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Re: [Patch] sext_hwi: Avoid left shift of negative value undefined behaviour

From: Jeff Law <law at redhat dot com>
To: Mikael Morin <mikael dot morin at sfr dot fr>, gcc-patches <gcc-patches at gcc dot gnu dot org>
Date: Tue, 11 Aug 2015 13:49:24 -0600
Subject: Re: [Patch] sext_hwi: Avoid left shift of negative value undefined behaviour
Authentication-results: sourceware.org; auth=none
References: <55C33636 dot 7020907 at sfr dot fr>

On 08/06/2015 04:25 AM, Mikael Morin wrote:

Hello,

this avoids an error found with bootstrap-ubsan.
Regression tested on x86_64-unknown-linux-gnu.  OK for trunk?

Mikael


noub_sext.CL


2015-08-05  Mikael Morin<mikael@gcc.gnu.org>

	* hwint.h (sext_hwi): Rewrite without undefined behaviour on
	negative SRC.

OK. Hopefully most of the time the precision is known at compile-timewhich would allow for optimization of the resulting code back to thepair-of-shifts form by combine.





jeff

Follow-Ups:
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  - From: Richard Biener

References:
- [Patch] sext_hwi: Avoid left shift of negative value undefined behaviour
  - From: Mikael Morin

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