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

[Aleksey Shipilev]

On Mon, 7 Dec 2020 20:39:05 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 426:
> 
>> 424:     return false;
>> 425:   }
>> 426:   guarantee(UnlockDiagnosticVMOptions, "Checked during initial parsing");
> 
> You can move it up right after `check_predicate`: `check_predicate(CompileCommand::Blackhole, method)` is allowed to return `true` iff `UnlockDiagnosticVMOptions` is set. 
> 
> Not sure `guarantee` is well-justified here, IMO `assert` would suffice.

`UnlockDiagnosticVMOptions` is `trueInDebug`, so `assert` is useless. We really care about "release" mode here.

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