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 tree-optimization/98908] Failure to optimize arithmetic involving struct members into operating on the entire struct
Date: Fri, 03 Sep 2021 00:59:28 +0000 [thread overview]
Message-ID: <bug-98908-4-laTrsLZK0d@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-98908-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98908
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|WAITING |RESOLVED
Target Milestone|--- |9.0
Resolution|--- |FIXED
--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Gabriel Ravier from comment #6)
> Also the second example wasn't misoptimized, on the contrary it was the most
> reasonable portable function I could write that would work equivalently to
> the first *and* that GCC would optimize ideally.
GCC 7.1.0 produces:
f(reg):
.LFB0:
.cfi_startproc
mov edx, edi
xor eax, eax
mov ecx, edi
and edx, -2
mov al, dl
movzx edx, ch
and edx, -128
mov ah, dl
ret
f1(reg):
.LFB1:
.cfi_startproc
and di, -32514
xor eax, eax
movzx edx, di
mov al, dil
sar edx, 8
mov ah, dl
ret
f is your first example and f1 is the second.
As you can see GCC before GCC 8 did neither.
In GCC 8, the second function produces:
_1 = x.l;
_2 = (signed short) _1;
_3 = x.h;
_4 = (int) _3;
_5 = _4 << 8;
_6 = (signed short) _5;
_7 = _2 | _6;
_8 = (short unsigned int) _7;
tmp_14 = _8 & 33022;
MEM[(unsigned char *)&D.2500] = tmp_14;
And is only opimitized in GCC 9 with bswap producing what I mentioned before
So fixed for GCC 9.
next prev parent reply other threads:[~2021-09-03 0:59 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-01 8:10 [Bug tree-optimization/98908] New: " gabravier at gmail dot com
2021-02-02 7:58 ` [Bug tree-optimization/98908] " rguenth at gcc dot gnu.org
2021-09-03 0:15 ` gabravier at gmail dot com
2021-09-03 0:27 ` pinskia at gcc dot gnu.org
2021-09-03 0:28 ` pinskia at gcc dot gnu.org
2021-09-03 0:31 ` gabravier at gmail dot com
2021-09-03 0:41 ` gabravier at gmail dot com
2021-09-03 0:59 ` pinskia at gcc dot gnu.org [this message]
2021-09-03 1:09 ` gabravier at gmail dot com
2021-09-03 1:11 ` gabravier at gmail dot com
2021-09-03 1:31 ` [Bug tree-optimization/98908] [11 Regression] arithmetic involving struct members into operating on the entire struct fails at -O3 pinskia at gcc dot gnu.org
2021-09-03 1:38 ` pinskia at gcc dot gnu.org
2022-04-21 7:48 ` rguenth at gcc dot gnu.org
2023-05-29 10:04 ` 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-98908-4-laTrsLZK0d@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).