Re: [Qemu-devel] qemu optimization

[Paul Brook <paul@codesourcery.com>]

> > Without them, there is no native code run by qemu - everything is
> > translated.
>
> Yep. But even in that situation, there will always be room for
> improvement in how the dynamic code generator works.
>
> I wonder, has anyone tried doing a peephole optimizer? Translate key
> instruction sequences to macro instructions? There have got to be a few
> such high-traffic sequences that run all the time in Windows or Linux
> that could be implemented in the dynamically generated dynamic code
> generator.

You might want to look at my hand-coded backed for qemu. The intention is that 
this will eventually replace dyngen/gcc altogether. Currently everything 
except the experimental m68k target uses a mixture of the old and the 
micro-ops.

One of the differences is that most of the semantics and guest CPU state 
accesses are explicit, so it should be possible to use conventional 
optimisation techniques (including peepholes).

Source and patches can be found at
https://nowt.dyndns.org

As proof-of-concept I also implemented a simple register propagation pass, and 
got a 15% speedup on the nbench benchmark.

Paul