Reappl "[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@gmail.com>.

Reviewers: kuhar, brzycki, dmgreen, grosser, davide

Reviewed By: kuhar, brzycki

Author: NutshellySima

Subscribers: vsk, mgorny, llvm-commits

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

llvm-svn: 336163

llvm/include/llvm/IR/DomTreeUpdater.h

@@ -0,0 +1,244 @@
+//===- 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 <functional>
+#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,
+                        std::function<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,
+                       std::function<void(BasicBlock *)> Callback)
+        : CallbackVH(V), DelBB(V), Callback_(Callback) {}
+
+  private:
+    BasicBlock *DelBB = nullptr;
+    std::function<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

llvm/include/llvm/module.modulemap

@@ -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 * }

llvm/lib/IR/CMakeLists.txt

@@ -21,6 +21,7 @@ add_llvm_library(LLVMCore
   DiagnosticInfo.cpp
   DiagnosticPrinter.cpp
   Dominators.cpp
+  DomTreeUpdater.cpp
   Function.cpp
   GVMaterializer.cpp
   Globals.cpp