unbind_to performance tuning

* src/alloc.c (which_symbols):
* src/dispnew.c (Fredisplay):
* src/editfns.c (Fsubst_char_in_region):
* src/fileio.c (Fdo_auto_save):
* src/indent.c (Fvertical_motion):
* src/keymap.c (Fcurrent_active_maps):
* src/lread.c (Feval_buffer):
* src/minibuf.c (get_minibuffer):
* src/sysdep.c (system_process_attributes):
* src/textprop.c (Fnext_single_char_property_change)
(Fprevious_single_char_property_change):
* src/window.c (Fscroll_other_window, Fscroll_other_window_down):
* src/xdisp.c (Fformat_mode_line):
Help the compiler eliminate tail recursion in call to unbind_to.
* src/coding.c (decode_coding_gap):
Omit unnecessary unbind_to, as we’re about to call unbind_to anyway.
* src/coding.c (Fread_coding_system):
* src/eval.c (eval_sub):
* src/xdisp.c (handle_single_display_spec, decode_mode_spec):
* src/xselect.c (x_get_local_selection):
Avoid need to save a machine register when calling unbind_to.
* src/minibuf.c (Ftry_completion, Fall_completions):
Omit unnecessary assignment.

src/alloc.c

@@ -7206,8 +7206,7 @@ which_symbols (Lisp_Object obj, EMACS_INT find_max)
      }
 
   out:
-   unbind_to (gc_count, Qnil);
-   return found;
+   return unbind_to (gc_count, found);
 }
 
 #ifdef SUSPICIOUS_OBJECT_CHECKING

src/coding.c

@@ -8005,7 +8005,6 @@ decode_coding_gap (struct coding_system *coding,
       ptrdiff_t prev_Z = Z, prev_Z_BYTE = Z_BYTE;
       Lisp_Object val;
       Lisp_Object undo_list = BVAR (current_buffer, undo_list);
-      ptrdiff_t count1 = SPECPDL_INDEX ();
 
       record_unwind_protect (coding_restore_undo_list,
 			     Fcons (undo_list, Fcurrent_buffer ()));
@@ -8016,7 +8015,6 @@ decode_coding_gap (struct coding_system *coding,
       CHECK_NATNUM (val);
       coding->produced_char += Z - prev_Z;
       coding->produced += Z_BYTE - prev_Z_BYTE;
-      unbind_to (count1, Qnil);
     }
 
   unbind_to (count, Qnil);
@@ -8545,7 +8543,7 @@ are lower-case).  */)
   val = Fcompleting_read (prompt, Vcoding_system_alist, Qnil,
 			  Qt, Qnil, Qcoding_system_history,
 			  default_coding_system, Qnil);
-  unbind_to (count, Qnil);
+  val = unbind_to (count, val);
   return (SCHARS (val) == 0 ? Qnil : Fintern (val, Qnil));
 }
 

src/dispnew.c

@@ -5828,8 +5828,7 @@ immediately by pending input.  */)
   if (!NILP (force) && !redisplay_dont_pause)
     specbind (Qredisplay_dont_pause, Qt);
   redisplay_preserve_echo_area (2);
-  unbind_to (count, Qnil);
-  return Qt;
+  return unbind_to (count, Qt);
 }
 
 

src/editfns.c

@@ -3531,8 +3531,7 @@ Both characters must have the same length of multi-byte form.  */)
       update_compositions (changed, last_changed, CHECK_ALL);
     }
 
-  unbind_to (count, Qnil);
-  return Qnil;
+  return unbind_to (count, Qnil);
 }
 
 

src/eval.c

@@ -2366,7 +2366,7 @@ eval_sub (Lisp_Object form)
 	  specbind (Qlexical_binding,
 		    NILP (Vinternal_interpreter_environment) ? Qnil : Qt);
 	  exp = apply1 (Fcdr (fun), original_args);
-	  unbind_to (count1, Qnil);
+	  exp = unbind_to (count1, exp);
 	  val = eval_sub (exp);
 	}
       else if (EQ (funcar, Qlambda)

src/fileio.c

@@ -5767,8 +5767,7 @@ A non-nil CURRENT-ONLY argument means save only current buffer.  */)
   Vquit_flag = oquit;
 
   /* This restores the message-stack status.  */
-  unbind_to (count, Qnil);
-  return Qnil;
+  return unbind_to (count, Qnil);
 }
 
 DEFUN ("set-buffer-auto-saved", Fset_buffer_auto_saved,

src/indent.c

@@ -2356,9 +2356,7 @@ whether or not it is currently displayed in some window.  */)
       bidi_unshelve_cache (itdata, 0);
     }
 
-  unbind_to (count, Qnil);
-
-  return make_number (it.vpos);
+  return unbind_to (count, make_number (it.vpos));
 }
 
 

src/keymap.c

@@ -1608,9 +1608,7 @@ like in the respective argument of `key-binding'.  */)
 	keymaps = Fcons (otlp, keymaps);
     }
 
-  unbind_to (count, Qnil);
-
-  return keymaps;
+  return unbind_to (count, keymaps);
 }
 
 /* GC is possible in this function if it autoloads a keymap.  */

src/lread.c

@@ -2143,9 +2143,7 @@ This function preserves the position of point.  */)
   BUF_TEMP_SET_PT (XBUFFER (buf), BUF_BEGV (XBUFFER (buf)));
   readevalloop (buf, 0, filename,
 		!NILP (printflag), unibyte, Qnil, Qnil, Qnil);
-  unbind_to (count, Qnil);
-
-  return Qnil;
+  return unbind_to (count, Qnil);
 }
 
 DEFUN ("eval-region", Feval_region, Seval_region, 2, 4, "r",

src/minibuf.c

@@ -755,7 +755,7 @@ get_minibuffer (EMACS_INT depth)
 	call0 (intern ("minibuffer-inactive-mode"));
       else
         Fkill_all_local_variables ();
-      unbind_to (count, Qnil);
+      buf = unbind_to (count, buf);
     }
 
   return buf;
@@ -1274,11 +1274,12 @@ is used to further constrain the set of candidates.  */)
 	    for (regexps = Vcompletion_regexp_list; CONSP (regexps);
 		 regexps = XCDR (regexps))
 	      {
-		if (bindcount < 0) {
-		  bindcount = SPECPDL_INDEX ();
-		  specbind (Qcase_fold_search,
-			    completion_ignore_case ? Qt : Qnil);
-		}
+		if (bindcount < 0)
+		  {
+		    bindcount = SPECPDL_INDEX ();
+		    specbind (Qcase_fold_search,
+			      completion_ignore_case ? Qt : Qnil);
+		  }
 		tem = Fstring_match (XCAR (regexps), eltstring, zero);
 		if (NILP (tem))
 		  break;
@@ -1377,10 +1378,8 @@ is used to further constrain the set of candidates.  */)
 	}
     }
 
-  if (bindcount >= 0) {
+  if (bindcount >= 0)
     unbind_to (bindcount, Qnil);
-    bindcount = -1;
-  }
 
   if (NILP (bestmatch))
     return Qnil;		/* No completions found.  */
@@ -1534,11 +1533,12 @@ with a space are ignored unless STRING itself starts with a space.  */)
 	    for (regexps = Vcompletion_regexp_list; CONSP (regexps);
 		 regexps = XCDR (regexps))
 	      {
-		if (bindcount < 0) {
-		  bindcount = SPECPDL_INDEX ();
-		  specbind (Qcase_fold_search,
-			    completion_ignore_case ? Qt : Qnil);
-		}
+		if (bindcount < 0)
+		  {
+		    bindcount = SPECPDL_INDEX ();
+		    specbind (Qcase_fold_search,
+			      completion_ignore_case ? Qt : Qnil);
+		  }
 		tem = Fstring_match (XCAR (regexps), eltstring, zero);
 		if (NILP (tem))
 		  break;
@@ -1556,10 +1556,11 @@ with a space are ignored unless STRING itself starts with a space.  */)
 		tem = Fcommandp (elt, Qnil);
 	      else
 		{
-		  if (bindcount >= 0) {
-		    unbind_to (bindcount, Qnil);
-		    bindcount = -1;
-		  }
+		  if (bindcount >= 0)
+		    {
+		      unbind_to (bindcount, Qnil);
+		      bindcount = -1;
+		    }
 		  tem = type == 3
 		    ? call2 (predicate, elt,
 			     HASH_VALUE (XHASH_TABLE (collection), idx - 1))
@@ -1572,10 +1573,8 @@ with a space are ignored unless STRING itself starts with a space.  */)
 	}
     }
 
-  if (bindcount >= 0) {
+  if (bindcount >= 0)
     unbind_to (bindcount, Qnil);
-    bindcount = -1;
-  }
 
   return Fnreverse (allmatches);
 }

src/sysdep.c

@@ -3592,8 +3592,7 @@ system_process_attributes (Lisp_Object pid)
 						  Vlocale_coding_system, 0);
       attrs = Fcons (Fcons (Qargs, decoded_cmd), attrs);
     }
-  unbind_to (count, Qnil);
-  return attrs;
+  return unbind_to (count, attrs);
 }
 
 #elif defined __FreeBSD__

src/textprop.c

@@ -826,7 +826,7 @@ last valid position in OBJECT.  */)
 	      break;
 	  }
 
-      unbind_to (count, Qnil);
+      position = unbind_to (count, position);
     }
 
   return position;
@@ -920,7 +920,7 @@ first valid position in OBJECT.  */)
 	    }
 	}
 
-      unbind_to (count, Qnil);
+      position = unbind_to (count, position);
     }
 
   return position;

src/window.c

@@ -5771,8 +5771,7 @@ which see.  */)
 {
   ptrdiff_t count = SPECPDL_INDEX ();
   scroll_command (Fother_window_for_scrolling (), arg, 1);
-  unbind_to (count, Qnil);
-  return Qnil;
+  return unbind_to (count, Qnil);
 }
 
 DEFUN ("scroll-other-window-down", Fscroll_other_window_down,
@@ -5783,8 +5782,7 @@ For more details, see the documentation for `scroll-other-window'.  */)
 {
   ptrdiff_t count = SPECPDL_INDEX ();
   scroll_command (Fother_window_for_scrolling (), arg, -1);
-  unbind_to (count, Qnil);
-  return Qnil;
+  return unbind_to (count, Qnil);
 }
 
 DEFUN ("scroll-left", Fscroll_left, Sscroll_left, 0, 2, "^P\np",

src/xdisp.c

@@ -4937,7 +4937,7 @@ handle_single_display_spec (struct it *it, Lisp_Object spec, Lisp_Object object,
       specbind (Qposition, make_number (CHARPOS (*position)));
       specbind (Qbuffer_position, make_number (bufpos));
       form = safe_eval (form);
-      unbind_to (count, Qnil);
+      form = unbind_to (count, form);
     }
 
   if (NILP (form))
@@ -5000,7 +5000,7 @@ handle_single_display_spec (struct it *it, Lisp_Object spec, Lisp_Object object,
 
 		  specbind (Qheight, face->lface[LFACE_HEIGHT_INDEX]);
 		  value = safe_eval (it->font_height);
-		  unbind_to (count, Qnil);
+		  value = unbind_to (count, value);
 
 		  if (NUMBERP (value))
 		    new_height = XFLOATINT (value);
@@ -24183,8 +24183,7 @@ are the selected window and the WINDOW's buffer).  */)
 			empty_unibyte_string);
     }
 
-  unbind_to (count, Qnil);
-  return str;
+  return unbind_to (count, str);
 }
 
 /* Write a null-terminated, right justified decimal representation of
@@ -24804,7 +24803,7 @@ decode_mode_spec (struct window *w, register int c, int field_width,
 	if (STRINGP (curdir))
 	  val = call1 (intern ("file-remote-p"), curdir);
 
-	unbind_to (count, Qnil);
+	val = unbind_to (count, val);
 
 	if (NILP (val))
 	  return "-";

src/xselect.c

@@ -387,7 +387,7 @@ x_get_local_selection (Lisp_Object selection_symbol, Lisp_Object target_type,
 		       XCAR (XCDR (local_value)));
       else
 	value = Qnil;
-      unbind_to (count, Qnil);
+      value = unbind_to (count, value);
     }
 
   /* Make sure this value is of a type that we could transmit