Index: include/clang/Lex/Preprocessor.h
===================================================================
--- include/clang/Lex/Preprocessor.h
+++ include/clang/Lex/Preprocessor.h
@@ -147,6 +147,7 @@
   IdentifierInfo *Ident__DATE__, *Ident__TIME__;   // __DATE__, __TIME__
   IdentifierInfo *Ident__INCLUDE_LEVEL__;          // __INCLUDE_LEVEL__
   IdentifierInfo *Ident__BASE_FILE__;              // __BASE_FILE__
+  IdentifierInfo *Ident__FILE_NAME__;              // __FILE_NAME__
   IdentifierInfo *Ident__TIMESTAMP__;              // __TIMESTAMP__
   IdentifierInfo *Ident__COUNTER__;                // __COUNTER__
   IdentifierInfo *Ident_Pragma, *Ident__pragma;    // _Pragma, __pragma
Index: lib/Lex/PPMacroExpansion.cpp
===================================================================
--- lib/Lex/PPMacroExpansion.cpp
+++ lib/Lex/PPMacroExpansion.cpp
@@ -363,6 +363,7 @@
   }
 
   // Clang Extensions.
+  Ident__FILE_NAME__      = RegisterBuiltinMacro(*this, "__FILE_NAME__");
   Ident__has_feature      = RegisterBuiltinMacro(*this, "__has_feature");
   Ident__has_extension    = RegisterBuiltinMacro(*this, "__has_extension");
   Ident__has_builtin      = RegisterBuiltinMacro(*this, "__has_builtin");
@@ -1474,7 +1475,8 @@
     // __LINE__ expands to a simple numeric value.
     OS << (PLoc.isValid()? PLoc.getLine() : 1);
     Tok.setKind(tok::numeric_constant);
-  } else if (II == Ident__FILE__ || II == Ident__BASE_FILE__) {
+  } else if (II == Ident__FILE__ || II == Ident__BASE_FILE__ ||
+             II == Ident__FILE_NAME__) {
     // C99 6.10.8: "__FILE__: The presumed name of the current source file (a
     // character string literal)". This can be affected by #line.
     PresumedLoc PLoc = SourceMgr.getPresumedLoc(Tok.getLocation());
@@ -1495,7 +1497,21 @@
     // Escape this filename.  Turn '\' -> '\\' '"' -> '\"'
     SmallString<128> FN;
     if (PLoc.isValid()) {
-      FN += PLoc.getFilename();
+      // __FILE_NAME__ is a Clang-specific extension that expands to the
+      // the last part of __FILE__.
+      if (II == Ident__FILE_NAME__) {
+        // Try to get the last path component.
+        StringRef PLFileName = PLoc.getFilename(); 
+        size_t LastSep = PLFileName.find_last_of('/');        
+        // Skip the separator and get the last part, otherwise fall back on
+        // returning the original full filename.
+        if (LastSep != StringRef::npos)
+          FN += PLFileName.substr(LastSep+1);
+        else
+          FN += PLFileName;
+      } else {
+        FN += PLoc.getFilename();
+      }
       Lexer::Stringify(FN);
       OS << '"' << FN << '"';
     }
Index: test/Preprocessor/Inputs/include-subdir/file_name_macro_include.h
===================================================================
--- test/Preprocessor/Inputs/include-subdir/file_name_macro_include.h
+++ test/Preprocessor/Inputs/include-subdir/file_name_macro_include.h
@@ -0,0 +1,6 @@
+3: __FILE_NAME__
+4: "file_name_macro_include.h"
+#ifdef MS
+// Should be the same even when included with backslash.
+5: __FILE_NAME__
+#endif
Index: test/Preprocessor/Inputs/include-subdir/h
===================================================================
--- test/Preprocessor/Inputs/include-subdir/h
+++ test/Preprocessor/Inputs/include-subdir/h
@@ -0,0 +1 @@
+6: __FILE_NAME__
Index: test/Preprocessor/Inputs/include-subdir/subdir1/hdr1.h
===================================================================
--- test/Preprocessor/Inputs/include-subdir/subdir1/hdr1.h
+++ test/Preprocessor/Inputs/include-subdir/subdir1/hdr1.h
@@ -0,0 +1 @@
+7: __FILE_NAME__
Index: test/Preprocessor/Inputs/include-subdir/subdir1/hdr2.h
===================================================================
--- test/Preprocessor/Inputs/include-subdir/subdir1/hdr2.h
+++ test/Preprocessor/Inputs/include-subdir/subdir1/hdr2.h
@@ -0,0 +1 @@
+8: __FILE_NAME__
Index: test/Preprocessor/file_name_macro.c
===================================================================
--- test/Preprocessor/file_name_macro.c
+++ test/Preprocessor/file_name_macro.c
@@ -0,0 +1,44 @@
+// RUN: %clang_cc1 -E %s -I%S/Inputs | FileCheck -strict-whitespace %s
+// RUN: %clang_cc1 -fms-compatibility -DMS -E %s -I%S/Inputs | FileCheck -check-prefix=CHECK-MS -strict-whitespace %s 
+// RUN: %clang_cc1 -E %s -I%S/Inputs -DBADINC -verify
+
+#ifdef BADINC
+
+// Paranoia.
+
+__FILE_NAME__
+#include <include-subdir/> // expected-error {{file not found}}
+__FILE_NAME__
+
+#else
+
+// Reference.
+1: "file_name_macro.c"
+
+// Ensure it expands correctly for this file.
+2: __FILE_NAME__
+
+// CHECK: {{^}}1: "file_name_macro.c"
+// CHECK: {{^}}2: "file_name_macro.c"
+
+// Test if inclusion works right.
+#ifdef MS
+#include <include-subdir\file_name_macro_include.h>
+// MS compatibility allows for mixed separators in paths.
+#include <include-subdir/subdir1\hdr1.h>
+#include <include-subdir\subdir1/hdr2.h>
+#else
+#include <include-subdir/file_name_macro_include.h>
+#endif
+
+#include <include-subdir/h>
+
+// CHECK: {{^}}3: "file_name_macro_include.h"
+// CHECK: {{^}}4: "file_name_macro_include.h"
+// CHECK-NOT: {{^}}5: "file_name_macro_include.h"
+// CHECK-MS: {{^}}5: "file_name_macro_include.h"
+// CHECK: {{^}}6: "h"
+// CHECK-MS: {{^}}7: "hdr1.h"
+// CHECK-MS: {{^}}8: "hdr2.h"
+
+#endif