[llvm] [VPlan] Dispatch to multiple exit blocks via middle blocks. (PR #112138)

[David Sherwood via llvm-commits]

================
@@ -921,8 +915,18 @@ VPlanPtr VPlan::createInitialVPlan(Type *InductionTy,
   //    we unconditionally branch to the scalar preheader.  Do nothing.
   // 3) Otherwise, construct a runtime check.
   BasicBlock *IRExitBlock = TheLoop->getUniqueExitBlock();
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david-arm wrote:

I think you should just be able to do

```
  BasicBlock *IRExitBlock = TheLoop->getUniqueLatchExitBlock();
```

here and remove the logic below.

https://github.com/llvm/llvm-project/pull/112138