From: Eli Zaretskii <eliz@gnu.org>
To: Pip Cet <pipcet@gmail.com>
Cc: rpluim@gmail.com, eggert@cs.ucla.edu, emacs-devel@gnu.org
Subject: Re: Floating-point constant folding in Emacs byte compiler
Date: Mon, 02 Apr 2018 14:22:27 +0300 [thread overview]
Message-ID: <83370d7szw.fsf@gnu.org> (raw)
In-Reply-To: <CAOqdjBeoLGZgzsJZ7vnoxdqpC3brgjBmPKxSch8WcWoEz7U8nQ@mail.gmail.com> (message from Pip Cet on Mon, 2 Apr 2018 10:56:25 +0000)
> From: Pip Cet <pipcet@gmail.com>
> Date: Mon, 2 Apr 2018 10:56:25 +0000
> Cc: Robert Pluim <rpluim@gmail.com>, emacs-devel@gnu.org
>
> I believe the currently-documented behavior is that it's undefined;
> however, merely leaving it undefined doesn't make bytecode compilation
> reproducible. To do that, right now, I redefine EQ to be true for
> same-value floats. I'd prefer the byte compiler to be fixed
> (unfortunately, flet-binding eq around the invocation of the byte
> compiler isn't an option since byte-compiled code won't let you
> redefine eq), but there appear to be several places where the
> assumption is built into it, and I haven't found them all. The
> half-fixed compiler generates obviously-suboptimal bytecode sequences
> like "const X; const X;".
>
> I think it makes sense to say that bytecode should be portable but not
> necessarily identical between implementations, provided there's also a
> way to canonicalize bytecode generation so the result is actually
> target-independent (in the sense that if there are still bytecode
> differences between targets, that's a bug in the Lisp code); I hope
> redefining EQ is sufficient for that.
Can you make a step back and explain what is it that you are trying to
achieve, and why? Making potentially backward-incompatible changes
without a very good reason is not something we should be enthusiastic
about, IMO. E.g., the fact that two floats are never EQ is burned
into too many muscle memories, and I expect subtle problems with at
least C code that uses EQ.
Thanks.
next prev parent reply other threads:[~2018-04-02 11:22 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-22 23:04 Floating-point constant folding in Emacs byte compiler Paul Eggert
2018-03-23 1:26 ` Stefan Monnier
2018-03-23 5:22 ` Paul Eggert
2018-03-23 8:24 ` Eli Zaretskii
2018-03-23 20:00 ` Paul Eggert
2018-03-23 8:15 ` Eli Zaretskii
2018-03-23 20:52 ` Pip Cet
2018-03-24 6:25 ` Eli Zaretskii
2018-03-26 9:39 ` Robert Pluim
2018-03-26 15:13 ` Eli Zaretskii
2018-03-26 15:57 ` Robert Pluim
2018-03-26 16:02 ` Eli Zaretskii
2018-03-26 18:23 ` Pip Cet
2018-03-26 18:29 ` Eli Zaretskii
2018-03-27 0:28 ` Paul Eggert
2018-03-27 23:28 ` Paul Eggert
2018-03-30 16:26 ` Pip Cet
2018-03-30 16:31 ` Noam Postavsky
2018-03-30 16:39 ` Paul Eggert
2018-04-02 10:56 ` Pip Cet
2018-04-02 11:22 ` Eli Zaretskii [this message]
2018-04-02 11:42 ` Pip Cet
2018-04-02 12:50 ` Eli Zaretskii
2018-04-02 14:50 ` Stefan Monnier
2018-04-02 15:02 ` Pip Cet
2018-04-02 12:57 ` Noam Postavsky
2018-04-02 13:30 ` Eli Zaretskii
2018-04-02 14:48 ` Stefan Monnier
2018-04-02 19:20 ` Paul Eggert
2018-04-02 19:39 ` Pip Cet
2018-04-02 19:58 ` Eli Zaretskii
2018-04-02 20:55 ` Pip Cet
[not found] ` <<83y3i568i0.fsf@gnu.org>
2018-04-02 13:37 ` Drew Adams
2018-04-02 14:05 ` Eli Zaretskii
2018-04-02 14:54 ` Pip Cet
2018-04-02 15:02 ` Drew Adams
2018-03-26 17:52 ` Stefan Monnier
2018-03-26 18:30 ` Eli Zaretskii
2018-03-27 0:08 ` Paul Eggert
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