Index: include/llvm/IR/ModuleSummaryIndex.h
===================================================================
--- include/llvm/IR/ModuleSummaryIndex.h
+++ include/llvm/IR/ModuleSummaryIndex.h
@@ -1023,6 +1023,13 @@
     return &*ModulePathStringTable.insert({ModPath, {ModId, Hash}}).first;
   }
 
+  /// Return module entry for module with the given \p ModPath.
+  ModuleInfo *getModule(StringRef ModPath) {
+    auto It = ModulePathStringTable.find(ModPath);
+    assert(It != ModulePathStringTable.end() && "Module not registered");
+    return &*It;
+  }
+
   /// Check if the given Module has any functions available for exporting
   /// in the index. We consider any module present in the ModulePathStringTable
   /// to have exported functions.
Index: lib/Bitcode/Reader/BitcodeReader.cpp
===================================================================
--- lib/Bitcode/Reader/BitcodeReader.cpp
+++ lib/Bitcode/Reader/BitcodeReader.cpp
@@ -753,6 +753,7 @@
   getValueInfoFromValueId(unsigned ValueId);
 
   ModuleSummaryIndex::ModuleInfo *addThisModule();
+  ModuleSummaryIndex::ModuleInfo *getThisModule();
 };
 
 } // end anonymous namespace
@@ -4812,6 +4813,11 @@
   return TheIndex.addModule(ModulePath, ModuleId);
 }
 
+ModuleSummaryIndex::ModuleInfo *
+ModuleSummaryIndexBitcodeReader::getThisModule() {
+  return TheIndex.getModule(ModulePath);
+}
+
 std::pair<ValueInfo, GlobalValue::GUID>
 ModuleSummaryIndexBitcodeReader::getValueInfoFromValueId(unsigned ValueId) {
   auto VGI = ValueIdToValueInfoMap[ValueId];
@@ -4965,6 +4971,9 @@
         break;
       case bitc::GLOBALVAL_SUMMARY_BLOCK_ID:
       case bitc::FULL_LTO_GLOBALVAL_SUMMARY_BLOCK_ID:
+        // Add the module if it is a per-module index (has a source file name).
+        if (!SourceFileName.empty())
+          addThisModule();
         assert(!SeenValueSymbolTable &&
                "Already read VST when parsing summary block?");
         // We might not have a VST if there were no values in the
@@ -5010,7 +5019,7 @@
         case bitc::MODULE_CODE_HASH: {
           if (Record.size() != 5)
             return error("Invalid hash length " + Twine(Record.size()).str());
-          auto &Hash = addThisModule()->second.second;
+          auto &Hash = getThisModule()->second.second;
           int Pos = 0;
           for (auto &Val : Record) {
             assert(!(Val >> 32) && "Unexpected high bits set");
@@ -5272,7 +5281,7 @@
       PendingTypeTestAssumeConstVCalls.clear();
       PendingTypeCheckedLoadConstVCalls.clear();
       auto VIAndOriginalGUID = getValueInfoFromValueId(ValueID);
-      FS->setModulePath(addThisModule()->first());
+      FS->setModulePath(getThisModule()->first());
       FS->setOriginalName(VIAndOriginalGUID.second);
       TheIndex.addGlobalValueSummary(VIAndOriginalGUID.first, std::move(FS));
       break;
@@ -5291,7 +5300,7 @@
       // string table section in the per-module index, we create a single
       // module path string table entry with an empty (0) ID to take
       // ownership.
-      AS->setModulePath(addThisModule()->first());
+      AS->setModulePath(getThisModule()->first());
 
       GlobalValue::GUID AliaseeGUID =
           getValueInfoFromValueId(AliaseeID).first.getGUID();
@@ -5315,7 +5324,7 @@
       std::vector<ValueInfo> Refs =
           makeRefList(ArrayRef<uint64_t>(Record).slice(2));
       auto FS = llvm::make_unique<GlobalVarSummary>(Flags, std::move(Refs));
-      FS->setModulePath(addThisModule()->first());
+      FS->setModulePath(getThisModule()->first());
       auto GUID = getValueInfoFromValueId(ValueID);
       FS->setOriginalName(GUID.second);
       TheIndex.addGlobalValueSummary(GUID.first, std::move(FS));
Index: test/LTO/Resolution/X86/mod-asm-used.ll
===================================================================
--- test/LTO/Resolution/X86/mod-asm-used.ll
+++ test/LTO/Resolution/X86/mod-asm-used.ll
@@ -1,7 +1,11 @@
 ; RUN: opt -module-summary -o %t.bc %s
 ; RUN: opt -module-summary -o %t2.bc %S/Inputs/mod-asm-used.ll
-; RUN: llvm-lto2 run %t.bc -r %t.bc,foo,l %t2.bc -r %t2.bc,foo,pl -o %t3
-; RUN: llvm-nm %t3.* | FileCheck %s
+; RUN: llvm-lto2 run %t.bc -r %t.bc,foo,l %t2.bc -r %t2.bc,foo,pl -o %t3 -save-temps
+; RUN: llvm-nm %t3.? | FileCheck %s
+
+; RUN: llvm-dis %t3.index.bc -o - | FileCheck %s --check-prefix=INDEX
+; INDEX: ^0 = module: (path: "{{.*}}mod-asm-used.ll.tmp.bc"
+; INDEX: ^1 = module: (path: "{{.*}}mod-asm-used.ll.tmp2.bc"
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"