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llvm / llvm / refs/heads/release_29 / . / lib / CodeGen / RegAllocGreedy.cpp
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//===-- RegAllocGreedy.cpp - greedy register allocator --------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the RAGreedy function pass for register allocation in
// optimized builds.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "regalloc"
#include "AllocationOrder.h"
#include "LiveIntervalUnion.h"
#include "LiveRangeEdit.h"
#include "RegAllocBase.h"
#include "Spiller.h"
#include "SpillPlacement.h"
#include "SplitKit.h"
#include "VirtRegMap.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Function.h"
#include "llvm/PassAnalysisSupport.h"
#include "llvm/CodeGen/CalcSpillWeights.h"
#include "llvm/CodeGen/EdgeBundles.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveStackAnalysis.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineLoopRanges.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegAllocRegistry.h"
#include "llvm/CodeGen/RegisterCoalescer.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/Timer.h"
#include <queue>
using namespace llvm;
STATISTIC(NumGlobalSplits, "Number of split global live ranges");
STATISTIC(NumLocalSplits, "Number of split local live ranges");
STATISTIC(NumReassigned, "Number of interferences reassigned");
STATISTIC(NumEvicted, "Number of interferences evicted");
static RegisterRegAlloc greedyRegAlloc("greedy", "greedy register allocator",
createGreedyRegisterAllocator);
namespace {
class RAGreedy : public MachineFunctionPass, public RegAllocBase {
// context
MachineFunction *MF;
BitVector ReservedRegs;
// analyses
SlotIndexes *Indexes;
LiveStacks *LS;
MachineDominatorTree *DomTree;
MachineLoopInfo *Loops;
MachineLoopRanges *LoopRanges;
EdgeBundles *Bundles;
SpillPlacement *SpillPlacer;
// state
std::auto_ptr<Spiller> SpillerInstance;
std::priority_queue<std::pair<unsigned, unsigned> > Queue;
// Live ranges pass through a number of stages as we try to allocate them.
// Some of the stages may also create new live ranges:
//
// - Region splitting.
// - Per-block splitting.
// - Local splitting.
// - Spilling.
//
// Ranges produced by one of the stages skip the previous stages when they are
// dequeued. This improves performance because we can skip interference checks
// that are unlikely to give any results. It also guarantees that the live
// range splitting algorithm terminates, something that is otherwise hard to
// ensure.
enum LiveRangeStage {
RS_Original, ///< Never seen before, never split.
RS_Second, ///< Second time in the queue.
RS_Region, ///< Produced by region splitting.
RS_Block, ///< Produced by per-block splitting.
RS_Local, ///< Produced by local splitting.
RS_Spill ///< Produced by spilling.
};
IndexedMap<unsigned char, VirtReg2IndexFunctor> LRStage;
LiveRangeStage getStage(const LiveInterval &VirtReg) const {
return LiveRangeStage(LRStage[VirtReg.reg]);
}
template<typename Iterator>
void setStage(Iterator Begin, Iterator End, LiveRangeStage NewStage) {
LRStage.resize(MRI->getNumVirtRegs());
for (;Begin != End; ++Begin)
LRStage[(*Begin)->reg] = NewStage;
}
// splitting state.
std::auto_ptr<SplitAnalysis> SA;
std::auto_ptr<SplitEditor> SE;
/// All basic blocks where the current register is live.
SmallVector<SpillPlacement::BlockConstraint, 8> SplitConstraints;
typedef std::pair<SlotIndex, SlotIndex> IndexPair;
/// Global live range splitting candidate info.
struct GlobalSplitCandidate {
unsigned PhysReg;
SmallVector<IndexPair, 8> Interference;
BitVector LiveBundles;
};
/// Candidate info for for each PhysReg in AllocationOrder.
/// This vector never shrinks, but grows to the size of the largest register
/// class.
SmallVector<GlobalSplitCandidate, 32> GlobalCand;
/// For every instruction in SA->UseSlots, store the previous non-copy
/// instruction.
SmallVector<SlotIndex, 8> PrevSlot;
public:
RAGreedy();
/// Return the pass name.
virtual const char* getPassName() const {
return "Greedy Register Allocator";
}
/// RAGreedy analysis usage.
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual void releaseMemory();
virtual Spiller &spiller() { return *SpillerInstance; }
virtual void enqueue(LiveInterval *LI);
virtual LiveInterval *dequeue();
virtual unsigned selectOrSplit(LiveInterval&,
SmallVectorImpl<LiveInterval*>&);
/// Perform register allocation.
virtual bool runOnMachineFunction(MachineFunction &mf);
static char ID;
private:
bool checkUncachedInterference(LiveInterval&, unsigned);
LiveInterval *getSingleInterference(LiveInterval&, unsigned);
bool reassignVReg(LiveInterval &InterferingVReg, unsigned OldPhysReg);
void mapGlobalInterference(unsigned, SmallVectorImpl<IndexPair>&);
float calcSplitConstraints(const SmallVectorImpl<IndexPair>&);
float calcGlobalSplitCost(const BitVector&);
void splitAroundRegion(LiveInterval&, unsigned, const BitVector&,
SmallVectorImpl<LiveInterval*>&);
void calcGapWeights(unsigned, SmallVectorImpl<float>&);
SlotIndex getPrevMappedIndex(const MachineInstr*);
void calcPrevSlots();
unsigned nextSplitPoint(unsigned);
bool canEvictInterference(LiveInterval&, unsigned, float&);
unsigned tryReassign(LiveInterval&, AllocationOrder&,
SmallVectorImpl<LiveInterval*>&);
unsigned tryEvict(LiveInterval&, AllocationOrder&,
SmallVectorImpl<LiveInterval*>&);
unsigned tryRegionSplit(LiveInterval&, AllocationOrder&,
SmallVectorImpl<LiveInterval*>&);
unsigned tryLocalSplit(LiveInterval&, AllocationOrder&,
SmallVectorImpl<LiveInterval*>&);
unsigned trySplit(LiveInterval&, AllocationOrder&,
SmallVectorImpl<LiveInterval*>&);
};
} // end anonymous namespace
char RAGreedy::ID = 0;
FunctionPass* llvm::createGreedyRegisterAllocator() {
return new RAGreedy();
}
RAGreedy::RAGreedy(): MachineFunctionPass(ID), LRStage(RS_Original) {
initializeSlotIndexesPass(*PassRegistry::getPassRegistry());
initializeLiveIntervalsPass(*PassRegistry::getPassRegistry());
initializeSlotIndexesPass(*PassRegistry::getPassRegistry());
initializeStrongPHIEliminationPass(*PassRegistry::getPassRegistry());
initializeRegisterCoalescerAnalysisGroup(*PassRegistry::getPassRegistry());
initializeCalculateSpillWeightsPass(*PassRegistry::getPassRegistry());
initializeLiveStacksPass(*PassRegistry::getPassRegistry());
initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry());
initializeMachineLoopInfoPass(*PassRegistry::getPassRegistry());
initializeMachineLoopRangesPass(*PassRegistry::getPassRegistry());
initializeVirtRegMapPass(*PassRegistry::getPassRegistry());
initializeEdgeBundlesPass(*PassRegistry::getPassRegistry());
initializeSpillPlacementPass(*PassRegistry::getPassRegistry());
}
void RAGreedy::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<AliasAnalysis>();
AU.addPreserved<AliasAnalysis>();
AU.addRequired<LiveIntervals>();
AU.addRequired<SlotIndexes>();
AU.addPreserved<SlotIndexes>();
if (StrongPHIElim)
AU.addRequiredID(StrongPHIEliminationID);
AU.addRequiredTransitive<RegisterCoalescer>();
AU.addRequired<CalculateSpillWeights>();
AU.addRequired<LiveStacks>();
AU.addPreserved<LiveStacks>();
AU.addRequired<MachineDominatorTree>();
AU.addPreserved<MachineDominatorTree>();
AU.addRequired<MachineLoopInfo>();
AU.addPreserved<MachineLoopInfo>();
AU.addRequired<MachineLoopRanges>();
AU.addPreserved<MachineLoopRanges>();
AU.addRequired<VirtRegMap>();
AU.addPreserved<VirtRegMap>();
AU.addRequired<EdgeBundles>();
AU.addRequired<SpillPlacement>();
MachineFunctionPass::getAnalysisUsage(AU);
}
void RAGreedy::releaseMemory() {
SpillerInstance.reset(0);
LRStage.clear();
RegAllocBase::releaseMemory();
}
void RAGreedy::enqueue(LiveInterval *LI) {
// Prioritize live ranges by size, assigning larger ranges first.
// The queue holds (size, reg) pairs.
const unsigned Size = LI->getSize();
const unsigned Reg = LI->reg;
assert(TargetRegisterInfo::isVirtualRegister(Reg) &&
"Can only enqueue virtual registers");
unsigned Prio;
LRStage.grow(Reg);
if (LRStage[Reg] == RS_Original)
// 1st generation ranges are handled first, long -> short.
Prio = (1u << 31) + Size;
else
// Repeat offenders are handled second, short -> long
Prio = (1u << 30) - Size;
// Boost ranges that have a physical register hint.
const unsigned Hint = VRM->getRegAllocPref(Reg);
if (TargetRegisterInfo::isPhysicalRegister(Hint))
Prio |= (1u << 30);
Queue.push(std::make_pair(Prio, Reg));
}
LiveInterval *RAGreedy::dequeue() {
if (Queue.empty())
return 0;
LiveInterval *LI = &LIS->getInterval(Queue.top().second);
Queue.pop();
return LI;
}
//===----------------------------------------------------------------------===//
// Register Reassignment
//===----------------------------------------------------------------------===//
// Check interference without using the cache.
bool RAGreedy::checkUncachedInterference(LiveInterval &VirtReg,
unsigned PhysReg) {
for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI) {
LiveIntervalUnion::Query subQ(&VirtReg, &PhysReg2LiveUnion[*AliasI]);
if (subQ.checkInterference())
return true;
}
return false;
}
/// getSingleInterference - Return the single interfering virtual register
/// assigned to PhysReg. Return 0 if more than one virtual register is
/// interfering.
LiveInterval *RAGreedy::getSingleInterference(LiveInterval &VirtReg,
unsigned PhysReg) {
// Check physreg and aliases.
LiveInterval *Interference = 0;
for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI) {
LiveIntervalUnion::Query &Q = query(VirtReg, *AliasI);
if (Q.checkInterference()) {
if (Interference)
return 0;
if (Q.collectInterferingVRegs(2) > 1)
return 0;
Interference = Q.interferingVRegs().front();
}
}
return Interference;
}
// Attempt to reassign this virtual register to a different physical register.
//
// FIXME: we are not yet caching these "second-level" interferences discovered
// in the sub-queries. These interferences can change with each call to
// selectOrSplit. However, we could implement a "may-interfere" cache that
// could be conservatively dirtied when we reassign or split.
//
// FIXME: This may result in a lot of alias queries. We could summarize alias
// live intervals in their parent register's live union, but it's messy.
bool RAGreedy::reassignVReg(LiveInterval &InterferingVReg,
unsigned WantedPhysReg) {
assert(TargetRegisterInfo::isVirtualRegister(InterferingVReg.reg) &&
"Can only reassign virtual registers");
assert(TRI->regsOverlap(WantedPhysReg, VRM->getPhys(InterferingVReg.reg)) &&
"inconsistent phys reg assigment");
AllocationOrder Order(InterferingVReg.reg, *VRM, ReservedRegs);
while (unsigned PhysReg = Order.next()) {
// Don't reassign to a WantedPhysReg alias.
if (TRI->regsOverlap(PhysReg, WantedPhysReg))
continue;
if (checkUncachedInterference(InterferingVReg, PhysReg))
continue;
// Reassign the interfering virtual reg to this physical reg.
unsigned OldAssign = VRM->getPhys(InterferingVReg.reg);
DEBUG(dbgs() << "reassigning: " << InterferingVReg << " from " <<
TRI->getName(OldAssign) << " to " << TRI->getName(PhysReg) << '\n');
unassign(InterferingVReg, OldAssign);
assign(InterferingVReg, PhysReg);
++NumReassigned;
return true;
}
return false;
}
/// tryReassign - Try to reassign a single interference to a different physreg.
/// @param VirtReg Currently unassigned virtual register.
/// @param Order Physregs to try.
/// @return Physreg to assign VirtReg, or 0.
unsigned RAGreedy::tryReassign(LiveInterval &VirtReg, AllocationOrder &Order,
SmallVectorImpl<LiveInterval*> &NewVRegs){
NamedRegionTimer T("Reassign", TimerGroupName, TimePassesIsEnabled);
Order.rewind();
while (unsigned PhysReg = Order.next()) {
LiveInterval *InterferingVReg = getSingleInterference(VirtReg, PhysReg);
if (!InterferingVReg)
continue;
if (TargetRegisterInfo::isPhysicalRegister(InterferingVReg->reg))
continue;
if (reassignVReg(*InterferingVReg, PhysReg))
return PhysReg;
}
return 0;
}
//===----------------------------------------------------------------------===//
// Interference eviction
//===----------------------------------------------------------------------===//
/// canEvict - Return true if all interferences between VirtReg and PhysReg can
/// be evicted. Set maxWeight to the maximal spill weight of an interference.
bool RAGreedy::canEvictInterference(LiveInterval &VirtReg, unsigned PhysReg,
float &MaxWeight) {
float Weight = 0;
for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI) {
LiveIntervalUnion::Query &Q = query(VirtReg, *AliasI);
// If there is 10 or more interferences, chances are one is smaller.
if (Q.collectInterferingVRegs(10) >= 10)
return false;
// Check if any interfering live range is heavier than VirtReg.
for (unsigned i = 0, e = Q.interferingVRegs().size(); i != e; ++i) {
LiveInterval *Intf = Q.interferingVRegs()[i];
if (TargetRegisterInfo::isPhysicalRegister(Intf->reg))
return false;
if (Intf->weight >= VirtReg.weight)
return false;
Weight = std::max(Weight, Intf->weight);
}
}
MaxWeight = Weight;
return true;
}
/// tryEvict - Try to evict all interferences for a physreg.
/// @param VirtReg Currently unassigned virtual register.
/// @param Order Physregs to try.
/// @return Physreg to assign VirtReg, or 0.
unsigned RAGreedy::tryEvict(LiveInterval &VirtReg,
AllocationOrder &Order,
SmallVectorImpl<LiveInterval*> &NewVRegs){
NamedRegionTimer T("Evict", TimerGroupName, TimePassesIsEnabled);
// Keep track of the lightest single interference seen so far.
float BestWeight = 0;
unsigned BestPhys = 0;
Order.rewind();
while (unsigned PhysReg = Order.next()) {
float Weight = 0;
if (!canEvictInterference(VirtReg, PhysReg, Weight))
continue;
// This is an eviction candidate.
DEBUG(dbgs() << "max " << PrintReg(PhysReg, TRI) << " interference = "
<< Weight << '\n');
if (BestPhys && Weight >= BestWeight)
continue;
// Best so far.
BestPhys = PhysReg;
BestWeight = Weight;
// Stop if the hint can be used.
if (Order.isHint(PhysReg))
break;
}
if (!BestPhys)
return 0;
DEBUG(dbgs() << "evicting " << PrintReg(BestPhys, TRI) << " interference\n");
for (const unsigned *AliasI = TRI->getOverlaps(BestPhys); *AliasI; ++AliasI) {
LiveIntervalUnion::Query &Q = query(VirtReg, *AliasI);
assert(Q.seenAllInterferences() && "Didn't check all interfererences.");
for (unsigned i = 0, e = Q.interferingVRegs().size(); i != e; ++i) {
LiveInterval *Intf = Q.interferingVRegs()[i];
unassign(*Intf, VRM->getPhys(Intf->reg));
++NumEvicted;
NewVRegs.push_back(Intf);
}
}
return BestPhys;
}
//===----------------------------------------------------------------------===//
// Region Splitting
//===----------------------------------------------------------------------===//
/// mapGlobalInterference - Compute a map of the interference from PhysReg and
/// its aliases in each block in SA->LiveBlocks.
/// If LiveBlocks[i] is live-in, Ranges[i].first is the first interference.
/// If LiveBlocks[i] is live-out, Ranges[i].second is the last interference.
void RAGreedy::mapGlobalInterference(unsigned PhysReg,
SmallVectorImpl<IndexPair> &Ranges) {
Ranges.assign(SA->LiveBlocks.size(), IndexPair());
LiveInterval &VirtReg = const_cast<LiveInterval&>(SA->getParent());
for (const unsigned *AI = TRI->getOverlaps(PhysReg); *AI; ++AI) {
if (!query(VirtReg, *AI).checkInterference())
continue;
LiveIntervalUnion::SegmentIter IntI =
PhysReg2LiveUnion[*AI].find(VirtReg.beginIndex());
if (!IntI.valid())
continue;
for (unsigned i = 0, e = SA->LiveBlocks.size(); i != e; ++i) {
const SplitAnalysis::BlockInfo &BI = SA->LiveBlocks[i];
IndexPair &IP = Ranges[i];
// Skip interference-free blocks.
if (IntI.start() >= BI.Stop)
continue;
// First interference in block.
if (BI.LiveIn) {
IntI.advanceTo(BI.Start);
if (!IntI.valid())
break;
if (IntI.start() >= BI.Stop)
continue;
if (!IP.first.isValid() || IntI.start() < IP.first)
IP.first = IntI.start();
}
// Last interference in block.
if (BI.LiveOut) {
IntI.advanceTo(BI.Stop);
if (!IntI.valid() || IntI.start() >= BI.Stop)
--IntI;
if (IntI.stop() <= BI.Start)
continue;
if (!IP.second.isValid() || IntI.stop() > IP.second)
IP.second = IntI.stop();
}
}
}
}
/// calcSplitConstraints - Fill out the SplitConstraints vector based on the
/// interference pattern in Intf. Return the static cost of this split,
/// assuming that all preferences in SplitConstraints are met.
float RAGreedy::calcSplitConstraints(const SmallVectorImpl<IndexPair> &Intf) {
// Reset interference dependent info.
SplitConstraints.resize(SA->LiveBlocks.size());
float StaticCost = 0;
for (unsigned i = 0, e = SA->LiveBlocks.size(); i != e; ++i) {
SplitAnalysis::BlockInfo &BI = SA->LiveBlocks[i];
SpillPlacement::BlockConstraint &BC = SplitConstraints[i];
IndexPair IP = Intf[i];
BC.Number = BI.MBB->getNumber();
BC.Entry = (BI.Uses && BI.LiveIn) ?
SpillPlacement::PrefReg : SpillPlacement::DontCare;
BC.Exit = (BI.Uses && BI.LiveOut) ?
SpillPlacement::PrefReg : SpillPlacement::DontCare;
// Number of spill code instructions to insert.
unsigned Ins = 0;
// Interference for the live-in value.
if (IP.first.isValid()) {
if (IP.first <= BI.Start)
BC.Entry = SpillPlacement::MustSpill, Ins += BI.Uses;
else if (!BI.Uses)
BC.Entry = SpillPlacement::PrefSpill;
else if (IP.first < BI.FirstUse)
BC.Entry = SpillPlacement::PrefSpill, ++Ins;
else if (IP.first < (BI.LiveThrough ? BI.LastUse : BI.Kill))
++Ins;
}
// Interference for the live-out value.
if (IP.second.isValid()) {
if (IP.second >= BI.LastSplitPoint)
BC.Exit = SpillPlacement::MustSpill, Ins += BI.Uses;
else if (!BI.Uses)
BC.Exit = SpillPlacement::PrefSpill;
else if (IP.second > BI.LastUse)
BC.Exit = SpillPlacement::PrefSpill, ++Ins;
else if (IP.second > (BI.LiveThrough ? BI.FirstUse : BI.Def))
++Ins;
}
// Accumulate the total frequency of inserted spill code.
if (Ins)
StaticCost += Ins * SpillPlacer->getBlockFrequency(BC.Number);
}
return StaticCost;
}
/// calcGlobalSplitCost - Return the global split cost of following the split
/// pattern in LiveBundles. This cost should be added to the local cost of the
/// interference pattern in SplitConstraints.
///
float RAGreedy::calcGlobalSplitCost(const BitVector &LiveBundles) {
float GlobalCost = 0;
for (unsigned i = 0, e = SA->LiveBlocks.size(); i != e; ++i) {
SplitAnalysis::BlockInfo &BI = SA->LiveBlocks[i];
SpillPlacement::BlockConstraint &BC = SplitConstraints[i];
bool RegIn = LiveBundles[Bundles->getBundle(BC.Number, 0)];
bool RegOut = LiveBundles[Bundles->getBundle(BC.Number, 1)];
unsigned Ins = 0;
if (!BI.Uses)
Ins += RegIn != RegOut;
else {
if (BI.LiveIn)
Ins += RegIn != (BC.Entry == SpillPlacement::PrefReg);
if (BI.LiveOut)
Ins += RegOut != (BC.Exit == SpillPlacement::PrefReg);
}
if (Ins)
GlobalCost += Ins * SpillPlacer->getBlockFrequency(BC.Number);
}
return GlobalCost;
}
/// splitAroundRegion - Split VirtReg around the region determined by
/// LiveBundles. Make an effort to avoid interference from PhysReg.
///
/// The 'register' interval is going to contain as many uses as possible while
/// avoiding interference. The 'stack' interval is the complement constructed by
/// SplitEditor. It will contain the rest.
///
void RAGreedy::splitAroundRegion(LiveInterval &VirtReg, unsigned PhysReg,
const BitVector &LiveBundles,
SmallVectorImpl<LiveInterval*> &NewVRegs) {
DEBUG({
dbgs() << "Splitting around region for " << PrintReg(PhysReg, TRI)
<< " with bundles";
for (int i = LiveBundles.find_first(); i>=0; i = LiveBundles.find_next(i))
dbgs() << " EB#" << i;
dbgs() << ".\n";
});
// First compute interference ranges in the live blocks.
SmallVector<IndexPair, 8> InterferenceRanges;
mapGlobalInterference(PhysReg, InterferenceRanges);
LiveRangeEdit LREdit(VirtReg, NewVRegs);
SE->reset(LREdit);
// Create the main cross-block interval.
SE->openIntv();
// First add all defs that are live out of a block.
for (unsigned i = 0, e = SA->LiveBlocks.size(); i != e; ++i) {
SplitAnalysis::BlockInfo &BI = SA->LiveBlocks[i];
bool RegIn = LiveBundles[Bundles->getBundle(BI.MBB->getNumber(), 0)];
bool RegOut = LiveBundles[Bundles->getBundle(BI.MBB->getNumber(), 1)];
// Should the register be live out?
if (!BI.LiveOut || !RegOut)
continue;
IndexPair &IP = InterferenceRanges[i];
DEBUG(dbgs() << "BB#" << BI.MBB->getNumber() << " -> EB#"
<< Bundles->getBundle(BI.MBB->getNumber(), 1)
<< " intf [" << IP.first << ';' << IP.second << ')');
// The interference interval should either be invalid or overlap MBB.
assert((!IP.first.isValid() || IP.first < BI.Stop) && "Bad interference");
assert((!IP.second.isValid() || IP.second > BI.Start)
&& "Bad interference");
// Check interference leaving the block.
if (!IP.second.isValid()) {
// Block is interference-free.
DEBUG(dbgs() << ", no interference");
if (!BI.Uses) {
assert(BI.LiveThrough && "No uses, but not live through block?");
// Block is live-through without interference.
DEBUG(dbgs() << ", no uses"
<< (RegIn ? ", live-through.\n" : ", stack in.\n"));
if (!RegIn)
SE->enterIntvAtEnd(*BI.MBB);
continue;
}
if (!BI.LiveThrough) {
DEBUG(dbgs() << ", not live-through.\n");
SE->useIntv(SE->enterIntvBefore(BI.Def), BI.Stop);
continue;
}
if (!RegIn) {
// Block is live-through, but entry bundle is on the stack.
// Reload just before the first use.
DEBUG(dbgs() << ", not live-in, enter before first use.\n");
SE->useIntv(SE->enterIntvBefore(BI.FirstUse), BI.Stop);
continue;
}
DEBUG(dbgs() << ", live-through.\n");
continue;
}
// Block has interference.
DEBUG(dbgs() << ", interference to " << IP.second);
if (!BI.LiveThrough && IP.second <= BI.Def) {
// The interference doesn't reach the outgoing segment.
DEBUG(dbgs() << " doesn't affect def from " << BI.Def << '\n');
SE->useIntv(BI.Def, BI.Stop);
continue;
}
if (!BI.Uses) {
// No uses in block, avoid interference by reloading as late as possible.
DEBUG(dbgs() << ", no uses.\n");
SlotIndex SegStart = SE->enterIntvAtEnd(*BI.MBB);
assert(SegStart >= IP.second && "Couldn't avoid interference");
continue;
}
if (IP.second.getBoundaryIndex() < BI.LastUse) {
// There are interference-free uses at the end of the block.
// Find the first use that can get the live-out register.
SmallVectorImpl<SlotIndex>::const_iterator UI =
std::lower_bound(SA->UseSlots.begin(), SA->UseSlots.end(),
IP.second.getBoundaryIndex());
assert(UI != SA->UseSlots.end() && "Couldn't find last use");
SlotIndex Use = *UI;
assert(Use <= BI.LastUse && "Couldn't find last use");
// Only attempt a split befroe the last split point.
if (Use.getBaseIndex() <= BI.LastSplitPoint) {
DEBUG(dbgs() << ", free use at " << Use << ".\n");
SlotIndex SegStart = SE->enterIntvBefore(Use);
assert(SegStart >= IP.second && "Couldn't avoid interference");
assert(SegStart < BI.LastSplitPoint && "Impossible split point");
SE->useIntv(SegStart, BI.Stop);
continue;
}
}
// Interference is after the last use.
DEBUG(dbgs() << " after last use.\n");
SlotIndex SegStart = SE->enterIntvAtEnd(*BI.MBB);
assert(SegStart >= IP.second && "Couldn't avoid interference");
}
// Now all defs leading to live bundles are handled, do everything else.
for (unsigned i = 0, e = SA->LiveBlocks.size(); i != e; ++i) {
SplitAnalysis::BlockInfo &BI = SA->LiveBlocks[i];
bool RegIn = LiveBundles[Bundles->getBundle(BI.MBB->getNumber(), 0)];
bool RegOut = LiveBundles[Bundles->getBundle(BI.MBB->getNumber(), 1)];
// Is the register live-in?
if (!BI.LiveIn || !RegIn)
continue;
// We have an incoming register. Check for interference.
IndexPair &IP = InterferenceRanges[i];
DEBUG(dbgs() << "EB#" << Bundles->getBundle(BI.MBB->getNumber(), 0)
<< " -> BB#" << BI.MBB->getNumber());
// Check interference entering the block.
if (!IP.first.isValid()) {
// Block is interference-free.
DEBUG(dbgs() << ", no interference");
if (!BI.Uses) {
assert(BI.LiveThrough && "No uses, but not live through block?");
// Block is live-through without interference.
if (RegOut) {
DEBUG(dbgs() << ", no uses, live-through.\n");
SE->useIntv(BI.Start, BI.Stop);
} else {
DEBUG(dbgs() << ", no uses, stack-out.\n");
SE->leaveIntvAtTop(*BI.MBB);
}
continue;
}
if (!BI.LiveThrough) {
DEBUG(dbgs() << ", killed in block.\n");
SE->useIntv(BI.Start, SE->leaveIntvAfter(BI.Kill));
continue;
}
if (!RegOut) {
// Block is live-through, but exit bundle is on the stack.
// Spill immediately after the last use.
if (BI.LastUse < BI.LastSplitPoint) {
DEBUG(dbgs() << ", uses, stack-out.\n");
SE->useIntv(BI.Start, SE->leaveIntvAfter(BI.LastUse));
continue;
}
// The last use is after the last split point, it is probably an
// indirect jump.
DEBUG(dbgs() << ", uses at " << BI.LastUse << " after split point "
<< BI.LastSplitPoint << ", stack-out.\n");
SlotIndex SegEnd = SE->leaveIntvBefore(BI.LastSplitPoint);
SE->useIntv(BI.Start, SegEnd);
// Run a double interval from the split to the last use.
// This makes it possible to spill the complement without affecting the
// indirect branch.
SE->overlapIntv(SegEnd, BI.LastUse);
continue;
}
// Register is live-through.
DEBUG(dbgs() << ", uses, live-through.\n");
SE->useIntv(BI.Start, BI.Stop);
continue;
}
// Block has interference.
DEBUG(dbgs() << ", interference from " << IP.first);
if (!BI.LiveThrough && IP.first >= BI.Kill) {
// The interference doesn't reach the outgoing segment.
DEBUG(dbgs() << " doesn't affect kill at " << BI.Kill << '\n');
SE->useIntv(BI.Start, BI.Kill);
continue;
}
if (!BI.Uses) {
// No uses in block, avoid interference by spilling as soon as possible.
DEBUG(dbgs() << ", no uses.\n");
SlotIndex SegEnd = SE->leaveIntvAtTop(*BI.MBB);
assert(SegEnd <= IP.first && "Couldn't avoid interference");
continue;
}
if (IP.first.getBaseIndex() > BI.FirstUse) {
// There are interference-free uses at the beginning of the block.
// Find the last use that can get the register.
SmallVectorImpl<SlotIndex>::const_iterator UI =
std::lower_bound(SA->UseSlots.begin(), SA->UseSlots.end(),
IP.first.getBaseIndex());
assert(UI != SA->UseSlots.begin() && "Couldn't find first use");
SlotIndex Use = (--UI)->getBoundaryIndex();
DEBUG(dbgs() << ", free use at " << *UI << ".\n");
SlotIndex SegEnd = SE->leaveIntvAfter(Use);
assert(SegEnd <= IP.first && "Couldn't avoid interference");
SE->useIntv(BI.Start, SegEnd);
continue;
}
// Interference is before the first use.
DEBUG(dbgs() << " before first use.\n");
SlotIndex SegEnd = SE->leaveIntvAtTop(*BI.MBB);
assert(SegEnd <= IP.first && "Couldn't avoid interference");
}
SE->closeIntv();
// FIXME: Should we be more aggressive about splitting the stack region into
// per-block segments? The current approach allows the stack region to
// separate into connected components. Some components may be allocatable.
SE->finish();
++NumGlobalSplits;
if (VerifyEnabled) {
MF->verify(this, "After splitting live range around region");
#ifndef NDEBUG
// Make sure that at least one of the new intervals can allocate to PhysReg.
// That was the whole point of splitting the live range.
bool found = false;
for (LiveRangeEdit::iterator I = LREdit.begin(), E = LREdit.end(); I != E;
++I)
if (!checkUncachedInterference(**I, PhysReg)) {
found = true;
break;
}
assert(found && "No allocatable intervals after pointless splitting");
#endif
}
}
unsigned RAGreedy::tryRegionSplit(LiveInterval &VirtReg, AllocationOrder &Order,
SmallVectorImpl<LiveInterval*> &NewVRegs) {
BitVector LiveBundles, BestBundles;
float BestCost = 0;
unsigned BestReg = 0;
Order.rewind();
for (unsigned Cand = 0; unsigned PhysReg = Order.next(); ++Cand) {
if (GlobalCand.size() <= Cand)
GlobalCand.resize(Cand+1);
GlobalCand[Cand].PhysReg = PhysReg;
mapGlobalInterference(PhysReg, GlobalCand[Cand].Interference);
float Cost = calcSplitConstraints(GlobalCand[Cand].Interference);
DEBUG(dbgs() << PrintReg(PhysReg, TRI) << "\tstatic = " << Cost);
if (BestReg && Cost >= BestCost) {
DEBUG(dbgs() << " higher.\n");
continue;
}
SpillPlacer->placeSpills(SplitConstraints, LiveBundles);
// No live bundles, defer to splitSingleBlocks().
if (!LiveBundles.any()) {
DEBUG(dbgs() << " no bundles.\n");
continue;
}
Cost += calcGlobalSplitCost(LiveBundles);
DEBUG({
dbgs() << ", total = " << Cost << " with bundles";
for (int i = LiveBundles.find_first(); i>=0; i = LiveBundles.find_next(i))
dbgs() << " EB#" << i;
dbgs() << ".\n";
});
if (!BestReg || Cost < BestCost) {
BestReg = PhysReg;
BestCost = 0.98f * Cost; // Prevent rounding effects.
BestBundles.swap(LiveBundles);
}
}
if (!BestReg)
return 0;
splitAroundRegion(VirtReg, BestReg, BestBundles, NewVRegs);
setStage(NewVRegs.begin(), NewVRegs.end(), RS_Region);
return 0;
}
//===----------------------------------------------------------------------===//
// Local Splitting
//===----------------------------------------------------------------------===//
/// calcGapWeights - Compute the maximum spill weight that needs to be evicted
/// in order to use PhysReg between two entries in SA->UseSlots.
///
/// GapWeight[i] represents the gap between UseSlots[i] and UseSlots[i+1].
///
void RAGreedy::calcGapWeights(unsigned PhysReg,
SmallVectorImpl<float> &GapWeight) {
assert(SA->LiveBlocks.size() == 1 && "Not a local interval");
const SplitAnalysis::BlockInfo &BI = SA->LiveBlocks.front();
const SmallVectorImpl<SlotIndex> &Uses = SA->UseSlots;
const unsigned NumGaps = Uses.size()-1;
// Start and end points for the interference check.
SlotIndex StartIdx = BI.LiveIn ? BI.FirstUse.getBaseIndex() : BI.FirstUse;
SlotIndex StopIdx = BI.LiveOut ? BI.LastUse.getBoundaryIndex() : BI.LastUse;
GapWeight.assign(NumGaps, 0.0f);
// Add interference from each overlapping register.
for (const unsigned *AI = TRI->getOverlaps(PhysReg); *AI; ++AI) {
if (!query(const_cast<LiveInterval&>(SA->getParent()), *AI)
.checkInterference())
continue;
// We know that VirtReg is a continuous interval from FirstUse to LastUse,
// so we don't need InterferenceQuery.
//
// Interference that overlaps an instruction is counted in both gaps
// surrounding the instruction. The exception is interference before
// StartIdx and after StopIdx.
//
LiveIntervalUnion::SegmentIter IntI = PhysReg2LiveUnion[*AI].find(StartIdx);
for (unsigned Gap = 0; IntI.valid() && IntI.start() < StopIdx; ++IntI) {
// Skip the gaps before IntI.
while (Uses[Gap+1].getBoundaryIndex() < IntI.start())
if (++Gap == NumGaps)
break;
if (Gap == NumGaps)
break;
// Update the gaps covered by IntI.
const float weight = IntI.value()->weight;
for (; Gap != NumGaps; ++Gap) {
GapWeight[Gap] = std::max(GapWeight[Gap], weight);
if (Uses[Gap+1].getBaseIndex() >= IntI.stop())
break;
}
if (Gap == NumGaps)
break;
}
}
}
/// getPrevMappedIndex - Return the slot index of the last non-copy instruction
/// before MI that has a slot index. If MI is the first mapped instruction in
/// its block, return the block start index instead.
///
SlotIndex RAGreedy::getPrevMappedIndex(const MachineInstr *MI) {
assert(MI && "Missing MachineInstr");
const MachineBasicBlock *MBB = MI->getParent();
MachineBasicBlock::const_iterator B = MBB->begin(), I = MI;
while (I != B)
if (!(--I)->isDebugValue() && !I->isCopy())
return Indexes->getInstructionIndex(I);
return Indexes->getMBBStartIdx(MBB);
}
/// calcPrevSlots - Fill in the PrevSlot array with the index of the previous
/// real non-copy instruction for each instruction in SA->UseSlots.
///
void RAGreedy::calcPrevSlots() {
const SmallVectorImpl<SlotIndex> &Uses = SA->UseSlots;
PrevSlot.clear();
PrevSlot.reserve(Uses.size());
for (unsigned i = 0, e = Uses.size(); i != e; ++i) {
const MachineInstr *MI = Indexes->getInstructionFromIndex(Uses[i]);
PrevSlot.push_back(getPrevMappedIndex(MI).getDefIndex());
}
}
/// nextSplitPoint - Find the next index into SA->UseSlots > i such that it may
/// be beneficial to split before UseSlots[i].
///
/// 0 is always a valid split point
unsigned RAGreedy::nextSplitPoint(unsigned i) {
const SmallVectorImpl<SlotIndex> &Uses = SA->UseSlots;
const unsigned Size = Uses.size();
assert(i != Size && "No split points after the end");
// Allow split before i when Uses[i] is not adjacent to the previous use.
while (++i != Size && PrevSlot[i].getBaseIndex() <= Uses[i-1].getBaseIndex())
;
return i;
}
/// tryLocalSplit - Try to split VirtReg into smaller intervals inside its only
/// basic block.
///
unsigned RAGreedy::tryLocalSplit(LiveInterval &VirtReg, AllocationOrder &Order,
SmallVectorImpl<LiveInterval*> &NewVRegs) {
assert(SA->LiveBlocks.size() == 1 && "Not a local interval");
const SplitAnalysis::BlockInfo &BI = SA->LiveBlocks.front();
// Note that it is possible to have an interval that is live-in or live-out
// while only covering a single block - A phi-def can use undef values from
// predecessors, and the block could be a single-block loop.
// We don't bother doing anything clever about such a case, we simply assume
// that the interval is continuous from FirstUse to LastUse. We should make
// sure that we don't do anything illegal to such an interval, though.
const SmallVectorImpl<SlotIndex> &Uses = SA->UseSlots;
if (Uses.size() <= 2)
return 0;
const unsigned NumGaps = Uses.size()-1;
DEBUG({
dbgs() << "tryLocalSplit: ";
for (unsigned i = 0, e = Uses.size(); i != e; ++i)
dbgs() << ' ' << SA->UseSlots[i];
dbgs() << '\n';
});
// For every use, find the previous mapped non-copy instruction.
// We use this to detect valid split points, and to estimate new interval
// sizes.
calcPrevSlots();
unsigned BestBefore = NumGaps;
unsigned BestAfter = 0;
float BestDiff = 0;
const float blockFreq = SpillPlacer->getBlockFrequency(BI.MBB->getNumber());
SmallVector<float, 8> GapWeight;
Order.rewind();
while (unsigned PhysReg = Order.next()) {
// Keep track of the largest spill weight that would need to be evicted in
// order to make use of PhysReg between UseSlots[i] and UseSlots[i+1].
calcGapWeights(PhysReg, GapWeight);
// Try to find the best sequence of gaps to close.
// The new spill weight must be larger than any gap interference.
// We will split before Uses[SplitBefore] and after Uses[SplitAfter].
unsigned SplitBefore = 0, SplitAfter = nextSplitPoint(1) - 1;
// MaxGap should always be max(GapWeight[SplitBefore..SplitAfter-1]).
// It is the spill weight that needs to be evicted.
float MaxGap = GapWeight[0];
for (unsigned i = 1; i != SplitAfter; ++i)
MaxGap = std::max(MaxGap, GapWeight[i]);
for (;;) {
// Live before/after split?
const bool LiveBefore = SplitBefore != 0 || BI.LiveIn;
const bool LiveAfter = SplitAfter != NumGaps || BI.LiveOut;
DEBUG(dbgs() << PrintReg(PhysReg, TRI) << ' '
<< Uses[SplitBefore] << '-' << Uses[SplitAfter]
<< " i=" << MaxGap);
// Stop before the interval gets so big we wouldn't be making progress.
if (!LiveBefore && !LiveAfter) {
DEBUG(dbgs() << " all\n");
break;
}
// Should the interval be extended or shrunk?
bool Shrink = true;
if (MaxGap < HUGE_VALF) {
// Estimate the new spill weight.
//
// Each instruction reads and writes the register, except the first
// instr doesn't read when !FirstLive, and the last instr doesn't write
// when !LastLive.
//
// We will be inserting copies before and after, so the total number of
// reads and writes is 2 * EstUses.
//
const unsigned EstUses = 2*(SplitAfter - SplitBefore) +
2*(LiveBefore + LiveAfter);
// Try to guess the size of the new interval. This should be trivial,
// but the slot index of an inserted copy can be a lot smaller than the
// instruction it is inserted before if there are many dead indexes
// between them.
//
// We measure the distance from the instruction before SplitBefore to
// get a conservative estimate.
//
// The final distance can still be different if inserting copies
// triggers a slot index renumbering.
//
const float EstWeight = normalizeSpillWeight(blockFreq * EstUses,
PrevSlot[SplitBefore].distance(Uses[SplitAfter]));
// Would this split be possible to allocate?
// Never allocate all gaps, we wouldn't be making progress.
float Diff = EstWeight - MaxGap;
DEBUG(dbgs() << " w=" << EstWeight << " d=" << Diff);
if (Diff > 0) {
Shrink = false;
if (Diff > BestDiff) {
DEBUG(dbgs() << " (best)");
BestDiff = Diff;
BestBefore = SplitBefore;
BestAfter = SplitAfter;
}
}
}
// Try to shrink.
if (Shrink) {
SplitBefore = nextSplitPoint(SplitBefore);
if (SplitBefore < SplitAfter) {
DEBUG(dbgs() << " shrink\n");
// Recompute the max when necessary.
if (GapWeight[SplitBefore - 1] >= MaxGap) {
MaxGap = GapWeight[SplitBefore];
for (unsigned i = SplitBefore + 1; i != SplitAfter; ++i)
MaxGap = std::max(MaxGap, GapWeight[i]);
}
continue;
}
MaxGap = 0;
}
// Try to extend the interval.
if (SplitAfter >= NumGaps) {
DEBUG(dbgs() << " end\n");
break;
}
DEBUG(dbgs() << " extend\n");
for (unsigned e = nextSplitPoint(SplitAfter + 1) - 1;
SplitAfter != e; ++SplitAfter)
MaxGap = std::max(MaxGap, GapWeight[SplitAfter]);
continue;
}
}
// Didn't find any candidates?
if (BestBefore == NumGaps)
return 0;
DEBUG(dbgs() << "Best local split range: " << Uses[BestBefore]
<< '-' << Uses[BestAfter] << ", " << BestDiff
<< ", " << (BestAfter - BestBefore + 1) << " instrs\n");
LiveRangeEdit LREdit(VirtReg, NewVRegs);
SE->reset(LREdit);
SE->openIntv();
SlotIndex SegStart = SE->enterIntvBefore(Uses[BestBefore]);
SlotIndex SegStop = SE->leaveIntvAfter(Uses[BestAfter]);
SE->useIntv(SegStart, SegStop);
SE->closeIntv();
SE->finish();
setStage(NewVRegs.begin(), NewVRegs.end(), RS_Local);
++NumLocalSplits;
return 0;
}
//===----------------------------------------------------------------------===//
// Live Range Splitting
//===----------------------------------------------------------------------===//
/// trySplit - Try to split VirtReg or one of its interferences, making it
/// assignable.
/// @return Physreg when VirtReg may be assigned and/or new NewVRegs.
unsigned RAGreedy::trySplit(LiveInterval &VirtReg, AllocationOrder &Order,
SmallVectorImpl<LiveInterval*>&NewVRegs) {
// Local intervals are handled separately.
if (LIS->intervalIsInOneMBB(VirtReg)) {
NamedRegionTimer T("Local Splitting", TimerGroupName, TimePassesIsEnabled);
SA->analyze(&VirtReg);
return tryLocalSplit(VirtReg, Order, NewVRegs);
}
NamedRegionTimer T("Global Splitting", TimerGroupName, TimePassesIsEnabled);
// Don't iterate global splitting.
// Move straight to spilling if this range was produced by a global split.
LiveRangeStage Stage = getStage(VirtReg);
if (Stage >= RS_Block)
return 0;
SA->analyze(&VirtReg);
// First try to split around a region spanning multiple blocks.
if (Stage < RS_Region) {
unsigned PhysReg = tryRegionSplit(VirtReg, Order, NewVRegs);
if (PhysReg || !NewVRegs.empty())
return PhysReg;
}
// Then isolate blocks with multiple uses.
if (Stage < RS_Block) {
SplitAnalysis::BlockPtrSet Blocks;
if (SA->getMultiUseBlocks(Blocks)) {
LiveRangeEdit LREdit(VirtReg, NewVRegs);
SE->reset(LREdit);
SE->splitSingleBlocks(Blocks);
setStage(NewVRegs.begin(), NewVRegs.end(), RS_Block);
if (VerifyEnabled)
MF->verify(this, "After splitting live range around basic blocks");
}
}
// Don't assign any physregs.
return 0;
}
//===----------------------------------------------------------------------===//
// Main Entry Point
//===----------------------------------------------------------------------===//
unsigned RAGreedy::selectOrSplit(LiveInterval &VirtReg,
SmallVectorImpl<LiveInterval*> &NewVRegs) {
LiveRangeStage Stage = getStage(VirtReg);
if (Stage == RS_Original)
LRStage[VirtReg.reg] = RS_Second;
// First try assigning a free register.
AllocationOrder Order(VirtReg.reg, *VRM, ReservedRegs);
while (unsigned PhysReg = Order.next()) {
if (!checkPhysRegInterference(VirtReg, PhysReg))
return PhysReg;
}
if (unsigned PhysReg = tryReassign(VirtReg, Order, NewVRegs))
return PhysReg;
if (unsigned PhysReg = tryEvict(VirtReg, Order, NewVRegs))
return PhysReg;
assert(NewVRegs.empty() && "Cannot append to existing NewVRegs");
// The first time we see a live range, don't try to split or spill.
// Wait until the second time, when all smaller ranges have been allocated.
// This gives a better picture of the interference to split around.
if (Stage == RS_Original) {
NewVRegs.push_back(&VirtReg);
return 0;
}
assert(Stage < RS_Spill && "Cannot allocate after spilling");
// Try splitting VirtReg or interferences.
unsigned PhysReg = trySplit(VirtReg, Order, NewVRegs);
if (PhysReg || !NewVRegs.empty())
return PhysReg;
// Finally spill VirtReg itself.
NamedRegionTimer T("Spiller", TimerGroupName, TimePassesIsEnabled);
SmallVector<LiveInterval*, 1> pendingSpills;
spiller().spill(&VirtReg, NewVRegs, pendingSpills);
// The live virtual register requesting allocation was spilled, so tell
// the caller not to allocate anything during this round.
return 0;
}
bool RAGreedy::runOnMachineFunction(MachineFunction &mf) {
DEBUG(dbgs() << "********** GREEDY REGISTER ALLOCATION **********\n"
<< "********** Function: "
<< ((Value*)mf.getFunction())->getName() << '\n');
MF = &mf;
if (VerifyEnabled)
MF->verify(this, "Before greedy register allocator");
RegAllocBase::init(getAnalysis<VirtRegMap>(), getAnalysis<LiveIntervals>());
Indexes = &getAnalysis<SlotIndexes>();
DomTree = &getAnalysis<MachineDominatorTree>();
ReservedRegs = TRI->getReservedRegs(*MF);
SpillerInstance.reset(createInlineSpiller(*this, *MF, *VRM));
Loops = &getAnalysis<MachineLoopInfo>();
LoopRanges = &getAnalysis<MachineLoopRanges>();
Bundles = &getAnalysis<EdgeBundles>();
SpillPlacer = &getAnalysis<SpillPlacement>();
SA.reset(new SplitAnalysis(*VRM, *LIS, *Loops));
SE.reset(new SplitEditor(*SA, *LIS, *VRM, *DomTree));
LRStage.clear();
LRStage.resize(MRI->getNumVirtRegs());
allocatePhysRegs();
addMBBLiveIns(MF);
LIS->addKillFlags();
// Run rewriter
{
NamedRegionTimer T("Rewriter", TimerGroupName, TimePassesIsEnabled);
VRM->rewrite(Indexes);
}
// The pass output is in VirtRegMap. Release all the transient data.
releaseMemory();
return true;
}