concurrent sweeping --merge fixes

src/gc.c

@@ -3160,6 +3160,14 @@ static int _jl_gc_collect(jl_ptls_t ptls, jl_gc_collection_t collection)
     JL_PROBE_GC_MARK_BEGIN();
     uint64_t start_mark_time = jl_hrtime();
 
+    // 1. fix GC bits of objects in the remset.
+    assert(gc_n_threads);
+    for (int t_i = 0; t_i < gc_n_threads; t_i++) {
+        jl_ptls_t ptls2 = gc_all_tls_states[t_i];
+        if (ptls2 != NULL)
+            gc_premark(ptls2);
+    }
+
     assert(gc_n_threads);
     int single_threaded = (jl_n_gcthreads == 0 || gc_heap_snapshot_enabled);
     for (int t_i = 0; t_i < gc_n_threads; t_i++) {

src/jloptions.c

@@ -849,13 +849,6 @@ JL_DLLEXPORT void jl_parse_opts(int *argcp, char ***argvp)
             else
                 jl_errorf("julia: invalid argument to --permalloc-pkgimg={yes|no} (%s)", optarg);
             break;
-        case opt_gc_threads:
-            errno = 0;
-            long ngcthreads = strtol(optarg, &endptr, 10);
-            if (errno != 0 || optarg == endptr || *endptr != 0 || ngcthreads < 1 || ngcthreads >= INT16_MAX)
-                jl_errorf("julia: --gcthreads=<n>; n must be an integer >= 1");
-            jl_options.ngcthreads = (int16_t)ngcthreads;
-            break;
         default:
             jl_errorf("julia: unhandled option -- %c\n"
                       "This is a bug, please report it.", c);