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5907d86365
llvm-6502/lib/CodeGen/RegAllocGreedy.cpp
Jakob Stoklund Olesen 5907d86365 Add an InterferenceCache class for caching per-block interference ranges. 
When the greedy register allocator is splitting multiple global live ranges, it
tends to look at the same interference data many times. The InterferenceCache
class caches queries for unaltered LiveIntervalUnions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128764 91177308-0d34-0410-b5e6-96231b3b80d8
2011-04-02 06:03:35 +00:00

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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 "InterferenceCache.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(NumEvicted, "Number of interferences evicted");
static RegisterRegAlloc greedyRegAlloc("greedy", "greedy register allocator",
createGreedyRegisterAllocator);
namespace {
class RAGreedy : public MachineFunctionPass,
public RegAllocBase,
private LiveRangeEdit::Delegate {
// 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_New, ///< Never seen before.
RS_First, ///< First time in the queue.
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) {
unsigned Reg = (*Begin)->reg;
if (LRStage[Reg] == RS_New)
LRStage[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:
void LRE_WillEraseInstruction(MachineInstr*);
bool LRE_CanEraseVirtReg(unsigned);
void LRE_WillShrinkVirtReg(unsigned);
void LRE_DidCloneVirtReg(unsigned, unsigned);
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 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_New) {
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);
}
//===----------------------------------------------------------------------===//
// LiveRangeEdit delegate methods
//===----------------------------------------------------------------------===//
void RAGreedy::LRE_WillEraseInstruction(MachineInstr *MI) {
// LRE itself will remove from SlotIndexes and parent basic block.
VRM->RemoveMachineInstrFromMaps(MI);
}
bool RAGreedy::LRE_CanEraseVirtReg(unsigned VirtReg) {
if (unsigned PhysReg = VRM->getPhys(VirtReg)) {
unassign(LIS->getInterval(VirtReg), PhysReg);
return true;
}
// Unassigned virtreg is probably in the priority queue.
// RegAllocBase will erase it after dequeueing.
return false;
}
void RAGreedy::LRE_WillShrinkVirtReg(unsigned VirtReg) {
unsigned PhysReg = VRM->getPhys(VirtReg);
if (!PhysReg)
return;
// Register is assigned, put it back on the queue for reassignment.
LiveInterval &LI = LIS->getInterval(VirtReg);
unassign(LI, PhysReg);
enqueue(&LI);
}
void RAGreedy::LRE_DidCloneVirtReg(unsigned New, unsigned Old) {
// LRE may clone a virtual register because dead code elimination causes it to
// be split into connected components. Ensure that the new register gets the
// same stage as the parent.
LRStage.grow(New);
LRStage[New] = LRStage[Old];
}
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_New)
LRStage[Reg] = RS_First;
if (LRStage[Reg] == RS_Second)
// Unsplit ranges that couldn't be allocated immediately are deferred until
// everything else has been allocated. Long ranges are allocated last so
// they are split against realistic interference.
Prio = (1u << 31) - Size;
else {
// Everything else is allocated in long->short order. Long ranges that don't
// fit should be spilled ASAP so they don't create interference.
Prio = (1u << 31) + Size;
// Boost ranges that have a physical register hint.
if (TargetRegisterInfo::isPhysicalRegister(VRM->getRegAllocPref(Reg)))
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;
}
//===----------------------------------------------------------------------===//
// 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, this);
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)
<< " [" << BI.Start << ';' << BI.LastSplitPoint << '-'
<< BI.Stop << ") 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() << " [" << BI.Start << ';'
<< BI.LastSplitPoint << '-' << BI.Stop << ')');
// 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");
}
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, this);
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, this);
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) {
// 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 = 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.
LiveRangeStage Stage = getStage(VirtReg);
if (Stage == RS_First) {
LRStage[VirtReg.reg] = RS_Second;
DEBUG(dbgs() << "wait for second round\n");
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);
LiveRangeEdit LRE(VirtReg, NewVRegs, this);
spiller().spill(LRE);
setStage(NewVRegs.begin(), NewVRegs.end(), RS_Spill);
if (VerifyEnabled)
MF->verify(this, "After spilling");
// 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;
}
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