Index: lib/CodeGen/BackendUtil.cpp
===================================================================
--- lib/CodeGen/BackendUtil.cpp
+++ lib/CodeGen/BackendUtil.cpp
@@ -998,7 +998,7 @@
                               std::unique_ptr<raw_pwrite_stream> OS,
                               std::string SampleProfile,
                               BackendAction Action) {
-  StringMap<std::map<GlobalValue::GUID, GlobalValueSummary *>>
+  StringMap<DenseMap<GlobalValue::GUID, GlobalValueSummary *>>
       ModuleToDefinedGVSummaries;
   CombinedIndex->collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);