[Analysis] Avoid repeated hash lookups (NFC) (#125462)

Author: kazutakahirata

llvm/include/llvm/Analysis/ScalarEvolutionExpressions.h

@@ -944,10 +944,11 @@ class SCEVLoopAddRecRewriter
       Operands.push_back(visit(Op));
 
     const Loop *L = Expr->getLoop();
-    if (0 == Map.count(L))
+    auto It = Map.find(L);
+    if (It == Map.end())
       return SE.getAddRecExpr(Operands, L, Expr->getNoWrapFlags());
 
-    return SCEVAddRecExpr::evaluateAtIteration(Operands, Map[L], SE);
+    return SCEVAddRecExpr::evaluateAtIteration(Operands, It->second, SE);
   }
 
 private: