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Simplification pass prunes all unreachable continuations

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* module/language/cps/simplify.scm (prune-continuations): Prune
  continuations as a post-pass with a fresh DFG.  Using a
  pre-eta-conversion DFG as we were doing before missed some cases.
This commit is contained in:
Andy Wingo 2014-02-25 21:32:36 +01:00
parent 546efe2514
commit 4b3d7a2b7c
1 changed files with 44 additions and 42 deletions
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86
module/language/cps/simplify.scm
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@ -40,6 +40,46 @@
;; aren't used), making it useful for this pass to include its own ;; aren't used), making it useful for this pass to include its own
;; little pruner. ;; little pruner.
(define* (prune-continuations fun #:optional (dfg (compute-dfg fun)))
(let ((cfa (analyze-control-flow fun dfg)))
(define (must-visit-cont cont)
(or (visit-cont cont)
(error "cont must be reachable" cont)))
(define (visit-cont cont)
(match cont
(($ $cont sym cont)
(and (cfa-k-idx cfa sym #:default (lambda (k) #f))
(rewrite-cps-cont cont
(($ $kargs names syms body)
(sym ($kargs names syms ,(visit-term body))))
(($ $kentry self tail clauses)
(sym ($kentry self ,tail ,(visit-conts clauses))))
(($ $kclause arity body)
(sym ($kclause ,arity ,(must-visit-cont body))))
((or ($ $kreceive) ($ $kif))
(sym ,cont)))))))
(define (visit-conts conts)
(filter-map visit-cont conts))
(define (visit-term term)
(match term
(($ $letk conts body)
(let ((body (visit-term body)))
(match (visit-conts conts)
(() body)
(conts (build-cps-term ($letk ,conts ,body))))))
(($ $letrec names syms funs body)
(build-cps-term
($letrec names syms (map (cut prune-continuations <> dfg) funs)
,(visit-term body))))
(($ $continue k src (and fun ($ $fun)))
(build-cps-term
($continue k src ,(prune-continuations fun dfg))))
(($ $continue k src exp)
term)))
(rewrite-cps-exp fun
(($ $fun src meta free body)
($fun src meta free ,(must-visit-cont body))))))
(define (compute-eta-reductions fun) (define (compute-eta-reductions fun)
(let ((table (make-hash-table))) (let ((table (make-hash-table)))
(define (visit-cont cont) (define (visit-cont cont)
@ -73,42 +113,6 @@
(visit-fun fun) (visit-fun fun)
table)) table))
(define (locally-prune-continuations fun dfg)
(let ((cfa (analyze-control-flow fun dfg)))
(define (must-visit-cont cont)
(or (visit-cont cont)
(error "cont must be reachable" cont)))
(define (visit-cont cont)
(match cont
(($ $cont sym cont)
(and (cfa-k-idx cfa sym #:default (lambda (k) #f))
(rewrite-cps-cont cont
(($ $kargs names syms body)
(sym ($kargs names syms ,(visit-term body))))
(($ $kentry self tail clauses)
(sym ($kentry self ,tail ,(visit-conts clauses))))
(($ $kclause arity body)
(sym ($kclause ,arity ,(must-visit-cont body))))
((or ($ $kreceive) ($ $kif))
(sym ,cont)))))))
(define (visit-conts conts)
(filter-map visit-cont conts))
(define (visit-term term)
(match term
(($ $letk conts body)
(let ((body (visit-term body)))
(match (visit-conts conts)
(() body)
(conts (build-cps-term ($letk ,conts ,body))))))
(($ $letrec names syms funs body)
(build-cps-term
($letrec names syms funs ,(visit-term body))))
(($ $continue k src exp)
term)))
(rewrite-cps-exp fun
(($ $fun src meta free body)
($fun src meta free ,(must-visit-cont body))))))
(define (eta-reduce fun) (define (eta-reduce fun)
(let ((table (compute-eta-reductions fun)) (let ((table (compute-eta-reductions fun))
(dfg (compute-dfg fun))) (dfg (compute-dfg fun)))
@ -154,11 +158,9 @@
(($ $continue k src exp) (($ $continue k src exp)
($continue (reduce k scope) src ,exp)))) ($continue (reduce k scope) src ,exp))))
(define (visit-fun fun) (define (visit-fun fun)
(locally-prune-continuations (rewrite-cps-exp fun
(rewrite-cps-exp fun (($ $fun src meta free body)
(($ $fun src meta free body) ($fun src meta free ,(visit-cont body #f)))))
($fun src meta free ,(visit-cont body #f))))
dfg))
(visit-fun fun))) (visit-fun fun)))
(define (compute-beta-reductions fun) (define (compute-beta-reductions fun)
@ -273,4 +275,4 @@
(visit-fun fun))) (visit-fun fun)))
(define (simplify fun) (define (simplify fun)
(eta-reduce (beta-reduce fun))) (prune-continuations (eta-reduce (beta-reduce fun))))