anchor.diff:              epilog = epilog
               compileDelta = compileDelta
               startDefragmentation = fun _ _ _ -> Task.FromResult TimeSpan.Zero
  -            run = fun() -> GLVM.vmRun(prolog, mode, &stats)
  +            run = fun() -> 
  +                let mutable stats = VMStats()
  +                GLVM.vmRun(prolog, mode, &stats)
               memorySize = fun () -> 0L
               alloc = fun code -> 
                   let ptr = GLVM.vmCreate()
  
positive.code:                     | [| a; b; c; d; e |] -> GLVM.vmAppend5(frag, id, i.Operation, a, b, c, d, e)
                      | _ -> failwithf "invalid instruction: %A" i
  
          let mutable stats = Unchecked.defaultof<_>
          {
              compileNeedsPrev = true
              nativeCallCount = ref 0
  
negative.code: 
              writeNext = fun prev next -> GLVM.vmLink(prev, next); 0
              isNext = fun prev frag -> GLVM.vmGetNext prev = frag
              dispose = fun () -> GLVM.vmDelete prolog; GLVM.vmDelete epilog
          }
  
      let glvmOptimized (compile : Option<PreparedRenderObject> -> PreparedRenderObject -> IAdaptiveCode<Instruction>) () =
  