RFR: 8340012: [C2] assert(KlassEncodingMetaspaceMax > pd) failed: change encoding max if new encoding after 8338526

[Martin Doerr]

On Fri, 13 Sep 2024 15:44:35 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> Which CPUs are affected? Only PPC64?

The C2 transformation is used on aarch64, ppc64, riscv, s390. The issue has been observed on AIX only so far. It may be possible to trigger it on other platforms by extra flags.

> use CompressedClassSpaceBaseAddress to enforce a low base address, e.g. 1GB.

Thanks for the hints! We need `CompressedKlassPointers::base() == nullptr` to trigger the problem. Otherwise, C2 will not use the transformation.

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PR Comment: https://git.openjdk.org/jdk/pull/20971#issuecomment-2349291099