[lld] Explicitly ignore comdat groups when parsing LTO object(s)

Any symbols defined in the LTO object are by definition the ones we
want in the final output so we skip the comdat group checking in those
cases.

This change makes the ELF code more explicit about this and means
that wasm and ELF do this in the same way.

Differential Revision: https://reviews.llvm.org/D62884

llvm-svn: 362625

lld/ELF/Driver.cpp

@@ -1506,9 +1506,8 @@ template <class ELFT> void LinkerDriver::compileBitcodeFiles() {
     LTO->add(*File);
 
   for (InputFile *File : LTO->compile()) {
-    DenseMap<CachedHashStringRef, const InputFile *> DummyGroups;
     auto *Obj = cast<ObjFile<ELFT>>(File);
-    Obj->parse(DummyGroups);
+    Obj->parse(/*IgnoreComdats=*/true);
     for (Symbol *Sym : Obj->getGlobalSymbols())
       Sym->parseSymbolVersion();
     ObjectFiles.push_back(File);

lld/ELF/InputFiles.cpp

@@ -178,13 +178,13 @@ template <class ELFT> static void doParseFile(InputFile *File) {
   // LLVM bitcode file
   if (auto *F = dyn_cast<BitcodeFile>(File)) {
     BitcodeFiles.push_back(F);
-    F->parse<ELFT>(Symtab->ComdatGroups);
+    F->parse<ELFT>();
     return;
   }
 
   // Regular object file
   ObjectFiles.push_back(File);
-  cast<ObjFile<ELFT>>(File)->parse(Symtab->ComdatGroups);
+  cast<ObjFile<ELFT>>(File)->parse();
 }
 
 // Add symbols in File to the symbol table.
@@ -449,14 +449,12 @@ template <class ELFT> ArrayRef<Symbol *> ObjFile<ELFT>::getGlobalSymbols() {
   return makeArrayRef(this->Symbols).slice(this->FirstGlobal);
 }
 
-template <class ELFT>
-void ObjFile<ELFT>::parse(
-    DenseMap<CachedHashStringRef, const InputFile *> &ComdatGroups) {
+template <class ELFT> void ObjFile<ELFT>::parse(bool IgnoreComdats) {
   // Read a section table. JustSymbols is usually false.
   if (this->JustSymbols)
     initializeJustSymbols();
   else
-    initializeSections(ComdatGroups);
+    initializeSections(IgnoreComdats);
 
   // Read a symbol table.
   initializeSymbols();
@@ -564,8 +562,7 @@ static void addDependentLibrary(StringRef Specifier, const InputFile *F) {
 }
 
 template <class ELFT>
-void ObjFile<ELFT>::initializeSections(
-    DenseMap<CachedHashStringRef, const InputFile *> &ComdatGroups) {
+void ObjFile<ELFT>::initializeSections(bool IgnoreComdats) {
   const ELFFile<ELFT> &Obj = this->getObj();
 
   ArrayRef<Elf_Shdr> ObjSections = CHECK(Obj.sections(), this);
@@ -625,7 +622,9 @@ void ObjFile<ELFT>::initializeSections(
         fatal(toString(this) + ": unsupported SHT_GROUP format");
 
       bool IsNew =
-          ComdatGroups.try_emplace(CachedHashStringRef(Signature), this).second;
+          IgnoreComdats ||
+          Symtab->ComdatGroups.try_emplace(CachedHashStringRef(Signature), this)
+              .second;
       if (IsNew) {
         if (Config->Relocatable)
           this->Sections[I] = createInputSection(Sec);
@@ -1478,13 +1477,11 @@ static Symbol *createBitcodeSymbol(const std::vector<bool> &KeptComdats,
   return Symtab->addSymbol(New);
 }
 
-template <class ELFT>
-void BitcodeFile::parse(
-    DenseMap<CachedHashStringRef, const InputFile *> &ComdatGroups) {
+template <class ELFT> void BitcodeFile::parse() {
   std::vector<bool> KeptComdats;
   for (StringRef S : Obj->getComdatTable())
     KeptComdats.push_back(
-        ComdatGroups.try_emplace(CachedHashStringRef(S), this).second);
+        Symtab->ComdatGroups.try_emplace(CachedHashStringRef(S), this).second);
 
   for (const lto::InputFile::Symbol &ObjSym : Obj->symbols())
     Symbols.push_back(createBitcodeSymbol<ELFT>(KeptComdats, ObjSym, *this));
@@ -1617,14 +1614,10 @@ std::string elf::replaceThinLTOSuffix(StringRef Path) {
   return Path;
 }
 
-template void
-BitcodeFile::parse<ELF32LE>(DenseMap<CachedHashStringRef, const InputFile *> &);
-template void
-BitcodeFile::parse<ELF32BE>(DenseMap<CachedHashStringRef, const InputFile *> &);
-template void
-BitcodeFile::parse<ELF64LE>(DenseMap<CachedHashStringRef, const InputFile *> &);
-template void
-BitcodeFile::parse<ELF64BE>(DenseMap<CachedHashStringRef, const InputFile *> &);
+template void BitcodeFile::parse<ELF32LE>();
+template void BitcodeFile::parse<ELF32BE>();
+template void BitcodeFile::parse<ELF64LE>();
+template void BitcodeFile::parse<ELF64BE>();
 
 template void LazyObjFile::parse<ELF32LE>();
 template void LazyObjFile::parse<ELF32BE>();

lld/ELF/InputFiles.h

@@ -201,8 +201,7 @@ public:
     this->ArchiveName = ArchiveName;
   }
 
-  void parse(llvm::DenseMap<llvm::CachedHashStringRef, const InputFile *>
-                 &ComdatGroups);
+  void parse(bool IgnoreComdats = false);
 
   StringRef getShtGroupSignature(ArrayRef<Elf_Shdr> Sections,
                                  const Elf_Shdr &Sec);
@@ -250,8 +249,7 @@ public:
   ArrayRef<Elf_CGProfile> CGProfile;
 
 private:
-  void initializeSections(llvm::DenseMap<llvm::CachedHashStringRef,
-                                         const InputFile *> &ComdatGroups);
+  void initializeSections(bool IgnoreComdats);
   void initializeSymbols();
   void initializeJustSymbols();
   void initializeDwarf();
@@ -340,9 +338,7 @@ public:
   BitcodeFile(MemoryBufferRef M, StringRef ArchiveName,
               uint64_t OffsetInArchive);
   static bool classof(const InputFile *F) { return F->kind() == BitcodeKind; }
-  template <class ELFT>
-  void parse(llvm::DenseMap<llvm::CachedHashStringRef, const InputFile *>
-                 &ComdatGroups);
+  template <class ELFT> void parse();
   std::unique_ptr<llvm::lto::InputFile> Obj;
 };
 

lld/wasm/InputFiles.cpp

@@ -306,11 +306,10 @@ void ObjFile::parse(bool IgnoreComdats) {
   TypeIsUsed.resize(getWasmObj()->types().size(), false);
 
   ArrayRef<StringRef> Comdats = WasmObj->linkingData().Comdats;
-  for (unsigned I = 0; I < Comdats.size(); ++I)
-    if (IgnoreComdats)
-      KeptComdats.push_back(true);
-    else
-      KeptComdats.push_back(Symtab->addComdat(Comdats[I]));
+  for (unsigned I = 0; I < Comdats.size(); ++I) {
+    bool IsNew = IgnoreComdats || Symtab->addComdat(Comdats[I]);
+    KeptComdats.push_back(IsNew);
+  }
 
   // Populate `Segments`.
   for (const WasmSegment &S : WasmObj->dataSegments())
@@ -535,10 +534,7 @@ void BitcodeFile::parse(bool IgnoreComdats) {
   }
   std::vector<bool> KeptComdats;
   for (StringRef S : Obj->getComdatTable())
-    if (IgnoreComdats)
-      KeptComdats.push_back(true);
-    else
-      KeptComdats.push_back(Symtab->addComdat(S));
+    KeptComdats.push_back(Symtab->addComdat(S));
 
   for (const lto::InputFile::Symbol &ObjSym : Obj->symbols())
     Symbols.push_back(createBitcodeSymbol(KeptComdats, ObjSym, *this));