RFR: 8370405: C2: mismatched store from MergeStores wrongly scalarized in allocation elimination

[Quan Anh Mai]

On Wed, 29 Oct 2025 14:50:48 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> It seems that we don't trust the return type of a method call (look at `TypeFunc::make(ciMethod*)` where we pass `ignore_interfaces` into `TypeTuple::make_domain` and `TypeTuple::make_range`). I don't understand why, though, interfaces are weird.
>> 
>> However, `tmp` is trusted because it is created with `anewarray`. In `Parse::do_anewarray`, we pass `trusted_interfaces` to `TypeKlassPtr::make`.
>> 
>> The question is, why are we storing an `Object` into an array of `Enumeration`s?
>
> Right, I follow you all the way up to your question. I would answer like this:
> 
> `tmp` knows that its elements (the fields) have type `java/lang/Object (java/util/Enumeration)`, so they must be `Object` of interface `Enumeration`. But the projection from the call does not trust the interface, and so it just knows that it produces an `Object`.
> 
> I'll try to strip interface information from both, and see if I get a match that way. Does that sound reasonable?

@eme64 But `aastore` does a check cast before the store. Since `Object` is not a subtype of `Object(Enumeration)`, should we do a check cast and the value to store is a `CheckCastPP` with the appropriate type?

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PR Review Comment: https://git.openjdk.org/jdk/pull/27997#discussion_r2473619411