1 //===- llvm/Analysis/MemoryDependenceAnalysis.h - Memory Deps --*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the MemoryDependenceAnalysis analysis pass.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_ANALYSIS_MEMORYDEPENDENCEANALYSIS_H
15 #define LLVM_ANALYSIS_MEMORYDEPENDENCEANALYSIS_H
17 #include "llvm/ADT/DenseMap.h"
18 #include "llvm/ADT/PointerIntPair.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/Analysis/AliasAnalysis.h"
21 #include "llvm/IR/BasicBlock.h"
22 #include "llvm/IR/ValueHandle.h"
23 #include "llvm/Pass.h"
32 class MemoryDependenceAnalysis;
33 class PredIteratorCache;
37 /// MemDepResult - A memory dependence query can return one of three different
38 /// answers, described below.
41 /// Invalid - Clients of MemDep never see this.
44 /// Clobber - This is a dependence on the specified instruction which
45 /// clobbers the desired value. The pointer member of the MemDepResult
46 /// pair holds the instruction that clobbers the memory. For example,
47 /// this occurs when we see a may-aliased store to the memory location we
50 /// There are several cases that may be interesting here:
51 /// 1. Loads are clobbered by may-alias stores.
52 /// 2. Loads are considered clobbered by partially-aliased loads. The
53 /// client may choose to analyze deeper into these cases.
56 /// Def - This is a dependence on the specified instruction which
57 /// defines/produces the desired memory location. The pointer member of
58 /// the MemDepResult pair holds the instruction that defines the memory.
59 /// Cases of interest:
60 /// 1. This could be a load or store for dependence queries on
61 /// load/store. The value loaded or stored is the produced value.
62 /// Note that the pointer operand may be different than that of the
63 /// queried pointer due to must aliases and phi translation. Note
64 /// that the def may not be the same type as the query, the pointers
65 /// may just be must aliases.
66 /// 2. For loads and stores, this could be an allocation instruction. In
67 /// this case, the load is loading an undef value or a store is the
68 /// first store to (that part of) the allocation.
69 /// 3. Dependence queries on calls return Def only when they are
70 /// readonly calls or memory use intrinsics with identical callees
71 /// and no intervening clobbers. No validation is done that the
72 /// operands to the calls are the same.
75 /// Other - This marker indicates that the query has no known dependency
76 /// in the specified block. More detailed state info is encoded in the
77 /// upper part of the pair (i.e. the Instruction*)
80 /// If DepType is "Other", the upper part of the pair
81 /// (i.e. the Instruction* part) is instead used to encode more detailed
82 /// type information as follows
84 /// NonLocal - This marker indicates that the query has no dependency in
85 /// the specified block. To find out more, the client should query other
86 /// predecessor blocks.
88 /// NonFuncLocal - This marker indicates that the query has no
89 /// dependency in the specified function.
91 /// Unknown - This marker indicates that the query dependency
96 typedef PointerIntPair<Instruction*, 2, DepType> PairTy;
98 explicit MemDepResult(PairTy V) : Value(V) {}
100 MemDepResult() : Value(nullptr, Invalid) {}
102 /// get methods: These are static ctor methods for creating various
103 /// MemDepResult kinds.
104 static MemDepResult getDef(Instruction *Inst) {
105 assert(Inst && "Def requires inst");
106 return MemDepResult(PairTy(Inst, Def));
108 static MemDepResult getClobber(Instruction *Inst) {
109 assert(Inst && "Clobber requires inst");
110 return MemDepResult(PairTy(Inst, Clobber));
112 static MemDepResult getNonLocal() {
114 PairTy(reinterpret_cast<Instruction*>(NonLocal), Other));
116 static MemDepResult getNonFuncLocal() {
118 PairTy(reinterpret_cast<Instruction*>(NonFuncLocal), Other));
120 static MemDepResult getUnknown() {
122 PairTy(reinterpret_cast<Instruction*>(Unknown), Other));
125 /// isClobber - Return true if this MemDepResult represents a query that is
126 /// an instruction clobber dependency.
127 bool isClobber() const { return Value.getInt() == Clobber; }
129 /// isDef - Return true if this MemDepResult represents a query that is
130 /// an instruction definition dependency.
131 bool isDef() const { return Value.getInt() == Def; }
133 /// isNonLocal - Return true if this MemDepResult represents a query that
134 /// is transparent to the start of the block, but where a non-local hasn't
136 bool isNonLocal() const {
137 return Value.getInt() == Other
138 && Value.getPointer() == reinterpret_cast<Instruction*>(NonLocal);
141 /// isNonFuncLocal - Return true if this MemDepResult represents a query
142 /// that is transparent to the start of the function.
143 bool isNonFuncLocal() const {
144 return Value.getInt() == Other
145 && Value.getPointer() == reinterpret_cast<Instruction*>(NonFuncLocal);
148 /// isUnknown - Return true if this MemDepResult represents a query which
149 /// cannot and/or will not be computed.
150 bool isUnknown() const {
151 return Value.getInt() == Other
152 && Value.getPointer() == reinterpret_cast<Instruction*>(Unknown);
155 /// getInst() - If this is a normal dependency, return the instruction that
156 /// is depended on. Otherwise, return null.
157 Instruction *getInst() const {
158 if (Value.getInt() == Other) return nullptr;
159 return Value.getPointer();
162 bool operator==(const MemDepResult &M) const { return Value == M.Value; }
163 bool operator!=(const MemDepResult &M) const { return Value != M.Value; }
164 bool operator<(const MemDepResult &M) const { return Value < M.Value; }
165 bool operator>(const MemDepResult &M) const { return Value > M.Value; }
167 friend class MemoryDependenceAnalysis;
168 /// Dirty - Entries with this marker occur in a LocalDeps map or
169 /// NonLocalDeps map when the instruction they previously referenced was
170 /// removed from MemDep. In either case, the entry may include an
171 /// instruction pointer. If so, the pointer is an instruction in the
172 /// block where scanning can start from, saving some work.
174 /// In a default-constructed MemDepResult object, the type will be Dirty
175 /// and the instruction pointer will be null.
178 /// isDirty - Return true if this is a MemDepResult in its dirty/invalid.
180 bool isDirty() const { return Value.getInt() == Invalid; }
182 static MemDepResult getDirty(Instruction *Inst) {
183 return MemDepResult(PairTy(Inst, Invalid));
187 /// NonLocalDepEntry - This is an entry in the NonLocalDepInfo cache. For
188 /// each BasicBlock (the BB entry) it keeps a MemDepResult.
189 class NonLocalDepEntry {
193 NonLocalDepEntry(BasicBlock *bb, MemDepResult result)
194 : BB(bb), Result(result) {}
196 // This is used for searches.
197 NonLocalDepEntry(BasicBlock *bb) : BB(bb) {}
199 // BB is the sort key, it can't be changed.
200 BasicBlock *getBB() const { return BB; }
202 void setResult(const MemDepResult &R) { Result = R; }
204 const MemDepResult &getResult() const { return Result; }
206 bool operator<(const NonLocalDepEntry &RHS) const {
211 /// NonLocalDepResult - This is a result from a NonLocal dependence query.
212 /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the
213 /// (potentially phi translated) address that was live in the block.
214 class NonLocalDepResult {
215 NonLocalDepEntry Entry;
218 NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address)
219 : Entry(bb, result), Address(address) {}
221 // BB is the sort key, it can't be changed.
222 BasicBlock *getBB() const { return Entry.getBB(); }
224 void setResult(const MemDepResult &R, Value *Addr) {
229 const MemDepResult &getResult() const { return Entry.getResult(); }
231 /// getAddress - Return the address of this pointer in this block. This can
232 /// be different than the address queried for the non-local result because
233 /// of phi translation. This returns null if the address was not available
234 /// in a block (i.e. because phi translation failed) or if this is a cached
235 /// result and that address was deleted.
237 /// The address is always null for a non-local 'call' dependence.
238 Value *getAddress() const { return Address; }
241 /// MemoryDependenceAnalysis - This is an analysis that determines, for a
242 /// given memory operation, what preceding memory operations it depends on.
243 /// It builds on alias analysis information, and tries to provide a lazy,
244 /// caching interface to a common kind of alias information query.
246 /// The dependency information returned is somewhat unusual, but is pragmatic.
247 /// If queried about a store or call that might modify memory, the analysis
248 /// will return the instruction[s] that may either load from that memory or
249 /// store to it. If queried with a load or call that can never modify memory,
250 /// the analysis will return calls and stores that might modify the pointer,
251 /// but generally does not return loads unless a) they are volatile, or
252 /// b) they load from *must-aliased* pointers. Returning a dependence on
253 /// must-alias'd pointers instead of all pointers interacts well with the
254 /// internal caching mechanism.
256 class MemoryDependenceAnalysis : public FunctionPass {
257 // A map from instructions to their dependency.
258 typedef DenseMap<Instruction*, MemDepResult> LocalDepMapType;
259 LocalDepMapType LocalDeps;
262 typedef std::vector<NonLocalDepEntry> NonLocalDepInfo;
264 /// ValueIsLoadPair - This is a pair<Value*, bool> where the bool is true if
265 /// the dependence is a read only dependence, false if read/write.
266 typedef PointerIntPair<const Value*, 1, bool> ValueIsLoadPair;
268 /// BBSkipFirstBlockPair - This pair is used when caching information for a
269 /// block. If the pointer is null, the cache value is not a full query that
270 /// starts at the specified block. If non-null, the bool indicates whether
271 /// or not the contents of the block was skipped.
272 typedef PointerIntPair<BasicBlock*, 1, bool> BBSkipFirstBlockPair;
274 /// NonLocalPointerInfo - This record is the information kept for each
275 /// (value, is load) pair.
276 struct NonLocalPointerInfo {
277 /// Pair - The pair of the block and the skip-first-block flag.
278 BBSkipFirstBlockPair Pair;
279 /// NonLocalDeps - The results of the query for each relevant block.
280 NonLocalDepInfo NonLocalDeps;
281 /// Size - The maximum size of the dereferences of the
282 /// pointer. May be UnknownSize if the sizes are unknown.
284 /// TBAATag - The TBAA tag associated with dereferences of the
285 /// pointer. May be null if there are no tags or conflicting tags.
286 const MDNode *TBAATag;
288 NonLocalPointerInfo()
289 : Size(AliasAnalysis::UnknownSize), TBAATag(nullptr) {}
292 /// CachedNonLocalPointerInfo - This map stores the cached results of doing
293 /// a pointer lookup at the bottom of a block. The key of this map is the
294 /// pointer+isload bit, the value is a list of <bb->result> mappings.
295 typedef DenseMap<ValueIsLoadPair,
296 NonLocalPointerInfo> CachedNonLocalPointerInfo;
297 CachedNonLocalPointerInfo NonLocalPointerDeps;
299 // A map from instructions to their non-local pointer dependencies.
300 typedef DenseMap<Instruction*,
301 SmallPtrSet<ValueIsLoadPair, 4> > ReverseNonLocalPtrDepTy;
302 ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps;
305 /// PerInstNLInfo - This is the instruction we keep for each cached access
306 /// that we have for an instruction. The pointer is an owning pointer and
307 /// the bool indicates whether we have any dirty bits in the set.
308 typedef std::pair<NonLocalDepInfo, bool> PerInstNLInfo;
310 // A map from instructions to their non-local dependencies.
311 typedef DenseMap<Instruction*, PerInstNLInfo> NonLocalDepMapType;
313 NonLocalDepMapType NonLocalDeps;
315 // A reverse mapping from dependencies to the dependees. This is
316 // used when removing instructions to keep the cache coherent.
317 typedef DenseMap<Instruction*,
318 SmallPtrSet<Instruction*, 4> > ReverseDepMapType;
319 ReverseDepMapType ReverseLocalDeps;
321 // A reverse mapping from dependencies to the non-local dependees.
322 ReverseDepMapType ReverseNonLocalDeps;
324 /// Current AA implementation, just a cache.
326 const DataLayout *DL;
328 std::unique_ptr<PredIteratorCache> PredCache;
331 MemoryDependenceAnalysis();
332 ~MemoryDependenceAnalysis();
335 /// Pass Implementation stuff. This doesn't do any analysis eagerly.
336 bool runOnFunction(Function &) override;
338 /// Clean up memory in between runs
339 void releaseMemory() override;
341 /// getAnalysisUsage - Does not modify anything. It uses Value Numbering
342 /// and Alias Analysis.
344 void getAnalysisUsage(AnalysisUsage &AU) const override;
346 /// getDependency - Return the instruction on which a memory operation
347 /// depends. See the class comment for more details. It is illegal to call
348 /// this on non-memory instructions.
349 MemDepResult getDependency(Instruction *QueryInst);
351 /// getNonLocalCallDependency - Perform a full dependency query for the
352 /// specified call, returning the set of blocks that the value is
353 /// potentially live across. The returned set of results will include a
354 /// "NonLocal" result for all blocks where the value is live across.
356 /// This method assumes the instruction returns a "NonLocal" dependency
357 /// within its own block.
359 /// This returns a reference to an internal data structure that may be
360 /// invalidated on the next non-local query or when an instruction is
361 /// removed. Clients must copy this data if they want it around longer than
363 const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS);
366 /// getNonLocalPointerDependency - Perform a full dependency query for an
367 /// access to the specified (non-volatile) memory location, returning the
368 /// set of instructions that either define or clobber the value.
370 /// This method assumes the pointer has a "NonLocal" dependency within BB.
371 void getNonLocalPointerDependency(const AliasAnalysis::Location &Loc,
372 bool isLoad, BasicBlock *BB,
373 SmallVectorImpl<NonLocalDepResult> &Result);
375 /// removeInstruction - Remove an instruction from the dependence analysis,
376 /// updating the dependence of instructions that previously depended on it.
377 void removeInstruction(Instruction *InstToRemove);
379 /// invalidateCachedPointerInfo - This method is used to invalidate cached
380 /// information about the specified pointer, because it may be too
381 /// conservative in memdep. This is an optional call that can be used when
382 /// the client detects an equivalence between the pointer and some other
383 /// value and replaces the other value with ptr. This can make Ptr available
384 /// in more places that cached info does not necessarily keep.
385 void invalidateCachedPointerInfo(Value *Ptr);
387 /// invalidateCachedPredecessors - Clear the PredIteratorCache info.
388 /// This needs to be done when the CFG changes, e.g., due to splitting
390 void invalidateCachedPredecessors();
392 /// getPointerDependencyFrom - Return the instruction on which a memory
393 /// location depends. If isLoad is true, this routine ignores may-aliases
394 /// with read-only operations. If isLoad is false, this routine ignores
395 /// may-aliases with reads from read-only locations. If possible, pass
396 /// the query instruction as well; this function may take advantage of
397 /// the metadata annotated to the query instruction to refine the result.
399 /// Note that this is an uncached query, and thus may be inefficient.
401 MemDepResult getPointerDependencyFrom(const AliasAnalysis::Location &Loc,
403 BasicBlock::iterator ScanIt,
405 Instruction *QueryInst = nullptr);
408 /// getLoadLoadClobberFullWidthSize - This is a little bit of analysis that
409 /// looks at a memory location for a load (specified by MemLocBase, Offs,
410 /// and Size) and compares it against a load. If the specified load could
411 /// be safely widened to a larger integer load that is 1) still efficient,
412 /// 2) safe for the target, and 3) would provide the specified memory
413 /// location value, then this function returns the size in bytes of the
414 /// load width to use. If not, this returns zero.
415 static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase,
419 const DataLayout &DL);
422 MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall,
423 BasicBlock::iterator ScanIt,
425 bool getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
426 const AliasAnalysis::Location &Loc,
427 bool isLoad, BasicBlock *BB,
428 SmallVectorImpl<NonLocalDepResult> &Result,
429 DenseMap<BasicBlock*, Value*> &Visited,
430 bool SkipFirstBlock = false);
431 MemDepResult GetNonLocalInfoForBlock(const AliasAnalysis::Location &Loc,
432 bool isLoad, BasicBlock *BB,
433 NonLocalDepInfo *Cache,
434 unsigned NumSortedEntries);
436 void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P);
438 /// verifyRemoved - Verify that the specified instruction does not occur
439 /// in our internal data structures.
440 void verifyRemoved(Instruction *Inst) const;
444 } // End llvm namespace