public inbox for gcc-help@gcc.gnu.org
 help / color / mirror / Atom feed
From: Tom Kacvinsky <tkacvins@gmail.com>
To: gcc-help@gnu.org
Subject: -march=x86_64 -mtune=generic question
Date: Wed, 25 May 2022 14:58:06 -0400	[thread overview]
Message-ID: <CAG_eJLcU1AVOu=4vHO1zKTqt+xkSt=HmMPZrr_ivV76_qWAVtg@mail.gmail.com> (raw)

Perhaps this is a question for the gcc development list, but I thought
I'd try here first.

I am trying to figure out why GCC 12.1 generated object code is
executing a hair slower than GCC 8.3.0 generated object code.

I did run gcc with -fverbose-asm and -S, examined the assembly, and saw
that -march=x86_64 -mtune=generic was used for compilation options.

Reading the documentation. I see that -mtune=generic can change from GCC
release to release based on the most prevalent processors in use at the
time.

I did poke around at the gcc source code and (gcc/config/i386/*) to see
if I could figure out what changed from release to release and admit defeat.

Does anyone have a quick rundown on what would have changed between GCC
8.3.0 and 12.1.0 in terms of what -mtune=generic does for optimizations?

Thanks,

Tom

             reply	other threads:[~2022-05-25 18:58 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-25 18:58 Tom Kacvinsky [this message]
2022-05-26  7:11 ` Andrew Haley
2022-05-26 10:13   ` Tom Kacvinsky
2022-05-26 11:05     ` Jonathan Wakely

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='CAG_eJLcU1AVOu=4vHO1zKTqt+xkSt=HmMPZrr_ivV76_qWAVtg@mail.gmail.com' \
    --to=tkacvins@gmail.com \
    --cc=gcc-help@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).