Move solution and projects to src

11 files changed, 2514 insertions, 0 deletions

diff --git a/src/ARMeilleure/CodeGen/RegisterAllocators/AllocationResult.cs b/src/ARMeilleure/CodeGen/RegisterAllocators/AllocationResult.cs
new file mode 100644
index 00000000..43e5c7e2
--- /dev/null
+++ b/src/ARMeilleure/CodeGen/RegisterAllocators/AllocationResult.cs
@@ -0,0 +1,19 @@
+namespace ARMeilleure.CodeGen.RegisterAllocators
+{
+    readonly struct AllocationResult
+    {
+        public int IntUsedRegisters { get; }
+        public int VecUsedRegisters { get; }
+        public int SpillRegionSize  { get; }
+
+        public AllocationResult(
+            int intUsedRegisters,
+            int vecUsedRegisters,
+            int spillRegionSize)
+        {
+            IntUsedRegisters = intUsedRegisters;
+            VecUsedRegisters = vecUsedRegisters;
+            SpillRegionSize  = spillRegionSize;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/ARMeilleure/CodeGen/RegisterAllocators/CopyResolver.cs b/src/ARMeilleure/CodeGen/RegisterAllocators/CopyResolver.cs
new file mode 100644
index 00000000..587b1a02
--- /dev/null
+++ b/src/ARMeilleure/CodeGen/RegisterAllocators/CopyResolver.cs
@@ -0,0 +1,259 @@
+using ARMeilleure.IntermediateRepresentation;
+using System;
+using System.Collections.Generic;
+
+using static ARMeilleure.IntermediateRepresentation.Operand.Factory;
+using static ARMeilleure.IntermediateRepresentation.Operation.Factory;
+
+namespace ARMeilleure.CodeGen.RegisterAllocators
+{
+    class CopyResolver
+    {
+        private class ParallelCopy
+        {
+            private readonly struct Copy
+            {
+                public Register Dest   { get; }
+                public Register Source { get; }
+
+                public OperandType Type { get; }
+
+                public Copy(Register dest, Register source, OperandType type)
+                {
+                    Dest   = dest;
+                    Source = source;
+                    Type   = type;
+                }
+            }
+
+            private readonly List<Copy> _copies;
+
+            public int Count => _copies.Count;
+
+            public ParallelCopy()
+            {
+                _copies = new List<Copy>();
+            }
+
+            public void AddCopy(Register dest, Register source, OperandType type)
+            {
+                _copies.Add(new Copy(dest, source, type));
+            }
+
+            public void Sequence(List<Operation> sequence)
+            {
+                Dictionary<Register, Register> locations = new Dictionary<Register, Register>();
+                Dictionary<Register, Register> sources   = new Dictionary<Register, Register>();
+
+                Dictionary<Register, OperandType> types = new Dictionary<Register, OperandType>();
+
+                Queue<Register> pendingQueue = new Queue<Register>();
+                Queue<Register> readyQueue   = new Queue<Register>();
+
+                foreach (Copy copy in _copies)
+                {
+                    locations[copy.Source] = copy.Source;
+                    sources[copy.Dest]     = copy.Source;
+                    types[copy.Dest]       = copy.Type;
+
+                    pendingQueue.Enqueue(copy.Dest);
+                }
+
+                foreach (Copy copy in _copies)
+                {
+                    // If the destination is not used anywhere, we can assign it immediately.
+                    if (!locations.ContainsKey(copy.Dest))
+                    {
+                        readyQueue.Enqueue(copy.Dest);
+                    }
+                }
+
+                while (pendingQueue.TryDequeue(out Register current))
+                {
+                    Register copyDest;
+                    Register origSource;
+                    Register copySource;
+
+                    while (readyQueue.TryDequeue(out copyDest))
+                    {
+                        origSource = sources[copyDest];
+                        copySource = locations[origSource];
+
+                        OperandType type = types[copyDest];
+
+                        EmitCopy(sequence, GetRegister(copyDest, type), GetRegister(copySource, type));
+
+                        locations[origSource] = copyDest;
+
+                        if (origSource == copySource && sources.ContainsKey(origSource))
+                        {
+                            readyQueue.Enqueue(origSource);
+                        }
+                    }
+
+                    copyDest   = current;
+                    origSource = sources[copyDest];
+                    copySource = locations[origSource];
+
+                    if (copyDest != copySource)
+                    {
+                        OperandType type = types[copyDest];
+
+                        type = type.IsInteger() ? OperandType.I64 : OperandType.V128;
+
+                        EmitXorSwap(sequence, GetRegister(copyDest, type), GetRegister(copySource, type));
+
+                        locations[origSource] = copyDest;
+
+                        Register swapOther = copySource;
+
+                        if (copyDest != locations[sources[copySource]])
+                        {
+                            // Find the other swap destination register.
+                            // To do that, we search all the pending registers, and pick
+                            // the one where the copy source register is equal to the
+                            // current destination register being processed (copyDest).
+                            foreach (Register pending in pendingQueue)
+                            {
+                                // Is this a copy of pending <- copyDest?
+                                if (copyDest == locations[sources[pending]])
+                                {
+                                    swapOther = pending;
+
+                                    break;
+                                }
+                            }
+                        }
+
+                        // The value that was previously at "copyDest" now lives on
+                        // "copySource" thanks to the swap, now we need to update the
+                        // location for the next copy that is supposed to copy the value
+                        // that used to live on "copyDest".
+                        locations[sources[swapOther]] = copySource;
+                    }
+                }
+            }
+
+            private static void EmitCopy(List<Operation> sequence, Operand x, Operand y)
+            {
+                sequence.Add(Operation(Instruction.Copy, x, y));
+            }
+
+            private static void EmitXorSwap(List<Operation> sequence, Operand x, Operand y)
+            {
+                sequence.Add(Operation(Instruction.BitwiseExclusiveOr, x, x, y));
+                sequence.Add(Operation(Instruction.BitwiseExclusiveOr, y, y, x));
+                sequence.Add(Operation(Instruction.BitwiseExclusiveOr, x, x, y));
+            }
+        }
+
+        private Queue<Operation> _fillQueue = null;
+        private Queue<Operation> _spillQueue = null;
+        private ParallelCopy _parallelCopy = null;
+
+        public bool HasCopy { get; private set; }
+
+        public void AddSplit(LiveInterval left, LiveInterval right)
+        {
+            if (left.Local != right.Local)
+            {
+                throw new ArgumentException("Intervals of different variables are not allowed.");
+            }
+
+            OperandType type = left.Local.Type;
+
+            if (left.IsSpilled && !right.IsSpilled)
+            {
+                // Move from the stack to a register.
+                AddSplitFill(left, right, type);
+            }
+            else if (!left.IsSpilled && right.IsSpilled)
+            {
+                // Move from a register to the stack.
+                AddSplitSpill(left, right, type);
+            }
+            else if (!left.IsSpilled && !right.IsSpilled && left.Register != right.Register)
+            {
+                // Move from one register to another.
+                AddSplitCopy(left, right, type);
+            }
+            else if (left.SpillOffset != right.SpillOffset)
+            {
+                // This would be the stack-to-stack move case, but this is not supported.
+                throw new ArgumentException("Both intervals were spilled.");
+            }
+        }
+
+        private void AddSplitFill(LiveInterval left, LiveInterval right, OperandType type)
+        {
+            if (_fillQueue == null)
+            {
+                _fillQueue = new Queue<Operation>();
+            }
+
+            Operand register = GetRegister(right.Register, type);
+            Operand offset = Const(left.SpillOffset);
+
+            _fillQueue.Enqueue(Operation(Instruction.Fill, register, offset));
+
+            HasCopy = true;
+        }
+
+        private void AddSplitSpill(LiveInterval left, LiveInterval right, OperandType type)
+        {
+            if (_spillQueue == null)
+            {
+                _spillQueue = new Queue<Operation>();
+            }
+
+            Operand offset = Const(right.SpillOffset);
+            Operand register = GetRegister(left.Register, type);
+
+            _spillQueue.Enqueue(Operation(Instruction.Spill, default, offset, register));
+
+            HasCopy = true;
+        }
+
+        private void AddSplitCopy(LiveInterval left, LiveInterval right, OperandType type)
+        {
+            if (_parallelCopy == null)
+            {
+                _parallelCopy = new ParallelCopy();
+            }
+
+            _parallelCopy.AddCopy(right.Register, left.Register, type);
+
+            HasCopy = true;
+        }
+
+        public Operation[] Sequence()
+        {
+            List<Operation> sequence = new List<Operation>();
+
+            if (_spillQueue != null)
+            {
+                while (_spillQueue.TryDequeue(out Operation spillOp))
+                {
+                    sequence.Add(spillOp);
+                }
+            }
+
+            _parallelCopy?.Sequence(sequence);
+
+            if (_fillQueue != null)
+            {
+                while (_fillQueue.TryDequeue(out Operation fillOp))
+                {
+                    sequence.Add(fillOp);
+                }
+            }
+
+            return sequence.ToArray();
+        }
+
+        private static Operand GetRegister(Register reg, OperandType type)
+        {
+            return Register(reg.Index, reg.Type, type);
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/ARMeilleure/CodeGen/RegisterAllocators/HybridAllocator.cs b/src/ARMeilleure/CodeGen/RegisterAllocators/HybridAllocator.cs
new file mode 100644
index 00000000..25952c77
--- /dev/null
+++ b/src/ARMeilleure/CodeGen/RegisterAllocators/HybridAllocator.cs
@@ -0,0 +1,454 @@
+using ARMeilleure.IntermediateRepresentation;
+using ARMeilleure.Translation;
+using System;
+using System.Diagnostics;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+using static ARMeilleure.IntermediateRepresentation.Operand.Factory;
+using static ARMeilleure.IntermediateRepresentation.Operation.Factory;
+
+namespace ARMeilleure.CodeGen.RegisterAllocators
+{
+    class HybridAllocator : IRegisterAllocator
+    {
+        private readonly struct BlockInfo
+        {
+            public bool HasCall { get; }
+
+            public int IntFixedRegisters { get; }
+            public int VecFixedRegisters { get; }
+
+            public BlockInfo(bool hasCall, int intFixedRegisters, int vecFixedRegisters)
+            {
+                HasCall           = hasCall;
+                IntFixedRegisters = intFixedRegisters;
+                VecFixedRegisters = vecFixedRegisters;
+            }
+        }
+
+        private struct LocalInfo
+        {
+            public int Uses { get; set; }
+            public int UsesAllocated { get; set; }
+            public int Sequence { get; set; }
+            public Operand Temp { get; set; }
+            public Operand Register { get; set; }
+            public Operand SpillOffset { get; set; }
+            public OperandType Type { get; }
+
+            private int _first;
+            private int _last;
+
+            public bool IsBlockLocal => _first == _last;
+
+            public LocalInfo(OperandType type, int uses, int blkIndex)
+            {
+                Uses = uses;
+                Type = type;
+
+                UsesAllocated = 0;
+                Sequence = 0;
+                Temp = default;
+                Register = default;
+                SpillOffset = default;
+
+                _first = -1;
+                _last  = -1;
+
+                SetBlockIndex(blkIndex);
+            }
+
+            public void SetBlockIndex(int blkIndex)
+            {
+                if (_first == -1 || blkIndex < _first)
+                {
+                    _first = blkIndex;
+                }
+
+                if (_last == -1 || blkIndex > _last)
+                {
+                    _last = blkIndex;
+                }
+            }
+        }
+
+        private const int MaxIROperands = 4;
+        // The "visited" state is stored in the MSB of the local's value.
+        private const ulong VisitedMask = 1ul << 63;
+
+        private BlockInfo[] _blockInfo;
+        private LocalInfo[] _localInfo;
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static bool IsVisited(Operand local)
+        {
+            Debug.Assert(local.Kind == OperandKind.LocalVariable);
+
+            return (local.GetValueUnsafe() & VisitedMask) != 0;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void SetVisited(Operand local)
+        {
+            Debug.Assert(local.Kind == OperandKind.LocalVariable);
+
+            local.GetValueUnsafe() |= VisitedMask;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private ref LocalInfo GetLocalInfo(Operand local)
+        {
+            Debug.Assert(local.Kind == OperandKind.LocalVariable);
+            Debug.Assert(IsVisited(local), "Local variable not visited. Used before defined?");
+
+            return ref _localInfo[(uint)local.GetValueUnsafe() - 1];
+        }
+
+        public AllocationResult RunPass(ControlFlowGraph cfg, StackAllocator stackAlloc, RegisterMasks regMasks)
+        {
+            int intUsedRegisters = 0;
+            int vecUsedRegisters = 0;
+
+            int intFreeRegisters = regMasks.IntAvailableRegisters;
+            int vecFreeRegisters = regMasks.VecAvailableRegisters;
+
+            _blockInfo = new BlockInfo[cfg.Blocks.Count];
+            _localInfo = new LocalInfo[cfg.Blocks.Count * 3];
+
+            int localInfoCount = 0;
+
+            for (int index = cfg.PostOrderBlocks.Length - 1; index >= 0; index--)
+            {
+                BasicBlock block = cfg.PostOrderBlocks[index];
+
+                int intFixedRegisters = 0;
+                int vecFixedRegisters = 0;
+
+                bool hasCall = false;
+
+                for (Operation node = block.Operations.First; node != default; node = node.ListNext)
+                {
+                    if (node.Instruction == Instruction.Call)
+                    {
+                        hasCall = true;
+                    }
+
+                    foreach (Operand source in node.SourcesUnsafe)
+                    {
+                        if (source.Kind == OperandKind.LocalVariable)
+                        {
+                            GetLocalInfo(source).SetBlockIndex(block.Index);
+                        }
+                        else if (source.Kind == OperandKind.Memory)
+                        {
+                            MemoryOperand memOp = source.GetMemory();
+
+                            if (memOp.BaseAddress != default)
+                            {
+                                GetLocalInfo(memOp.BaseAddress).SetBlockIndex(block.Index);
+                            }
+
+                            if (memOp.Index != default)
+                            {
+                                GetLocalInfo(memOp.Index).SetBlockIndex(block.Index);
+                            }
+                        }
+                    }
+
+                    foreach (Operand dest in node.DestinationsUnsafe)
+                    {
+                        if (dest.Kind == OperandKind.LocalVariable)
+                        {
+                            if (IsVisited(dest))
+                            {
+                                GetLocalInfo(dest).SetBlockIndex(block.Index);
+                            }
+                            else
+                            {
+                                dest.NumberLocal(++localInfoCount);
+
+                                if (localInfoCount > _localInfo.Length)
+                                {
+                                    Array.Resize(ref _localInfo, localInfoCount * 2);
+                                }
+
+                                SetVisited(dest);
+                                GetLocalInfo(dest) = new LocalInfo(dest.Type, UsesCount(dest), block.Index);
+                            }
+                        }
+                        else if (dest.Kind == OperandKind.Register)
+                        {
+                            if (dest.Type.IsInteger())
+                            {
+                                intFixedRegisters |= 1 << dest.GetRegister().Index;
+                            }
+                            else
+                            {
+                                vecFixedRegisters |= 1 << dest.GetRegister().Index;
+                            }
+                        }
+                    }
+                }
+
+                _blockInfo[block.Index] = new BlockInfo(hasCall, intFixedRegisters, vecFixedRegisters);
+            }
+
+            int sequence = 0;
+
+            for (int index = cfg.PostOrderBlocks.Length - 1; index >= 0; index--)
+            {
+                BasicBlock block = cfg.PostOrderBlocks[index];
+
+                ref BlockInfo blkInfo = ref _blockInfo[block.Index];
+
+                int intLocalFreeRegisters = intFreeRegisters & ~blkInfo.IntFixedRegisters;
+                int vecLocalFreeRegisters = vecFreeRegisters & ~blkInfo.VecFixedRegisters;
+
+                int intCallerSavedRegisters = blkInfo.HasCall ? regMasks.IntCallerSavedRegisters : 0;
+                int vecCallerSavedRegisters = blkInfo.HasCall ? regMasks.VecCallerSavedRegisters : 0;
+
+                int intSpillTempRegisters = SelectSpillTemps(
+                    intCallerSavedRegisters & ~blkInfo.IntFixedRegisters,
+                    intLocalFreeRegisters);
+                int vecSpillTempRegisters = SelectSpillTemps(
+                    vecCallerSavedRegisters & ~blkInfo.VecFixedRegisters,
+                    vecLocalFreeRegisters);
+
+                intLocalFreeRegisters &= ~(intSpillTempRegisters | intCallerSavedRegisters);
+                vecLocalFreeRegisters &= ~(vecSpillTempRegisters | vecCallerSavedRegisters);
+
+                for (Operation node = block.Operations.First; node != default; node = node.ListNext)
+                {
+                    int intLocalUse = 0;
+                    int vecLocalUse = 0;
+
+                    Operand AllocateRegister(Operand local)
+                    {
+                        ref LocalInfo info = ref GetLocalInfo(local);
+
+                        info.UsesAllocated++;
+
+                        Debug.Assert(info.UsesAllocated <= info.Uses);
+
+                        if (info.Register != default)
+                        {
+                            if (info.UsesAllocated == info.Uses)
+                            {
+                                Register reg = info.Register.GetRegister();
+
+                                if (local.Type.IsInteger())
+                                {
+                                    intLocalFreeRegisters |= 1 << reg.Index;
+                                }
+                                else
+                                {
+                                    vecLocalFreeRegisters |= 1 << reg.Index;
+                                }
+                            }
+
+                            return info.Register;
+                        }
+                        else
+                        {
+                            Operand temp = info.Temp;
+
+                            if (temp == default || info.Sequence != sequence)
+                            {
+                                temp = local.Type.IsInteger()
+                                    ? GetSpillTemp(local, intSpillTempRegisters, ref intLocalUse)
+                                    : GetSpillTemp(local, vecSpillTempRegisters, ref vecLocalUse);
+
+                                info.Sequence = sequence;
+                                info.Temp = temp;
+                            }
+
+                            Operation fillOp = Operation(Instruction.Fill, temp, info.SpillOffset);
+
+                            block.Operations.AddBefore(node, fillOp);
+
+                            return temp;
+                        }
+                    }
+
+                    bool folded = false;
+
+                    // If operation is a copy of a local and that local is living on the stack, we turn the copy into
+                    // a fill, instead of inserting a fill before it.
+                    if (node.Instruction == Instruction.Copy)
+                    {
+                        Operand source = node.GetSource(0);
+
+                        if (source.Kind == OperandKind.LocalVariable)
+                        {
+                            ref LocalInfo info = ref GetLocalInfo(source);
+
+                            if (info.Register == default)
+                            {
+                                Operation fillOp = Operation(Instruction.Fill, node.Destination, info.SpillOffset);
+
+                                block.Operations.AddBefore(node, fillOp);
+                                block.Operations.Remove(node);
+
+                                node = fillOp;
+
+                                folded = true;
+                            }
+                        }
+                    }
+
+                    if (!folded)
+                    {
+                        foreach (ref Operand source in node.SourcesUnsafe)
+                        {
+                            if (source.Kind == OperandKind.LocalVariable)
+                            {
+                                source = AllocateRegister(source);
+                            }
+                            else if (source.Kind == OperandKind.Memory)
+                            {
+                                MemoryOperand memOp = source.GetMemory();
+
+                                if (memOp.BaseAddress != default)
+                                {
+                                    memOp.BaseAddress = AllocateRegister(memOp.BaseAddress);
+                                }
+
+                                if (memOp.Index != default)
+                                {
+                                    memOp.Index = AllocateRegister(memOp.Index);
+                                }
+                            }
+                        }
+                    }
+
+                    int intLocalAsg = 0;
+                    int vecLocalAsg = 0;
+
+                    foreach (ref Operand dest in node.DestinationsUnsafe)
+                    {
+                        if (dest.Kind != OperandKind.LocalVariable)
+                        {
+                            continue;
+                        }
+
+                        ref LocalInfo info = ref GetLocalInfo(dest);
+
+                        if (info.UsesAllocated == 0)
+                        {
+                            int mask = dest.Type.IsInteger()
+                                ? intLocalFreeRegisters
+                                : vecLocalFreeRegisters;
+
+                            if (info.IsBlockLocal && mask != 0)
+                            {
+                                int selectedReg = BitOperations.TrailingZeroCount(mask);
+
+                                info.Register = Register(selectedReg, info.Type.ToRegisterType(), info.Type);
+
+                                if (dest.Type.IsInteger())
+                                {
+                                    intLocalFreeRegisters &= ~(1 << selectedReg);
+                                    intUsedRegisters      |=   1 << selectedReg;
+                                }
+                                else
+                                {
+                                    vecLocalFreeRegisters &= ~(1 << selectedReg);
+                                    vecUsedRegisters      |=   1 << selectedReg;
+                                }
+                            }
+                            else
+                            {
+                                info.Register    = default;
+                                info.SpillOffset = Const(stackAlloc.Allocate(dest.Type.GetSizeInBytes()));
+                            }
+                        }
+
+                        info.UsesAllocated++;
+
+                        Debug.Assert(info.UsesAllocated <= info.Uses);
+
+                        if (info.Register != default)
+                        {
+                            dest = info.Register;
+                        }
+                        else
+                        {
+                            Operand temp = info.Temp;
+
+                            if (temp == default || info.Sequence != sequence)
+                            {
+                                temp = dest.Type.IsInteger()
+                                    ? GetSpillTemp(dest, intSpillTempRegisters, ref intLocalAsg)
+                                    : GetSpillTemp(dest, vecSpillTempRegisters, ref vecLocalAsg);
+
+                                info.Sequence = sequence;
+                                info.Temp     = temp;
+                            }
+
+                            dest = temp;
+
+                            Operation spillOp = Operation(Instruction.Spill, default, info.SpillOffset, temp);
+
+                            block.Operations.AddAfter(node, spillOp);
+
+                            node = spillOp;
+                        }
+                    }
+
+                    sequence++;
+
+                    intUsedRegisters |= intLocalAsg | intLocalUse;
+                    vecUsedRegisters |= vecLocalAsg | vecLocalUse;
+                }
+            }
+
+            return new AllocationResult(intUsedRegisters, vecUsedRegisters, stackAlloc.TotalSize);
+        }
+
+        private static int SelectSpillTemps(int mask0, int mask1)
+        {
+            int selection = 0;
+            int count     = 0;
+
+            while (count < MaxIROperands && mask0 != 0)
+            {
+                int mask = mask0 & -mask0;
+
+                selection |= mask;
+
+                mask0 &= ~mask;
+
+                count++;
+            }
+
+            while (count < MaxIROperands && mask1 != 0)
+            {
+                int mask = mask1 & -mask1;
+
+                selection |= mask;
+
+                mask1 &= ~mask;
+
+                count++;
+            }
+
+            Debug.Assert(count == MaxIROperands, "No enough registers for spill temps.");
+
+            return selection;
+        }
+
+        private static Operand GetSpillTemp(Operand local, int freeMask, ref int useMask)
+        {
+            int selectedReg = BitOperations.TrailingZeroCount(freeMask & ~useMask);
+
+            useMask |= 1 << selectedReg;
+
+            return Register(selectedReg, local.Type.ToRegisterType(), local.Type);
+        }
+
+        private static int UsesCount(Operand local)
+        {
+            return local.AssignmentsCount + local.UsesCount;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/ARMeilleure/CodeGen/RegisterAllocators/IRegisterAllocator.cs b/src/ARMeilleure/CodeGen/RegisterAllocators/IRegisterAllocator.cs
new file mode 100644
index 00000000..8f236c25
--- /dev/null
+++ b/src/ARMeilleure/CodeGen/RegisterAllocators/IRegisterAllocator.cs
@@ -0,0 +1,12 @@
+using ARMeilleure.Translation;
+
+namespace ARMeilleure.CodeGen.RegisterAllocators
+{
+    interface IRegisterAllocator
+    {
+        AllocationResult RunPass(
+            ControlFlowGraph cfg,
+            StackAllocator stackAlloc,
+            RegisterMasks regMasks);
+    }
+}
\ No newline at end of file
diff --git a/src/ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs b/src/ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs
new file mode 100644
index 00000000..d80157af
--- /dev/null
+++ b/src/ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs
@@ -0,0 +1,1101 @@
+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 HashSet<int> _blockEdges;
+        private LiveRange[] _blockRanges;
+        private BitMap[] _blockLiveIn;
+
+        private List<LiveInterval> _intervals;
+        private LiveInterval[] _parentIntervals;
+
+        private List<(IntrusiveList<Operation>, 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[masks.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<int> 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, regMasks.RegistersCount);
+
+            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.IsFixedAndUsed)
+                    {
+                        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, regMasks.RegistersCount);
+            }
+
+            for (int index = regMasks.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, int registersCount)
+        {
+            // 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, registersCount))
+            {
+                AllocateRegWithSpill(context, current, cIndex, registersCount);
+            }
+        }
+
+        private bool TryAllocateRegWithoutSpill(AllocationContext context, LiveInterval current, int cIndex, int registersCount)
+        {
+            RegisterType regType = current.Local.Type.ToRegisterType();
+
+            Span<int> 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, registersCount);
+                }
+                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, int registersCount)
+        {
+            RegisterType regType = current.Local.Type.ToRegisterType();
+
+            Span<int> usePositions = stackalloc int[registersCount];
+            Span<int> 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, registersCount);
+
+                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, registersCount);
+
+                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, registersCount);
+                }
+                else
+                {
+                    Spill(context, splitChild);
+                }
+
+                SplitAndSpillOverlappingIntervals(context, current, registersCount);
+
+                context.Active.Set(cIndex);
+            }
+        }
+
+        private static int GetHighestValueIndex(Span<int> span)
+        {
+            int highest = int.MinValue;
+
+            int selected = 0;
+
+            for (int index = 0; 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, int registersCount)
+        {
+            foreach (int iIndex in context.Active)
+            {
+                LiveInterval interval = _intervals[iIndex];
+
+                if (!interval.IsFixed && interval.Register == current.Register)
+                {
+                    SplitAndSpillOverlappingInterval(context, current, interval, registersCount);
+
+                    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, registersCount);
+
+                    context.Inactive.Clear(iIndex);
+                }
+            }
+        }
+
+        private void SplitAndSpillOverlappingInterval(
+            AllocationContext context,
+            LiveInterval      current,
+            LiveInterval      interval,
+            int               registersCount)
+        {
+            // 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, registersCount);
+            }
+            else
+            {
+                Spill(context, splitChild);
+            }
+        }
+
+        private void InsertInterval(LiveInterval interval, int registersCount)
+        {
+            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<int, CopyResolver> copyResolvers = new Dictionary<int, CopyResolver>();
+
+            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<int, CopyResolver> kv in copyResolvers)
+            {
+                CopyResolver copyResolver = kv.Value;
+
+                if (!copyResolver.HasCopy)
+                {
+                    continue;
+                }
+
+                int splitPosition = kv.Key;
+
+                (IntrusiveList<Operation> 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>, Operation) GetOperationNode(int position)
+        {
+            return _operationNodes[position / InstructionGap];
+        }
+
+        private void NumberLocals(ControlFlowGraph cfg, int registersCount)
+        {
+            _operationNodes = new List<(IntrusiveList<Operation>, Operation)>();
+            _intervals = new List<LiveInterval>();
+
+            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<int>();
+
+            // 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)];
+
+                        if (interval.IsFixed)
+                        {
+                            interval.IsFixedAndUsed = true;
+                        }
+
+                        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;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/ARMeilleure/CodeGen/RegisterAllocators/LiveInterval.cs b/src/ARMeilleure/CodeGen/RegisterAllocators/LiveInterval.cs
new file mode 100644
index 00000000..d739ad28
--- /dev/null
+++ b/src/ARMeilleure/CodeGen/RegisterAllocators/LiveInterval.cs
@@ -0,0 +1,396 @@
+using ARMeilleure.IntermediateRepresentation;
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+
+namespace ARMeilleure.CodeGen.RegisterAllocators
+{
+    unsafe readonly struct LiveInterval : IComparable<LiveInterval>
+    {
+        public const int NotFound = -1;
+
+        private struct Data
+        {
+            public int End;
+            public int SpillOffset;
+
+            public LiveRange FirstRange;
+            public LiveRange PrevRange;
+            public LiveRange CurrRange;
+
+            public LiveInterval Parent;
+
+            public UseList Uses;
+            public LiveIntervalList Children;
+
+            public Operand Local;
+            public Register Register;
+
+            public bool IsFixed;
+            public bool IsFixedAndUsed;
+        }
+
+        private readonly Data* _data;
+
+        private ref int End => ref _data->End;
+        private ref LiveRange FirstRange => ref _data->FirstRange;
+        private ref LiveRange CurrRange => ref _data->CurrRange;
+        private ref LiveRange PrevRange => ref _data->PrevRange;
+        private ref LiveInterval Parent => ref _data->Parent;
+        private ref UseList Uses => ref _data->Uses;
+        private ref LiveIntervalList Children => ref _data->Children;
+
+        public Operand Local => _data->Local;
+        public ref Register Register => ref _data->Register;
+        public ref int SpillOffset => ref _data->SpillOffset;
+
+        public bool IsFixed => _data->IsFixed;
+        public ref bool IsFixedAndUsed => ref _data->IsFixedAndUsed;
+        public bool IsEmpty => FirstRange == default;
+        public bool IsSplit => Children.Count != 0;
+        public bool IsSpilled => SpillOffset != -1;
+
+        public int UsesCount => Uses.Count;
+
+        public LiveInterval(Operand local = default, LiveInterval parent = default)
+        {
+            _data = Allocators.LiveIntervals.Allocate<Data>();
+            *_data = default;
+
+            _data->IsFixed = false;
+            _data->Local = local;
+
+            Parent = parent == default ? this : parent;
+            Uses = new UseList();
+            Children = new LiveIntervalList();
+
+            FirstRange = default;
+            CurrRange = default;
+            PrevRange = default;
+
+            SpillOffset = -1;
+        }
+
+        public LiveInterval(Register register) : this(local: default, parent: default)
+        {
+            _data->IsFixed = true;
+
+            Register = register;
+        }
+
+        public void Reset()
+        {
+            PrevRange = default;
+            CurrRange = FirstRange;
+        }
+
+        public void Forward(int position)
+        {
+            LiveRange prev = PrevRange;
+            LiveRange curr = CurrRange;
+
+            while (curr != default && curr.Start < position && !curr.Overlaps(position))
+            {
+                prev = curr;
+                curr = curr.Next;
+            }
+
+            PrevRange = prev;
+            CurrRange = curr;
+        }
+
+        public int GetStart()
+        {
+            Debug.Assert(!IsEmpty, "Empty LiveInterval cannot have a start position.");
+
+            return FirstRange.Start;
+        }
+
+        public void SetStart(int position)
+        {
+            if (FirstRange != default)
+            {
+                Debug.Assert(position != FirstRange.End);
+
+                FirstRange.Start = position;
+            }
+            else
+            {
+                FirstRange = new LiveRange(position, position + 1);
+                End = position + 1;
+            }
+        }
+
+        public int GetEnd()
+        {
+            Debug.Assert(!IsEmpty, "Empty LiveInterval cannot have an end position.");
+
+            return End;
+        }
+
+        public void AddRange(int start, int end)
+        {
+            Debug.Assert(start < end, $"Invalid range start position {start}, {end}");
+
+            if (FirstRange != default)
+            {
+                // If the new range ends exactly where the first range start, then coalesce together.
+                if (end == FirstRange.Start)
+                {
+                    FirstRange.Start = start;
+
+                    return;
+                }
+                // If the new range is already contained, then coalesce together.
+                else if (FirstRange.Overlaps(start, end))
+                {
+                    FirstRange.Start = Math.Min(FirstRange.Start, start);
+                    FirstRange.End = Math.Max(FirstRange.End, end);
+                    End = Math.Max(End, end);
+
+                    Debug.Assert(FirstRange.Next == default || !FirstRange.Overlaps(FirstRange.Next));
+                    return;
+                }
+            }
+
+            FirstRange = new LiveRange(start, end, FirstRange);
+            End = Math.Max(End, end);
+
+            Debug.Assert(FirstRange.Next == default || !FirstRange.Overlaps(FirstRange.Next));
+        }
+
+        public void AddUsePosition(int position)
+        {
+            Uses.Add(position);
+        }
+
+        public bool Overlaps(int position)
+        {
+            LiveRange curr = CurrRange;
+
+            while (curr != default && curr.Start <= position)
+            {
+                if (curr.Overlaps(position))
+                {
+                    return true;
+                }
+
+                curr = curr.Next;
+            }
+
+            return false;
+        }
+
+        public bool Overlaps(LiveInterval other)
+        {
+            return GetOverlapPosition(other) != NotFound;
+        }
+
+        public int GetOverlapPosition(LiveInterval other)
+        {
+            LiveRange a = CurrRange;
+            LiveRange b = other.CurrRange;
+
+            while (a != default)
+            {
+                while (b != default && b.Start < a.Start)
+                {
+                    if (a.Overlaps(b))
+                    {
+                        return a.Start;
+                    }
+
+                    b = b.Next;
+                }
+
+                if (b == default)
+                {
+                    break;
+                }
+                else if (a.Overlaps(b))
+                {
+                    return a.Start;
+                }
+
+                a = a.Next;
+            }
+
+            return NotFound;
+        }
+
+        public ReadOnlySpan<LiveInterval> SplitChildren()
+        {
+            return Parent.Children.Span;
+        }
+
+        public ReadOnlySpan<int> UsePositions()
+        {
+            return Uses.Span;
+        }
+
+        public int FirstUse()
+        {
+            return Uses.FirstUse;
+        }
+
+        public int NextUseAfter(int position)
+        {
+            return Uses.NextUse(position);
+        }
+
+        public LiveInterval Split(int position)
+        {
+            LiveInterval result = new(Local, Parent);
+            result.End = End;
+
+            LiveRange prev = PrevRange;
+            LiveRange curr = CurrRange;
+
+            while (curr != default && curr.Start < position && !curr.Overlaps(position))
+            {
+                prev = curr;
+                curr = curr.Next;
+            }
+
+            if (curr.Start >= position)
+            {
+                prev.Next = default;
+
+                result.FirstRange = curr;
+
+                End = prev.End;
+            }
+            else
+            {
+                result.FirstRange = new LiveRange(position, curr.End, curr.Next);
+
+                curr.End = position;
+                curr.Next = default;
+
+                End = curr.End;
+            }
+
+            result.Uses = Uses.Split(position);
+
+            AddSplitChild(result);
+
+            Debug.Assert(!IsEmpty, "Left interval is empty after split.");
+            Debug.Assert(!result.IsEmpty, "Right interval is empty after split.");
+
+            // Make sure the iterator in the new split is pointing to the start.
+            result.Reset();
+
+            return result;
+        }
+
+        private void AddSplitChild(LiveInterval child)
+        {
+            Debug.Assert(!child.IsEmpty, "Trying to insert an empty interval.");
+
+            Parent.Children.Add(child);
+        }
+
+        public LiveInterval GetSplitChild(int position)
+        {
+            if (Overlaps(position))
+            {
+                return this;
+            }
+
+            foreach (LiveInterval splitChild in SplitChildren())
+            {
+                if (splitChild.Overlaps(position))
+                {
+                    return splitChild;
+                }
+                else if (splitChild.GetStart() > position)
+                {
+                    break;
+                }
+            }
+
+            return default;
+        }
+
+        public bool TrySpillWithSiblingOffset()
+        {
+            foreach (LiveInterval splitChild in SplitChildren())
+            {
+                if (splitChild.IsSpilled)
+                {
+                    Spill(splitChild.SpillOffset);
+
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        public void Spill(int offset)
+        {
+            SpillOffset = offset;
+        }
+
+        public int CompareTo(LiveInterval interval)
+        {
+            if (FirstRange == default || interval.FirstRange == default)
+            {
+                return 0;
+            }
+
+            return GetStart().CompareTo(interval.GetStart());
+        }
+
+        public bool Equals(LiveInterval interval)
+        {
+            return interval._data == _data;
+        }
+
+        public override bool Equals(object obj)
+        {
+            return obj is LiveInterval interval && Equals(interval);
+        }
+
+        public static bool operator ==(LiveInterval a, LiveInterval b)
+        {
+            return a.Equals(b);
+        }
+
+        public static bool operator !=(LiveInterval a, LiveInterval b)
+        {
+            return !a.Equals(b);
+        }
+
+        public override int GetHashCode()
+        {
+            return HashCode.Combine((IntPtr)_data);
+        }
+
+        public override string ToString()
+        {
+            LiveInterval self = this;
+
+            IEnumerable<string> GetRanges()
+            {
+                LiveRange curr = self.CurrRange;
+
+                while (curr != default)
+                {
+                    if (curr == self.CurrRange)
+                    {
+                        yield return "*" + curr;
+                    }
+                    else
+                    {
+                        yield return curr.ToString();
+                    }
+
+                    curr = curr.Next;
+                }
+            }
+
+            return string.Join(", ", GetRanges());
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/ARMeilleure/CodeGen/RegisterAllocators/LiveIntervalList.cs b/src/ARMeilleure/CodeGen/RegisterAllocators/LiveIntervalList.cs
new file mode 100644
index 00000000..06b979ea
--- /dev/null
+++ b/src/ARMeilleure/CodeGen/RegisterAllocators/LiveIntervalList.cs
@@ -0,0 +1,40 @@
+using System;
+
+namespace ARMeilleure.CodeGen.RegisterAllocators
+{
+    unsafe struct LiveIntervalList
+    {
+        private LiveInterval* _items;
+        private int _count;
+        private int _capacity;
+
+        public int Count => _count;
+        public Span<LiveInterval> Span => new(_items, _count);
+
+        public void Add(LiveInterval interval)
+        {
+            if (_count + 1 > _capacity)
+            {
+                var oldSpan = Span;
+
+                _capacity = Math.Max(4, _capacity * 2);
+                _items = Allocators.References.Allocate<LiveInterval>((uint)_capacity);
+
+                var newSpan = Span;
+
+                oldSpan.CopyTo(newSpan);
+            }
+
+            int position = interval.GetStart();
+            int i = _count - 1;
+
+            while (i >= 0 && _items[i].GetStart() > position)
+            {
+                _items[i + 1] = _items[i--];
+            }
+
+            _items[i + 1] = interval;
+            _count++;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/ARMeilleure/CodeGen/RegisterAllocators/LiveRange.cs b/src/ARMeilleure/CodeGen/RegisterAllocators/LiveRange.cs
new file mode 100644
index 00000000..e38b5190
--- /dev/null
+++ b/src/ARMeilleure/CodeGen/RegisterAllocators/LiveRange.cs
@@ -0,0 +1,74 @@
+using System;
+
+namespace ARMeilleure.CodeGen.RegisterAllocators
+{
+    unsafe readonly struct LiveRange : IEquatable<LiveRange>
+    {
+        private struct Data
+        {
+            public int Start;
+            public int End;
+            public LiveRange Next;
+        }
+
+        private readonly Data* _data;
+
+        public ref int Start => ref _data->Start;
+        public ref int End => ref _data->End;
+        public ref LiveRange Next => ref _data->Next;
+
+        public LiveRange(int start, int end, LiveRange next = default)
+        {
+            _data = Allocators.LiveRanges.Allocate<Data>();
+
+            Start = start;
+            End = end;
+            Next = next;
+        }
+
+        public bool Overlaps(int start, int end)
+        {
+            return Start < end && start < End;
+        }
+
+        public bool Overlaps(LiveRange range)
+        {
+            return Start < range.End && range.Start < End;
+        }
+
+        public bool Overlaps(int position)
+        {
+            return position >= Start && position < End;
+        }
+
+        public bool Equals(LiveRange range)
+        {
+            return range._data == _data;
+        }
+
+        public override bool Equals(object obj)
+        {
+            return obj is LiveRange range && Equals(range);
+        }
+
+        public static bool operator ==(LiveRange a, LiveRange b)
+        {
+            return a.Equals(b);
+        }
+
+        public static bool operator !=(LiveRange a, LiveRange b)
+        {
+            return !a.Equals(b);
+        }
+
+        public override int GetHashCode()
+        {
+            return HashCode.Combine((IntPtr)_data);
+        }
+
+        public override string ToString()
+        {
+            return $"[{Start}, {End})";
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/ARMeilleure/CodeGen/RegisterAllocators/RegisterMasks.cs b/src/ARMeilleure/CodeGen/RegisterAllocators/RegisterMasks.cs
new file mode 100644
index 00000000..bc948f95
--- /dev/null
+++ b/src/ARMeilleure/CodeGen/RegisterAllocators/RegisterMasks.cs
@@ -0,0 +1,50 @@
+using ARMeilleure.IntermediateRepresentation;
+using System;
+
+namespace ARMeilleure.CodeGen.RegisterAllocators
+{
+    readonly struct RegisterMasks
+    {
+        public int IntAvailableRegisters   { get; }
+        public int VecAvailableRegisters   { get; }
+        public int IntCallerSavedRegisters { get; }
+        public int VecCallerSavedRegisters { get; }
+        public int IntCalleeSavedRegisters { get; }
+        public int VecCalleeSavedRegisters { get; }
+        public int RegistersCount { get; }
+
+        public RegisterMasks(
+            int intAvailableRegisters,
+            int vecAvailableRegisters,
+            int intCallerSavedRegisters,
+            int vecCallerSavedRegisters,
+            int intCalleeSavedRegisters,
+            int vecCalleeSavedRegisters,
+            int registersCount)
+        {
+            IntAvailableRegisters   = intAvailableRegisters;
+            VecAvailableRegisters   = vecAvailableRegisters;
+            IntCallerSavedRegisters = intCallerSavedRegisters;
+            VecCallerSavedRegisters = vecCallerSavedRegisters;
+            IntCalleeSavedRegisters = intCalleeSavedRegisters;
+            VecCalleeSavedRegisters = vecCalleeSavedRegisters;
+            RegistersCount          = registersCount;
+        }
+
+        public int GetAvailableRegisters(RegisterType type)
+        {
+            if (type == RegisterType.Integer)
+            {
+                return IntAvailableRegisters;
+            }
+            else if (type == RegisterType.Vector)
+            {
+                return VecAvailableRegisters;
+            }
+            else
+            {
+                throw new ArgumentException($"Invalid register type \"{type}\".");
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/ARMeilleure/CodeGen/RegisterAllocators/StackAllocator.cs b/src/ARMeilleure/CodeGen/RegisterAllocators/StackAllocator.cs
new file mode 100644
index 00000000..038312fe
--- /dev/null
+++ b/src/ARMeilleure/CodeGen/RegisterAllocators/StackAllocator.cs
@@ -0,0 +1,25 @@
+using ARMeilleure.IntermediateRepresentation;
+
+namespace ARMeilleure.CodeGen.RegisterAllocators
+{
+    class StackAllocator
+    {
+        private int _offset;
+
+        public int TotalSize => _offset;
+
+        public int Allocate(OperandType type)
+        {
+            return Allocate(type.GetSizeInBytes());
+        }
+
+        public int Allocate(int sizeInBytes)
+        {
+            int offset = _offset;
+
+            _offset += sizeInBytes;
+
+            return offset;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/ARMeilleure/CodeGen/RegisterAllocators/UseList.cs b/src/ARMeilleure/CodeGen/RegisterAllocators/UseList.cs
new file mode 100644
index 00000000..c89f0854
--- /dev/null
+++ b/src/ARMeilleure/CodeGen/RegisterAllocators/UseList.cs
@@ -0,0 +1,84 @@
+using System;
+
+namespace ARMeilleure.CodeGen.RegisterAllocators
+{
+    unsafe struct UseList
+    {
+        private int* _items;
+        private int _capacity;
+        private int _count;
+
+        public int Count => _count;
+        public int FirstUse => _count > 0 ? _items[_count - 1] : LiveInterval.NotFound;
+        public Span<int> Span => new(_items, _count);
+
+        public void Add(int position)
+        {
+            if (_count + 1 > _capacity)
+            {
+                var oldSpan = Span;
+
+                _capacity = Math.Max(4, _capacity * 2);
+                _items = Allocators.Default.Allocate<int>((uint)_capacity);
+
+                var newSpan = Span;
+
+                oldSpan.CopyTo(newSpan);
+            }
+
+            // Use positions are usually inserted in descending order, so inserting in descending order is faster,
+            // since the number of half exchanges is reduced.
+            int i = _count - 1;
+
+            while (i >= 0 && _items[i] < position)
+            {
+                _items[i + 1] = _items[i--];
+            }
+
+            _items[i + 1] = position;
+            _count++;
+        }
+
+        public int NextUse(int position)
+        {
+            int index = NextUseIndex(position);
+
+            return index != LiveInterval.NotFound ? _items[index] : LiveInterval.NotFound;
+        }
+
+        public int NextUseIndex(int position)
+        {
+            int i = _count - 1;
+
+            if (i == -1 || position > _items[0])
+            {
+                return LiveInterval.NotFound;
+            }
+
+            while (i >= 0 && _items[i] < position)
+            {
+                i--;
+            }
+
+            return i;
+        }
+
+        public UseList Split(int position)
+        {
+            int index = NextUseIndex(position);
+
+            // Since the list is in descending order, the new split list takes the front of the list and the current
+            // list takes the back of the list.
+            UseList result = new();
+            result._count = index + 1;
+            result._capacity = result._count;
+            result._items = _items;
+
+            _count = _count - result._count;
+            _capacity = _count;
+            _items = _items + result._count;
+
+            return result;
+        }
+    }
+}
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