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

[Andrew Haley]

On Mon, 5 Oct 2020 17:36:14 GMT, Boris Ulasevich <bulasevich at openjdk.org> wrote:

> Let me revive the change request [3] to C2 and AArch64 that applies Bitfield Insert instruction in the expression "(v1
> & 0xFF) | ((v2 & 0xFF) << 8)".
>  
> Compared to the last round of review [2] I updated the transformation to apply BFI in more cases and added a jtreg test.
> 
> As before, compared to the original patch [1], the transformation logic is now in the common C2 code: a new
> BitfieldInsert node has been introduced to replace Or+Shift+And sequence when possible, on AARCH a single BFI
> instruction is emitted for the new node.
>  
> [1] https://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2020-July/039161.html
> [2] https://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2020-August/039653.html
> [3] https://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2020-August/039792.html

Please add your microbenchmark to this pull request.

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