RFR: 8251462: Remove legacy compilation policy [v4]

[Igor Veresov]

On Fri, 22 Jan 2021 01:25:25 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 62:
> 
>> 60:       }
>> 61:     } else if (strcmp(CompilationMode, "high-only") == 0) {
>> 62:       if (!CompilerConfig::has_c2() && !CompilerConfig::is_jvmci_compiler()) {
> 
> Is using `!is_c2_or_jvmci_compiler_available()` better here? All flags should be processed at this point. And we could have some `TieredStopAtLevel` flags.
> It looks like you have cross dependency between CompilerConfig and CompilationModeFlag which make using `is_c2_or_jvmci_compiler_available()` impossible here.

Yes, there is an unfortunate cross dependency. It would probably work fine since ```_mode``` is initialized to ```NORMAL``` before parsing the flag. But I wanted to not use any function that would depend on the value of the ```_mode``` during parsing. It could create trouble in the future. I'll put more comments about that.

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