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Re: [Qemu-devel] [PATCH 5/8] tcg: Add interpreter for bytecode

From: Andi Kleen
Subject: Re: [Qemu-devel] [PATCH 5/8] tcg: Add interpreter for bytecode
Date: Mon, 19 Sep 2011 08:52:05 +0200
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> I think it also improves branch target prediction - if you have a tight
> loop of a few opcodes the predictor can guess where you're headed (since
> there is a separate lookup key for each opcode), whereas with the
> original code, there's a single key which cannot be used to predict the
> branch target.

At least usually. I caught at least one version of gcc to CSE the jump
instruction into a common location in one of my interpreters
:-( But not all do it at least, and I hope gcc gets fixed.

It's still faster for other reasons usually.


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