RFR: 8356027: Print enhanced compilation timings [v4]

[Ashutosh Mehra]

On Mon, 5 May 2025 16:37:00 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> In Leyden, we have the extended compilation timings printouts with -XX:+PrintCompilation / UL, that are very useful to study compiler dynamics. These timings include:
>>  1. Time spent before queuing: shows the compilation queue bottlenecks
>>  2. Time spent in the queue: shows delays caused by queue bottlenecks and compiler load
>>  3. Time spent actually compiling: shows the per-method compilation costs
>> 
>> We should consider the same kind of printout for mainline. This would also require us to print the compilation task _after_ the compilation, not only before it. This improvement would also obviate any need for `PrintCompilation2` flag, [JDK-8356028](https://bugs.openjdk.org/browse/JDK-8356028).
>> 
>> The difference from the output format we ship in Leyden:
>>  1. This output prints before/after the compilation to maintain old behavior partially. The "before" printout is now prepended with `started` to clearly mark it as such.
>>  2. The output is raw number in microseconds. In Leyden repo, we have these prepended with characters, like `C0.1`, but that prepending makes it a bit inconvenient with scripts. This PR also does microseconds, instead of fractional milliseconds. This should be enough to capture the wide range of durations.
>> 
>> See the sample `-XX:+PrintCompilation` output in the comments.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 server fastdebug, `compiler`
>>  - [x]  Linux x86_64 server fastdebug, `all`
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Revert the shared printing block

Marked as reviewed by asmehra (Committer).

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PR Review: https://git.openjdk.org/jdk/pull/24984#pullrequestreview-2815605291