From: Jiufu Guo <guojiufu@linux.ibm.com>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: "Kewen.Lin" <linkw@linux.ibm.com>,
dje.gcc@gmail.com, linkw@gcc.gnu.org, gcc-patches@gcc.gnu.org
Subject: Re: [PATCH V2] rs6000: Support to build constants by li/lis+oris/xoris
Date: Tue, 29 Nov 2022 17:08:57 +0800 [thread overview]
Message-ID: <7e8rjuyvo6.fsf@pike.rch.stglabs.ibm.com> (raw)
In-Reply-To: <20221128141822.GM25951@gate.crashing.org> (Segher Boessenkool's message of "Mon, 28 Nov 2022 08:18:23 -0600")
Hi Segher,
Thanks for your review!
Segher Boessenkool <segher@kernel.crashing.org> writes:
> On Mon, Nov 28, 2022 at 11:37:34AM +0800, Jiufu Guo wrote:
>> Segher Boessenkool <segher@kernel.crashing.org> writes:
>> > On Fri, Nov 25, 2022 at 04:11:49PM +0800, Kewen.Lin wrote:
>> >> on 2022/10/26 19:40, Jiufu Guo wrote:
>> >> for "li/lis + oris/xoris", I interpreted it into four combinations:
>> >>
>> >> li + oris, lis + oris, li + xoris, lis + xoris.
>> >>
>> >> not sure just me interpreting like that, but the actual combinations
>> >> which this patch adopts are:
>> >>
>> >> li + oris, li + xoris, lis + xoris.
>> >>
>> >> It's a bit off, but not a big deal, up to you to reword it or not. :)
>> >
>> > The first two are obvious, but the last one is almost never a good idea,
>> > there usually are better ways to do the same. I cannot even think of
>> > any case where this is best? A lis;rl* is always prefered (it can
>> > optimise better, be combined with other insns).
>> I understant your point here. The first two: 'li' for lowest 16bits,
>> 'oris/xoris' for next 16bits.
>>
>> While for 'lis + xoris', it may not obvious, because both 'lis' and
>> 'xoris' operates on 17-31bits.
>> 'lis + xoris' is for case "32(1) || 1(0) || 15(x) || 16(0)". xoris is
>> used to clean bit31. This case seems hard to be supported by 'rlxx'.
>
> Please put that in a separate patch? First do a patch with just
> lis;x?oris. They are unrelated and different in almost every way.
Sure, Thanks for the advice!
>
>> I hit to find this case when I analyze what kind of constants can be
>> build by two instructions. Checked the posssible combinations:
>> "addi/addis" + "neg/ori/../xoris/rldX/rlwX/../sradi/extswsli"(those
>> instructions which accept one register and one immediate).
>>
>> I also drafted the patch to use "li/lis+rlxx" to build constant.
>> https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601276.html
>> https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601277.html
>
> Those seem to do many things in one patch as well :-( It is very hard
> to review such things, it takes many hours each to do properly.
Sorry, I will try to seperate them to smaller granularities!
BR,
Jeff (Jiufu)
>
>
> Segher
next prev parent reply other threads:[~2022-11-29 9:09 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-26 11:40 Jiufu Guo
2022-10-27 5:19 ` Jiufu Guo
2022-11-09 3:29 ` Ping: " Jiufu Guo
2022-11-25 8:11 ` Kewen.Lin
2022-11-25 12:41 ` Jiufu Guo
2022-11-25 14:43 ` Segher Boessenkool
2022-11-28 3:37 ` Jiufu Guo
2022-11-28 7:51 ` Jiufu Guo
2022-11-28 17:19 ` Segher Boessenkool
2022-11-29 13:14 ` Jiufu Guo
2022-12-01 1:48 ` Jiufu Guo
2022-11-28 14:18 ` Segher Boessenkool
2022-11-29 9:08 ` Jiufu Guo [this message]
2022-12-01 8:56 ` Jiufu Guo
2022-11-30 4:30 ` Jiufu Guo
2022-12-01 1:51 ` Jiufu Guo
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=7e8rjuyvo6.fsf@pike.rch.stglabs.ibm.com \
--to=guojiufu@linux.ibm.com \
--cc=dje.gcc@gmail.com \
--cc=gcc-patches@gcc.gnu.org \
--cc=linkw@gcc.gnu.org \
--cc=linkw@linux.ibm.com \
--cc=segher@kernel.crashing.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 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).