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/sparc-tdep.h b/gdb/sparc-tdep.h
index c4ea4ff..2d8c507 100644
--- a/gdb/sparc-tdep.h
+++ b/gdb/sparc-tdep.h
@@ -85,7 +85,7 @@ struct sparc_gdbarch_tdep : gdbarch_tdep_base
   size_t plt_entry_size = 0;
 
   /* Alternative location for trap return.  Used for single-stepping.  */
-  CORE_ADDR (*step_trap) (frame_info_ptr frame, unsigned long insn)
+  CORE_ADDR (*step_trap) (const frame_info_ptr &frame, unsigned long insn)
     = nullptr;
 
   /* ISA-specific data types.  */
@@ -207,10 +207,10 @@ extern CORE_ADDR sparc_analyze_prologue (struct gdbarch *gdbarch,
 					 struct sparc_frame_cache *cache);
 
 extern struct sparc_frame_cache *
-  sparc_frame_cache (frame_info_ptr this_frame, void **this_cache);
+  sparc_frame_cache (const frame_info_ptr &this_frame, void **this_cache);
 
 extern struct sparc_frame_cache *
-  sparc32_frame_cache (frame_info_ptr this_frame, void **this_cache);
+  sparc32_frame_cache (const frame_info_ptr &this_frame, void **this_cache);
 
 extern int
   sparc_stack_frame_destroyed_p (struct gdbarch *gdbarch, CORE_ADDR pc);
@@ -255,13 +255,13 @@ extern const struct sparc_gregmap sparc32nbsd_gregmap;
 
 /* Return the address of a system call's alternative return
    address.  */
-extern CORE_ADDR sparcnbsd_step_trap (frame_info_ptr frame,
+extern CORE_ADDR sparcnbsd_step_trap (const frame_info_ptr &frame,
 				      unsigned long insn);
 
 extern void sparc32nbsd_init_abi (struct gdbarch_info info,
 				  struct gdbarch *gdbarch);
 
 extern struct trad_frame_saved_reg *
-  sparc32nbsd_sigcontext_saved_regs (frame_info_ptr next_frame);
+  sparc32nbsd_sigcontext_saved_regs (const frame_info_ptr &next_frame);
 
 #endif /* sparc-tdep.h */