RFR: 8365570: C2 fails assert(false) failed: Unexpected node in SuperWord truncation: CastII [v2]

[Christian Hagedorn]

On Thu, 21 Aug 2025 15:21:48 GMT, Jasmine Karthikeyan <jkarthikeyan at openjdk.org> wrote:

>> Hi all,
>> This is a quick patch for the assert failure in superword truncation with CastII. I've added a check for all constraint cast nodes, and attached a reduced version of the fuzzer test. Thanks!
>
> Jasmine Karthikeyan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update comment for constraint casts

The fix looks good to me, too! I only have one comment about the test.

test/hotspot/jtreg/compiler/vectorization/TestSubwordTruncation.java line 431:

> 429:     }
> 430: 
> 431:     @Test(compLevel = CompLevel.C2)

Any particular reason you've chosen `C2` here and not let the IR framework handle it? (by default it's `ANY` which will compile at the highest available tier). I'm also wondering if this test would fail if someone ran the test with a build without C2.

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PR Review: https://git.openjdk.org/jdk/pull/26827#pullrequestreview-3228138075
PR Review Comment: https://git.openjdk.org/jdk/pull/26827#discussion_r2351288090