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[Bug tree-optimization/32309] Unnecessary conversion from short to unsigend short breaks vectorization
- From: "pinskia at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 12 Jun 2007 17:56:44 -0000
- Subject: [Bug tree-optimization/32309] Unnecessary conversion from short to unsigend short breaks vectorization
- References: <bug-32309-14687@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #6 from pinskia at gmail dot com 2007-06-12 17:56 -------
Subject: Re: Unnecessary conversion from short to unsigend short breaks
vectorization
On 12 Jun 2007 17:53:19 -0000, gangren at google dot com
<gcc-bugzilla@gcc.gnu.org> wrote:
> I'm aware of integral promotion. But not quite understand why we can optimize
> (short)((int)short_var + (int)short_var) to (short)((unsigned short)short_var +
> (unsigned short)short_var), but not to (short)((short)short_var +
> (short)short_var)? Is it because unsigned short has different overflow
> handling?
Yes, signed short has undefined overflow, while unsigned is defined as
wrapping.
--Pinski
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32309