Index: lib/CodeGen/CodeGenAction.cpp
===================================================================
--- lib/CodeGen/CodeGenAction.cpp
+++ lib/CodeGen/CodeGenAction.cpp
@@ -551,9 +551,12 @@
     LinkModuleToUse = ModuleOrErr.get();
   }
 
+  StringRef mainFileName = getCompilerInstance().getCodeGenOpts().MainFileName;
+  if (mainFileName.empty())
+    mainFileName = InFile;
   BEConsumer = new BackendConsumer(BA, CI.getDiagnostics(), CI.getCodeGenOpts(),
                                    CI.getTargetOpts(), CI.getLangOpts(),
-                                   CI.getFrontendOpts().ShowTimers, InFile,
+                                   CI.getFrontendOpts().ShowTimers, mainFileName,
                                    LinkModuleToUse, OS.release(), *VMContext);
   return BEConsumer;
 }
Index: test/Misc/main-file-name.c
===================================================================
--- /dev/null
+++ test/Misc/main-file-name.c
@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -emit-llvm -o - %s -main-file-name some.name | FileCheck -check-prefix NAMED %s
+
+// CHECK: ; ModuleID = '{{.*}}main-file-name.c'
+// NAMED: ; ModuleID = 'some.name'
+