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

[Florian Hahn via llvm-commits]

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@@ -0,0 +1,298 @@
+//===-- 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 {
+struct VPPredicator {
+  using BlockMaskCacheTy = DenseMap<VPBasicBlock *, VPValue *>;
+  VPPredicator(BlockMaskCacheTy &BlockMaskCache)
+      : BlockMaskCache(BlockMaskCache) {}
+
+  /// 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;
+
+  /// Returns the previously computed predicate of the edge between \p Src and
+  /// \p Dst.
+  VPValue *getEdgeMask(const VPBasicBlock *Src, const VPBasicBlock *Dst) const {
+    return EdgeMaskCache.lookup({Src, 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(!BlockMaskCache.contains(VPBB) && "Mask already set");
+    BlockMaskCache[VPBB] = Mask;
+  }
+
+  /// Compute and return the mask for the vector loop header block.
+  void createHeaderMask(VPBasicBlock *HeaderVPBB, bool FoldTail);
+
+  /// Compute and return the predicate of \p VPBB, assuming that the header
+  /// block of the loop is set to True or the loop mask when tail folding.
+  VPValue *createBlockInMask(VPBasicBlock *VPBB);
+
+  /// Computes and return the predicate of the edge between \p Src and \p Dst.
+  VPValue *createEdgeMask(VPBasicBlock *Src, VPBasicBlock *Dst);
+
+  /// Create an edge mask for every destination of cases and/or default.
+  void createSwitchEdgeMasks(VPInstruction *SI);
+};
+} // namespace
+
+VPValue *VPPredicator::createEdgeMask(VPBasicBlock *Src, VPBasicBlock *Dst) {
+  assert(is_contained(Dst->getPredecessors(), Src) && "Invalid edge");
+
+  // Look for cached value.
+  VPValue *EdgeMask = getEdgeMask(Src, Dst);
+  if (EdgeMask)
+    return EdgeMask;
+
+  VPValue *SrcMask = getBlockInMask(Src);
+
+  // The terminator has to be a branch inst!
+  if (Src->empty() || Src->getNumSuccessors() == 1) {
+    EdgeMaskCache[{Src, Dst}] = SrcMask;
+    return SrcMask;
+  }
+
+  auto *Term = cast<VPInstruction>(Src->getTerminator());
+  if (Term->getOpcode() == Instruction::Switch) {
+    createSwitchEdgeMasks(Term);
+    return getEdgeMask(Src, Dst);
+  }
+
+  auto *BI = cast<VPInstruction>(Src->getTerminator());
+  assert(BI->getOpcode() == VPInstruction::BranchOnCond);
+  if (Src->getSuccessors()[0] == Src->getSuccessors()[1]) {
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fhahn wrote:

Will look into that separately, will probably warrant a generalization of removeBranchOnTrue, as we need to take care of updating the phi nodes

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