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/Optional.h"
19 #include "llvm/ADT/PointerEmbeddedInt.h"
20 #include "llvm/ADT/PointerIntPair.h"
21 #include "llvm/ADT/PointerSumType.h"
22 #include "llvm/ADT/SmallPtrSet.h"
23 #include "llvm/Analysis/AliasAnalysis.h"
24 #include "llvm/Analysis/MemoryLocation.h"
25 #include "llvm/IR/BasicBlock.h"
26 #include "llvm/IR/Metadata.h"
27 #include "llvm/IR/PassManager.h"
28 #include "llvm/IR/PredIteratorCache.h"
29 #include "llvm/Pass.h"
30 #include "llvm/Support/ErrorHandling.h"
38 class AssumptionCache;
45 class TargetLibraryInfo;
48 /// A memory dependence query can return one of three different answers.
51 /// Clients of MemDep never see this.
53 /// Entries with this marker occur in a LocalDeps map or NonLocalDeps map
54 /// when the instruction they previously referenced was removed from
55 /// MemDep. In either case, the entry may include an instruction pointer.
56 /// If so, the pointer is an instruction in the block where scanning can
57 /// start from, saving some work.
59 /// In a default-constructed MemDepResult object, the type will be Invalid
60 /// and the instruction pointer will be null.
63 /// This is a dependence on the specified instruction which clobbers the
64 /// desired value. The pointer member of the MemDepResult pair holds the
65 /// instruction that clobbers the memory. For example, this occurs when we
66 /// see a may-aliased store to the memory location we care about.
68 /// There are several cases that may be interesting here:
69 /// 1. Loads are clobbered by may-alias stores.
70 /// 2. Loads are considered clobbered by partially-aliased loads. The
71 /// client may choose to analyze deeper into these cases.
74 /// This is a dependence on the specified instruction which defines or
75 /// produces the desired memory location. The pointer member of the
76 /// MemDepResult pair holds the instruction that defines the memory.
78 /// Cases of interest:
79 /// 1. This could be a load or store for dependence queries on
80 /// load/store. The value loaded or stored is the produced value.
81 /// Note that the pointer operand may be different than that of the
82 /// queried pointer due to must aliases and phi translation. Note
83 /// that the def may not be the same type as the query, the pointers
84 /// may just be must aliases.
85 /// 2. For loads and stores, this could be an allocation instruction. In
86 /// this case, the load is loading an undef value or a store is the
87 /// first store to (that part of) the allocation.
88 /// 3. Dependence queries on calls return Def only when they are readonly
89 /// calls or memory use intrinsics with identical callees and no
90 /// intervening clobbers. No validation is done that the operands to
91 /// the calls are the same.
94 /// This marker indicates that the query has no known dependency in the
97 /// More detailed state info is encoded in the upper part of the pair (i.e.
102 /// If DepType is "Other", the upper part of the sum type is an encoding of
103 /// the following more detailed type information.
105 /// This marker indicates that the query has no dependency in the specified
108 /// To find out more, the client should query other predecessor blocks.
110 /// This marker indicates that the query has no dependency in the specified
113 /// This marker indicates that the query dependency is unknown.
117 using ValueTy = PointerSumType<
118 DepType, PointerSumTypeMember<Invalid, Instruction *>,
119 PointerSumTypeMember<Clobber, Instruction *>,
120 PointerSumTypeMember<Def, Instruction *>,
121 PointerSumTypeMember<Other, PointerEmbeddedInt<OtherType, 3>>>;
124 explicit MemDepResult(ValueTy V) : Value(V) {}
127 MemDepResult() = default;
129 /// get methods: These are static ctor methods for creating various
130 /// MemDepResult kinds.
131 static MemDepResult getDef(Instruction *Inst) {
132 assert(Inst && "Def requires inst");
133 return MemDepResult(ValueTy::create<Def>(Inst));
135 static MemDepResult getClobber(Instruction *Inst) {
136 assert(Inst && "Clobber requires inst");
137 return MemDepResult(ValueTy::create<Clobber>(Inst));
139 static MemDepResult getNonLocal() {
140 return MemDepResult(ValueTy::create<Other>(NonLocal));
142 static MemDepResult getNonFuncLocal() {
143 return MemDepResult(ValueTy::create<Other>(NonFuncLocal));
145 static MemDepResult getUnknown() {
146 return MemDepResult(ValueTy::create<Other>(Unknown));
149 /// Tests if this MemDepResult represents a query that is an instruction
150 /// clobber dependency.
151 bool isClobber() const { return Value.is<Clobber>(); }
153 /// Tests if this MemDepResult represents a query that is an instruction
154 /// definition dependency.
155 bool isDef() const { return Value.is<Def>(); }
157 /// Tests if this MemDepResult represents a query that is transparent to the
158 /// start of the block, but where a non-local hasn't been done.
159 bool isNonLocal() const {
160 return Value.is<Other>() && Value.cast<Other>() == NonLocal;
163 /// Tests if this MemDepResult represents a query that is transparent to the
164 /// start of the function.
165 bool isNonFuncLocal() const {
166 return Value.is<Other>() && Value.cast<Other>() == NonFuncLocal;
169 /// Tests if this MemDepResult represents a query which cannot and/or will
171 bool isUnknown() const {
172 return Value.is<Other>() && Value.cast<Other>() == Unknown;
175 /// If this is a normal dependency, returns the instruction that is depended
176 /// on. Otherwise, returns null.
177 Instruction *getInst() const {
178 switch (Value.getTag()) {
180 return Value.cast<Invalid>();
182 return Value.cast<Clobber>();
184 return Value.cast<Def>();
188 llvm_unreachable("Unknown discriminant!");
191 bool operator==(const MemDepResult &M) const { return Value == M.Value; }
192 bool operator!=(const MemDepResult &M) const { return Value != M.Value; }
193 bool operator<(const MemDepResult &M) const { return Value < M.Value; }
194 bool operator>(const MemDepResult &M) const { return Value > M.Value; }
197 friend class MemoryDependenceResults;
199 /// Tests if this is a MemDepResult in its dirty/invalid. state.
200 bool isDirty() const { return Value.is<Invalid>(); }
202 static MemDepResult getDirty(Instruction *Inst) {
203 return MemDepResult(ValueTy::create<Invalid>(Inst));
207 /// This is an entry in the NonLocalDepInfo cache.
209 /// For each BasicBlock (the BB entry) it keeps a MemDepResult.
210 class NonLocalDepEntry {
215 NonLocalDepEntry(BasicBlock *bb, MemDepResult result)
216 : BB(bb), Result(result) {}
218 // This is used for searches.
219 NonLocalDepEntry(BasicBlock *bb) : BB(bb) {}
221 // BB is the sort key, it can't be changed.
222 BasicBlock *getBB() const { return BB; }
224 void setResult(const MemDepResult &R) { Result = R; }
226 const MemDepResult &getResult() const { return Result; }
228 bool operator<(const NonLocalDepEntry &RHS) const { return BB < RHS.BB; }
231 /// This is a result from a NonLocal dependence query.
233 /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the
234 /// (potentially phi translated) address that was live in the block.
235 class NonLocalDepResult {
236 NonLocalDepEntry Entry;
240 NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address)
241 : Entry(bb, result), Address(address) {}
243 // BB is the sort key, it can't be changed.
244 BasicBlock *getBB() const { return Entry.getBB(); }
246 void setResult(const MemDepResult &R, Value *Addr) {
251 const MemDepResult &getResult() const { return Entry.getResult(); }
253 /// Returns the address of this pointer in this block.
255 /// This can be different than the address queried for the non-local result
256 /// because of phi translation. This returns null if the address was not
257 /// available in a block (i.e. because phi translation failed) or if this is
258 /// a cached result and that address was deleted.
260 /// The address is always null for a non-local 'call' dependence.
261 Value *getAddress() const { return Address; }
264 /// Provides a lazy, caching interface for making common memory aliasing
265 /// information queries, backed by LLVM's alias analysis passes.
267 /// The dependency information returned is somewhat unusual, but is pragmatic.
268 /// If queried about a store or call that might modify memory, the analysis
269 /// will return the instruction[s] that may either load from that memory or
270 /// store to it. If queried with a load or call that can never modify memory,
271 /// the analysis will return calls and stores that might modify the pointer,
272 /// but generally does not return loads unless a) they are volatile, or
273 /// b) they load from *must-aliased* pointers. Returning a dependence on
274 /// must-alias'd pointers instead of all pointers interacts well with the
275 /// internal caching mechanism.
276 class MemoryDependenceResults {
277 // A map from instructions to their dependency.
278 using LocalDepMapType = DenseMap<Instruction *, MemDepResult>;
279 LocalDepMapType LocalDeps;
282 using NonLocalDepInfo = std::vector<NonLocalDepEntry>;
285 /// A pair<Value*, bool> where the bool is true if the dependence is a read
286 /// only dependence, false if read/write.
287 using ValueIsLoadPair = PointerIntPair<const Value *, 1, bool>;
289 /// This pair is used when caching information for a block.
291 /// If the pointer is null, the cache value is not a full query that starts
292 /// at the specified block. If non-null, the bool indicates whether or not
293 /// the contents of the block was skipped.
294 using BBSkipFirstBlockPair = PointerIntPair<BasicBlock *, 1, bool>;
296 /// This record is the information kept for each (value, is load) pair.
297 struct NonLocalPointerInfo {
298 /// The pair of the block and the skip-first-block flag.
299 BBSkipFirstBlockPair Pair;
300 /// The results of the query for each relevant block.
301 NonLocalDepInfo NonLocalDeps;
302 /// The maximum size of the dereferences of the pointer.
304 /// May be UnknownSize if the sizes are unknown.
305 uint64_t Size = MemoryLocation::UnknownSize;
306 /// The AA tags associated with dereferences of the pointer.
308 /// The members may be null if there are no tags or conflicting tags.
311 NonLocalPointerInfo() = default;
314 /// Cache storing single nonlocal def for the instruction.
315 /// It is set when nonlocal def would be found in function returning only
316 /// local dependencies.
317 DenseMap<Instruction *, NonLocalDepResult> NonLocalDefsCache;
319 /// This map stores the cached results of doing a pointer lookup at the
320 /// bottom of a block.
322 /// The key of this map is the pointer+isload bit, the value is a list of
323 /// <bb->result> mappings.
324 using CachedNonLocalPointerInfo =
325 DenseMap<ValueIsLoadPair, NonLocalPointerInfo>;
326 CachedNonLocalPointerInfo NonLocalPointerDeps;
328 // A map from instructions to their non-local pointer dependencies.
329 using ReverseNonLocalPtrDepTy =
330 DenseMap<Instruction *, SmallPtrSet<ValueIsLoadPair, 4>>;
331 ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps;
333 /// This is the instruction we keep for each cached access that we have for
336 /// The pointer is an owning pointer and the bool indicates whether we have
337 /// any dirty bits in the set.
338 using PerInstNLInfo = std::pair<NonLocalDepInfo, bool>;
340 // A map from instructions to their non-local dependencies.
341 using NonLocalDepMapType = DenseMap<Instruction *, PerInstNLInfo>;
343 NonLocalDepMapType NonLocalDeps;
345 // A reverse mapping from dependencies to the dependees. This is
346 // used when removing instructions to keep the cache coherent.
347 using ReverseDepMapType =
348 DenseMap<Instruction *, SmallPtrSet<Instruction *, 4>>;
349 ReverseDepMapType ReverseLocalDeps;
351 // A reverse mapping from dependencies to the non-local dependees.
352 ReverseDepMapType ReverseNonLocalDeps;
354 /// Current AA implementation, just a cache.
357 const TargetLibraryInfo &TLI;
359 PredIteratorCache PredCache;
362 MemoryDependenceResults(AliasAnalysis &AA, AssumptionCache &AC,
363 const TargetLibraryInfo &TLI,
365 : AA(AA), AC(AC), TLI(TLI), DT(DT) {}
367 /// Handle invalidation in the new PM.
368 bool invalidate(Function &F, const PreservedAnalyses &PA,
369 FunctionAnalysisManager::Invalidator &Inv);
371 /// Some methods limit the number of instructions they will examine.
372 /// The return value of this method is the default limit that will be
373 /// used if no limit is explicitly passed in.
374 unsigned getDefaultBlockScanLimit() const;
376 /// Returns the instruction on which a memory operation depends.
378 /// See the class comment for more details. It is illegal to call this on
379 /// non-memory instructions.
380 MemDepResult getDependency(Instruction *QueryInst);
382 /// Perform a full dependency query for the specified call, returning the set
383 /// of blocks that the value is potentially live across.
385 /// The returned set of results will include a "NonLocal" result for all
386 /// blocks where the value is live across.
388 /// This method assumes the instruction returns a "NonLocal" dependency
389 /// within its own block.
391 /// This returns a reference to an internal data structure that may be
392 /// invalidated on the next non-local query or when an instruction is
393 /// removed. Clients must copy this data if they want it around longer than
395 const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS);
397 /// Perform a full dependency query for an access to the QueryInst's
398 /// specified memory location, returning the set of instructions that either
399 /// define or clobber the value.
401 /// Warning: For a volatile query instruction, the dependencies will be
402 /// accurate, and thus usable for reordering, but it is never legal to
403 /// remove the query instruction.
405 /// This method assumes the pointer has a "NonLocal" dependency within
406 /// QueryInst's parent basic block.
407 void getNonLocalPointerDependency(Instruction *QueryInst,
408 SmallVectorImpl<NonLocalDepResult> &Result);
410 /// Removes an instruction from the dependence analysis, updating the
411 /// dependence of instructions that previously depended on it.
412 void removeInstruction(Instruction *InstToRemove);
414 /// Invalidates cached information about the specified pointer, because it
415 /// may be too conservative in memdep.
417 /// This is an optional call that can be used when the client detects an
418 /// equivalence between the pointer and some other value and replaces the
419 /// other value with ptr. This can make Ptr available in more places that
420 /// cached info does not necessarily keep.
421 void invalidateCachedPointerInfo(Value *Ptr);
423 /// Clears the PredIteratorCache info.
425 /// This needs to be done when the CFG changes, e.g., due to splitting
427 void invalidateCachedPredecessors();
429 /// Returns the instruction on which a memory location depends.
431 /// If isLoad is true, this routine ignores may-aliases with read-only
432 /// operations. If isLoad is false, this routine ignores may-aliases
433 /// with reads from read-only locations. If possible, pass the query
434 /// instruction as well; this function may take advantage of the metadata
435 /// annotated to the query instruction to refine the result. \p Limit
436 /// can be used to set the maximum number of instructions that will be
437 /// examined to find the pointer dependency. On return, it will be set to
438 /// the number of instructions left to examine. If a null pointer is passed
439 /// in, the limit will default to the value of -memdep-block-scan-limit.
441 /// Note that this is an uncached query, and thus may be inefficient.
442 MemDepResult getPointerDependencyFrom(const MemoryLocation &Loc, bool isLoad,
443 BasicBlock::iterator ScanIt,
445 Instruction *QueryInst = nullptr,
446 unsigned *Limit = nullptr);
448 MemDepResult getSimplePointerDependencyFrom(const MemoryLocation &MemLoc,
450 BasicBlock::iterator ScanIt,
452 Instruction *QueryInst,
453 unsigned *Limit = nullptr);
455 /// This analysis looks for other loads and stores with invariant.group
456 /// metadata and the same pointer operand. Returns Unknown if it does not
457 /// find anything, and Def if it can be assumed that 2 instructions load or
458 /// store the same value and NonLocal which indicate that non-local Def was
459 /// found, which can be retrieved by calling getNonLocalPointerDependency
460 /// with the same queried instruction.
461 MemDepResult getInvariantGroupPointerDependency(LoadInst *LI, BasicBlock *BB);
463 /// Looks at a memory location for a load (specified by MemLocBase, Offs, and
464 /// Size) and compares it against a load.
466 /// If the specified load could be safely widened to a larger integer load
467 /// that is 1) still efficient, 2) safe for the target, and 3) would provide
468 /// the specified memory location value, then this function returns the size
469 /// in bytes of the load width to use. If not, this returns zero.
470 static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase,
475 /// Release memory in caches.
476 void releaseMemory();
479 MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall,
480 BasicBlock::iterator ScanIt,
482 bool getNonLocalPointerDepFromBB(Instruction *QueryInst,
483 const PHITransAddr &Pointer,
484 const MemoryLocation &Loc, bool isLoad,
486 SmallVectorImpl<NonLocalDepResult> &Result,
487 DenseMap<BasicBlock *, Value *> &Visited,
488 bool SkipFirstBlock = false);
489 MemDepResult GetNonLocalInfoForBlock(Instruction *QueryInst,
490 const MemoryLocation &Loc, bool isLoad,
491 BasicBlock *BB, NonLocalDepInfo *Cache,
492 unsigned NumSortedEntries);
494 void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P);
496 void verifyRemoved(Instruction *Inst) const;
499 /// An analysis that produces \c MemoryDependenceResults for a function.
501 /// This is essentially a no-op because the results are computed entirely
503 class MemoryDependenceAnalysis
504 : public AnalysisInfoMixin<MemoryDependenceAnalysis> {
505 friend AnalysisInfoMixin<MemoryDependenceAnalysis>;
507 static AnalysisKey Key;
510 using Result = MemoryDependenceResults;
512 MemoryDependenceResults run(Function &F, FunctionAnalysisManager &AM);
515 /// A wrapper analysis pass for the legacy pass manager that exposes a \c
516 /// MemoryDepnedenceResults instance.
517 class MemoryDependenceWrapperPass : public FunctionPass {
518 Optional<MemoryDependenceResults> MemDep;
523 MemoryDependenceWrapperPass();
524 ~MemoryDependenceWrapperPass() override;
526 /// Pass Implementation stuff. This doesn't do any analysis eagerly.
527 bool runOnFunction(Function &) override;
529 /// Clean up memory in between runs
530 void releaseMemory() override;
532 /// Does not modify anything. It uses Value Numbering and Alias Analysis.
533 void getAnalysisUsage(AnalysisUsage &AU) const override;
535 MemoryDependenceResults &getMemDep() { return *MemDep; }
538 } // end namespace llvm
540 #endif // LLVM_ANALYSIS_MEMORYDEPENDENCEANALYSIS_H