defalias vs. defsubst (Emacs Lisp)

example.el

;;; -*- lexical-binding: t; -*-

;; $ emacs -Q --batch -f batch-byte-compile example.el
;; $ emacs -Q --batch -l example.elc -f disas
;; $ emacs -Q --batch -l example.elc -f bench

(defun add (a b)
  (+ (car a) (car b)))

(defalias 'car-alias #'car)
(defun add-alias (a b)
  (+ (car-alias a) (car-alias b)))

(defsubst car-subst (x) (car x))
(defun add-subst (a b)
  (+ (car-subst a) (car-subst b)))

(require 'cl-lib)
(defun add-cl-first (a b)
  (+ (cl-first a) (cl-first b)))

(defun disas ()
  (dolist (func '(add add-alias add-subst add-cl-first))
    (disassemble func)
    (princ (with-current-buffer "*Disassemble*" (buffer-string)))))

(defun bench ()
  (let ((a (list 2))
        (b (list 3)))
    (print (benchmark-run 10000000 (add a b)))
    (print (benchmark-run 10000000 (add-alias a b)))
    (print (benchmark-run 10000000 (add-subst a b)))
    (print (benchmark-run 10000000 (add-cl-first a b)))))