GH-121784: Generate an error during code gen if a variable is marked unused, but is used and thus cached in a prior uop. (#121788)

* Reject uop definitions that declare values as 'unused' that are already cached by prior uops

* Track which variables are defined and only load from memory when needed

* Support explicit `flush` in macro definitions. 

* Make sure stack is flushed in where needed.

Author: markshannon

Lib/test/test_generated_cases.py

@@ -3448,7 +3448,7 @@ dummy_func(
             }
         }
 
-        op(_CHECK_FUNCTION_VERSION, (func_version/2, callable, unused, unused[oparg] -- callable, unused, unused[oparg])) {
+        op(_CHECK_FUNCTION_VERSION, (func_version/2, callable, self_or_null, unused[oparg] -- callable, self_or_null, unused[oparg])) {
             PyObject *callable_o = PyStackRef_AsPyObjectBorrow(callable);
             EXIT_IF(!PyFunction_Check(callable_o));
             PyFunctionObject *func = (PyFunctionObject *)callable_o;
@@ -3479,7 +3479,6 @@ dummy_func(
             assert(PyStackRef_IsNull(null));
             assert(Py_TYPE(callable_o) == &PyMethod_Type);
             self = PyStackRef_FromPyObjectNew(((PyMethodObject *)callable_o)->im_self);
-            stack_pointer[-1 - oparg] = self;  // Patch stack as it is used by _PY_FRAME_GENERAL
             method = PyStackRef_FromPyObjectNew(((PyMethodObject *)callable_o)->im_func);
             assert(PyFunction_Check(PyStackRef_AsPyObjectBorrow(method)));
             PyStackRef_CLOSE(callable);
@@ -3490,6 +3489,7 @@ dummy_func(
             _CHECK_PEP_523 +
             _CHECK_METHOD_VERSION +
             _EXPAND_METHOD +
+            flush + // so that self is in the argument array
             _PY_FRAME_GENERAL +
             _SAVE_RETURN_OFFSET +
             _PUSH_FRAME;
@@ -3544,16 +3544,12 @@ dummy_func(
             EXIT_IF(Py_TYPE(PyStackRef_AsPyObjectBorrow(callable)) != &PyMethod_Type);
         }
 
-        op(_INIT_CALL_BOUND_METHOD_EXACT_ARGS, (callable, unused, unused[oparg] -- func, self, unused[oparg])) {
+        op(_INIT_CALL_BOUND_METHOD_EXACT_ARGS, (callable, null, unused[oparg] -- func, self, unused[oparg])) {
             PyObject *callable_o = PyStackRef_AsPyObjectBorrow(callable);
             STAT_INC(CALL, hit);
-            stack_pointer[-1 - oparg] = PyStackRef_FromPyObjectNew(((PyMethodObject *)callable_o)->im_self);  // Patch stack as it is used by _INIT_CALL_PY_EXACT_ARGS
-            stack_pointer[-2 - oparg] = PyStackRef_FromPyObjectNew(((PyMethodObject *)callable_o)->im_func);  // This is used by CALL, upon deoptimization
-            self = stack_pointer[-1 - oparg];
-            func = stack_pointer[-2 - oparg];
+            self = PyStackRef_FromPyObjectNew(((PyMethodObject *)callable_o)->im_self);
+            func = PyStackRef_FromPyObjectNew(((PyMethodObject *)callable_o)->im_func);
             PyStackRef_CLOSE(callable);
-            // self may be unused in tier 1, so silence warnings.
-            (void)self;
         }
 
         op(_CHECK_PEP_523, (--)) {
@@ -3568,7 +3564,7 @@ dummy_func(
             EXIT_IF(code->co_argcount != oparg + (!PyStackRef_IsNull(self_or_null)));
         }
 
-        op(_CHECK_STACK_SPACE, (callable, unused, unused[oparg] -- callable, unused, unused[oparg])) {
+        op(_CHECK_STACK_SPACE, (callable, self_or_null, unused[oparg] -- callable, self_or_null, unused[oparg])) {
             PyObject *callable_o = PyStackRef_AsPyObjectBorrow(callable);
             PyFunctionObject *func = (PyFunctionObject *)callable_o;
             PyCodeObject *code = (PyCodeObject *)func->func_code;
@@ -3609,6 +3605,7 @@ dummy_func(
             _CHECK_PEP_523 +
             _CHECK_CALL_BOUND_METHOD_EXACT_ARGS +
             _INIT_CALL_BOUND_METHOD_EXACT_ARGS +
+            flush + // In case the following deopt
             _CHECK_FUNCTION_VERSION +
             _CHECK_FUNCTION_EXACT_ARGS +
             _CHECK_STACK_SPACE +