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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/61559] FAIL: gcc.dg/builtin-bswap-8.c on i686 with -mmovbe
Date: Thu, 04 Sep 2014 09:52:00 -0000 [thread overview]
Message-ID: <bug-61559-4-JxqZsifThF@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-61559-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61559
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Aren't these optimizations actually a pessimization for -mmovbe if the inner
bswap is on a read from memory? Assuming the load and bswap instruction is
cheap, then e.g. loading two values with bswap on them and doing say xor on
them afterwards might be cheaper than load the two values, xor them and then
bswap them (because for that bswap you don't have a load+bswap instruction).
next prev parent reply other threads:[~2014-09-04 9:52 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-19 9:16 [Bug rtl-optimization/61559] New: " ubizjak at gmail dot com
2014-06-19 9:18 ` [Bug rtl-optimization/61559] " ubizjak at gmail dot com
2014-06-25 5:13 ` thopre01 at gcc dot gnu.org
2014-06-25 6:22 ` ebotcazou at gcc dot gnu.org
2014-09-03 17:11 ` [Bug tree-optimization/61559] " ubizjak at gmail dot com
2014-09-04 8:56 ` rguenth at gcc dot gnu.org
2014-09-04 9:52 ` jakub at gcc dot gnu.org [this message]
2014-09-04 9:59 ` rguenther at suse dot de
2014-09-04 11:36 ` ubizjak at gmail dot com
2014-09-04 11:52 ` rguenther at suse dot de
2014-09-04 12:08 ` jakub at gcc dot gnu.org
2014-11-13 8:46 ` rguenth at gcc dot gnu.org
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