[mypyc] feat: stararg fastpath when calling fn(*args) with tuple (#19623)

There are 3 safe cases where we can reuse a tuple when calling a python
function:
fn(*args)
fn(*args, **kwargs)
fn(*args, k=1, k2=2, **kwargs)

This PR covers the first two cases.

The IR diff will probably demonstrate this change better than I can
explain it.

Author: BobTheBuidler

mypyc/irbuild/ll_builder.py

@@ -789,6 +789,18 @@ def _construct_varargs(
         for value, kind, name in args:
             if kind == ARG_STAR:
                 if star_result is None:
+                    # fast path if star expr is a tuple:
+                    # we can pass the immutable tuple straight into the function call.
+                    if is_tuple_rprimitive(value.type):
+                        if len(args) == 1:
+                            # fn(*args)
+                            return value, self._create_dict([], [], line)
+                        elif len(args) == 2 and args[1][1] == ARG_STAR2:
+                            # fn(*args, **kwargs)
+                            star_result = value
+                            continue
+                        # elif ...: TODO extend this to optimize fn(*args, k=1, **kwargs) case
+                    # TODO optimize this case using the length utils - currently in review
                     star_result = self.new_list_op(star_values, line)
                 self.primitive_op(list_extend_op, [star_result, value], line)
             elif kind == ARG_STAR2:
@@ -886,9 +898,11 @@ def _construct_varargs(
             # tuple. Otherwise create the tuple from the list.
             if star_result is None:
                 star_result = self.new_tuple(star_values, line)
-            else:
+            elif not is_tuple_rprimitive(star_result.type):
+                # if star_result is a tuple we took the fast path
                 star_result = self.primitive_op(list_tuple_op, [star_result], line)
         if has_star2 and star2_result is None:
+            # TODO: use dict_copy_op for simple cases of **kwargs
             star2_result = self._create_dict(star2_keys, star2_values, line)
 
         return star_result, star2_result

mypyc/test-data/irbuild-generics.test

@@ -166,25 +166,18 @@ execute(f, 1)
 def execute(func, args, kwargs):
     func :: object
     args :: tuple
-    kwargs :: dict
-    r0 :: list
-    r1 :: object
-    r2 :: dict
-    r3 :: i32
-    r4 :: bit
-    r5 :: tuple
-    r6 :: object
-    r7 :: int
+    kwargs, r0 :: dict
+    r1 :: i32
+    r2 :: bit
+    r3 :: object
+    r4 :: int
 L0:
-    r0 = PyList_New(0)
-    r1 = CPyList_Extend(r0, args)
-    r2 = PyDict_New()
-    r3 = CPyDict_UpdateInDisplay(r2, kwargs)
-    r4 = r3 >= 0 :: signed
-    r5 = PyList_AsTuple(r0)
-    r6 = PyObject_Call(func, r5, r2)
-    r7 = unbox(int, r6)
-    return r7
+    r0 = PyDict_New()
+    r1 = CPyDict_UpdateInDisplay(r0, kwargs)
+    r2 = r1 >= 0 :: signed
+    r3 = PyObject_Call(func, args, r0)
+    r4 = unbox(int, r3)
+    return r4
 def f(x):
     x :: int
 L0:
@@ -709,14 +702,11 @@ def inner_deco_obj.__call__(__mypyc_self__, args, kwargs):
     can_dictcomp :: dict
     r22, can_iter, r23, can_use_keys, r24, can_use_values :: list
     r25 :: object
-    r26 :: list
-    r27 :: object
-    r28 :: dict
-    r29 :: i32
-    r30 :: bit
-    r31 :: tuple
-    r32 :: object
-    r33 :: int
+    r26 :: dict
+    r27 :: i32
+    r28 :: bit
+    r29 :: object
+    r30 :: int
 L0:
     r0 = __mypyc_self__.__mypyc_env__
     r1 = var_object_size args
@@ -768,15 +758,12 @@ L9:
     r24 = CPyDict_Values(kwargs)
     can_use_values = r24
     r25 = r0.func
-    r26 = PyList_New(0)
-    r27 = CPyList_Extend(r26, args)
-    r28 = PyDict_New()
-    r29 = CPyDict_UpdateInDisplay(r28, kwargs)
-    r30 = r29 >= 0 :: signed
-    r31 = PyList_AsTuple(r26)
-    r32 = PyObject_Call(r25, r31, r28)
-    r33 = unbox(int, r32)
-    return r33
+    r26 = PyDict_New()
+    r27 = CPyDict_UpdateInDisplay(r26, kwargs)
+    r28 = r27 >= 0 :: signed
+    r29 = PyObject_Call(r25, args, r26)
+    r30 = unbox(int, r29)
+    return r30
 def deco(func):
     func :: object
     r0 :: __main__.deco_env