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From: Michael Marks <Michael.Marks@internetmachines.com>
To: nobody@gcc.gnu.org
Cc: gcc-prs@gcc.gnu.org,
Subject: RE: c/10226: unsigned short promotion with bitwise inversion
Date: Thu, 27 Mar 2003 00:16:00 -0000 [thread overview]
Message-ID: <20030326231601.1327.qmail@sources.redhat.com> (raw)
The following reply was made to PR c/10226; it has been noted by GNATS.
From: Michael Marks <Michael.Marks@internetmachines.com>
To: 'Falk Hueffner' <falk.hueffner@student.uni-tuebingen.de>,
Glen Nakamura <glen@imodulo.com>
Cc: gcc-gnats@gcc.gnu.org
Subject: RE: c/10226: unsigned short promotion with bitwise inversion
Date: Wed, 26 Mar 2003 15:10:54 -0800
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Guys,
How about...
warning: comparison will will promote to ~(unsigned) which will zero extend
before ~ operation
-----Original Message-----
From: Falk Hueffner [mailto:falk.hueffner@student.uni-tuebingen.de]
Sent: Wednesday, March 26, 2003 2:54 PM
To: Glen Nakamura
Cc: Michael Marks; gcc-gnats@gcc.gnu.org
Subject: Re: c/10226: unsigned short promotion with bitwise inversion
Glen Nakamura <glen@imodulo.com> writes:
> On Wed, Mar 26, 2003 at 11:19:58PM +0100, Falk Hueffner wrote:
> > Glen Nakamura <glen@imodulo.com> writes:
> > > How about one of these:
> > > warning: comparison of promoted ~unsigned with unsigned is always
false
> > > warning: comparison of ~(promoted unsigned) with unsigned is always
false
> >
> > Yes, that makes it even clearer. I'd prefer the second variant. (BTW,
> > funny, the optimizer doesn't seem to realize it's always false...)
>
> It does on my system (GCC 3.3):
Well, yeah, it's simply constant folding there. What I meant is that
gcc doesn't optimize
int f(unsigned short a, unsigned short b) { return b == ~a; }
to
int f(unsigned short a, unsigned short b) { return 0; }
--
Falk
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<TITLE>RE: c/10226: unsigned short promotion with bitwise =
inversion</TITLE>
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<BODY>
<P><FONT SIZE=3D2>Guys,</FONT>
<BR><FONT SIZE=3D2>How about...</FONT>
<BR><FONT SIZE=3D2>warning: comparison will will promote to ~(unsigned) =
which will zero extend before ~ operation</FONT>
</P>
<P><FONT SIZE=3D2>-----Original Message-----</FONT>
<BR><FONT SIZE=3D2>From: Falk Hueffner [<A =
HREF=3D"mailto:falk.hueffner@student.uni-tuebingen.de">mailto:falk.hueff=
ner@student.uni-tuebingen.de</A>]</FONT>
<BR><FONT SIZE=3D2>Sent: Wednesday, March 26, 2003 2:54 PM</FONT>
<BR><FONT SIZE=3D2>To: Glen Nakamura</FONT>
<BR><FONT SIZE=3D2>Cc: Michael Marks; gcc-gnats@gcc.gnu.org</FONT>
<BR><FONT SIZE=3D2>Subject: Re: c/10226: unsigned short promotion with =
bitwise inversion</FONT>
</P>
<BR>
<P><FONT SIZE=3D2>Glen Nakamura <glen@imodulo.com> writes:</FONT>
</P>
<P><FONT SIZE=3D2>> On Wed, Mar 26, 2003 at 11:19:58PM +0100, Falk =
Hueffner wrote:</FONT>
<BR><FONT SIZE=3D2>> > Glen Nakamura <glen@imodulo.com> =
writes:</FONT>
<BR><FONT SIZE=3D2>> > > How about one of these:</FONT>
<BR><FONT SIZE=3D2>> > > warning: comparison of promoted =
~unsigned with unsigned is always false</FONT>
<BR><FONT SIZE=3D2>> > > warning: comparison of ~(promoted =
unsigned) with unsigned is always false</FONT>
<BR><FONT SIZE=3D2>> > </FONT>
<BR><FONT SIZE=3D2>> > Yes, that makes it even clearer. I'd =
prefer the second variant. (BTW,</FONT>
<BR><FONT SIZE=3D2>> > funny, the optimizer doesn't seem to =
realize it's always false...)</FONT>
<BR><FONT SIZE=3D2>> </FONT>
<BR><FONT SIZE=3D2>> It does on my system (GCC 3.3):</FONT>
</P>
<P><FONT SIZE=3D2>Well, yeah, it's simply constant folding there. What =
I meant is that</FONT>
<BR><FONT SIZE=3D2>gcc doesn't optimize</FONT>
</P>
<P><FONT SIZE=3D2>int f(unsigned short a, unsigned short b) { return b =
=3D=3D ~a; }</FONT>
</P>
<P><FONT SIZE=3D2>to</FONT>
</P>
<P><FONT SIZE=3D2>int f(unsigned short a, unsigned short b) { return 0; =
}</FONT>
</P>
<P><FONT SIZE=3D2>-- </FONT>
<BR> <FONT =
SIZE=3D2>Falk</FONT>
</P>
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next reply other threads:[~2003-03-26 23:16 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-03-27 0:16 Michael Marks [this message]
-- strict thread matches above, loose matches on Subject: below --
2003-03-26 23:06 Falk Hueffner
2003-03-26 22:36 Glen Nakamura
2003-03-26 22:26 Falk Hueffner
2003-03-26 22:26 Glen Nakamura
2003-03-26 22:06 Michael Marks
2003-03-26 21:56 Glen Nakamura
2003-03-26 21:56 Falk Hueffner
2003-03-26 21:16 Michael Marks
2003-03-26 21:16 ebotcazou
2003-03-26 20:36 Glen Nakamura
2003-03-26 19:56 Michael Marks
2003-03-26 18:26 Falk Hueffner
2003-03-26 18:16 mmarks
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