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/arch-utils.h b/gdb/arch-utils.h
index 0f37aaf..2dcd8f6 100644
--- a/gdb/arch-utils.h
+++ b/gdb/arch-utils.h
@@ -158,7 +158,7 @@ struct value *default_get_memtag (struct gdbarch *gdbarch,
 				  struct value *address,
 				  memtag_type tag_type);
 
-extern CORE_ADDR generic_skip_trampoline_code (frame_info_ptr frame,
+extern CORE_ADDR generic_skip_trampoline_code (const frame_info_ptr &frame,
 					       CORE_ADDR pc);
 
 extern CORE_ADDR generic_skip_solib_resolver (struct gdbarch *gdbarch,
@@ -171,7 +171,7 @@ extern int generic_stack_frame_destroyed_p (struct gdbarch *gdbarch,
 					    CORE_ADDR pc);
 
 extern int default_code_of_frame_writable (struct gdbarch *gdbarch,
-					   frame_info_ptr frame);
+					   const frame_info_ptr &frame);
 
 /* By default, registers are not convertible.  */
 extern int generic_convert_register_p (struct gdbarch *gdbarch, int regnum,
@@ -295,7 +295,7 @@ extern ULONGEST default_type_align (struct gdbarch *gdbarch,
 				    struct type *type);
 
 /* Default implementation of gdbarch get_pc_address_flags method.  */
-extern std::string default_get_pc_address_flags (frame_info_ptr frame,
+extern std::string default_get_pc_address_flags (const frame_info_ptr &frame,
 						 CORE_ADDR pc);
 
 /* Default implementation of gdbarch read_core_file_mappings method.  */
@@ -313,7 +313,7 @@ extern bool default_use_target_description_from_corefile_notes
 
 /* Default implementation of gdbarch default_get_return_buf_addr method.  */
 extern CORE_ADDR default_get_return_buf_addr (struct type *val_typegdbarch,
-					      frame_info_ptr cur_frame);
+					      const frame_info_ptr &cur_frame);
 
 /* Default implementation of gdbarch default_dwarf2_omit_typedef_p method.  */
 extern bool default_dwarf2_omit_typedef_p (struct type *target_type,