GH-100762: Don't call gen.throw() in gen.close(), unless necessary.

Doc/library/dis.rst

@@ -700,7 +700,10 @@ iterations of the loop.
  Yields ``STACK.pop()`` from a :term:`generator`.
 
  .. versionchanged:: 3.11
- oparg set to be the stack depth, for efficient handling on frames.
+ oparg set to be the stack depth.
+
+ .. versionchanged:: 3.12
+ oparg set to be the exception block depth, for efficient closing of generators.
 
 
 .. opcode:: SETUP_ANNOTATIONS

Lib/importlib/_bootstrap_external.py

@@ -429,7 +429,8 @@ def _write_atomic(path, data, mode=0o666):
 # Python 3.12a1 3513 (Add CALL_INTRINSIC_1 instruction, removed STOPITERATION_ERROR, PRINT_EXPR, IMPORT_STAR)
 # Python 3.12a1 3514 (Remove ASYNC_GEN_WRAP, LIST_TO_TUPLE, and UNARY_POSITIVE)
 # Python 3.12a1 3515 (Embed jump mask in COMPARE_OP oparg)
-# Python 3.12a1 3516 (Add COMAPRE_AND_BRANCH instruction)
+# Python 3.12a1 3516 (Add COMPARE_AND_BRANCH instruction)
+# Python 3.12a1 3517 (Change YIELD_VALUE oparg to exception block depth)
 
 # Python 3.13 will start with 3550
 
@@ -442,7 +443,7 @@ 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 = (3516).to_bytes(2, 'little') + b'\r\n'
+MAGIC_NUMBER = (3517).to_bytes(2, 'little') + b'\r\n'
 
 _RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little') # For import.c
 

Lib/test/test_dis.py

@@ -492,7 +492,7 @@ async def _asyncwith(c):
  GET_AWAITABLE 1
  LOAD_CONST 0 (None)
  >> SEND 3 (to 22)
- YIELD_VALUE 3
+ YIELD_VALUE 2
  RESUME 3
  JUMP_BACKWARD_NO_INTERRUPT 4 (to 14)
  >> POP_TOP
@@ -526,7 +526,7 @@ async def _asyncwith(c):
  GET_AWAITABLE 2
  LOAD_CONST 0 (None)
  >> SEND 4 (to 92)
- YIELD_VALUE 6
+ YIELD_VALUE 3
  RESUME 3
  JUMP_BACKWARD_NO_INTERRUPT 4 (to 82)
  >> CLEANUP_THROW

Misc/NEWS.d/next/Core and Builtins/2023-01-13-12-56-20.gh-issue-100762.YvHaQJ.rst

@@ -0,0 +1,3 @@
+Record the (virtual) exception block depth in the oparg of
+:opcode:`YIELD_VALUE`. Use this to avoid the expensive ``throw()`` when
+closing generators (and coroutines) that can be closed trivially.

Objects/genobject.c

@@ -354,15 +354,37 @@ gen_close(PyGenObject *gen, PyObject *args)
  PyObject *yf = _PyGen_yf(gen);
  int err = 0;
 
+ if (gen->gi_frame_state == FRAME_CREATED){
+ gen->gi_frame_state = FRAME_COMPLETED;
+ Py_RETURN_NONE;
+ }
+ if (gen->gi_frame_state >= FRAME_COMPLETED){
+ Py_RETURN_NONE;
+ }
  if (yf){
  PyFrameState state = gen->gi_frame_state;
  gen->gi_frame_state = FRAME_EXECUTING;
  err = gen_close_iter(yf);
  gen->gi_frame_state = state;
  Py_DECREF(yf);
  }
- if (err == 0)
+ _PyInterpreterFrame *frame = (_PyInterpreterFrame *)gen->gi_iframe;
+ /* It is possible for the previous instruction to not be a
+ * YIELD_VALUE if the debugger has changed the lineno. */
+ if (err == 0 && frame->prev_instr->opcode == YIELD_VALUE){
+ assert(frame->prev_instr[1].opcode == RESUME);
+ int exception_handler_depth = frame->prev_instr->oparg;
+ assert(exception_handler_depth > 0);
+ /* We can safely ignore the outermost try block
+ * as it automatically generated to handle
+ * StopIteration. */
+ if (exception_handler_depth == 1){
+ Py_RETURN_NONE;
+ }
+ }
+ if (err == 0){
  PyErr_SetNone(PyExc_GeneratorExit);
+ }
  retval = gen_send_ex(gen, Py_None, 1, 1);
  if (retval){
  const char *msg = "generator ignored GeneratorExit"

Python/bytecodes.c

@@ -720,7 +720,6 @@ dummy_func(
  // NOTE: It's important that YIELD_VALUE never raises an exception!
  // The compiler treats any exception raised here as a failed close()
  // or throw() call.
- assert(oparg == STACK_LEVEL());
  assert(frame != &entry_frame);
  PyGenObject *gen = _PyFrame_GetGenerator(frame);
  gen->gi_frame_state = FRAME_SUSPENDED;

Python/compile.c

@@ -7162,9 +7162,6 @@ stackdepth(basicblock *entryblock, int code_flags)
  next = NULL;
  break;
  }
- if (instr->i_opcode == YIELD_VALUE){
- instr->i_oparg = depth;
- }
  }
  if (next != NULL){
  assert(BB_HAS_FALLTHROUGH(b));
@@ -7332,6 +7329,9 @@ label_exception_targets(basicblock *entryblock){
  }
  }
  else{
+ if (instr->i_opcode == YIELD_VALUE){
+ instr->i_oparg = except_stack->depth;
+ }
  instr->i_except = handler;
  }
  }

Python/opcode_metadata.h

@@ -59,7 +59,7 @@ static const struct{
  [GET_ANEXT] ={1, 2, DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
  [GET_AWAITABLE] ={1, 1, DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IB },
  [SEND] ={-1, -1, DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IB },
- [YIELD_VALUE] ={1, 1, DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IB },
+ [YIELD_VALUE] ={1, 1, DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
  [POP_EXCEPT] ={1, 0, DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
  [RERAISE] ={-1, -1, DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IB },
  [PREP_RERAISE_STAR] ={2, 1, DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },