LLVM  3.7.0
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"
19 #include "llvm/ADT/SmallPtrSet.h"
21 #include "llvm/IR/BasicBlock.h"
23 #include "llvm/IR/ValueHandle.h"
24 #include "llvm/Pass.h"
25 
26 namespace llvm {
27  class Function;
28  class FunctionPass;
29  class Instruction;
30  class CallSite;
31  class AliasAnalysis;
32  class AssumptionCache;
33  class MemoryDependenceAnalysis;
34  class PredIteratorCache;
35  class DominatorTree;
36  class PHITransAddr;
37 
38  /// MemDepResult - A memory dependence query can return one of three different
39  /// answers, described below.
40  class MemDepResult {
41  enum DepType {
42  /// Invalid - Clients of MemDep never see this.
43  Invalid = 0,
44 
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
49  /// care about.
50  ///
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.
55  Clobber,
56 
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.
74  Def,
75 
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*)
79  Other
80  };
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
84  enum OtherType {
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.
88  NonLocal = 0x4,
89  /// NonFuncLocal - This marker indicates that the query has no
90  /// dependency in the specified function.
91  NonFuncLocal = 0x8,
92  /// Unknown - This marker indicates that the query dependency
93  /// is unknown.
94  Unknown = 0xc
95  };
96 
98  PairTy Value;
99  explicit MemDepResult(PairTy V) : Value(V) {}
100  public:
101  MemDepResult() : Value(nullptr, Invalid) {}
102 
103  /// get methods: These are static ctor methods for creating various
104  /// MemDepResult kinds.
106  assert(Inst && "Def requires inst");
107  return MemDepResult(PairTy(Inst, Def));
108  }
110  assert(Inst && "Clobber requires inst");
111  return MemDepResult(PairTy(Inst, Clobber));
112  }
114  return MemDepResult(
115  PairTy(reinterpret_cast<Instruction*>(NonLocal), Other));
116  }
118  return MemDepResult(
119  PairTy(reinterpret_cast<Instruction*>(NonFuncLocal), Other));
120  }
122  return MemDepResult(
123  PairTy(reinterpret_cast<Instruction*>(Unknown), Other));
124  }
125 
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; }
129 
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; }
133 
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
136  /// been done.
137  bool isNonLocal() const {
138  return Value.getInt() == Other
139  && Value.getPointer() == reinterpret_cast<Instruction*>(NonLocal);
140  }
141 
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);
147  }
148 
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);
154  }
155 
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();
161  }
162 
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; }
167  private:
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.
174  ///
175  /// In a default-constructed MemDepResult object, the type will be Dirty
176  /// and the instruction pointer will be null.
177  ///
178 
179  /// isDirty - Return true if this is a MemDepResult in its dirty/invalid.
180  /// state.
181  bool isDirty() const { return Value.getInt() == Invalid; }
182 
183  static MemDepResult getDirty(Instruction *Inst) {
184  return MemDepResult(PairTy(Inst, Invalid));
185  }
186  };
187 
188  /// NonLocalDepEntry - This is an entry in the NonLocalDepInfo cache. For
189  /// each BasicBlock (the BB entry) it keeps a MemDepResult.
191  BasicBlock *BB;
192  MemDepResult Result;
193  public:
195  : BB(bb), Result(result) {}
196 
197  // This is used for searches.
198  NonLocalDepEntry(BasicBlock *bb) : BB(bb) {}
199 
200  // BB is the sort key, it can't be changed.
201  BasicBlock *getBB() const { return BB; }
202 
203  void setResult(const MemDepResult &R) { Result = R; }
204 
205  const MemDepResult &getResult() const { return Result; }
206 
207  bool operator<(const NonLocalDepEntry &RHS) const {
208  return BB < RHS.BB;
209  }
210  };
211 
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.
216  NonLocalDepEntry Entry;
217  Value *Address;
218  public:
220  : Entry(bb, result), Address(address) {}
221 
222  // BB is the sort key, it can't be changed.
223  BasicBlock *getBB() const { return Entry.getBB(); }
224 
225  void setResult(const MemDepResult &R, Value *Addr) {
226  Entry.setResult(R);
227  Address = Addr;
228  }
229 
230  const MemDepResult &getResult() const { return Entry.getResult(); }
231 
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.
237  ///
238  /// The address is always null for a non-local 'call' dependence.
239  Value *getAddress() const { return Address; }
240  };
241 
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.
246  ///
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.
256  ///
258  // A map from instructions to their dependency.
260  LocalDepMapType LocalDeps;
261 
262  public:
263  typedef std::vector<NonLocalDepEntry> NonLocalDepInfo;
264  private:
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.
268 
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.
274 
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.
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.
284  uint64_t Size;
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.
288  AAMDNodes AATags;
289 
290  NonLocalPointerInfo() : Size(MemoryLocation::UnknownSize) {}
291  };
292 
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;
299 
300  // A map from instructions to their non-local pointer dependencies.
301  typedef DenseMap<Instruction*,
302  SmallPtrSet<ValueIsLoadPair, 4> > ReverseNonLocalPtrDepTy;
303  ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps;
304 
305 
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;
310 
311  // A map from instructions to their non-local dependencies.
312  typedef DenseMap<Instruction*, PerInstNLInfo> NonLocalDepMapType;
313 
314  NonLocalDepMapType NonLocalDeps;
315 
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;
321 
322  // A reverse mapping from dependencies to the non-local dependees.
323  ReverseDepMapType ReverseNonLocalDeps;
324 
325  /// Current AA implementation, just a cache.
326  AliasAnalysis *AA;
327  DominatorTree *DT;
328  AssumptionCache *AC;
329  PredIteratorCache PredCache;
330 
331  public:
333  ~MemoryDependenceAnalysis() override;
334  static char ID;
335 
336  /// Pass Implementation stuff. This doesn't do any analysis eagerly.
337  bool runOnFunction(Function &) override;
338 
339  /// Clean up memory in between runs
340  void releaseMemory() override;
341 
342  /// getAnalysisUsage - Does not modify anything. It uses Value Numbering
343  /// and Alias Analysis.
344  ///
345  void getAnalysisUsage(AnalysisUsage &AU) const override;
346 
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.
351 
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.
356  ///
357  /// This method assumes the instruction returns a "NonLocal" dependency
358  /// within its own block.
359  ///
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
363  /// that.
365 
366 
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.
370  ///
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.
374  ///
375  /// This method assumes the pointer has a "NonLocal" dependency within
376  /// QueryInst's parent basic block.
379 
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);
383 
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.
391 
392  /// invalidateCachedPredecessors - Clear the PredIteratorCache info.
393  /// This needs to be done when the CFG changes, e.g., due to splitting
394  /// critical edges.
396 
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.
403  ///
404  /// Note that this is an uncached query, and thus may be inefficient.
405  ///
407  bool isLoad,
408  BasicBlock::iterator ScanIt,
409  BasicBlock *BB,
410  Instruction *QueryInst = nullptr);
411 
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,
420  int64_t MemLocOffs,
421  unsigned MemLocSize,
422  const LoadInst *LI);
423 
424  private:
425  MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall,
426  BasicBlock::iterator ScanIt,
427  BasicBlock *BB);
428  bool getNonLocalPointerDepFromBB(Instruction *QueryInst,
429  const PHITransAddr &Pointer,
430  const MemoryLocation &Loc, bool isLoad,
431  BasicBlock *BB,
434  bool SkipFirstBlock = false);
435  MemDepResult GetNonLocalInfoForBlock(Instruction *QueryInst,
436  const MemoryLocation &Loc, bool isLoad,
437  BasicBlock *BB, NonLocalDepInfo *Cache,
438  unsigned NumSortedEntries);
439 
440  void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P);
441 
442  /// verifyRemoved - Verify that the specified instruction does not occur
443  /// in our internal data structures.
444  void verifyRemoved(Instruction *Inst) const;
445 
446  };
447 
448 } // End llvm namespace
449 
450 #endif
void invalidateCachedPointerInfo(Value *Ptr)
invalidateCachedPointerInfo - This method is used to invalidate cached information about the specifie...
bool isDef() const
isDef - Return true if this MemDepResult represents a query that is an instruction definition depende...
bool operator<(const MemDepResult &M) const
A cache of .assume calls within a function.
LoadInst - an instruction for reading from memory.
Definition: Instructions.h:177
void setResult(const MemDepResult &R, Value *Addr)
bool isUnknown() const
isUnknown - Return true if this MemDepResult represents a query which cannot and/or will not be compu...
bool isClobber() const
isClobber - Return true if this MemDepResult represents a query that is an instruction clobber depend...
bool runOnFunction(Function &) override
Pass Implementation stuff. This doesn't do any analysis eagerly.
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: APInt.h:33
static MemDepResult getDef(Instruction *Inst)
get methods: These are static ctor methods for creating various MemDepResult kinds.
MemoryDependenceAnalysis - This is an analysis that determines, for a given memory operation...
Value * getAddress() const
getAddress - Return the address of this pointer in this block.
void releaseMemory() override
Clean up memory in between runs.
PredIteratorCache - This class is an extremely trivial cache for predecessor iterator queries...
bool operator==(const MemDepResult &M) const
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:67
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Does not modify anything.
static MemDepResult getUnknown()
MemDepResult getPointerDependencyFrom(const MemoryLocation &Loc, bool isLoad, BasicBlock::iterator ScanIt, BasicBlock *BB, Instruction *QueryInst=nullptr)
getPointerDependencyFrom - Return the instruction on which a memory location depends.
#define P(N)
LLVM Basic Block Representation.
Definition: BasicBlock.h:65
PHITransAddr - An address value which tracks and handles phi translation.
Definition: PHITransAddr.h:36
bool operator>(const MemDepResult &M) const
NonLocalDepResult - This is a result from a NonLocal dependence query.
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:294
const MemDepResult & getResult() const
void setResult(const MemDepResult &R)
MemDepResult - A memory dependence query can return one of three different answers, described below.
Representation for a specific memory location.
NonLocalDepEntry(BasicBlock *bb, MemDepResult result)
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements...
Definition: SmallPtrSet.h:299
static MemDepResult getClobber(Instruction *Inst)
A collection of metadata nodes that might be associated with a memory access used by the alias-analys...
Definition: Metadata.h:548
bool isNonLocal() const
isNonLocal - Return true if this MemDepResult represents a query that is transparent to the start of ...
std::vector< NonLocalDepEntry > NonLocalDepInfo
bool operator<(const NonLocalDepEntry &RHS) const
Instruction * getInst() const
getInst() - If this is a normal dependency, return the instruction that is depended on...
MemDepResult getDependency(Instruction *QueryInst)
getDependency - Return the instruction on which a memory operation depends.
void invalidateCachedPredecessors()
invalidateCachedPredecessors - Clear the PredIteratorCache info.
const NonLocalDepInfo & getNonLocalCallDependency(CallSite QueryCS)
getNonLocalCallDependency - Perform a full dependency query for the specified call, returning the set of blocks that the value is potentially live across.
LLVM Value Representation.
Definition: Value.h:69
const MemDepResult & getResult() const
NonLocalDepEntry - This is an entry in the NonLocalDepInfo cache.
static MemDepResult getNonLocal()
static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase, int64_t MemLocOffs, unsigned MemLocSize, const LoadInst *LI)
getLoadLoadClobberFullWidthSize - This is a little bit of analysis that looks at a memory location fo...
bool isNonFuncLocal() const
isNonFuncLocal - Return true if this MemDepResult represents a query that is transparent to the start...
bool operator!=(const MemDepResult &M) const
void removeInstruction(Instruction *InstToRemove)
removeInstruction - Remove an instruction from the dependence analysis, updating the dependence of in...
void getNonLocalPointerDependency(Instruction *QueryInst, SmallVectorImpl< NonLocalDepResult > &Result)
getNonLocalPointerDependency - Perform a full dependency query for an access to the QueryInst's speci...