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1 //===----- llvm/Analysis/CaptureTracking.h - Pointer capture ----*- 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 contains routines that help determine which pointers are captured.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_ANALYSIS_CAPTURETRACKING_H
15 #define LLVM_ANALYSIS_CAPTURETRACKING_H
16 
17 namespace llvm {
18 
19   class Value;
20   class Use;
21   class Instruction;
22   class DominatorTree;
23   class OrderedBasicBlock;
24 
25   /// PointerMayBeCaptured - Return true if this pointer value may be captured
26   /// by the enclosing function (which is required to exist).  This routine can
27   /// be expensive, so consider caching the results.  The boolean ReturnCaptures
28   /// specifies whether returning the value (or part of it) from the function
29   /// counts as capturing it or not.  The boolean StoreCaptures specified
30   /// whether storing the value (or part of it) into memory anywhere
31   /// automatically counts as capturing it or not.
32   bool PointerMayBeCaptured(const Value *V,
33                             bool ReturnCaptures,
34                             bool StoreCaptures);
35 
36   /// PointerMayBeCapturedBefore - Return true if this pointer value may be
37   /// captured by the enclosing function (which is required to exist). If a
38   /// DominatorTree is provided, only captures which happen before the given
39   /// instruction are considered. This routine can be expensive, so consider
40   /// caching the results.  The boolean ReturnCaptures specifies whether
41   /// returning the value (or part of it) from the function counts as capturing
42   /// it or not.  The boolean StoreCaptures specified whether storing the value
43   /// (or part of it) into memory anywhere automatically counts as capturing it
44   /// or not. Captures by the provided instruction are considered if the
45   /// final parameter is true. An ordered basic block in \p OBB could be used
46   /// to speed up capture-tracker queries.
47   bool PointerMayBeCapturedBefore(const Value *V, bool ReturnCaptures,
48                                   bool StoreCaptures, const Instruction *I,
49                                   DominatorTree *DT, bool IncludeI = false,
50                                   OrderedBasicBlock *OBB = nullptr);
51 
52   /// This callback is used in conjunction with PointerMayBeCaptured. In
53   /// addition to the interface here, you'll need to provide your own getters
54   /// to see whether anything was captured.
55   struct CaptureTracker {
56     virtual ~CaptureTracker();
57 
58     /// tooManyUses - The depth of traversal has breached a limit. There may be
59     /// capturing instructions that will not be passed into captured().
60     virtual void tooManyUses() = 0;
61 
62     /// shouldExplore - This is the use of a value derived from the pointer.
63     /// To prune the search (ie., assume that none of its users could possibly
64     /// capture) return false. To search it, return true.
65     ///
66     /// U->getUser() is always an Instruction.
67     virtual bool shouldExplore(const Use *U);
68 
69     /// captured - Information about the pointer was captured by the user of
70     /// use U. Return true to stop the traversal or false to continue looking
71     /// for more capturing instructions.
72     virtual bool captured(const Use *U) = 0;
73   };
74 
75   /// PointerMayBeCaptured - Visit the value and the values derived from it and
76   /// find values which appear to be capturing the pointer value. This feeds
77   /// results into and is controlled by the CaptureTracker object.
78   void PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker);
79 } // end namespace llvm
80 
81 #endif
82