RFR: JDK-8241503: C2: Share MacroAssembler between mach nodes during code emission [v6]

[Vladimir Kozlov]

On Mon, 18 Dec 2023 20:19:49 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

>> Cesar Soares Lucas has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains seven commits:
>> 
>>  - Merge with origin/master
>>  - Fix build, copyright dates, m4 files.
>>  - Fix merge
>>  - Catch up with master branch.
>>    
>>    Merge remote-tracking branch 'origin/master' into reuse-macroasm
>>  - Some inst_mark fixes; Catch up with master.
>>  - Catch up with changes on master
>>  - Reuse same C2_MacroAssembler object to emit instructions.
>
> Cleanup is not bad. Fewer objects and a bit shorter code at some places are an advantage.
> Maybe Vladimir had some more reasons in mind when filing the issue. It's linked to https://bugs.openjdk.org/browse/JDK-8239472. It'd be nice if you or Vladimir could add a bit of motivation to the description of the PR or the JBS issue.

@TheRealMDoerr  motivation is to reduce memory consumption and speed up C2. `C2_MacroAssembler`  is based on `ResourceObj` which allocates in compiler arena. Each small  `C2_MacroAssembler masm()` will add allocation to arena until we finish compilation. Also speedup because we don't need to do such allocations.

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PR Comment: https://git.openjdk.org/jdk/pull/16484#issuecomment-1863321348