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)

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