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Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT a4b18c6] tcg/x86_64: genera
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From: |
Laurent Desnogues |
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Subject: |
Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT a4b18c6] tcg/x86_64: generated dec/inc instead of sub/addwhen possible |
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Date: |
Mon, 28 Sep 2009 10:21:43 +0200 |
On Mon, Sep 28, 2009 at 9:51 AM, Avi Kivity <address@hidden> wrote:
> On 09/27/2009 06:13 PM, Anthony Liguori wrote:
>>
>> From: Aurelien Jarno<address@hidden>
>>
>
> Intel recommends not using inc/dec. Since these instructions don't update
> all of the flags, they cannot be issued in parallel to previous instructions
> that do.
That's true, but I think Icache misses will cost you more than
the false dependencies; due to code size expansion in the
translation process, optimizing rules should not be obeyed
blindly. I guess this should be measured.
Laurent