Identify Analysis pass.
Do not run analysis pass again if analysis info is still available.
This fixes PR1441.

llvm-svn: 48476
diff --git a/llvm/lib/Analysis/AliasAnalysisEvaluator.cpp b/llvm/lib/Analysis/AliasAnalysisEvaluator.cpp
index 1ed0680..51fdec4 100644
--- a/llvm/lib/Analysis/AliasAnalysisEvaluator.cpp
+++ b/llvm/lib/Analysis/AliasAnalysisEvaluator.cpp
@@ -70,6 +70,9 @@
       return false;
     }
 
+    /// isAnalysis - Return true if this pass is  implementing an analysis pass.
+    virtual bool isAnalysis() const { return true; }
+
     bool runOnFunction(Function &F);
     bool doFinalization(Module &M);
   };