RFR: 8350177: C2 SuperWord: Integer.numberOfLeadingZeros, numberOfTrailingZeros, reverse and bitCount have input types wrongly turncated for byte and short [v3]

[Jasmine Karthikeyan]

On Mon, 16 Jun 2025 06:06:23 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> src/hotspot/share/opto/superword.cpp line 2538:
>> 
>>> 2536:     break;
>>> 2537:   default:
>>> 2538:     assert(false, "Unexpected node: %s", NodeClassNames[in->Opcode()]);
>> 
>> Suggestion:
>> 
>>     // If this assert it hit, that means that we need to determine if the node can be safely truncated,
>>     // and then add it to the list of truncatable nodes or the list of non-truncatable ones just above.
>>     // In product, we just return false, which is always correct.
>>     assert(false, "Unexpected node: %s", NodeClassNames[in->Opcode()]);
>
> I'm fairly sure that we will hit this assert with a fuzzer or some other RFE soon, and then it will be nice to know quickly what kind of failure we have here.

This is a good point, I've made this change.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25440#discussion_r2153586302