utils, backends: add and use unique_list

backends.py has an interesting idiom for keeping the unique
elements of a list.  This is much faster than OrderedSet:

* dict.fromkeys() vs. OrderedSet.__init__(): 35% faster on Python
  3.13, 50-60% faster on Python 3.10

* list(d) (d is a dict) vs. list(os) (os is an OrderedSet): up to
  25% faster on Python 3.13, up to 15% faster on Python 3.10
  though it tapers out after a few hundred elements.

Add a function to mesonlib to encapsulate this idiom.

Signed-off-by: Paolo Bonzini <[email protected]>

Author: bonzini

mesonbuild/backend/backends.py

@@ -29,7 +29,7 @@
     File, MachineChoice, MesonException, MesonBugException, OrderedSet,
     ExecutableSerialisation, EnvironmentException,
     classify_unity_sources, get_compiler_for_source,
-    get_rsp_threshold,
+    get_rsp_threshold, unique_list
 )
 from ..options import OptionKey
 
@@ -471,11 +471,11 @@ def relpath(todir: str, fromdir: str) -> str:
     def flatten_object_list(self, target: build.BuildTarget, proj_dir_to_build_root: str = ''
                             ) -> T.Tuple[T.List[str], T.List[build.BuildTargetTypes]]:
         obj_list, deps = self._flatten_object_list(target, target.get_objects(), proj_dir_to_build_root)
-        return list(dict.fromkeys(obj_list)), deps
+        return unique_list(obj_list), deps
 
     def determine_ext_objs(self, objects: build.ExtractedObjects) -> T.List[str]:
         obj_list, _ = self._flatten_object_list(objects.target, [objects], '')
-        return list(dict.fromkeys(obj_list))
+        return unique_list(obj_list)
 
     def _flatten_object_list(self, target: build.BuildTarget,
                              objects: T.Sequence[T.Union[str, 'File', build.ExtractedObjects]],

mesonbuild/utils/universal.py

@@ -154,6 +154,7 @@ class _VerPickleLoadable(Protocol):
     'substitute_values',
     'substring_is_in_list',
     'typeslistify',
+    'unique_list',
     'verbose_git',
     'version_compare',
     'version_compare_condition_with_min',
@@ -2081,6 +2082,10 @@ def substring_is_in_list(substr: str, strlist: T.List[str]) -> bool:
     return False
 
 
+def unique_list(x: T.Iterable[_T]) -> T.List[_T]:
+    return list(dict.fromkeys(x))
+
+
 class OrderedSet(T.MutableSet[_T]):
     """A set that preserves the order in which items are added, by first
     insertion.