From: Al Viro <viro@ZenIV.linux.org.uk>
To: Chen Gang <chengang@emindsoft.com.cn>
Cc: dhowells@redhat.com, akpm@linux-foundation.org,
nicolas.iooss_linux@m4x.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] fs: dcache: Use bool return value instead of int
Date: Wed, 13 Jan 2016 22:54:46 +0000 [thread overview]
Message-ID: <20160113225446.GU17997@ZenIV.linux.org.uk> (raw)
In-Reply-To: <5696D239.2000605@emindsoft.com.cn>
On Thu, Jan 14, 2016 at 06:39:53AM +0800, Chen Gang wrote:
> > As for the inlines... frankly, if gcc generates a different code from having
> > replaced int with bool in those, it's time to do something very nasty to
> > gcc developers.
> >
>
> Could you provide the related proof?
static inline _Bool f(.....)
{
return <int expression>;
}
...
if (f(.....))
should generate the code identical to
if ((_Bool)<int expression>)
which, in turn, should generate the code identical to
if (<int expression> != 0)
and
if (<int expression>)
Neither explicit nor implicit conversion to _Bool (the former by the explicit
cast, the latter - by declaring f() to return _Bool) matters at all when the
damn thing is inlined in a condition context. Conversion to _Bool is
equivalent to comparison with 0, and so is the use in condition of if() and
friends.
For something not inlined you might get different code generated due to a
difference in calling sequences of _Bool(...) and int(...); for inlined
case having one of those variants produce a better code means that compiler
has managed to miss some trivial optimization in all other variants.
And I'm yet to see any proof that gcc *does* fuck up in that fashion. It
might - dumb bugs happen to everyone, but I would not assume that they'd
managed to do something that bogys without experimental evidence.
next prev parent reply other threads:[~2016-01-13 22:54 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-11 21:30 [PATCH] fs: dcache: Use bool return value instead of int chengang
2016-01-11 22:51 ` Al Viro
2016-01-12 21:42 ` Chen Gang
2016-01-12 22:21 ` Al Viro
2016-01-13 22:39 ` Chen Gang
2016-01-13 22:54 ` Al Viro [this message]
2016-01-14 15:39 ` Chen Gang
2016-01-24 21:19 ` Chen Gang
2016-01-24 21:27 ` Al Viro
2016-01-25 21:24 ` Chen Gang
2016-01-12 0:33 ` David Howells
2016-01-12 1:02 ` Al Viro
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
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160113225446.GU17997@ZenIV.linux.org.uk \
--to=viro@zeniv.linux.org.uk \
--cc=akpm@linux-foundation.org \
--cc=chengang@emindsoft.com.cn \
--cc=dhowells@redhat.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=nicolas.iooss_linux@m4x.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.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.