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Steffen Mueller
February 27, 2013 20:42
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Sorry for the late reply.

On 02/27/2013 10:08 AM, bulk88 wrote:
> Why? remove a branch and turn it into a separate non branching opcode?
> (not saying I dont like your idea).

Yes, that was the intention. Apart from cache-size issues, we basically 
*know* that it ought to be faster that way. On top of that, PADSVs are 
very common, too.

Initial artificial benchmarking showed an improvement on the order of 
2-3%. Further (marginally more sophisticated) benchmarking showed that 
that is compatible with the noise and bias induced by the environment 
and matters such as linker order and alignment.

It's really just the usual frustration: Benchmarking micro-optimizations 
is nigh-on impossible.

Since this particular change is non-trivial (new OP etc), I won't go 
ahead and clean it up/push it. But I do believe that there is an 
opportunity in analysing hot OPs (not necessarily the same as pp_hot) 
for similar opportunities and looking at the performance impact of 
specializing a few more OPs.


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