do not repeatedly dereference use_iterator

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@107963 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/IPA/CallGraph.cpp b/lib/Analysis/IPA/CallGraph.cpp
index 2bde56d..65c7c6e 100644
--- a/lib/Analysis/IPA/CallGraph.cpp
+++ b/lib/Analysis/IPA/CallGraph.cpp
@@ -126,13 +126,15 @@
     }
 
     // Loop over all of the users of the function, looking for non-call uses.
-    for (Value::use_iterator I = F->use_begin(), E = F->use_end(); I != E; ++I)
-      if ((!isa<CallInst>(I) && !isa<InvokeInst>(I))
-          || !CallSite(cast<Instruction>(I)).isCallee(I)) {
+    for (Value::use_iterator I = F->use_begin(), E = F->use_end(); I != E; ++I){
+      User *U = *I;
+      if ((!isa<CallInst>(U) && !isa<InvokeInst>(U))
+          || !CallSite(cast<Instruction>(U)).isCallee(I)) {
         // Not a call, or being used as a parameter rather than as the callee.
         ExternalCallingNode->addCalledFunction(CallSite(), Node);
         break;
       }
+    }
 
     // If this function is not defined in this translation unit, it could call
     // anything.