Investigate codegen for Vector128.GetUpper

[tannergooding]

As per #53450 (comment), it would like be beneficial to investigate changing the codegen of Vector128.GetUpper to use DUP rather than EXT on ARM64.

category:cq
theme:codegen

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Issue Details

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As per #53450 (comment), it would like be beneficial to investigate changing the codegen of Vector128.GetUpper to use DUP rather than EXT on ARM64.

Author:	tannergooding
Assignees:	tannergooding
Labels:	arch-arm64, tenet-performance, area-CodeGen-coreclr, untriaged
Milestone:	-

[JulieLeeMSFT]

Cc @dotnet/jit-contrib

[TIHan]

@TamarChristinaArm , I have a question, looking at the A78 Optimization Guide, EXT D-form and DUP D-form both have the same latency and throughput, is this indeed true? If so, then there wouldn't be a benefit to emitting DUP instead of EXT here.