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Re: [Bug tree-optimization/32309] Unnecessary conversion from short to unsigend short breaks vectorization

From: "Andrew Pinski" <pinskia at gmail dot com>
To: gcc-bugzilla at gcc dot gnu dot org
Cc: gcc-bugs at gcc dot gnu dot org
Date: Tue, 12 Jun 2007 10:56:36 -0700
Subject: Re: [Bug tree-optimization/32309] Unnecessary conversion from short to unsigend short breaks vectorization
References: <bug-32309-14687@http.gcc.gnu.org/bugzilla/> <20070612175319.30673.qmail@sourceware.org>

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

References:
- [Bug tree-optimization/32309] New: Unnecessary conversion from short to unsigend short breaks vectorization
  - From: gangren at google dot com
- [Bug tree-optimization/32309] Unnecessary conversion from short to unsigend short breaks vectorization
  - From: gangren at google dot com

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