visit_reachable: replace release-mode test with an assert. (GH-16866)
It should be impossible for an untracked object to have the collecting
flag set. Back when state was stored in gc_refs, it obviously was
impossible (gc_refs couldn't possibly have a positive & negative value
simultaneously). While the _implementation_ of "state" has gotten much
more complicated, it's still _logically_ just as impossible.
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index 9750d2a..1307aa3 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -468,13 +468,16 @@
PyGC_Head *gc = AS_GC(op);
const Py_ssize_t gc_refs = gc_get_refs(gc);
- // Ignore untracked objects and objects in other generation.
+ // Ignore objects in other generation.
// This also skips objects "to the left" of the current position in
// move_unreachable's scan of the 'young' list - they've already been
// traversed, and no longer have the PREV_MASK_COLLECTING flag.
- if (gc->_gc_next == 0 || !gc_is_collecting(gc)) {
+ if (! gc_is_collecting(gc)) {
return 0;
}
+ // It would be a logic error elsewhere if the collecting flag were set on
+ // an untracked object.
+ assert(gc->_gc_next != 0);
if (gc->_gc_next & NEXT_MASK_UNREACHABLE) {
/* This had gc_refs = 0 when move_unreachable got