Identify Analysis pass.

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


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48476 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/AliasAnalysisEvaluator.cpp

@@ -70,6 +70,9 @@ namespace {
       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);
   };