diff --git a/include/llvm/Pass.h b/include/llvm/Pass.h
index af15516c72b..601420eb37e 100644
--- a/include/llvm/Pass.h
+++ b/include/llvm/Pass.h
@@ -119,8 +119,13 @@ public:
   void print(std::ostream *O, const Module *M) const { if (O) print(*O, M); }
   void dump() const; // dump - call print(std::cerr, 0);
 
+  /// Each pass is responsible for assigning a pass manager to itself.
+  /// PMS is the stack of available pass manager. 
   virtual void assignPassManager(PMStack &PMS, 
 				 PassManagerType T = PMT_Unknown) {}
+  /// Check if available pass managers are suitable for this pass or not.
+  virtual void preparePassManager(PMStack &PMS) {}
+
   // Access AnalysisResolver
   inline void setResolver(AnalysisResolver *AR) { Resolver = AR; }
   inline AnalysisResolver *getResolver() { return Resolver; }
diff --git a/lib/VMCore/PassManager.cpp b/lib/VMCore/PassManager.cpp
index 23a26130fc3..25353082433 100644
--- a/lib/VMCore/PassManager.cpp
+++ b/lib/VMCore/PassManager.cpp
@@ -385,6 +385,9 @@ void PMTopLevelManager::schedulePass(Pass *P) {
   if (findAnalysisPass(P->getPassInfo()))
       return;
 
+  // Give pass a chance to prepare the stage.
+  P->preparePassManager(activeStack);
+
   AnalysisUsage AnUsage;
   P->getAnalysisUsage(AnUsage);
   const std::vector<AnalysisID> &RequiredSet = AnUsage.getRequiredSet();