RFR: 8266962: Add arch supporting check for "Op_VectorLoadConst" before creating the node

[Xiaohong Gong]

On Fri, 14 May 2021 15:42:53 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> The fix makes perfect sense, but I'm curious why do we have `VectorLoadConst` in the first place.
> 
> It exposes JVM support for the iota vector constant materialization, but it's not clear to me what benefits it brings compared to feeding the intrinsic with the vector materialized on JDK side.

Thanks for looking at this PR @iwanowww ! As far as I know the `VectorLoadConst` is used here to get the initial shuffle iota of the vector.  I'm not so clear about what the `iota vector constant materialization` you mean. Could you please elaborate more about it? Thanks so much!

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PR: https://git.openjdk.java.net/jdk/pull/4023