[llvm] [LV] Tidy up early bail outs related to runtime checks (PR #228077)

[David Sherwood via llvm-commits]

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david-arm wrote:

It's intentional, because I couldn't find any tests that broke when I introduced an unreachable. It also isn't exposed anywhere in the LLVM test suite so to me it looks like dead code. If you know of a test case that would expose this code path I'm happy to add one, but ideally it would be nice to avoid additional complexity for situations that cannot arise.

https://github.com/llvm/llvm-project/pull/228077