No longer let the GC replace dead keys with the LJ_TDEADKEY tag.

Important: this changes the semantics of the write barrier!
Carefully read the big comment block in lj_obj.h
This helps HREFK key slot specialization and allows safely hoisting
HREF/HREFK across GC steps, too (fix for a barely reproducible bug).
Dead keys are only removed during a table resize (as before).

1 files changed, 1 insertions, 7 deletions

diff --git a/src/lj_gc.c b/src/lj_gc.c
index b97fb955..b457c424 100644
--- a/src/lj_gc.c
+++ b/src/lj_gc.c
@@ -186,13 +186,10 @@ static int gc_traverse_tab(global_State *g, GCtab *t)
     MSize i, hmask = t->hmask;
     for (i = 0; i <= hmask; i++) {
       Node *n = &node[i];
-      lua_assert(itype(&n->key) != LJ_TDEADKEY || tvisnil(&n->val));
       if (!tvisnil(&n->val)) {  /* Mark non-empty slot. */
         lua_assert(!tvisnil(&n->key));
         if (!(weak & LJ_GC_WEAKKEY)) gc_marktv(g, &n->key);
         if (!(weak & LJ_GC_WEAKVAL)) gc_marktv(g, &n->val);
-      } else if (tvisgcv(&n->key)) {  /* Leave GC key in, but mark as dead. */
-        setitype(&n->key, LJ_TDEADKEY);
       }
     }
   }
@@ -424,11 +421,8 @@ static void gc_clearweak(GCobj *o)
         Node *n = &node[i];
         /* Clear hash slot when key or value is about to be collected. */
         if (!tvisnil(&n->val) && (gc_mayclear(&n->key, 0) ||
-                                  gc_mayclear(&n->val, 1))) {
+                                  gc_mayclear(&n->val, 1)))
           setnilV(&n->val);
-          if (tvisgcv(&n->key))  /* Leave GC key in, but mark as dead. */
-            setitype(&n->key, LJ_TDEADKEY);
-        }
       }
     }
     o = gcref(t->gclist);