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, 2 insertions, 2 deletions

diff --git a/gdb/valops.c b/gdb/valops.c
index 399d0f1..be90744 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -976,7 +976,7 @@ value_one (struct type *type)
    e.g. in case the type is a variable length array.  */
 
 static struct value *
-get_value_at (struct type *type, CORE_ADDR addr, frame_info_ptr frame,
+get_value_at (struct type *type, CORE_ADDR addr, const frame_info_ptr &frame,
 	      int lazy)
 {
   struct value *val;
@@ -1029,7 +1029,7 @@ value_at_non_lval (struct type *type, CORE_ADDR addr)
    e.g. in case the type is a variable length array.  */
 
 struct value *
-value_at_lazy (struct type *type, CORE_ADDR addr, frame_info_ptr frame)
+value_at_lazy (struct type *type, CORE_ADDR addr, const frame_info_ptr &frame)
 {
   return get_value_at (type, addr, frame, 1);
 }