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/riscv-tdep.c b/gdb/riscv-tdep.c
index 9a7cfa3..68ef323 100644
--- a/gdb/riscv-tdep.c
+++ b/gdb/riscv-tdep.c
@@ -165,7 +165,7 @@ static const reggroup *csr_reggroup = nullptr;
 /* Callback function for user_reg_add.  */
 
 static struct value *
-value_of_riscv_user_reg (frame_info_ptr frame, const void *baton)
+value_of_riscv_user_reg (const frame_info_ptr &frame, const void *baton)
 {
   const int *reg_p = (const int *) baton;
   return value_of_register (*reg_p, get_next_frame_sentinel_okay (frame));
@@ -1135,7 +1135,7 @@ riscv_register_type (struct gdbarch *gdbarch, int regnum)
 static void
 riscv_print_one_register_info (struct gdbarch *gdbarch,
 			       struct ui_file *file,
-			       frame_info_ptr frame,
+			       const frame_info_ptr &frame,
 			       int regnum)
 {
   const char *name = gdbarch_register_name (gdbarch, regnum);
@@ -1504,7 +1504,7 @@ riscv_pseudo_register_reggroup_p (struct gdbarch *gdbarch, int regnum,
 static void
 riscv_print_registers_info (struct gdbarch *gdbarch,
 			    struct ui_file *file,
-			    frame_info_ptr frame,
+			    const frame_info_ptr &frame,
 			    int regnum, int print_all)
 {
   if (regnum != -1)
@@ -3806,7 +3806,7 @@ riscv_frame_align (struct gdbarch *gdbarch, CORE_ADDR addr)
    unwinder.  */
 
 static struct riscv_unwind_cache *
-riscv_frame_cache (frame_info_ptr this_frame, void **this_cache)
+riscv_frame_cache (const frame_info_ptr &this_frame, void **this_cache)
 {
   CORE_ADDR pc, start_addr;
   struct riscv_unwind_cache *cache;
@@ -3866,7 +3866,7 @@ riscv_frame_cache (frame_info_ptr this_frame, void **this_cache)
 /* Implement the this_id callback for RiscV frame unwinder.  */
 
 static void
-riscv_frame_this_id (frame_info_ptr this_frame,
+riscv_frame_this_id (const frame_info_ptr &this_frame,
 		     void **prologue_cache,
 		     struct frame_id *this_id)
 {
@@ -3887,7 +3887,7 @@ riscv_frame_this_id (frame_info_ptr this_frame,
 /* Implement the prev_register callback for RiscV frame unwinder.  */
 
 static struct value *
-riscv_frame_prev_register (frame_info_ptr this_frame,
+riscv_frame_prev_register (const frame_info_ptr &this_frame,
 			   void **prologue_cache,
 			   int regnum)
 {