RFR: 8251462: Remove legacy compilation policy [v4]

[Igor Veresov]

On Fri, 22 Jan 2021 01:37:53 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Igor Veresov has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Check legacy flags validity before deriving flag values for emulation mode.
>
> src/hotspot/share/compiler/compilerDefinitions.cpp line 84:
> 
>> 82:     } else if (CompilerConfig::is_c2_or_jvmci_compiler_only()) {
>> 83:       _mode = Mode::HIGH_ONLY;
>> 84:     } else if (CompilerConfig::is_jvmci_compiler() && !TieredCompilation) {
> 
> Should you check `CompilerConfig::is_tiered()` instead of `TieredCompilation` flag?

I wanted to be explicit about what's happening here. I'd like it to be obvious that the we're switching to ```HIGH_ONLY_QUICK_INTERNAL``` mode as a result of the user specifying -XX:-TieredCompilation on the command line.

There is a bug on this line however. I should be checking if c1 is present and enabled.

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PR: https://git.openjdk.java.net/jdk/pull/1985