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;;; Continuation-passing style (CPS) intermediate language (IL)
;; Copyright (C) 2013, 2014, 2015 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:
;;;
;;; Primcalls that don't correspond to VM instructions are treated as if
;;; they are calls, and indeed the later reify-primitives pass turns
;;; them into calls. Because no return arity checking is done for these
;;; primitives, if a later optimization pass simplifies the primcall to
;;; a VM operation, the tail of the simplification has to be a
;;; primcall to 'values. Most of these primcalls can be elided, and
;;; that is the job of this pass.
;;;
;;; Code:
(define-module (language cps elide-values)
#:use-module (ice-9 match)
#:use-module (srfi srfi-26)
#:use-module (language cps)
#:use-module (language cps dfg)
#:export (elide-values))
(define (elide-values* fun conts)
(define (visit-cont cont)
(rewrite-cps-cont cont
(($ $cont sym ($ $kargs names syms body))
(sym ($kargs names syms ,(visit-term body))))
(($ $cont sym ($ $kfun src meta self tail clause))
(sym ($kfun src meta self ,tail ,(and clause (visit-cont clause)))))
(($ $cont sym ($ $kclause arity body alternate))
(sym ($kclause ,arity ,(visit-cont body)
,(and alternate (visit-cont alternate)))))
(($ $cont)
,cont)))
(define (visit-term term)
(rewrite-cps-term term
(($ $letk conts body)
($letk ,(map visit-cont conts)
,(visit-term body)))
(($ $continue k src ($ $primcall 'values vals))
,(rewrite-cps-term (vector-ref conts k)
(($ $ktail)
($continue k src ($values vals)))
(($ $kreceive ($ $arity req () rest () #f) kargs)
,(cond
((and (not rest) (= (length vals) (length req)))
(build-cps-term
($continue kargs src ($values vals))))
((and rest (>= (length vals) (length req)))
(let-fresh (krest) (rest)
(let ((vals* (append (list-head vals (length req))
(list rest))))
(build-cps-term
($letk ((krest ($kargs ('rest) (rest)
($continue kargs src
($values vals*)))))
,(let lp ((tail (list-tail vals (length req)))
(k krest))
(match tail
(()
(build-cps-term ($continue k src
($const '()))))
((v . tail)
(let-fresh (krest) (rest)
(build-cps-term
($letk ((krest ($kargs ('rest) (rest)
($continue k src
($primcall 'cons
(v rest))))))
,(lp tail krest))))))))))))
(else term)))
(($ $kargs args)
,(if (< (length vals) (length args))
term
(let ((vals (list-head vals (length args))))
(build-cps-term
($continue k src ($values vals))))))))
(($ $continue k src (and fun ($ $fun)))
($continue k src ,(visit-fun fun)))
(($ $continue k src ($ $rec names syms funs))
($continue k src ($rec names syms (map visit-fun funs))))
(($ $continue)
,term)))
(define (visit-fun fun)
(rewrite-cps-exp fun
(($ $fun cont)
($fun ,(visit-cont cont)))))
(visit-cont fun))
(define (elide-values fun)
(with-fresh-name-state fun
(let ((conts (build-cont-table fun)))
(elide-values* fun conts))))
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