GPU: Use a bitmap to track buffer modified flags. (#3775)

* Initial implementation

* Some improvements.

* Fix incorrect cast

* Performance improvement and improved correctness

* Add very fast path when all handles are checked.

* Slightly faster

* Add comment

* De-virtualize region handle

All region handles are now bitmap backed.

* Remove non-bitmap tracking

* Remove unused methods

* Add docs, remove unused methods

* Address Feedback

* Rename file

Ryujinx.Memory/Tracking/ConcurrentBitmap.cs

@@ -0,0 +1,161 @@
+using System;
+using System.Threading;
+
+namespace Ryujinx.Memory.Tracking
+{
+    /// <summary>
+    /// A bitmap that can be safely modified from multiple threads.
+    /// </summary>
+    internal class ConcurrentBitmap
+    {
+        public const int IntSize = 64;
+
+        public const int IntShift = 6;
+        public const int IntMask = IntSize - 1;
+
+        /// <summary>
+        /// Masks representing the bitmap. Least significant bit first, 64-bits per mask.
+        /// </summary>
+        public readonly long[] Masks;
+
+        /// <summary>
+        /// Create a new multithreaded bitmap.
+        /// </summary>
+        /// <param name="count">The number of bits to reserve</param>
+        /// <param name="set">Whether the bits should be initially set or not</param>
+        public ConcurrentBitmap(int count, bool set)
+        {
+            Masks = new long[(count + IntMask) / IntSize];
+
+            if (set)
+            {
+                Array.Fill(Masks, -1L);
+            }
+        }
+
+        /// <summary>
+        /// Check if any bit in the bitmap is set.
+        /// </summary>
+        /// <returns>True if any bits are set, false otherwise</returns>
+        public bool AnySet()
+        {
+            for (int i = 0; i < Masks.Length; i++)
+            {
+                if (Volatile.Read(ref Masks[i]) != 0)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Check if a bit in the bitmap is set.
+        /// </summary>
+        /// <param name="bit">The bit index to check</param>
+        /// <returns>True if the bit is set, false otherwise</returns>
+        public bool IsSet(int bit)
+        {
+            int wordIndex = bit >> IntShift;
+            int wordBit = bit & IntMask;
+
+            long wordMask = 1L << wordBit;
+
+            return (Volatile.Read(ref Masks[wordIndex]) & wordMask) != 0;
+        }
+
+        /// <summary>
+        /// Check if any bit in a range of bits in the bitmap are set. (inclusive)
+        /// </summary>
+        /// <param name="start">The first bit index to check</param>
+        /// <param name="end">The last bit index to check</param>
+        /// <returns>True if a bit is set, false otherwise</returns>
+        public bool IsSet(int start, int end)
+        {
+            if (start == end)
+            {
+                return IsSet(start);
+            }
+
+            int startIndex = start >> IntShift;
+            int startBit = start & IntMask;
+            long startMask = -1L << startBit;
+
+            int endIndex = end >> IntShift;
+            int endBit = end & IntMask;
+            long endMask = (long)(ulong.MaxValue >> (IntMask - endBit));
+
+            long startValue = Volatile.Read(ref Masks[startIndex]);
+
+            if (startIndex == endIndex)
+            {
+                return (startValue & startMask & endMask) != 0;
+            }
+
+            if ((startValue & startMask) != 0)
+            {
+                return true;
+            }
+
+            for (int i = startIndex + 1; i < endIndex; i++)
+            {
+                if (Volatile.Read(ref Masks[i]) != 0)
+                {
+                    return true;
+                }
+            }
+
+            long endValue = Volatile.Read(ref Masks[endIndex]);
+
+            if ((endValue & endMask) != 0)
+            {
+                return true;
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Set a bit at a specific index to either true or false.
+        /// </summary>
+        /// <param name="bit">The bit index to set</param>
+        /// <param name="value">Whether the bit should be set or not</param>
+        public void Set(int bit, bool value)
+        {
+            int wordIndex = bit >> IntShift;
+            int wordBit = bit & IntMask;
+
+            long wordMask = 1L << wordBit;
+
+            long existing;
+            long newValue;
+
+            do
+            {
+                existing = Volatile.Read(ref Masks[wordIndex]);
+
+                if (value)
+                {
+                    newValue = existing | wordMask;
+                }
+                else
+                {
+                    newValue = existing & ~wordMask;
+                }
+            }
+            while (Interlocked.CompareExchange(ref Masks[wordIndex], newValue, existing) != existing);
+        }
+
+        /// <summary>
+        /// Clear the bitmap entirely, setting all bits to 0.
+        /// </summary>
+        public void Clear()
+        {
+            for (int i = 0; i < Masks.Length; i++)
+            {
+                Volatile.Write(ref Masks[i], 0);
+            }
+        }
+    }
+}