Index: lib/CodeGen/BackendUtil.cpp
===================================================================
--- lib/CodeGen/BackendUtil.cpp
+++ lib/CodeGen/BackendUtil.cpp
@@ -862,7 +862,8 @@
 }
 
 static void runThinLTOBackend(ModuleSummaryIndex *CombinedIndex, Module *M,
-                              std::unique_ptr<raw_pwrite_stream> OS) {
+                              std::unique_ptr<raw_pwrite_stream> OS,
+                              std::string SampleProfile) {
   StringMap<std::map<GlobalValue::GUID, GlobalValueSummary *>>
       ModuleToDefinedGVSummaries;
   CombinedIndex->collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
@@ -930,6 +931,7 @@
     return llvm::make_unique<lto::NativeObjectStream>(std::move(OS));
   };
   lto::Config Conf;
+  Conf.SampleProfile = SampleProfile;
   if (Error E = thinBackend(
           Conf, 0, AddStream, *M, *CombinedIndex, ImportList,
           ModuleToDefinedGVSummaries[M->getModuleIdentifier()], ModuleMap)) {
@@ -965,7 +967,8 @@
     // of an error).
     bool DoThinLTOBackend = CombinedIndex != nullptr;
     if (DoThinLTOBackend) {
-      runThinLTOBackend(CombinedIndex.get(), M, std::move(OS));
+      runThinLTOBackend(CombinedIndex.get(), M, std::move(OS),
+                        CGOpts.SampleProfileFile);
       return;
     }
   }
Index: test/CodeGen/thinlto_backend.ll
===================================================================
--- test/CodeGen/thinlto_backend.ll
+++ test/CodeGen/thinlto_backend.ll
@@ -8,6 +8,10 @@
 ; RUN: not %clang_cc1 -O2 -o %t1.o -x c %s -c -fthinlto-index=%t.thinlto.bc 2>&1 | FileCheck %s -check-prefix=CHECK-WARNING
 ; CHECK-WARNING: error: invalid argument '-fthinlto-index={{.*}}' only allowed with '-x ir'
 
+; Ensure sample profile pass are passed to backend
+; RUN: %clang -O2 -o %t4.o -x ir %t1.o -c -fthinlto-index=%t.thinlto.bc -fprofile-sample-use=%S/Inputs/pgo-sample.prof -mllvm -debug-pass=Structure 2>&1 | FileCheck %s -check-prefix=CHECK-SAMPLEPGO
+; CHECK-SAMPLEPGO: Sample profile pass
+
 ; Ensure we get expected error for missing index file
 ; RUN: %clang -O2 -o %t4.o -x ir %t1.o -c -fthinlto-index=bad.thinlto.bc 2>&1 | FileCheck %s -check-prefix=CHECK-ERROR1
 ; CHECK-ERROR1: Error loading index file 'bad.thinlto.bc'