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, 3 insertions, 3 deletions

diff --git a/gdb/riscv-linux-tdep.c b/gdb/riscv-linux-tdep.c
index 9dfbe78..0267dc6 100644
--- a/gdb/riscv-linux-tdep.c
+++ b/gdb/riscv-linux-tdep.c
@@ -86,7 +86,7 @@ riscv_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
 /* Signal trampoline support.  */
 
 static void riscv_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);
 
@@ -125,7 +125,7 @@ static const struct tramp_frame riscv_linux_sigframe = {
 
 static void
 riscv_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)
 {
@@ -163,7 +163,7 @@ riscv_linux_sigframe_init (const struct tramp_frame *self,
    instruction to be executed.  */
 
 static CORE_ADDR
-riscv_linux_syscall_next_pc (frame_info_ptr frame)
+riscv_linux_syscall_next_pc (const frame_info_ptr &frame)
 {
   const CORE_ADDR pc = get_frame_pc (frame);
   const ULONGEST a7 = get_frame_register_unsigned (frame, RISCV_A7_REGNUM);