GH-87849: Simplify stack effect of SEND and specialize it for generators and coroutines. (GH-101788)

15 files changed, 185 insertions, 99 deletions

diff --git a/Include/internal/pycore_code.h b/Include/internal/pycore_code.h
index a287250..10f1e32 100644
--- a/Include/internal/pycore_code.h
+++ b/Include/internal/pycore_code.h
@@ -92,6 +92,12 @@ typedef struct {
 
 #define INLINE_CACHE_ENTRIES_FOR_ITER CACHE_ENTRIES(_PyForIterCache)
 
+typedef struct {
+    uint16_t counter;
+} _PySendCache;
+
+#define INLINE_CACHE_ENTRIES_SEND CACHE_ENTRIES(_PySendCache)
+
 // Borrowed references to common callables:
 struct callable_cache {
     PyObject *isinstance;
@@ -233,6 +239,7 @@ extern void _Py_Specialize_CompareAndBranch(PyObject *lhs, PyObject *rhs,
 extern void _Py_Specialize_UnpackSequence(PyObject *seq, _Py_CODEUNIT *instr,
                                           int oparg);
 extern void _Py_Specialize_ForIter(PyObject *iter, _Py_CODEUNIT *instr, int oparg);
+extern void _Py_Specialize_Send(PyObject *receiver, _Py_CODEUNIT *instr);
 
 /* Finalizer function for static codeobjects used in deepfreeze.py */
 extern void _PyStaticCode_Fini(PyCodeObject *co);
diff --git a/Include/internal/pycore_opcode.h b/Include/internal/pycore_opcode.h
index 47c8472..5e65ade 100644
--- a/Include/internal/pycore_opcode.h
+++ b/Include/internal/pycore_opcode.h
@@ -50,6 +50,7 @@ const uint8_t _PyOpcode_Caches[256] = {
     [COMPARE_OP] = 1,
     [LOAD_GLOBAL] = 5,
     [BINARY_OP] = 1,
+    [SEND] = 1,
     [COMPARE_AND_BRANCH] = 1,
     [CALL] = 4,
 };
@@ -196,6 +197,7 @@ const uint8_t _PyOpcode_Deopt[256] = {
     [RETURN_GENERATOR] = RETURN_GENERATOR,
     [RETURN_VALUE] = RETURN_VALUE,
     [SEND] = SEND,
+    [SEND_GEN] = SEND,
     [SETUP_ANNOTATIONS] = SETUP_ANNOTATIONS,
     [SET_ADD] = SET_ADD,
     [SET_UPDATE] = SET_UPDATE,
@@ -395,7 +397,7 @@ static const char *const _PyOpcode_OpName[263] = {
     [SET_UPDATE] = "SET_UPDATE",
     [DICT_MERGE] = "DICT_MERGE",
     [DICT_UPDATE] = "DICT_UPDATE",
-    [166] = "<166>",
+    [SEND_GEN] = "SEND_GEN",
     [167] = "<167>",
     [168] = "<168>",
     [169] = "<169>",
@@ -496,7 +498,6 @@ static const char *const _PyOpcode_OpName[263] = {
 #endif
 
 #define EXTRA_CASES \
-    case 166: \
     case 167: \
     case 168: \
     case 169: \
diff --git a/Include/opcode.h b/Include/opcode.h
index 77ad7c224..d643741 100644
--- a/Include/opcode.h
+++ b/Include/opcode.h
@@ -187,6 +187,7 @@ extern "C" {
 #define UNPACK_SEQUENCE_LIST                   159
 #define UNPACK_SEQUENCE_TUPLE                  160
 #define UNPACK_SEQUENCE_TWO_TUPLE              161
+#define SEND_GEN                               166
 #define DO_TRACING                             255
 
 #define HAS_ARG(op) ((((op) >= HAVE_ARGUMENT) && (!IS_PSEUDO_OPCODE(op)))\
diff --git a/Lib/dis.py b/Lib/dis.py
index a692100..9edde6a 100644
--- a/Lib/dis.py
+++ b/Lib/dis.py
@@ -39,6 +39,7 @@ LOAD_GLOBAL = opmap['LOAD_GLOBAL']
 BINARY_OP = opmap['BINARY_OP']
 JUMP_BACKWARD = opmap['JUMP_BACKWARD']
 FOR_ITER = opmap['FOR_ITER']
+SEND = opmap['SEND']
 LOAD_ATTR = opmap['LOAD_ATTR']
 
 CACHE = opmap["CACHE"]
@@ -453,6 +454,7 @@ def _get_instructions_bytes(code, varname_from_oparg=None,
         argrepr = ''
         positions = Positions(*next(co_positions, ()))
         deop = _deoptop(op)
+        caches = _inline_cache_entries[deop]
         if arg is not None:
             #  Set argval to the dereferenced value of the argument when
             #  available, and argrepr to the string representation of argval.
@@ -478,8 +480,7 @@ def _get_instructions_bytes(code, varname_from_oparg=None,
             elif deop in hasjrel:
                 signed_arg = -arg if _is_backward_jump(deop) else arg
                 argval = offset + 2 + signed_arg*2
-                if deop == FOR_ITER:
-                    argval += 2
+                argval += 2 * caches
                 argrepr = "to " + repr(argval)
             elif deop in haslocal or deop in hasfree:
                 argval, argrepr = _get_name_info(arg, varname_from_oparg)
@@ -633,12 +634,12 @@ def findlabels(code):
     for offset, op, arg in _unpack_opargs(code):
         if arg is not None:
             deop = _deoptop(op)
+            caches = _inline_cache_entries[deop]
             if deop in hasjrel:
                 if _is_backward_jump(deop):
                     arg = -arg
                 label = offset + 2 + arg*2
-                if deop == FOR_ITER:
-                    label += 2
+                label += 2 * caches
             elif deop in hasjabs:
                 label = arg*2
             else:
diff --git a/Lib/importlib/_bootstrap_external.py b/Lib/importlib/_bootstrap_external.py
index 933c8c7..38d4a38 100644
--- a/Lib/importlib/_bootstrap_external.py
+++ b/Lib/importlib/_bootstrap_external.py
@@ -432,6 +432,7 @@ _code_type = type(_write_atomic.__code__)
 #     Python 3.12a5 3516 (Add COMPARE_AND_BRANCH instruction)
 #     Python 3.12a5 3517 (Change YIELD_VALUE oparg to exception block depth)
 #     Python 3.12a5 3518 (Add RETURN_CONST instruction)
+#     Python 3.12a5 3519 (Modify SEND instruction)
 
 #     Python 3.13 will start with 3550
 
@@ -444,7 +445,7 @@ _code_type = type(_write_atomic.__code__)
 # Whenever MAGIC_NUMBER is changed, the ranges in the magic_values array
 # in PC/launcher.c must also be updated.
 
-MAGIC_NUMBER = (3518).to_bytes(2, 'little') + b'\r\n'
+MAGIC_NUMBER = (3519).to_bytes(2, 'little') + b'\r\n'
 
 _RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # For import.c
 
diff --git a/Lib/opcode.py b/Lib/opcode.py
index 5f163d2..b69cd1b 100644
--- a/Lib/opcode.py
+++ b/Lib/opcode.py
@@ -167,7 +167,7 @@ def_op('COPY', 120)
 def_op('RETURN_CONST', 121)
 hasconst.append(121)
 def_op('BINARY_OP', 122)
-jrel_op('SEND', 123) # Number of bytes to skip
+jrel_op('SEND', 123)            # Number of words to skip
 def_op('LOAD_FAST', 124)        # Local variable number, no null check
 haslocal.append(124)
 def_op('STORE_FAST', 125)       # Local variable number
@@ -370,6 +370,9 @@ _specializations = {
         "UNPACK_SEQUENCE_TUPLE",
         "UNPACK_SEQUENCE_TWO_TUPLE",
     ],
+    "SEND": [
+        "SEND_GEN",
+    ],
 }
 _specialized_instructions = [
     opcode for family in _specializations.values() for opcode in family
@@ -429,6 +432,9 @@ _cache_format = {
     "STORE_SUBSCR": {
         "counter": 1,
     },
+    "SEND": {
+        "counter": 1,
+    },
 }
 
 _inline_cache_entries = [
diff --git a/Lib/test/test_dis.py b/Lib/test/test_dis.py
index 1050b15..9086824 100644
--- a/Lib/test/test_dis.py
+++ b/Lib/test/test_dis.py
@@ -475,11 +475,13 @@ dis_asyncwith = """\
            BEFORE_ASYNC_WITH
            GET_AWAITABLE            1
            LOAD_CONST               0 (None)
-        >> SEND                     3 (to 22)
+        >> SEND                     3 (to 24)
            YIELD_VALUE              2
            RESUME                   3
-           JUMP_BACKWARD_NO_INTERRUPT     4 (to 14)
-        >> POP_TOP
+           JUMP_BACKWARD_NO_INTERRUPT     5 (to 14)
+        >> SWAP                     2
+           POP_TOP
+           POP_TOP
 
 %3d        LOAD_CONST               1 (1)
            STORE_FAST               1 (x)
@@ -490,30 +492,33 @@ dis_asyncwith = """\
            CALL                     2
            GET_AWAITABLE            2
            LOAD_CONST               0 (None)
-        >> SEND                     3 (to 56)
+        >> SEND                     3 (to 64)
            YIELD_VALUE              2
            RESUME                   3
-           JUMP_BACKWARD_NO_INTERRUPT     4 (to 48)
+           JUMP_BACKWARD_NO_INTERRUPT     5 (to 54)
         >> POP_TOP
+           POP_TOP
 
 %3d        LOAD_CONST               2 (2)
            STORE_FAST               2 (y)
            RETURN_CONST             0 (None)
 
 %3d     >> CLEANUP_THROW
-           JUMP_BACKWARD           23 (to 22)
+           JUMP_BACKWARD           27 (to 24)
         >> CLEANUP_THROW
-           JUMP_BACKWARD            8 (to 56)
+           JUMP_BACKWARD            9 (to 64)
         >> PUSH_EXC_INFO
            WITH_EXCEPT_START
            GET_AWAITABLE            2
            LOAD_CONST               0 (None)
-        >> SEND                     4 (to 90)
+        >> SEND                     4 (to 102)
            YIELD_VALUE              3
            RESUME                   3
-           JUMP_BACKWARD_NO_INTERRUPT     4 (to 80)
+           JUMP_BACKWARD_NO_INTERRUPT     5 (to 90)
         >> CLEANUP_THROW
-        >> POP_JUMP_IF_TRUE         1 (to 94)
+        >> SWAP                     2
+           POP_TOP
+           POP_JUMP_IF_TRUE         1 (to 110)
            RERAISE                  2
         >> POP_TOP
            POP_EXCEPT
diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-02-10-15-54-57.gh-issue-87849.IUVvPz.rst b/Misc/NEWS.d/next/Core and Builtins/2023-02-10-15-54-57.gh-issue-87849.IUVvPz.rst
new file mode 100644
index 0000000..da5f3ff
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2023-02-10-15-54-57.gh-issue-87849.IUVvPz.rst
@@ -0,0 +1,3 @@
+Change the ``SEND`` instruction to leave the receiver on the stack. This
+allows the specialized form of ``SEND`` to skip the chain of C calls and jump
+directly to the ``RESUME`` in the generator or coroutine.
diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index 0e52a3e..581ed2d 100644
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -334,10 +334,10 @@ mark_stacks(PyCodeObject *code_obj, int len)
                     break;
                 }
                 case SEND:
-                    j = get_arg(code, i) + i + 1;
+                    j = get_arg(code, i) + i + INLINE_CACHE_ENTRIES_SEND + 1;
                     assert(j < len);
-                    assert(stacks[j] == UNINITIALIZED || stacks[j] == pop_value(next_stack));
-                    stacks[j] = pop_value(next_stack);
+                    assert(stacks[j] == UNINITIALIZED || stacks[j] == next_stack);
+                    stacks[j] = next_stack;
                     stacks[i+1] = next_stack;
                     break;
                 case JUMP_FORWARD:
diff --git a/Python/bytecodes.c b/Python/bytecodes.c
index 2b9f12f..429cd7f 100644
--- a/Python/bytecodes.c
+++ b/Python/bytecodes.c
@@ -680,51 +680,66 @@ dummy_func(
             PREDICT(LOAD_CONST);
         }
 
-        inst(SEND, (receiver, v -- receiver if (!jump), retval)) {
+        family(for_iter, INLINE_CACHE_ENTRIES_FOR_ITER) = {
+            SEND,
+            SEND_GEN,
+        };
+
+        inst(SEND, (unused/1, receiver, v -- receiver, retval)) {
+            #if ENABLE_SPECIALIZATION
+            _PySendCache *cache = (_PySendCache *)next_instr;
+            if (ADAPTIVE_COUNTER_IS_ZERO(cache->counter)) {
+                assert(cframe.use_tracing == 0);
+                next_instr--;
+                _Py_Specialize_Send(receiver, next_instr);
+                DISPATCH_SAME_OPARG();
+            }
+            STAT_INC(SEND, deferred);
+            DECREMENT_ADAPTIVE_COUNTER(cache->counter);
+            #endif  /* ENABLE_SPECIALIZATION */
             assert(frame != &entry_frame);
-            bool jump = false;
-            PySendResult gen_status;
-            if (tstate->c_tracefunc == NULL) {
-                gen_status = PyIter_Send(receiver, v, &retval);
-            } else {
-                if (Py_IsNone(v) && PyIter_Check(receiver)) {
-                    retval = Py_TYPE(receiver)->tp_iternext(receiver);
-                }
-                else {
-                    retval = PyObject_CallMethodOneArg(receiver, &_Py_ID(send), v);
-                }
-                if (retval == NULL) {
-                    if (tstate->c_tracefunc != NULL
-                            && _PyErr_ExceptionMatches(tstate, PyExc_StopIteration))
-                        call_exc_trace(tstate->c_tracefunc, tstate->c_traceobj, tstate, frame);
-                    if (_PyGen_FetchStopIterationValue(&retval) == 0) {
-                        gen_status = PYGEN_RETURN;
-                    }
-                    else {
-                        gen_status = PYGEN_ERROR;
-                    }
+            if (Py_IsNone(v) && PyIter_Check(receiver)) {
+                retval = Py_TYPE(receiver)->tp_iternext(receiver);
+            }
+            else {
+                retval = PyObject_CallMethodOneArg(receiver, &_Py_ID(send), v);
+            }
+            if (retval == NULL) {
+                if (tstate->c_tracefunc != NULL
+                        && _PyErr_ExceptionMatches(tstate, PyExc_StopIteration))
+                    call_exc_trace(tstate->c_tracefunc, tstate->c_traceobj, tstate, frame);
+                if (_PyGen_FetchStopIterationValue(&retval) == 0) {
+                    assert(retval != NULL);
+                    JUMPBY(oparg);
                 }
                 else {
-                    gen_status = PYGEN_NEXT;
+                    assert(retval == NULL);
+                    goto error;
                 }
             }
-            if (gen_status == PYGEN_ERROR) {
-                assert(retval == NULL);
-                goto error;
-            }
-            Py_DECREF(v);
-            if (gen_status == PYGEN_RETURN) {
-                assert(retval != NULL);
-                Py_DECREF(receiver);
-                JUMPBY(oparg);
-                jump = true;
-            }
             else {
-                assert(gen_status == PYGEN_NEXT);
                 assert(retval != NULL);
             }
         }
 
+        inst(SEND_GEN, (unused/1, receiver, v -- receiver)) {
+            assert(cframe.use_tracing == 0);
+            PyGenObject *gen = (PyGenObject *)receiver;
+            DEOPT_IF(Py_TYPE(gen) != &PyGen_Type &&
+                     Py_TYPE(gen) != &PyCoro_Type, SEND);
+            DEOPT_IF(gen->gi_frame_state >= FRAME_EXECUTING, SEND);
+            STAT_INC(SEND, hit);
+            _PyInterpreterFrame *gen_frame = (_PyInterpreterFrame *)gen->gi_iframe;
+            frame->yield_offset = oparg;
+            STACK_SHRINK(1);
+            _PyFrame_StackPush(gen_frame, v);
+            gen->gi_frame_state = FRAME_EXECUTING;
+            gen->gi_exc_state.previous_item = tstate->exc_info;
+            tstate->exc_info = &gen->gi_exc_state;
+            JUMPBY(INLINE_CACHE_ENTRIES_SEND + oparg);
+            DISPATCH_INLINED(gen_frame);
+        }
+
         inst(YIELD_VALUE, (retval -- unused)) {
             // NOTE: It's important that YIELD_VALUE never raises an exception!
             // The compiler treats any exception raised here as a failed close()
@@ -796,12 +811,13 @@ dummy_func(
             }
         }
 
-        inst(CLEANUP_THROW, (sub_iter, last_sent_val, exc_value -- value)) {
+        inst(CLEANUP_THROW, (sub_iter, last_sent_val, exc_value -- none, value)) {
             assert(throwflag);
             assert(exc_value && PyExceptionInstance_Check(exc_value));
             if (PyErr_GivenExceptionMatches(exc_value, PyExc_StopIteration)) {
                 value = Py_NewRef(((PyStopIterationObject *)exc_value)->value);
                 DECREF_INPUTS();
+                none = Py_NewRef(Py_None);
             }
             else {
                 _PyErr_SetRaisedException(tstate, Py_NewRef(exc_value));
diff --git a/Python/compile.c b/Python/compile.c
index a3c915c..b49eda3 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -1789,6 +1789,8 @@ compiler_add_yield_from(struct compiler *c, location loc, int await)
     ADDOP(c, loc, CLEANUP_THROW);
 
     USE_LABEL(c, exit);
+    ADDOP_I(c, loc, SWAP, 2);
+    ADDOP(c, loc, POP_TOP);
     return SUCCESS;
 }
 
diff --git a/Python/generated_cases.c.h b/Python/generated_cases.c.h
index a224d4e..093ebff 100644
--- a/Python/generated_cases.c.h
+++ b/Python/generated_cases.c.h
@@ -882,57 +882,69 @@
         }
 
         TARGET(SEND) {
+            PREDICTED(SEND);
             PyObject *v = PEEK(1);
             PyObject *receiver = PEEK(2);
             PyObject *retval;
+            #if ENABLE_SPECIALIZATION
+            _PySendCache *cache = (_PySendCache *)next_instr;
+            if (ADAPTIVE_COUNTER_IS_ZERO(cache->counter)) {
+                assert(cframe.use_tracing == 0);
+                next_instr--;
+                _Py_Specialize_Send(receiver, next_instr);
+                DISPATCH_SAME_OPARG();
+            }
+            STAT_INC(SEND, deferred);
+            DECREMENT_ADAPTIVE_COUNTER(cache->counter);
+            #endif  /* ENABLE_SPECIALIZATION */
             assert(frame != &entry_frame);
-            bool jump = false;
-            PySendResult gen_status;
-            if (tstate->c_tracefunc == NULL) {
-                gen_status = PyIter_Send(receiver, v, &retval);
-            } else {
-                if (Py_IsNone(v) && PyIter_Check(receiver)) {
-                    retval = Py_TYPE(receiver)->tp_iternext(receiver);
-                }
-                else {
-                    retval = PyObject_CallMethodOneArg(receiver, &_Py_ID(send), v);
-                }
-                if (retval == NULL) {
-                    if (tstate->c_tracefunc != NULL
-                            && _PyErr_ExceptionMatches(tstate, PyExc_StopIteration))
-                        call_exc_trace(tstate->c_tracefunc, tstate->c_traceobj, tstate, frame);
-                    if (_PyGen_FetchStopIterationValue(&retval) == 0) {
-                        gen_status = PYGEN_RETURN;
-                    }
-                    else {
-                        gen_status = PYGEN_ERROR;
-                    }
+            if (Py_IsNone(v) && PyIter_Check(receiver)) {
+                retval = Py_TYPE(receiver)->tp_iternext(receiver);
+            }
+            else {
+                retval = PyObject_CallMethodOneArg(receiver, &_Py_ID(send), v);
+            }
+            if (retval == NULL) {
+                if (tstate->c_tracefunc != NULL
+                        && _PyErr_ExceptionMatches(tstate, PyExc_StopIteration))
+                    call_exc_trace(tstate->c_tracefunc, tstate->c_traceobj, tstate, frame);
+                if (_PyGen_FetchStopIterationValue(&retval) == 0) {
+                    assert(retval != NULL);
+                    JUMPBY(oparg);
                 }
                 else {
-                    gen_status = PYGEN_NEXT;
+                    assert(retval == NULL);
+                    goto error;
                 }
             }
-            if (gen_status == PYGEN_ERROR) {
-                assert(retval == NULL);
-                goto error;
-            }
-            Py_DECREF(v);
-            if (gen_status == PYGEN_RETURN) {
-                assert(retval != NULL);
-                Py_DECREF(receiver);
-                JUMPBY(oparg);
-                jump = true;
-            }
             else {
-                assert(gen_status == PYGEN_NEXT);
                 assert(retval != NULL);
             }
-            STACK_SHRINK(1);
-            STACK_GROW(((!jump) ? 1 : 0));
             POKE(1, retval);
+            JUMPBY(1);
             DISPATCH();
         }
 
+        TARGET(SEND_GEN) {
+            PyObject *v = PEEK(1);
+            PyObject *receiver = PEEK(2);
+            assert(cframe.use_tracing == 0);
+            PyGenObject *gen = (PyGenObject *)receiver;
+            DEOPT_IF(Py_TYPE(gen) != &PyGen_Type &&
+                     Py_TYPE(gen) != &PyCoro_Type, SEND);
+            DEOPT_IF(gen->gi_frame_state >= FRAME_EXECUTING, SEND);
+            STAT_INC(SEND, hit);
+            _PyInterpreterFrame *gen_frame = (_PyInterpreterFrame *)gen->gi_iframe;
+            frame->yield_offset = oparg;
+            STACK_SHRINK(1);
+            _PyFrame_StackPush(gen_frame, v);
+            gen->gi_frame_state = FRAME_EXECUTING;
+            gen->gi_exc_state.previous_item = tstate->exc_info;
+            tstate->exc_info = &gen->gi_exc_state;
+            JUMPBY(INLINE_CACHE_ENTRIES_SEND + oparg);
+            DISPATCH_INLINED(gen_frame);
+        }
+
         TARGET(YIELD_VALUE) {
             PyObject *retval = PEEK(1);
             // NOTE: It's important that YIELD_VALUE never raises an exception!
@@ -1026,6 +1038,7 @@
             PyObject *exc_value = PEEK(1);
             PyObject *last_sent_val = PEEK(2);
             PyObject *sub_iter = PEEK(3);
+            PyObject *none;
             PyObject *value;
             assert(throwflag);
             assert(exc_value && PyExceptionInstance_Check(exc_value));
@@ -1034,13 +1047,15 @@
                 Py_DECREF(sub_iter);
                 Py_DECREF(last_sent_val);
                 Py_DECREF(exc_value);
+                none = Py_NewRef(Py_None);
             }
             else {
                 _PyErr_SetRaisedException(tstate, Py_NewRef(exc_value));
                 goto exception_unwind;
             }
-            STACK_SHRINK(2);
+            STACK_SHRINK(1);
             POKE(1, value);
+            POKE(2, none);
             DISPATCH();
         }
 
diff --git a/Python/opcode_metadata.h b/Python/opcode_metadata.h
index db1dfd3..d622eb1 100644
--- a/Python/opcode_metadata.h
+++ b/Python/opcode_metadata.h
@@ -104,6 +104,8 @@ _PyOpcode_num_popped(int opcode, int oparg, bool jump) {
             return 1;
         case SEND:
             return 2;
+        case SEND_GEN:
+            return 2;
         case YIELD_VALUE:
             return 1;
         case POP_EXCEPT:
@@ -453,7 +455,9 @@ _PyOpcode_num_pushed(int opcode, int oparg, bool jump) {
         case GET_AWAITABLE:
             return 1;
         case SEND:
-            return ((!jump) ? 1 : 0) + 1;
+            return 2;
+        case SEND_GEN:
+            return 1;
         case YIELD_VALUE:
             return 1;
         case POP_EXCEPT:
@@ -465,7 +469,7 @@ _PyOpcode_num_pushed(int opcode, int oparg, bool jump) {
         case END_ASYNC_FOR:
             return 0;
         case CLEANUP_THROW:
-            return 1;
+            return 2;
         case LOAD_ASSERTION_ERROR:
             return 1;
         case LOAD_BUILD_CLASS:
@@ -763,7 +767,8 @@ const struct opcode_metadata _PyOpcode_opcode_metadata[256] = {
     [GET_AITER] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
     [GET_ANEXT] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
     [GET_AWAITABLE] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IB },
-    [SEND] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IB },
+    [SEND] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IBC },
+    [SEND_GEN] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IBC },
     [YIELD_VALUE] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
     [POP_EXCEPT] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IX },
     [RERAISE] = { DIR_NONE, DIR_NONE, DIR_NONE, true, INSTR_FMT_IB },
diff --git a/Python/opcode_targets.h b/Python/opcode_targets.h
index eceb246..301ec6e 100644
--- a/Python/opcode_targets.h
+++ b/Python/opcode_targets.h
@@ -165,7 +165,7 @@ static void *opcode_targets[256] = {
     &&TARGET_SET_UPDATE,
     &&TARGET_DICT_MERGE,
     &&TARGET_DICT_UPDATE,
-    &&_unknown_opcode,
+    &&TARGET_SEND_GEN,
     &&_unknown_opcode,
     &&_unknown_opcode,
     &&_unknown_opcode,
diff --git a/Python/specialize.c b/Python/specialize.c
index 908ad6d..4ede312 100644
--- a/Python/specialize.c
+++ b/Python/specialize.c
@@ -128,6 +128,7 @@ print_spec_stats(FILE *out, OpcodeStats *stats)
     fprintf(out, "opcode[%d].specializable : 1\n", BINARY_SLICE);
     fprintf(out, "opcode[%d].specializable : 1\n", COMPARE_OP);
     fprintf(out, "opcode[%d].specializable : 1\n", STORE_SLICE);
+    fprintf(out, "opcode[%d].specializable : 1\n", SEND);
     for (int i = 0; i < 256; i++) {
         if (_PyOpcode_Caches[i]) {
             fprintf(out, "opcode[%d].specializable : 1\n", i);
@@ -1084,7 +1085,7 @@ PyObject *descr, DescriptorClassification kind)
             if (dict) {
                 SPECIALIZATION_FAIL(LOAD_ATTR, SPEC_FAIL_ATTR_NOT_MANAGED_DICT);
                 return 0;
-            }  
+            }
             assert(owner_cls->tp_dictoffset > 0);
             assert(owner_cls->tp_dictoffset <= INT16_MAX);
             _py_set_opcode(instr, LOAD_ATTR_METHOD_LAZY_DICT);
@@ -2183,3 +2184,25 @@ success:
     STAT_INC(FOR_ITER, success);
     cache->counter = adaptive_counter_cooldown();
 }
+
+void
+_Py_Specialize_Send(PyObject *receiver, _Py_CODEUNIT *instr)
+{
+    assert(ENABLE_SPECIALIZATION);
+    assert(_PyOpcode_Caches[SEND] == INLINE_CACHE_ENTRIES_SEND);
+    _PySendCache *cache = (_PySendCache *)(instr + 1);
+    PyTypeObject *tp = Py_TYPE(receiver);
+    if (tp == &PyGen_Type || tp == &PyCoro_Type) {
+        _py_set_opcode(instr, SEND_GEN);
+        goto success;
+    }
+    SPECIALIZATION_FAIL(SEND,
+                        _PySpecialization_ClassifyIterator(receiver));
+    STAT_INC(SEND, failure);
+    _py_set_opcode(instr, SEND);
+    cache->counter = adaptive_counter_backoff(cache->counter);
+    return;
+success:
+    STAT_INC(SEND, success);
+    cache->counter = adaptive_counter_cooldown();
+}