[llvm] [Transforms][Utils] Add LoopSplitUtils for iteration-space loop splitting (PR #205995)

[Ramkumar Ramachandra via llvm-commits]

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artagnon wrote:

```suggestion
  if (!L->getLoopPreheader() || !L->getLoopLatch() ||
      !L->getExitingBlock() || !L->getExitBlock() ||
      L->getExitingBlock() != L->getLoopLatch() ||
      !L->isLCSSAForm(*DT)) {
    LLVM_DEBUG(dbgs() << DEBUG_TYPE ": loop not in expected form\n");
    return false;
  }
```

Not sure what value there is in splitting it out? Please use DEBUG_TYPE to prefix the debug-output?

https://github.com/llvm/llvm-project/pull/205995