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+;;; Continuation-passing style (CPS) intermediate language (IL)
+
+;; Copyright (C) 2014, 2015, 2017 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:
+;;;
+;;; A simple pass to prune unneeded top-level scopes.
+;;;
+;;; Code:
+
+(define-module (language cps prune-top-level-scopes)
+ #:use-module (ice-9 match)
+ #:use-module (language cps)
+ #:use-module (language cps utils)
+ #:use-module (language cps intmap)
+ #:use-module (language cps intset)
+ #:export (prune-top-level-scopes))
+
+(define (compute-used-scopes conts)
+ (persistent-intset
+ (intmap-fold
+ (lambda (label cont used-scopes)
+ (match cont
+ (($ $kargs _ _
+ ($ $continue k src
+ ($ $primcall 'cached-toplevel-box (scope name bound?))))
+ (intset-add! used-scopes scope))
+ (_
+ used-scopes)))
+ conts
+ empty-intset)))
+
+(define (prune-top-level-scopes conts)
+ (let* ((used-scopes (compute-used-scopes conts)))
+ (intmap-map
+ (lambda (label cont)
+ (match cont
+ (($ $kargs names vars
+ ($ $continue k src
+ ($ $primcall 'cache-current-module! (scope-id) (module))))
+ (if (intset-ref used-scopes scope-id)
+ cont
+ (build-cont ($kargs names vars
+ ($continue k src ($values ()))))))
+ (_
+ cont)))
+ conts)))