Don't crash on a query where the block is not in any loop. Thanks to

Sameer D. Sahasrabuddhe for pointing this out!

llvm-svn: 22314

llvm/include/llvm/Analysis/LoopInfo.h

@@ -250,7 +250,8 @@ public:
 
   // isLoopHeader - True if the block is a loop header node
   bool isLoopHeader(BasicBlock *BB) const {
-    return getLoopFor(BB)->getHeader() == BB;
+    const Loop *L = getLoopFor(BB);
+    return L && L->getHeader() == BB;
   }
 
   /// runOnFunction - Calculate the natural loop information.