LLVM  10.0.0svn
LazyRandomTypeCollection.h
Go to the documentation of this file.
1 //===- LazyRandomTypeCollection.h -------------------------------*- 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 #ifndef LLVM_DEBUGINFO_CODEVIEW_LAZYRANDOMTYPECOLLECTION_H
10 #define LLVM_DEBUGINFO_CODEVIEW_LAZYRANDOMTYPECOLLECTION_H
11 
12 #include "llvm/ADT/ArrayRef.h"
13 #include "llvm/ADT/Optional.h"
14 #include "llvm/ADT/StringRef.h"
18 #include "llvm/Support/Allocator.h"
20 #include "llvm/Support/Error.h"
22 #include <cstdint>
23 #include <vector>
24 
25 namespace llvm {
26 namespace codeview {
27 
28 /// Provides amortized O(1) random access to a CodeView type stream.
29 /// Normally to access a type from a type stream, you must know its byte
30 /// offset into the type stream, because type records are variable-lengthed.
31 /// However, this is not the way we prefer to access them. For example, given
32 /// a symbol record one of the fields may be the TypeIndex of the symbol's
33 /// type record. Or given a type record such as an array type, there might
34 /// be a TypeIndex for the element type. Sequential access is perfect when
35 /// we're just dumping every entry, but it's very poor for real world usage.
36 ///
37 /// Type streams in PDBs contain an additional field which is a list of pairs
38 /// containing indices and their corresponding offsets, roughly every ~8KB of
39 /// record data. This general idea need not be confined to PDBs though. By
40 /// supplying such an array, the producer of a type stream can allow the
41 /// consumer much better access time, because the consumer can find the nearest
42 /// index in this array, and do a linear scan forward only from there.
43 ///
44 /// LazyRandomTypeCollection implements this algorithm, but additionally goes
45 /// one step further by caching offsets of every record that has been visited at
46 /// least once. This way, even repeated visits of the same record will never
47 /// require more than one linear scan. For a type stream of N elements divided
48 /// into M chunks of roughly equal size, this yields a worst case lookup time
49 /// of O(N/M) and an amortized time of O(1).
52 
53  struct CacheEntry {
54  CVType Type;
57  };
58 
59 public:
60  explicit LazyRandomTypeCollection(uint32_t RecordCountHint);
63  LazyRandomTypeCollection(const CVTypeArray &Types, uint32_t RecordCountHint,
64  PartialOffsetArray PartialOffsets);
65  LazyRandomTypeCollection(const CVTypeArray &Types, uint32_t RecordCountHint);
66 
67  void reset(ArrayRef<uint8_t> Data, uint32_t RecordCountHint);
68  void reset(StringRef Data, uint32_t RecordCountHint);
69  void reset(BinaryStreamReader &Reader, uint32_t RecordCountHint);
70 
72 
74 
75  CVType getType(TypeIndex Index) override;
76  StringRef getTypeName(TypeIndex Index) override;
77  bool contains(TypeIndex Index) override;
78  uint32_t size() override;
79  uint32_t capacity() override;
80  Optional<TypeIndex> getFirst() override;
81  Optional<TypeIndex> getNext(TypeIndex Prev) override;
82 
83 private:
84  Error ensureTypeExists(TypeIndex Index);
85  void ensureCapacityFor(TypeIndex Index);
86 
87  Error visitRangeForType(TypeIndex TI);
88  Error fullScanForType(TypeIndex TI);
89  void visitRange(TypeIndex Begin, uint32_t BeginOffset, TypeIndex End);
90 
91  /// Number of actual records.
92  uint32_t Count = 0;
93 
94  /// The largest type index which we've visited.
95  TypeIndex LargestTypeIndex = TypeIndex::None();
96 
98  StringSaver NameStorage;
99 
100  /// The type array to allow random access visitation of.
101  CVTypeArray Types;
102 
103  std::vector<CacheEntry> Records;
104 
105  /// An array of index offsets for the given type stream, allowing log(N)
106  /// lookups of a type record by index. Similar to KnownOffsets but only
107  /// contains offsets for some type indices, some of which may not have
108  /// ever been visited.
109  PartialOffsetArray PartialOffsets;
110 };
111 
112 } // end namespace codeview
113 } // end namespace llvm
114 
115 #endif // LLVM_DEBUGINFO_CODEVIEW_LAZYRANDOMTYPECOLLECTION_H
This class represents lattice values for constants.
Definition: AllocatorList.h:23
amdgpu Simplify well known AMD library false FunctionCallee Value const Twine & Name
This file defines the MallocAllocator and BumpPtrAllocator interfaces.
Optional< TypeIndex > getNext(TypeIndex Prev) override
void reset(ArrayRef< uint8_t > Data, uint32_t RecordCountHint)
A 32-bit type reference.
Definition: TypeIndex.h:95
The instances of the Type class are immutable: once they are created, they are never changed...
Definition: Type.h:45
Allocate memory in an ever growing pool, as if by bump-pointer.
Definition: Allocator.h:140
Optional< CVType > tryGetType(TypeIndex Index)
StringRef getTypeName(TypeIndex Index) override
Basic Register Allocator
Saves strings in the provided stable storage and returns a StringRef with a stable character pointer...
Definition: StringSaver.h:21
Lightweight error class with error context and mandatory checking.
Definition: Error.h:157
Provides read only access to a subclass of BinaryStream.
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:48
static TypeIndex None()
Definition: TypeIndex.h:138
Provides amortized O(1) random access to a CodeView type stream.