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/AliasSetTracker.cpp

@@ -558,6 +558,9 @@ namespace {
       AU.addRequired<AliasAnalysis>();
     }
 
+    /// isAnalysis - Return true if this pass is  implementing an analysis pass.
+    virtual bool isAnalysis() const { return true; }
+
     virtual bool runOnFunction(Function &F) {
       Tracker = new AliasSetTracker(getAnalysis<AliasAnalysis>());