From: "Maciej W. Rozycki" <macro@imgtec.com>
To: Robert Suchanek <Robert.Suchanek@imgtec.com>
Cc: "Catherine_Moore@mentor.com" <Catherine_Moore@mentor.com>,
Matthew Fortune <Matthew.Fortune@imgtec.com>,
"gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH][MIPS] Don't split shifts by default for MIPS16.
Date: Thu, 09 Jun 2016 15:46:00 -0000 [thread overview]
Message-ID: <alpine.DEB.2.00.1606091622150.10382@tp.orcam.me.uk> (raw)
In-Reply-To: <B5E67142681B53468FAF6B7C313565624F4EDCB2@hhmail02.hh.imgtec.org>
On Tue, 24 May 2016, Robert Suchanek wrote:
> The following changes the default behaviour of shift splitting
> for MIPS16 e.g. the shifts will be split only when used with
> undocumented -mno-debugd option that is now switched on by default.
>
> This appears to enable better optimization in certain cases, and hence,
> giving slightly better performance.
Thank you for your contribution, however I have some issues with your
proposal.
First of all since TARGET_DEBUG_D_MODE is used across several places I
think this really should be split into two separate pieces, independently
reviewed.
Then we have two parts:
1. The change to the expander is probably all but obviously correct as it
complements a similar one applied to the corresponding splitters eons
ago (back in 2001), although I wonder why we need to have both the
splitters and instructions split manually in the expander in the first
place. Can you please investigatie it?
2. The other change is far from obvious since it flips the splitting
default, which has been there since forever (or the addition of MIPS16
support back in 1998). So I think it needs a justification more
elaborate than just "certain cases", and perhaps a proper command-line
option defined rather than using an obscure debugging hook. It may
also make sense to set the default dynamically from the CPU tuning
selected -- if the "certain cases" change from CPU to CPU, that is.
Can you please look into it?
Maciej
prev parent reply other threads:[~2016-06-09 15:46 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-24 15:49 Robert Suchanek
2016-06-09 15:46 ` Maciej W. Rozycki [this message]
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=alpine.DEB.2.00.1606091622150.10382@tp.orcam.me.uk \
--to=macro@imgtec.com \
--cc=Catherine_Moore@mentor.com \
--cc=Matthew.Fortune@imgtec.com \
--cc=Robert.Suchanek@imgtec.com \
--cc=gcc-patches@gcc.gnu.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).