Be lazy about refreshing the windows in tui_show_frame_info (PR tui/13378)

tui_show_frame_info is responsible for updating the visible windows
following a change in frame information (that being the currently
selected frame, PC, line number, etc).  Currently it always redraws and
refreshes each window even if frame information has not changed.  This
behavior is inefficient and helps contribute to the occassional
flickering of the TUI as described in the mentioned PR.

This patch makes tui_show_frame_info refresh the windows only if frame
information has changed.  Determining whether frame information has
changed is done indirectly by determining whether the locator has
changed.  This approach is convenient and yet sensible because the
locator contains all the relevant info we need to check anyway: the
current PC, the line number, the name of the executable and the name of
the current function.  Probably only the PC is really necessary to
check, but it doesn't hurt to check every field.

Effectively, with this patch, consecutive calls to select_frame with the
same frame/PC no longer cause TUI's frame information to be updated
multiple times.

gdb/ChangeLog:

	PR tui/13378
	* tui/tui-stack.c (tui_set_locator_info): Change prototype to
	return an int instead of void.  Return whether the locator
	window has changed.
	(tui_show_frame_info): If the locator info has not changed, then
	bail out early to avoid refreshing the windows.

1 files changed, 55 insertions, 16 deletions

diff --git a/gdb/tui/tui-stack.c b/gdb/tui/tui-stack.c
index b17d303..65d18fe 100644
--- a/gdb/tui/tui-stack.c
+++ b/gdb/tui/tui-stack.c
@@ -48,10 +48,10 @@ static char *tui_get_function_from_frame (struct frame_info *fi);
 static void tui_set_locator_fullname (const char *fullname);
 
 /* Update the locator, with the provided arguments.  */
-static void tui_set_locator_info (struct gdbarch *gdbarch,
-				  const char *fullname,
-				  const char *procname,
-                                  int lineno, CORE_ADDR addr);
+static int tui_set_locator_info (struct gdbarch *gdbarch,
+				 const char *fullname,
+				 const char *procname,
+                                 int lineno, CORE_ADDR addr);
 
 static void tui_update_command (char *, int);
 
@@ -292,8 +292,12 @@ tui_set_locator_fullname (const char *fullname)
   strcat_to_buf (element->full_name, MAX_LOCATOR_ELEMENT_LEN, fullname);
 }
 
-/* Update the locator, with the provided arguments.  */
-static void
+/* Update the locator, with the provided arguments.
+
+   Returns 1 if any of the locator's fields were actually changed,
+   and 0 otherwise.  */
+
+static int
 tui_set_locator_info (struct gdbarch *gdbarch,
 		      const char *fullname,
 		      const char *procname, 
@@ -302,21 +306,40 @@ tui_set_locator_info (struct gdbarch *gdbarch,
 {
   struct tui_gen_win_info *locator = tui_locator_win_info_ptr ();
   struct tui_locator_element *element;
+  int locator_changed_p = 0;
 
   /* Allocate the locator content if necessary.  */
   if (locator->content_size <= 0)
     {
       locator->content = tui_alloc_content (1, LOCATOR_WIN);
       locator->content_size = 1;
+      locator_changed_p = 1;
     }
 
+  if (procname == NULL)
+    procname = "";
+
+  if (fullname == NULL)
+    fullname = "";
+
   element = &locator->content[0]->which_element.locator;
+
+  locator_changed_p |= strncmp (element->proc_name, procname,
+				MAX_LOCATOR_ELEMENT_LEN) != 0;
+  locator_changed_p |= lineno != element->line_no;
+  locator_changed_p |= addr != element->addr;
+  locator_changed_p |= gdbarch != element->gdbarch;
+  locator_changed_p |= strncmp (element->full_name, fullname,
+				MAX_LOCATOR_ELEMENT_LEN) != 0;
+
   element->proc_name[0] = (char) 0;
   strcat_to_buf (element->proc_name, MAX_LOCATOR_ELEMENT_LEN, procname);
   element->line_no = lineno;
   element->addr = addr;
   element->gdbarch = gdbarch;
   tui_set_locator_fullname (fullname);
+
+  return locator_changed_p;
 }
 
 /* Update only the full_name portion of the locator.  */
@@ -327,11 +350,14 @@ tui_update_locator_fullname (const char *fullname)
   tui_show_locator_content ();
 }
 
-/* Function to print the frame information for the TUI.  */
+/* Function to print the frame information for the TUI.  The windows are
+   refreshed only if frame information has changed since the last refresh.  */
+
 void
 tui_show_frame_info (struct frame_info *fi)
 {
   struct tui_win_info *win_info;
+  int locator_changed_p;
   int i;
 
   if (fi)
@@ -349,15 +375,23 @@ tui_show_frame_info (struct frame_info *fi)
         && tui_source_is_displayed (symtab_to_fullname (sal.symtab));
 
       if (get_frame_pc_if_available (fi, &pc))
-	tui_set_locator_info (get_frame_arch (fi),
-			      (sal.symtab == 0
-			       ? "??" : symtab_to_fullname (sal.symtab)),
-			      tui_get_function_from_frame (fi),
-			      sal.line,
-			      pc);
+	locator_changed_p
+	  = tui_set_locator_info (get_frame_arch (fi),
+				  (sal.symtab == 0
+				   ? "??" : symtab_to_fullname (sal.symtab)),
+				  tui_get_function_from_frame (fi),
+				  sal.line,
+				  pc);
       else
-	tui_set_locator_info (get_frame_arch (fi),
-			      "??", _("<unavailable>"), sal.line, 0);
+	locator_changed_p
+	  = tui_set_locator_info (get_frame_arch (fi),
+				  "??", _("<unavailable>"), sal.line, 0);
+
+      /* If the locator information has not changed, then frame information has
+	 not changed.  If frame information has not changed, then the windows'
+	 contents will not change.  So don't bother refreshing the windows.  */
+      if (!locator_changed_p)
+	return;
 
       tui_show_locator_content ();
       start_line = 0;
@@ -431,7 +465,12 @@ tui_show_frame_info (struct frame_info *fi)
     }
   else
     {
-      tui_set_locator_info (NULL, NULL, NULL, 0, (CORE_ADDR) 0);
+      locator_changed_p
+	= tui_set_locator_info (NULL, NULL, NULL, 0, (CORE_ADDR) 0);
+
+      if (!locator_changed_p)
+	return;
+
       tui_show_locator_content ();
       for (i = 0; i < (tui_source_windows ())->count; i++)
 	{