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, 11 insertions, 11 deletions

diff --git a/gdb/csky-tdep.c b/gdb/csky-tdep.c
index 2aa6c0a..c1ce8a5 100644
--- a/gdb/csky-tdep.c
+++ b/gdb/csky-tdep.c
@@ -958,7 +958,7 @@ csky_analyze_prologue (struct gdbarch *gdbarch,
 		       CORE_ADDR start_pc,
 		       CORE_ADDR limit_pc,
 		       CORE_ADDR end_pc,
-		       frame_info_ptr this_frame,
+		       const frame_info_ptr &this_frame,
 		       struct csky_unwind_cache *this_cache,
 		       lr_type_t lr_type)
 {
@@ -2063,7 +2063,7 @@ csky_analyze_lr_type (struct gdbarch *gdbarch,
 /* Heuristic unwinder.  */
 
 static struct csky_unwind_cache *
-csky_frame_unwind_cache (frame_info_ptr this_frame)
+csky_frame_unwind_cache (const frame_info_ptr &this_frame)
 {
   CORE_ADDR prologue_start, prologue_end, func_end, prev_pc, block_addr;
   struct csky_unwind_cache *cache;
@@ -2122,7 +2122,7 @@ csky_frame_unwind_cache (frame_info_ptr this_frame)
 /* Implement the this_id function for the normal unwinder.  */
 
 static void
-csky_frame_this_id (frame_info_ptr this_frame,
+csky_frame_this_id (const frame_info_ptr &this_frame,
 		    void **this_prologue_cache, struct frame_id *this_id)
 {
   struct csky_unwind_cache *cache;
@@ -2143,7 +2143,7 @@ csky_frame_this_id (frame_info_ptr this_frame,
 /* Implement the prev_register function for the normal unwinder.  */
 
 static struct value *
-csky_frame_prev_register (frame_info_ptr this_frame,
+csky_frame_prev_register (const frame_info_ptr &this_frame,
 			  void **this_prologue_cache, int regnum)
 {
   struct csky_unwind_cache *cache;
@@ -2172,7 +2172,7 @@ static const struct frame_unwind csky_unwind_cache = {
 };
 
 static CORE_ADDR
-csky_check_long_branch (frame_info_ptr frame, CORE_ADDR pc)
+csky_check_long_branch (const frame_info_ptr &frame, CORE_ADDR pc)
 {
   gdb_byte buf[8];
   struct gdbarch *gdbarch = get_frame_arch (frame);
@@ -2209,7 +2209,7 @@ csky_check_long_branch (frame_info_ptr frame, CORE_ADDR pc)
 
 static int
 csky_stub_unwind_sniffer (const struct frame_unwind *self,
-			  frame_info_ptr this_frame,
+			  const frame_info_ptr &this_frame,
 			  void **this_prologue_cache)
 {
   CORE_ADDR addr_in_block, pc;
@@ -2240,7 +2240,7 @@ csky_stub_unwind_sniffer (const struct frame_unwind *self,
 }
 
 static struct csky_unwind_cache *
-csky_make_stub_cache (frame_info_ptr this_frame)
+csky_make_stub_cache (const frame_info_ptr &this_frame)
 {
   struct csky_unwind_cache *cache;
 
@@ -2252,7 +2252,7 @@ csky_make_stub_cache (frame_info_ptr this_frame)
 }
 
 static void
-csky_stub_this_id (frame_info_ptr this_frame,
+csky_stub_this_id (const frame_info_ptr &this_frame,
 		  void **this_cache,
 		  struct frame_id *this_id)
 {
@@ -2267,7 +2267,7 @@ csky_stub_this_id (frame_info_ptr this_frame,
 }
 
 static struct value *
-csky_stub_prev_register (frame_info_ptr this_frame,
+csky_stub_prev_register (const frame_info_ptr &this_frame,
 			    void **this_cache,
 			    int prev_regnum)
 {
@@ -2307,7 +2307,7 @@ static frame_unwind csky_stub_unwind = {
    for the normal unwinder.  */
 
 static CORE_ADDR
-csky_frame_base_address (frame_info_ptr this_frame, void **this_cache)
+csky_frame_base_address (const frame_info_ptr &this_frame, void **this_cache)
 {
   struct csky_unwind_cache *cache;
 
@@ -2330,7 +2330,7 @@ static const struct frame_base csky_frame_base = {
 static void
 csky_dwarf2_frame_init_reg (struct gdbarch *gdbarch, int regnum,
 			    struct dwarf2_frame_state_reg *reg,
-			    frame_info_ptr this_frame)
+			    const frame_info_ptr &this_frame)
 {
   if (regnum == gdbarch_pc_regnum (gdbarch))
     reg->how = DWARF2_FRAME_REG_RA;