bug#6996: `byte-compile-report-ops', `byte-code-meter', `byte-metering-on', what are they?

bug#6996: `byte-compile-report-ops', `byte-code-meter', `byte-metering-on', what are they?

[MON KEY]

`byte-compile-report-ops', `byte-code-meter', `byte-metering-on', what are they?

Following files:
 src/bytecode.c
 lisp/emacs-lisp/bytecomp.el

define the variables `byte-code-meter', `byte-metering-on' and a function
`byte-compile-report-ops'.

there is this comment in bytecomp.el
 ";;; report metering (see the hacks in bytecode.c)"

I can't find reference to these anywher in docs, archives, etc.
What do these things do?

(byte-compile-report-ops)
=> Debugger entered--Lisp error: (void-variable byte-code-meter)

--
/s_P\

bug#6996: `byte-compile-report-ops', `byte-code-meter', `byte-metering-on', what are they?

[Glenn Morris]

MON KEY wrote (on Tue, 7 Sep 2010 at 17:33 -0400):

> `byte-compile-report-ops', `byte-code-meter', `byte-metering-on', what are they?
> 
> Following files:
>  src/bytecode.c
>  lisp/emacs-lisp/bytecomp.el
> 
> define the variables `byte-code-meter', `byte-metering-on' and a function
> `byte-compile-report-ops'.

From src/bytecode.c:

#ifdef BYTE_CODE_METER
  DEFVAR_LISP ("byte-code-meter", &Vbyte_code_meter,...
...
#endif

In the comments in the same file:

  define BYTE_CODE_METER to enable generation of a byte-op usage
  histogram.

So if you are interested, why not define it, re-build and see what
happens?

I have no idea what it does, but since it is not on by default since
1991, and is not documented anywhere, I don't see it as a bug if it
doesn't do whatever it is supposed to do. At the worst it is dead code
that could be deleted.

bug#6996: Acknowledgement (`byte-compile-report-ops', `byte-code-meter', `byte-metering-on', what are they?)

[MON KEY]

> I have no idea what it does,

If you don't I doubt few others do either, maybe Jim Blandy?

> but since it is not on by default since 1991,

That's nearly 20 years ago!

> and is not documented anywhere, I don't see it as a bug if it
> doesn't do whatever it is supposed to do.

Its a bug b/c bytecomp.el exposes/provides it.

> At the worst it is dead code that could be deleted.

At the very least there must be _some_ reason the code has
persisted... Hence, my tepid curiosity.

--
/s_P\

bug#6996: Acknowledgement (`byte-compile-report-ops', `byte-code-meter', `byte-metering-on', what are they?)

[Stefan Monnier]

>> At the worst it is dead code that could be deleted.
> At the very least there must be _some_ reason the code has
> persisted... Hence, my tepid curiosity.

From the description it was code that tried to figure out which
byte-codes were used more often.  Probably this was used at some point
to help decide which byte-code to add/keep as well as how much to
optimize paticular byte-codes.


        Stefan