[Analysis] Avoid repeated hash lookups (NFC) (#127574)

Author: kazutakahirata

llvm/lib/Analysis/InlineCost.cpp

@@ -795,17 +795,19 @@ class InlineCostCallAnalyzer final : public CallAnalyzer {
     // the given instruction was assessed.
     if (!PrintInstructionComments)
       return;
-    InstructionCostDetailMap[I].CostBefore = Cost;
-    InstructionCostDetailMap[I].ThresholdBefore = Threshold;
+    auto &CostDetail = InstructionCostDetailMap[I];
+    CostDetail.CostBefore = Cost;
+    CostDetail.ThresholdBefore = Threshold;
   }
 
   void onInstructionAnalysisFinish(const Instruction *I) override {
     // This function is called to find new values of cost and threshold after
     // the instruction has been assessed.
     if (!PrintInstructionComments)
       return;
-    InstructionCostDetailMap[I].CostAfter = Cost;
-    InstructionCostDetailMap[I].ThresholdAfter = Threshold;
+    auto &CostDetail = InstructionCostDetailMap[I];
+    CostDetail.CostAfter = Cost;
+    CostDetail.ThresholdAfter = Threshold;
   }
 
   bool isCostBenefitAnalysisEnabled() {