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" 15 #include "llvm/DebugInfo/CodeView/TypeCollection.h" 16 #include "llvm/DebugInfo/CodeView/TypeIndex.h" 17 #include "llvm/DebugInfo/CodeView/TypeRecord.h" 18 #include "llvm/Support/Allocator.h" 19 #include "llvm/Support/BinaryStreamArray.h" 20 #include "llvm/Support/Error.h" 21 #include "llvm/Support/StringSaver.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). 50 class LazyRandomTypeCollection : public TypeCollection { 51 using PartialOffsetArray = FixedStreamArray<TypeIndexOffset>; 52 53 struct CacheEntry { 54 CVType Type; 55 uint32_t Offset; 56 StringRef Name; 57 }; 58 59 public: 60 explicit LazyRandomTypeCollection(uint32_t RecordCountHint); 61 LazyRandomTypeCollection(StringRef Data, uint32_t RecordCountHint); 62 LazyRandomTypeCollection(ArrayRef<uint8_t> Data, 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 71 uint32_t getOffsetOfType(TypeIndex Index); 72 73 Optional<CVType> tryGetType(TypeIndex Index); 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 bool replaceType(TypeIndex &Index, CVType Data, bool Stabilize) override; 83 84 private: 85 Error ensureTypeExists(TypeIndex Index); 86 void ensureCapacityFor(TypeIndex Index); 87 88 Error visitRangeForType(TypeIndex TI); 89 Error fullScanForType(TypeIndex TI); 90 void visitRange(TypeIndex Begin, uint32_t BeginOffset, TypeIndex End); 91 92 /// Number of actual records. 93 uint32_t Count = 0; 94 95 /// The largest type index which we've visited. 96 TypeIndex LargestTypeIndex = TypeIndex::None(); 97 98 BumpPtrAllocator Allocator; 99 StringSaver NameStorage; 100 101 /// The type array to allow random access visitation of. 102 CVTypeArray Types; 103 104 std::vector<CacheEntry> Records; 105 106 /// An array of index offsets for the given type stream, allowing log(N) 107 /// lookups of a type record by index. Similar to KnownOffsets but only 108 /// contains offsets for some type indices, some of which may not have 109 /// ever been visited. 110 PartialOffsetArray PartialOffsets; 111 }; 112 113 } // end namespace codeview 114 } // end namespace llvm 115 116 #endif // LLVM_DEBUGINFO_CODEVIEW_LAZYRANDOMTYPECOLLECTION_H 117