Index: llvm/lib/LTO/LTO.cpp
===================================================================
--- llvm/lib/LTO/LTO.cpp
+++ llvm/lib/LTO/LTO.cpp
@@ -446,6 +446,11 @@
     if (GV.hasAppendingLinkage())
       Keep.push_back(&GV);
 
+  DenseSet<GlobalObject *> AliasedGlobals;
+  for (auto &GA : M.aliases())
+    if (GlobalObject *GO = GA.getBaseObject())
+      AliasedGlobals.insert(GO);
+
   for (const InputFile::Symbol &Sym :
        make_range(InputFile::symbol_iterator(SymTab.symbols().begin(), SymTab,
                                              nullptr),
@@ -455,20 +460,33 @@
     SymbolResolution Res = *ResI++;
     addSymbolToGlobalRes(Used, Sym, Res, 0);
 
-    if (Sym.getFlags() & object::BasicSymbolRef::SF_Undefined)
-      continue;
-    if (Res.Prevailing && Sym.isGV()) {
+    if (Sym.isGV()) {
       GlobalValue *GV = Sym.getGV();
-      Keep.push_back(GV);
-      switch (GV->getLinkage()) {
-      default:
-        break;
-      case GlobalValue::LinkOnceAnyLinkage:
-        GV->setLinkage(GlobalValue::WeakAnyLinkage);
-        break;
-      case GlobalValue::LinkOnceODRLinkage:
-        GV->setLinkage(GlobalValue::WeakODRLinkage);
-        break;
+      if (Res.Prevailing) {
+        if (Sym.getFlags() & object::BasicSymbolRef::SF_Undefined)
+          continue;
+        Keep.push_back(GV);
+        switch (GV->getLinkage()) {
+        default:
+          break;
+        case GlobalValue::LinkOnceAnyLinkage:
+          GV->setLinkage(GlobalValue::WeakAnyLinkage);
+          break;
+        case GlobalValue::LinkOnceODRLinkage:
+          GV->setLinkage(GlobalValue::WeakODRLinkage);
+          break;
+        }
+      } else if (isa<GlobalObject>(GV) &&
+                 (GV->hasLinkOnceODRLinkage() || GV->hasWeakODRLinkage()) &&
+                 !AliasedGlobals.count(cast<GlobalObject>(GV))) {
+        // Either of the above two types of linkage indicates that the chosen
+        // prevailing symbol will have the same semantics as this copy of the
+        // symbol, so we can set its linkage to available_externally. This
+        // causes the IR mover to link the symbol if it does not already have a
+        // definition in the combined module.
+        // FIXME: Consider moving to IRMover?
+        GV->setLinkage(GlobalValue::AvailableExternallyLinkage);
+        cast<GlobalObject>(GV)->setComdat(nullptr);
       }
     }
     // Common resolution: collect the maximum size/alignment over all commons.
Index: llvm/lib/Linker/IRMover.cpp
===================================================================
--- llvm/lib/Linker/IRMover.cpp
+++ llvm/lib/Linker/IRMover.cpp
@@ -870,7 +870,7 @@
   if (DGV && !DGV->isDeclarationForLinker())
     return false;
 
-  if (SGV.hasAvailableExternallyLinkage())
+  if (SGV.hasAvailableExternallyLinkage() && (!DGV || DGV->isDeclaration()))
     return true;
 
   if (SGV.isDeclaration() || DoneLinkingBodies)
Index: llvm/test/LTO/Resolution/X86/Inputs/link-availextern.ll
===================================================================
--- /dev/null
+++ llvm/test/LTO/Resolution/X86/Inputs/link-availextern.ll
@@ -0,0 +1,11 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define linkonce_odr i32 @f() {
+  ret i32 2
+}
+
+define void @f3() {
+  %x = call i32 @f()
+  ret void
+}
Index: llvm/test/LTO/Resolution/X86/link-availextern.ll
===================================================================
--- /dev/null
+++ llvm/test/LTO/Resolution/X86/link-availextern.ll
@@ -0,0 +1,30 @@
+; RUN: llvm-as %s -o %t1
+; RUN: llvm-as %S/Inputs/link-availextern.ll -o %t2
+
+; RUN: llvm-lto2 -o %t3 %t1 -r %t1,f, -r %t1,f2,p -save-temps
+; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=SINGLE %s
+
+; RUN: llvm-lto2 -o %t3 %t1 %t2 -r %t1,f, -r %t1,f2,p -r %t2,f, -r %t2,f3,p -save-temps
+; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=SINGLE %s
+
+; RUN: llvm-lto2 -o %t3 %t1 %t2 -r %t1,f, -r %t1,f2,p -r %t2,f,p -r %t2,f3,p -save-temps
+; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=BOTH %s
+
+; RUN: llvm-lto2 -o %t3 %t2 %t1 -r %t1,f, -r %t1,f2,p -r %t2,f,p -r %t2,f3,p -save-temps
+; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=BOTH %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; SINGLE: define available_externally i32 @f()
+; SINGLE-NEXT: ret i32 1
+; BOTH: define weak_odr i32 @f()
+; BOTH-NEXT: ret i32 2
+define linkonce_odr i32 @f() {
+  ret i32 1
+}
+
+define void @f2() {
+  %x = call i32 @f()
+  ret void
+}