[master] RFR: JDK-8325104: Lilliput: Shrink Classpointers [v3]

[Stefan Karlsson]

On Sat, 10 Feb 2024 14:52:43 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> src/hotspot/share/gc/shared/c2/barrierSetC2.cpp line 661:
>> 
>>> 659:   if (base_off % BytesPerLong != 0) {
>>> 660:     assert(UseCompressedClassPointers, "");
>>> 661:     assert(!UseCompactObjectHeaders, "");
>> 
>> What is that for? Is it important?
>
> Mostly for documentation. The various asserts like this helped me understand a lot of code.

It could be nice to include compact headers in the comment above. Maybe something like this. It would make it clearer why this assert was added.

  // 8  - 32-bit VM
  // 8  - 64-bit VM, compact object headers
  // 12 - 64-bit VM, compressed klass
  // 16 - 64-bit VM, normal klass

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PR Review Comment: https://git.openjdk.org/lilliput/pull/128#discussion_r1540760038