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/nds32-tdep.c b/gdb/nds32-tdep.c
index d4be42c..e453cd0 100644
--- a/gdb/nds32-tdep.c
+++ b/gdb/nds32-tdep.c
@@ -265,7 +265,7 @@ static const struct
    register.  */
 
 static struct value *
-value_of_nds32_reg (frame_info_ptr frame, const void *baton)
+value_of_nds32_reg (const frame_info_ptr &frame, const void *baton)
 {
   return value_of_register ((int) (intptr_t) baton,
 			    get_next_frame_sentinel_okay (frame));
@@ -902,7 +902,7 @@ nds32_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc)
    a pointer to the current nds32_frame_cache in *THIS_CACHE.  */
 
 static struct nds32_frame_cache *
-nds32_frame_cache (frame_info_ptr this_frame, void **this_cache)
+nds32_frame_cache (const frame_info_ptr &this_frame, void **this_cache)
 {
   struct gdbarch *gdbarch = get_frame_arch (this_frame);
   struct nds32_frame_cache *cache;
@@ -953,7 +953,7 @@ nds32_frame_cache (frame_info_ptr this_frame, void **this_cache)
    PC and the caller's SP when we were called.  */
 
 static void
-nds32_frame_this_id (frame_info_ptr this_frame,
+nds32_frame_this_id (const frame_info_ptr &this_frame,
 		     void **this_cache, struct frame_id *this_id)
 {
   struct nds32_frame_cache *cache = nds32_frame_cache (this_frame, this_cache);
@@ -968,7 +968,7 @@ nds32_frame_this_id (frame_info_ptr this_frame,
 /* Implement the "prev_register" frame_unwind method.  */
 
 static struct value *
-nds32_frame_prev_register (frame_info_ptr this_frame, void **this_cache,
+nds32_frame_prev_register (const frame_info_ptr &this_frame, void **this_cache,
 			   int regnum)
 {
   struct nds32_frame_cache *cache = nds32_frame_cache (this_frame, this_cache);
@@ -1002,7 +1002,7 @@ static const struct frame_unwind nds32_frame_unwind =
 /* Return the frame base address of *THIS_FRAME.  */
 
 static CORE_ADDR
-nds32_frame_base_address (frame_info_ptr this_frame, void **this_cache)
+nds32_frame_base_address (const frame_info_ptr &this_frame, void **this_cache)
 {
   struct nds32_frame_cache *cache = nds32_frame_cache (this_frame, this_cache);
 
@@ -1288,7 +1288,7 @@ nds32_stack_frame_destroyed_p (struct gdbarch *gdbarch, CORE_ADDR addr)
 
 static int
 nds32_epilogue_frame_sniffer (const struct frame_unwind *self,
-			      frame_info_ptr this_frame, void **this_cache)
+			      const frame_info_ptr &this_frame, void **this_cache)
 {
   if (frame_relative_level (this_frame) == 0)
     return nds32_stack_frame_destroyed_p (get_frame_arch (this_frame),
@@ -1303,7 +1303,7 @@ nds32_epilogue_frame_sniffer (const struct frame_unwind *self,
    *THIS_CACHE.  */
 
 static struct nds32_frame_cache *
-nds32_epilogue_frame_cache (frame_info_ptr this_frame, void **this_cache)
+nds32_epilogue_frame_cache (const frame_info_ptr &this_frame, void **this_cache)
 {
   struct gdbarch *gdbarch = get_frame_arch (this_frame);
   struct nds32_frame_cache *cache;
@@ -1335,7 +1335,7 @@ nds32_epilogue_frame_cache (frame_info_ptr this_frame, void **this_cache)
 /* Implement the "this_id" frame_unwind method.  */
 
 static void
-nds32_epilogue_frame_this_id (frame_info_ptr this_frame,
+nds32_epilogue_frame_this_id (const frame_info_ptr &this_frame,
 			      void **this_cache, struct frame_id *this_id)
 {
   struct nds32_frame_cache *cache
@@ -1351,7 +1351,7 @@ nds32_epilogue_frame_this_id (frame_info_ptr this_frame,
 /* Implement the "prev_register" frame_unwind method.  */
 
 static struct value *
-nds32_epilogue_frame_prev_register (frame_info_ptr this_frame,
+nds32_epilogue_frame_prev_register (const frame_info_ptr &this_frame,
 				    void **this_cache, int regnum)
 {
   struct nds32_frame_cache *cache
@@ -1825,7 +1825,7 @@ nds32_return_value (struct gdbarch *gdbarch, struct value *func_type,
 /* Implement the "get_longjmp_target" gdbarch method.  */
 
 static int
-nds32_get_longjmp_target (frame_info_ptr frame, CORE_ADDR *pc)
+nds32_get_longjmp_target (const frame_info_ptr &frame, CORE_ADDR *pc)
 {
   gdb_byte buf[4];
   CORE_ADDR jb_addr;