From: Paolo Bonzini <pbonzini@redhat.com>
To: Aurelien Jarno <aurelien@aurel32.net>
Cc: qemu-devel@nongnu.org, Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-devel] [PATCH] tcg-i386: Use MOVBE if available
Date: Sun, 22 Dec 2013 14:39:48 +0100 [thread overview]
Message-ID: <52B6EBA4.6050803@redhat.com> (raw)
In-Reply-To: <20131222122450.GB4326@ohm.rr44.fr>
Il 22/12/2013 13:24, Aurelien Jarno ha scritto:
> On Sat, Dec 21, 2013 at 03:08:21PM +0100, Paolo Bonzini wrote:
>> Il 21/12/2013 00:00, Richard Henderson ha scritto:
>>> + if (real_bswap && have_movbe) {
>>> + tcg_out_modrm_offset(s, OPC_MOVBE_GyMy + P_DATA16 + seg,
>>> + datalo, base, ofs);
>>> + tcg_out_ext16u(s, datalo, datalo);
>>
>> Do partial register stalls still exist on Atom and Haswell? I don't
>> remember exactly what you had to do to prevent them, but IIRC you first
>> moved zero to the register and then overwrote the the low 16 bits.
>
> Note that for unsigned 16-bit load you can do either movzw + bswap or
> movbe + movzw.
Yeah, I was asking if xor + movbe would be faster. Benchmarking could
tell, but anyway xor + movbe is likely the smallest code you can produce.
Paolo
next prev parent reply other threads:[~2013-12-22 13:40 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-20 23:00 [Qemu-devel] [PATCH] tcg-i386: Use MOVBE if available Richard Henderson
2013-12-21 14:08 ` Paolo Bonzini
2013-12-22 12:24 ` Aurelien Jarno
2013-12-22 13:39 ` Paolo Bonzini [this message]
2013-12-22 16:38 ` Richard Henderson
2013-12-22 20:03 ` Aurelien Jarno
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