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/AliasAnalysisCounter.cpp

@@ -72,6 +72,9 @@ namespace {
       }
     }
 
+    /// isAnalysis - Return true if this pass is  implementing an analysis pass.
+    virtual bool isAnalysis() const { return true; }
+
     bool runOnModule(Module &M) {
       this->M = &M;
       InitializeAliasAnalysis(this);