[Second check-in attempt; last night's was backed out, but I claim it was because of bad dependencies or timestamp problems in the Win32 builds. /be] Add cx->lastAtom, a long overdue addition to the per-context GC root set (196461, r=shaver).

js/src/jsapi.c

@@ -1518,6 +1518,7 @@ JS_ClearNewbornRoots(JSContext *cx)
 
     for (i = 0; i < GCX_NTYPES; i++)
         cx->newborn[i] = NULL;
+    cx->lastAtom = NULL;
 }
 
 #include "jshash.h" /* Added by JSIFY */

js/src/jsatom.c

@@ -459,6 +459,7 @@ js_AtomizeHashedKey(JSContext *cx, jsval key, JSHashNumber keyHash, uintN flags)
 
     atom = (JSAtom *)he;
     atom->flags |= flags;
+    cx->lastAtom = atom;
 out:
     JS_UNLOCK(&state->lock,cx);
     return atom;
@@ -549,6 +550,7 @@ js_AtomizeDouble(JSContext *cx, jsdouble d, uintN flags)
 
     atom = (JSAtom *)he;
     atom->flags |= flags;
+    cx->lastAtom = atom;
 out:
     JS_UNLOCK(&state->lock,cx);
     return atom;
@@ -611,6 +613,7 @@ js_AtomizeString(JSContext *cx, JSString *str, uintN flags)
 
     atom = (JSAtom *)he;
     atom->flags |= flags & (ATOM_PINNED | ATOM_INTERNED);
+    cx->lastAtom = atom;
 out:
     JS_UNLOCK(&state->lock,cx);
     return atom;

js/src/jscntxt.h

@@ -317,6 +317,9 @@ struct JSContext {
     /* Most recently created things by type, members of the GC's root set. */
     JSGCThing           *newborn[GCX_NTYPES];
 
+    /* Atom root for the last-looked-up atom on this context. */
+    JSAtom              *lastAtom;
+
     /* Regular expression class statics (XXX not shared globally). */
     JSRegExpStatics     regExpStatics;
 

js/src/jsgc.c

@@ -759,7 +759,7 @@ gc_dump_thing(JSGCThing *thing, uint8 flags, GCMarkNode *prev, FILE *fp)
                                   ? NULL
                                   : JSVAL_TO_PRIVATE(privateValue);
         const char *className = gc_object_class_name(thing);
-        fprintf(fp, "object %08p %s", privateThing, className);
+        fprintf(fp, "object %8p %s", privateThing, className);
         break;
       }
       case GCX_DOUBLE:
@@ -989,6 +989,7 @@ js_ForceGC(JSContext *cx, uintN gcflags)
 
     for (i = 0; i < GCX_NTYPES; i++)
         cx->newborn[i] = NULL;
+    cx->lastAtom = NULL;
     cx->runtime->gcPoke = JS_TRUE;
     js_GC(cx, gcflags);
     JS_ArenaFinish();
@@ -1261,6 +1262,8 @@ restart:
                 NULL);
         for (i = GCX_EXTERNAL_STRING; i < GCX_NTYPES; i++)
             GC_MARK(cx, acx->newborn[i], "newborn external string", NULL);
+        if (acx->lastAtom)
+            GC_MARK_ATOM(cx, acx->lastAtom, NULL);
 #if JS_HAS_EXCEPTIONS
         if (acx->throwing && JSVAL_IS_GCTHING(acx->exception))
             GC_MARK(cx, JSVAL_TO_GCTHING(acx->exception), "exception", NULL);