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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/109907] Missed optimization for bit extraction (uses shift instead of single bit-test)
Date: Fri, 19 May 2023 15:42:25 +0000 [thread overview]
Message-ID: <bug-109907-4-pJvOOSfdup@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-109907-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109907
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2023-05-19
Ever confirmed|0 |1
Assignee|unassigned at gcc dot gnu.org |pinskia at gcc dot gnu.org
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed. I am going to try to fix this.
The code which does this is in expr.cc and starts with the following comment:
/* If this is an equality or inequality test of a single bit, we can
do this by shifting the bit being tested to the low-order bit and
masking the result with the constant 1. If the condition was EQ,
we xor it with 1. This does not require an scc insn and is faster
than an scc insn even if we have it.
Which makes it sound like it is always true but it is not as shown by the avr
generated code.
next prev parent reply other threads:[~2023-05-19 15:42 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-19 10:10 [Bug middle-end/109907] New: [avr] " gjl at gcc dot gnu.org
2023-05-19 14:14 ` [Bug middle-end/109907] " pinskia at gcc dot gnu.org
2023-05-19 15:42 ` pinskia at gcc dot gnu.org [this message]
2023-05-19 15:45 ` [Bug middle-end/109907] " pinskia at gcc dot gnu.org
2023-05-19 20:03 ` pinskia at gcc dot gnu.org
2023-05-19 20:12 ` pinskia at gcc dot gnu.org
2023-05-19 20:41 ` gjl at gcc dot gnu.org
2023-05-19 20:55 ` pinskia at gcc dot gnu.org
2023-05-19 20:59 ` gjl at gcc dot gnu.org
2023-05-20 0:46 ` pinskia at gcc dot gnu.org
2023-05-20 5:09 ` pinskia at gcc dot gnu.org
2023-05-20 7:36 ` gjl at gcc dot gnu.org
2023-05-20 7:50 ` gjl at gcc dot gnu.org
2023-05-20 22:23 ` pinskia at gcc dot gnu.org
2023-05-20 22:40 ` pinskia at gcc dot gnu.org
2023-05-21 5:15 ` pinskia at gcc dot gnu.org
2023-05-21 5:36 ` pinskia at gcc dot gnu.org
2023-05-21 9:09 ` gjl at gcc dot gnu.org
2023-05-21 9:55 ` gjl at gcc dot gnu.org
2023-05-23 9:58 ` gjl at gcc dot gnu.org
2023-05-26 8:49 ` gjl at gcc dot gnu.org
2023-05-26 11:14 ` gjl at gcc dot gnu.org
2023-05-26 15:21 ` pinskia at gcc dot gnu.org
2023-05-26 16:08 ` gjl at gcc dot gnu.org
2023-05-26 23:11 ` pinskia at gcc dot gnu.org
2023-05-26 23:34 ` pinskia at gcc dot gnu.org
2023-05-26 23:49 ` pinskia at gcc dot gnu.org
2023-05-27 0:36 ` pinskia at gcc dot gnu.org
2023-05-27 4:02 ` pinskia at gcc dot gnu.org
2023-05-27 20:09 ` pinskia at gcc dot gnu.org
2023-06-11 9:22 ` cvs-commit at gcc dot gnu.org
2023-06-11 9:26 ` gjl at gcc dot gnu.org
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