Index: lldb/source/Commands/CommandObjectProcess.cpp
===================================================================
--- lldb/source/Commands/CommandObjectProcess.cpp
+++ lldb/source/Commands/CommandObjectProcess.cpp
@@ -357,6 +357,26 @@
             interpreter, CommandCompletions::eProcessPluginCompletion, request,
             nullptr);
         break;
+
+      case 'p':
+        PlatformSP platform_sp(interpreter.GetPlatform(true));
+        if (!platform_sp)
+          return;
+        ProcessInstanceInfoList process_infos;
+        ProcessInstanceInfoMatch match_info;
+        platform_sp->FindProcesses(match_info, process_infos);
+        const size_t num_matches = process_infos.size();
+        if (num_matches == 0)
+          return;
+        for (size_t i = 0; i < num_matches; ++i) {
+          const llvm::StringRef process_name =
+              process_infos[i].GetNameAsStringRef();
+          if (process_name.empty())
+            continue;
+          request.TryCompleteCurrentArg(
+              std::to_string(process_infos[i].GetProcessID()), process_name);
+        }
+        break;
       }
     }
 
Index: lldb/test/API/functionalities/completion/TestCompletion.py
===================================================================
--- lldb/test/API/functionalities/completion/TestCompletion.py
+++ lldb/test/API/functionalities/completion/TestCompletion.py
@@ -5,6 +5,7 @@
 
 
 import os
+from multiprocessing import Process
 import lldb
 from lldbsuite.test.decorators import *
 from lldbsuite.test.lldbtest import *
@@ -92,6 +93,17 @@
             self.complete_from_to('process ' + subcommand + ' mac',
                                   'process ' + subcommand + ' mach-o-core')
 
+    def test_process_attach_dash_p(self):
+        def test():
+            while True:
+                pass
+        
+        p = Process(target=test)
+        p.daemon = True
+        p.start()
+        self.complete_from_to('process attach -p ', [str(p.pid)])
+        p.terminate()
+
     def test_process_signal(self):
         # The tab completion for "process signal"  won't work without a running process.
         self.complete_from_to('process signal ',