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, 4 insertions, 4 deletions

diff --git a/gdb/amdgpu-tdep.c b/gdb/amdgpu-tdep.c
index 44252e5..ac137d9 100644
--- a/gdb/amdgpu-tdep.c
+++ b/gdb/amdgpu-tdep.c
@@ -846,7 +846,7 @@ struct amdgpu_frame_cache
 };
 
 static amdgpu_frame_cache *
-amdgpu_frame_cache (frame_info_ptr this_frame, void **this_cache)
+amdgpu_frame_cache (const frame_info_ptr &this_frame, void **this_cache)
 {
   if (*this_cache != nullptr)
     return (struct amdgpu_frame_cache *) *this_cache;
@@ -862,7 +862,7 @@ amdgpu_frame_cache (frame_info_ptr this_frame, void **this_cache)
 }
 
 static void
-amdgpu_frame_this_id (frame_info_ptr this_frame, void **this_cache,
+amdgpu_frame_this_id (const frame_info_ptr &this_frame, void **this_cache,
 		      frame_id *this_id)
 {
   struct amdgpu_frame_cache *cache
@@ -880,13 +880,13 @@ amdgpu_frame_this_id (frame_info_ptr this_frame, void **this_cache,
 }
 
 static frame_id
-amdgpu_dummy_id (struct gdbarch *gdbarch, frame_info_ptr this_frame)
+amdgpu_dummy_id (struct gdbarch *gdbarch, const frame_info_ptr &this_frame)
 {
   return frame_id_build (0, get_frame_pc (this_frame));
 }
 
 static struct value *
-amdgpu_frame_prev_register (frame_info_ptr this_frame, void **this_cache,
+amdgpu_frame_prev_register (const frame_info_ptr &this_frame, void **this_cache,
 			    int regnum)
 {
   return frame_unwind_got_register (this_frame, regnum, regnum);