Index: llvm/test/Assembler/summary-flags2.ll
===================================================================
--- /dev/null
+++ llvm/test/Assembler/summary-flags2.ll
@@ -0,0 +1,8 @@
+; Check that we can assemble/disassemble empty index with non-trivial flags
+; RUN: llvm-as %s -o - | llvm-dis -o - | FileCheck %s
+
+; ModuleID = 'index.bc'
+source_filename = "index.bc"
+
+^0 = flags: 2
+; CHECK: ^0 = flags: 2
Index: llvm/tools/llvm-as/llvm-as.cpp
===================================================================
--- llvm/tools/llvm-as/llvm-as.cpp
+++ llvm/tools/llvm-as/llvm-as.cpp
@@ -92,7 +92,7 @@
     const ModuleSummaryIndex *IndexToWrite = nullptr;
     // Don't attempt to write a summary index unless it contains any entries.
     // Otherwise we get an empty summary section.
-    if (Index && Index->begin() != Index->end())
+    if (Index && (Index->begin() != Index->end() || Index->getFlags()))
       IndexToWrite = Index;
     if (!IndexToWrite || (M && (!M->empty() || !M->global_empty())))
       // If we have a non-empty Module, then we write the Module plus