Revert "Don't use exchange in the hot path of the GC (#50021)"

This reverts commit 0a2d6fc.

Author: d-netto

src/gc.c

@@ -799,7 +799,7 @@ STATIC_INLINE void gc_queue_big_marked(jl_ptls_t ptls, bigval_t *hdr,
 FORCE_INLINE int gc_try_setmark_tag(jl_taggedvalue_t *o, uint8_t mark_mode) JL_NOTSAFEPOINT
 {
     assert(gc_marked(mark_mode));
-    uintptr_t tag = jl_atomic_load_relaxed((_Atomic(uintptr_t)*)&o->header);
+    uintptr_t tag = o->header;
     if (gc_marked(tag))
         return 0;
     if (mark_reset_age) {
@@ -813,9 +813,9 @@ FORCE_INLINE int gc_try_setmark_tag(jl_taggedvalue_t *o, uint8_t mark_mode) JL_N
         tag = tag | mark_mode;
         assert((tag & 0x3) == mark_mode);
     }
-    jl_atomic_store_relaxed((_Atomic(uintptr_t)*)&o->header, tag); //xchg here was slower than
-    verify_val(jl_valueof(o));                                     //potentially redoing work because of a stale tag.
-    return 1;
+    tag = jl_atomic_exchange_relaxed((_Atomic(uintptr_t)*)&o->header, tag);
+    verify_val(jl_valueof(o));
+    return !gc_marked(tag);
 }
 
 // This function should be called exactly once during marking for each big