From: "H.J. Lu" <hjl.tools@gmail.com>
To: Noah Goldstein <goldstein.w.n@gmail.com>
Cc: libc-alpha@sourceware.org, carlos@systemhalted.org
Subject: Re: [PATCH v2] x86-64: Replace `and %ah` write with `test %ah` read
Date: Mon, 13 Mar 2023 19:00:29 -0700 [thread overview]
Message-ID: <CAMe9rOrcQizwXJTtJcKd3OeCnOuvLqYx5BukksLUHLVNyBp2ig@mail.gmail.com> (raw)
In-Reply-To: <20230313205056.419587-1-goldstein.w.n@gmail.com>
On Mon, Mar 13, 2023 at 1:51 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> High8 partial registers can incur a stall when being modified (if not
> renamed seperately), or at the very least incur extra backend uops (if
> renamed seperately). Either way read only `testl $0x4, %ah` is preferable
> to `andb $0x4, %ah`.
>
> Function size is unchanged when accounting for 16-byte padding.
> ---
> sysdeps/x86_64/fpu/e_fmodl.S | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/sysdeps/x86_64/fpu/e_fmodl.S b/sysdeps/x86_64/fpu/e_fmodl.S
> index d754668bce..e9a76178f9 100644
> --- a/sysdeps/x86_64/fpu/e_fmodl.S
> +++ b/sysdeps/x86_64/fpu/e_fmodl.S
> @@ -13,7 +13,7 @@ ENTRY(__ieee754_fmodl)
> fldt 8(%rsp)
> 1: fprem
> fstsw %ax
> - and $04,%ah
> + testb $0x4,%ah
> jnz 1b
> fstp %st(1)
> ret
> --
> 2.34.1
>
OK.
Thanks.
--
H.J.
prev parent reply other threads:[~2023-03-14 2:01 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-10 2:44 [PATCH v1] x86-64: Replace `%ah` write with `%eax` read Noah Goldstein
2023-03-10 16:38 ` H.J. Lu
2023-03-13 8:03 ` Florian Weimer
2023-03-13 16:59 ` Noah Goldstein
2023-03-13 17:30 ` Florian Weimer
2023-03-13 20:49 ` Noah Goldstein
2023-03-13 20:50 ` [PATCH v2] x86-64: Replace `and %ah` write with `test %ah` read Noah Goldstein
2023-03-14 2:00 ` H.J. Lu [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=CAMe9rOrcQizwXJTtJcKd3OeCnOuvLqYx5BukksLUHLVNyBp2ig@mail.gmail.com \
--to=hjl.tools@gmail.com \
--cc=carlos@systemhalted.org \
--cc=goldstein.w.n@gmail.com \
--cc=libc-alpha@sourceware.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).