Index: cfe/trunk/lib/CodeGen/CGDebugInfo.cpp
===================================================================
--- cfe/trunk/lib/CodeGen/CGDebugInfo.cpp
+++ cfe/trunk/lib/CodeGen/CGDebugInfo.cpp
@@ -29,6 +29,7 @@
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/Version.h"
 #include "clang/Frontend/CodeGenOptions.h"
+#include "clang/Frontend/FrontendOptions.h"
 #include "clang/Lex/HeaderSearchOptions.h"
 #include "clang/Lex/ModuleMap.h"
 #include "clang/Lex/PreprocessorOptions.h"
@@ -495,6 +496,16 @@
       llvm::sys::path::append(MainFileDirSS, MainFileName);
       MainFileName = MainFileDirSS.str();
     }
+    // If the main file name provided is identical to the input file name, and
+    // if the input file is a preprocessed source, use the module name for
+    // debug info. The module name comes from the name specified in the first
+    // linemarker if the input is a preprocessed source.
+    if (MainFile->getName() == MainFileName &&
+        FrontendOptions::getInputKindForExtension(
+            MainFile->getName().rsplit('.').second)
+            .isPreprocessed())
+      MainFileName = CGM.getModule().getName().str();
+
     CSKind = computeChecksum(SM.getMainFileID(), Checksum);
   }
 
Index: cfe/trunk/test/CodeGen/debug-info-preprocessed-file.i
===================================================================
--- cfe/trunk/test/CodeGen/debug-info-preprocessed-file.i
+++ cfe/trunk/test/CodeGen/debug-info-preprocessed-file.i
@@ -0,0 +1,11 @@
+# 1 "/foo/bar/preprocessed-input.c"
+# 1 "<built-in>" 1
+# 1 "<built-in>" 3
+# 318 "<built-in>" 3
+# 1 "<command line>" 1
+# 1 "<built-in>" 2
+# 1 "preprocessed-input.c" 2
+
+// RUN: %clang -g -c -S -emit-llvm -o - %s | FileCheck %s
+// CHECK: !DICompileUnit(language: DW_LANG_C99, file: ![[FILE:[0-9]+]] 
+// CHECK: ![[FILE]] = !DIFile(filename: "/foo/bar/preprocessed-input.c"