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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 PhiValues;
48 class Value;
49 
50 /// A memory dependence query can return one of three different answers.
51 class MemDepResult {
52  enum DepType {
53  /// Clients of MemDep never see this.
54  ///
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.
60  ///
61  /// In a default-constructed MemDepResult object, the type will be Invalid
62  /// and the instruction pointer will be null.
63  Invalid = 0,
64 
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.
69  ///
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.
74  Clobber,
75 
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.
79  ///
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.
94  Def,
95 
96  /// This marker indicates that the query has no known dependency in the
97  /// specified block.
98  ///
99  /// More detailed state info is encoded in the upper part of the pair (i.e.
100  /// the Instruction*)
101  Other
102  };
103 
104  /// If DepType is "Other", the upper part of the sum type is an encoding of
105  /// the following more detailed type information.
106  enum OtherType {
107  /// This marker indicates that the query has no dependency in the specified
108  /// block.
109  ///
110  /// To find out more, the client should query other predecessor blocks.
111  NonLocal = 1,
112  /// This marker indicates that the query has no dependency in the specified
113  /// function.
114  NonFuncLocal,
115  /// This marker indicates that the query dependency is unknown.
116  Unknown
117  };
118 
119  using ValueTy = PointerSumType<
124  ValueTy Value;
125 
126  explicit MemDepResult(ValueTy V) : Value(V) {}
127 
128 public:
129  MemDepResult() = default;
130 
131  /// get methods: These are static ctor methods for creating various
132  /// MemDepResult kinds.
134  assert(Inst && "Def requires inst");
135  return MemDepResult(ValueTy::create<Def>(Inst));
136  }
138  assert(Inst && "Clobber requires inst");
139  return MemDepResult(ValueTy::create<Clobber>(Inst));
140  }
142  return MemDepResult(ValueTy::create<Other>(NonLocal));
143  }
145  return MemDepResult(ValueTy::create<Other>(NonFuncLocal));
146  }
148  return MemDepResult(ValueTy::create<Other>(Unknown));
149  }
150 
151  /// Tests if this MemDepResult represents a query that is an instruction
152  /// clobber dependency.
153  bool isClobber() const { return Value.is<Clobber>(); }
154 
155  /// Tests if this MemDepResult represents a query that is an instruction
156  /// definition dependency.
157  bool isDef() const { return Value.is<Def>(); }
158 
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;
163  }
164 
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;
169  }
170 
171  /// Tests if this MemDepResult represents a query which cannot and/or will
172  /// not be computed.
173  bool isUnknown() const {
174  return Value.is<Other>() && Value.cast<Other>() == Unknown;
175  }
176 
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()) {
181  case Invalid:
182  return Value.cast<Invalid>();
183  case Clobber:
184  return Value.cast<Clobber>();
185  case Def:
186  return Value.cast<Def>();
187  case Other:
188  return nullptr;
189  }
190  llvm_unreachable("Unknown discriminant!");
191  }
192 
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; }
197 
198 private:
200 
201  /// Tests if this is a MemDepResult in its dirty/invalid. state.
202  bool isDirty() const { return Value.is<Invalid>(); }
203 
204  static MemDepResult getDirty(Instruction *Inst) {
205  return MemDepResult(ValueTy::create<Invalid>(Inst));
206  }
207 };
208 
209 /// This is an entry in the NonLocalDepInfo cache.
210 ///
211 /// For each BasicBlock (the BB entry) it keeps a MemDepResult.
213  BasicBlock *BB;
215 
216 public:
218  : BB(bb), Result(result) {}
219 
220  // This is used for searches.
221  NonLocalDepEntry(BasicBlock *bb) : BB(bb) {}
222 
223  // BB is the sort key, it can't be changed.
224  BasicBlock *getBB() const { return BB; }
225 
226  void setResult(const MemDepResult &R) { Result = R; }
227 
228  const MemDepResult &getResult() const { return Result; }
229 
230  bool operator<(const NonLocalDepEntry &RHS) const { return BB < RHS.BB; }
231 };
232 
233 /// This is a result from a NonLocal dependence query.
234 ///
235 /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the
236 /// (potentially phi translated) address that was live in the block.
238  NonLocalDepEntry Entry;
239  Value *Address;
240 
241 public:
242  NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address)
243  : Entry(bb, result), Address(address) {}
244 
245  // BB is the sort key, it can't be changed.
246  BasicBlock *getBB() const { return Entry.getBB(); }
247 
248  void setResult(const MemDepResult &R, Value *Addr) {
249  Entry.setResult(R);
250  Address = Addr;
251  }
252 
253  const MemDepResult &getResult() const { return Entry.getResult(); }
254 
255  /// Returns the address of this pointer in this block.
256  ///
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.
261  ///
262  /// The address is always null for a non-local 'call' dependence.
263  Value *getAddress() const { return Address; }
264 };
265 
266 /// Provides a lazy, caching interface for making common memory aliasing
267 /// information queries, backed by LLVM's alias analysis passes.
268 ///
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.
279  // A map from instructions to their dependency.
281  LocalDepMapType LocalDeps;
282 
283 public:
284  using NonLocalDepInfo = std::vector<NonLocalDepEntry>;
285 
286 private:
287  /// A pair<Value*, bool> where the bool is true if the dependence is a read
288  /// only dependence, false if read/write.
290 
291  /// This pair is used when caching information for a block.
292  ///
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.
297 
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.
302  /// The results of the query for each relevant block.
303  NonLocalDepInfo NonLocalDeps;
304  /// The maximum size of the dereferences of the pointer.
305  ///
306  /// May be UnknownSize if the sizes are unknown.
308  /// The AA tags associated with dereferences of the pointer.
309  ///
310  /// The members may be null if there are no tags or conflicting tags.
311  AAMDNodes AATags;
312 
313  NonLocalPointerInfo() = default;
314  };
315 
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.
322  ReverseNonLocalDefsCacheTy ReverseNonLocalDefsCache;
323 
324  /// This map stores the cached results of doing a pointer lookup at the
325  /// bottom of a block.
326  ///
327  /// The key of this map is the pointer+isload bit, the value is a list of
328  /// <bb->result> mappings.
331  CachedNonLocalPointerInfo NonLocalPointerDeps;
332 
333  // A map from instructions to their non-local pointer dependencies.
336  ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps;
337 
338  /// This is the instruction we keep for each cached access that we have for
339  /// an instruction.
340  ///
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>;
344 
345  // A map from instructions to their non-local dependencies.
347 
348  NonLocalDepMapType NonLocalDeps;
349 
350  // A reverse mapping from dependencies to the dependees. This is
351  // used when removing instructions to keep the cache coherent.
352  using ReverseDepMapType =
354  ReverseDepMapType ReverseLocalDeps;
355 
356  // A reverse mapping from dependencies to the non-local dependees.
357  ReverseDepMapType ReverseNonLocalDeps;
358 
359  /// Current AA implementation, just a cache.
360  AliasAnalysis &AA;
361  AssumptionCache &AC;
362  const TargetLibraryInfo &TLI;
363  DominatorTree &DT;
364  PhiValues &PV;
365  PredIteratorCache PredCache;
366 
367 public:
369  const TargetLibraryInfo &TLI,
370  DominatorTree &DT, PhiValues &PV)
371  : AA(AA), AC(AC), TLI(TLI), DT(DT), PV(PV) {}
372 
373  /// Handle invalidation in the new PM.
374  bool invalidate(Function &F, const PreservedAnalyses &PA,
376 
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;
381 
382  /// Returns the instruction on which a memory operation depends.
383  ///
384  /// See the class comment for more details. It is illegal to call this on
385  /// non-memory instructions.
386  MemDepResult getDependency(Instruction *QueryInst);
387 
388  /// Perform a full dependency query for the specified call, returning the set
389  /// of blocks that the value is potentially live across.
390  ///
391  /// The returned set of results will include a "NonLocal" result for all
392  /// blocks where the value is live across.
393  ///
394  /// This method assumes the instruction returns a "NonLocal" dependency
395  /// within its own block.
396  ///
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
400  /// that.
401  const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS);
402 
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.
406  ///
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.
410  ///
411  /// This method assumes the pointer has a "NonLocal" dependency within
412  /// QueryInst's parent basic block.
413  void getNonLocalPointerDependency(Instruction *QueryInst,
415 
416  /// Removes an instruction from the dependence analysis, updating the
417  /// dependence of instructions that previously depended on it.
418  void removeInstruction(Instruction *InstToRemove);
419 
420  /// Invalidates cached information about the specified pointer, because it
421  /// may be too conservative in memdep.
422  ///
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);
428 
429  /// Clears the PredIteratorCache info.
430  ///
431  /// This needs to be done when the CFG changes, e.g., due to splitting
432  /// critical edges.
433  void invalidateCachedPredecessors();
434 
435  /// Returns the instruction on which a memory location depends.
436  ///
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.
446  ///
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,
450  BasicBlock *BB,
451  Instruction *QueryInst = nullptr,
452  unsigned *Limit = nullptr);
453 
454  MemDepResult getSimplePointerDependencyFrom(const MemoryLocation &MemLoc,
455  bool isLoad,
456  BasicBlock::iterator ScanIt,
457  BasicBlock *BB,
458  Instruction *QueryInst,
459  unsigned *Limit = nullptr);
460 
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);
468 
469  /// Looks at a memory location for a load (specified by MemLocBase, Offs, and
470  /// Size) and compares it against a load.
471  ///
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,
477  int64_t MemLocOffs,
478  unsigned MemLocSize,
479  const LoadInst *LI);
480 
481  /// Release memory in caches.
482  void releaseMemory();
483 
484 private:
485  MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall,
486  BasicBlock::iterator ScanIt,
487  BasicBlock *BB);
488  bool getNonLocalPointerDepFromBB(Instruction *QueryInst,
489  const PHITransAddr &Pointer,
490  const MemoryLocation &Loc, bool isLoad,
491  BasicBlock *BB,
494  bool SkipFirstBlock = false);
495  MemDepResult GetNonLocalInfoForBlock(Instruction *QueryInst,
496  const MemoryLocation &Loc, bool isLoad,
497  BasicBlock *BB, NonLocalDepInfo *Cache,
498  unsigned NumSortedEntries);
499 
500  void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P);
501 
502  void verifyRemoved(Instruction *Inst) const;
503 };
504 
505 /// An analysis that produces \c MemoryDependenceResults for a function.
506 ///
507 /// This is essentially a no-op because the results are computed entirely
508 /// lazily.
510  : public AnalysisInfoMixin<MemoryDependenceAnalysis> {
512 
513  static AnalysisKey Key;
514 
515 public:
517 
519 };
520 
521 /// A wrapper analysis pass for the legacy pass manager that exposes a \c
522 /// MemoryDepnedenceResults instance.
525 
526 public:
527  static char ID;
528 
530  ~MemoryDependenceWrapperPass() override;
531 
532  /// Pass Implementation stuff. This doesn't do any analysis eagerly.
533  bool runOnFunction(Function &) override;
534 
535  /// Clean up memory in between runs
536  void releaseMemory() override;
537 
538  /// Does not modify anything. It uses Value Numbering and Alias Analysis.
539  void getAnalysisUsage(AnalysisUsage &AU) const override;
540 
541  MemoryDependenceResults &getMemDep() { return *MemDep; }
542 };
543 
544 } // end namespace llvm
545 
546 #endif // LLVM_ANALYSIS_MEMORYDEPENDENCEANALYSIS_H
uint64_t CallInst * C
uint64_t LocationSize
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.
MemoryDependenceResults(AliasAnalysis &AA, AssumptionCache &AC, const TargetLibraryInfo &TLI, DominatorTree &DT, PhiValues &PV)
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:145
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.
Class for calculating and caching the underlying values of phis in a function.
Definition: PhiValues.h:43
MemDepResult()=default
uint32_t Size
Definition: Profile.cpp:47
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
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