bpo-44990: Change layout of evaluation frames. "Layout B" (GH-27933)

Places the locals between the specials and stack. This is the more "natural" layout for a C struct, makes the code simpler and gives a slight speedup (~1%)

Author: markshannon

Include/internal/pycore_frame.h

@@ -29,10 +29,9 @@ typedef struct _interpreter_frame {
     PyObject *generator;
     struct _interpreter_frame *previous;
     int f_lasti;       /* Last instruction if called */
-    int stackdepth;  /* Depth of value stack */
-    int nlocalsplus;
-    PyFrameState f_state;       /* What state the frame is in */
-    PyObject *stack[1];
+    int stacktop;     /* Offset of TOS from localsplus  */
+    PyFrameState f_state;  /* What state the frame is in */
+    PyObject *localsplus[1];
 } InterpreterFrame;
 
 static inline int _PyFrame_IsRunnable(InterpreterFrame *f) {
@@ -47,6 +46,26 @@ static inline int _PyFrameHasCompleted(InterpreterFrame *f) {
     return f->f_state > FRAME_EXECUTING;
 }
 
+static inline PyObject **_PyFrame_Stackbase(InterpreterFrame *f) {
+    return f->localsplus + f->f_code->co_nlocalsplus;
+}
+
+static inline PyObject *_PyFrame_StackPeek(InterpreterFrame *f) {
+    assert(f->stacktop > f->f_code->co_nlocalsplus);
+    return f->localsplus[f->stacktop-1];
+}
+
+static inline PyObject *_PyFrame_StackPop(InterpreterFrame *f) {
+    assert(f->stacktop > f->f_code->co_nlocalsplus);
+    f->stacktop--;
+    return f->localsplus[f->stacktop];
+}
+
+static inline void _PyFrame_StackPush(InterpreterFrame *f, PyObject *value) {
+    f->localsplus[f->stacktop] = value;
+    f->stacktop++;
+}
+
 #define FRAME_SPECIALS_SIZE ((sizeof(InterpreterFrame)-1)/sizeof(PyObject *))
 
 InterpreterFrame *
@@ -61,8 +80,7 @@ _PyFrame_InitializeSpecials(
     frame->f_builtins = Py_NewRef(con->fc_builtins);
     frame->f_globals = Py_NewRef(con->fc_globals);
     frame->f_locals = Py_XNewRef(locals);
-    frame->nlocalsplus = nlocalsplus;
-    frame->stackdepth = 0;
+    frame->stacktop = nlocalsplus;
     frame->frame_obj = NULL;
     frame->generator = NULL;
     frame->f_lasti = -1;
@@ -75,7 +93,19 @@ _PyFrame_InitializeSpecials(
 static inline PyObject**
 _PyFrame_GetLocalsArray(InterpreterFrame *frame)
 {
-    return ((PyObject **)frame) - frame->nlocalsplus;
+    return frame->localsplus;
+}
+
+static inline PyObject**
+_PyFrame_GetStackPointer(InterpreterFrame *frame)
+{
+    return frame->localsplus+frame->stacktop;
+}
+
+static inline void
+_PyFrame_SetStackPointer(InterpreterFrame *frame, PyObject **stack_pointer)
+{
+    frame->stacktop = (int)(stack_pointer - frame->localsplus);
 }
 
 /* For use by _PyFrame_GetFrameObject

Objects/frameobject.c

@@ -397,9 +397,7 @@ first_line_not_before(int *lines, int len, int line)
 static void
 frame_stack_pop(PyFrameObject *f)
 {
-    assert(f->f_frame->stackdepth > 0);
-    f->f_frame->stackdepth--;
-    PyObject *v = f->f_frame->stack[f->f_frame->stackdepth];
+    PyObject *v = _PyFrame_StackPop(f->f_frame);
     Py_DECREF(v);
 }
 
@@ -633,14 +631,10 @@ frame_dealloc(PyFrameObject *f)
         Py_CLEAR(frame->f_builtins);
         Py_CLEAR(frame->f_locals);
         PyObject **locals = _PyFrame_GetLocalsArray(frame);
-        for (int i = 0; i < co->co_nlocalsplus; i++) {
+        for (int i = 0; i < frame->stacktop; i++) {
             Py_CLEAR(locals[i]);
         }
-        /* stack */
-        for (int i = 0; i < frame->stackdepth; i++) {
-            Py_CLEAR(frame->stack[i]);
-        }
-        PyMem_Free(locals);
+        PyMem_Free(frame);
     }
     Py_CLEAR(f->f_back);
     Py_CLEAR(f->f_trace);
@@ -686,17 +680,13 @@ frame_tp_clear(PyFrameObject *f)
 
     Py_CLEAR(f->f_trace);
 
-    /* locals */
+    /* locals and stack */
     PyObject **locals = _PyFrame_GetLocalsArray(f->f_frame);
-    for (int i = 0; i < f->f_frame->nlocalsplus; i++) {
+    assert(f->f_frame->stacktop >= 0);
+    for (int i = 0; i < f->f_frame->stacktop; i++) {
         Py_CLEAR(locals[i]);
     }
-
-    /* stack */
-    for (int i = 0; i < f->f_frame->stackdepth; i++) {
-        Py_CLEAR(f->f_frame->stack[i]);
-    }
-    f->f_frame->stackdepth = 0;
+    f->f_frame->stacktop = 0;
     return 0;
 }
 

Objects/genobject.c

@@ -190,8 +190,7 @@ gen_send_ex2(PyGenObject *gen, PyObject *arg, PyObject **presult,
     /* Push arg onto the frame's value stack */
     result = arg ? arg : Py_None;
     Py_INCREF(result);
-    frame->stack[frame->stackdepth] = result;
-    frame->stackdepth++;
+    _PyFrame_StackPush(frame, result);
 
     frame->previous = tstate->frame;
 
@@ -350,8 +349,7 @@ _PyGen_yf(PyGenObject *gen)
 
         if (code[(frame->f_lasti+1)*sizeof(_Py_CODEUNIT)] != YIELD_FROM)
             return NULL;
-        assert(frame->stackdepth > 0);
-        yf = frame->stack[frame->stackdepth-1];
+        yf = _PyFrame_StackPeek(frame);
         Py_INCREF(yf);
     }
 
@@ -469,9 +467,7 @@ _gen_throw(PyGenObject *gen, int close_on_genexit,
         if (!ret) {
             PyObject *val;
             /* Pop subiterator from stack */
-            assert(gen->gi_xframe->stackdepth > 0);
-            gen->gi_xframe->stackdepth--;
-            ret = gen->gi_xframe->stack[gen->gi_xframe->stackdepth];
+            ret = _PyFrame_StackPop(gen->gi_xframe);
             assert(ret == yf);
             Py_DECREF(ret);
             /* Termination repetition of YIELD_FROM */

Objects/typeobject.c

@@ -8874,7 +8874,7 @@ super_init_without_args(PyFrameObject *f, PyCodeObject *co,
         return -1;
     }
 
-    assert(f->f_frame->nlocalsplus > 0);
+    assert(f->f_frame->f_code->co_nlocalsplus > 0);
     PyObject *firstarg = _PyFrame_GetLocalsArray(f->f_frame)[0];
     // The first argument might be a cell.
     if (firstarg != NULL && (_PyLocals_GetKind(co->co_localspluskinds, 0) & CO_FAST_CELL)) {