bpo-43693: Un-revert commits 2c1e258 and b2bf2bc. (gh-26577)

These were reverted in gh-26530 (commit 17c4edc) due to refleaks.

* 2c1e258 - Compute deref offsets in compiler (gh-25152)
* b2bf2bc - Add new internal code objects fields: co_fastlocalnames and co_fastlocalkinds. (gh-26388)

This change fixes the refleaks.

https://bugs.python.org/issue43693

2 files changed, 78 insertions, 9 deletions

diff --git a/Include/cpython/code.h b/Include/cpython/code.h
index 98d728b..c81f9f3 100644
--- a/Include/cpython/code.h
+++ b/Include/cpython/code.h
@@ -3,6 +3,8 @@
 #endif
 
 typedef uint16_t _Py_CODEUNIT;
+// Each oparg must fit in the second half of _Py_CODEUNIT, hence 8 bits.
+#define _Py_MAX_OPARG 255
 
 #ifdef WORDS_BIGENDIAN
 #  define _Py_OPCODE(word) ((word) >> 8)
@@ -16,6 +18,11 @@ typedef uint16_t _Py_CODEUNIT;
 
 typedef struct _PyOpcache _PyOpcache;
 
+
+// These are duplicated from pycore_code.h.
+typedef unsigned char _PyLocalsPlusKind;
+typedef _PyLocalsPlusKind *_PyLocalsPlusKinds;
+
 /* Bytecode object */
 struct PyCodeObject {
     PyObject_HEAD
@@ -47,7 +54,9 @@ struct PyCodeObject {
     // The hottest fields (in the eval loop) are grouped here at the top.
     PyObject *co_consts;        /* list (constants used) */
     PyObject *co_names;         /* list of strings (names used) */
-    _Py_CODEUNIT *co_firstinstr; /* Pointer to first instruction, used for quickening */
+    _Py_CODEUNIT *co_firstinstr; /* Pointer to first instruction, used for quickening.
+                                    Unlike the other "hot" fields, this one is
+                                    actually derived from co_code. */
     PyObject *co_exceptiontable; /* Byte string encoding exception handling table */
     int co_flags;               /* CO_..., see below */
     int co_warmup;              /* Warmup counter for quickening */
@@ -59,9 +68,8 @@ struct PyCodeObject {
     int co_stacksize;           /* #entries needed for evaluation stack */
     int co_firstlineno;         /* first source line number */
     PyObject *co_code;          /* instruction opcodes */
-    PyObject *co_varnames;      /* tuple of strings (local variable names) */
-    PyObject *co_cellvars;      /* tuple of strings (cell variable names) */
-    PyObject *co_freevars;      /* tuple of strings (free variable names) */
+    PyObject *co_localsplusnames;  /* tuple mapping offsets to names */
+    _PyLocalsPlusKinds co_localspluskinds; /* array mapping to local kinds */
     PyObject *co_filename;      /* unicode (where it was loaded from) */
     PyObject *co_name;          /* unicode (name, for reference) */
     PyObject *co_linetable;     /* string (encoding addr<->lineno mapping) See
@@ -70,11 +78,15 @@ struct PyCodeObject {
     /* These fields are set with computed values on new code objects. */
 
     int *co_cell2arg;           /* Maps cell vars which are arguments. */
-    // These are redundant but offer some performance benefit.
+    // redundant values (derived from co_localsplusnames and co_localspluskinds)
     int co_nlocalsplus;         /* number of local + cell + free variables */
     int co_nlocals;             /* number of local variables */
     int co_ncellvars;           /* number of cell variables */
     int co_nfreevars;           /* number of free variables */
+    // lazily-computed values
+    PyObject *co_varnames;      /* tuple of strings (local variable names) */
+    PyObject *co_cellvars;      /* tuple of strings (cell variable names) */
+    PyObject *co_freevars;      /* tuple of strings (free variable names) */
 
     /* The remaining fields are zeroed out on new code objects. */
 
@@ -152,7 +164,7 @@ struct PyCodeObject {
 PyAPI_DATA(PyTypeObject) PyCode_Type;
 
 #define PyCode_Check(op) Py_IS_TYPE(op, &PyCode_Type)
-#define PyCode_GetNumFree(op) (PyTuple_GET_SIZE((op)->co_freevars))
+#define PyCode_GetNumFree(op) ((op)->co_nfreevars)
 
 /* Public interface */
 PyAPI_FUNC(PyCodeObject *) PyCode_New(
diff --git a/Include/internal/pycore_code.h b/Include/internal/pycore_code.h
index cb72350..d1ff597 100644
--- a/Include/internal/pycore_code.h
+++ b/Include/internal/pycore_code.h
@@ -150,6 +150,58 @@ int _Py_Quicken(PyCodeObject *code);
 
 extern Py_ssize_t _Py_QuickenedCount;
 
+
+/* "Locals plus" for a code object is the set of locals + cell vars +
+ * free vars.  This relates to variable names as well as offsets into
+ * the "fast locals" storage array of execution frames.  The compiler
+ * builds the list of names, their offsets, and the corresponding
+ * kind of local.
+ *
+ * Those kinds represent the source of the initial value and the
+ * variable's scope (as related to closures).  A "local" is an
+ * argument or other variable defined in the current scope.  A "free"
+ * variable is one that is defined in an outer scope and comes from
+ * the function's closure.  A "cell" variable is a local that escapes
+ * into an inner function as part of a closure, and thus must be
+ * wrapped in a cell.  Any "local" can also be a "cell", but the
+ * "free" kind is mutually exclusive with both.
+ */
+
+// We would use an enum if C let us specify the storage type.
+typedef unsigned char _PyLocalsPlusKind;
+/* Note that these all fit within _PyLocalsPlusKind, as do combinations. */
+// Later, we will use the smaller numbers to differentiate the different
+// kinds of locals (e.g. pos-only arg, varkwargs, local-only).
+#define CO_FAST_LOCAL   0x20
+#define CO_FAST_CELL    0x40
+#define CO_FAST_FREE    0x80
+
+typedef _PyLocalsPlusKind *_PyLocalsPlusKinds;
+
+static inline int
+_PyCode_InitLocalsPlusKinds(int num, _PyLocalsPlusKinds *pkinds)
+{
+    if (num == 0) {
+        *pkinds = NULL;
+        return 0;
+    }
+    _PyLocalsPlusKinds kinds = PyMem_NEW(_PyLocalsPlusKind, num);
+    if (kinds == NULL) {
+        PyErr_NoMemory();
+        return -1;
+    }
+    *pkinds = kinds;
+    return 0;
+}
+
+static inline void
+_PyCode_ClearLocalsPlusKinds(_PyLocalsPlusKinds kinds)
+{
+    if (kinds != NULL) {
+        PyMem_Free(kinds);
+    }
+}
+
 struct _PyCodeConstructor {
     /* metadata */
     PyObject *filename;
@@ -166,13 +218,13 @@ struct _PyCodeConstructor {
     PyObject *names;
 
     /* mapping frame offsets to information */
-    PyObject *varnames;
-    PyObject *cellvars;
-    PyObject *freevars;
+    PyObject *localsplusnames;
+    _PyLocalsPlusKinds localspluskinds;
 
     /* args (within varnames) */
     int argcount;
     int posonlyargcount;
+    // XXX Replace argcount with posorkwargcount (argcount - posonlyargcount).
     int kwonlyargcount;
 
     /* needed to create the frame */
@@ -199,6 +251,11 @@ PyAPI_FUNC(PyCodeObject *) _PyCode_New(struct _PyCodeConstructor *);
 
 int _PyCode_InitOpcache(PyCodeObject *co);
 
+/* Getters for internal PyCodeObject data. */
+PyAPI_FUNC(PyObject *) _PyCode_GetVarnames(PyCodeObject *);
+PyAPI_FUNC(PyObject *) _PyCode_GetCellvars(PyCodeObject *);
+PyAPI_FUNC(PyObject *) _PyCode_GetFreevars(PyCodeObject *);
+
 
 #ifdef __cplusplus
 }