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#include "llvm/ADT/DenseMap.h"
17
18namespace llvm {
19
20 class Value;
21 class Use;
22 class DataLayout;
23 class Instruction;
24 class DominatorTree;
25
26 /// getDefaultMaxUsesToExploreForCaptureTracking - Return default value of
27 /// the maximal number of uses to explore before giving up. It is used by
28 /// PointerMayBeCaptured family analysis.
29 unsigned getDefaultMaxUsesToExploreForCaptureTracking();
30
31 /// PointerMayBeCaptured - Return true if this pointer value may be captured
32 /// by the enclosing function (which is required to exist). This routine can
33 /// be expensive, so consider caching the results. The boolean ReturnCaptures
34 /// specifies whether returning the value (or part of it) from the function
35 /// counts as capturing it or not. The boolean StoreCaptures specified
36 /// whether storing the value (or part of it) into memory anywhere
37 /// automatically counts as capturing it or not.
38 /// MaxUsesToExplore specifies how many uses the analysis should explore for
39 /// one value before giving up due too "too many uses". If MaxUsesToExplore
40 /// is zero, a default value is assumed.
41 bool PointerMayBeCaptured(const Value *V, bool ReturnCaptures,
42 bool StoreCaptures,
43 unsigned MaxUsesToExplore = 0);
44
45 /// PointerMayBeCapturedBefore - Return true if this pointer value may be
46 /// captured by the enclosing function (which is required to exist). If a
47 /// DominatorTree is provided, only captures which happen before the given
48 /// instruction are considered. This routine can be expensive, so consider
49 /// caching the results. The boolean ReturnCaptures specifies whether
50 /// returning the value (or part of it) from the function counts as capturing
51 /// it or not. The boolean StoreCaptures specified whether storing the value
52 /// (or part of it) into memory anywhere automatically counts as capturing it
53 /// or not. Captures by the provided instruction are considered if the
54 /// final parameter is true.
55 /// MaxUsesToExplore specifies how many uses the analysis should explore for
56 /// one value before giving up due too "too many uses". If MaxUsesToExplore
57 /// is zero, a default value is assumed.
58 bool PointerMayBeCapturedBefore(
59 const Value *V, bool ReturnCaptures, bool StoreCaptures,
60 const Instruction *I, const DominatorTree *DT, bool IncludeI = false,
61 unsigned MaxUsesToExplore = 0);
62
63 /// This callback is used in conjunction with PointerMayBeCaptured. In
64 /// addition to the interface here, you'll need to provide your own getters
65 /// to see whether anything was captured.
66 struct CaptureTracker {
67 virtual ~CaptureTracker();
68
69 /// tooManyUses - The depth of traversal has breached a limit. There may be
70 /// capturing instructions that will not be passed into captured().
71 virtual void tooManyUses() = 0;
72
73 /// shouldExplore - This is the use of a value derived from the pointer.
74 /// To prune the search (ie., assume that none of its users could possibly
75 /// capture) return false. To search it, return true.
76 ///
77 /// U->getUser() is always an Instruction.
78 virtual bool shouldExplore(const Use *U);
79
80 /// captured - Information about the pointer was captured by the user of
81 /// use U. Return true to stop the traversal or false to continue looking
82 /// for more capturing instructions.
83 virtual bool captured(const Use *U) = 0;
84
85 /// isDereferenceableOrNull - Overload to allow clients with additional
86 /// knowledge about pointer dereferenceability to provide it and thereby
87 /// avoid conservative responses when a pointer is compared to null.
88 virtual bool isDereferenceableOrNull(Value *O, const DataLayout &DL);
89 };
90
91 /// PointerMayBeCaptured - Visit the value and the values derived from it and
92 /// find values which appear to be capturing the pointer value. This feeds
93 /// results into and is controlled by the CaptureTracker object.
94 /// MaxUsesToExplore specifies how many uses the analysis should explore for
95 /// one value before giving up due too "too many uses". If MaxUsesToExplore
96 /// is zero, a default value is assumed.
97 void PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker,
98 unsigned MaxUsesToExplore = 0);
99
100 /// Returns true if the pointer is to a function-local object that never
101 /// escapes from the function.
102 bool isNonEscapingLocalObject(
103 const Value *V,
104 SmallDenseMap<const Value *, bool, 8> *IsCapturedCache = nullptr);
105} // end namespace llvm
106
107#endif
108