Revert "GH-126491: GC: Mark objects reachable from roots before doing cycle collection (GH-126502)" (#126983)

5 files changed, 6 insertions, 15 deletions

diff --git a/Include/internal/pycore_dict.h b/Include/internal/pycore_dict.h
index f7d747c..c5399ad 100644
--- a/Include/internal/pycore_dict.h
+++ b/Include/internal/pycore_dict.h
@@ -43,6 +43,8 @@ extern int _PyDict_Next(
 
 extern int _PyDict_HasOnlyStringKeys(PyObject *mp);
 
+extern void _PyDict_MaybeUntrack(PyObject *mp);
+
 // Export for '_ctypes' shared extension
 PyAPI_FUNC(Py_ssize_t) _PyDict_SizeOf(PyDictObject *);
 
diff --git a/Include/internal/pycore_frame.h b/Include/internal/pycore_frame.h
index b786c5f..8c01003 100644
--- a/Include/internal/pycore_frame.h
+++ b/Include/internal/pycore_frame.h
@@ -75,7 +75,6 @@ typedef struct _PyInterpreterFrame {
     _PyStackRef *stackpointer;
     uint16_t return_offset;  /* Only relevant during a function call */
     char owner;
-    char visited;
     /* Locals and stack */
     _PyStackRef localsplus[1];
 } _PyInterpreterFrame;
@@ -208,7 +207,6 @@ _PyFrame_Initialize(
 #endif
     frame->return_offset = 0;
     frame->owner = FRAME_OWNED_BY_THREAD;
-    frame->visited = 0;
 
     for (int i = null_locals_from; i < code->co_nlocalsplus; i++) {
         frame->localsplus[i] = PyStackRef_NULL;
@@ -391,7 +389,6 @@ _PyFrame_PushTrampolineUnchecked(PyThreadState *tstate, PyCodeObject *code, int
     frame->instr_ptr = _PyCode_CODE(code);
 #endif
     frame->owner = FRAME_OWNED_BY_THREAD;
-    frame->visited = 0;
     frame->return_offset = 0;
 
 #ifdef Py_GIL_DISABLED
diff --git a/Include/internal/pycore_gc.h b/Include/internal/pycore_gc.h
index c81e7a1..38a1c56 100644
--- a/Include/internal/pycore_gc.h
+++ b/Include/internal/pycore_gc.h
@@ -10,11 +10,11 @@ extern "C" {
 
 /* GC information is stored BEFORE the object structure. */
 typedef struct {
-    // Tagged pointer to next object in the list.
+    // Pointer to next object in the list.
     // 0 means the object is not tracked
     uintptr_t _gc_next;
 
-    // Tagged pointer to previous object in the list.
+    // Pointer to previous object in the list.
     // Lowest two bits are used for flags documented later.
     uintptr_t _gc_prev;
 } PyGC_Head;
@@ -302,11 +302,6 @@ struct gc_generation_stats {
     Py_ssize_t uncollectable;
 };
 
-enum _GCPhase {
-    GC_PHASE_MARK = 0,
-    GC_PHASE_COLLECT = 1
-};
-
 struct _gc_runtime_state {
     /* List of objects that still need to be cleaned up, singly linked
      * via their gc headers' gc_prev pointers.  */
@@ -330,12 +325,10 @@ struct _gc_runtime_state {
     /* a list of callbacks to be invoked when collection is performed */
     PyObject *callbacks;
 
-    Py_ssize_t prior_heap_size;
     Py_ssize_t heap_size;
     Py_ssize_t work_to_do;
     /* Which of the old spaces is the visited space */
     int visited_space;
-    int phase;
 
 #ifdef Py_GIL_DISABLED
     /* This is the number of objects that survived the last full
diff --git a/Include/internal/pycore_object.h b/Include/internal/pycore_object.h
index 0cba7bc..c7af720 100644
--- a/Include/internal/pycore_object.h
+++ b/Include/internal/pycore_object.h
@@ -466,8 +466,8 @@ static inline void _PyObject_GC_TRACK(
     PyGC_Head *last = (PyGC_Head*)(generation0->_gc_prev);
     _PyGCHead_SET_NEXT(last, gc);
     _PyGCHead_SET_PREV(gc, last);
-    uintptr_t not_visited = 1 ^ interp->gc.visited_space;
-    gc->_gc_next = ((uintptr_t)generation0) | not_visited;
+    /* Young objects will be moved into the visited space during GC, so set the bit here */
+    gc->_gc_next = ((uintptr_t)generation0) | (uintptr_t)interp->gc.visited_space;
     generation0->_gc_prev = (uintptr_t)gc;
 #endif
 }
diff --git a/Include/internal/pycore_runtime_init.h b/Include/internal/pycore_runtime_init.h
index ce116ad..8a8f476 100644
--- a/Include/internal/pycore_runtime_init.h
+++ b/Include/internal/pycore_runtime_init.h
@@ -134,7 +134,6 @@ extern PyTypeObject _PyExc_MemoryError;
                 { .threshold = 0, }, \
             }, \
             .work_to_do = -5000, \
-            .phase = GC_PHASE_MARK, \
         }, \
         .qsbr = { \
             .wr_seq = QSBR_INITIAL, \