--- /dev/null
+#| -*-Scheme-*-
+
+$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/compiler/back/mermap.scm,v 1.1 1988/11/07 13:57:49 cph Exp $
+
+Copyright (c) 1988 Massachusetts Institute of Technology
+
+This material was developed by the Scheme project at the Massachusetts
+Institute of Technology, Department of Electrical Engineering and
+Computer Science. Permission to copy this software, to redistribute
+it, and to use it for any purpose is granted, subject to the following
+restrictions and understandings.
+
+1. Any copy made of this software must include this copyright notice
+in full.
+
+2. Users of this software agree to make their best efforts (a) to
+return to the MIT Scheme project any improvements or extensions that
+they make, so that these may be included in future releases; and (b)
+to inform MIT of noteworthy uses of this software.
+
+3. All materials developed as a consequence of the use of this
+software shall duly acknowledge such use, in accordance with the usual
+standards of acknowledging credit in academic research.
+
+4. MIT has made no warrantee or representation that the operation of
+this software will be error-free, and MIT is under no obligation to
+provide any services, by way of maintenance, update, or otherwise.
+
+5. In conjunction with products arising from the use of this material,
+there shall be no use of the name of the Massachusetts Institute of
+Technology nor of any adaptation thereof in any advertising,
+promotional, or sales literature without prior written consent from
+MIT in each case. |#
+
+;;;; LAP Generator: Merge Register Maps
+
+(declare (usual-integrations))
+\f
+(define (merge-register-maps maps weights)
+ ;; This plays merry hell with the map entry order. An attempt has
+ ;; been made to preserve the order in simple cases, but in general
+ ;; there isn't enough information to do a really good job.
+ (let ((entries
+ (reduce add-weighted-entries
+ '()
+ (if (not weights)
+ (map (lambda (map)
+ (map->weighted-entries map 1))
+ maps)
+ (map map->weighted-entries maps weights)))))
+ (for-each eliminate-unlikely-aliases! entries)
+ (eliminate-conflicting-aliases! entries)
+ (weighted-entries->map entries)))
+
+(define (weighted-entries->map entries)
+ (let loop
+ ((entries entries)
+ (map-entries '())
+ (map-registers available-machine-registers))
+ (if (null? entries)
+ (make-register-map (reverse! map-entries)
+ (sort-machine-registers map-registers))
+ (let ((aliases (map car (vector-ref (car entries) 2))))
+ (if (null? aliases)
+ (loop (cdr entries) map-entries map-registers)
+ (loop (cdr entries)
+ (cons (make-map-entry
+ (vector-ref (car entries) 0)
+ (positive? (vector-ref (car entries) 1))
+ aliases)
+ map-entries)
+ (eqv-set-delete map-registers aliases)))))))
+\f
+(define (eliminate-conflicting-aliases! entries)
+ (for-each (lambda (conflicting-alias)
+ (let ((homes (cdr conflicting-alias)))
+ (let ((maximum (apply max (map cdr homes))))
+ (let ((winner
+ (list-search-positive homes
+ (lambda (home)
+ (= (cdr home) maximum)))))
+ (for-each
+ (lambda (home)
+ (if (not (eq? home winner))
+ (let ((entry
+ (find-weighted-entry (car home) entries)))
+ (vector-set! entry 2
+ (del-assv! (car conflicting-alias)
+ (vector-ref entry 2))))))
+ homes)))))
+ (conflicting-aliases entries)))
+
+(define (conflicting-aliases entries)
+ (let ((alist '()))
+ (for-each
+ (lambda (entry)
+ (let ((home (vector-ref entry 0)))
+ (for-each
+ (lambda (alias-weight)
+ (let ((alist-entry (assv (car alias-weight) alist))
+ (element (cons home (cdr alias-weight))))
+ (if alist-entry
+ (set-cdr! alist-entry (cons element (cdr alist-entry)))
+ (set! alist
+ (cons (list (car alias-weight) element) alist)))))
+ (vector-ref entry 2))))
+ entries)
+ (list-transform-negative alist
+ (lambda (alist-entry)
+ (null? (cddr alist-entry))))))
+
+(define (eliminate-unlikely-aliases! entry)
+ (let ((home-weight (vector-ref entry 1))
+ (alias-weights (vector-ref entry 2)))
+ (let ((maximum (max home-weight (apply max (map cdr alias-weights)))))
+ (if (not (= home-weight maximum))
+ (vector-set! entry 1 0))
+ (vector-set! entry 2
+ ((list-deletor!
+ (lambda (alias-weight)
+ (not (= (cdr alias-weight) maximum))))
+ alias-weights)))))
+\f
+(define (map->weighted-entries register-map weight)
+ (map (lambda (entry)
+ (vector (map-entry-home entry)
+ (if (map-entry-saved-into-home? entry) weight 0)
+ (map (lambda (alias) (cons alias weight))
+ (map-entry-aliases entry))))
+ (map-entries register-map)))
+
+(define (add-weighted-entries x-entries y-entries)
+ (merge-entries x-entries y-entries
+ (lambda (entry entries)
+ (list-search-positive entries
+ (let ((home (vector-ref entry 0)))
+ (lambda (entry)
+ (eqv? home (vector-ref entry 0))))))
+ (lambda (x-entry y-entry)
+ (vector (vector-ref x-entry 0)
+ (+ (vector-ref x-entry 1) (vector-ref y-entry 1))
+ (merge-entries (vector-ref x-entry 2) (vector-ref y-entry 2)
+ (lambda (entry entries)
+ (assq (car entry) entries))
+ (lambda (x-entry y-entry)
+ (cons (car x-entry) (+ (cdr x-entry) (cdr y-entry)))))))))
+
+(define (merge-entries x-entries y-entries find-entry merge-entry)
+ (let loop
+ ((x-entries x-entries)
+ (y-entries (list-copy y-entries))
+ (result '()))
+ (if (null? x-entries)
+ ;; This (feebly) attempts to preserve the entry order.
+ (append! (reverse! result) y-entries)
+ (let ((x-entry (car x-entries))
+ (x-entries (cdr x-entries)))
+ (let ((y-entry (find-entry x-entry y-entries)))
+ (if y-entry
+ (loop x-entries
+ (delq! y-entry y-entries)
+ (cons (merge-entry x-entry y-entry) result))
+ (loop x-entries
+ y-entries
+ (cons x-entry result))))))))
+
+(define find-weighted-entry
+ (association-procedure eqv? (lambda (entry) (vector-ref entry 0))))
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