[llvm] r336114 - [Dominators] Add the DomTreeUpdater class

Jakub Kuderski via llvm-commits llvm-commits at lists.llvm.org
Mon Jul 2 08:37:41 PDT 2018


Author: kuhar
Date: Mon Jul  2 08:37:41 2018
New Revision: 336114

URL: http://llvm.org/viewvc/llvm-project?rev=336114&view=rev
Log:
[Dominators] Add the DomTreeUpdater class

Summary:
This patch is the first in a series of patches related to the [[ http://lists.llvm.org/pipermail/llvm-dev/2018-June/123883.html | RFC - A new dominator tree updater for LLVM ]].

This patch introduces the DomTreeUpdater class, which provides a cleaner API to perform updates on available dominator trees (none, only DomTree, only PostDomTree, both) using different update strategies (eagerly or lazily) to simplify the updating process.

—Prior to the patch—

   - Directly calling update functions of DominatorTree updates the data structure eagerly while DeferredDominance does updates lazily.
   - DeferredDominance class cannot be used when a PostDominatorTree also needs to be updated.
   - Functions receiving DT/DDT need to branch a lot which is currently necessary.
   - Functions using both DomTree and PostDomTree need to call the update function separately on both trees.
   - People need to construct an additional DeferredDominance class to use functions only receiving DDT.

—After the patch—

Patch by Chijun Sima <simachijun at gmail.com>.

Reviewers: kuhar, brzycki, dmgreen, grosser, davide

Reviewed By: kuhar, brzycki

Subscribers: vsk, mgorny, llvm-commits

Author: NutshellySima

Differential Revision: https://reviews.llvm.org/D48383

Added:
    llvm/trunk/include/llvm/IR/DomTreeUpdater.h
    llvm/trunk/lib/IR/DomTreeUpdater.cpp
    llvm/trunk/unittests/IR/DomTreeUpdaterTest.cpp
Modified:
    llvm/trunk/include/llvm/module.modulemap
    llvm/trunk/lib/IR/CMakeLists.txt
    llvm/trunk/unittests/IR/CMakeLists.txt

Added: llvm/trunk/include/llvm/IR/DomTreeUpdater.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/DomTreeUpdater.h?rev=336114&view=auto
==============================================================================
--- llvm/trunk/include/llvm/IR/DomTreeUpdater.h (added)
+++ llvm/trunk/include/llvm/IR/DomTreeUpdater.h Mon Jul  2 08:37:41 2018
@@ -0,0 +1,242 @@
+//===- DomTreeUpdater.h - DomTree/Post DomTree Updater ----------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the DomTreeUpdater class, which provides a uniform way to
+// update dominator tree related data structures.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_DOMTREEUPDATER_H
+#define LLVM_DOMTREEUPDATER_H
+
+#include "llvm/Analysis/PostDominators.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/ValueHandle.h"
+#include "llvm/Support/GenericDomTree.h"
+#include <vector>
+
+namespace llvm {
+class DomTreeUpdater {
+public:
+  enum class UpdateStrategy : unsigned char { Eager = 0, Lazy = 1 };
+
+  explicit DomTreeUpdater(UpdateStrategy Strategy_) : Strategy(Strategy_) {}
+  DomTreeUpdater(DominatorTree &DT_, UpdateStrategy Strategy_)
+      : DT(&DT_), Strategy(Strategy_) {}
+  DomTreeUpdater(PostDominatorTree &PDT_, UpdateStrategy Strategy_)
+      : PDT(&PDT_), Strategy(Strategy_) {}
+  DomTreeUpdater(DominatorTree &DT_, PostDominatorTree &PDT_,
+                 UpdateStrategy Strategy_)
+      : DT(&DT_), PDT(&PDT_), Strategy(Strategy_) {}
+
+  ~DomTreeUpdater() { flush(); }
+
+  /// Returns the UpdateStrategy of the class instance.
+  UpdateStrategy getUpdateStrategy() const { return Strategy; };
+
+  /// Returns true if it holds a DominatorTree.
+  bool hasDomTree() const { return DT != nullptr; }
+
+  /// Returns true if it holds a PostDominatorTree.
+  bool hasPostDomTree() const { return PDT != nullptr; }
+
+  /// Returns true if there is BasicBlock awaiting deletion.
+  /// The deletion will only happen until a flush event and
+  /// all available trees are up-to-date.
+  /// Returns false under Eager UpdateStrategy.
+  bool hasPendingDeletedBB() const { return !DeletedBBs.empty(); }
+
+  /// Returns true if DelBB is awaiting deletion.
+  /// Returns false under Eager UpdateStrategy.
+  bool isBBPendingDeletion(BasicBlock *DelBB) const;
+
+  /// Returns true if either of DT or PDT is valid and the tree has at
+  /// least one update pending. If DT or PDT is nullptr it is treated
+  /// as having no pending updates. This function does not check
+  /// whether there is BasicBlock awaiting deletion.
+  /// Returns false under Eager UpdateStrategy.
+  bool hasPendingUpdates() const;
+
+  /// Returns true if there are DominatorTree updates queued.
+  /// Returns false under Eager UpdateStrategy.
+  bool hasPendingDomTreeUpdates() const;
+
+  /// Returns true if there are PostDominatorTree updates queued.
+  /// Returns false under Eager UpdateStrategy.
+  bool hasPendingPostDomTreeUpdates() const;
+
+  /// Apply updates on all available trees. Under Eager UpdateStrategy with
+  /// ForceRemoveDuplicates enabled or under Lazy UpdateStrategy, it will
+  /// discard duplicated updates and self-dominance updates. The Eager
+  /// Strategy applies the updates immediately while the Lazy Strategy
+  /// queues the updates. It is required for the state of
+  /// the LLVM IR to be updated *before* applying the Updates because the
+  /// internal update routine will analyze the current state of the relationship
+  /// between a pair of (From, To) BasicBlocks to determine whether a single
+  /// update needs to be discarded.
+  void applyUpdates(ArrayRef<DominatorTree::UpdateType> Updates,
+                    bool ForceRemoveDuplicates = false);
+
+  /// Notify all available trees on an edge insertion. Under either Strategy,
+  /// self-dominance update will be removed. The Eager Strategy applies
+  /// the update immediately while the Lazy Strategy queues the update.
+  /// It is recommended to only use this method when you have exactly one
+  /// insertion (and no deletions). It is recommended to use applyUpdates() in
+  /// all other cases. This function has to be called *after* making the update
+  /// on the actual CFG. An internal functions checks if the edge exists in the
+  /// CFG in DEBUG mode.
+  void insertEdge(BasicBlock *From, BasicBlock *To);
+
+  /// Notify all available trees on an edge insertion.
+  /// Under either Strategy, these updates will be discard silently in the
+  /// following sequence
+  /// 1. Invalid - Inserting an edge that does not exist in the CFG.
+  /// 2. Self-dominance update.
+  /// The Eager Strategy applies the update immediately while the Lazy Strategy
+  /// queues the update. It is recommended to only use this method when you have
+  /// exactly one insertion (and no deletions) and want to discard an invalid
+  /// update. Returns true if the update is valid.
+  bool insertEdgeRelaxed(BasicBlock *From, BasicBlock *To);
+
+  /// Notify all available trees on an edge deletion. Under either Strategy,
+  /// self-dominance update will be removed. The Eager Strategy applies
+  /// the update immediately while the Lazy Strategy queues the update.
+  /// It is recommended to only use this method when you have exactly one
+  /// deletion (and no insertions). It is recommended to use applyUpdates() in
+  /// all other cases. This function has to be called *after* making the update
+  /// on the actual CFG. An internal functions checks if the edge doesn't exist
+  /// in the CFG in DEBUG mode.
+  void deleteEdge(BasicBlock *From, BasicBlock *To);
+
+  /// Notify all available trees on an edge deletion.
+  /// Under either Strategy, these updates will be discard silently in the
+  /// following sequence:
+  /// 1. Invalid - Deleting an edge that still exists in the CFG.
+  /// 2. Self-dominance update.
+  /// The Eager Strategy applies the update immediately while the Lazy Strategy
+  /// queues the update. It is recommended to only use this method when you have
+  /// exactly one deletion (and no insertions) and want to discard an invalid
+  /// update. Returns true if the update is valid.
+  bool deleteEdgeRelaxed(BasicBlock *From, BasicBlock *To);
+
+  /// Delete DelBB. DelBB will be removed from its Parent and
+  /// erased from available trees if it exists and finally get deleted.
+  /// Under Eager UpdateStrategy, DelBB will be processed immediately.
+  /// Under Lazy UpdateStrategy, DelBB will be queued until a flush event and
+  /// all available trees are up-to-date.
+  void deleteBB(BasicBlock *DelBB);
+
+  /// Delete DelBB. DelBB will be removed from its Parent and
+  /// erased from available trees if it exists. Then the callback will
+  /// be called. Finally, DelBB will be deleted.
+  /// Under Eager UpdateStrategy, DelBB will be processed immediately.
+  /// Under Lazy UpdateStrategy, DelBB will be queued until a flush event and
+  /// all available trees are up-to-date.
+  /// Multiple callbacks can be queued for one DelBB under Lazy UpdateStrategy.
+  void callbackDeleteBB(BasicBlock *DelBB,
+                        function_ref<void(BasicBlock *)> Callback);
+
+  /// Recalculate all available trees.
+  /// Under Lazy Strategy, available trees will only be recalculated if there
+  /// are pending updates or there is BasicBlock awaiting deletion. Returns true
+  /// if at least one tree is recalculated.
+  bool recalculate(Function &F);
+
+  /// Flush DomTree updates and return DomTree.
+  /// It also flush out of date updates applied by all available trees
+  /// and flush Deleted BBs if both trees are up-to-date.
+  /// It must only be called when it has a DomTree.
+  DominatorTree &getDomTree();
+
+  /// Flush PostDomTree updates and return PostDomTree.
+  /// It also flush out of date updates applied by all available trees
+  /// and flush Deleted BBs if both trees are up-to-date.
+  /// It must only be called when it has a PostDomTree.
+  PostDominatorTree &getPostDomTree();
+
+  /// Apply all pending updates to available trees and flush all BasicBlocks
+  /// awaiting deletion.
+  /// Does nothing under Eager UpdateStrategy.
+  void flush();
+
+  /// Debug method to help view the internal state of this class.
+  LLVM_DUMP_METHOD void dump() const;
+
+private:
+  class CallBackOnDeletion final : public CallbackVH {
+  public:
+    CallBackOnDeletion(BasicBlock *V, function_ref<void(BasicBlock *)> Callback)
+        : CallbackVH(V), DelBB(V), Callback_(Callback) {}
+
+  private:
+    BasicBlock *DelBB = nullptr;
+    function_ref<void(BasicBlock *)> Callback_;
+
+    void deleted() override {
+      Callback_(DelBB);
+      CallbackVH::deleted();
+    }
+  };
+
+  SmallVector<DominatorTree::UpdateType, 16> PendUpdates;
+  size_t PendDTUpdateIndex = 0;
+  size_t PendPDTUpdateIndex = 0;
+  DominatorTree *DT = nullptr;
+  PostDominatorTree *PDT = nullptr;
+  const UpdateStrategy Strategy;
+  SmallPtrSet<BasicBlock *, 8> DeletedBBs;
+  std::vector<CallBackOnDeletion> Callbacks;
+  bool IsRecalculatingDomTree = false;
+  bool IsRecalculatingPostDomTree = false;
+
+  /// First remove all the instructions of DelBB and then make sure DelBB has a
+  /// valid terminator instruction which is necessary to have when DelBB still
+  /// has to be inside of its parent Function while awaiting deletion under Lazy
+  /// UpdateStrategy to prevent other routines from asserting the state of the
+  /// IR is inconsistent. Assert if DelBB is nullptr or has predecessors.
+  void validateDeleteBB(BasicBlock *DelBB);
+
+  /// Returns true if at least one BasicBlock is deleted.
+  bool forceFlushDeletedBB();
+
+  /// Deduplicate and remove unnecessary updates (no-ops) when using Lazy
+  /// UpdateStrategy. Returns true if the update is queued for update.
+  bool applyLazyUpdate(DominatorTree::UpdateKind Kind, BasicBlock *From,
+                       BasicBlock *To);
+
+  /// Helper function to apply all pending DomTree updates.
+  void applyDomTreeUpdates();
+
+  /// Helper function to apply all pending PostDomTree updates.
+  void applyPostDomTreeUpdates();
+
+  /// Helper function to flush deleted BasicBlocks if all available
+  /// trees are up-to-date.
+  void tryFlushDeletedBB();
+
+  /// Drop all updates applied by all available trees and delete BasicBlocks if
+  /// all available trees are up-to-date.
+  void dropOutOfDateUpdates();
+
+  /// Erase Basic Block node that has been unlinked from Function
+  /// in the DomTree and PostDomTree.
+  void eraseDelBBNode(BasicBlock *DelBB);
+
+  /// Returns true if the update appears in the LLVM IR.
+  /// It is used to check whether an update is valid in
+  /// insertEdge/deleteEdge or is unnecessary in the batch update.
+  bool isUpdateValid(DominatorTree::UpdateType Update) const;
+
+  /// Returns true if the update is self dominance.
+  bool isSelfDominance(DominatorTree::UpdateType Update) const;
+};
+} // namespace llvm
+
+#endif // LLVM_DOMTREEUPDATER_H

Modified: llvm/trunk/include/llvm/module.modulemap
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/module.modulemap?rev=336114&r1=336113&r2=336114&view=diff
==============================================================================
--- llvm/trunk/include/llvm/module.modulemap (original)
+++ llvm/trunk/include/llvm/module.modulemap Mon Jul  2 08:37:41 2018
@@ -196,6 +196,8 @@ module LLVM_intrinsic_gen {
   module IR_CFG { header "IR/CFG.h" export * }
   module IR_ConstantRange { header "IR/ConstantRange.h" export * }
   module IR_Dominators { header "IR/Dominators.h" export * }
+  module Analysis_PostDominators { header "Analysis/PostDominators.h" export * }
+  module IR_DomTreeUpdater { header "IR/DomTreeUpdater.h" export * }
   module IR_IRBuilder { header "IR/IRBuilder.h" export * }
   module IR_PassManager { header "IR/PassManager.h" export * }
   module IR_PredIteratorCache { header "IR/PredIteratorCache.h" export * }

Modified: llvm/trunk/lib/IR/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/CMakeLists.txt?rev=336114&r1=336113&r2=336114&view=diff
==============================================================================
--- llvm/trunk/lib/IR/CMakeLists.txt (original)
+++ llvm/trunk/lib/IR/CMakeLists.txt Mon Jul  2 08:37:41 2018
@@ -21,6 +21,7 @@ add_llvm_library(LLVMCore
   DiagnosticInfo.cpp
   DiagnosticPrinter.cpp
   Dominators.cpp
+  DomTreeUpdater.cpp
   Function.cpp
   GVMaterializer.cpp
   Globals.cpp

Added: llvm/trunk/lib/IR/DomTreeUpdater.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/DomTreeUpdater.cpp?rev=336114&view=auto
==============================================================================
--- llvm/trunk/lib/IR/DomTreeUpdater.cpp (added)
+++ llvm/trunk/lib/IR/DomTreeUpdater.cpp Mon Jul  2 08:37:41 2018
@@ -0,0 +1,511 @@
+//===- DomTreeUpdater.cpp - DomTree/Post DomTree Updater --------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the DomTreeUpdater class, which provides a uniform way
+// to update dominator tree related data structures.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/DomTreeUpdater.h"
+#include "llvm/Analysis/PostDominators.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/Support/GenericDomTree.h"
+#include <algorithm>
+
+namespace llvm {
+
+bool DomTreeUpdater::isUpdateValid(
+    const DominatorTree::UpdateType Update) const {
+  const auto *From = Update.getFrom();
+  const auto *To = Update.getTo();
+  const auto Kind = Update.getKind();
+
+  // Discard updates by inspecting the current state of successors of From.
+  // Since isUpdateValid() must be called *after* the Terminator of From is
+  // altered we can determine if the update is unnecessary for batch updates
+  // or invalid for a single update.
+  const bool HasEdge = llvm::any_of(
+      successors(From), [To](const BasicBlock *B) { return B == To; });
+
+  // If the IR does not match the update,
+  // 1. In batch updates, this update is unnecessary.
+  // 2. When called by insertEdge*()/deleteEdge*(), this update is invalid.
+  // Edge does not exist in IR.
+  if (Kind == DominatorTree::Insert && !HasEdge)
+    return false;
+
+  // Edge exists in IR.
+  if (Kind == DominatorTree::Delete && HasEdge)
+    return false;
+
+  return true;
+}
+
+bool DomTreeUpdater::isSelfDominance(
+    const DominatorTree::UpdateType Update) const {
+  // Won't affect DomTree and PostDomTree.
+  return Update.getFrom() == Update.getTo();
+}
+
+bool DomTreeUpdater::applyLazyUpdate(DominatorTree::UpdateKind Kind,
+                                     BasicBlock *From, BasicBlock *To) {
+  assert(Strategy == DomTreeUpdater::UpdateStrategy::Lazy &&
+         "Call applyLazyUpdate() with Eager strategy error");
+  // Analyze pending updates to determine if the update is unnecessary.
+  const DominatorTree::UpdateType Update = {Kind, From, To};
+  const DominatorTree::UpdateType Invert = {Kind != DominatorTree::Insert
+                                                ? DominatorTree::Insert
+                                                : DominatorTree::Delete,
+                                            From, To};
+  // Only check duplicates in updates that are not applied by both trees.
+  auto I =
+      PendUpdates.begin() + std::max(PendDTUpdateIndex, PendPDTUpdateIndex);
+  const auto E = PendUpdates.end();
+
+  assert(I <= E && "Iterator out of range.");
+
+  for (; I != E; ++I) {
+    if (Update == *I)
+      return false; // Discard duplicate updates.
+
+    if (Invert == *I) {
+      // Update and Invert are both valid (equivalent to a no-op). Remove
+      // Invert from PendUpdates and discard the Update.
+      PendUpdates.erase(I);
+      return false;
+    }
+  }
+
+  PendUpdates.push_back(Update); // Save the valid update.
+  return true;
+}
+
+void DomTreeUpdater::applyDomTreeUpdates() {
+  // No pending DomTreeUpdates.
+  if (Strategy != UpdateStrategy::Lazy || !DT)
+    return;
+
+  // Only apply updates not are applied by DomTree.
+  if (hasPendingDomTreeUpdates()) {
+    const auto I = PendUpdates.begin() + PendDTUpdateIndex;
+    const auto E = PendUpdates.end();
+    assert(I < E && "Iterator range invalid; there should be DomTree updates.");
+    DT->applyUpdates(ArrayRef<DominatorTree::UpdateType>(I, E));
+    PendDTUpdateIndex = PendUpdates.size();
+  }
+}
+
+void DomTreeUpdater::flush() {
+  applyDomTreeUpdates();
+  applyPostDomTreeUpdates();
+  dropOutOfDateUpdates();
+}
+
+void DomTreeUpdater::applyPostDomTreeUpdates() {
+  // No pending PostDomTreeUpdates.
+  if (Strategy != UpdateStrategy::Lazy || !PDT)
+    return;
+
+  // Only apply updates not are applied by PostDomTree.
+  if (hasPendingPostDomTreeUpdates()) {
+    const auto I = PendUpdates.begin() + PendPDTUpdateIndex;
+    const auto E = PendUpdates.end();
+    assert(I < E &&
+           "Iterator range invalid; there should be PostDomTree updates.");
+    PDT->applyUpdates(ArrayRef<DominatorTree::UpdateType>(I, E));
+    PendPDTUpdateIndex = PendUpdates.size();
+  }
+}
+
+void DomTreeUpdater::tryFlushDeletedBB() {
+  if (!hasPendingUpdates())
+    forceFlushDeletedBB();
+}
+
+bool DomTreeUpdater::forceFlushDeletedBB() {
+  if (DeletedBBs.empty())
+    return false;
+
+  for (auto *BB : DeletedBBs) {
+    BB->removeFromParent();
+    eraseDelBBNode(BB);
+    delete BB;
+  }
+  DeletedBBs.clear();
+  Callbacks.clear();
+  return true;
+}
+
+bool DomTreeUpdater::recalculate(Function &F) {
+  if (!DT && !PDT)
+    return false;
+
+  if (Strategy == UpdateStrategy::Eager) {
+    if (DT)
+      DT->recalculate(F);
+    if (PDT)
+      PDT->recalculate(F);
+    return true;
+  }
+
+  // Prevent forceFlushDeletedBB() from erasing DomTree or PostDomTree nodes.
+  IsRecalculatingDomTree = IsRecalculatingPostDomTree = true;
+
+  // Because all trees are going to be up-to-date after recalculation,
+  // flush awaiting deleted BasicBlocks.
+  if (forceFlushDeletedBB() || hasPendingUpdates()) {
+    if (DT)
+      DT->recalculate(F);
+    if (PDT)
+      PDT->recalculate(F);
+
+    // Resume forceFlushDeletedBB() to erase DomTree or PostDomTree nodes.
+    IsRecalculatingDomTree = IsRecalculatingPostDomTree = false;
+    PendDTUpdateIndex = PendPDTUpdateIndex = PendUpdates.size();
+    dropOutOfDateUpdates();
+    return true;
+  }
+
+  // Resume forceFlushDeletedBB() to erase DomTree or PostDomTree nodes.
+  IsRecalculatingDomTree = IsRecalculatingPostDomTree = false;
+  return false;
+}
+
+bool DomTreeUpdater::hasPendingUpdates() const {
+  return hasPendingDomTreeUpdates() || hasPendingPostDomTreeUpdates();
+}
+
+bool DomTreeUpdater::hasPendingDomTreeUpdates() const {
+  if (!DT)
+    return false;
+  return PendUpdates.size() != PendDTUpdateIndex;
+}
+
+bool DomTreeUpdater::hasPendingPostDomTreeUpdates() const {
+  if (!PDT)
+    return false;
+  return PendUpdates.size() != PendPDTUpdateIndex;
+}
+
+bool DomTreeUpdater::isBBPendingDeletion(llvm::BasicBlock *DelBB) const {
+  if (Strategy == UpdateStrategy::Eager || DeletedBBs.empty())
+    return false;
+  return DeletedBBs.count(DelBB) != 0;
+}
+
+// The DT and PDT require the nodes related to updates
+// are not deleted when update functions are called.
+// So BasicBlock deletions must be pended when the
+// UpdateStrategy is Lazy. When the UpdateStrategy is
+// Eager, the BasicBlock will be deleted immediately.
+void DomTreeUpdater::deleteBB(BasicBlock *DelBB) {
+  validateDeleteBB(DelBB);
+  if (Strategy == UpdateStrategy::Lazy) {
+    DeletedBBs.insert(DelBB);
+    return;
+  }
+
+  DelBB->removeFromParent();
+  eraseDelBBNode(DelBB);
+  delete DelBB;
+}
+
+void DomTreeUpdater::callbackDeleteBB(
+    BasicBlock *DelBB, function_ref<void(BasicBlock *)> Callback) {
+  validateDeleteBB(DelBB);
+  if (Strategy == UpdateStrategy::Lazy) {
+    Callbacks.push_back(CallBackOnDeletion(DelBB, Callback));
+    DeletedBBs.insert(DelBB);
+    return;
+  }
+
+  DelBB->removeFromParent();
+  eraseDelBBNode(DelBB);
+  Callback(DelBB);
+  delete DelBB;
+}
+
+void DomTreeUpdater::eraseDelBBNode(BasicBlock *DelBB) {
+  if (DT && !IsRecalculatingDomTree)
+    if (DT->getNode(DelBB))
+      DT->eraseNode(DelBB);
+
+  if (PDT && !IsRecalculatingPostDomTree)
+    if (PDT->getNode(DelBB))
+      PDT->eraseNode(DelBB);
+}
+
+void DomTreeUpdater::validateDeleteBB(BasicBlock *DelBB) {
+  assert(DelBB && "Invalid push_back of nullptr DelBB.");
+  assert(pred_empty(DelBB) && "DelBB has one or more predecessors.");
+  // DelBB is unreachable and all its instructions are dead.
+  while (!DelBB->empty()) {
+    Instruction &I = DelBB->back();
+    // Replace used instructions with an arbitrary value (undef).
+    if (!I.use_empty())
+      I.replaceAllUsesWith(llvm::UndefValue::get(I.getType()));
+    DelBB->getInstList().pop_back();
+  }
+  // Make sure DelBB has a valid terminator instruction. As long as DelBB is a
+  // Child of Function F it must contain valid IR.
+  new UnreachableInst(DelBB->getContext(), DelBB);
+}
+
+void DomTreeUpdater::applyUpdates(ArrayRef<DominatorTree::UpdateType> Updates,
+                                  bool ForceRemoveDuplicates) {
+  if (Strategy == UpdateStrategy::Lazy || ForceRemoveDuplicates) {
+    SmallVector<DominatorTree::UpdateType, 8> Seen;
+    for (const auto U : Updates)
+      // For Lazy UpdateStrategy, avoid duplicates to applyLazyUpdate() to save
+      // on analysis.
+      if (llvm::none_of(
+              Seen,
+              [U](const DominatorTree::UpdateType S) { return S == U; }) &&
+          isUpdateValid(U) && !isSelfDominance(U)) {
+        Seen.push_back(U);
+        if (Strategy == UpdateStrategy::Lazy)
+          applyLazyUpdate(U.getKind(), U.getFrom(), U.getTo());
+      }
+    if (Strategy == UpdateStrategy::Lazy)
+      return;
+
+    if (DT)
+      DT->applyUpdates(Seen);
+    if (PDT)
+      PDT->applyUpdates(Seen);
+    return;
+  }
+
+  if (DT)
+    DT->applyUpdates(Updates);
+  if (PDT)
+    PDT->applyUpdates(Updates);
+}
+
+DominatorTree &DomTreeUpdater::getDomTree() {
+  assert(DT && "Invalid acquisition of a null DomTree");
+  applyDomTreeUpdates();
+  dropOutOfDateUpdates();
+  return *DT;
+}
+
+PostDominatorTree &DomTreeUpdater::getPostDomTree() {
+  assert(PDT && "Invalid acquisition of a null PostDomTree");
+  applyPostDomTreeUpdates();
+  dropOutOfDateUpdates();
+  return *PDT;
+}
+
+void DomTreeUpdater::insertEdge(BasicBlock *From, BasicBlock *To) {
+
+#ifndef NDEBUG
+  assert(isUpdateValid({DominatorTree::Insert, From, To}) &&
+         "Inserted edge does not appear in the CFG");
+#endif
+
+  // Won't affect DomTree and PostDomTree; discard update.
+  if (From == To)
+    return;
+
+  if (Strategy == UpdateStrategy::Eager) {
+    if (DT)
+      DT->insertEdge(From, To);
+    if (PDT)
+      PDT->insertEdge(From, To);
+    return;
+  }
+
+  applyLazyUpdate(DominatorTree::Insert, From, To);
+}
+
+bool DomTreeUpdater::insertEdgeRelaxed(BasicBlock *From, BasicBlock *To) {
+  if (!isUpdateValid({DominatorTree::Insert, From, To}))
+    return false;
+
+  if (From == To)
+    return true;
+
+  if (Strategy == UpdateStrategy::Eager) {
+    if (DT)
+      DT->insertEdge(From, To);
+    if (PDT)
+      PDT->insertEdge(From, To);
+    return true;
+  }
+
+  applyLazyUpdate(DominatorTree::Insert, From, To);
+  return true;
+}
+
+void DomTreeUpdater::deleteEdge(BasicBlock *From, BasicBlock *To) {
+
+#ifndef NDEBUG
+  assert(isUpdateValid({DominatorTree::Delete, From, To}) &&
+         "Deleted edge still exists in the CFG!");
+#endif
+
+  // Won't affect DomTree and PostDomTree; discard update.
+  if (From == To)
+    return;
+
+  if (Strategy == UpdateStrategy::Eager) {
+    if (DT)
+      DT->deleteEdge(From, To);
+    if (PDT)
+      PDT->deleteEdge(From, To);
+    return;
+  }
+
+  applyLazyUpdate(DominatorTree::Delete, From, To);
+}
+
+bool DomTreeUpdater::deleteEdgeRelaxed(BasicBlock *From, BasicBlock *To) {
+  if (!isUpdateValid({DominatorTree::Delete, From, To}))
+    return false;
+
+  if (From == To)
+    return true;
+
+  if (Strategy == UpdateStrategy::Eager) {
+    if (DT)
+      DT->deleteEdge(From, To);
+    if (PDT)
+      PDT->deleteEdge(From, To);
+    return true;
+  }
+
+  applyLazyUpdate(DominatorTree::Delete, From, To);
+  return true;
+}
+
+void DomTreeUpdater::dropOutOfDateUpdates() {
+  if (Strategy == DomTreeUpdater::UpdateStrategy::Eager)
+    return;
+
+  tryFlushDeletedBB();
+
+  // Drop all updates applied by both trees.
+  if (!DT)
+    PendDTUpdateIndex = PendUpdates.size();
+  if (!PDT)
+    PendPDTUpdateIndex = PendUpdates.size();
+
+  const size_t dropIndex = std::min(PendDTUpdateIndex, PendPDTUpdateIndex);
+  const auto B = PendUpdates.begin();
+  const auto E = PendUpdates.begin() + dropIndex;
+  assert(B <= E && "Iterator out of range.");
+  PendUpdates.erase(B, E);
+  // Calculate current index.
+  PendDTUpdateIndex -= dropIndex;
+  PendPDTUpdateIndex -= dropIndex;
+}
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+LLVM_DUMP_METHOD void DomTreeUpdater::dump() const {
+  raw_ostream &OS = llvm::dbgs();
+
+  OS << "Available Trees: ";
+  if (DT || PDT) {
+    if (DT)
+      OS << "DomTree ";
+    if (PDT)
+      OS << "PostDomTree ";
+    OS << "\n";
+  } else
+    OS << "None\n";
+
+  OS << "UpdateStrategy: ";
+  if (Strategy == UpdateStrategy::Eager) {
+    OS << "Eager\n";
+    return;
+  } else
+    OS << "Lazy\n";
+  int Index = 0;
+
+  auto printUpdates =
+      [&](ArrayRef<DominatorTree::UpdateType>::const_iterator begin,
+          ArrayRef<DominatorTree::UpdateType>::const_iterator end) {
+        if (begin == end)
+          OS << "  None\n";
+        Index = 0;
+        for (auto It = begin, ItEnd = end; It != ItEnd; ++It) {
+          auto U = *It;
+          OS << "  " << Index << " : ";
+          ++Index;
+          if (U.getKind() == DominatorTree::Insert)
+            OS << "Insert, ";
+          else
+            OS << "Delete, ";
+          BasicBlock *From = U.getFrom();
+          if (From) {
+            auto S = From->getName();
+            if (!From->hasName())
+              S = "(no name)";
+            OS << S << "(" << From << "), ";
+          } else {
+            OS << "(badref), ";
+          }
+          BasicBlock *To = U.getTo();
+          if (To) {
+            auto S = To->getName();
+            if (!To->hasName())
+              S = "(no_name)";
+            OS << S << "(" << To << ")\n";
+          } else {
+            OS << "(badref)\n";
+          }
+        }
+      };
+
+  if (DT) {
+    const auto I = PendUpdates.begin() + PendDTUpdateIndex;
+    assert(PendUpdates.begin() <= I && I <= PendUpdates.end() &&
+           "Iterator out of range.");
+    OS << "Applied but not cleared DomTreeUpdates:\n";
+    printUpdates(PendUpdates.begin(), I);
+    OS << "Pending DomTreeUpdates:\n";
+    printUpdates(I, PendUpdates.end());
+  }
+
+  if (PDT) {
+    const auto I = PendUpdates.begin() + PendPDTUpdateIndex;
+    assert(PendUpdates.begin() <= I && I <= PendUpdates.end() &&
+           "Iterator out of range.");
+    OS << "Applied but not cleared PostDomTreeUpdates:\n";
+    printUpdates(PendUpdates.begin(), I);
+    OS << "Pending PostDomTreeUpdates:\n";
+    printUpdates(I, PendUpdates.end());
+  }
+
+  OS << "Pending DeletedBBs:\n";
+  Index = 0;
+  for (auto BB : DeletedBBs) {
+    OS << "  " << Index << " : ";
+    ++Index;
+    if (BB->hasName())
+      OS << BB->getName() << "(";
+    else
+      OS << "(no_name)(";
+    OS << BB << ")\n";
+  }
+
+  OS << "Pending Callbacks:\n";
+  Index = 0;
+  for (auto BB : Callbacks) {
+    OS << "  " << Index << " : ";
+    ++Index;
+    if (BB->hasName())
+      OS << BB->getName() << "(";
+    else
+      OS << "(no_name)(";
+    OS << BB << ")\n";
+  }
+}
+#endif
+} // namespace llvm

Modified: llvm/trunk/unittests/IR/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/IR/CMakeLists.txt?rev=336114&r1=336113&r2=336114&view=diff
==============================================================================
--- llvm/trunk/unittests/IR/CMakeLists.txt (original)
+++ llvm/trunk/unittests/IR/CMakeLists.txt Mon Jul  2 08:37:41 2018
@@ -18,6 +18,7 @@ add_llvm_unittest(IRTests
   DeferredDominanceTest.cpp
   DominatorTreeTest.cpp
   DominatorTreeBatchUpdatesTest.cpp
+  DomTreeUpdaterTest.cpp
   FunctionTest.cpp
   PassBuilderCallbacksTest.cpp
   IRBuilderTest.cpp

Added: llvm/trunk/unittests/IR/DomTreeUpdaterTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/IR/DomTreeUpdaterTest.cpp?rev=336114&view=auto
==============================================================================
--- llvm/trunk/unittests/IR/DomTreeUpdaterTest.cpp (added)
+++ llvm/trunk/unittests/IR/DomTreeUpdaterTest.cpp Mon Jul  2 08:37:41 2018
@@ -0,0 +1,693 @@
+//==- llvm/unittests/IR/DomTreeUpdaterTest.cpp - DomTreeUpdater unit tests ===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/IR/DomTreeUpdater.h"
+#include "llvm/Analysis/PostDominators.h"
+#include "llvm/AsmParser/Parser.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Support/SourceMgr.h"
+#include "gtest/gtest.h"
+#include <algorithm>
+
+using namespace llvm;
+
+static std::unique_ptr<Module> makeLLVMModule(LLVMContext &Context,
+                                              StringRef ModuleStr) {
+  SMDiagnostic Err;
+  std::unique_ptr<Module> M = parseAssemblyString(ModuleStr, Err, Context);
+  assert(M && "Bad LLVM IR?");
+  return M;
+}
+
+TEST(DomTreeUpdater, EagerUpdateBasicOperations) {
+  StringRef FuncName = "f";
+  StringRef ModuleString = R"(
+                          define i32 @f(i32 %i, i32 *%p) {
+                          bb0:
+                             store i32 %i, i32 *%p
+                             switch i32 %i, label %bb1 [
+                               i32 1, label %bb2
+                               i32 2, label %bb3
+                             ]
+                          bb1:
+                             ret i32 1
+                          bb2:
+                             ret i32 2
+                          bb3:
+                             ret i32 3
+                          })";
+  // Make the module.
+  LLVMContext Context;
+  std::unique_ptr<Module> M = makeLLVMModule(Context, ModuleString);
+  Function *F = M->getFunction(FuncName);
+
+  // Make the DomTreeUpdater.
+  DominatorTree DT(*F);
+  PostDominatorTree PDT(*F);
+  DomTreeUpdater DTU(DT, PDT, DomTreeUpdater::UpdateStrategy::Eager);
+
+  ASSERT_TRUE(DTU.hasDomTree());
+  ASSERT_TRUE(DTU.hasPostDomTree());
+  ASSERT_EQ(DTU.getUpdateStrategy(), DomTreeUpdater::UpdateStrategy::Eager);
+  ASSERT_TRUE(DTU.getDomTree().verify());
+  ASSERT_TRUE(DTU.getPostDomTree().verify());
+  ASSERT_FALSE(DTU.hasPendingUpdates());
+
+  Function::iterator FI = F->begin();
+  BasicBlock *BB0 = &*FI++;
+  BasicBlock *BB1 = &*FI++;
+  BasicBlock *BB2 = &*FI++;
+  BasicBlock *BB3 = &*FI++;
+  SwitchInst *SI = dyn_cast<SwitchInst>(BB0->getTerminator());
+  ASSERT_NE(SI, nullptr) << "Couldn't get SwitchInst.";
+
+  ASSERT_FALSE(DTU.insertEdgeRelaxed(BB0, BB0));
+  ASSERT_TRUE(DTU.deleteEdgeRelaxed(BB0, BB0));
+
+  // Delete edge bb0 -> bb3 and push the update twice to verify duplicate
+  // entries are discarded.
+  std::vector<DominatorTree::UpdateType> Updates;
+  Updates.reserve(4);
+  Updates.push_back({DominatorTree::Delete, BB0, BB3});
+  Updates.push_back({DominatorTree::Delete, BB0, BB3});
+
+  // Invalid Insert: no edge bb1 -> bb2 after change to bb0.
+  Updates.push_back({DominatorTree::Insert, BB1, BB2});
+  // Invalid Delete: edge exists bb0 -> bb1 after change to bb0.
+  Updates.push_back({DominatorTree::Delete, BB0, BB1});
+
+  // CFG Change: remove edge bb0 -> bb3.
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 3u);
+  BB3->removePredecessor(BB0);
+  for (auto i = SI->case_begin(), e = SI->case_end(); i != e; ++i) {
+    if (i->getCaseSuccessor() == BB3) {
+      SI->removeCase(i);
+      break;
+    }
+  }
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 2u);
+  // Deletion of a BasicBlock is an immediate event. We remove all uses to the
+  // contained Instructions and change the Terminator to "unreachable" when
+  // queued for deletion.
+  ASSERT_FALSE(isa<UnreachableInst>(BB3->getTerminator()));
+  EXPECT_FALSE(DTU.isBBPendingDeletion(BB3));
+  DTU.applyUpdates(Updates, /*ForceRemoveDuplicates*/ true);
+  ASSERT_FALSE(DTU.hasPendingUpdates());
+
+  // Invalid Insert: no edge bb1 -> bb2 after change to bb0.
+  ASSERT_FALSE(DTU.insertEdgeRelaxed(BB1, BB2));
+  // Invalid Delete: edge exists bb0 -> bb1 after change to bb0.
+  ASSERT_FALSE(DTU.deleteEdgeRelaxed(BB0, BB1));
+
+  // DTU working with Eager UpdateStrategy does not need to flush.
+  ASSERT_TRUE(DT.verify());
+  ASSERT_TRUE(PDT.verify());
+
+  // Test callback utils.
+  ASSERT_EQ(BB3->getParent(), F);
+  DTU.callbackDeleteBB(BB3,
+                       [&F](BasicBlock *BB) { ASSERT_NE(BB->getParent(), F); });
+
+  ASSERT_TRUE(DT.verify());
+  ASSERT_TRUE(PDT.verify());
+  ASSERT_FALSE(DTU.hasPendingUpdates());
+
+  // Unnecessary flush() test
+  DTU.flush();
+  EXPECT_TRUE(DT.verify());
+  EXPECT_TRUE(PDT.verify());
+
+  // Remove all case branch to BB2 to test Eager recalculation.
+  // Code section from llvm::ConstantFoldTerminator
+  for (auto i = SI->case_begin(), e = SI->case_end(); i != e;) {
+    if (i->getCaseSuccessor() == BB2) {
+      // Remove this entry.
+      BB2->removePredecessor(BB0);
+      i = SI->removeCase(i);
+      e = SI->case_end();
+    } else
+      ++i;
+  }
+  ASSERT_FALSE(DT.verify());
+  ASSERT_FALSE(PDT.verify());
+  DTU.recalculate(*F);
+  ASSERT_TRUE(DT.verify());
+  ASSERT_TRUE(PDT.verify());
+}
+
+TEST(DomTreeUpdater, EagerUpdateReplaceEntryBB) {
+  StringRef FuncName = "f";
+  StringRef ModuleString = R"(
+                           define i32 @f() {
+                           bb0:
+                              br label %bb1
+                            bb1:
+                              ret i32 1
+                           }
+                           )";
+  // Make the module.
+  LLVMContext Context;
+  std::unique_ptr<Module> M = makeLLVMModule(Context, ModuleString);
+  Function *F = M->getFunction(FuncName);
+
+  // Make the DTU.
+  DominatorTree DT(*F);
+  PostDominatorTree PDT(*F);
+  DomTreeUpdater DTU(DT, PDT, DomTreeUpdater::UpdateStrategy::Eager);
+  ASSERT_TRUE(DTU.hasDomTree());
+  ASSERT_TRUE(DTU.hasPostDomTree());
+  ASSERT_EQ(DTU.getUpdateStrategy(), DomTreeUpdater::UpdateStrategy::Eager);
+  ASSERT_TRUE(DT.verify());
+  ASSERT_TRUE(PDT.verify());
+
+  Function::iterator FI = F->begin();
+  BasicBlock *BB0 = &*FI++;
+  BasicBlock *BB1 = &*FI++;
+
+  // Add a block as the new function entry BB. We also link it to BB0.
+  BasicBlock *NewEntry =
+      BasicBlock::Create(F->getContext(), "new_entry", F, BB0);
+  BranchInst::Create(BB0, NewEntry);
+  EXPECT_EQ(F->begin()->getName(), NewEntry->getName());
+  EXPECT_TRUE(&F->getEntryBlock() == NewEntry);
+
+  ASSERT_TRUE(DTU.insertEdgeRelaxed(NewEntry, BB0));
+
+  // Changing the Entry BB requires a full recalculation of DomTree.
+  DTU.recalculate(*F);
+  ASSERT_TRUE(DT.verify());
+  ASSERT_TRUE(PDT.verify());
+
+  // CFG Change: remove new_edge -> bb0 and redirect to new_edge -> bb1.
+  EXPECT_EQ(NewEntry->getTerminator()->getNumSuccessors(), 1u);
+  NewEntry->getTerminator()->eraseFromParent();
+  BranchInst::Create(BB1, NewEntry);
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 1u);
+
+  // Update the DTU. At this point bb0 now has no predecessors but is still a
+  // Child of F.
+  DTU.applyUpdates({{DominatorTree::Delete, NewEntry, BB0},
+                    {DominatorTree::Insert, NewEntry, BB1}});
+  ASSERT_TRUE(DT.verify());
+  ASSERT_TRUE(PDT.verify());
+
+  // Now remove bb0 from F.
+  ASSERT_FALSE(isa<UnreachableInst>(BB0->getTerminator()));
+  EXPECT_FALSE(DTU.isBBPendingDeletion(BB0));
+  DTU.deleteBB(BB0);
+  ASSERT_TRUE(DT.verify());
+  ASSERT_TRUE(PDT.verify());
+}
+
+TEST(DomTreeUpdater, LazyUpdateDTBasicOperations) {
+  StringRef FuncName = "f";
+  StringRef ModuleString = R"(
+                           define i32 @f(i32 %i, i32 *%p) {
+                            bb0:
+                              store i32 %i, i32 *%p
+                              switch i32 %i, label %bb1 [
+                                i32 0, label %bb2
+                                i32 1, label %bb2
+                                i32 2, label %bb3
+                              ]
+                            bb1:
+                              ret i32 1
+                            bb2:
+                              ret i32 2
+                            bb3:
+                              ret i32 3
+                           }
+                           )";
+  // Make the module.
+  LLVMContext Context;
+  std::unique_ptr<Module> M = makeLLVMModule(Context, ModuleString);
+  Function *F = M->getFunction(FuncName);
+
+  // Make the DTU.
+  DominatorTree DT(*F);
+  DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
+  ASSERT_TRUE(DTU.hasDomTree());
+  ASSERT_FALSE(DTU.hasPostDomTree());
+  ASSERT_EQ(DTU.getUpdateStrategy(), DomTreeUpdater::UpdateStrategy::Lazy);
+  ASSERT_TRUE(DTU.getDomTree().verify());
+
+  Function::iterator FI = F->begin();
+  BasicBlock *BB0 = &*FI++;
+  BasicBlock *BB1 = &*FI++;
+  BasicBlock *BB2 = &*FI++;
+  BasicBlock *BB3 = &*FI++;
+
+  // Test discards of self-domination update.
+  DTU.deleteEdge(BB0, BB0);
+  ASSERT_FALSE(DTU.hasPendingDomTreeUpdates());
+
+  // Delete edge bb0 -> bb3 and push the update twice to verify duplicate
+  // entries are discarded.
+  std::vector<DominatorTree::UpdateType> Updates;
+  Updates.reserve(4);
+  Updates.push_back({DominatorTree::Delete, BB0, BB3});
+  Updates.push_back({DominatorTree::Delete, BB0, BB3});
+
+  // Invalid Insert: no edge bb1 -> bb2 after change to bb0.
+  Updates.push_back({DominatorTree::Insert, BB1, BB2});
+  // Invalid Delete: edge exists bb0 -> bb1 after change to bb0.
+  Updates.push_back({DominatorTree::Delete, BB0, BB1});
+
+  // CFG Change: remove edge bb0 -> bb3 and one duplicate edge bb0 -> bb2.
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 4u);
+  BB0->getTerminator()->eraseFromParent();
+  BranchInst::Create(BB1, BB2, ConstantInt::getTrue(F->getContext()), BB0);
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 2u);
+
+  // Verify. Updates to DTU must be applied *after* all changes to the CFG
+  // (including block deletion).
+  DTU.applyUpdates(Updates);
+  ASSERT_TRUE(DTU.getDomTree().verify());
+
+  // Deletion of a BasicBlock is an immediate event. We remove all uses to the
+  // contained Instructions and change the Terminator to "unreachable" when
+  // queued for deletion. Its parent is still F until all the pending updates
+  // are applied to all trees held by the DomTreeUpdater (DomTree/PostDomTree).
+  // We don't defer this action because it can cause problems for other
+  // transforms or analysis as it's part of the actual CFG. We only defer
+  // updates to the DominatorTrees. This code will crash if it is placed before
+  // the BranchInst::Create() call above. After a deletion of a BasicBlock. Only
+  // an explicit flush event can trigger the flushing of deleteBBs. Because some
+  // passes using Lazy UpdateStrategy rely on this behavior.
+
+  ASSERT_FALSE(isa<UnreachableInst>(BB3->getTerminator()));
+  EXPECT_FALSE(DTU.isBBPendingDeletion(BB3));
+  EXPECT_FALSE(DTU.hasPendingDeletedBB());
+  DTU.deleteBB(BB3);
+  EXPECT_TRUE(DTU.isBBPendingDeletion(BB3));
+  EXPECT_TRUE(DTU.hasPendingDeletedBB());
+  ASSERT_TRUE(isa<UnreachableInst>(BB3->getTerminator()));
+  EXPECT_EQ(BB3->getParent(), F);
+  DTU.recalculate(*F);
+
+  EXPECT_FALSE(DTU.hasPendingDeletedBB());
+}
+
+TEST(DomTreeUpdater, LazyUpdateDTInheritedPreds) {
+  StringRef FuncName = "f";
+  StringRef ModuleString = R"(
+                           define i32 @f(i32 %i, i32 *%p) {
+                            bb0:
+                              store i32 %i, i32 *%p
+                              switch i32 %i, label %bb1 [
+                                i32 2, label %bb2
+                                i32 3, label %bb3
+                              ]
+                            bb1:
+                              br label %bb3
+                            bb2:
+                              br label %bb3
+                            bb3:
+                              ret i32 3
+                           }
+                           )";
+  // Make the module.
+  LLVMContext Context;
+  std::unique_ptr<Module> M = makeLLVMModule(Context, ModuleString);
+  Function *F = M->getFunction(FuncName);
+
+  // Make the DTU.
+  DominatorTree DT(*F);
+  DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Lazy);
+  ASSERT_TRUE(DTU.hasDomTree());
+  ASSERT_FALSE(DTU.hasPostDomTree());
+  ASSERT_EQ(DTU.getUpdateStrategy(), DomTreeUpdater::UpdateStrategy::Lazy);
+  ASSERT_TRUE(DTU.getDomTree().verify());
+
+  Function::iterator FI = F->begin();
+  BasicBlock *BB0 = &*FI++;
+  BasicBlock *BB1 = &*FI++;
+  BasicBlock *BB2 = &*FI++;
+  BasicBlock *BB3 = &*FI++;
+
+  // There are several CFG locations where we have:
+  //
+  //   pred1..predN
+  //    |        |
+  //    +> curr <+    converted into:   pred1..predN curr
+  //        |                            |        |
+  //        v                            +> succ <+
+  //       succ
+  //
+  // There is a specific shape of this we have to be careful of:
+  //
+  //   pred1..predN
+  //   ||        |
+  //   |+> curr <+    converted into:   pred1..predN curr
+  //   |    |                            |        |
+  //   |    v                            +> succ <+
+  //   +-> succ
+  //
+  // While the final CFG form is functionally identical the updates to
+  // DTU are not. In the first case we must have DTU.insertEdge(Pred1, Succ)
+  // while in the latter case we must *NOT* have DTU.insertEdge(Pred1, Succ).
+
+  // CFG Change: bb0 now only has bb0 -> bb1 and bb0 -> bb3. We are preparing to
+  // remove bb2.
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 3u);
+  BB0->getTerminator()->eraseFromParent();
+  BranchInst::Create(BB1, BB3, ConstantInt::getTrue(F->getContext()), BB0);
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 2u);
+
+  // Test callback utils.
+  std::vector<BasicBlock *> BasicBlocks;
+  BasicBlocks.push_back(BB1);
+  BasicBlocks.push_back(BB2);
+  auto Eraser = [&](BasicBlock *BB) {
+    BasicBlocks.erase(
+        std::remove_if(BasicBlocks.begin(), BasicBlocks.end(),
+                       [&](const BasicBlock *i) { return i == BB; }),
+        BasicBlocks.end());
+  };
+  ASSERT_EQ(BasicBlocks.size(), static_cast<size_t>(2));
+  // Remove bb2 from F. This has to happen before the call to applyUpdates() for
+  // DTU to detect there is no longer an edge between bb2 -> bb3. The deleteBB()
+  // method converts bb2's TI into "unreachable".
+  ASSERT_FALSE(isa<UnreachableInst>(BB2->getTerminator()));
+  EXPECT_FALSE(DTU.isBBPendingDeletion(BB2));
+  DTU.callbackDeleteBB(BB2, Eraser);
+  EXPECT_TRUE(DTU.isBBPendingDeletion(BB2));
+  ASSERT_TRUE(isa<UnreachableInst>(BB2->getTerminator()));
+  EXPECT_EQ(BB2->getParent(), F);
+
+  // Queue up the DTU updates.
+  std::vector<DominatorTree::UpdateType> Updates;
+  Updates.reserve(4);
+  Updates.push_back({DominatorTree::Delete, BB0, BB2});
+  Updates.push_back({DominatorTree::Delete, BB2, BB3});
+
+  // Handle the specific shape case next.
+  // CFG Change: bb0 now only branches to bb3. We are preparing to remove bb1.
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 2u);
+  BB0->getTerminator()->eraseFromParent();
+  BranchInst::Create(BB3, BB0);
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 1u);
+
+  // Remove bb1 from F. This has to happen before the call to applyUpdates() for
+  // DTU to detect there is no longer an edge between bb1 -> bb3. The deleteBB()
+  // method converts bb1's TI into "unreachable".
+  ASSERT_FALSE(isa<UnreachableInst>(BB1->getTerminator()));
+  EXPECT_FALSE(DTU.isBBPendingDeletion(BB1));
+  DTU.callbackDeleteBB(BB1, Eraser);
+  EXPECT_TRUE(DTU.isBBPendingDeletion(BB1));
+  ASSERT_TRUE(isa<UnreachableInst>(BB1->getTerminator()));
+  EXPECT_EQ(BB1->getParent(), F);
+
+  // Update the DTU. In this case we don't call DTU.insertEdge(BB0, BB3) because
+  // the edge previously existed at the start of this test when DT was first
+  // created.
+  Updates.push_back({DominatorTree::Delete, BB0, BB1});
+  Updates.push_back({DominatorTree::Delete, BB1, BB3});
+
+  // Verify everything.
+  DTU.applyUpdates(Updates);
+  ASSERT_EQ(BasicBlocks.size(), static_cast<size_t>(2));
+  DTU.flush();
+  ASSERT_EQ(BasicBlocks.size(), static_cast<size_t>(0));
+  ASSERT_TRUE(DT.verify());
+}
+
+TEST(DomTreeUpdater, LazyUpdateBasicOperations) {
+  StringRef FuncName = "f";
+  StringRef ModuleString = R"(
+                           define i32 @f(i32 %i, i32 *%p) {
+                            bb0:
+                              store i32 %i, i32 *%p
+                              switch i32 %i, label %bb1 [
+                                i32 0, label %bb2
+                                i32 1, label %bb2
+                                i32 2, label %bb3
+                              ]
+                            bb1:
+                              ret i32 1
+                            bb2:
+                              ret i32 2
+                            bb3:
+                              ret i32 3
+                           }
+                           )";
+  // Make the module.
+  LLVMContext Context;
+  std::unique_ptr<Module> M = makeLLVMModule(Context, ModuleString);
+  Function *F = M->getFunction(FuncName);
+
+  // Make the DTU.
+  DominatorTree DT(*F);
+  PostDominatorTree PDT(*F);
+  DomTreeUpdater DTU(DT, PDT, DomTreeUpdater::UpdateStrategy::Lazy);
+  ASSERT_TRUE(DTU.hasDomTree());
+  ASSERT_TRUE(DTU.hasPostDomTree());
+  ASSERT_EQ(DTU.getUpdateStrategy(), DomTreeUpdater::UpdateStrategy::Lazy);
+  ASSERT_TRUE(DTU.getDomTree().verify());
+  ASSERT_TRUE(DTU.getPostDomTree().verify());
+
+  Function::iterator FI = F->begin();
+  BasicBlock *BB0 = &*FI++;
+  BasicBlock *BB1 = &*FI++;
+  BasicBlock *BB2 = &*FI++;
+  BasicBlock *BB3 = &*FI++;
+  // Test discards of self-domination update.
+  DTU.deleteEdge(BB0, BB0);
+
+  // Delete edge bb0 -> bb3 and push the update twice to verify duplicate
+  // entries are discarded.
+  std::vector<DominatorTree::UpdateType> Updates;
+  Updates.reserve(4);
+  Updates.push_back({DominatorTree::Delete, BB0, BB3});
+  Updates.push_back({DominatorTree::Delete, BB0, BB3});
+
+  // Unnecessary Insert: no edge bb1 -> bb2 after change to bb0.
+  Updates.push_back({DominatorTree::Insert, BB1, BB2});
+  // Unnecessary Delete: edge exists bb0 -> bb1 after change to bb0.
+  Updates.push_back({DominatorTree::Delete, BB0, BB1});
+
+  // CFG Change: remove edge bb0 -> bb3 and one duplicate edge bb0 -> bb2.
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 4u);
+  BB0->getTerminator()->eraseFromParent();
+  BranchInst::Create(BB1, BB2, ConstantInt::getTrue(F->getContext()), BB0);
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 2u);
+
+  // Deletion of a BasicBlock is an immediate event. We remove all uses to the
+  // contained Instructions and change the Terminator to "unreachable" when
+  // queued for deletion. Its parent is still F until DTU.flushDomTree is
+  // called. We don't defer this action because it can cause problems for other
+  // transforms or analysis as it's part of the actual CFG. We only defer
+  // updates to the DominatorTree. This code will crash if it is placed before
+  // the BranchInst::Create() call above.
+  bool CallbackFlag = false;
+  ASSERT_FALSE(isa<UnreachableInst>(BB3->getTerminator()));
+  EXPECT_FALSE(DTU.isBBPendingDeletion(BB3));
+  DTU.callbackDeleteBB(BB3, [&](BasicBlock *) { CallbackFlag = true; });
+  EXPECT_TRUE(DTU.isBBPendingDeletion(BB3));
+  ASSERT_TRUE(isa<UnreachableInst>(BB3->getTerminator()));
+  EXPECT_EQ(BB3->getParent(), F);
+
+  // Verify. Updates to DTU must be applied *after* all changes to the CFG
+  // (including block deletion).
+  DTU.applyUpdates(Updates);
+  ASSERT_TRUE(DTU.getDomTree().verify());
+  ASSERT_TRUE(DTU.hasPendingUpdates());
+  ASSERT_TRUE(DTU.hasPendingPostDomTreeUpdates());
+  ASSERT_FALSE(DTU.hasPendingDomTreeUpdates());
+  ASSERT_TRUE(DTU.hasPendingDeletedBB());
+  ASSERT_TRUE(DTU.getPostDomTree().verify());
+  ASSERT_FALSE(DTU.hasPendingUpdates());
+  ASSERT_FALSE(DTU.hasPendingPostDomTreeUpdates());
+  ASSERT_FALSE(DTU.hasPendingDomTreeUpdates());
+  ASSERT_FALSE(DTU.hasPendingDeletedBB());
+  ASSERT_EQ(CallbackFlag, true);
+}
+
+TEST(DomTreeUpdater, LazyUpdateReplaceEntryBB) {
+  StringRef FuncName = "f";
+  StringRef ModuleString = R"(
+                           define i32 @f() {
+                           bb0:
+                              br label %bb1
+                            bb1:
+                              ret i32 1
+                           }
+                           )";
+  // Make the module.
+  LLVMContext Context;
+  std::unique_ptr<Module> M = makeLLVMModule(Context, ModuleString);
+  Function *F = M->getFunction(FuncName);
+
+  // Make the DTU.
+  DominatorTree DT(*F);
+  PostDominatorTree PDT(*F);
+  DomTreeUpdater DTU(DT, PDT, DomTreeUpdater::UpdateStrategy::Lazy);
+  ASSERT_TRUE(DTU.hasDomTree());
+  ASSERT_TRUE(DTU.hasPostDomTree());
+  ASSERT_EQ(DTU.getUpdateStrategy(), DomTreeUpdater::UpdateStrategy::Lazy);
+  ASSERT_TRUE(DTU.getDomTree().verify());
+  ASSERT_TRUE(DTU.getPostDomTree().verify());
+
+  Function::iterator FI = F->begin();
+  BasicBlock *BB0 = &*FI++;
+  BasicBlock *BB1 = &*FI++;
+
+  // Add a block as the new function entry BB. We also link it to BB0.
+  BasicBlock *NewEntry =
+      BasicBlock::Create(F->getContext(), "new_entry", F, BB0);
+  BranchInst::Create(BB0, NewEntry);
+  EXPECT_EQ(F->begin()->getName(), NewEntry->getName());
+  EXPECT_TRUE(&F->getEntryBlock() == NewEntry);
+
+  // Insert the new edge between new_entry -> bb0. Without this the
+  // recalculate() call below will not actually recalculate the DT as there
+  // are no changes pending and no blocks deleted.
+  DTU.insertEdge(NewEntry, BB0);
+
+  // Changing the Entry BB requires a full recalculation.
+  DTU.recalculate(*F);
+  ASSERT_TRUE(DTU.getDomTree().verify());
+  ASSERT_TRUE(DTU.getPostDomTree().verify());
+
+  // CFG Change: remove new_edge -> bb0 and redirect to new_edge -> bb1.
+  EXPECT_EQ(NewEntry->getTerminator()->getNumSuccessors(), 1u);
+  NewEntry->getTerminator()->eraseFromParent();
+  BranchInst::Create(BB1, NewEntry);
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 1u);
+
+  // Update the DTU. At this point bb0 now has no predecessors but is still a
+  // Child of F.
+  DTU.applyUpdates({{DominatorTree::Delete, NewEntry, BB0},
+                    {DominatorTree::Insert, NewEntry, BB1}});
+  DTU.flush();
+  ASSERT_TRUE(DT.verify());
+  ASSERT_TRUE(PDT.verify());
+
+  // Now remove bb0 from F.
+  ASSERT_FALSE(isa<UnreachableInst>(BB0->getTerminator()));
+  EXPECT_FALSE(DTU.isBBPendingDeletion(BB0));
+  DTU.deleteBB(BB0);
+  EXPECT_TRUE(DTU.isBBPendingDeletion(BB0));
+  ASSERT_TRUE(isa<UnreachableInst>(BB0->getTerminator()));
+  EXPECT_EQ(BB0->getParent(), F);
+
+  // Perform a full recalculation of the DTU. It is not necessary here but we
+  // do this to test the case when there are no pending DT updates but there are
+  // pending deleted BBs.
+  ASSERT_TRUE(DTU.hasPendingDeletedBB());
+  DTU.recalculate(*F);
+  ASSERT_FALSE(DTU.hasPendingDeletedBB());
+}
+
+TEST(DomTreeUpdater, LazyUpdateStepTest) {
+  // This test focus on testing a DTU holding both trees applying multiple
+  // updates and DT/PDT not flushed together.
+  StringRef FuncName = "f";
+  StringRef ModuleString = R"(
+                           define i32 @f(i32 %i, i32 *%p) {
+                            bb0:
+                              store i32 %i, i32 *%p
+                              switch i32 %i, label %bb1 [
+                                i32 0, label %bb1
+                                i32 1, label %bb2
+                                i32 2, label %bb3
+                                i32 3, label %bb1
+                              ]
+                            bb1:
+                              ret i32 1
+                            bb2:
+                              ret i32 2
+                            bb3:
+                              ret i32 3
+                           }
+                           )";
+  // Make the module.
+  LLVMContext Context;
+  std::unique_ptr<Module> M = makeLLVMModule(Context, ModuleString);
+  Function *F = M->getFunction(FuncName);
+
+  // Make the DomTreeUpdater.
+  DominatorTree DT(*F);
+  PostDominatorTree PDT(*F);
+  DomTreeUpdater DTU(DT, PDT, DomTreeUpdater::UpdateStrategy::Lazy);
+
+  ASSERT_TRUE(DTU.hasDomTree());
+  ASSERT_TRUE(DTU.hasPostDomTree());
+  ASSERT_EQ(DTU.getUpdateStrategy(), DomTreeUpdater::UpdateStrategy::Lazy);
+  ASSERT_TRUE(DTU.getDomTree().verify());
+  ASSERT_TRUE(DTU.getPostDomTree().verify());
+  ASSERT_FALSE(DTU.hasPendingUpdates());
+
+  Function::iterator FI = F->begin();
+  BasicBlock *BB0 = &*FI++;
+  FI++;
+  BasicBlock *BB2 = &*FI++;
+  BasicBlock *BB3 = &*FI++;
+  SwitchInst *SI = dyn_cast<SwitchInst>(BB0->getTerminator());
+  ASSERT_NE(SI, nullptr) << "Couldn't get SwitchInst.";
+
+  // Delete edge bb0 -> bb3 and push the update twice to verify duplicate
+  // entries are discarded.
+  std::vector<DominatorTree::UpdateType> Updates;
+  Updates.reserve(1);
+  Updates.push_back({DominatorTree::Delete, BB0, BB3});
+
+  // CFG Change: remove edge bb0 -> bb3.
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 5u);
+  BB3->removePredecessor(BB0);
+  for (auto i = SI->case_begin(), e = SI->case_end(); i != e; ++i) {
+    if (i->getCaseIndex() == 2) {
+      SI->removeCase(i);
+      break;
+    }
+  }
+  EXPECT_EQ(BB0->getTerminator()->getNumSuccessors(), 4u);
+  // Deletion of a BasicBlock is an immediate event. We remove all uses to the
+  // contained Instructions and change the Terminator to "unreachable" when
+  // queued for deletion.
+  ASSERT_FALSE(isa<UnreachableInst>(BB3->getTerminator()));
+  EXPECT_FALSE(DTU.isBBPendingDeletion(BB3));
+  DTU.applyUpdates(Updates);
+
+  // Only flush DomTree.
+  ASSERT_TRUE(DTU.getDomTree().verify());
+  ASSERT_TRUE(DTU.hasPendingPostDomTreeUpdates());
+  ASSERT_FALSE(DTU.hasPendingDomTreeUpdates());
+
+  ASSERT_EQ(BB3->getParent(), F);
+  DTU.deleteBB(BB3);
+
+  Updates.clear();
+
+  // Remove all case branch to BB2 to test Eager recalculation.
+  // Code section from llvm::ConstantFoldTerminator
+  for (auto i = SI->case_begin(), e = SI->case_end(); i != e;) {
+    if (i->getCaseSuccessor() == BB2) {
+      // Remove this entry.
+      BB2->removePredecessor(BB0);
+      i = SI->removeCase(i);
+      e = SI->case_end();
+      Updates.push_back({DominatorTree::Delete, BB0, BB2});
+    } else
+      ++i;
+  }
+
+  DTU.applyUpdates(Updates);
+  // flush PostDomTree
+  ASSERT_TRUE(DTU.getPostDomTree().verify());
+  ASSERT_FALSE(DTU.hasPendingPostDomTreeUpdates());
+  ASSERT_TRUE(DTU.hasPendingDomTreeUpdates());
+  // flush both trees
+  DTU.flush();
+  ASSERT_TRUE(DT.verify());
+}




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