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, 6 insertions, 6 deletions

diff --git a/gdb/m68k-linux-tdep.c b/gdb/m68k-linux-tdep.c
index 9004b2e..eca4ede 100644
--- a/gdb/m68k-linux-tdep.c
+++ b/gdb/m68k-linux-tdep.c
@@ -61,7 +61,7 @@
    non-RT and RT signal trampolines.  */
 
 static int
-m68k_linux_pc_in_sigtramp (frame_info_ptr this_frame)
+m68k_linux_pc_in_sigtramp (const frame_info_ptr &this_frame)
 {
   struct gdbarch *gdbarch = get_frame_arch (this_frame);
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
@@ -219,7 +219,7 @@ m68k_linux_inferior_created (inferior *inf)
 }
 
 static struct m68k_linux_sigtramp_info
-m68k_linux_get_sigtramp_info (frame_info_ptr this_frame)
+m68k_linux_get_sigtramp_info (const frame_info_ptr &this_frame)
 {
   struct gdbarch *gdbarch = get_frame_arch (this_frame);
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
@@ -248,7 +248,7 @@ m68k_linux_get_sigtramp_info (frame_info_ptr this_frame)
 /* Signal trampolines.  */
 
 static struct trad_frame_cache *
-m68k_linux_sigtramp_frame_cache (frame_info_ptr this_frame,
+m68k_linux_sigtramp_frame_cache (const frame_info_ptr &this_frame,
 				 void **this_cache)
 {
   struct frame_id this_id;
@@ -286,7 +286,7 @@ m68k_linux_sigtramp_frame_cache (frame_info_ptr this_frame,
 }
 
 static void
-m68k_linux_sigtramp_frame_this_id (frame_info_ptr this_frame,
+m68k_linux_sigtramp_frame_this_id (const frame_info_ptr &this_frame,
 				   void **this_cache,
 				   struct frame_id *this_id)
 {
@@ -296,7 +296,7 @@ m68k_linux_sigtramp_frame_this_id (frame_info_ptr this_frame,
 }
 
 static struct value *
-m68k_linux_sigtramp_frame_prev_register (frame_info_ptr this_frame,
+m68k_linux_sigtramp_frame_prev_register (const frame_info_ptr &this_frame,
 					 void **this_cache,
 					 int regnum)
 {
@@ -308,7 +308,7 @@ m68k_linux_sigtramp_frame_prev_register (frame_info_ptr this_frame,
 
 static int
 m68k_linux_sigtramp_frame_sniffer (const struct frame_unwind *self,
-				   frame_info_ptr this_frame,
+				   const frame_info_ptr &this_frame,
 				   void **this_prologue_cache)
 {
   return m68k_linux_pc_in_sigtramp (this_frame);