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 06:01:17 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> src/hotspot/share/opto/superword.cpp line 2521:
>> 
>>> 2519:   if (VectorNode::is_shift_opcode(opc)) {
>>> 2520:     return false;
>>> 2521:   }
>> 
>> Is right shift also not truncatable? Can you add a comment why?
>
> Here you did a return in assert.

Shifts are the special case I mentioned earlier, where we consider them non-truncating to get a more precise type from input loads. I've added a comment mentioning it.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25440#discussion_r2153589837