diff --git a/Include/cpython/code.h b/Include/cpython/code.h
index 0cf49f06c87..fba9296aedc 100644
--- a/Include/cpython/code.h
+++ b/Include/cpython/code.h
@@ -19,21 +19,35 @@ extern "C" {
 typedef union {
     uint16_t cache;
     struct {
-        uint8_t opcode;
-        uint8_t oparg;
-    };
+        uint8_t code;
+        uint8_t arg;
+    } op;
 } _Py_CODEUNIT;
 
-#define _Py_OPCODE(word) ((word).opcode)
-#define _Py_OPARG(word) ((word).oparg)
+
+/* These macros only remain defined for compatibility. */
+#define _Py_OPCODE(word) ((word).op.code)
+#define _Py_OPARG(word) ((word).op.arg)
+
+static inline _Py_CODEUNIT
+_py_make_codeunit(uint8_t opcode, uint8_t oparg)
+{
+    // No designated initialisers because of C++ compat
+    _Py_CODEUNIT word;
+    word.op.code = opcode;
+    word.op.arg = oparg;
+    return word;
+}
 
 static inline void
 _py_set_opcode(_Py_CODEUNIT *word, uint8_t opcode)
 {
-    word->opcode = opcode;
+    word->op.code = opcode;
 }
 
-#define _Py_SET_OPCODE(word, opcode) _py_set_opocde(&(word), opcode)
+#define _Py_MAKE_CODEUNIT(opcode, oparg) _py_make_codeunit((opcode), (oparg))
+#define _Py_SET_OPCODE(word, opcode) _py_set_opcode(&(word), (opcode))
+
 
 typedef struct {
     PyObject *_co_code;
diff --git a/Misc/NEWS.d/next/C API/2023-02-14-15-53-01.gh-issue-101907.HgF1N2.rst b/Misc/NEWS.d/next/C API/2023-02-14-15-53-01.gh-issue-101907.HgF1N2.rst
new file mode 100644
index 00000000000..cfc0d72cdbc
--- /dev/null
+++ b/Misc/NEWS.d/next/C API/2023-02-14-15-53-01.gh-issue-101907.HgF1N2.rst	
@@ -0,0 +1 @@
+Removes use of non-standard C++ extension in public header files.
diff --git a/Objects/codeobject.c b/Objects/codeobject.c
index ab31b6582cd..a03b14edea8 100644
--- a/Objects/codeobject.c
+++ b/Objects/codeobject.c
@@ -413,7 +413,7 @@ init_code(PyCodeObject *co, struct _PyCodeConstructor *con)
            PyBytes_GET_SIZE(con->code));
     int entry_point = 0;
     while (entry_point < Py_SIZE(co) &&
-        _Py_OPCODE(_PyCode_CODE(co)[entry_point]) != RESUME) {
+        _PyCode_CODE(co)[entry_point].op.code != RESUME) {
         entry_point++;
     }
     co->_co_firsttraceable = entry_point;
@@ -1505,12 +1505,12 @@ deopt_code(_Py_CODEUNIT *instructions, Py_ssize_t len)
 {
     for (int i = 0; i < len; i++) {
         _Py_CODEUNIT instruction = instructions[i];
-        int opcode = _PyOpcode_Deopt[_Py_OPCODE(instruction)];
+        int opcode = _PyOpcode_Deopt[instruction.op.code];
         int caches = _PyOpcode_Caches[opcode];
-        instructions[i].opcode = opcode;
+        instructions[i].op.code = opcode;
         while (caches--) {
-            instructions[++i].opcode = CACHE;
-            instructions[i].oparg = 0;
+            instructions[++i].op.code = CACHE;
+            instructions[i].op.arg = 0;
         }
     }
 }
@@ -1763,13 +1763,13 @@ code_richcompare(PyObject *self, PyObject *other, int op)
     for (int i = 0; i < Py_SIZE(co); i++) {
         _Py_CODEUNIT co_instr = _PyCode_CODE(co)[i];
         _Py_CODEUNIT cp_instr = _PyCode_CODE(cp)[i];
-        co_instr.opcode = _PyOpcode_Deopt[_Py_OPCODE(co_instr)];
-        cp_instr.opcode =_PyOpcode_Deopt[_Py_OPCODE(cp_instr)];
+        co_instr.op.code = _PyOpcode_Deopt[co_instr.op.code];
+        cp_instr.op.code = _PyOpcode_Deopt[cp_instr.op.code];
         eq = co_instr.cache == cp_instr.cache;
         if (!eq) {
             goto unequal;
         }
-        i += _PyOpcode_Caches[_Py_OPCODE(co_instr)];
+        i += _PyOpcode_Caches[co_instr.op.code];
     }
 
     /* compare constants */
@@ -1848,9 +1848,9 @@ code_hash(PyCodeObject *co)
     SCRAMBLE_IN(co->co_firstlineno);
     SCRAMBLE_IN(Py_SIZE(co));
     for (int i = 0; i < Py_SIZE(co); i++) {
-        int deop = _PyOpcode_Deopt[_Py_OPCODE(_PyCode_CODE(co)[i])];
+        int deop = _PyOpcode_Deopt[_PyCode_CODE(co)[i].op.code];
         SCRAMBLE_IN(deop);
-        SCRAMBLE_IN(_Py_OPARG(_PyCode_CODE(co)[i]));
+        SCRAMBLE_IN(_PyCode_CODE(co)[i].op.arg);
         i += _PyOpcode_Caches[deop];
     }
     if ((Py_hash_t)uhash == -1) {
diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index 581ed2d214c..34143c9a40b 100644
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -111,13 +111,13 @@ static unsigned int
 get_arg(const _Py_CODEUNIT *codestr, Py_ssize_t i)
 {
     _Py_CODEUNIT word;
-    unsigned int oparg = _Py_OPARG(codestr[i]);
-    if (i >= 1 && _Py_OPCODE(word = codestr[i-1]) == EXTENDED_ARG) {
-        oparg |= _Py_OPARG(word) << 8;
-        if (i >= 2 && _Py_OPCODE(word = codestr[i-2]) == EXTENDED_ARG) {
-            oparg |= _Py_OPARG(word) << 16;
-            if (i >= 3 && _Py_OPCODE(word = codestr[i-3]) == EXTENDED_ARG) {
-                oparg |= _Py_OPARG(word) << 24;
+    unsigned int oparg = codestr[i].op.arg;
+    if (i >= 1 && (word = codestr[i-1]).op.code == EXTENDED_ARG) {
+        oparg |= word.op.arg << 8;
+        if (i >= 2 && (word = codestr[i-2]).op.code == EXTENDED_ARG) {
+            oparg |= word.op.arg << 16;
+            if (i >= 3 && (word = codestr[i-3]).op.code == EXTENDED_ARG) {
+                oparg |= word.op.arg << 24;
             }
         }
     }
@@ -304,7 +304,7 @@ mark_stacks(PyCodeObject *code_obj, int len)
             if (next_stack == UNINITIALIZED) {
                 continue;
             }
-            opcode = _Py_OPCODE(code[i]);
+            opcode = code[i].op.code;
             switch (opcode) {
                 case JUMP_IF_FALSE_OR_POP:
                 case JUMP_IF_TRUE_OR_POP:
@@ -610,7 +610,7 @@ _PyFrame_GetState(PyFrameObject *frame)
             if (_PyInterpreterFrame_LASTI(frame->f_frame) < 0) {
                 return FRAME_CREATED;
             }
-            switch (_Py_OPCODE(*frame->f_frame->prev_instr))
+            switch (frame->f_frame->prev_instr->op.code)
             {
                 case COPY_FREE_VARS:
                 case MAKE_CELL:
@@ -1092,8 +1092,8 @@ _PyFrame_OpAlreadyRan(_PyInterpreterFrame *frame, int opcode, int oparg)
     for (_Py_CODEUNIT *instruction = _PyCode_CODE(frame->f_code);
          instruction < frame->prev_instr; instruction++)
     {
-        int check_opcode = _PyOpcode_Deopt[_Py_OPCODE(*instruction)];
-        check_oparg |= _Py_OPARG(*instruction);
+        int check_opcode = _PyOpcode_Deopt[instruction->op.code];
+        check_oparg |= instruction->op.arg;
         if (check_opcode == opcode && check_oparg == oparg) {
             return 1;
         }
@@ -1117,7 +1117,7 @@ frame_init_get_vars(_PyInterpreterFrame *frame)
     // here:
     PyCodeObject *co = frame->f_code;
     int lasti = _PyInterpreterFrame_LASTI(frame);
-    if (!(lasti < 0 && _Py_OPCODE(_PyCode_CODE(co)[0]) == COPY_FREE_VARS
+    if (!(lasti < 0 && _PyCode_CODE(co)->op.code == COPY_FREE_VARS
           && PyFunction_Check(frame->f_funcobj)))
     {
         /* Free vars are initialized */
diff --git a/Objects/genobject.c b/Objects/genobject.c
index 35246653c45..aec64ca7004 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -332,11 +332,11 @@ _PyGen_yf(PyGenObject *gen)
             /* Return immediately if the frame didn't start yet. SEND
                always come after LOAD_CONST: a code object should not start
                with SEND */
-            assert(_Py_OPCODE(_PyCode_CODE(gen->gi_code)[0]) != SEND);
+            assert(_PyCode_CODE(gen->gi_code)[0].op.code != SEND);
             return NULL;
         }
         _Py_CODEUNIT next = frame->prev_instr[1];
-        if (_Py_OPCODE(next) != RESUME || _Py_OPARG(next) < 2)
+        if (next.op.code != RESUME || next.op.arg < 2)
         {
             /* Not in a yield from */
             return NULL;
@@ -371,9 +371,9 @@ gen_close(PyGenObject *gen, PyObject *args)
     _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;
+    if (err == 0 && frame->prev_instr[0].op.code == YIELD_VALUE) {
+        assert(frame->prev_instr[1].op.code == RESUME);
+        int exception_handler_depth = frame->prev_instr[0].op.code;
         assert(exception_handler_depth > 0);
         /* We can safely ignore the outermost try block
          * as it automatically generated to handle
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index f2e8092aa37..2d1220a0695 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -9507,8 +9507,8 @@ super_init_without_args(_PyInterpreterFrame *cframe, PyCodeObject *co,
         if (_PyInterpreterFrame_LASTI(cframe) >= 0) {
             // MAKE_CELL and COPY_FREE_VARS have no quickened forms, so no need
             // to use _PyOpcode_Deopt here:
-            assert(_Py_OPCODE(_PyCode_CODE(co)[0]) == MAKE_CELL ||
-                   _Py_OPCODE(_PyCode_CODE(co)[0]) == COPY_FREE_VARS);
+            assert(_PyCode_CODE(co)[0].op.code == MAKE_CELL ||
+                   _PyCode_CODE(co)[0].op.code == COPY_FREE_VARS);
             assert(PyCell_Check(firstarg));
             firstarg = PyCell_GET(firstarg);
         }
diff --git a/Python/bytecodes.c b/Python/bytecodes.c
index 84747f1758e..c5959f2f994 100644
--- a/Python/bytecodes.c
+++ b/Python/bytecodes.c
@@ -246,9 +246,9 @@ dummy_func(
             DEOPT_IF(!PyUnicode_CheckExact(left), BINARY_OP);
             DEOPT_IF(Py_TYPE(right) != Py_TYPE(left), BINARY_OP);
             _Py_CODEUNIT true_next = next_instr[INLINE_CACHE_ENTRIES_BINARY_OP];
-            assert(_Py_OPCODE(true_next) == STORE_FAST ||
-                   _Py_OPCODE(true_next) == STORE_FAST__LOAD_FAST);
-            PyObject **target_local = &GETLOCAL(_Py_OPARG(true_next));
+            assert(true_next.op.code == STORE_FAST ||
+                   true_next.op.code == STORE_FAST__LOAD_FAST);
+            PyObject **target_local = &GETLOCAL(true_next.op.arg);
             DEOPT_IF(*target_local != left, BINARY_OP);
             STAT_INC(BINARY_OP, hit);
             /* Handle `left = left + right` or `left += right` for str.
@@ -1748,10 +1748,10 @@ dummy_func(
             Py_DECREF(left);
             Py_DECREF(right);
             ERROR_IF(cond == NULL, error);
-            assert(_Py_OPCODE(next_instr[1]) == POP_JUMP_IF_FALSE ||
-                   _Py_OPCODE(next_instr[1]) == POP_JUMP_IF_TRUE);
-            bool jump_on_true = _Py_OPCODE(next_instr[1]) == POP_JUMP_IF_TRUE;
-            int offset = _Py_OPARG(next_instr[1]);
+            assert(next_instr[1].op.code == POP_JUMP_IF_FALSE ||
+                   next_instr[1].op.code == POP_JUMP_IF_TRUE);
+            bool jump_on_true = next_instr[1].op.code == POP_JUMP_IF_TRUE;
+            int offset = next_instr[1].op.arg;
             int err = PyObject_IsTrue(cond);
             Py_DECREF(cond);
             if (err < 0) {
@@ -1774,7 +1774,7 @@ dummy_func(
             _Py_DECREF_SPECIALIZED(left, _PyFloat_ExactDealloc);
             _Py_DECREF_SPECIALIZED(right, _PyFloat_ExactDealloc);
             if (sign_ish & oparg) {
-                int offset = _Py_OPARG(next_instr[1]);
+                int offset = next_instr[1].op.arg;
                 JUMPBY(offset);
             }
         }
@@ -1795,7 +1795,7 @@ dummy_func(
             _Py_DECREF_SPECIALIZED(left, (destructor)PyObject_Free);
             _Py_DECREF_SPECIALIZED(right, (destructor)PyObject_Free);
             if (sign_ish & oparg) {
-                int offset = _Py_OPARG(next_instr[1]);
+                int offset = next_instr[1].op.arg;
                 JUMPBY(offset);
             }
         }
@@ -1814,7 +1814,7 @@ dummy_func(
             assert((oparg & 0xf) == COMPARISON_NOT_EQUALS || (oparg & 0xf) == COMPARISON_EQUALS);
             assert(COMPARISON_NOT_EQUALS + 1 == COMPARISON_EQUALS);
             if ((res + COMPARISON_NOT_EQUALS) & oparg) {
-                int offset = _Py_OPARG(next_instr[1]);
+                int offset = next_instr[1].op.arg;
                 JUMPBY(offset);
             }
         }
@@ -2122,7 +2122,7 @@ dummy_func(
                     _PyErr_Clear(tstate);
                 }
                 /* iterator ended normally */
-                assert(_Py_OPCODE(next_instr[INLINE_CACHE_ENTRIES_FOR_ITER + oparg]) == END_FOR);
+                assert(next_instr[INLINE_CACHE_ENTRIES_FOR_ITER + oparg].op.code == END_FOR);
                 Py_DECREF(iter);
                 STACK_SHRINK(1);
                 /* Jump forward oparg, then skip following END_FOR instruction */
@@ -2186,7 +2186,7 @@ dummy_func(
             DEOPT_IF(Py_TYPE(r) != &PyRangeIter_Type, FOR_ITER);
             STAT_INC(FOR_ITER, hit);
             _Py_CODEUNIT next = next_instr[INLINE_CACHE_ENTRIES_FOR_ITER];
-            assert(_PyOpcode_Deopt[_Py_OPCODE(next)] == STORE_FAST);
+            assert(_PyOpcode_Deopt[next.op.code] == STORE_FAST);
             if (r->len <= 0) {
                 STACK_SHRINK(1);
                 Py_DECREF(r);
@@ -2197,7 +2197,7 @@ dummy_func(
                 long value = r->start;
                 r->start = value + r->step;
                 r->len--;
-                if (_PyLong_AssignValue(&GETLOCAL(_Py_OPARG(next)), value) < 0) {
+                if (_PyLong_AssignValue(&GETLOCAL(next.op.arg), value) < 0) {
                     goto error;
                 }
                 // The STORE_FAST is already done.
@@ -2220,7 +2220,7 @@ dummy_func(
             gen->gi_exc_state.previous_item = tstate->exc_info;
             tstate->exc_info = &gen->gi_exc_state;
             JUMPBY(INLINE_CACHE_ENTRIES_FOR_ITER + oparg);
-            assert(_Py_OPCODE(*next_instr) == END_FOR);
+            assert(next_instr->op.code == END_FOR);
             DISPATCH_INLINED(gen_frame);
         }
 
@@ -2809,7 +2809,7 @@ dummy_func(
             STACK_SHRINK(3);
             // CALL + POP_TOP
             JUMPBY(INLINE_CACHE_ENTRIES_CALL + 1);
-            assert(_Py_OPCODE(next_instr[-1]) == POP_TOP);
+            assert(next_instr[-1].op.code == POP_TOP);
             DISPATCH();
         }
 
@@ -3118,8 +3118,8 @@ dummy_func(
         inst(EXTENDED_ARG, (--)) {
             assert(oparg);
             assert(cframe.use_tracing == 0);
-            opcode = _Py_OPCODE(*next_instr);
-            oparg = oparg << 8 | _Py_OPARG(*next_instr);
+            opcode = next_instr->op.code;
+            oparg = oparg << 8 | next_instr->op.arg;
             PRE_DISPATCH_GOTO();
             DISPATCH_GOTO();
         }
diff --git a/Python/ceval.c b/Python/ceval.c
index 308ef52259d..b85231a1df8 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -132,8 +132,8 @@ lltrace_instruction(_PyInterpreterFrame *frame,
        objects enters the interpreter recursively. It is also slow.
        So you might want to comment it out. */
     dump_stack(frame, stack_pointer);
-    int oparg = _Py_OPARG(*next_instr);
-    int opcode = _Py_OPCODE(*next_instr);
+    int oparg = next_instr->op.arg;
+    int opcode = next_instr->op.code;
     const char *opname = _PyOpcode_OpName[opcode];
     assert(opname != NULL);
     int offset = (int)(next_instr - _PyCode_CODE(frame->f_code));
@@ -920,8 +920,8 @@ handle_eval_breaker:
             // CPython hasn't ever traced the instruction after an EXTENDED_ARG.
             // Inline the EXTENDED_ARG here, so we can avoid branching there:
             INSTRUCTION_START(EXTENDED_ARG);
-            opcode = _Py_OPCODE(*next_instr);
-            oparg = oparg << 8 | _Py_OPARG(*next_instr);
+            opcode = next_instr->op.code;
+            oparg = oparg << 8 | next_instr->op.arg;
             // Make sure the next instruction isn't a RESUME, since that needs
             // to trace properly (and shouldn't have an EXTENDED_ARG, anyways):
             assert(opcode != RESUME);
@@ -946,7 +946,7 @@ handle_eval_breaker:
 #endif
             /* Tell C compilers not to hold the opcode variable in the loop.
                next_instr points the current instruction without TARGET(). */
-            opcode = _Py_OPCODE(*next_instr);
+            opcode = next_instr->op.code;
             _PyErr_Format(tstate, PyExc_SystemError,
                           "%U:%d: unknown opcode %d",
                           frame->f_code->co_filename,
@@ -2196,7 +2196,7 @@ maybe_call_line_trace(Py_tracefunc func, PyObject *obj,
             (_PyInterpreterFrame_LASTI(frame) < instr_prev &&
              // SEND has no quickened forms, so no need to use _PyOpcode_Deopt
              // here:
-             _Py_OPCODE(*frame->prev_instr) != SEND);
+             frame->prev_instr->op.code != SEND);
         if (trace) {
             result = call_trace(func, obj, tstate, frame, PyTrace_LINE, Py_None);
         }
diff --git a/Python/ceval_macros.h b/Python/ceval_macros.h
index 691bf8e1caa..ac1fec77dac 100644
--- a/Python/ceval_macros.h
+++ b/Python/ceval_macros.h
@@ -100,7 +100,7 @@
 
 #define DISPATCH_SAME_OPARG() \
     { \
-        opcode = _Py_OPCODE(*next_instr); \
+        opcode = next_instr->op.code; \
         PRE_DISPATCH_GOTO(); \
         opcode |= cframe.use_tracing OR_DTRACE_LINE; \
         DISPATCH_GOTO(); \
@@ -143,8 +143,8 @@ GETITEM(PyObject *v, Py_ssize_t i) {
 #define INSTR_OFFSET() ((int)(next_instr - _PyCode_CODE(frame->f_code)))
 #define NEXTOPARG()  do { \
         _Py_CODEUNIT word = *next_instr; \
-        opcode = _Py_OPCODE(word); \
-        oparg = _Py_OPARG(word); \
+        opcode = word.op.code; \
+        oparg = word.op.arg; \
     } while (0)
 #define JUMPTO(x)       (next_instr = _PyCode_CODE(frame->f_code) + (x))
 #define JUMPBY(x)       (next_instr += (x))
@@ -180,14 +180,14 @@ GETITEM(PyObject *v, Py_ssize_t i) {
 #if USE_COMPUTED_GOTOS
 #define PREDICT(op)             if (0) goto PREDICT_ID(op)
 #else
-#define PREDICT(op) \
+#define PREDICT(next_op) \
     do { \
         _Py_CODEUNIT word = *next_instr; \
-        opcode = _Py_OPCODE(word) | cframe.use_tracing OR_DTRACE_LINE; \
-        if (opcode == op) { \
-            oparg = _Py_OPARG(word); \
-            INSTRUCTION_START(op); \
-            goto PREDICT_ID(op); \
+        opcode = word.op.code | cframe.use_tracing OR_DTRACE_LINE; \
+        if (opcode == next_op) { \
+            oparg = word.op.arg; \
+            INSTRUCTION_START(next_op); \
+            goto PREDICT_ID(next_op); \
         } \
     } while(0)
 #endif
diff --git a/Python/compile.c b/Python/compile.c
index c3b344c7af2..3f620beb0d0 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -274,31 +274,31 @@ write_instr(_Py_CODEUNIT *codestr, struct instr *instruction, int ilen)
     int caches = _PyOpcode_Caches[opcode];
     switch (ilen - caches) {
         case 4:
-            codestr->opcode = EXTENDED_ARG;
-            codestr->oparg = (oparg >> 24) & 0xFF;
+            codestr->op.code = EXTENDED_ARG;
+            codestr->op.arg = (oparg >> 24) & 0xFF;
             codestr++;
             /* fall through */
         case 3:
-            codestr->opcode = EXTENDED_ARG;
-            codestr->oparg = (oparg >> 16) & 0xFF;
+            codestr->op.code = EXTENDED_ARG;
+            codestr->op.arg = (oparg >> 16) & 0xFF;
             codestr++;
             /* fall through */
         case 2:
-            codestr->opcode = EXTENDED_ARG;
-            codestr->oparg = (oparg >> 8) & 0xFF;
+            codestr->op.code = EXTENDED_ARG;
+            codestr->op.arg = (oparg >> 8) & 0xFF;
             codestr++;
             /* fall through */
         case 1:
-            codestr->opcode = opcode;
-            codestr->oparg = oparg & 0xFF;
+            codestr->op.code = opcode;
+            codestr->op.arg = oparg & 0xFF;
             codestr++;
             break;
         default:
             Py_UNREACHABLE();
     }
     while (caches--) {
-        codestr->opcode = CACHE;
-        codestr->oparg = 0;
+        codestr->op.code = CACHE;
+        codestr->op.arg = 0;
         codestr++;
     }
 }
diff --git a/Python/generated_cases.c.h b/Python/generated_cases.c.h
index 730dfb7426a..487e63d855d 100644
--- a/Python/generated_cases.c.h
+++ b/Python/generated_cases.c.h
@@ -339,9 +339,9 @@
             DEOPT_IF(!PyUnicode_CheckExact(left), BINARY_OP);
             DEOPT_IF(Py_TYPE(right) != Py_TYPE(left), BINARY_OP);
             _Py_CODEUNIT true_next = next_instr[INLINE_CACHE_ENTRIES_BINARY_OP];
-            assert(_Py_OPCODE(true_next) == STORE_FAST ||
-                   _Py_OPCODE(true_next) == STORE_FAST__LOAD_FAST);
-            PyObject **target_local = &GETLOCAL(_Py_OPARG(true_next));
+            assert(true_next.op.code == STORE_FAST ||
+                   true_next.op.code == STORE_FAST__LOAD_FAST);
+            PyObject **target_local = &GETLOCAL(true_next.op.arg);
             DEOPT_IF(*target_local != left, BINARY_OP);
             STAT_INC(BINARY_OP, hit);
             /* Handle `left = left + right` or `left += right` for str.
@@ -2199,10 +2199,10 @@
             Py_DECREF(left);
             Py_DECREF(right);
             if (cond == NULL) goto pop_2_error;
-            assert(_Py_OPCODE(next_instr[1]) == POP_JUMP_IF_FALSE ||
-                   _Py_OPCODE(next_instr[1]) == POP_JUMP_IF_TRUE);
-            bool jump_on_true = _Py_OPCODE(next_instr[1]) == POP_JUMP_IF_TRUE;
-            int offset = _Py_OPARG(next_instr[1]);
+            assert(next_instr[1].op.code == POP_JUMP_IF_FALSE ||
+                   next_instr[1].op.code == POP_JUMP_IF_TRUE);
+            bool jump_on_true = next_instr[1].op.code == POP_JUMP_IF_TRUE;
+            int offset = next_instr[1].op.arg;
             int err = PyObject_IsTrue(cond);
             Py_DECREF(cond);
             if (err < 0) {
@@ -2230,7 +2230,7 @@
             _Py_DECREF_SPECIALIZED(left, _PyFloat_ExactDealloc);
             _Py_DECREF_SPECIALIZED(right, _PyFloat_ExactDealloc);
             if (sign_ish & oparg) {
-                int offset = _Py_OPARG(next_instr[1]);
+                int offset = next_instr[1].op.arg;
                 JUMPBY(offset);
             }
             STACK_SHRINK(2);
@@ -2255,7 +2255,7 @@
             _Py_DECREF_SPECIALIZED(left, (destructor)PyObject_Free);
             _Py_DECREF_SPECIALIZED(right, (destructor)PyObject_Free);
             if (sign_ish & oparg) {
-                int offset = _Py_OPARG(next_instr[1]);
+                int offset = next_instr[1].op.arg;
                 JUMPBY(offset);
             }
             STACK_SHRINK(2);
@@ -2278,7 +2278,7 @@
             assert((oparg & 0xf) == COMPARISON_NOT_EQUALS || (oparg & 0xf) == COMPARISON_EQUALS);
             assert(COMPARISON_NOT_EQUALS + 1 == COMPARISON_EQUALS);
             if ((res + COMPARISON_NOT_EQUALS) & oparg) {
-                int offset = _Py_OPARG(next_instr[1]);
+                int offset = next_instr[1].op.arg;
                 JUMPBY(offset);
             }
             STACK_SHRINK(2);
@@ -2682,7 +2682,7 @@
                     _PyErr_Clear(tstate);
                 }
                 /* iterator ended normally */
-                assert(_Py_OPCODE(next_instr[INLINE_CACHE_ENTRIES_FOR_ITER + oparg]) == END_FOR);
+                assert(next_instr[INLINE_CACHE_ENTRIES_FOR_ITER + oparg].op.code == END_FOR);
                 Py_DECREF(iter);
                 STACK_SHRINK(1);
                 /* Jump forward oparg, then skip following END_FOR instruction */
@@ -2761,7 +2761,7 @@
             DEOPT_IF(Py_TYPE(r) != &PyRangeIter_Type, FOR_ITER);
             STAT_INC(FOR_ITER, hit);
             _Py_CODEUNIT next = next_instr[INLINE_CACHE_ENTRIES_FOR_ITER];
-            assert(_PyOpcode_Deopt[_Py_OPCODE(next)] == STORE_FAST);
+            assert(_PyOpcode_Deopt[next.op.code] == STORE_FAST);
             if (r->len <= 0) {
                 STACK_SHRINK(1);
                 Py_DECREF(r);
@@ -2772,7 +2772,7 @@
                 long value = r->start;
                 r->start = value + r->step;
                 r->len--;
-                if (_PyLong_AssignValue(&GETLOCAL(_Py_OPARG(next)), value) < 0) {
+                if (_PyLong_AssignValue(&GETLOCAL(next.op.arg), value) < 0) {
                     goto error;
                 }
                 // The STORE_FAST is already done.
@@ -2795,7 +2795,7 @@
             gen->gi_exc_state.previous_item = tstate->exc_info;
             tstate->exc_info = &gen->gi_exc_state;
             JUMPBY(INLINE_CACHE_ENTRIES_FOR_ITER + oparg);
-            assert(_Py_OPCODE(*next_instr) == END_FOR);
+            assert(next_instr->op.code == END_FOR);
             DISPATCH_INLINED(gen_frame);
         }
 
@@ -3516,7 +3516,7 @@
             STACK_SHRINK(3);
             // CALL + POP_TOP
             JUMPBY(INLINE_CACHE_ENTRIES_CALL + 1);
-            assert(_Py_OPCODE(next_instr[-1]) == POP_TOP);
+            assert(next_instr[-1].op.code == POP_TOP);
             DISPATCH();
         }
 
@@ -3903,8 +3903,8 @@
         TARGET(EXTENDED_ARG) {
             assert(oparg);
             assert(cframe.use_tracing == 0);
-            opcode = _Py_OPCODE(*next_instr);
-            oparg = oparg << 8 | _Py_OPARG(*next_instr);
+            opcode = next_instr->op.code;
+            oparg = oparg << 8 | next_instr->op.arg;
             PRE_DISPATCH_GOTO();
             DISPATCH_GOTO();
         }
diff --git a/Python/specialize.c b/Python/specialize.c
index 4ede3122d38..c9555f8ad4d 100644
--- a/Python/specialize.c
+++ b/Python/specialize.c
@@ -282,7 +282,7 @@ _PyCode_Quicken(PyCodeObject *code)
     _Py_CODEUNIT *instructions = _PyCode_CODE(code);
     for (int i = 0; i < Py_SIZE(code); i++) {
         int previous_opcode = opcode;
-        opcode = _PyOpcode_Deopt[_Py_OPCODE(instructions[i])];
+        opcode = _PyOpcode_Deopt[instructions[i].op.code];
         int caches = _PyOpcode_Caches[opcode];
         if (caches) {
             instructions[i + 1].cache = adaptive_counter_warmup();
@@ -291,31 +291,31 @@ _PyCode_Quicken(PyCodeObject *code)
         }
         switch (previous_opcode << 8 | opcode) {
             case LOAD_CONST << 8 | LOAD_FAST:
-                instructions[i - 1].opcode = LOAD_CONST__LOAD_FAST;
+                instructions[i - 1].op.code = LOAD_CONST__LOAD_FAST;
                 break;
             case LOAD_FAST << 8 | LOAD_CONST:
-                instructions[i - 1].opcode = LOAD_FAST__LOAD_CONST;
+                instructions[i - 1].op.code = LOAD_FAST__LOAD_CONST;
                 break;
             case LOAD_FAST << 8 | LOAD_FAST:
-                instructions[i - 1].opcode = LOAD_FAST__LOAD_FAST;
+                instructions[i - 1].op.code = LOAD_FAST__LOAD_FAST;
                 break;
             case STORE_FAST << 8 | LOAD_FAST:
-                instructions[i - 1].opcode = STORE_FAST__LOAD_FAST;
+                instructions[i - 1].op.code = STORE_FAST__LOAD_FAST;
                 break;
             case STORE_FAST << 8 | STORE_FAST:
-                instructions[i - 1].opcode = STORE_FAST__STORE_FAST;
+                instructions[i - 1].op.code = STORE_FAST__STORE_FAST;
                 break;
             case COMPARE_OP << 8 | POP_JUMP_IF_TRUE:
             case COMPARE_OP << 8 | POP_JUMP_IF_FALSE:
             {
-                int oparg = instructions[i - 1 - INLINE_CACHE_ENTRIES_COMPARE_OP].oparg;
+                int oparg = instructions[i - 1 - INLINE_CACHE_ENTRIES_COMPARE_OP].op.arg;
                 assert((oparg >> 4) <= Py_GE);
                 int mask = compare_masks[oparg >> 4];
                 if (opcode == POP_JUMP_IF_FALSE) {
                     mask = mask ^ 0xf;
                 }
-                instructions[i - 1 - INLINE_CACHE_ENTRIES_COMPARE_OP].opcode = COMPARE_AND_BRANCH;
-                instructions[i - 1 - INLINE_CACHE_ENTRIES_COMPARE_OP].oparg = (oparg & 0xf0) | mask;
+                instructions[i - 1 - INLINE_CACHE_ENTRIES_COMPARE_OP].op.code = COMPARE_AND_BRANCH;
+                instructions[i - 1 - INLINE_CACHE_ENTRIES_COMPARE_OP].op.arg = (oparg & 0xf0) | mask;
                 break;
             }
         }
@@ -519,7 +519,7 @@ specialize_module_load_attr(
     }
     write_u32(cache->version, keys_version);
     cache->index = (uint16_t)index;
-    _py_set_opcode(instr, LOAD_ATTR_MODULE);
+    instr->op.code = LOAD_ATTR_MODULE;
     return 0;
 }
 
@@ -674,7 +674,7 @@ specialize_dict_access(
         }
         write_u32(cache->version, type->tp_version_tag);
         cache->index = (uint16_t)index;
-        _py_set_opcode(instr, values_op);
+        instr->op.code = values_op;
     }
     else {
         PyDictObject *dict = (PyDictObject *)_PyDictOrValues_GetDict(dorv);
@@ -694,7 +694,7 @@ specialize_dict_access(
         }
         cache->index = (uint16_t)index;
         write_u32(cache->version, type->tp_version_tag);
-        _py_set_opcode(instr, hint_op);
+        instr->op.code = hint_op;
     }
     return 1;
 }
@@ -739,7 +739,7 @@ _Py_Specialize_LoadAttr(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name)
             goto fail;
         case METHOD:
         {
-            int oparg = _Py_OPARG(*instr);
+            int oparg = instr->op.arg;
             if (oparg & 1) {
                 if (specialize_attr_loadmethod(owner, instr, name, descr, kind)) {
                     goto success;
@@ -775,7 +775,7 @@ _Py_Specialize_LoadAttr(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name)
             write_u32(lm_cache->type_version, type->tp_version_tag);
             /* borrowed */
             write_obj(lm_cache->descr, fget);
-            _py_set_opcode(instr, LOAD_ATTR_PROPERTY);
+            instr->op.code = LOAD_ATTR_PROPERTY;
             goto success;
         }
         case OBJECT_SLOT:
@@ -799,7 +799,7 @@ _Py_Specialize_LoadAttr(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name)
             assert(offset > 0);
             cache->index = (uint16_t)offset;
             write_u32(cache->version, type->tp_version_tag);
-            _py_set_opcode(instr, LOAD_ATTR_SLOT);
+            instr->op.code = LOAD_ATTR_SLOT;
             goto success;
         }
         case DUNDER_CLASS:
@@ -808,7 +808,7 @@ _Py_Specialize_LoadAttr(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name)
             assert(offset == (uint16_t)offset);
             cache->index = (uint16_t)offset;
             write_u32(cache->version, type->tp_version_tag);
-            _py_set_opcode(instr, LOAD_ATTR_SLOT);
+            instr->op.code = LOAD_ATTR_SLOT;
             goto success;
         }
         case OTHER_SLOT:
@@ -836,7 +836,7 @@ _Py_Specialize_LoadAttr(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name)
             /* borrowed */
             write_obj(lm_cache->descr, descr);
             write_u32(lm_cache->type_version, type->tp_version_tag);
-            _py_set_opcode(instr, LOAD_ATTR_GETATTRIBUTE_OVERRIDDEN);
+            instr->op.code = LOAD_ATTR_GETATTRIBUTE_OVERRIDDEN;
             goto success;
         }
         case BUILTIN_CLASSMETHOD:
@@ -867,7 +867,7 @@ _Py_Specialize_LoadAttr(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name)
 fail:
     STAT_INC(LOAD_ATTR, failure);
     assert(!PyErr_Occurred());
-    _py_set_opcode(instr, LOAD_ATTR);
+    instr->op.code = LOAD_ATTR;
     cache->counter = adaptive_counter_backoff(cache->counter);
     return;
 success:
@@ -927,7 +927,7 @@ _Py_Specialize_StoreAttr(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name)
             assert(offset > 0);
             cache->index = (uint16_t)offset;
             write_u32(cache->version, type->tp_version_tag);
-            _py_set_opcode(instr, STORE_ATTR_SLOT);
+            instr->op.code = STORE_ATTR_SLOT;
             goto success;
         }
         case DUNDER_CLASS:
@@ -963,7 +963,7 @@ _Py_Specialize_StoreAttr(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name)
 fail:
     STAT_INC(STORE_ATTR, failure);
     assert(!PyErr_Occurred());
-    _py_set_opcode(instr, STORE_ATTR);
+    instr->op.code = STORE_ATTR;
     cache->counter = adaptive_counter_backoff(cache->counter);
     return;
 success:
@@ -1027,7 +1027,7 @@ specialize_class_load_attr(PyObject *owner, _Py_CODEUNIT *instr,
         case NON_DESCRIPTOR:
             write_u32(cache->type_version, ((PyTypeObject *)owner)->tp_version_tag);
             write_obj(cache->descr, descr);
-            _py_set_opcode(instr, LOAD_ATTR_CLASS);
+            instr->op.code = LOAD_ATTR_CLASS;
             return 0;
 #ifdef Py_STATS
         case ABSENT:
@@ -1069,7 +1069,7 @@ PyObject *descr, DescriptorClassification kind)
             return 0;
         }
         write_u32(cache->keys_version, keys_version);
-        _py_set_opcode(instr, LOAD_ATTR_METHOD_WITH_VALUES);
+        instr->op.code = LOAD_ATTR_METHOD_WITH_VALUES;
     }
     else {
         Py_ssize_t dictoffset = owner_cls->tp_dictoffset;
@@ -1078,7 +1078,7 @@ PyObject *descr, DescriptorClassification kind)
             return 0;
         }
         if (dictoffset == 0) {
-            _py_set_opcode(instr, LOAD_ATTR_METHOD_NO_DICT);
+            instr->op.code = LOAD_ATTR_METHOD_NO_DICT;
         }
         else {
             PyObject *dict = *(PyObject **) ((char *)owner + dictoffset);
@@ -1088,7 +1088,7 @@ PyObject *descr, DescriptorClassification kind)
             }
             assert(owner_cls->tp_dictoffset > 0);
             assert(owner_cls->tp_dictoffset <= INT16_MAX);
-            _py_set_opcode(instr, LOAD_ATTR_METHOD_LAZY_DICT);
+            instr->op.code = LOAD_ATTR_METHOD_LAZY_DICT;
         }
     }
     /* `descr` is borrowed. This is safe for methods (even inherited ones from
@@ -1146,7 +1146,7 @@ _Py_Specialize_LoadGlobal(
         }
         cache->index = (uint16_t)index;
         write_u32(cache->module_keys_version, keys_version);
-        _py_set_opcode(instr, LOAD_GLOBAL_MODULE);
+        instr->op.code = LOAD_GLOBAL_MODULE;
         goto success;
     }
     if (!PyDict_CheckExact(builtins)) {
@@ -1184,12 +1184,12 @@ _Py_Specialize_LoadGlobal(
     cache->index = (uint16_t)index;
     write_u32(cache->module_keys_version, globals_version);
     cache->builtin_keys_version = (uint16_t)builtins_version;
-    _py_set_opcode(instr, LOAD_GLOBAL_BUILTIN);
+    instr->op.code = LOAD_GLOBAL_BUILTIN;
     goto success;
 fail:
     STAT_INC(LOAD_GLOBAL, failure);
     assert(!PyErr_Occurred());
-    _py_set_opcode(instr, LOAD_GLOBAL);
+    instr->op.code = LOAD_GLOBAL;
     cache->counter = adaptive_counter_backoff(cache->counter);
     return;
 success:
@@ -1295,7 +1295,7 @@ _Py_Specialize_BinarySubscr(
     if (container_type == &PyList_Type) {
         if (PyLong_CheckExact(sub)) {
             if (Py_SIZE(sub) == 0 || Py_SIZE(sub) == 1) {
-                _py_set_opcode(instr, BINARY_SUBSCR_LIST_INT);
+                instr->op.code = BINARY_SUBSCR_LIST_INT;
                 goto success;
             }
             SPECIALIZATION_FAIL(BINARY_SUBSCR, SPEC_FAIL_OUT_OF_RANGE);
@@ -1308,7 +1308,7 @@ _Py_Specialize_BinarySubscr(
     if (container_type == &PyTuple_Type) {
         if (PyLong_CheckExact(sub)) {
             if (Py_SIZE(sub) == 0 || Py_SIZE(sub) == 1) {
-                _py_set_opcode(instr, BINARY_SUBSCR_TUPLE_INT);
+                instr->op.code = BINARY_SUBSCR_TUPLE_INT;
                 goto success;
             }
             SPECIALIZATION_FAIL(BINARY_SUBSCR, SPEC_FAIL_OUT_OF_RANGE);
@@ -1319,7 +1319,7 @@ _Py_Specialize_BinarySubscr(
         goto fail;
     }
     if (container_type == &PyDict_Type) {
-        _py_set_opcode(instr, BINARY_SUBSCR_DICT);
+        instr->op.code = BINARY_SUBSCR_DICT;
         goto success;
     }
     PyTypeObject *cls = Py_TYPE(container);
@@ -1350,7 +1350,7 @@ _Py_Specialize_BinarySubscr(
         }
         cache->func_version = version;
         ((PyHeapTypeObject *)container_type)->_spec_cache.getitem = descriptor;
-        _py_set_opcode(instr, BINARY_SUBSCR_GETITEM);
+        instr->op.code = BINARY_SUBSCR_GETITEM;
         goto success;
     }
     SPECIALIZATION_FAIL(BINARY_SUBSCR,
@@ -1358,7 +1358,7 @@ _Py_Specialize_BinarySubscr(
 fail:
     STAT_INC(BINARY_SUBSCR, failure);
     assert(!PyErr_Occurred());
-    _py_set_opcode(instr, BINARY_SUBSCR);
+    instr->op.code = BINARY_SUBSCR;
     cache->counter = adaptive_counter_backoff(cache->counter);
     return;
 success:
@@ -1378,7 +1378,7 @@ _Py_Specialize_StoreSubscr(PyObject *container, PyObject *sub, _Py_CODEUNIT *ins
             if ((Py_SIZE(sub) == 0 || Py_SIZE(sub) == 1)
                 && ((PyLongObject *)sub)->long_value.ob_digit[0] < (size_t)PyList_GET_SIZE(container))
             {
-                _py_set_opcode(instr, STORE_SUBSCR_LIST_INT);
+                instr->op.code = STORE_SUBSCR_LIST_INT;
                 goto success;
             }
             else {
@@ -1396,8 +1396,8 @@ _Py_Specialize_StoreSubscr(PyObject *container, PyObject *sub, _Py_CODEUNIT *ins
         }
     }
     if (container_type == &PyDict_Type) {
-        _py_set_opcode(instr, STORE_SUBSCR_DICT);
-         goto success;
+        instr->op.code = STORE_SUBSCR_DICT;
+        goto success;
     }
 #ifdef Py_STATS
     PyMappingMethods *as_mapping = container_type->tp_as_mapping;
@@ -1463,7 +1463,7 @@ _Py_Specialize_StoreSubscr(PyObject *container, PyObject *sub, _Py_CODEUNIT *ins
 fail:
     STAT_INC(STORE_SUBSCR, failure);
     assert(!PyErr_Occurred());
-    _py_set_opcode(instr, STORE_SUBSCR);
+    instr->op.code = STORE_SUBSCR;
     cache->counter = adaptive_counter_backoff(cache->counter);
     return;
 success:
@@ -1482,23 +1482,23 @@ specialize_class_call(PyObject *callable, _Py_CODEUNIT *instr, int nargs,
         return -1;
     }
     if (tp->tp_flags & Py_TPFLAGS_IMMUTABLETYPE) {
-        int oparg = _Py_OPARG(*instr);
+        int oparg = instr->op.arg;
         if (nargs == 1 && kwnames == NULL && oparg == 1) {
             if (tp == &PyUnicode_Type) {
-                _py_set_opcode(instr, CALL_NO_KW_STR_1);
+                instr->op.code = CALL_NO_KW_STR_1;
                 return 0;
             }
             else if (tp == &PyType_Type) {
-                _py_set_opcode(instr, CALL_NO_KW_TYPE_1);
+                instr->op.code = CALL_NO_KW_TYPE_1;
                 return 0;
             }
             else if (tp == &PyTuple_Type) {
-                _py_set_opcode(instr, CALL_NO_KW_TUPLE_1);
+                instr->op.code = CALL_NO_KW_TUPLE_1;
                 return 0;
             }
         }
         if (tp->tp_vectorcall != NULL) {
-            _py_set_opcode(instr, CALL_BUILTIN_CLASS);
+            instr->op.code = CALL_BUILTIN_CLASS;
             return 0;
         }
         SPECIALIZATION_FAIL(CALL, tp == &PyUnicode_Type ?
@@ -1573,7 +1573,7 @@ specialize_method_descriptor(PyMethodDescrObject *descr, _Py_CODEUNIT *instr,
                 SPECIALIZATION_FAIL(CALL, SPEC_FAIL_WRONG_NUMBER_ARGUMENTS);
                 return -1;
             }
-            _py_set_opcode(instr, CALL_NO_KW_METHOD_DESCRIPTOR_NOARGS);
+            instr->op.code = CALL_NO_KW_METHOD_DESCRIPTOR_NOARGS;
             return 0;
         }
         case METH_O: {
@@ -1584,21 +1584,21 @@ specialize_method_descriptor(PyMethodDescrObject *descr, _Py_CODEUNIT *instr,
             PyInterpreterState *interp = _PyInterpreterState_GET();
             PyObject *list_append = interp->callable_cache.list_append;
             _Py_CODEUNIT next = instr[INLINE_CACHE_ENTRIES_CALL + 1];
-            bool pop = (_Py_OPCODE(next) == POP_TOP);
-            int oparg = _Py_OPARG(*instr);
+            bool pop = (next.op.code == POP_TOP);
+            int oparg = instr->op.arg;
             if ((PyObject *)descr == list_append && oparg == 1 && pop) {
-                _py_set_opcode(instr, CALL_NO_KW_LIST_APPEND);
+                instr->op.code = CALL_NO_KW_LIST_APPEND;
                 return 0;
             }
-            _py_set_opcode(instr, CALL_NO_KW_METHOD_DESCRIPTOR_O);
+            instr->op.code = CALL_NO_KW_METHOD_DESCRIPTOR_O;
             return 0;
         }
         case METH_FASTCALL: {
-            _py_set_opcode(instr, CALL_NO_KW_METHOD_DESCRIPTOR_FAST);
+            instr->op.code = CALL_NO_KW_METHOD_DESCRIPTOR_FAST;
             return 0;
         }
         case METH_FASTCALL | METH_KEYWORDS: {
-            _py_set_opcode(instr, CALL_METHOD_DESCRIPTOR_FAST_WITH_KEYWORDS);
+            instr->op.code = CALL_METHOD_DESCRIPTOR_FAST_WITH_KEYWORDS;
             return 0;
         }
     }
@@ -1649,14 +1649,14 @@ specialize_py_call(PyFunctionObject *func, _Py_CODEUNIT *instr, int nargs,
     write_u32(cache->func_version, version);
     cache->min_args = min_args;
     if (argcount == nargs) {
-        _py_set_opcode(instr, bound_method ? CALL_BOUND_METHOD_EXACT_ARGS : CALL_PY_EXACT_ARGS);
+        instr->op.code = bound_method ? CALL_BOUND_METHOD_EXACT_ARGS : CALL_PY_EXACT_ARGS;
     }
     else if (bound_method) {
         SPECIALIZATION_FAIL(CALL, SPEC_FAIL_CALL_BOUND_METHOD);
         return -1;
     }
     else {
-        _py_set_opcode(instr, CALL_PY_WITH_DEFAULTS);
+        instr->op.code = CALL_PY_WITH_DEFAULTS;
     }
     return 0;
 }
@@ -1683,10 +1683,10 @@ specialize_c_call(PyObject *callable, _Py_CODEUNIT *instr, int nargs,
             /* len(o) */
             PyInterpreterState *interp = _PyInterpreterState_GET();
             if (callable == interp->callable_cache.len) {
-                _py_set_opcode(instr, CALL_NO_KW_LEN);
+                instr->op.code = CALL_NO_KW_LEN;
                 return 0;
             }
-            _py_set_opcode(instr, CALL_NO_KW_BUILTIN_O);
+            instr->op.code = CALL_NO_KW_BUILTIN_O;
             return 0;
         }
         case METH_FASTCALL: {
@@ -1698,15 +1698,15 @@ specialize_c_call(PyObject *callable, _Py_CODEUNIT *instr, int nargs,
                 /* isinstance(o1, o2) */
                 PyInterpreterState *interp = _PyInterpreterState_GET();
                 if (callable == interp->callable_cache.isinstance) {
-                    _py_set_opcode(instr, CALL_NO_KW_ISINSTANCE);
+                    instr->op.code = CALL_NO_KW_ISINSTANCE;
                     return 0;
                 }
             }
-            _py_set_opcode(instr, CALL_NO_KW_BUILTIN_FAST);
+            instr->op.code = CALL_NO_KW_BUILTIN_FAST;
             return 0;
         }
         case METH_FASTCALL | METH_KEYWORDS: {
-            _py_set_opcode(instr, CALL_BUILTIN_FAST_WITH_KEYWORDS);
+            instr->op.code = CALL_BUILTIN_FAST_WITH_KEYWORDS;
             return 0;
         }
         default:
@@ -1785,7 +1785,7 @@ _Py_Specialize_Call(PyObject *callable, _Py_CODEUNIT *instr, int nargs,
     if (fail) {
         STAT_INC(CALL, failure);
         assert(!PyErr_Occurred());
-        _py_set_opcode(instr, CALL);
+        instr->op.code = CALL;
         cache->counter = adaptive_counter_backoff(cache->counter);
     }
     else {
@@ -1880,21 +1880,21 @@ _Py_Specialize_BinaryOp(PyObject *lhs, PyObject *rhs, _Py_CODEUNIT *instr,
             }
             if (PyUnicode_CheckExact(lhs)) {
                 _Py_CODEUNIT next = instr[INLINE_CACHE_ENTRIES_BINARY_OP + 1];
-                bool to_store = (_Py_OPCODE(next) == STORE_FAST ||
-                                 _Py_OPCODE(next) == STORE_FAST__LOAD_FAST);
-                if (to_store && locals[_Py_OPARG(next)] == lhs) {
-                    _py_set_opcode(instr, BINARY_OP_INPLACE_ADD_UNICODE);
+                bool to_store = (next.op.code == STORE_FAST ||
+                                 next.op.code == STORE_FAST__LOAD_FAST);
+                if (to_store && locals[next.op.arg] == lhs) {
+                    instr->op.code = BINARY_OP_INPLACE_ADD_UNICODE;
                     goto success;
                 }
-                _py_set_opcode(instr, BINARY_OP_ADD_UNICODE);
+                instr->op.code = BINARY_OP_ADD_UNICODE;
                 goto success;
             }
             if (PyLong_CheckExact(lhs)) {
-                _py_set_opcode(instr, BINARY_OP_ADD_INT);
+                instr->op.code = BINARY_OP_ADD_INT;
                 goto success;
             }
             if (PyFloat_CheckExact(lhs)) {
-                _py_set_opcode(instr, BINARY_OP_ADD_FLOAT);
+                instr->op.code = BINARY_OP_ADD_FLOAT;
                 goto success;
             }
             break;
@@ -1904,11 +1904,11 @@ _Py_Specialize_BinaryOp(PyObject *lhs, PyObject *rhs, _Py_CODEUNIT *instr,
                 break;
             }
             if (PyLong_CheckExact(lhs)) {
-                _py_set_opcode(instr, BINARY_OP_MULTIPLY_INT);
+                instr->op.code = BINARY_OP_MULTIPLY_INT;
                 goto success;
             }
             if (PyFloat_CheckExact(lhs)) {
-                _py_set_opcode(instr, BINARY_OP_MULTIPLY_FLOAT);
+                instr->op.code = BINARY_OP_MULTIPLY_FLOAT;
                 goto success;
             }
             break;
@@ -1918,18 +1918,18 @@ _Py_Specialize_BinaryOp(PyObject *lhs, PyObject *rhs, _Py_CODEUNIT *instr,
                 break;
             }
             if (PyLong_CheckExact(lhs)) {
-                _py_set_opcode(instr, BINARY_OP_SUBTRACT_INT);
+                instr->op.code = BINARY_OP_SUBTRACT_INT;
                 goto success;
             }
             if (PyFloat_CheckExact(lhs)) {
-                _py_set_opcode(instr, BINARY_OP_SUBTRACT_FLOAT);
+                instr->op.code = BINARY_OP_SUBTRACT_FLOAT;
                 goto success;
             }
             break;
     }
     SPECIALIZATION_FAIL(BINARY_OP, binary_op_fail_kind(oparg, lhs, rhs));
     STAT_INC(BINARY_OP, failure);
-    _py_set_opcode(instr, BINARY_OP);
+    instr->op.code = BINARY_OP;
     cache->counter = adaptive_counter_backoff(cache->counter);
     return;
 success:
@@ -1981,7 +1981,7 @@ _Py_Specialize_CompareAndBranch(PyObject *lhs, PyObject *rhs, _Py_CODEUNIT *inst
     assert(_PyOpcode_Caches[COMPARE_AND_BRANCH] == INLINE_CACHE_ENTRIES_COMPARE_OP);
     _PyCompareOpCache *cache = (_PyCompareOpCache *)(instr + 1);
 #ifndef NDEBUG
-    int next_opcode = _Py_OPCODE(instr[INLINE_CACHE_ENTRIES_COMPARE_OP + 1]);
+    int next_opcode = instr[INLINE_CACHE_ENTRIES_COMPARE_OP + 1].op.code;
     assert(next_opcode == POP_JUMP_IF_FALSE || next_opcode == POP_JUMP_IF_TRUE);
 #endif
     if (Py_TYPE(lhs) != Py_TYPE(rhs)) {
@@ -1989,12 +1989,12 @@ _Py_Specialize_CompareAndBranch(PyObject *lhs, PyObject *rhs, _Py_CODEUNIT *inst
         goto failure;
     }
     if (PyFloat_CheckExact(lhs)) {
-        _py_set_opcode(instr, COMPARE_AND_BRANCH_FLOAT);
+        instr->op.code = COMPARE_AND_BRANCH_FLOAT;
         goto success;
     }
     if (PyLong_CheckExact(lhs)) {
         if (Py_ABS(Py_SIZE(lhs)) <= 1 && Py_ABS(Py_SIZE(rhs)) <= 1) {
-            _py_set_opcode(instr, COMPARE_AND_BRANCH_INT);
+            instr->op.code = COMPARE_AND_BRANCH_INT;
             goto success;
         }
         else {
@@ -2009,14 +2009,14 @@ _Py_Specialize_CompareAndBranch(PyObject *lhs, PyObject *rhs, _Py_CODEUNIT *inst
             goto failure;
         }
         else {
-            _py_set_opcode(instr, COMPARE_AND_BRANCH_STR);
+            instr->op.code = COMPARE_AND_BRANCH_STR;
             goto success;
         }
     }
     SPECIALIZATION_FAIL(COMPARE_AND_BRANCH, compare_op_fail_kind(lhs, rhs));
 failure:
     STAT_INC(COMPARE_AND_BRANCH, failure);
-    _py_set_opcode(instr, COMPARE_AND_BRANCH);
+    instr->op.code = COMPARE_AND_BRANCH;
     cache->counter = adaptive_counter_backoff(cache->counter);
     return;
 success:
@@ -2051,10 +2051,10 @@ _Py_Specialize_UnpackSequence(PyObject *seq, _Py_CODEUNIT *instr, int oparg)
             goto failure;
         }
         if (PyTuple_GET_SIZE(seq) == 2) {
-            _py_set_opcode(instr, UNPACK_SEQUENCE_TWO_TUPLE);
+            instr->op.code = UNPACK_SEQUENCE_TWO_TUPLE;
             goto success;
         }
-        _py_set_opcode(instr, UNPACK_SEQUENCE_TUPLE);
+        instr->op.code = UNPACK_SEQUENCE_TUPLE;
         goto success;
     }
     if (PyList_CheckExact(seq)) {
@@ -2062,13 +2062,13 @@ _Py_Specialize_UnpackSequence(PyObject *seq, _Py_CODEUNIT *instr, int oparg)
             SPECIALIZATION_FAIL(UNPACK_SEQUENCE, SPEC_FAIL_EXPECTED_ERROR);
             goto failure;
         }
-        _py_set_opcode(instr, UNPACK_SEQUENCE_LIST);
+        instr->op.code = UNPACK_SEQUENCE_LIST;
         goto success;
     }
     SPECIALIZATION_FAIL(UNPACK_SEQUENCE, unpack_sequence_fail_kind(seq));
 failure:
     STAT_INC(UNPACK_SEQUENCE, failure);
-    _py_set_opcode(instr, UNPACK_SEQUENCE);
+    instr->op.code = UNPACK_SEQUENCE;
     cache->counter = adaptive_counter_backoff(cache->counter);
     return;
 success:
@@ -2156,28 +2156,28 @@ _Py_Specialize_ForIter(PyObject *iter, _Py_CODEUNIT *instr, int oparg)
     _PyForIterCache *cache = (_PyForIterCache *)(instr + 1);
     PyTypeObject *tp = Py_TYPE(iter);
     _Py_CODEUNIT next = instr[1+INLINE_CACHE_ENTRIES_FOR_ITER];
-    int next_op = _PyOpcode_Deopt[_Py_OPCODE(next)];
+    int next_op = _PyOpcode_Deopt[next.op.code];
     if (tp == &PyListIter_Type) {
-        _py_set_opcode(instr, FOR_ITER_LIST);
+        instr->op.code = FOR_ITER_LIST;
         goto success;
     }
     else if (tp == &PyTupleIter_Type) {
-        _py_set_opcode(instr, FOR_ITER_TUPLE);
+        instr->op.code = FOR_ITER_TUPLE;
         goto success;
     }
     else if (tp == &PyRangeIter_Type && next_op == STORE_FAST) {
-        _py_set_opcode(instr, FOR_ITER_RANGE);
+        instr->op.code = FOR_ITER_RANGE;
         goto success;
     }
     else if (tp == &PyGen_Type && oparg <= SHRT_MAX) {
-        assert(_Py_OPCODE(instr[oparg + INLINE_CACHE_ENTRIES_FOR_ITER + 1]) == END_FOR);
-        _py_set_opcode(instr, FOR_ITER_GEN);
+        assert(instr[oparg + INLINE_CACHE_ENTRIES_FOR_ITER + 1].op.code == END_FOR);
+        instr->op.code = FOR_ITER_GEN;
         goto success;
     }
     SPECIALIZATION_FAIL(FOR_ITER,
                         _PySpecialization_ClassifyIterator(iter));
     STAT_INC(FOR_ITER, failure);
-    _py_set_opcode(instr, FOR_ITER);
+    instr->op.code = FOR_ITER;
     cache->counter = adaptive_counter_backoff(cache->counter);
     return;
 success:
@@ -2193,13 +2193,13 @@ _Py_Specialize_Send(PyObject *receiver, _Py_CODEUNIT *instr)
     _PySendCache *cache = (_PySendCache *)(instr + 1);
     PyTypeObject *tp = Py_TYPE(receiver);
     if (tp == &PyGen_Type || tp == &PyCoro_Type) {
-        _py_set_opcode(instr, SEND_GEN);
+        instr->op.code = SEND_GEN;
         goto success;
     }
     SPECIALIZATION_FAIL(SEND,
                         _PySpecialization_ClassifyIterator(receiver));
     STAT_INC(SEND, failure);
-    _py_set_opcode(instr, SEND);
+    instr->op.code = SEND;
     cache->counter = adaptive_counter_backoff(cache->counter);
     return;
 success:
diff --git a/Tools/cases_generator/generate_cases.py b/Tools/cases_generator/generate_cases.py
index aa8e14075c8..c7f52b55a5e 100644
--- a/Tools/cases_generator/generate_cases.py
+++ b/Tools/cases_generator/generate_cases.py
@@ -8,6 +8,7 @@ import argparse
 import contextlib
 import dataclasses
 import os
+import posixpath
 import re
 import sys
 import typing
@@ -17,7 +18,7 @@ from parser import StackEffect
 
 HERE = os.path.dirname(__file__)
 ROOT = os.path.join(HERE, "../..")
-THIS = os.path.relpath(__file__, ROOT)
+THIS = os.path.relpath(__file__, ROOT).replace(os.path.sep, posixpath.sep)
 
 DEFAULT_INPUT = os.path.relpath(os.path.join(ROOT, "Python/bytecodes.c"))
 DEFAULT_OUTPUT = os.path.relpath(os.path.join(ROOT, "Python/generated_cases.c.h"))
@@ -930,7 +931,7 @@ class Analyzer:
         with open(self.metadata_filename, "w") as f:
             # Write provenance header
             f.write(f"// This file is generated by {THIS} --metadata\n")
-            f.write(f"// from {os.path.relpath(self.filename, ROOT)}\n")
+            f.write(f"// from {os.path.relpath(self.filename, ROOT).replace(os.path.sep, posixpath.sep)}\n")
             f.write(f"// Do not edit!\n")
 
             # Create formatter; the rest of the code uses this
@@ -1009,7 +1010,7 @@ class Analyzer:
         with open(self.output_filename, "w") as f:
             # Write provenance header
             f.write(f"// This file is generated by {THIS}\n")
-            f.write(f"// from {os.path.relpath(self.filename, ROOT)}\n")
+            f.write(f"// from {os.path.relpath(self.filename, ROOT).replace(os.path.sep, posixpath.sep)}\n")
             f.write(f"// Do not edit!\n")
 
             # Create formatter; the rest of the code uses this