Optimize some SegmentedArrayHelper members for JIT (#67558)

Author: EgorBo

src/Dependencies/Collections/Internal/SegmentedArrayHelper.cs

@@ -16,16 +16,12 @@ internal static class SegmentedArrayHelper
         // Large value types may benefit from a smaller number.
         internal const int IntrosortSizeThreshold = 16;
 
-        /// <summary>
-        /// A combination of <see cref="MethodImplOptions.AggressiveInlining"/> and
-        /// <see cref="F:System.Runtime.CompilerServices.MethodImplOptions.AggressiveOptimization"/>.
-        /// </summary>
-        [SuppressMessage("Documentation", "CA1200:Avoid using cref tags with a prefix", Justification = "The field is not supported in all compilation targets.")]
-        internal const MethodImplOptions FastPathMethodImplOptions = MethodImplOptions.AggressiveInlining | (MethodImplOptions)512;
-
-        [MethodImpl(FastPathMethodImplOptions)]
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal static int GetSegmentSize<T>()
         {
+#if NETCOREAPP3_0_OR_NEWER
+            return InlineCalculateSegmentSize(Unsafe.SizeOf<T>());
+#else
             if (Unsafe.SizeOf<T>() == Unsafe.SizeOf<object>())
             {
                 return ReferenceTypeSegmentHelper.SegmentSize;
@@ -34,11 +30,15 @@ internal static int GetSegmentSize<T>()
             {
                 return ValueTypeSegmentHelper<T>.SegmentSize;
             }
+#endif
         }
 
-        [MethodImpl(FastPathMethodImplOptions)]
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal static int GetSegmentShift<T>()
         {
+#if NETCOREAPP3_0_OR_NEWER
+            return InlineCalculateSegmentShift(Unsafe.SizeOf<T>());
+#else
             if (Unsafe.SizeOf<T>() == Unsafe.SizeOf<object>())
             {
                 return ReferenceTypeSegmentHelper.SegmentShift;
@@ -47,11 +47,15 @@ internal static int GetSegmentShift<T>()
             {
                 return ValueTypeSegmentHelper<T>.SegmentShift;
             }
+#endif
         }
 
-        [MethodImpl(FastPathMethodImplOptions)]
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal static int GetOffsetMask<T>()
         {
+#if NETCOREAPP3_0_OR_NEWER
+            return InlineCalculateOffsetMask(Unsafe.SizeOf<T>());
+#else
             if (Unsafe.SizeOf<T>() == Unsafe.SizeOf<object>())
             {
                 return ReferenceTypeSegmentHelper.OffsetMask;
@@ -60,6 +64,7 @@ internal static int GetOffsetMask<T>()
             {
                 return ValueTypeSegmentHelper<T>.OffsetMask;
             }
+#endif
         }
 
         /// <summary>
@@ -121,6 +126,31 @@ private static int CalculateOffsetMask(int segmentSize)
             return segmentSize - 1;
         }
 
+        // Faster inline implementation for NETCOREAPP to avoid static constructors and non-inlineable
+        // generics with runtime lookups
+#if NETCOREAPP3_0_OR_NEWER
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static int InlineCalculateSegmentSize(int elementSize)
+        {
+            return 1 << InlineCalculateSegmentShift(elementSize);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static int InlineCalculateSegmentShift(int elementSize)
+        {
+            // Default Large Object Heap size threshold
+            // https://github.com/dotnet/runtime/blob/c9d69e38d0e54bea5d188593ef6c3b30139f3ab1/src/coreclr/src/gc/gc.h#L111
+            const uint Threshold = 85000;
+            return System.Numerics.BitOperations.Log2((uint)((Threshold / elementSize) - (2 * Unsafe.SizeOf<object>())));
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static int InlineCalculateOffsetMask(int elementSize)
+        {
+            return InlineCalculateSegmentSize(elementSize) - 1;
+        }
+#endif
+
         internal static class TestAccessor
         {
             public static int CalculateSegmentSize(int elementSize)

src/Dependencies/Collections/SegmentedArray`1.cs

@@ -32,7 +32,6 @@ namespace Microsoft.CodeAnalysis.Collections
         /// </remarks>
         private static int SegmentSize
         {
-            [MethodImpl(SegmentedArrayHelper.FastPathMethodImplOptions)]
             get
             {
                 return SegmentedArrayHelper.GetSegmentSize<T>();
@@ -44,7 +43,6 @@ private static int SegmentSize
         /// </summary>
         private static int SegmentShift
         {
-            [MethodImpl(SegmentedArrayHelper.FastPathMethodImplOptions)]
             get
             {
                 return SegmentedArrayHelper.GetSegmentShift<T>();
@@ -56,7 +54,6 @@ private static int SegmentShift
         /// </summary>
         private static int OffsetMask
         {
-            [MethodImpl(SegmentedArrayHelper.FastPathMethodImplOptions)]
             get
             {
                 return SegmentedArrayHelper.GetOffsetMask<T>();
@@ -115,7 +112,7 @@ private SegmentedArray(int length, T[][] items)
 
         public ref T this[int index]
         {
-            [MethodImpl(SegmentedArrayHelper.FastPathMethodImplOptions)]
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
             get
             {
                 return ref _items[index >> SegmentShift][index & OffsetMask];