Index: test/tools/gold/X86/Inputs/thinlto_linkonceresolution.ll
===================================================================
--- test/tools/gold/X86/Inputs/thinlto_linkonceresolution.ll
+++ test/tools/gold/X86/Inputs/thinlto_linkonceresolution.ll
@@ -2,3 +2,6 @@
 define linkonce_odr hidden void @f() {
   ret void
 }
+define linkonce hidden void @h() {
+  ret void
+}
Index: test/tools/gold/X86/Inputs/thinlto_weakresolution.ll
===================================================================
--- /dev/null
+++ test/tools/gold/X86/Inputs/thinlto_weakresolution.ll
@@ -0,0 +1,7 @@
+target triple = "x86_64-unknown-linux-gnu"
+define weak_odr hidden void @f() {
+  ret void
+}
+define weak hidden void @h() {
+  ret void
+}
Index: test/tools/gold/X86/thinlto_linkonceresolution.ll
===================================================================
--- test/tools/gold/X86/thinlto_linkonceresolution.ll
+++ test/tools/gold/X86/thinlto_linkonceresolution.ll
@@ -11,22 +11,35 @@
 ; RUN:     --plugin-opt=thinlto \
 ; RUN:     --plugin-opt=-import-instr-limit=0 \
 ; RUN:     --plugin-opt=save-temps \
+; RUN:     --plugin-opt=O0 \
 ; RUN:     -o %t3.o %t2.o %t.o
 ; RUN: llvm-nm %t3.o | FileCheck %s
 ; RUN: llvm-dis %t.o.opt.bc -o - | FileCheck --check-prefix=OPT %s
 ; RUN: llvm-dis %t2.o.opt.bc -o - | FileCheck --check-prefix=OPT2 %s
 
-; Ensure that f() is defined in resulting object file, and also
-; confirm the weak linkage directly in the saved opt bitcode files.
+; Ensure that f() and h() are defined in resulting object file.
 ; CHECK-NOT: U f
-; OPT: declare extern_weak hidden void @f()
+; CHECK-NOT: U h
+
+; The non-prevailing copy can be changed to available_externally in the
+; linkonce_odr case, but must remain linkonce in the non-ODR case (which
+; is eventually changed to an extern_weak declaration).
+; OPT: define available_externally hidden void @f()
+; OPT: declare extern_weak hidden void @h()
+
+; The prevailing copy must be converted to weak so that it is kept.
 ; OPT2: define weak_odr hidden void @f()
+; OPT2: define weak hidden void @h()
 
 target triple = "x86_64-unknown-linux-gnu"
 define i32 @g() {
   call void @f()
+  call void @h()
   ret i32 0
 }
 define linkonce_odr hidden void @f() {
   ret void
 }
+define linkonce hidden void @h() {
+  ret void
+}
Index: test/tools/gold/X86/thinlto_weakresolution.ll
===================================================================
--- /dev/null
+++ test/tools/gold/X86/thinlto_weakresolution.ll
@@ -0,0 +1,46 @@
+; RUN: llvm-as -module-summary %s -o %t.o
+; RUN: llvm-as -module-summary %p/Inputs/thinlto_weakresolution.ll -o %t2.o
+
+; Check that for ThinLTO the plugin converts the preempted copy of a
+; weak symbol to available_externally if it is weak_odr, or leaves it
+; alone in the non-ODR case.
+; Note that gold picks the first copy of f() as the prevailing one,
+; so listing %t2.o first is sufficient to ensure that this copy is
+; preempted. Also, set the import-instr-limit to 0 to prevent any effects
+; from importing.
+; RUN: %gold -m elf_x86_64 -plugin %llvmshlibdir/LLVMgold.so \
+; RUN:     --plugin-opt=thinlto \
+; RUN:     --plugin-opt=-import-instr-limit=0 \
+; RUN:     --plugin-opt=save-temps \
+; RUN:     --plugin-opt=O0 \
+; RUN:     -o %t3.o %t2.o %t.o
+; RUN: llvm-nm %t3.o | FileCheck %s
+; RUN: llvm-dis %t.o.opt.bc -o - | FileCheck --check-prefix=OPT %s
+; RUN: llvm-dis %t2.o.opt.bc -o - | FileCheck --check-prefix=OPT2 %s
+
+; Ensure that f() and h() are defined in resulting object file.
+; CHECK-NOT: U f
+; CHECK-NOT: U h
+
+; The non-prevailing copy can be changed to available_externally in the
+; weak_odr case, but must remain weak in the non-ODR case (which
+; is eventually changed to an extern_weak declaration).
+; OPT: define available_externally hidden void @f()
+; OPT: declare extern_weak hidden void @h()
+
+; The prevailing copy remains weak so that it is kept.
+; OPT2: define weak_odr hidden void @f()
+; OPT2: define weak hidden void @h()
+
+target triple = "x86_64-unknown-linux-gnu"
+define i32 @g() {
+  call void @f()
+  call void @h()
+  ret i32 0
+}
+define weak_odr hidden void @f() {
+  ret void
+}
+define weak hidden void @h() {
+  ret void
+}
Index: tools/gold/gold-plugin.cpp
===================================================================
--- tools/gold/gold-plugin.cpp
+++ tools/gold/gold-plugin.cpp
@@ -759,8 +759,24 @@
     case LDPR_RESOLVED_IR:
     case LDPR_RESOLVED_EXEC:
     case LDPR_RESOLVED_DYN:
+      break;
+
     case LDPR_PREEMPTED_IR:
     case LDPR_PREEMPTED_REG:
+      // For ThinLTO we can change the linkage type of preempted non-comdat
+      // symbols to available_externally so that they can be dropped during
+      // the ThinLTO backend compile step. This is unnecessary for full LTO
+      // where all copies will be merged into a single one. Note that we
+      // already ensure the prevailing copy gets weak linkage in the ThinLTO
+      // so that it isn't eliminated if unreferenced in its module.
+      // FIXME: For can preempted Comdat members be dropped from their
+      // Comdat so they can use available_externally linkage?
+      if (options::thinlto && !GV->hasComdat() &&
+          // Can't do this for WeakAny/LinkOnceAny since they may be overridden
+          // and are thus ineligible for optimizations such as being inlined.
+          // FIXME: In the non-ODR case drop the definitions.
+          (GV->hasWeakODRLinkage() || GV->hasLinkOnceODRLinkage()))
+        GV->setLinkage(GlobalValue::AvailableExternallyLinkage);
       break;
 
     case LDPR_UNDEF: