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llvm-mirror/lib/CodeGen/RegAllocLinearScan.cpp
Chris Lattner 8b6f0daaae Add some comments. 
llvm-svn: 27133
2006-03-25 23:00:56 +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/CodeGen/LiveIntervalAnalysis.h"
#include "PhysRegTracker.h"
#include "VirtRegMap.h"
#include "llvm/Function.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 "llvm/ADT/EquivalenceClasses.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Debug.h"
#include <algorithm>
#include <cmath>
#include <iostream>
#include <set>
#include <queue>
#include <memory>
using namespace llvm;
namespace {
Statistic<double> efficiency
("regalloc", "Ratio of intervals processed over total intervals");
Statistic<> NumBacktracks("regalloc", "Number of times we had to backtrack");
static unsigned numIterations = 0;
static unsigned numIntervals = 0;
struct RA : public MachineFunctionPass {
typedef std::pair<LiveInterval*, LiveInterval::iterator> IntervalPtr;
typedef std::vector<IntervalPtr> IntervalPtrs;
private:
/// RelatedRegClasses - This structure is built the first time a function is
/// compiled, and keeps track of which register classes have registers that
/// belong to multiple classes or have aliases that are in other classes.
EquivalenceClasses<const TargetRegisterClass*> RelatedRegClasses;
std::map<unsigned, const TargetRegisterClass*> OneClassForEachPhysReg;
MachineFunction* mf_;
const TargetMachine* tm_;
const MRegisterInfo* mri_;
LiveIntervals* li_;
bool *PhysRegsUsed;
/// handled_ - Intervals are added to the handled_ set in the order of their
/// start value. This is uses for backtracking.
std::vector<LiveInterval*> handled_;
/// fixed_ - Intervals that correspond to machine registers.
///
IntervalPtrs fixed_;
/// active_ - Intervals that are currently being processed, and which have a
/// live range active for the current point.
IntervalPtrs active_;
/// inactive_ - Intervals that are currently being processed, but which have
/// a hold at the current point.
IntervalPtrs inactive_;
typedef std::priority_queue<LiveInterval*,
std::vector<LiveInterval*>,
greater_ptr<LiveInterval> > IntervalHeap;
IntervalHeap unhandled_;
std::auto_ptr<PhysRegTracker> prt_;
std::auto_ptr<VirtRegMap> vrm_;
std::auto_ptr<Spiller> spiller_;
public:
virtual const char* getPassName() const {
return "Linear Scan Register Allocator";
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LiveIntervals>();
MachineFunctionPass::getAnalysisUsage(AU);
}
/// runOnMachineFunction - register allocate the whole function
bool runOnMachineFunction(MachineFunction&);
private:
/// linearScan - the linear scan algorithm
void linearScan();
/// initIntervalSets - initialize the interval sets.
///
void initIntervalSets();
/// processActiveIntervals - expire old intervals and move non-overlapping
/// ones to the inactive list.
void processActiveIntervals(unsigned CurPoint);
/// processInactiveIntervals - expire old intervals and move overlapping
/// ones to the active list.
void processInactiveIntervals(unsigned CurPoint);
/// 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);
void ComputeRelatedRegClasses();
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->first << " -> ";
unsigned reg = i->first->reg;
if (MRegisterInfo::isVirtualRegister(reg)) {
reg = vrm_->getPhys(reg);
}
std::cerr << mri_->getName(reg) << '\n';
}
}
};
}
void RA::ComputeRelatedRegClasses() {
const MRegisterInfo &MRI = *mri_;
// First pass, add all reg classes to the union, and determine at least one
// reg class that each register is in.
bool HasAliases = false;
for (MRegisterInfo::regclass_iterator RCI = MRI.regclass_begin(),
E = MRI.regclass_end(); RCI != E; ++RCI) {
RelatedRegClasses.insert(*RCI);
for (TargetRegisterClass::iterator I = (*RCI)->begin(), E = (*RCI)->end();
I != E; ++I) {
HasAliases = HasAliases || *MRI.getAliasSet(*I) != 0;
const TargetRegisterClass *&PRC = OneClassForEachPhysReg[*I];
if (PRC) {
// Already processed this register. Just make sure we know that
// multiple register classes share a register.
RelatedRegClasses.unionSets(PRC, *RCI);
} else {
PRC = *RCI;
}
}
}
// Second pass, now that we know conservatively what register classes each reg
// belongs to, add info about aliases. We don't need to do this for targets
// without register aliases.
if (HasAliases)
for (std::map<unsigned, const TargetRegisterClass*>::iterator
I = OneClassForEachPhysReg.begin(), E = OneClassForEachPhysReg.end();
I != E; ++I)
for (const unsigned *AS = MRI.getAliasSet(I->first); *AS; ++AS)
RelatedRegClasses.unionSets(I->second, OneClassForEachPhysReg[*AS]);
}
bool RA::runOnMachineFunction(MachineFunction &fn) {
mf_ = &fn;
tm_ = &fn.getTarget();
mri_ = tm_->getRegisterInfo();
li_ = &getAnalysis<LiveIntervals>();
// If this is the first function compiled, compute the related reg classes.
if (RelatedRegClasses.empty())
ComputeRelatedRegClasses();
PhysRegsUsed = new bool[mri_->getNumRegs()];
std::fill(PhysRegsUsed, PhysRegsUsed+mri_->getNumRegs(), false);
fn.setUsedPhysRegs(PhysRegsUsed);
if (!prt_.get()) prt_.reset(new PhysRegTracker(*mri_));
vrm_.reset(new VirtRegMap(*mf_));
if (!spiller_.get()) spiller_.reset(createSpiller());
initIntervalSets();
linearScan();
// Rewrite spill code and update the PhysRegsUsed set.
spiller_->runOnMachineFunction(*mf_, *vrm_);
vrm_.reset(); // Free the VirtRegMap
while (!unhandled_.empty()) unhandled_.pop();
fixed_.clear();
active_.clear();
inactive_.clear();
handled_.clear();
return true;
}
/// initIntervalSets - initialize the interval sets.
///
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) {
if (MRegisterInfo::isPhysicalRegister(i->second.reg)) {
PhysRegsUsed[i->second.reg] = true;
fixed_.push_back(std::make_pair(&i->second, i->second.begin()));
} else
unhandled_.push(&i->second);
}
}
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->beginNumber());
processInactiveIntervals(cur->beginNumber());
assert(MRegisterInfo::isVirtualRegister(cur->reg) &&
"Can only allocate virtual registers!");
// Allocating a virtual register. try to find a free
// physical register or spill an interval (possibly this one) in order to
// assign it one.
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->first->reg;
DEBUG(std::cerr << "\tinterval " << *i->first << " expired\n");
assert(MRegisterInfo::isVirtualRegister(reg) &&
"Can only allocate virtual registers!");
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->first << " expired\n");
i = IntervalPtrs::reverse_iterator(inactive_.erase(i.base()-1));
}
DEBUG(std::cerr << *vrm_);
}
/// processActiveIntervals - expire old intervals and move non-overlapping ones
/// to the inactive list.
void RA::processActiveIntervals(unsigned CurPoint)
{
DEBUG(std::cerr << "\tprocessing active intervals:\n");
for (unsigned i = 0, e = active_.size(); i != e; ++i) {
LiveInterval *Interval = active_[i].first;
LiveInterval::iterator IntervalPos = active_[i].second;
unsigned reg = Interval->reg;
IntervalPos = Interval->advanceTo(IntervalPos, CurPoint);
if (IntervalPos == Interval->end()) { // Remove expired intervals.
DEBUG(std::cerr << "\t\tinterval " << *Interval << " expired\n");
assert(MRegisterInfo::isVirtualRegister(reg) &&
"Can only allocate virtual registers!");
reg = vrm_->getPhys(reg);
prt_->delRegUse(reg);
// Pop off the end of the list.
active_[i] = active_.back();
active_.pop_back();
--i; --e;
} else if (IntervalPos->start > CurPoint) {
// Move inactive intervals to inactive list.
DEBUG(std::cerr << "\t\tinterval " << *Interval << " inactive\n");
assert(MRegisterInfo::isVirtualRegister(reg) &&
"Can only allocate virtual registers!");
reg = vrm_->getPhys(reg);
prt_->delRegUse(reg);
// add to inactive.
inactive_.push_back(std::make_pair(Interval, IntervalPos));
// Pop off the end of the list.
active_[i] = active_.back();
active_.pop_back();
--i; --e;
} else {
// Otherwise, just update the iterator position.
active_[i].second = IntervalPos;
}
}
}
/// processInactiveIntervals - expire old intervals and move overlapping
/// ones to the active list.
void RA::processInactiveIntervals(unsigned CurPoint)
{
DEBUG(std::cerr << "\tprocessing inactive intervals:\n");
for (unsigned i = 0, e = inactive_.size(); i != e; ++i) {
LiveInterval *Interval = inactive_[i].first;
LiveInterval::iterator IntervalPos = inactive_[i].second;
unsigned reg = Interval->reg;
IntervalPos = Interval->advanceTo(IntervalPos, CurPoint);
if (IntervalPos == Interval->end()) { // remove expired intervals.
DEBUG(std::cerr << "\t\tinterval " << *Interval << " expired\n");
// Pop off the end of the list.
inactive_[i] = inactive_.back();
inactive_.pop_back();
--i; --e;
} else if (IntervalPos->start <= CurPoint) {
// move re-activated intervals in active list
DEBUG(std::cerr << "\t\tinterval " << *Interval << " active\n");
assert(MRegisterInfo::isVirtualRegister(reg) &&
"Can only allocate virtual registers!");
reg = vrm_->getPhys(reg);
prt_->addRegUse(reg);
// add to active
active_.push_back(std::make_pair(Interval, IntervalPos));
// Pop off the end of the list.
inactive_[i] = inactive_.back();
inactive_.pop_back();
--i; --e;
} else {
// Otherwise, just update the iterator position.
inactive_[i].second = IntervalPos;
}
}
}
/// updateSpillWeights - updates the spill weights of the specifed physical
/// register and its weight.
static void updateSpillWeights(std::vector<float> &Weights,
unsigned reg, float weight,
const MRegisterInfo *MRI) {
Weights[reg] += weight;
for (const unsigned* as = MRI->getAliasSet(reg); *as; ++as)
Weights[*as] += weight;
}
static RA::IntervalPtrs::iterator FindIntervalInVector(RA::IntervalPtrs &IP,
LiveInterval *LI) {
for (RA::IntervalPtrs::iterator I = IP.begin(), E = IP.end(); I != E; ++I)
if (I->first == LI) return I;
return IP.end();
}
static void RevertVectorIteratorsTo(RA::IntervalPtrs &V, unsigned Point) {
for (unsigned i = 0, e = V.size(); i != e; ++i) {
RA::IntervalPtr &IP = V[i];
LiveInterval::iterator I = std::upper_bound(IP.first->begin(),
IP.second, Point);
if (I != IP.first->begin()) --I;
IP.second = I;
}
}
/// assignRegOrStackSlotAtInterval - assign a register if one is available, or
/// spill.
void RA::assignRegOrStackSlotAtInterval(LiveInterval* cur)
{
DEBUG(std::cerr << "\tallocating current interval: ");
PhysRegTracker backupPrt = *prt_;
std::vector<std::pair<unsigned, float> > SpillWeightsToAdd;
unsigned StartPosition = cur->beginNumber();
const TargetRegisterClass *RC = mf_->getSSARegMap()->getRegClass(cur->reg);
const TargetRegisterClass *RCLeader = RelatedRegClasses.getLeaderValue(RC);
// 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) {
unsigned Reg = i->first->reg;
assert(MRegisterInfo::isVirtualRegister(Reg) &&
"Can only allocate virtual registers!");
const TargetRegisterClass *RegRC = mf_->getSSARegMap()->getRegClass(Reg);
// If this is not in a related reg class to the register we're allocating,
// don't check it.
if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader &&
cur->overlapsFrom(*i->first, i->second-1)) {
Reg = vrm_->getPhys(Reg);
prt_->addRegUse(Reg);
SpillWeightsToAdd.push_back(std::make_pair(Reg, i->first->weight));
}
}
// Speculatively check to see if we can get a register right now. If not,
// we know we won't be able to by adding more constraints. If so, we can
// check to see if it is valid. Doing an exhaustive search of the fixed_ list
// is very bad (it contains all callee clobbered registers for any functions
// with a call), so we want to avoid doing that if possible.
unsigned physReg = getFreePhysReg(cur);
if (physReg) {
// We got a register. However, if it's in the fixed_ list, we might
// conflict with it. Check to see if we conflict with it or any of its
// aliases.
std::set<unsigned> RegAliases;
for (const unsigned *AS = mri_->getAliasSet(physReg); *AS; ++AS)
RegAliases.insert(*AS);
bool ConflictsWithFixed = false;
for (unsigned i = 0, e = fixed_.size(); i != e; ++i) {
if (physReg == fixed_[i].first->reg ||
RegAliases.count(fixed_[i].first->reg)) {
// Okay, this reg is on the fixed list. Check to see if we actually
// conflict.
IntervalPtr &IP = fixed_[i];
LiveInterval *I = IP.first;
if (I->endNumber() > StartPosition) {
LiveInterval::iterator II = I->advanceTo(IP.second, StartPosition);
IP.second = II;
if (II != I->begin() && II->start > StartPosition)
--II;
if (cur->overlapsFrom(*I, II)) {
ConflictsWithFixed = true;
break;
}
}
}
}
// Okay, the register picked by our speculative getFreePhysReg call turned
// out to be in use. Actually add all of the conflicting fixed registers to
// prt so we can do an accurate query.
if (ConflictsWithFixed) {
// For every interval in fixed we overlap with, mark the register as not
// free and update spill weights.
for (unsigned i = 0, e = fixed_.size(); i != e; ++i) {
IntervalPtr &IP = fixed_[i];
LiveInterval *I = IP.first;
const TargetRegisterClass *RegRC = OneClassForEachPhysReg[I->reg];
if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader &&
I->endNumber() > StartPosition) {
LiveInterval::iterator II = I->advanceTo(IP.second, StartPosition);
IP.second = II;
if (II != I->begin() && II->start > StartPosition)
--II;
if (cur->overlapsFrom(*I, II)) {
unsigned reg = I->reg;
prt_->addRegUse(reg);
SpillWeightsToAdd.push_back(std::make_pair(reg, I->weight));
}
}
}
// Using the newly updated prt_ object, which includes conflicts in the
// future, see if there are any registers available.
physReg = getFreePhysReg(cur);
}
}
// Restore the physical register tracker, removing information about the
// future.
*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(std::make_pair(cur, cur->begin()));
handled_.push_back(cur);
return;
}
DEBUG(std::cerr << "no free registers\n");
// Compile the spill weights into an array that is better for scanning.
std::vector<float> SpillWeights(mri_->getNumRegs(), 0.0);
for (std::vector<std::pair<unsigned, float> >::iterator
I = SpillWeightsToAdd.begin(), E = SpillWeightsToAdd.end(); I != E; ++I)
updateSpillWeights(SpillWeights, I->first, I->second, mri_);
// for each interval in active, update spill weights.
for (IntervalPtrs::const_iterator i = active_.begin(), e = active_.end();
i != e; ++i) {
unsigned reg = i->first->reg;
assert(MRegisterInfo::isVirtualRegister(reg) &&
"Can only allocate virtual registers!");
reg = vrm_->getPhys(reg);
updateSpillWeights(SpillWeights, reg, i->first->weight, mri_);
}
DEBUG(std::cerr << "\tassigning stack slot at interval "<< *cur << ":\n");
// Find a register to spill.
float minWeight = float(HUGE_VAL);
unsigned minReg = 0;
for (TargetRegisterClass::iterator i = RC->allocation_order_begin(*mf_),
e = RC->allocation_order_end(*mf_); i != e; ++i) {
unsigned reg = *i;
if (minWeight > SpillWeights[reg]) {
minWeight = SpillWeights[reg];
minReg = reg;
}
}
// If we didn't find a register that is spillable, try aliases?
// FIXME: assert(minReg && "Didn't find any 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;
}
++NumBacktracks;
// 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->beginNumber();
// 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->first->reg;
if (//MRegisterInfo::isVirtualRegister(reg) &&
toSpill[vrm_->getPhys(reg)] &&
cur->overlapsFrom(*i->first, i->second)) {
DEBUG(std::cerr << "\t\t\tspilling(a): " << *i->first << '\n');
earliestStart = std::min(earliestStart, i->first->beginNumber());
int slot = vrm_->assignVirt2StackSlot(i->first->reg);
std::vector<LiveInterval*> newIs =
li_->addIntervalsForSpills(*i->first, *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->first->reg;
if (//MRegisterInfo::isVirtualRegister(reg) &&
toSpill[vrm_->getPhys(reg)] &&
cur->overlapsFrom(*i->first, i->second-1)) {
DEBUG(std::cerr << "\t\t\tspilling(i): " << *i->first << '\n');
earliestStart = std::min(earliestStart, i->first->beginNumber());
int slot = vrm_->assignVirt2StackSlot(reg);
std::vector<LiveInterval*> newIs =
li_->addIntervalsForSpills(*i->first, *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 earliest 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->beginNumber() < 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 = FindIntervalInVector(active_, i)) != active_.end()) {
active_.erase(it);
assert(!MRegisterInfo::isPhysicalRegister(i->reg));
if (!spilled.count(i->reg))
unhandled_.push(i);
prt_->delRegUse(vrm_->getPhys(i->reg));
vrm_->clearVirt(i->reg);
} else if ((it = FindIntervalInVector(inactive_, i)) != inactive_.end()) {
inactive_.erase(it);
assert(!MRegisterInfo::isPhysicalRegister(i->reg));
if (!spilled.count(i->reg))
unhandled_.push(i);
vrm_->clearVirt(i->reg);
} else {
assert(MRegisterInfo::isVirtualRegister(i->reg) &&
"Can only allocate virtual registers!");
vrm_->clearVirt(i->reg);
unhandled_.push(i);
}
}
// Rewind the iterators in the active, inactive, and fixed lists back to the
// point we reverted to.
RevertVectorIteratorsTo(active_, earliestStart);
RevertVectorIteratorsTo(inactive_, earliestStart);
RevertVectorIteratorsTo(fixed_, earliestStart);
// 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)
for (unsigned i = 0, e = handled_.size(); i != e; ++i) {
LiveInterval *HI = handled_[i];
if (!HI->expiredAt(earliestStart) &&
HI->expiredAt(cur->beginNumber())) {
DEBUG(std::cerr << "\t\t\tundo changes for: " << *HI << '\n');
active_.push_back(std::make_pair(HI, HI->begin()));
assert(!MRegisterInfo::isPhysicalRegister(HI->reg));
prt_->addRegUse(vrm_->getPhys(HI->reg));
}
}
// merge added with unhandled
for (unsigned i = 0, e = added.size(); i != e; ++i)
unhandled_.push(added[i]);
}
/// getFreePhysReg - return a free physical register for this virtual register
/// interval if we have one, otherwise return 0.
unsigned RA::getFreePhysReg(LiveInterval *cur) {
std::vector<unsigned> inactiveCounts(mri_->getNumRegs(), 0);
unsigned MaxInactiveCount = 0;
const TargetRegisterClass *RC = mf_->getSSARegMap()->getRegClass(cur->reg);
const TargetRegisterClass *RCLeader = RelatedRegClasses.getLeaderValue(RC);
for (IntervalPtrs::iterator i = inactive_.begin(), e = inactive_.end();
i != e; ++i) {
unsigned reg = i->first->reg;
assert(MRegisterInfo::isVirtualRegister(reg) &&
"Can only allocate virtual registers!");
// If this is not in a related reg class to the register we're allocating,
// don't check it.
const TargetRegisterClass *RegRC = mf_->getSSARegMap()->getRegClass(reg);
if (RelatedRegClasses.getLeaderValue(RegRC) == RCLeader) {
reg = vrm_->getPhys(reg);
++inactiveCounts[reg];
MaxInactiveCount = std::max(MaxInactiveCount, inactiveCounts[reg]);
}
}
const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
unsigned FreeReg = 0;
unsigned FreeRegInactiveCount = 0;
// Scan for the first available register.
TargetRegisterClass::iterator I = rc->allocation_order_begin(*mf_);
TargetRegisterClass::iterator E = rc->allocation_order_end(*mf_);
for (; I != E; ++I)
if (prt_->isRegAvail(*I)) {
FreeReg = *I;
FreeRegInactiveCount = inactiveCounts[FreeReg];
break;
}
// If there are no free regs, or if this reg has the max inactive count,
// return this register.
if (FreeReg == 0 || FreeRegInactiveCount == MaxInactiveCount) return FreeReg;
// Continue scanning the registers, looking for the one with the highest
// inactive count. Alkis found that this reduced register pressure very
// slightly on X86 (in rev 1.94 of this file), though this should probably be
// reevaluated now.
for (; I != E; ++I) {
unsigned Reg = *I;
if (prt_->isRegAvail(Reg) && FreeRegInactiveCount < inactiveCounts[Reg]) {
FreeReg = Reg;
FreeRegInactiveCount = inactiveCounts[Reg];
if (FreeRegInactiveCount == MaxInactiveCount)
break; // We found the one with the max inactive count.
}
}
return FreeReg;
}
FunctionPass* llvm::createLinearScanRegisterAllocator() {
return new RA();
}
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