Possible to inline is_zombie check?

[Eric Caspole]

Hi hotspot team,
While profiling a customer app, I saw "nmethod::is_zombie() const"  
surprisingly high in the profile. It turns out that is_zombie() is  
virtual in CodeBlob, so it is always a call. But there is only one  
"guarantee" in CodeCache that takes advantage of the virtualness that  
can be coded around.

I have a simple microbenchmark, attached, mimicking the real app,  
attached, where "nmethod::is_zombie() const" is exercised due to  
frequent stack-walking. This webrev removes is_zombie as a virtual  
call so it can be inlined, and improves the performance of the  
microbenchmark by a few percent.

  http://cr.openjdk.java.net/~ecaspole/inline_zombie_check/webrev.00/

Regards,
Eric

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