[llvm] [PowerPC] Optimize bitcast(truncate) patterns using vbpermq/vbpermd (PR #181233)

[Nemanja Ivanovic via llvm-commits]

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nemanjai wrote:

I am not sure such a TRUNC would ever be triggered since it would be a truncation to an illegal type.

https://github.com/llvm/llvm-project/pull/181233