From: Stefan Monnier <monnier@iro.umontreal.ca>
Date: Thu, 27 Oct 2016 05:18:16 +0000 (-0400)
Subject: Reduce lread substitutions.
X-Git-Tag: emacs-26.0.90~521^2~18^2~3
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=6af67b4a8842fd3b949fa5bfb68811f62a521ae2;p=emacs.git

Reduce lread substitutions.

* src/lread.c (read1): After reading an object using the "#n=" syntax,
if the read object is a cons cell, instead of recursively substituting
the placeholder with the new object, mutate the placeholder cons cell
itself to have the correct car and cdr values.
---

diff --git a/src/lread.c b/src/lread.c
index 263638651db..a6d04ec5af7 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -2990,12 +2990,21 @@ read1 (Lisp_Object readcharfun, int *pch, bool first_in_list)
 		      tem = read0 (readcharfun);
 
 		      /* Now put it everywhere the placeholder was...  */
-		      Fsubstitute_object_in_subtree (tem, placeholder);
+                      if (CONSP (tem))
+                        {
+                          Fsetcar (placeholder, XCAR (tem));
+                          Fsetcdr (placeholder, XCDR (tem));
+                          return placeholder;
+                        }
+                      else
+                        {
+		          Fsubstitute_object_in_subtree (tem, placeholder);
 
-		      /* ...and #n# will use the real value from now on.  */
-		      Fsetcdr (cell, tem);
+		          /* ...and #n# will use the real value from now on.  */
+		          Fsetcdr (cell, tem);
 
-		      return tem;
+		          return tem;
+                        }
 		    }
 
 		  /* #n# returns a previously read object.  */