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, 3 insertions, 12 deletions

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);