RFR: 8251462: Remove legacy compilation policy

[Chris Plummer]

On Thu, 7 Jan 2021 18:43:51 GMT, Igor Veresov <iveresov at openjdk.org> wrote:

> This change removes the legacy compilation policy and an emulation mode to the tiered policy to simulate the old behavior with ```-XX:-TieredCompilation```. The change removed a bunch of interpreter code, devirtualizes the compilation policy API, adds a consistent way to query compiler configuration with the new ```CompilerConfig``` API.
> 
> I've tested this with hs-tier{1,2,3,4,5}. And also made sure it builds and works with C1/C2-Graal/AOT being enabled/disabled.
> 
> Since there are platform-specific changes I would greatly appreciate some help from the maintainers of the specific ports to verify the build and run basic smoke tests. I've already tested x64 and aarch64. Thanks!

test/hotspot/jtreg/vmTestbase/nsk/jvmti/scenarios/hotswap/HS203/hs203t004/hs203t004.java line 35:

> 33:  *     While running the thread, it calls a method (doTask2() ) for number of times (10000).
> 34:  *     That would cause this method to be compiled, which causes a jvmti callback for compiled method load.
> 35:  *     (Hint : to force method compilation -XX:CompileThreshold=900 is used).

The test still uses (and the comments state it uses) -XX:CompileThreshold=900 to force compilation, yet it looks like you needed to bump the number of times the method is called from 1000 to 10000 to keep this test working. Why doesn't 1000 still work?

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