[vectorIntrinsics] RFR: 8283413: Add C2 mid-end and x86 back-end implementation for bit REVERSE and REVERSE_BYTES operation [v6]

[Jatin Bhateja]

On Fri, 22 Jul 2022 07:58:39 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Please refer to the PR https://github.com/openjdk/jdk/pull/9565. Thanks a lot!
>
>> Yeah, I know that is used to skip the transformations. I'm just curious why we need to skip the optimizations if it is used by a `VectorBlend`. Did you met any issues or something others? Thanks! I want to add a transformation such as `(ReverseBytesV src) => src` if the basic element type is T_BYTE. I cannot see the reason that I need to also skip this transformation for VectorBlend used ReverseBytesV. Maybe we can continue the discussion after I created a PR for it. WDYT?
> 
> It was purely to skip matching over bigger graph pallet at that point, with blends pattern matching will be slightly complex and will need to be handled in VectorBlend idealization routines.

I think we can have a separate PR to handle cascaded complementary masked operations over non-predicated targets to handle all the cases in one shot i.e. REVERSE, REVERSEBYTES, NOT.

Other interesting transforms could be  ROR X+ ROL X by same shift = X,   
complementary casts/re-interprets.,  X2Y + Y2X = X

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