Index: include/clang/Lex/Preprocessor.h
===================================================================
--- include/clang/Lex/Preprocessor.h
+++ include/clang/Lex/Preprocessor.h
@@ -33,6 +33,7 @@
 #include "llvm/ADT/TinyPtrVector.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Registry.h"
+#include "llvm/Support/Timer.h"
 #include <memory>
 #include <vector>
 
@@ -624,6 +625,9 @@
   unsigned NumFastMacroExpanded, NumTokenPaste, NumFastTokenPaste;
   unsigned NumSkipped;
 
+  // A timer to keep track of how much time was spent on preprocessing.
+  llvm::Timer PreprocessingTimer;
+
   /// \brief The predefined macros that preprocessor should use from the
   /// command line etc.
   std::string Predefines;
Index: include/clang/Lex/PreprocessorOptions.h
===================================================================
--- include/clang/Lex/PreprocessorOptions.h
+++ include/clang/Lex/PreprocessorOptions.h
@@ -127,7 +127,11 @@
   /// manipulation of the compiler invocation object, in cases where the 
   /// compiler invocation and its buffers will be reused.
   bool RetainRemappedFileBuffers;
-  
+
+  /// \brief Whether to measure the amount of time spent in code related to
+  /// preprocessing. This flag defaults to false.
+  bool ShowTimers;
+
   /// \brief The Objective-C++ ARC standard library that we should support,
   /// by providing appropriate definitions to retrofit the standard library
   /// with support for lifetime-qualified pointers.
@@ -164,6 +168,7 @@
                           GeneratePreamble(false),
                           RemappedFilesKeepOriginalName(true),
                           RetainRemappedFileBuffers(false),
+                          ShowTimers(false),
                           ObjCXXARCStandardLibrary(ARCXX_nolib) { }
 
   void addMacroDef(StringRef Name) { Macros.emplace_back(Name, false); }
Index: lib/Frontend/CompilerInstance.cpp
===================================================================
--- lib/Frontend/CompilerInstance.cpp
+++ lib/Frontend/CompilerInstance.cpp
@@ -367,7 +367,9 @@
 // Preprocessor
 
 void CompilerInstance::createPreprocessor(TranslationUnitKind TUKind) {
-  const PreprocessorOptions &PPOpts = getPreprocessorOpts();
+  PreprocessorOptions &PPOpts = getPreprocessorOpts();
+  if (getFrontendOpts().ShowTimers)
+    PPOpts.ShowTimers = true;
 
   // Create a PTH manager if we are using some form of a token cache.
   PTHManager *PTHMgr = nullptr;
Index: lib/Lex/PPDirectives.cpp
===================================================================
--- lib/Lex/PPDirectives.cpp
+++ lib/Lex/PPDirectives.cpp
@@ -871,6 +871,8 @@
 /// lexer/preprocessor state, and advances the lexer(s) so that the next token
 /// read is the correct one.
 void Preprocessor::HandleDirective(Token &Result) {
+  llvm::TimeRegion(PPOpts->ShowTimers ? &PreprocessingTimer : nullptr);
+
   // FIXME: Traditional: # with whitespace before it not recognized by K&R?
 
   // We just parsed a # character at the start of a line, so we're in directive
Index: lib/Lex/Preprocessor.cpp
===================================================================
--- lib/Lex/Preprocessor.cpp
+++ lib/Lex/Preprocessor.cpp
@@ -88,6 +88,7 @@
       CurDirLookup(nullptr), CurLexerKind(CLK_Lexer),
       CurLexerSubmodule(nullptr), Callbacks(nullptr),
       CurSubmoduleState(&NullSubmoduleState), MacroArgCache(nullptr),
+      PreprocessingTimer("preprocessor", "Preprocessing"),
       Record(nullptr), MIChainHead(nullptr) {
   OwnsHeaderSearch = OwnsHeaders;
   
@@ -656,6 +657,8 @@
 
   IdentifierInfo &II = *Identifier.getIdentifierInfo();
 
+  llvm::TimeRegion(PPOpts->ShowTimers ? &PreprocessingTimer : nullptr);
+
   // If the information about this identifier is out of date, update it from
   // the external source.
   // We have to treat __VA_ARGS__ in a special way, since it gets