RFR: 8292847: Zero: Allow ergonomics to select the GC

[Thomas Schatzl]

On Wed, 24 Aug 2022 06:01:05 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> Zero is currently defaulting to Serial GC on all machines, due to the fact that `NeverActAsServerClassMachine` is `true`. It is set in `compiler_globals.pd` under `#if !defined(COMPILER1) && !defined(COMPILER2) && !INCLUDE_JVMCI`. `NeverActAsServerClassMachine` mostly affects compiler ergonomics, which Zero does not need, but it also affects the selection of default GC.
> 
> After [JDK-8256497](https://bugs.openjdk.org/browse/JDK-8256497), we can let Zero default to G1. After [JDK-8292329](https://bugs.openjdk.org/browse/JDK-8292329), it would help Zero to use the CDS shared heap.
> 
> Additional testing:
>  - [x] Linux x86_64 Zero fastdebug, `make bootcycle-images`
>  - [x]  Linux x86_64 Zero fastdebug, `tier1` tests (many known failures)

Marked as reviewed by tschatzl (Reviewer).

-------------

PR: https://git.openjdk.org/jdk/pull/9994