MemoryDependenceAnalysis.h revision 4034e14985af013f71f7884fa275415a3be27778
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 26namespace 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 return MemDepResult(PairTy(Inst, Def)); 94 } 95 static MemDepResult getClobber(Instruction *Inst) { 96 return MemDepResult(PairTy(Inst, Clobber)); 97 } 98 static MemDepResult getNonLocal() { 99 return MemDepResult(PairTy(0, NonLocal)); 100 } 101 102 /// isClobber - Return true if this MemDepResult represents a query that is 103 /// a instruction clobber dependency. 104 bool isClobber() const { return Value.getInt() == Clobber; } 105 106 /// isDef - Return true if this MemDepResult represents a query that is 107 /// a instruction definition dependency. 108 bool isDef() const { return Value.getInt() == Def; } 109 110 /// isNonLocal - Return true if this MemDepResult represents a query that 111 /// is transparent to the start of the block, but where a non-local hasn't 112 /// been done. 113 bool isNonLocal() const { return Value.getInt() == NonLocal; } 114 115 /// getInst() - If this is a normal dependency, return the instruction that 116 /// is depended on. Otherwise, return null. 117 Instruction *getInst() const { return Value.getPointer(); } 118 119 bool operator==(const MemDepResult &M) const { return Value == M.Value; } 120 bool operator!=(const MemDepResult &M) const { return Value != M.Value; } 121 bool operator<(const MemDepResult &M) const { return Value < M.Value; } 122 bool operator>(const MemDepResult &M) const { return Value > M.Value; } 123 private: 124 friend class MemoryDependenceAnalysis; 125 /// Dirty - Entries with this marker occur in a LocalDeps map or 126 /// NonLocalDeps map when the instruction they previously referenced was 127 /// removed from MemDep. In either case, the entry may include an 128 /// instruction pointer. If so, the pointer is an instruction in the 129 /// block where scanning can start from, saving some work. 130 /// 131 /// In a default-constructed MemDepResult object, the type will be Dirty 132 /// and the instruction pointer will be null. 133 /// 134 135 /// isDirty - Return true if this is a MemDepResult in its dirty/invalid. 136 /// state. 137 bool isDirty() const { return Value.getInt() == Invalid; } 138 139 static MemDepResult getDirty(Instruction *Inst) { 140 return MemDepResult(PairTy(Inst, Invalid)); 141 } 142 }; 143 144 /// NonLocalDepEntry - This is an entry in the NonLocalDepInfo cache. For 145 /// each BasicBlock (the BB entry) it keeps a MemDepResult. 146 class NonLocalDepEntry { 147 BasicBlock *BB; 148 MemDepResult Result; 149 public: 150 NonLocalDepEntry(BasicBlock *bb, MemDepResult result) 151 : BB(bb), Result(result) {} 152 153 // This is used for searches. 154 NonLocalDepEntry(BasicBlock *bb) : BB(bb) {} 155 156 // BB is the sort key, it can't be changed. 157 BasicBlock *getBB() const { return BB; } 158 159 void setResult(const MemDepResult &R) { Result = R; } 160 161 const MemDepResult &getResult() const { return Result; } 162 163 bool operator<(const NonLocalDepEntry &RHS) const { 164 return BB < RHS.BB; 165 } 166 }; 167 168 /// NonLocalDepResult - This is a result from a NonLocal dependence query. 169 /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the 170 /// (potentially phi translated) address that was live in the block. 171 class NonLocalDepResult { 172 NonLocalDepEntry Entry; 173 Value *Address; 174 public: 175 NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address) 176 : Entry(bb, result), Address(address) {} 177 178 // BB is the sort key, it can't be changed. 179 BasicBlock *getBB() const { return Entry.getBB(); } 180 181 void setResult(const MemDepResult &R, Value *Addr) { 182 Entry.setResult(R); 183 Address = Addr; 184 } 185 186 const MemDepResult &getResult() const { return Entry.getResult(); } 187 188 /// getAddress - Return the address of this pointer in this block. This can 189 /// be different than the address queried for the non-local result because 190 /// of phi translation. This returns null if the address was not available 191 /// in a block (i.e. because phi translation failed) or if this is a cached 192 /// result and that address was deleted. 193 /// 194 /// The address is always null for a non-local 'call' dependence. 195 Value *getAddress() const { return Address; } 196 }; 197 198 /// MemoryDependenceAnalysis - This is an analysis that determines, for a 199 /// given memory operation, what preceding memory operations it depends on. 200 /// It builds on alias analysis information, and tries to provide a lazy, 201 /// caching interface to a common kind of alias information query. 202 /// 203 /// The dependency information returned is somewhat unusual, but is pragmatic. 204 /// If queried about a store or call that might modify memory, the analysis 205 /// will return the instruction[s] that may either load from that memory or 206 /// store to it. If queried with a load or call that can never modify memory, 207 /// the analysis will return calls and stores that might modify the pointer, 208 /// but generally does not return loads unless a) they are volatile, or 209 /// b) they load from *must-aliased* pointers. Returning a dependence on 210 /// must-alias'd pointers instead of all pointers interacts well with the 211 /// internal caching mechanism. 212 /// 213 class MemoryDependenceAnalysis : public FunctionPass { 214 // A map from instructions to their dependency. 215 typedef DenseMap<Instruction*, MemDepResult> LocalDepMapType; 216 LocalDepMapType LocalDeps; 217 218 public: 219 typedef std::vector<NonLocalDepEntry> NonLocalDepInfo; 220 private: 221 /// ValueIsLoadPair - This is a pair<Value*, bool> where the bool is true if 222 /// the dependence is a read only dependence, false if read/write. 223 typedef PointerIntPair<const Value*, 1, bool> ValueIsLoadPair; 224 225 /// BBSkipFirstBlockPair - This pair is used when caching information for a 226 /// block. If the pointer is null, the cache value is not a full query that 227 /// starts at the specified block. If non-null, the bool indicates whether 228 /// or not the contents of the block was skipped. 229 typedef PointerIntPair<BasicBlock*, 1, bool> BBSkipFirstBlockPair; 230 231 /// NonLocalPointerInfo - This record is the information kept for each 232 /// (value, is load) pair. 233 struct NonLocalPointerInfo { 234 /// Pair - The pair of the block and the skip-first-block flag. 235 BBSkipFirstBlockPair Pair; 236 /// NonLocalDeps - The results of the query for each relevant block. 237 NonLocalDepInfo NonLocalDeps; 238 /// Size - The maximum size of the dereferences of the 239 /// pointer. May be UnknownSize if the sizes are unknown. 240 uint64_t Size; 241 /// TBAATag - The TBAA tag associated with dereferences of the 242 /// pointer. May be null if there are no tags or conflicting tags. 243 const MDNode *TBAATag; 244 245 NonLocalPointerInfo() : Size(AliasAnalysis::UnknownSize), TBAATag(0) {} 246 }; 247 248 /// CachedNonLocalPointerInfo - This map stores the cached results of doing 249 /// a pointer lookup at the bottom of a block. The key of this map is the 250 /// pointer+isload bit, the value is a list of <bb->result> mappings. 251 typedef DenseMap<ValueIsLoadPair, 252 NonLocalPointerInfo> CachedNonLocalPointerInfo; 253 CachedNonLocalPointerInfo NonLocalPointerDeps; 254 255 // A map from instructions to their non-local pointer dependencies. 256 typedef DenseMap<Instruction*, 257 SmallPtrSet<ValueIsLoadPair, 4> > ReverseNonLocalPtrDepTy; 258 ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps; 259 260 261 /// PerInstNLInfo - This is the instruction we keep for each cached access 262 /// that we have for an instruction. The pointer is an owning pointer and 263 /// the bool indicates whether we have any dirty bits in the set. 264 typedef std::pair<NonLocalDepInfo, bool> PerInstNLInfo; 265 266 // A map from instructions to their non-local dependencies. 267 typedef DenseMap<Instruction*, PerInstNLInfo> NonLocalDepMapType; 268 269 NonLocalDepMapType NonLocalDeps; 270 271 // A reverse mapping from dependencies to the dependees. This is 272 // used when removing instructions to keep the cache coherent. 273 typedef DenseMap<Instruction*, 274 SmallPtrSet<Instruction*, 4> > ReverseDepMapType; 275 ReverseDepMapType ReverseLocalDeps; 276 277 // A reverse mapping from dependencies to the non-local dependees. 278 ReverseDepMapType ReverseNonLocalDeps; 279 280 /// Current AA implementation, just a cache. 281 AliasAnalysis *AA; 282 TargetData *TD; 283 OwningPtr<PredIteratorCache> PredCache; 284 public: 285 MemoryDependenceAnalysis(); 286 ~MemoryDependenceAnalysis(); 287 static char ID; 288 289 /// Pass Implementation stuff. This doesn't do any analysis eagerly. 290 bool runOnFunction(Function &); 291 292 /// Clean up memory in between runs 293 void releaseMemory(); 294 295 /// getAnalysisUsage - Does not modify anything. It uses Value Numbering 296 /// and Alias Analysis. 297 /// 298 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 299 300 /// getDependency - Return the instruction on which a memory operation 301 /// depends. See the class comment for more details. It is illegal to call 302 /// this on non-memory instructions. 303 MemDepResult getDependency(Instruction *QueryInst); 304 305 /// getNonLocalCallDependency - Perform a full dependency query for the 306 /// specified call, returning the set of blocks that the value is 307 /// potentially live across. The returned set of results will include a 308 /// "NonLocal" result for all blocks where the value is live across. 309 /// 310 /// This method assumes the instruction returns a "NonLocal" dependency 311 /// within its own block. 312 /// 313 /// This returns a reference to an internal data structure that may be 314 /// invalidated on the next non-local query or when an instruction is 315 /// removed. Clients must copy this data if they want it around longer than 316 /// that. 317 const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS); 318 319 320 /// getNonLocalPointerDependency - Perform a full dependency query for an 321 /// access to the specified (non-volatile) memory location, returning the 322 /// set of instructions that either define or clobber the value. 323 /// 324 /// This method assumes the pointer has a "NonLocal" dependency within BB. 325 void getNonLocalPointerDependency(const AliasAnalysis::Location &Loc, 326 bool isLoad, BasicBlock *BB, 327 SmallVectorImpl<NonLocalDepResult> &Result); 328 329 /// removeInstruction - Remove an instruction from the dependence analysis, 330 /// updating the dependence of instructions that previously depended on it. 331 void removeInstruction(Instruction *InstToRemove); 332 333 /// invalidateCachedPointerInfo - This method is used to invalidate cached 334 /// information about the specified pointer, because it may be too 335 /// conservative in memdep. This is an optional call that can be used when 336 /// the client detects an equivalence between the pointer and some other 337 /// value and replaces the other value with ptr. This can make Ptr available 338 /// in more places that cached info does not necessarily keep. 339 void invalidateCachedPointerInfo(Value *Ptr); 340 341 /// invalidateCachedPredecessors - Clear the PredIteratorCache info. 342 /// This needs to be done when the CFG changes, e.g., due to splitting 343 /// critical edges. 344 void invalidateCachedPredecessors(); 345 346 /// getPointerDependencyFrom - Return the instruction on which a memory 347 /// location depends. If isLoad is true, this routine ignores may-aliases 348 /// with read-only operations. If isLoad is false, this routine ignores 349 /// may-aliases with reads from read-only locations. 350 /// 351 /// Note that this is an uncached query, and thus may be inefficient. 352 /// 353 MemDepResult getPointerDependencyFrom(const AliasAnalysis::Location &Loc, 354 bool isLoad, 355 BasicBlock::iterator ScanIt, 356 BasicBlock *BB); 357 358 359 /// getLoadLoadClobberFullWidthSize - This is a little bit of analysis that 360 /// looks at a memory location for a load (specified by MemLocBase, Offs, 361 /// and Size) and compares it against a load. If the specified load could 362 /// be safely widened to a larger integer load that is 1) still efficient, 363 /// 2) safe for the target, and 3) would provide the specified memory 364 /// location value, then this function returns the size in bytes of the 365 /// load width to use. If not, this returns zero. 366 static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase, 367 int64_t MemLocOffs, 368 unsigned MemLocSize, 369 const LoadInst *LI, 370 const TargetData &TD); 371 372 private: 373 MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall, 374 BasicBlock::iterator ScanIt, 375 BasicBlock *BB); 376 bool getNonLocalPointerDepFromBB(const PHITransAddr &Pointer, 377 const AliasAnalysis::Location &Loc, 378 bool isLoad, BasicBlock *BB, 379 SmallVectorImpl<NonLocalDepResult> &Result, 380 DenseMap<BasicBlock*, Value*> &Visited, 381 bool SkipFirstBlock = false); 382 MemDepResult GetNonLocalInfoForBlock(const AliasAnalysis::Location &Loc, 383 bool isLoad, BasicBlock *BB, 384 NonLocalDepInfo *Cache, 385 unsigned NumSortedEntries); 386 387 void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P); 388 389 /// verifyRemoved - Verify that the specified instruction does not occur 390 /// in our internal data structures. 391 void verifyRemoved(Instruction *Inst) const; 392 393 }; 394 395} // End llvm namespace 396 397#endif 398