diff --git a/include/clang/Basic/DiagnosticFrontendKinds.td b/include/clang/Basic/DiagnosticFrontendKinds.td
index 9dbd9cfa21..50d997c986 100644
--- a/include/clang/Basic/DiagnosticFrontendKinds.td
+++ b/include/clang/Basic/DiagnosticFrontendKinds.td
@@ -33,6 +33,10 @@ def err_fe_expected_compiler_job : Error<
     "unable to handle compilation, expected exactly one compiler job in '%0'">;
 def err_fe_expected_clang_command : Error<
     "expected a clang compiler command">;
+def err_fe_remap_missing_to_file : Error<
+    "could not remap file '%0' to the contents of file '%1'">, DefaultFatal;
+def err_fe_remap_missing_from_file : Error<
+    "could not remap from missing file '%0'">, DefaultFatal;
 
 def err_verify_bogus_characters : Error<
     "bogus characters before '{{' in expected string">;
diff --git a/include/clang/Frontend/PreprocessorOptions.h b/include/clang/Frontend/PreprocessorOptions.h
index f0c1d3c2c3..c43a1feb8c 100644
--- a/include/clang/Frontend/PreprocessorOptions.h
+++ b/include/clang/Frontend/PreprocessorOptions.h
@@ -13,6 +13,7 @@
 #include "llvm/ADT/StringRef.h"
 #include <cassert>
 #include <string>
+#include <utility>
 #include <vector>
 
 namespace clang {
@@ -41,6 +42,21 @@ public:
   /// If given, a PTH cache file to use for speeding up header parsing.
   std::string TokenCache;
 
+  /// \brief The set of file remappings, which take existing files on
+  /// the system (the first part of each pair) and gives them the
+  /// contents of other files on the system (the second part of each
+  /// pair).
+  std::vector<std::pair<std::string, std::string> >  RemappedFiles;
+
+  typedef std::vector<std::pair<std::string, std::string> >::const_iterator
+    remapped_file_iterator;
+  remapped_file_iterator remapped_file_begin() const { 
+    return RemappedFiles.begin();
+  }
+  remapped_file_iterator remapped_file_end() const { 
+    return RemappedFiles.end();
+  }
+
 public:
   PreprocessorOptions() : UsePredefines(true) {}
 
@@ -50,6 +66,9 @@ public:
   void addMacroUndef(llvm::StringRef Name) {
     Macros.push_back(std::make_pair(Name, true));
   }
+  void addRemappedFile(llvm::StringRef From, llvm::StringRef To) {
+    RemappedFiles.push_back(std::make_pair(From, To));
+  }
 };
 
 } // end namespace clang
diff --git a/lib/Frontend/CompilerInstance.cpp b/lib/Frontend/CompilerInstance.cpp
index 2d58beead8..02b24b4976 100644
--- a/lib/Frontend/CompilerInstance.cpp
+++ b/lib/Frontend/CompilerInstance.cpp
@@ -190,6 +190,45 @@ CompilerInstance::createPreprocessor(Diagnostic &Diags,
     PP->setPTHManager(PTHMgr);
   }
 
+  // Remap files in the source manager.
+  for (PreprocessorOptions::remapped_file_iterator
+         Remap = PPOpts.remapped_file_begin(),
+         RemapEnd = PPOpts.remapped_file_end();
+       Remap != RemapEnd;
+       ++Remap) {
+    // Find the file that we're mapping to.
+    const FileEntry *ToFile = FileMgr.getFile(Remap->second);
+    if (!ToFile) {
+      Diags.Report(diag::err_fe_remap_missing_to_file)
+        << Remap->first << Remap->second;
+      continue;
+    }
+
+    // Find the file that we're mapping from.
+    const FileEntry *FromFile = FileMgr.getFile(Remap->first);
+    if (!FromFile) {
+      // FIXME: We could actually recover from this, by faking a
+      // FileEntry based on the "ToFile".
+      Diags.Report(diag::err_fe_remap_missing_from_file)
+        << Remap->first;
+      continue;
+    }
+
+    // Load the contents of the file we're mapping to.
+    std::string ErrorStr;
+    const llvm::MemoryBuffer *Buffer
+      = llvm::MemoryBuffer::getFile(ToFile->getName(), &ErrorStr);
+    if (!Buffer) {
+      Diags.Report(diag::err_fe_error_opening)
+        << Remap->second << ErrorStr;
+      continue;
+    }
+
+    // Override the contents of the "from" file with the contents of
+    // the "to" file.
+    SourceMgr.overrideFileContents(FromFile, Buffer);
+  }
+
   InitializePreprocessor(*PP, PPOpts, HSOpts);
 
   // Handle generating dependencies, if requested.
diff --git a/test/Misc/Inputs/remapped-file b/test/Misc/Inputs/remapped-file
new file mode 100644
index 0000000000..657613ed14
--- /dev/null
+++ b/test/Misc/Inputs/remapped-file
@@ -0,0 +1 @@
+int *f(float *fp) { return fp; }
diff --git a/test/Misc/remap-file.c b/test/Misc/remap-file.c
new file mode 100644
index 0000000000..e8aa3e44cc
--- /dev/null
+++ b/test/Misc/remap-file.c
@@ -0,0 +1,5 @@
+// RUN: clang-cc -remap-file="%s;%S/Inputs/remapped-file" -fsyntax-only %s 2>&1 | FileCheck %s
+
+// CHECK: remap-file.c:1:28: warning: incompatible pointer types
+
+int
diff --git a/tools/clang-cc/Options.cpp b/tools/clang-cc/Options.cpp
index a18598ef7c..c97d4ca8c9 100644
--- a/tools/clang-cc/Options.cpp
+++ b/tools/clang-cc/Options.cpp
@@ -673,6 +673,10 @@ static llvm::cl::opt<bool>
 UndefMacros("undef", llvm::cl::value_desc("macro"),
             llvm::cl::desc("undef all system defines"));
 
+static llvm::cl::list<std::string>
+RemappedFiles("remap-file", llvm::cl::value_desc("<from>;<to>"),
+              llvm::cl::desc("replace the contents of the <from> file with the contents of the <to> file"));
+
 }
 
 //===----------------------------------------------------------------------===//
@@ -1071,6 +1075,20 @@ void clang::InitializePreprocessorOptions(PreprocessorOptions &Opts) {
 
   for (unsigned i = 0, e = OrderedPaths.size(); i != e; ++i)
     Opts.Includes.push_back(*OrderedPaths[i].second);
+
+  // Handle file remapping.
+  for (unsigned i = 0, e = RemappedFiles.size(); i != e; ++i) {
+    std::string::size_type Semi = RemappedFiles[i].find(';');
+    if (Semi == std::string::npos) {
+      // FIXME: Don't fail like this.
+      fprintf(stderr, 
+              "error: -remap-file not of the form <from-file>;<to-file>\n");
+      continue;
+    }
+
+    Opts.addRemappedFile(llvm::StringRef(RemappedFiles[i].c_str(), Semi),
+                         llvm::StringRef(RemappedFiles[i].c_str() + Semi + 1));
+  }
 }
 
 void clang::InitializeLangOptions(LangOptions &Options,