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Micro optimization and improved similarity with gas' output:

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When two section names share a suffix, reuse the entry in shstrtab.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129115 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola 2011-04-07 23:21:52 +00:00
parent 60d490cdc7
commit d5321da8d2
1 changed files with 38 additions and 10 deletions
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48
lib/MC/ELFObjectWriter.cpp
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@ -544,6 +544,9 @@ void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm,
StringMap<uint64_t> StringIndexMap;
StringTable += '\x00';
// FIXME: We could optimize suffixes in strtab in the same way we
// optimize them in shstrtab.
// Add the data for the symbols.
for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
ie = Asm.symbol_end(); it != ie; ++it) {
@ -748,6 +751,24 @@ void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
}
}
static int compareBySuffix(const void *a, const void *b) {
const MCSectionELF *secA = *static_cast<const MCSectionELF* const *>(a);
const MCSectionELF *secB = *static_cast<const MCSectionELF* const *>(b);
const StringRef &NameA = secA->getSectionName();
const StringRef &NameB = secB->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,
@ -806,6 +827,15 @@ void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
F = new MCDataFragment(&ShstrtabSD);
std::vector<const MCSectionELF*> Sections;
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(it->getSection());
Sections.push_back(&Section);
}
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
@ -813,22 +843,20 @@ void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
uint64_t Index = 1;
F->getContents() += '\x00';
StringMap<uint64_t> SecStringMap;
for (MCAssembler::const_iterator it = Asm.begin(),
ie = Asm.end(); it != ie; ++it) {
const MCSectionELF &Section =
static_cast<const MCSectionELF&>(it->getSection());
// FIXME: We could merge suffixes like in .text and .rela.text.
for (unsigned int I = 0, E = Sections.size(); I != E; ++I) {
const MCSectionELF &Section = *Sections[I];
StringRef Name = Section.getSectionName();
if (SecStringMap.count(Name)) {
SectionStringTableIndex[&Section] = SecStringMap[Name];
continue;
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;
SecStringMap[Name] = Index;
Index += Name.size() + 1;
F->getContents() += Name;