CodeGen Optimisations (LSRA and Translator) (#978)

* Start of JIT garbage collection improvements

- thread static pool for Operand, MemoryOperand, Operation
- Operands and Operations are always to be constructed via their static
helper classes, so they can be pooled.
- removing LinkedList from Node for sources/destinations (replaced with
List<>s for now, but probably could do arrays since size is bounded)
- removing params constructors from Node
- LinkedList<> to List<> with Clear() for Operand assignments/uses
- ThreadStaticPool is very simple and basically just exists for the
purpose of our specific translation allocation problem. Right now it
will stay at the worst case allocation count for that thread (so far) -
the pool can never shrink.

- Still some cases of Operand[] that haven't been removed yet. Will need
to evaluate them (eg. is there a reasonable max number of params for
Calls?)

* ConcurrentStack instead of ConcurrentQueue for Rejit

* Optimize some parts of LSRA

- BitMap now operates on 64-bit int rather than 32-bit
- BitMap is now pooled in a ThreadStatic pool (within lrsa)
- BitMap now is now its own iterator. Marginally speeds up iterating
through the bits.
- A few cases where enumerators were generated have been converted to
forms that generate less garbage.
- New data structure for sorting _usePositions in LiveIntervals. Much
faster split, NextUseAfter, initial insertion. Random insertion is
slightly slower.
- That last one is WIP since you need to insert the values backwards. It
would be ideal if it just flipped it for you, uncomplicating things on
the caller side.

* Use a static pool of thread static pools. (yes.)

Prevents each execution thread creating its own lowCq pool and making me cry.

* Move constant value to top, change naming convention.

* Fix iteration of memory operands.

* Increase max thread count.

* Address Feedback

4 files changed, 89 insertions, 77 deletions

diff --git a/ARMeilleure/CodeGen/RegisterAllocators/CopyResolver.cs b/ARMeilleure/CodeGen/RegisterAllocators/CopyResolver.cs
index 65901e80..417f3bae 100644
--- a/ARMeilleure/CodeGen/RegisterAllocators/CopyResolver.cs
+++ b/ARMeilleure/CodeGen/RegisterAllocators/CopyResolver.cs
@@ -2,6 +2,9 @@ using ARMeilleure.IntermediateRepresentation;
 using System;
 using System.Collections.Generic;
 
+using static ARMeilleure.IntermediateRepresentation.OperandHelper;
+using static ARMeilleure.IntermediateRepresentation.OperationHelper;
+
 namespace ARMeilleure.CodeGen.RegisterAllocators
 {
     class CopyResolver
@@ -133,14 +136,14 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
             private static void EmitCopy(List<Operation> sequence, Operand x, Operand y)
             {
-                sequence.Add(new Operation(Instruction.Copy, x, y));
+                sequence.Add(Operation(Instruction.Copy, x, y));
             }
 
             private static void EmitXorSwap(List<Operation> sequence, Operand x, Operand y)
             {
-                sequence.Add(new Operation(Instruction.BitwiseExclusiveOr, x, x, y));
-                sequence.Add(new Operation(Instruction.BitwiseExclusiveOr, y, y, x));
-                sequence.Add(new Operation(Instruction.BitwiseExclusiveOr, x, x, 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));
             }
         }
 
@@ -194,20 +197,20 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
         {
             Operand register = GetRegister(right.Register, type);
 
-            Operand offset = new Operand(left.SpillOffset);
+            Operand offset = Const(left.SpillOffset);
 
-            _fillQueue.Enqueue(new Operation(Instruction.Fill, register, offset));
+            _fillQueue.Enqueue(Operation(Instruction.Fill, register, offset));
 
             HasCopy = true;
         }
 
         private void AddSplitSpill(LiveInterval left, LiveInterval right, OperandType type)
         {
-            Operand offset = new Operand(right.SpillOffset);
+            Operand offset = Const(right.SpillOffset);
 
             Operand register = GetRegister(left.Register, type);
 
-            _spillQueue.Enqueue(new Operation(Instruction.Spill, null, offset, register));
+            _spillQueue.Enqueue(Operation(Instruction.Spill, null, offset, register));
 
             HasCopy = true;
         }
@@ -240,7 +243,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
         private static Operand GetRegister(Register reg, OperandType type)
         {
-            return new Operand(reg.Index, reg.Type, type);
+            return Register(reg.Index, reg.Type, type);
         }
     }
 }
\ No newline at end of file
diff --git a/ARMeilleure/CodeGen/RegisterAllocators/HybridAllocator.cs b/ARMeilleure/CodeGen/RegisterAllocators/HybridAllocator.cs
index ce7936f9..21470a66 100644
--- a/ARMeilleure/CodeGen/RegisterAllocators/HybridAllocator.cs
+++ b/ARMeilleure/CodeGen/RegisterAllocators/HybridAllocator.cs
@@ -1,10 +1,11 @@
-using ARMeilleure.Common;
 using ARMeilleure.IntermediateRepresentation;
 using ARMeilleure.Translation;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Numerics;
 
 using static ARMeilleure.IntermediateRepresentation.OperandHelper;
+using static ARMeilleure.IntermediateRepresentation.OperationHelper;
 
 namespace ARMeilleure.CodeGen.RegisterAllocators
 {
@@ -265,7 +266,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
                                 node.SetSource(srcIndex, temp);
                             }
 
-                            Operation fillOp = new Operation(Instruction.Fill, temp, Const(info.SpillOffset));
+                            Operation fillOp = Operation(Instruction.Fill, temp, Const(info.SpillOffset));
 
                             block.Operations.AddBefore(node, fillOp);
                         }
@@ -317,7 +318,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
                             if (info.IsBlockLocal && mask != 0)
                             {
-                                int selectedReg = BitUtils.LowestBitSet(mask);
+                                int selectedReg = BitOperations.TrailingZeroCount(mask);
 
                                 info.Register = selectedReg;
 
@@ -363,7 +364,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
                             node.SetDestination(dstIndex, temp);
 
-                            Operation spillOp = new Operation(Instruction.Spill, null, Const(info.SpillOffset), temp);
+                            Operation spillOp = Operation(Instruction.Spill, null, Const(info.SpillOffset), temp);
 
                             block.Operations.AddAfter(node, spillOp);
 
@@ -415,7 +416,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
         private static Operand GetSpillTemp(Operand local, int freeMask, ref int useMask)
         {
-            int selectedReg = BitUtils.LowestBitSet(freeMask & ~useMask);
+            int selectedReg = BitOperations.TrailingZeroCount(freeMask & ~useMask);
 
             useMask |= 1 << selectedReg;
 
diff --git a/ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs b/ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs
index 1dc6ad73..01bb9554 100644
--- a/ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs
+++ b/ARMeilleure/CodeGen/RegisterAllocators/LinearScanAllocator.cs
@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Numerics;
 
 namespace ARMeilleure.CodeGen.RegisterAllocators
 {
@@ -32,7 +33,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
         private int _operationsCount;
 
-        private class AllocationContext
+        private class AllocationContext : IDisposable
         {
             public RegisterMasks Masks { get; }
 
@@ -49,8 +50,8 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
                 StackAlloc = stackAlloc;
                 Masks      = masks;
 
-                Active   = new BitMap(intervalsCount);
-                Inactive = new BitMap(intervalsCount);
+                Active   = BitMapPool.Allocate(intervalsCount);
+                Inactive = BitMapPool.Allocate(intervalsCount);
             }
 
             public void MoveActiveToInactive(int bit)
@@ -69,6 +70,11 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
                 dest.Set(bit);
             }
+
+            public void Dispose()
+            {
+                BitMapPool.Release();
+            }
         }
 
         public AllocationResult RunPass(
@@ -121,10 +127,14 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
             InsertSplitCopies();
             InsertSplitCopiesAtEdges(cfg);
 
-            return new AllocationResult(
+            AllocationResult result = new AllocationResult(
                 context.IntUsedRegisters,
                 context.VecUsedRegisters,
                 context.StackAlloc.TotalSize);
+
+            context.Dispose();
+
+            return result;
         }
 
         private void AllocateInterval(AllocationContext context, LiveInterval current, int cIndex)
@@ -618,15 +628,22 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
                 bool hasSingleOrNoSuccessor = block.Next == null || block.Branch == null;
 
-                foreach (BasicBlock successor in Successors(block))
+                for (int i = 0; i < 2; i++)
                 {
+                    // This used to use an enumerable, but it ended up generating a lot of garbage, so now it is a loop.
+                    BasicBlock successor = (i == 0) ? block.Next : block.Branch;
+                    if (successor == null)
+                    {
+                        continue;
+                    }
+
                     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 = Successors(successor).First().Index;
+                        succIndex = FirstSuccessor(successor).Index;
                     }
 
                     CopyResolver copyResolver = new CopyResolver();
@@ -699,8 +716,10 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
         {
             Operand register = GetRegister(current);
 
-            foreach (int usePosition in current.UsePositions())
+            IList<int> usePositions = current.UsePositions();
+            for (int i = usePositions.Count - 1; i >= 0; i--)
             {
+                int usePosition = -usePositions[i];
                 (_, Node operation) = GetOperationNode(usePosition);
 
                 for (int index = 0; index < operation.SourcesCount; index++)
@@ -743,7 +762,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
         {
             Debug.Assert(!interval.IsSpilled, "Spilled intervals are not allowed.");
 
-            return new Operand(
+            return OperandHelper.Register(
                 interval.Register.Index,
                 interval.Register.Type,
                 interval.Local.Type);
@@ -778,8 +797,9 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
                 {
                     _operationNodes.Add((block.Operations, node));
 
-                    foreach (Operand dest in Destinations(node))
+                    for (int i = 0; i < node.DestinationsCount; i++)
                     {
+                        Operand dest = node.GetDestination(i);
                         if (dest.Kind == OperandKind.LocalVariable && visited.Add(dest))
                         {
                             dest.NumberLocal(_intervals.Count);
@@ -815,12 +835,12 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
             // Compute local live sets.
             for (BasicBlock block = cfg.Blocks.First; block != null; block = block.ListNext)
             {
-                BitMap liveGen  = new BitMap(mapSize);
-                BitMap liveKill = new BitMap(mapSize);
+                BitMap liveGen  = BitMapPool.Allocate(mapSize);
+                BitMap liveKill = BitMapPool.Allocate(mapSize);
 
                 for (Node node = block.Operations.First; node != null; node = node.ListNext)
                 {
-                    foreach (Operand source in Sources(node))
+                    Sources(node, (source) =>
                     {
                         int id = GetOperandId(source);
 
@@ -828,10 +848,11 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
                         {
                             liveGen.Set(id);
                         }
-                    }
+                    });
 
-                    foreach (Operand dest in Destinations(node))
+                    for (int i = 0; i < node.DestinationsCount; i++)
                     {
+                        Operand dest = node.GetDestination(i);
                         liveKill.Set(GetOperandId(dest));
                     }
                 }
@@ -846,8 +867,8 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
             for (int index = 0; index < cfg.Blocks.Count; index++)
             {
-                blkLiveIn [index] = new BitMap(mapSize);
-                blkLiveOut[index] = new BitMap(mapSize);
+                blkLiveIn [index] = BitMapPool.Allocate(mapSize);
+                blkLiveOut[index] = BitMapPool.Allocate(mapSize);
             }
 
             bool modified;
@@ -862,12 +883,10 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
                     BitMap liveOut = blkLiveOut[block.Index];
 
-                    foreach (BasicBlock successor in Successors(block))
+                    if ((block.Next != null && liveOut.Set(blkLiveIn[block.Next.Index])) || 
+                        (block.Branch != null && liveOut.Set(blkLiveIn[block.Branch.Index])))
                     {
-                        if (liveOut.Set(blkLiveIn[successor.Index]))
-                        {
-                            modified = true;
-                        }
+                        modified = true;
                     }
 
                     BitMap liveIn = blkLiveIn[block.Index];
@@ -920,21 +939,22 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
                 {
                     operationPos -= InstructionGap;
 
-                    foreach (Operand dest in Destinations(node))
+                    for (int i = 0; i < node.DestinationsCount; i++)
                     {
+                        Operand dest = node.GetDestination(i);
                         LiveInterval interval = _intervals[GetOperandId(dest)];
 
                         interval.SetStart(operationPos + 1);
                         interval.AddUsePosition(operationPos + 1);
                     }
 
-                    foreach (Operand source in Sources(node))
+                    Sources(node, (source) =>
                     {
                         LiveInterval interval = _intervals[GetOperandId(source)];
 
                         interval.AddRange(blockStart, operationPos + 1);
                         interval.AddUsePosition(operationPos);
-                    }
+                    });
 
                     if (node is Operation operation && operation.Instruction == Instruction.Call)
                     {
@@ -949,7 +969,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
         {
             while (mask != 0)
             {
-                int regIndex = BitUtils.LowestBitSet(mask);
+                int regIndex = BitOperations.TrailingZeroCount(mask);
 
                 Register callerSavedReg = new Register(regIndex, regType);
 
@@ -982,17 +1002,9 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
             return (register.Index << 1) | (register.Type == RegisterType.Vector ? 1 : 0);
         }
 
-        private static IEnumerable<BasicBlock> Successors(BasicBlock block)
+        private static BasicBlock FirstSuccessor(BasicBlock block)
         {
-            if (block.Next != null)
-            {
-                yield return block.Next;
-            }
-
-            if (block.Branch != null)
-            {
-                yield return block.Branch;
-            }
+            return block.Next ?? block.Branch;
         }
 
         private static IEnumerable<Node> BottomOperations(BasicBlock block)
@@ -1007,15 +1019,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
             }
         }
 
-        private static IEnumerable<Operand> Destinations(Node node)
-        {
-            for (int index = 0; index < node.DestinationsCount; index++)
-            {
-                yield return node.GetDestination(index);
-            }
-        }
-
-        private static IEnumerable<Operand> Sources(Node node)
+        private static void Sources(Node node, Action<Operand> action)
         {
             for (int index = 0; index < node.SourcesCount; index++)
             {
@@ -1023,7 +1027,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
                 if (IsLocalOrRegister(source.Kind))
                 {
-                    yield return source;
+                    action(source);
                 }
                 else if (source.Kind == OperandKind.Memory)
                 {
@@ -1031,12 +1035,12 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
                     if (memOp.BaseAddress != null)
                     {
-                        yield return memOp.BaseAddress;
+                        action(memOp.BaseAddress);
                     }
 
                     if (memOp.Index != null)
                     {
-                        yield return memOp.Index;
+                        action(memOp.Index);
                     }
                 }
             }
diff --git a/ARMeilleure/CodeGen/RegisterAllocators/LiveInterval.cs b/ARMeilleure/CodeGen/RegisterAllocators/LiveInterval.cs
index 18858a76..6e786061 100644
--- a/ARMeilleure/CodeGen/RegisterAllocators/LiveInterval.cs
+++ b/ARMeilleure/CodeGen/RegisterAllocators/LiveInterval.cs
@@ -1,3 +1,4 @@
+using ARMeilleure.Common;
 using ARMeilleure.IntermediateRepresentation;
 using System;
 using System.Collections.Generic;
@@ -12,7 +13,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
         private LiveInterval _parent;
 
-        private SortedSet<int> _usePositions;
+        private SortedIntegerList _usePositions;
 
         public int UsesCount => _usePositions.Count;
 
@@ -38,7 +39,7 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
             Local   = local;
             _parent = parent ?? this;
 
-            _usePositions = new SortedSet<int>();
+            _usePositions = new SortedIntegerList();
 
             _ranges = new List<LiveRange>();
 
@@ -196,7 +197,9 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
 
         public void AddUsePosition(int position)
         {
-            _usePositions.Add(position);
+            // Inserts are in descending order, but ascending is faster for SortedIntegerList<>.
+            // We flip the ordering, then iterate backwards when using the final list.
+            _usePositions.Add(-position);
         }
 
         public bool Overlaps(int position)
@@ -247,9 +250,9 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
             return _childs.Values;
         }
 
-        public IEnumerable<int> UsePositions()
+        public IList<int> UsePositions()
         {
-            return _usePositions;
+            return _usePositions.GetList();
         }
 
         public int FirstUse()
@@ -259,20 +262,19 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
                 return NotFound;
             }
 
-            return _usePositions.First();
+            return -_usePositions.Last();
         }
 
         public int NextUseAfter(int position)
         {
-            foreach (int usePosition in _usePositions)
-            {
-                if (usePosition >= position)
-                {
-                    return usePosition;
-                }
-            }
+            int index = _usePositions.FindLessEqualIndex(-position);
+            return (index >= 0) ? -_usePositions[index] : NotFound;
+        }
 
-            return NotFound;
+        public void RemoveAfter(int position)
+        {
+            int index = _usePositions.FindLessEqualIndex(-position);
+            _usePositions.RemoveRange(0, index + 1);
         }
 
         public LiveInterval Split(int position)
@@ -311,12 +313,14 @@ namespace ARMeilleure.CodeGen.RegisterAllocators
                 _ranges.RemoveRange(splitIndex, count);
             }
 
-            foreach (int usePosition in _usePositions.Where(x => x >= position))
+            int addAfter = _usePositions.FindLessEqualIndex(-position);
+            for (int index = addAfter; index >= 0; index--)
             {
+                int usePosition = _usePositions[index];
                 right._usePositions.Add(usePosition);
             }
 
-            _usePositions.RemoveWhere(x => x >= position);
+            RemoveAfter(position);
 
             Debug.Assert(_ranges.Count != 0, "Left interval is empty after split.");