RFR: 8293170: Improve encoding of the debuginfo nmethod section

[Evgeny Astigeevich]

On Thu, 25 Aug 2022 14:35:32 GMT, Boris Ulasevich <bulasevich at openjdk.org> wrote:

> The nmethod "scopes data" section is 10% of the size of nmethod. Now the data is compressed using the Pack200 algorithm, which is good for encoding small integers (LineNumberTable, etc). Using the fact that half of the data in the partition contains zeros, I reduce its size by another 30%.
>  
> Testing: jtreg hotspot&jdk, Renaissance benchmarks

src/hotspot/share/code/compressedStream.cpp line 152:

> 150: }
> 151: 
> 152: int CompressedSparseDataWriteStream::position() {

The function with a side effect looks strange to me. I see an assert in `DebugInformationRecorder::DebugInformationRecorder(OopRecorder* oop_recorder)` which uses it for checking.  So the assert can cause side affects. I am not sure it is expected.

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PR: https://git.openjdk.org/jdk/pull/10025