llvm-6502/lib/CodeGen/RegAllocLinearScan.cpp

537 lines
18 KiB
C++
Raw Normal View History

//===-- RegAllocLinearScan.cpp - Linear Scan register allocator -----------===//
//
// 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 a linear scan register allocator.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "regalloc"
#include "llvm/Function.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/SSARegMap.h"
#include "llvm/Target/MRegisterInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "Support/Debug.h"
#include "Support/Statistic.h"
#include "Support/STLExtras.h"
#include "LiveIntervalAnalysis.h"
#include "PhysRegTracker.h"
#include "VirtRegMap.h"
#include <algorithm>
#include <cmath>
#include <set>
#include <queue>
using namespace llvm;
namespace {
Statistic<double> efficiency
("regalloc", "Ratio of intervals processed over total intervals");
static unsigned numIterations = 0;
static unsigned numIntervals = 0;
class RA : public MachineFunctionPass {
private:
MachineFunction* mf_;
const TargetMachine* tm_;
const MRegisterInfo* mri_;
LiveIntervals* li_;
typedef std::vector<LiveInterval*> IntervalPtrs;
IntervalPtrs handled_, fixed_, active_, inactive_;
typedef std::priority_queue<LiveInterval*,
IntervalPtrs,
greater_ptr<LiveInterval> > IntervalHeap;
IntervalHeap unhandled_;
std::auto_ptr<PhysRegTracker> prt_;
std::auto_ptr<VirtRegMap> vrm_;
std::auto_ptr<Spiller> spiller_;
typedef std::vector<float> SpillWeights;
SpillWeights spillWeights_;
public:
virtual const char* getPassName() const {
return "Linear Scan Register Allocator";
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LiveVariables>();
AU.addRequired<LiveIntervals>();
MachineFunctionPass::getAnalysisUsage(AU);
}
/// runOnMachineFunction - register allocate the whole function
bool runOnMachineFunction(MachineFunction&);
void releaseMemory();
private:
/// linearScan - the linear scan algorithm
void linearScan();
/// initIntervalSets - initializa the four interval sets:
/// unhandled, fixed, active and inactive
void initIntervalSets();
/// processActiveIntervals - expire old intervals and move
/// non-overlapping ones to the incative list
void processActiveIntervals(LiveInterval* cur);
/// processInactiveIntervals - expire old intervals and move
/// overlapping ones to the active list
void processInactiveIntervals(LiveInterval* cur);
/// updateSpillWeights - updates the spill weights of the
/// specifed physical register and its weight
void updateSpillWeights(unsigned reg, SpillWeights::value_type weight);
/// assignRegOrStackSlotAtInterval - assign a register if one
/// is available, or spill.
void assignRegOrStackSlotAtInterval(LiveInterval* cur);
///
/// register handling helpers
///
/// getFreePhysReg - return a free physical register for this
/// virtual register interval if we have one, otherwise return
/// 0
unsigned getFreePhysReg(LiveInterval* cur);
/// assignVirt2StackSlot - assigns this virtual register to a
/// stack slot. returns the stack slot
int assignVirt2StackSlot(unsigned virtReg);
template <typename ItTy>
void printIntervals(const char* const str, ItTy i, ItTy e) const {
if (str) std::cerr << str << " intervals:\n";
for (; i != e; ++i) {
std::cerr << "\t" << **i << " -> ";
unsigned reg = (*i)->reg;
if (MRegisterInfo::isVirtualRegister(reg)) {
reg = vrm_->getPhys(reg);
}
std::cerr << mri_->getName(reg) << '\n';
}
}
};
}
void RA::releaseMemory()
{
while (!unhandled_.empty()) unhandled_.pop();
fixed_.clear();
active_.clear();
inactive_.clear();
handled_.clear();
}
bool RA::runOnMachineFunction(MachineFunction &fn) {
mf_ = &fn;
tm_ = &fn.getTarget();
mri_ = tm_->getRegisterInfo();
li_ = &getAnalysis<LiveIntervals>();
if (!prt_.get()) prt_.reset(new PhysRegTracker(*mri_));
vrm_.reset(new VirtRegMap(*mf_));
if (!spiller_.get()) spiller_.reset(createSpiller());
initIntervalSets();
linearScan();
spiller_->runOnMachineFunction(*mf_, *vrm_);
return true;
}
void RA::linearScan()
{
// linear scan algorithm
DEBUG(std::cerr << "********** LINEAR SCAN **********\n");
DEBUG(std::cerr << "********** Function: "
<< mf_->getFunction()->getName() << '\n');
// DEBUG(printIntervals("unhandled", unhandled_.begin(), unhandled_.end()));
DEBUG(printIntervals("fixed", fixed_.begin(), fixed_.end()));
DEBUG(printIntervals("active", active_.begin(), active_.end()));
DEBUG(printIntervals("inactive", inactive_.begin(), inactive_.end()));
while (!unhandled_.empty()) {
// pick the interval with the earliest start point
LiveInterval* cur = unhandled_.top();
unhandled_.pop();
++numIterations;
DEBUG(std::cerr << "\n*** CURRENT ***: " << *cur << '\n');
processActiveIntervals(cur);
processInactiveIntervals(cur);
// if this register is fixed we are done
if (MRegisterInfo::isPhysicalRegister(cur->reg)) {
prt_->addRegUse(cur->reg);
active_.push_back(cur);
handled_.push_back(cur);
}
// otherwise we are allocating a virtual register. try to find
// a free physical register or spill an interval in order to
// assign it one (we could spill the current though).
else {
assignRegOrStackSlotAtInterval(cur);
}
DEBUG(printIntervals("active", active_.begin(), active_.end()));
DEBUG(printIntervals("inactive", inactive_.begin(), inactive_.end()));
}
numIntervals += li_->getNumIntervals();
efficiency = double(numIterations) / double(numIntervals);
// expire any remaining active intervals
for (IntervalPtrs::reverse_iterator
i = active_.rbegin(); i != active_.rend(); ) {
unsigned reg = (*i)->reg;
DEBUG(std::cerr << "\tinterval " << **i << " expired\n");
if (MRegisterInfo::isVirtualRegister(reg))
reg = vrm_->getPhys(reg);
prt_->delRegUse(reg);
i = IntervalPtrs::reverse_iterator(active_.erase(i.base()-1));
}
// expire any remaining inactive intervals
for (IntervalPtrs::reverse_iterator
i = inactive_.rbegin(); i != inactive_.rend(); ) {
DEBUG(std::cerr << "\tinterval " << **i << " expired\n");
i = IntervalPtrs::reverse_iterator(inactive_.erase(i.base()-1));
}
DEBUG(std::cerr << *vrm_);
}
void RA::initIntervalSets()
{
assert(unhandled_.empty() && fixed_.empty() &&
active_.empty() && inactive_.empty() &&
"interval sets should be empty on initialization");
for (LiveIntervals::iterator i = li_->begin(), e = li_->end(); i != e; ++i){
unhandled_.push(&i->second);
if (MRegisterInfo::isPhysicalRegister(i->second.reg))
fixed_.push_back(&i->second);
}
}
void RA::processActiveIntervals(IntervalPtrs::value_type cur)
{
DEBUG(std::cerr << "\tprocessing active intervals:\n");
for (IntervalPtrs::reverse_iterator
i = active_.rbegin(); i != active_.rend();) {
unsigned reg = (*i)->reg;
// remove expired intervals
if ((*i)->expiredAt(cur->start())) {
DEBUG(std::cerr << "\t\tinterval " << **i << " expired\n");
if (MRegisterInfo::isVirtualRegister(reg))
reg = vrm_->getPhys(reg);
prt_->delRegUse(reg);
// remove from active
i = IntervalPtrs::reverse_iterator(active_.erase(i.base()-1));
}
// move inactive intervals to inactive list
else if (!(*i)->liveAt(cur->start())) {
DEBUG(std::cerr << "\t\tinterval " << **i << " inactive\n");
if (MRegisterInfo::isVirtualRegister(reg))
reg = vrm_->getPhys(reg);
prt_->delRegUse(reg);
// add to inactive
inactive_.push_back(*i);
// remove from active
i = IntervalPtrs::reverse_iterator(active_.erase(i.base()-1));
}
else {
++i;
}
}
}
void RA::processInactiveIntervals(IntervalPtrs::value_type cur)
{
DEBUG(std::cerr << "\tprocessing inactive intervals:\n");
for (IntervalPtrs::reverse_iterator
i = inactive_.rbegin(); i != inactive_.rend();) {
unsigned reg = (*i)->reg;
// remove expired intervals
if ((*i)->expiredAt(cur->start())) {
DEBUG(std::cerr << "\t\tinterval " << **i << " expired\n");
// remove from inactive
i = IntervalPtrs::reverse_iterator(inactive_.erase(i.base()-1));
}
// move re-activated intervals in active list
else if ((*i)->liveAt(cur->start())) {
DEBUG(std::cerr << "\t\tinterval " << **i << " active\n");
if (MRegisterInfo::isVirtualRegister(reg))
reg = vrm_->getPhys(reg);
prt_->addRegUse(reg);
// add to active
active_.push_back(*i);
// remove from inactive
i = IntervalPtrs::reverse_iterator(inactive_.erase(i.base()-1));
}
else {
++i;
}
}
}
void RA::updateSpillWeights(unsigned reg, SpillWeights::value_type weight)
{
spillWeights_[reg] += weight;
for (const unsigned* as = mri_->getAliasSet(reg); *as; ++as)
spillWeights_[*as] += weight;
}
void RA::assignRegOrStackSlotAtInterval(LiveInterval* cur)
{
DEBUG(std::cerr << "\tallocating current interval: ");
PhysRegTracker backupPrt = *prt_;
spillWeights_.assign(mri_->getNumRegs(), 0.0);
// for each interval in active update spill weights
for (IntervalPtrs::const_iterator i = active_.begin(), e = active_.end();
i != e; ++i) {
unsigned reg = (*i)->reg;
if (MRegisterInfo::isVirtualRegister(reg))
reg = vrm_->getPhys(reg);
updateSpillWeights(reg, (*i)->weight);
}
// for every interval in inactive we overlap with, mark the
// register as not free and update spill weights
for (IntervalPtrs::const_iterator i = inactive_.begin(),
e = inactive_.end(); i != e; ++i) {
if (cur->overlaps(**i)) {
unsigned reg = (*i)->reg;
if (MRegisterInfo::isVirtualRegister(reg))
reg = vrm_->getPhys(reg);
prt_->addRegUse(reg);
updateSpillWeights(reg, (*i)->weight);
}
}
// for every interval in fixed we overlap with,
// mark the register as not free and update spill weights
for (IntervalPtrs::const_iterator i = fixed_.begin(),
e = fixed_.end(); i != e; ++i) {
if (cur->overlaps(**i)) {
unsigned reg = (*i)->reg;
prt_->addRegUse(reg);
updateSpillWeights(reg, (*i)->weight);
}
}
unsigned physReg = getFreePhysReg(cur);
// restore the physical register tracker
*prt_ = backupPrt;
// if we find a free register, we are done: assign this virtual to
// the free physical register and add this interval to the active
// list.
if (physReg) {
DEBUG(std::cerr << mri_->getName(physReg) << '\n');
vrm_->assignVirt2Phys(cur->reg, physReg);
prt_->addRegUse(physReg);
active_.push_back(cur);
handled_.push_back(cur);
return;
}
DEBUG(std::cerr << "no free registers\n");
DEBUG(std::cerr << "\tassigning stack slot at interval "<< *cur << ":\n");
float minWeight = HUGE_VAL;
unsigned minReg = 0;
const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_);
i != rc->allocation_order_end(*mf_); ++i) {
unsigned reg = *i;
if (minWeight > spillWeights_[reg]) {
minWeight = spillWeights_[reg];
minReg = reg;
}
}
DEBUG(std::cerr << "\t\tregister with min weight: "
<< mri_->getName(minReg) << " (" << minWeight << ")\n");
// if the current has the minimum weight, we need to spill it and
// add any added intervals back to unhandled, and restart
// linearscan.
if (cur->weight <= minWeight) {
DEBUG(std::cerr << "\t\t\tspilling(c): " << *cur << '\n';);
int slot = vrm_->assignVirt2StackSlot(cur->reg);
std::vector<LiveInterval*> added =
li_->addIntervalsForSpills(*cur, *vrm_, slot);
if (added.empty())
return; // Early exit if all spills were folded.
// Merge added with unhandled. Note that we know that
// addIntervalsForSpills returns intervals sorted by their starting
// point.
for (unsigned i = 0, e = added.size(); i != e; ++i)
unhandled_.push(added[i]);
return;
}
// push the current interval back to unhandled since we are going
// to re-run at least this iteration. Since we didn't modify it it
// should go back right in the front of the list
unhandled_.push(cur);
// otherwise we spill all intervals aliasing the register with
// minimum weight, rollback to the interval with the earliest
// start point and let the linear scan algorithm run again
std::vector<LiveInterval*> added;
assert(MRegisterInfo::isPhysicalRegister(minReg) &&
"did not choose a register to spill?");
std::vector<bool> toSpill(mri_->getNumRegs(), false);
// we are going to spill minReg and all its aliases
toSpill[minReg] = true;
for (const unsigned* as = mri_->getAliasSet(minReg); *as; ++as)
toSpill[*as] = true;
// the earliest start of a spilled interval indicates up to where
// in handled we need to roll back
unsigned earliestStart = cur->start();
// set of spilled vregs (used later to rollback properly)
std::set<unsigned> spilled;
// spill live intervals of virtual regs mapped to the physical
// register we want to clear (and its aliases). we only spill
// those that overlap with the current interval as the rest do not
// affect its allocation. we also keep track of the earliest start
// of all spilled live intervals since this will mark our rollback
// point
for (IntervalPtrs::iterator
i = active_.begin(); i != active_.end(); ++i) {
unsigned reg = (*i)->reg;
if (MRegisterInfo::isVirtualRegister(reg) &&
toSpill[vrm_->getPhys(reg)] &&
cur->overlaps(**i)) {
DEBUG(std::cerr << "\t\t\tspilling(a): " << **i << '\n');
earliestStart = std::min(earliestStart, (*i)->start());
int slot = vrm_->assignVirt2StackSlot((*i)->reg);
std::vector<LiveInterval*> newIs =
li_->addIntervalsForSpills(**i, *vrm_, slot);
std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
spilled.insert(reg);
}
}
for (IntervalPtrs::iterator
i = inactive_.begin(); i != inactive_.end(); ++i) {
unsigned reg = (*i)->reg;
if (MRegisterInfo::isVirtualRegister(reg) &&
toSpill[vrm_->getPhys(reg)] &&
cur->overlaps(**i)) {
DEBUG(std::cerr << "\t\t\tspilling(i): " << **i << '\n');
earliestStart = std::min(earliestStart, (*i)->start());
int slot = vrm_->assignVirt2StackSlot((*i)->reg);
std::vector<LiveInterval*> newIs =
li_->addIntervalsForSpills(**i, *vrm_, slot);
std::copy(newIs.begin(), newIs.end(), std::back_inserter(added));
spilled.insert(reg);
}
}
DEBUG(std::cerr << "\t\trolling back to: " << earliestStart << '\n');
// scan handled in reverse order up to the earliaset start of a
// spilled live interval and undo each one, restoring the state of
// unhandled
while (!handled_.empty()) {
LiveInterval* i = handled_.back();
// if this interval starts before t we are done
if (i->start() < earliestStart)
break;
DEBUG(std::cerr << "\t\t\tundo changes for: " << *i << '\n');
handled_.pop_back();
// when undoing a live interval allocation we must know if it
// is active or inactive to properly update the PhysRegTracker
// and the VirtRegMap
IntervalPtrs::iterator it;
if ((it = find(active_.begin(), active_.end(), i)) != active_.end()) {
active_.erase(it);
if (MRegisterInfo::isPhysicalRegister(i->reg)) {
prt_->delRegUse(i->reg);
unhandled_.push(i);
}
else {
if (!spilled.count(i->reg))
unhandled_.push(i);
prt_->delRegUse(vrm_->getPhys(i->reg));
vrm_->clearVirt(i->reg);
}
}
else if ((it = find(inactive_.begin(), inactive_.end(), i)) != inactive_.end()) {
inactive_.erase(it);
if (MRegisterInfo::isPhysicalRegister(i->reg))
unhandled_.push(i);
else {
if (!spilled.count(i->reg))
unhandled_.push(i);
vrm_->clearVirt(i->reg);
}
}
else {
if (MRegisterInfo::isVirtualRegister(i->reg))
vrm_->clearVirt(i->reg);
unhandled_.push(i);
}
}
// scan the rest and undo each interval that expired after t and
// insert it in active (the next iteration of the algorithm will
// put it in inactive if required)
IntervalPtrs::iterator i = handled_.begin(), e = handled_.end();
for (; i != e; ++i) {
if (!(*i)->expiredAt(earliestStart) && (*i)->expiredAt(cur->start())) {
DEBUG(std::cerr << "\t\t\tundo changes for: " << **i << '\n');
active_.push_back(*i);
if (MRegisterInfo::isPhysicalRegister((*i)->reg))
prt_->addRegUse((*i)->reg);
else
prt_->addRegUse(vrm_->getPhys((*i)->reg));
}
}
std::sort(added.begin(), added.end(), less_ptr<LiveInterval>());
// merge added with unhandled
for (unsigned i = 0, e = added.size(); i != e; ++i)
unhandled_.push(added[i]);
}
unsigned RA::getFreePhysReg(LiveInterval* cur)
{
const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_);
i != rc->allocation_order_end(*mf_); ++i) {
unsigned reg = *i;
if (prt_->isRegAvail(reg))
return reg;
}
return 0;
}
FunctionPass* llvm::createLinearScanRegisterAllocator() {
return new RA();
}