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llvm-6502/lib/CodeGen/RegAllocGreedy.cpp
Jakob Stoklund Olesen 9f4b893b84 Add a safe-guard against repeated splitting for some rare cases. 
The number of blocks covered by a live range must be strictly decreasing when
splitting, otherwise we can't allow repeated splitting.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130249 91177308-0d34-0410-b5e6-96231b3b80d8
2011-04-26 22:33:12 +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 "LiveDebugVariables.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_Global, ///< Produced by global 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;
/// Cached per-block interference maps
InterferenceCache IntfCache;
/// All basic blocks where the current register has uses.
SmallVector<SpillPlacement::BlockConstraint, 8> SplitConstraints;
/// Global live range splitting candidate info.
struct GlobalSplitCandidate {
unsigned PhysReg;
BitVector LiveBundles;
SmallVector<unsigned, 8> ActiveBlocks;
void reset(unsigned Reg) {
PhysReg = Reg;
LiveBundles.clear();
ActiveBlocks.clear();
}
};
/// 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);
float calcSpillCost();
bool addSplitConstraints(InterferenceCache::Cursor, float&);
void addThroughConstraints(InterferenceCache::Cursor, ArrayRef<unsigned>);
void growRegion(GlobalSplitCandidate &Cand, InterferenceCache::Cursor);
float calcGlobalSplitCost(GlobalSplitCandidate&, InterferenceCache::Cursor);
void splitAroundRegion(LiveInterval&, GlobalSplitCandidate&,
SmallVectorImpl<LiveInterval*>&);
void calcGapWeights(unsigned, SmallVectorImpl<float>&);
SlotIndex getPrevMappedIndex(const MachineInstr*);
void calcPrevSlots();
unsigned nextSplitPoint(unsigned);
bool canEvictInterference(LiveInterval&, unsigned, float&);
unsigned tryAssign(LiveInterval&, AllocationOrder&,
SmallVectorImpl<LiveInterval*>&);
unsigned tryEvict(LiveInterval&, AllocationOrder&,
SmallVectorImpl<LiveInterval*>&, unsigned = ~0u);
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;
// Hysteresis to use when comparing floats.
// This helps stabilize decisions based on float comparisons.
const float Hysteresis = 0.98f;
FunctionPass* llvm::createGreedyRegisterAllocator() {
return new RAGreedy();
}
RAGreedy::RAGreedy(): MachineFunctionPass(ID), LRStage(RS_New) {
initializeLiveDebugVariablesPass(*PassRegistry::getPassRegistry());
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>();
AU.addRequired<LiveDebugVariables>();
AU.addPreserved<LiveDebugVariables>();
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();
GlobalCand.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;
}
//===----------------------------------------------------------------------===//
// Direct Assignment
//===----------------------------------------------------------------------===//
/// tryAssign - Try to assign VirtReg to an available register.
unsigned RAGreedy::tryAssign(LiveInterval &VirtReg,
AllocationOrder &Order,
SmallVectorImpl<LiveInterval*> &NewVRegs) {
Order.rewind();
unsigned PhysReg;
while ((PhysReg = Order.next()))
if (!checkPhysRegInterference(VirtReg, PhysReg))
break;
if (!PhysReg || Order.isHint(PhysReg))
return PhysReg;
// PhysReg is available. Try to evict interference from a cheaper alternative.
unsigned Cost = TRI->getCostPerUse(PhysReg);
// Most registers have 0 additional cost.
if (!Cost)
return PhysReg;
DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " is available at cost " << Cost
<< '\n');
unsigned CheapReg = tryEvict(VirtReg, Order, NewVRegs, Cost);
return CheapReg ? CheapReg : PhysReg;
}
//===----------------------------------------------------------------------===//
// Interference eviction
//===----------------------------------------------------------------------===//
/// canEvict - Return true if all interferences between VirtReg and PhysReg can
/// be evicted.
/// Return false if any interference is heavier than MaxWeight.
/// On return, 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 heavier.
if (Q.collectInterferingVRegs(10, MaxWeight) >= 10)
return false;
// Check if any interfering live range is heavier than MaxWeight.
for (unsigned i = Q.interferingVRegs().size(); i; --i) {
LiveInterval *Intf = Q.interferingVRegs()[i - 1];
if (TargetRegisterInfo::isPhysicalRegister(Intf->reg))
return false;
if (Intf->weight >= MaxWeight)
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,
unsigned CostPerUseLimit) {
NamedRegionTimer T("Evict", TimerGroupName, TimePassesIsEnabled);
// Keep track of the lightest single interference seen so far.
float BestWeight = VirtReg.weight;
unsigned BestPhys = 0;
Order.rewind();
while (unsigned PhysReg = Order.next()) {
if (TRI->getCostPerUse(PhysReg) >= CostPerUseLimit)
continue;
// The first use of a register in a function has cost 1.
if (CostPerUseLimit == 1 && !MRI->isPhysRegUsed(PhysReg))
continue;
float Weight = BestWeight;
if (!canEvictInterference(VirtReg, PhysReg, Weight))
continue;
// This is an eviction candidate.
DEBUG(dbgs() << 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
//===----------------------------------------------------------------------===//
/// addSplitConstraints - Fill out the SplitConstraints vector based on the
/// interference pattern in Physreg and its aliases. Add the constraints to
/// SpillPlacement and return the static cost of this split in Cost, assuming
/// that all preferences in SplitConstraints are met.
/// Return false if there are no bundles with positive bias.
bool RAGreedy::addSplitConstraints(InterferenceCache::Cursor Intf,
float &Cost) {
ArrayRef<SplitAnalysis::BlockInfo> UseBlocks = SA->getUseBlocks();
// Reset interference dependent info.
SplitConstraints.resize(UseBlocks.size());
float StaticCost = 0;
for (unsigned i = 0; i != UseBlocks.size(); ++i) {
const SplitAnalysis::BlockInfo &BI = UseBlocks[i];
SpillPlacement::BlockConstraint &BC = SplitConstraints[i];
BC.Number = BI.MBB->getNumber();
Intf.moveToBlock(BC.Number);
BC.Entry = BI.LiveIn ? SpillPlacement::PrefReg : SpillPlacement::DontCare;
BC.Exit = BI.LiveOut ? SpillPlacement::PrefReg : SpillPlacement::DontCare;
if (!Intf.hasInterference())
continue;
// Number of spill code instructions to insert.
unsigned Ins = 0;
// Interference for the live-in value.
if (BI.LiveIn) {
if (Intf.first() <= Indexes->getMBBStartIdx(BC.Number))
BC.Entry = SpillPlacement::MustSpill, ++Ins;
else if (Intf.first() < BI.FirstUse)
BC.Entry = SpillPlacement::PrefSpill, ++Ins;
else if (Intf.first() < (BI.LiveThrough ? BI.LastUse : BI.Kill))
++Ins;
}
// Interference for the live-out value.
if (BI.LiveOut) {
if (Intf.last() >= SA->getLastSplitPoint(BC.Number))
BC.Exit = SpillPlacement::MustSpill, ++Ins;
else if (Intf.last() > BI.LastUse)
BC.Exit = SpillPlacement::PrefSpill, ++Ins;
else if (Intf.last() > (BI.LiveThrough ? BI.FirstUse : BI.Def))
++Ins;
}
// Accumulate the total frequency of inserted spill code.
if (Ins)
StaticCost += Ins * SpillPlacer->getBlockFrequency(BC.Number);
}
Cost = StaticCost;
// Add constraints for use-blocks. Note that these are the only constraints
// that may add a positive bias, it is downhill from here.
SpillPlacer->addConstraints(SplitConstraints);
return SpillPlacer->scanActiveBundles();
}
/// addThroughConstraints - Add constraints and links to SpillPlacer from the
/// live-through blocks in Blocks.
void RAGreedy::addThroughConstraints(InterferenceCache::Cursor Intf,
ArrayRef<unsigned> Blocks) {
const unsigned GroupSize = 8;
SpillPlacement::BlockConstraint BCS[GroupSize];
unsigned TBS[GroupSize];
unsigned B = 0, T = 0;
for (unsigned i = 0; i != Blocks.size(); ++i) {
unsigned Number = Blocks[i];
Intf.moveToBlock(Number);
if (!Intf.hasInterference()) {
assert(T < GroupSize && "Array overflow");
TBS[T] = Number;
if (++T == GroupSize) {
SpillPlacer->addLinks(ArrayRef<unsigned>(TBS, T));
T = 0;
}
continue;
}
assert(B < GroupSize && "Array overflow");
BCS[B].Number = Number;
// Interference for the live-in value.
if (Intf.first() <= Indexes->getMBBStartIdx(Number))
BCS[B].Entry = SpillPlacement::MustSpill;
else
BCS[B].Entry = SpillPlacement::PrefSpill;
// Interference for the live-out value.
if (Intf.last() >= SA->getLastSplitPoint(Number))
BCS[B].Exit = SpillPlacement::MustSpill;
else
BCS[B].Exit = SpillPlacement::PrefSpill;
if (++B == GroupSize) {
ArrayRef<SpillPlacement::BlockConstraint> Array(BCS, B);
SpillPlacer->addConstraints(Array);
B = 0;
}
}
ArrayRef<SpillPlacement::BlockConstraint> Array(BCS, B);
SpillPlacer->addConstraints(Array);
SpillPlacer->addLinks(ArrayRef<unsigned>(TBS, T));
}
void RAGreedy::growRegion(GlobalSplitCandidate &Cand,
InterferenceCache::Cursor Intf) {
// Keep track of through blocks that have not been added to SpillPlacer.
BitVector Todo = SA->getThroughBlocks();
SmallVectorImpl<unsigned> &ActiveBlocks = Cand.ActiveBlocks;
unsigned AddedTo = 0;
#ifndef NDEBUG
unsigned Visited = 0;
#endif
for (;;) {
ArrayRef<unsigned> NewBundles = SpillPlacer->getRecentPositive();
if (NewBundles.empty())
break;
// Find new through blocks in the periphery of PrefRegBundles.
for (int i = 0, e = NewBundles.size(); i != e; ++i) {
unsigned Bundle = NewBundles[i];
// Look at all blocks connected to Bundle in the full graph.
ArrayRef<unsigned> Blocks = Bundles->getBlocks(Bundle);
for (ArrayRef<unsigned>::iterator I = Blocks.begin(), E = Blocks.end();
I != E; ++I) {
unsigned Block = *I;
if (!Todo.test(Block))
continue;
Todo.reset(Block);
// This is a new through block. Add it to SpillPlacer later.
ActiveBlocks.push_back(Block);
#ifndef NDEBUG
++Visited;
#endif
}
}
// Any new blocks to add?
if (ActiveBlocks.size() > AddedTo) {
ArrayRef<unsigned> Add(&ActiveBlocks[AddedTo],
ActiveBlocks.size() - AddedTo);
addThroughConstraints(Intf, Add);
AddedTo = ActiveBlocks.size();
}
// Perhaps iterating can enable more bundles?
SpillPlacer->iterate();
}
DEBUG(dbgs() << ", v=" << Visited);
}
/// calcSpillCost - Compute how expensive it would be to split the live range in
/// SA around all use blocks instead of forming bundle regions.
float RAGreedy::calcSpillCost() {
float Cost = 0;
const LiveInterval &LI = SA->getParent();
ArrayRef<SplitAnalysis::BlockInfo> UseBlocks = SA->getUseBlocks();
for (unsigned i = 0; i != UseBlocks.size(); ++i) {
const SplitAnalysis::BlockInfo &BI = UseBlocks[i];
unsigned Number = BI.MBB->getNumber();
// We normally only need one spill instruction - a load or a store.
Cost += SpillPlacer->getBlockFrequency(Number);
// Unless the value is redefined in the block.
if (BI.LiveIn && BI.LiveOut) {
SlotIndex Start, Stop;
tie(Start, Stop) = Indexes->getMBBRange(Number);
LiveInterval::const_iterator I = LI.find(Start);
assert(I != LI.end() && "Expected live-in value");
// Is there a different live-out value? If so, we need an extra spill
// instruction.
if (I->end < Stop)
Cost += SpillPlacer->getBlockFrequency(Number);
}
}
return Cost;
}
/// 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(GlobalSplitCandidate &Cand,
InterferenceCache::Cursor Intf) {
float GlobalCost = 0;
const BitVector &LiveBundles = Cand.LiveBundles;
ArrayRef<SplitAnalysis::BlockInfo> UseBlocks = SA->getUseBlocks();
for (unsigned i = 0; i != UseBlocks.size(); ++i) {
const SplitAnalysis::BlockInfo &BI = UseBlocks[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.LiveIn)
Ins += RegIn != (BC.Entry == SpillPlacement::PrefReg);
if (BI.LiveOut)
Ins += RegOut != (BC.Exit == SpillPlacement::PrefReg);
if (Ins)
GlobalCost += Ins * SpillPlacer->getBlockFrequency(BC.Number);
}
for (unsigned i = 0, e = Cand.ActiveBlocks.size(); i != e; ++i) {
unsigned Number = Cand.ActiveBlocks[i];
bool RegIn = LiveBundles[Bundles->getBundle(Number, 0)];
bool RegOut = LiveBundles[Bundles->getBundle(Number, 1)];
if (!RegIn && !RegOut)
continue;
if (RegIn && RegOut) {
// We need double spill code if this block has interference.
Intf.moveToBlock(Number);
if (Intf.hasInterference())
GlobalCost += 2*SpillPlacer->getBlockFrequency(Number);
continue;
}
// live-in / stack-out or stack-in live-out.
GlobalCost += SpillPlacer->getBlockFrequency(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,
GlobalSplitCandidate &Cand,
SmallVectorImpl<LiveInterval*> &NewVRegs) {
const BitVector &LiveBundles = Cand.LiveBundles;
DEBUG({
dbgs() << "Splitting around region for " << PrintReg(Cand.PhysReg, TRI)
<< " with bundles";
for (int i = LiveBundles.find_first(); i>=0; i = LiveBundles.find_next(i))
dbgs() << " EB#" << i;
dbgs() << ".\n";
});
InterferenceCache::Cursor Intf(IntfCache, Cand.PhysReg);
LiveRangeEdit LREdit(VirtReg, NewVRegs, this);
SE->reset(LREdit);
// Create the main cross-block interval.
const unsigned MainIntv = SE->openIntv();
// First add all defs that are live out of a block.
ArrayRef<SplitAnalysis::BlockInfo> UseBlocks = SA->getUseBlocks();
for (unsigned i = 0; i != UseBlocks.size(); ++i) {
const SplitAnalysis::BlockInfo &BI = UseBlocks[i];
bool RegIn = LiveBundles[Bundles->getBundle(BI.MBB->getNumber(), 0)];
bool RegOut = LiveBundles[Bundles->getBundle(BI.MBB->getNumber(), 1)];
// Create separate intervals for isolated blocks with multiple uses.
if (!RegIn && !RegOut && BI.FirstUse != BI.LastUse) {
DEBUG(dbgs() << "BB#" << BI.MBB->getNumber() << " isolated.\n");
SE->splitSingleBlock(BI);
SE->selectIntv(MainIntv);
continue;
}
// Should the register be live out?
if (!BI.LiveOut || !RegOut)
continue;
SlotIndex Start, Stop;
tie(Start, Stop) = Indexes->getMBBRange(BI.MBB);
Intf.moveToBlock(BI.MBB->getNumber());
DEBUG(dbgs() << "BB#" << BI.MBB->getNumber() << " -> EB#"
<< Bundles->getBundle(BI.MBB->getNumber(), 1)
<< " [" << Start << ';'
<< SA->getLastSplitPoint(BI.MBB->getNumber()) << '-' << Stop
<< ") intf [" << Intf.first() << ';' << Intf.last() << ')');
// The interference interval should either be invalid or overlap MBB.
assert((!Intf.hasInterference() || Intf.first() < Stop)
&& "Bad interference");
assert((!Intf.hasInterference() || Intf.last() > Start)
&& "Bad interference");
// Check interference leaving the block.
if (!Intf.hasInterference()) {
// Block is interference-free.
DEBUG(dbgs() << ", no interference");
if (!BI.LiveThrough) {
DEBUG(dbgs() << ", not live-through.\n");
SE->useIntv(SE->enterIntvBefore(BI.Def), 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), Stop);
continue;
}
DEBUG(dbgs() << ", live-through.\n");
continue;
}
// Block has interference.
DEBUG(dbgs() << ", interference to " << Intf.last());
if (!BI.LiveThrough && Intf.last() <= BI.Def) {
// The interference doesn't reach the outgoing segment.
DEBUG(dbgs() << " doesn't affect def from " << BI.Def << '\n');
SE->useIntv(BI.Def, Stop);
continue;
}
SlotIndex LastSplitPoint = SA->getLastSplitPoint(BI.MBB->getNumber());
if (Intf.last().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(),
Intf.last().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() <= LastSplitPoint) {
DEBUG(dbgs() << ", free use at " << Use << ".\n");
SlotIndex SegStart = SE->enterIntvBefore(Use);
assert(SegStart >= Intf.last() && "Couldn't avoid interference");
assert(SegStart < LastSplitPoint && "Impossible split point");
SE->useIntv(SegStart, Stop);
continue;
}
}
// Interference is after the last use.
DEBUG(dbgs() << " after last use.\n");
SlotIndex SegStart = SE->enterIntvAtEnd(*BI.MBB);
assert(SegStart >= Intf.last() && "Couldn't avoid interference");
}
// Now all defs leading to live bundles are handled, do everything else.
for (unsigned i = 0; i != UseBlocks.size(); ++i) {
const SplitAnalysis::BlockInfo &BI = UseBlocks[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.
SlotIndex Start, Stop;
tie(Start, Stop) = Indexes->getMBBRange(BI.MBB);
Intf.moveToBlock(BI.MBB->getNumber());
DEBUG(dbgs() << "EB#" << Bundles->getBundle(BI.MBB->getNumber(), 0)
<< " -> BB#" << BI.MBB->getNumber() << " [" << Start << ';'
<< SA->getLastSplitPoint(BI.MBB->getNumber()) << '-' << Stop
<< ')');
// Check interference entering the block.
if (!Intf.hasInterference()) {
// Block is interference-free.
DEBUG(dbgs() << ", no interference");
if (!BI.LiveThrough) {
DEBUG(dbgs() << ", killed in block.\n");
SE->useIntv(Start, SE->leaveIntvAfter(BI.Kill));
continue;
}
if (!RegOut) {
SlotIndex LastSplitPoint = SA->getLastSplitPoint(BI.MBB->getNumber());
// Block is live-through, but exit bundle is on the stack.
// Spill immediately after the last use.
if (BI.LastUse < LastSplitPoint) {
DEBUG(dbgs() << ", uses, stack-out.\n");
SE->useIntv(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 "
<< LastSplitPoint << ", stack-out.\n");
SlotIndex SegEnd = SE->leaveIntvBefore(LastSplitPoint);
SE->useIntv(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(Start, Stop);
continue;
}
// Block has interference.
DEBUG(dbgs() << ", interference from " << Intf.first());
if (!BI.LiveThrough && Intf.first() >= BI.Kill) {
// The interference doesn't reach the outgoing segment.
DEBUG(dbgs() << " doesn't affect kill at " << BI.Kill << '\n');
SE->useIntv(Start, BI.Kill);
continue;
}
if (Intf.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(),
Intf.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 <= Intf.first() && "Couldn't avoid interference");
SE->useIntv(Start, SegEnd);
continue;
}
// Interference is before the first use.
DEBUG(dbgs() << " before first use.\n");
SlotIndex SegEnd = SE->leaveIntvAtTop(*BI.MBB);
assert(SegEnd <= Intf.first() && "Couldn't avoid interference");
}
// Handle live-through blocks.
for (unsigned i = 0, e = Cand.ActiveBlocks.size(); i != e; ++i) {
unsigned Number = Cand.ActiveBlocks[i];
bool RegIn = LiveBundles[Bundles->getBundle(Number, 0)];
bool RegOut = LiveBundles[Bundles->getBundle(Number, 1)];
DEBUG(dbgs() << "Live through BB#" << Number << '\n');
if (RegIn && RegOut) {
Intf.moveToBlock(Number);
if (!Intf.hasInterference()) {
SE->useIntv(Indexes->getMBBStartIdx(Number),
Indexes->getMBBEndIdx(Number));
continue;
}
}
MachineBasicBlock *MBB = MF->getBlockNumbered(Number);
if (RegIn)
SE->leaveIntvAtTop(*MBB);
if (RegOut)
SE->enterIntvAtEnd(*MBB);
}
++NumGlobalSplits;
SmallVector<unsigned, 8> IntvMap;
SE->finish(&IntvMap);
LRStage.resize(MRI->getNumVirtRegs());
unsigned OrigBlocks = SA->getNumThroughBlocks() + SA->getUseBlocks().size();
// Sort out the new intervals created by splitting. We get four kinds:
// - Remainder intervals should not be split again.
// - Candidate intervals can be assigned to Cand.PhysReg.
// - Block-local splits are candidates for local splitting.
// - DCE leftovers should go back on the queue.
for (unsigned i = 0, e = LREdit.size(); i != e; ++i) {
unsigned Reg = LREdit.get(i)->reg;
// Ignore old intervals from DCE.
if (LRStage[Reg] != RS_New)
continue;
// Remainder interval. Don't try splitting again, spill if it doesn't
// allocate.
if (IntvMap[i] == 0) {
LRStage[Reg] = RS_Global;
continue;
}
// Main interval. Allow repeated splitting as long as the number of live
// blocks is strictly decreasing.
if (IntvMap[i] == MainIntv) {
if (SA->countLiveBlocks(LREdit.get(i)) >= OrigBlocks) {
DEBUG(dbgs() << "Main interval covers the same " << OrigBlocks
<< " blocks as original.\n");
// Don't allow repeated splitting as a safe guard against looping.
LRStage[Reg] = RS_Global;
}
continue;
}
// Other intervals are treated as new. This includes local intervals created
// for blocks with multiple uses, and anything created by DCE.
}
if (VerifyEnabled)
MF->verify(this, "After splitting live range around region");
}
unsigned RAGreedy::tryRegionSplit(LiveInterval &VirtReg, AllocationOrder &Order,
SmallVectorImpl<LiveInterval*> &NewVRegs) {
float BestCost = Hysteresis * calcSpillCost();
DEBUG(dbgs() << "Cost of isolating all blocks = " << BestCost << '\n');
const unsigned NoCand = ~0u;
unsigned BestCand = NoCand;
Order.rewind();
for (unsigned Cand = 0; unsigned PhysReg = Order.next(); ++Cand) {
if (GlobalCand.size() <= Cand)
GlobalCand.resize(Cand+1);
GlobalCand[Cand].reset(PhysReg);
SpillPlacer->prepare(GlobalCand[Cand].LiveBundles);
float Cost;
InterferenceCache::Cursor Intf(IntfCache, PhysReg);
if (!addSplitConstraints(Intf, Cost)) {
DEBUG(dbgs() << PrintReg(PhysReg, TRI) << "\tno positive bundles\n");
continue;
}
DEBUG(dbgs() << PrintReg(PhysReg, TRI) << "\tstatic = " << Cost);
if (Cost >= BestCost) {
DEBUG({
if (BestCand == NoCand)
dbgs() << " worse than no bundles\n";
else
dbgs() << " worse than "
<< PrintReg(GlobalCand[BestCand].PhysReg, TRI) << '\n';
});
continue;
}
growRegion(GlobalCand[Cand], Intf);
SpillPlacer->finish();
// No live bundles, defer to splitSingleBlocks().
if (!GlobalCand[Cand].LiveBundles.any()) {
DEBUG(dbgs() << " no bundles.\n");
continue;
}
Cost += calcGlobalSplitCost(GlobalCand[Cand], Intf);
DEBUG({
dbgs() << ", total = " << Cost << " with bundles";
for (int i = GlobalCand[Cand].LiveBundles.find_first(); i>=0;
i = GlobalCand[Cand].LiveBundles.find_next(i))
dbgs() << " EB#" << i;
dbgs() << ".\n";
});
if (Cost < BestCost) {
BestCand = Cand;
BestCost = Hysteresis * Cost; // Prevent rounding effects.
}
}
if (BestCand == NoCand)
return 0;
splitAroundRegion(VirtReg, GlobalCand[BestCand], NewVRegs);
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->getUseBlocks().size() == 1 && "Not a local interval");
const SplitAnalysis::BlockInfo &BI = SA->getUseBlocks().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->getUseBlocks().size() == 1 && "Not a local interval");
const SplitAnalysis::BlockInfo &BI = SA->getUseBlocks().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->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.
if (getStage(VirtReg) >= RS_Global)
return 0;
SA->analyze(&VirtReg);
// First try to split around a region spanning multiple blocks.
unsigned PhysReg = tryRegionSplit(VirtReg, Order, NewVRegs);
if (PhysReg || !NewVRegs.empty())
return PhysReg;
// Then isolate blocks with multiple uses.
SplitAnalysis::BlockPtrSet Blocks;
if (SA->getMultiUseBlocks(Blocks)) {
LiveRangeEdit LREdit(VirtReg, NewVRegs, this);
SE->reset(LREdit);
SE->splitSingleBlocks(Blocks);
setStage(NewVRegs.begin(), NewVRegs.end(), RS_Global);
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);
if (unsigned PhysReg = tryAssign(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.
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());
IntfCache.init(MF, &PhysReg2LiveUnion[0], Indexes, TRI);
allocatePhysRegs();
addMBBLiveIns(MF);
LIS->addKillFlags();
// Run rewriter
{
NamedRegionTimer T("Rewriter", TimerGroupName, TimePassesIsEnabled);
VRM->rewrite(Indexes);
}
// Write out new DBG_VALUE instructions.
getAnalysis<LiveDebugVariables>().emitDebugValues(VRM);
// The pass output is in VirtRegMap. Release all the transient data.
releaseMemory();
return true;
}
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