On Wed, 25 Feb 2026 12:16:53 GMT, Christian Hagedorn <[email protected]> wrote:
> `compute_flat_in_array_if_unknown()` computes the flat in array property if > we don't know it. We additionally added some assertions that when we have > `FlatInArray::NotFlat` or `FlatInArray::Flat`, we are either dealing with a > non-value class or a value class, respectively. This worked in most cases. > > We now found cases with type speculation where this breaks: We could > speculatively assume that something is `FlatInArray::NotFlat/Flat`, propagate > that further and then later find that this contradicts the flat in array > property of some non-speculative type. > > I've first tried to avoid introducing these inconsistencies when starting to > use a speculative type. This sometimes work but not always: We could find an > inconsistency way further down in the graph later which is then hard to fix. > > I therefore propose to accept the fact that the flat in array property can be > inconsistent (i.e. being not flat in array, when actually dealing with an > always flat in array value class etc.): > - We set not flat in array even though the type could theoretically be flat > in array. > - We set flat in array even though the type could theoretically be non flat > in array. > > We only use the flat in array property for `SubTypeCheck` and `CmpP` nodes in > `Value()`. When facing such an inconsistency, we could end up "wrongly" > folding a compare node. But in that case, we would trap earlier because the > speculated type turns out to be wrong (see `testSuperNotFlatSubFlat()` as an > example). > > To make this work properly, we also need to adjust `SubTypeCheck::sub()` to > not only check the case when the super class is flat in array and the sub > class is not but also the other way round (this missing piece was now also > found as a missed optimization opportunity in the CI independently of these > changes). > > Thanks, > Christian This pull request has now been integrated. Changeset: 94f14342 Author: Christian Hagedorn <[email protected]> Committer: Tobias Hartmann <[email protected]> URL: https://git.openjdk.org/valhalla/commit/94f14342eaa6ef40bcb7926eac401affa9807312 Stats: 274 lines in 5 files changed: 255 ins; 7 del; 12 mod 8373878: [lworld] C2: Assertions about flat in array properties are too strong in TypePtr::compute_flat_in_array_if_unknown() Reviewed-by: thartmann ------------- PR: https://git.openjdk.org/valhalla/pull/2162
