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/i386-tdep.h b/gdb/i386-tdep.h
index e7699f0..a85e0a9 100644
--- a/gdb/i386-tdep.h
+++ b/gdb/i386-tdep.h
@@ -227,10 +227,10 @@ struct i386_gdbarch_tdep : gdbarch_tdep_base
   CORE_ADDR sigtramp_end = 0;
 
   /* Detect sigtramp.  */
-  int (*sigtramp_p) (frame_info_ptr) = nullptr;
+  int (*sigtramp_p) (const frame_info_ptr &) = nullptr;
 
   /* Get address of sigcontext for sigtramp.  */
-  CORE_ADDR (*sigcontext_addr) (frame_info_ptr) = nullptr;
+  CORE_ADDR (*sigcontext_addr) (const frame_info_ptr &) = nullptr;
 
   /* Offset of registers in `struct sigcontext'.  */
   int *sc_reg_offset = 0;
@@ -377,11 +377,11 @@ extern struct type *i386_pseudo_register_type (struct gdbarch *gdbarch,
 					       int regnum);
 
 extern value *i386_pseudo_register_read_value (gdbarch *gdbarch,
-					       frame_info_ptr next_frame,
+					       const frame_info_ptr &next_frame,
 					       int regnum);
 
 extern void i386_pseudo_register_write (gdbarch *gdbarch,
-					frame_info_ptr next_frame, int regnum,
+					const frame_info_ptr &next_frame, int regnum,
 					gdb::array_view<const gdb_byte> buf);
 
 extern int i386_ax_pseudo_register_collect (struct gdbarch *gdbarch,
@@ -398,7 +398,7 @@ extern int i386_ax_pseudo_register_collect (struct gdbarch *gdbarch,
 #define I386_MAX_INSN_LEN (16)
 
 /* Functions exported from i386-tdep.c.  */
-extern CORE_ADDR i386_pe_skip_trampoline_code (frame_info_ptr frame,
+extern CORE_ADDR i386_pe_skip_trampoline_code (const frame_info_ptr &frame,
 					       CORE_ADDR pc, char *name);
 extern CORE_ADDR i386_skip_main_prologue (struct gdbarch *gdbarch,
 					  CORE_ADDR pc);
@@ -417,7 +417,7 @@ extern CORE_ADDR i386_thiscall_push_dummy_call (struct gdbarch *gdbarch,
 						bool thiscall);
 
 /* Return whether the THIS_FRAME corresponds to a sigtramp routine.  */
-extern int i386_sigtramp_p (frame_info_ptr this_frame);
+extern int i386_sigtramp_p (const frame_info_ptr &this_frame);
 
 /* Return non-zero if REGNUM is a member of the specified group.  */
 extern int i386_register_reggroup_p (struct gdbarch *gdbarch, int regnum,