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c8b9f33ac0
* Do not put fixed registers into the unhandled set. This means they will never find their way into the inactive, active, or handled sets, so we can simplify a bunch of code. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@17945 91177308-0d34-0410-b5e6-96231b3b80d8
624 lines
22 KiB
C++
624 lines
22 KiB
C++
//===-- RegAllocLinearScan.cpp - Linear Scan register allocator -----------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements a linear scan register allocator.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "regalloc"
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#include "llvm/Function.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstr.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/CodeGen/SSARegMap.h"
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#include "llvm/Target/MRegisterInfo.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/STLExtras.h"
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#include "LiveIntervalAnalysis.h"
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#include "PhysRegTracker.h"
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#include "VirtRegMap.h"
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#include <algorithm>
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#include <cmath>
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#include <set>
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#include <queue>
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using namespace llvm;
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namespace {
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Statistic<double> efficiency
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("regalloc", "Ratio of intervals processed over total intervals");
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Statistic<> NumBacktracks("regalloc", "Number of times we had to backtrack");
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static unsigned numIterations = 0;
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static unsigned numIntervals = 0;
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struct RA : public MachineFunctionPass {
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typedef std::pair<LiveInterval*, LiveInterval::iterator> IntervalPtr;
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typedef std::vector<IntervalPtr> IntervalPtrs;
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private:
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MachineFunction* mf_;
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const TargetMachine* tm_;
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const MRegisterInfo* mri_;
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LiveIntervals* li_;
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/// handled_ - Intervals are added to the handled_ set in the order of their
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/// start value. This is uses for backtracking.
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std::vector<LiveInterval*> handled_;
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/// fixed_ - Intervals that correspond to machine registers.
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///
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IntervalPtrs fixed_;
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/// active_ - Intervals that are currently being processed, and which have a
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/// live range active for the current point.
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IntervalPtrs active_;
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/// inactive_ - Intervals that are currently being processed, but which have
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/// a hold at the current point.
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IntervalPtrs inactive_;
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typedef std::priority_queue<LiveInterval*,
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std::vector<LiveInterval*>,
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greater_ptr<LiveInterval> > IntervalHeap;
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IntervalHeap unhandled_;
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std::auto_ptr<PhysRegTracker> prt_;
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std::auto_ptr<VirtRegMap> vrm_;
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std::auto_ptr<Spiller> spiller_;
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public:
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virtual const char* getPassName() const {
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return "Linear Scan Register Allocator";
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<LiveIntervals>();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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/// runOnMachineFunction - register allocate the whole function
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bool runOnMachineFunction(MachineFunction&);
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private:
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/// linearScan - the linear scan algorithm
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void linearScan();
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/// initIntervalSets - initialize the interval sets.
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///
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void initIntervalSets();
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/// processActiveIntervals - expire old intervals and move non-overlapping
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/// ones to the inactive list.
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void processActiveIntervals(unsigned CurPoint);
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/// processInactiveIntervals - expire old intervals and move overlapping
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/// ones to the active list.
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void processInactiveIntervals(unsigned CurPoint);
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/// assignRegOrStackSlotAtInterval - assign a register if one
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/// is available, or spill.
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void assignRegOrStackSlotAtInterval(LiveInterval* cur);
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///
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/// register handling helpers
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///
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/// getFreePhysReg - return a free physical register for this virtual
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/// register interval if we have one, otherwise return 0.
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unsigned getFreePhysReg(LiveInterval* cur);
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/// assignVirt2StackSlot - assigns this virtual register to a
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/// stack slot. returns the stack slot
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int assignVirt2StackSlot(unsigned virtReg);
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template <typename ItTy>
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void printIntervals(const char* const str, ItTy i, ItTy e) const {
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if (str) std::cerr << str << " intervals:\n";
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for (; i != e; ++i) {
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std::cerr << "\t" << *i->first << " -> ";
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unsigned reg = i->first->reg;
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if (MRegisterInfo::isVirtualRegister(reg)) {
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reg = vrm_->getPhys(reg);
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}
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std::cerr << mri_->getName(reg) << '\n';
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}
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}
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};
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}
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bool RA::runOnMachineFunction(MachineFunction &fn) {
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mf_ = &fn;
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tm_ = &fn.getTarget();
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mri_ = tm_->getRegisterInfo();
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li_ = &getAnalysis<LiveIntervals>();
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if (!prt_.get()) prt_.reset(new PhysRegTracker(*mri_));
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vrm_.reset(new VirtRegMap(*mf_));
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if (!spiller_.get()) spiller_.reset(createSpiller());
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initIntervalSets();
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linearScan();
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spiller_->runOnMachineFunction(*mf_, *vrm_);
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vrm_.reset(); // Free the VirtRegMap
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while (!unhandled_.empty()) unhandled_.pop();
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fixed_.clear();
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active_.clear();
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inactive_.clear();
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handled_.clear();
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return true;
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}
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/// initIntervalSets - initialize the interval sets.
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///
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void RA::initIntervalSets()
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{
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assert(unhandled_.empty() && fixed_.empty() &&
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active_.empty() && inactive_.empty() &&
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"interval sets should be empty on initialization");
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for (LiveIntervals::iterator i = li_->begin(), e = li_->end(); i != e; ++i) {
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if (MRegisterInfo::isPhysicalRegister(i->second.reg))
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fixed_.push_back(std::make_pair(&i->second, i->second.begin()));
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else
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unhandled_.push(&i->second);
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}
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}
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void RA::linearScan()
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{
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// linear scan algorithm
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DEBUG(std::cerr << "********** LINEAR SCAN **********\n");
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DEBUG(std::cerr << "********** Function: "
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<< mf_->getFunction()->getName() << '\n');
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// DEBUG(printIntervals("unhandled", unhandled_.begin(), unhandled_.end()));
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DEBUG(printIntervals("fixed", fixed_.begin(), fixed_.end()));
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DEBUG(printIntervals("active", active_.begin(), active_.end()));
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DEBUG(printIntervals("inactive", inactive_.begin(), inactive_.end()));
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while (!unhandled_.empty()) {
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// pick the interval with the earliest start point
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LiveInterval* cur = unhandled_.top();
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unhandled_.pop();
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++numIterations;
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DEBUG(std::cerr << "\n*** CURRENT ***: " << *cur << '\n');
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processActiveIntervals(cur->beginNumber());
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processInactiveIntervals(cur->beginNumber());
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assert(MRegisterInfo::isVirtualRegister(cur->reg) &&
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"Can only allocate virtual registers!");
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// Allocating a virtual register. try to find a free
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// physical register or spill an interval (possibly this one) in order to
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// assign it one.
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assignRegOrStackSlotAtInterval(cur);
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DEBUG(printIntervals("active", active_.begin(), active_.end()));
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DEBUG(printIntervals("inactive", inactive_.begin(), inactive_.end()));
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}
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numIntervals += li_->getNumIntervals();
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efficiency = double(numIterations) / double(numIntervals);
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// expire any remaining active intervals
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for (IntervalPtrs::reverse_iterator
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i = active_.rbegin(); i != active_.rend(); ) {
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unsigned reg = i->first->reg;
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DEBUG(std::cerr << "\tinterval " << *i->first << " expired\n");
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assert(MRegisterInfo::isVirtualRegister(reg) &&
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"Can only allocate virtual registers!");
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reg = vrm_->getPhys(reg);
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prt_->delRegUse(reg);
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i = IntervalPtrs::reverse_iterator(active_.erase(i.base()-1));
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}
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// expire any remaining inactive intervals
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for (IntervalPtrs::reverse_iterator
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i = inactive_.rbegin(); i != inactive_.rend(); ) {
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DEBUG(std::cerr << "\tinterval " << *i->first << " expired\n");
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i = IntervalPtrs::reverse_iterator(inactive_.erase(i.base()-1));
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}
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DEBUG(std::cerr << *vrm_);
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}
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/// processActiveIntervals - expire old intervals and move non-overlapping ones
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/// to the inactive list.
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void RA::processActiveIntervals(unsigned CurPoint)
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{
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DEBUG(std::cerr << "\tprocessing active intervals:\n");
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for (unsigned i = 0, e = active_.size(); i != e; ++i) {
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LiveInterval *Interval = active_[i].first;
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LiveInterval::iterator IntervalPos = active_[i].second;
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unsigned reg = Interval->reg;
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IntervalPos = Interval->advanceTo(IntervalPos, CurPoint);
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if (IntervalPos == Interval->end()) { // Remove expired intervals.
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DEBUG(std::cerr << "\t\tinterval " << *Interval << " expired\n");
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assert(MRegisterInfo::isVirtualRegister(reg) &&
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"Can only allocate virtual registers!");
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reg = vrm_->getPhys(reg);
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prt_->delRegUse(reg);
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// Pop off the end of the list.
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active_[i] = active_.back();
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active_.pop_back();
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--i; --e;
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} else if (IntervalPos->start > CurPoint) {
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// Move inactive intervals to inactive list.
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DEBUG(std::cerr << "\t\tinterval " << *Interval << " inactive\n");
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assert(MRegisterInfo::isVirtualRegister(reg) &&
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"Can only allocate virtual registers!");
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reg = vrm_->getPhys(reg);
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prt_->delRegUse(reg);
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// add to inactive.
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inactive_.push_back(std::make_pair(Interval, IntervalPos));
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// Pop off the end of the list.
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active_[i] = active_.back();
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active_.pop_back();
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--i; --e;
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} else {
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// Otherwise, just update the iterator position.
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active_[i].second = IntervalPos;
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}
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}
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}
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/// processInactiveIntervals - expire old intervals and move overlapping
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/// ones to the active list.
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void RA::processInactiveIntervals(unsigned CurPoint)
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{
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DEBUG(std::cerr << "\tprocessing inactive intervals:\n");
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for (unsigned i = 0, e = inactive_.size(); i != e; ++i) {
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LiveInterval *Interval = inactive_[i].first;
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LiveInterval::iterator IntervalPos = inactive_[i].second;
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unsigned reg = Interval->reg;
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IntervalPos = Interval->advanceTo(IntervalPos, CurPoint);
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if (IntervalPos == Interval->end()) { // remove expired intervals.
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DEBUG(std::cerr << "\t\tinterval " << *Interval << " expired\n");
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// Pop off the end of the list.
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inactive_[i] = inactive_.back();
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inactive_.pop_back();
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--i; --e;
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} else if (IntervalPos->start <= CurPoint) {
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// move re-activated intervals in active list
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DEBUG(std::cerr << "\t\tinterval " << *Interval << " active\n");
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assert(MRegisterInfo::isVirtualRegister(reg) &&
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"Can only allocate virtual registers!");
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reg = vrm_->getPhys(reg);
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prt_->addRegUse(reg);
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// add to active
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active_.push_back(std::make_pair(Interval, IntervalPos));
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// Pop off the end of the list.
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inactive_[i] = inactive_.back();
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inactive_.pop_back();
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--i; --e;
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} else {
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// Otherwise, just update the iterator position.
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inactive_[i].second = IntervalPos;
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}
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}
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}
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/// updateSpillWeights - updates the spill weights of the specifed physical
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/// register and its weight.
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static void updateSpillWeights(std::vector<float> &Weights,
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unsigned reg, float weight,
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const MRegisterInfo *MRI) {
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Weights[reg] += weight;
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for (const unsigned* as = MRI->getAliasSet(reg); *as; ++as)
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Weights[*as] += weight;
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}
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static RA::IntervalPtrs::iterator FindIntervalInVector(RA::IntervalPtrs &IP,
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LiveInterval *LI) {
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for (RA::IntervalPtrs::iterator I = IP.begin(), E = IP.end(); I != E; ++I)
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if (I->first == LI) return I;
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return IP.end();
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}
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static void RevertVectorIteratorsTo(RA::IntervalPtrs &V, unsigned Point) {
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for (unsigned i = 0, e = V.size(); i != e; ++i) {
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RA::IntervalPtr &IP = V[i];
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LiveInterval::iterator I = std::upper_bound(IP.first->begin(),
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IP.second, Point);
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if (I != IP.first->begin()) --I;
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IP.second = I;
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}
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}
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/// assignRegOrStackSlotAtInterval - assign a register if one is available, or
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/// spill.
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void RA::assignRegOrStackSlotAtInterval(LiveInterval* cur)
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{
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DEBUG(std::cerr << "\tallocating current interval: ");
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PhysRegTracker backupPrt = *prt_;
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std::vector<float> SpillWeights;
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SpillWeights.assign(mri_->getNumRegs(), 0.0);
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unsigned StartPosition = cur->beginNumber();
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// for each interval in active, update spill weights.
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for (IntervalPtrs::const_iterator i = active_.begin(), e = active_.end();
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i != e; ++i) {
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unsigned reg = i->first->reg;
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assert(MRegisterInfo::isVirtualRegister(reg) &&
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"Can only allocate virtual registers!");
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reg = vrm_->getPhys(reg);
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updateSpillWeights(SpillWeights, reg, i->first->weight, mri_);
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}
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// for every interval in inactive we overlap with, mark the
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// register as not free and update spill weights
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for (IntervalPtrs::const_iterator i = inactive_.begin(),
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e = inactive_.end(); i != e; ++i) {
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if (cur->overlapsFrom(*i->first, i->second-1)) {
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unsigned reg = i->first->reg;
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assert(MRegisterInfo::isVirtualRegister(reg) &&
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"Can only allocate virtual registers!");
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reg = vrm_->getPhys(reg);
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prt_->addRegUse(reg);
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updateSpillWeights(SpillWeights, reg, i->first->weight, mri_);
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}
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}
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// For every interval in fixed we overlap with, mark the register as not free
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// and update spill weights.
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for (unsigned i = 0, e = fixed_.size(); i != e; ++i) {
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IntervalPtr &IP = fixed_[i];
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LiveInterval *I = IP.first;
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if (I->endNumber() > StartPosition) {
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LiveInterval::iterator II = I->advanceTo(IP.second, StartPosition);
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IP.second = II;
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if (II != I->begin() && II->start > StartPosition)
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--II;
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if (cur->overlapsFrom(*I, II)) {
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unsigned reg = I->reg;
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prt_->addRegUse(reg);
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updateSpillWeights(SpillWeights, reg, I->weight, mri_);
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}
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}
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}
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unsigned physReg = getFreePhysReg(cur);
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// restore the physical register tracker
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*prt_ = backupPrt;
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// if we find a free register, we are done: assign this virtual to
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// the free physical register and add this interval to the active
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// list.
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if (physReg) {
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DEBUG(std::cerr << mri_->getName(physReg) << '\n');
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vrm_->assignVirt2Phys(cur->reg, physReg);
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prt_->addRegUse(physReg);
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active_.push_back(std::make_pair(cur, cur->begin()));
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handled_.push_back(cur);
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return;
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}
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DEBUG(std::cerr << "no free registers\n");
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DEBUG(std::cerr << "\tassigning stack slot at interval "<< *cur << ":\n");
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float minWeight = HUGE_VAL;
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unsigned minReg = 0;
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const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
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for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_);
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i != rc->allocation_order_end(*mf_); ++i) {
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unsigned reg = *i;
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if (minWeight > SpillWeights[reg]) {
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minWeight = SpillWeights[reg];
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minReg = reg;
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}
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}
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DEBUG(std::cerr << "\t\tregister with min weight: "
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<< mri_->getName(minReg) << " (" << minWeight << ")\n");
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// if the current has the minimum weight, we need to spill it and
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// add any added intervals back to unhandled, and restart
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// linearscan.
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if (cur->weight <= minWeight) {
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DEBUG(std::cerr << "\t\t\tspilling(c): " << *cur << '\n';);
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int slot = vrm_->assignVirt2StackSlot(cur->reg);
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std::vector<LiveInterval*> added =
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li_->addIntervalsForSpills(*cur, *vrm_, slot);
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if (added.empty())
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return; // Early exit if all spills were folded.
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// Merge added with unhandled. Note that we know that
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// addIntervalsForSpills returns intervals sorted by their starting
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// point.
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for (unsigned i = 0, e = added.size(); i != e; ++i)
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unhandled_.push(added[i]);
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return;
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}
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++NumBacktracks;
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// push the current interval back to unhandled since we are going
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// to re-run at least this iteration. Since we didn't modify it it
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// should go back right in the front of the list
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unhandled_.push(cur);
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// otherwise we spill all intervals aliasing the register with
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// minimum weight, rollback to the interval with the earliest
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// start point and let the linear scan algorithm run again
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std::vector<LiveInterval*> added;
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assert(MRegisterInfo::isPhysicalRegister(minReg) &&
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"did not choose a register to spill?");
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std::vector<bool> toSpill(mri_->getNumRegs(), false);
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// We are going to spill minReg and all its aliases.
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toSpill[minReg] = true;
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for (const unsigned* as = mri_->getAliasSet(minReg); *as; ++as)
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toSpill[*as] = true;
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// the earliest start of a spilled interval indicates up to where
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// in handled we need to roll back
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unsigned earliestStart = cur->beginNumber();
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// set of spilled vregs (used later to rollback properly)
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std::set<unsigned> spilled;
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// spill live intervals of virtual regs mapped to the physical register we
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// want to clear (and its aliases). We only spill those that overlap with the
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// current interval as the rest do not affect its allocation. we also keep
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// track of the earliest start of all spilled live intervals since this will
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// mark our rollback point.
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for (IntervalPtrs::iterator i = active_.begin(); i != active_.end(); ++i) {
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unsigned reg = i->first->reg;
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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);
|
|
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!");
|
|
reg = vrm_->getPhys(reg);
|
|
++inactiveCounts[reg];
|
|
}
|
|
|
|
const TargetRegisterClass* rc = mf_->getSSARegMap()->getRegClass(cur->reg);
|
|
|
|
unsigned freeReg = 0;
|
|
for (TargetRegisterClass::iterator i = rc->allocation_order_begin(*mf_);
|
|
i != rc->allocation_order_end(*mf_); ++i) {
|
|
unsigned reg = *i;
|
|
if (prt_->isRegAvail(reg) &&
|
|
(!freeReg || inactiveCounts[freeReg] < inactiveCounts[reg]))
|
|
freeReg = reg;
|
|
}
|
|
return freeReg;
|
|
}
|
|
|
|
FunctionPass* llvm::createLinearScanRegisterAllocator() {
|
|
return new RA();
|
|
}
|