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/PredIteratorCache.h"
23 #include "llvm/IR/ValueHandle.h"
24 #include "llvm/Pass.h"
32 class AssumptionCache;
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 /// 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.
57 /// Def - This is a dependence on the specified instruction which
58 /// defines/produces the desired memory location. The pointer member of
59 /// the MemDepResult pair holds the instruction that defines the memory.
60 /// Cases of interest:
61 /// 1. This could be a load or store for dependence queries on
62 /// load/store. The value loaded or stored is the produced value.
63 /// Note that the pointer operand may be different than that of the
64 /// queried pointer due to must aliases and phi translation. Note
65 /// that the def may not be the same type as the query, the pointers
66 /// may just be must aliases.
67 /// 2. For loads and stores, this could be an allocation instruction. In
68 /// this case, the load is loading an undef value or a store is the
69 /// first store to (that part of) the allocation.
70 /// 3. Dependence queries on calls return Def only when they are
71 /// readonly calls or memory use intrinsics with identical callees
72 /// and no intervening clobbers. No validation is done that the
73 /// operands to the calls are the same.
76 /// Other - This marker indicates that the query has no known dependency
77 /// in the specified block. More detailed state info is encoded in the
78 /// upper part of the pair (i.e. the Instruction*)
81 /// If DepType is "Other", the upper part of the pair
82 /// (i.e. the Instruction* part) is instead used to encode more detailed
83 /// type information as follows
85 /// NonLocal - This marker indicates that the query has no dependency in
86 /// the specified block. To find out more, the client should query other
87 /// predecessor blocks.
89 /// NonFuncLocal - This marker indicates that the query has no
90 /// dependency in the specified function.
92 /// Unknown - This marker indicates that the query dependency
97 typedef PointerIntPair<Instruction*, 2, DepType> PairTy;
99 explicit MemDepResult(PairTy V) : Value(V) {}
101 MemDepResult() : Value(nullptr, Invalid) {}
103 /// get methods: These are static ctor methods for creating various
104 /// MemDepResult kinds.
105 static MemDepResult getDef(Instruction *Inst) {
106 assert(Inst && "Def requires inst");
107 return MemDepResult(PairTy(Inst, Def));
109 static MemDepResult getClobber(Instruction *Inst) {
110 assert(Inst && "Clobber requires inst");
111 return MemDepResult(PairTy(Inst, Clobber));
113 static MemDepResult getNonLocal() {
115 PairTy(reinterpret_cast<Instruction*>(NonLocal), Other));
117 static MemDepResult getNonFuncLocal() {
119 PairTy(reinterpret_cast<Instruction*>(NonFuncLocal), Other));
121 static MemDepResult getUnknown() {
123 PairTy(reinterpret_cast<Instruction*>(Unknown), Other));
126 /// isClobber - Return true if this MemDepResult represents a query that is
127 /// an instruction clobber dependency.
128 bool isClobber() const { return Value.getInt() == Clobber; }
130 /// isDef - Return true if this MemDepResult represents a query that is
131 /// an instruction definition dependency.
132 bool isDef() const { return Value.getInt() == Def; }
134 /// isNonLocal - Return true if this MemDepResult represents a query that
135 /// is transparent to the start of the block, but where a non-local hasn't
137 bool isNonLocal() const {
138 return Value.getInt() == Other
139 && Value.getPointer() == reinterpret_cast<Instruction*>(NonLocal);
142 /// isNonFuncLocal - Return true if this MemDepResult represents a query
143 /// that is transparent to the start of the function.
144 bool isNonFuncLocal() const {
145 return Value.getInt() == Other
146 && Value.getPointer() == reinterpret_cast<Instruction*>(NonFuncLocal);
149 /// isUnknown - Return true if this MemDepResult represents a query which
150 /// cannot and/or will not be computed.
151 bool isUnknown() const {
152 return Value.getInt() == Other
153 && Value.getPointer() == reinterpret_cast<Instruction*>(Unknown);
156 /// getInst() - If this is a normal dependency, return the instruction that
157 /// is depended on. Otherwise, return null.
158 Instruction *getInst() const {
159 if (Value.getInt() == Other) return nullptr;
160 return Value.getPointer();
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; }
166 bool operator>(const MemDepResult &M) const { return Value > M.Value; }
168 friend class MemoryDependenceAnalysis;
169 /// Dirty - Entries with this marker occur in a LocalDeps map or
170 /// NonLocalDeps map when the instruction they previously referenced was
171 /// removed from MemDep. In either case, the entry may include an
172 /// instruction pointer. If so, the pointer is an instruction in the
173 /// block where scanning can start from, saving some work.
175 /// In a default-constructed MemDepResult object, the type will be Dirty
176 /// and the instruction pointer will be null.
179 /// isDirty - Return true if this is a MemDepResult in its dirty/invalid.
181 bool isDirty() const { return Value.getInt() == Invalid; }
183 static MemDepResult getDirty(Instruction *Inst) {
184 return MemDepResult(PairTy(Inst, Invalid));
188 /// NonLocalDepEntry - This is an entry in the NonLocalDepInfo cache. For
189 /// each BasicBlock (the BB entry) it keeps a MemDepResult.
190 class NonLocalDepEntry {
194 NonLocalDepEntry(BasicBlock *bb, MemDepResult result)
195 : BB(bb), Result(result) {}
197 // This is used for searches.
198 NonLocalDepEntry(BasicBlock *bb) : BB(bb) {}
200 // BB is the sort key, it can't be changed.
201 BasicBlock *getBB() const { return BB; }
203 void setResult(const MemDepResult &R) { Result = R; }
205 const MemDepResult &getResult() const { return Result; }
207 bool operator<(const NonLocalDepEntry &RHS) const {
212 /// NonLocalDepResult - This is a result from a NonLocal dependence query.
213 /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the
214 /// (potentially phi translated) address that was live in the block.
215 class NonLocalDepResult {
216 NonLocalDepEntry Entry;
219 NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address)
220 : Entry(bb, result), Address(address) {}
222 // BB is the sort key, it can't be changed.
223 BasicBlock *getBB() const { return Entry.getBB(); }
225 void setResult(const MemDepResult &R, Value *Addr) {
230 const MemDepResult &getResult() const { return Entry.getResult(); }
232 /// getAddress - Return the address of this pointer in this block. This can
233 /// be different than the address queried for the non-local result because
234 /// of phi translation. This returns null if the address was not available
235 /// in a block (i.e. because phi translation failed) or if this is a cached
236 /// result and that address was deleted.
238 /// The address is always null for a non-local 'call' dependence.
239 Value *getAddress() const { return Address; }
242 /// MemoryDependenceAnalysis - This is an analysis that determines, for a
243 /// given memory operation, what preceding memory operations it depends on.
244 /// It builds on alias analysis information, and tries to provide a lazy,
245 /// caching interface to a common kind of alias information query.
247 /// The dependency information returned is somewhat unusual, but is pragmatic.
248 /// If queried about a store or call that might modify memory, the analysis
249 /// will return the instruction[s] that may either load from that memory or
250 /// store to it. If queried with a load or call that can never modify memory,
251 /// the analysis will return calls and stores that might modify the pointer,
252 /// but generally does not return loads unless a) they are volatile, or
253 /// b) they load from *must-aliased* pointers. Returning a dependence on
254 /// must-alias'd pointers instead of all pointers interacts well with the
255 /// internal caching mechanism.
257 class MemoryDependenceAnalysis : public FunctionPass {
258 // A map from instructions to their dependency.
259 typedef DenseMap<Instruction*, MemDepResult> LocalDepMapType;
260 LocalDepMapType LocalDeps;
263 typedef std::vector<NonLocalDepEntry> NonLocalDepInfo;
265 /// ValueIsLoadPair - This is a pair<Value*, bool> where the bool is true if
266 /// the dependence is a read only dependence, false if read/write.
267 typedef PointerIntPair<const Value*, 1, bool> ValueIsLoadPair;
269 /// BBSkipFirstBlockPair - This pair is used when caching information for a
270 /// block. If the pointer is null, the cache value is not a full query that
271 /// starts at the specified block. If non-null, the bool indicates whether
272 /// or not the contents of the block was skipped.
273 typedef PointerIntPair<BasicBlock*, 1, bool> BBSkipFirstBlockPair;
275 /// NonLocalPointerInfo - This record is the information kept for each
276 /// (value, is load) pair.
277 struct NonLocalPointerInfo {
278 /// Pair - The pair of the block and the skip-first-block flag.
279 BBSkipFirstBlockPair Pair;
280 /// NonLocalDeps - The results of the query for each relevant block.
281 NonLocalDepInfo NonLocalDeps;
282 /// Size - The maximum size of the dereferences of the
283 /// pointer. May be UnknownSize if the sizes are unknown.
285 /// AATags - The AA tags associated with dereferences of the
286 /// pointer. The members may be null if there are no tags or
287 /// conflicting tags.
290 NonLocalPointerInfo() : Size(MemoryLocation::UnknownSize) {}
293 /// CachedNonLocalPointerInfo - This map stores the cached results of doing
294 /// a pointer lookup at the bottom of a block. The key of this map is the
295 /// pointer+isload bit, the value is a list of <bb->result> mappings.
296 typedef DenseMap<ValueIsLoadPair,
297 NonLocalPointerInfo> CachedNonLocalPointerInfo;
298 CachedNonLocalPointerInfo NonLocalPointerDeps;
300 // A map from instructions to their non-local pointer dependencies.
301 typedef DenseMap<Instruction*,
302 SmallPtrSet<ValueIsLoadPair, 4> > ReverseNonLocalPtrDepTy;
303 ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps;
306 /// PerInstNLInfo - This is the instruction we keep for each cached access
307 /// that we have for an instruction. The pointer is an owning pointer and
308 /// the bool indicates whether we have any dirty bits in the set.
309 typedef std::pair<NonLocalDepInfo, bool> PerInstNLInfo;
311 // A map from instructions to their non-local dependencies.
312 typedef DenseMap<Instruction*, PerInstNLInfo> NonLocalDepMapType;
314 NonLocalDepMapType NonLocalDeps;
316 // A reverse mapping from dependencies to the dependees. This is
317 // used when removing instructions to keep the cache coherent.
318 typedef DenseMap<Instruction*,
319 SmallPtrSet<Instruction*, 4> > ReverseDepMapType;
320 ReverseDepMapType ReverseLocalDeps;
322 // A reverse mapping from dependencies to the non-local dependees.
323 ReverseDepMapType ReverseNonLocalDeps;
325 /// Current AA implementation, just a cache.
329 PredIteratorCache PredCache;
332 MemoryDependenceAnalysis();
333 ~MemoryDependenceAnalysis() override;
336 /// Pass Implementation stuff. This doesn't do any analysis eagerly.
337 bool runOnFunction(Function &) override;
339 /// Clean up memory in between runs
340 void releaseMemory() override;
342 /// getAnalysisUsage - Does not modify anything. It uses Value Numbering
343 /// and Alias Analysis.
345 void getAnalysisUsage(AnalysisUsage &AU) const override;
347 /// getDependency - Return the instruction on which a memory operation
348 /// depends. See the class comment for more details. It is illegal to call
349 /// this on non-memory instructions.
350 MemDepResult getDependency(Instruction *QueryInst);
352 /// getNonLocalCallDependency - Perform a full dependency query for the
353 /// specified call, returning the set of blocks that the value is
354 /// potentially live across. The returned set of results will include a
355 /// "NonLocal" result for all blocks where the value is live across.
357 /// This method assumes the instruction returns a "NonLocal" dependency
358 /// within its own block.
360 /// This returns a reference to an internal data structure that may be
361 /// invalidated on the next non-local query or when an instruction is
362 /// removed. Clients must copy this data if they want it around longer than
364 const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS);
367 /// getNonLocalPointerDependency - Perform a full dependency query for an
368 /// access to the QueryInst's specified memory location, returning the set
369 /// of instructions that either define or clobber the value.
371 /// Warning: For a volatile query instruction, the dependencies will be
372 /// accurate, and thus usable for reordering, but it is never legal to
373 /// remove the query instruction.
375 /// This method assumes the pointer has a "NonLocal" dependency within
376 /// QueryInst's parent basic block.
377 void getNonLocalPointerDependency(Instruction *QueryInst,
378 SmallVectorImpl<NonLocalDepResult> &Result);
380 /// removeInstruction - Remove an instruction from the dependence analysis,
381 /// updating the dependence of instructions that previously depended on it.
382 void removeInstruction(Instruction *InstToRemove);
384 /// invalidateCachedPointerInfo - This method is used to invalidate cached
385 /// information about the specified pointer, because it may be too
386 /// conservative in memdep. This is an optional call that can be used when
387 /// the client detects an equivalence between the pointer and some other
388 /// value and replaces the other value with ptr. This can make Ptr available
389 /// in more places that cached info does not necessarily keep.
390 void invalidateCachedPointerInfo(Value *Ptr);
392 /// invalidateCachedPredecessors - Clear the PredIteratorCache info.
393 /// This needs to be done when the CFG changes, e.g., due to splitting
395 void invalidateCachedPredecessors();
397 /// getPointerDependencyFrom - Return the instruction on which a memory
398 /// location depends. If isLoad is true, this routine ignores may-aliases
399 /// with read-only operations. If isLoad is false, this routine ignores
400 /// may-aliases with reads from read-only locations. If possible, pass
401 /// the query instruction as well; this function may take advantage of
402 /// the metadata annotated to the query instruction to refine the result.
404 /// Note that this is an uncached query, and thus may be inefficient.
406 MemDepResult getPointerDependencyFrom(const MemoryLocation &Loc,
408 BasicBlock::iterator ScanIt,
410 Instruction *QueryInst = nullptr);
412 /// getLoadLoadClobberFullWidthSize - This is a little bit of analysis that
413 /// looks at a memory location for a load (specified by MemLocBase, Offs,
414 /// and Size) and compares it against a load. If the specified load could
415 /// be safely widened to a larger integer load that is 1) still efficient,
416 /// 2) safe for the target, and 3) would provide the specified memory
417 /// location value, then this function returns the size in bytes of the
418 /// load width to use. If not, this returns zero.
419 static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase,
425 MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall,
426 BasicBlock::iterator ScanIt,
428 bool getNonLocalPointerDepFromBB(Instruction *QueryInst,
429 const PHITransAddr &Pointer,
430 const MemoryLocation &Loc, bool isLoad,
432 SmallVectorImpl<NonLocalDepResult> &Result,
433 DenseMap<BasicBlock *, Value *> &Visited,
434 bool SkipFirstBlock = false);
435 MemDepResult GetNonLocalInfoForBlock(Instruction *QueryInst,
436 const MemoryLocation &Loc, bool isLoad,
437 BasicBlock *BB, NonLocalDepInfo *Cache,
438 unsigned NumSortedEntries);
440 void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P);
442 /// verifyRemoved - Verify that the specified instruction does not occur
443 /// in our internal data structures.
444 void verifyRemoved(Instruction *Inst) const;