- reduce the heap allocations

src/Lucene.Net/Index/AbstractAllTermDocs.cs

@@ -71,7 +71,7 @@ public bool Next(IState state)
             return SkipTo(internalDoc + 1, state);
         }
 
-        public int Read(int[] docs, int[] freqs, IState state)
+        public int Read(Span<int> docs, Span<int> freqs, IState state)
         {
             int length = docs.Length;
             int i = 0;

src/Lucene.Net/Index/DirectoryReader.cs

@@ -1394,7 +1394,7 @@ public virtual bool Next(IState state)
             }
 
             /// <summary>Optimized implementation. </summary>
-            public virtual int Read(int[] docs, int[] freqs, IState state)
+            public virtual int Read(Span<int> docs, Span<int> freqs, IState state)
             {
                 while (true)
                 {

src/Lucene.Net/Index/FilterIndexReader.cs

@@ -69,7 +69,7 @@ public virtual bool Next(IState state)
 			{
 				return in_Renamed.Next(state);
 			}
-			public virtual int Read(int[] docs, int[] freqs, IState state)
+			public virtual int Read(Span<int> docs, Span<int> freqs, IState state)
 			{
 				return in_Renamed.Read(docs, freqs, state);
 			}

src/Lucene.Net/Index/MultipleTermPositions.cs

@@ -226,7 +226,7 @@ public virtual void Seek(TermEnum termEnum, IState state)
 
 		/// <summary> Not implemented.</summary>
 		/// <throws>  UnsupportedOperationException </throws>
-		public virtual int Read(int[] arg0, int[] arg1, IState state)
+		public virtual int Read(Span<int> arg0, Span<int> arg1, IState state)
 		{
 			throw new System.NotSupportedException();
 		}

src/Lucene.Net/Index/ParallelReader.cs

@@ -723,7 +723,7 @@ public virtual bool Next(IState state)
 				return termDocs.Next(state);
 			}
 
-			public virtual int Read(int[] docs, int[] freqs, IState state)
+			public virtual int Read(Span<int> docs, Span<int> freqs, IState state)
 			{
 				if (termDocs == null)
 					return 0;

src/Lucene.Net/Index/SegmentTermDocs.cs

@@ -182,7 +182,7 @@ public virtual bool Next(IState state)
 		}
 
 		/// <summary>Optimized implementation. </summary>
-		public virtual int Read(int[] docs, int[] freqs, IState state)
+		public virtual int Read(Span<int> docs, Span<int> freqs, IState state)
 		{
 			int length = docs.Length;
 			if (currentFieldOmitTermFreqAndPositions)
@@ -216,7 +216,7 @@ public virtual int Read(int[] docs, int[] freqs, IState state)
 			}
 		}
 
-		private int ReadNoTf(int[] docs, int[] freqs, int length, IState state)
+		private int ReadNoTf(Span<int> docs, Span<int> freqs, int length, IState state)
 		{
 			int i = 0;
 			while (i < length && count < df)

src/Lucene.Net/Index/SegmentTermPositions.cs

@@ -115,7 +115,7 @@ public override bool Next(IState state)
 			return false;
 		}
 
-		public override int Read(int[] docs, int[] freqs, IState state)
+		public override int Read(Span<int> docs, Span<int> freqs, IState state)
 		{
 			throw new System.NotSupportedException("TermPositions does not support processing multiple documents in one call. Use TermDocs instead.");
 		}

src/Lucene.Net/Index/TermDocs.cs

@@ -62,7 +62,7 @@ public interface TermDocs : IDisposable
 		/// <p/>Returns the number of entries read.  Zero is only returned when the
 		/// stream has been exhausted.  
 		/// </summary>
-		int Read(int[] docs, int[] freqs, IState state);
+		int Read(Span<int> docs, Span<int> freqs, IState state);
 
 		/// <summary>Skips entries to the first beyond the current whose document number is
 		/// greater than or equal to <i>target</i>. <p/>Returns true iff there is such

src/Lucene.Net/Search/MultiTermQueryWrapperFilter.cs

@@ -114,8 +114,9 @@ public override DocIdSet GetDocIdSet(IndexReader reader, IState state)
                     return DocIdSet.EMPTY_DOCIDSET;
                 // else fill into an OpenBitSet
                 OpenBitSet bitSet = new OpenBitSet(reader.MaxDoc);
-                int[] docs = new int[32];
-                int[] freqs = new int[32];
+                Span<int> docs = stackalloc int[32];
+                Span<int> freqs = stackalloc int[32];
+
                 TermDocs termDocs = reader.TermDocs(state);
                 try
                 {