From: Chris Hanson <org/chris-hanson/cph>
Date: Fri, 3 Jun 1988 14:56:55 +0000 (+0000)
Subject: (invalidate-memory-destination!) Optimize this -- if both class and
X-Git-Tag: 20090517-FFI~12742
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=0c07901d729bde76164a87e4fa20647a8806e2b1;p=mit-scheme.git

(invalidate-memory-destination!) Optimize this -- if both class and
hash are not given, don't bother to insert the element in the hash
table, because it will have no useful effect.
---

diff --git a/v7/src/compiler/rtlopt/rcse2.scm b/v7/src/compiler/rtlopt/rcse2.scm
index 710e799f6..5795faeb7 100644
--- a/v7/src/compiler/rtlopt/rcse2.scm
+++ b/v7/src/compiler/rtlopt/rcse2.scm
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/compiler/rtlopt/rcse2.scm,v 4.6 1988/05/09 19:54:06 mhwu Exp $
+$Header: /Users/cph/tmp/foo/mit-scheme/mit-scheme/v7/src/compiler/rtlopt/rcse2.scm,v 4.7 1988/06/03 14:56:55 cph Exp $
 
 Copyright (c) 1987 Massachusetts Institute of Technology
 
@@ -191,7 +191,12 @@ MIT in each case. |#
 (define (insert-memory-destination! expression element hash)
   (let ((class (element->class element)))
     (mention-registers! expression)
-    (set-element-in-memory?! (hash-table-insert! hash expression class) true)))
+    ;; Optimization: if class and hash are both false, hash-table-insert!
+    ;; makes an element which is not connected to the rest of the table.
+    ;; In that case, there is no need to make an element at all.
+    (if (or class hash)
+	(set-element-in-memory?! (hash-table-insert! hash expression class)
+				 true))))
 
 (define (mention-registers! expression)
   (if (rtl:register? expression)