1 //===- MemorySSAUpdater.h - Memory SSA 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 // \file 10 // An automatic updater for MemorySSA that handles arbitrary insertion, 11 // deletion, and moves. It performs phi insertion where necessary, and 12 // automatically updates the MemorySSA IR to be correct. 13 // While updating loads or removing instructions is often easy enough to not 14 // need this, updating stores should generally not be attemped outside this 15 // API. 16 // 17 // Basic API usage: 18 // Create the memory access you want for the instruction (this is mainly so 19 // we know where it is, without having to duplicate the entire set of create 20 // functions MemorySSA supports). 21 // Call insertDef or insertUse depending on whether it's a MemoryUse or a 22 // MemoryDef. 23 // That's it. 24 // 25 // For moving, first, move the instruction itself using the normal SSA 26 // instruction moving API, then just call moveBefore, moveAfter,or moveTo with 27 // the right arguments. 28 // 29 //===----------------------------------------------------------------------===// 30 31 #ifndef LLVM_ANALYSIS_MEMORYSSAUPDATER_H 32 #define LLVM_ANALYSIS_MEMORYSSAUPDATER_H 33 34 #include "llvm/ADT/SmallPtrSet.h" 35 #include "llvm/ADT/SmallSet.h" 36 #include "llvm/ADT/SmallVector.h" 37 #include "llvm/Analysis/MemorySSA.h" 38 #include "llvm/IR/ValueHandle.h" 39 #include "llvm/IR/ValueMap.h" 40 #include "llvm/Support/CFGDiff.h" 41 42 namespace llvm { 43 44 class BasicBlock; 45 class DominatorTree; 46 class Instruction; 47 class LoopBlocksRPO; 48 template <typename T, unsigned int N> class SmallSetVector; 49 50 using ValueToValueMapTy = ValueMap<const Value *, WeakTrackingVH>; 51 using PhiToDefMap = SmallDenseMap<MemoryPhi *, MemoryAccess *>; 52 using CFGUpdate = cfg::Update<BasicBlock *>; 53 54 class MemorySSAUpdater { 55 private: 56 MemorySSA *MSSA; 57 58 /// We use WeakVH rather than a costly deletion to deal with dangling pointers. 59 /// MemoryPhis are created eagerly and sometimes get zapped shortly afterwards. 60 SmallVector<WeakVH, 16> InsertedPHIs; 61 62 SmallPtrSet<BasicBlock *, 8> VisitedBlocks; 63 SmallSet<AssertingVH<MemoryPhi>, 8> NonOptPhis; 64 65 public: MemorySSAUpdater(MemorySSA * MSSA)66 MemorySSAUpdater(MemorySSA *MSSA) : MSSA(MSSA) {} 67 68 /// Insert a definition into the MemorySSA IR. RenameUses will rename any use 69 /// below the new def block (and any inserted phis). RenameUses should be set 70 /// to true if the definition may cause new aliases for loads below it. This 71 /// is not the case for hoisting or sinking or other forms of code *movement*. 72 /// It *is* the case for straight code insertion. 73 /// For example: 74 /// store a 75 /// if (foo) { } 76 /// load a 77 /// 78 /// Moving the store into the if block, and calling insertDef, does not 79 /// require RenameUses. 80 /// However, changing it to: 81 /// store a 82 /// if (foo) { store b } 83 /// load a 84 /// Where a mayalias b, *does* require RenameUses be set to true. 85 void insertDef(MemoryDef *Def, bool RenameUses = false); 86 void insertUse(MemoryUse *Use, bool RenameUses = false); 87 /// Update the MemoryPhi in `To` following an edge deletion between `From` and 88 /// `To`. If `To` becomes unreachable, a call to removeBlocks should be made. 89 void removeEdge(BasicBlock *From, BasicBlock *To); 90 /// Update the MemoryPhi in `To` to have a single incoming edge from `From`, 91 /// following a CFG change that replaced multiple edges (switch) with a direct 92 /// branch. 93 void removeDuplicatePhiEdgesBetween(const BasicBlock *From, 94 const BasicBlock *To); 95 /// Update MemorySSA when inserting a unique backedge block for a loop. 96 void updatePhisWhenInsertingUniqueBackedgeBlock(BasicBlock *LoopHeader, 97 BasicBlock *LoopPreheader, 98 BasicBlock *BackedgeBlock); 99 /// Update MemorySSA after a loop was cloned, given the blocks in RPO order, 100 /// the exit blocks and a 1:1 mapping of all blocks and instructions 101 /// cloned. This involves duplicating all defs and uses in the cloned blocks 102 /// Updating phi nodes in exit block successors is done separately. 103 void updateForClonedLoop(const LoopBlocksRPO &LoopBlocks, 104 ArrayRef<BasicBlock *> ExitBlocks, 105 const ValueToValueMapTy &VM, 106 bool IgnoreIncomingWithNoClones = false); 107 // Block BB was fully or partially cloned into its predecessor P1. Map 108 // contains the 1:1 mapping of instructions cloned and VM[BB]=P1. 109 void updateForClonedBlockIntoPred(BasicBlock *BB, BasicBlock *P1, 110 const ValueToValueMapTy &VM); 111 /// Update phi nodes in exit block successors following cloning. Exit blocks 112 /// that were not cloned don't have additional predecessors added. 113 void updateExitBlocksForClonedLoop(ArrayRef<BasicBlock *> ExitBlocks, 114 const ValueToValueMapTy &VMap, 115 DominatorTree &DT); 116 void updateExitBlocksForClonedLoop( 117 ArrayRef<BasicBlock *> ExitBlocks, 118 ArrayRef<std::unique_ptr<ValueToValueMapTy>> VMaps, DominatorTree &DT); 119 120 /// Apply CFG updates, analogous with the DT edge updates. By default, the 121 /// DT is assumed to be already up to date. If UpdateDTFirst is true, first 122 /// update the DT with the same updates. 123 void applyUpdates(ArrayRef<CFGUpdate> Updates, DominatorTree &DT, 124 bool UpdateDTFirst = false); 125 /// Apply CFG insert updates, analogous with the DT edge updates. 126 void applyInsertUpdates(ArrayRef<CFGUpdate> Updates, DominatorTree &DT); 127 128 void moveBefore(MemoryUseOrDef *What, MemoryUseOrDef *Where); 129 void moveAfter(MemoryUseOrDef *What, MemoryUseOrDef *Where); 130 void moveToPlace(MemoryUseOrDef *What, BasicBlock *BB, 131 MemorySSA::InsertionPlace Where); 132 /// `From` block was spliced into `From` and `To`. There is a CFG edge from 133 /// `From` to `To`. Move all accesses from `From` to `To` starting at 134 /// instruction `Start`. `To` is newly created BB, so empty of 135 /// MemorySSA::MemoryAccesses. Edges are already updated, so successors of 136 /// `To` with MPhi nodes need to update incoming block. 137 /// |------| |------| 138 /// | From | | From | 139 /// | | |------| 140 /// | | || 141 /// | | => \/ 142 /// | | |------| <- Start 143 /// | | | To | 144 /// |------| |------| 145 void moveAllAfterSpliceBlocks(BasicBlock *From, BasicBlock *To, 146 Instruction *Start); 147 /// `From` block was merged into `To`. There is a CFG edge from `To` to 148 /// `From`.`To` still branches to `From`, but all instructions were moved and 149 /// `From` is now an empty block; `From` is about to be deleted. Move all 150 /// accesses from `From` to `To` starting at instruction `Start`. `To` may 151 /// have multiple successors, `From` has a single predecessor. `From` may have 152 /// successors with MPhi nodes, replace their incoming block with `To`. 153 /// |------| |------| 154 /// | To | | To | 155 /// |------| | | 156 /// || => | | 157 /// \/ | | 158 /// |------| | | <- Start 159 /// | From | | | 160 /// |------| |------| 161 void moveAllAfterMergeBlocks(BasicBlock *From, BasicBlock *To, 162 Instruction *Start); 163 /// A new empty BasicBlock (New) now branches directly to Old. Some of 164 /// Old's predecessors (Preds) are now branching to New instead of Old. 165 /// If New is the only predecessor, move Old's Phi, if present, to New. 166 /// Otherwise, add a new Phi in New with appropriate incoming values, and 167 /// update the incoming values in Old's Phi node too, if present. 168 void wireOldPredecessorsToNewImmediatePredecessor( 169 BasicBlock *Old, BasicBlock *New, ArrayRef<BasicBlock *> Preds, 170 bool IdenticalEdgesWereMerged = true); 171 // The below are utility functions. Other than creation of accesses to pass 172 // to insertDef, and removeAccess to remove accesses, you should generally 173 // not attempt to update memoryssa yourself. It is very non-trivial to get 174 // the edge cases right, and the above calls already operate in near-optimal 175 // time bounds. 176 177 /// Create a MemoryAccess in MemorySSA at a specified point in a block. 178 /// 179 /// When used by itself, this method will only insert the new MemoryAccess 180 /// into the access list, but not make any other changes, such as inserting 181 /// MemoryPHI nodes, or updating users to point to the new MemoryAccess. You 182 /// must specify a correct Definition in this case. 183 /// 184 /// Usually, this API is instead combined with insertUse() or insertDef(), 185 /// which will perform all the necessary MSSA updates. If these APIs are used, 186 /// then nullptr can be used as Definition, as the correct defining access 187 /// will be automatically determined. 188 /// 189 /// Note: If a MemoryAccess already exists for I, this function will make it 190 /// inaccessible and it *must* have removeMemoryAccess called on it. 191 MemoryAccess *createMemoryAccessInBB(Instruction *I, MemoryAccess *Definition, 192 const BasicBlock *BB, 193 MemorySSA::InsertionPlace Point); 194 195 /// Create a MemoryAccess in MemorySSA before an existing MemoryAccess. 196 /// 197 /// See createMemoryAccessInBB() for usage details. 198 MemoryUseOrDef *createMemoryAccessBefore(Instruction *I, 199 MemoryAccess *Definition, 200 MemoryUseOrDef *InsertPt); 201 /// Create a MemoryAccess in MemorySSA after an existing MemoryAccess. 202 /// 203 /// See createMemoryAccessInBB() for usage details. 204 MemoryUseOrDef *createMemoryAccessAfter(Instruction *I, 205 MemoryAccess *Definition, 206 MemoryAccess *InsertPt); 207 208 /// Remove a MemoryAccess from MemorySSA, including updating all 209 /// definitions and uses. 210 /// This should be called when a memory instruction that has a MemoryAccess 211 /// associated with it is erased from the program. For example, if a store or 212 /// load is simply erased (not replaced), removeMemoryAccess should be called 213 /// on the MemoryAccess for that store/load. 214 void removeMemoryAccess(MemoryAccess *, bool OptimizePhis = false); 215 216 /// Remove MemoryAccess for a given instruction, if a MemoryAccess exists. 217 /// This should be called when an instruction (load/store) is deleted from 218 /// the program. 219 void removeMemoryAccess(const Instruction *I, bool OptimizePhis = false) { 220 if (MemoryAccess *MA = MSSA->getMemoryAccess(I)) 221 removeMemoryAccess(MA, OptimizePhis); 222 } 223 224 /// Remove all MemoryAcceses in a set of BasicBlocks about to be deleted. 225 /// Assumption we make here: all uses of deleted defs and phi must either 226 /// occur in blocks about to be deleted (thus will be deleted as well), or 227 /// they occur in phis that will simply lose an incoming value. 228 /// Deleted blocks still have successor info, but their predecessor edges and 229 /// Phi nodes may already be updated. Instructions in DeadBlocks should be 230 /// deleted after this call. 231 void removeBlocks(const SmallSetVector<BasicBlock *, 8> &DeadBlocks); 232 233 /// Instruction I will be changed to an unreachable. Remove all accesses in 234 /// I's block that follow I (inclusive), and update the Phis in the blocks' 235 /// successors. 236 void changeToUnreachable(const Instruction *I); 237 238 /// Get handle on MemorySSA. getMemorySSA()239 MemorySSA* getMemorySSA() const { return MSSA; } 240 241 private: 242 // Move What before Where in the MemorySSA IR. 243 template <class WhereType> 244 void moveTo(MemoryUseOrDef *What, BasicBlock *BB, WhereType Where); 245 // Move all memory accesses from `From` to `To` starting at `Start`. 246 // Restrictions apply, see public wrappers of this method. 247 void moveAllAccesses(BasicBlock *From, BasicBlock *To, Instruction *Start); 248 MemoryAccess *getPreviousDef(MemoryAccess *); 249 MemoryAccess *getPreviousDefInBlock(MemoryAccess *); 250 MemoryAccess * 251 getPreviousDefFromEnd(BasicBlock *, 252 DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> &); 253 MemoryAccess * 254 getPreviousDefRecursive(BasicBlock *, 255 DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> &); 256 MemoryAccess *recursePhi(MemoryAccess *Phi); 257 MemoryAccess *tryRemoveTrivialPhi(MemoryPhi *Phi); 258 template <class RangeType> 259 MemoryAccess *tryRemoveTrivialPhi(MemoryPhi *Phi, RangeType &Operands); 260 void tryRemoveTrivialPhis(ArrayRef<WeakVH> UpdatedPHIs); 261 void fixupDefs(const SmallVectorImpl<WeakVH> &); 262 // Clone all uses and defs from BB to NewBB given a 1:1 map of all 263 // instructions and blocks cloned, and a map of MemoryPhi : Definition 264 // (MemoryAccess Phi or Def). VMap maps old instructions to cloned 265 // instructions and old blocks to cloned blocks. MPhiMap, is created in the 266 // caller of this private method, and maps existing MemoryPhis to new 267 // definitions that new MemoryAccesses must point to. These definitions may 268 // not necessarily be MemoryPhis themselves, they may be MemoryDefs. As such, 269 // the map is between MemoryPhis and MemoryAccesses, where the MemoryAccesses 270 // may be MemoryPhis or MemoryDefs and not MemoryUses. 271 // If CloneWasSimplified = true, the clone was exact. Otherwise, assume that 272 // the clone involved simplifications that may have: (1) turned a MemoryUse 273 // into an instruction that MemorySSA has no representation for, or (2) turned 274 // a MemoryDef into a MemoryUse or an instruction that MemorySSA has no 275 // representation for. No other cases are supported. 276 void cloneUsesAndDefs(BasicBlock *BB, BasicBlock *NewBB, 277 const ValueToValueMapTy &VMap, PhiToDefMap &MPhiMap, 278 bool CloneWasSimplified = false); 279 template <typename Iter> 280 void privateUpdateExitBlocksForClonedLoop(ArrayRef<BasicBlock *> ExitBlocks, 281 Iter ValuesBegin, Iter ValuesEnd, 282 DominatorTree &DT); 283 void applyInsertUpdates(ArrayRef<CFGUpdate>, DominatorTree &DT, 284 const GraphDiff<BasicBlock *> *GD); 285 }; 286 } // end namespace llvm 287 288 #endif // LLVM_ANALYSIS_MEMORYSSAUPDATER_H 289