From: Taylor R. Campbell <net/mumble/campbell>
Date: Mon, 24 Oct 2005 05:07:38 +0000 (+0000)
Subject: Fix bug in parser optimizer whereby local bindings for the buffer
X-Git-Tag: 20090517-FFI~1201
X-Git-Url: https://birchwood-abbey.net/git?a=commitdiff_plain;h=b56ddae388d08a1c97ff2a114332ef13a8a66a16;p=mit-scheme.git

Fix bug in parser optimizer whereby local bindings for the buffer
pointer would be eliminated due to ostensible lack of reference, even
if the user code contained references to them, because the reference
counter won't descend into the user code.  Also, reintroduce the new
rule, which was previously removed, for turning redundant bindings of
the buffer pointer into aliases.  Cases affected independently by each
optimization should now be covered correctly & safely.
---

diff --git a/v7/src/star-parser/shared.scm b/v7/src/star-parser/shared.scm
index c3d115f37..740e456ec 100644
--- a/v7/src/star-parser/shared.scm
+++ b/v7/src/star-parser/shared.scm
@@ -1,6 +1,6 @@
 #| -*-Scheme-*-
 
-$Id: shared.scm,v 1.31 2005/06/04 23:44:05 cph Exp $
+$Id: shared.scm,v 1.32 2005/10/24 05:07:38 riastradh Exp $
 
 Copyright 2001,2002,2003,2005 Massachusetts Institute of Technology
 
@@ -808,16 +808,30 @@ USA.
 	       ,(new-pointer tail identifier pointers)))))))
 
 (define-pointer-optimization '(('LAMBDA (IDENTIFIER) EXPRESSION)
-			       ('GET-PARSER-BUFFER-POINTER EXPRESSION))
+                               ('GET-PARSER-BUFFER-POINTER EXPRESSION))
   (lambda (expression pointers)
     (let ((identifier (car (cadr (car expression))))
-	  (operand (cadr expression))
-	  (body (caddr (car expression))))
-      (let ((body (new-pointer body identifier pointers)))
-	(if (= (car (count-references (list identifier) body)) 0)
-	    ;; IDENTIFIER is an alias, so don't bind it.
-	    body
-	    `((LAMBDA (,identifier) ,body) ,operand))))))
+          (operand (cadr expression))
+          (body (caddr (car expression))))
+      (let ((optimized-body (new-pointer body identifier pointers)))
+        ;; Don't bind the identifier if it is internal and unused.  The
+        ;; condition that the identifier be internal avoids a problem
+        ;; of not counting references that are in the user's code,
+        ;; which COUNT-REFERENCES can't descend into.
+        (if (and (internal-identifier? identifier)
+                 (zero? (car (count-references (list identifier)
+                                               optimized-body))))
+            optimized-body
+            `((LAMBDA (,identifier)
+                ;++ If we already have a pointer, the optimizer ought
+                ;++ to introduce a (DECLARE (INTEGRATE ,identifier))
+                ;++ here so that the scode optimizer will integrate the
+                ;++ variable, even though the parser optimizer won't,
+                ;++ but later passes of the parser optimizer can't
+                ;++ handle LAMBDAs with more than one subform.
+                ,optimized-body)
+              ,(or (car pointers)
+                   operand)))))))
 
 (define-pointer-optimization '('PROTECT EXPRESSION)
   (lambda (expression pointers)