From: Eli Zaretskii <eliz@gnu.org>
To: Paul Eggert <eggert@cs.ucla.edu>
Cc: emacs-devel@gnu.org
Subject: Re: FACE_FROM_ID vs FACE_OPT_FROM_ID
Date: Sat, 02 Jul 2016 12:50:57 +0300 [thread overview]
Message-ID: <831t3ctlku.fsf@gnu.org> (raw)
In-Reply-To: <576EF8FC.1040507@cs.ucla.edu> (message from Paul Eggert on Sat, 25 Jun 2016 23:34:52 +0200)
> Cc: emacs-devel@gnu.org
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Sat, 25 Jun 2016 23:34:52 +0200
>
> > . Define FACE_FROM_ID as it was before:
> >
> > #define FACE_FROM_ID(F, ID) \
> > (UNSIGNED_CMP (ID, <, FRAME_FACE_CACHE (F)->used) \
> > ? FRAME_FACE_CACHE (F)->faces_by_id[ID] \
> > : NULL)
> >
> > . In every place that calls FACE_FROM_ID and doesn't already include
> > code to deal with a NULL value, do this:
> >
> > face = FACE_FROM_ID (f, face_id);
> > if (!face)
> > emacs_abort ();
> >
> > . Remove FACE_OPT_FROM_ID
> >
>
> If we go this route, I suggest having a function NONNULL_FACE_FROM_ID
> that packages up those three lines of code (which will occur in many
> places). That is, instead of this:
>
> face = FACE_FROM_ID (f, face_id);
> if (!face)
> emacs_abort ();
>
> we should write this:
>
> face = NONNULL_FACE_FROM_ID (f, face_id);
>
> to mean the same thing. (Or perhaps you can think of a better name than
> NONNULL_FACE_FROM_ID.)
>
> This sort of thing should also suffice to remove the warning. A downside
> is that it inserts unnecessary runtime checks in production code, as the
> "if (!face) emacs_abort ();" won't detect errors in production usefully
> earlier than the existing code does when it dereferences the pointer. In
> practice the unnecessary checks probably won't cost that much, so it's
> OK if nobody else cares about the performance degradation in production
> code. (I tried hard to avoid slowing down Emacs merely to pacify GCC,
> and if we go this route we'd be departing slightly from that tradition.)
OK, thanks. I took all these arguments under consideration, and made
the corresponding changes in master commit 55d38fc. Most of it is
just renaming FACE_OPT_FROM_ID to FACE_FROM_ID_OR_NULL (the latter is
IMO more telling about its purpose), but some of the changes change
the macro we call, either because the calling code can cope with a
NULL face pointer, or because it cannot, but the dereference was too
far for GCC 6 to notice it.
I decided not to abort when ENABLE_CHECKING is not defined, because
you convinced me that is unnecessary.
prev parent reply other threads:[~2016-07-02 9:50 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-23 20:03 FACE_FROM_ID vs FACE_OPT_FROM_ID Eli Zaretskii
2016-06-24 0:23 ` Paul Eggert
2016-06-24 8:49 ` Eli Zaretskii
2016-06-24 9:27 ` Paul Eggert
2016-06-24 9:57 ` Eli Zaretskii
2016-06-24 10:00 ` Eli Zaretskii
2016-06-24 11:17 ` Paul Eggert
2016-06-24 13:43 ` Eli Zaretskii
2016-06-24 21:34 ` Paul Eggert
2016-06-25 7:48 ` Eli Zaretskii
2016-06-25 21:34 ` Paul Eggert
2016-07-02 9:50 ` Eli Zaretskii [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://www.gnu.org/software/emacs/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=831t3ctlku.fsf@gnu.org \
--to=eliz@gnu.org \
--cc=eggert@cs.ucla.edu \
--cc=emacs-devel@gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.savannah.gnu.org/cgit/emacs.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).