[llvm] [LoopVectorize] Perform loop versioning for some early exit loops (PR #120603)

[Jacob Lifshay via llvm-commits]

programmerjake wrote:

I proposed a similar speculative load instruction here: https://discourse.llvm.org/t/rfc-supporting-more-early-exit-loops/84690/2?u=programmerjake

https://github.com/llvm/llvm-project/pull/120603