llvm-6502/lib/CodeGen/LiveIntervalAnalysis.cpp
2004-02-15 10:24:21 +00:00

659 lines
23 KiB
C++

//===-- LiveIntervals.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/LiveIntervals.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/CFG.h"
#include "Support/CommandLine.h"
#include "Support/Debug.h"
#include "Support/Statistic.h"
#include "Support/STLExtras.h"
#include <cmath>
#include <iostream>
#include <limits>
using namespace llvm;
namespace {
RegisterAnalysis<LiveIntervals> X("liveintervals",
"Live Interval Analysis");
Statistic<> numIntervals("liveintervals", "Number of intervals");
Statistic<> numJoined ("liveintervals", "Number of joined intervals");
Statistic<> numPeep ("liveintervals", "Number of identity moves "
"eliminated after coalescing");
cl::opt<bool>
join("join-liveintervals",
cl::desc("Join compatible live intervals"),
cl::init(true));
};
void LiveIntervals::getAnalysisUsage(AnalysisUsage &AU) const
{
AU.addPreserved<LiveVariables>();
AU.addRequired<LiveVariables>();
AU.addPreservedID(PHIEliminationID);
AU.addRequiredID(PHIEliminationID);
AU.addRequiredID(TwoAddressInstructionPassID);
AU.addRequired<LoopInfo>();
MachineFunctionPass::getAnalysisUsage(AU);
}
void LiveIntervals::releaseMemory()
{
mbbi2mbbMap_.clear();
mi2iMap_.clear();
i2miMap_.clear();
r2iMap_.clear();
r2rMap_.clear();
intervals_.clear();
}
/// runOnMachineFunction - Register allocate the whole function
///
bool LiveIntervals::runOnMachineFunction(MachineFunction &fn) {
DEBUG(std::cerr << "MACHINE FUNCTION: "; fn.print(std::cerr));
mf_ = &fn;
tm_ = &fn.getTarget();
mri_ = tm_->getRegisterInfo();
lv_ = &getAnalysis<LiveVariables>();
// number MachineInstrs
unsigned miIndex = 0;
for (MachineFunction::iterator mbb = mf_->begin(), mbbEnd = mf_->end();
mbb != mbbEnd; ++mbb) {
const std::pair<MachineBasicBlock*, unsigned>& entry =
lv_->getMachineBasicBlockInfo(mbb);
bool inserted = mbbi2mbbMap_.insert(std::make_pair(entry.second,
entry.first)).second;
assert(inserted && "multiple index -> MachineBasicBlock");
for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
mi != miEnd; ++mi) {
inserted = mi2iMap_.insert(std::make_pair(mi, miIndex)).second;
assert(inserted && "multiple MachineInstr -> index mappings");
i2miMap_.push_back(mi);
miIndex += 2;
}
}
computeIntervals();
numIntervals += intervals_.size();
// join intervals if requested
if (join) joinIntervals();
// perform a final pass over the instructions and compute spill
// weights, coalesce virtual registers and remove identity moves
const LoopInfo& loopInfo = getAnalysis<LoopInfo>();
const TargetInstrInfo& tii = tm_->getInstrInfo();
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; ) {
for (unsigned i = 0; i < mii->getNumOperands(); ++i) {
const MachineOperand& mop = mii->getOperand(i);
if (mop.isRegister()) {
// replace register with representative register
unsigned reg = rep(mop.getReg());
mii->SetMachineOperandReg(i, reg);
if (MRegisterInfo::isVirtualRegister(reg)) {
Reg2IntervalMap::iterator r2iit = r2iMap_.find(reg);
assert(r2iit != r2iMap_.end());
r2iit->second->weight += pow(10.0F, loopDepth);
}
}
}
// if the move is now an identity move delete it
unsigned srcReg, dstReg;
if (tii.isMoveInstr(*mii, srcReg, dstReg) && srcReg == dstReg) {
// remove index -> MachineInstr and
// MachineInstr -> index mappings
Mi2IndexMap::iterator mi2i = mi2iMap_.find(mii);
if (mi2i != mi2iMap_.end()) {
i2miMap_[mi2i->second/2] = 0;
mi2iMap_.erase(mi2i);
}
mii = mbbi->erase(mii);
++numPeep;
}
else
++mii;
}
}
intervals_.sort(StartPointComp());
DEBUG(std::cerr << "*** INTERVALS ***\n");
DEBUG(std::copy(intervals_.begin(), intervals_.end(),
std::ostream_iterator<Interval>(std::cerr, "\n")));
DEBUG(std::cerr << "*** MACHINEINSTRS ***\n");
DEBUG(
for (unsigned i = 0; i != i2miMap_.size(); ++i) {
if (const MachineInstr* mi = i2miMap_[i]) {
std:: cerr << i*2 << '\t';
mi->print(std::cerr, *tm_);
}
});
return true;
}
void LiveIntervals::updateSpilledInterval(Interval& li)
{
assert(li.weight != std::numeric_limits<float>::infinity() &&
"attempt to spill already spilled interval!");
Interval::Ranges oldRanges;
swap(oldRanges, li.ranges);
for (Interval::Ranges::iterator i = oldRanges.begin(), e = oldRanges.end();
i != e; ++i) {
unsigned index = i->first & ~1;
unsigned end = i->second;
for (; index < end; index += 2) {
// skip deleted instructions
while (!getInstructionFromIndex(index)) index += 2;
MachineInstr* mi = getInstructionFromIndex(index);
for (unsigned i = 0; i < mi->getNumOperands(); ++i) {
MachineOperand& mop = mi->getOperand(i);
if (mop.isRegister()) {
unsigned reg = mop.getReg();
if (rep(reg) == li.reg) {
li.addRange(index, index + 2);
}
}
}
}
}
// the new spill weight is now infinity as it cannot be spilled again
li.weight = std::numeric_limits<float>::infinity();
}
void LiveIntervals::printRegName(unsigned reg) const
{
if (MRegisterInfo::isPhysicalRegister(reg))
std::cerr << mri_->getName(reg);
else
std::cerr << '%' << reg;
}
void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock* mbb,
MachineBasicBlock::iterator mi,
unsigned reg)
{
DEBUG(std::cerr << "\t\tregister: ";printRegName(reg); std::cerr << '\n');
LiveVariables::VarInfo& vi = lv_->getVarInfo(reg);
Interval* interval = 0;
Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
if (r2iit == r2iMap_.end() || r2iit->first != reg) {
// add new interval
intervals_.push_back(Interval(reg));
// update interval index for this register
r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
interval = &intervals_.back();
// iterate over all of the blocks that the variable is
// completely live in, adding them to the live
// interval. obviously we only need to do this once.
for (unsigned i = 0, e = vi.AliveBlocks.size(); i != e; ++i) {
if (vi.AliveBlocks[i]) {
MachineBasicBlock* mbb = lv_->getIndexMachineBasicBlock(i);
if (!mbb->empty()) {
interval->addRange(getInstructionIndex(&mbb->front()),
getInstructionIndex(&mbb->back()) + 1);
}
}
}
}
else {
interval = &*r2iit->second;
}
// we consider defs to happen at the second time slot of the
// instruction
unsigned instrIndex = getInstructionIndex(mi) + 1;
bool killedInDefiningBasicBlock = false;
for (int i = 0, e = vi.Kills.size(); i != e; ++i) {
MachineBasicBlock* killerBlock = vi.Kills[i].first;
MachineInstr* killerInstr = vi.Kills[i].second;
unsigned start = (mbb == killerBlock ?
instrIndex :
getInstructionIndex(&killerBlock->front()));
unsigned end = (killerInstr == mi ?
instrIndex + 1 : // dead
getInstructionIndex(killerInstr) + 1); // killed
// we do not want to add invalid ranges. these can happen when
// a variable has its latest use and is redefined later on in
// the same basic block (common with variables introduced by
// PHI elimination)
if (start < end) {
killedInDefiningBasicBlock |= mbb == killerBlock;
interval->addRange(start, end);
}
}
if (!killedInDefiningBasicBlock) {
unsigned end = getInstructionIndex(&mbb->back()) + 1;
interval->addRange(instrIndex, end);
}
}
void LiveIntervals::handlePhysicalRegisterDef(MachineBasicBlock* mbb,
MachineBasicBlock::iterator mi,
unsigned reg)
{
typedef LiveVariables::killed_iterator KillIter;
DEBUG(std::cerr << "\t\tregister: "; printRegName(reg));
MachineBasicBlock::iterator e = mbb->end();
// we consider defs to happen at the second time slot of the
// instruction
unsigned start, end;
start = end = getInstructionIndex(mi) + 1;
// a variable can be dead by the instruction defining it
for (KillIter ki = lv_->dead_begin(mi), ke = lv_->dead_end(mi);
ki != ke; ++ki) {
if (reg == ki->second) {
DEBUG(std::cerr << " dead\n");
++end;
goto exit;
}
}
// a variable can only be killed by subsequent instructions
do {
++mi;
end += 2;
for (KillIter ki = lv_->killed_begin(mi), ke = lv_->killed_end(mi);
ki != ke; ++ki) {
if (reg == ki->second) {
DEBUG(std::cerr << " killed\n");
goto exit;
}
}
} while (mi != e);
exit:
assert(start < end && "did not find end of interval?");
Reg2IntervalMap::iterator r2iit = r2iMap_.lower_bound(reg);
if (r2iit != r2iMap_.end() && r2iit->first == reg) {
r2iit->second->addRange(start, end);
}
else {
intervals_.push_back(Interval(reg));
// update interval index for this register
r2iMap_.insert(r2iit, std::make_pair(reg, --intervals_.end()));
intervals_.back().addRange(start, end);
}
}
void LiveIntervals::handleRegisterDef(MachineBasicBlock* mbb,
MachineBasicBlock::iterator mi,
unsigned reg)
{
if (MRegisterInfo::isPhysicalRegister(reg)) {
if (lv_->getAllocatablePhysicalRegisters()[reg]) {
handlePhysicalRegisterDef(mbb, mi, reg);
for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
handlePhysicalRegisterDef(mbb, mi, *as);
}
}
else {
handleVirtualRegisterDef(mbb, mi, reg);
}
}
unsigned LiveIntervals::getInstructionIndex(MachineInstr* instr) const
{
Mi2IndexMap::const_iterator it = mi2iMap_.find(instr);
return it == mi2iMap_.end() ? std::numeric_limits<unsigned>::max() : it->second;
}
MachineInstr* LiveIntervals::getInstructionFromIndex(unsigned index) const
{
index /= 2; // convert index to vector index
assert(index < i2miMap_.size() &&
"index does not correspond to an instruction");
return i2miMap_[index];
}
/// 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()
{
DEBUG(std::cerr << "*** COMPUTING LIVE INTERVALS ***\n");
for (MbbIndex2MbbMap::iterator
it = mbbi2mbbMap_.begin(), itEnd = mbbi2mbbMap_.end();
it != itEnd; ++it) {
MachineBasicBlock* mbb = it->second;
DEBUG(std::cerr << mbb->getBasicBlock()->getName() << ":\n");
for (MachineBasicBlock::iterator mi = mbb->begin(), miEnd = mbb->end();
mi != miEnd; ++mi) {
const TargetInstrDescriptor& tid =
tm_->getInstrInfo().get(mi->getOpcode());
DEBUG(std::cerr << "[" << getInstructionIndex(mi) << "]\t";
mi->print(std::cerr, *tm_););
// handle implicit defs
for (const unsigned* id = tid.ImplicitDefs; *id; ++id)
handleRegisterDef(mbb, mi, *id);
// handle explicit defs
for (int i = mi->getNumOperands() - 1; i >= 0; --i) {
MachineOperand& mop = mi->getOperand(i);
// handle register defs - build intervals
if (mop.isRegister() && mop.isDef())
handleRegisterDef(mbb, mi, mop.getReg());
}
}
}
}
unsigned LiveIntervals::rep(unsigned reg)
{
Reg2RegMap::iterator it = r2rMap_.find(reg);
if (it != r2rMap_.end())
return it->second = rep(it->second);
return reg;
}
void LiveIntervals::joinIntervals()
{
DEBUG(std::cerr << "** JOINING INTERVALS ***\n");
const TargetInstrInfo& tii = tm_->getInstrInfo();
for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
mbbi != mbbe; ++mbbi) {
MachineBasicBlock* mbb = mbbi;
DEBUG(std::cerr << mbb->getBasicBlock()->getName() << ":\n");
for (MachineBasicBlock::iterator mi = mbb->begin(), mie = mbb->end();
mi != mie; ++mi) {
const TargetInstrDescriptor& tid =
tm_->getInstrInfo().get(mi->getOpcode());
DEBUG(std::cerr << "[" << getInstructionIndex(mi) << "]\t";
mi->print(std::cerr, *tm_););
// we only join virtual registers with allocatable
// physical registers since we do not have liveness information
// on not allocatable physical registers
unsigned regA, regB;
if (tii.isMoveInstr(*mi, regA, regB) &&
(MRegisterInfo::isVirtualRegister(regA) ||
lv_->getAllocatablePhysicalRegisters()[regA]) &&
(MRegisterInfo::isVirtualRegister(regB) ||
lv_->getAllocatablePhysicalRegisters()[regB])) {
// get representative registers
regA = rep(regA);
regB = rep(regB);
// if they are already joined we continue
if (regA == regB)
continue;
Reg2IntervalMap::iterator r2iA = r2iMap_.find(regA);
assert(r2iA != r2iMap_.end());
Reg2IntervalMap::iterator r2iB = r2iMap_.find(regB);
assert(r2iB != r2iMap_.end());
Intervals::iterator intA = r2iA->second;
Intervals::iterator intB = r2iB->second;
// both A and B are virtual registers
if (MRegisterInfo::isVirtualRegister(intA->reg) &&
MRegisterInfo::isVirtualRegister(intB->reg)) {
const TargetRegisterClass *rcA, *rcB;
rcA = mf_->getSSARegMap()->getRegClass(intA->reg);
rcB = mf_->getSSARegMap()->getRegClass(intB->reg);
assert(rcA == rcB && "registers must be of the same class");
// if their intervals do not overlap we join them
if (!intB->overlaps(*intA)) {
intA->join(*intB);
r2iB->second = r2iA->second;
r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
intervals_.erase(intB);
++numJoined;
}
}
else if (MRegisterInfo::isPhysicalRegister(intA->reg) ^
MRegisterInfo::isPhysicalRegister(intB->reg)) {
if (MRegisterInfo::isPhysicalRegister(intB->reg)) {
std::swap(regA, regB);
std::swap(intA, intB);
std::swap(r2iA, r2iB);
}
assert(MRegisterInfo::isPhysicalRegister(intA->reg) &&
MRegisterInfo::isVirtualRegister(intB->reg) &&
"A must be physical and B must be virtual");
if (!intA->overlaps(*intB) &&
!overlapsAliases(*intA, *intB)) {
intA->join(*intB);
r2iB->second = r2iA->second;
r2rMap_.insert(std::make_pair(intB->reg, intA->reg));
intervals_.erase(intB);
++numJoined;
}
}
}
}
}
}
bool LiveIntervals::overlapsAliases(const Interval& lhs,
const Interval& rhs) const
{
assert(MRegisterInfo::isPhysicalRegister(lhs.reg) &&
"first interval must describe a physical register");
for (const unsigned* as = mri_->getAliasSet(lhs.reg); *as; ++as) {
Reg2IntervalMap::const_iterator r2i = r2iMap_.find(*as);
assert(r2i != r2iMap_.end() && "alias does not have interval?");
if (rhs.overlaps(*r2i->second))
return true;
}
return false;
}
LiveIntervals::Interval::Interval(unsigned r)
: reg(r),
weight((MRegisterInfo::isPhysicalRegister(r) ?
std::numeric_limits<float>::infinity() : 0.0F))
{
}
// An example for liveAt():
//
// this = [1,2), liveAt(0) will return false. The instruction defining
// this spans slots [0,1]. Since it is a definition we say that it is
// live in the second slot onwards. By ending the lifetime of this
// interval at 2 it means that it is not used at all. liveAt(1)
// returns true which means that this clobbers a register at
// instruction at 0.
//
// this = [1,4), liveAt(0) will return false and liveAt(2) will return
// true. The variable is defined at instruction 0 and last used at 2.
bool LiveIntervals::Interval::liveAt(unsigned index) const
{
Range dummy(index, index+1);
Ranges::const_iterator r = std::upper_bound(ranges.begin(),
ranges.end(),
dummy);
if (r == ranges.begin())
return false;
--r;
return index >= r->first && index < r->second;
}
// An example for overlaps():
//
// 0: A = ...
// 2: B = ...
// 4: C = A + B ;; last use of A
//
// The live intervals should look like:
//
// A = [1, 5)
// B = [3, x)
// C = [5, y)
//
// A->overlaps(C) should return false since we want to be able to join
// A and C.
bool LiveIntervals::Interval::overlaps(const Interval& other) const
{
Ranges::const_iterator i = ranges.begin();
Ranges::const_iterator ie = ranges.end();
Ranges::const_iterator j = other.ranges.begin();
Ranges::const_iterator je = other.ranges.end();
if (i->first < j->first) {
i = std::upper_bound(i, ie, *j);
if (i != ranges.begin()) --i;
}
else if (j->first < i->first) {
j = std::upper_bound(j, je, *i);
if (j != other.ranges.begin()) --j;
}
while (i != ie && j != je) {
if (i->first == j->first) {
return true;
}
else {
if (i->first > j->first) {
swap(i, j);
swap(ie, je);
}
assert(i->first < j->first);
if (i->second > j->first) {
return true;
}
else {
++i;
}
}
}
return false;
}
void LiveIntervals::Interval::addRange(unsigned start, unsigned end)
{
assert(start < end && "Invalid range to add!");
DEBUG(std::cerr << "\t\t\tadding range: [" << start <<','<< end << ") -> ");
//assert(start < end && "invalid range?");
Range range = std::make_pair(start, end);
Ranges::iterator it =
ranges.insert(std::upper_bound(ranges.begin(), ranges.end(), range),
range);
it = mergeRangesForward(it);
it = mergeRangesBackward(it);
DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
}
void LiveIntervals::Interval::join(const LiveIntervals::Interval& other)
{
DEBUG(std::cerr << "\t\t\t\tjoining intervals: "
<< other << " and " << *this << '\n');
Ranges::iterator cur = ranges.begin();
for (Ranges::const_iterator i = other.ranges.begin(),
e = other.ranges.end(); i != e; ++i) {
cur = ranges.insert(std::upper_bound(cur, ranges.end(), *i), *i);
cur = mergeRangesForward(cur);
cur = mergeRangesBackward(cur);
}
if (MRegisterInfo::isVirtualRegister(reg))
weight += other.weight;
DEBUG(std::cerr << "\t\t\t\tafter merging: " << *this << '\n');
}
LiveIntervals::Interval::Ranges::iterator
LiveIntervals::Interval::mergeRangesForward(Ranges::iterator it)
{
for (Ranges::iterator next = it + 1;
next != ranges.end() && it->second >= next->first; ) {
it->second = std::max(it->second, next->second);
next = ranges.erase(next);
}
return it;
}
LiveIntervals::Interval::Ranges::iterator
LiveIntervals::Interval::mergeRangesBackward(Ranges::iterator it)
{
while (it != ranges.begin()) {
Ranges::iterator prev = it - 1;
if (it->first > prev->second) break;
it->first = std::min(it->first, prev->first);
it->second = std::max(it->second, prev->second);
it = ranges.erase(prev);
}
return it;
}
std::ostream& llvm::operator<<(std::ostream& os,
const LiveIntervals::Interval& li)
{
os << "%reg" << li.reg << ',' << li.weight << " = ";
for (LiveIntervals::Interval::Ranges::const_iterator
i = li.ranges.begin(), e = li.ranges.end(); i != e; ++i) {
os << "[" << i->first << "," << i->second << ")";
}
return os;
}