ELFObjectWriter: deduplicate suffices in strtab
We already do this for shstrtab, so might as well do it for strtab. This
extracts the string table building code into a separate class. The idea
is to use it for other object formats too.
I mostly wanted to do this for the general principle, but it does save a
little bit on object file size. I tried this on a clang bootstrap and
saved 0.54% on the sum of object file sizes (1.14 MB out of 212 MB for
a release build).
Differential Revision: http://reviews.llvm.org/D3533
llvm-svn: 207670
diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index 2e07e22..ebcc691f 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -28,6 +28,7 @@
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/MC/MCValue.h"
+#include "llvm/Object/StringTableBuilder.h"
#include "llvm/Support/Compression.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Endian.h"
@@ -132,11 +133,11 @@
MCSymbolData *SymbolData;
uint64_t StringIndex;
uint32_t SectionIndex;
+ StringRef Name;
// Support lexicographic sorting.
bool operator<(const ELFSymbolData &RHS) const {
- return SymbolData->getSymbol().getName() <
- RHS.SymbolData->getSymbol().getName();
+ return Name < RHS.Name;
}
};
@@ -149,13 +150,13 @@
llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
Relocations;
- DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
+ StringTableBuilder ShStrTabBuilder;
/// @}
/// @name Symbol Table Data
/// @{
- SmallString<256> StringTable;
+ StringTableBuilder StrTabBuilder;
std::vector<uint64_t> FileSymbolData;
std::vector<ELFSymbolData> LocalSymbolData;
std::vector<ELFSymbolData> ExternalSymbolData;
@@ -676,7 +677,6 @@
SectionIndexMapTy &SectionIndexMap) {
// The string table must be emitted first because we need the index
// into the string table for all the symbol names.
- assert(StringTable.size() && "Missing string table");
// FIXME: Make sure the start of the symbol table is aligned.
@@ -1031,27 +1031,6 @@
MCELF::SetBinding(Data, ELF::STB_GLOBAL);
}
- // Index 0 is always the empty string.
- StringMap<uint64_t> StringIndexMap;
- StringTable += '\x00';
-
- // FIXME: We could optimize suffixes in strtab in the same way we
- // optimize them in shstrtab.
-
- for (MCAssembler::const_file_name_iterator it = Asm.file_names_begin(),
- ie = Asm.file_names_end();
- it != ie;
- ++it) {
- StringRef Name = *it;
- uint64_t &Entry = StringIndexMap[Name];
- if (!Entry) {
- Entry = StringTable.size();
- StringTable += Name;
- StringTable += '\x00';
- }
- FileSymbolData.push_back(Entry);
- }
-
// Add the data for the symbols.
for (MCSymbolData &SD : Asm.symbols()) {
const MCSymbol &Symbol = SD.getSymbol();
@@ -1102,7 +1081,6 @@
// @@ in defined ones.
StringRef Name = Symbol.getName();
SmallString<32> Buf;
-
size_t Pos = Name.find("@@@");
if (Pos != StringRef::npos) {
Buf += Name.substr(0, Pos);
@@ -1110,14 +1088,8 @@
Buf += Name.substr(Pos + Skip);
Name = Buf;
}
+ MSD.Name = StrTabBuilder.add(Name);
- uint64_t &Entry = StringIndexMap[Name];
- if (!Entry) {
- Entry = StringTable.size();
- StringTable += Name;
- StringTable += '\x00';
- }
- MSD.StringIndex = Entry;
if (MSD.SectionIndex == ELF::SHN_UNDEF)
UndefinedSymbolData.push_back(MSD);
else if (Local)
@@ -1126,6 +1098,21 @@
ExternalSymbolData.push_back(MSD);
}
+ for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
+ StrTabBuilder.add(*i);
+
+ StrTabBuilder.finalize();
+
+ for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
+ FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
+
+ for (ELFSymbolData& MSD : LocalSymbolData)
+ MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
+ for (ELFSymbolData& MSD : ExternalSymbolData)
+ MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
+ for (ELFSymbolData& MSD : UndefinedSymbolData)
+ MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
+
// Symbols are required to be in lexicographic order.
array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
@@ -1436,23 +1423,6 @@
}
}
-static int compareBySuffix(const MCSectionELF *const *a,
- const MCSectionELF *const *b) {
- const StringRef &NameA = (*a)->getSectionName();
- const StringRef &NameB = (*b)->getSectionName();
- const unsigned sizeA = NameA.size();
- const unsigned sizeB = NameB.size();
- const unsigned len = std::min(sizeA, sizeB);
- for (unsigned int i = 0; i < len; ++i) {
- char ca = NameA[sizeA - i - 1];
- char cb = NameB[sizeB - i - 1];
- if (ca != cb)
- return cb - ca;
- }
-
- return sizeB - sizeA;
-}
-
void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
MCAsmLayout &Layout,
SectionIndexMapTy &SectionIndexMap,
@@ -1493,45 +1463,20 @@
WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
F = new MCDataFragment(&StrtabSD);
- F->getContents().append(StringTable.begin(), StringTable.end());
+ F->getContents().append(StrTabBuilder.data().begin(),
+ StrTabBuilder.data().end());
F = new MCDataFragment(&ShstrtabSD);
- std::vector<const MCSectionELF*> Sections;
- for (MCAssembler::const_iterator it = Asm.begin(),
- ie = Asm.end(); it != ie; ++it) {
+ // Section header string table.
+ for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(it->getSection());
- Sections.push_back(&Section);
+ ShStrTabBuilder.add(Section.getSectionName());
}
- array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix);
-
- // Section header string table.
- //
- // The first entry of a string table holds a null character so skip
- // section 0.
- uint64_t Index = 1;
- F->getContents().push_back('\x00');
-
- for (unsigned int I = 0, E = Sections.size(); I != E; ++I) {
- const MCSectionELF &Section = *Sections[I];
-
- StringRef Name = Section.getSectionName();
- if (I != 0) {
- StringRef PreviousName = Sections[I - 1]->getSectionName();
- if (PreviousName.endswith(Name)) {
- SectionStringTableIndex[&Section] = Index - Name.size() - 1;
- continue;
- }
- }
- // Remember the index into the string table so we can write it
- // into the sh_name field of the section header table.
- SectionStringTableIndex[&Section] = Index;
-
- Index += Name.size() + 1;
- F->getContents().append(Name.begin(), Name.end());
- F->getContents().push_back('\x00');
- }
+ ShStrTabBuilder.finalize();
+ F->getContents().append(ShStrTabBuilder.data().begin(),
+ ShStrTabBuilder.data().end());
}
void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
@@ -1599,7 +1544,7 @@
switch(Section.getType()) {
case ELF::SHT_DYNAMIC:
- sh_link = SectionStringTableIndex[&Section];
+ sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
sh_info = 0;
break;
@@ -1680,7 +1625,8 @@
}
}
- WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(),
+ WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
+ Section.getType(),
Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
Alignment, Section.getEntrySize());
}