Index: llvm/trunk/include/llvm/BinaryFormat/Wasm.h
===================================================================
--- llvm/trunk/include/llvm/BinaryFormat/Wasm.h
+++ llvm/trunk/include/llvm/BinaryFormat/Wasm.h
@@ -101,7 +101,7 @@
   uint32_t CodeSectionOffset;
   uint32_t Size;
   StringRef Name; // from the "linking" or "names" section
-  StringRef Comdat; // from the "comdat info" section
+  uint32_t Comdat; // from the "comdat info" section
 };
 
 struct WasmDataSegment {
@@ -111,7 +111,7 @@
   StringRef Name;
   uint32_t Alignment;
   uint32_t Flags;
-  StringRef Comdat; // from the "comdat info" section
+  uint32_t Comdat; // from the "comdat info" section
 };
 
 struct WasmElemSegment {
@@ -160,6 +160,7 @@
 
 struct WasmLinkingData {
   std::vector<WasmInitFunc> InitFunctions;
+  std::vector<StringRef> Comdats;
   std::vector<WasmSymbolInfo> SymbolTable;
 };
 
Index: llvm/trunk/include/llvm/Object/Wasm.h
===================================================================
--- llvm/trunk/include/llvm/Object/Wasm.h
+++ llvm/trunk/include/llvm/Object/Wasm.h
@@ -141,7 +141,6 @@
   ArrayRef<wasm::WasmElemSegment> elements() const { return ElemSegments; }
   ArrayRef<WasmSegment> dataSegments() const { return DataSegments; }
   ArrayRef<wasm::WasmFunction> functions() const { return Functions; }
-  ArrayRef<StringRef> comdats() const { return Comdats; }
   ArrayRef<wasm::WasmFunctionName> debugNames() const { return DebugNames; }
   uint32_t startFunction() const { return StartFunction; }
   uint32_t getNumImportedGlobals() const { return NumImportedGlobals; }
@@ -255,7 +254,6 @@
   std::vector<WasmSegment> DataSegments;
   std::vector<wasm::WasmFunction> Functions;
   std::vector<WasmSymbol> Symbols;
-  std::vector<StringRef> Comdats;
   std::vector<wasm::WasmFunctionName> DebugNames;
   uint32_t StartFunction = -1;
   bool HasLinkingSection = false;
Index: llvm/trunk/lib/Object/WasmObjectFile.cpp
===================================================================
--- llvm/trunk/lib/Object/WasmObjectFile.cpp
+++ llvm/trunk/lib/Object/WasmObjectFile.cpp
@@ -485,12 +485,12 @@
 {
   uint32_t ComdatCount = readVaruint32(Ptr);
   StringSet<> ComdatSet;
-  while (ComdatCount--) {
+  for (unsigned ComdatIndex = 0; ComdatIndex < ComdatCount; ++ComdatIndex) {
     StringRef Name = readString(Ptr);
     if (Name.empty() || !ComdatSet.insert(Name).second)
       return make_error<GenericBinaryError>("Bad/duplicate COMDAT name " + Twine(Name),
                                             object_error::parse_failed);
-    Comdats.emplace_back(Name);
+    LinkingData.Comdats.emplace_back(Name);
     uint32_t Flags = readVaruint32(Ptr);
     if (Flags != 0)
       return make_error<GenericBinaryError>("Unsupported COMDAT flags",
@@ -508,19 +508,19 @@
         if (Index >= DataSegments.size())
           return make_error<GenericBinaryError>("COMDAT data index out of range",
                                                 object_error::parse_failed);
-        if (!DataSegments[Index].Data.Comdat.empty())
+        if (DataSegments[Index].Data.Comdat != UINT32_MAX)
           return make_error<GenericBinaryError>("Data segment in two COMDATs",
                                                 object_error::parse_failed);
-        DataSegments[Index].Data.Comdat = Name;
+        DataSegments[Index].Data.Comdat = ComdatIndex;
         break;
       case wasm::WASM_COMDAT_FUNCTION:
         if (!isDefinedFunctionIndex(Index))
           return make_error<GenericBinaryError>("COMDAT function index out of range",
                                                 object_error::parse_failed);
-        if (!getDefinedFunction(Index).Comdat.empty())
+        if (getDefinedFunction(Index).Comdat != UINT32_MAX)
           return make_error<GenericBinaryError>("Function in two COMDATs",
                                                 object_error::parse_failed);
-        getDefinedFunction(Index).Comdat = Name;
+        getDefinedFunction(Index).Comdat = ComdatIndex;
         break;
       }
     }
@@ -878,6 +878,8 @@
 
     uint32_t BodySize = FunctionEnd - Ptr;
     Function.Body = ArrayRef<uint8_t>(Ptr, BodySize);
+    // This will be set later when reading in the linking metadata section.
+    Function.Comdat = UINT32_MAX;
     Ptr += BodySize;
     assert(Ptr == FunctionEnd);
     Functions.push_back(Function);
@@ -924,8 +926,11 @@
       return Err;
     uint32_t Size = readVaruint32(Ptr);
     Segment.Data.Content = ArrayRef<uint8_t>(Ptr, Size);
+    // The rest of these Data fields are set later, when reading in the linking
+    // metadata section.
     Segment.Data.Alignment = 0;
     Segment.Data.Flags = 0;
+    Segment.Data.Comdat = UINT32_MAX;
     Segment.SectionOffset = Ptr - Start;
     Ptr += Size;
     DataSegments.push_back(Segment);
Index: llvm/trunk/tools/obj2yaml/wasm2yaml.cpp
===================================================================
--- llvm/trunk/tools/obj2yaml/wasm2yaml.cpp
+++ llvm/trunk/tools/obj2yaml/wasm2yaml.cpp
@@ -62,15 +62,12 @@
     CustomSec = std::move(NameSec);
   } else if (WasmSec.Name == "linking") {
     std::unique_ptr<WasmYAML::LinkingSection> LinkingSec = make_unique<WasmYAML::LinkingSection>();
-    std::map<StringRef,size_t> ComdatIndexes;
-    for (StringRef ComdatName : Obj.comdats()) {
-      ComdatIndexes[ComdatName] = LinkingSec->Comdats.size();
+    ArrayRef<StringRef> Comdats = Obj.linkingData().Comdats;
+    for (StringRef ComdatName : Comdats)
       LinkingSec->Comdats.emplace_back(WasmYAML::Comdat{ComdatName, {}});
-    }
     for (auto &Func : Obj.functions()) {
-      if (!Func.Comdat.empty()) {
-        auto &Comdat = LinkingSec->Comdats[ComdatIndexes[Func.Comdat]];
-        Comdat.Entries.emplace_back(
+      if (Func.Comdat != UINT32_MAX) {
+        LinkingSec->Comdats[Func.Comdat].Entries.emplace_back(
                 WasmYAML::ComdatEntry{wasm::WASM_COMDAT_FUNCTION, Func.Index});
       }
     }
@@ -84,9 +81,8 @@
         SegmentInfo.Flags = Segment.Data.Flags;
         LinkingSec->SegmentInfos.push_back(SegmentInfo);
       }
-      if (!Segment.Data.Comdat.empty()) {
-        auto &Comdat = LinkingSec->Comdats[ComdatIndexes[Segment.Data.Comdat]];
-        Comdat.Entries.emplace_back(
+      if (Segment.Data.Comdat != UINT32_MAX) {
+        LinkingSec->Comdats[Segment.Data.Comdat].Entries.emplace_back(
             WasmYAML::ComdatEntry{wasm::WASM_COMDAT_DATA, SegmentIndex});
       }
       SegmentIndex++;