gdb: pass frames as `const frame_info_ptr &`

We currently pass frames to function by value, as `frame_info_ptr`.
This is somewhat expensive:

 - the size of `frame_info_ptr` is 64 bytes, which is a bit big to pass
   by value
 - the constructors and destructor link/unlink the object in the global
   `frame_info_ptr::frame_list` list.  This is an `intrusive_list`, so
   it's not so bad: it's just assigning a few points, there's no memory
   allocation as if it was `std::list`, but still it's useless to do
   that over and over.

As suggested by Tom Tromey, change many function signatures to accept
`const frame_info_ptr &` instead of `frame_info_ptr`.

Some functions reassign their `frame_info_ptr` parameter, like:

  void
  the_func (frame_info_ptr frame)
  {
    for (; frame != nullptr; frame = get_prev_frame (frame))
      {
        ...
      }
  }

I wondered what to do about them, do I leave them as-is or change them
(and need to introduce a separate local variable that can be
re-assigned).  I opted for the later for consistency.  It might not be
clear why some functions take `const frame_info_ptr &` while others take
`frame_info_ptr`.  Also, if a function took a `frame_info_ptr` because
it did re-assign its parameter, I doubt that we would think to change it
to `const frame_info_ptr &` should the implementation change such that
it doesn't need to take `frame_info_ptr` anymore.  It seems better to
have a simple rule and apply it everywhere.

Change-Id: I59d10addef687d157f82ccf4d54f5dde9a963fd0
Approved-By: Andrew Burgess <aburgess@redhat.com>

1 files changed, 7 insertions, 7 deletions

diff --git a/gdb/python/py-framefilter.c b/gdb/python/py-framefilter.c
index fd2757d..768e3a6 100644
--- a/gdb/python/py-framefilter.c
+++ b/gdb/python/py-framefilter.c
@@ -416,7 +416,7 @@ enumerate_args (PyObject *iter,
 		enum ext_lang_frame_args args_type,
 		bool raw_frame_args,
 		int print_args_field,
-		frame_info_ptr frame)
+		const frame_info_ptr &frame)
 {
   struct value_print_options opts;
 
@@ -548,7 +548,7 @@ enumerate_locals (PyObject *iter,
 		  int indent,
 		  enum ext_lang_frame_args args_type,
 		  int print_args_field,
-		  frame_info_ptr frame)
+		  const frame_info_ptr &frame)
 {
   struct value_print_options opts;
 
@@ -636,7 +636,7 @@ static enum ext_lang_bt_status
 py_mi_print_variables (PyObject *filter, struct ui_out *out,
 		       struct value_print_options *opts,
 		       enum ext_lang_frame_args args_type,
-		       frame_info_ptr frame,
+		       const frame_info_ptr &frame,
 		       bool raw_frame_args_p)
 {
   gdbpy_ref<> args_iter (get_py_iter_from_func (filter, "frame_args"));
@@ -671,7 +671,7 @@ py_print_locals (PyObject *filter,
 		 struct ui_out *out,
 		 enum ext_lang_frame_args args_type,
 		 int indent,
-		 frame_info_ptr frame)
+		 const frame_info_ptr &frame)
 {
   gdbpy_ref<> locals_iter (get_py_iter_from_func (filter, "frame_locals"));
   if (locals_iter == NULL)
@@ -697,7 +697,7 @@ py_print_args (PyObject *filter,
 	       struct ui_out *out,
 	       enum ext_lang_frame_args args_type,
 	       bool raw_frame_args,
-	       frame_info_ptr frame)
+	       const frame_info_ptr &frame)
 {
   gdbpy_ref<> args_iter (get_py_iter_from_func (filter, "frame_args"));
   if (args_iter == NULL)
@@ -1082,7 +1082,7 @@ py_print_frame (PyObject *filter, frame_filter_flags flags,
    frame FRAME.  */
 
 static PyObject *
-bootstrap_python_frame_filters (frame_info_ptr frame,
+bootstrap_python_frame_filters (const frame_info_ptr &frame,
 				int frame_low, int frame_high)
 {
   gdbpy_ref<> frame_obj (frame_info_to_frame_object (frame));
@@ -1137,7 +1137,7 @@ bootstrap_python_frame_filters (frame_info_ptr frame,
 
 enum ext_lang_bt_status
 gdbpy_apply_frame_filter (const struct extension_language_defn *extlang,
-			  frame_info_ptr frame, frame_filter_flags flags,
+			  const frame_info_ptr &frame, frame_filter_flags flags,
 			  enum ext_lang_frame_args args_type,
 			  struct ui_out *out, int frame_low, int frame_high)
 {