RFR: 8249893: AARCH64: optimize the construction of the value from the bits of the other two [v6]

[Boris Ulasevich]

On Wed, 30 Mar 2022 08:15:08 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>>>  why you need to delay application of this transform to a new post-loops optimization stage
>> 
>> Unfortunately, BitfieldInsert transformation conflicts with vectorization:
>> - if or/and/shift was converted to BFI it is no longer vectorized
>> - vectorized or/and/shift operations are faster than BFI
>> 
>> I delayed my transformation to be sure loop and vectorization transformations is already done at the moment.
>
> @bulasevich any plans to re-open and fix this?

@TobiHartmann 

The original fix was a complicated rule in aarch64.ad file.
I was suggested [1] to move the logic to early stages, but the result is bulky anyway.
I myself am not happy with this change, and I have two negative reviews [2][3].
I decided to discard this change, and I have no plans to re-open and fix this.

[1] https://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2020-August/039373.html
[2] https://github.com/openjdk/jdk/pull/511#pullrequestreview-524294415
[3] https://github.com/openjdk/jdk/pull/511#issuecomment-722992744

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PR: https://git.openjdk.java.net/jdk/pull/511