[llvm] [LICM] Use DomTreeUpdater version of SplitBlockPredecessors, nfc (PR #107190)

[Nikita Popov via llvm-commits]

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nikic wrote:

TBH, I think I'd prefer just not having a test for this than having *this* test. Presumably this is making the stars align in exactly the right way to trigger a crash, but it's probably not going to still be doing that half a year form now when something, somewhere changes in a small way. If there's no way to make the issue more reliably reproducible (e.g. via an extra assert somewhere) then this test isn't adding much, and will likely be a PITA to update in the future for random changes across four passes.

https://github.com/llvm/llvm-project/pull/107190