gh-105775: Convert LOAD_CLOSURE to a pseudo-op (#106059)

This enables super-instruction formation,
removal of checks for uninitialized variables,
and frees up an instruction.

Doc/library/dis.rst

@@ -1291,18 +1291,6 @@ iterations of the loop.
    .. versionadded:: 3.11
 
 
-.. opcode:: LOAD_CLOSURE (i)
-
-   Pushes a reference to the cell contained in slot ``i`` of the "fast locals"
-   storage.  The name of the variable is ``co_fastlocalnames[i]``.
-
-   Note that ``LOAD_CLOSURE`` is effectively an alias for ``LOAD_FAST``.
-   It exists to keep bytecode a little more readable.
-
-   .. versionchanged:: 3.11
-      ``i`` is no longer offset by the length of ``co_varnames``.
-
-
 .. opcode:: LOAD_DEREF (i)
 
    Loads the cell contained in slot ``i`` of the "fast locals" storage.
@@ -1725,6 +1713,17 @@ but are replaced by real opcodes or removed before bytecode is generated.
    Undirected relative jump instructions which are replaced by their
    directed (forward/backward) counterparts by the assembler.
 
+.. opcode:: LOAD_CLOSURE (i)
+
+   Pushes a reference to the cell contained in slot ``i`` of the "fast locals"
+   storage.
+
+   Note that ``LOAD_CLOSURE`` is replaced with ``LOAD_FAST`` in the assembler.
+
+   .. versionchanged:: 3.13
+      This opcode is now a pseudo-instruction.
+
+
 .. opcode:: LOAD_METHOD
 
    Optimized unbound method lookup. Emitted as a ``LOAD_ATTR`` opcode

Lib/importlib/_bootstrap_external.py

@@ -451,6 +451,7 @@ def _write_atomic(path, data, mode=0o666):
 #     Python 3.13a1 3553 (Add SET_FUNCTION_ATTRIBUTE)
 #     Python 3.13a1 3554 (more efficient bytecodes for f-strings)
 #     Python 3.13a1 3555 (generate specialized opcodes metadata from bytecodes.c)
+#     Python 3.13a1 3556 (Convert LOAD_CLOSURE to a pseudo-op)
 
 #     Python 3.14 will start with 3600
 
@@ -467,7 +468,7 @@ def _write_atomic(path, data, mode=0o666):
 # Whenever MAGIC_NUMBER is changed, the ranges in the magic_values array
 # in PC/launcher.c must also be updated.
 
-MAGIC_NUMBER = (3555).to_bytes(2, 'little') + b'\r\n'
+MAGIC_NUMBER = (3556).to_bytes(2, 'little') + b'\r\n'
 
 _RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # For import.c
 

Lib/opcode.py

@@ -198,8 +198,6 @@ def pseudo_op(name, op, real_ops):
 jrel_op('JUMP_BACKWARD_NO_INTERRUPT', 134) # Number of words to skip (backwards)
 def_op('MAKE_CELL', 135)
 hasfree.append(135)
-def_op('LOAD_CLOSURE', 136)
-hasfree.append(136)
 def_op('LOAD_DEREF', 137)
 hasfree.append(137)
 def_op('STORE_DEREF', 138)
@@ -293,6 +291,7 @@ def pseudo_op(name, op, real_ops):
 pseudo_op('LOAD_ZERO_SUPER_ATTR', 265, ['LOAD_SUPER_ATTR'])
 
 pseudo_op('STORE_FAST_MAYBE_NULL', 266, ['STORE_FAST'])
+pseudo_op('LOAD_CLOSURE', 267, ['LOAD_FAST'])
 
 MAX_PSEUDO_OPCODE = MIN_PSEUDO_OPCODE + len(_pseudo_ops) - 1
 

Lib/test/test_compiler_assemble.py

@@ -70,3 +70,41 @@ def test_simple_expr(self):
         ]
         expected = {(3, 4) : 3.5, (-100, 200) : 50, (10, 18) : 14}
         self.assemble_test(insts, metadata, expected)
+
+
+    def test_expression_with_pseudo_instruction_load_closure(self):
+
+        def mod_two(x):
+            def inner():
+                return x
+            return inner() % 2
+
+        inner_code = mod_two.__code__.co_consts[1]
+        assert isinstance(inner_code, types.CodeType)
+
+        metadata = {
+            'filename' : 'mod_two.py',
+            'name'     : 'mod_two',
+            'qualname' : 'nested.mod_two',
+            'cellvars' : {'x' : 0},
+            'consts': {None: 0, inner_code: 1, 2: 2},
+            'argcount' : 1,
+            'varnames' : {'x' : 0},
+        }
+
+        instructions = [
+            ('RESUME', 0,),
+            ('PUSH_NULL', 0, 1),
+            ('LOAD_CLOSURE', 0, 1),
+            ('BUILD_TUPLE', 1, 1),
+            ('LOAD_CONST', 1, 1),
+            ('MAKE_FUNCTION', 0, 2),
+            ('SET_FUNCTION_ATTRIBUTE', 8, 2),
+            ('CALL', 0, 2),                     # (lambda: x)()
+            ('LOAD_CONST', 2, 2),               # 2
+            ('BINARY_OP', 6, 2),                # %
+            ('RETURN_VALUE', 0, 2)
+        ]
+
+        expected = {(0,): 0, (1,): 1, (2,): 0, (120,): 0, (121,): 1}
+        self.assemble_test(instructions, metadata, expected)

Lib/test/test_dis.py

@@ -685,7 +685,7 @@ def foo(x):
 
 %3d        RESUME                   0
 
-%3d        LOAD_CLOSURE             0 (y)
+%3d        LOAD_FAST                0 (y)
            BUILD_TUPLE              1
            LOAD_CONST               1 (<code object foo at 0x..., file "%s", line %d>)
            MAKE_FUNCTION
@@ -709,7 +709,7 @@ def foo(x):
 %3d        RESUME                   0
 
 %3d        LOAD_GLOBAL              1 (NULL + list)
-           LOAD_CLOSURE             0 (x)
+           LOAD_FAST                0 (x)
            BUILD_TUPLE              1
            LOAD_CONST               1 (<code object <genexpr> at 0x..., file "%s", line %d>)
            MAKE_FUNCTION
@@ -1596,8 +1596,8 @@ def _prepare_test_cases():
   Instruction(opname='MAKE_CELL', opcode=135, arg=1, argval='b', argrepr='b', offset=2, start_offset=2, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='RESUME', opcode=151, arg=0, argval=0, argrepr='', offset=4, start_offset=4, starts_line=1, is_jump_target=False, positions=None),
   Instruction(opname='LOAD_CONST', opcode=100, arg=5, argval=(3, 4), argrepr='(3, 4)', offset=6, start_offset=6, starts_line=2, is_jump_target=False, positions=None),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=0, argval='a', argrepr='a', offset=8, start_offset=8, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=1, argval='b', argrepr='b', offset=10, start_offset=10, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='LOAD_FAST', opcode=124, arg=0, argval='a', argrepr='a', offset=8, start_offset=8, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='LOAD_FAST', opcode=124, arg=1, argval='b', argrepr='b', offset=10, start_offset=10, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='BUILD_TUPLE', opcode=102, arg=2, argval=2, argrepr='', offset=12, start_offset=12, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='LOAD_CONST', opcode=100, arg=1, argval=code_object_f, argrepr=repr(code_object_f), offset=14, start_offset=14, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='MAKE_FUNCTION', opcode=24, arg=None, argval=None, argrepr='', offset=16, start_offset=16, starts_line=None, is_jump_target=False, positions=None),
@@ -1624,10 +1624,10 @@ def _prepare_test_cases():
   Instruction(opname='MAKE_CELL', opcode=135, arg=1, argval='d', argrepr='d', offset=4, start_offset=4, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='RESUME', opcode=151, arg=0, argval=0, argrepr='', offset=6, start_offset=6, starts_line=2, is_jump_target=False, positions=None),
   Instruction(opname='LOAD_CONST', opcode=100, arg=2, argval=(5, 6), argrepr='(5, 6)', offset=8, start_offset=8, starts_line=3, is_jump_target=False, positions=None),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=3, argval='a', argrepr='a', offset=10, start_offset=10, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=4, argval='b', argrepr='b', offset=12, start_offset=12, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=0, argval='c', argrepr='c', offset=14, start_offset=14, starts_line=None, is_jump_target=False, positions=None),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=1, argval='d', argrepr='d', offset=16, start_offset=16, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='LOAD_FAST', opcode=124, arg=3, argval='a', argrepr='a', offset=10, start_offset=10, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='LOAD_FAST', opcode=124, arg=4, argval='b', argrepr='b', offset=12, start_offset=12, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='LOAD_FAST', opcode=124, arg=0, argval='c', argrepr='c', offset=14, start_offset=14, starts_line=None, is_jump_target=False, positions=None),
+  Instruction(opname='LOAD_FAST', opcode=124, arg=1, argval='d', argrepr='d', offset=16, start_offset=16, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='BUILD_TUPLE', opcode=102, arg=4, argval=4, argrepr='', offset=18, start_offset=18, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='LOAD_CONST', opcode=100, arg=1, argval=code_object_inner, argrepr=repr(code_object_inner), offset=20, start_offset=20, starts_line=None, is_jump_target=False, positions=None),
   Instruction(opname='MAKE_FUNCTION', opcode=24, arg=None, argval=None, argrepr='', offset=22, start_offset=22, starts_line=None, is_jump_target=False, positions=None),

Misc/NEWS.d/next/Core and Builtins/2023-06-24-10-34-27.gh-issue-105775.OqjoGV.rst

@@ -0,0 +1 @@
+:opcode:`LOAD_CLOSURE` is now a pseudo-op.

PC/launcher.c

@@ -1270,6 +1270,7 @@ static PYC_MAGIC magic_values[] = {
     /* Allow 50 magic numbers per version from here on */
     { 3450, 3499, L"3.11" },
     { 3500, 3549, L"3.12" },
+    { 3550, 3599, L"3.13" },
     { 0 }
 };
 

Python/bytecodes.c

@@ -175,12 +175,9 @@ dummy_func(
             }
         }
 
-        inst(LOAD_CLOSURE, (-- value)) {
-            /* We keep LOAD_CLOSURE so that the bytecode stays more readable. */
-            value = GETLOCAL(oparg);
-            ERROR_IF(value == NULL, unbound_local_error);
-            Py_INCREF(value);
-        }
+        pseudo(LOAD_CLOSURE) = {
+            LOAD_FAST,
+        };
 
         inst(LOAD_FAST_CHECK, (-- value)) {
             value = GETLOCAL(oparg);

Python/compile.c

@@ -836,6 +836,8 @@ stack_effect(int opcode, int oparg, int jump)
 
         case STORE_FAST_MAYBE_NULL:
             return -1;
+        case LOAD_CLOSURE:
+            return 1;
         case LOAD_METHOD:
             return 1;
         case LOAD_SUPER_METHOD: