Don't build print-number-table unless it will be used

There are only a few users of print-number-table, and none of them use
it when print-circle is nil.  A couple of them used to.  print_object
was changed in 2012-04-20 "* src/print.c (print_preprocess): Only
check print_depth if print-circle is nil".
byte-compile-output-docform which uses print-number-table binds
print-circle to t before printing unless
byte-compile-disable-print-circle is set, but that variable has been
marked obsolete since 24.1.

* src/print.c (print_preprocess): Assert Vprint_circle is non-nil.
Remove code handling the case when Vprint_circle is nil.
(print, Fprint_preprocess): Don't call print_preprocess unless
Vprint_circle is non-nil.
(print_object): Remove comment referencing removed code in
print_preprocess.

1 files changed, 39 insertions, 53 deletions

diff --git a/src/print.c b/src/print.c
index 18330b0fbf4..c870aa5a088 100644
--- a/src/print.c
+++ b/src/print.c
@@ -1120,8 +1120,8 @@ print (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag)
       Vprint_number_table = Qnil;
     }
 
-  /* Construct Vprint_number_table for print-gensym and print-circle.  */
-  if (!NILP (Vprint_gensym) || !NILP (Vprint_circle))
+  /* Construct Vprint_number_table for print-circle.  */
+  if (!NILP (Vprint_circle))
     {
       /* Construct Vprint_number_table.
          This increments print_number_index for the objects added.  */
@@ -1163,13 +1163,14 @@ print (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag)
        && SYMBOLP (obj)                                    \
        && !SYMBOL_INTERNED_P (obj)))
 
-/* Construct Vprint_number_table according to the structure of OBJ.
-   OBJ itself and all its elements will be added to Vprint_number_table
-   recursively if it is a list, vector, compiled function, char-table,
-   string (its text properties will be traced), or a symbol that has
-   no obarray (this is for the print-gensym feature).
-   The status fields of Vprint_number_table mean whether each object appears
-   more than once in OBJ: Qnil at the first time, and Qt after that.  */
+/* Construct Vprint_number_table for the print-circle feature
+   according to the structure of OBJ.  OBJ itself and all its elements
+   will be added to Vprint_number_table recursively if it is a list,
+   vector, compiled function, char-table, string (its text properties
+   will be traced), or a symbol that has no obarray (this is for the
+   print-gensym feature).  The status fields of Vprint_number_table
+   mean whether each object appears more than once in OBJ: Qnil at the
+   first time, and Qt after that.  */
 static void
 print_preprocess (Lisp_Object obj)
 {
@@ -1178,20 +1179,7 @@ print_preprocess (Lisp_Object obj)
   int loop_count = 0;
   Lisp_Object halftail;
 
-  /* Avoid infinite recursion for circular nested structure
-     in the case where Vprint_circle is nil.  */
-  if (NILP (Vprint_circle))
-    {
-      /* Give up if we go so deep that print_object will get an error.  */
-      /* See similar code in print_object.  */
-      if (print_depth >= PRINT_CIRCLE)
-        error ("Apparently circular structure being printed");
-
-      for (i = 0; i < print_depth; i++)
-        if (EQ (obj, being_printed[i]))
-          return;
-      being_printed[print_depth] = obj;
-    }
+  eassert (!NILP (Vprint_circle));
 
   print_depth++;
   halftail = obj;
@@ -1202,33 +1190,28 @@ print_preprocess (Lisp_Object obj)
       if (!HASH_TABLE_P (Vprint_number_table))
         Vprint_number_table = CALLN (Fmake_hash_table, QCtest, Qeq);
 
-      /* In case print-circle is nil and print-gensym is t,
-         add OBJ to Vprint_number_table only when OBJ is a symbol.  */
-      if (! NILP (Vprint_circle) || SYMBOLP (obj))
-        {
-          Lisp_Object num = Fgethash (obj, Vprint_number_table, Qnil);
-          if (!NILP (num)
-              /* If Vprint_continuous_numbering is non-nil and OBJ is a gensym,
-                 always print the gensym with a number.  This is a special for
-                 the lisp function byte-compile-output-docform.  */
-              || (!NILP (Vprint_continuous_numbering)
-                  && SYMBOLP (obj)
-                  && !SYMBOL_INTERNED_P (obj)))
-            { /* OBJ appears more than once.    Let's remember that.  */
-              if (!FIXNUMP (num))
-                {
-                  print_number_index++;
-                  /* Negative number indicates it hasn't been printed yet.  */
-                  Fputhash (obj, make_fixnum (- print_number_index),
-                            Vprint_number_table);
-                }
-              print_depth--;
-              return;
+      Lisp_Object num = Fgethash (obj, Vprint_number_table, Qnil);
+      if (!NILP (num)
+          /* If Vprint_continuous_numbering is non-nil and OBJ is a gensym,
+             always print the gensym with a number.  This is a special for
+             the lisp function byte-compile-output-docform.  */
+          || (!NILP (Vprint_continuous_numbering)
+              && SYMBOLP (obj)
+              && !SYMBOL_INTERNED_P (obj)))
+        { /* OBJ appears more than once.  Let's remember that.  */
+          if (!FIXNUMP (num))
+            {
+              print_number_index++;
+              /* Negative number indicates it hasn't been printed yet.  */
+              Fputhash (obj, make_fixnum (- print_number_index),
+                        Vprint_number_table);
             }
-          else
-            /* OBJ is not yet recorded.  Let's add to the table.  */
-            Fputhash (obj, Qt, Vprint_number_table);
+          print_depth--;
+          return;
         }
+      else
+        /* OBJ is not yet recorded.  Let's add to the table.  */
+        Fputhash (obj, Qt, Vprint_number_table);
 
       switch (XTYPE (obj))
         {
@@ -1275,11 +1258,15 @@ print_preprocess (Lisp_Object obj)
 
 DEFUN ("print--preprocess", Fprint_preprocess, Sprint_preprocess, 1, 1, 0,
        doc: /* Extract sharing info from OBJECT needed to print it.
-Fills `print-number-table'.  */)
-  (Lisp_Object object)
+Fills `print-number-table' if `print-circle' is non-nil.  Does nothing
+if `print-circle' is nil.  */)
+     (Lisp_Object object)
 {
-  print_number_index = 0;
-  print_preprocess (object);
+  if (!NILP (Vprint_circle))
+    {
+      print_number_index = 0;
+      print_preprocess (object);
+    }
   return Qnil;
 }
 
@@ -1864,7 +1851,6 @@ print_object (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag)
       /* Simple but incomplete way.  */
       int i;
 
-      /* See similar code in print_preprocess.  */
       if (print_depth >= PRINT_CIRCLE)
         error ("Apparently circular structure being printed");