Index: include/clang/Frontend/PrecompiledPreamble.h
===================================================================
--- include/clang/Frontend/PrecompiledPreamble.h
+++ include/clang/Frontend/PrecompiledPreamble.h
@@ -244,6 +244,10 @@
 public:
   virtual ~PreambleCallbacks() = default;
 
+  /// Called before FrontendAction::BeginSourceFile.
+  /// Can be used to store references to various CompilerInstance fields
+  /// (e.g. SourceManager) that may be interesting to the consumers of other callbacks.
+  virtual void BeforeExecute(CompilerInstance &CI);
   /// Called after FrontendAction::Execute(), but before
   /// FrontendAction::EndSourceFile(). Can be used to transfer ownership of
   /// various CompilerInstance fields before they are destroyed.
Index: lib/Frontend/PrecompiledPreamble.cpp
===================================================================
--- lib/Frontend/PrecompiledPreamble.cpp
+++ lib/Frontend/PrecompiledPreamble.cpp
@@ -333,6 +333,7 @@
   std::unique_ptr<PrecompilePreambleAction> Act;
   Act.reset(new PrecompilePreambleAction(
       StoreInMemory ? &Storage.asMemory().Data : nullptr, Callbacks));
+  Callbacks.BeforeExecute(*Clang);
   if (!Act->BeginSourceFile(*Clang.get(), Clang->getFrontendOpts().Inputs[0]))
     return BuildPreambleError::BeginSourceFileFailed;
 
@@ -694,6 +695,7 @@
   }
 }
 
+void PreambleCallbacks::BeforeExecute(CompilerInstance &CI) {}
 void PreambleCallbacks::AfterExecute(CompilerInstance &CI) {}
 void PreambleCallbacks::AfterPCHEmitted(ASTWriter &Writer) {}
 void PreambleCallbacks::HandleTopLevelDecl(DeclGroupRef DG) {}