(rep(MO.getReg()), Reg))
MO.unsetIsKill();
}
}
/// hasRegisterDef - True if the instruction defines the specific register.
///
bool LiveIntervals::hasRegisterDef(MachineInstr *MI, unsigned Reg) {
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isDef() &&
mri_->regsOverlap(rep(MO.getReg()), Reg))
return true;
}
return false;
}
LiveInterval LiveIntervals::createInterval(unsigned reg) {
float Weight = MRegisterInfo::isPhysicalRegister(reg) ?
HUGE_VALF : 0.0F;
return LiveInterval(reg, Weight);
}
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