[lworld] RFR: 8370450: [lworld] Alternate implementation of the substitutability test method [v2]

[Frederic Parain]

On Thu, 23 Oct 2025 18:13:38 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Frederic Parain has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:
>> 
>>  - Merge remote-tracking branch 'upstream/lworld' into new_acmp
>>  - Add alternate version of the substitutability method
>
> src/hotspot/share/classfile/fieldLayoutBuilder.cpp line 1361:
> 
>> 1359:   _nonoop_acmp_map = new GrowableArray<Pair<int,int>>();
>> 1360:   _oop_acmp_map = new GrowableArray<int>();
>> 1361:   if (_is_empty_inline_class) return;
> 
> Why not return first before allocating these GrowableArray in resource area?

It streamlines the code in InstanceKlass::fill_instance_klass() by not having to handle the null map case.

> src/hotspot/share/interpreter/bytecodeTracer.cpp line 95:
> 
>> 93:   void trace(const methodHandle& method, address bcp, uintptr_t tos, uintptr_t tos2, outputStream* st) {
>> 94:     ResourceMark rm;
>> 95:     ttyLocker ttyl;
> 
> This should be removed with [JDK-8370044](https://bugs.openjdk.org/browse/JDK-8370044)

It is just a quick hack because I needed to use TraceBytecode to evaluate the new acmp.
I'll remove it before pushing.

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

PR Review Comment: https://git.openjdk.org/valhalla/pull/1695#discussion_r2457297856
PR Review Comment: https://git.openjdk.org/valhalla/pull/1695#discussion_r2457288265