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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 (language cps)
#:use-module (language cps utils)
#:use-module (language cps with-cps)
#:use-module (language cps intmap)
#:export (elide-values))
(define (inline-values cps k src args)
(match (intmap-ref cps k)
(($ $ktail)
(with-cps cps
(build-term
($continue k src ($values args)))))
(($ $kreceive ($ $arity req () rest () #f) kargs)
(cond
((and (not rest) (= (length args) (length req)))
(with-cps cps
(build-term
($continue kargs src ($values args)))))
((and rest (>= (length args) (length req)))
(let ()
(define (build-rest cps k tail)
(match tail
(()
(with-cps cps
(build-term ($continue k src ($const '())))))
((v . tail)
(with-cps cps
(letv rest)
(letk krest ($kargs ('rest) (rest)
($continue k src ($primcall 'cons (v rest)))))
($ (build-rest krest tail))))))
(with-cps cps
(letv rest)
(letk krest ($kargs ('rest) (rest)
($continue kargs src
($values ,(append (list-head args (length req))
(list rest))))))
($ (build-rest krest (list-tail args (length req)))))))
(else (with-cps cps #f))))))
(define (elide-values conts)
(with-fresh-name-state conts
(persistent-intmap
(intmap-fold
(lambda (label cont out)
(match cont
(($ $kargs names vars ($ $continue k src ($ $primcall 'values args)))
(call-with-values (lambda () (inline-values out k src args))
(lambda (out term)
(if term
(let ((cont (build-cont ($kargs names vars ,term))))
(intmap-replace! out label cont))
out))))
(_ out)))
conts
conts))))
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