bug#34757: Invalid bytecode from byte compiler

[Eli Zaretskii]

> From: Pip Cet <pipcet@gmail.com>
> Date: Fri, 8 Mar 2019 21:13:37 +0000
> Cc: 34757@debbugs.gnu.org
> 
> On Tue, Mar 5, 2019 at 3:30 PM chuntaro <chuntaro@sakura-games.jp> wrote:
> >
> > Invalid bytecode is output and error occurs when executed.
> 
> If I'm looking at this correctly, the problem is that the byte code
> which is generated in an intermediate step:
> 
> 0       constant  2
> 1       constant  print
> 2       constant  1
> 3       call      1
> 4       discard
> 5       constant  3
> 6       return
> 
> is considered a "trivial function" by byte-compile-out-toplevel, which
> assumes that all values on the stack are used by the call.
> 
> We could fix byte-compile-out-toplevel to properly analyze how many
> stack arguments the call takes, but this patch simply treats forms
> like this as nontrivial:
> 
> diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
> index 0b8f8824b4c..4e54e08ce14 100644
> --- a/lisp/emacs-lisp/bytecomp.el
> +++ b/lisp/emacs-lisp/bytecomp.el
> @@ -3025,6 +3025,7 @@ byte-compile-out-toplevel
>                         (or (null (cdr rest))
>                             (and (memq output-type '(file progn t))
>                                  (cdr (cdr rest))
> +                                (eql (length body) (cdr (car rest)))
>                                  (eq (car (nth 1 rest)) 'byte-discard)
>                                  (progn (setq rest (cdr rest)) t))))
>                    (setq maycall nil)    ; Only allow one real function call.

Stefan, any comments?