;; lib/perf-smoke.sx — substrate perf smoke test
;;
;; Four micro-benchmarks exercising different substrate hot paths. Each
;; emits its own elapsed-ms via clock-milliseconds. A wrapper script
;; (scripts/perf-smoke.sh) parses the output and compares to reference
;; numbers, exiting non-zero on any 5× or worse regression.
;;
;; Workloads are chosen for distinct failure modes:
;;   bench-fib       — function-call dispatch (recursive arithmetic)
;;   bench-let-chain — env construction (deep let bindings × N)
;;   bench-map-sq    — HO-form dispatch + lambda creation
;;   bench-tail-loop — TCO + primitive dispatch in tight loop

(define (bench-fib n)
  (let ((fib (fn (n) (if (< n 2) n (+ (fib (- n 1)) (fib (- n 2)))))))
    (let ((s (clock-milliseconds)))
      (fib n)
      (- (clock-milliseconds) s))))

(define (bench-let-chain iters)
  (let ((s (clock-milliseconds)))
    (let loop ((i 0) (acc 0))
      (if (= i iters)
          (- (clock-milliseconds) s)
          (loop
            (+ i 1)
            (let ((a 1) (b 2) (c 3) (d 4) (e 5) (f 6) (g 7) (h 8))
              (+ a b c d e f g h acc)))))))

(define (bench-map-sq n)
  (let ((s (clock-milliseconds)))
    (map (fn (x) (* x x)) (range 1 (+ n 1)))
    (- (clock-milliseconds) s)))

(define (bench-tail-loop iters)
  (let ((s (clock-milliseconds)))
    (let loop ((i 0))
      (if (= i iters)
          (- (clock-milliseconds) s)
          (loop (+ i 1))))))

(define (perf-smoke)
  ;; Warm-up: populate JIT cache so the timed pass sees the steady state.
  (bench-fib 12)
  (bench-let-chain 200)
  (bench-map-sq 100)
  (bench-tail-loop 500)
  ;; Timed pass. Sizes tuned for ~50-200 ms each on a quiet machine.
  (let ((r-fib  (bench-fib 18))
        (r-let  (bench-let-chain 1000))
        (r-map  (bench-map-sq 500))
        (r-tail (bench-tail-loop 5000)))
    (str "perf-smoke fib18=" r-fib
         " let1000=" r-let
         " map500=" r-map
         " tail5000=" r-tail)))