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/SetVector.h" 35 #include "llvm/ADT/SmallPtrSet.h" 36 #include "llvm/ADT/SmallSet.h" 37 #include "llvm/ADT/SmallVector.h" 38 #include "llvm/Analysis/LoopInfo.h" 39 #include "llvm/Analysis/LoopIterator.h" 40 #include "llvm/Analysis/MemorySSA.h" 41 #include "llvm/IR/BasicBlock.h" 42 #include "llvm/IR/CFGDiff.h" 43 #include "llvm/IR/Dominators.h" 44 #include "llvm/IR/Module.h" 45 #include "llvm/IR/OperandTraits.h" 46 #include "llvm/IR/Type.h" 47 #include "llvm/IR/Use.h" 48 #include "llvm/IR/User.h" 49 #include "llvm/IR/Value.h" 50 #include "llvm/IR/ValueHandle.h" 51 #include "llvm/IR/ValueMap.h" 52 #include "llvm/Pass.h" 53 #include "llvm/Support/Casting.h" 54 #include "llvm/Support/ErrorHandling.h" 55 56 namespace llvm { 57 58 class Function; 59 class Instruction; 60 class MemoryAccess; 61 class LLVMContext; 62 class raw_ostream; 63 64 using ValueToValueMapTy = ValueMap<const Value *, WeakTrackingVH>; 65 using PhiToDefMap = SmallDenseMap<MemoryPhi *, MemoryAccess *>; 66 using CFGUpdate = cfg::Update<BasicBlock *>; 67 using GraphDiffInvBBPair = 68 std::pair<const GraphDiff<BasicBlock *> *, Inverse<BasicBlock *>>; 69 70 class MemorySSAUpdater { 71 private: 72 MemorySSA *MSSA; 73 74 /// We use WeakVH rather than a costly deletion to deal with dangling pointers. 75 /// MemoryPhis are created eagerly and sometimes get zapped shortly afterwards. 76 SmallVector<WeakVH, 16> InsertedPHIs; 77 78 SmallPtrSet<BasicBlock *, 8> VisitedBlocks; 79 SmallSet<AssertingVH<MemoryPhi>, 8> NonOptPhis; 80 81 public: 82 MemorySSAUpdater(MemorySSA *MSSA) : MSSA(MSSA) {} 83 84 /// Insert a definition into the MemorySSA IR. RenameUses will rename any use 85 /// below the new def block (and any inserted phis). RenameUses should be set 86 /// to true if the definition may cause new aliases for loads below it. This 87 /// is not the case for hoisting or sinking or other forms of code *movement*. 88 /// It *is* the case for straight code insertion. 89 /// For example: 90 /// store a 91 /// if (foo) { } 92 /// load a 93 /// 94 /// Moving the store into the if block, and calling insertDef, does not 95 /// require RenameUses. 96 /// However, changing it to: 97 /// store a 98 /// if (foo) { store b } 99 /// load a 100 /// Where a mayalias b, *does* require RenameUses be set to true. 101 void insertDef(MemoryDef *Def, bool RenameUses = false); 102 void insertUse(MemoryUse *Use, bool RenameUses = false); 103 /// Update the MemoryPhi in `To` following an edge deletion between `From` and 104 /// `To`. If `To` becomes unreachable, a call to removeBlocks should be made. 105 void removeEdge(BasicBlock *From, BasicBlock *To); 106 /// Update the MemoryPhi in `To` to have a single incoming edge from `From`, 107 /// following a CFG change that replaced multiple edges (switch) with a direct 108 /// branch. 109 void removeDuplicatePhiEdgesBetween(const BasicBlock *From, 110 const BasicBlock *To); 111 /// Update MemorySSA when inserting a unique backedge block for a loop. 112 void updatePhisWhenInsertingUniqueBackedgeBlock(BasicBlock *LoopHeader, 113 BasicBlock *LoopPreheader, 114 BasicBlock *BackedgeBlock); 115 /// Update MemorySSA after a loop was cloned, given the blocks in RPO order, 116 /// the exit blocks and a 1:1 mapping of all blocks and instructions 117 /// cloned. This involves duplicating all defs and uses in the cloned blocks 118 /// Updating phi nodes in exit block successors is done separately. 119 void updateForClonedLoop(const LoopBlocksRPO &LoopBlocks, 120 ArrayRef<BasicBlock *> ExitBlocks, 121 const ValueToValueMapTy &VM, 122 bool IgnoreIncomingWithNoClones = false); 123 // Block BB was fully or partially cloned into its predecessor P1. Map 124 // contains the 1:1 mapping of instructions cloned and VM[BB]=P1. 125 void updateForClonedBlockIntoPred(BasicBlock *BB, BasicBlock *P1, 126 const ValueToValueMapTy &VM); 127 /// Update phi nodes in exit block successors following cloning. Exit blocks 128 /// that were not cloned don't have additional predecessors added. 129 void updateExitBlocksForClonedLoop(ArrayRef<BasicBlock *> ExitBlocks, 130 const ValueToValueMapTy &VMap, 131 DominatorTree &DT); 132 void updateExitBlocksForClonedLoop( 133 ArrayRef<BasicBlock *> ExitBlocks, 134 ArrayRef<std::unique_ptr<ValueToValueMapTy>> VMaps, DominatorTree &DT); 135 136 /// Apply CFG updates, analogous with the DT edge updates. 137 void applyUpdates(ArrayRef<CFGUpdate> Updates, DominatorTree &DT); 138 /// Apply CFG insert updates, analogous with the DT edge updates. 139 void applyInsertUpdates(ArrayRef<CFGUpdate> Updates, DominatorTree &DT); 140 141 void moveBefore(MemoryUseOrDef *What, MemoryUseOrDef *Where); 142 void moveAfter(MemoryUseOrDef *What, MemoryUseOrDef *Where); 143 void moveToPlace(MemoryUseOrDef *What, BasicBlock *BB, 144 MemorySSA::InsertionPlace Where); 145 /// `From` block was spliced into `From` and `To`. There is a CFG edge from 146 /// `From` to `To`. Move all accesses from `From` to `To` starting at 147 /// instruction `Start`. `To` is newly created BB, so empty of 148 /// MemorySSA::MemoryAccesses. Edges are already updated, so successors of 149 /// `To` with MPhi nodes need to update incoming block. 150 /// |------| |------| 151 /// | From | | From | 152 /// | | |------| 153 /// | | || 154 /// | | => \/ 155 /// | | |------| <- Start 156 /// | | | To | 157 /// |------| |------| 158 void moveAllAfterSpliceBlocks(BasicBlock *From, BasicBlock *To, 159 Instruction *Start); 160 /// `From` block was merged into `To`. There is a CFG edge from `To` to 161 /// `From`.`To` still branches to `From`, but all instructions were moved and 162 /// `From` is now an empty block; `From` is about to be deleted. Move all 163 /// accesses from `From` to `To` starting at instruction `Start`. `To` may 164 /// have multiple successors, `From` has a single predecessor. `From` may have 165 /// successors with MPhi nodes, replace their incoming block with `To`. 166 /// |------| |------| 167 /// | To | | To | 168 /// |------| | | 169 /// || => | | 170 /// \/ | | 171 /// |------| | | <- Start 172 /// | From | | | 173 /// |------| |------| 174 void moveAllAfterMergeBlocks(BasicBlock *From, BasicBlock *To, 175 Instruction *Start); 176 /// A new empty BasicBlock (New) now branches directly to Old. Some of 177 /// Old's predecessors (Preds) are now branching to New instead of Old. 178 /// If New is the only predecessor, move Old's Phi, if present, to New. 179 /// Otherwise, add a new Phi in New with appropriate incoming values, and 180 /// update the incoming values in Old's Phi node too, if present. 181 void wireOldPredecessorsToNewImmediatePredecessor( 182 BasicBlock *Old, BasicBlock *New, ArrayRef<BasicBlock *> Preds, 183 bool IdenticalEdgesWereMerged = true); 184 // The below are utility functions. Other than creation of accesses to pass 185 // to insertDef, and removeAccess to remove accesses, you should generally 186 // not attempt to update memoryssa yourself. It is very non-trivial to get 187 // the edge cases right, and the above calls already operate in near-optimal 188 // time bounds. 189 190 /// Create a MemoryAccess in MemorySSA at a specified point in a block, 191 /// with a specified clobbering definition. 192 /// 193 /// Returns the new MemoryAccess. 194 /// This should be called when a memory instruction is created that is being 195 /// used to replace an existing memory instruction. It will *not* create PHI 196 /// nodes, or verify the clobbering definition. The insertion place is used 197 /// solely to determine where in the memoryssa access lists the instruction 198 /// will be placed. The caller is expected to keep ordering the same as 199 /// instructions. 200 /// It will return the new MemoryAccess. 201 /// Note: If a MemoryAccess already exists for I, this function will make it 202 /// inaccessible and it *must* have removeMemoryAccess called on it. 203 MemoryAccess *createMemoryAccessInBB(Instruction *I, MemoryAccess *Definition, 204 const BasicBlock *BB, 205 MemorySSA::InsertionPlace Point); 206 207 /// Create a MemoryAccess in MemorySSA before or after an existing 208 /// MemoryAccess. 209 /// 210 /// Returns the new MemoryAccess. 211 /// This should be called when a memory instruction is created that is being 212 /// used to replace an existing memory instruction. It will *not* create PHI 213 /// nodes, or verify the clobbering definition. 214 /// 215 /// Note: If a MemoryAccess already exists for I, this function will make it 216 /// inaccessible and it *must* have removeMemoryAccess called on it. 217 MemoryUseOrDef *createMemoryAccessBefore(Instruction *I, 218 MemoryAccess *Definition, 219 MemoryUseOrDef *InsertPt); 220 MemoryUseOrDef *createMemoryAccessAfter(Instruction *I, 221 MemoryAccess *Definition, 222 MemoryAccess *InsertPt); 223 224 /// Remove a MemoryAccess from MemorySSA, including updating all 225 /// definitions and uses. 226 /// This should be called when a memory instruction that has a MemoryAccess 227 /// associated with it is erased from the program. For example, if a store or 228 /// load is simply erased (not replaced), removeMemoryAccess should be called 229 /// on the MemoryAccess for that store/load. 230 void removeMemoryAccess(MemoryAccess *, bool OptimizePhis = false); 231 232 /// Remove MemoryAccess for a given instruction, if a MemoryAccess exists. 233 /// This should be called when an instruction (load/store) is deleted from 234 /// the program. 235 void removeMemoryAccess(const Instruction *I, bool OptimizePhis = false) { 236 if (MemoryAccess *MA = MSSA->getMemoryAccess(I)) 237 removeMemoryAccess(MA, OptimizePhis); 238 } 239 240 /// Remove all MemoryAcceses in a set of BasicBlocks about to be deleted. 241 /// Assumption we make here: all uses of deleted defs and phi must either 242 /// occur in blocks about to be deleted (thus will be deleted as well), or 243 /// they occur in phis that will simply lose an incoming value. 244 /// Deleted blocks still have successor info, but their predecessor edges and 245 /// Phi nodes may already be updated. Instructions in DeadBlocks should be 246 /// deleted after this call. 247 void removeBlocks(const SmallSetVector<BasicBlock *, 8> &DeadBlocks); 248 249 /// Instruction I will be changed to an unreachable. Remove all accesses in 250 /// I's block that follow I (inclusive), and update the Phis in the blocks' 251 /// successors. 252 void changeToUnreachable(const Instruction *I); 253 254 /// Conditional branch BI is changed or replaced with an unconditional branch 255 /// to `To`. Update Phis in BI's successors to remove BI's BB. 256 void changeCondBranchToUnconditionalTo(const BranchInst *BI, 257 const BasicBlock *To); 258 259 /// Get handle on MemorySSA. 260 MemorySSA* getMemorySSA() const { return MSSA; } 261 262 private: 263 // Move What before Where in the MemorySSA IR. 264 template <class WhereType> 265 void moveTo(MemoryUseOrDef *What, BasicBlock *BB, WhereType Where); 266 // Move all memory accesses from `From` to `To` starting at `Start`. 267 // Restrictions apply, see public wrappers of this method. 268 void moveAllAccesses(BasicBlock *From, BasicBlock *To, Instruction *Start); 269 MemoryAccess *getPreviousDef(MemoryAccess *); 270 MemoryAccess *getPreviousDefInBlock(MemoryAccess *); 271 MemoryAccess * 272 getPreviousDefFromEnd(BasicBlock *, 273 DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> &); 274 MemoryAccess * 275 getPreviousDefRecursive(BasicBlock *, 276 DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> &); 277 MemoryAccess *recursePhi(MemoryAccess *Phi); 278 MemoryAccess *tryRemoveTrivialPhi(MemoryPhi *Phi); 279 template <class RangeType> 280 MemoryAccess *tryRemoveTrivialPhi(MemoryPhi *Phi, RangeType &Operands); 281 void tryRemoveTrivialPhis(ArrayRef<WeakVH> UpdatedPHIs); 282 void fixupDefs(const SmallVectorImpl<WeakVH> &); 283 // Clone all uses and defs from BB to NewBB given a 1:1 map of all 284 // instructions and blocks cloned, and a map of MemoryPhi : Definition 285 // (MemoryAccess Phi or Def). VMap maps old instructions to cloned 286 // instructions and old blocks to cloned blocks. MPhiMap, is created in the 287 // caller of this private method, and maps existing MemoryPhis to new 288 // definitions that new MemoryAccesses must point to. These definitions may 289 // not necessarily be MemoryPhis themselves, they may be MemoryDefs. As such, 290 // the map is between MemoryPhis and MemoryAccesses, where the MemoryAccesses 291 // may be MemoryPhis or MemoryDefs and not MemoryUses. 292 // If CloneWasSimplified = true, the clone was exact. Otherwise, assume that 293 // the clone involved simplifications that may have: (1) turned a MemoryUse 294 // into an instruction that MemorySSA has no representation for, or (2) turned 295 // a MemoryDef into a MemoryUse or an instruction that MemorySSA has no 296 // representation for. No other cases are supported. 297 void cloneUsesAndDefs(BasicBlock *BB, BasicBlock *NewBB, 298 const ValueToValueMapTy &VMap, PhiToDefMap &MPhiMap, 299 bool CloneWasSimplified = false); 300 template <typename Iter> 301 void privateUpdateExitBlocksForClonedLoop(ArrayRef<BasicBlock *> ExitBlocks, 302 Iter ValuesBegin, Iter ValuesEnd, 303 DominatorTree &DT); 304 void applyInsertUpdates(ArrayRef<CFGUpdate>, DominatorTree &DT, 305 const GraphDiff<BasicBlock *> *GD); 306 }; 307 } // end namespace llvm 308 309 #endif // LLVM_ANALYSIS_MEMORYSSAUPDATER_H 310