using ARMeilleure.Common; using ARMeilleure.IntermediateRepresentation; using ARMeilleure.Translation; using System; using System.Collections.Generic; using System.Diagnostics; using System.Linq; using System.Numerics; namespace ARMeilleure.CodeGen.RegisterAllocators { // Based on: // "Linear Scan Register Allocation for the Java(tm) HotSpot Client Compiler". // http://www.christianwimmer.at/Publications/Wimmer04a/Wimmer04a.pdf class LinearScanAllocator : IRegisterAllocator { private const int InstructionGap = 2; private const int InstructionGapMask = InstructionGap - 1; private const int RegistersCount = 16; private HashSet _blockEdges; private LiveRange[] _blockRanges; private BitMap[] _blockLiveIn; private List _intervals; private LiveInterval[] _parentIntervals; private List<(IntrusiveList, Operation)> _operationNodes; private int _operationsCount; private class AllocationContext { public RegisterMasks Masks { get; } public StackAllocator StackAlloc { get; } public BitMap Active { get; } public BitMap Inactive { get; } public int IntUsedRegisters { get; set; } public int VecUsedRegisters { get; set; } private readonly int[] _intFreePositions; private readonly int[] _vecFreePositions; private readonly int _intFreePositionsCount; private readonly int _vecFreePositionsCount; public AllocationContext(StackAllocator stackAlloc, RegisterMasks masks, int intervalsCount) { StackAlloc = stackAlloc; Masks = masks; Active = new BitMap(Allocators.Default, intervalsCount); Inactive = new BitMap(Allocators.Default, intervalsCount); PopulateFreePositions(RegisterType.Integer, out _intFreePositions, out _intFreePositionsCount); PopulateFreePositions(RegisterType.Vector, out _vecFreePositions, out _vecFreePositionsCount); void PopulateFreePositions(RegisterType type, out int[] positions, out int count) { positions = new int[RegistersCount]; count = BitOperations.PopCount((uint)masks.GetAvailableRegisters(type)); int mask = masks.GetAvailableRegisters(type); for (int i = 0; i < positions.Length; i++) { if ((mask & (1 << i)) != 0) { positions[i] = int.MaxValue; } } } } public void GetFreePositions(RegisterType type, in Span positions, out int count) { if (type == RegisterType.Integer) { _intFreePositions.CopyTo(positions); count = _intFreePositionsCount; } else { Debug.Assert(type == RegisterType.Vector); _vecFreePositions.CopyTo(positions); count = _vecFreePositionsCount; } } public void MoveActiveToInactive(int bit) { Move(Active, Inactive, bit); } public void MoveInactiveToActive(int bit) { Move(Inactive, Active, bit); } private static void Move(BitMap source, BitMap dest, int bit) { source.Clear(bit); dest.Set(bit); } } public AllocationResult RunPass( ControlFlowGraph cfg, StackAllocator stackAlloc, RegisterMasks regMasks) { NumberLocals(cfg); var context = new AllocationContext(stackAlloc, regMasks, _intervals.Count); BuildIntervals(cfg, context); for (int index = 0; index < _intervals.Count; index++) { LiveInterval current = _intervals[index]; if (current.IsEmpty) { continue; } if (current.IsFixed) { context.Active.Set(index); if (current.Register.Type == RegisterType.Integer) { context.IntUsedRegisters |= 1 << current.Register.Index; } else /* if (interval.Register.Type == RegisterType.Vector) */ { context.VecUsedRegisters |= 1 << current.Register.Index; } continue; } AllocateInterval(context, current, index); } for (int index = RegistersCount * 2; index < _intervals.Count; index++) { if (!_intervals[index].IsSpilled) { ReplaceLocalWithRegister(_intervals[index]); } } InsertSplitCopies(); InsertSplitCopiesAtEdges(cfg); return new AllocationResult(context.IntUsedRegisters, context.VecUsedRegisters, context.StackAlloc.TotalSize); } private void AllocateInterval(AllocationContext context, LiveInterval current, int cIndex) { // Check active intervals that already ended. foreach (int iIndex in context.Active) { LiveInterval interval = _intervals[iIndex]; interval.Forward(current.GetStart()); if (interval.GetEnd() < current.GetStart()) { context.Active.Clear(iIndex); } else if (!interval.Overlaps(current.GetStart())) { context.MoveActiveToInactive(iIndex); } } // Check inactive intervals that already ended or were reactivated. foreach (int iIndex in context.Inactive) { LiveInterval interval = _intervals[iIndex]; interval.Forward(current.GetStart()); if (interval.GetEnd() < current.GetStart()) { context.Inactive.Clear(iIndex); } else if (interval.Overlaps(current.GetStart())) { context.MoveInactiveToActive(iIndex); } } if (!TryAllocateRegWithoutSpill(context, current, cIndex)) { AllocateRegWithSpill(context, current, cIndex); } } private bool TryAllocateRegWithoutSpill(AllocationContext context, LiveInterval current, int cIndex) { RegisterType regType = current.Local.Type.ToRegisterType(); Span freePositions = stackalloc int[RegistersCount]; context.GetFreePositions(regType, freePositions, out int freePositionsCount); foreach (int iIndex in context.Active) { LiveInterval interval = _intervals[iIndex]; Register reg = interval.Register; if (reg.Type == regType) { freePositions[reg.Index] = 0; freePositionsCount--; } } // If all registers are already active, return early. No point in inspecting the inactive set to look for // holes. if (freePositionsCount == 0) { return false; } foreach (int iIndex in context.Inactive) { LiveInterval interval = _intervals[iIndex]; Register reg = interval.Register; ref int freePosition = ref freePositions[reg.Index]; if (reg.Type == regType && freePosition != 0) { int overlapPosition = interval.GetOverlapPosition(current); if (overlapPosition != LiveInterval.NotFound && freePosition > overlapPosition) { freePosition = overlapPosition; } } } int selectedReg = GetHighestValueIndex(freePositions); int selectedNextUse = freePositions[selectedReg]; // Intervals starts and ends at odd positions, unless they span an entire // block, in this case they will have ranges at a even position. // When a interval is loaded from the stack to a register, we can only // do the split at a odd position, because otherwise the split interval // that is inserted on the list to be processed may clobber a register // used by the instruction at the same position as the split. // The problem only happens when a interval ends exactly at this instruction, // because otherwise they would interfere, and the register wouldn't be selected. // When the interval is aligned and the above happens, there's no problem as // the instruction that is actually with the last use is the one // before that position. selectedNextUse &= ~InstructionGapMask; if (selectedNextUse <= current.GetStart()) { return false; } else if (selectedNextUse < current.GetEnd()) { LiveInterval splitChild = current.Split(selectedNextUse); if (splitChild.UsesCount != 0) { Debug.Assert(splitChild.GetStart() > current.GetStart(), "Split interval has an invalid start position."); InsertInterval(splitChild); } else { Spill(context, splitChild); } } current.Register = new Register(selectedReg, regType); if (regType == RegisterType.Integer) { context.IntUsedRegisters |= 1 << selectedReg; } else /* if (regType == RegisterType.Vector) */ { context.VecUsedRegisters |= 1 << selectedReg; } context.Active.Set(cIndex); return true; } private void AllocateRegWithSpill(AllocationContext context, LiveInterval current, int cIndex) { RegisterType regType = current.Local.Type.ToRegisterType(); Span usePositions = stackalloc int[RegistersCount]; Span blockedPositions = stackalloc int[RegistersCount]; context.GetFreePositions(regType, usePositions, out _); context.GetFreePositions(regType, blockedPositions, out _); foreach (int iIndex in context.Active) { LiveInterval interval = _intervals[iIndex]; Register reg = interval.Register; if (reg.Type == regType) { ref int usePosition = ref usePositions[reg.Index]; ref int blockedPosition = ref blockedPositions[reg.Index]; if (interval.IsFixed) { usePosition = 0; blockedPosition = 0; } else { int nextUse = interval.NextUseAfter(current.GetStart()); if (nextUse != LiveInterval.NotFound && usePosition > nextUse) { usePosition = nextUse; } } } } foreach (int iIndex in context.Inactive) { LiveInterval interval = _intervals[iIndex]; Register reg = interval.Register; if (reg.Type == regType) { ref int usePosition = ref usePositions[reg.Index]; ref int blockedPosition = ref blockedPositions[reg.Index]; if (interval.IsFixed) { int overlapPosition = interval.GetOverlapPosition(current); if (overlapPosition != LiveInterval.NotFound) { blockedPosition = Math.Min(blockedPosition, overlapPosition); usePosition = Math.Min(usePosition, overlapPosition); } } else if (interval.Overlaps(current)) { int nextUse = interval.NextUseAfter(current.GetStart()); if (nextUse != LiveInterval.NotFound && usePosition > nextUse) { usePosition = nextUse; } } } } int selectedReg = GetHighestValueIndex(usePositions); int currentFirstUse = current.FirstUse(); Debug.Assert(currentFirstUse >= 0, "Current interval has no uses."); if (usePositions[selectedReg] < currentFirstUse) { // All intervals on inactive and active are being used before current, // so spill the current interval. Debug.Assert(currentFirstUse > current.GetStart(), "Trying to spill a interval currently being used."); LiveInterval splitChild = current.Split(currentFirstUse); Debug.Assert(splitChild.GetStart() > current.GetStart(), "Split interval has an invalid start position."); InsertInterval(splitChild); Spill(context, current); } else if (blockedPositions[selectedReg] > current.GetEnd()) { // Spill made the register available for the entire current lifetime, // so we only need to split the intervals using the selected register. current.Register = new Register(selectedReg, regType); SplitAndSpillOverlappingIntervals(context, current); context.Active.Set(cIndex); } else { // There are conflicts even after spill due to the use of fixed registers // that can't be spilled, so we need to also split current at the point of // the first fixed register use. current.Register = new Register(selectedReg, regType); int splitPosition = blockedPositions[selectedReg] & ~InstructionGapMask; Debug.Assert(splitPosition > current.GetStart(), "Trying to split a interval at a invalid position."); LiveInterval splitChild = current.Split(splitPosition); if (splitChild.UsesCount != 0) { Debug.Assert(splitChild.GetStart() > current.GetStart(), "Split interval has an invalid start position."); InsertInterval(splitChild); } else { Spill(context, splitChild); } SplitAndSpillOverlappingIntervals(context, current); context.Active.Set(cIndex); } } private static int GetHighestValueIndex(Span span) { int highest = span[0]; if (highest == int.MaxValue) { return 0; } int selected = 0; for (int index = 1; index < span.Length; index++) { int current = span[index]; if (highest < current) { highest = current; selected = index; if (current == int.MaxValue) { break; } } } return selected; } private void SplitAndSpillOverlappingIntervals(AllocationContext context, LiveInterval current) { foreach (int iIndex in context.Active) { LiveInterval interval = _intervals[iIndex]; if (!interval.IsFixed && interval.Register == current.Register) { SplitAndSpillOverlappingInterval(context, current, interval); context.Active.Clear(iIndex); } } foreach (int iIndex in context.Inactive) { LiveInterval interval = _intervals[iIndex]; if (!interval.IsFixed && interval.Register == current.Register && interval.Overlaps(current)) { SplitAndSpillOverlappingInterval(context, current, interval); context.Inactive.Clear(iIndex); } } } private void SplitAndSpillOverlappingInterval( AllocationContext context, LiveInterval current, LiveInterval interval) { // If there's a next use after the start of the current interval, // we need to split the spilled interval twice, and re-insert it // on the "pending" list to ensure that it will get a new register // on that use position. int nextUse = interval.NextUseAfter(current.GetStart()); LiveInterval splitChild; if (interval.GetStart() < current.GetStart()) { splitChild = interval.Split(current.GetStart()); } else { splitChild = interval; } if (nextUse != -1) { Debug.Assert(nextUse > current.GetStart(), "Trying to spill a interval currently being used."); if (nextUse > splitChild.GetStart()) { LiveInterval right = splitChild.Split(nextUse); Spill(context, splitChild); splitChild = right; } InsertInterval(splitChild); } else { Spill(context, splitChild); } } private void InsertInterval(LiveInterval interval) { Debug.Assert(interval.UsesCount != 0, "Trying to insert a interval without uses."); Debug.Assert(!interval.IsEmpty, "Trying to insert a empty interval."); Debug.Assert(!interval.IsSpilled, "Trying to insert a spilled interval."); int startIndex = RegistersCount * 2; int insertIndex = _intervals.BinarySearch(startIndex, _intervals.Count - startIndex, interval, null); if (insertIndex < 0) { insertIndex = ~insertIndex; } _intervals.Insert(insertIndex, interval); } private void Spill(AllocationContext context, LiveInterval interval) { Debug.Assert(!interval.IsFixed, "Trying to spill a fixed interval."); Debug.Assert(interval.UsesCount == 0, "Trying to spill a interval with uses."); // We first check if any of the siblings were spilled, if so we can reuse // the stack offset. Otherwise, we allocate a new space on the stack. // This prevents stack-to-stack copies being necessary for a split interval. if (!interval.TrySpillWithSiblingOffset()) { interval.Spill(context.StackAlloc.Allocate(interval.Local.Type)); } } private void InsertSplitCopies() { Dictionary copyResolvers = new Dictionary(); CopyResolver GetCopyResolver(int position) { if (!copyResolvers.TryGetValue(position, out CopyResolver copyResolver)) { copyResolver = new CopyResolver(); copyResolvers.Add(position, copyResolver); } return copyResolver; } foreach (LiveInterval interval in _intervals.Where(x => x.IsSplit)) { LiveInterval previous = interval; foreach (LiveInterval splitChild in interval.SplitChildren()) { int splitPosition = splitChild.GetStart(); if (!_blockEdges.Contains(splitPosition) && previous.GetEnd() == splitPosition) { GetCopyResolver(splitPosition).AddSplit(previous, splitChild); } previous = splitChild; } } foreach (KeyValuePair kv in copyResolvers) { CopyResolver copyResolver = kv.Value; if (!copyResolver.HasCopy) { continue; } int splitPosition = kv.Key; (IntrusiveList nodes, Operation node) = GetOperationNode(splitPosition); Operation[] sequence = copyResolver.Sequence(); nodes.AddBefore(node, sequence[0]); node = sequence[0]; for (int index = 1; index < sequence.Length; index++) { nodes.AddAfter(node, sequence[index]); node = sequence[index]; } } } private void InsertSplitCopiesAtEdges(ControlFlowGraph cfg) { int blocksCount = cfg.Blocks.Count; bool IsSplitEdgeBlock(BasicBlock block) { return block.Index >= blocksCount; } // Reset iterators to beginning because GetSplitChild depends on the state of the iterator. foreach (LiveInterval interval in _intervals) { interval.Reset(); } for (BasicBlock block = cfg.Blocks.First; block != null; block = block.ListNext) { if (IsSplitEdgeBlock(block)) { continue; } bool hasSingleOrNoSuccessor = block.SuccessorsCount <= 1; for (int i = 0; i < block.SuccessorsCount; i++) { BasicBlock successor = block.GetSuccessor(i); int succIndex = successor.Index; // If the current node is a split node, then the actual successor node // (the successor before the split) should be right after it. if (IsSplitEdgeBlock(successor)) { succIndex = successor.GetSuccessor(0).Index; } CopyResolver copyResolver = null; foreach (int iIndex in _blockLiveIn[succIndex]) { LiveInterval interval = _parentIntervals[iIndex]; if (!interval.IsSplit) { continue; } int lEnd = _blockRanges[block.Index].End - 1; int rStart = _blockRanges[succIndex].Start; LiveInterval left = interval.GetSplitChild(lEnd); LiveInterval right = interval.GetSplitChild(rStart); if (left != default && right != default && left != right) { if (copyResolver == null) { copyResolver = new CopyResolver(); } copyResolver.AddSplit(left, right); } } if (copyResolver == null || !copyResolver.HasCopy) { continue; } Operation[] sequence = copyResolver.Sequence(); if (hasSingleOrNoSuccessor) { foreach (Operation operation in sequence) { block.Append(operation); } } else if (successor.Predecessors.Count == 1) { successor.Operations.AddFirst(sequence[0]); Operation prependNode = sequence[0]; for (int index = 1; index < sequence.Length; index++) { Operation operation = sequence[index]; successor.Operations.AddAfter(prependNode, operation); prependNode = operation; } } else { // Split the critical edge. BasicBlock splitBlock = cfg.SplitEdge(block, successor); foreach (Operation operation in sequence) { splitBlock.Append(operation); } } } } } private void ReplaceLocalWithRegister(LiveInterval current) { Operand register = GetRegister(current); foreach (int usePosition in current.UsePositions()) { (_, Operation operation) = GetOperationNode(usePosition); for (int index = 0; index < operation.SourcesCount; index++) { Operand source = operation.GetSource(index); if (source == current.Local) { operation.SetSource(index, register); } else if (source.Kind == OperandKind.Memory) { MemoryOperand memOp = source.GetMemory(); if (memOp.BaseAddress == current.Local) { memOp.BaseAddress = register; } if (memOp.Index == current.Local) { memOp.Index = register; } } } for (int index = 0; index < operation.DestinationsCount; index++) { Operand dest = operation.GetDestination(index); if (dest == current.Local) { operation.SetDestination(index, register); } } } } private static Operand GetRegister(LiveInterval interval) { Debug.Assert(!interval.IsSpilled, "Spilled intervals are not allowed."); return Operand.Factory.Register( interval.Register.Index, interval.Register.Type, interval.Local.Type); } private (IntrusiveList, Operation) GetOperationNode(int position) { return _operationNodes[position / InstructionGap]; } private void NumberLocals(ControlFlowGraph cfg) { _operationNodes = new List<(IntrusiveList, Operation)>(); _intervals = new List(); for (int index = 0; index < RegistersCount; index++) { _intervals.Add(new LiveInterval(new Register(index, RegisterType.Integer))); _intervals.Add(new LiveInterval(new Register(index, RegisterType.Vector))); } // The "visited" state is stored in the MSB of the local's value. const ulong VisitedMask = 1ul << 63; bool IsVisited(Operand local) { return (local.GetValueUnsafe() & VisitedMask) != 0; } void SetVisited(Operand local) { local.GetValueUnsafe() |= VisitedMask; } _operationsCount = 0; for (int index = cfg.PostOrderBlocks.Length - 1; index >= 0; index--) { BasicBlock block = cfg.PostOrderBlocks[index]; for (Operation node = block.Operations.First; node != default; node = node.ListNext) { _operationNodes.Add((block.Operations, node)); for (int i = 0; i < node.DestinationsCount; i++) { Operand dest = node.GetDestination(i); if (dest.Kind == OperandKind.LocalVariable && !IsVisited(dest)) { dest.NumberLocal(_intervals.Count); _intervals.Add(new LiveInterval(dest)); SetVisited(dest); } } } _operationsCount += block.Operations.Count * InstructionGap; if (block.Operations.Count == 0) { // Pretend we have a dummy instruction on the empty block. _operationNodes.Add((default, default)); _operationsCount += InstructionGap; } } _parentIntervals = _intervals.ToArray(); } private void BuildIntervals(ControlFlowGraph cfg, AllocationContext context) { _blockRanges = new LiveRange[cfg.Blocks.Count]; int mapSize = _intervals.Count; BitMap[] blkLiveGen = new BitMap[cfg.Blocks.Count]; BitMap[] blkLiveKill = new BitMap[cfg.Blocks.Count]; // Compute local live sets. for (BasicBlock block = cfg.Blocks.First; block != null; block = block.ListNext) { BitMap liveGen = new BitMap(Allocators.Default, mapSize); BitMap liveKill = new BitMap(Allocators.Default, mapSize); for (Operation node = block.Operations.First; node != default; node = node.ListNext) { for (int i = 0; i < node.SourcesCount; i++) { VisitSource(node.GetSource(i)); } for (int i = 0; i < node.DestinationsCount; i++) { VisitDestination(node.GetDestination(i)); } void VisitSource(Operand source) { if (IsLocalOrRegister(source.Kind)) { int id = GetOperandId(source); if (!liveKill.IsSet(id)) { liveGen.Set(id); } } else if (source.Kind == OperandKind.Memory) { MemoryOperand memOp = source.GetMemory(); if (memOp.BaseAddress != default) { VisitSource(memOp.BaseAddress); } if (memOp.Index != default) { VisitSource(memOp.Index); } } } void VisitDestination(Operand dest) { liveKill.Set(GetOperandId(dest)); } } blkLiveGen [block.Index] = liveGen; blkLiveKill[block.Index] = liveKill; } // Compute global live sets. BitMap[] blkLiveIn = new BitMap[cfg.Blocks.Count]; BitMap[] blkLiveOut = new BitMap[cfg.Blocks.Count]; for (int index = 0; index < cfg.Blocks.Count; index++) { blkLiveIn [index] = new BitMap(Allocators.Default, mapSize); blkLiveOut[index] = new BitMap(Allocators.Default, mapSize); } bool modified; do { modified = false; for (int index = 0; index < cfg.PostOrderBlocks.Length; index++) { BasicBlock block = cfg.PostOrderBlocks[index]; BitMap liveOut = blkLiveOut[block.Index]; for (int i = 0; i < block.SuccessorsCount; i++) { BasicBlock succ = block.GetSuccessor(i); modified |= liveOut.Set(blkLiveIn[succ.Index]); } BitMap liveIn = blkLiveIn[block.Index]; liveIn.Set (liveOut); liveIn.Clear(blkLiveKill[block.Index]); liveIn.Set (blkLiveGen [block.Index]); } } while (modified); _blockLiveIn = blkLiveIn; _blockEdges = new HashSet(); // Compute lifetime intervals. int operationPos = _operationsCount; for (int index = 0; index < cfg.PostOrderBlocks.Length; index++) { BasicBlock block = cfg.PostOrderBlocks[index]; // We handle empty blocks by pretending they have a dummy instruction, // because otherwise the block would have the same start and end position, // and this is not valid. int instCount = Math.Max(block.Operations.Count, 1); int blockStart = operationPos - instCount * InstructionGap; int blockEnd = operationPos; _blockRanges[block.Index] = new LiveRange(blockStart, blockEnd); _blockEdges.Add(blockStart); BitMap liveOut = blkLiveOut[block.Index]; foreach (int id in liveOut) { _intervals[id].AddRange(blockStart, blockEnd); } if (block.Operations.Count == 0) { operationPos -= InstructionGap; continue; } for (Operation node = block.Operations.Last; node != default; node = node.ListPrevious) { operationPos -= InstructionGap; for (int i = 0; i < node.DestinationsCount; i++) { VisitDestination(node.GetDestination(i)); } for (int i = 0; i < node.SourcesCount; i++) { VisitSource(node.GetSource(i)); } if (node.Instruction == Instruction.Call) { AddIntervalCallerSavedReg(context.Masks.IntCallerSavedRegisters, operationPos, RegisterType.Integer); AddIntervalCallerSavedReg(context.Masks.VecCallerSavedRegisters, operationPos, RegisterType.Vector); } void VisitSource(Operand source) { if (IsLocalOrRegister(source.Kind)) { LiveInterval interval = _intervals[GetOperandId(source)]; interval.AddRange(blockStart, operationPos + 1); interval.AddUsePosition(operationPos); } else if (source.Kind == OperandKind.Memory) { MemoryOperand memOp = source.GetMemory(); if (memOp.BaseAddress != default) { VisitSource(memOp.BaseAddress); } if (memOp.Index != default) { VisitSource(memOp.Index); } } } void VisitDestination(Operand dest) { LiveInterval interval = _intervals[GetOperandId(dest)]; interval.SetStart(operationPos + 1); interval.AddUsePosition(operationPos + 1); } } } foreach (LiveInterval interval in _parentIntervals) { interval.Reset(); } } private void AddIntervalCallerSavedReg(int mask, int operationPos, RegisterType regType) { while (mask != 0) { int regIndex = BitOperations.TrailingZeroCount(mask); Register callerSavedReg = new Register(regIndex, regType); LiveInterval interval = _intervals[GetRegisterId(callerSavedReg)]; interval.AddRange(operationPos + 1, operationPos + InstructionGap); mask &= ~(1 << regIndex); } } private static int GetOperandId(Operand operand) { if (operand.Kind == OperandKind.LocalVariable) { return operand.GetLocalNumber(); } else if (operand.Kind == OperandKind.Register) { return GetRegisterId(operand.GetRegister()); } else { throw new ArgumentException($"Invalid operand kind \"{operand.Kind}\"."); } } private static int GetRegisterId(Register register) { return (register.Index << 1) | (register.Type == RegisterType.Vector ? 1 : 0); } private static bool IsLocalOrRegister(OperandKind kind) { return kind == OperandKind.LocalVariable || kind == OperandKind.Register; } } }