Make more use of get_dirs_from_args

_pytest/config.py

@@ -1121,26 +1121,27 @@ def get_common_ancestor(args):
     return common_ancestor
 
 def get_dirs_from_args(args):
-    return [py.path.local(x) for x in args if not str(x).startswith("-")]
+    return [d for d in (py.path.local(x) for x in args if not
+                        str(x).startswith("-")) if d.exists()]
 
 def determine_setup(inifile, args):
+    dirs = get_dirs_from_args(args)
     if inifile:
         iniconfig = py.iniconfig.IniConfig(inifile)
         try:
             inicfg = iniconfig["pytest"]
         except KeyError:
             inicfg = None
-        rootdir = get_common_ancestor(args)
+        rootdir = get_common_ancestor(dirs)
     else:
-        ancestor = get_common_ancestor(args)
+        ancestor = get_common_ancestor(dirs)
         rootdir, inifile, inicfg = getcfg(
             [ancestor], ["pytest.ini", "tox.ini", "setup.cfg"])
         if rootdir is None:
             for rootdir in ancestor.parts(reverse=True):
                 if rootdir.join("setup.py").exists():
                     break
             else:
-                dirs = get_dirs_from_args(args)
                 rootdir, inifile, inicfg = getcfg(
                     dirs, ["pytest.ini", "tox.ini", "setup.cfg"])
                 if rootdir is None: