Changed TensorSpan and ReadOnlyTensorSpan layout for better performan…

…ce. (dotnet#103244)

* TensorShape

* fixed TensorShape issue

* removed extra inline buffer type. Fixed tests. Added large dimension testing

* removed typo

* adding unsaved files

* changes to use const for stack alloc comparison

* changes from pr comments

src/libraries/System.Numerics.Tensors/src/System.Numerics.Tensors.csproj

@@ -16,6 +16,7 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'">
+    <Compile Include="System\Numerics\Tensors\netcore\TensorShape.cs" />
     <Compile Include="System\Numerics\Tensors\netcore\TensorHelpers.cs" />
     <Compile Include="System\Numerics\Tensors\netcore\TensorExtensions.cs" />
     <Compile Include="System\Numerics\Tensors\netcore\Tensor.Factory.cs" />

src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/Tensor.Factory.cs

@@ -153,16 +153,16 @@ public static Tensor<T> CreateUninitialized<T>(scoped ReadOnlySpan<nint> lengths
 
         public static ref readonly TensorSpan<T> FillGaussianNormalDistribution<T>(in TensorSpan<T> destination) where T : IFloatingPoint<T>
         {
-            Span<T> span = MemoryMarshal.CreateSpan<T>(ref destination._reference, (int)destination._flattenedLength);
+            Span<T> span = MemoryMarshal.CreateSpan<T>(ref destination._reference, (int)destination._shape._memoryLength);
 
-            GaussianDistribution<T>(span, destination._flattenedLength);
+            GaussianDistribution<T>(span, destination._shape._memoryLength);
 
             return ref destination;
         }
 
         public static ref readonly TensorSpan<T> FillUniformDistribution<T>(in TensorSpan<T> destination) where T : IFloatingPoint<T>
         {
-            Span<T> span = MemoryMarshal.CreateSpan<T>(ref destination._reference, (int)destination._flattenedLength);
+            Span<T> span = MemoryMarshal.CreateSpan<T>(ref destination._reference, (int)destination._shape._memoryLength);
 
             for (int i = 0; i < span.Length; i++)
                 span[i] = T.CreateChecked(Random.Shared.NextDouble());

src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorHelpers.cs

@@ -17,7 +17,7 @@ internal static class TensorHelpers
         /// <returns>How many boolean values are true.</returns>
         public static nint CountTrueElements(scoped in ReadOnlyTensorSpan<bool> filter)
         {
-            Span<bool> filterSpan = MemoryMarshal.CreateSpan(ref filter._reference, (int)filter._flattenedLength);
+            Span<bool> filterSpan = MemoryMarshal.CreateSpan(ref filter._reference, (int)filter._shape._memoryLength);
             nint count = 0;
             for (int i = 0; i < filterSpan.Length; i++)
             {
@@ -83,11 +83,14 @@ internal static nint[] GetIntermediateShape(ReadOnlySpan<nint> shape1, int shape
             return newShape;
         }
 
+        internal static bool IsUnderlyingStorageSameSize<T>(scoped in ReadOnlyTensorSpan<T> tensor1, scoped in ReadOnlyTensorSpan<T> tensor2)
+            => tensor1._shape._memoryLength == tensor2._shape._memoryLength;
+
         internal static bool IsUnderlyingStorageSameSize<T>(Tensor<T> tensor1, Tensor<T> tensor2)
-            => tensor1.Lengths.Length == tensor2.Lengths.Length;
+    => tensor1._values.Length == tensor2._values.Length;
 
-        internal static bool AreLengthsTheSame<T>(ReadOnlyTensorSpan<T> tensor1, ReadOnlyTensorSpan<T> tensor2)
-            => tensor1._lengths.SequenceEqual(tensor2._lengths);
+        internal static bool AreLengthsTheSame<T>(scoped in ReadOnlyTensorSpan<T> tensor1, scoped in ReadOnlyTensorSpan<T> tensor2)
+            => tensor1.Lengths.SequenceEqual(tensor2.Lengths);
 
         internal static bool AreLengthsTheSame(ReadOnlySpan<nint> lengths1, ReadOnlySpan<nint> lengths2)
             => lengths1.SequenceEqual(lengths2);

src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorShape.cs

@@ -0,0 +1,64 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace System.Numerics.Tensors
+{
+    internal readonly struct TensorShape
+    {
+        // Used to determine when we need to allocate a metadata array
+        public const int MaxInlineArraySize = 5;
+
+        // Used to determine when we can stack alloc for indexing vs when we need to allocate
+        public const int MaxInlineRank = 8;
+
+        internal readonly nint[]? _metadata;      // 8 bytes
+
+        internal readonly nint _memoryLength;   // 8 bytes
+        internal readonly int _rank;              // 4 bytes
+
+        private readonly NintBuffer _lengths;
+        private readonly NintBuffer _strides;
+
+        internal TensorShape(nint memoryLength, ReadOnlySpan<nint> lengths, ReadOnlySpan<nint> strides)
+        {
+            _memoryLength = memoryLength;
+            _rank = lengths.Length;
+            if (lengths.Length > MaxInlineArraySize)
+            {
+                _metadata = new nint[lengths.Length + strides.Length];
+                lengths.CopyTo(MemoryMarshal.CreateSpan(ref _metadata[0], lengths.Length));
+                strides.CopyTo(MemoryMarshal.CreateSpan(ref _metadata[lengths.Length], strides.Length));
+            }
+            else
+            {
+                lengths.CopyTo(_lengths);
+                strides.CopyTo(_strides);
+            }
+        }
+
+        [InlineArray(MaxInlineArraySize)] // 5x8 bytes (40)
+        private struct NintBuffer
+        {
+            public nint e0;
+        }
+
+        [UnscopedRef]
+        public ReadOnlySpan<nint> Lengths => (_metadata is null)
+                                           ? ((ReadOnlySpan<nint>)_lengths).Slice(0, _rank)
+                                           : MemoryMarshal.CreateReadOnlySpan(ref MemoryMarshal.GetArrayDataReference(_metadata), _rank);
+
+        [UnscopedRef]
+        public ReadOnlySpan<nint> Strides => (_metadata is null)
+                                           ? ((ReadOnlySpan<nint>)_strides).Slice(0, _rank)
+                                           : MemoryMarshal.CreateReadOnlySpan(ref MemoryMarshal.GetArrayDataReference(_metadata), _rank * 2).Slice(_rank);
+
+        public nint FlattenedLength => TensorSpanHelpers.CalculateTotalLength(Lengths);
+
+        public bool IsEmpty => FlattenedLength == 0;
+    }
+}