RFR: 8252505: C1/C2 compiler support for blackholes [v11]

[Aleksey Shipilev]

On 12/2/20 7:26 PM, Vladimir Ivanov wrote:
> 
>> Unfortunately, not. In JMH, `Blackhole` methods are instance methods (they have state), and that plays nicely with compatibility: when JIT fails to provide blackholing, it would naturally fall back to old behavior. I think null check for receiver is the fair behavior here, as subsequent optimization may expect receiver null-checked after the call. I have not seen null-checks in my `perfasm` runs with C1, though.
> 
> It will "consume" and keep it alive the receiver, but have you
> considered passing receiver explicitly as an argument?

I cannot parse what you are saying here. Please elaborate?

> If you want to keep instance method support, please, double-check that
> null check stays there for correctness.

OK, that looks empirically verifiable (i.e. with the jtreg test), will od.

-- 
Thanks,
-Aleksey