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/PointerIntPair.h"
19#include "llvm/ADT/SmallPtrSet.h"
20#include "llvm/Analysis/AliasAnalysis.h"
21#include "llvm/IR/BasicBlock.h"
22#include "llvm/IR/ValueHandle.h"
23#include "llvm/Pass.h"
24
25namespace llvm {
26  class Function;
27  class FunctionPass;
28  class Instruction;
29  class CallSite;
30  class AliasAnalysis;
31  class DataLayout;
32  class MemoryDependenceAnalysis;
33  class PredIteratorCache;
34  class DominatorTree;
35  class PHITransAddr;
36
37  /// MemDepResult - A memory dependence query can return one of three different
38  /// answers, described below.
39  class MemDepResult {
40    enum DepType {
41      /// Invalid - Clients of MemDep never see this.
42      Invalid = 0,
43
44      /// Clobber - This is a dependence on the specified instruction which
45      /// clobbers the desired value.  The pointer member of the MemDepResult
46      /// pair holds the instruction that clobbers the memory.  For example,
47      /// this occurs when we see a may-aliased store to the memory location we
48      /// care about.
49      ///
50      /// There are several cases that may be interesting here:
51      ///   1. Loads are clobbered by may-alias stores.
52      ///   2. Loads are considered clobbered by partially-aliased loads.  The
53      ///      client may choose to analyze deeper into these cases.
54      Clobber,
55
56      /// Def - This is a dependence on the specified instruction which
57      /// defines/produces the desired memory location.  The pointer member of
58      /// the MemDepResult pair holds the instruction that defines the memory.
59      /// Cases of interest:
60      ///   1. This could be a load or store for dependence queries on
61      ///      load/store.  The value loaded or stored is the produced value.
62      ///      Note that the pointer operand may be different than that of the
63      ///      queried pointer due to must aliases and phi translation.  Note
64      ///      that the def may not be the same type as the query, the pointers
65      ///      may just be must aliases.
66      ///   2. For loads and stores, this could be an allocation instruction. In
67      ///      this case, the load is loading an undef value or a store is the
68      ///      first store to (that part of) the allocation.
69      ///   3. Dependence queries on calls return Def only when they are
70      ///      readonly calls or memory use intrinsics with identical callees
71      ///      and no intervening clobbers.  No validation is done that the
72      ///      operands to the calls are the same.
73      Def,
74
75      /// Other - This marker indicates that the query has no known dependency
76      /// in the specified block.  More detailed state info is encoded in the
77      /// upper part of the pair (i.e. the Instruction*)
78      Other
79    };
80    /// If DepType is "Other", the upper part of the pair
81    /// (i.e. the Instruction* part) is instead used to encode more detailed
82    /// type information as follows
83    enum OtherType {
84      /// NonLocal - This marker indicates that the query has no dependency in
85      /// the specified block.  To find out more, the client should query other
86      /// predecessor blocks.
87      NonLocal = 0x4,
88      /// NonFuncLocal - This marker indicates that the query has no
89      /// dependency in the specified function.
90      NonFuncLocal = 0x8,
91      /// Unknown - This marker indicates that the query dependency
92      /// is unknown.
93      Unknown = 0xc
94    };
95
96    typedef PointerIntPair<Instruction*, 2, DepType> PairTy;
97    PairTy Value;
98    explicit MemDepResult(PairTy V) : Value(V) {}
99  public:
100    MemDepResult() : Value(nullptr, Invalid) {}
101
102    /// get methods: These are static ctor methods for creating various
103    /// MemDepResult kinds.
104    static MemDepResult getDef(Instruction *Inst) {
105      assert(Inst && "Def requires inst");
106      return MemDepResult(PairTy(Inst, Def));
107    }
108    static MemDepResult getClobber(Instruction *Inst) {
109      assert(Inst && "Clobber requires inst");
110      return MemDepResult(PairTy(Inst, Clobber));
111    }
112    static MemDepResult getNonLocal() {
113      return MemDepResult(
114        PairTy(reinterpret_cast<Instruction*>(NonLocal), Other));
115    }
116    static MemDepResult getNonFuncLocal() {
117      return MemDepResult(
118        PairTy(reinterpret_cast<Instruction*>(NonFuncLocal), Other));
119    }
120    static MemDepResult getUnknown() {
121      return MemDepResult(
122        PairTy(reinterpret_cast<Instruction*>(Unknown), Other));
123    }
124
125    /// isClobber - Return true if this MemDepResult represents a query that is
126    /// an instruction clobber dependency.
127    bool isClobber() const { return Value.getInt() == Clobber; }
128
129    /// isDef - Return true if this MemDepResult represents a query that is
130    /// an instruction definition dependency.
131    bool isDef() const { return Value.getInt() == Def; }
132
133    /// isNonLocal - Return true if this MemDepResult represents a query that
134    /// is transparent to the start of the block, but where a non-local hasn't
135    /// been done.
136    bool isNonLocal() const {
137      return Value.getInt() == Other
138        && Value.getPointer() == reinterpret_cast<Instruction*>(NonLocal);
139    }
140
141    /// isNonFuncLocal - Return true if this MemDepResult represents a query
142    /// that is transparent to the start of the function.
143    bool isNonFuncLocal() const {
144      return Value.getInt() == Other
145        && Value.getPointer() == reinterpret_cast<Instruction*>(NonFuncLocal);
146    }
147
148    /// isUnknown - Return true if this MemDepResult represents a query which
149    /// cannot and/or will not be computed.
150    bool isUnknown() const {
151      return Value.getInt() == Other
152        && Value.getPointer() == reinterpret_cast<Instruction*>(Unknown);
153    }
154
155    /// getInst() - If this is a normal dependency, return the instruction that
156    /// is depended on.  Otherwise, return null.
157    Instruction *getInst() const {
158      if (Value.getInt() == Other) return nullptr;
159      return Value.getPointer();
160    }
161
162    bool operator==(const MemDepResult &M) const { return Value == M.Value; }
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  private:
167    friend class MemoryDependenceAnalysis;
168    /// Dirty - Entries with this marker occur in a LocalDeps map or
169    /// NonLocalDeps map when the instruction they previously referenced was
170    /// removed from MemDep.  In either case, the entry may include an
171    /// instruction pointer.  If so, the pointer is an instruction in the
172    /// block where scanning can start from, saving some work.
173    ///
174    /// In a default-constructed MemDepResult object, the type will be Dirty
175    /// and the instruction pointer will be null.
176    ///
177
178    /// isDirty - Return true if this is a MemDepResult in its dirty/invalid.
179    /// state.
180    bool isDirty() const { return Value.getInt() == Invalid; }
181
182    static MemDepResult getDirty(Instruction *Inst) {
183      return MemDepResult(PairTy(Inst, Invalid));
184    }
185  };
186
187  /// NonLocalDepEntry - This is an entry in the NonLocalDepInfo cache.  For
188  /// each BasicBlock (the BB entry) it keeps a MemDepResult.
189  class NonLocalDepEntry {
190    BasicBlock *BB;
191    MemDepResult Result;
192  public:
193    NonLocalDepEntry(BasicBlock *bb, MemDepResult result)
194      : BB(bb), Result(result) {}
195
196    // This is used for searches.
197    NonLocalDepEntry(BasicBlock *bb) : BB(bb) {}
198
199    // BB is the sort key, it can't be changed.
200    BasicBlock *getBB() const { return BB; }
201
202    void setResult(const MemDepResult &R) { Result = R; }
203
204    const MemDepResult &getResult() const { return Result; }
205
206    bool operator<(const NonLocalDepEntry &RHS) const {
207      return BB < RHS.BB;
208    }
209  };
210
211  /// NonLocalDepResult - This is a result from a NonLocal dependence query.
212  /// For each BasicBlock (the BB entry) it keeps a MemDepResult and the
213  /// (potentially phi translated) address that was live in the block.
214  class NonLocalDepResult {
215    NonLocalDepEntry Entry;
216    Value *Address;
217  public:
218    NonLocalDepResult(BasicBlock *bb, MemDepResult result, Value *address)
219      : Entry(bb, result), Address(address) {}
220
221    // BB is the sort key, it can't be changed.
222    BasicBlock *getBB() const { return Entry.getBB(); }
223
224    void setResult(const MemDepResult &R, Value *Addr) {
225      Entry.setResult(R);
226      Address = Addr;
227    }
228
229    const MemDepResult &getResult() const { return Entry.getResult(); }
230
231    /// getAddress - Return the address of this pointer in this block.  This can
232    /// be different than the address queried for the non-local result because
233    /// of phi translation.  This returns null if the address was not available
234    /// in a block (i.e. because phi translation failed) or if this is a cached
235    /// result and that address was deleted.
236    ///
237    /// The address is always null for a non-local 'call' dependence.
238    Value *getAddress() const { return Address; }
239  };
240
241  /// MemoryDependenceAnalysis - This is an analysis that determines, for a
242  /// given memory operation, what preceding memory operations it depends on.
243  /// It builds on alias analysis information, and tries to provide a lazy,
244  /// caching interface to a common kind of alias information query.
245  ///
246  /// The dependency information returned is somewhat unusual, but is pragmatic.
247  /// If queried about a store or call that might modify memory, the analysis
248  /// will return the instruction[s] that may either load from that memory or
249  /// store to it.  If queried with a load or call that can never modify memory,
250  /// the analysis will return calls and stores that might modify the pointer,
251  /// but generally does not return loads unless a) they are volatile, or
252  /// b) they load from *must-aliased* pointers.  Returning a dependence on
253  /// must-alias'd pointers instead of all pointers interacts well with the
254  /// internal caching mechanism.
255  ///
256  class MemoryDependenceAnalysis : public FunctionPass {
257    // A map from instructions to their dependency.
258    typedef DenseMap<Instruction*, MemDepResult> LocalDepMapType;
259    LocalDepMapType LocalDeps;
260
261  public:
262    typedef std::vector<NonLocalDepEntry> NonLocalDepInfo;
263  private:
264    /// ValueIsLoadPair - This is a pair<Value*, bool> where the bool is true if
265    /// the dependence is a read only dependence, false if read/write.
266    typedef PointerIntPair<const Value*, 1, bool> ValueIsLoadPair;
267
268    /// BBSkipFirstBlockPair - This pair is used when caching information for a
269    /// block.  If the pointer is null, the cache value is not a full query that
270    /// starts at the specified block.  If non-null, the bool indicates whether
271    /// or not the contents of the block was skipped.
272    typedef PointerIntPair<BasicBlock*, 1, bool> BBSkipFirstBlockPair;
273
274    /// NonLocalPointerInfo - This record is the information kept for each
275    /// (value, is load) pair.
276    struct NonLocalPointerInfo {
277      /// Pair - The pair of the block and the skip-first-block flag.
278      BBSkipFirstBlockPair Pair;
279      /// NonLocalDeps - The results of the query for each relevant block.
280      NonLocalDepInfo NonLocalDeps;
281      /// Size - The maximum size of the dereferences of the
282      /// pointer. May be UnknownSize if the sizes are unknown.
283      uint64_t Size;
284      /// TBAATag - The TBAA tag associated with dereferences of the
285      /// pointer. May be null if there are no tags or conflicting tags.
286      const MDNode *TBAATag;
287
288      NonLocalPointerInfo()
289        : Size(AliasAnalysis::UnknownSize), TBAATag(nullptr) {}
290    };
291
292    /// CachedNonLocalPointerInfo - This map stores the cached results of doing
293    /// a pointer lookup at the bottom of a block.  The key of this map is the
294    /// pointer+isload bit, the value is a list of <bb->result> mappings.
295    typedef DenseMap<ValueIsLoadPair,
296                     NonLocalPointerInfo> CachedNonLocalPointerInfo;
297    CachedNonLocalPointerInfo NonLocalPointerDeps;
298
299    // A map from instructions to their non-local pointer dependencies.
300    typedef DenseMap<Instruction*,
301                     SmallPtrSet<ValueIsLoadPair, 4> > ReverseNonLocalPtrDepTy;
302    ReverseNonLocalPtrDepTy ReverseNonLocalPtrDeps;
303
304
305    /// PerInstNLInfo - This is the instruction we keep for each cached access
306    /// that we have for an instruction.  The pointer is an owning pointer and
307    /// the bool indicates whether we have any dirty bits in the set.
308    typedef std::pair<NonLocalDepInfo, bool> PerInstNLInfo;
309
310    // A map from instructions to their non-local dependencies.
311    typedef DenseMap<Instruction*, PerInstNLInfo> NonLocalDepMapType;
312
313    NonLocalDepMapType NonLocalDeps;
314
315    // A reverse mapping from dependencies to the dependees.  This is
316    // used when removing instructions to keep the cache coherent.
317    typedef DenseMap<Instruction*,
318                     SmallPtrSet<Instruction*, 4> > ReverseDepMapType;
319    ReverseDepMapType ReverseLocalDeps;
320
321    // A reverse mapping from dependencies to the non-local dependees.
322    ReverseDepMapType ReverseNonLocalDeps;
323
324    /// Current AA implementation, just a cache.
325    AliasAnalysis *AA;
326    const DataLayout *DL;
327    DominatorTree *DT;
328    std::unique_ptr<PredIteratorCache> PredCache;
329
330  public:
331    MemoryDependenceAnalysis();
332    ~MemoryDependenceAnalysis();
333    static char ID;
334
335    /// Pass Implementation stuff.  This doesn't do any analysis eagerly.
336    bool runOnFunction(Function &) override;
337
338    /// Clean up memory in between runs
339    void releaseMemory() override;
340
341    /// getAnalysisUsage - Does not modify anything.  It uses Value Numbering
342    /// and Alias Analysis.
343    ///
344    void getAnalysisUsage(AnalysisUsage &AU) const override;
345
346    /// getDependency - Return the instruction on which a memory operation
347    /// depends.  See the class comment for more details.  It is illegal to call
348    /// this on non-memory instructions.
349    MemDepResult getDependency(Instruction *QueryInst);
350
351    /// getNonLocalCallDependency - Perform a full dependency query for the
352    /// specified call, returning the set of blocks that the value is
353    /// potentially live across.  The returned set of results will include a
354    /// "NonLocal" result for all blocks where the value is live across.
355    ///
356    /// This method assumes the instruction returns a "NonLocal" dependency
357    /// within its own block.
358    ///
359    /// This returns a reference to an internal data structure that may be
360    /// invalidated on the next non-local query or when an instruction is
361    /// removed.  Clients must copy this data if they want it around longer than
362    /// that.
363    const NonLocalDepInfo &getNonLocalCallDependency(CallSite QueryCS);
364
365
366    /// getNonLocalPointerDependency - Perform a full dependency query for an
367    /// access to the specified (non-volatile) memory location, returning the
368    /// set of instructions that either define or clobber the value.
369    ///
370    /// This method assumes the pointer has a "NonLocal" dependency within BB.
371    void getNonLocalPointerDependency(const AliasAnalysis::Location &Loc,
372                                      bool isLoad, BasicBlock *BB,
373                                    SmallVectorImpl<NonLocalDepResult> &Result);
374
375    /// removeInstruction - Remove an instruction from the dependence analysis,
376    /// updating the dependence of instructions that previously depended on it.
377    void removeInstruction(Instruction *InstToRemove);
378
379    /// invalidateCachedPointerInfo - This method is used to invalidate cached
380    /// information about the specified pointer, because it may be too
381    /// conservative in memdep.  This is an optional call that can be used when
382    /// the client detects an equivalence between the pointer and some other
383    /// value and replaces the other value with ptr. This can make Ptr available
384    /// in more places that cached info does not necessarily keep.
385    void invalidateCachedPointerInfo(Value *Ptr);
386
387    /// invalidateCachedPredecessors - Clear the PredIteratorCache info.
388    /// This needs to be done when the CFG changes, e.g., due to splitting
389    /// critical edges.
390    void invalidateCachedPredecessors();
391
392    /// getPointerDependencyFrom - Return the instruction on which a memory
393    /// location depends.  If isLoad is true, this routine ignores may-aliases
394    /// with read-only operations.  If isLoad is false, this routine ignores
395    /// may-aliases with reads from read-only locations. If possible, pass
396    /// the query instruction as well; this function may take advantage of
397    /// the metadata annotated to the query instruction to refine the result.
398    ///
399    /// Note that this is an uncached query, and thus may be inefficient.
400    ///
401    MemDepResult getPointerDependencyFrom(const AliasAnalysis::Location &Loc,
402                                          bool isLoad,
403                                          BasicBlock::iterator ScanIt,
404                                          BasicBlock *BB,
405                                          Instruction *QueryInst = nullptr);
406
407
408    /// getLoadLoadClobberFullWidthSize - This is a little bit of analysis that
409    /// looks at a memory location for a load (specified by MemLocBase, Offs,
410    /// and Size) and compares it against a load.  If the specified load could
411    /// be safely widened to a larger integer load that is 1) still efficient,
412    /// 2) safe for the target, and 3) would provide the specified memory
413    /// location value, then this function returns the size in bytes of the
414    /// load width to use.  If not, this returns zero.
415    static unsigned getLoadLoadClobberFullWidthSize(const Value *MemLocBase,
416                                                    int64_t MemLocOffs,
417                                                    unsigned MemLocSize,
418                                                    const LoadInst *LI,
419                                                    const DataLayout &DL);
420
421  private:
422    MemDepResult getCallSiteDependencyFrom(CallSite C, bool isReadOnlyCall,
423                                           BasicBlock::iterator ScanIt,
424                                           BasicBlock *BB);
425    bool getNonLocalPointerDepFromBB(const PHITransAddr &Pointer,
426                                     const AliasAnalysis::Location &Loc,
427                                     bool isLoad, BasicBlock *BB,
428                                     SmallVectorImpl<NonLocalDepResult> &Result,
429                                     DenseMap<BasicBlock*, Value*> &Visited,
430                                     bool SkipFirstBlock = false);
431    MemDepResult GetNonLocalInfoForBlock(const AliasAnalysis::Location &Loc,
432                                         bool isLoad, BasicBlock *BB,
433                                         NonLocalDepInfo *Cache,
434                                         unsigned NumSortedEntries);
435
436    void RemoveCachedNonLocalPointerDependencies(ValueIsLoadPair P);
437
438    /// verifyRemoved - Verify that the specified instruction does not occur
439    /// in our internal data structures.
440    void verifyRemoved(Instruction *Inst) const;
441
442  };
443
444} // End llvm namespace
445
446#endif
447