Introduce x_uncatch_errors_after_check to reduce XSync calls.

Both x_had_errors_p and x_check_errors call XSync, so if they're
immediately followed by x_uncatch_errors, its XSync call will be
redundant, resulting in a wasted round trip to the X server.

* src/xterm.c (x_uncatch_errors_after_check): New routine; a copy of
x_uncatch_errors without the XSync call.
(XTmouse_position, x_wm_supports):
* src/xfns.c (x_set_mouse_color):
* src/xmenu.c (Fx_menu_bar_open_internal):
* src/xselect.c (x_own_selection, x_get_foreign_selection):
(Fx_get_atom_name): Call it instead of x_uncatch_errors.
* src/xterm.h (x_uncatch_errors_after_check): Declare.

src/xfns.c

@@ -759,7 +759,7 @@ x_set_mouse_color (struct frame *f, Lisp_Object arg, Lisp_Object oldval)
 
   /* Check and report errors with the above calls.  */
   x_check_errors (dpy, "can't set cursor shape: %s");
-  x_uncatch_errors ();
+  x_uncatch_errors_after_check ();
 
   {
     XColor fore_color, back_color;

src/xmenu.c

@@ -325,7 +325,7 @@ If FRAME is nil or not given, use the selected frame.  */)
                              /* Child of win.  */
                              &child);
       error_p = x_had_errors_p (FRAME_X_DISPLAY (f));
-      x_uncatch_errors ();
+      x_uncatch_errors_after_check ();
 
       if (! error_p)
         {

src/xselect.c

@@ -316,7 +316,7 @@ x_own_selection (Lisp_Object selection_name, Lisp_Object selection_value,
   x_catch_errors (display);
   XSetSelectionOwner (display, selection_atom, selecting_window, timestamp);
   x_check_errors (display, "Can't set selection: %s");
-  x_uncatch_errors ();
+  x_uncatch_errors_after_check ();
   unblock_input ();
 
   /* Now update the local cache */
@@ -1179,7 +1179,7 @@ x_get_foreign_selection (Lisp_Object selection_symbol, Lisp_Object target_type,
   XConvertSelection (display, selection_atom, type_atom, target_property,
 		     requestor_window, requestor_time);
   x_check_errors (display, "Can't convert selection: %s");
-  x_uncatch_errors ();
+  x_uncatch_errors_after_check ();
 
   /* Prepare to block until the reply has been read.  */
   reading_selection_window = requestor_window;
@@ -2364,7 +2364,7 @@ If the value is 0 or the atom is not known, return the empty string.  */)
   x_catch_errors (dpy);
   name = atom ? XGetAtomName (dpy, atom) : empty;
   had_errors_p = x_had_errors_p (dpy);
-  x_uncatch_errors ();
+  x_uncatch_errors_after_check ();
 
   if (!had_errors_p)
     ret = build_string (name);

src/xterm.c

@@ -4992,7 +4992,7 @@ XTmouse_position (struct frame **fp, int insist, Lisp_Object *bar_window,
 	if (x_had_errors_p (FRAME_X_DISPLAY (*fp)))
 	  f1 = 0;
 
-	x_uncatch_errors ();
+	x_uncatch_errors_after_check ();
 
 	/* If not, is it one of our scroll bars?  */
 	if (! f1)
@@ -9217,7 +9217,10 @@ x_error_catcher (Display *display, XErrorEvent *event)
    Calling x_check_errors signals an Emacs error if an X error has
    occurred since the last call to x_catch_errors or x_check_errors.
 
-   Calling x_uncatch_errors resumes the normal error handling.  */
+   Calling x_uncatch_errors resumes the normal error handling.
+   Calling x_uncatch_errors_after_check is similar, but skips an XSync
+   to the server, and should be used only immediately after
+   x_had_errors_p or x_check_errors.  */
 
 void
 x_catch_errors (Display *dpy)
@@ -9233,6 +9236,25 @@ x_catch_errors (Display *dpy)
   x_error_message = data;
 }
 
+/* Undo the last x_catch_errors call.
+   DPY should be the display that was passed to x_catch_errors.
+
+   This version should be used only if the immediately preceding
+   X-protocol-related thing was x_check_errors or x_had_error_p, both
+   of which issue XSync calls, so we don't need to re-sync here.  */
+
+void
+x_uncatch_errors_after_check (void)
+{
+  struct x_error_message_stack *tmp;
+
+  block_input ();
+  tmp = x_error_message;
+  x_error_message = x_error_message->prev;
+  xfree (tmp);
+  unblock_input ();
+}
+
 /* Undo the last x_catch_errors call.
    DPY should be the display that was passed to x_catch_errors.  */
 
@@ -9928,7 +9950,7 @@ x_wm_supports (struct frame *f, Atom want_atom)
   XSelectInput (dpy, wmcheck_window, StructureNotifyMask);
   if (x_had_errors_p (dpy))
     {
-      x_uncatch_errors ();
+      x_uncatch_errors_after_check ();
       unblock_input ();
       return false;
     }

src/xterm.h

@@ -1030,6 +1030,7 @@ extern void x_check_errors (Display *, const char *)
   ATTRIBUTE_FORMAT_PRINTF (2, 0);
 extern bool x_had_errors_p (Display *);
 extern void x_uncatch_errors (void);
+extern void x_uncatch_errors_after_check (void);
 extern void x_clear_errors (Display *);
 extern void xembed_request_focus (struct frame *);
 extern void x_ewmh_activate_frame (struct frame *);