[Pass] Avoid repeated hash lookups (NFC) (#107761)

Author: kazutakahirata

mlir/lib/Pass/Pass.cpp

@@ -938,11 +938,9 @@ AnalysisManager AnalysisManager::nestImmediate(Operation *op) {
   assert(impl->getOperation() == op->getParentOp() &&
          "expected immediate child operation");
 
-  auto it = impl->childAnalyses.find(op);
-  if (it == impl->childAnalyses.end())
-    it = impl->childAnalyses
-             .try_emplace(op, std::make_unique<NestedAnalysisMap>(op, impl))
-             .first;
+  auto [it, inserted] = impl->childAnalyses.try_emplace(op);
+  if (inserted)
+    it->second = std::make_unique<NestedAnalysisMap>(op, impl);
   return {it->second.get()};
 }