diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 2d1f498..5509797 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -12,6 +12,10 @@
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
+#include "clang/Lex/HeaderSearch.h"
+#include "clang/Lex/Preprocessor.h"
+#include "clang/Lex/PTHManager.h"
+#include "clang/Frontend/Utils.h"
 #include "llvm/LLVMContext.h"
 using namespace clang;
 
@@ -33,3 +37,51 @@
 void CompilerInstance::createSourceManager() {
   SourceMgr.reset(new SourceManager());
 }
+
+void CompilerInstance::createPreprocessor() {
+  PP.reset(createPreprocessor(getDiagnostics(), getLangOpts(),
+                              getPreprocessorOpts(), getHeaderSearchOpts(),
+                              getDependencyOutputOpts(), getTarget(),
+                              getSourceManager(), getFileManager()));
+}
+
+Preprocessor *
+CompilerInstance::createPreprocessor(Diagnostic &Diags,
+                                     const LangOptions &LangInfo,
+                                     const PreprocessorOptions &PPOpts,
+                                     const HeaderSearchOptions &HSOpts,
+                                     const DependencyOutputOptions &DepOpts,
+                                     const TargetInfo &Target,
+                                     SourceManager &SourceMgr,
+                                     FileManager &FileMgr) {
+  // Create a PTH manager if we are using some form of a token cache.
+  PTHManager *PTHMgr = 0;
+  if (!PPOpts.getTokenCache().empty())
+    PTHMgr = PTHManager::Create(PPOpts.getTokenCache(), Diags);
+
+  // FIXME: Don't fail like this.
+  if (Diags.hasErrorOccurred())
+    exit(1);
+
+  // Create the Preprocessor.
+  HeaderSearch *HeaderInfo = new HeaderSearch(FileMgr);
+  Preprocessor *PP = new Preprocessor(Diags, LangInfo, Target,
+                                      SourceMgr, *HeaderInfo, PTHMgr,
+                                      /*OwnsHeaderSearch=*/true);
+
+  // Note that this is different then passing PTHMgr to Preprocessor's ctor.
+  // That argument is used as the IdentifierInfoLookup argument to
+  // IdentifierTable's ctor.
+  if (PTHMgr) {
+    PTHMgr->setPreprocessor(PP);
+    PP->setPTHManager(PTHMgr);
+  }
+
+  InitializePreprocessor(*PP, PPOpts, HSOpts);
+
+  // Handle generating dependencies, if requested.
+  if (!DepOpts.OutputFile.empty())
+    AttachDependencyFileGen(*PP, DepOpts);
+
+  return PP;
+}