RFR: 8363986: Heap region in CDS archive is not at deterministic address [v2]

[Ioi Lam]

On Tue, 18 Nov 2025 19:21:45 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Ioi Lam has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains seven commits:
>> 
>>  - clean up of old C++ class name ArchiveHeapWriter
>>  - @ashu-mehra comment -- simplified the criteria for _is_writing_deterministic_heap
>>  - Merge branch 'master' into 8363986-heap-region-in-aot-cache-not-determinitic-address
>>  - More clean up
>>  - fixed aot map
>>  - clean up
>>  - 8363986: Heap region in CDS archive is not at deterministic address
>
> src/hotspot/share/cds/aotMappedHeapWriter.cpp line 109:
> 
>> 107:       // optimizations such as AOT compiled code require the same compressed oop
>> 108:       // encoding to be used in the assembly phase and production run, so we cannot
>> 109:       // force (zero-based, no shift) encoding.
> 
> In Leyden we do force encoding `(base, shift)` with `-XX:+UseCompatibleCompressedOops` flag in Leyden when AOT code is generated and used:
> https://github.com/openjdk/leyden/blob/premain/src/hotspot/share/oops/compressedOops.cpp#L51
> 
> The flag is enabled by default when AOT code is used:
> https://github.com/openjdk/leyden/blob/premain/src/hotspot/share/cds/cdsConfig.cpp#L121
> 
> It allows to use different heap size in production runs.

I have updated the comments to avoid discussing future AOT optimizations. Instead, it says:


// Determninistic output is not supported by the new AOT workflow, so
// we don't force the (zero-based, no shift) encoding. This way, it is more
// likely that we can avoid oop relocation in the production run.

> src/hotspot/share/cds/aotMappedHeapWriter.cpp line 588:
> 
>> 586: //     In the production run, if different COOPS encodings are used:
>> 587: //         - The heap contents needs to be relocated.
>> 588: //         - AOTCodeCache will be disabled.
> 
> Not true by default. See my first comment.

I have deleted the comment about AOTCodeCache.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/28052#discussion_r2539579548
PR Review Comment: https://git.openjdk.org/jdk/pull/28052#discussion_r2539581224