On Tue, 20 Jan 2026 12:54:01 GMT, Marc Chevalier <[email protected]> wrote:
>> src/hotspot/share/ci/ciFlatArray.cpp line 136:
>>
>>> 134:
>>> 135: ciConstant ciFlatArray::field_value(int index, ciField* field) {
>>> 136: auto get_field_from_object_constant = [field](const ciConstant& v)
>>> -> ciConstant {
>>
>> I don't really agree with this fix, `ciFlatArray::field_value` should be
>> dumber, it is the caller who knows that we do not fold the load if the
>> element is `null`, the callee should just return the field as it is.
>
> I fear I don't understand. Let's say, I have a flat array `MyValue[] arr`
> where `MyValue` is a value class with a single field `f`. Let's also assume
> `arr[0] == null`, `arr.field_value(0, f)` (assuming the `ci...` versions of
> it with matching names) tries to get the constant value of the field `f` of
> `arr[0]`, and `arr[0].f` is not null, it's rather undefined. It's not about
> stability and folding. On the other hand, if `arr[0]` is not null, but
> `arr[0].f` is null, `arr.field_value(0, f)` already returns `null` (the
> `ciConstant` that means that).
>
> Am I missing something?
That is only true from the Java perspective. From the VM perspective, a flat
array would be something like (C++ pseudocode):
class MyValuePayload {
oop* f;
bool null_marker;
};
MyValuePayload* arr = new MyValuePayload[n];
Then, it is clear that even if `arr[0].null_marker == false`, `arr[0].f` is
still defined and has a value (which should be `nullptr`).
-------------
PR Review Comment:
https://git.openjdk.org/valhalla/pull/1923#discussion_r2708268808
