[llvm] [ConstantTime][LLVM] Add llvm.ct.select intrinsic with generic SelectionDAG lowering (PR #166702)

[Julius Alexandre via llvm-commits]

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wizardengineer wrote:

This is covered by the move to the legalizer. Non-legal types blend at the widest legal integer with ext-load and trunc-store tails, and the scalable-vector and non-legal-scalar cases are handled in f4383a332170.

https://github.com/llvm/llvm-project/pull/166702