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, 3 insertions, 3 deletions

diff --git a/gdb/i387-tdep.c b/gdb/i387-tdep.c
index d73e3ba..3d979e2 100644
--- a/gdb/i387-tdep.c
+++ b/gdb/i387-tdep.c
@@ -202,7 +202,7 @@ print_i387_control_word (int control_p,
 
 void
 i387_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)
 {
   i386_gdbarch_tdep *tdep = gdbarch_tdep<i386_gdbarch_tdep> (gdbarch);
   ULONGEST fctrl;
@@ -345,7 +345,7 @@ i387_convert_register_p (struct gdbarch *gdbarch, int regnum,
    return its contents in TO.  */
 
 int
-i387_register_to_value (frame_info_ptr frame, int regnum,
+i387_register_to_value (const frame_info_ptr &frame, int regnum,
 			struct type *type, gdb_byte *to,
 			int *optimizedp, int *unavailablep)
 {
@@ -380,7 +380,7 @@ i387_register_to_value (frame_info_ptr frame, int regnum,
    REGNUM in frame FRAME.  */
 
 void
-i387_value_to_register (frame_info_ptr frame, int regnum,
+i387_value_to_register (const frame_info_ptr &frame, int regnum,
 			struct type *type, const gdb_byte *from)
 {
   struct gdbarch *gdbarch = get_frame_arch (frame);