From: Paul Eggert <eggert@cs.ucla.edu>
To: Bruno Haible <bruno@clisp.org>, Pip Cet <pipcet@gmail.com>
Cc: 36370@debbugs.gnu.org, bug-gnulib@gnu.org
Subject: Re: bug#36370: 27.0.50; XFIXNAT called on negative numbers
Date: Sat, 29 Jun 2019 10:11:40 -0700 [thread overview]
Message-ID: <99bacb9f-1192-1315-85d7-5ab4924dfef8@cs.ucla.edu> (raw)
In-Reply-To: <2515002.Q0mBYvUW8C@omega>
[-- Attachment #1: Type: text/plain, Size: 1008 bytes --]
Bruno Haible wrote:
> + If you want the use of this macro to improve, not deteriorate,
> + performance, R should not contain function calls except to functions
> + that are declared 'inline __attribute__((__always_inline__))'. */
A reader of that might incorrectly conclude that using such functions will
always improve performance, compared to using functions not declared that way.
And I'm leery of putting such GCC-specific info into the documentation of a
generic macro.
Also, given Pip Cet's misunderstanding it'd be helpful to add a word or two
about the intent of 'assume (R)'.
How about the attached patch?
> - evaluated. Behavior is undefined if R is false. */
> + evaluated. The behavior is undefined if R is false.
This is a nit, but to my ears the shorter version is better, and has a
more-accurate connotation as "the behavior" connotes "the behavior of 'assume
(R)'", whereas behavior is also undefined for code before or after a call to an
incorrect 'assume (R)'.
[-- Attachment #2: verify.diff --]
[-- Type: text/x-patch, Size: 800 bytes --]
diff --git a/lib/verify.h b/lib/verify.h
index f8e4eff02..168a7afdb 100644
--- a/lib/verify.h
+++ b/lib/verify.h
@@ -259,9 +259,11 @@ template <int w>
# define __has_builtin(x) 0
#endif
-/* Assume that R always holds. This lets the compiler optimize
- accordingly. R should not have side-effects; it may or may not be
- evaluated. Behavior is undefined if R is false. */
+/* Assume that R always holds. Behavior is undefined if R is false.
+ R should lack side effects, as it may be evaluated only partially.
+ Although 'assume (R)' is typically intended to help performance,
+ performance may degrade if R uses hard-to-optimize features
+ such as calls to non-inlined functions. */
#if (__has_builtin (__builtin_unreachable) \
|| 4 < __GNUC__ + (5 <= __GNUC_MINOR__))
next prev parent reply other threads:[~2019-06-29 17:12 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAOqdjBcM09RbDv19xNF7HxmykU2oAJ4Vsm45Y65aYXZbOO9u3g@mail.gmail.com>
[not found] ` <e7d67132-4c2e-5c3a-74ae-78c8d67b8132@cs.ucla.edu>
[not found] ` <CAOqdjBct1qJ43dAL5642B52ZXH9M1x_qYOZX3GzJi6YvckoS7Q@mail.gmail.com>
[not found] ` <de8a8fa5-176c-f22a-fa56-c5d54fd42352@cs.ucla.edu>
[not found] ` <CAOqdjBd7FXkSd=brysRa8bc+o5uHTBshQ2XxQ2ZSyt=naJgp0g@mail.gmail.com>
[not found] ` <7ef599ae-0a1d-e86f-2bed-a1503455833f@cs.ucla.edu>
[not found] ` <CAOqdjBcyT17XDSAEm2NVtFbJLyEc4m9jj_9sX-nyOUKca2aUwA@mail.gmail.com>
2019-06-27 21:13 ` bug#36370: 27.0.50; XFIXNAT called on negative numbers Paul Eggert
2019-06-27 21:37 ` Pip Cet
2019-06-27 23:45 ` Bruno Haible
2019-06-28 0:04 ` Paul Eggert
2019-06-28 11:06 ` Pip Cet
2019-06-28 12:14 ` Bruno Haible
2019-06-28 12:29 ` Bruno Haible
2019-06-28 13:51 ` Pip Cet
2019-06-28 17:46 ` Paul Eggert
2019-06-28 19:15 ` Pip Cet
2019-06-28 19:56 ` Bruno Haible
2019-06-28 21:08 ` Pip Cet
2019-06-29 5:41 ` Paul Eggert
2019-06-29 6:48 ` Pip Cet
2019-06-29 17:31 ` Paul Eggert
2019-06-30 9:21 ` Pip Cet
2019-06-28 19:11 ` Bruno Haible
2019-06-28 21:07 ` Pip Cet
2019-06-28 23:30 ` Bruno Haible
2019-06-29 5:40 ` Paul Eggert
2019-06-29 5:44 ` Pip Cet
2019-06-29 10:31 ` Bruno Haible
2019-06-29 17:11 ` Paul Eggert [this message]
2019-06-29 17:48 ` Bruno Haible
2019-06-30 15:30 ` Pip Cet
2019-06-30 15:45 ` Bruno Haible
2019-07-02 23:39 ` Paul Eggert
2019-07-01 1:46 ` Richard Stallman
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