anchor.diff:                     ;; Copy values out of the MV area.
                      `(sys.lap-x86:lea64 :rdi (:rsp 8))
                      `(sys.lap-x86:mov32 :esi ,(+ (- 8 sys.int::+tag-object+)
  -                                                (* sys.int::+stack-group-offset-mv-slots+ 8)))
  +                                                ;; fixme. should be +thread-mv-slots-start+
  +                                                (* #+(or)sys.int::+stack-group-offset-mv-slots+ 32 8)))
                      save-loop-head
                      `(sys.lap-x86:gs)
                      `(sys.lap-x86:mov64 :rbx (:rsi))
  
positive.code:                 (load-in-reg :r13 value t)
                  (emit `(sys.lap-x86:gs)
                        `(sys.lap-x86:mov64 (,(+ (- 8 sys.int::+tag-object+)
                                                 (* sys.int::+stack-group-offset-mv-slots+ 8)
                                                 (* i 8)))
                                            :r13))
                  (emit-gc-info :multiple-values 1)
  
negative.code:                             ;; Copy values.
                              `(sys.lap-x86:mov64 :rdi :rsp)
                              `(sys.lap-x86:mov32 :esi ,(+ (- 8 sys.int::+tag-object+)
                                                           ;; fixme. should be +thread-mv-slots-start+
                                                           (* #+(or)sys.int::+stack-group-offset-mv-slots+ 32 8))))
                        ;; Switch to the right GC mode.
                        (emit-gc-info :pushed-values -5 :pushed-values-register :rcx :multiple-values 0)
                        (emit loop-head
  