[llvm] [DominanceFrontier] Support post-dominators on graphs with single root (PR #179336)

[Ramkumar Ramachandra via llvm-commits]

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@@ -0,0 +1,94 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "../lib/Transforms/Vectorize/VPlan.h"
+
+#include "VPlanTestBase.h"
+#include "llvm/Analysis/DominanceFrontier.h"
+#include "llvm/Analysis/DominanceFrontierImpl.h"
+#include "gtest/gtest.h"
+
+namespace llvm {
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artagnon wrote:

```suggestion
using namespace llvm;
```

https://github.com/llvm/llvm-project/pull/179336