Give preference to registers over other expressions, even if they have

the same cost.  The RTL combiner and rewriting passes can always
make for cheaper expressions if necessary.

diff --git a/v7/src/compiler/rtlopt/rcseht.scm b/v7/src/compiler/rtlopt/rcseht.scm
index d9ab9db639ebc2d7b27f649cbe636fa569718638..0a9c85c4f9e1922acc4e3483f7df70a66e091108 100644 (file)
--- a/v7/src/compiler/rtlopt/rcseht.scm
+++ b/v7/src/compiler/rtlopt/rcseht.scm
@@ -1,8 +1,8 @@
 #| -*-Scheme-*-
 
-$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/compiler/rtlopt/rcseht.scm,v 4.11 1990/01/23 22:44:12 cph Rel $
+$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/compiler/rtlopt/rcseht.scm,v 4.12 1992/02/17 21:10:22 jinx Exp $
 
-Copyright (c) 1988, 1989, 1990 Massachusetts Institute of Technology
+Copyright (c) 1988-1992 Massachusetts Institute of Technology
 
 This material was developed by the Scheme project at the Massachusetts
 Institute of Technology, Department of Electrical Engineering and
@@ -34,6 +34,7 @@ MIT in each case. |#
 
 ;;;; RTL Common Subexpression Elimination: Hash Table Abstraction
 ;;;  Based on the GNU C Compiler
+;;; package: (compiler rtl-cse)
 
 (declare (usual-integrations))
 \f
@@ -86,7 +87,10 @@ MIT in each case. |#
          (hash-table-set! hash element)))
     (cond ((not class)
           (set-element-first-value! element element))
-         ((< cost (element-cost class))
+         ((or (< cost (element-cost class))
+              (and (= cost (element-cost class))
+                   (rtl:register? expression)
+                   (not (rtl:register? (element-expression class)))))
           (set-element-next-value! element class)
           (set-element-previous-value! class element)
           (let loop ((x element))
@@ -101,7 +105,11 @@ MIT in each case. |#
                    (set-element-next-value! element false)
                    (set-element-next-value! previous element)
                    (set-element-previous-value! element previous))
-                  ((<= cost (element-cost next))
+                  ((or (< cost (element-cost next))
+                       (and (= cost (element-cost next))
+                            (or (rtl:register? expression)
+                                (not (rtl:register?
+                                      (element-expression next))))))
                    (set-element-next-value! element next)
                    (set-element-previous-value! next element)
                    (set-element-next-value! previous element)