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//==- include/llvm/CodeGen/AccelTable.h - Accelerator Tables -----*- C++ -*-==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
/// \file
/// This file contains support for writing accelerator tables.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_CODEGEN_ACCELTABLE_H
#define LLVM_CODEGEN_ACCELTABLE_H
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/STLFunctionalExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/CodeGen/DIE.h"
#include "llvm/CodeGen/DwarfStringPoolEntry.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/DJB.h"
#include "llvm/Support/Debug.h"
#include <cstdint>
#include <variant>
#include <vector>
/// \file
/// The DWARF and Apple accelerator tables are an indirect hash table optimized
/// for null lookup rather than access to known data. The Apple accelerator
/// tables are a precursor of the newer DWARF v5 accelerator tables. Both
/// formats share common design ideas.
///
/// The Apple accelerator table are output into an on-disk format that looks
/// like this:
///
/// .------------------.
/// | HEADER |
/// |------------------|
/// | BUCKETS |
/// |------------------|
/// | HASHES |
/// |------------------|
/// | OFFSETS |
/// |------------------|
/// | DATA |
/// `------------------'
///
/// The header contains a magic number, version, type of hash function,
/// the number of buckets, total number of hashes, and room for a special struct
/// of data and the length of that struct.
///
/// The buckets contain an index (e.g. 6) into the hashes array. The hashes
/// section contains all of the 32-bit hash values in contiguous memory, and the
/// offsets contain the offset into the data area for the particular hash.
///
/// For a lookup example, we could hash a function name and take it modulo the
/// number of buckets giving us our bucket. From there we take the bucket value
/// as an index into the hashes table and look at each successive hash as long
/// as the hash value is still the same modulo result (bucket value) as earlier.
/// If we have a match we look at that same entry in the offsets table and grab
/// the offset in the data for our final match.
///
/// The DWARF v5 accelerator table consists of zero or more name indices that
/// are output into an on-disk format that looks like this:
///
/// .------------------.
/// | HEADER |
/// |------------------|
/// | CU LIST |
/// |------------------|
/// | LOCAL TU LIST |
/// |------------------|
/// | FOREIGN TU LIST |
/// |------------------|
/// | HASH TABLE |
/// |------------------|
/// | NAME TABLE |
/// |------------------|
/// | ABBREV TABLE |
/// |------------------|
/// | ENTRY POOL |
/// `------------------'
///
/// For the full documentation please refer to the DWARF 5 standard.
///
///
/// This file defines the class template AccelTable, which is represents an
/// abstract view of an Accelerator table, without any notion of an on-disk
/// layout. This class is parameterized by an entry type, which should derive
/// from AccelTableData. This is the type of individual entries in the table,
/// and it should store the data necessary to emit them. AppleAccelTableData is
/// the base class for Apple Accelerator Table entries, which have a uniform
/// structure based on a sequence of Atoms. There are different sub-classes
/// derived from AppleAccelTable, which differ in the set of Atoms and how they
/// obtain their values.
///
/// An Apple Accelerator Table can be serialized by calling emitAppleAccelTable
/// function.
namespace llvm {
class AsmPrinter;
class DwarfDebug;
class DwarfTypeUnit;
class MCSymbol;
class raw_ostream;
/// Interface which the different types of accelerator table data have to
/// conform. It serves as a base class for different values of the template
/// argument of the AccelTable class template.
class AccelTableData {
public:
virtual ~AccelTableData() = default;
bool operator<(const AccelTableData &Other) const {
return order() < Other.order();
}
// Subclasses should implement:
// static uint32_t hash(StringRef Name);
#ifndef NDEBUG
virtual void print(raw_ostream &OS) const = 0;
#endif
protected:
virtual uint64_t order() const = 0;
};
/// A base class holding non-template-dependant functionality of the AccelTable
/// class. Clients should not use this class directly but rather instantiate
/// AccelTable with a type derived from AccelTableData.
class AccelTableBase {
public:
using HashFn = uint32_t(StringRef);
/// Represents a group of entries with identical name (and hence, hash value).
struct HashData {
DwarfStringPoolEntryRef Name;
uint32_t HashValue;
std::vector<AccelTableData *> Values;
MCSymbol *Sym;
/// Get all AccelTableData cast as a `T`.
template <typename T = AccelTableData *> auto getValues() const {
static_assert(std::is_pointer<T>());
static_assert(
std::is_base_of<AccelTableData, std::remove_pointer_t<T>>());
return map_range(
Values, [](AccelTableData *Data) { return static_cast<T>(Data); });
}
#ifndef NDEBUG
void print(raw_ostream &OS) const;
void dump() const { print(dbgs()); }
#endif
};
using HashList = std::vector<HashData *>;
using BucketList = std::vector<HashList>;
protected:
/// Allocator for HashData and Values.
BumpPtrAllocator Allocator;
using StringEntries = MapVector<StringRef, HashData>;
StringEntries Entries;
HashFn *Hash;
uint32_t BucketCount = 0;
uint32_t UniqueHashCount = 0;
HashList Hashes;
BucketList Buckets;
void computeBucketCount();
AccelTableBase(HashFn *Hash) : Hash(Hash) {}
public:
void finalize(AsmPrinter *Asm, StringRef Prefix);
ArrayRef<HashList> getBuckets() const { return Buckets; }
uint32_t getBucketCount() const { return BucketCount; }
uint32_t getUniqueHashCount() const { return UniqueHashCount; }
uint32_t getUniqueNameCount() const { return Entries.size(); }
#ifndef NDEBUG
void print(raw_ostream &OS) const;
void dump() const { print(dbgs()); }
#endif
AccelTableBase(const AccelTableBase &) = delete;
void operator=(const AccelTableBase &) = delete;
};
/// This class holds an abstract representation of an Accelerator Table,
/// consisting of a sequence of buckets, each bucket containint a sequence of
/// HashData entries. The class is parameterized by the type of entries it
/// holds. The type template parameter also defines the hash function to use for
/// hashing names.
template <typename DataT> class AccelTable : public AccelTableBase {
public:
AccelTable() : AccelTableBase(DataT::hash) {}
template <typename... Types>
void addName(DwarfStringPoolEntryRef Name, Types &&... Args);
void clear() { Entries.clear(); }
void addEntries(AccelTable<DataT> &Table);
const StringEntries getEntries() const { return Entries; }
};
template <typename AccelTableDataT>
template <typename... Types>
void AccelTable<AccelTableDataT>::addName(DwarfStringPoolEntryRef Name,
Types &&... Args) {
assert(Buckets.empty() && "Already finalized!");
// If the string is in the list already then add this die to the list
// otherwise add a new one.
auto &It = Entries[Name.getString()];
if (It.Values.empty()) {
It.Name = Name;
It.HashValue = Hash(Name.getString());
}
It.Values.push_back(new (Allocator)
AccelTableDataT(std::forward<Types>(Args)...));
}
/// A base class for different implementations of Data classes for Apple
/// Accelerator Tables. The columns in the table are defined by the static Atoms
/// variable defined on the subclasses.
class AppleAccelTableData : public AccelTableData {
public:
/// An Atom defines the form of the data in an Apple accelerator table.
/// Conceptually it is a column in the accelerator consisting of a type and a
/// specification of the form of its data.
struct Atom {
/// Atom Type.
const uint16_t Type;
/// DWARF Form.
const uint16_t Form;
constexpr Atom(uint16_t Type, uint16_t Form) : Type(Type), Form(Form) {}
#ifndef NDEBUG
void print(raw_ostream &OS) const;
void dump() const { print(dbgs()); }
#endif
};
// Subclasses should define:
// static constexpr Atom Atoms[];
virtual void emit(AsmPrinter *Asm) const = 0;
static uint32_t hash(StringRef Buffer) { return djbHash(Buffer); }
};
/// Helper class to identify an entry in DWARF5AccelTable based on their DIE
/// offset and UnitID.
struct OffsetAndUnitID {
uint64_t Offset = 0;
uint32_t UnitID = 0;
bool IsTU = false;
OffsetAndUnitID() = delete;
OffsetAndUnitID(uint64_t Offset, uint32_t UnitID, bool IsTU)
: Offset(Offset), UnitID(UnitID), IsTU(IsTU) {}
uint64_t offset() const { return Offset; };
uint32_t unitID() const { return UnitID; };
bool isTU() const { return IsTU; }
};
template <> struct DenseMapInfo<OffsetAndUnitID> {
static inline OffsetAndUnitID getEmptyKey() {
return OffsetAndUnitID(-1, -1, false);
}
static inline OffsetAndUnitID getTombstoneKey() {
return OffsetAndUnitID(-2, -2, false);
}
static unsigned getHashValue(const OffsetAndUnitID &Val) {
return (unsigned)llvm::hash_combine(Val.offset(), Val.unitID(), Val.IsTU);
}
static bool isEqual(const OffsetAndUnitID &LHS, const OffsetAndUnitID &RHS) {
return LHS.offset() == RHS.offset() && LHS.unitID() == RHS.unitID() &&
LHS.IsTU == RHS.isTU();
}
};
/// The Data class implementation for DWARF v5 accelerator table. Unlike the
/// Apple Data classes, this class is just a DIE wrapper, and does not know to
/// serialize itself. The complete serialization logic is in the
/// emitDWARF5AccelTable function.
class DWARF5AccelTableData : public AccelTableData {
public:
static uint32_t hash(StringRef Name) { return caseFoldingDjbHash(Name); }
DWARF5AccelTableData(const DIE &Die, const uint32_t UnitID, const bool IsTU);
DWARF5AccelTableData(const uint64_t DieOffset,
const std::optional<uint64_t> DefiningParentOffset,
const unsigned DieTag, const unsigned UnitID,
const bool IsTU)
: OffsetVal(DieOffset), ParentOffset(DefiningParentOffset),
DieTag(DieTag), AbbrevNumber(0), IsTU(IsTU), UnitID(UnitID) {}
#ifndef NDEBUG
void print(raw_ostream &OS) const override;
#endif
uint64_t getDieOffset() const {
assert(isNormalized() && "Accessing DIE Offset before normalizing.");
return std::get<uint64_t>(OffsetVal);
}
OffsetAndUnitID getDieOffsetAndUnitID() const {
return {getDieOffset(), getUnitID(), isTU()};
}
unsigned getDieTag() const { return DieTag; }
unsigned getUnitID() const { return UnitID; }
bool isTU() const { return IsTU; }
void normalizeDIEToOffset() {
assert(!isNormalized() && "Accessing offset after normalizing.");
const DIE *Entry = std::get<const DIE *>(OffsetVal);
ParentOffset = getDefiningParentDieOffset(*Entry);
OffsetVal = Entry->getOffset();
}
bool isNormalized() const {
return std::holds_alternative<uint64_t>(OffsetVal);
}
std::optional<uint64_t> getParentDieOffset() const {
if (auto OffsetAndId = getParentDieOffsetAndUnitID())
return OffsetAndId->offset();
return {};
}
std::optional<OffsetAndUnitID> getParentDieOffsetAndUnitID() const {
assert(isNormalized() && "Accessing DIE Offset before normalizing.");
if (!ParentOffset)
return std::nullopt;
return OffsetAndUnitID(*ParentOffset, getUnitID(), isTU());
}
/// Sets AbbrevIndex for an Entry.
void setAbbrevNumber(uint16_t AbbrevNum) { AbbrevNumber = AbbrevNum; }
/// Returns AbbrevIndex for an Entry.
uint16_t getAbbrevNumber() const { return AbbrevNumber; }
/// If `Die` has a non-null parent and the parent is not a declaration,
/// return its offset.
static std::optional<uint64_t> getDefiningParentDieOffset(const DIE &Die);
protected:
std::variant<const DIE *, uint64_t> OffsetVal;
std::optional<uint64_t> ParentOffset;
uint32_t DieTag : 16;
uint32_t AbbrevNumber : 15;
uint32_t IsTU : 1;
uint32_t UnitID;
uint64_t order() const override { return getDieOffset(); }
};
class DebugNamesAbbrev : public FoldingSetNode {
public:
uint32_t DieTag;
uint32_t Number;
struct AttributeEncoding {
dwarf::Index Index;
dwarf::Form Form;
};
DebugNamesAbbrev(uint32_t DieTag) : DieTag(DieTag), Number(0) {}
/// Add attribute encoding to an abbreviation.
void addAttribute(const DebugNamesAbbrev::AttributeEncoding &Attr) {
AttrVect.push_back(Attr);
}
/// Set abbreviation tag index.
void setNumber(uint32_t AbbrevNumber) { Number = AbbrevNumber; }
/// Get abbreviation tag index.
uint32_t getNumber() const { return Number; }
/// Get DIE Tag.
uint32_t getDieTag() const { return DieTag; }
/// Used to gather unique data for the abbreviation folding set.
void Profile(FoldingSetNodeID &ID) const;
/// Returns attributes for an abbreviation.
const SmallVector<AttributeEncoding, 1> &getAttributes() const {
return AttrVect;
}
private:
SmallVector<AttributeEncoding, 1> AttrVect;
};
struct TypeUnitMetaInfo {
// Symbol for start of the TU section or signature if this is SplitDwarf.
std::variant<MCSymbol *, uint64_t> LabelOrSignature;
// Unique ID of Type Unit.
unsigned UniqueID;
};
using TUVectorTy = SmallVector<TypeUnitMetaInfo, 1>;
class DWARF5AccelTable : public AccelTable<DWARF5AccelTableData> {
// Symbols to start of all the TU sections that were generated.
TUVectorTy TUSymbolsOrHashes;
public:
struct UnitIndexAndEncoding {
unsigned Index;
DebugNamesAbbrev::AttributeEncoding Encoding;
};
/// Returns type units that were constructed.
const TUVectorTy &getTypeUnitsSymbols() { return TUSymbolsOrHashes; }
/// Add a type unit start symbol.
void addTypeUnitSymbol(DwarfTypeUnit &U);
/// Add a type unit Signature.
void addTypeUnitSignature(DwarfTypeUnit &U);
/// Convert DIE entries to explicit offset.
/// Needs to be called after DIE offsets are computed.
void convertDieToOffset() {
for (auto &Entry : Entries) {
for (auto *Data : Entry.second.getValues<DWARF5AccelTableData *>()) {
// For TU we normalize as each Unit is emitted.
// So when this is invoked after CU construction we will be in mixed
// state.
if (!Data->isNormalized())
Data->normalizeDIEToOffset();
}
}
}
void addTypeEntries(DWARF5AccelTable &Table) {
for (auto &Entry : Table.getEntries()) {
for (auto *Data : Entry.second.getValues<DWARF5AccelTableData *>()) {
addName(Entry.second.Name, Data->getDieOffset(),
Data->getParentDieOffset(), Data->getDieTag(),
Data->getUnitID(), Data->isTU());
}
}
}
};
void emitAppleAccelTableImpl(AsmPrinter *Asm, AccelTableBase &Contents,
StringRef Prefix, const MCSymbol *SecBegin,
ArrayRef<AppleAccelTableData::Atom> Atoms);
/// Emit an Apple Accelerator Table consisting of entries in the specified
/// AccelTable. The DataT template parameter should be derived from
/// AppleAccelTableData.
template <typename DataT>
void emitAppleAccelTable(AsmPrinter *Asm, AccelTable<DataT> &Contents,
StringRef Prefix, const MCSymbol *SecBegin) {
static_assert(std::is_convertible<DataT *, AppleAccelTableData *>::value);
emitAppleAccelTableImpl(Asm, Contents, Prefix, SecBegin, DataT::Atoms);
}
void emitDWARF5AccelTable(AsmPrinter *Asm, DWARF5AccelTable &Contents,
const DwarfDebug &DD,
ArrayRef<std::unique_ptr<DwarfCompileUnit>> CUs);
/// Emit a DWARFv5 Accelerator Table consisting of entries in the specified
/// AccelTable. The \p CUs contains either symbols keeping offsets to the
/// start of compilation unit, either offsets to the start of compilation
/// unit themselves.
void emitDWARF5AccelTable(
AsmPrinter *Asm, DWARF5AccelTable &Contents,
ArrayRef<std::variant<MCSymbol *, uint64_t>> CUs,
llvm::function_ref<std::optional<DWARF5AccelTable::UnitIndexAndEncoding>(
const DWARF5AccelTableData &)>
getIndexForEntry);
/// Accelerator table data implementation for simple Apple accelerator tables
/// with just a DIE reference.
class AppleAccelTableOffsetData : public AppleAccelTableData {
public:
AppleAccelTableOffsetData(const DIE &D) : Die(D) {}
void emit(AsmPrinter *Asm) const override;
static constexpr Atom Atoms[] = {
Atom(dwarf::DW_ATOM_die_offset, dwarf::DW_FORM_data4)};
#ifndef NDEBUG
void print(raw_ostream &OS) const override;
#endif
protected:
uint64_t order() const override { return Die.getOffset(); }
const DIE &Die;
};
/// Accelerator table data implementation for Apple type accelerator tables.
class AppleAccelTableTypeData : public AppleAccelTableOffsetData {
public:
AppleAccelTableTypeData(const DIE &D) : AppleAccelTableOffsetData(D) {}
void emit(AsmPrinter *Asm) const override;
static constexpr Atom Atoms[] = {
Atom(dwarf::DW_ATOM_die_offset, dwarf::DW_FORM_data4),
Atom(dwarf::DW_ATOM_die_tag, dwarf::DW_FORM_data2),
Atom(dwarf::DW_ATOM_type_flags, dwarf::DW_FORM_data1)};
#ifndef NDEBUG
void print(raw_ostream &OS) const override;
#endif
};
/// Accelerator table data implementation for simple Apple accelerator tables
/// with a DIE offset but no actual DIE pointer.
class AppleAccelTableStaticOffsetData : public AppleAccelTableData {
public:
AppleAccelTableStaticOffsetData(uint32_t Offset) : Offset(Offset) {}
void emit(AsmPrinter *Asm) const override;
static constexpr Atom Atoms[] = {
Atom(dwarf::DW_ATOM_die_offset, dwarf::DW_FORM_data4)};
#ifndef NDEBUG
void print(raw_ostream &OS) const override;
#endif
protected:
uint64_t order() const override { return Offset; }
uint32_t Offset;
};
/// Accelerator table data implementation for type accelerator tables with
/// a DIE offset but no actual DIE pointer.
class AppleAccelTableStaticTypeData : public AppleAccelTableStaticOffsetData {
public:
AppleAccelTableStaticTypeData(uint32_t Offset, uint16_t Tag,
bool ObjCClassIsImplementation,
uint32_t QualifiedNameHash)
: AppleAccelTableStaticOffsetData(Offset),
QualifiedNameHash(QualifiedNameHash), Tag(Tag),
ObjCClassIsImplementation(ObjCClassIsImplementation) {}
void emit(AsmPrinter *Asm) const override;
static constexpr Atom Atoms[] = {
Atom(dwarf::DW_ATOM_die_offset, dwarf::DW_FORM_data4),
Atom(dwarf::DW_ATOM_die_tag, dwarf::DW_FORM_data2),
Atom(5, dwarf::DW_FORM_data1), Atom(6, dwarf::DW_FORM_data4)};
#ifndef NDEBUG
void print(raw_ostream &OS) const override;
#endif
protected:
uint64_t order() const override { return Offset; }
uint32_t QualifiedNameHash;
uint16_t Tag;
bool ObjCClassIsImplementation;
};
} // end namespace llvm
#endif // LLVM_CODEGEN_ACCELTABLE_H
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