On Tue, 20 Jan 2026 11:30:38 GMT, Quan Anh Mai <[email protected]> wrote:
>> Some code added by >> [JDK-8372700](https://bugs.openjdk.org/browse/JDK-8372700) can compute the >> constant value of a field of a (flatten) element in a flat array. We get a >> crash when the element of the array is known to be `null`, and so the field >> doesn't exist. >> >> So, let's just check in `ciConstant ciFlatArray::field_value(int index, >> ciField* field)` whether we get a null constant before interpreting it as a >> `ciInstance` and trying to retrieve a field from there. This should be >> enough since a `ciObject` is (directly) derived by `ciNullObject`, >> `ciInstance` and `ciArray`. Since we are looking up a value of a flat array, >> an element cannot be a `ciArray` (arrays have identities and can't be >> contained in a flat array). After looking up whether the flat array element >> is null, the `obj->as_instance()` cast acts as an assert, should we ever add >> another derived class from `ciObject`. >> >> In case of a null array element, `field_value` simply returns an invalid >> `ciConstant`. >> >> Tested with >> tier1,tier2,tier3,hs-precheckin-comp,hs-comp-stress,valhalla-comp-stress. >> Looks good. >> >> Thanks, >> Marc > > 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? ------------- PR Review Comment: https://git.openjdk.org/valhalla/pull/1923#discussion_r2708233184
