Unusually high polymorphic dispatch costs?

[Rémi Forax]

On 05/01/2011 09:58 PM, Charles Oliver Nutter wrote:
> On Sun, May 1, 2011 at 1:01 PM, Mark Roos<mroos at roos.com>  wrote:
>> With respect to chaining gwt handles.
>>
>> Any thoughts on at what depth the chain should be converted to some other
>> form of dispatch?
>> I am currently just letting them build
>>
>> In smalltalk it seems that around 10-20 inline tests are about the same as a
>> hash lookup but I
>> would think it could be different after the JIT gets to it.
> I think it's going to vary widely by how much code is in the target
> methods, how expensive the test is, how "balanced" the chain is (e.g.
> most frequently-hit at the front) and so on. Obviously if you have a
> megamorphic site that's seeing hundreds of methods you wouldn't want
> to chain GWT to that length.
>
> I'm going to write a benchmark with variable-morphology(?) to see
> where the line is in JRuby.
>
> The other question is whether a mostly mono or bimorphic call site
> should keep those at the head of the chain, speeding up those calls,
> and just have the IC at the end of the chain as a catch-all. I'm also
> trying to think of low-cost ways of tracking which branches are
> getting followed in the chain, so they could potentially be rebalanced
> periodically.
>

Could you also include a test with -XX:+TieredCompilation ?
I wonder how profile information are propagated between tiers.

> - Charlie

cheers,
Rémi