Updating Load512 for WideningLoader for performance increase

Author: khushal1996

src/libraries/System.Private.CoreLib/src/System/Text/Ascii.Equality.cs

@@ -536,8 +536,19 @@ public static Vector256<ushort> Load256(ref byte ptr)
             [MethodImpl(MethodImplOptions.AggressiveInlining)]
             public static Vector512<ushort> Load512(ref byte ptr)
             {
-                (Vector256<ushort> lower, Vector256<ushort> upper) = Vector256.Widen(Vector256.LoadUnsafe(ref ptr));
-                return Vector512.Create(lower, upper);
+                // This is done here for performance gain.
+                // A similar implementation would be as below:
+                //
+                //      (Vector256<ushort> lower, Vector256<ushort> upper) = Vector256.Widen(Vector256.LoadUnsafe(ref ptr));
+                //      return Vector512.Create(lower, upper);
+                //
+                // This is similar to what is done for Load256 here. But
+                // for Vector512, this implementation is low performance
+                // since a load and widen on Vector256 followed by a
+                // create on Vector512 is leading to a performance lower
+                // than that of similar implementationfor Vector256.
+                (Vector512<ushort> lower, Vector512<ushort> _) = Vector512.Widen(Vector256.LoadUnsafe(ref ptr).ToVector512());
+                return lower;
             }
 
             [MethodImpl(MethodImplOptions.AggressiveInlining)]