On Wed, 1 Jul 2026 05:12:57 GMT, Tobias Hartmann <[email protected]> wrote:
>> When slightly modifying the test that I added for >> [JDK-8386067](https://bugs.openjdk.org/browse/JDK-8386067), I hit an assert >> in `CallStaticJavaNode::replace_is_substitutable` because expansion of the >> substitutability call failed and `emit_substitutability_check` returned >> `nullptr` although `can_emit_substitutability_check` returned `true`. >> >> In the new test, the problematic field is `ObjectHolder::obj` which, >> although it is of type `Object`, is always `exact` and therefore can't be a >> value object and does not require a substitutability test. >> `InlineTypeNode::can_emit_substitutability_check` correctly returns `true`: >> https://github.com/openjdk/valhalla/blob/2ae8e47da016bb4d7718e7923c964c2b91c638e6/src/hotspot/share/opto/inlinetypenode.cpp#L611-L614 >> >> >> However, during recursive expansion, nullable value object fields are >> null-checked and then compared field-by-field: >> https://github.com/openjdk/valhalla/blob/2ae8e47da016bb4d7718e7923c964c2b91c638e6/src/hotspot/share/opto/inlinetypenode.cpp#L910 >> >> The code unconditionally rebuilt those fields with >> `InlineTypeNode::make_from_oop` after the null and type checks because >> there's a `CastPP` in-between: >> https://github.com/openjdk/valhalla/blob/2ae8e47da016bb4d7718e7923c964c2b91c638e6/src/hotspot/share/opto/inlinetypenode.cpp#L955-L960 >> >> If the field was already scalarized, this discarded the existing >> `InlineTypeNode` and reloaded fields from the oop, losing precise >> information such as exact Object field Phis. The later Object field >> comparison then looks non-exact and `emit_substitutability_check_pointer` >> returns `nullptr`: >> https://github.com/openjdk/valhalla/blob/2ae8e47da016bb4d7718e7923c964c2b91c638e6/src/hotspot/share/opto/inlinetypenode.cpp#L722-L724 >> >> The fix is to preserve already-scalarized recursive field operands when >> their inline klass matches the comparison klass, and only checkcast/reload >> operands that are not scalarized. With the fix, exact type information is >> preserved and we emit a pointer comparison for the exact object fields: >> https://github.com/openjdk/valhalla/blob/2ae8e47da016bb4d7718e7923c964c2b91c638e6/src/hotspot/share/opto/inlinetypenode.cpp#L700-L702 >> >> The IR Framework test verifies this successful expansion. >> >> Note: The null and type checks are not immediately folded because by GVN >> because we need to set `set_delay_transform` here: >> https://github.com/openjdk/valhalla/blob/2ae8e47da016bb4d7718e7923c964c2b91c638e6/src/hotspot/share/opto/callnode.cpp#L141... > > Tobias Hartmann has updated the pull request incrementally with one > additional commit since the last revision: > > New attempt at comment Thanks for the review Quan Anh! ------------- PR Comment: https://git.openjdk.org/valhalla/pull/2602#issuecomment-4851543866
