1 //===- llvm/Analysis/MemoryDependenceAnalysis.h - Memory Deps --*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file defines the MemoryDependenceAnalysis analysis pass. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_ANALYSIS_MEMORY_DEPENDENCE_H 15 #define LLVM_ANALYSIS_MEMORY_DEPENDENCE_H 16 17 #include "llvm/BasicBlock.h" 18 #include "llvm/Pass.h" 19 #include "llvm/Support/ValueHandle.h" 20 #include "llvm/Analysis/AliasAnalysis.h" 21 #include "llvm/ADT/DenseMap.h" 22 #include "llvm/ADT/SmallPtrSet.h" 23 #include "llvm/ADT/OwningPtr.h" 24 #include "llvm/ADT/PointerIntPair.h" 25 26 namespace llvm { 27 class Function; 28 class FunctionPass; 29 class Instruction; 30 class CallSite; 31 class AliasAnalysis; 32 class TargetData; 33 class MemoryDependenceAnalysis; 34 class PredIteratorCache; 35 class DominatorTree; 36 class PHITransAddr; 37 38 /// MemDepResult - A memory dependence query can return one of three different 39 /// answers, described below. 40 class MemDepResult { 41 enum DepType { 42 /// Invalid - Clients of MemDep never see this. 43 Invalid = 0, 44 45 /// Clobber - This is a dependence on the specified instruction which 46 /// clobbers the desired value. The pointer member of the MemDepResult 47 /// pair holds the instruction that clobbers the memory. For example, 48 /// this occurs when we see a may-aliased store to the memory location we 49 /// care about. 50 /// 51 /// There are several cases that may be interesting here: 52 /// 1. Loads are clobbered by may-alias stores. 53 /// 2. Loads are considered clobbered by partially-aliased loads. The 54 /// client may choose to analyze deeper into these cases. 55 /// 56 /// A dependence query on the first instruction of the entry block will 57 /// return a clobber(self) result. 58 Clobber, 59 60 /// Def - This is a dependence on the specified instruction which 61 /// defines/produces the desired memory location. The pointer member of 62 /// the MemDepResult pair holds the instruction that defines the memory. 63 /// Cases of interest: 64 /// 1. This could be a load or store for dependence queries on 65 /// load/store. The value loaded or stored is the produced value. 66 /// Note that the pointer operand may be different than that of the 67 /// queried pointer due to must aliases and phi translation. Note 68 /// that the def may not be the same type as the query, the pointers 69 /// may just be must aliases. 70 /// 2. For loads and stores, this could be an allocation instruction. In 71 /// this case, the load is loading an undef value or a store is the 72 /// first store to (that part of) the allocation. 73 /// 3. Dependence queries on calls return Def only when they are 74 /// readonly calls or memory use intrinsics with identical callees 75 /// and no intervening clobbers. No validation is done that the 76 /// operands to the calls are the same. 77 Def, 78 79 /// NonLocal - This marker indicates that the query has no dependency in 80 /// the specified block. To find out more, the client should query other 81 /// predecessor blocks. 82 NonLocal 83 }; 84 typedef PointerIntPair<Instruction*, 2, DepType> PairTy; 85 PairTy Value; 86 explicit MemDepResult(PairTy V) : Value(V) {} 87 public: 88 MemDepResult() : Value(0, Invalid) {} 89 90 /// get methods: These are static ctor methods for creating various 91 /// MemDepResult kinds. 92 static MemDepResult getDef(Instruction *Inst) { 93 assert(Inst && "Def requires inst"); 94 return MemDepResult(PairTy(Inst, Def)); 95 } 96 static MemDepResult getClobber(Instruction *Inst) { 97 assert(Inst && "Clobber requires inst"); 98 return MemDepResult(PairTy(Inst, Clobber)); 99 } 100 static MemDepResult getNonLocal() { 101 return MemDepResult(PairTy(0, NonLocal)); 102 } 103 static MemDepResult getUnknown() { 104 return MemDepResult(PairTy(0, Clobber)); 105 } 106 107 /// isClobber - Return true if this MemDepResult represents a query that is 108 /// a instruction clobber dependency. 109 bool isClobber() const { return Value.getInt() == Clobber && getInst(); } 110 111 /// isUnknown - Return true if this MemDepResult represents a query which 112 /// cannot and/or will not be computed. 113 bool isUnknown() const { return Value.getInt() == Clobber && !getInst(); } 114 115 /// isDef - Return true if this MemDepResult represents a query that is 116 /// a instruction definition dependency. 117 bool isDef() const { return Value.getInt() == Def; } 118 119 /// isNonLocal - Return true if this MemDepResult represents a query that 120 /// is transparent to the start of the block, but where a non-local hasn't 121 /// been done. 122 bool isNonLocal() const { return Value.getInt() == NonLocal; } 123 124 /// getInst() - If this is a normal dependency, return the instruction that 125 /// is depended on. Otherwise, return null. 126 Instruction *getInst() const { return Value.getPointer(); } 127 128 bool operator==(const MemDepResult &M) const { return Value == M.Value; } 129 bool operator!=(const MemDepResult &M) const { return Value != M.Value; } 130 bool operator<(const MemDepResult &M) const { return Value < M.Value; } 131 bool operator>(const MemDepResult &M) const { return Value > M.Value; } 132 private: 133 friend class MemoryDependenceAnalysis; 134 /// Dirty - Entries with this marker occur in a LocalDeps map or 135 /// NonLocalDeps map when the instruction they previously referenced was 136 /// removed from MemDep. In either case, the entry may include an 137 /// instruction pointer. If so, the pointer is an instruction in the 138 /// block where scanning can start from, saving some work. 139 /// 140 /// In a default-constructed MemDepResult object, the type will be Dirty 141 /// and the instruction pointer will be null. 142 /// 143 144 /// isDirty - Return true if this is a MemDepResult in its dirty/invalid. 145 /// state. 146 bool isDirty() const { return Value.getInt() == Invalid; } 147 148 static MemDepResult getDirty(Instruction *Inst) { 149 return MemDepResult(PairTy(Inst, Invalid)); 150 } 151 }; 152 153 /// NonLocalDepEntry - This is an entry in the NonLocalDepInfo cache. For 154 /// each BasicBlock (the BB entry) it keeps a MemDepResult. 155 class NonLocalDepEntry { 156 BasicBlock *BB; 157 MemDepResult Result; 158 public: 159 NonLocalDepEntry(BasicBlock *bb, MemDepResult result) 160 : BB(bb), Result(result) {} 161 162 // This is used for searches. 163 NonLocalDepEntry(BasicBlock *bb) : BB(bb) {} 164 165 // BB is the sort key, it can't be changed. 166 BasicBlock *getBB() const { return BB; } 167 168 void setResult(const MemDepResult &R) { Result = R; } 169 170 const MemDepResult &getResult() const { return Result; } 171 172 bool operator<(const NonLocalDepEntry &RHS) const { 173 return BB < RHS.BB; 174 } 175 }; 176 177 /// NonLocalDepResult - This is a result from a NonLocal dependence query. 178 /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the 179 /// (potentially phi translated) address that was live in the block. 180 class NonLocalDepResult { 181 NonLocalDepEntry Entry; 182 Value *Address; 183 public: 184 NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address) 185 : Entry(bb, result), Address(address) {} 186 187 // BB is the sort key, it can't be changed. 188 BasicBlock *getBB() const { return Entry.getBB(); } 189 190 void setResult(const MemDepResult &R, Value *Addr) { 191 Entry.setResult(R); 192 Address = Addr; 193 } 194 195 const MemDepResult &getResult() const { return Entry.getResult(); } 196 197 /// getAddress - Return the address of this pointer in this block. This can 198 /// be different than the address queried for the non-local result because 199 /// of phi translation. This returns null if the address was not available 200 /// in a block (i.e. because phi translation failed) or if this is a cached 201 /// result and that address was deleted. 202 /// 203 /// The address is always null for a non-local 'call' dependence. 204 Value *getAddress() const { return Address; } 205 }; 206 207 /// MemoryDependenceAnalysis - This is an analysis that determines, for a 208 /// given memory operation, what preceding memory operations it depends on. 209 /// It builds on alias analysis information, and tries to provide a lazy, 210 /// caching interface to a common kind of alias information query. 211 /// 212 /// The dependency information returned is somewhat unusual, but is pragmatic. 213 /// If queried about a store or call that might modify memory, the analysis 214 /// will return the instruction[s] that may either load from that memory or 215 /// store to it. If queried with a load or call that can never modify memory, 216 /// the analysis will return calls and stores that might modify the pointer, 217 /// but generally does not return loads unless a) they are volatile, or 218 /// b) they load from *must-aliased* pointers. Returning a dependence on 219 /// must-alias'd pointers instead of all pointers interacts well with the 220 /// internal caching mechanism. 221 /// 222 class MemoryDependenceAnalysis : public FunctionPass { 223 // A map from instructions to their dependency. 224 typedef DenseMap<Instruction*, MemDepResult> LocalDepMapType; 225 LocalDepMapType LocalDeps; 226 227 public: 228 typedef std::vector<NonLocalDepEntry> NonLocalDepInfo; 229 private: 230 /// ValueIsLoadPair - This is a pair<Value*, bool> where the bool is true if 231 /// the dependence is a read only dependence, false if read/write. 232 typedef PointerIntPair<const Value*, 1, bool> ValueIsLoadPair; 233 234 /// BBSkipFirstBlockPair - This pair is used when caching information for a 235 /// block. If the pointer is null, the cache value is not a full query that 236 /// starts at the specified block. If non-null, the bool indicates whether 237 /// or not the contents of the block was skipped. 238 typedef PointerIntPair<BasicBlock*, 1, bool> BBSkipFirstBlockPair; 239 240 /// NonLocalPointerInfo - This record is the information kept for each 241 /// (value, is load) pair. 242 struct NonLocalPointerInfo { 243 /// Pair - The pair of the block and the skip-first-block flag. 244 BBSkipFirstBlockPair Pair; 245 /// NonLocalDeps - The results of the query for each relevant block. 246 NonLocalDepInfo NonLocalDeps; 247 /// Size - The maximum size of the dereferences of the 248 /// pointer. May be UnknownSize if the sizes are unknown. 249 uint64_t Size; 250 /// TBAATag - The TBAA tag associated with dereferences of the 251 /// pointer. May be null if there are no tags or conflicting tags. 252 const MDNode *TBAATag; 253 254 NonLocalPointerInfo() : Size(AliasAnalysis::UnknownSize), TBAATag(0) {} 255 }; 256 257 /// CachedNonLocalPointerInfo - This map stores the cached results of doing 258 /// a pointer lookup at the bottom of a block. The key of this map is the 259 /// pointer+isload bit, the value is a list of <bb->result> mappings. 260 typedef DenseMap<ValueIsLoadPair, 261 NonLocalPointerInfo> CachedNonLocalPointerInfo; 262 CachedNonLocalPointerInfo NonLocalPointerDeps; 263 264 // A map from instructions to their non-local pointer dependencies. 265 typedef DenseMap<Instruction*, 266 SmallPtrSet<ValueIsLoadPair, 4> > ReverseNonLocalPtrDepTy; 267 ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps; 268 269 270 /// PerInstNLInfo - This is the instruction we keep for each cached access 271 /// that we have for an instruction. The pointer is an owning pointer and 272 /// the bool indicates whether we have any dirty bits in the set. 273 typedef std::pair<NonLocalDepInfo, bool> PerInstNLInfo; 274 275 // A map from instructions to their non-local dependencies. 276 typedef DenseMap<Instruction*, PerInstNLInfo> NonLocalDepMapType; 277 278 NonLocalDepMapType NonLocalDeps; 279 280 // A reverse mapping from dependencies to the dependees. This is 281 // used when removing instructions to keep the cache coherent. 282 typedef DenseMap<Instruction*, 283 SmallPtrSet<Instruction*, 4> > ReverseDepMapType; 284 ReverseDepMapType ReverseLocalDeps; 285 286 // A reverse mapping from dependencies to the non-local dependees. 287 ReverseDepMapType ReverseNonLocalDeps; 288 289 /// Current AA implementation, just a cache. 290 AliasAnalysis *AA; 291 TargetData *TD; 292 OwningPtr<PredIteratorCache> PredCache; 293 public: 294 MemoryDependenceAnalysis(); 295 ~MemoryDependenceAnalysis(); 296 static char ID; 297 298 /// Pass Implementation stuff. This doesn't do any analysis eagerly. 299 bool runOnFunction(Function &); 300 301 /// Clean up memory in between runs 302 void releaseMemory(); 303 304 /// getAnalysisUsage - Does not modify anything. It uses Value Numbering 305 /// and Alias Analysis. 306 /// 307 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 308 309 /// getDependency - Return the instruction on which a memory operation 310 /// depends. See the class comment for more details. It is illegal to call 311 /// this on non-memory instructions. 312 MemDepResult getDependency(Instruction *QueryInst); 313 314 /// getNonLocalCallDependency - Perform a full dependency query for the 315 /// specified call, returning the set of blocks that the value is 316 /// potentially live across. The returned set of results will include a 317 /// "NonLocal" result for all blocks where the value is live across. 318 /// 319 /// This method assumes the instruction returns a "NonLocal" dependency 320 /// within its own block. 321 /// 322 /// This returns a reference to an internal data structure that may be 323 /// invalidated on the next non-local query or when an instruction is 324 /// removed. Clients must copy this data if they want it around longer than 325 /// that. 326 const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS); 327 328 329 /// getNonLocalPointerDependency - Perform a full dependency query for an 330 /// access to the specified (non-volatile) memory location, returning the 331 /// set of instructions that either define or clobber the value. 332 /// 333 /// This method assumes the pointer has a "NonLocal" dependency within BB. 334 void getNonLocalPointerDependency(const AliasAnalysis::Location &Loc, 335 bool isLoad, BasicBlock *BB, 336 SmallVectorImpl<NonLocalDepResult> &Result); 337 338 /// removeInstruction - Remove an instruction from the dependence analysis, 339 /// updating the dependence of instructions that previously depended on it. 340 void removeInstruction(Instruction *InstToRemove); 341 342 /// invalidateCachedPointerInfo - This method is used to invalidate cached 343 /// information about the specified pointer, because it may be too 344 /// conservative in memdep. This is an optional call that can be used when 345 /// the client detects an equivalence between the pointer and some other 346 /// value and replaces the other value with ptr. This can make Ptr available 347 /// in more places that cached info does not necessarily keep. 348 void invalidateCachedPointerInfo(Value *Ptr); 349 350 /// invalidateCachedPredecessors - Clear the PredIteratorCache info. 351 /// This needs to be done when the CFG changes, e.g., due to splitting 352 /// critical edges. 353 void invalidateCachedPredecessors(); 354 355 /// getPointerDependencyFrom - Return the instruction on which a memory 356 /// location depends. If isLoad is true, this routine ignores may-aliases 357 /// with read-only operations. If isLoad is false, this routine ignores 358 /// may-aliases with reads from read-only locations. 359 /// 360 /// Note that this is an uncached query, and thus may be inefficient. 361 /// 362 MemDepResult getPointerDependencyFrom(const AliasAnalysis::Location &Loc, 363 bool isLoad, 364 BasicBlock::iterator ScanIt, 365 BasicBlock *BB); 366 367 368 /// getLoadLoadClobberFullWidthSize - This is a little bit of analysis that 369 /// looks at a memory location for a load (specified by MemLocBase, Offs, 370 /// and Size) and compares it against a load. If the specified load could 371 /// be safely widened to a larger integer load that is 1) still efficient, 372 /// 2) safe for the target, and 3) would provide the specified memory 373 /// location value, then this function returns the size in bytes of the 374 /// load width to use. If not, this returns zero. 375 static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase, 376 int64_t MemLocOffs, 377 unsigned MemLocSize, 378 const LoadInst *LI, 379 const TargetData &TD); 380 381 private: 382 MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall, 383 BasicBlock::iterator ScanIt, 384 BasicBlock *BB); 385 bool getNonLocalPointerDepFromBB(const PHITransAddr &Pointer, 386 const AliasAnalysis::Location &Loc, 387 bool isLoad, BasicBlock *BB, 388 SmallVectorImpl<NonLocalDepResult> &Result, 389 DenseMap<BasicBlock*, Value*> &Visited, 390 bool SkipFirstBlock = false); 391 MemDepResult GetNonLocalInfoForBlock(const AliasAnalysis::Location &Loc, 392 bool isLoad, BasicBlock *BB, 393 NonLocalDepInfo *Cache, 394 unsigned NumSortedEntries); 395 396 void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P); 397 398 /// verifyRemoved - Verify that the specified instruction does not occur 399 /// in our internal data structures. 400 void verifyRemoved(Instruction *Inst) const; 401 402 }; 403 404 } // End llvm namespace 405 406 #endif 407
