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Diffstat (limited to 'contrib/llvm/lib/CodeGen/RegAllocGreedy.cpp')
| -rw-r--r-- | contrib/llvm/lib/CodeGen/RegAllocGreedy.cpp | 1708 |
1 files changed, 1708 insertions, 0 deletions
diff --git a/contrib/llvm/lib/CodeGen/RegAllocGreedy.cpp b/contrib/llvm/lib/CodeGen/RegAllocGreedy.cpp new file mode 100644 index 0000000..3f2a617 --- /dev/null +++ b/contrib/llvm/lib/CodeGen/RegAllocGreedy.cpp @@ -0,0 +1,1708 @@ +//===-- 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 "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/LiveRangeEdit.h" +#include "llvm/CodeGen/LiveStackAnalysis.h" +#include "llvm/CodeGen/MachineDominators.h" +#include "llvm/CodeGen/MachineFunctionPass.h" +#include "llvm/CodeGen/MachineLoopInfo.h" +#include "llvm/CodeGen/MachineRegisterInfo.h" +#include "llvm/CodeGen/Passes.h" +#include "llvm/CodeGen/RegAllocRegistry.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<SplitEditor::ComplementSpillMode> +SplitSpillMode("split-spill-mode", cl::Hidden, + cl::desc("Spill mode for splitting live ranges"), + cl::values(clEnumValN(SplitEditor::SM_Partition, "default", "Default"), + clEnumValN(SplitEditor::SM_Size, "size", "Optimize for size"), + clEnumValN(SplitEditor::SM_Speed, "speed", "Optimize for speed"), + clEnumValEnd), + cl::init(SplitEditor::SM_Partition)); + +static RegisterRegAlloc greedyRegAlloc("greedy", "greedy register allocator", + createGreedyRegisterAllocator); + +namespace { +class RAGreedy : public MachineFunctionPass, + public RegAllocBase, + private LiveRangeEdit::Delegate { + + // context + MachineFunction *MF; + + // analyses + SlotIndexes *Indexes; + LiveStacks *LS; + MachineDominatorTree *DomTree; + MachineLoopInfo *Loops; + EdgeBundles *Bundles; + SpillPlacement *SpillPlacer; + LiveDebugVariables *DebugVars; + + // state + std::auto_ptr<Spiller> SpillerInstance; + std::priority_queue<std::pair<unsigned, unsigned> > Queue; + unsigned NextCascade; + + // 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 { + /// Newly created live range that has never been queued. + RS_New, + + /// Only attempt assignment and eviction. Then requeue as RS_Split. + RS_Assign, + + /// Attempt live range splitting if assignment is impossible. + RS_Split, + + /// Attempt more aggressive live range splitting that is guaranteed to make + /// progress. This is used for split products that may not be making + /// progress. + RS_Split2, + + /// Live range will be spilled. No more splitting will be attempted. + RS_Spill, + + /// There is nothing more we can do to this live range. Abort compilation + /// if it can't be assigned. + RS_Done + }; + + static const char *const StageName[]; + + // RegInfo - Keep additional information about each live range. + struct RegInfo { + LiveRangeStage Stage; + + // Cascade - Eviction loop prevention. See canEvictInterference(). + unsigned Cascade; + + RegInfo() : Stage(RS_New), Cascade(0) {} + }; + + IndexedMap<RegInfo, VirtReg2IndexFunctor> ExtraRegInfo; + + LiveRangeStage getStage(const LiveInterval &VirtReg) const { + return ExtraRegInfo[VirtReg.reg].Stage; + } + + void setStage(const LiveInterval &VirtReg, LiveRangeStage Stage) { + ExtraRegInfo.resize(MRI->getNumVirtRegs()); + ExtraRegInfo[VirtReg.reg].Stage = Stage; + } + + template<typename Iterator> + void setStage(Iterator Begin, Iterator End, LiveRangeStage NewStage) { + ExtraRegInfo.resize(MRI->getNumVirtRegs()); + for (;Begin != End; ++Begin) { + unsigned Reg = (*Begin)->reg; + if (ExtraRegInfo[Reg].Stage == RS_New) + ExtraRegInfo[Reg].Stage = NewStage; + } + } + + /// Cost of evicting interference. + struct EvictionCost { + unsigned BrokenHints; ///< Total number of broken hints. + float MaxWeight; ///< Maximum spill weight evicted. + + EvictionCost(unsigned B = 0) : BrokenHints(B), MaxWeight(0) {} + + bool operator<(const EvictionCost &O) const { + if (BrokenHints != O.BrokenHints) + return BrokenHints < O.BrokenHints; + return MaxWeight < O.MaxWeight; + } + }; + + // Register mask interference. The current VirtReg is checked for register + // mask interference on entry to selectOrSplit(). If there is no + // interference, UsableRegs is left empty. If there is interference, + // UsableRegs has a bit mask of registers that can be used without register + // mask interference. + BitVector UsableRegs; + + /// clobberedByRegMask - Returns true if PhysReg is not directly usable + /// because of register mask clobbers. + bool clobberedByRegMask(unsigned PhysReg) const { + return !UsableRegs.empty() && !UsableRegs.test(PhysReg); + } + + // 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 { + // Register intended for assignment, or 0. + unsigned PhysReg; + + // SplitKit interval index for this candidate. + unsigned IntvIdx; + + // Interference for PhysReg. + InterferenceCache::Cursor Intf; + + // Bundles where this candidate should be live. + BitVector LiveBundles; + SmallVector<unsigned, 8> ActiveBlocks; + + void reset(InterferenceCache &Cache, unsigned Reg) { + PhysReg = Reg; + IntvIdx = 0; + Intf.setPhysReg(Cache, Reg); + LiveBundles.clear(); + ActiveBlocks.clear(); + } + + // Set B[i] = C for every live bundle where B[i] was NoCand. + unsigned getBundles(SmallVectorImpl<unsigned> &B, unsigned C) { + unsigned Count = 0; + for (int i = LiveBundles.find_first(); i >= 0; + i = LiveBundles.find_next(i)) + if (B[i] == NoCand) { + B[i] = C; + Count++; + } + return Count; + } + }; + + /// 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; + + enum { NoCand = ~0u }; + + /// Candidate map. Each edge bundle is assigned to a GlobalCand entry, or to + /// NoCand which indicates the stack interval. + SmallVector<unsigned, 32> BundleCand; + +public: + RAGreedy(); + + /// Return the pass name. + virtual const char* getPassName() const { + return "Greedy Register Allocator"; + } + + /// RAGreedy analysis usage. + virtual void getAnalysisUsage(AnalysisUsage &AU) const; + virtual void releaseMemory(); + virtual Spiller &spiller() { return *SpillerInstance; } + virtual void enqueue(LiveInterval *LI); + virtual LiveInterval *dequeue(); + virtual unsigned selectOrSplit(LiveInterval&, + SmallVectorImpl<LiveInterval*>&); + + /// Perform register allocation. + virtual bool runOnMachineFunction(MachineFunction &mf); + + static char ID; + +private: + bool 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); + float calcGlobalSplitCost(GlobalSplitCandidate&); + bool calcCompactRegion(GlobalSplitCandidate&); + void splitAroundRegion(LiveRangeEdit&, ArrayRef<unsigned>); + void calcGapWeights(unsigned, SmallVectorImpl<float>&); + bool shouldEvict(LiveInterval &A, bool, LiveInterval &B, bool); + bool canEvictInterference(LiveInterval&, unsigned, bool, EvictionCost&); + void evictInterference(LiveInterval&, unsigned, + SmallVectorImpl<LiveInterval*>&); + + unsigned tryAssign(LiveInterval&, AllocationOrder&, + SmallVectorImpl<LiveInterval*>&); + unsigned tryEvict(LiveInterval&, AllocationOrder&, + SmallVectorImpl<LiveInterval*>&, unsigned = ~0u); + unsigned tryRegionSplit(LiveInterval&, AllocationOrder&, + SmallVectorImpl<LiveInterval*>&); + unsigned tryBlockSplit(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_Assign", + "RS_Split", + "RS_Split2", + "RS_Spill", + "RS_Done" +}; +#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) { + initializeLiveDebugVariablesPass(*PassRegistry::getPassRegistry()); + initializeSlotIndexesPass(*PassRegistry::getPassRegistry()); + initializeLiveIntervalsPass(*PassRegistry::getPassRegistry()); + initializeSlotIndexesPass(*PassRegistry::getPassRegistry()); + initializeRegisterCoalescerPass(*PassRegistry::getPassRegistry()); + initializeMachineSchedulerPass(*PassRegistry::getPassRegistry()); + initializeCalculateSpillWeightsPass(*PassRegistry::getPassRegistry()); + initializeLiveStacksPass(*PassRegistry::getPassRegistry()); + initializeMachineDominatorTreePass(*PassRegistry::getPassRegistry()); + initializeMachineLoopInfoPass(*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>(); + AU.addRequired<CalculateSpillWeights>(); + AU.addRequired<LiveStacks>(); + AU.addPreserved<LiveStacks>(); + AU.addRequired<MachineDominatorTree>(); + AU.addPreserved<MachineDominatorTree>(); + AU.addRequired<MachineLoopInfo>(); + AU.addPreserved<MachineLoopInfo>(); + AU.addRequired<VirtRegMap>(); + AU.addPreserved<VirtRegMap>(); + AU.addRequired<EdgeBundles>(); + AU.addRequired<SpillPlacement>(); + MachineFunctionPass::getAnalysisUsage(AU); +} + + +//===----------------------------------------------------------------------===// +// LiveRangeEdit delegate methods +//===----------------------------------------------------------------------===// + +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) { + // Cloning a register we haven't even heard about yet? Just ignore it. + if (!ExtraRegInfo.inBounds(Old)) + return; + + // LRE may clone a virtual register because dead code elimination causes it to + // be split into connected components. The new components are much smaller + // than the original, so they should get a new chance at being assigned. + // same stage as the parent. + ExtraRegInfo[Old].Stage = RS_Assign; + ExtraRegInfo.grow(New); + ExtraRegInfo[New] = ExtraRegInfo[Old]; +} + +void RAGreedy::releaseMemory() { + SpillerInstance.reset(0); + ExtraRegInfo.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; + + ExtraRegInfo.grow(Reg); + if (ExtraRegInfo[Reg].Stage == RS_New) + ExtraRegInfo[Reg].Stage = RS_Assign; + + if (ExtraRegInfo[Reg].Stage == RS_Split) { + // Unsplit ranges that couldn't be allocated immediately are deferred until + // everything else has been allocated. + Prio = Size; + } else { + // Everything is allocated in long->short order. Long ranges that don't fit + // should be spilled (or split) 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 (clobberedByRegMask(PhysReg)) + continue; + if (!checkPhysRegInterference(VirtReg, PhysReg)) + break; + } + if (!PhysReg || Order.isHint(PhysReg)) + return PhysReg; + + // PhysReg is available, but there may be a better choice. + + // If we missed a simple hint, try to cheaply evict interference from the + // preferred register. + if (unsigned Hint = MRI->getSimpleHint(VirtReg.reg)) + if (Order.isHint(Hint) && !clobberedByRegMask(Hint)) { + DEBUG(dbgs() << "missed hint " << PrintReg(Hint, TRI) << '\n'); + EvictionCost MaxCost(1); + if (canEvictInterference(VirtReg, Hint, true, MaxCost)) { + evictInterference(VirtReg, Hint, NewVRegs); + return Hint; + } + } + + // 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 +//===----------------------------------------------------------------------===// + +/// shouldEvict - determine if A should 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. +/// +/// Cascade numbers are used to prevent infinite loops if this function is a +/// cyclic relation. +/// +/// @param A The live range to be assigned. +/// @param IsHint True when A is about to be assigned to its preferred +/// register. +/// @param B The live range to be evicted. +/// @param BreaksHint True when B is already assigned to its preferred register. +bool RAGreedy::shouldEvict(LiveInterval &A, bool IsHint, + LiveInterval &B, bool BreaksHint) { + bool CanSplit = getStage(B) < RS_Spill; + + // Be fairly aggressive about following hints as long as the evictee can be + // split. + if (CanSplit && IsHint && !BreaksHint) + return true; + + return A.weight > B.weight; +} + +/// canEvictInterference - Return true if all interferences between VirtReg and +/// PhysReg can be evicted. When OnlyCheap is set, don't do anything +/// +/// @param VirtReg Live range that is about to be assigned. +/// @param PhysReg Desired register for assignment. +/// @prarm IsHint True when PhysReg is VirtReg's preferred register. +/// @param MaxCost Only look for cheaper candidates and update with new cost +/// when returning true. +/// @returns True when interference can be evicted cheaper than MaxCost. +bool RAGreedy::canEvictInterference(LiveInterval &VirtReg, unsigned PhysReg, + bool IsHint, EvictionCost &MaxCost) { + // Find VirtReg's cascade number. This will be unassigned if VirtReg was never + // involved in an eviction before. If a cascade number was assigned, deny + // evicting anything with the same or a newer cascade number. This prevents + // infinite eviction loops. + // + // This works out so a register without a cascade number is allowed to evict + // anything, and it can be evicted by anything. + unsigned Cascade = ExtraRegInfo[VirtReg.reg].Cascade; + if (!Cascade) + Cascade = NextCascade; + + EvictionCost Cost; + for (const uint16_t *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) >= 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; + // Never evict spill products. They cannot split or spill. + if (getStage(*Intf) == RS_Done) + return false; + // Once a live range becomes small enough, it is urgent that we find a + // register for it. This is indicated by an infinite spill weight. These + // urgent live ranges get to evict almost anything. + bool Urgent = !VirtReg.isSpillable() && Intf->isSpillable(); + // Only evict older cascades or live ranges without a cascade. + unsigned IntfCascade = ExtraRegInfo[Intf->reg].Cascade; + if (Cascade <= IntfCascade) { + if (!Urgent) + return false; + // We permit breaking cascades for urgent evictions. It should be the + // last resort, though, so make it really expensive. + Cost.BrokenHints += 10; + } + // Would this break a satisfied hint? + bool BreaksHint = VRM->hasPreferredPhys(Intf->reg); + // Update eviction cost. + Cost.BrokenHints += BreaksHint; + Cost.MaxWeight = std::max(Cost.MaxWeight, Intf->weight); + // Abort if this would be too expensive. + if (!(Cost < MaxCost)) + return false; + // Finally, apply the eviction policy for non-urgent evictions. + if (!Urgent && !shouldEvict(VirtReg, IsHint, *Intf, BreaksHint)) + return false; + } + } + MaxCost = Cost; + return true; +} + +/// evictInterference - Evict any interferring registers that prevent VirtReg +/// from being assigned to Physreg. This assumes that canEvictInterference +/// returned true. +void RAGreedy::evictInterference(LiveInterval &VirtReg, unsigned PhysReg, + SmallVectorImpl<LiveInterval*> &NewVRegs) { + // Make sure that VirtReg has a cascade number, and assign that cascade + // number to every evicted register. These live ranges than then only be + // evicted by a newer cascade, preventing infinite loops. + unsigned Cascade = ExtraRegInfo[VirtReg.reg].Cascade; + if (!Cascade) + Cascade = ExtraRegInfo[VirtReg.reg].Cascade = NextCascade++; + + DEBUG(dbgs() << "evicting " << PrintReg(PhysReg, TRI) + << " interference: Cascade " << Cascade << '\n'); + for (const uint16_t *AliasI = TRI->getOverlaps(PhysReg); *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)); + assert((ExtraRegInfo[Intf->reg].Cascade < Cascade || + VirtReg.isSpillable() < Intf->isSpillable()) && + "Cannot decrease cascade number, illegal eviction"); + ExtraRegInfo[Intf->reg].Cascade = Cascade; + ++NumEvicted; + NewVRegs.push_back(Intf); + } + } +} + +/// 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 cheapest interference seen so far. + EvictionCost BestCost(~0u); + unsigned BestPhys = 0; + + // When we are just looking for a reduced cost per use, don't break any + // hints, and only evict smaller spill weights. + if (CostPerUseLimit < ~0u) { + BestCost.BrokenHints = 0; + BestCost.MaxWeight = VirtReg.weight; + } + + Order.rewind(); + while (unsigned PhysReg = Order.next()) { + if (clobberedByRegMask(PhysReg)) + continue; + if (TRI->getCostPerUse(PhysReg) >= CostPerUseLimit) + continue; + // The first use of a callee-saved register in a function has cost 1. + // Don't start using a CSR when the CostPerUseLimit is low. + if (CostPerUseLimit == 1) + if (unsigned CSR = RegClassInfo.getLastCalleeSavedAlias(PhysReg)) + if (!MRI->isPhysRegUsed(CSR)) { + DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " would clobber CSR " + << PrintReg(CSR, TRI) << '\n'); + continue; + } + + if (!canEvictInterference(VirtReg, PhysReg, false, BestCost)) + continue; + + // Best so far. + BestPhys = PhysReg; + + // Stop if the hint can be used. + if (Order.isHint(PhysReg)) + break; + } + + if (!BestPhys) + return 0; + + evictInterference(VirtReg, BestPhys, NewVRegs); + 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; + BC.ChangesValue = BI.FirstDef; + + 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.FirstInstr) + BC.Entry = SpillPlacement::PrefSpill, ++Ins; + else if (Intf.first() < BI.LastInstr) + ++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.LastInstr) + BC.Exit = SpillPlacement::PrefSpill, ++Ins; + else if (Intf.last() > BI.FirstInstr) + ++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(makeArrayRef(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(makeArrayRef(TBS, T)); +} + +void RAGreedy::growRegion(GlobalSplitCandidate &Cand) { + // 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(); + // 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) + break; + + // Compute through constraints from the interference, or assume that all + // through blocks prefer spilling when forming compact regions. + ArrayRef<unsigned> NewBlocks = makeArrayRef(ActiveBlocks).slice(AddedTo); + if (Cand.PhysReg) + addThroughConstraints(Cand.Intf, NewBlocks); + else + // Provide a strong negative bias on through blocks to prevent unwanted + // liveness on loop backedges. + SpillPlacer->addPrefSpill(NewBlocks, /* Strong= */ true); + AddedTo = ActiveBlocks.size(); + + // Perhaps iterating can enable more bundles? + SpillPlacer->iterate(); + } + DEBUG(dbgs() << ", v=" << Visited); +} + +/// calcCompactRegion - Compute the set of edge bundles that should be live +/// when splitting the current live range into compact regions. Compact +/// regions can be computed without looking at interference. They are the +/// regions formed by removing all the live-through blocks from the live range. +/// +/// Returns false if the current live range is already compact, or if the +/// compact regions would form single block regions anyway. +bool RAGreedy::calcCompactRegion(GlobalSplitCandidate &Cand) { + // Without any through blocks, the live range is already compact. + if (!SA->getNumThroughBlocks()) + return false; + + // Compact regions don't correspond to any physreg. + Cand.reset(IntfCache, 0); + + DEBUG(dbgs() << "Compact region bundles"); + + // Use the spill placer to determine the live bundles. GrowRegion pretends + // that all the through blocks have interference when PhysReg is unset. + SpillPlacer->prepare(Cand.LiveBundles); + + // The static split cost will be zero since Cand.Intf reports no interference. + float Cost; + if (!addSplitConstraints(Cand.Intf, Cost)) { + DEBUG(dbgs() << ", none.\n"); + return false; + } + + growRegion(Cand); + SpillPlacer->finish(); + + if (!Cand.LiveBundles.any()) { + DEBUG(dbgs() << ", none.\n"); + return false; + } + + DEBUG({ + for (int i = Cand.LiveBundles.find_first(); i>=0; + i = Cand.LiveBundles.find_next(i)) + dbgs() << " EB#" << i; + dbgs() << ".\n"; + }); + return true; +} + +/// 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; + 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 && BI.FirstDef) + 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) { + 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. + Cand.Intf.moveToBlock(Number); + if (Cand.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 the current live range around the regions +/// determined by BundleCand and GlobalCand. +/// +/// Before calling this function, GlobalCand and BundleCand must be initialized +/// so each bundle is assigned to a valid candidate, or NoCand for the +/// stack-bound bundles. The shared SA/SE SplitAnalysis and SplitEditor +/// objects must be initialized for the current live range, and intervals +/// created for the used candidates. +/// +/// @param LREdit The LiveRangeEdit object handling the current split. +/// @param UsedCands List of used GlobalCand entries. Every BundleCand value +/// must appear in this list. +void RAGreedy::splitAroundRegion(LiveRangeEdit &LREdit, + ArrayRef<unsigned> UsedCands) { + // These are the intervals created for new global ranges. We may create more + // intervals for local ranges. + const unsigned NumGlobalIntvs = LREdit.size(); + DEBUG(dbgs() << "splitAroundRegion with " << NumGlobalIntvs << " globals.\n"); + assert(NumGlobalIntvs && "No global intervals configured"); + + // Isolate even single instructions when dealing with a proper sub-class. + // That guarantees register class inflation for the stack interval because it + // is all copies. + unsigned Reg = SA->getParent().reg; + bool SingleInstrs = RegClassInfo.isProperSubClass(MRI->getRegClass(Reg)); + + // First handle all the blocks with uses. + 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(); + unsigned IntvIn = 0, IntvOut = 0; + SlotIndex IntfIn, IntfOut; + if (BI.LiveIn) { + unsigned CandIn = BundleCand[Bundles->getBundle(Number, 0)]; + if (CandIn != NoCand) { + GlobalSplitCandidate &Cand = GlobalCand[CandIn]; + IntvIn = Cand.IntvIdx; + Cand.Intf.moveToBlock(Number); + IntfIn = Cand.Intf.first(); + } + } + if (BI.LiveOut) { + unsigned CandOut = BundleCand[Bundles->getBundle(Number, 1)]; + if (CandOut != NoCand) { + GlobalSplitCandidate &Cand = GlobalCand[CandOut]; + IntvOut = Cand.IntvIdx; + Cand.Intf.moveToBlock(Number); + IntfOut = Cand.Intf.last(); + } + } + + // Create separate intervals for isolated blocks with multiple uses. + if (!IntvIn && !IntvOut) { + DEBUG(dbgs() << "BB#" << BI.MBB->getNumber() << " isolated.\n"); + if (SA->shouldSplitSingleBlock(BI, SingleInstrs)) + SE->splitSingleBlock(BI); + continue; + } + + if (IntvIn && IntvOut) + SE->splitLiveThroughBlock(Number, IntvIn, IntfIn, IntvOut, IntfOut); + else if (IntvIn) + SE->splitRegInBlock(BI, IntvIn, IntfIn); + else + SE->splitRegOutBlock(BI, IntvOut, IntfOut); + } + + // Handle live-through blocks. The relevant live-through blocks are stored in + // the ActiveBlocks list with each candidate. We need to filter out + // duplicates. + BitVector Todo = SA->getThroughBlocks(); + for (unsigned c = 0; c != UsedCands.size(); ++c) { + ArrayRef<unsigned> Blocks = GlobalCand[UsedCands[c]].ActiveBlocks; + for (unsigned i = 0, e = Blocks.size(); i != e; ++i) { + unsigned Number = Blocks[i]; + if (!Todo.test(Number)) + continue; + Todo.reset(Number); + + unsigned IntvIn = 0, IntvOut = 0; + SlotIndex IntfIn, IntfOut; + + unsigned CandIn = BundleCand[Bundles->getBundle(Number, 0)]; + if (CandIn != NoCand) { + GlobalSplitCandidate &Cand = GlobalCand[CandIn]; + IntvIn = Cand.IntvIdx; + Cand.Intf.moveToBlock(Number); + IntfIn = Cand.Intf.first(); + } + + unsigned CandOut = BundleCand[Bundles->getBundle(Number, 1)]; + if (CandOut != NoCand) { + GlobalSplitCandidate &Cand = GlobalCand[CandOut]; + IntvOut = Cand.IntvIdx; + Cand.Intf.moveToBlock(Number); + IntfOut = Cand.Intf.last(); + } + if (!IntvIn && !IntvOut) + continue; + SE->splitLiveThroughBlock(Number, IntvIn, IntfIn, IntvOut, IntfOut); + } + } + + ++NumGlobalSplits; + + SmallVector<unsigned, 8> IntvMap; + SE->finish(&IntvMap); + DebugVars->splitRegister(Reg, LREdit.regs()); + + ExtraRegInfo.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) { + LiveInterval &Reg = *LREdit.get(i); + + // Ignore old intervals from DCE. + if (getStage(Reg) != RS_New) + continue; + + // Remainder interval. Don't try splitting again, spill if it doesn't + // allocate. + if (IntvMap[i] == 0) { + setStage(Reg, RS_Spill); + continue; + } + + // Global intervals. Allow repeated splitting as long as the number of live + // blocks is strictly decreasing. + if (IntvMap[i] < NumGlobalIntvs) { + if (SA->countLiveBlocks(&Reg) >= OrigBlocks) { + DEBUG(dbgs() << "Main interval covers the same " << OrigBlocks + << " blocks as original.\n"); + // Don't allow repeated splitting as a safe guard against looping. + setStage(Reg, RS_Split2); + } + 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) { + unsigned NumCands = 0; + unsigned BestCand = NoCand; + float BestCost; + SmallVector<unsigned, 8> UsedCands; + + // Check if we can split this live range around a compact region. + bool HasCompact = calcCompactRegion(GlobalCand.front()); + if (HasCompact) { + // Yes, keep GlobalCand[0] as the compact region candidate. + NumCands = 1; + BestCost = HUGE_VALF; + } else { + // No benefit from the compact region, our fallback will be per-block + // splitting. Make sure we find a solution that is cheaper than spilling. + BestCost = Hysteresis * calcSpillCost(); + DEBUG(dbgs() << "Cost of isolating all blocks = " << BestCost << '\n'); + } + + Order.rewind(); + while (unsigned PhysReg = Order.next()) { + // Discard bad candidates before we run out of interference cache cursors. + // This will only affect register classes with a lot of registers (>32). + if (NumCands == IntfCache.getMaxCursors()) { + unsigned WorstCount = ~0u; + unsigned Worst = 0; + for (unsigned i = 0; i != NumCands; ++i) { + if (i == BestCand || !GlobalCand[i].PhysReg) + continue; + unsigned Count = GlobalCand[i].LiveBundles.count(); + if (Count < WorstCount) + Worst = i, WorstCount = Count; + } + --NumCands; + GlobalCand[Worst] = GlobalCand[NumCands]; + if (BestCand == NumCands) + BestCand = Worst; + } + + if (GlobalCand.size() <= NumCands) + GlobalCand.resize(NumCands+1); + GlobalSplitCandidate &Cand = GlobalCand[NumCands]; + Cand.reset(IntfCache, PhysReg); + + SpillPlacer->prepare(Cand.LiveBundles); + float Cost; + if (!addSplitConstraints(Cand.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(Cand); + + SpillPlacer->finish(); + + // No live bundles, defer to splitSingleBlocks(). + if (!Cand.LiveBundles.any()) { + DEBUG(dbgs() << " no bundles.\n"); + continue; + } + + Cost += calcGlobalSplitCost(Cand); + DEBUG({ + dbgs() << ", total = " << Cost << " with bundles"; + for (int i = Cand.LiveBundles.find_first(); i>=0; + i = Cand.LiveBundles.find_next(i)) + dbgs() << " EB#" << i; + dbgs() << ".\n"; + }); + if (Cost < BestCost) { + BestCand = NumCands; + BestCost = Hysteresis * Cost; // Prevent rounding effects. + } + ++NumCands; + } + + // No solutions found, fall back to single block splitting. + if (!HasCompact && BestCand == NoCand) + return 0; + + // Prepare split editor. + LiveRangeEdit LREdit(VirtReg, NewVRegs, *MF, *LIS, VRM, this); + SE->reset(LREdit, SplitSpillMode); + + // Assign all edge bundles to the preferred candidate, or NoCand. + BundleCand.assign(Bundles->getNumBundles(), NoCand); + + // Assign bundles for the best candidate region. + if (BestCand != NoCand) { + GlobalSplitCandidate &Cand = GlobalCand[BestCand]; + if (unsigned B = Cand.getBundles(BundleCand, BestCand)) { + UsedCands.push_back(BestCand); + Cand.IntvIdx = SE->openIntv(); + DEBUG(dbgs() << "Split for " << PrintReg(Cand.PhysReg, TRI) << " in " + << B << " bundles, intv " << Cand.IntvIdx << ".\n"); + (void)B; + } + } + + // Assign bundles for the compact region. + if (HasCompact) { + GlobalSplitCandidate &Cand = GlobalCand.front(); + assert(!Cand.PhysReg && "Compact region has no physreg"); + if (unsigned B = Cand.getBundles(BundleCand, 0)) { + UsedCands.push_back(0); + Cand.IntvIdx = SE->openIntv(); + DEBUG(dbgs() << "Split for compact region in " << B << " bundles, intv " + << Cand.IntvIdx << ".\n"); + (void)B; + } + } + + splitAroundRegion(LREdit, UsedCands); + return 0; +} + + +//===----------------------------------------------------------------------===// +// Per-Block Splitting +//===----------------------------------------------------------------------===// + +/// tryBlockSplit - Split a global live range around every block with uses. This +/// creates a lot of local live ranges, that will be split by tryLocalSplit if +/// they don't allocate. +unsigned RAGreedy::tryBlockSplit(LiveInterval &VirtReg, AllocationOrder &Order, + SmallVectorImpl<LiveInterval*> &NewVRegs) { + assert(&SA->getParent() == &VirtReg && "Live range wasn't analyzed"); + unsigned Reg = VirtReg.reg; + bool SingleInstrs = RegClassInfo.isProperSubClass(MRI->getRegClass(Reg)); + LiveRangeEdit LREdit(VirtReg, NewVRegs, *MF, *LIS, VRM, this); + SE->reset(LREdit, SplitSpillMode); + ArrayRef<SplitAnalysis::BlockInfo> UseBlocks = SA->getUseBlocks(); + for (unsigned i = 0; i != UseBlocks.size(); ++i) { + const SplitAnalysis::BlockInfo &BI = UseBlocks[i]; + if (SA->shouldSplitSingleBlock(BI, SingleInstrs)) + SE->splitSingleBlock(BI); + } + // No blocks were split. + if (LREdit.empty()) + return 0; + + // We did split for some blocks. + SmallVector<unsigned, 8> IntvMap; + SE->finish(&IntvMap); + + // Tell LiveDebugVariables about the new ranges. + DebugVars->splitRegister(Reg, LREdit.regs()); + + ExtraRegInfo.resize(MRI->getNumVirtRegs()); + + // Sort out the new intervals created by splitting. The remainder interval + // goes straight to spilling, the new local ranges get to stay RS_New. + for (unsigned i = 0, e = LREdit.size(); i != e; ++i) { + LiveInterval &LI = *LREdit.get(i); + if (getStage(LI) == RS_New && IntvMap[i] == 0) + setStage(LI, RS_Spill); + } + + if (VerifyEnabled) + MF->verify(this, "After splitting live range around basic blocks"); + 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(); + ArrayRef<SlotIndex> Uses = SA->getUseSlots(); + const unsigned NumGaps = Uses.size()-1; + + // Start and end points for the interference check. + SlotIndex StartIdx = + BI.LiveIn ? BI.FirstInstr.getBaseIndex() : BI.FirstInstr; + SlotIndex StopIdx = + BI.LiveOut ? BI.LastInstr.getBoundaryIndex() : BI.LastInstr; + + GapWeight.assign(NumGaps, 0.0f); + + // Add interference from each overlapping register. + for (const uint16_t *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 FirstInstr to + // LastInstr, 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 = getLiveUnion(*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; + } + } +} + +/// 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 FirstInstr to LastInstr. We should + // make sure that we don't do anything illegal to such an interval, though. + + ArrayRef<SlotIndex> Uses = SA->getUseSlots(); + 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() << ' ' << Uses[i]; + dbgs() << '\n'; + }); + + // If VirtReg is live across any register mask operands, compute a list of + // gaps with register masks. + SmallVector<unsigned, 8> RegMaskGaps; + if (!UsableRegs.empty()) { + // Get regmask slots for the whole block. + ArrayRef<SlotIndex> RMS = LIS->getRegMaskSlotsInBlock(BI.MBB->getNumber()); + DEBUG(dbgs() << RMS.size() << " regmasks in block:"); + // Constrain to VirtReg's live range. + unsigned ri = std::lower_bound(RMS.begin(), RMS.end(), + Uses.front().getRegSlot()) - RMS.begin(); + unsigned re = RMS.size(); + for (unsigned i = 0; i != NumGaps && ri != re; ++i) { + // Look for Uses[i] <= RMS <= Uses[i+1]. + assert(!SlotIndex::isEarlierInstr(RMS[ri], Uses[i])); + if (SlotIndex::isEarlierInstr(Uses[i+1], RMS[ri])) + continue; + // Skip a regmask on the same instruction as the last use. It doesn't + // overlap the live range. + if (SlotIndex::isSameInstr(Uses[i+1], RMS[ri]) && i+1 == NumGaps) + break; + DEBUG(dbgs() << ' ' << RMS[ri] << ':' << Uses[i] << '-' << Uses[i+1]); + RegMaskGaps.push_back(i); + // Advance ri to the next gap. A regmask on one of the uses counts in + // both gaps. + while (ri != re && SlotIndex::isEarlierInstr(RMS[ri], Uses[i+1])) + ++ri; + } + DEBUG(dbgs() << '\n'); + } + + // Since we allow local split results to be split again, there is a risk of + // creating infinite loops. It is tempting to require that the new live + // ranges have less instructions than the original. That would guarantee + // convergence, but it is too strict. A live range with 3 instructions can be + // split 2+3 (including the COPY), and we want to allow that. + // + // Instead we use these rules: + // + // 1. Allow any split for ranges with getStage() < RS_Split2. (Except for the + // noop split, of course). + // 2. Require progress be made for ranges with getStage() == RS_Split2. All + // the new ranges must have fewer instructions than before the split. + // 3. New ranges with the same number of instructions are marked RS_Split2, + // smaller ranges are marked RS_New. + // + // These rules allow a 3 -> 2+3 split once, which we need. They also prevent + // excessive splitting and infinite loops. + // + bool ProgressRequired = getStage(VirtReg) >= RS_Split2; + + // Best split candidate. + 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); + + // Remove any gaps with regmask clobbers. + if (clobberedByRegMask(PhysReg)) + for (unsigned i = 0, e = RegMaskGaps.size(); i != e; ++i) + GapWeight[RegMaskGaps[i]] = HUGE_VALF; + + // 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 = 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 (;;) { + // 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; + + // How many gaps would the new range have? + unsigned NewGaps = LiveBefore + SplitAfter - SplitBefore + LiveAfter; + + // Legally, without causing looping? + bool Legal = !ProgressRequired || NewGaps < NumGaps; + + if (Legal && MaxGap < HUGE_VALF) { + // Estimate the new spill weight. Each instruction reads or writes the + // register. Conservatively assume there are no read-modify-write + // instructions. + // + // Try to guess the size of the new interval. + const float EstWeight = normalizeSpillWeight(blockFreq * (NewGaps + 1), + Uses[SplitBefore].distance(Uses[SplitAfter]) + + (LiveBefore + LiveAfter)*SlotIndex::InstrDist); + // 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) { + 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"); + MaxGap = std::max(MaxGap, GapWeight[SplitAfter++]); + } + } + + // 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, *MF, *LIS, VRM, this); + SE->reset(LREdit); + + SE->openIntv(); + SlotIndex SegStart = SE->enterIntvBefore(Uses[BestBefore]); + SlotIndex SegStop = SE->leaveIntvAfter(Uses[BestAfter]); + SE->useIntv(SegStart, SegStop); + SmallVector<unsigned, 8> IntvMap; + SE->finish(&IntvMap); + DebugVars->splitRegister(VirtReg.reg, LREdit.regs()); + + // If the new range has the same number of instructions as before, mark it as + // RS_Split2 so the next split will be forced to make progress. Otherwise, + // leave the new intervals as RS_New so they can compete. + bool LiveBefore = BestBefore != 0 || BI.LiveIn; + bool LiveAfter = BestAfter != NumGaps || BI.LiveOut; + unsigned NewGaps = LiveBefore + BestAfter - BestBefore + LiveAfter; + if (NewGaps >= NumGaps) { + DEBUG(dbgs() << "Tagging non-progress ranges: "); + assert(!ProgressRequired && "Didn't make progress when it was required."); + for (unsigned i = 0, e = IntvMap.size(); i != e; ++i) + if (IntvMap[i] == 1) { + setStage(*LREdit.get(i), RS_Split2); + DEBUG(dbgs() << PrintReg(LREdit.get(i)->reg)); + } + DEBUG(dbgs() << '\n'); + } + ++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) { + // Ranges must be Split2 or less. + if (getStage(VirtReg) >= RS_Spill) + return 0; + + // 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); + + 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. RS_Split2 + // ranges already made dubious progress with region splitting, so they go + // straight to single block splitting. + if (getStage(VirtReg) < RS_Split2) { + unsigned PhysReg = tryRegionSplit(VirtReg, Order, NewVRegs); + if (PhysReg || !NewVRegs.empty()) + return PhysReg; + } + + // Then isolate blocks. + return tryBlockSplit(VirtReg, Order, NewVRegs); +} + + +//===----------------------------------------------------------------------===// +// Main Entry Point +//===----------------------------------------------------------------------===// + +unsigned RAGreedy::selectOrSplit(LiveInterval &VirtReg, + SmallVectorImpl<LiveInterval*> &NewVRegs) { + // Check if VirtReg is live across any calls. + UsableRegs.clear(); + if (LIS->checkRegMaskInterference(VirtReg, UsableRegs)) + DEBUG(dbgs() << "Live across regmasks.\n"); + + // First try assigning a free register. + AllocationOrder Order(VirtReg.reg, *VRM, RegClassInfo); + if (unsigned PhysReg = tryAssign(VirtReg, Order, NewVRegs)) + return PhysReg; + + LiveRangeStage Stage = getStage(VirtReg); + DEBUG(dbgs() << StageName[Stage] + << " Cascade " << ExtraRegInfo[VirtReg.reg].Cascade << '\n'); + + // Try to evict a less worthy live range, but only for ranges from the primary + // queue. The RS_Split ranges already failed to do this, and they should not + // get a second chance until they have been split. + if (Stage != RS_Split) + 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_Split) { + setStage(VirtReg, RS_Split); + 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_Done || !VirtReg.isSpillable()) + 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, *MF, *LIS, VRM, this); + spiller().spill(LRE); + setStage(NewVRegs.begin(), NewVRegs.end(), RS_Done); + + 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>(); + SpillerInstance.reset(createInlineSpiller(*this, *MF, *VRM)); + Loops = &getAnalysis<MachineLoopInfo>(); + Bundles = &getAnalysis<EdgeBundles>(); + SpillPlacer = &getAnalysis<SpillPlacement>(); + DebugVars = &getAnalysis<LiveDebugVariables>(); + + SA.reset(new SplitAnalysis(*VRM, *LIS, *Loops)); + SE.reset(new SplitEditor(*SA, *LIS, *VRM, *DomTree)); + ExtraRegInfo.clear(); + ExtraRegInfo.resize(MRI->getNumVirtRegs()); + NextCascade = 1; + IntfCache.init(MF, &getLiveUnion(0), Indexes, LIS, TRI); + GlobalCand.resize(32); // This will grow as needed. + + allocatePhysRegs(); + addMBBLiveIns(MF); + LIS->addKillFlags(); + + // Run rewriter + { + NamedRegionTimer T("Rewriter", TimerGroupName, TimePassesIsEnabled); + VRM->rewrite(Indexes); + } + + // Write out new DBG_VALUE instructions. + { + NamedRegionTimer T("Emit Debug Info", TimerGroupName, TimePassesIsEnabled); + DebugVars->emitDebugValues(VRM); + } + + // All machine operands and other references to virtual registers have been + // replaced. Remove the virtual registers and release all the transient data. + VRM->clearAllVirt(); + MRI->clearVirtRegs(); + releaseMemory(); + + return true; +} |
