RFR: JDK-8317683: Add JIT memory statistics [v2]

[Thomas Stuefe]

On Wed, 11 Oct 2023 12:25:54 GMT, Andrew Dinn <adinn at openjdk.org> wrote:

>> Thomas Stuefe has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:
>> 
>>  - Feedback Vladimir
>>  - Compilation memory statistic
>
> Also, I know it is not currently an option to specify enum values for cflag types but it would be more coherent from a user perspective if there was one compiler directive with 3 possible values
> 
>   MemStat = Off*/Collect/Print     *=default

Hi @adinn and @vnkozlov ,

I followed Andrew's advice and reworked the command once more. Now we have a just single command called "memstat". It has two valid values, "compile" and "print". The value can be left out for convenience, so that means "collect".

So:
`-XX:CompileCommand=memstat,*.*` synonymous with `-XX:CompileCommand=memstat,*.*,collect` : collects but does not print
`-XX:CompileCommand=memstat,*.*,print` does print

The option itself is an int. That fits nicely into the enum-ish shape. I think some future improvement could generalize that idea into a general enum-value-string-to-int converter.

This was a bit tricky because of the templatized nature of the value. I wish we had just a normal C-like union, this code would be a lot simple :-/

Does this look okay?

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PR Comment: https://git.openjdk.org/jdk/pull/16076#issuecomment-1761263754