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More robust contification

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* module/language/cps/contification.scm (contify): It could be that
  visiting pending contifications could enqueue more contifications, so
  iterate to a fixed point.  Signal an error if there are any pending
  contifications at the end of an iteration.
This commit is contained in:
Andy Wingo 2013-10-21 16:59:42 +02:00
parent c8ad7426e2
commit e92e0bbe9c
1 changed files with 97 additions and 82 deletions
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179
module/language/cps/contification.scm
View file

@ -59,17 +59,31 @@
(lift-definition! k scope dfg)))
conts)
(hashq-set! pending-contifications scope
(append conts
(hashq-ref pending-contifications scope '()))))
(define (finish-pending-contifications call term-k)
(append conts (hashq-ref pending-contifications scope '()))))
(define (flush-pending-contifications term-k term)
(match (hashq-ref pending-contifications term-k)
(#f call)
(#f term)
((cont ...)
;; Catch any possible double-contification bug.
(hashq-set! pending-contifications term-k 'poison)
(build-cps-term
($letk ,(map visit-cont cont)
,call)))))
(hashq-remove! pending-contifications term-k)
;; Visiting the pending continuations can enqueue more
;; contifications in this same scope, so iterate until there
;; are none left.
(flush-pending-contifications
term-k
(let lp ((term term))
(rewrite-cps-term term
(($ $letrec names syms funs body)
($letrec names syms funs ,(lp body)))
(($ $letk conts* body)
($letk ,(append conts* (map visit-cont cont))
,body))
(body
($letk ,(map visit-cont cont)
,body))))))))
(define (report-pending-contifications)
(hash-for-each (lambda (sym pending)
(error 'pending-contification sym pending))
pending-contifications))
(define (contify-call proc args)
(and=> (assq-ref call-substs proc)
@ -150,7 +164,7 @@
;; (1) Find the scope at which to contify.
(let ((scope (if (continuation-bound-in? k term-k dfg)
term-k
(lookup-def k dfg))))
(pk 'contify-from term-k 'at k (lookup-block-scope k dfg)))))
;; (2) Mark all SYMs for replacement in calls, and
;; mark the tail continuations for replacement by K.
(for-each (lambda (sym tail arities bodies)
@ -184,76 +198,77 @@
(($ $cont)
,cont)))
(define (visit-term term term-k)
(match term
(($ $letk conts body)
;; Visit the body first, so we visit depth-first.
(let lp ((body (visit-term body term-k)))
;; Because we attach contified functions on a particular
;; term-k, and one term-k can correspond to an arbitrarily
;; nested sequence of $letrec and $letk instances, normalize
;; so that all continuations are bound by one $letk --
;; guaranteeing that they are in the same scope.
(rewrite-cps-term body
(($ $letrec names syms funs body)
($letrec names syms funs ,(lp body)))
(($ $letk conts* body)
($letk ,(append conts* (map visit-cont conts))
,body))
(body
($letk ,(map visit-cont conts)
,body)))))
(($ $letrec names syms funs body)
(define (split-components nsf)
;; FIXME: Compute strongly-connected components. Currently
;; we just put non-recursive functions in their own
;; components, and lump everything else in the remaining
;; component.
(define (recursive? k)
(or-map (cut variable-free-in? <> k dfg) syms))
(let lp ((nsf nsf) (rec '()))
(match nsf
(()
(if (null? rec)
'()
(list rec)))
(((and elt (n s ($ $fun meta free ($ $cont kentry))))
. nsf)
(if (recursive? kentry)
(lp nsf (cons elt rec))
(cons (list elt) (lp nsf rec)))))))
(define (visit-components components)
(match components
(() (visit-term body term-k))
((((name sym fun) ...) . components)
(match fun
((($ $fun meta free
($ $cont fun-k _
($ $kentry self
($ $cont tail-k _ ($ $ktail))
(($ $cont _ _ ($ $kclause arity body))
...))))
...)
(if (contify-funs term-k sym self tail-k arity body)
(visit-components components)
(build-cps-term
($letrec name sym (map visit-fun fun)
,(visit-components components)))))))))
(visit-components (split-components (map list names syms funs))))
(($ $continue k exp)
(let ((k* (lookup-return-cont k)))
(define (default)
(rewrite-cps-term exp
(($ $fun) ($continue k* ,(visit-fun exp)))
(($ $primcall 'return (val))
,(if (eq? k k*)
(build-cps-term ($continue k* ,exp))
(build-cps-term ($continue k* ($values (val))))))
(($ $primcall 'return-values vals)
,(if (eq? k k*)
(build-cps-term ($continue k* ,exp))
(build-cps-term ($continue k* ($values vals)))))
(_ ($continue k* ,exp))))
(finish-pending-contifications
(flush-pending-contifications
term-k
(match term
(($ $letk conts body)
;; Visit the body first, so we visit depth-first.
(let lp ((body (visit-term body term-k)))
;; Because we attach contified functions on a particular
;; term-k, and one term-k can correspond to an arbitrarily
;; nested sequence of $letrec and $letk instances, normalize
;; so that all continuations are bound by one $letk --
;; guaranteeing that they are in the same scope.
(rewrite-cps-term body
(($ $letrec names syms funs body)
($letrec names syms funs ,(lp body)))
(($ $letk conts* body)
($letk ,(append conts* (map visit-cont conts))
,body))
(body
($letk ,(map visit-cont conts)
,body)))))
(($ $letrec names syms funs body)
(define (split-components nsf)
;; FIXME: Compute strongly-connected components. Currently
;; we just put non-recursive functions in their own
;; components, and lump everything else in the remaining
;; component.
(define (recursive? k)
(or-map (cut variable-free-in? <> k dfg) syms))
(let lp ((nsf nsf) (rec '()))
(match nsf
(()
(if (null? rec)
'()
(list rec)))
(((and elt (n s ($ $fun meta free ($ $cont kentry))))
. nsf)
(if (recursive? kentry)
(lp nsf (cons elt rec))
(cons (list elt) (lp nsf rec)))))))
(define (visit-components components)
(match components
(() (visit-term body term-k))
((((name sym fun) ...) . components)
(match fun
((($ $fun meta free
($ $cont fun-k _
($ $kentry self
($ $cont tail-k _ ($ $ktail))
(($ $cont _ _ ($ $kclause arity body))
...))))
...)
(if (contify-funs term-k sym self tail-k arity body)
(visit-components components)
(build-cps-term
($letrec name sym (map visit-fun fun)
,(visit-components components)))))))))
(visit-components (split-components (map list names syms funs))))
(($ $continue k exp)
(let ((k* (lookup-return-cont k)))
(define (default)
(rewrite-cps-term exp
(($ $fun) ($continue k* ,(visit-fun exp)))
(($ $primcall 'return (val))
,(if (eq? k k*)
(build-cps-term ($continue k* ,exp))
(build-cps-term ($continue k* ($values (val))))))
(($ $primcall 'return-values vals)
,(if (eq? k k*)
(build-cps-term ($continue k* ,exp))
(build-cps-term ($continue k* ($values vals)))))
(_ ($continue k* ,exp))))
(match exp
(($ $fun meta free
($ $cont fun-k _
@ -269,10 +284,10 @@
(($ $call proc args)
(or (contify-call proc args)
(default)))
(_ (default)))
term-k)))))
(_ (default))))))))
(let ((fun (visit-fun fun)))
(report-pending-contifications)
(if (null? call-substs)
fun
;; Iterate to fixed point.