bpo-44878: _PyEval_EvalFrameDefault readability improvements (GH-27725)

* Move a few variable declarations to point of definition.

* Factor out tracing of function entry into helper function.

Python/ceval.c

@@ -1392,56 +1392,9 @@ eval_frame_handle_pending(PyThreadState *tstate)
 #define BUILTINS() frame->f_builtins
 #define LOCALS() frame->f_locals
 
-PyObject* _Py_HOT_FUNCTION
+static int
-_PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int throwflag)
+trace_function_entry(PyThreadState *tstate, InterpreterFrame *frame)
 {
-    _Py_EnsureTstateNotNULL(tstate);
-
-#if USE_COMPUTED_GOTOS
-/* Import the static jump table */
-#include "opcode_targets.h"
-#endif
-
-#ifdef DXPAIRS
-    int lastopcode = 0;
-#endif
-    PyObject **stack_pointer;  /* Next free slot in value stack */
-    _Py_CODEUNIT *next_instr;
-    int opcode;        /* Current opcode */
-    int oparg;         /* Current opcode argument, if any */
-    PyObject **localsplus;
-    PyObject *retval = NULL;            /* Return value */
-    _Py_atomic_int * const eval_breaker = &tstate->interp->ceval.eval_breaker;
-    PyCodeObject *co;
-
-    _Py_CODEUNIT *first_instr;
-    PyObject *names;
-    PyObject *consts;
-
-#ifdef LLTRACE
-    _Py_IDENTIFIER(__ltrace__);
-#endif
-
-    if (_Py_EnterRecursiveCall(tstate, "")) {
-        return NULL;
-    }
-
-    CFrame cframe;
-
-    /* WARNING: Because the CFrame lives on the C stack,
-     * but can be accessed from a heap allocated object (tstate)
-     * strict stack discipline must be maintained.
-     */
-    CFrame *prev_cframe = tstate->cframe;
-    cframe.use_tracing = prev_cframe->use_tracing;
-    cframe.previous = prev_cframe;
-    tstate->cframe = &cframe;
-
-    /* push frame */
-    tstate->frame = frame;
-    co = frame->f_code;
-
-    if (cframe.use_tracing) {
     if (tstate->c_tracefunc != NULL) {
         /* tstate->c_tracefunc, if defined, is a
             function that will be called on *every* entry
@@ -1461,7 +1414,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
                                     tstate, frame,
                                     PyTrace_CALL, Py_None)) {
             /* Trace function raised an error */
-                goto exit_eval_frame;
+            return -1;
         }
     }
     if (tstate->c_profilefunc != NULL) {
@@ -1472,14 +1425,58 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
                                     tstate, frame,
                                     PyTrace_CALL, Py_None)) {
             /* Profile function raised an error */
-                goto exit_eval_frame;
+            return -1;
         }
     }
+    return 0;
+}
+
+PyObject* _Py_HOT_FUNCTION
+_PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int throwflag)
+{
+    _Py_EnsureTstateNotNULL(tstate);
+
+#if USE_COMPUTED_GOTOS
+/* Import the static jump table */
+#include "opcode_targets.h"
+#endif
+
+#ifdef DXPAIRS
+    int lastopcode = 0;
+#endif
+    int opcode;        /* Current opcode */
+    int oparg;         /* Current opcode argument, if any */
+    PyObject *retval = NULL;            /* Return value */
+    _Py_atomic_int * const eval_breaker = &tstate->interp->ceval.eval_breaker;
+
+    if (_Py_EnterRecursiveCall(tstate, "")) {
+        return NULL;
+    }
+
+    CFrame cframe;
+
+    /* WARNING: Because the CFrame lives on the C stack,
+     * but can be accessed from a heap allocated object (tstate)
+     * strict stack discipline must be maintained.
+     */
+    CFrame *prev_cframe = tstate->cframe;
+    cframe.use_tracing = prev_cframe->use_tracing;
+    cframe.previous = prev_cframe;
+    tstate->cframe = &cframe;
+
+    /* push frame */
+    tstate->frame = frame;
+
+    if (cframe.use_tracing) {
+        if (trace_function_entry(tstate, frame)) {
+            goto exit_eval_frame;
+        }
     }
 
     if (PyDTrace_FUNCTION_ENTRY_ENABLED())
         dtrace_function_entry(frame);
 
+    PyCodeObject *co = frame->f_code;
     /* Increment the warmup counter and quicken if warm enough
      * _Py_Quicken is idempotent so we don't worry about overflow */
     if (!PyCodeObject_IsWarmedUp(co)) {
@@ -1492,10 +1489,10 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
     }
 
 
-    names = co->co_names;
+    PyObject *names = co->co_names;
-    consts = co->co_consts;
+    PyObject *consts = co->co_consts;
-    localsplus = _PyFrame_GetLocalsArray(frame);
+    PyObject **localsplus = _PyFrame_GetLocalsArray(frame);
-    first_instr = co->co_firstinstr;
+    _Py_CODEUNIT *first_instr = co->co_firstinstr;
     /*
        frame->f_lasti refers to the index of the last instruction,
        unless it's -1 in which case next_instr should be first_instr.
@@ -1512,8 +1509,8 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
        to the beginning of the combined pair.)
     */
     assert(frame->f_lasti >= -1);
-    next_instr = first_instr + frame->f_lasti + 1;
+    _Py_CODEUNIT *next_instr = first_instr + frame->f_lasti + 1;
-    stack_pointer = frame->stack + frame->stackdepth;
+    PyObject **stack_pointer = frame->stack + frame->stackdepth;
     /* Set stackdepth to -1.
      * Update when returning or calling trace function.
        Having f_stackdepth <= 0 ensures that invalid
@@ -1524,6 +1521,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
     frame->f_state = FRAME_EXECUTING;
 
 #ifdef LLTRACE
+    _Py_IDENTIFIER(__ltrace__);
     {
         int r = _PyDict_ContainsId(GLOBALS(), &PyId___ltrace__);
         if (r < 0) {