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llvm-mirror/lib/CodeGen/RegAllocLinearScan.cpp
Alkis Evlogimenos 81c6957eab Make the set of fixed (preallocated) intervals be a fixed superset of 
unhandled + handled. So unhandled is now including all fixed intervals
and fixed intervals never changes when processing a function.

llvm-svn: 12462
2004-03-17 00:48:59 +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_;
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(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();
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(li_->getIntervals());
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
IntervalPtrs::value_type cur = unhandled_.front();
unhandled_.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) {
unhandled_.push_back(&*i);
if (MRegisterInfo::isPhysicalRegister(i->reg))
fixed_.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, *vrm_, 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, *vrm_, 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, *vrm_, slot);
}
}
DEBUG(std::cerr << "\t\trolling back to: " << earliestStart << '\n');
// scan handled in reverse order and undo each one, restoring the
// state of unhandled
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)) {
prt_->delRegUse(i->reg);
unhandled_.push_front(i);
}
else {
prt_->delRegUse(vrm_->getPhys(i->reg));
vrm_->clearVirt(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))
unhandled_.push_front(i);
else {
vrm_->clearVirt(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::isVirtualRegister(i->reg))
vrm_->clearVirt(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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