RFR: 8376822: UseCompactObjectHeaders: fill Klass alignment gaps in AOT cache [v2]

[Ioi Lam]

On Tue, 24 Feb 2026 11:12:39 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   moved offset != 0 check
>
> src/hotspot/share/cds/archiveUtils.cpp line 293:
> 
>> 291: using AllocGapNode = RBNode<DumpRegion::AllocGap, Empty>;
>> 292: 
>> 293: class DumpRegion::AllocGapTree : public RBTreeCHeap<AllocGap, Empty, AllocGapCmp, mtClassShared> {
> 
> Is there a reason that we're subclassing here instead of having a RBTreeCHeap as a member of this class?

Since I named the class `AllocGapTree`, I think subclassing makes more sense.

> src/hotspot/share/cds/archiveUtils.cpp line 310:
> 
>> 308:   }
>> 309: 
>> 310:   char* allocate_from_gap(size_t num_bytes) {
> 
> `precond` that `num_bytes` is divisble by `SharedSpaceObjectAlignment`?

The condition is checked inside the `AllocGap` constructor just below this line. I do the `preconds` there to avoid sprinkling alignment checks all over the code.

> src/hotspot/share/cds/archiveUtils.cpp line 318:
> 
>> 316:     AllocGapNode* node = closest_ge(target);
>> 317:     if (node == nullptr) {
>> 318:       return nullptr; // Didn't find any useable gap.
> 
> Sp nit: 'usable' is preferred

Fixed.

> src/hotspot/share/cds/archiveUtils.cpp line 373:
> 
>> 371:   if (alignment == SharedSpaceObjectAlignment && type != MetaspaceClosureType::SymbolType) {
>> 372:     // The addresses of Symbols must be in the same order as they are in ArchiveBuilder::SourceObjList.
>> 373:     // If we put them in gaps, their orders will change.
> 
> "orders" -> "order"

Fixed.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/29869#discussion_r2854632657
PR Review Comment: https://git.openjdk.org/jdk/pull/29869#discussion_r2854633466
PR Review Comment: https://git.openjdk.org/jdk/pull/29869#discussion_r2854633176
PR Review Comment: https://git.openjdk.org/jdk/pull/29869#discussion_r2854634033