RFR: 8266074: Vtable-based CHA implementation

[Vladimir Ivanov]

On Fri, 30 Apr 2021 20:13:19 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> The test assumes `UseVtableBasedCHA` is on and some of the assertions it makes fail with `-XX:-UseVtableBasedCHA`. So, it would require all the changes in the test logic have to be guarded by a check whether UseVtableBasedCHA is on or off.
>> 
>> Considering `UseVtableBasedCHA` is turned on by default in the PR, I don't see much value in complicating the test.
>
> So only new implementation is tested with these changes in test. Got it. May be use:
> `@requires vm.opt.final.UseVtableBasedCHA == true`

I'm fine with both approaches. 

Explicitly setting the flag looked to me more robust and clearer communicating the intent. But if you prefer `@requires`, I'll use it.

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PR: https://git.openjdk.java.net/jdk/pull/3727