RFR: 8257848: -XX:CompileCommand=blackhole, * should be diagnostic [v4]

[Aleksey Shipilev]

On Mon, 7 Dec 2020 19:30:01 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Check blackhole unlocking at startup
>
> src/hotspot/share/compiler/compilerOracle.cpp line 416:
> 
>> 414:     return false;
>> 415:   }
>> 416:   if (!UnlockDiagnosticVMOptions) {
> 
> The check happens too late (during compilation when JIT encounters marked method).
> 
> IMO it should happen during command-line parsing at startup: `CompilerOracle::parse_from_line()` or `register_command()` look suitable.

Right. I moved it to `register_command`, and `guarantee`-d in `CompilerOracle::should_blackhole` that we ever get there (that is, predicate matched) if diagnostic options were unlocked. Still passes tests in both release and fastdebug.

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PR: https://git.openjdk.java.net/jdk/pull/1674