[Transforms] Avoid repeated hash lookups (NFC) (#112654)

Author: kazutakahirata

llvm/lib/Transforms/Utils/LoopPeel.cpp

@@ -206,13 +206,11 @@ PhiAnalyzer::PhiAnalyzer(const Loop &L, unsigned MaxIterations)
 //   G(%y) = Unknown otherwise (including phi not in header block)
 PhiAnalyzer::PeelCounter PhiAnalyzer::calculate(const Value &V) {
   // If we already know the answer, take it from the map.
-  auto I = IterationsToInvariance.find(&V);
-  if (I != IterationsToInvariance.end())
-    return I->second;
-
-  // Place Unknown to map to avoid infinite recursion. Such
+  // Otherwise, place Unknown to map to avoid infinite recursion. Such
   // cycles can never stop on an invariant.
-  IterationsToInvariance[&V] = Unknown;
+  auto [I, Inserted] = IterationsToInvariance.try_emplace(&V, Unknown);
+  if (!Inserted)
+    return I->second;
 
   if (L.isLoopInvariant(&V))
     // Loop invariant so known at start.