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From: Richard Henderson <rth@twiddle.net>
To: qemu-devel@nongnu.org
Cc: laurent.desnogues@gmail.com, aurelien@aurel32.net
Subject: Re: [Qemu-devel] [PATCH 2/2] tcg-x86_64: Avoid unnecessary REX.B prefixes.
Date: Tue, 05 Jan 2010 20:16:35 -0800	[thread overview]
Message-ID: <4B440EA3.9040502@twiddle.net> (raw)
In-Reply-To: <20100106010537.9C9D2CBB@are.twiddle.net>

On 01/05/2010 04:31 PM, Richard Henderson wrote:
> A while ago Laurent pointed out that the setcc opcode emitted by
> the setcond patch had unnecessary REX prefixes.
>
> The existing P_REXB internal opcode flag unconditionally emits
> the REX prefix.  Technically it's not needed if the register in
> question is %al, %bl, %cl, %dl.

I should perhaps mention that this patch doesn't help out all
that much.  Only EBX is free for use by the code generator, so
more often than not we're using %bpl, which does require the
REX prefix.


r~

  reply	other threads:[~2010-01-06  4:16 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-01-06  0:31 [Qemu-devel] [PATCH 2/2] tcg-x86_64: Avoid unnecessary REX.B prefixes Richard Henderson
2010-01-06  4:16 ` Richard Henderson [this message]
2010-01-14 16:10 ` Aurelien Jarno
2010-01-14 18:09   ` Richard Henderson
2010-01-14 18:51     ` Aurelien Jarno
2010-01-14 22:59       ` [Qemu-devel] [PATCH] " Richard Henderson
2010-01-15  8:30         ` [Qemu-devel] " Aurelien Jarno
2010-01-15  1:37     ` [Qemu-devel] [PATCH 2/2] " Jamie Lokier

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