public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/109057] Does GCC interpret assembly when deciding to optimize away a variable?
Date: Tue, 07 Mar 2023 17:32:53 +0000	[thread overview]
Message-ID: <bug-109057-4-MLBGaF9RNZ@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-109057-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109057

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #5)
> (In reply to Andrew Pinski from comment #2)
> > No it is not. you just don't notice it there because goldbolt is hiding
> > things because it thinks it is unused.
> 
> This actually isn't godbolt hiding anything (which it does sometimes), but
> because
> nothing is printed in the asm nothing needs to be printed into the assembly
> output.
> It still acts as a black box to the compiler.
Kinda.

>More importantly, the entire static array LUT was optimized away from the object file. 
the asm code still has LUT array (godbolt does hide unused lables by default).
Using the original code we do get:

        .type   LUT, @object
        .size   LUT, 8
LUT:
        .string "\001\005\003"
        .ascii  "\002\007\001\002"

  parent reply	other threads:[~2023-03-07 17:32 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-07 17:07 [Bug c++/109057] New: " hbucher at gmail dot com
2023-03-07 17:17 ` [Bug middle-end/109057] " hbucher at gmail dot com
2023-03-07 17:22 ` pinskia at gcc dot gnu.org
2023-03-07 17:27 ` jakub at gcc dot gnu.org
2023-03-07 17:28 ` hbucher at gmail dot com
2023-03-07 17:29 ` jakub at gcc dot gnu.org
2023-03-07 17:31 ` hbucher at gmail dot com
2023-03-07 17:32 ` jakub at gcc dot gnu.org
2023-03-07 17:32 ` pinskia at gcc dot gnu.org [this message]
2023-03-07 17:38 ` hbucher at gmail dot com
2023-03-07 17:44 ` jakub at gcc dot gnu.org

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=bug-109057-4-MLBGaF9RNZ@http.gcc.gnu.org/bugzilla/ \
    --to=gcc-bugzilla@gcc.gnu.org \
    --cc=gcc-bugs@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).