LLVM  10.0.0svn
CaptureTracking.h
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1 //===----- llvm/Analysis/CaptureTracking.h - Pointer capture ----*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file contains routines that help determine which pointers are captured.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_ANALYSIS_CAPTURETRACKING_H
14 #define LLVM_ANALYSIS_CAPTURETRACKING_H
15 
16 namespace llvm {
17 
18  class Value;
19  class Use;
20  class DataLayout;
21  class Instruction;
22  class DominatorTree;
23  class OrderedBasicBlock;
24 
25  /// The default value for MaxUsesToExplore argument. It's relatively small to
26  /// keep the cost of analysis reasonable for clients like BasicAliasAnalysis,
27  /// where the results can't be cached.
28  /// TODO: we should probably introduce a caching CaptureTracking analysis and
29  /// use it where possible. The caching version can use much higher limit or
30  /// don't have this cap at all.
31  unsigned constexpr DefaultMaxUsesToExplore = 20;
32 
33  /// PointerMayBeCaptured - Return true if this pointer value may be captured
34  /// by the enclosing function (which is required to exist). This routine can
35  /// be expensive, so consider caching the results. The boolean ReturnCaptures
36  /// specifies whether returning the value (or part of it) from the function
37  /// counts as capturing it or not. The boolean StoreCaptures specified
38  /// whether storing the value (or part of it) into memory anywhere
39  /// automatically counts as capturing it or not.
40  /// MaxUsesToExplore specifies how many uses should the analysis explore for
41  /// one value before giving up due too "too many uses".
42  bool PointerMayBeCaptured(const Value *V,
43  bool ReturnCaptures,
44  bool StoreCaptures,
45  unsigned MaxUsesToExplore = DefaultMaxUsesToExplore);
46 
47  /// PointerMayBeCapturedBefore - Return true if this pointer value may be
48  /// captured by the enclosing function (which is required to exist). If a
49  /// DominatorTree is provided, only captures which happen before the given
50  /// instruction are considered. This routine can be expensive, so consider
51  /// caching the results. The boolean ReturnCaptures specifies whether
52  /// returning the value (or part of it) from the function counts as capturing
53  /// it or not. The boolean StoreCaptures specified whether storing the value
54  /// (or part of it) into memory anywhere automatically counts as capturing it
55  /// or not. Captures by the provided instruction are considered if the
56  /// final parameter is true. An ordered basic block in \p OBB could be used
57  /// to speed up capture-tracker queries.
58  /// MaxUsesToExplore specifies how many uses should the analysis explore for
59  /// one value before giving up due too "too many uses".
60  bool PointerMayBeCapturedBefore(const Value *V, bool ReturnCaptures,
61  bool StoreCaptures, const Instruction *I,
62  const DominatorTree *DT, bool IncludeI = false,
63  OrderedBasicBlock *OBB = nullptr,
64  unsigned MaxUsesToExplore = DefaultMaxUsesToExplore);
65 
66  /// This callback is used in conjunction with PointerMayBeCaptured. In
67  /// addition to the interface here, you'll need to provide your own getters
68  /// to see whether anything was captured.
69  struct CaptureTracker {
70  virtual ~CaptureTracker();
71 
72  /// tooManyUses - The depth of traversal has breached a limit. There may be
73  /// capturing instructions that will not be passed into captured().
74  virtual void tooManyUses() = 0;
75 
76  /// shouldExplore - This is the use of a value derived from the pointer.
77  /// To prune the search (ie., assume that none of its users could possibly
78  /// capture) return false. To search it, return true.
79  ///
80  /// U->getUser() is always an Instruction.
81  virtual bool shouldExplore(const Use *U);
82 
83  /// captured - Information about the pointer was captured by the user of
84  /// use U. Return true to stop the traversal or false to continue looking
85  /// for more capturing instructions.
86  virtual bool captured(const Use *U) = 0;
87 
88  /// isDereferenceableOrNull - Overload to allow clients with additional
89  /// knowledge about pointer dereferenceability to provide it and thereby
90  /// avoid conservative responses when a pointer is compared to null.
91  virtual bool isDereferenceableOrNull(Value *O, const DataLayout &DL);
92  };
93 
94  /// PointerMayBeCaptured - Visit the value and the values derived from it and
95  /// find values which appear to be capturing the pointer value. This feeds
96  /// results into and is controlled by the CaptureTracker object.
97  /// MaxUsesToExplore specifies how many uses should the analysis explore for
98  /// one value before giving up due too "too many uses".
99  void PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker,
100  unsigned MaxUsesToExplore = DefaultMaxUsesToExplore);
101 } // end namespace llvm
102 
103 #endif
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:111
virtual void tooManyUses()=0
tooManyUses - The depth of traversal has breached a limit.
This callback is used in conjunction with PointerMayBeCaptured.
This class represents lattice values for constants.
Definition: AllocatorList.h:23
unsigned constexpr DefaultMaxUsesToExplore
The default value for MaxUsesToExplore argument.
virtual bool shouldExplore(const Use *U)
shouldExplore - This is the use of a value derived from the pointer.
virtual bool isDereferenceableOrNull(Value *O, const DataLayout &DL)
isDereferenceableOrNull - Overload to allow clients with additional knowledge about pointer dereferen...
A Use represents the edge between a Value definition and its users.
Definition: Use.h:55
virtual bool captured(const Use *U)=0
captured - Information about the pointer was captured by the user of use U.
bool PointerMayBeCapturedBefore(const Value *V, bool ReturnCaptures, bool StoreCaptures, const Instruction *I, const DominatorTree *DT, bool IncludeI=false, OrderedBasicBlock *OBB=nullptr, unsigned MaxUsesToExplore=DefaultMaxUsesToExplore)
PointerMayBeCapturedBefore - Return true if this pointer value may be captured by the enclosing funct...
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree...
Definition: Dominators.h:144
#define I(x, y, z)
Definition: MD5.cpp:58
LLVM Value Representation.
Definition: Value.h:74
bool PointerMayBeCaptured(const Value *V, bool ReturnCaptures, bool StoreCaptures, unsigned MaxUsesToExplore=DefaultMaxUsesToExplore)
PointerMayBeCaptured - Return true if this pointer value may be captured by the enclosing function (w...