//===-- 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"); 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; } } // 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); if (MRegisterInfo::isPhysicalRegister(i->reg)) { assert(0 && "daksjlfd"); 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 = FindIntervalInVector(inactive_, i)) != inactive_.end()) { inactive_.erase(it); if (MRegisterInfo::isPhysicalRegister(i->reg)) { assert(0 && "daksjlfd"); unhandled_.push(i); } else { 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())); if (MRegisterInfo::isPhysicalRegister(HI->reg)) { assert(0 &&"sdflkajsdf"); prt_->addRegUse(HI->reg); } else 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(); }