[Scalar] Avoid repeated hash lookups (NFC)

Author: kazutakahirata

llvm/lib/Transforms/Scalar/ConstantHoisting.cpp

@@ -274,8 +274,7 @@ static void findBestInsertionSet(DominatorTree &DT, BlockFrequencyInfo &BFI,
   InsertPtsMap.reserve(Orders.size() + 1);
   for (BasicBlock *Node : llvm::reverse(Orders)) {
     bool NodeInBBs = BBs.count(Node);
-    auto &InsertPts = InsertPtsMap[Node].first;
-    BlockFrequency &InsertPtsFreq = InsertPtsMap[Node].second;
+    auto &[InsertPts, InsertPtsFreq] = InsertPtsMap[Node];
 
     // Return the optimal insert points in BBs.
     if (Node == Entry) {