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_MEMORY_DEPENDENCE_H
15 #define LLVM_ANALYSIS_MEMORY_DEPENDENCE_H
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"
33 class MemoryDependenceAnalysis;
34 class PredIteratorCache;
38 /// MemDepResult - A memory dependence query can return one of three different
39 /// answers, described below.
42 /// Invalid - Clients of MemDep never see this.
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
51 /// A dependence query on the first instruction of the entry block will
52 /// return a clobber(self) result.
55 /// Def - This is a dependence on the specified instruction which
56 /// defines/produces the desired memory location. The pointer member of
57 /// the MemDepResult pair holds the instruction that defines the memory.
58 /// Cases of interest:
59 /// 1. This could be a load or store for dependence queries on
60 /// load/store. The value loaded or stored is the produced value.
61 /// Note that the pointer operand may be different than that of the
62 /// queried pointer due to must aliases and phi translation. Note
63 /// that the def may not be the same type as the query, the pointers
64 /// may just be must aliases.
65 /// 2. For loads and stores, this could be an allocation instruction. In
66 /// this case, the load is loading an undef value or a store is the
67 /// first store to (that part of) the allocation.
68 /// 3. Dependence queries on calls return Def only when they are
69 /// readonly calls or memory use intrinsics with identical callees
70 /// and no intervening clobbers. No validation is done that the
71 /// operands to the calls are the same.
74 /// NonLocal - This marker indicates that the query has no dependency in
75 /// the specified block. To find out more, the client should query other
76 /// predecessor blocks.
79 typedef PointerIntPair<Instruction*, 2, DepType> PairTy;
81 explicit MemDepResult(PairTy V) : Value(V) {}
83 MemDepResult() : Value(0, Invalid) {}
85 /// get methods: These are static ctor methods for creating various
86 /// MemDepResult kinds.
87 static MemDepResult getDef(Instruction *Inst) {
88 return MemDepResult(PairTy(Inst, Def));
90 static MemDepResult getClobber(Instruction *Inst) {
91 return MemDepResult(PairTy(Inst, Clobber));
93 static MemDepResult getNonLocal() {
94 return MemDepResult(PairTy(0, NonLocal));
97 /// isClobber - Return true if this MemDepResult represents a query that is
98 /// a instruction clobber dependency.
99 bool isClobber() const { return Value.getInt() == Clobber; }
101 /// isDef - Return true if this MemDepResult represents a query that is
102 /// a instruction definition dependency.
103 bool isDef() const { return Value.getInt() == Def; }
105 /// isNonLocal - Return true if this MemDepResult represents a query that
106 /// is transparent to the start of the block, but where a non-local hasn't
108 bool isNonLocal() const { return Value.getInt() == NonLocal; }
110 /// getInst() - If this is a normal dependency, return the instruction that
111 /// is depended on. Otherwise, return null.
112 Instruction *getInst() const { return Value.getPointer(); }
114 bool operator==(const MemDepResult &M) const { return Value == M.Value; }
115 bool operator!=(const MemDepResult &M) const { return Value != M.Value; }
116 bool operator<(const MemDepResult &M) const { return Value < M.Value; }
117 bool operator>(const MemDepResult &M) const { return Value > M.Value; }
119 friend class MemoryDependenceAnalysis;
120 /// Dirty - Entries with this marker occur in a LocalDeps map or
121 /// NonLocalDeps map when the instruction they previously referenced was
122 /// removed from MemDep. In either case, the entry may include an
123 /// instruction pointer. If so, the pointer is an instruction in the
124 /// block where scanning can start from, saving some work.
126 /// In a default-constructed MemDepResult object, the type will be Dirty
127 /// and the instruction pointer will be null.
130 /// isDirty - Return true if this is a MemDepResult in its dirty/invalid.
132 bool isDirty() const { return Value.getInt() == Invalid; }
134 static MemDepResult getDirty(Instruction *Inst) {
135 return MemDepResult(PairTy(Inst, Invalid));
139 /// NonLocalDepEntry - This is an entry in the NonLocalDepInfo cache. For
140 /// each BasicBlock (the BB entry) it keeps a MemDepResult.
141 class NonLocalDepEntry {
145 NonLocalDepEntry(BasicBlock *bb, MemDepResult result)
146 : BB(bb), Result(result) {}
148 // This is used for searches.
149 NonLocalDepEntry(BasicBlock *bb) : BB(bb) {}
151 // BB is the sort key, it can't be changed.
152 BasicBlock *getBB() const { return BB; }
154 void setResult(const MemDepResult &R) { Result = R; }
156 const MemDepResult &getResult() const { return Result; }
158 bool operator<(const NonLocalDepEntry &RHS) const {
163 /// NonLocalDepResult - This is a result from a NonLocal dependence query.
164 /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the
165 /// (potentially phi translated) address that was live in the block.
166 class NonLocalDepResult {
167 NonLocalDepEntry Entry;
170 NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address)
171 : Entry(bb, result), Address(address) {}
173 // BB is the sort key, it can't be changed.
174 BasicBlock *getBB() const { return Entry.getBB(); }
176 void setResult(const MemDepResult &R, Value *Addr) {
181 const MemDepResult &getResult() const { return Entry.getResult(); }
183 /// getAddress - Return the address of this pointer in this block. This can
184 /// be different than the address queried for the non-local result because
185 /// of phi translation. This returns null if the address was not available
186 /// in a block (i.e. because phi translation failed) or if this is a cached
187 /// result and that address was deleted.
189 /// The address is always null for a non-local 'call' dependence.
190 Value *getAddress() const { return Address; }
193 /// MemoryDependenceAnalysis - This is an analysis that determines, for a
194 /// given memory operation, what preceding memory operations it depends on.
195 /// It builds on alias analysis information, and tries to provide a lazy,
196 /// caching interface to a common kind of alias information query.
198 /// The dependency information returned is somewhat unusual, but is pragmatic.
199 /// If queried about a store or call that might modify memory, the analysis
200 /// will return the instruction[s] that may either load from that memory or
201 /// store to it. If queried with a load or call that can never modify memory,
202 /// the analysis will return calls and stores that might modify the pointer,
203 /// but generally does not return loads unless a) they are volatile, or
204 /// b) they load from *must-aliased* pointers. Returning a dependence on
205 /// must-alias'd pointers instead of all pointers interacts well with the
206 /// internal caching mechanism.
208 class MemoryDependenceAnalysis : public FunctionPass {
209 // A map from instructions to their dependency.
210 typedef DenseMap<Instruction*, MemDepResult> LocalDepMapType;
211 LocalDepMapType LocalDeps;
214 typedef std::vector<NonLocalDepEntry> NonLocalDepInfo;
216 /// ValueIsLoadPair - This is a pair<Value*, bool> where the bool is true if
217 /// the dependence is a read only dependence, false if read/write.
218 typedef PointerIntPair<const Value*, 1, bool> ValueIsLoadPair;
220 /// BBSkipFirstBlockPair - This pair is used when caching information for a
221 /// block. If the pointer is null, the cache value is not a full query that
222 /// starts at the specified block. If non-null, the bool indicates whether
223 /// or not the contents of the block was skipped.
224 typedef PointerIntPair<BasicBlock*, 1, bool> BBSkipFirstBlockPair;
226 /// NonLocalPointerInfo - This record is the information kept for each
227 /// (value, is load) pair.
228 struct NonLocalPointerInfo {
229 /// Pair - The pair of the block and the skip-first-block flag.
230 BBSkipFirstBlockPair Pair;
231 /// NonLocalDeps - The results of the query for each relevant block.
232 NonLocalDepInfo NonLocalDeps;
233 /// Size - The maximum size of the dereferences of the
234 /// pointer. May be UnknownSize if the sizes are unknown.
236 /// TBAATag - The TBAA tag associated with dereferences of the
237 /// pointer. May be null if there are no tags or conflicting tags.
238 const MDNode *TBAATag;
240 NonLocalPointerInfo() : Size(AliasAnalysis::UnknownSize), TBAATag(0) {}
243 /// CachedNonLocalPointerInfo - This map stores the cached results of doing
244 /// a pointer lookup at the bottom of a block. The key of this map is the
245 /// pointer+isload bit, the value is a list of <bb->result> mappings.
246 typedef DenseMap<ValueIsLoadPair,
247 NonLocalPointerInfo> CachedNonLocalPointerInfo;
248 CachedNonLocalPointerInfo NonLocalPointerDeps;
250 // A map from instructions to their non-local pointer dependencies.
251 typedef DenseMap<Instruction*,
252 SmallPtrSet<ValueIsLoadPair, 4> > ReverseNonLocalPtrDepTy;
253 ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps;
256 /// PerInstNLInfo - This is the instruction we keep for each cached access
257 /// that we have for an instruction. The pointer is an owning pointer and
258 /// the bool indicates whether we have any dirty bits in the set.
259 typedef std::pair<NonLocalDepInfo, bool> PerInstNLInfo;
261 // A map from instructions to their non-local dependencies.
262 typedef DenseMap<Instruction*, PerInstNLInfo> NonLocalDepMapType;
264 NonLocalDepMapType NonLocalDeps;
266 // A reverse mapping from dependencies to the dependees. This is
267 // used when removing instructions to keep the cache coherent.
268 typedef DenseMap<Instruction*,
269 SmallPtrSet<Instruction*, 4> > ReverseDepMapType;
270 ReverseDepMapType ReverseLocalDeps;
272 // A reverse mapping from dependencies to the non-local dependees.
273 ReverseDepMapType ReverseNonLocalDeps;
275 /// Current AA implementation, just a cache.
278 OwningPtr<PredIteratorCache> PredCache;
280 MemoryDependenceAnalysis();
281 ~MemoryDependenceAnalysis();
284 /// Pass Implementation stuff. This doesn't do any analysis eagerly.
285 bool runOnFunction(Function &);
287 /// Clean up memory in between runs
288 void releaseMemory();
290 /// getAnalysisUsage - Does not modify anything. It uses Value Numbering
291 /// and Alias Analysis.
293 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
295 /// getDependency - Return the instruction on which a memory operation
296 /// depends. See the class comment for more details. It is illegal to call
297 /// this on non-memory instructions.
298 MemDepResult getDependency(Instruction *QueryInst);
300 /// getNonLocalCallDependency - Perform a full dependency query for the
301 /// specified call, returning the set of blocks that the value is
302 /// potentially live across. The returned set of results will include a
303 /// "NonLocal" result for all blocks where the value is live across.
305 /// This method assumes the instruction returns a "NonLocal" dependency
306 /// within its own block.
308 /// This returns a reference to an internal data structure that may be
309 /// invalidated on the next non-local query or when an instruction is
310 /// removed. Clients must copy this data if they want it around longer than
312 const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS);
315 /// getNonLocalPointerDependency - Perform a full dependency query for an
316 /// access to the specified (non-volatile) memory location, returning the
317 /// set of instructions that either define or clobber the value.
319 /// This method assumes the pointer has a "NonLocal" dependency within BB.
320 void getNonLocalPointerDependency(const AliasAnalysis::Location &Loc,
321 bool isLoad, BasicBlock *BB,
322 SmallVectorImpl<NonLocalDepResult> &Result);
324 /// removeInstruction - Remove an instruction from the dependence analysis,
325 /// updating the dependence of instructions that previously depended on it.
326 void removeInstruction(Instruction *InstToRemove);
328 /// invalidateCachedPointerInfo - This method is used to invalidate cached
329 /// information about the specified pointer, because it may be too
330 /// conservative in memdep. This is an optional call that can be used when
331 /// the client detects an equivalence between the pointer and some other
332 /// value and replaces the other value with ptr. This can make Ptr available
333 /// in more places that cached info does not necessarily keep.
334 void invalidateCachedPointerInfo(Value *Ptr);
336 /// invalidateCachedPredecessors - Clear the PredIteratorCache info.
337 /// This needs to be done when the CFG changes, e.g., due to splitting
339 void invalidateCachedPredecessors();
341 /// getPointerDependencyFrom - Return the instruction on which a memory
342 /// location depends. If isLoad is true, this routine ignores may-aliases
343 /// with read-only operations. If isLoad is false, this routine ignores
344 /// may-aliases with reads from read-only locations.
346 /// Note that this is an uncached query, and thus may be inefficient.
348 MemDepResult getPointerDependencyFrom(const AliasAnalysis::Location &Loc,
350 BasicBlock::iterator ScanIt,
354 MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall,
355 BasicBlock::iterator ScanIt,
357 bool getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
358 const AliasAnalysis::Location &Loc,
359 bool isLoad, BasicBlock *BB,
360 SmallVectorImpl<NonLocalDepResult> &Result,
361 DenseMap<BasicBlock*, Value*> &Visited,
362 bool SkipFirstBlock = false);
363 MemDepResult GetNonLocalInfoForBlock(const AliasAnalysis::Location &Loc,
364 bool isLoad, BasicBlock *BB,
365 NonLocalDepInfo *Cache,
366 unsigned NumSortedEntries);
368 void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P);
370 /// verifyRemoved - Verify that the specified instruction does not occur
371 /// in our internal data structures.
372 void verifyRemoved(Instruction *Inst) const;
376 } // End llvm namespace