Stephen Hines | c6ca60f | 2023-05-09 02:19:22 -0700 | [diff] [blame^] | 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 |