[llvm] [AArch64] Optimize two large shifts and a combine into a single combine and shift (PR #99480)

[via llvm-commits]

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+; RUN: llc < %s -verify-machineinstrs -mtriple=aarch64-none-linux-gnu -mattr=neon | FileCheck %s
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sopyb wrote:

It took me an embarrassingly long time to figure this out. I kept thinking it was more complicated than it actually was, which caused me to delay addressing it for nearly two days. :woman_facepalming: 

https://github.com/llvm/llvm-project/pull/99480