Index: llvm/trunk/test/tools/gold/X86/Inputs/thinlto_linkonceresolution.ll
===================================================================
--- llvm/trunk/test/tools/gold/X86/Inputs/thinlto_linkonceresolution.ll
+++ llvm/trunk/test/tools/gold/X86/Inputs/thinlto_linkonceresolution.ll
@@ -0,0 +1,4 @@
+target triple = "x86_64-unknown-linux-gnu"
+define linkonce_odr hidden void @f() {
+  ret void
+}
Index: llvm/trunk/test/tools/gold/X86/thinlto_linkonceresolution.ll
===================================================================
--- llvm/trunk/test/tools/gold/X86/thinlto_linkonceresolution.ll
+++ llvm/trunk/test/tools/gold/X86/thinlto_linkonceresolution.ll
@@ -0,0 +1,32 @@
+; RUN: llvm-as -function-summary %s -o %t.o
+; RUN: llvm-as -function-summary %p/Inputs/thinlto_linkonceresolution.ll -o %t2.o
+
+; Ensure the plugin ensures that for ThinLTO the prevailing copy of a
+; linkonce symbol is changed to weak to ensure it is not eliminated.
+; 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 f() from
+; being imported from %t2.o which hides the problem.
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold.so \
+; RUN:     --plugin-opt=thinlto \
+; RUN:     --plugin-opt=-import-instr-limit=0 \
+; RUN:     --plugin-opt=save-temps \
+; 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.
+; CHECK-NOT: U f
+; OPT: declare extern_weak hidden void @f()
+; OPT2: define weak_odr hidden void @f()
+
+target triple = "x86_64-unknown-linux-gnu"
+define i32 @g() {
+  call void @f()
+  ret i32 0
+}
+define linkonce_odr hidden void @f() {
+  ret void
+}
Index: llvm/trunk/tools/gold/gold-plugin.cpp
===================================================================
--- llvm/trunk/tools/gold/gold-plugin.cpp
+++ llvm/trunk/tools/gold/gold-plugin.cpp
@@ -709,6 +709,16 @@
     if (Resolution == LDPR_PREVAILING_DEF_IRONLY_EXP && !Res.IsLinkonceOdr)
       Resolution = LDPR_PREVAILING_DEF;
 
+    // In ThinLTO mode change all prevailing resolutions to LDPR_PREVAILING_DEF.
+    // For ThinLTO the IR files are compiled through the backend independently,
+    // so we need to ensure that any prevailing linkonce copy will be emitted
+    // into the object file by making it weak. Additionally, we can skip the
+    // IRONLY handling for internalization, which isn't performed in ThinLTO
+    // mode currently anyway.
+    if (options::thinlto && (Resolution == LDPR_PREVAILING_DEF_IRONLY_EXP ||
+                             Resolution == LDPR_PREVAILING_DEF_IRONLY))
+      Resolution = LDPR_PREVAILING_DEF;
+
     GV->setUnnamedAddr(Res.UnnamedAddr);
     GV->setVisibility(Res.Visibility);