Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -649,8 +649,9 @@
   Opts.NoUseJumpTables = Args.hasArg(OPT_fno_jump_tables);
 
   Opts.PrepareForLTO = Args.hasArg(OPT_flto, OPT_flto_EQ);
-  const Arg *A = Args.getLastArg(OPT_flto, OPT_flto_EQ);
-  Opts.EmitSummaryIndex = A && A->containsValue("thin");
+  Opts.EmitSummaryIndex =
+      Args.hasArg(OPT_flto_EQ) &&
+      StringRef(Args.getLastArgValue(OPT_flto_EQ)) == "thin";
   Opts.LTOUnit = Args.hasFlag(OPT_flto_unit, OPT_fno_lto_unit, false);
   if (Arg *A = Args.getLastArg(OPT_fthinlto_index_EQ)) {
     if (IK.getLanguage() != InputKind::LLVM_IR)