[vectorIntrinsics] RFR: 8283413: Add C2 mid-end and x86 back-end implementation for bit REVERSE operation [v2]

[Jatin Bhateja]

On Mon, 21 Mar 2022 08:12:43 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

>> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8283413: Adding Ideal transform for (ReverseV (ReverseV VEC)) => VEC and (ReverseV (ReverseV VEC MASK) MASK)) => VEC
>
> src/hotspot/share/opto/compile.cpp line 3425:
> 
>> 3423:     }
>> 3424:     break;
>> 3425:   }
> 
> The mid-end part looks good to me.  Thanks! BTW, may I ask why you add this transformation here while not in the `ReverseVNode::Idea()` ? Thanks so much！

Blend IR node is created in a subsequent step after ReverseV node creation and are not visible to during eager identity transformation of ReverseV;   Final graph reshaping gives us opportunity to perform point transformation on graph patterns which cannot be easily handled through gvn based transformations.

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PR: https://git.openjdk.java.net/panama-vector/pull/182