From: Marc Lehmann <pcg@goof.com>
To: egcs@cygnus.com
Subject: Re: [EGCS] Re: double alignment patch for x86
Date: Sun, 17 Aug 1997 21:48:08 -0000 [thread overview]
Message-ID: <E0x0BO4-0004OH-00.1997-08-17-21-53-20_pgcc_forever_@cerebro> (raw)
In-Reply-To: 199708171940.PAA05296@jfc.
John Carr wrote:
>
>byte alignment. 8 byte alignment is desirable (and has always been --
>Sun made a bad choice 10 years ago). gcc copies misaligned double
>arguments to aligned locations on the stack. Doing this on x86 might
I thinkt the patch already does this with -mstack-align-double
the (broken) -marg-align-double is just to squeeze out
the last bit of performance ;)
>help performance without breaking compatibility (or it might not: on x86
>there is only a cost if the dynamic value of the pointer is not aligned
>but SPARC requires two instructions instead of one to support possibly
>misaligned pointers).
It takes 2 additional cycles per double access.. this can sum up
to 30% runtime penalty on important algorithms like
matrix multiply...
It was a actually physicist that actually pointed this out to me
(and H.J.Lu for the libc, I believe).
-----==-
----==-- _
---==---(_)__ __ ____ __ Marc Lehmann
--==---/ / _ \/ // /\ \/ / pcg@goof.com
-=====/_/_//_/\_,_/ /_/\_\
The choice of a GNU generation
next reply other threads:[~1997-08-17 21:48 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
1997-08-17 21:48 Marc Lehmann [this message]
1997-08-17 21:48 Toon Moene
1997-08-18 8:22 2 (small?) problems Thomas Hiller
1997-08-18 13:29 ` [EGCS] Re: double alignment patch for x86 Dave Love
1997-08-19 19:45 Marc Lehmann
1998-02-09 2:10 ` Jeffrey A Law
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=E0x0BO4-0004OH-00.1997-08-17-21-53-20_pgcc_forever_@cerebro \
--to=pcg@goof.com \
--cc=egcs@cygnus.com \
/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).