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

[Vladimir Ivanov]

On Fri, 14 May 2021 06:04:45 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

> When creating the vector shuffle, the `"VectorLoadConstNode"` will be created to get an initial index vector. Before creating it, the compiler should check whether the current platform supports this opcode in case the jvm crashes with `"bad ad file"`. The compiler should finish the intrinsification and go back to the default java implementation if the backend doesn't support it.
> 
> Tested tier1 and jdk::tier3.

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.

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Marked as reviewed by vlivanov (Reviewer).

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