Remove all checks and inline blit

Author: forki

src/fsharp/FSharp.Core/array.fs

@@ -83,17 +83,8 @@ namespace Microsoft.FSharp.Collections
 
         [<CodeAnalysis.SuppressMessage("Microsoft.Naming","CA1704:IdentifiersShouldBeSpelledCorrectly")>]
         [<CompiledName("CopyTo")>]
-        let blit (source : 'T[]) sourceIndex (target: 'T[]) targetIndex count = 
-            checkNonNull "source" source
-            checkNonNull "target" target
-            if sourceIndex < 0 then invalidArg "sourceIndex" (SR.GetString(SR.inputMustBeNonNegative))
-            if count < 0 then invalidArg "count" (SR.GetString(SR.inputMustBeNonNegative))
-            if targetIndex < 0 then invalidArg "targetIndex" (SR.GetString(SR.inputMustBeNonNegative))
-            if sourceIndex + count > source.Length then invalidArg "count" (SR.GetString(SR.outOfRange))
-            if targetIndex + count > target.Length then invalidArg "count" (SR.GetString(SR.outOfRange))
+        let inline blit (source : 'T[]) (sourceIndex:int) (target: 'T[]) (targetIndex:int) (count:int) = 
             Array.Copy(source, sourceIndex, target, targetIndex, count)
-            // for i = 0 to count - 1 do 
-            //    target.[targetIndex+i] <- source.[sourceIndex + i]
 
         let rec concatAddLengths (arrs:'T[][]) i acc =
             if i >= arrs.Length then acc 

src/fsharp/FSharp.Core/array.fsi

@@ -62,7 +62,7 @@ namespace Microsoft.FSharp.Collections
         /// <exception cref="System.ArgumentException">Thrown when any of sourceIndex, targetIndex or count are negative,
         /// or when there aren't enough elements in source or target.</exception>
         [<CompiledName("CopyTo")>]
-        val blit: source:'T[] -> sourceIndex:int -> target:'T[] -> targetIndex:int -> count:int -> unit
+        val inline blit: source:'T[] -> sourceIndex:int -> target:'T[] -> targetIndex:int -> count:int -> unit
 
         /// <summary>For each element of the array, applies the given function. Concatenates all the results and return the combined array.</summary>
         /// <param name="mapping">The function to create sub-arrays from the input array elements.</param>