[llvm] [VPlan] Introduce scalar loop header in plan, remove VPLiveOut. (PR #109975)

[via llvm-commits]

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@@ -455,8 +455,12 @@ void VPIRBasicBlock::execute(VPTransformState *State) {
          "VPIRBasicBlock can have at most two successors at the moment!");
   State->Builder.SetInsertPoint(IRBB->getTerminator());
   executeRecipes(State, IRBB);
-  if (getSingleSuccessor()) {
-    assert(isa<UnreachableInst>(IRBB->getTerminator()));
+  // Prepare branch instruction in IRBB. If there are no successors, there's
+  // nothing to do. If IRBB's terminator is already a BranchInst, there's
+  // nothing to do here. If it is unreachable, we don't cannot re-use an
+  // existing branch and no branch has been created during recipe execution.
+  // Create it now.
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ayalz wrote:

```suggestion
  //  Create a branch instruction to terminate IRBB if one was not created yet and needed.
```


https://github.com/llvm/llvm-project/pull/109975