Index: llvm/trunk/lib/Linker/LinkModules.cpp
===================================================================
--- llvm/trunk/lib/Linker/LinkModules.cpp
+++ llvm/trunk/lib/Linker/LinkModules.cpp
@@ -509,6 +509,8 @@
       ComdatsChosen;
   bool getComdatResult(const Comdat *SrcC, Comdat::SelectionKind &SK,
                        bool &LinkFromSrc);
+  // Keep track of the global value members of each comdat in source.
+  DenseMap<const Comdat *, std::vector<GlobalValue *>> ComdatMembers;
 
   /// Given a global in the source module, return the global in the
   /// destination module that is being linked to, if any.
@@ -1386,6 +1388,7 @@
     std::tie(SK, LinkFromSrc) = ComdatsChosen[SC];
     C = DstM->getOrInsertComdat(SC->getName());
     C->setSelectionKind(SK);
+    ComdatMembers[SC].push_back(SGV);
   } else if (DGV) {
     if (shouldLinkFromSource(LinkFromSrc, *DGV, *SGV))
       return true;
@@ -1589,6 +1592,19 @@
 bool ModuleLinker::linkGlobalValueBody(GlobalValue &Src) {
   Value *Dst = ValueMap[&Src];
   assert(Dst);
+  if (const Comdat *SC = Src.getComdat()) {
+    // To ensure that we don't generate an incomplete comdat group,
+    // we must materialize and map in any other members that are not
+    // yet materialized in Dst, which also ensures their definitions
+    // are linked in. Otherwise, linkonce and other lazy linked GVs will
+    // not be materialized if they aren't referenced.
+    for (auto *SGV : ComdatMembers[SC]) {
+      if (ValueMap[SGV])
+        continue;
+      Value *NewV = ValMaterializer.materializeValueFor(SGV);
+      ValueMap[SGV] = NewV;
+    }
+  }
   if (shouldInternalizeLinkedSymbols())
     if (auto *DGV = dyn_cast<GlobalValue>(Dst))
       DGV->setLinkage(GlobalValue::InternalLinkage);
Index: llvm/trunk/test/Linker/Inputs/only-needed-named-metadata.ll
===================================================================
--- llvm/trunk/test/Linker/Inputs/only-needed-named-metadata.ll
+++ llvm/trunk/test/Linker/Inputs/only-needed-named-metadata.ll
@@ -2,11 +2,8 @@
 
 declare i32 @foo()
 
-declare void @c1_a()
-
 define void @bar() {
 	load i32, i32* @X
 	call i32 @foo()
-	call void @c1_a()
 	ret void
 }
Index: llvm/trunk/test/Linker/comdat_group.ll
===================================================================
--- llvm/trunk/test/Linker/comdat_group.ll
+++ llvm/trunk/test/Linker/comdat_group.ll
@@ -0,0 +1,20 @@
+; RUN: llvm-as -function-summary %s -o %t.bc
+
+; Ensure complete comdat group is materialized
+; RUN: llvm-link %t.bc -S | FileCheck %s
+; CHECK: $linkoncecomdat = comdat any
+; CHECK: @linkoncecomdat = linkonce global i32 2
+; CHECK: @linkoncecomdat_unref_var = linkonce global i32 2, comdat($linkoncecomdat)
+; CHECK: define linkonce void @linkoncecomdat_unref_func() comdat($linkoncecomdat)
+
+$linkoncecomdat = comdat any
+@linkoncecomdat = linkonce global i32 2, comdat($linkoncecomdat)
+@linkoncecomdat_unref_var = linkonce global i32 2, comdat($linkoncecomdat)
+define linkonce void @linkoncecomdat_unref_func() comdat($linkoncecomdat) {
+  ret void
+}
+; Reference one member of comdat so that comdat is generated.
+define void @ref_linkoncecomdat() {
+  load i32, i32* @linkoncecomdat, align 4
+  ret void
+}
Index: llvm/trunk/test/Linker/only-needed-named-metadata.ll
===================================================================
--- llvm/trunk/test/Linker/only-needed-named-metadata.ll
+++ llvm/trunk/test/Linker/only-needed-named-metadata.ll
@@ -25,17 +25,6 @@
 ; ONLYNEEDED-NOT:@globalfunc1()
 ; ONLYNEEDED-NOT:@analias
 ; ONLYNEEDED-NOT:@globalfunc2()
-; ONLYNEEDED-NOT:@c1_c
-; ONLYNEEDED-NOT:@c1()
-
-$c1 = comdat any
-@c1_c = global i32 0, comdat($c1)
-define void @c1() comdat {
-  ret void
-}
-define void @c1_a() comdat($c1) {
-  ret void
-}
 
 @X = global i32 5
 @U = global i32 6
@@ -64,7 +53,7 @@
   ret void
 }
 
-!llvm.named = !{!0, !1, !2, !3, !4, !5, !6, !7}
+!llvm.named = !{!0, !1, !2, !3, !4, !5, !6}
 !0 = !{i32 ()* @unused}
 !1 = !{i32* @U}
 !2 = !{i32 ()* @unused_linkonce}
@@ -72,4 +61,3 @@
 !4 = !{void (...)* @weakalias}
 !5 = !{void (...)* @analias}
 !6 = !{void (...)* @linkoncealias}
-!7 = !{void ()* @c1}