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llvm-6502/lib/CodeGen/RegAllocLinearScan.cpp
Alkis Evlogimenos 0d6c5b6489 Move machine code rewriter and spiller outside the register 
allocator.

The implementation is completely rewritten and now employs several
optimizations not exercised before. For example for 164.gzip we have
997 loads and 699 stores vs the 1221 loads and 880 stores we have
before.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11798 91177308-0d34-0410-b5e6-96231b3b80d8
2004-02-24 08:58:30 +00:00

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//===-- 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 "LiveIntervals.h"
#include "PhysRegTracker.h"
#include "VirtRegMap.h"
#include <algorithm>
#include <iostream>
using namespace llvm;
namespace {
class RA : public MachineFunctionPass {
private:
MachineFunction* mf_;
const TargetMachine* tm_;
const MRegisterInfo* mri_;
LiveIntervals* li_;
typedef std::list<LiveIntervals::Interval*> IntervalPtrs;
IntervalPtrs unhandled_, fixed_, active_, inactive_, handled_;
std::auto_ptr<PhysRegTracker> prt_;
std::auto_ptr<VirtRegMap> vrm_;
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(LiveIntervals::Intervals& li);
/// processActiveIntervals - expire old intervals and move
/// non-overlapping ones to the incative list
void processActiveIntervals(IntervalPtrs::value_type cur);
/// processInactiveIntervals - expire old intervals and move
/// overlapping ones to the active list
void processInactiveIntervals(IntervalPtrs::value_type 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(IntervalPtrs::value_type cur);
///
/// register handling helpers
///
/// getFreePhysReg - return a free physical register for this
/// virtual register interval if we have one, otherwise return
/// 0
unsigned getFreePhysReg(IntervalPtrs::value_type cur);
/// assignVirt2StackSlot - assigns this virtual register to a
/// stack slot. returns the stack slot
int assignVirt2StackSlot(unsigned virtReg);
void printIntervals(const char* const str,
RA::IntervalPtrs::const_iterator i,
RA::IntervalPtrs::const_iterator 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 verifyAssignment() const {
// for (Virt2PhysMap::const_iterator i = v2pMap_.begin(),
// e = v2pMap_.end(); i != e; ++i)
// for (Virt2PhysMap::const_iterator i2 = next(i); i2 != e; ++i2)
// if (MRegisterInfo::isVirtualRegister(i->second) &&
// (i->second == i2->second ||
// mri_->areAliases(i->second, i2->second))) {
// const LiveIntervals::Interval
// &in = li_->getInterval(i->second),
// &in2 = li_->getInterval(i2->second);
// if (in.overlaps(in2)) {
// std::cerr << in << " overlaps " << in2 << '\n';
// assert(0);
// }
// }
// }
};
}
void RA::releaseMemory()
{
unhandled_.clear();
active_.clear();
inactive_.clear();
fixed_.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_));
initIntervalSets(li_->getIntervals());
linearScan();
eliminateVirtRegs(*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() || !fixed_.empty()) {
// pick the interval with the earliest start point
IntervalPtrs::value_type cur;
if (fixed_.empty()) {
cur = unhandled_.front();
unhandled_.pop_front();
}
else if (unhandled_.empty()) {
cur = fixed_.front();
fixed_.pop_front();
}
else if (unhandled_.front()->start() < fixed_.front()->start()) {
cur = unhandled_.front();
unhandled_.pop_front();
}
else {
cur = fixed_.front();
fixed_.pop_front();
}
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()));
// DEBUG(verifyAssignment());
}
// expire any remaining active intervals
for (IntervalPtrs::iterator i = active_.begin(); i != active_.end(); ++i) {
unsigned reg = (*i)->reg;
DEBUG(std::cerr << "\tinterval " << **i << " expired\n");
if (MRegisterInfo::isVirtualRegister(reg))
reg = vrm_->getPhys(reg);
prt_->delRegUse(reg);
}
DEBUG(std::cerr << *vrm_);
}
void RA::initIntervalSets(LiveIntervals::Intervals& li)
{
assert(unhandled_.empty() && fixed_.empty() &&
active_.empty() && inactive_.empty() &&
"interval sets should be empty on initialization");
for (LiveIntervals::Intervals::iterator i = li.begin(), e = li.end();
i != e; ++i) {
if (MRegisterInfo::isPhysicalRegister(i->reg))
fixed_.push_back(&*i);
else
unhandled_.push_back(&*i);
}
}
void RA::processActiveIntervals(IntervalPtrs::value_type cur)
{
DEBUG(std::cerr << "\tprocessing active intervals:\n");
for (IntervalPtrs::iterator i = active_.begin(); i != active_.end();) {
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 = active_.erase(i);
}
// 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 = active_.erase(i);
}
else {
++i;
}
}
}
void RA::processInactiveIntervals(IntervalPtrs::value_type cur)
{
DEBUG(std::cerr << "\tprocessing inactive intervals:\n");
for (IntervalPtrs::iterator i = inactive_.begin(); i != inactive_.end();) {
unsigned reg = (*i)->reg;
// remove expired intervals
if ((*i)->expiredAt(cur->start())) {
DEBUG(std::cerr << "\t\tinterval " << **i << " expired\n");
// remove from inactive
i = inactive_.erase(i);
}
// 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 = inactive_.erase(i);
}
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(IntervalPtrs::value_type 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 = std::numeric_limits<float>::infinity();
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 modify it,
// push it back in unhandled and let the linear scan algorithm run
// again
if (cur->weight <= minWeight) {
DEBUG(std::cerr << "\t\t\tspilling(c): " << *cur << '\n';);
int slot = vrm_->assignVirt2StackSlot(cur->reg);
li_->updateSpilledInterval(*cur, slot);
// if we didn't eliminate the interval find where to add it
// back to unhandled. We need to scan since unhandled are
// sorted on earliest start point and we may have changed our
// start point.
if (!cur->empty()) {
IntervalPtrs::iterator it = unhandled_.begin();
while (it != unhandled_.end() && (*it)->start() < cur->start())
++it;
unhandled_.insert(it, cur);
}
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_front(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
assert(MRegisterInfo::isPhysicalRegister(minReg) &&
"did not choose a register to spill?");
std::vector<bool> toSpill(mri_->getNumRegs(), false);
toSpill[minReg] = true;
for (const unsigned* as = mri_->getAliasSet(minReg); *as; ++as)
toSpill[*as] = true;
unsigned earliestStart = cur->start();
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);
li_->updateSpilledInterval(**i, slot);
}
}
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);
li_->updateSpilledInterval(**i, slot);
}
}
DEBUG(std::cerr << "\t\trolling back to: " << earliestStart << '\n');
// scan handled in reverse order and undo each one, restoring the
// state of unhandled and fixed
while (!handled_.empty()) {
IntervalPtrs::value_type i = handled_.back();
// if this interval starts before t we are done
if (!i->empty() && i->start() < earliestStart)
break;
DEBUG(std::cerr << "\t\t\tundo changes for: " << *i << '\n');
handled_.pop_back();
IntervalPtrs::iterator it;
if ((it = find(active_.begin(), active_.end(), i)) != active_.end()) {
active_.erase(it);
if (MRegisterInfo::isPhysicalRegister(i->reg)) {
fixed_.push_front(i);
prt_->delRegUse(i->reg);
}
else {
prt_->delRegUse(vrm_->getPhys(i->reg));
vrm_->clearVirtReg(i->reg);
if (i->spilled()) {
if (!i->empty()) {
IntervalPtrs::iterator it = unhandled_.begin();
while (it != unhandled_.end() &&
(*it)->start() < i->start())
++it;
unhandled_.insert(it, i);
}
}
else
unhandled_.push_front(i);
}
}
else if ((it = find(inactive_.begin(), inactive_.end(), i)) != inactive_.end()) {
inactive_.erase(it);
if (MRegisterInfo::isPhysicalRegister(i->reg))
fixed_.push_front(i);
else {
vrm_->clearVirtReg(i->reg);
if (i->spilled()) {
if (!i->empty()) {
IntervalPtrs::iterator it = unhandled_.begin();
while (it != unhandled_.end() &&
(*it)->start() < i->start())
++it;
unhandled_.insert(it, i);
}
}
else
unhandled_.push_front(i);
}
}
else {
if (MRegisterInfo::isPhysicalRegister(i->reg))
fixed_.push_front(i);
else {
vrm_->clearVirtReg(i->reg);
unhandled_.push_front(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));
}
}
}
unsigned RA::getFreePhysReg(IntervalPtrs::value_type 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();
}
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