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%.

3 files changed, 17 insertions, 28 deletions

diff --git a/Include/cpython/code.h b/Include/cpython/code.h
index e810eb4..330f1f5 100644
--- a/Include/cpython/code.h
+++ b/Include/cpython/code.h
@@ -40,6 +40,7 @@ struct PyCodeObject {
     PyObject *co_name;          /* unicode (name, for reference) */
     PyObject *co_linetable;     /* string (encoding addr<->lineno mapping) See
                                    Objects/lnotab_notes.txt for details. */
+    PyObject *co_exceptiontable; /* Byte string encoding exception handling table */
     void *co_zombieframe;       /* for optimization only (see frameobject.c) */
     PyObject *co_weakreflist;   /* to support weakrefs to code objects */
     /* Scratch space for extra data relating to the code object.
@@ -117,12 +118,12 @@ PyAPI_DATA(PyTypeObject) PyCode_Type;
 PyAPI_FUNC(PyCodeObject *) PyCode_New(
         int, int, int, int, int, PyObject *, PyObject *,
         PyObject *, PyObject *, PyObject *, PyObject *,
-        PyObject *, PyObject *, int, PyObject *);
+        PyObject *, PyObject *, int, PyObject *, PyObject *);
 
 PyAPI_FUNC(PyCodeObject *) PyCode_NewWithPosOnlyArgs(
         int, int, int, int, int, int, PyObject *, PyObject *,
         PyObject *, PyObject *, PyObject *, PyObject *,
-        PyObject *, PyObject *, int, PyObject *);
+        PyObject *, PyObject *, int, PyObject *, PyObject *);
         /* same as struct above */
 
 /* Creates a new empty code object with the specified source location. */
diff --git a/Include/cpython/frameobject.h b/Include/cpython/frameobject.h
index 5122ec4..0c2206c0 100644
--- a/Include/cpython/frameobject.h
+++ b/Include/cpython/frameobject.h
@@ -34,18 +34,14 @@ struct _frame {
     PyObject *f_locals;         /* local symbol table (any mapping) */
     PyObject **f_valuestack;    /* points after the last local */
     PyObject *f_trace;          /* Trace function */
-    int f_stackdepth;           /* Depth of value stack */
-    char f_trace_lines;         /* Emit per-line trace events? */
-    char f_trace_opcodes;       /* Emit per-opcode trace events? */
-
     /* Borrowed reference to a generator, or NULL */
     PyObject *f_gen;
-
+    int f_stackdepth;           /* Depth of value stack */
     int f_lasti;                /* Last instruction if called */
     int f_lineno;               /* Current line number. Only valid if non-zero */
-    int f_iblock;               /* index in f_blockstack */
     PyFrameState f_state;       /* What state the frame is in */
-    PyTryBlock f_blockstack[CO_MAXBLOCKS]; /* for try and loop blocks */
+    char f_trace_lines;         /* Emit per-line trace events? */
+    char f_trace_opcodes;       /* Emit per-opcode trace events? */
     PyObject *f_localsplus[1];  /* locals+stack, dynamically sized */
 };
 
@@ -77,11 +73,6 @@ _PyFrame_New_NoTrack(PyThreadState *, PyFrameConstructor *, PyObject *);
 
 /* The rest of the interface is specific for frame objects */
 
-/* Block management functions */
-
-PyAPI_FUNC(void) PyFrame_BlockSetup(PyFrameObject *, int, int, int);
-PyAPI_FUNC(PyTryBlock *) PyFrame_BlockPop(PyFrameObject *);
-
 /* Conversions between "fast locals" and locals in dictionary */
 
 PyAPI_FUNC(void) PyFrame_LocalsToFast(PyFrameObject *, int);
diff --git a/Include/opcode.h b/Include/opcode.h
index 5203975..1e44e1f 100644
--- a/Include/opcode.h
+++ b/Include/opcode.h
@@ -35,10 +35,13 @@ extern "C" {
 #define MATCH_SEQUENCE           32
 #define MATCH_KEYS               33
 #define COPY_DICT_WITHOUT_KEYS   34
+#define PUSH_EXC_INFO            35
+#define POP_EXCEPT_AND_RERAISE   37
 #define WITH_EXCEPT_START        49
 #define GET_AITER                50
 #define GET_ANEXT                51
 #define BEFORE_ASYNC_WITH        52
+#define BEFORE_WITH              53
 #define END_ASYNC_FOR            54
 #define INPLACE_ADD              55
 #define INPLACE_SUBTRACT         56
@@ -69,7 +72,6 @@ extern "C" {
 #define IMPORT_STAR              84
 #define SETUP_ANNOTATIONS        85
 #define YIELD_VALUE              86
-#define POP_BLOCK                87
 #define POP_EXCEPT               89
 #define HAVE_ARGUMENT            90
 #define STORE_NAME               90
@@ -103,7 +105,6 @@ extern "C" {
 #define CONTAINS_OP             118
 #define RERAISE                 119
 #define JUMP_IF_NOT_EXC_MATCH   121
-#define SETUP_FINALLY           122
 #define LOAD_FAST               124
 #define STORE_FAST              125
 #define DELETE_FAST             126
@@ -118,14 +119,12 @@ extern "C" {
 #define DELETE_DEREF            138
 #define CALL_FUNCTION_KW        141
 #define CALL_FUNCTION_EX        142
-#define SETUP_WITH              143
 #define EXTENDED_ARG            144
 #define LIST_APPEND             145
 #define SET_ADD                 146
 #define MAP_ADD                 147
 #define LOAD_CLASSDEREF         148
 #define MATCH_CLASS             152
-#define SETUP_ASYNC_WITH        154
 #define FORMAT_VALUE            155
 #define BUILD_CONST_KEY_MAP     156
 #define BUILD_STRING            157
@@ -140,8 +139,8 @@ static uint32_t _PyOpcode_RelativeJump[8] = {
     0U,
     0U,
     536870912U,
-    67125248U,
-    67141632U,
+    16384U,
+    0U,
     0U,
     0U,
     0U,
@@ -150,22 +149,20 @@ static uint32_t _PyOpcode_Jump[8] = {
     0U,
     0U,
     536870912U,
-    101695488U,
-    67141632U,
+    34586624U,
+    0U,
     0U,
     0U,
     0U,
 };
 #endif /* OPCODE_TABLES */
 
-/* EXCEPT_HANDLER is a special, implicit block type which is created when
-   entering an except handler. It is not an opcode but we define it here
-   as we want it to be available to both frameobject.c and ceval.c, while
-   remaining private.*/
-#define EXCEPT_HANDLER 257
-
 #define HAS_ARG(op) ((op) >= HAVE_ARGUMENT)
 
+/* Reserve some bytecodes for internal use in the compiler.
+ * The value of 240 is arbitrary. */
+#define IS_ARTIFICIAL(op) ((op) > 240)
+
 #ifdef __cplusplus
 }
 #endif