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/sparc-netbsd-tdep.c b/gdb/sparc-netbsd-tdep.c
index 486381f..d2b1a4b 100644
--- a/gdb/sparc-netbsd-tdep.c
+++ b/gdb/sparc-netbsd-tdep.c
@@ -95,7 +95,7 @@ sparc32nbsd_pc_in_sigtramp (CORE_ADDR pc, const char *name)
 }
 
 trad_frame_saved_reg *
-sparc32nbsd_sigcontext_saved_regs (frame_info_ptr this_frame)
+sparc32nbsd_sigcontext_saved_regs (const frame_info_ptr &this_frame)
 {
   struct gdbarch *gdbarch = get_frame_arch (this_frame);
   trad_frame_saved_reg *saved_regs;
@@ -180,7 +180,7 @@ sparc32nbsd_sigcontext_saved_regs (frame_info_ptr this_frame)
 }
 
 static struct sparc_frame_cache *
-sparc32nbsd_sigcontext_frame_cache (frame_info_ptr this_frame,
+sparc32nbsd_sigcontext_frame_cache (const frame_info_ptr &this_frame,
 				    void **this_cache)
 {
   struct sparc_frame_cache *cache;
@@ -211,7 +211,7 @@ sparc32nbsd_sigcontext_frame_cache (frame_info_ptr this_frame,
 }
 
 static void
-sparc32nbsd_sigcontext_frame_this_id (frame_info_ptr this_frame,
+sparc32nbsd_sigcontext_frame_this_id (const frame_info_ptr &this_frame,
 				      void **this_cache,
 				      struct frame_id *this_id)
 {
@@ -222,7 +222,7 @@ sparc32nbsd_sigcontext_frame_this_id (frame_info_ptr this_frame,
 }
 
 static struct value *
-sparc32nbsd_sigcontext_frame_prev_register (frame_info_ptr this_frame,
+sparc32nbsd_sigcontext_frame_prev_register (const frame_info_ptr &this_frame,
 					    void **this_cache, int regnum)
 {
   struct sparc_frame_cache *cache =
@@ -233,7 +233,7 @@ sparc32nbsd_sigcontext_frame_prev_register (frame_info_ptr this_frame,
 
 static int
 sparc32nbsd_sigcontext_frame_sniffer (const struct frame_unwind *self,
-				      frame_info_ptr this_frame,
+				      const frame_info_ptr &this_frame,
 				      void **this_cache)
 {
   CORE_ADDR pc = get_frame_pc (this_frame);
@@ -264,7 +264,7 @@ static const struct frame_unwind sparc32nbsd_sigcontext_frame_unwind =
    address.  */
 
 CORE_ADDR
-sparcnbsd_step_trap (frame_info_ptr frame, unsigned long insn)
+sparcnbsd_step_trap (const frame_info_ptr &frame, unsigned long insn)
 {
   if ((X_I (insn) == 0 && X_RS1 (insn) == 0 && X_RS2 (insn) == 0)
       || (X_I (insn) == 1 && X_RS1 (insn) == 0 && (insn & 0x7f) == 0))