bpo-40222: "Zero cost" exception handling (GH-25729)

"Zero cost" exception handling.

* Uses a lookup table to determine how to handle exceptions.
* Removes SETUP_FINALLY and POP_TOP block instructions, eliminating (most of) the runtime overhead of try statements.
* Reduces the size of the frame object by about 60%.

1 files changed, 23 insertions, 12 deletions

diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index c76ac90..e981e39 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -119,7 +119,7 @@ PyCode_NewWithPosOnlyArgs(int argcount, int posonlyargcount, int kwonlyargcount,
                           PyObject *code, PyObject *consts, PyObject *names,
                           PyObject *varnames, PyObject *freevars, PyObject *cellvars,
                           PyObject *filename, PyObject *name, int firstlineno,
-                          PyObject *linetable)
+                          PyObject *linetable, PyObject *exceptiontable)
 {
     PyCodeObject *co;
     Py_ssize_t *cell2arg = NULL;
@@ -137,7 +137,8 @@ PyCode_NewWithPosOnlyArgs(int argcount, int posonlyargcount, int kwonlyargcount,
         cellvars == NULL || !PyTuple_Check(cellvars) ||
         name == NULL || !PyUnicode_Check(name) ||
         filename == NULL || !PyUnicode_Check(filename) ||
-        linetable == NULL || !PyBytes_Check(linetable)) {
+        linetable == NULL || !PyBytes_Check(linetable) ||
+        exceptiontable == NULL || !PyBytes_Check(exceptiontable)) {
         PyErr_BadInternalCall();
         return NULL;
     }
@@ -260,6 +261,8 @@ PyCode_NewWithPosOnlyArgs(int argcount, int posonlyargcount, int kwonlyargcount,
     co->co_firstlineno = firstlineno;
     Py_INCREF(linetable);
     co->co_linetable = linetable;
+    Py_INCREF(exceptiontable);
+    co->co_exceptiontable = exceptiontable;
     co->co_zombieframe = NULL;
     co->co_weakreflist = NULL;
     co->co_extra = NULL;
@@ -277,12 +280,12 @@ PyCode_New(int argcount, int kwonlyargcount,
            PyObject *code, PyObject *consts, PyObject *names,
            PyObject *varnames, PyObject *freevars, PyObject *cellvars,
            PyObject *filename, PyObject *name, int firstlineno,
-           PyObject *linetable)
+           PyObject *linetable, PyObject *exceptiontable)
 {
     return PyCode_NewWithPosOnlyArgs(argcount, 0, kwonlyargcount, nlocals,
                                      stacksize, flags, code, consts, names,
                                      varnames, freevars, cellvars, filename,
-                                     name, firstlineno, linetable);
+                                     name, firstlineno, linetable, exceptiontable);
 }
 
 int
@@ -369,7 +372,8 @@ PyCode_NewEmpty(const char *filename, const char *funcname, int firstlineno)
                 filename_ob,                    /* filename */
                 funcname_ob,                    /* name */
                 firstlineno,                    /* firstlineno */
-                emptystring                     /* linetable */
+                emptystring,                    /* linetable */
+                emptystring                     /* exception table */
                 );
 
 failed:
@@ -397,6 +401,7 @@ static PyMemberDef code_memberlist[] = {
     {"co_name",         T_OBJECT,       OFF(co_name),            READONLY},
     {"co_firstlineno",  T_INT,          OFF(co_firstlineno),     READONLY},
     {"co_linetable",    T_OBJECT,       OFF(co_linetable),       READONLY},
+    {"co_exceptiontable",    T_OBJECT,  OFF(co_exceptiontable),  READONLY},
     {NULL}      /* Sentinel */
 };
 
@@ -538,6 +543,7 @@ code.__new__ as code_new
     name: unicode
     firstlineno: int
     linetable: object(subclass_of="&PyBytes_Type")
+    exceptiontable: object(subclass_of="&PyBytes_Type")
     freevars: object(subclass_of="&PyTuple_Type", c_default="NULL") = ()
     cellvars: object(subclass_of="&PyTuple_Type", c_default="NULL") = ()
     /
@@ -550,9 +556,9 @@ code_new_impl(PyTypeObject *type, int argcount, int posonlyargcount,
               int kwonlyargcount, int nlocals, int stacksize, int flags,
               PyObject *code, PyObject *consts, PyObject *names,
               PyObject *varnames, PyObject *filename, PyObject *name,
-              int firstlineno, PyObject *linetable, PyObject *freevars,
-              PyObject *cellvars)
-/*[clinic end generated code: output=42c1839b082ba293 input=0ec80da632b99f57]*/
+              int firstlineno, PyObject *linetable, PyObject *exceptiontable,
+              PyObject *freevars, PyObject *cellvars)
+/*[clinic end generated code: output=a3899259c3b4cace input=f823c686da4b3a03]*/
 {
     PyObject *co = NULL;
     PyObject *ournames = NULL;
@@ -618,7 +624,9 @@ code_new_impl(PyTypeObject *type, int argcount, int posonlyargcount,
                                                code, consts, ournames,
                                                ourvarnames, ourfreevars,
                                                ourcellvars, filename,
-                                               name, firstlineno, linetable);
+                                               name, firstlineno, linetable,
+                                               exceptiontable
+                                              );
   cleanup:
     Py_XDECREF(ournames);
     Py_XDECREF(ourvarnames);
@@ -663,6 +671,7 @@ code_dealloc(PyCodeObject *co)
     Py_XDECREF(co->co_filename);
     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_zombieframe != NULL)
@@ -715,6 +724,7 @@ code.replace
     co_filename: unicode(c_default="self->co_filename") = None
     co_name: unicode(c_default="self->co_name") = None
     co_linetable: PyBytesObject(c_default="(PyBytesObject *)self->co_linetable") = None
+    co_exceptiontable: PyBytesObject(c_default="(PyBytesObject *)self->co_exceptiontable") = None
 
 Return a copy of the code object with new values for the specified fields.
 [clinic start generated code]*/
@@ -727,8 +737,9 @@ code_replace_impl(PyCodeObject *self, int co_argcount,
                   PyObject *co_consts, PyObject *co_names,
                   PyObject *co_varnames, PyObject *co_freevars,
                   PyObject *co_cellvars, PyObject *co_filename,
-                  PyObject *co_name, PyBytesObject *co_linetable)
-/*[clinic end generated code: output=50d77e668d3b449b input=a5f997b173d7f636]*/
+                  PyObject *co_name, PyBytesObject *co_linetable,
+                  PyBytesObject *co_exceptiontable)
+/*[clinic end generated code: output=80957472b7f78ed6 input=38376b1193efbbae]*/
 {
 #define CHECK_INT_ARG(ARG) \
         if (ARG < 0) { \
@@ -758,7 +769,7 @@ code_replace_impl(PyCodeObject *self, int co_argcount,
         co_argcount, co_posonlyargcount, co_kwonlyargcount, co_nlocals,
         co_stacksize, co_flags, (PyObject*)co_code, co_consts, co_names,
         co_varnames, co_freevars, co_cellvars, co_filename, co_name,
-        co_firstlineno, (PyObject*)co_linetable);
+        co_firstlineno, (PyObject*)co_linetable, (PyObject*)co_exceptiontable);
 }
 
 static PyObject *