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/arm-tdep.h b/gdb/arm-tdep.h
index 506387b..11839b0 100644
--- a/gdb/arm-tdep.h
+++ b/gdb/arm-tdep.h
@@ -279,7 +279,7 @@ extern void
 		       arm_displaced_step_copy_insn_closure *dsc, int regno,
 		       ULONGEST val, enum pc_write_style write_pc);
 
-CORE_ADDR arm_skip_stub (frame_info_ptr, CORE_ADDR);
+CORE_ADDR arm_skip_stub (const frame_info_ptr &, CORE_ADDR);
 
 ULONGEST arm_get_next_pcs_read_memory_unsigned_integer (CORE_ADDR memaddr,
 							int len,
@@ -292,7 +292,7 @@ int arm_get_next_pcs_is_thumb (struct arm_get_next_pcs *self);
 
 std::vector<CORE_ADDR> arm_software_single_step (struct regcache *);
 int arm_is_thumb (struct regcache *regcache);
-int arm_frame_is_thumb (frame_info_ptr frame);
+int arm_frame_is_thumb (const frame_info_ptr &frame);
 
 extern void arm_displaced_step_fixup (struct gdbarch *,
 				      displaced_step_copy_insn_closure *,