Use MemoryMarshal.GetReference.

"If in your code by construction you know that the span will not be
empty, you can choose to instead use MemoryMarshal.GetReference, which
performs the same operation but without the length check."

https://devblogs.microsoft.com/dotnet/performance-improvements-in-net-core-3-0/

Author: bgrainger

src/MySqlConnector/Utilities/Utility.cs

@@ -38,16 +38,16 @@ public static string GetString(this Encoding encoding, ReadOnlySpan<byte> span)
 #else
 			unsafe
 			{
-				fixed (byte* ptr = span)
+				fixed (byte* ptr = &MemoryMarshal.GetReference(span))
 					return encoding.GetString(ptr, span.Length);
 			}
 #endif
 		}
 
 		public static unsafe void GetBytes(this Encoding encoding, ReadOnlySpan<char> chars, Span<byte> bytes)
 		{
-			fixed (char* charsPtr = chars)
-			fixed (byte* bytesPtr = bytes)
+			fixed (char* charsPtr = &MemoryMarshal.GetReference(chars))
+			fixed (byte* bytesPtr = &MemoryMarshal.GetReference(bytes))
 			{
 				encoding.GetBytes(charsPtr, chars.Length, bytesPtr, bytes.Length);
 			}
@@ -57,8 +57,8 @@ public static unsafe void GetBytes(this Encoding encoding, ReadOnlySpan<char> ch
 #if NET461 || NET471 || NETSTANDARD2_0
 		public static unsafe void Convert(this Encoder encoder, ReadOnlySpan<char> chars, Span<byte> bytes, bool flush, out int charsUsed, out int bytesUsed, out bool completed)
 		{
-			fixed (char* charsPtr = chars)
-			fixed (byte* bytesPtr = bytes)
+			fixed (char* charsPtr = &MemoryMarshal.GetReference(chars))
+			fixed (byte* bytesPtr = &MemoryMarshal.GetReference(bytes))
 			{
 				// MemoryMarshal.GetNonNullPinnableReference is internal, so fake it by using an invalid but non-null pointer; this
 				// prevents Convert from throwing an exception when the output buffer is empty