From: David Wohlferd <dw@LimeGreenSocks.com>
To: "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
Cc: Richard Henderson <rth@redhat.com>,
Sandra Loosemore <sandra@codesourcery.com>,
Joseph Myers <joseph@codesourcery.com>,
David Wohlferd <dw@LimeGreenSocks.com>
Subject: Re: [DOC Patch] Add sample for @cc constraint
Date: Wed, 23 Mar 2016 07:02:00 -0000 [thread overview]
Message-ID: <56F1F24D.9080304@LimeGreenSocks.com> (raw)
In-Reply-To: <56E4E5D6.4030500@LimeGreenSocks.com>
Ping? (link to original post:
https://gcc.gnu.org/ml/gcc-patches/2016-03/msg00743.html )
This patch adds a sample for a new-to-v6 feature. Is this not the right
time for doc improvements?
I considered adding some assembler output. Something like:
------------------------
Before this feature, you had to write code like this:
asm("bt $0, %1 ; setc %0" : "=q" (a) : "r" (value) : "cc");
if (a)
This would generate code like this:
bt $0, %ebx
setc %al <--------- Convert flags to byte
testb %al, %al <------ Convert byte back to flags
jne .L5
Using @cc, this code
asm("bt $0, %1" : "=@ccc" (a) : "r" (value) );
if (a)
produces this output:
bt $0, %ebx
jc .L5 <--------- Use the flags directly
----------------
While this helps show the benefit of the feature, it just seemed like
too much detail. Showing people the c code and reminding them to enable
optimizations (what the current patch does) seems like it should be
sufficient.
dw
On 3/12/2016 8:00 PM, David Wohlferd wrote:
> The docs for the new(-ish) @cc constraint need an example. Attached.
>
> ChangeLog:
>
> 2016-03-12 David Wohlferd <dw@LimeGreenSocks.com>
>
> * doc/extend.texi: Add sample for @cc constraint
>
> Note that while I have a release on file with FSF, I don't have write
> access to SVN.
>
> dw
next prev parent reply other threads:[~2016-03-23 1:33 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-13 4:01 David Wohlferd
2016-03-23 7:02 ` David Wohlferd [this message]
2016-03-24 15:21 ` Bernd Schmidt
2016-03-24 17:59 ` Sandra Loosemore
2016-03-27 22:34 ` David Wohlferd
2016-03-29 12:10 ` Bernd Schmidt
2016-04-01 23:39 ` David Wohlferd
2016-04-11 22:49 ` David Wohlferd
2016-04-12 13:06 ` Bernd Schmidt
2016-04-15 23:13 ` David Wohlferd
2016-04-25 9:51 ` Bernd Schmidt
2016-04-26 0:16 ` David Wohlferd
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