GH-108866: Guarantee forward progress in executors. (GH-113006)

3 files changed, 13 insertions, 18 deletions

diff --git a/Python/bytecodes.c b/Python/bytecodes.c
index e0f3735..1ae8342 100644
--- a/Python/bytecodes.c
+++ b/Python/bytecodes.c
@@ -2352,20 +2352,17 @@ dummy_func(
 
             PyCodeObject *code = _PyFrame_GetCode(frame);
             _PyExecutorObject *executor = (_PyExecutorObject *)code->co_executors->executors[oparg&255];
-            int original_oparg = executor->vm_data.oparg | (oparg & 0xfffff00);
-            JUMPBY(1-original_oparg);
-            frame->instr_ptr = next_instr;
             Py_INCREF(executor);
             if (executor->execute == _PyUOpExecute) {
                 current_executor = (_PyUOpExecutorObject *)executor;
                 GOTO_TIER_TWO();
             }
-            frame = executor->execute(executor, frame, stack_pointer);
-            if (frame == NULL) {
-                frame = tstate->current_frame;
+            next_instr = executor->execute(executor, frame, stack_pointer);
+            frame = tstate->current_frame;
+            if (next_instr == NULL) {
                 goto resume_with_error;
             }
-            goto enter_tier_one;
+            stack_pointer = _PyFrame_GetStackPointer(frame);
         }
 
         replaced op(_POP_JUMP_IF_FALSE, (unused/1, cond -- )) {
diff --git a/Python/generated_cases.c.h b/Python/generated_cases.c.h
index 8f68bc6..65e6f11 100644
--- a/Python/generated_cases.c.h
+++ b/Python/generated_cases.c.h
@@ -2328,20 +2328,18 @@
             CHECK_EVAL_BREAKER();
             PyCodeObject *code = _PyFrame_GetCode(frame);
             _PyExecutorObject *executor = (_PyExecutorObject *)code->co_executors->executors[oparg&255];
-            int original_oparg = executor->vm_data.oparg | (oparg & 0xfffff00);
-            JUMPBY(1-original_oparg);
-            frame->instr_ptr = next_instr;
             Py_INCREF(executor);
             if (executor->execute == _PyUOpExecute) {
                 current_executor = (_PyUOpExecutorObject *)executor;
                 GOTO_TIER_TWO();
             }
-            frame = executor->execute(executor, frame, stack_pointer);
-            if (frame == NULL) {
-                frame = tstate->current_frame;
+            next_instr = executor->execute(executor, frame, stack_pointer);
+            frame = tstate->current_frame;
+            if (next_instr == NULL) {
                 goto resume_with_error;
             }
-            goto enter_tier_one;
+            stack_pointer = _PyFrame_GetStackPointer(frame);
+            DISPATCH();
         }
 
         TARGET(EXIT_INIT_CHECK) {
diff --git a/Python/optimizer.c b/Python/optimizer.c
index dd24fbe..7c46bd6 100644
--- a/Python/optimizer.c
+++ b/Python/optimizer.c
@@ -167,6 +167,7 @@ _PyOptimizer_BackEdge(_PyInterpreterFrame *frame, _Py_CODEUNIT *src, _Py_CODEUNI
     }
     _PyOptimizerObject *opt = interp->optimizer;
     _PyExecutorObject *executor = NULL;
+    /* Start optimizing at the destination to guarantee forward progress */
     int err = opt->optimize(opt, code, dest, &executor, (int)(stack_pointer - _PyFrame_Stackbase(frame)));
     if (err <= 0) {
         assert(executor == NULL);
@@ -247,14 +248,13 @@ PyTypeObject _PyCounterExecutor_Type = {
     .tp_methods = executor_methods,
 };
 
-static _PyInterpreterFrame *
+static _Py_CODEUNIT *
 counter_execute(_PyExecutorObject *self, _PyInterpreterFrame *frame, PyObject **stack_pointer)
 {
     ((_PyCounterExecutorObject *)self)->optimizer->count++;
     _PyFrame_SetStackPointer(frame, stack_pointer);
-    frame->instr_ptr = ((_PyCounterExecutorObject *)self)->next_instr;
     Py_DECREF(self);
-    return frame;
+    return ((_PyCounterExecutorObject *)self)->next_instr;
 }
 
 static int
@@ -891,7 +891,7 @@ uop_optimize(
 /* Dummy execute() function for UOp Executor.
  * The actual implementation is inlined in ceval.c,
  * in _PyEval_EvalFrameDefault(). */
-_PyInterpreterFrame *
+_Py_CODEUNIT *
 _PyUOpExecute(_PyExecutorObject *executor, _PyInterpreterFrame *frame, PyObject **stack_pointer)
 {
     Py_FatalError("Tier 2 is now inlined into Tier 1");