compopt.lisp

;;; -*- Mode: Lisp; Syntax: Common-Lisp; -*-
;;; Code from Paradigms of Artificial Intelligence Programming
;;; Copyright (c) 1991 Peter Norvig

;;;; File compopt.lisp:  Optimizers for Scheme compiler (compile3.lisp).

(def-optimizer (:LABEL) (instr code all-code)
  ;; ... L ... => ... ... ;if no reference to L
  (when (not (find instr all-code :key #'arg1))
    (setf (first code) (second code)
          (rest code) (rest2 code))
    t))

(def-optimizer (GSET LSET) (instr code all-code)
  ;; ex: (begin (set! x y) (if x z))
  ;; (SET X) (POP) (VAR X) ==> (SET X)
  (when (and (is (second code) 'POP)
             (is (third code) '(GVAR LVAR))
             (eq (arg1 instr) (arg1 (third code))))
    (setf (rest code) (nthcdr 3 code))
    t))

(def-optimizer (JUMP CALL CALLJ RETURN) (instr code all-code)
  ;; (JUMP L1) ...dead code... L2 ==> (JUMP L1) L2
  (setf (rest code) (member-if #'label-p (rest code)))
  ;; (JUMP L1) ... L1 (JUMP L2) ==> (JUMP L2)  ... L1 (JUMP L2)
  (when (and (is instr 'JUMP)
             (is (target instr code) '(JUMP RETURN))
    (setf (first code) (copy-list (target instr code)))
    t)))

(def-optimizer (TJUMP FJUMP) (instr code all-code)
  ;; (FJUMP L1) ... L1 (JUMP L2) ==> (FJUMP L2) ... L1 (JUMP L2)
  (when (is (target instr code) 'JUMP)
    (setf (second instr) (arg1 (target instr code)))
    t))

(def-optimizer (T -1 0 1 2) (instr code all-code)
  (case (opcode (second code))
    (NOT ;; (T) (NOT) ==> NIL
     (setf (first code) (gen1 'NIL)
           (rest code) (rest2 code))
     t)
    (FJUMP ;; (T) (FJUMP L) ... => ...
     (setf (first code) (third code)
           (rest code) (rest3 code))
     t)
    (TJUMP ;; (T) (TJUMP L) ... => (JUMP L) ...
     (setf (first code) (gen1 'JUMP (arg1 (next-instr code))))
     t)))

(def-optimizer (NIL) (instr code all-code)
  (case (opcode (second code))
    (NOT ;; (NIL) (NOT) ==> T
     (setf (first code) (gen1 'T)
           (rest code) (rest2 code))
     t)
    (TJUMP ;; (NIL) (TJUMP L) ... => ...
     (setf (first code) (third code)
             (rest code) (rest3 code))
     t)
    (FJUMP ;; (NIL) (FJUMP L) ==> (JUMP L)
     (setf (first code) (gen1 'JUMP (arg1 (next-instr code))))
     t)))