[LiveDebugValues] Avoid repeated hash lookups (NFC) (llvm#109242)

Author: kazutakahirata

llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.h

@@ -484,22 +484,16 @@ class DbgOpIDMap {
 
 private:
   DbgOpID insertConstOp(MachineOperand &MO) {
-    auto ExistingIt = ConstOpToID.find(MO);
-    if (ExistingIt != ConstOpToID.end())
-      return ExistingIt->second;
-    DbgOpID ID(true, ConstOps.size());
-    ConstOpToID.insert(std::make_pair(MO, ID));
-    ConstOps.push_back(MO);
-    return ID;
+    auto [It, Inserted] = ConstOpToID.try_emplace(MO, true, ConstOps.size());
+    if (Inserted)
+      ConstOps.push_back(MO);
+    return It->second;
   }
   DbgOpID insertValueOp(ValueIDNum VID) {
-    auto ExistingIt = ValueOpToID.find(VID);
-    if (ExistingIt != ValueOpToID.end())
-      return ExistingIt->second;
-    DbgOpID ID(false, ValueOps.size());
-    ValueOpToID.insert(std::make_pair(VID, ID));
-    ValueOps.push_back(VID);
-    return ID;
+    auto [It, Inserted] = ValueOpToID.try_emplace(VID, false, ValueOps.size());
+    if (Inserted)
+      ValueOps.push_back(VID);
+    return It->second;
   }
 };