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, 6 insertions, 5 deletions

diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index 4e17a6b..c1fdbb3 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -1743,7 +1743,7 @@ finish_backward (struct finish_command_fsm *sm)
    frame that called the function we're about to step out of.  */
 
 static void
-finish_forward (struct finish_command_fsm *sm, frame_info_ptr frame)
+finish_forward (struct finish_command_fsm *sm, const frame_info_ptr &frame)
 {
   struct frame_id frame_id = get_frame_id (frame);
   struct gdbarch *gdbarch = get_frame_arch (frame);
@@ -1768,9 +1768,10 @@ finish_forward (struct finish_command_fsm *sm, frame_info_ptr frame)
 /* Skip frames for "finish".  */
 
 static frame_info_ptr
-skip_finish_frames (frame_info_ptr frame)
+skip_finish_frames (const frame_info_ptr &initial_frame)
 {
   frame_info_ptr start;
+  frame_info_ptr frame = initial_frame;
 
   do
     {
@@ -2256,7 +2257,7 @@ default_print_one_register_info (struct ui_file *file,
 void
 default_print_registers_info (struct gdbarch *gdbarch,
 			      struct ui_file *file,
-			      frame_info_ptr frame,
+			      const frame_info_ptr &frame,
 			      int regnum, int print_all)
 {
   int i;
@@ -2416,7 +2417,7 @@ info_registers_command (const char *addr_exp, int from_tty)
 
 static void
 print_vector_info (struct ui_file *file,
-		   frame_info_ptr frame, const char *args)
+		   const frame_info_ptr &frame, const char *args)
 {
   struct gdbarch *gdbarch = get_frame_arch (frame);
 
@@ -2953,7 +2954,7 @@ interrupt_command (const char *args, int from_tty)
 
 void
 default_print_float_info (struct gdbarch *gdbarch, struct ui_file *file,
-			  frame_info_ptr frame, const char *args)
+			  const frame_info_ptr &frame, const char *args)
 {
   int regnum;
   int printed_something = 0;