[CodeGen] Avoid repeated hash lookups (NFC) (#125160)

Author: kazutakahirata

llvm/lib/CodeGen/WindowScheduler.cpp

@@ -356,8 +356,8 @@ void WindowScheduler::generateTripleMBB() {
           // ==================================
           //          < Terminators >
           // ==================================
-          if (DefPairs.count(NewUse))
-            NewUse = DefPairs[NewUse];
+          if (auto It = DefPairs.find(NewUse); It != DefPairs.end())
+            NewUse = It->second;
           NewMI->substituteRegister(DefRegPair.first, NewUse, 0, *TRI);
         }
       // DefPairs is updated at last.
@@ -581,9 +581,10 @@ DenseMap<MachineInstr *, int> WindowScheduler::getIssueOrder(unsigned Offset,
   DenseMap<MachineInstr *, int> IssueOrder;
   int Id = 0;
   for (int Cycle = 0; Cycle < (int)II; ++Cycle) {
-    if (!CycleToMIs.count(Cycle))
+    auto It = CycleToMIs.find(Cycle);
+    if (It == CycleToMIs.end())
       continue;
-    for (auto *MI : CycleToMIs[Cycle])
+    for (auto *MI : It->second)
       IssueOrder[MI] = Id++;
   }
   return IssueOrder;