Emitted IL

emitted.il

    .method public static 
           default void countdown (int32 n)  cil managed 
    {
        // Method begins at RVA 0x2064
        // Code size 18 (0x12)
        .maxstack 4
        IL_0000:  ldarg.0 
        IL_0001:  switch (
          IL_0011)
        IL_000a:  ldarg.0 
        IL_000b:  ldc.i4.1 
        IL_000c:  sub 
        IL_000d:  starg.s 0
        IL_000f:  br.s IL_0000

        IL_0011:  ret 
    } // end of method Test3::countdown

test.f#

let n = 1000000

let rec countdown n =
    match n with
    | 0 -> ()
    | _ -> countdown (n-1)

countdown n
printfn "Done"