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Date: Tue, 17 Mar 2009 13:18:20 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] branches are expensive
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To: qemu-devel@nongnu.org

Steffen Liebergeld wrote:
> Hi,
>
> while measuring the execution of an ARM guest, I encountered that branches are
> extremely expensive in terms of executed host instructions. A single ARM
> branch takes 148 to 152 host instructions. In my setup host and guest use the
> ARM instruction set architecture.
>
> My question is what makes branches so expensive? What code is run when
> executing a branch? Other instructions are translated to 14 to 40
> instructions.
>   

I'm no tcg guru, but if branches are not chained, you'd need an 
expensive lookup to find the next translation block.  If branches are 
chained they'll probably be much faster.

-- 
error compiling committee.c: too many arguments to function