From: Paul Eggert <eggert@cs.ucla.edu>
To: Po Lu <luangruo@yahoo.com>
Cc: Spencer Baugh <sbaugh@janestreet.com>, 63556@debbugs.gnu.org
Subject: bug#63556: 29.0.90; Use of _Generic breaks Emacs build on GCC <4.9
Date: Thu, 18 May 2023 07:40:47 -0700 [thread overview]
Message-ID: <d31e2c64-be6a-13fc-1f5a-98b6ea971dcf@cs.ucla.edu> (raw)
In-Reply-To: <87v8gp51ys.fsf@yahoo.com>
On 5/18/23 04:11, Po Lu wrote:
> Would anyone mind if I made configure check for that?
There would be problems in doing that. GCC and Clang both have problems
with _Generic (suggested by this original bug report), and some of them
have to do with which warnings you've enabled. The configure-time check
would run without the warnings whereas the build would run with them.
This is partly why intprops-internal.h has given up on _Generic with GCC
and Clang; see its ifdefs. I assumed that these problems didn't apply to
their simple use in elogb, but apparently I assumed incorrectly.
> Btw, couldn't the macro be defined to something along the lines of this
> when the compiler only supports C99?
>
> #define foo(expression) \
> (sizeof (expression) == sizeof (signed char) \
That wouldn't work on unusual platforms that have padding bits. Of
course we could simply refuse to port to targets like that; still, I'd
be reluctant to do that just for this little issue.
> The problem of using `long long' on systems with less than 64
> significant bits in their words. I don't think that's a particularly
> good idea -- once such uses pile up, Emacs will gradually become slower
> and slower on such systems.
I couldn't measure the slowdown in this case. Until it's measurable I
wouldn't worry about it. To some extent I put in that _Generic
originally more as documentation than as an actual attempt to speed
things up.
next prev parent reply other threads:[~2023-05-18 14:40 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-17 17:38 bug#63556: 29.0.90; Use of _Generic breaks Emacs build on GCC <4.9 Spencer Baugh
2023-05-17 17:45 ` Eli Zaretskii
2023-05-17 17:57 ` Paul Eggert
2023-05-18 11:11 ` Po Lu via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-05-18 11:42 ` Eli Zaretskii
2023-05-18 13:21 ` Po Lu via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-05-18 14:12 ` Eli Zaretskii
2023-05-18 14:40 ` Paul Eggert [this message]
2023-05-19 0:46 ` Po Lu via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-05-19 3:05 ` Paul Eggert
2023-05-19 3:18 ` Po Lu via Bug reports for GNU Emacs, the Swiss army knife of text editors
2023-05-18 20:32 ` Paul Eggert
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