Index: llvm/trunk/lib/Transforms/IPO/FunctionImport.cpp
===================================================================
--- llvm/trunk/lib/Transforms/IPO/FunctionImport.cpp
+++ llvm/trunk/lib/Transforms/IPO/FunctionImport.cpp
@@ -58,6 +58,16 @@
     DontForceImportReferencedDiscardableSymbols("disable-force-link-odr",
                                                 cl::init(false), cl::Hidden);
 
+static cl::opt<bool> EnableImportMetadata(
+    "enable-import-metadata", cl::init(
+#if !defined(NDEBUG)
+                                  true /*Enabled with asserts.*/
+#else
+                                  false
+#endif
+                                  ),
+    cl::Hidden, cl::desc("Enable import metadata like 'thinlto_src_module'"));
+
 // Load lazily a module from \p FileName in \p Context.
 static std::unique_ptr<Module> loadFile(const std::string &FileName,
                                         LLVMContext &Context) {
@@ -591,12 +601,15 @@
                    << SrcModule->getSourceFileName() << "\n");
       if (Import) {
         F.materialize();
-        // Add 'thinlto_src_module' metadata for statistics and debugging.
-        F.setMetadata("thinlto_src_module",
-                      llvm::MDNode::get(DestModule.getContext(),
-                                        {llvm::MDString::get(
-                                            DestModule.getContext(),
-                                            SrcModule->getSourceFileName())}));
+        if (EnableImportMetadata) {
+          // Add 'thinlto_src_module' metadata for statistics and debugging.
+          F.setMetadata(
+              "thinlto_src_module",
+              llvm::MDNode::get(
+                  DestModule.getContext(),
+                  {llvm::MDString::get(DestModule.getContext(),
+                                       SrcModule->getSourceFileName())}));
+        }
         GlobalsToImport.insert(&F);
       }
     }
Index: llvm/trunk/test/Transforms/FunctionImport/funcimport.ll
===================================================================
--- llvm/trunk/test/Transforms/FunctionImport/funcimport.ll
+++ llvm/trunk/test/Transforms/FunctionImport/funcimport.ll
@@ -4,12 +4,12 @@
 ; RUN: llvm-lto -thinlto -print-summary-global-ids -o %t3 %t.bc %t2.bc 2>&1 | FileCheck %s --check-prefix=GUID
 
 ; Do the import now
-; RUN: opt -disable-force-link-odr -function-import -stats -print-imports -summary-file %t3.thinlto.bc %t.bc -S 2>&1 | FileCheck %s --check-prefix=CHECK --check-prefix=INSTLIMDEF
+; RUN: opt -disable-force-link-odr -function-import -stats -print-imports -enable-import-metadata -summary-file %t3.thinlto.bc %t.bc -S 2>&1 | FileCheck %s --check-prefix=CHECK --check-prefix=INSTLIMDEF
 ; "-stats" requires +Asserts.
-; REQUIRES: asserts
+; REQUIRES asserts
 
 ; Test import with smaller instruction limit
-; RUN: opt -disable-force-link-odr -function-import -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=5 -S | FileCheck %s --check-prefix=CHECK --check-prefix=INSTLIM5
+; RUN: opt -disable-force-link-odr -function-import -enable-import-metadata  -summary-file %t3.thinlto.bc %t.bc -import-instr-limit=5 -S | FileCheck %s --check-prefix=CHECK --check-prefix=INSTLIM5
 ; INSTLIM5-NOT: @staticfunc.llvm.
 
 ; Test import with smaller instruction limit and without the -disable-force-link-odr