bpo-43693: Eliminate unused "fast locals".

Include/cpython/code.h

@@ -83,11 +83,11 @@ struct PyCodeObject {
 
     /* These fields are set with computed values on new code objects. */
 
-    int *co_cell2arg;           /* Maps cell vars which are arguments. */
     // 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_nplaincellvars;      /* number of non-arg cell variables */
+    int co_ncellvars;           /* total number of cell variables */
     int co_nfreevars;           /* number of free variables */
     // lazily-computed values
     PyObject *co_varnames;      /* tuple of strings (local variable names) */
@@ -142,10 +142,6 @@ struct PyCodeObject {
 #define CO_FUTURE_GENERATOR_STOP  0x800000
 #define CO_FUTURE_ANNOTATIONS    0x1000000
 
-/* This value is found in the co_cell2arg array when the associated cell
-   variable does not correspond to an argument. */
-#define CO_CELL_NOT_AN_ARG (-1)
-
 /* This should be defined if a future statement modifies the syntax.
    For example, when a keyword is added.
 */

Include/internal/pycore_frame.h

@@ -32,8 +32,6 @@ _PyFrame_GetBuiltins(PyFrameObject *f)
 
 int _PyFrame_TakeLocals(PyFrameObject *f);
 
-PyAPI_FUNC(int) _PyFrame_OpAlreadyRan(PyFrameObject *f, int opcode, int oparg);
-
 #ifdef __cplusplus
 }
 #endif

Lib/importlib/_bootstrap_external.py

@@ -358,6 +358,7 @@ def _write_atomic(path, data, mode=0o666):
 #     Python 3.11a1 3453 (add co_fastlocalnames and co_fastlocalkinds)
 #     Python 3.11a1 3454 (compute cell offsets relative to locals bpo-43693)
 #     Python 3.11a1 3455 (add MAKE_CELL bpo-43693)
+#     Python 3.11a1 3456 (interleave cell args bpo-43693)
 
 #
 # MAGIC must change whenever the bytecode emitted by the compiler may no
@@ -367,7 +368,7 @@ 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 = (3455).to_bytes(2, 'little') + b'\r\n'
+MAGIC_NUMBER = (3456).to_bytes(2, 'little') + b'\r\n'
 _RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # For import.c
 
 _PYCACHE = '__pycache__'

Lib/test/test_dis.py

@@ -427,9 +427,9 @@ def foo(x):
     return foo
 
 dis_nested_0 = """\
-              0 MAKE_CELL                2 (y)
+              0 MAKE_CELL                0 (y)
 
-%3d           2 LOAD_CLOSURE             2 (y)
+%3d           2 LOAD_CLOSURE             0 (y)
               4 BUILD_TUPLE              1
               6 LOAD_CONST               1 (<code object foo at 0x..., file "%s", line %d>)
               8 LOAD_CONST               2 ('_h.<locals>.foo')
@@ -446,14 +446,14 @@ def foo(x):
 
 dis_nested_1 = """%s
 Disassembly of <code object foo at 0x..., file "%s", line %d>:
-              0 MAKE_CELL                1 (x)
+              0 MAKE_CELL                0 (x)
 
-%3d           2 LOAD_CLOSURE             1 (x)
+%3d           2 LOAD_CLOSURE             0 (x)
               4 BUILD_TUPLE              1
               6 LOAD_CONST               1 (<code object <listcomp> at 0x..., file "%s", line %d>)
               8 LOAD_CONST               2 ('_h.<locals>.foo.<locals>.<listcomp>')
              10 MAKE_FUNCTION            8 (closure)
-             12 LOAD_DEREF               2 (y)
+             12 LOAD_DEREF               1 (y)
              14 GET_ITER
              16 CALL_FUNCTION            1
              18 RETURN_VALUE
@@ -966,19 +966,19 @@ def jumpy():
 
 Instruction = dis.Instruction
 expected_opinfo_outer = [
-  Instruction(opname='MAKE_CELL', opcode=135, arg=3, argval='a', argrepr='a', offset=0, starts_line=None, is_jump_target=False),
-  Instruction(opname='MAKE_CELL', opcode=135, arg=4, argval='b', argrepr='b', offset=2, starts_line=None, is_jump_target=False),
+  Instruction(opname='MAKE_CELL', opcode=135, arg=0, argval='a', argrepr='a', offset=0, starts_line=None, is_jump_target=False),
+  Instruction(opname='MAKE_CELL', opcode=135, arg=1, argval='b', argrepr='b', offset=2, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=8, argval=(3, 4), argrepr='(3, 4)', offset=4, starts_line=2, is_jump_target=False),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=3, argval='a', argrepr='a', offset=6, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=4, argval='b', argrepr='b', offset=8, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=0, argval='a', argrepr='a', offset=6, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=1, argval='b', argrepr='b', offset=8, starts_line=None, is_jump_target=False),
   Instruction(opname='BUILD_TUPLE', opcode=102, arg=2, argval=2, argrepr='', offset=10, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=3, argval=code_object_f, argrepr=repr(code_object_f), offset=12, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=4, argval='outer.<locals>.f', argrepr="'outer.<locals>.f'", offset=14, starts_line=None, is_jump_target=False),
   Instruction(opname='MAKE_FUNCTION', opcode=132, arg=9, argval=9, argrepr='defaults, closure', offset=16, starts_line=None, is_jump_target=False),
   Instruction(opname='STORE_FAST', opcode=125, arg=2, argval='f', argrepr='f', offset=18, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_GLOBAL', opcode=116, arg=0, argval='print', argrepr='print', offset=20, starts_line=7, is_jump_target=False),
-  Instruction(opname='LOAD_DEREF', opcode=137, arg=3, argval='a', argrepr='a', offset=22, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_DEREF', opcode=137, arg=4, argval='b', argrepr='b', offset=24, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_DEREF', opcode=137, arg=0, argval='a', argrepr='a', offset=22, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_DEREF', opcode=137, arg=1, argval='b', argrepr='b', offset=24, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=5, argval='', argrepr="''", offset=26, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=6, argval=1, argrepr='1', offset=28, starts_line=None, is_jump_target=False),
   Instruction(opname='BUILD_LIST', opcode=103, arg=0, argval=0, argrepr='', offset=30, starts_line=None, is_jump_target=False),
@@ -991,23 +991,23 @@ def jumpy():
 ]
 
 expected_opinfo_f = [
-  Instruction(opname='MAKE_CELL', opcode=135, arg=3, argval='c', argrepr='c', offset=0, starts_line=None, is_jump_target=False),
-  Instruction(opname='MAKE_CELL', opcode=135, arg=4, argval='d', argrepr='d', offset=2, starts_line=None, is_jump_target=False),
+  Instruction(opname='MAKE_CELL', opcode=135, arg=0, argval='c', argrepr='c', offset=0, starts_line=None, is_jump_target=False),
+  Instruction(opname='MAKE_CELL', opcode=135, arg=1, argval='d', argrepr='d', offset=2, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=5, argval=(5, 6), argrepr='(5, 6)', offset=4, starts_line=3, is_jump_target=False),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=5, argval='a', argrepr='a', offset=6, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=6, argval='b', argrepr='b', offset=8, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=3, argval='c', argrepr='c', offset=10, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=4, argval='d', argrepr='d', offset=12, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=3, argval='a', argrepr='a', offset=6, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=4, argval='b', argrepr='b', offset=8, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=0, argval='c', argrepr='c', offset=10, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_CLOSURE', opcode=136, arg=1, argval='d', argrepr='d', offset=12, starts_line=None, is_jump_target=False),
   Instruction(opname='BUILD_TUPLE', opcode=102, arg=4, argval=4, argrepr='', offset=14, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=3, argval=code_object_inner, argrepr=repr(code_object_inner), offset=16, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_CONST', opcode=100, arg=4, argval='outer.<locals>.f.<locals>.inner', argrepr="'outer.<locals>.f.<locals>.inner'", offset=18, starts_line=None, is_jump_target=False),
   Instruction(opname='MAKE_FUNCTION', opcode=132, arg=9, argval=9, argrepr='defaults, closure', offset=20, starts_line=None, is_jump_target=False),
   Instruction(opname='STORE_FAST', opcode=125, arg=2, argval='inner', argrepr='inner', offset=22, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_GLOBAL', opcode=116, arg=0, argval='print', argrepr='print', offset=24, starts_line=5, is_jump_target=False),
-  Instruction(opname='LOAD_DEREF', opcode=137, arg=5, argval='a', argrepr='a', offset=26, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_DEREF', opcode=137, arg=6, argval='b', argrepr='b', offset=28, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_DEREF', opcode=137, arg=3, argval='c', argrepr='c', offset=30, starts_line=None, is_jump_target=False),
-  Instruction(opname='LOAD_DEREF', opcode=137, arg=4, argval='d', argrepr='d', offset=32, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_DEREF', opcode=137, arg=3, argval='a', argrepr='a', offset=26, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_DEREF', opcode=137, arg=4, argval='b', argrepr='b', offset=28, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_DEREF', opcode=137, arg=0, argval='c', argrepr='c', offset=30, starts_line=None, is_jump_target=False),
+  Instruction(opname='LOAD_DEREF', opcode=137, arg=1, argval='d', argrepr='d', offset=32, starts_line=None, is_jump_target=False),
   Instruction(opname='CALL_FUNCTION', opcode=131, arg=4, argval=4, argrepr='', offset=34, starts_line=None, is_jump_target=False),
   Instruction(opname='POP_TOP', opcode=1, arg=None, argval=None, argrepr='', offset=36, starts_line=None, is_jump_target=False),
   Instruction(opname='LOAD_FAST', opcode=124, arg=2, argval='inner', argrepr='inner', offset=38, starts_line=6, is_jump_target=False),

Misc/NEWS.d/next/Core and Builtins/2021-06-07-15-13-44.bpo-43693.c_zDeY.rst

@@ -0,0 +1,4 @@
+Computation of the offsets of cell variables is done in the compiler instead
+of at runtime. This reduces the overhead of handling cell and free
+variables, especially in the case where a variable is both an argument and
+cell variable.

Objects/codeobject.c

@@ -162,43 +162,28 @@ _Py_set_localsplus_info(int offset, PyObject *name, _PyLocalsPlusKind kind,
     Py_INCREF(name);
     PyTuple_SET_ITEM(names, offset, name);
     kinds[offset] = kind;
-
-    if (kind == CO_FAST_CELL) {
-        // Cells can overlap with args, so mark those cases.
-        int nlocalsplus = (int)PyTuple_GET_SIZE(names);
-        for (int i = 0; i < nlocalsplus; i++) {
-            _PyLocalsPlusKind kind = kinds[i];
-            if (kind && !(kind & CO_FAST_LOCAL)) {
-                // We've moved past the locals.
-                break;
-            }
-            PyObject *varname = PyTuple_GET_ITEM(names, i);
-            int cmp = PyUnicode_Compare(name, varname);
-            if (cmp == 0) {
-                kinds[i] |= CO_FAST_CELL;
-                break;
-            }
-            assert(cmp > 0 || !PyErr_Occurred());
-        }
-    }
 }
 
 static void
 get_localsplus_counts(PyObject *names, _PyLocalsPlusKinds kinds,
-                      int *pnlocals, int *pncellvars,
+                      int *pnlocals, int *pnplaincellvars, int *pncellvars,
                       int *pnfreevars)
 {
     int nlocals = 0;
+    int nplaincellvars = 0;
     int ncellvars = 0;
     int nfreevars = 0;
-    int nlocalsplus = Py_SAFE_DOWNCAST(PyTuple_GET_SIZE(names),
-                                       Py_ssize_t, int);
+    Py_ssize_t nlocalsplus = PyTuple_GET_SIZE(names);
     for (int i = 0; i < nlocalsplus; i++) {
         if (kinds[i] & CO_FAST_LOCAL) {
             nlocals += 1;
+            if (kinds[i] & CO_FAST_CELL) {
+                ncellvars += 1;
+            }
         }
         else if (kinds[i] & CO_FAST_CELL) {
             ncellvars += 1;
+            nplaincellvars += 1;
         }
         else if (kinds[i] & CO_FAST_FREE) {
             nfreevars += 1;
@@ -207,6 +192,9 @@ get_localsplus_counts(PyObject *names, _PyLocalsPlusKinds kinds,
     if (pnlocals != NULL) {
         *pnlocals = nlocals;
     }
+    if (pnplaincellvars != NULL) {
+        *pnplaincellvars = nplaincellvars;
+    }
     if (pncellvars != NULL) {
         *pncellvars = ncellvars;
     }
@@ -227,10 +215,6 @@ get_localsplus_names(PyCodeObject *co, _PyLocalsPlusKind kind, int num)
         if ((co->co_localspluskinds[offset] & kind) == 0) {
             continue;
         }
-        // For now there may be duplicates, which we ignore.
-        if (kind == CO_FAST_CELL && co->co_localspluskinds[offset] != kind) {
-            continue;
-        }
         assert(index < num);
         PyObject *name = PyTuple_GET_ITEM(co->co_localsplusnames, offset);
         Py_INCREF(name);
@@ -283,7 +267,7 @@ _PyCode_Validate(struct _PyCodeConstructor *con)
      * here to avoid the possibility of overflow (however remote). */
     int nlocals;
     get_localsplus_counts(con->localsplusnames, con->localspluskinds,
-                          &nlocals, NULL, NULL);
+                          &nlocals, NULL, NULL, NULL);
     int nplainlocals = nlocals -
                        con->argcount -
                        con->kwonlyargcount -
@@ -301,9 +285,9 @@ static void
 init_code(PyCodeObject *co, struct _PyCodeConstructor *con)
 {
     int nlocalsplus = (int)PyTuple_GET_SIZE(con->localsplusnames);
-    int nlocals, ncellvars, nfreevars;
+    int nlocals, nplaincellvars, ncellvars, nfreevars;
     get_localsplus_counts(con->localsplusnames, con->localspluskinds,
-                          &nlocals, &ncellvars, &nfreevars);
+                          &nlocals, &nplaincellvars, &ncellvars, &nfreevars);
 
     Py_INCREF(con->filename);
     co->co_filename = con->filename;
@@ -338,9 +322,9 @@ init_code(PyCodeObject *co, struct _PyCodeConstructor *con)
     co->co_exceptiontable = con->exceptiontable;
 
     /* derived values */
-    co->co_cell2arg = NULL;  // This will be set soon.
     co->co_nlocalsplus = nlocalsplus;
     co->co_nlocals = nlocals;
+    co->co_nplaincellvars = nplaincellvars;
     co->co_ncellvars = ncellvars;
     co->co_nfreevars = nfreevars;
     co->co_varnames = NULL;
@@ -392,44 +376,6 @@ _PyCode_New(struct _PyCodeConstructor *con)
         co->co_flags &= ~CO_NOFREE;
     }
 
-    /* Create mapping between cells and arguments if needed. */
-    if (co->co_ncellvars) {
-        int totalargs = co->co_argcount +
-                        co->co_kwonlyargcount +
-                        ((co->co_flags & CO_VARARGS) != 0) +
-                        ((co->co_flags & CO_VARKEYWORDS) != 0);
-        assert(totalargs <= co->co_nlocals);
-        /* Find cells which are also arguments. */
-        for (int i = 0; i < co->co_ncellvars; i++) {
-            PyObject *cellname = PyTuple_GET_ITEM(co->co_localsplusnames,
-                                                  i + co->co_nlocals);
-            for (int j = 0; j < totalargs; j++) {
-                PyObject *argname = PyTuple_GET_ITEM(co->co_localsplusnames, j);
-                int cmp = PyUnicode_Compare(cellname, argname);
-                if (cmp == -1 && PyErr_Occurred()) {
-                    Py_DECREF(co);
-                    return NULL;
-                }
-                if (cmp == 0) {
-                    if (co->co_cell2arg == NULL) {
-                        co->co_cell2arg = PyMem_NEW(int, co->co_ncellvars);
-                        if (co->co_cell2arg == NULL) {
-                            Py_DECREF(co);
-                            PyErr_NoMemory();
-                            return NULL;
-                        }
-                        for (int k = 0; k < co->co_ncellvars; k++) {
-                            co->co_cell2arg[k] = CO_CELL_NOT_AN_ARG;
-                        }
-                    }
-                    co->co_cell2arg[i] = j;
-                    // Go to the next cell name.
-                    break;
-                }
-            }
-        }
-    }
-
     return co;
 }
 
@@ -478,6 +424,23 @@ PyCode_NewWithPosOnlyArgs(int argcount, int posonlyargcount, int kwonlyargcount,
     }
     for (int i = 0; i < ncellvars; i++, offset++) {
         PyObject *name = PyTuple_GET_ITEM(cellvars, i);
+        int argoffset = -1;
+        for (int j = 0; j < nvarnames; j++) {
+            int cmp = PyUnicode_Compare(PyTuple_GET_ITEM(varnames, j),
+                                        name);
+            assert(!PyErr_Occurred());
+            if (cmp == 0) {
+                argoffset = j;
+                break;
+            }
+        }
+        if (argoffset >= 0) {
+            // Merge the localsplus indices.
+            nlocalsplus -= 1;
+            offset -= 1;
+            localspluskinds[argoffset] |= CO_FAST_CELL;
+            continue;
+        }
         _Py_set_localsplus_info(offset, name, CO_FAST_CELL,
                                localsplusnames, localspluskinds);
     }
@@ -486,6 +449,11 @@ PyCode_NewWithPosOnlyArgs(int argcount, int posonlyargcount, int kwonlyargcount,
         _Py_set_localsplus_info(offset, name, CO_FAST_FREE,
                                localsplusnames, localspluskinds);
     }
+    // If any cells were args then nlocalsplus will have shrunk.
+    // We don't bother resizing localspluskinds.
+    if (_PyTuple_Resize(&localsplusnames, nlocalsplus) < 0) {
+        goto error;
+    }
 
     struct _PyCodeConstructor con = {
         .filename = filename,
@@ -1182,8 +1150,6 @@ code_dealloc(PyCodeObject *co)
     Py_XDECREF(co->co_name);
     Py_XDECREF(co->co_linetable);
     Py_XDECREF(co->co_exceptiontable);
-    if (co->co_cell2arg != NULL)
-        PyMem_Free(co->co_cell2arg);
     if (co->co_weakreflist != NULL)
         PyObject_ClearWeakRefs((PyObject*)co);
     if (co->co_quickened) {
@@ -1377,10 +1343,6 @@ code_sizeof(PyCodeObject *co, PyObject *Py_UNUSED(args))
                (co_extra->ce_size-1) * sizeof(co_extra->ce_extras[0]);
     }
 
-    if (co->co_cell2arg != NULL && co->co_cellvars != NULL) {
-        res += co->co_ncellvars * sizeof(Py_ssize_t);
-    }
-
     if (co->co_quickened != NULL) {
         Py_ssize_t count = co->co_quickened[0].entry.zero.cache_count;
         count += (PyBytes_GET_SIZE(co->co_code)+sizeof(SpecializedCacheEntry)-1)/