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, 10 insertions, 10 deletions

diff --git a/gdb/arc-tdep.c b/gdb/arc-tdep.c
index 84e211c..12d8aee 100644
--- a/gdb/arc-tdep.c
+++ b/gdb/arc-tdep.c
@@ -998,7 +998,7 @@ arc_store_return_value (struct gdbarch *gdbarch, struct type *type,
 /* Implement the "get_longjmp_target" gdbarch method.  */
 
 static int
-arc_get_longjmp_target (frame_info_ptr frame, CORE_ADDR *pc)
+arc_get_longjmp_target (const frame_info_ptr &frame, CORE_ADDR *pc)
 {
   arc_debug_printf ("called");
 
@@ -1062,7 +1062,7 @@ arc_return_value (struct gdbarch *gdbarch, struct value *function,
    frame pointer.  */
 
 static CORE_ADDR
-arc_frame_base_address (frame_info_ptr this_frame, void **prologue_cache)
+arc_frame_base_address (const frame_info_ptr &this_frame, void **prologue_cache)
 {
   return (CORE_ADDR) get_frame_register_unsigned (this_frame, ARC_FP_REGNUM);
 }
@@ -1643,7 +1643,7 @@ arc_print_frame_cache (struct gdbarch *gdbarch, const char *message,
 /* Frame unwinder for normal frames.  */
 
 static struct arc_frame_cache *
-arc_make_frame_cache (frame_info_ptr this_frame)
+arc_make_frame_cache (const frame_info_ptr &this_frame)
 {
   arc_debug_printf ("called");
 
@@ -1710,7 +1710,7 @@ arc_make_frame_cache (frame_info_ptr this_frame)
 /* Implement the "this_id" frame_unwind method.  */
 
 static void
-arc_frame_this_id (frame_info_ptr this_frame, void **this_cache,
+arc_frame_this_id (const frame_info_ptr &this_frame, void **this_cache,
 		   struct frame_id *this_id)
 {
   arc_debug_printf ("called");
@@ -1755,7 +1755,7 @@ arc_frame_this_id (frame_info_ptr this_frame, void **this_cache,
 /* Implement the "prev_register" frame_unwind method.  */
 
 static struct value *
-arc_frame_prev_register (frame_info_ptr this_frame,
+arc_frame_prev_register (const frame_info_ptr &this_frame,
 			 void **this_cache, int regnum)
 {
   if (*this_cache == NULL)
@@ -1792,7 +1792,7 @@ arc_frame_prev_register (frame_info_ptr this_frame,
 static void
 arc_dwarf2_frame_init_reg (struct gdbarch *gdbarch, int regnum,
 			   struct dwarf2_frame_state_reg *reg,
-			   frame_info_ptr info)
+			   const frame_info_ptr &info)
 {
   if (regnum == gdbarch_pc_regnum (gdbarch))
     /* The return address column.  */
@@ -1806,7 +1806,7 @@ arc_dwarf2_frame_init_reg (struct gdbarch *gdbarch, int regnum,
     from within signal handlers.  */
 
 static struct arc_frame_cache *
-arc_make_sigtramp_frame_cache (frame_info_ptr this_frame)
+arc_make_sigtramp_frame_cache (const frame_info_ptr &this_frame)
 {
   arc_debug_printf ("called");
 
@@ -1845,7 +1845,7 @@ arc_make_sigtramp_frame_cache (frame_info_ptr this_frame)
    frames.  */
 
 static void
-arc_sigtramp_frame_this_id (frame_info_ptr this_frame,
+arc_sigtramp_frame_this_id (const frame_info_ptr &this_frame,
 			    void **this_cache, struct frame_id *this_id)
 {
   arc_debug_printf ("called");
@@ -1864,7 +1864,7 @@ arc_sigtramp_frame_this_id (frame_info_ptr this_frame,
 /* Get a register from a signal handler frame.  */
 
 static struct value *
-arc_sigtramp_frame_prev_register (frame_info_ptr this_frame,
+arc_sigtramp_frame_prev_register (const frame_info_ptr &this_frame,
 				  void **this_cache, int regnum)
 {
   arc_debug_printf ("regnum = %d", regnum);
@@ -1882,7 +1882,7 @@ arc_sigtramp_frame_prev_register (frame_info_ptr this_frame,
 
 static int
 arc_sigtramp_frame_sniffer (const struct frame_unwind *self,
-			    frame_info_ptr this_frame,
+			    const frame_info_ptr &this_frame,
 			    void **this_cache)
 {
   arc_debug_printf ("called");