[lworld] RFR: 8375441: [lworld] C2: assert(is_instance()) failed: bad cast [v2]

[Quan Anh Mai]

On Wed, 4 Feb 2026 10:38:24 GMT, Marc Chevalier <mchevalier at openjdk.org> wrote:

>> src/hotspot/share/ci/ciInstance.cpp line 95:
>> 
>>> 93:         InlineLayoutInfo* layout_info = holder->inline_layout_info_adr(index);
>>> 94:         InlineKlass* vk = layout_info->klass();
>>> 95:         oop res = vk->read_payload_from_addr(obj, offset, layout_info->kind(), THREAD);
>> 
>> It seems to imply that this access is required to be atomic, what if it is a non-atomic field?
>
> I think the problem isn't here, but in `field_value`: in case we need a non-atomic field, we don't need to find the containing field and cache that. If the containing field turns out not to be atomic, we can simply get the leaf field directly, and cache that. For now, I've made an error to ask for a flat declared field in case it's non-atomic: one probably want/should (but at least can) query the leaf fields individually.

What if we have something like this:

    @Stable
    static final VeryLargeValueType[] ARRAY = new null-free-non-atomic VeryLargeValyeType[100];

The program uses a non-atomic layout because it will not do racy accesses on this array, but the compiler may, and what should we do in this case? Probably just give up?

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1923#discussion_r2763396079