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/sparc64-linux-tdep.c b/gdb/sparc64-linux-tdep.c
index ba9d694..33da532 100644
--- a/gdb/sparc64-linux-tdep.c
+++ b/gdb/sparc64-linux-tdep.c
@@ -52,7 +52,7 @@
 /* Signal trampoline support.  */
 
 static void sparc64_linux_sigframe_init (const struct tramp_frame *self,
-					 frame_info_ptr this_frame,
+					 const frame_info_ptr &this_frame,
 					 struct trad_frame_cache *this_cache,
 					 CORE_ADDR func);
 
@@ -73,7 +73,7 @@ static const struct tramp_frame sparc64_linux_rt_sigframe =
 
 static void
 sparc64_linux_sigframe_init (const struct tramp_frame *self,
-			     frame_info_ptr this_frame,
+			     const frame_info_ptr &this_frame,
 			     struct trad_frame_cache *this_cache,
 			     CORE_ADDR func)
 {
@@ -176,7 +176,7 @@ sparc64_linux_report_signal_info (struct gdbarch *gdbarch, struct ui_out *uiout,
    address.  */
 
 static CORE_ADDR
-sparc64_linux_step_trap (frame_info_ptr frame, unsigned long insn)
+sparc64_linux_step_trap (const frame_info_ptr &frame, unsigned long insn)
 {
   /* __NR_rt_sigreturn is 101  */
   if ((insn == 0x91d0206d)
@@ -306,7 +306,7 @@ sparc64_linux_get_syscall_number (struct gdbarch *gdbarch,
 /* Implement the "get_longjmp_target" gdbarch method.  */
 
 static int
-sparc64_linux_get_longjmp_target (frame_info_ptr frame, CORE_ADDR *pc)
+sparc64_linux_get_longjmp_target (const frame_info_ptr &frame, CORE_ADDR *pc)
 {
   struct gdbarch *gdbarch = get_frame_arch (frame);
   CORE_ADDR jb_addr;