[ELF] Add ELFFileBase::{elfShdrs,numELFShdrs} to avoid duplicate llvm…

…::object::ELFFile::sections() This mainly avoid `relsOrRelas` cost in `InputSectionBase::relocate`. `llvm::object::ELFFile::sections()` has redundant and expensive checks.
b-sh · Dec 25, 2021 · b5a0f0f · b5a0f0f
1 parent 2709fd1
commit b5a0f0f
Show file tree

Hide file tree

Showing 6 changed files with 23 additions and 19 deletions.
diff --git a/lld/ELF/DWARF.cpp b/lld/ELF/DWARF.cpp
@@ -27,8 +27,7 @@ using namespace lld::elf;
 
 template <class ELFT> LLDDwarfObj<ELFT>::LLDDwarfObj(ObjFile<ELFT> *obj) {
   // Get the ELF sections to retrieve sh_flags. See the SHF_GROUP comment below.
-  ArrayRef<typename ELFT::Shdr> objSections =
-      CHECK(obj->getObj().sections(), obj);
+  ArrayRef<typename ELFT::Shdr> objSections = obj->template getELFShdrs<ELFT>();
   assert(objSections.size() == obj->getSections().size());
   for (auto it : llvm::enumerate(obj->getSections())) {
     InputSectionBase *sec = it.value();

diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp
@@ -846,14 +846,13 @@ static bool
 processCallGraphRelocations(SmallVector<uint32_t, 32> &symbolIndices,
                             ArrayRef<typename ELFT::CGProfile> &cgProfile,
                             ObjFile<ELFT> *inputObj) {
-  symbolIndices.clear();
-  const ELFFile<ELFT> &obj = inputObj->getObj();
-  ArrayRef<Elf_Shdr_Impl<ELFT>> objSections =
-      CHECK(obj.sections(), "could not retrieve object sections");
-
   if (inputObj->cgProfileSectionIndex == SHN_UNDEF)
     return false;
 
+  ArrayRef<Elf_Shdr_Impl<ELFT>> objSections =
+      inputObj->template getELFShdrs<ELFT>();
+  symbolIndices.clear();
+  const ELFFile<ELFT> &obj = inputObj->getObj();
   cgProfile =
       check(obj.template getSectionContentsAsArray<typename ELFT::CGProfile>(
           objSections[inputObj->cgProfileSectionIndex]));

diff --git a/lld/ELF/InputFiles.cpp b/lld/ELF/InputFiles.cpp
@@ -370,6 +370,8 @@ template <class ELFT> void ELFFileBase::init() {
   abiVersion = obj.getHeader().e_ident[llvm::ELF::EI_ABIVERSION];
 
   ArrayRef<Elf_Shdr> sections = CHECK(obj.sections(), this);
+  elfShdrs = sections.data();
+  numELFShdrs = sections.size();
 
   // Find a symbol table.
   bool isDSO =
@@ -477,8 +479,7 @@ bool ObjFile<ELFT>::shouldMerge(const Elf_Shdr &sec, StringRef name) {
 // When the option is given, we link "just symbols". The section table is
 // initialized with null pointers.
 template <class ELFT> void ObjFile<ELFT>::initializeJustSymbols() {
-  ArrayRef<Elf_Shdr> sections = CHECK(this->getObj().sections(), this);
-  this->sections.resize(sections.size());
+  sections.resize(numELFShdrs);
 }
 
 // An ELF object file may contain a `.deplibs` section. If it exists, the
@@ -544,7 +545,7 @@ template <class ELFT>
 void ObjFile<ELFT>::initializeSections(bool ignoreComdats) {
   const ELFFile<ELFT> &obj = this->getObj();
 
-  ArrayRef<Elf_Shdr> objSections = CHECK(obj.sections(), this);
+  ArrayRef<Elf_Shdr> objSections = getELFShdrs<ELFT>();
   StringRef shstrtab = CHECK(obj.getSectionStringTable(objSections), this);
   uint64_t size = objSections.size();
   this->sections.resize(size);
@@ -1410,7 +1411,7 @@ template <class ELFT> void SharedFile::parse() {
 
   ArrayRef<Elf_Dyn> dynamicTags;
   const ELFFile<ELFT> obj = this->getObj<ELFT>();
-  ArrayRef<Elf_Shdr> sections = CHECK(obj.sections(), this);
+  ArrayRef<Elf_Shdr> sections = getELFShdrs<ELFT>();
 
   const Elf_Shdr *versymSec = nullptr;
   const Elf_Shdr *verdefSec = nullptr;

diff --git a/lld/ELF/InputFiles.h b/lld/ELF/InputFiles.h
@@ -189,6 +189,10 @@ class ELFFileBase : public InputFile {
         .slice(firstGlobal);
   }
 
+  template <typename ELFT> typename ELFT::ShdrRange getELFShdrs() const {
+    return typename ELFT::ShdrRange(
+        reinterpret_cast<const typename ELFT::Shdr *>(elfShdrs), numELFShdrs);
+  }
   template <typename ELFT> typename ELFT::SymRange getELFSyms() const {
     return typename ELFT::SymRange(
         reinterpret_cast<const typename ELFT::Sym *>(elfSyms), numELFSyms);
@@ -201,7 +205,9 @@ class ELFFileBase : public InputFile {
   // Initializes this class's member variables.
   template <typename ELFT> void init();
 
+  const void *elfShdrs = nullptr;
   const void *elfSyms = nullptr;
+  uint32_t numELFShdrs = 0;
   uint32_t numELFSyms = 0;
   uint32_t firstGlobal = 0;
   StringRef stringTable;

diff --git a/lld/ELF/InputSection.cpp b/lld/ELF/InputSection.cpp
@@ -163,16 +163,16 @@ template <class ELFT> RelsOrRelas<ELFT> InputSectionBase::relsOrRelas() const {
   if (relSecIdx == 0)
     return {};
   RelsOrRelas<ELFT> ret;
-  const ELFFile<ELFT> obj = cast<ELFFileBase>(file)->getObj<ELFT>();
-  typename ELFT::Shdr shdr = cantFail(obj.sections())[relSecIdx];
+  typename ELFT::Shdr shdr =
+      cast<ELFFileBase>(file)->getELFShdrs<ELFT>()[relSecIdx];
   if (shdr.sh_type == SHT_REL) {
     ret.rels = makeArrayRef(reinterpret_cast<const typename ELFT::Rel *>(
-                                obj.base() + shdr.sh_offset),
+                                file->mb.getBufferStart() + shdr.sh_offset),
                             shdr.sh_size / sizeof(typename ELFT::Rel));
   } else {
     assert(shdr.sh_type == SHT_RELA);
     ret.relas = makeArrayRef(reinterpret_cast<const typename ELFT::Rela *>(
-                                 obj.base() + shdr.sh_offset),
+                                 file->mb.getBufferStart() + shdr.sh_offset),
                              shdr.sh_size / sizeof(typename ELFT::Rela));
   }
   return ret;
@@ -433,8 +433,7 @@ void InputSection::copyRelocations(uint8_t *buf, ArrayRef<RelTy> rels) {
             sec->name != ".gcc_except_table" && sec->name != ".got2" &&
             sec->name != ".toc") {
           uint32_t secIdx = cast<Undefined>(sym).discardedSecIdx;
-          Elf_Shdr_Impl<ELFT> sec =
-              CHECK(file->getObj().sections(), file)[secIdx];
+          Elf_Shdr_Impl<ELFT> sec = file->template getELFShdrs<ELFT>()[secIdx];
           warn("relocation refers to a discarded section: " +
                CHECK(file->getObj().getSectionName(sec), file) +
                "\n>>> referenced by " + getObjMsg(p->r_offset));

diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp
@@ -472,8 +472,8 @@ static std::string maybeReportDiscarded(Undefined &sym) {
   if (!file || !sym.discardedSecIdx ||
       file->getSections()[sym.discardedSecIdx] != &InputSection::discarded)
     return "";
-  ArrayRef<Elf_Shdr_Impl<ELFT>> objSections =
-      CHECK(file->getObj().sections(), file);
+  ArrayRef<typename ELFT::Shdr> objSections =
+      file->template getELFShdrs<ELFT>();
 
   std::string msg;
   if (sym.type == ELF::STT_SECTION) {