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86 lines
3.1 KiB
Scheme
86 lines
3.1 KiB
Scheme
;;; Continuation-passing style (CPS) intermediate language (IL)
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;; Copyright (C) 2013, 2014, 2015 Free Software Foundation, Inc.
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;;;; This library is free software; you can redistribute it and/or
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;;;; modify it under the terms of the GNU Lesser General Public
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;;;; License as published by the Free Software Foundation; either
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;;;; version 3 of the License, or (at your option) any later version.
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;;;;
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;;;; This library is distributed in the hope that it will be useful,
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;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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;;;; Lesser General Public License for more details.
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;;;;
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;;;; You should have received a copy of the GNU Lesser General Public
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;;;; License along with this library; if not, write to the Free Software
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;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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;;; Commentary:
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;;;
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;;; A pass that prunes successors of expressions that bail out.
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;;;
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;;; Code:
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(define-module (language cps prune-bailouts)
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#:use-module (ice-9 match)
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#:use-module (language cps)
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#:use-module (language cps utils)
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#:use-module (language cps with-cps)
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#:use-module (language cps intmap)
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#:use-module (language cps intset)
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#:export (prune-bailouts))
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(define (compute-tails conts)
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"For each LABEL->CONT entry in the intmap CONTS, compute a
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LABEL->TAIL-LABEL indicating the tail continuation of each expression's
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containing function. In some cases TAIL-LABEL might not be available,
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for example if there is a stale $kfun pointing at a body, or for
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unreferenced terms. In that case TAIL-LABEL is either absent or #f."
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(intmap-fold
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(lambda (label cont out)
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(match cont
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(($ $kfun src meta self tail clause)
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(intset-fold (lambda (label out)
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(intmap-add out label tail (lambda (old new) #f)))
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(compute-function-body conts label)
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out))
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(_ out)))
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conts
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empty-intmap))
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(define (prune-bailout out tails k src exp)
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(match (intmap-ref out k)
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(($ $ktail)
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(with-cps out #f))
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(_
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(match (intmap-ref tails k (lambda (_) #f))
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(#f
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(with-cps out #f))
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(ktail
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(with-cps out
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(letv prim rest)
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(letk kresult ($kargs ('rest) (rest)
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($continue ktail src ($values ()))))
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(letk kreceive ($kreceive '() 'rest kresult))
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(build-term ($continue kreceive src ,exp))))))))
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(define (prune-bailouts conts)
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(let ((tails (compute-tails conts)))
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(with-fresh-name-state conts
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(persistent-intmap
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(intmap-fold
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(lambda (label cont out)
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(match cont
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(($ $kargs names vars
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($ $continue k src
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(and exp ($ $primcall (or 'error 'scm-error 'throw)))))
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(call-with-values (lambda () (prune-bailout out tails k src exp))
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(lambda (out term)
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(if term
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(let ((cont (build-cont ($kargs names vars ,term))))
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(intmap-replace! out label cont))
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out))))
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(_ out)))
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conts
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conts)))))
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