[lld] r319133 - Reland r319090, "COFF: Do not create SectionChunks for discarded comdat sections." with a fix for debug sections.

Peter Collingbourne via llvm-commits llvm-commits at lists.llvm.org
Mon Nov 27 17:30:07 PST 2017


Author: pcc
Date: Mon Nov 27 17:30:07 2017
New Revision: 319133

URL: http://llvm.org/viewvc/llvm-project?rev=319133&view=rev
Log:
Reland r319090, "COFF: Do not create SectionChunks for discarded comdat sections." with a fix for debug sections.

If /debug was not specified, readSection will return a null
pointer for debug sections. If the debug section is associative with
another section, we need to make sure that the section returned from
readSection is not a null pointer before adding it as an associative
section.

Differential Revision: https://reviews.llvm.org/D40533

Modified:
    lld/trunk/COFF/Chunks.cpp
    lld/trunk/COFF/Chunks.h
    lld/trunk/COFF/InputFiles.cpp
    lld/trunk/COFF/InputFiles.h
    lld/trunk/COFF/MarkLive.cpp
    lld/trunk/COFF/SymbolTable.cpp
    lld/trunk/COFF/SymbolTable.h
    lld/trunk/COFF/Symbols.h
    lld/trunk/test/COFF/pdb-comdat.test
    lld/trunk/test/COFF/reloc-discarded.s

Modified: lld/trunk/COFF/Chunks.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/Chunks.cpp?rev=319133&r1=319132&r2=319133&view=diff
==============================================================================
--- lld/trunk/COFF/Chunks.cpp (original)
+++ lld/trunk/COFF/Chunks.cpp Mon Nov 27 17:30:07 2017
@@ -38,9 +38,6 @@ SectionChunk::SectionChunk(ObjFile *F, c
 
   Alignment = Header->getAlignment();
 
-  // Chunks may be discarded during comdat merging.
-  Discarded = false;
-
   // If linker GC is disabled, every chunk starts out alive.  If linker GC is
   // enabled, treat non-comdat sections as roots. Generally optimized object
   // files will be built with -ffunction-sections or /Gy, so most things worth
@@ -362,12 +359,8 @@ bool SectionChunk::isCOMDAT() const {
 void SectionChunk::printDiscardedMessage() const {
   // Removed by dead-stripping. If it's removed by ICF, ICF already
   // printed out the name, so don't repeat that here.
-  if (Sym && this == Repl) {
-    if (Discarded)
-      message("Discarded comdat symbol " + Sym->getName());
-    else if (!Live)
-      message("Discarded " + Sym->getName());
-  }
+  if (Sym && this == Repl)
+    message("Discarded " + Sym->getName());
 }
 
 StringRef SectionChunk::getDebugName() {

Modified: lld/trunk/COFF/Chunks.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/Chunks.h?rev=319133&r1=319132&r2=319133&view=diff
==============================================================================
--- lld/trunk/COFF/Chunks.h (original)
+++ lld/trunk/COFF/Chunks.h Mon Nov 27 17:30:07 2017
@@ -159,10 +159,9 @@ public:
   void addAssociative(SectionChunk *Child);
 
   StringRef getDebugName() override;
-  void setSymbol(DefinedRegular *S) { if (!Sym) Sym = S; }
 
-  // Returns true if the chunk was not dropped by GC or COMDAT deduplication.
-  bool isLive() { return Live && !Discarded; }
+  // Returns true if the chunk was not dropped by GC.
+  bool isLive() { return Live; }
 
   // Used by the garbage collector.
   void markLive() {
@@ -171,13 +170,6 @@ public:
     Live = true;
   }
 
-  // Returns true if this chunk was dropped by COMDAT deduplication.
-  bool isDiscarded() const { return Discarded; }
-
-  // Used by the SymbolTable when discarding unused comdat sections. This is
-  // redundant when GC is enabled, as all comdat sections will start out dead.
-  void markDiscarded() { Discarded = true; }
-
   // True if this is a codeview debug info chunk. These will not be laid out in
   // the image. Instead they will end up in the PDB, if one is requested.
   bool isCodeView() const {
@@ -213,24 +205,21 @@ public:
   // The file that this chunk was created from.
   ObjFile *File;
 
+  // The COMDAT leader symbol if this is a COMDAT chunk.
+  DefinedRegular *Sym = nullptr;
+
 private:
   StringRef SectionName;
   std::vector<SectionChunk *> AssocChildren;
   llvm::iterator_range<const coff_relocation *> Relocs;
   size_t NumRelocs;
 
-  // True if this chunk was discarded because it was a duplicate comdat section.
-  bool Discarded;
-
   // Used by the garbage collector.
   bool Live;
 
   // Used for ICF (Identical COMDAT Folding)
   void replace(SectionChunk *Other);
   uint32_t Class[2] = {0, 0};
-
-  // Sym points to a section symbol if this is a COMDAT chunk.
-  DefinedRegular *Sym = nullptr;
 };
 
 // A chunk for common symbols. Common chunks don't have actual data.

Modified: lld/trunk/COFF/InputFiles.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/InputFiles.cpp?rev=319133&r1=319132&r2=319133&view=diff
==============================================================================
--- lld/trunk/COFF/InputFiles.cpp (original)
+++ lld/trunk/COFF/InputFiles.cpp Mon Nov 27 17:30:07 2017
@@ -119,86 +119,159 @@ void ObjFile::parse() {
   initializeSEH();
 }
 
+// We set SectionChunk pointers in the SparseChunks vector to this value
+// temporarily to mark comdat sections as having an unknown resolution. As we
+// walk the object file's symbol table, once we visit either a leader symbol or
+// an associative section definition together with the parent comdat's leader,
+// we set the pointer to either nullptr (to mark the section as discarded) or a
+// valid SectionChunk for that section.
+static SectionChunk *const PendingComdat = reinterpret_cast<SectionChunk *>(1);
+
 void ObjFile::initializeChunks() {
   uint32_t NumSections = COFFObj->getNumberOfSections();
   Chunks.reserve(NumSections);
   SparseChunks.resize(NumSections + 1);
   for (uint32_t I = 1; I < NumSections + 1; ++I) {
     const coff_section *Sec;
-    StringRef Name;
     if (auto EC = COFFObj->getSection(I, Sec))
       fatal("getSection failed: #" + Twine(I) + ": " + EC.message());
-    if (auto EC = COFFObj->getSectionName(Sec, Name))
-      fatal("getSectionName failed: #" + Twine(I) + ": " + EC.message());
-    if (Name == ".sxdata") {
-      SXData = Sec;
-      continue;
-    }
-    if (Name == ".drectve") {
-      ArrayRef<uint8_t> Data;
-      COFFObj->getSectionContents(Sec, Data);
-      Directives = std::string((const char *)Data.data(), Data.size());
-      continue;
-    }
 
-    // Object files may have DWARF debug info or MS CodeView debug info
-    // (or both).
-    //
-    // DWARF sections don't need any special handling from the perspective
-    // of the linker; they are just a data section containing relocations.
-    // We can just link them to complete debug info.
-    //
-    // CodeView needs a linker support. We need to interpret and debug
-    // info, and then write it to a separate .pdb file.
-
-    // Ignore debug info unless /debug is given.
-    if (!Config->Debug && Name.startswith(".debug"))
-      continue;
-
-    if (Sec->Characteristics & llvm::COFF::IMAGE_SCN_LNK_REMOVE)
-      continue;
-    auto *C = make<SectionChunk>(this, Sec);
-
-    // CodeView sections are stored to a different vector because they are not
-    // linked in the regular manner.
-    if (C->isCodeView())
-      DebugChunks.push_back(C);
+    if (Sec->Characteristics & IMAGE_SCN_LNK_COMDAT)
+      SparseChunks[I] = PendingComdat;
     else
-      Chunks.push_back(C);
+      SparseChunks[I] = readSection(I, nullptr);
+  }
+}
+
+SectionChunk *ObjFile::readSection(uint32_t SectionNumber,
+                                   const coff_aux_section_definition *Def) {
+  const coff_section *Sec;
+  StringRef Name;
+  if (auto EC = COFFObj->getSection(SectionNumber, Sec))
+    fatal("getSection failed: #" + Twine(SectionNumber) + ": " + EC.message());
+  if (auto EC = COFFObj->getSectionName(Sec, Name))
+    fatal("getSectionName failed: #" + Twine(SectionNumber) + ": " +
+          EC.message());
+  if (Name == ".sxdata") {
+    SXData = Sec;
+    return nullptr;
+  }
+  if (Name == ".drectve") {
+    ArrayRef<uint8_t> Data;
+    COFFObj->getSectionContents(Sec, Data);
+    Directives = std::string((const char *)Data.data(), Data.size());
+    return nullptr;
+  }
 
-    SparseChunks[I] = C;
+  // Object files may have DWARF debug info or MS CodeView debug info
+  // (or both).
+  //
+  // DWARF sections don't need any special handling from the perspective
+  // of the linker; they are just a data section containing relocations.
+  // We can just link them to complete debug info.
+  //
+  // CodeView needs a linker support. We need to interpret and debug
+  // info, and then write it to a separate .pdb file.
+
+  // Ignore debug info unless /debug is given.
+  if (!Config->Debug && Name.startswith(".debug"))
+    return nullptr;
+
+  if (Sec->Characteristics & llvm::COFF::IMAGE_SCN_LNK_REMOVE)
+    return nullptr;
+  auto *C = make<SectionChunk>(this, Sec);
+  if (Def)
+    C->Checksum = Def->CheckSum;
+
+  // CodeView sections are stored to a different vector because they are not
+  // linked in the regular manner.
+  if (C->isCodeView())
+    DebugChunks.push_back(C);
+  else
+    Chunks.push_back(C);
+
+  return C;
+}
+
+void ObjFile::readAssociativeDefinition(
+    COFFSymbolRef Sym, const coff_aux_section_definition *Def) {
+  SectionChunk *Parent = SparseChunks[Def->getNumber(Sym.isBigObj())];
+
+  // If the parent is pending, it probably means that its section definition
+  // appears after us in the symbol table. Leave the associated section as
+  // pending; we will handle it during the second pass in initializeSymbols().
+  if (Parent == PendingComdat)
+    return;
+
+  // Check whether the parent is prevailing. If it is, so are we, and we read
+  // the section; otherwise mark it as discarded.
+  int32_t SectionNumber = Sym.getSectionNumber();
+  if (Parent) {
+    SparseChunks[SectionNumber] = readSection(SectionNumber, Def);
+    if (SparseChunks[SectionNumber])
+      Parent->addAssociative(SparseChunks[SectionNumber]);
+  } else {
+    SparseChunks[SectionNumber] = nullptr;
   }
 }
 
+Symbol *ObjFile::createRegular(COFFSymbolRef Sym) {
+  SectionChunk *SC = SparseChunks[Sym.getSectionNumber()];
+  if (Sym.isExternal()) {
+    StringRef Name;
+    COFFObj->getSymbolName(Sym, Name);
+    if (SC)
+      return Symtab->addRegular(this, Name, Sym.getGeneric(), SC);
+    return Symtab->addUndefined(Name, this, false);
+  }
+  if (SC)
+    return make<DefinedRegular>(this, /*Name*/ "", false,
+                                /*IsExternal*/ false, Sym.getGeneric(), SC);
+  return nullptr;
+}
+
 void ObjFile::initializeSymbols() {
   uint32_t NumSymbols = COFFObj->getNumberOfSymbols();
   Symbols.resize(NumSymbols);
 
   SmallVector<std::pair<Symbol *, uint32_t>, 8> WeakAliases;
-  int32_t LastSectionNumber = 0;
+  std::vector<uint32_t> PendingIndexes;
+  PendingIndexes.reserve(NumSymbols);
+
+  std::vector<const coff_aux_section_definition *> ComdatDefs(
+      COFFObj->getNumberOfSections() + 1);
 
   for (uint32_t I = 0; I < NumSymbols; ++I) {
     COFFSymbolRef COFFSym = check(COFFObj->getSymbol(I));
-
-    const void *AuxP = nullptr;
-    if (COFFSym.getNumberOfAuxSymbols())
-      AuxP = check(COFFObj->getSymbol(I + 1)).getRawPtr();
-    bool IsFirst = (LastSectionNumber != COFFSym.getSectionNumber());
-
-    Symbol *Sym = nullptr;
     if (COFFSym.isUndefined()) {
-      Sym = createUndefined(COFFSym);
+      Symbols[I] = createUndefined(COFFSym);
     } else if (COFFSym.isWeakExternal()) {
-      Sym = createUndefined(COFFSym);
-      uint32_t TagIndex =
-          static_cast<const coff_aux_weak_external *>(AuxP)->TagIndex;
-      WeakAliases.emplace_back(Sym, TagIndex);
+      Symbols[I] = createUndefined(COFFSym);
+      uint32_t TagIndex = COFFSym.getAux<coff_aux_weak_external>()->TagIndex;
+      WeakAliases.emplace_back(Symbols[I], TagIndex);
+    } else if (Optional<Symbol *> OptSym = createDefined(COFFSym, ComdatDefs)) {
+      Symbols[I] = *OptSym;
     } else {
-      Sym = createDefined(COFFSym, AuxP, IsFirst);
+      // createDefined() returns None if a symbol belongs to a section that
+      // was pending at the point when the symbol was read. This can happen in
+      // two cases:
+      // 1) section definition symbol for a comdat leader;
+      // 2) symbol belongs to a comdat section associated with a section whose
+      //    section definition symbol appears later in the symbol table.
+      // In both of these cases, we can expect the section to be resolved by
+      // the time we finish visiting the remaining symbols in the symbol
+      // table. So we postpone the handling of this symbol until that time.
+      PendingIndexes.push_back(I);
     }
-    Symbols[I] = Sym;
     I += COFFSym.getNumberOfAuxSymbols();
-    LastSectionNumber = COFFSym.getSectionNumber();
+  }
+
+  for (uint32_t I : PendingIndexes) {
+    COFFSymbolRef Sym = check(COFFObj->getSymbol(I));
+    if (auto *Def = Sym.getSectionDefinition())
+      if (Def->Selection == IMAGE_COMDAT_SELECT_ASSOCIATIVE)
+        readAssociativeDefinition(Sym, Def);
+    Symbols[I] = createRegular(Sym);
   }
 
   for (auto &KV : WeakAliases) {
@@ -214,8 +287,9 @@ Symbol *ObjFile::createUndefined(COFFSym
   return Symtab->addUndefined(Name, this, Sym.isWeakExternal());
 }
 
-Symbol *ObjFile::createDefined(COFFSymbolRef Sym, const void *AuxP,
-                               bool IsFirst) {
+Optional<Symbol *> ObjFile::createDefined(
+    COFFSymbolRef Sym,
+    std::vector<const coff_aux_section_definition *> &ComdatDefs) {
   StringRef Name;
   if (Sym.isCommon()) {
     auto *C = make<CommonChunk>(Sym);
@@ -254,37 +328,46 @@ Symbol *ObjFile::createDefined(COFFSymbo
   if ((uint32_t)SectionNumber >= SparseChunks.size())
     fatal("broken object file: " + toString(this));
 
-  // Nothing else to do without a section chunk.
-  auto *SC = SparseChunks[SectionNumber];
-  if (!SC)
-    return nullptr;
-
-  // Handle section definitions
-  if (IsFirst && AuxP) {
-    auto *Aux = reinterpret_cast<const coff_aux_section_definition *>(AuxP);
-    if (Aux->Selection == IMAGE_COMDAT_SELECT_ASSOCIATIVE)
-      if (auto *ParentSC = SparseChunks[Aux->getNumber(Sym.isBigObj())]) {
-        ParentSC->addAssociative(SC);
-        // If we already discarded the parent, discard the child.
-        if (ParentSC->isDiscarded())
-          SC->markDiscarded();
-      }
-    SC->Checksum = Aux->CheckSum;
+  // Handle comdat leader symbols.
+  if (const coff_aux_section_definition *Def = ComdatDefs[SectionNumber]) {
+    ComdatDefs[SectionNumber] = nullptr;
+    Symbol *Leader;
+    bool Prevailing;
+    if (Sym.isExternal()) {
+      COFFObj->getSymbolName(Sym, Name);
+      std::tie(Leader, Prevailing) =
+          Symtab->addComdat(this, Name, Sym.getGeneric());
+    } else {
+      Leader = make<DefinedRegular>(this, /*Name*/ "", false,
+                                    /*IsExternal*/ false, Sym.getGeneric());
+      Prevailing = true;
+    }
+    if (Prevailing) {
+      SectionChunk *C = readSection(SectionNumber, Def);
+      SparseChunks[SectionNumber] = C;
+      C->Sym = cast<DefinedRegular>(Leader);
+      cast<DefinedRegular>(Leader)->Data = &C->Repl;
+    } else {
+      SparseChunks[SectionNumber] = nullptr;
+    }
+    return Leader;
   }
 
-  DefinedRegular *B;
-  if (Sym.isExternal()) {
-    COFFObj->getSymbolName(Sym, Name);
-    Symbol *S =
-        Symtab->addRegular(this, Name, SC->isCOMDAT(), Sym.getGeneric(), SC);
-    B = cast<DefinedRegular>(S);
-  } else
-    B = make<DefinedRegular>(this, /*Name*/ "", SC->isCOMDAT(),
-                             /*IsExternal*/ false, Sym.getGeneric(), SC);
-  if (SC->isCOMDAT() && Sym.getValue() == 0 && !AuxP)
-    SC->setSymbol(B);
+  // Read associative section definitions and prepare to handle the comdat
+  // leader symbol by setting the section's ComdatDefs pointer if we encounter a
+  // non-associative comdat.
+  if (SparseChunks[SectionNumber] == PendingComdat) {
+    if (auto *Def = Sym.getSectionDefinition()) {
+      if (Def->Selection == IMAGE_COMDAT_SELECT_ASSOCIATIVE)
+        readAssociativeDefinition(Sym, Def);
+      else
+        ComdatDefs[SectionNumber] = Def;
+    }
+  }
 
-  return B;
+  if (SparseChunks[SectionNumber] == PendingComdat)
+    return None;
+  return createRegular(Sym);
 }
 
 void ObjFile::initializeSEH() {
@@ -361,8 +444,12 @@ void ImportFile::parse() {
 void BitcodeFile::parse() {
   Obj = check(lto::InputFile::create(MemoryBufferRef(
       MB.getBuffer(), Saver.save(ParentName + MB.getBufferIdentifier()))));
+  std::vector<std::pair<Symbol *, bool>> Comdat(Obj->getComdatTable().size());
+  for (size_t I = 0; I != Obj->getComdatTable().size(); ++I)
+    Comdat[I] = Symtab->addComdat(this, Saver.save(Obj->getComdatTable()[I]));
   for (const lto::InputFile::Symbol &ObjSym : Obj->symbols()) {
     StringRef SymName = Saver.save(ObjSym.getName());
+    int ComdatIndex = ObjSym.getComdatIndex();
     Symbol *Sym;
     if (ObjSym.isUndefined()) {
       Sym = Symtab->addUndefined(SymName, this, false);
@@ -374,9 +461,15 @@ void BitcodeFile::parse() {
       std::string Fallback = ObjSym.getCOFFWeakExternalFallback();
       Symbol *Alias = Symtab->addUndefined(Saver.save(Fallback));
       checkAndSetWeakAlias(Symtab, this, Sym, Alias);
+    } else if (ComdatIndex != -1) {
+      if (SymName == Obj->getComdatTable()[ComdatIndex])
+        Sym = Comdat[ComdatIndex].first;
+      else if (Comdat[ComdatIndex].second)
+        Sym = Symtab->addRegular(this, SymName);
+      else
+        Sym = Symtab->addUndefined(SymName, this, false);
     } else {
-      bool IsCOMDAT = ObjSym.getComdatIndex() != -1;
-      Sym = Symtab->addRegular(this, SymName, IsCOMDAT);
+      Sym = Symtab->addRegular(this, SymName);
     }
     SymbolBodies.push_back(Sym);
   }

Modified: lld/trunk/COFF/InputFiles.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/InputFiles.h?rev=319133&r1=319132&r2=319133&view=diff
==============================================================================
--- lld/trunk/COFF/InputFiles.h (original)
+++ lld/trunk/COFF/InputFiles.h Mon Nov 27 17:30:07 2017
@@ -142,7 +142,19 @@ private:
   void initializeSymbols();
   void initializeSEH();
 
-  Symbol *createDefined(COFFSymbolRef Sym, const void *Aux, bool IsFirst);
+  SectionChunk *
+  readSection(uint32_t SectionNumber,
+              const llvm::object::coff_aux_section_definition *Def);
+
+  void readAssociativeDefinition(
+      COFFSymbolRef COFFSym,
+      const llvm::object::coff_aux_section_definition *Def);
+
+  llvm::Optional<Symbol *>
+  createDefined(COFFSymbolRef Sym,
+                std::vector<const llvm::object::coff_aux_section_definition *>
+                    &ComdatDefs);
+  Symbol *createRegular(COFFSymbolRef Sym);
   Symbol *createUndefined(COFFSymbolRef Sym);
 
   std::unique_ptr<COFFObjectFile> COFFObj;

Modified: lld/trunk/COFF/MarkLive.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/MarkLive.cpp?rev=319133&r1=319132&r2=319133&view=diff
==============================================================================
--- lld/trunk/COFF/MarkLive.cpp (original)
+++ lld/trunk/COFF/MarkLive.cpp Mon Nov 27 17:30:07 2017
@@ -52,13 +52,6 @@ void markLive(const std::vector<Chunk *>
 
   while (!Worklist.empty()) {
     SectionChunk *SC = Worklist.pop_back_val();
-
-    // If this section was discarded, there are relocations referring to
-    // discarded sections. Ignore these sections to avoid crashing. They will be
-    // diagnosed during relocation processing.
-    if (SC->isDiscarded())
-      continue;
-
     assert(SC->isLive() && "We mark as live when pushing onto the worklist!");
 
     // Mark all symbols listed in the relocation table for this section.

Modified: lld/trunk/COFF/SymbolTable.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/SymbolTable.cpp?rev=319133&r1=319132&r2=319133&view=diff
==============================================================================
--- lld/trunk/COFF/SymbolTable.cpp (original)
+++ lld/trunk/COFF/SymbolTable.cpp Mon Nov 27 17:30:07 2017
@@ -24,36 +24,6 @@ using namespace llvm;
 namespace lld {
 namespace coff {
 
-enum SymbolPreference {
-  SP_EXISTING = -1,
-  SP_CONFLICT = 0,
-  SP_NEW = 1,
-};
-
-/// Checks if an existing symbol S should be kept or replaced by a new symbol.
-/// Returns SP_EXISTING when S should be kept, SP_NEW when the new symbol
-/// should be kept, and SP_CONFLICT if no valid resolution exists.
-static SymbolPreference compareDefined(Symbol *S, bool WasInserted,
-                                       bool NewIsCOMDAT) {
-  // If the symbol wasn't previously known, the new symbol wins by default.
-  if (WasInserted || !isa<Defined>(S))
-    return SP_NEW;
-
-  // If the existing symbol is a DefinedRegular, both it and the new symbol
-  // must be comdats. In that case, we have no reason to prefer one symbol
-  // over the other, and we keep the existing one. If one of the symbols
-  // is not a comdat, we report a conflict.
-  if (auto *R = dyn_cast<DefinedRegular>(S)) {
-    if (NewIsCOMDAT && R->isCOMDAT())
-      return SP_EXISTING;
-    else
-      return SP_CONFLICT;
-  }
-
-  // Existing symbol is not a DefinedRegular; new symbol wins.
-  return SP_NEW;
-}
-
 SymbolTable *Symtab;
 
 void SymbolTable::addFile(InputFile *File) {
@@ -239,7 +209,7 @@ Symbol *SymbolTable::addSynthetic(String
   return S;
 }
 
-Symbol *SymbolTable::addRegular(InputFile *F, StringRef N, bool IsCOMDAT,
+Symbol *SymbolTable::addRegular(InputFile *F, StringRef N,
                                 const coff_symbol_generic *Sym,
                                 SectionChunk *C) {
   Symbol *S;
@@ -247,22 +217,32 @@ Symbol *SymbolTable::addRegular(InputFil
   std::tie(S, WasInserted) = insert(N);
   if (!isa<BitcodeFile>(F))
     S->IsUsedInRegularObj = true;
-  SymbolPreference SP = compareDefined(S, WasInserted, IsCOMDAT);
-  if (SP == SP_CONFLICT) {
+  if (WasInserted || !isa<DefinedRegular>(S))
+    replaceSymbol<DefinedRegular>(S, F, N, /*IsCOMDAT*/ false,
+                                  /*IsExternal*/ true, Sym, C);
+  else
     reportDuplicate(S, F);
-  } else if (SP == SP_NEW) {
-    replaceSymbol<DefinedRegular>(S, F, N, IsCOMDAT, /*IsExternal*/ true, Sym,
-                                  C);
-  } else if (SP == SP_EXISTING && IsCOMDAT && C) {
-    C->markDiscarded();
-    // Discard associative chunks that we've parsed so far. No need to recurse
-    // because an associative section cannot have children.
-    for (SectionChunk *Child : C->children())
-      Child->markDiscarded();
-  }
   return S;
 }
 
+std::pair<Symbol *, bool>
+SymbolTable::addComdat(InputFile *F, StringRef N,
+                       const coff_symbol_generic *Sym) {
+  Symbol *S;
+  bool WasInserted;
+  std::tie(S, WasInserted) = insert(N);
+  if (!isa<BitcodeFile>(F))
+    S->IsUsedInRegularObj = true;
+  if (WasInserted || !isa<DefinedRegular>(S)) {
+    replaceSymbol<DefinedRegular>(S, F, N, /*IsCOMDAT*/ true,
+                                  /*IsExternal*/ true, Sym, nullptr);
+    return {S, true};
+  }
+  if (!cast<DefinedRegular>(S)->isCOMDAT())
+    reportDuplicate(S, F);
+  return {S, false};
+}
+
 Symbol *SymbolTable::addCommon(InputFile *F, StringRef N, uint64_t Size,
                                const coff_symbol_generic *Sym, CommonChunk *C) {
   Symbol *S;

Modified: lld/trunk/COFF/SymbolTable.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/SymbolTable.h?rev=319133&r1=319132&r2=319133&view=diff
==============================================================================
--- lld/trunk/COFF/SymbolTable.h (original)
+++ lld/trunk/COFF/SymbolTable.h Mon Nov 27 17:30:07 2017
@@ -83,9 +83,12 @@ public:
   Symbol *addUndefined(StringRef Name, InputFile *F, bool IsWeakAlias);
   void addLazy(ArchiveFile *F, const Archive::Symbol Sym);
   Symbol *addAbsolute(StringRef N, COFFSymbolRef S);
-  Symbol *addRegular(InputFile *F, StringRef N, bool IsCOMDAT,
+  Symbol *addRegular(InputFile *F, StringRef N,
                      const llvm::object::coff_symbol_generic *S = nullptr,
                      SectionChunk *C = nullptr);
+  std::pair<Symbol *, bool>
+  addComdat(InputFile *F, StringRef N,
+            const llvm::object::coff_symbol_generic *S = nullptr);
   Symbol *addCommon(InputFile *F, StringRef N, uint64_t Size,
                     const llvm::object::coff_symbol_generic *S = nullptr,
                     CommonChunk *C = nullptr);

Modified: lld/trunk/COFF/Symbols.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/Symbols.h?rev=319133&r1=319132&r2=319133&view=diff
==============================================================================
--- lld/trunk/COFF/Symbols.h (original)
+++ lld/trunk/COFF/Symbols.h Mon Nov 27 17:30:07 2017
@@ -169,7 +169,6 @@ public:
   SectionChunk *getChunk() const { return *Data; }
   uint32_t getValue() const { return Sym->Value; }
 
-private:
   SectionChunk **Data;
 };
 

Modified: lld/trunk/test/COFF/pdb-comdat.test
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/COFF/pdb-comdat.test?rev=319133&r1=319132&r2=319133&view=diff
==============================================================================
--- lld/trunk/test/COFF/pdb-comdat.test (original)
+++ lld/trunk/test/COFF/pdb-comdat.test Mon Nov 27 17:30:07 2017
@@ -107,3 +107,6 @@ REORDER-LABEL:   Mod 0001 | `{{.*}}pdb_c
 REORDER:       c:\src\llvm-project\build\pdb_comdat_main.c
 REORDER-NOT:       c:\src\llvm-project\build\foo.h
 REORDER-LABEL:   Mod 0002 | `* Linker *`:
+
+Make sure that we don't crash on non-prevailing debug sections if -debug is not enabled.
+RUN: lld-link pdb_comdat_main.obj pdb_comdat_bar.obj -out:%t.exe -nodefaultlib -entry:main

Modified: lld/trunk/test/COFF/reloc-discarded.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/COFF/reloc-discarded.s?rev=319133&r1=319132&r2=319133&view=diff
==============================================================================
--- lld/trunk/test/COFF/reloc-discarded.s (original)
+++ lld/trunk/test/COFF/reloc-discarded.s Mon Nov 27 17:30:07 2017
@@ -18,7 +18,6 @@ main_global:
 
 	.section	.CRT$XCU,"dr",associative,main_global
 	.p2align	3
-	.globl assoc_global
 assoc_global:
 	.quad	main_global
 




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