Index: test/wasm/Inputs/comdat1.ll
===================================================================
--- /dev/null
+++ test/wasm/Inputs/comdat1.ll
@@ -0,0 +1,11 @@
+$inlineFn = comdat any
+@constantData = weak_odr constant [3 x i8] c"abc", comdat($inlineFn)
+define linkonce_odr i32 @inlineFn() comdat {
+entry:
+  ret i32 ptrtoint ([3 x i8]* @constantData to i32)
+}
+
+define i32 @callInline1() {
+entry:
+    ret i32 ptrtoint (i32 ()* @inlineFn to i32)
+}
Index: test/wasm/Inputs/comdat2.ll
===================================================================
--- /dev/null
+++ test/wasm/Inputs/comdat2.ll
@@ -0,0 +1,11 @@
+$inlineFn = comdat any
+@constantData = weak_odr constant [3 x i8] c"abc", comdat($inlineFn)
+define linkonce_odr i32 @inlineFn() comdat {
+entry:
+  ret i32 ptrtoint ([3 x i8]* @constantData to i32)
+}
+
+define i32 @callInline2() {
+entry:
+    ret i32 ptrtoint (i32 ()* @inlineFn to i32)
+}
Index: test/wasm/comdats.ll
===================================================================
--- /dev/null
+++ test/wasm/comdats.ll
@@ -0,0 +1,62 @@
+; RUN: llc -filetype=obj -mtriple=wasm32-unknown-uknown-wasm %p/Inputs/comdat1.ll -o %t1.o
+; RUN: llc -filetype=obj -mtriple=wasm32-unknown-uknown-wasm %p/Inputs/comdat2.ll -o %t2.o
+; RUN: llc -filetype=obj -mtriple=wasm32-unknown-uknown-wasm %s -o %t.o
+; RUN: lld -flavor wasm -o %t.wasm %t.o %t1.o %t2.o
+; RUN: obj2yaml %t.wasm | FileCheck %s
+
+declare i32 @inlineFn()
+
+define void @_start() local_unnamed_addr {
+entry:
+  %call = call i32 @inlineFn()
+  ret void
+}
+
+; CHECK:       - Type:            GLOBAL
+; CHECK-NEXT:    Globals:
+; CHECK-NEXT:      - Type:            I32
+; CHECK-NEXT:        Mutable:         true
+; CHECK-NEXT:        InitExpr:
+; CHECK-NEXT:          Opcode:          I32_CONST
+; CHECK-NEXT:          Value:           66576
+; CHECK-NEXT:  - Type:            EXPORT
+; CHECK-NEXT:    Exports:
+; CHECK-NEXT:      - Name:            memory
+; CHECK-NEXT:        Kind:            MEMORY
+; CHECK-NEXT:        Index:           0
+; CHECK-NEXT:      - Name:            _start
+; CHECK-NEXT:        Kind:            FUNCTION
+; CHECK-NEXT:        Index:           0
+; CHECK-NEXT:      - Name:            inlineFn
+; CHECK-NEXT:        Kind:            FUNCTION
+; CHECK-NEXT:        Index:           1
+; CHECK-NEXT:      - Name:            callInline1
+; CHECK-NEXT:        Kind:            FUNCTION
+; CHECK-NEXT:        Index:           2
+; CHECK-NEXT:      - Name:            callInline2
+; CHECK-NEXT:        Kind:            FUNCTION
+; CHECK-NEXT:        Index:           3
+; CHECK-NEXT:  - Type:            ELEM
+; CHECK-NEXT:    Segments:
+; CHECK-NEXT:      - Offset:
+; CHECK-NEXT:          Opcode:          I32_CONST
+; CHECK-NEXT:          Value:           1
+; CHECK-NEXT:        Functions:       [ 1 ]
+; CHECK-NEXT:  - Type:            CODE
+; CHECK-NEXT:    Functions:
+; CHECK-NEXT:      - Locals:
+; CHECK-NEXT:        Body:            1081808080001A0B
+; CHECK-NEXT:      - Locals:
+; CHECK-NEXT:        Body:            4180888080000B
+; CHECK-NEXT:      - Locals:
+; CHECK-NEXT:        Body:            4181808080000B
+; CHECK-NEXT:      - Locals:
+; CHECK-NEXT:        Body:            4181808080000B
+; CHECK-NEXT:  - Type:            DATA
+; CHECK-NEXT:    Segments:
+; CHECK-NEXT:      - SectionOffset:   7
+; CHECK-NEXT:        MemoryIndex:     0
+; CHECK-NEXT:        Offset:
+; CHECK-NEXT:          Opcode:          I32_CONST
+; CHECK-NEXT:          Value:           1024
+; CHECK-NEXT:        Content:         '616263'
Index: wasm/InputFiles.cpp
===================================================================
--- wasm/InputFiles.cpp
+++ wasm/InputFiles.cpp
@@ -141,8 +141,7 @@
       return Segment;
     }
   }
-  error("symbol not found in any segment: " + WasmSym.Name);
-  return nullptr;
+  fatal("symbol not found in any segment: " + WasmSym.Name);
 }
 
 static void copyRelocationsRange(std::vector<WasmRelocation> &To,
@@ -188,6 +187,9 @@
     }
   }
 
+  for (const auto &C : WasmObj->comdats())
+    Symtab->addComdat(C.first(), this);
+
   FunctionSymbols.resize(NumFunctionImports + WasmObj->functions().size());
   GlobalSymbols.resize(NumGlobalImports + WasmObj->globals().size());
 
@@ -254,10 +256,20 @@
   // the weak symbol), then it's discardable.  We aren't considering here
   // whether the Symbol is actually ever called.
   for (uint32_t I = 0; I < Funcs.size(); ++I) {
-    if (!ReachedFunctions[I])
+    StringRef Comdat = Functions[I]->Function->Comdat;
+    ObjFile *ComdatFile = Comdat.empty() ? this : Symtab->findComdat(Comdat);
+    if (!ReachedFunctions[I] || ComdatFile != this)
       Functions[I] = &InputFunction::Discarded;
   }
 
+  for (InputSegment *&Seg : Segments) {
+    StringRef Comdat = Seg->Segment->Data.Comdat;
+    if (!Comdat.empty() && Symtab->findComdat(Comdat) != this) {
+      DEBUG(dbgs() << "discarding segment: " << Seg->getName() << "\n");
+      Seg = &InputSegment::Discarded;
+    }
+  }
+
   // Populate `TableSymbols` with all symbols that are called indirectly
   uint32_t SegmentCount = WasmObj->elements().size();
   if (SegmentCount) {
Index: wasm/SymbolTable.h
===================================================================
--- wasm/SymbolTable.h
+++ wasm/SymbolTable.h
@@ -58,11 +58,15 @@
   Symbol *addDefinedGlobal(StringRef Name);
   void addLazy(ArchiveFile *F, const Archive::Symbol *Sym);
 
+  bool addComdat(StringRef Name, ObjFile *);
+  ObjFile *findComdat(StringRef Name) const;
+
 private:
   std::pair<Symbol *, bool> insert(StringRef Name);
 
   llvm::DenseMap<llvm::CachedHashStringRef, Symbol *> SymMap;
   std::vector<Symbol *> SymVector;
+  llvm::DenseMap<llvm::CachedHashStringRef, ObjFile *> ComdatMap;
 };
 
 extern SymbolTable *Symtab;
Index: wasm/SymbolTable.cpp
===================================================================
--- wasm/SymbolTable.cpp
+++ wasm/SymbolTable.cpp
@@ -225,3 +225,19 @@
     F->addMember(Sym);
   }
 }
+
+bool SymbolTable::addComdat(StringRef Name, ObjFile *F) {
+  DEBUG(dbgs() << "addComdat: " << Name << "\n");
+  ObjFile *&File = ComdatMap[CachedHashStringRef(Name)];
+  if (File) {
+    DEBUG(dbgs() << "COMDAT already defined\n");
+    return false;
+  }
+  File = F;
+  return true;
+}
+
+ObjFile *SymbolTable::findComdat(StringRef Name) const {
+  auto It = ComdatMap.find(CachedHashStringRef(Name));
+  return It == ComdatMap.end() ? nullptr : It->second;
+}
Index: wasm/Writer.cpp
===================================================================
--- wasm/Writer.cpp
+++ wasm/Writer.cpp
@@ -408,6 +408,10 @@
     SubSection.finalizeContents();
     SubSection.writeToStream(OS);
   }
+
+  // TODO How important is relocatable output - do we need to output the Comdats?
+  // In that case we may need to fiddling with how we merge InputSegments into
+  // OutputSegments so that we can write out the Comdats here.
 }
 
 // Create the custom "name" section containing debug symbol names.