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/IR/ValueHandle.h"
30 #include "llvm/Pass.h"
31 #include "llvm/Support/ErrorHandling.h"
39 class AssumptionCache;
46 class TargetLibraryInfo;
50 /// A memory dependence query can return one of three different answers.
53 /// Clients of MemDep never see this.
55 /// Entries with this marker occur in a LocalDeps map or NonLocalDeps map
56 /// when the instruction they previously referenced was removed from
57 /// MemDep. In either case, the entry may include an instruction pointer.
58 /// If so, the pointer is an instruction in the block where scanning can
59 /// start from, saving some work.
61 /// In a default-constructed MemDepResult object, the type will be Invalid
62 /// and the instruction pointer will be null.
65 /// This is a dependence on the specified instruction which clobbers the
66 /// desired value. The pointer member of the MemDepResult pair holds the
67 /// instruction that clobbers the memory. For example, this occurs when we
68 /// see a may-aliased store to the memory location we care about.
70 /// There are several cases that may be interesting here:
71 /// 1. Loads are clobbered by may-alias stores.
72 /// 2. Loads are considered clobbered by partially-aliased loads. The
73 /// client may choose to analyze deeper into these cases.
76 /// This is a dependence on the specified instruction which defines or
77 /// produces the desired memory location. The pointer member of the
78 /// MemDepResult pair holds the instruction that defines the memory.
80 /// Cases of interest:
81 /// 1. This could be a load or store for dependence queries on
82 /// load/store. The value loaded or stored is the produced value.
83 /// Note that the pointer operand may be different than that of the
84 /// queried pointer due to must aliases and phi translation. Note
85 /// that the def may not be the same type as the query, the pointers
86 /// may just be must aliases.
87 /// 2. For loads and stores, this could be an allocation instruction. In
88 /// this case, the load is loading an undef value or a store is the
89 /// first store to (that part of) the allocation.
90 /// 3. Dependence queries on calls return Def only when they are readonly
91 /// calls or memory use intrinsics with identical callees and no
92 /// intervening clobbers. No validation is done that the operands to
93 /// the calls are the same.
96 /// This marker indicates that the query has no known dependency in the
99 /// More detailed state info is encoded in the upper part of the pair (i.e.
100 /// the Instruction*)
104 /// If DepType is "Other", the upper part of the sum type is an encoding of
105 /// the following more detailed type information.
107 /// This marker indicates that the query has no dependency in the specified
110 /// To find out more, the client should query other predecessor blocks.
112 /// This marker indicates that the query has no dependency in the specified
115 /// This marker indicates that the query dependency is unknown.
119 using ValueTy = PointerSumType<
120 DepType, PointerSumTypeMember<Invalid, Instruction *>,
121 PointerSumTypeMember<Clobber, Instruction *>,
122 PointerSumTypeMember<Def, Instruction *>,
123 PointerSumTypeMember<Other, PointerEmbeddedInt<OtherType, 3>>>;
126 explicit MemDepResult(ValueTy V) : Value(V) {}
129 MemDepResult() = default;
131 /// get methods: These are static ctor methods for creating various
132 /// MemDepResult kinds.
133 static MemDepResult getDef(Instruction *Inst) {
134 assert(Inst && "Def requires inst");
135 return MemDepResult(ValueTy::create<Def>(Inst));
137 static MemDepResult getClobber(Instruction *Inst) {
138 assert(Inst && "Clobber requires inst");
139 return MemDepResult(ValueTy::create<Clobber>(Inst));
141 static MemDepResult getNonLocal() {
142 return MemDepResult(ValueTy::create<Other>(NonLocal));
144 static MemDepResult getNonFuncLocal() {
145 return MemDepResult(ValueTy::create<Other>(NonFuncLocal));
147 static MemDepResult getUnknown() {
148 return MemDepResult(ValueTy::create<Other>(Unknown));
151 /// Tests if this MemDepResult represents a query that is an instruction
152 /// clobber dependency.
153 bool isClobber() const { return Value.is<Clobber>(); }
155 /// Tests if this MemDepResult represents a query that is an instruction
156 /// definition dependency.
157 bool isDef() const { return Value.is<Def>(); }
159 /// Tests if this MemDepResult represents a query that is transparent to the
160 /// start of the block, but where a non-local hasn't been done.
161 bool isNonLocal() const {
162 return Value.is<Other>() && Value.cast<Other>() == NonLocal;
165 /// Tests if this MemDepResult represents a query that is transparent to the
166 /// start of the function.
167 bool isNonFuncLocal() const {
168 return Value.is<Other>() && Value.cast<Other>() == NonFuncLocal;
171 /// Tests if this MemDepResult represents a query which cannot and/or will
173 bool isUnknown() const {
174 return Value.is<Other>() && Value.cast<Other>() == Unknown;
177 /// If this is a normal dependency, returns the instruction that is depended
178 /// on. Otherwise, returns null.
179 Instruction *getInst() const {
180 switch (Value.getTag()) {
182 return Value.cast<Invalid>();
184 return Value.cast<Clobber>();
186 return Value.cast<Def>();
190 llvm_unreachable("Unknown discriminant!");
193 bool operator==(const MemDepResult &M) const { return Value == M.Value; }
194 bool operator!=(const MemDepResult &M) const { return Value != M.Value; }
195 bool operator<(const MemDepResult &M) const { return Value < M.Value; }
196 bool operator>(const MemDepResult &M) const { return Value > M.Value; }
199 friend class MemoryDependenceResults;
201 /// Tests if this is a MemDepResult in its dirty/invalid. state.
202 bool isDirty() const { return Value.is<Invalid>(); }
204 static MemDepResult getDirty(Instruction *Inst) {
205 return MemDepResult(ValueTy::create<Invalid>(Inst));
209 /// This is an entry in the NonLocalDepInfo cache.
211 /// For each BasicBlock (the BB entry) it keeps a MemDepResult.
212 class NonLocalDepEntry {
217 NonLocalDepEntry(BasicBlock *bb, MemDepResult result)
218 : BB(bb), Result(result) {}
220 // This is used for searches.
221 NonLocalDepEntry(BasicBlock *bb) : BB(bb) {}
223 // BB is the sort key, it can't be changed.
224 BasicBlock *getBB() const { return BB; }
226 void setResult(const MemDepResult &R) { Result = R; }
228 const MemDepResult &getResult() const { return Result; }
230 bool operator<(const NonLocalDepEntry &RHS) const { return BB < RHS.BB; }
233 /// This is a result from a NonLocal dependence query.
235 /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the
236 /// (potentially phi translated) address that was live in the block.
237 class NonLocalDepResult {
238 NonLocalDepEntry Entry;
242 NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address)
243 : Entry(bb, result), Address(address) {}
245 // BB is the sort key, it can't be changed.
246 BasicBlock *getBB() const { return Entry.getBB(); }
248 void setResult(const MemDepResult &R, Value *Addr) {
253 const MemDepResult &getResult() const { return Entry.getResult(); }
255 /// Returns the address of this pointer in this block.
257 /// This can be different than the address queried for the non-local result
258 /// because of phi translation. This returns null if the address was not
259 /// available in a block (i.e. because phi translation failed) or if this is
260 /// a cached result and that address was deleted.
262 /// The address is always null for a non-local 'call' dependence.
263 Value *getAddress() const { return Address; }
266 /// Provides a lazy, caching interface for making common memory aliasing
267 /// information queries, backed by LLVM's alias analysis passes.
269 /// The dependency information returned is somewhat unusual, but is pragmatic.
270 /// If queried about a store or call that might modify memory, the analysis
271 /// will return the instruction[s] that may either load from that memory or
272 /// store to it. If queried with a load or call that can never modify memory,
273 /// the analysis will return calls and stores that might modify the pointer,
274 /// but generally does not return loads unless a) they are volatile, or
275 /// b) they load from *must-aliased* pointers. Returning a dependence on
276 /// must-alias'd pointers instead of all pointers interacts well with the
277 /// internal caching mechanism.
278 class MemoryDependenceResults {
279 // A map from instructions to their dependency.
280 using LocalDepMapType = DenseMap<Instruction *, MemDepResult>;
281 LocalDepMapType LocalDeps;
284 using NonLocalDepInfo = std::vector<NonLocalDepEntry>;
287 /// A pair<Value*, bool> where the bool is true if the dependence is a read
288 /// only dependence, false if read/write.
289 using ValueIsLoadPair = PointerIntPair<const Value *, 1, bool>;
291 /// This pair is used when caching information for a block.
293 /// If the pointer is null, the cache value is not a full query that starts
294 /// at the specified block. If non-null, the bool indicates whether or not
295 /// the contents of the block was skipped.
296 using BBSkipFirstBlockPair = PointerIntPair<BasicBlock *, 1, bool>;
298 /// This record is the information kept for each (value, is load) pair.
299 struct NonLocalPointerInfo {
300 /// The pair of the block and the skip-first-block flag.
301 BBSkipFirstBlockPair Pair;
302 /// The results of the query for each relevant block.
303 NonLocalDepInfo NonLocalDeps;
304 /// The maximum size of the dereferences of the pointer.
306 /// May be UnknownSize if the sizes are unknown.
307 LocationSize Size = MemoryLocation::UnknownSize;
308 /// The AA tags associated with dereferences of the pointer.
310 /// The members may be null if there are no tags or conflicting tags.
313 NonLocalPointerInfo() = default;
316 /// Cache storing single nonlocal def for the instruction.
317 /// It is set when nonlocal def would be found in function returning only
318 /// local dependencies.
319 DenseMap<AssertingVH<const Value>, NonLocalDepResult> NonLocalDefsCache;
320 using ReverseNonLocalDefsCacheTy =
321 DenseMap<Instruction *, SmallPtrSet<const Value*, 4>>;
322 ReverseNonLocalDefsCacheTy ReverseNonLocalDefsCache;
324 /// This map stores the cached results of doing a pointer lookup at the
325 /// bottom of a block.
327 /// The key of this map is the pointer+isload bit, the value is a list of
328 /// <bb->result> mappings.
329 using CachedNonLocalPointerInfo =
330 DenseMap<ValueIsLoadPair, NonLocalPointerInfo>;
331 CachedNonLocalPointerInfo NonLocalPointerDeps;
333 // A map from instructions to their non-local pointer dependencies.
334 using ReverseNonLocalPtrDepTy =
335 DenseMap<Instruction *, SmallPtrSet<ValueIsLoadPair, 4>>;
336 ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps;
338 /// This is the instruction we keep for each cached access that we have for
341 /// The pointer is an owning pointer and the bool indicates whether we have
342 /// any dirty bits in the set.
343 using PerInstNLInfo = std::pair<NonLocalDepInfo, bool>;
345 // A map from instructions to their non-local dependencies.
346 using NonLocalDepMapType = DenseMap<Instruction *, PerInstNLInfo>;
348 NonLocalDepMapType NonLocalDeps;
350 // A reverse mapping from dependencies to the dependees. This is
351 // used when removing instructions to keep the cache coherent.
352 using ReverseDepMapType =
353 DenseMap<Instruction *, SmallPtrSet<Instruction *, 4>>;
354 ReverseDepMapType ReverseLocalDeps;
356 // A reverse mapping from dependencies to the non-local dependees.
357 ReverseDepMapType ReverseNonLocalDeps;
359 /// Current AA implementation, just a cache.
362 const TargetLibraryInfo &TLI;
365 PredIteratorCache PredCache;
368 MemoryDependenceResults(AliasAnalysis &AA, AssumptionCache &AC,
369 const TargetLibraryInfo &TLI,
370 DominatorTree &DT, PhiValues &PV)
371 : AA(AA), AC(AC), TLI(TLI), DT(DT), PV(PV) {}
373 /// Handle invalidation in the new PM.
374 bool invalidate(Function &F, const PreservedAnalyses &PA,
375 FunctionAnalysisManager::Invalidator &Inv);
377 /// Some methods limit the number of instructions they will examine.
378 /// The return value of this method is the default limit that will be
379 /// used if no limit is explicitly passed in.
380 unsigned getDefaultBlockScanLimit() const;
382 /// Returns the instruction on which a memory operation depends.
384 /// See the class comment for more details. It is illegal to call this on
385 /// non-memory instructions.
386 MemDepResult getDependency(Instruction *QueryInst);
388 /// Perform a full dependency query for the specified call, returning the set
389 /// of blocks that the value is potentially live across.
391 /// The returned set of results will include a "NonLocal" result for all
392 /// blocks where the value is live across.
394 /// This method assumes the instruction returns a "NonLocal" dependency
395 /// within its own block.
397 /// This returns a reference to an internal data structure that may be
398 /// invalidated on the next non-local query or when an instruction is
399 /// removed. Clients must copy this data if they want it around longer than
401 const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS);
403 /// Perform a full dependency query for an access to the QueryInst's
404 /// specified memory location, returning the set of instructions that either
405 /// define or clobber the value.
407 /// Warning: For a volatile query instruction, the dependencies will be
408 /// accurate, and thus usable for reordering, but it is never legal to
409 /// remove the query instruction.
411 /// This method assumes the pointer has a "NonLocal" dependency within
412 /// QueryInst's parent basic block.
413 void getNonLocalPointerDependency(Instruction *QueryInst,
414 SmallVectorImpl<NonLocalDepResult> &Result);
416 /// Removes an instruction from the dependence analysis, updating the
417 /// dependence of instructions that previously depended on it.
418 void removeInstruction(Instruction *InstToRemove);
420 /// Invalidates cached information about the specified pointer, because it
421 /// may be too conservative in memdep.
423 /// This is an optional call that can be used when the client detects an
424 /// equivalence between the pointer and some other value and replaces the
425 /// other value with ptr. This can make Ptr available in more places that
426 /// cached info does not necessarily keep.
427 void invalidateCachedPointerInfo(Value *Ptr);
429 /// Clears the PredIteratorCache info.
431 /// This needs to be done when the CFG changes, e.g., due to splitting
433 void invalidateCachedPredecessors();
435 /// Returns the instruction on which a memory location depends.
437 /// If isLoad is true, this routine ignores may-aliases with read-only
438 /// operations. If isLoad is false, this routine ignores may-aliases
439 /// with reads from read-only locations. If possible, pass the query
440 /// instruction as well; this function may take advantage of the metadata
441 /// annotated to the query instruction to refine the result. \p Limit
442 /// can be used to set the maximum number of instructions that will be
443 /// examined to find the pointer dependency. On return, it will be set to
444 /// the number of instructions left to examine. If a null pointer is passed
445 /// in, the limit will default to the value of -memdep-block-scan-limit.
447 /// Note that this is an uncached query, and thus may be inefficient.
448 MemDepResult getPointerDependencyFrom(const MemoryLocation &Loc, bool isLoad,
449 BasicBlock::iterator ScanIt,
451 Instruction *QueryInst = nullptr,
452 unsigned *Limit = nullptr);
454 MemDepResult getSimplePointerDependencyFrom(const MemoryLocation &MemLoc,
456 BasicBlock::iterator ScanIt,
458 Instruction *QueryInst,
459 unsigned *Limit = nullptr);
461 /// This analysis looks for other loads and stores with invariant.group
462 /// metadata and the same pointer operand. Returns Unknown if it does not
463 /// find anything, and Def if it can be assumed that 2 instructions load or
464 /// store the same value and NonLocal which indicate that non-local Def was
465 /// found, which can be retrieved by calling getNonLocalPointerDependency
466 /// with the same queried instruction.
467 MemDepResult getInvariantGroupPointerDependency(LoadInst *LI, BasicBlock *BB);
469 /// Looks at a memory location for a load (specified by MemLocBase, Offs, and
470 /// Size) and compares it against a load.
472 /// If the specified load could be safely widened to a larger integer load
473 /// that is 1) still efficient, 2) safe for the target, and 3) would provide
474 /// the specified memory location value, then this function returns the size
475 /// in bytes of the load width to use. If not, this returns zero.
476 static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase,
481 /// Release memory in caches.
482 void releaseMemory();
485 MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall,
486 BasicBlock::iterator ScanIt,
488 bool getNonLocalPointerDepFromBB(Instruction *QueryInst,
489 const PHITransAddr &Pointer,
490 const MemoryLocation &Loc, bool isLoad,
492 SmallVectorImpl<NonLocalDepResult> &Result,
493 DenseMap<BasicBlock *, Value *> &Visited,
494 bool SkipFirstBlock = false);
495 MemDepResult GetNonLocalInfoForBlock(Instruction *QueryInst,
496 const MemoryLocation &Loc, bool isLoad,
497 BasicBlock *BB, NonLocalDepInfo *Cache,
498 unsigned NumSortedEntries);
500 void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P);
502 void verifyRemoved(Instruction *Inst) const;
505 /// An analysis that produces \c MemoryDependenceResults for a function.
507 /// This is essentially a no-op because the results are computed entirely
509 class MemoryDependenceAnalysis
510 : public AnalysisInfoMixin<MemoryDependenceAnalysis> {
511 friend AnalysisInfoMixin<MemoryDependenceAnalysis>;
513 static AnalysisKey Key;
516 using Result = MemoryDependenceResults;
518 MemoryDependenceResults run(Function &F, FunctionAnalysisManager &AM);
521 /// A wrapper analysis pass for the legacy pass manager that exposes a \c
522 /// MemoryDepnedenceResults instance.
523 class MemoryDependenceWrapperPass : public FunctionPass {
524 Optional<MemoryDependenceResults> MemDep;
529 MemoryDependenceWrapperPass();
530 ~MemoryDependenceWrapperPass() override;
532 /// Pass Implementation stuff. This doesn't do any analysis eagerly.
533 bool runOnFunction(Function &) override;
535 /// Clean up memory in between runs
536 void releaseMemory() override;
538 /// Does not modify anything. It uses Value Numbering and Alias Analysis.
539 void getAnalysisUsage(AnalysisUsage &AU) const override;
541 MemoryDependenceResults &getMemDep() { return *MemDep; }
544 } // end namespace llvm
546 #endif // LLVM_ANALYSIS_MEMORYDEPENDENCEANALYSIS_H