[llvm] [VPlan] Move EVL-based transforms to VPlanEVLTransforms.cpp (NFC) (PR #209883)

[Luke Lau via llvm-commits]

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@@ -0,0 +1,657 @@
+//===- VPlanEVLTransforms.cpp - Explicit Vector Length transforms ---------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file implements the VPlan-to-VPlan transforms related to explicit
+/// vector length (EVL) support.
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lukel97 wrote:

EVL on its own doesn't mean too much, it's just an argument to a VP intrinsic. It would be good to explicitly have tail folding in the file name, maybe something like VPlanEVLTailFolding.cpp?

```suggestion
/// vector length (EVL) tail folding support.
```

https://github.com/llvm/llvm-project/pull/209883