[bpt/guile.git] / module / language / cps / closure-conversion.scm

;;; Continuation-passing style (CPS) intermediate language (IL)

;; Copyright (C) 2013, 2014 Free Software Foundation, Inc.

;;;; This library is free software; you can redistribute it and/or
;;;; modify it under the terms of the GNU Lesser General Public
;;;; License as published by the Free Software Foundation; either
;;;; version 3 of the License, or (at your option) any later version.
;;;;
;;;; This library is distributed in the hope that it will be useful,
;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
;;;; Lesser General Public License for more details.
;;;;
;;;; You should have received a copy of the GNU Lesser General Public
;;;; License along with this library; if not, write to the Free Software
;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

;;; Commentary:
;;;
;;; This pass converts a CPS term in such a way that no function has any
;;; free variables.  Instead, closures are built explicitly with
;;; make-closure primcalls, and free variables are referenced through
;;; the closure.
;;;
;;; Closure conversion also removes any $letrec forms that contification
;;; did not handle.  See (language cps) for a further discussion of
;;; $letrec.
;;;
;;; Code:

(define-module (language cps closure-conversion)
  #:use-module (ice-9 match)
  #:use-module ((srfi srfi-1) #:select (fold
                                        lset-union lset-difference
                                        list-index))
  #:use-module (ice-9 receive)
  #:use-module (srfi srfi-26)
  #:use-module (language cps)
  #:export (convert-closures))

(define (union s1 s2)
  (lset-union eq? s1 s2))

(define (difference s1 s2)
  (lset-difference eq? s1 s2))

;; bound := sym ...
;; free := sym ...

(define (convert-free-var sym self bound k)
  "Convert one possibly free variable reference to a bound reference.

If @var{sym} is free (i.e., not present in @var{bound},), it is replaced
by a closure reference via a @code{free-ref} primcall, and @var{k} is
called with the new var.  Otherwise @var{sym} is bound, so @var{k} is
called with @var{sym}.

@var{k} should return two values: a term and a list of additional free
values in the term."
  (if (memq sym bound)
      (k sym)
      (let-fresh (k*) (sym*)
        (receive (exp free) (k sym*)
          (values (build-cps-term
                    ($letk ((k* ($kargs (sym*) (sym*) ,exp)))
                      ($continue k* #f ($primcall 'free-ref (self sym)))))
                  (cons sym free))))))
  
(define (convert-free-vars syms self bound k)
  "Convert a number of possibly free references to bound references.
@var{k} is called with the bound references, and should return two
values: the term and a list of additional free variables in the term."
  (match syms
    (() (k '()))
    ((sym . syms)
     (convert-free-var sym self bound
                       (lambda (sym)
                         (convert-free-vars syms self bound
                                            (lambda (syms)
                                              (k (cons sym syms)))))))))
  
(define (init-closure src v free outer-self outer-bound body)
  "Initialize the free variables @var{free} in a closure bound to
@var{v}, and continue with @var{body}.  @var{outer-self} must be the
label of the outer procedure, where the initialization will be
performed, and @var{outer-bound} is the list of bound variables there."
  (fold (lambda (free idx body)
          (let-fresh (k) (idxsym)
            (build-cps-term
              ($letk ((k ($kargs () () ,body)))
                ,(convert-free-var
                  free outer-self outer-bound
                  (lambda (free)
                    (values (build-cps-term
                              ($letconst (('idx idxsym idx))
                                ($continue k src
                                  ($primcall 'free-set! (v idxsym free)))))
                            '())))))))
        body
        free
        (iota (length free))))

(define (cc* exps self bound)
  "Convert all free references in the list of expressions @var{exps} to
bound references, and convert functions to flat closures.  Returns two
values: the transformed list, and a cumulative set of free variables."
  (let lp ((exps exps) (exps* '()) (free '()))
    (match exps
      (() (values (reverse exps*) free))
      ((exp . exps)
       (receive (exp* free*) (cc exp self bound)
         (lp exps (cons exp* exps*) (union free free*)))))))

;; Closure conversion.
(define (cc exp self bound)
  "Convert all free references in @var{exp} to bound references, and
convert functions to flat closures."
  (match exp
    (($ $letk conts body)
     (receive (conts free) (cc* conts self bound)
       (receive (body free*) (cc body self bound)
         (values (build-cps-term ($letk ,conts ,body))
                 (union free free*)))))

    (($ $cont sym ($ $kargs names syms body))
     (receive (body free) (cc body self (append syms bound))
       (values (build-cps-cont (sym ($kargs names syms ,body)))
               free)))

    (($ $cont sym ($ $kentry self tail clause))
     (receive (clause free) (if clause
                                (cc clause self (list self))
                                (values #f '()))
       (values (build-cps-cont (sym ($kentry self ,tail ,clause)))
               free)))

    (($ $cont sym ($ $kclause arity body alternate))
     (receive (body free) (cc body self bound)
       (receive (alternate free*) (if alternate
                                      (cc alternate self bound)
                                      (values #f '()))
         (values (build-cps-cont (sym ($kclause ,arity ,body ,alternate)))
                 (union free free*)))))

    (($ $cont)
     ;; Other kinds of continuations don't bind values and don't have
     ;; bodies.
     (values exp '()))

    ;; Remove letrec.
    (($ $letrec names syms funs body)
     (let ((bound (append bound syms)))
       (receive (body free) (cc body self bound)
         (let lp ((in (map list names syms funs))
                  (bindings (lambda (body) body))
                  (body body)
                  (free free))
           (match in
             (() (values (bindings body) free))
             (((name sym ($ $fun src meta () fun-body)) . in)
              (receive (fun-body fun-free) (cc fun-body #f '())
                (lp in
                    (lambda (body)
                      (let-fresh (k) ()
                        (build-cps-term
                          ($letk ((k ($kargs (name) (sym) ,(bindings body))))
                            ($continue k src
                              ($fun src meta fun-free ,fun-body))))))
                    (init-closure src sym fun-free self bound body)
                    (union free (difference fun-free bound))))))))))

    (($ $continue k src
        (or ($ $void)
            ($ $const)
            ($ $prim)))
     (values exp '()))

    (($ $continue k src ($ $fun src* meta () body))
     (receive (body free) (cc body #f '())
       (match free
         (()
          (values (build-cps-term
                    ($continue k src ($fun src* meta free ,body)))
                  free))
         (_
          (values
           (let-fresh (kinit) (v)
             (build-cps-term
               ($letk ((kinit ($kargs (v) (v)
                                ,(init-closure
                                  src v free self bound
                                  (build-cps-term
                                    ($continue k src ($values (v))))))))
                 ($continue kinit src ($fun src* meta free ,body)))))
           (difference free bound))))))

    (($ $continue k src ($ $call proc args))
     (convert-free-vars (cons proc args) self bound
                        (match-lambda
                         ((proc . args)
                          (values (build-cps-term
                                    ($continue k src ($call proc args)))
                                  '())))))

    (($ $continue k src ($ $callk k* proc args))
     (convert-free-vars (cons proc args) self bound
                        (match-lambda
                         ((proc . args)
                          (values (build-cps-term
                                    ($continue k src ($callk k* proc args)))
                                  '())))))

    (($ $continue k src ($ $primcall name args))
     (convert-free-vars args self bound
                        (lambda (args)
                          (values (build-cps-term
                                    ($continue k src ($primcall name args)))
                                  '()))))

    (($ $continue k src ($ $values args))
     (convert-free-vars args self bound
                        (lambda (args)
                          (values (build-cps-term
                                    ($continue k src ($values args)))
                                  '()))))

    (($ $continue k src ($ $prompt escape? tag handler))
     (convert-free-var
      tag self bound
      (lambda (tag)
        (values (build-cps-term
                  ($continue k src ($prompt escape? tag handler)))
                '()))))

    (_ (error "what" exp))))

;; Convert the slot arguments of 'free-ref' primcalls from symbols to
;; indices.
(define (convert-to-indices body free)
  (define (free-index sym)
    (or (list-index (cut eq? <> sym) free)
        (error "free variable not found!" sym free)))
  (define (visit-term term)
    (rewrite-cps-term term
      (($ $letk conts body)
       ($letk ,(map visit-cont conts) ,(visit-term body)))
      (($ $continue k src ($ $primcall 'free-ref (closure sym)))
       ,(let-fresh () (idx)
          (build-cps-term
            ($letconst (('idx idx (free-index sym)))
              ($continue k src ($primcall 'free-ref (closure idx)))))))
      (($ $continue k src ($ $fun src* meta free body))
       ($continue k src
         ($fun src* meta free ,(convert-to-indices body free))))
      (($ $continue)
       ,term)))
  (define (visit-cont cont)
    (rewrite-cps-cont cont
      (($ $cont sym ($ $kargs names syms body))
       (sym ($kargs names syms ,(visit-term body))))
      (($ $cont sym ($ $kclause arity body alternate))
       (sym ($kclause ,arity ,(visit-cont body)
                      ,(and alternate (visit-cont alternate)))))
      ;; Other kinds of continuations don't bind values and don't have
      ;; bodies.
      (($ $cont)
       ,cont)))

  (rewrite-cps-cont body
    (($ $cont sym ($ $kentry self tail clause))
     (sym ($kentry self ,tail ,(and clause (visit-cont clause)))))))

(define (convert-closures exp)
  "Convert free reference in @var{exp} to primcalls to @code{free-ref},
and allocate and initialize flat closures."
  (with-fresh-name-state exp
    (match exp
      (($ $fun src meta () body)
       (receive (body free) (cc body #f '())
         (unless (null? free)
           (error "Expected no free vars in toplevel thunk" exp body free))
         (build-cps-exp
           ($fun src meta free ,(convert-to-indices body free))))))))
Commit	Line	Data
4b8de65e AW	1	;;; Continuation-passing style (CPS) intermediate language (IL)
4b8de65e AW	2
7ab76a83	3	;; Copyright (C) 2013, 2014 Free Software Foundation, Inc.
4b8de65e AW	4
	5	;;;; This library is free software; you can redistribute it and/or
	6	;;;; modify it under the terms of the GNU Lesser General Public
	7	;;;; License as published by the Free Software Foundation; either
	8	;;;; version 3 of the License, or (at your option) any later version.
	9	;;;;
	10	;;;; This library is distributed in the hope that it will be useful,
	11	;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
	12	;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	13	;;;; Lesser General Public License for more details.
	14	;;;;
	15	;;;; You should have received a copy of the GNU Lesser General Public
	16	;;;; License along with this library; if not, write to the Free Software
	17	;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	18
	19	;;; Commentary:
	20	;;;
	21	;;; This pass converts a CPS term in such a way that no function has any
	22	;;; free variables. Instead, closures are built explicitly with
	23	;;; make-closure primcalls, and free variables are referenced through
	24	;;; the closure.
	25	;;;
	26	;;; Closure conversion also removes any $letrec forms that contification
	27	;;; did not handle. See (language cps) for a further discussion of
	28	;;; $letrec.
	29	;;;
	30	;;; Code:
	31
	32	(define-module (language cps closure-conversion)
	33	#:use-module (ice-9 match)
	34	#:use-module ((srfi srfi-1) #:select (fold
	35	lset-union lset-difference
	36	list-index))
	37	#:use-module (ice-9 receive)
	38	#:use-module (srfi srfi-26)
	39	#:use-module (language cps)
	40	#:export (convert-closures))
	41
	42	(define (union s1 s2)
	43	(lset-union eq? s1 s2))
	44
	45	(define (difference s1 s2)
	46	(lset-difference eq? s1 s2))
	47
	48	;; bound := sym ...
	49	;; free := sym ...
	50
	51	(define (convert-free-var sym self bound k)
	52	"Convert one possibly free variable reference to a bound reference.
	53
	54	If @var{sym} is free (i.e., not present in @var{bound},), it is replaced
	55	by a closure reference via a @code{free-ref} primcall, and @var{k} is
	56	called with the new var. Otherwise @var{sym} is bound, so @var{k} is
	57	called with @var{sym}.
	58
	59	@var{k} should return two values: a term and a list of additional free
	60	values in the term."
	61	(if (memq sym bound)
	62	(k sym)
828ed944	63	(let-fresh (k) (sym)
4b8de65e AW	64	(receive (exp free) (k sym*)
4b8de65e AW	65	(values (build-cps-term
6e422a35 AW	66	($letk ((k* ($kargs (sym) (sym) ,exp)))
6e422a35 AW	67	($continue k* #f ($primcall 'free-ref (self sym)))))
4b8de65e AW	68	(cons sym free))))))
	69
	70	(define (convert-free-vars syms self bound k)
	71	"Convert a number of possibly free references to bound references.
	72	@var{k} is called with the bound references, and should return two
	73	values: the term and a list of additional free variables in the term."
	74	(match syms
	75	(() (k '()))
	76	((sym . syms)
	77	(convert-free-var sym self bound
	78	(lambda (sym)
	79	(convert-free-vars syms self bound
	80	(lambda (syms)
	81	(k (cons sym syms)))))))))
	82
	83	(define (init-closure src v free outer-self outer-bound body)
	84	"Initialize the free variables @var{free} in a closure bound to
	85	@var{v}, and continue with @var{body}. @var{outer-self} must be the
	86	label of the outer procedure, where the initialization will be
	87	performed, and @var{outer-bound} is the list of bound variables there."
	88	(fold (lambda (free idx body)
828ed944	89	(let-fresh (k) (idxsym)
4b8de65e	90	(build-cps-term
6e422a35	91	($letk ((k ($kargs () () ,body)))
4b8de65e AW	92	,(convert-free-var
	93	free outer-self outer-bound
	94	(lambda (free)
	95	(values (build-cps-term
	96	($letconst (('idx idxsym idx))
6e422a35	97	($continue k src
4b8de65e AW	98	($primcall 'free-set! (v idxsym free)))))
	99	'())))))))
	100	body
	101	free
	102	(iota (length free))))
	103
	104	(define (cc* exps self bound)
	105	"Convert all free references in the list of expressions @var{exps} to
	106	bound references, and convert functions to flat closures. Returns two
	107	values: the transformed list, and a cumulative set of free variables."
	108	(let lp ((exps exps) (exps* '()) (free '()))
	109	(match exps
	110	(() (values (reverse exps*) free))
	111	((exp . exps)
	112	(receive (exp* free*) (cc exp self bound)
	113	(lp exps (cons exp* exps) (union free free)))))))
	114
	115	;; Closure conversion.
	116	(define (cc exp self bound)
	117	"Convert all free references in @var{exp} to bound references, and
	118	convert functions to flat closures."
	119	(match exp
	120	(($ $letk conts body)
	121	(receive (conts free) (cc* conts self bound)
	122	(receive (body free*) (cc body self bound)
	123	(values (build-cps-term ($letk ,conts ,body))
	124	(union free free*)))))
	125
6e422a35	126	(($ $cont sym ($ $kargs names syms body))
4b8de65e	127	(receive (body free) (cc body self (append syms bound))
6e422a35	128	(values (build-cps-cont (sym ($kargs names syms ,body)))
4b8de65e AW	129	free)))
4b8de65e AW	130
90dce16d AW	131	(($ $cont sym ($ $kentry self tail clause))
	132	(receive (clause free) (if clause
	133	(cc clause self (list self))
	134	(values #f '()))
	135	(values (build-cps-cont (sym ($kentry self ,tail ,clause)))
4b8de65e AW	136	free)))
4b8de65e AW	137
90dce16d	138	(($ $cont sym ($ $kclause arity body alternate))
4b8de65e	139	(receive (body free) (cc body self bound)
90dce16d AW	140	(receive (alternate free*) (if alternate
	141	(cc alternate self bound)
	142	(values #f '()))
	143	(values (build-cps-cont (sym ($kclause ,arity ,body ,alternate)))
	144	(union free free*)))))
4b8de65e AW	145
	146	(($ $cont)
	147	;; Other kinds of continuations don't bind values and don't have
	148	;; bodies.
	149	(values exp '()))
	150
	151	;; Remove letrec.
	152	(($ $letrec names syms funs body)
	153	(let ((bound (append bound syms)))
	154	(receive (body free) (cc body self bound)
	155	(let lp ((in (map list names syms funs))
	156	(bindings (lambda (body) body))
	157	(body body)
	158	(free free))
	159	(match in
	160	(() (values (bindings body) free))
6e422a35	161	(((name sym ($ $fun src meta () fun-body)) . in)
4b8de65e AW	162	(receive (fun-body fun-free) (cc fun-body #f '())
	163	(lp in
	164	(lambda (body)
828ed944	165	(let-fresh (k) ()
4b8de65e	166	(build-cps-term
6e422a35 AW	167	($letk ((k ($kargs (name) (sym) ,(bindings body))))
	168	($continue k src
	169	($fun src meta fun-free ,fun-body))))))
	170	(init-closure src sym fun-free self bound body)
4b8de65e AW	171	(union free (difference fun-free bound))))))))))
4b8de65e AW	172
6e422a35	173	(($ $continue k src
4b8de65e AW	174	(or ($ $void)
	175	($ $const)
	176	($ $prim)))
	177	(values exp '()))
	178
6e422a35	179	(($ $continue k src ($ $fun src* meta () body))
4b8de65e AW	180	(receive (body free) (cc body #f '())
	181	(match free
	182	(()
	183	(values (build-cps-term
6e422a35	184	($continue k src ($fun src* meta free ,body)))
4b8de65e AW	185	free))
	186	(_
	187	(values
828ed944	188	(let-fresh (kinit) (v)
4b8de65e	189	(build-cps-term
6e422a35	190	($letk ((kinit ($kargs (v) (v)
13085a82 AW	191	,(init-closure
	192	src v free self bound
	193	(build-cps-term
	194	($continue k src ($values (v))))))))
6e422a35	195	($continue kinit src ($fun src* meta free ,body)))))
4b8de65e AW	196	(difference free bound))))))
4b8de65e AW	197
6e422a35	198	(($ $continue k src ($ $call proc args))
4b8de65e AW	199	(convert-free-vars (cons proc args) self bound
	200	(match-lambda
	201	((proc . args)
	202	(values (build-cps-term
6e422a35	203	($continue k src ($call proc args)))
4b8de65e AW	204	'())))))
4b8de65e AW	205
b3ae2b50 AW	206	(($ $continue k src ($ $callk k* proc args))
	207	(convert-free-vars (cons proc args) self bound
	208	(match-lambda
	209	((proc . args)
	210	(values (build-cps-term
	211	($continue k src ($callk k* proc args)))
	212	'())))))
	213
6e422a35	214	(($ $continue k src ($ $primcall name args))
4b8de65e AW	215	(convert-free-vars args self bound
	216	(lambda (args)
	217	(values (build-cps-term
6e422a35	218	($continue k src ($primcall name args)))
4b8de65e AW	219	'()))))
4b8de65e AW	220
6e422a35	221	(($ $continue k src ($ $values args))
4b8de65e AW	222	(convert-free-vars args self bound
	223	(lambda (args)
	224	(values (build-cps-term
6e422a35	225	($continue k src ($values args)))
4b8de65e AW	226	'()))))
4b8de65e AW	227
7ab76a83	228	(($ $continue k src ($ $prompt escape? tag handler))
4b8de65e AW	229	(convert-free-var
	230	tag self bound
	231	(lambda (tag)
	232	(values (build-cps-term
7ab76a83	233	($continue k src ($prompt escape? tag handler)))
4b8de65e AW	234	'()))))
	235
	236	(_ (error "what" exp))))
	237
	238	;; Convert the slot arguments of 'free-ref' primcalls from symbols to
	239	;; indices.
	240	(define (convert-to-indices body free)
	241	(define (free-index sym)
	242	(or (list-index (cut eq? <> sym) free)
	243	(error "free variable not found!" sym free)))
	244	(define (visit-term term)
	245	(rewrite-cps-term term
	246	(($ $letk conts body)
	247	($letk ,(map visit-cont conts) ,(visit-term body)))
6e422a35	248	(($ $continue k src ($ $primcall 'free-ref (closure sym)))
828ed944	249	,(let-fresh () (idx)
4b8de65e AW	250	(build-cps-term
4b8de65e AW	251	($letconst (('idx idx (free-index sym)))
6e422a35 AW	252	($continue k src ($primcall 'free-ref (closure idx)))))))
	253	(($ $continue k src ($ $fun src* meta free body))
	254	($continue k src
	255	($fun src* meta free ,(convert-to-indices body free))))
4b8de65e AW	256	(($ $continue)
	257	,term)))
	258	(define (visit-cont cont)
	259	(rewrite-cps-cont cont
6e422a35 AW	260	(($ $cont sym ($ $kargs names syms body))
6e422a35 AW	261	(sym ($kargs names syms ,(visit-term body))))
90dce16d AW	262	(($ $cont sym ($ $kclause arity body alternate))
	263	(sym ($kclause ,arity ,(visit-cont body)
	264	,(and alternate (visit-cont alternate)))))
4b8de65e AW	265	;; Other kinds of continuations don't bind values and don't have
	266	;; bodies.
	267	(($ $cont)
	268	,cont)))
	269
	270	(rewrite-cps-cont body
90dce16d AW	271	(($ $cont sym ($ $kentry self tail clause))
90dce16d AW	272	(sym ($kentry self ,tail ,(and clause (visit-cont clause)))))))
4b8de65e AW	273
	274	(define (convert-closures exp)
	275	"Convert free reference in @var{exp} to primcalls to @code{free-ref},
	276	and allocate and initialize flat closures."
828ed944 AW	277	(with-fresh-name-state exp
	278	(match exp
	279	(($ $fun src meta () body)
	280	(receive (body free) (cc body #f '())
	281	(unless (null? free)
	282	(error "Expected no free vars in toplevel thunk" exp body free))
	283	(build-cps-exp
	284	($fun src meta free ,(convert-to-indices body free))))))))