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llvm-6502/lib/CodeGen/RegAllocGreedy.cpp
Jakob Stoklund Olesen d2056e51c6 Simplify the eviction policy by making the failsafe explicit. 
When assigned ranges are evicted, they are put in the RS_Evicted stage and are
not allowed to evict anything else. That prevents looping automatically.

When evicting ranges just to get a cheaper register, use only spill weights to
find the possible candidates. Avoid breaking hints for this purpose, it is not
worth it.

Start implementing more complex eviction heuristics, guarded by the temporary
-complex-eviction flag. The initial version permits a heavier range to be
evicted if it doesn't have any uses where the evicting range is live. This makes
it a good candidate for live ranfge splitting.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132358 91177308-0d34-0410-b5e6-96231b3b80d8
2011-05-31 21:02:44 +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/CommandLine.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 cl::opt<bool>
ComplexEviction("complex-eviction", cl::Hidden,
cl::desc("Use complex eviction heuristics"));
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;
LiveDebugVariables *DebugVars;
// 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_Evicted, ///< Requeued after being evicted.
RS_Second, ///< Second time in the queue, ready for splitting.
RS_Global, ///< Produced by global splitting.
RS_Local, ///< Produced by local splitting.
RS_Spill ///< Produced by spilling.
};
static const char *const StageName[];
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 hasDefInRange(const LiveInterval&, const LiveInterval&);
bool hasUseInRange(const LiveInterval&, const LiveInterval&);
bool canEvict(LiveInterval &A, LiveInterval &B);
bool canEvictInterference(LiveInterval&, unsigned, float&, bool);
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;
#ifndef NDEBUG
const char *const RAGreedy::StageName[] = {
"RS_New",
"RS_First",
"RS_Evicted",
"RS_Second",
"RS_Global",
"RS_Local",
"RS_Spill"
};
#endif
// 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
//===----------------------------------------------------------------------===//
/// hasDefInRange - Returns true when any def of A happens where B is live.
///
/// The SSA form of live intervals guarantees:
///
/// A.overlaps(B) == hasDefInRange(A, B) || hasDefInRange(B, A)
///
bool RAGreedy::hasDefInRange(const LiveInterval &A, const LiveInterval &B) {
for (LiveInterval::const_vni_iterator I = A.vni_begin(), E = A.vni_end();
I != E; ++I) {
const VNInfo *VNI = *I;
if (VNI->isUnused())
continue;
if (B.liveAt(VNI->def))
return true;
}
return false;
}
/// hasUseInRange - Returns true when any def or use of A happens where B is
/// live. The following is always true:
///
/// A.overlaps(B) == hasUseInRange(A, B) || hasUseInRange(B, A)
///
bool RAGreedy::hasUseInRange(const LiveInterval &A, const LiveInterval &B) {
if (hasDefInRange(A, B))
return true;
for (MachineRegisterInfo::use_nodbg_iterator I = MRI->use_nodbg_begin(A.reg),
E = MRI->use_nodbg_end(); I != E; ++I) {
if (I.getOperand().isUndef())
continue;
SlotIndex Idx = Indexes->getInstructionIndex(&*I).getDefIndex();
if (B.liveAt(Idx))
return true;
}
return false;
}
/// canEvict - determine if A can evict the assigned live range B. The eviction
/// policy defined by this function together with the allocation order defined
/// by enqueue() decides which registers ultimately end up being split and
/// spilled.
///
/// Safeguards ensure that canEvict can never cause an infinite loop.
///
bool RAGreedy::canEvict(LiveInterval &A, LiveInterval &B) {
if (!ComplexEviction)
return A.weight > B.weight;
// Evict B if it has no uses in A's live range.
if (!hasUseInRange(B, A)) {
DEBUG(dbgs() << "Bypass: " << B << '\n');
return true;
}
return A.weight > B.weight;
}
/// 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, bool OnlyCheap) {
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 (getStage(*Intf) == RS_Spill)
return false;
if (Intf->weight >= MaxWeight)
return false;
// When we are simply looking for a cheaper alternative, don't try too
// hard. The evicted range shouldn't end up getting split.
if (OnlyCheap) {
// Don't evict something that won't be able to reevict something else.
if (getStage(*Intf) != RS_First)
return false;
// Don't break a satisfied hint.
if (VRM->getRegAllocPref(Intf->reg) == *AliasI)
return false;
}
if (VirtReg.isSpillable() && !canEvict(VirtReg, *Intf))
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.
/// @param CostPerUseLimit Only look at physregs below this cost per use.
/// @return Physreg to assign VirtReg, or 0.
unsigned RAGreedy::tryEvict(LiveInterval &VirtReg,
AllocationOrder &Order,
SmallVectorImpl<LiveInterval*> &NewVRegs,
unsigned CostPerUseLimit) {
// Ranges that may have been evicted or requeued for splitting may never evict
// other ranges. That could cause looping.
// Spill ranges can always evict.
LiveRangeStage Stage = getStage(VirtReg);
if (Stage >= RS_Evicted && VirtReg.isSpillable())
return 0;
NamedRegionTimer T("Evict", TimerGroupName, TimePassesIsEnabled);
bool OnlyCheap = CostPerUseLimit != ~0u;
// Keep track of the lightest single interference seen so far.
// When scavenging for a cheap register, never consider evicting heavier
// ranges.
float BestWeight = OnlyCheap ? VirtReg.weight : HUGE_VALF;
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, OnlyCheap))
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);
// Prevent looping by marking the evicted ranges as RS_Evicted.
// When OnlyCheap is set, Intf is guaranteed to have a smaller spill
// weight which also prevents looping.
if (!OnlyCheap && getStage(*Intf) < RS_Evicted)
LRStage[Intf->reg] = RS_Evicted;
}
}
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.LastUse)
++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.FirstUse)
++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.FirstUse), 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.FirstUse) {
// The interference doesn't reach the outgoing segment.
DEBUG(dbgs() << " doesn't affect def from " << BI.FirstUse << '\n');
SE->useIntv(BI.FirstUse, 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.LastUse));
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.LastUse) {
// The interference doesn't reach the outgoing segment.
DEBUG(dbgs() << " doesn't affect kill at " << BI.LastUse << '\n');
SE->useIntv(Start, BI.LastUse);
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);
DebugVars->splitRegister(VirtReg.reg, LREdit.regs());
LRStage.resize(MRI->getNumVirtRegs());
unsigned OrigBlocks = SA->getNumLiveBlocks();
// 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.
DEBUG(dbgs() << " w=" << EstWeight);
if (EstWeight * Hysteresis >= MaxGap) {
Shrink = false;
float Diff = EstWeight - MaxGap;
if (Diff > BestDiff) {
DEBUG(dbgs() << " (best)");
BestDiff = Hysteresis * 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();
DebugVars->splitRegister(VirtReg.reg, LREdit.regs());
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);
// FIXME: SplitAnalysis may repair broken live ranges coming from the
// coalescer. That may cause the range to become allocatable which means that
// tryRegionSplit won't be making progress. This check should be replaced with
// an assertion when the coalescer is fixed.
if (SA->didRepairRange()) {
// VirtReg has changed, so all cached queries are invalid.
invalidateVirtRegs();
if (unsigned PhysReg = tryAssign(VirtReg, Order, NewVRegs))
return PhysReg;
}
// 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;
LiveRangeStage Stage = getStage(VirtReg);
DEBUG(dbgs() << StageName[Stage] << '\n');
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_First) {
LRStage[VirtReg.reg] = RS_Second;
DEBUG(dbgs() << "wait for second round\n");
NewVRegs.push_back(&VirtReg);
return 0;
}
// If we couldn't allocate a register from spilling, there is probably some
// invalid inline assembly. The base class wil report it.
if (Stage >= RS_Spill)
return ~0u;
// 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>();
DebugVars = &getAnalysis<LiveDebugVariables>();
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.
DebugVars->emitDebugValues(VRM);
// The pass output is in VirtRegMap. Release all the transient data.
releaseMemory();
return true;
}
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