[TypePromotion] Use return value from SmallPtrSet::insert to avoid a call to SmallPtrSet::count. NFC (#103008)

Author: topperc

llvm/lib/CodeGen/TypePromotion.cpp

@@ -834,11 +834,10 @@ bool TypePromotionImpl::TryToPromote(Value *V, unsigned PromotedWidth,
     // the tree has already been explored.
     // TODO: This could limit the transform, ie if we try to promote something
     // from an i8 and fail first, before trying an i16.
-    if (AllVisited.count(V))
+    if (!AllVisited.insert(V).second)
       return false;
 
     CurrentVisited.insert(V);
-    AllVisited.insert(V);
 
     // Calls can be both sources and sinks.
     if (isSink(V))