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GC entries of SHF_MERGE sections.

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It is a fairly direct extension of the gc algorithm. For merge sections
instead of remembering just a live bit, we remember which offsets were
used.

This reduces the .rodata sections in chromium from 9648861 to 9477472
bytes.

llvm-svn: 267164
This commit is contained in:
Rafael Espindola
2016-04-22 16:46:08 +00:00
parent 197d6a882f
commit caa831d85a
7 changed files with 251 additions and 48 deletions
Download Patch File Download Diff File Expand all files Collapse all files

73
lld/ELF/InputSection.cpp
View File

@@ -77,23 +77,41 @@ InputSectionBase<ELFT>::getOffset(const DefinedRegular<ELFT> &Sym) {
return getOffset(Sym.Value);
}
// Returns a section that Rel relocation is pointing to.
template <class ELFT>
InputSectionBase<ELFT> *
InputSectionBase<ELFT>::getRelocTarget(const Elf_Rel &Rel) const {
// Global symbol
static DefinedRegular<ELFT> *getRelocTargetSym(ObjectFile<ELFT> *File,
const typename ELFT::Rel &Rel) {
uint32_t SymIndex = Rel.getSymbol(Config->Mips64EL);
SymbolBody &B = File->getSymbolBody(SymIndex).repl();
if (auto *D = dyn_cast<DefinedRegular<ELFT>>(&B))
if (D->Section)
return D->Section->Repl;
return D;
return nullptr;
}
// Returns a section that Rel relocation is pointing to.
template <class ELFT>
InputSectionBase<ELFT> *
std::pair<InputSectionBase<ELFT> *, typename ELFT::uint>
InputSectionBase<ELFT>::getRelocTarget(const Elf_Rel &Rel) const {
auto *D = getRelocTargetSym(File, Rel);
if (!D)
return std::make_pair(nullptr, 0);
if (!D->isSection())
return std::make_pair(D->Section->Repl, D->Value);
const uint8_t *BufLoc = getSectionData().begin() + Rel.r_offset;
uintX_t Addend =
Target->getImplicitAddend(BufLoc, Rel.getType(Config->Mips64EL));
return std::make_pair(D->Section->Repl, D->Value + Addend);
}
template <class ELFT>
std::pair<InputSectionBase<ELFT> *, typename ELFT::uint>
InputSectionBase<ELFT>::getRelocTarget(const Elf_Rela &Rel) const {
return getRelocTarget(reinterpret_cast<const Elf_Rel &>(Rel));
auto *D = getRelocTargetSym(File, Rel);
if (!D)
return std::make_pair(nullptr, 0);
if (!D->isSection())
return std::make_pair(D->Section->Repl, D->Value);
return std::make_pair(D->Section->Repl, D->Value + Rel.r_addend);
}
template <class ELFT>
@@ -368,10 +386,49 @@ typename ELFT::uint EHInputSection<ELFT>::getOffset(uintX_t Offset) {
return Base + Addend;
}
static size_t findNull(StringRef S, size_t EntSize) {
// Optimize the common case.
if (EntSize == 1)
return S.find(0);
for (unsigned I = 0, N = S.size(); I != N; I += EntSize) {
const char *B = S.begin() + I;
if (std::all_of(B, B + EntSize, [](char C) { return C == 0; }))
return I;
}
return StringRef::npos;
}
template <class ELFT>
MergeInputSection<ELFT>::MergeInputSection(elf::ObjectFile<ELFT> *F,
const Elf_Shdr *Header)
: SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::Merge) {}
: SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::Merge) {
uintX_t EntSize = Header->sh_entsize;
ArrayRef<uint8_t> D = this->getSectionData();
StringRef Data((const char *)D.data(), D.size());
std::vector<std::pair<uintX_t, uintX_t>> &Offsets = this->Offsets;
uintX_t V = Config->GcSections ? -1 : 0;
if (Header->sh_flags & SHF_STRINGS) {
uintX_t Offset = 0;
while (!Data.empty()) {
size_t End = findNull(Data, EntSize);
if (End == StringRef::npos)
fatal("string is not null terminated");
Offsets.push_back(std::make_pair(Offset, V));
uintX_t Size = End + EntSize;
Data = Data.substr(Size);
Offset += Size;
}
return;
}
// If this is not of type string, every entry has the same size.
size_t Size = Data.size();
assert((Size % EntSize) == 0);
for (unsigned I = 0, N = Size; I != N; I += EntSize)
Offsets.push_back(std::make_pair(I, V));
}
template <class ELFT>
bool MergeInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {