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MemoryDependenceAnalysis.h
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1 //===- llvm/Analysis/MemoryDependenceAnalysis.h - Memory Deps ---*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines the MemoryDependenceAnalysis analysis pass.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_ANALYSIS_MEMORYDEPENDENCEANALYSIS_H
15 #define LLVM_ANALYSIS_MEMORYDEPENDENCEANALYSIS_H
16 
17 #include "llvm/ADT/DenseMap.h"
18 #include "llvm/ADT/Optional.h"
22 #include "llvm/ADT/SmallPtrSet.h"
25 #include "llvm/IR/BasicBlock.h"
26 #include "llvm/IR/Metadata.h"
27 #include "llvm/IR/PassManager.h"
29 #include "llvm/IR/ValueHandle.h"
30 #include "llvm/Pass.h"
32 #include <cassert>
33 #include <cstdint>
34 #include <utility>
35 #include <vector>
36 
37 namespace llvm {
38 
39 class AssumptionCache;
40 class CallSite;
41 class DominatorTree;
42 class Function;
43 class Instruction;
44 class LoadInst;
45 class PHITransAddr;
46 class TargetLibraryInfo;
47 class Value;
48 
49 /// A memory dependence query can return one of three different answers.
50 class MemDepResult {
51  enum DepType {
52  /// Clients of MemDep never see this.
53  ///
54  /// Entries with this marker occur in a LocalDeps map or NonLocalDeps map
55  /// when the instruction they previously referenced was removed from
56  /// MemDep. In either case, the entry may include an instruction pointer.
57  /// If so, the pointer is an instruction in the block where scanning can
58  /// start from, saving some work.
59  ///
60  /// In a default-constructed MemDepResult object, the type will be Invalid
61  /// and the instruction pointer will be null.
62  Invalid = 0,
63 
64  /// This is a dependence on the specified instruction which clobbers the
65  /// desired value. The pointer member of the MemDepResult pair holds the
66  /// instruction that clobbers the memory. For example, this occurs when we
67  /// see a may-aliased store to the memory location we care about.
68  ///
69  /// There are several cases that may be interesting here:
70  /// 1. Loads are clobbered by may-alias stores.
71  /// 2. Loads are considered clobbered by partially-aliased loads. The
72  /// client may choose to analyze deeper into these cases.
73  Clobber,
74 
75  /// This is a dependence on the specified instruction which defines or
76  /// produces the desired memory location. The pointer member of the
77  /// MemDepResult pair holds the instruction that defines the memory.
78  ///
79  /// Cases of interest:
80  /// 1. This could be a load or store for dependence queries on
81  /// load/store. The value loaded or stored is the produced value.
82  /// Note that the pointer operand may be different than that of the
83  /// queried pointer due to must aliases and phi translation. Note
84  /// that the def may not be the same type as the query, the pointers
85  /// may just be must aliases.
86  /// 2. For loads and stores, this could be an allocation instruction. In
87  /// this case, the load is loading an undef value or a store is the
88  /// first store to (that part of) the allocation.
89  /// 3. Dependence queries on calls return Def only when they are readonly
90  /// calls or memory use intrinsics with identical callees and no
91  /// intervening clobbers. No validation is done that the operands to
92  /// the calls are the same.
93  Def,
94 
95  /// This marker indicates that the query has no known dependency in the
96  /// specified block.
97  ///
98  /// More detailed state info is encoded in the upper part of the pair (i.e.
99  /// the Instruction*)
100  Other
101  };
102 
103  /// If DepType is "Other", the upper part of the sum type is an encoding of
104  /// the following more detailed type information.
105  enum OtherType {
106  /// This marker indicates that the query has no dependency in the specified
107  /// block.
108  ///
109  /// To find out more, the client should query other predecessor blocks.
110  NonLocal = 1,
111  /// This marker indicates that the query has no dependency in the specified
112  /// function.
113  NonFuncLocal,
114  /// This marker indicates that the query dependency is unknown.
115  Unknown
116  };
117 
118  using ValueTy = PointerSumType<
123  ValueTy Value;
124 
125  explicit MemDepResult(ValueTy V) : Value(V) {}
126 
127 public:
128  MemDepResult() = default;
129 
130  /// get methods: These are static ctor methods for creating various
131  /// MemDepResult kinds.
133  assert(Inst && "Def requires inst");
134  return MemDepResult(ValueTy::create<Def>(Inst));
135  }
137  assert(Inst && "Clobber requires inst");
138  return MemDepResult(ValueTy::create<Clobber>(Inst));
139  }
141  return MemDepResult(ValueTy::create<Other>(NonLocal));
142  }
144  return MemDepResult(ValueTy::create<Other>(NonFuncLocal));
145  }
147  return MemDepResult(ValueTy::create<Other>(Unknown));
148  }
149 
150  /// Tests if this MemDepResult represents a query that is an instruction
151  /// clobber dependency.
152  bool isClobber() const { return Value.is<Clobber>(); }
153 
154  /// Tests if this MemDepResult represents a query that is an instruction
155  /// definition dependency.
156  bool isDef() const { return Value.is<Def>(); }
157 
158  /// Tests if this MemDepResult represents a query that is transparent to the
159  /// start of the block, but where a non-local hasn't been done.
160  bool isNonLocal() const {
161  return Value.is<Other>() && Value.cast<Other>() == NonLocal;
162  }
163 
164  /// Tests if this MemDepResult represents a query that is transparent to the
165  /// start of the function.
166  bool isNonFuncLocal() const {
167  return Value.is<Other>() && Value.cast<Other>() == NonFuncLocal;
168  }
169 
170  /// Tests if this MemDepResult represents a query which cannot and/or will
171  /// not be computed.
172  bool isUnknown() const {
173  return Value.is<Other>() && Value.cast<Other>() == Unknown;
174  }
175 
176  /// If this is a normal dependency, returns the instruction that is depended
177  /// on. Otherwise, returns null.
178  Instruction *getInst() const {
179  switch (Value.getTag()) {
180  case Invalid:
181  return Value.cast<Invalid>();
182  case Clobber:
183  return Value.cast<Clobber>();
184  case Def:
185  return Value.cast<Def>();
186  case Other:
187  return nullptr;
188  }
189  llvm_unreachable("Unknown discriminant!");
190  }
191 
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; }
195  bool operator>(const MemDepResult &M) const { return Value > M.Value; }
196 
197 private:
199 
200  /// Tests if this is a MemDepResult in its dirty/invalid. state.
201  bool isDirty() const { return Value.is<Invalid>(); }
202 
203  static MemDepResult getDirty(Instruction *Inst) {
204  return MemDepResult(ValueTy::create<Invalid>(Inst));
205  }
206 };
207 
208 /// This is an entry in the NonLocalDepInfo cache.
209 ///
210 /// For each BasicBlock (the BB entry) it keeps a MemDepResult.
212  BasicBlock *BB;
213  MemDepResult Result;
214 
215 public:
217  : BB(bb), Result(result) {}
218 
219  // This is used for searches.
220  NonLocalDepEntry(BasicBlock *bb) : BB(bb) {}
221 
222  // BB is the sort key, it can't be changed.
223  BasicBlock *getBB() const { return BB; }
224 
225  void setResult(const MemDepResult &R) { Result = R; }
226 
227  const MemDepResult &getResult() const { return Result; }
228 
229  bool operator<(const NonLocalDepEntry &RHS) const { return BB < RHS.BB; }
230 };
231 
232 /// This is a result from a NonLocal dependence query.
233 ///
234 /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the
235 /// (potentially phi translated) address that was live in the block.
237  NonLocalDepEntry Entry;
238  Value *Address;
239 
240 public:
241  NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address)
242  : Entry(bb, result), Address(address) {}
243 
244  // BB is the sort key, it can't be changed.
245  BasicBlock *getBB() const { return Entry.getBB(); }
246 
247  void setResult(const MemDepResult &R, Value *Addr) {
248  Entry.setResult(R);
249  Address = Addr;
250  }
251 
252  const MemDepResult &getResult() const { return Entry.getResult(); }
253 
254  /// Returns the address of this pointer in this block.
255  ///
256  /// This can be different than the address queried for the non-local result
257  /// because of phi translation. This returns null if the address was not
258  /// available in a block (i.e. because phi translation failed) or if this is
259  /// a cached result and that address was deleted.
260  ///
261  /// The address is always null for a non-local 'call' dependence.
262  Value *getAddress() const { return Address; }
263 };
264 
265 /// Provides a lazy, caching interface for making common memory aliasing
266 /// information queries, backed by LLVM's alias analysis passes.
267 ///
268 /// The dependency information returned is somewhat unusual, but is pragmatic.
269 /// If queried about a store or call that might modify memory, the analysis
270 /// will return the instruction[s] that may either load from that memory or
271 /// store to it. If queried with a load or call that can never modify memory,
272 /// the analysis will return calls and stores that might modify the pointer,
273 /// but generally does not return loads unless a) they are volatile, or
274 /// b) they load from *must-aliased* pointers. Returning a dependence on
275 /// must-alias'd pointers instead of all pointers interacts well with the
276 /// internal caching mechanism.
278  // A map from instructions to their dependency.
280  LocalDepMapType LocalDeps;
281 
282 public:
283  using NonLocalDepInfo = std::vector<NonLocalDepEntry>;
284 
285 private:
286  /// A pair<Value*, bool> where the bool is true if the dependence is a read
287  /// only dependence, false if read/write.
289 
290  /// This pair is used when caching information for a block.
291  ///
292  /// If the pointer is null, the cache value is not a full query that starts
293  /// at the specified block. If non-null, the bool indicates whether or not
294  /// the contents of the block was skipped.
296 
297  /// This record is the information kept for each (value, is load) pair.
298  struct NonLocalPointerInfo {
299  /// The pair of the block and the skip-first-block flag.
301  /// The results of the query for each relevant block.
302  NonLocalDepInfo NonLocalDeps;
303  /// The maximum size of the dereferences of the pointer.
304  ///
305  /// May be UnknownSize if the sizes are unknown.
307  /// The AA tags associated with dereferences of the pointer.
308  ///
309  /// The members may be null if there are no tags or conflicting tags.
310  AAMDNodes AATags;
311 
312  NonLocalPointerInfo() = default;
313  };
314 
315  /// Cache storing single nonlocal def for the instruction.
316  /// It is set when nonlocal def would be found in function returning only
317  /// local dependencies.
321  ReverseNonLocalDefsCacheTy ReverseNonLocalDefsCache;
322 
323  /// This map stores the cached results of doing a pointer lookup at the
324  /// bottom of a block.
325  ///
326  /// The key of this map is the pointer+isload bit, the value is a list of
327  /// <bb->result> mappings.
330  CachedNonLocalPointerInfo NonLocalPointerDeps;
331 
332  // A map from instructions to their non-local pointer dependencies.
335  ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps;
336 
337  /// This is the instruction we keep for each cached access that we have for
338  /// an instruction.
339  ///
340  /// The pointer is an owning pointer and the bool indicates whether we have
341  /// any dirty bits in the set.
342  using PerInstNLInfo = std::pair<NonLocalDepInfo, bool>;
343 
344  // A map from instructions to their non-local dependencies.
346 
347  NonLocalDepMapType NonLocalDeps;
348 
349  // A reverse mapping from dependencies to the dependees. This is
350  // used when removing instructions to keep the cache coherent.
351  using ReverseDepMapType =
353  ReverseDepMapType ReverseLocalDeps;
354 
355  // A reverse mapping from dependencies to the non-local dependees.
356  ReverseDepMapType ReverseNonLocalDeps;
357 
358  /// Current AA implementation, just a cache.
359  AliasAnalysis &AA;
360  AssumptionCache &AC;
361  const TargetLibraryInfo &TLI;
362  DominatorTree &DT;
363  PredIteratorCache PredCache;
364 
365 public:
367  const TargetLibraryInfo &TLI,
368  DominatorTree &DT)
369  : AA(AA), AC(AC), TLI(TLI), DT(DT) {}
370 
371  /// Handle invalidation in the new PM.
372  bool invalidate(Function &F, const PreservedAnalyses &PA,
374 
375  /// Some methods limit the number of instructions they will examine.
376  /// The return value of this method is the default limit that will be
377  /// used if no limit is explicitly passed in.
378  unsigned getDefaultBlockScanLimit() const;
379 
380  /// Returns the instruction on which a memory operation depends.
381  ///
382  /// See the class comment for more details. It is illegal to call this on
383  /// non-memory instructions.
384  MemDepResult getDependency(Instruction *QueryInst);
385 
386  /// Perform a full dependency query for the specified call, returning the set
387  /// of blocks that the value is potentially live across.
388  ///
389  /// The returned set of results will include a "NonLocal" result for all
390  /// blocks where the value is live across.
391  ///
392  /// This method assumes the instruction returns a "NonLocal" dependency
393  /// within its own block.
394  ///
395  /// This returns a reference to an internal data structure that may be
396  /// invalidated on the next non-local query or when an instruction is
397  /// removed. Clients must copy this data if they want it around longer than
398  /// that.
399  const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS);
400 
401  /// Perform a full dependency query for an access to the QueryInst's
402  /// specified memory location, returning the set of instructions that either
403  /// define or clobber the value.
404  ///
405  /// Warning: For a volatile query instruction, the dependencies will be
406  /// accurate, and thus usable for reordering, but it is never legal to
407  /// remove the query instruction.
408  ///
409  /// This method assumes the pointer has a "NonLocal" dependency within
410  /// QueryInst's parent basic block.
411  void getNonLocalPointerDependency(Instruction *QueryInst,
413 
414  /// Removes an instruction from the dependence analysis, updating the
415  /// dependence of instructions that previously depended on it.
416  void removeInstruction(Instruction *InstToRemove);
417 
418  /// Invalidates cached information about the specified pointer, because it
419  /// may be too conservative in memdep.
420  ///
421  /// This is an optional call that can be used when the client detects an
422  /// equivalence between the pointer and some other value and replaces the
423  /// other value with ptr. This can make Ptr available in more places that
424  /// cached info does not necessarily keep.
425  void invalidateCachedPointerInfo(Value *Ptr);
426 
427  /// Clears the PredIteratorCache info.
428  ///
429  /// This needs to be done when the CFG changes, e.g., due to splitting
430  /// critical edges.
431  void invalidateCachedPredecessors();
432 
433  /// Returns the instruction on which a memory location depends.
434  ///
435  /// If isLoad is true, this routine ignores may-aliases with read-only
436  /// operations. If isLoad is false, this routine ignores may-aliases
437  /// with reads from read-only locations. If possible, pass the query
438  /// instruction as well; this function may take advantage of the metadata
439  /// annotated to the query instruction to refine the result. \p Limit
440  /// can be used to set the maximum number of instructions that will be
441  /// examined to find the pointer dependency. On return, it will be set to
442  /// the number of instructions left to examine. If a null pointer is passed
443  /// in, the limit will default to the value of -memdep-block-scan-limit.
444  ///
445  /// Note that this is an uncached query, and thus may be inefficient.
446  MemDepResult getPointerDependencyFrom(const MemoryLocation &Loc, bool isLoad,
447  BasicBlock::iterator ScanIt,
448  BasicBlock *BB,
449  Instruction *QueryInst = nullptr,
450  unsigned *Limit = nullptr);
451 
452  MemDepResult getSimplePointerDependencyFrom(const MemoryLocation &MemLoc,
453  bool isLoad,
454  BasicBlock::iterator ScanIt,
455  BasicBlock *BB,
456  Instruction *QueryInst,
457  unsigned *Limit = nullptr);
458 
459  /// This analysis looks for other loads and stores with invariant.group
460  /// metadata and the same pointer operand. Returns Unknown if it does not
461  /// find anything, and Def if it can be assumed that 2 instructions load or
462  /// store the same value and NonLocal which indicate that non-local Def was
463  /// found, which can be retrieved by calling getNonLocalPointerDependency
464  /// with the same queried instruction.
465  MemDepResult getInvariantGroupPointerDependency(LoadInst *LI, BasicBlock *BB);
466 
467  /// Looks at a memory location for a load (specified by MemLocBase, Offs, and
468  /// Size) and compares it against a load.
469  ///
470  /// If the specified load could be safely widened to a larger integer load
471  /// that is 1) still efficient, 2) safe for the target, and 3) would provide
472  /// the specified memory location value, then this function returns the size
473  /// in bytes of the load width to use. If not, this returns zero.
474  static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase,
475  int64_t MemLocOffs,
476  unsigned MemLocSize,
477  const LoadInst *LI);
478 
479  /// Release memory in caches.
480  void releaseMemory();
481 
482 private:
483  MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall,
484  BasicBlock::iterator ScanIt,
485  BasicBlock *BB);
486  bool getNonLocalPointerDepFromBB(Instruction *QueryInst,
487  const PHITransAddr &Pointer,
488  const MemoryLocation &Loc, bool isLoad,
489  BasicBlock *BB,
492  bool SkipFirstBlock = false);
493  MemDepResult GetNonLocalInfoForBlock(Instruction *QueryInst,
494  const MemoryLocation &Loc, bool isLoad,
495  BasicBlock *BB, NonLocalDepInfo *Cache,
496  unsigned NumSortedEntries);
497 
498  void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P);
499 
500  void verifyRemoved(Instruction *Inst) const;
501 };
502 
503 /// An analysis that produces \c MemoryDependenceResults for a function.
504 ///
505 /// This is essentially a no-op because the results are computed entirely
506 /// lazily.
508  : public AnalysisInfoMixin<MemoryDependenceAnalysis> {
510 
511  static AnalysisKey Key;
512 
513 public:
515 
517 };
518 
519 /// A wrapper analysis pass for the legacy pass manager that exposes a \c
520 /// MemoryDepnedenceResults instance.
523 
524 public:
525  static char ID;
526 
528  ~MemoryDependenceWrapperPass() override;
529 
530  /// Pass Implementation stuff. This doesn't do any analysis eagerly.
531  bool runOnFunction(Function &) override;
532 
533  /// Clean up memory in between runs
534  void releaseMemory() override;
535 
536  /// Does not modify anything. It uses Value Numbering and Alias Analysis.
537  void getAnalysisUsage(AnalysisUsage &AU) const override;
538 
539  MemoryDependenceResults &getMemDep() { return *MemDep; }
540 };
541 
542 } // end namespace llvm
543 
544 #endif // LLVM_ANALYSIS_MEMORYDEPENDENCEANALYSIS_H
uint64_t CallInst * C
uint64_t LocationSize
MemoryDependenceResults(AliasAnalysis &AA, AssumptionCache &AC, const TargetLibraryInfo &TLI, DominatorTree &DT)
Value * getAddress() const
Returns the address of this pointer in this block.
Provides a lazy, caching interface for making common memory aliasing information queries, backed by LLVM&#39;s alias analysis passes.
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
A compile time pair of an integer tag and the pointer-like type which it indexes within a sum type...
bool operator<(const NonLocalDepEntry &RHS) const
bool isNonLocal() const
Tests if this MemDepResult represents a query that is transparent to the start of the block...
This file contains the declarations for metadata subclasses.
bool operator>(const MemDepResult &M) const
A cache of @llvm.assume calls within a function.
F(f)
An instruction for reading from memory.
Definition: Instructions.h:168
void setResult(const MemDepResult &R, Value *Addr)
bool operator!=(const MemDepResult &M) const
bool isDef() const
Tests if this MemDepResult represents a query that is an instruction definition dependency.
bool isClobber() const
Tests if this MemDepResult represents a query that is an instruction clobber dependency.
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APFloat.h:42
static bool isLoad(int Opcode)
static MemDepResult getDef(Instruction *Inst)
get methods: These are static ctor methods for creating various MemDepResult kinds.
An analysis that produces MemoryDependenceResults for a function.
Key
PAL metadata keys.
PredIteratorCache - This class is an extremely trivial cache for predecessor iterator queries...
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:142
static MemDepResult getUnknown()
static bool runOnFunction(Function &F, bool PostInlining)
#define P(N)
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:153
LLVM Basic Block Representation.
Definition: BasicBlock.h:59
PointerIntPair - This class implements a pair of a pointer and small integer.
PHITransAddr - An address value which tracks and handles phi translation.
Definition: PHITransAddr.h:36
This is a result from a NonLocal dependence query.
A CRTP mix-in that provides informational APIs needed for analysis passes.
Definition: PassManager.h:382
NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address)
Represent the analysis usage information of a pass.
static MemDepResult getNonFuncLocal()
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:285
bool operator<(const MemDepResult &M) const
void setResult(const MemDepResult &R)
A wrapper analysis pass for the legacy pass manager that exposes a MemoryDepnedenceResults instance...
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
A memory dependence query can return one of three different answers.
Representation for a specific memory location.
const MemDepResult & getResult() const
NonLocalDepEntry(BasicBlock *bb, MemDepResult result)
Provides information about what library functions are available for the current target.
static MemDepResult getClobber(Instruction *Inst)
const MemDepResult & getResult() const
A collection of metadata nodes that might be associated with a memory access used by the alias-analys...
Definition: Metadata.h:642
InstListType::iterator iterator
Instruction iterators...
Definition: BasicBlock.h:91
bool isNonFuncLocal() const
Tests if this MemDepResult represents a query that is transparent to the start of the function...
std::vector< NonLocalDepEntry > NonLocalDepInfo
A sum type over pointer-like types.
bool isUnknown() const
Tests if this MemDepResult represents a query which cannot and/or will not be computed.
Instruction * getInst() const
If this is a normal dependency, returns the instruction that is depended on.
This file provides utility analysis objects describing memory locations.
MemDepResult()=default
API to communicate dependencies between analyses during invalidation.
Definition: PassManager.h:559
bool operator==(const MemDepResult &M) const
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
LLVM Value Representation.
Definition: Value.h:73
constexpr char Size[]
Key for Kernel::Arg::Metadata::mSize.
This is an entry in the NonLocalDepInfo cache.
A container for analyses that lazily runs them and caches their results.
This header defines various interfaces for pass management in LLVM.
static MemDepResult getNonLocal()
A special type used by analysis passes to provide an address that identifies that particular analysis...
Definition: PassManager.h:70