On Tue, 20 Jan 2026 11:25:59 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/opto/type.cpp line 414: > >> 412: >> 413: if (con.is_valid() && // not a mismatched access >> 414: !con.is_null_or_zero()) { // not a default value > > This is incorrect, the value is not constant if the element of the array is > `null`, not if the field we retrieved is `null`. I think you're correct. While being sound, we might miss opportunities where the value is actually constant but we discard it. `con.is_value()` already is enough to make sure the array element is not null (and constant). ------------- PR Review Comment: https://git.openjdk.org/valhalla/pull/1923#discussion_r2708249153
