[review] gdb: Add a class to track last display symtab and line information

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 312eed7..01f2425 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,32 @@ 
 2019-11-08  Andrew Burgess  <andrew.burgess@embecosm.com>
 
+	* stack.c (set_last_displayed_sal): Delete.
+	(last_displayed_sal_valid): Delete.
+	(last_displayed_pspace): Delete.
+	(last_displayed_addr): Delete.
+	(last_displayed_symtab): Delete.
+	(last_displayed_line): Delete.
+	(class last_displayed_symtab_info_type): New.
+	(last_displayed_symtab_info): New static global variable.
+	(print_frame_info): Call methods on last_displayed_symtab_info.
+	(clear_last_displayed_sal): Update header comment, and make use of
+	last_displayed_symtab_info.
+	(last_displayed_sal_is_valid): Likewise.
+	(get_last_displayed_pspace): Likewise.
+	(get_last_displayed_addr): Likewise.
+	(get_last_displayed_symtab): Likewise.
+	(get_last_displayed_line): Likewise.
+	(get_last_displayed_sal): Likewise.
+	* stack.h (clear_last_displayed_sal): Update header comment.
+	(last_displayed_sal_is_valid): Likewise.
+	(get_last_displayed_pspace): Likewise.
+	(get_last_displayed_addr): Likewise.
+	(get_last_displayed_symtab): Likewise.
+	(get_last_displayed_line): Likewise.
+	(get_last_displayed_sal): Likewise.
+
+2019-11-08  Andrew Burgess  <andrew.burgess@embecosm.com>
+
 	* stack.c (frame_show_address): Convert return type to bool.
 	* stack.h (frame_show_address): Likewise, and update header
 	comment.
diff --git a/gdb/stack.c b/gdb/stack.c
index 5af00c7..9d397bc 100644
--- a/gdb/stack.c
+++ b/gdb/stack.c
@@ -224,12 +224,6 @@ 
 			 enum print_what print_what,  int print_args,
 			 struct symtab_and_line sal);
 
-static void set_last_displayed_sal (int valid,
-				    struct program_space *pspace,
-				    CORE_ADDR addr,
-				    struct symtab *symtab,
-				    int line);
-
 static struct frame_info *find_frame_for_function (const char *);
 static struct frame_info *find_frame_for_address (CORE_ADDR);
 
@@ -241,13 +235,84 @@ 
 
 int annotation_level = 0;
 
-/* These variables hold the last symtab and line we displayed to the user.
- * This is where we insert a breakpoint or a skiplist entry by default.  */
-static int last_displayed_sal_valid = 0;
-static struct program_space *last_displayed_pspace = 0;
-static CORE_ADDR last_displayed_addr = 0;
-static struct symtab *last_displayed_symtab = 0;
-static int last_displayed_line = 0;
+/* Class used to manage tracking the last symtab we displayed.  */
+
+class last_displayed_symtab_info_type
+{
+public:
+  /* True if the cached information is valid.  */
+  bool is_valid () const
+  { return m_valid; }
+
+  /* Return the cached program_space.  If the cache is invalid nullptr is
+     returned.  */
+  struct program_space *pspace () const
+  { return m_pspace; }
+
+  /* Return the cached CORE_ADDR address.  If the cache is invalid 0 is
+     returned.  */
+  CORE_ADDR address () const
+  { return m_address; }
+
+  /* Return the cached symtab.  If the cache is invalid nullptr is
+     returned.  */
+  struct symtab *symtab () const
+  { return m_symtab; }
+
+  /* Return the cached line number.  If the cache is invalid 0 is
+     returned.  */
+  int line () const
+  { return m_line; }
+
+  /* Invalidate the cache, reset all the members to their default value.  */
+  void invalidate ()
+  {
+    m_valid = false;
+    m_pspace = nullptr;
+    m_address = 0;
+    m_symtab = nullptr;
+    m_line = 0;
+  }
+
+  /* Store a new set of values in the cache.  */
+  void set (struct program_space *pspace, CORE_ADDR address,
+	    struct symtab *symtab, int line)
+  {
+    m_valid = true;
+    m_pspace = pspace;
+    m_address = address;
+    m_symtab = symtab;
+    m_line = line;
+
+    if (pspace == nullptr)
+      {
+	invalidate ();
+	internal_error (__FILE__, __LINE__,
+			_("Trying to set NULL pspace."));
+      }
+  }
+
+private:
+  /* True when the cache is valid.  */
+  bool m_valid = false;
+
+  /* The last program space displayed.  */
+  struct program_space *m_pspace = nullptr;
+
+  /* The last address displayed.  */
+  CORE_ADDR m_address = 0;
+
+  /* The last symtab displayed.  */
+  struct symtab *m_symtab = nullptr;
+
+  /* The last line number displayed.  */
+  int m_line = 0;
+};
+
+/* An actual instance of the cache, holds information about the last symtab
+   displayed.  */
+static last_displayed_symtab_info_type last_displayed_symtab_info;
+
 
 
 /* See stack.h.  */
@@ -1105,9 +1170,9 @@ 
       CORE_ADDR pc;
 
       if (get_frame_pc_if_available (frame, &pc))
-	set_last_displayed_sal (1, sal.pspace, pc, sal.symtab, sal.line);
+	last_displayed_symtab_info.set (sal.pspace, pc, sal.symtab, sal.line);
       else
-	set_last_displayed_sal (0, 0, 0, 0, 0);
+	last_displayed_symtab_info.invalidate ();
     }
 
   annotate_frame_end ();
@@ -1115,103 +1180,67 @@ 
   gdb_flush (gdb_stdout);
 }
 
-/* Remember the last symtab and line we displayed, which we use e.g.
- * as the place to put a breakpoint when the `break' command is
- * invoked with no arguments.  */
-
-static void
-set_last_displayed_sal (int valid, struct program_space *pspace,
-			CORE_ADDR addr, struct symtab *symtab,
-			int line)
-{
-  last_displayed_sal_valid = valid;
-  last_displayed_pspace = pspace;
-  last_displayed_addr = addr;
-  last_displayed_symtab = symtab;
-  last_displayed_line = line;
-  if (valid && pspace == NULL)
-    {
-      clear_last_displayed_sal ();
-      internal_error (__FILE__, __LINE__,
-		      _("Trying to set NULL pspace."));
-    }
-}
-
-/* Forget the last sal we displayed.  */
+/* See stack.h.  */
 
 void
 clear_last_displayed_sal (void)
 {
-  last_displayed_sal_valid = 0;
-  last_displayed_pspace = 0;
-  last_displayed_addr = 0;
-  last_displayed_symtab = 0;
-  last_displayed_line = 0;
+  last_displayed_symtab_info.invalidate ();
 }
 
-/* Is our record of the last sal we displayed valid?  If not,
- * the get_last_displayed_* functions will return NULL or 0, as
- * appropriate.  */
+/* See stack.h.  */
 
-int
+bool
 last_displayed_sal_is_valid (void)
 {
-  return last_displayed_sal_valid;
+  return last_displayed_symtab_info.is_valid ();
 }
 
-/* Get the pspace of the last sal we displayed, if it's valid.  */
+/* See stack.h.  */
 
 struct program_space *
 get_last_displayed_pspace (void)
 {
-  if (last_displayed_sal_valid)
-    return last_displayed_pspace;
-  return 0;
+  return last_displayed_symtab_info.pspace ();
 }
 
-/* Get the address of the last sal we displayed, if it's valid.  */
+/* See stack.h.  */
 
 CORE_ADDR
 get_last_displayed_addr (void)
 {
-  if (last_displayed_sal_valid)
-    return last_displayed_addr;
-  return 0;
+  return last_displayed_symtab_info.address ();
 }
 
-/* Get the symtab of the last sal we displayed, if it's valid.  */
+/* See stack.h.  */
 
 struct symtab*
 get_last_displayed_symtab (void)
 {
-  if (last_displayed_sal_valid)
-    return last_displayed_symtab;
-  return 0;
+  return last_displayed_symtab_info.symtab ();
 }
 
-/* Get the line of the last sal we displayed, if it's valid.  */
+/* See stack.h.  */
 
 int
 get_last_displayed_line (void)
 {
-  if (last_displayed_sal_valid)
-    return last_displayed_line;
-  return 0;
+  return last_displayed_symtab_info.line ();
 }
 
-/* Get the last sal we displayed, if it's valid.  */
+/* See stack.h.  */
 
 symtab_and_line
 get_last_displayed_sal ()
 {
   symtab_and_line sal;
 
-  if (last_displayed_sal_valid)
+  if (last_displayed_symtab_info.is_valid ())
     {
-      sal.pspace = last_displayed_pspace;
-      sal.pc = last_displayed_addr;
-      sal.symtab = last_displayed_symtab;
-      sal.line = last_displayed_line;
+      sal.pspace = last_displayed_symtab_info.pspace ();
+      sal.pc = last_displayed_symtab_info.address ();
+      sal.symtab = last_displayed_symtab_info.symtab ();
+      sal.line = last_displayed_symtab_info.line ();
     }
 
   return sal;
diff --git a/gdb/stack.h b/gdb/stack.h
index 28d2273..9b038f0 100644
--- a/gdb/stack.h
+++ b/gdb/stack.h
@@ -54,14 +54,38 @@ 
 
 bool frame_show_address (struct frame_info *frame, struct symtab_and_line sal);
 
-/* Get or set the last displayed symtab and line, which is, e.g. where we set a
- * breakpoint when `break' is supplied with no arguments.  */
+/* Forget the last sal we displayed.  */
+
 void clear_last_displayed_sal (void);
-int last_displayed_sal_is_valid (void);
+
+/* Is our record of the last sal we displayed valid?  If not, the
+   get_last_displayed_* functions will return NULL or 0, as appropriate.  */
+
+bool last_displayed_sal_is_valid (void);
+
+/* Get the pspace of the last sal we displayed, if it's valid, otherwise
+   return nullptr.  */
+
 struct program_space* get_last_displayed_pspace (void);
+
+/* Get the address of the last sal we displayed, if it's valid, otherwise
+   return an address of 0.  */
+
 CORE_ADDR get_last_displayed_addr (void);
+
+/* Get the symtab of the last sal we displayed, if it's valid, otherwise
+   return nullptr.  */
+
 struct symtab* get_last_displayed_symtab (void);
+
+/* Get the line of the last sal we displayed, if it's valid, otherwise
+   return 0.  */
+
 int get_last_displayed_line (void);
+
+/* Get the last sal we displayed, if it's valid, otherwise return a
+   symtab_and_line constructed in its default state.  */
+
 symtab_and_line get_last_displayed_sal ();
 
 /* Completer for the "frame apply all" command.  */