bpo-42217: compiler: merge same co_code and co_linetable objects (pythonGH-23056)

Author: methane

Lib/test/test_compile.py

@@ -632,6 +632,17 @@ def check_same_constant(const):
  self.check_constant(f1, frozenset({0}))
  self.assertTrue(f1(0))
 
+ # Merging equal co_linetable and co_code is not a strict requirement
+ # for the Python semantics, it's a more an implementation detail.
+ @support.cpython_only
+ def test_merge_code_attrs(self):
+ # See https://bugs.python.org/issue42217
+ f1 = lambda x: x.y.z
+ f2 = lambda a: a.b.c
+
+ self.assertIs(f1.__code__.co_linetable, f2.__code__.co_linetable)
+ self.assertIs(f1.__code__.co_code, f2.__code__.co_code)
+
  # This is a regression test for a CPython specific peephole optimizer
  # implementation bug present in a few releases. It's assertion verifies
  # that peephole optimization was actually done though that isn't an

Misc/NEWS.d/next/Core and Builtins/2020-10-31-16-54-00.bpo-42217.GdcHe5.rst

@@ -0,0 +1 @@
+Make the compiler merges same co_code and co_linetable objects in a module like already did for co_consts.

Python/compile.c

@@ -5806,14 +5806,12 @@ compute_code_flags(struct compiler *c)
  return flags;
 }
 
-// Merge *tuple* with constant cache.
+// Merge *obj* with constant cache.
 // Unlike merge_consts_recursive(), this function doesn't work recursively.
 static int
-merge_const_tuple(struct compiler *c, PyObject **tuple)
+merge_const_one(struct compiler *c, PyObject **obj)
 {
- assert(PyTuple_CheckExact(*tuple));
-
- PyObject *key = _PyCode_ConstantKey(*tuple);
+ PyObject *key = _PyCode_ConstantKey(*obj);
  if (key == NULL) {
  return 0;
  }
@@ -5824,14 +5822,18 @@ merge_const_tuple(struct compiler *c, PyObject **tuple)
  if (t == NULL) {
  return 0;
  }
- if (t == key) { // tuple is new constant.
+ if (t == key) { // obj is new constant.
  return 1;
  }
 
- PyObject *u = PyTuple_GET_ITEM(t, 1);
- Py_INCREF(u);
- Py_DECREF(*tuple);
- *tuple = u;
+ if (PyTuple_CheckExact(t)) {
+ // t is still borrowed reference
+ t = PyTuple_GET_ITEM(t, 1);
+ }
+
+ Py_INCREF(t);
+ Py_DECREF(*obj);
+ *obj = t;
  return 1;
 }
 
@@ -5861,10 +5863,10 @@ makecode(struct compiler *c, struct assembler *a, PyObject *consts)
  if (!freevars)
  goto error;
 
- if (!merge_const_tuple(c, &names) ||
- !merge_const_tuple(c, &varnames) ||
- !merge_const_tuple(c, &cellvars) ||
- !merge_const_tuple(c, &freevars))
+ if (!merge_const_one(c, &names) ||
+ !merge_const_one(c, &varnames) ||
+ !merge_const_one(c, &cellvars) ||
+ !merge_const_one(c, &freevars))
  {
  goto error;
  }
@@ -5881,7 +5883,7 @@ makecode(struct compiler *c, struct assembler *a, PyObject *consts)
  if (consts == NULL) {
  goto error;
  }
- if (!merge_const_tuple(c, &consts)) {
+ if (!merge_const_one(c, &consts)) {
  Py_DECREF(consts);
  goto error;
  }
@@ -6028,10 +6030,18 @@ assemble(struct compiler *c, int addNone)
  goto error;
  }
 
- if (_PyBytes_Resize(&a.a_lnotab, a.a_lnotab_off) < 0)
+ if (_PyBytes_Resize(&a.a_lnotab, a.a_lnotab_off) < 0) {
  goto error;
- if (_PyBytes_Resize(&a.a_bytecode, a.a_offset * sizeof(_Py_CODEUNIT)) < 0)
+ }
+ if (!merge_const_one(c, &a.a_lnotab)) {
  goto error;
+ }
+ if (_PyBytes_Resize(&a.a_bytecode, a.a_offset * sizeof(_Py_CODEUNIT)) < 0) {
+ goto error;
+ }
+ if (!merge_const_one(c, &a.a_bytecode)) {
+ goto error;
+ }
 
  co = makecode(c, &a, consts);
  error: