RFR: 8354282: C2: more crashes in compiled code because of dependency on removed range check CastIIs [v8]

[Emanuel Peter]

On Tue, 2 Dec 2025 15:17:38 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> src/hotspot/share/opto/castnode.hpp line 108:
>> 
>>> 106:     // Floating: The Cast is only dependent on the single range check.
>>> 107:     // Narrowing: The Cast narrows the type to a positive index. If the input to the Cast is narrower, we can safely
>>> 108:     //            remove the cast because the array access will be safe.
>> 
>> The "Floating" part is a bit counter intuitive here, because the ctrl of the CastII is the RangeCheck, right?
>> So is it not therefore already pinned?
>> 
>> Maybe we can add some detail about what the "floating" explicitly means here. Is it that we can later move the CastII up in an optimization?
>
> Actually, I'm wondering if the term `hoistable` and `non-hoistable` would not be better terms...

At least we could say that it is allowed to hoist the RangeCheck,  and the CastII could float up to where the RC is hoisted.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24575#discussion_r2581649395