[llvm] [VPlan] Move predication to VPlanTransform (NFC). (PR #128420)

[via llvm-commits]

================
@@ -0,0 +1,301 @@
+//===-- VPlanPredicator.cpp - VPlan predicator ----------------------------===//
+//
+// 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 predication for VPlans.
+///
+//===----------------------------------------------------------------------===//
+
+#include "VPRecipeBuilder.h"
+#include "VPlan.h"
+#include "VPlanCFG.h"
+#include "VPlanTransforms.h"
+#include "VPlanUtils.h"
+#include "llvm/ADT/PostOrderIterator.h"
+
+using namespace llvm;
+
+namespace {
+class VPPredicator {
+  using BlockMaskCacheTy = DenseMap<VPBasicBlock *, VPValue *>;
+  /// Builder to construct recipes to compute masks.
+  VPBuilder Builder;
+
+  /// When we if-convert we need to create edge masks. We have to cache values
+  /// so that we don't end up with exponential recursion/IR.
+  using EdgeMaskCacheTy =
+      DenseMap<std::pair<const VPBasicBlock *, const VPBasicBlock *>,
+               VPValue *>;
+  EdgeMaskCacheTy EdgeMaskCache;
+
+  BlockMaskCacheTy &BlockMaskCache;
+
+  /// Create an edge mask for every destination of cases and/or default.
+  void createSwitchEdgeMasks(VPInstruction *SI);
+
+  /// Computes and return the predicate of the edge between \p Src and \p Dst.
+  VPValue *createEdgeMask(VPBasicBlock *Src, VPBasicBlock *Dst);
+
+  /// Returns the *entry* mask for \p VPBB.
+  VPValue *getBlockInMask(VPBasicBlock *VPBB) const {
+    return BlockMaskCache.lookup(VPBB);
+  }
+
+  void setBlockInMask(VPBasicBlock *VPBB, VPValue *Mask) {
+    // TODO: Include the masks as operands in the predicated VPlan directly to
+    // remove the need to keep a map of masks beyond the predication transform.
+    assert(!getBlockInMask(VPBB) && "Mask already set");
+    BlockMaskCache[VPBB] = Mask;
+  }
+
+  VPValue *setEdgeMask(const VPBasicBlock *Src, const VPBasicBlock *Dst,
----------------
ayalz wrote:

```suggestion
  /// Record \p Mask as the mask of the edge from \p Src to \p Dst. The edge is expected to not have a mask already.
  VPValue *setEdgeMask(const VPBasicBlock *Src, const VPBasicBlock *Dst,
```
also expecting no parallel edges - worth verifying?

https://github.com/llvm/llvm-project/pull/128420