1 | //===- DomTreeUpdater.h - DomTree/Post DomTree Updater ----------*- C++ -*-===// |
2 | // |
3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
4 | // See https://llvm.org/LICENSE.txt for license information. |
5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
6 | // |
7 | //===----------------------------------------------------------------------===// |
8 | // |
9 | // This file defines the DomTreeUpdater class, which provides a uniform way to |
10 | // update dominator tree related data structures. |
11 | // |
12 | //===----------------------------------------------------------------------===// |
13 | |
14 | #ifndef LLVM_ANALYSIS_DOMTREEUPDATER_H |
15 | #define LLVM_ANALYSIS_DOMTREEUPDATER_H |
16 | |
17 | #include "llvm/ADT/SmallPtrSet.h" |
18 | #include "llvm/IR/Dominators.h" |
19 | #include "llvm/IR/ValueHandle.h" |
20 | #include "llvm/Support/Compiler.h" |
21 | #include <cstddef> |
22 | #include <functional> |
23 | #include <vector> |
24 | |
25 | namespace llvm { |
26 | class PostDominatorTree; |
27 | |
28 | class DomTreeUpdater { |
29 | public: |
30 | enum class UpdateStrategy : unsigned char { Eager = 0, Lazy = 1 }; |
31 | |
32 | explicit DomTreeUpdater(UpdateStrategy Strategy_) : Strategy(Strategy_) {} |
33 | DomTreeUpdater(DominatorTree &DT_, UpdateStrategy Strategy_) |
34 | : DT(&DT_), Strategy(Strategy_) {} |
35 | DomTreeUpdater(DominatorTree *DT_, UpdateStrategy Strategy_) |
36 | : DT(DT_), Strategy(Strategy_) {} |
37 | DomTreeUpdater(PostDominatorTree &PDT_, UpdateStrategy Strategy_) |
38 | : PDT(&PDT_), Strategy(Strategy_) {} |
39 | DomTreeUpdater(PostDominatorTree *PDT_, UpdateStrategy Strategy_) |
40 | : PDT(PDT_), Strategy(Strategy_) {} |
41 | DomTreeUpdater(DominatorTree &DT_, PostDominatorTree &PDT_, |
42 | UpdateStrategy Strategy_) |
43 | : DT(&DT_), PDT(&PDT_), Strategy(Strategy_) {} |
44 | DomTreeUpdater(DominatorTree *DT_, PostDominatorTree *PDT_, |
45 | UpdateStrategy Strategy_) |
46 | : DT(DT_), PDT(PDT_), Strategy(Strategy_) {} |
47 | |
48 | ~DomTreeUpdater() { flush(); } |
49 | |
50 | /// Returns true if the current strategy is Lazy. |
51 | bool isLazy() const { return Strategy == UpdateStrategy::Lazy; }; |
52 | |
53 | /// Returns true if the current strategy is Eager. |
54 | bool isEager() const { return Strategy == UpdateStrategy::Eager; }; |
55 | |
56 | /// Returns true if it holds a DominatorTree. |
57 | bool hasDomTree() const { return DT != nullptr; } |
58 | |
59 | /// Returns true if it holds a PostDominatorTree. |
60 | bool hasPostDomTree() const { return PDT != nullptr; } |
61 | |
62 | /// Returns true if there is BasicBlock awaiting deletion. |
63 | /// The deletion will only happen until a flush event and |
64 | /// all available trees are up-to-date. |
65 | /// Returns false under Eager UpdateStrategy. |
66 | bool hasPendingDeletedBB() const { return !DeletedBBs.empty(); } |
67 | |
68 | /// Returns true if DelBB is awaiting deletion. |
69 | /// Returns false under Eager UpdateStrategy. |
70 | bool isBBPendingDeletion(BasicBlock *DelBB) const; |
71 | |
72 | /// Returns true if either of DT or PDT is valid and the tree has at |
73 | /// least one update pending. If DT or PDT is nullptr it is treated |
74 | /// as having no pending updates. This function does not check |
75 | /// whether there is BasicBlock awaiting deletion. |
76 | /// Returns false under Eager UpdateStrategy. |
77 | bool hasPendingUpdates() const; |
78 | |
79 | /// Returns true if there are DominatorTree updates queued. |
80 | /// Returns false under Eager UpdateStrategy or DT is nullptr. |
81 | bool hasPendingDomTreeUpdates() const; |
82 | |
83 | /// Returns true if there are PostDominatorTree updates queued. |
84 | /// Returns false under Eager UpdateStrategy or PDT is nullptr. |
85 | bool hasPendingPostDomTreeUpdates() const; |
86 | |
87 | ///@{ |
88 | /// \name Mutation APIs |
89 | /// |
90 | /// These methods provide APIs for submitting updates to the DominatorTree and |
91 | /// the PostDominatorTree. |
92 | /// |
93 | /// Note: There are two strategies to update the DominatorTree and the |
94 | /// PostDominatorTree: |
95 | /// 1. Eager UpdateStrategy: Updates are submitted and then flushed |
96 | /// immediately. |
97 | /// 2. Lazy UpdateStrategy: Updates are submitted but only flushed when you |
98 | /// explicitly call Flush APIs. It is recommended to use this update strategy |
99 | /// when you submit a bunch of updates multiple times which can then |
100 | /// add up to a large number of updates between two queries on the |
101 | /// DominatorTree. The incremental updater can reschedule the updates or |
102 | /// decide to recalculate the dominator tree in order to speedup the updating |
103 | /// process depending on the number of updates. |
104 | /// |
105 | /// Although GenericDomTree provides several update primitives, |
106 | /// it is not encouraged to use these APIs directly. |
107 | |
108 | /// Submit updates to all available trees. |
109 | /// The Eager Strategy flushes updates immediately while the Lazy Strategy |
110 | /// queues the updates. |
111 | /// |
112 | /// Note: The "existence" of an edge in a CFG refers to the CFG which DTU is |
113 | /// in sync with + all updates before that single update. |
114 | /// |
115 | /// CAUTION! |
116 | /// 1. It is required for the state of the LLVM IR to be updated |
117 | /// *before* submitting the updates because the internal update routine will |
118 | /// analyze the current state of the CFG to determine whether an update |
119 | /// is valid. |
120 | /// 2. It is illegal to submit any update that has already been submitted, |
121 | /// i.e., you are supposed not to insert an existent edge or delete a |
122 | /// nonexistent edge. |
123 | void applyUpdates(ArrayRef<DominatorTree::UpdateType> Updates); |
124 | |
125 | /// Submit updates to all available trees. It will also |
126 | /// 1. discard duplicated updates, |
127 | /// 2. remove invalid updates. (Invalid updates means deletion of an edge that |
128 | /// still exists or insertion of an edge that does not exist.) |
129 | /// The Eager Strategy flushes updates immediately while the Lazy Strategy |
130 | /// queues the updates. |
131 | /// |
132 | /// Note: The "existence" of an edge in a CFG refers to the CFG which DTU is |
133 | /// in sync with + all updates before that single update. |
134 | /// |
135 | /// CAUTION! |
136 | /// 1. It is required for the state of the LLVM IR to be updated |
137 | /// *before* submitting the updates because the internal update routine will |
138 | /// analyze the current state of the CFG to determine whether an update |
139 | /// is valid. |
140 | /// 2. It is illegal to submit any update that has already been submitted, |
141 | /// i.e., you are supposed not to insert an existent edge or delete a |
142 | /// nonexistent edge. |
143 | /// 3. It is only legal to submit updates to an edge in the order CFG changes |
144 | /// are made. The order you submit updates on different edges is not |
145 | /// restricted. |
146 | void applyUpdatesPermissive(ArrayRef<DominatorTree::UpdateType> Updates); |
147 | |
148 | /// Notify DTU that the entry block was replaced. |
149 | /// Recalculate all available trees and flush all BasicBlocks |
150 | /// awaiting deletion immediately. |
151 | void recalculate(Function &F); |
152 | |
153 | /// Delete DelBB. DelBB will be removed from its Parent and |
154 | /// erased from available trees if it exists and finally get deleted. |
155 | /// Under Eager UpdateStrategy, DelBB will be processed immediately. |
156 | /// Under Lazy UpdateStrategy, DelBB will be queued until a flush event and |
157 | /// all available trees are up-to-date. Assert if any instruction of DelBB is |
158 | /// modified while awaiting deletion. When both DT and PDT are nullptrs, DelBB |
159 | /// will be queued until flush() is called. |
160 | void deleteBB(BasicBlock *DelBB); |
161 | |
162 | /// Delete DelBB. DelBB will be removed from its Parent and |
163 | /// erased from available trees if it exists. Then the callback will |
164 | /// be called. Finally, DelBB will be deleted. |
165 | /// Under Eager UpdateStrategy, DelBB will be processed immediately. |
166 | /// Under Lazy UpdateStrategy, DelBB will be queued until a flush event and |
167 | /// all available trees are up-to-date. Assert if any instruction of DelBB is |
168 | /// modified while awaiting deletion. Multiple callbacks can be queued for one |
169 | /// DelBB under Lazy UpdateStrategy. |
170 | void callbackDeleteBB(BasicBlock *DelBB, |
171 | std::function<void(BasicBlock *)> Callback); |
172 | |
173 | ///@} |
174 | |
175 | ///@{ |
176 | /// \name Flush APIs |
177 | /// |
178 | /// CAUTION! By the moment these flush APIs are called, the current CFG needs |
179 | /// to be the same as the CFG which DTU is in sync with + all updates |
180 | /// submitted. |
181 | |
182 | /// Flush DomTree updates and return DomTree. |
183 | /// It flushes Deleted BBs if both trees are up-to-date. |
184 | /// It must only be called when it has a DomTree. |
185 | DominatorTree &getDomTree(); |
186 | |
187 | /// Flush PostDomTree updates and return PostDomTree. |
188 | /// It flushes Deleted BBs if both trees are up-to-date. |
189 | /// It must only be called when it has a PostDomTree. |
190 | PostDominatorTree &getPostDomTree(); |
191 | |
192 | /// Apply all pending updates to available trees and flush all BasicBlocks |
193 | /// awaiting deletion. |
194 | |
195 | void flush(); |
196 | |
197 | ///@} |
198 | |
199 | /// Debug method to help view the internal state of this class. |
200 | LLVM_DUMP_METHOD void dump() const; |
201 | |
202 | private: |
203 | class CallBackOnDeletion final : public CallbackVH { |
204 | public: |
205 | CallBackOnDeletion(BasicBlock *V, |
206 | std::function<void(BasicBlock *)> Callback) |
207 | : CallbackVH(V), DelBB(V), Callback_(Callback) {} |
208 | |
209 | private: |
210 | BasicBlock *DelBB = nullptr; |
211 | std::function<void(BasicBlock *)> Callback_; |
212 | |
213 | void deleted() override { |
214 | Callback_(DelBB); |
215 | CallbackVH::deleted(); |
216 | } |
217 | }; |
218 | |
219 | SmallVector<DominatorTree::UpdateType, 16> PendUpdates; |
220 | size_t PendDTUpdateIndex = 0; |
221 | size_t PendPDTUpdateIndex = 0; |
222 | DominatorTree *DT = nullptr; |
223 | PostDominatorTree *PDT = nullptr; |
224 | const UpdateStrategy Strategy; |
225 | SmallPtrSet<BasicBlock *, 8> DeletedBBs; |
226 | std::vector<CallBackOnDeletion> Callbacks; |
227 | bool IsRecalculatingDomTree = false; |
228 | bool IsRecalculatingPostDomTree = false; |
229 | |
230 | /// First remove all the instructions of DelBB and then make sure DelBB has a |
231 | /// valid terminator instruction which is necessary to have when DelBB still |
232 | /// has to be inside of its parent Function while awaiting deletion under Lazy |
233 | /// UpdateStrategy to prevent other routines from asserting the state of the |
234 | /// IR is inconsistent. Assert if DelBB is nullptr or has predecessors. |
235 | void validateDeleteBB(BasicBlock *DelBB); |
236 | |
237 | /// Returns true if at least one BasicBlock is deleted. |
238 | bool forceFlushDeletedBB(); |
239 | |
240 | /// Helper function to apply all pending DomTree updates. |
241 | void applyDomTreeUpdates(); |
242 | |
243 | /// Helper function to apply all pending PostDomTree updates. |
244 | void applyPostDomTreeUpdates(); |
245 | |
246 | /// Helper function to flush deleted BasicBlocks if all available |
247 | /// trees are up-to-date. |
248 | void tryFlushDeletedBB(); |
249 | |
250 | /// Drop all updates applied by all available trees and delete BasicBlocks if |
251 | /// all available trees are up-to-date. |
252 | void dropOutOfDateUpdates(); |
253 | |
254 | /// Erase Basic Block node that has been unlinked from Function |
255 | /// in the DomTree and PostDomTree. |
256 | void eraseDelBBNode(BasicBlock *DelBB); |
257 | |
258 | /// Returns true if the update appears in the LLVM IR. |
259 | /// It is used to check whether an update is valid in |
260 | /// insertEdge/deleteEdge or is unnecessary in the batch update. |
261 | bool isUpdateValid(DominatorTree::UpdateType Update) const; |
262 | |
263 | /// Returns true if the update is self dominance. |
264 | bool isSelfDominance(DominatorTree::UpdateType Update) const; |
265 | }; |
266 | } // namespace llvm |
267 | |
268 | #endif // LLVM_ANALYSIS_DOMTREEUPDATER_H |
269 | |