[llvm] [VPlan] Replace VPRegionBlock with explicit CFG before execute (NFCI). (PR #117506)

[via llvm-commits]

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@@ -240,6 +242,9 @@ class VPBlockUtils {
     VPBlockUtils::connectBlocks(From, BlockPtr, -1, SuccIdx);
     VPBlockUtils::connectBlocks(BlockPtr, To, PredIx, -1);
   }
+
+  /// Returns true if \p VPB is a loop header.
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ayalz wrote:

```suggestion
  /// Returns true if \p VPBB is a loop header, based on regions or \p VPDT in their absence.
```

https://github.com/llvm/llvm-project/pull/117506