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/Support/Allocator.h" 18 #include "llvm/Support/BinaryStreamArray.h" 19 #include "llvm/Support/Error.h" 20 #include "llvm/Support/StringSaver.h" 21 #include <cstdint> 22 #include <vector> 23 24 namespace llvm { 25 namespace codeview { 26 27 /// Provides amortized O(1) random access to a CodeView type stream. 28 /// Normally to access a type from a type stream, you must know its byte 29 /// offset into the type stream, because type records are variable-lengthed. 30 /// However, this is not the way we prefer to access them. For example, given 31 /// a symbol record one of the fields may be the TypeIndex of the symbol's 32 /// type record. Or given a type record such as an array type, there might 33 /// be a TypeIndex for the element type. Sequential access is perfect when 34 /// we're just dumping every entry, but it's very poor for real world usage. 35 /// 36 /// Type streams in PDBs contain an additional field which is a list of pairs 37 /// containing indices and their corresponding offsets, roughly every ~8KB of 38 /// record data. This general idea need not be confined to PDBs though. By 39 /// supplying such an array, the producer of a type stream can allow the 40 /// consumer much better access time, because the consumer can find the nearest 41 /// index in this array, and do a linear scan forward only from there. 42 /// 43 /// LazyRandomTypeCollection implements this algorithm, but additionally goes 44 /// one step further by caching offsets of every record that has been visited at 45 /// least once. This way, even repeated visits of the same record will never 46 /// require more than one linear scan. For a type stream of N elements divided 47 /// into M chunks of roughly equal size, this yields a worst case lookup time 48 /// of O(N/M) and an amortized time of O(1). 49 class LazyRandomTypeCollection : public TypeCollection { 50 using PartialOffsetArray = FixedStreamArray<TypeIndexOffset>; 51 52 struct CacheEntry { 53 CVType Type; 54 uint32_t Offset; 55 StringRef Name; 56 }; 57 58 public: 59 explicit LazyRandomTypeCollection(uint32_t RecordCountHint); 60 LazyRandomTypeCollection(StringRef Data, uint32_t RecordCountHint); 61 LazyRandomTypeCollection(ArrayRef<uint8_t> Data, uint32_t RecordCountHint); 62 LazyRandomTypeCollection(const CVTypeArray &Types, uint32_t RecordCountHint, 63 PartialOffsetArray PartialOffsets); 64 LazyRandomTypeCollection(const CVTypeArray &Types, uint32_t RecordCountHint); 65 66 void reset(ArrayRef<uint8_t> Data, uint32_t RecordCountHint); 67 void reset(StringRef Data, uint32_t RecordCountHint); 68 void reset(BinaryStreamReader &Reader, uint32_t RecordCountHint); 69 70 uint32_t getOffsetOfType(TypeIndex Index); 71 72 Optional<CVType> tryGetType(TypeIndex Index); 73 74 CVType getType(TypeIndex Index) override; 75 StringRef getTypeName(TypeIndex Index) override; 76 bool contains(TypeIndex Index) override; 77 uint32_t size() override; 78 uint32_t capacity() override; 79 Optional<TypeIndex> getFirst() override; 80 Optional<TypeIndex> getNext(TypeIndex Prev) override; 81 bool replaceType(TypeIndex &Index, CVType Data, bool Stabilize) 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 97 BumpPtrAllocator Allocator; 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 116