[MemProf] Stop cloning traversal on single allocation type

We were previously checking this after recursing on all callers, but if
we already have a single allocation type there is no need to even look
at any callers. Didn't show a significant improvement overall, but it
does reduce the count of times we enter the identifyClones and do other
checks.

Author: teresajohnson

llvm/lib/Transforms/IPO/MemProfContextDisambiguation.cpp

@@ -3407,6 +3407,10 @@ void CallsiteContextGraph<DerivedCCG, FuncTy, CallTy>::identifyClones(
   if (!Node->hasCall())
     return;
 
+  // No need to look at any callers if allocation type already unambiguous.
+  if (hasSingleAllocType(Node->AllocTypes))
+    return;
+
 #ifndef NDEBUG
   auto Insert =
 #endif