flambda-backend: Skip closure non-scannable environment in oldify_mopup (#2587)

* skip closure non scannable env

* edit

Author: TheNumbat

runtime/minor_gc.c

@@ -449,7 +449,16 @@ static void oldify_mopup (struct oldify_state* st, int do_ephemerons)
       oldify_one (st, f, Op_val (new_v));
     }
 
-    for (i = 1; i < scannable_wosize; i++){
+    i = 1;
+
+    if(Tag_val(new_v) == Closure_tag) {
+      mlsize_t non_scannable = Start_env_closinfo(Closinfo_val(v));
+      for (; i < non_scannable; i++) {
+        Field(new_v, i) = Field(v, i);
+      }
+    }
+
+    for (; i < scannable_wosize; i++){
       f = Field(v, i);
       CAMLassert (!Is_debug_tag(f));
       if (Is_block (f) && Is_young(f)) {

runtime4/minor_gc.c

@@ -340,7 +340,17 @@ void caml_oldify_mopup (void)
     if (Is_block (f) && Is_young (f)){
       caml_oldify_one (f, &Field (new_v, 0));
     }
-    for (i = 1; i < scannable_wosize; i++){
+
+    i = 1;
+
+    if(Tag_val(new_v) == Closure_tag) {
+      mlsize_t non_scannable = Start_env_closinfo(Closinfo_val(v));
+      for (; i < non_scannable; i++) {
+        Field(new_v, i) = Field(v, i);
+      }
+    }
+
+    for (; i < scannable_wosize; i++){
       f = Field (v, i);
       if (Is_block (f) && Is_young (f)){
         caml_oldify_one (f, &Field (new_v, i));