[Hexagon] Avoid repeated hash lookups (NFC) (llvm#131496)

Author: kazutakahirata

llvm/lib/Target/Hexagon/HexagonSubtarget.cpp

@@ -361,11 +361,13 @@ void HexagonSubtarget::CallMutation::apply(ScheduleDAGInstrs *DAGInstrs) {
           } else if (MO.isDef() && MO.getReg().isPhysical()) {
             for (MCRegAliasIterator AI(MO.getReg(), &TRI, true); AI.isValid();
                  ++AI) {
-              if (LastVRegUse.count(*AI) &&
-                  LastVRegUse[*AI] != &DAG->SUnits[su])
-                // %r0 = ...
-                DAG->addEdge(&DAG->SUnits[su], SDep(LastVRegUse[*AI], SDep::Barrier));
-              LastVRegUse.erase(*AI);
+              if (auto It = LastVRegUse.find(*AI); It != LastVRegUse.end()) {
+                if (It->second != &DAG->SUnits[su])
+                  // %r0 = ...
+                  DAG->addEdge(&DAG->SUnits[su],
+                               SDep(It->second, SDep::Barrier));
+                LastVRegUse.erase(It);
+              }
             }
           }
         }