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>

gdb/gdbarch_components.py

@@ -414,7 +414,7 @@ never be called.
 """,
     type="struct value *",
     name="pseudo_register_read_value",
-    params=[("frame_info_ptr", "next_frame"), ("int", "cookednum")],
+    params=[("const frame_info_ptr &", "next_frame"), ("int", "cookednum")],
     predicate=True,
 )
 
@@ -428,7 +428,7 @@ NEXT_FRAME.
     type="void",
     name="pseudo_register_write",
     params=[
-        ("frame_info_ptr", "next_frame"),
+        ("const frame_info_ptr &", "next_frame"),
         ("int", "pseudo_reg_num"),
         ("gdb::array_view<const gdb_byte>", "buf"),
     ],
@@ -628,7 +628,7 @@ frame.
 """,
     type="struct frame_id",
     name="dummy_id",
-    params=[("frame_info_ptr", "this_frame")],
+    params=[("const frame_info_ptr &", "this_frame")],
     predefault="default_dummy_id",
     invalid=False,
 )
@@ -689,7 +689,7 @@ Return true if the code of FRAME is writable.
 """,
     type="int",
     name="code_of_frame_writable",
-    params=[("frame_info_ptr", "frame")],
+    params=[("const frame_info_ptr &", "frame")],
     predefault="default_code_of_frame_writable",
     invalid=False,
 )
@@ -699,7 +699,7 @@ Method(
     name="print_registers_info",
     params=[
         ("struct ui_file *", "file"),
-        ("frame_info_ptr", "frame"),
+        ("const frame_info_ptr &", "frame"),
         ("int", "regnum"),
         ("int", "all"),
     ],
@@ -712,7 +712,7 @@ Method(
     name="print_float_info",
     params=[
         ("struct ui_file *", "file"),
-        ("frame_info_ptr", "frame"),
+        ("const frame_info_ptr &", "frame"),
         ("const char *", "args"),
     ],
     predefault="default_print_float_info",
@@ -724,7 +724,7 @@ Method(
     name="print_vector_info",
     params=[
         ("struct ui_file *", "file"),
-        ("frame_info_ptr", "frame"),
+        ("const frame_info_ptr &", "frame"),
         ("const char *", "args"),
     ],
     predicate=True,
@@ -767,7 +767,7 @@ FRAME corresponds to the longjmp frame.
 """,
     type="int",
     name="get_longjmp_target",
-    params=[("frame_info_ptr", "frame"), ("CORE_ADDR *", "pc")],
+    params=[("const frame_info_ptr &", "frame"), ("CORE_ADDR *", "pc")],
     predicate=True,
 )
 
@@ -789,7 +789,7 @@ Function(
     type="int",
     name="register_to_value",
     params=[
-        ("frame_info_ptr", "frame"),
+        ("const frame_info_ptr &", "frame"),
         ("int", "regnum"),
         ("struct type *", "type"),
         ("gdb_byte *", "buf"),
@@ -803,7 +803,7 @@ Function(
     type="void",
     name="value_to_register",
     params=[
-        ("frame_info_ptr", "frame"),
+        ("const frame_info_ptr &", "frame"),
         ("int", "regnum"),
         ("struct type *", "type"),
         ("const gdb_byte *", "buf"),
@@ -923,7 +923,7 @@ convention".
 May return 0 when unable to determine that address.""",
     type="CORE_ADDR",
     name="get_return_buf_addr",
-    params=[("struct type *", "val_type"), ("frame_info_ptr", "cur_frame")],
+    params=[("struct type *", "val_type"), ("const frame_info_ptr &", "cur_frame")],
     predefault="default_get_return_buf_addr",
     invalid=False,
 )
@@ -1157,7 +1157,7 @@ Value(
 Method(
     type="CORE_ADDR",
     name="unwind_pc",
-    params=[("frame_info_ptr", "next_frame")],
+    params=[("const frame_info_ptr &", "next_frame")],
     predefault="default_unwind_pc",
     invalid=False,
 )
@@ -1165,7 +1165,7 @@ Method(
 Method(
     type="CORE_ADDR",
     name="unwind_sp",
-    params=[("frame_info_ptr", "next_frame")],
+    params=[("const frame_info_ptr &", "next_frame")],
     predefault="default_unwind_sp",
     invalid=False,
 )
@@ -1177,7 +1177,7 @@ frame-base.  Enable frame-base before frame-unwind.
 """,
     type="int",
     name="frame_num_args",
-    params=[("frame_info_ptr", "frame")],
+    params=[("const frame_info_ptr &", "frame")],
     predicate=True,
 )
 
@@ -1357,7 +1357,7 @@ further single-step is needed before the instruction finishes.
 """,
     type="int",
     name="single_step_through_delay",
-    params=[("frame_info_ptr", "frame")],
+    params=[("const frame_info_ptr &", "frame")],
     predicate=True,
 )
 
@@ -1376,7 +1376,7 @@ disassembler.  Perhaps objdump can handle it?
 Function(
     type="CORE_ADDR",
     name="skip_trampoline_code",
-    params=[("frame_info_ptr", "frame"), ("CORE_ADDR", "pc")],
+    params=[("const frame_info_ptr &", "frame"), ("CORE_ADDR", "pc")],
     predefault="generic_skip_trampoline_code",
     invalid=False,
 )
@@ -1596,7 +1596,7 @@ Fetch the pointer to the ith function argument.
     type="CORE_ADDR",
     name="fetch_pointer_argument",
     params=[
-        ("frame_info_ptr", "frame"),
+        ("const frame_info_ptr &", "frame"),
         ("int", "argi"),
         ("struct type *", "type"),
     ],
@@ -2744,7 +2744,7 @@ Return a string containing any flags for the given PC in the given FRAME.
 """,
     type="std::string",
     name="get_pc_address_flags",
-    params=[("frame_info_ptr", "frame"), ("CORE_ADDR", "pc")],
+    params=[("const frame_info_ptr &", "frame"), ("CORE_ADDR", "pc")],
     predefault="default_get_pc_address_flags",
     invalid=False,
 )