[Scalar] Avoid repeated hash lookups (NFC)

Author: kazutakahirata

llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp

@@ -3296,12 +3296,12 @@ static void computeLiveInValues(DominatorTree &DT, Function &F,
       assert(!Data.LiveSet[&BB].count(Kill) && "live set contains kill");
 #endif
 
-    Data.LiveOut[&BB] = SetVector<Value *>();
-    computeLiveOutSeed(&BB, Data.LiveOut[&BB], GC);
-    Data.LiveIn[&BB] = Data.LiveSet[&BB];
-    Data.LiveIn[&BB].set_union(Data.LiveOut[&BB]);
-    Data.LiveIn[&BB].set_subtract(Data.KillSet[&BB]);
-    if (!Data.LiveIn[&BB].empty())
+    auto &Out = Data.LiveOut[&BB] = SetVector<Value *>();
+    computeLiveOutSeed(&BB, Out, GC);
+    auto &In = Data.LiveIn[&BB] = Data.LiveSet[&BB];
+    In.set_union(Out);
+    In.set_subtract(Data.KillSet[&BB]);
+    if (!In.empty())
       Worklist.insert_range(predecessors(&BB));
   }