Same changes around 'correctgraylist'

Instead of adding all tables and userdata back to the 'grayagain' list
to be checked by 'correctgraylist', the collector adds only the objects
that will remain in that list (objects aged TOUCHED1). This commit
also rewrites 'correctgraylist' with a clearer logic.

lgc.c

@@ -389,6 +389,32 @@ static void restartcollection (global_State *g) {
 ** =======================================================
 */
 
+
+/*
+** Check whether object 'o' should be kept in the 'grayagain' list for
+** post-processing by 'correctgraylist'. (It could put all old objects
+** in the list and leave all the work to 'correctgraylist', but it is
+** more efficient to avoid adding elements that will be removed.) Only
+** TOUCHED1 objects need to be in the list. TOUCHED2 doesn't need to go
+** back to a gray list, but then it must become OLD. (That is what
+** 'correctgraylist' does when it finds a TOUCHED2 object.)
+** It is defined as a macro because 'gclist' is not a unique field in
+** different collectable objects.
+*/
+#define genlink(g,o)	genlink_(g, obj2gco(o), &(o)->gclist)
+
+static void genlink_ (global_State *g, GCObject *o, GCObject **pnext) {
+  lua_assert(isblack(o));
+  if (getage(o) == G_TOUCHED1) {  /* touched in this cycle? */
+    *pnext = g->grayagain;  /* link it back in 'grayagain' */
+    g->grayagain = o;
+    black2gray(o);
+  }  /* everything else do not need to be linked back */
+  else if (getage(o) == G_TOUCHED2)
+    changeage(o, G_TOUCHED2, G_OLD);  /* advance age */
+}
+
+
 /*
 ** Traverse a table with weak values and link it to proper list. During
 ** propagate phase, keep it in 'grayagain' list, to be revisited in the
@@ -425,8 +451,9 @@ static void traverseweakvalue (global_State *g, Table *h) {
 ** the atomic phase, if table has any white->white entry, it has to
 ** be revisited during ephemeron convergence (as that key may turn
 ** black). Otherwise, if it has any white key, table has to be cleared
-** (in the atomic phase). In generational mode, it (like all visited
-** tables) must be kept in some gray list for post-processing.
+** (in the atomic phase). In generational mode, some tables
+** must be kept in some gray list for post-processing; this is done
+** by 'genlink'.
 */
 static int traverseephemeron (global_State *g, Table *h, int inv) {
   int marked = 0;  /* true if an object is marked in this traversal */
@@ -465,10 +492,10 @@ static int traverseephemeron (global_State *g, Table *h, int inv) {
     linkgclist(h, g->ephemeron);  /* have to propagate again */
   else if (hasclears)  /* table has white keys? */
     linkgclist(h, g->allweak);  /* may have to clean white keys */
-  else if (g->gckind == KGC_GEN)
-    linkgclist(h, g->grayagain);  /* keep it in some list */
-  else
-    gray2black(h);
+  else {
+    gray2black(h);  /* 'genlink' expects black objects */
+    genlink(g, h);  /* check whether collector still needs to see it */
+  }
   return marked;
 }
 
@@ -488,10 +515,7 @@ static void traversestrongtable (global_State *g, Table *h) {
       markvalue(g, gval(n));
     }
   }
-  if (g->gckind == KGC_GEN) {
-    linkgclist(h, g->grayagain);  /* keep it in some gray list */
-    black2gray(h);
-  }
+  genlink(g, h);
 }
 
 
@@ -503,7 +527,7 @@ static lu_mem traversetable (global_State *g, Table *h) {
       (cast_void(weakkey = strchr(svalue(mode), 'k')),
        cast_void(weakvalue = strchr(svalue(mode), 'v')),
        (weakkey || weakvalue))) {  /* is really weak? */
-    black2gray(h);  /* keep table gray */
+    black2gray(h);  /* turn it back to gray, as it probably goes to a list */
     if (!weakkey)  /* strong keys? */
       traverseweakvalue(g, h);
     else if (!weakvalue)  /* strong values? */
@@ -522,10 +546,7 @@ static int traverseudata (global_State *g, Udata *u) {
   markobjectN(g, u->metatable);  /* mark its metatable */
   for (i = 0; i < u->nuvalue; i++)
     markvalue(g, &u->uv[i].uv);
-  if (g->gckind == KGC_GEN) {
-    linkgclist(u, g->grayagain);  /* keep it in some gray list */
-    black2gray(u);
-  }
+  genlink(g, u);
   return 1 + u->nuvalue;
 }
 
@@ -1006,9 +1027,10 @@ static void sweep2old (lua_State *L, GCObject **p) {
 ** during the sweep. So, any white object must be dead.) For
 ** non-dead objects, advance their ages and clear the color of
 ** new objects. (Old objects keep their colors.)
-** The ages of G_TOUCHED1 and G_TOUCHED2 objects will advance
-** in 'correctgraylist'. (That function will also remove objects
-** turned white here from any gray list.)
+** The ages of G_TOUCHED1 and G_TOUCHED2 objects cannot be advanced
+** here, because these old-generation objects are usually not swept
+** here.  They will all be advanced in 'correctgraylist'. That function
+** will also remove objects turned white here from any gray list.
 */
 static GCObject **sweepgen (lua_State *L, global_State *g, GCObject **p,
                             GCObject *limit) {
@@ -1056,48 +1078,39 @@ static void whitelist (global_State *g, GCObject *p) {
 
 
 /*
-** Correct a list of gray objects.
+** Correct a list of gray objects. Return pointer to where rest of the
+** list should be linked.
 ** Because this correction is done after sweeping, young objects might
 ** be turned white and still be in the list. They are only removed.
-** For tables and userdata, advance 'touched1' to 'touched2'; 'touched2'
-** objects become regular old and are removed from the list.
-** For threads, just remove white ones from the list.
+** 'TOUCHED1' objects are advanced to 'TOUCHED2' and remain on the list;
+** Non-white threads also remain on the list; 'TOUCHED2' objects become
+** regular old; they and anything else are removed from the list.
 */
 static GCObject **correctgraylist (GCObject **p) {
   GCObject *curr;
   while ((curr = *p) != NULL) {
-    switch (curr->tt) {
-      case LUA_VTABLE: case LUA_VUSERDATA: {
-        GCObject **next = getgclist(curr);
-        if (getage(curr) == G_TOUCHED1) {  /* touched in this cycle? */
-          lua_assert(isgray(curr));
-          gray2black(curr);  /* make it black, for next barrier */
-          changeage(curr, G_TOUCHED1, G_TOUCHED2);
-          p = next;  /* keep it in the list and go to next element */
-        }
-        else {  /* everything else is removed */
-          /* white objects are simply removed */
-          if (!iswhite(curr)) {  /* not white? */
-            lua_assert(isold(curr));
-            if (getage(curr) == G_TOUCHED2)  /* advance from G_TOUCHED2... */
-              changeage(curr, G_TOUCHED2, G_OLD);  /* ... to G_OLD */
-            gray2black(curr);  /* make it black */
-          }
-          *p = *next;  /* remove 'curr' from gray list */
-        }
-        break;
-      }
-      case LUA_VTHREAD: {
-        lua_State *th = gco2th(curr);
-        lua_assert(!isblack(th));
-        if (iswhite(th))  /* new object? */
-          *p = th->gclist;  /* remove from gray list */
-        else  /* old threads remain gray */
-          p = &th->gclist;  /* go to next element */
-        break;
-      }
-      default: lua_assert(0);  /* nothing more could be gray here */
+    GCObject **next = getgclist(curr);
+    if (iswhite(curr))
+      goto remove;  /* remove all white objects */
+    else if (getage(curr) == G_TOUCHED1) {  /* touched in this cycle? */
+      lua_assert(isgray(curr));
+      gray2black(curr);  /* make it black, for next barrier */
+      changeage(curr, G_TOUCHED1, G_TOUCHED2);
+      goto remain;  /* keep it in the list and go to next element */
+    }
+    else if (curr->tt == LUA_VTHREAD) {
+      lua_assert(isgray(curr));
+      goto remain;  /* keep non-white threads on the list */
+    }
+    else {  /* everything else is removed */
+      lua_assert(isold(curr));  /* young objects should be white */
+      if (getage(curr) == G_TOUCHED2)  /* advance from G_TOUCHED2... */
+        changeage(curr, G_TOUCHED2, G_OLD);  /* ... to G_OLD */
+      gray2black(curr);  /* make object black */
+      goto remove;
     }
+    remove: *p = *next; continue;
+    remain: p = next; continue;
   }
   return p;
 }