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Re: [PATCH]: x86 gas: allow 'rep' prefix on 'bsf' and 'bsr' instructions
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Jan Beulich <JBeulich at suse dot com>
- Cc: Roland McGrath <mcgrathr at google dot com>, binutils at sourceware dot org
- Date: Fri, 6 Jul 2012 06:06:59 -0700
- Subject: Re: [PATCH]: x86 gas: allow 'rep' prefix on 'bsf' and 'bsr' instructions
- References: <firstname.lastname@example.org> <4FF6D163020000780008E021@nat28.tlf.novell.com>
On Fri, Jul 6, 2012 at 2:52 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>> On 21.06.12 at 23:36, Roland McGrath <email@example.com> wrote:
>> 'rep; bsf ...'/'rep; bsr ...' are encoded the same as 'tzcnt ...'/'lzcnt
> While tzcnt really is an extension of bsf, lzcnt is not one of bsr,
> so I don't really follow why it's useful to allow the prefix there.
It can be used to encode lzcnt with the older assembler,
similar to pause.