Provides amortized O(1) random access to a CodeView type stream. More...

#include "llvm/DebugInfo/CodeView/LazyRandomTypeCollection.h"

Inheritance diagram for llvm::codeview::LazyRandomTypeCollection:

Public Member Functions
	LazyRandomTypeCollection (uint32_t RecordCountHint)

	LazyRandomTypeCollection (StringRef Data, uint32_t RecordCountHint)

	LazyRandomTypeCollection (ArrayRef< uint8_t > Data, uint32_t RecordCountHint)

	LazyRandomTypeCollection (const CVTypeArray &Types, uint32_t RecordCountHint, PartialOffsetArray PartialOffsets)

	LazyRandomTypeCollection (const CVTypeArray &Types, uint32_t RecordCountHint)

void	reset (ArrayRef< uint8_t > Data, uint32_t RecordCountHint)

void	reset (StringRef Data, uint32_t RecordCountHint)

void	reset (BinaryStreamReader &Reader, uint32_t RecordCountHint)

uint32_t	getOffsetOfType (TypeIndex Index)

std::optional< CVType >	tryGetType (TypeIndex Index)

CVType	getType (TypeIndex Index) override

StringRef	getTypeName (TypeIndex Index) override

bool	contains (TypeIndex Index) override

uint32_t	size () override

uint32_t	capacity () override

std::optional< TypeIndex >	getFirst () override

std::optional< TypeIndex >	getNext (TypeIndex Prev) override

bool	replaceType (TypeIndex &Index, CVType Data, bool Stabilize) override

Public Member Functions inherited from llvm::codeview::TypeCollection
virtual	~TypeCollection ()=default

bool	empty ()

virtual std::optional< TypeIndex >	getFirst ()=0

virtual std::optional< TypeIndex >	getNext (TypeIndex Prev)=0

virtual CVType	getType (TypeIndex Index)=0

virtual StringRef	getTypeName (TypeIndex Index)=0

virtual bool	contains (TypeIndex Index)=0

virtual uint32_t	size ()=0

virtual uint32_t	capacity ()=0

virtual bool	replaceType (TypeIndex &Index, CVType Data, bool Stabilize)=0

template<typename TFunc >
void	ForEachRecord (TFunc Func)

Detailed Description

Provides amortized O(1) random access to a CodeView type stream.

Normally to access a type from a type stream, you must know its byte offset into the type stream, because type records are variable-lengthed. However, this is not the way we prefer to access them. For example, given a symbol record one of the fields may be the TypeIndex of the symbol's type record. Or given a type record such as an array type, there might be a TypeIndex for the element type. Sequential access is perfect when we're just dumping every entry, but it's very poor for real world usage.

Type streams in PDBs contain an additional field which is a list of pairs containing indices and their corresponding offsets, roughly every ~8KB of record data. This general idea need not be confined to PDBs though. By supplying such an array, the producer of a type stream can allow the consumer much better access time, because the consumer can find the nearest index in this array, and do a linear scan forward only from there.

LazyRandomTypeCollection implements this algorithm, but additionally goes one step further by caching offsets of every record that has been visited at least once. This way, even repeated visits of the same record will never require more than one linear scan. For a type stream of N elements divided into M chunks of roughly equal size, this yields a worst case lookup time of O(N/M) and an amortized time of O(1).

Definition at line 48 of file LazyRandomTypeCollection.h.