RFR: 8252505: C1/C2 compiler support for blackholes [v23]

[Aleksey Shipilev]

On Fri, 4 Dec 2020 09:35:31 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> As far as I can see, `CompilerOracle` prints warnings even with `quiet`. `quiet` seems to really only shun the successful messages. So this behavior is consistent. And frankly, it is a better UX: errors in compiler commands should be visible.
>
> IMO `CompileCommand=quiet` is fine here, but another option is to check `PrintWarnings`. I believe the output can be quite noisy and there's no way to turn it off.

Well, if users want to shun the warning, then they should not put incorrect compiler commands to JVM. For example, JMH does run with `quiet` to silence the "successful" command output, and I still want JVM to show warning messages when people put a `@CompilerControl(BLACKHOLE)` on a wrong method. It is better UX.

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PR: https://git.openjdk.java.net/jdk/pull/1203