1 //===- DomTreeUpdater.h - DomTree/Post DomTree Updater ----------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the DomTreeUpdater class, which provides a uniform way to
11 // update dominator tree related data structures.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_DOMTREEUPDATER_H
16 #define LLVM_DOMTREEUPDATER_H
18 #include "llvm/Analysis/PostDominators.h"
19 #include "llvm/IR/Dominators.h"
20 #include "llvm/IR/Instructions.h"
21 #include "llvm/IR/ValueHandle.h"
22 #include "llvm/Support/GenericDomTree.h"
27 class DomTreeUpdater {
29 enum class UpdateStrategy : unsigned char { Eager = 0, Lazy = 1 };
31 explicit DomTreeUpdater(UpdateStrategy Strategy_) : Strategy(Strategy_) {}
32 DomTreeUpdater(DominatorTree &DT_, UpdateStrategy Strategy_)
33 : DT(&DT_), Strategy(Strategy_) {}
34 DomTreeUpdater(DominatorTree *DT_, UpdateStrategy Strategy_)
35 : DT(DT_), Strategy(Strategy_) {}
36 DomTreeUpdater(PostDominatorTree &PDT_, UpdateStrategy Strategy_)
37 : PDT(&PDT_), Strategy(Strategy_) {}
38 DomTreeUpdater(PostDominatorTree *PDT_, UpdateStrategy Strategy_)
39 : PDT(PDT_), Strategy(Strategy_) {}
40 DomTreeUpdater(DominatorTree &DT_, PostDominatorTree &PDT_,
41 UpdateStrategy Strategy_)
42 : DT(&DT_), PDT(&PDT_), Strategy(Strategy_) {}
43 DomTreeUpdater(DominatorTree *DT_, PostDominatorTree *PDT_,
44 UpdateStrategy Strategy_)
45 : DT(DT_), PDT(PDT_), Strategy(Strategy_) {}
47 ~DomTreeUpdater() { flush(); }
49 /// Returns true if the current strategy is Lazy.
50 bool isLazy() const { return Strategy == UpdateStrategy::Lazy; };
52 /// Returns true if the current strategy is Eager.
53 bool isEager() const { return Strategy == UpdateStrategy::Eager; };
55 /// Returns true if it holds a DominatorTree.
56 bool hasDomTree() const { return DT != nullptr; }
58 /// Returns true if it holds a PostDominatorTree.
59 bool hasPostDomTree() const { return PDT != nullptr; }
61 /// Returns true if there is BasicBlock awaiting deletion.
62 /// The deletion will only happen until a flush event and
63 /// all available trees are up-to-date.
64 /// Returns false under Eager UpdateStrategy.
65 bool hasPendingDeletedBB() const { return !DeletedBBs.empty(); }
67 /// Returns true if DelBB is awaiting deletion.
68 /// Returns false under Eager UpdateStrategy.
69 bool isBBPendingDeletion(BasicBlock *DelBB) const;
71 /// Returns true if either of DT or PDT is valid and the tree has at
72 /// least one update pending. If DT or PDT is nullptr it is treated
73 /// as having no pending updates. This function does not check
74 /// whether there is BasicBlock awaiting deletion.
75 /// Returns false under Eager UpdateStrategy.
76 bool hasPendingUpdates() const;
78 /// Returns true if there are DominatorTree updates queued.
79 /// Returns false under Eager UpdateStrategy or DT is nullptr.
80 bool hasPendingDomTreeUpdates() const;
82 /// Returns true if there are PostDominatorTree updates queued.
83 /// Returns false under Eager UpdateStrategy or PDT is nullptr.
84 bool hasPendingPostDomTreeUpdates() const;
86 /// Apply updates on all available trees. Under Eager UpdateStrategy with
87 /// ForceRemoveDuplicates enabled or under Lazy UpdateStrategy, it will
88 /// discard duplicated updates and self-dominance updates. If both DT and PDT
89 /// are nullptrs, this function discards all updates. The Eager Strategy
90 /// applies the updates immediately while the Lazy Strategy queues the
91 /// updates. It is required for the state of the LLVM IR to be updated
92 /// *before* applying the Updates because the internal update routine will
93 /// analyze the current state of the relationship between a pair of (From, To)
94 /// BasicBlocks to determine whether a single update needs to be discarded.
95 void applyUpdates(ArrayRef<DominatorTree::UpdateType> Updates,
96 bool ForceRemoveDuplicates = false);
98 /// Notify all available trees on an edge insertion. If both DT and PDT are
99 /// nullptrs, this function discards the update. Under either Strategy,
100 /// self-dominance update will be removed. The Eager Strategy applies
101 /// the update immediately while the Lazy Strategy queues the update.
102 /// It is recommended to only use this method when you have exactly one
103 /// insertion (and no deletions). It is recommended to use applyUpdates() in
104 /// all other cases. This function has to be called *after* making the update
105 /// on the actual CFG. An internal functions checks if the edge exists in the
106 /// CFG in DEBUG mode.
107 void insertEdge(BasicBlock *From, BasicBlock *To);
109 /// Notify all available trees on an edge insertion.
110 /// Under either Strategy, the following updates will be discard silently
111 /// 1. Invalid - Inserting an edge that does not exist in the CFG.
112 /// 2. Self-dominance update.
113 /// 3. Both DT and PDT are nullptrs.
114 /// The Eager Strategy applies the update immediately while the Lazy Strategy
115 /// queues the update. It is recommended to only use this method when you have
116 /// exactly one insertion (and no deletions) and want to discard an invalid
118 void insertEdgeRelaxed(BasicBlock *From, BasicBlock *To);
120 /// Notify all available trees on an edge deletion. If both DT and PDT are
121 /// nullptrs, this function discards the update. Under either Strategy,
122 /// self-dominance update will be removed. The Eager Strategy applies
123 /// the update immediately while the Lazy Strategy queues the update.
124 /// It is recommended to only use this method when you have exactly one
125 /// deletion (and no insertions). It is recommended to use applyUpdates() in
126 /// all other cases. This function has to be called *after* making the update
127 /// on the actual CFG. An internal functions checks if the edge doesn't exist
128 /// in the CFG in DEBUG mode.
129 void deleteEdge(BasicBlock *From, BasicBlock *To);
131 /// Notify all available trees on an edge deletion.
132 /// Under either Strategy, the following updates will be discard silently
133 /// 1. Invalid - Deleting an edge that still exists in the CFG.
134 /// 2. Self-dominance update.
135 /// 3. Both DT and PDT are nullptrs.
136 /// The Eager Strategy applies the update immediately while the Lazy Strategy
137 /// queues the update. It is recommended to only use this method when you have
138 /// exactly one deletion (and no insertions) and want to discard an invalid
140 void deleteEdgeRelaxed(BasicBlock *From, BasicBlock *To);
142 /// Delete DelBB. DelBB will be removed from its Parent and
143 /// erased from available trees if it exists and finally get deleted.
144 /// Under Eager UpdateStrategy, DelBB will be processed immediately.
145 /// Under Lazy UpdateStrategy, DelBB will be queued until a flush event and
146 /// all available trees are up-to-date. Assert if any instruction of DelBB is
147 /// modified while awaiting deletion. When both DT and PDT are nullptrs, DelBB
148 /// will be queued until flush() is called.
149 void deleteBB(BasicBlock *DelBB);
151 /// Delete DelBB. DelBB will be removed from its Parent and
152 /// erased from available trees if it exists. Then the callback will
153 /// be called. Finally, DelBB will be deleted.
154 /// Under Eager UpdateStrategy, DelBB will be processed immediately.
155 /// Under Lazy UpdateStrategy, DelBB will be queued until a flush event and
156 /// all available trees are up-to-date. Assert if any instruction of DelBB is
157 /// modified while awaiting deletion. Multiple callbacks can be queued for one
158 /// DelBB under Lazy UpdateStrategy.
159 void callbackDeleteBB(BasicBlock *DelBB,
160 std::function<void(BasicBlock *)> Callback);
162 /// Recalculate all available trees and flush all BasicBlocks
163 /// awaiting deletion immediately.
164 void recalculate(Function &F);
166 /// Flush DomTree updates and return DomTree.
167 /// It also flush out of date updates applied by all available trees
168 /// and flush Deleted BBs if both trees are up-to-date.
169 /// It must only be called when it has a DomTree.
170 DominatorTree &getDomTree();
172 /// Flush PostDomTree updates and return PostDomTree.
173 /// It also flush out of date updates applied by all available trees
174 /// and flush Deleted BBs if both trees are up-to-date.
175 /// It must only be called when it has a PostDomTree.
176 PostDominatorTree &getPostDomTree();
178 /// Apply all pending updates to available trees and flush all BasicBlocks
179 /// awaiting deletion.
180 /// Does nothing under Eager UpdateStrategy.
183 /// Debug method to help view the internal state of this class.
184 LLVM_DUMP_METHOD void dump() const;
187 class CallBackOnDeletion final : public CallbackVH {
189 CallBackOnDeletion(BasicBlock *V,
190 std::function<void(BasicBlock *)> Callback)
191 : CallbackVH(V), DelBB(V), Callback_(Callback) {}
194 BasicBlock *DelBB = nullptr;
195 std::function<void(BasicBlock *)> Callback_;
197 void deleted() override {
199 CallbackVH::deleted();
203 SmallVector<DominatorTree::UpdateType, 16> PendUpdates;
204 size_t PendDTUpdateIndex = 0;
205 size_t PendPDTUpdateIndex = 0;
206 DominatorTree *DT = nullptr;
207 PostDominatorTree *PDT = nullptr;
208 const UpdateStrategy Strategy;
209 SmallPtrSet<BasicBlock *, 8> DeletedBBs;
210 std::vector<CallBackOnDeletion> Callbacks;
211 bool IsRecalculatingDomTree = false;
212 bool IsRecalculatingPostDomTree = false;
214 /// First remove all the instructions of DelBB and then make sure DelBB has a
215 /// valid terminator instruction which is necessary to have when DelBB still
216 /// has to be inside of its parent Function while awaiting deletion under Lazy
217 /// UpdateStrategy to prevent other routines from asserting the state of the
218 /// IR is inconsistent. Assert if DelBB is nullptr or has predecessors.
219 void validateDeleteBB(BasicBlock *DelBB);
221 /// Returns true if at least one BasicBlock is deleted.
222 bool forceFlushDeletedBB();
224 /// Deduplicate and remove unnecessary updates (no-ops) when using Lazy
225 /// UpdateStrategy. Returns true if the update is queued for update.
226 bool applyLazyUpdate(DominatorTree::UpdateKind Kind, BasicBlock *From,
229 /// Helper function to apply all pending DomTree updates.
230 void applyDomTreeUpdates();
232 /// Helper function to apply all pending PostDomTree updates.
233 void applyPostDomTreeUpdates();
235 /// Helper function to flush deleted BasicBlocks if all available
236 /// trees are up-to-date.
237 void tryFlushDeletedBB();
239 /// Drop all updates applied by all available trees and delete BasicBlocks if
240 /// all available trees are up-to-date.
241 void dropOutOfDateUpdates();
243 /// Erase Basic Block node that has been unlinked from Function
244 /// in the DomTree and PostDomTree.
245 void eraseDelBBNode(BasicBlock *DelBB);
247 /// Returns true if the update appears in the LLVM IR.
248 /// It is used to check whether an update is valid in
249 /// insertEdge/deleteEdge or is unnecessary in the batch update.
250 bool isUpdateValid(DominatorTree::UpdateType Update) const;
252 /// Returns true if the update is self dominance.
253 bool isSelfDominance(DominatorTree::UpdateType Update) const;
257 #endif // LLVM_DOMTREEUPDATER_H