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Closure conversion eliminates self-references introduced by fixpoint

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* module/language/cps/closure-conversion.scm (analyze-closures): Build a
  bound-vars set as well, to resolve introduced self-references.
  (prune-free-vars, convert-one): Arrange to eliminate self-references.
This commit is contained in:
Andy Wingo 2014-04-13 14:21:25 +02:00
parent 2920554a1e
commit fcb31f2953
1 changed files with 23 additions and 12 deletions
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35
module/language/cps/closure-conversion.scm
View file

@ -45,11 +45,16 @@
(define (analyze-closures exp dfg)
"Compute the set of free variables for all $fun instances in
@var{exp}."
(let ((free-vars (make-hash-table))
(let ((bound-vars (make-hash-table))
(free-vars (make-hash-table))
(named-funs (make-hash-table))
(well-known-vars (make-bitvector (var-counter) #t)))
(define (add-named-fun! var cont)
(hashq-set! named-funs var cont))
(hashq-set! named-funs var cont)
(match cont
(($ $cont label ($ $kfun src meta self))
(unless (eq? var self)
(hashq-set! bound-vars label var)))))
(define (clear-well-known! var)
(bitvector-set! well-known-vars var #f))
(define (compute-well-known-labels)
@ -131,7 +136,7 @@
(let ((free (visit-cont exp '())))
(unless (null? free)
(error "Expected no free vars in toplevel thunk" free exp))
(values free-vars named-funs (compute-well-known-labels)))))
(values bound-vars free-vars named-funs (compute-well-known-labels)))))
(define (prune-free-vars free-vars named-funs well-known var-aliases)
(define (well-known? label)
@ -158,7 +163,7 @@
;; Normally you wouldn't see duplicates in a free variable
;; list, but with aliases that is possible.
(if (memq elt list) list (cons elt list)))
(define (filter-out-eliminated free)
(define (prune-free closure-label free)
(match free
(() '())
((var . free)
@ -167,7 +172,7 @@
(($ $cont label)
(cond
((bitvector-ref eliminated label)
(filter-out-eliminated free))
(prune-free closure-label free))
((vector-ref label-aliases label)
=> (lambda (var)
(cond
@ -180,19 +185,23 @@
(bitvector-set! eliminated label #t)
(set! recurse? #t))
alias-stack)
(filter-out-eliminated free))
(prune-free closure-label free))
(else
(lp var (cons label alias-stack))))))
((eq? closure-label label)
;; Eliminate self-reference.
(pk 'hi)
(prune-free closure-label free))
(else
(adjoin var (filter-out-eliminated free)))))
(_ (adjoin var (filter-out-eliminated free))))))))
(adjoin var (prune-free closure-label free)))))
(_ (adjoin var (prune-free closure-label free))))))))
(hash-for-each-handle
(lambda (pair)
(match pair
((label . ()) #t)
((label . free)
(let ((orig-nfree (length free))
(free (filter-out-eliminated free)))
(free (prune-free label free)))
(set-cdr! pair free)
;; If we managed to eliminate one or more free variables
;; from a well-known function, it could be that we can
@ -219,7 +228,7 @@
(vector-set! var-aliases var alias))))))
named-funs)))
(define (convert-one label fun free-vars named-funs well-known aliases)
(define (convert-one bound label fun free-vars named-funs well-known aliases)
(define (well-known? label)
(bitvector-ref well-known label))
@ -259,6 +268,7 @@ Otherwise @var{var} is bound, so @var{k} is called with @var{var}."
(else 'vector-ref))
(self idx)))))))
($continue kidx #f ($const free-idx)))))))))
((eq? var bound) (k self))
(else (k var))))
(define (convert-free-vars vars k)
@ -509,13 +519,14 @@ and allocate and initialize flat closures."
(let ((dfg (compute-dfg fun)))
(with-fresh-name-state-from-dfg dfg
(call-with-values (lambda () (analyze-closures fun dfg))
(lambda (free-vars named-funs well-known)
(lambda (bound-vars free-vars named-funs well-known)
(let ((labels (sort (hash-map->list (lambda (k v) k) free-vars) <))
(aliases (make-vector (var-counter) #f)))
(prune-free-vars free-vars named-funs well-known aliases)
(build-cps-term
($program
,(map (lambda (label)
(convert-one label (lookup-cont label dfg)
(convert-one (hashq-ref bound-vars label) label
(lookup-cont label dfg)
free-vars named-funs well-known aliases))
labels)))))))))