remove unused docstring const

Author: WolframAlph

Include/internal/pycore_flowgraph.h

@@ -22,7 +22,7 @@ void _PyCfgBuilder_Free(struct _PyCfgBuilder *g);
 int _PyCfgBuilder_CheckSize(struct _PyCfgBuilder* g);
 
 int _PyCfg_OptimizeCodeUnit(struct _PyCfgBuilder *g, PyObject *consts, PyObject *const_cache,
-                            int nlocals, int nparams, int firstlineno);
+                            int nlocals, int nparams, int firstlineno, unsigned has_docstring);
 
 struct _PyCfgBuilder* _PyCfg_FromInstructionSequence(_PyInstructionSequence *seq);
 int _PyCfg_ToInstructionSequence(struct _PyCfgBuilder *g, _PyInstructionSequence *seq);

Lib/test/test_code.py

@@ -30,7 +30,7 @@
 freevars: ('x',)
 nlocals: 1
 flags: 19
-consts: ('None',)
+consts: ()
 
 >>> def h(x, y):
 ...     a = x + y
@@ -50,7 +50,7 @@
 freevars: ()
 nlocals: 5
 flags: 3
-consts: ('None',)
+consts: ()
 
 >>> def attrs(obj):
 ...     print(obj.attr1)
@@ -104,7 +104,7 @@
 freevars: ()
 nlocals: 3
 flags: 3
-consts: ('None',)
+consts: ()
 
 >>> def posonly_args(a,b,/,c):
 ...     return a,b,c
@@ -121,7 +121,7 @@
 freevars: ()
 nlocals: 3
 flags: 3
-consts: ('None',)
+consts: ()
 
 >>> def has_docstring(x: str):
 ...     'This is a one-line doc string'

Lib/test/test_compile.py

@@ -841,7 +841,7 @@ def f():
                 return "unused"
 
         self.assertEqual(f.__code__.co_consts,
-                         (True, "used"))
+                         ("used", ))
 
     @support.cpython_only
     def test_remove_unused_consts_extended_args(self):

Lib/test/test_dis.py

@@ -1425,9 +1425,9 @@ def get_disassembly(self, func, lasti=-1, wrapper=True, **kwargs):
 
 
 if dis.code_info.__doc__ is None:
-    code_info_consts = "0: None"
+    code_info_consts = ""
 else:
-    code_info_consts = "0: 'Formatted details of methods, functions, or code.'"
+    code_info_consts = "Constants:\n   0: 'Formatted details of methods, functions, or code.'"
 
 code_info_code_info = f"""\
 Name:              code_info
@@ -1438,8 +1438,7 @@ def get_disassembly(self, func, lasti=-1, wrapper=True, **kwargs):
 Number of locals:  1
 Stack size:        \\d+
 Flags:             OPTIMIZED, NEWLOCALS, HAS_DOCSTRING
-Constants:
-   {code_info_consts}
+{code_info_consts}
 Names:
    0: _format_code_info
    1: _get_code_object
@@ -1546,8 +1545,6 @@ def f(c=c):
 Number of locals:  0
 Stack size:        \\d+
 Flags:             0x0
-Constants:
-   0: None
 Names:
    0: x"""
 

Lib/test/test_peepholer.py

@@ -1057,16 +1057,16 @@ def test_conditional_jump_forward_non_const_condition(self):
         expected_insts = [
             ('LOAD_NAME', 1, 11),
             ('POP_JUMP_IF_TRUE', lbl := self.Label(), 12),
-            ('LOAD_CONST', 1, 13),
+            ('LOAD_CONST', 0, 13),
             ('RETURN_VALUE', None, 13),
             lbl,
-            ('LOAD_CONST', 2, 14),
+            ('LOAD_CONST', 1, 14),
             ('RETURN_VALUE', None, 14),
         ]
         self.cfg_optimization_test(insts,
                                    expected_insts,
                                    consts=[0, 1, 2, 3, 4],
-                                   expected_consts=[0, 2, 3])
+                                   expected_consts=[2, 3])
 
     def test_list_exceeding_stack_use_guideline(self):
         def f():
@@ -1107,10 +1107,10 @@ def test_multiple_foldings(self):
             ('RETURN_VALUE', None, 0)
         ]
         after = [
-            ('LOAD_CONST', 1, 0),
+            ('LOAD_CONST', 0, 0),
             ('RETURN_VALUE', None, 0)
         ]
-        self.cfg_optimization_test(before, after, consts=[], expected_consts=[(2,), (1, 2)])
+        self.cfg_optimization_test(before, after, consts=[], expected_consts=[(1, 2)])
 
     def test_build_empty_tuple(self):
         before = [
@@ -1277,13 +1277,13 @@ def test_conditional_jump_forward_const_condition(self):
         expected_insts = [
             ('NOP', None, 11),
             ('NOP', None, 12),
-            ('LOAD_CONST', 1, 14),
+            ('LOAD_CONST', 0, 14),
             ('RETURN_VALUE', None, 14),
         ]
         self.cfg_optimization_test(insts,
                                    expected_insts,
                                    consts=[0, 1, 2, 3, 4],
-                                   expected_consts=[0, 3])
+                                   expected_consts=[3])
 
     def test_conditional_jump_backward_non_const_condition(self):
         insts = [
@@ -1322,18 +1322,18 @@ def test_except_handler_label(self):
         insts = [
             ('SETUP_FINALLY', handler := self.Label(), 10),
             ('POP_BLOCK', None, -1),
-            ('LOAD_CONST', 1, 11),
+            ('LOAD_CONST', 0, 11),
             ('RETURN_VALUE', None, 11),
             handler,
-            ('LOAD_CONST', 2, 12),
+            ('LOAD_CONST', 1, 12),
             ('RETURN_VALUE', None, 12),
         ]
         expected_insts = [
             ('SETUP_FINALLY', handler := self.Label(), 10),
-            ('LOAD_CONST', 1, 11),
+            ('LOAD_CONST', 0, 11),
             ('RETURN_VALUE', None, 11),
             handler,
-            ('LOAD_CONST', 2, 12),
+            ('LOAD_CONST', 1, 12),
             ('RETURN_VALUE', None, 12),
         ]
         self.cfg_optimization_test(insts, expected_insts, consts=list(range(5)))

Python/compile.c

@@ -1325,7 +1325,7 @@ optimize_and_assemble_code_unit(struct compiler_unit *u, PyObject *const_cache,
     assert(u->u_metadata.u_firstlineno);
 
     if (_PyCfg_OptimizeCodeUnit(g, consts, const_cache, nlocals,
-                                nparams, u->u_metadata.u_firstlineno) < 0) {
+                                nparams, u->u_metadata.u_firstlineno, u->u_ste->ste_has_docstring) < 0) {
         goto error;
     }
 

Python/flowgraph.c

@@ -2281,7 +2281,7 @@ fast_scan_many_locals(basicblock *entryblock, int nlocals)
 }
 
 static int
-remove_unused_consts(basicblock *entryblock, PyObject *consts)
+remove_unused_consts(basicblock *entryblock, PyObject *consts, unsigned has_docstring)
 {
     assert(PyList_CheckExact(consts));
     Py_ssize_t nconsts = PyList_GET_SIZE(consts);
@@ -2297,11 +2297,15 @@ remove_unused_consts(basicblock *entryblock, PyObject *consts)
     if (index_map == NULL) {
         goto end;
     }
-    for (Py_ssize_t i = 1; i < nconsts; i++) {
+    for (Py_ssize_t i = 0; i < nconsts; i++) {
         index_map[i] = -1;
     }
     // The first constant may be docstring; keep it always.
-    index_map[0] = 0;
+    if (has_docstring) {
+        assert(PyList_Size(consts) >= 1);
+        assert(PyUnicode_CheckExact(PyList_GET_ITEM(consts, 0)));
+        index_map[0] = 0;
+    }
 
     /* mark used consts */
     for (basicblock *b = entryblock; b != NULL; b = b->b_next) {
@@ -2764,7 +2768,7 @@ resolve_line_numbers(cfg_builder *g, int firstlineno)
 
 int
 _PyCfg_OptimizeCodeUnit(cfg_builder *g, PyObject *consts, PyObject *const_cache,
-                        int nlocals, int nparams, int firstlineno)
+                        int nlocals, int nparams, int firstlineno, unsigned has_docstring)
 {
     assert(cfg_builder_check(g));
     /** Preprocessing **/
@@ -2775,7 +2779,7 @@ _PyCfg_OptimizeCodeUnit(cfg_builder *g, PyObject *consts, PyObject *const_cache,
 
     /** Optimization **/
     RETURN_IF_ERROR(optimize_cfg(g, consts, const_cache, firstlineno));
-    RETURN_IF_ERROR(remove_unused_consts(g->g_entryblock, consts));
+    RETURN_IF_ERROR(remove_unused_consts(g->g_entryblock, consts, has_docstring));
     RETURN_IF_ERROR(
         add_checks_for_loads_of_uninitialized_variables(
             g->g_entryblock, nlocals, nparams));
@@ -3191,7 +3195,7 @@ _PyCompile_OptimizeCfg(PyObject *seq, PyObject *consts, int nlocals)
     }
     int nparams = 0, firstlineno = 1;
     if (_PyCfg_OptimizeCodeUnit(g, consts, const_cache, nlocals,
-                                nparams, firstlineno) < 0) {
+                                nparams, firstlineno, 0) < 0) {
         goto error;
     }
     res = cfg_to_instruction_sequence(g);