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, 5 insertions, 5 deletions

diff --git a/gdb/ia64-libunwind-tdep.c b/gdb/ia64-libunwind-tdep.c
index a61e90f..24a5162 100644
--- a/gdb/ia64-libunwind-tdep.c
+++ b/gdb/ia64-libunwind-tdep.c
@@ -153,7 +153,7 @@ libunwind_frame_set_descr (struct gdbarch *gdbarch,
 }
 
 static struct libunwind_frame_cache *
-libunwind_frame_cache (frame_info_ptr this_frame, void **this_cache)
+libunwind_frame_cache (const frame_info_ptr &this_frame, void **this_cache)
 {
   unw_accessors_t *acc;
   unw_addr_space_t as;
@@ -247,7 +247,7 @@ libunwind_find_dyn_list (unw_addr_space_t as, unw_dyn_info_t *di, void *arg)
    libunwind frame unwinding.  */
 int
 libunwind_frame_sniffer (const struct frame_unwind *self,
-			 frame_info_ptr this_frame, void **this_cache)
+			 const frame_info_ptr &this_frame, void **this_cache)
 {
   unw_cursor_t cursor;
   unw_accessors_t *acc;
@@ -292,7 +292,7 @@ libunwind_frame_sniffer (const struct frame_unwind *self,
 }
 
 void
-libunwind_frame_this_id (frame_info_ptr this_frame, void **this_cache,
+libunwind_frame_this_id (const frame_info_ptr &this_frame, void **this_cache,
 			 struct frame_id *this_id)
 {
   struct libunwind_frame_cache *cache =
@@ -303,7 +303,7 @@ libunwind_frame_this_id (frame_info_ptr this_frame, void **this_cache,
 }
 
 struct value *
-libunwind_frame_prev_register (frame_info_ptr this_frame,
+libunwind_frame_prev_register (const frame_info_ptr &this_frame,
 			       void **this_cache, int regnum)
 {
   struct libunwind_frame_cache *cache =
@@ -387,7 +387,7 @@ libunwind_search_unwind_table (void *as, long ip, void *di,
 /* Verify if we are in a sigtramp frame and we can use libunwind to unwind.  */
 int
 libunwind_sigtramp_frame_sniffer (const struct frame_unwind *self,
-				  frame_info_ptr this_frame,
+				  const frame_info_ptr &this_frame,
 				  void **this_cache)
 {
   unw_cursor_t cursor;