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問題5.37

元の preserving から if の述語部と代替部を取り除く。

(define (preserving regs seq1 seq2)
  (if (null? regs)
      (append-instruction-sequences seq1 seq2)
      (let ((first-reg (car regs)))
           (preserving (cdr regs)
                       (make-instruction-sequence
                         (list-union (list first-reg)
                                     (registers-needed seq1))
                         (list-difference (registers-modified seq1)
                                          (list first-reg))
                         (append `((save ,first-reg))
                                 (statements seq1)
                                 `((restore ,first-reg))))
                       seq2))))

次の square 手続きで、常に save, restore 演算を生成する版と、修正前の preserving との比較を行う。

(parse-compiled-code
  (compile
    '(define (square x)
       (* x x))
    'val
    'next))

常に save, restore 演算を生成する版

(continue env)
(val)
  (save continue)
  (save env)
  (save continue)
  (assign val (op make-compiled-procedure) (label entry1) (reg env))
  (restore continue)
  (goto (label after-lambda2))
entry1
  (assign env (op compiled-procedure-env) (reg proc))
  (assign env (op extend-environment) (const (x)) (reg argl) (reg env))
  (save continue)
  (save env)
  (save continue)
  (assign proc (op lookup-variable-value) (const *) (reg env))
  (restore continue)
  (restore env)
  (restore continue)
  (save continue)
  (save proc)
  (save env)
  (save continue)
  (assign val (op lookup-variable-value) (const x) (reg env))
  (restore continue)
  (assign argl (op list) (reg val))
  (restore env)
  (save argl)
  (save continue)
  (assign val (op lookup-variable-value) (const x) (reg env))
  (restore continue)
  (restore argl)
  (assign argl (op cons) (reg val) (reg argl))
  (restore proc)
  (restore continue)
  (test (op primitive-procedure?) (reg proc))
  (branch (label primitive-branch3))
compiled-branch4
  (assign val (op compiled-procedure-entry) (reg proc))
  (goto (reg val))
primitive-branch3
  (save continue)
  (assign val (op apply-primitive-procedure) (reg proc) (reg argl))
  (restore continue)
  (goto (reg continue))
after-call5
after-lambda2
  (restore env)
  (perform (op define-variable!) (const square) (reg val) (reg env))
  (assign val (const ok))
  (restore continue)

スタック使用を最適化する preserving を使った版

(env)
(val)
  (assign val (op make-compiled-procedure) (label entry1) (reg env))
  (goto (label after-lambda2))
entry1
  (assign env (op compiled-procedure-env) (reg proc))
  (assign env (op extend-environment) (const (x)) (reg argl) (reg env))
  (assign proc (op lookup-variable-value) (const *) (reg env))
  (assign val (op lookup-variable-value) (const x) (reg env))
  (assign argl (op list) (reg val))
  (assign val (op lookup-variable-value) (const x) (reg env))
  (assign argl (op cons) (reg val) (reg argl))
  (test (op primitive-procedure?) (reg proc))
  (branch (label primitive-branch3))
compiled-branch4
  (assign val (op compiled-procedure-entry) (reg proc))
  (goto (reg val))
primitive-branch3
  (assign val (op apply-primitive-procedure) (reg proc) (reg argl))
  (goto (reg continue))
after-call5
after-lambda2
  (perform (op define-variable!) (const square) (reg val) (reg env))
  (assign val (const ok))

計算機プログラムの構造と解釈

posted with amazlet at 08.11.07

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