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llvm-project/llvm/lib/CodeGen/AsmPrinter/DwarfAccelTable.cpp

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//===- llvm/CodeGen/DwarfAccelTable.cpp - Dwarf Accelerator Tables --------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains support for writing dwarf accelerator tables.
//
//===----------------------------------------------------------------------===//
#include "DwarfAccelTable.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/Twine.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/CodeGen/DIE.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <limits>
#include <vector>
using namespace llvm;
// The length of the header data is always going to be 4 + 4 + 4*NumAtoms.
DwarfAccelTable::DwarfAccelTable(ArrayRef<DwarfAccelTable::Atom> atomList)
: Header(8 + (atomList.size() * 4)), HeaderData(atomList),
Entries(Allocator) {}
void DwarfAccelTable::AddName(DwarfStringPoolEntryRef Name, const DIE *die,
char Flags) {
assert(Data.empty() && "Already finalized!");
// If the string is in the list already then add this die to the list
// otherwise add a new one.
DataArray &DIEs = Entries[Name.getString()];
assert(!DIEs.Name || DIEs.Name == Name);
DIEs.Name = Name;
DIEs.Values.push_back(new (Allocator) HashDataContents(die, Flags));
}
void DwarfAccelTable::ComputeBucketCount() {
// First get the number of unique hashes.
std::vector<uint32_t> uniques(Data.size());
for (size_t i = 0, e = Data.size(); i < e; ++i)
uniques[i] = Data[i]->HashValue;
array_pod_sort(uniques.begin(), uniques.end());
std::vector<uint32_t>::iterator p =
std::unique(uniques.begin(), uniques.end());
uint32_t num = std::distance(uniques.begin(), p);
// Then compute the bucket size, minimum of 1 bucket.
if (num > 1024)
Header.bucket_count = num / 4;
else if (num > 16)
Header.bucket_count = num / 2;
else
Header.bucket_count = num > 0 ? num : 1;
Header.hashes_count = num;
}
// compareDIEs - comparison predicate that sorts DIEs by their offset.
static bool compareDIEs(const DwarfAccelTable::HashDataContents *A,
const DwarfAccelTable::HashDataContents *B) {
return A->Die->getOffset() < B->Die->getOffset();
}
void DwarfAccelTable::FinalizeTable(AsmPrinter *Asm, StringRef Prefix) {
// Create the individual hash data outputs.
Data.reserve(Entries.size());
for (StringMap<DataArray>::iterator EI = Entries.begin(), EE = Entries.end();
EI != EE; ++EI) {
// Unique the entries.
std::stable_sort(EI->second.Values.begin(), EI->second.Values.end(), compareDIEs);
EI->second.Values.erase(
std::unique(EI->second.Values.begin(), EI->second.Values.end()),
EI->second.Values.end());
HashData *Entry = new (Allocator) HashData(EI->getKey(), EI->second);
Data.push_back(Entry);
}
// Figure out how many buckets we need, then compute the bucket
// contents and the final ordering. We'll emit the hashes and offsets
// by doing a walk during the emission phase. We add temporary
// symbols to the data so that we can reference them during the offset
// later, we'll emit them when we emit the data.
ComputeBucketCount();
// Compute bucket contents and final ordering.
Buckets.resize(Header.bucket_count);
for (size_t i = 0, e = Data.size(); i < e; ++i) {
uint32_t bucket = Data[i]->HashValue % Header.bucket_count;
Buckets[bucket].push_back(Data[i]);
Data[i]->Sym = Asm->createTempSymbol(Prefix);
}
// Sort the contents of the buckets by hash value so that hash
// collisions end up together. Stable sort makes testing easier and
// doesn't cost much more.
for (size_t i = 0; i < Buckets.size(); ++i)
std::stable_sort(Buckets[i].begin(), Buckets[i].end(),
[] (HashData *LHS, HashData *RHS) {
return LHS->HashValue < RHS->HashValue;
});
}
// Emits the header for the table via the AsmPrinter.
void DwarfAccelTable::EmitHeader(AsmPrinter *Asm) {
Asm->OutStreamer->AddComment("Header Magic");
Asm->EmitInt32(Header.magic);
Asm->OutStreamer->AddComment("Header Version");
Asm->EmitInt16(Header.version);
Asm->OutStreamer->AddComment("Header Hash Function");
Asm->EmitInt16(Header.hash_function);
Asm->OutStreamer->AddComment("Header Bucket Count");
Asm->EmitInt32(Header.bucket_count);
Asm->OutStreamer->AddComment("Header Hash Count");
Asm->EmitInt32(Header.hashes_count);
Asm->OutStreamer->AddComment("Header Data Length");
Asm->EmitInt32(Header.header_data_len);
Asm->OutStreamer->AddComment("HeaderData Die Offset Base");
Asm->EmitInt32(HeaderData.die_offset_base);
Asm->OutStreamer->AddComment("HeaderData Atom Count");
Asm->EmitInt32(HeaderData.Atoms.size());
for (size_t i = 0; i < HeaderData.Atoms.size(); i++) {
Atom A = HeaderData.Atoms[i];
Asm->OutStreamer->AddComment(dwarf::AtomTypeString(A.type));
Asm->EmitInt16(A.type);
Asm->OutStreamer->AddComment(dwarf::FormEncodingString(A.form));
Asm->EmitInt16(A.form);
}
}
// Walk through and emit the buckets for the table. Each index is
// an offset into the list of hashes.
void DwarfAccelTable::EmitBuckets(AsmPrinter *Asm) {
unsigned index = 0;
for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
Asm->OutStreamer->AddComment("Bucket " + Twine(i));
if (!Buckets[i].empty())
Asm->EmitInt32(index);
else
Asm->EmitInt32(std::numeric_limits<uint32_t>::max());
// Buckets point in the list of hashes, not to the data. Do not
// increment the index multiple times in case of hash collisions.
uint64_t PrevHash = std::numeric_limits<uint64_t>::max();
for (auto *HD : Buckets[i]) {
uint32_t HashValue = HD->HashValue;
if (PrevHash != HashValue)
++index;
PrevHash = HashValue;
}
}
}
// Walk through the buckets and emit the individual hashes for each
// bucket.
void DwarfAccelTable::EmitHashes(AsmPrinter *Asm) {
uint64_t PrevHash = std::numeric_limits<uint64_t>::max();
for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
for (HashList::const_iterator HI = Buckets[i].begin(),
HE = Buckets[i].end();
HI != HE; ++HI) {
uint32_t HashValue = (*HI)->HashValue;
if (PrevHash == HashValue)
continue;
Asm->OutStreamer->AddComment("Hash in Bucket " + Twine(i));
Asm->EmitInt32(HashValue);
PrevHash = HashValue;
}
}
}
// Walk through the buckets and emit the individual offsets for each
// element in each bucket. This is done via a symbol subtraction from the
// beginning of the section. The non-section symbol will be output later
// when we emit the actual data.
void DwarfAccelTable::emitOffsets(AsmPrinter *Asm, const MCSymbol *SecBegin) {
uint64_t PrevHash = std::numeric_limits<uint64_t>::max();
for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
for (HashList::const_iterator HI = Buckets[i].begin(),
HE = Buckets[i].end();
HI != HE; ++HI) {
uint32_t HashValue = (*HI)->HashValue;
if (PrevHash == HashValue)
continue;
PrevHash = HashValue;
Asm->OutStreamer->AddComment("Offset in Bucket " + Twine(i));
MCContext &Context = Asm->OutStreamer->getContext();
const MCExpr *Sub = MCBinaryExpr::createSub(
MCSymbolRefExpr::create((*HI)->Sym, Context),
MCSymbolRefExpr::create(SecBegin, Context), Context);
Asm->OutStreamer->EmitValue(Sub, sizeof(uint32_t));
}
}
}
// Walk through the buckets and emit the full data for each element in
// the bucket. For the string case emit the dies and the various offsets.
// Terminate each HashData bucket with 0.
void DwarfAccelTable::EmitData(AsmPrinter *Asm, DwarfDebug *D) {
for (size_t i = 0, e = Buckets.size(); i < e; ++i) {
uint64_t PrevHash = std::numeric_limits<uint64_t>::max();
for (HashList::const_iterator HI = Buckets[i].begin(),
HE = Buckets[i].end();
HI != HE; ++HI) {
// Terminate the previous entry if there is no hash collision
// with the current one.
if (PrevHash != std::numeric_limits<uint64_t>::max() &&
PrevHash != (*HI)->HashValue)
Asm->EmitInt32(0);
// Remember to emit the label for our offset.
Asm->OutStreamer->EmitLabel((*HI)->Sym);
Asm->OutStreamer->AddComment((*HI)->Str);
Asm->emitDwarfStringOffset((*HI)->Data.Name);
Asm->OutStreamer->AddComment("Num DIEs");
Asm->EmitInt32((*HI)->Data.Values.size());
for (HashDataContents *HD : (*HI)->Data.Values) {
// Emit the DIE offset
Asm->EmitInt32(HD->Die->getDebugSectionOffset());
// If we have multiple Atoms emit that info too.
// FIXME: A bit of a hack, we either emit only one atom or all info.
if (HeaderData.Atoms.size() > 1) {
Asm->EmitInt16(HD->Die->getTag());
Asm->EmitInt8(HD->Flags);
}
}
PrevHash = (*HI)->HashValue;
}
// Emit the final end marker for the bucket.
if (!Buckets[i].empty())
Asm->EmitInt32(0);
}
}
// Emit the entire data structure to the output file.
void DwarfAccelTable::emit(AsmPrinter *Asm, const MCSymbol *SecBegin,
DwarfDebug *D) {
// Emit the header.
EmitHeader(Asm);
// Emit the buckets.
EmitBuckets(Asm);
// Emit the hashes.
EmitHashes(Asm);
// Emit the offsets.
emitOffsets(Asm, SecBegin);
// Emit the hash data.
EmitData(Asm, D);
}
#ifndef NDEBUG
void DwarfAccelTable::print(raw_ostream &OS) {
Header.print(OS);
HeaderData.print(OS);
OS << "Entries: \n";
for (StringMap<DataArray>::const_iterator EI = Entries.begin(),
EE = Entries.end();
EI != EE; ++EI) {
OS << "Name: " << EI->getKeyData() << "\n";
for (HashDataContents *HD : EI->second.Values)
HD->print(OS);
}
OS << "Buckets and Hashes: \n";
for (size_t i = 0, e = Buckets.size(); i < e; ++i)
for (HashList::const_iterator HI = Buckets[i].begin(),
HE = Buckets[i].end();
HI != HE; ++HI)
(*HI)->print(OS);
OS << "Data: \n";
for (std::vector<HashData *>::const_iterator DI = Data.begin(),
DE = Data.end();
DI != DE; ++DI)
(*DI)->print(OS);
}
#endif
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