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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/98865] Missed transform of (a >> 63) * b
Date: Wed, 18 May 2022 15:24:36 +0000 [thread overview]
Message-ID: <bug-98865-4-nTp2zkII7O@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-98865-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98865
--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Roger Sayle <sayle@gcc.gnu.org>:
https://gcc.gnu.org/g:4a9be8d51182076222d707d9d68f6eda78e8ee2c
commit r13-624-g4a9be8d51182076222d707d9d68f6eda78e8ee2c
Author: Roger Sayle <roger@nextmovesoftware.com>
Date: Wed May 18 16:23:01 2022 +0100
Correct ix86_rtx_cost for multi-word multiplication.
This is the i386 backend specific piece of my revised patch for
PR middle-end/98865, where Richard Biener has suggested that I perform
the desired transformation during RTL expansion where the backend can
control whether it is profitable to convert a multiplication into a
bit-wise AND and a negation. This works well for x86_64, but alas
exposes a latent bug with -m32, where a DImode multiplication incorrectly
appears to be cheaper than negdi2+anddi3(!?). The fix to ix86_rtx_costs
is to report that a DImode (multi-word) multiplication actually requires
three SImode multiplications and two SImode additions. This also corrects
the cost of TImode multiplication on TARGET_64BIT.
2022-05-18 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
* config/i386/i386.cc (ix86_rtx_costs) [MULT]: When mode size
is wider than word_mode, a multiplication costs three word_mode
multiplications and two word_mode additions.
next prev parent reply other threads:[~2022-05-18 15:24 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-28 13:38 [Bug middle-end/98865] New: " rguenth at gcc dot gnu.org
2021-01-28 13:40 ` [Bug middle-end/98865] " rguenth at gcc dot gnu.org
2021-01-28 14:26 ` jakub at gcc dot gnu.org
2021-03-07 2:46 ` pinskia at gcc dot gnu.org
2021-07-20 22:19 ` pinskia at gcc dot gnu.org
2021-09-22 18:19 ` cvs-commit at gcc dot gnu.org
2022-01-11 11:19 ` rguenth at gcc dot gnu.org
2022-05-18 15:24 ` cvs-commit at gcc dot gnu.org [this message]
2022-05-19 16:55 ` cvs-commit at gcc dot gnu.org
2022-05-27 8:02 ` cvs-commit at gcc dot gnu.org
2022-05-28 9:18 ` roger at nextmovesoftware dot com
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