From: Michael Matz <matz@suse.de>
To: Jeff Law <jeffreyalaw@gmail.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH] match.pd: Add bitwise and pattern [PR106243]
Date: Thu, 4 Aug 2022 12:34:08 +0000 (UTC) [thread overview]
Message-ID: <alpine.LSU.2.20.2208041229230.13939@wotan.suse.de> (raw)
In-Reply-To: <527a41b9-92a1-e662-da89-3176b77524fe@gmail.com>
Hello,
On Wed, 3 Aug 2022, Jeff Law via Gcc-patches wrote:
> > .optimized dump shows:
> > _1 = ABS_EXPR <x_2(D)>;
> > _3 = _1 & 1;
> > return _3;
> >
> > altho combine simplifies it to x & 1 on RTL, resulting in code-gen:
> > f1:
> > and w0, w0, 1
> > ret
> Doesn't the abs(x) & mask simplify to x & mask for any mask where the sign bit
> of x is off
No. Only the lowest bit remains the same between x and -x, all others
might or might not be inverted (first counter example: x=-3, mask=3).
Ciao,
Michael.
next prev parent reply other threads:[~2022-08-04 12:34 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-03 19:10 Sam Feifer
2022-08-03 20:44 ` Prathamesh Kulkarni
2022-08-03 22:39 ` Jeff Law
2022-08-04 7:08 ` Richard Biener
2022-08-04 12:34 ` Michael Matz [this message]
2022-08-04 7:06 ` Richard Biener
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