RFR: 8370666: VectorAPI: Add clear comments for vector mask relative code in c2

[Xiaohong Gong]

On Fri, 9 Jan 2026 13:27:35 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> src/hotspot/share/opto/vectornode.hpp line 1855:
>> 
>>> 1853: //------------------------------VectorLoadShuffleNode------------------------------
>>> 1854: // The target may not directly support the rearrange operation for an element type.
>>> 1855: // In those cases, we can transform the rearrange into a different element type.
>> 
>> Can you  specify a bit more about the inputs and outputs, and what exactly the transformation does?
>
> Is this a memory instruction? Because it is called `Load`. If not: can we rename it?

It's not a memory instruction. Like `VectorLoadMask`, it is used to convert a shuffle vector to a platform supported vector. Previously, the shuffle is a byte vector. And this node is used to convert the byte vector to a vector with real data element type. But now, it is not needed for some architectures, since the vector shuffle's payload has been changed to the same integer type of normal vector, i.e. byte, short, int, and long.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29130#discussion_r2680934137