;;;; A hot loop of struct copies.
;;;;
;;;; The suspected cost is `rep movsb`: this backend copies an aggregate by
;;;; block-moving bytes, where LLVM either keeps the thing in registers or
;;;; emits a handful of wide moves. Eight i64 fields is 64 bytes -- big
;;;; enough that a copy is a real copy, small enough that `rep movsb` is
;;;; paying its setup cost on every one of them, which is the shape the
;;;; instruction is worst at.

(defstruct Big [a i64  b i64  c i64  d i64  e i64  f i64  g i64  h i64])

(defn main [] i32
  (let [acc (i64 0)
        v (Big {.a 1 .b 2 .c 3 .d 4 .e 5 .f 6 .g 7 .h 8})]
    (dotimes [i 2000000]
      (let [w v]
        (set (.a v) (+ (.h w) 1))
        (set acc (+ acc (.a w)))))
    (print acc) (println ""))
  0)