Move is_start_of_object into Metaslab.

src/mem/alloc.h

@@ -1214,7 +1214,7 @@ namespace snmalloc
       Superslab* super, Slab* slab, void* p, sizeclass_t sizeclass)
     {
 #ifdef CHECK_CLIENT
-      if (!slab->is_start_of_object(super, p))
+      if (!slab->get_meta().is_start_of_object(p))
       {
         error("Not deallocating start of an object");
       }

src/mem/metaslab.h

@@ -150,6 +150,13 @@ namespace snmalloc
       return pointer_align_down<SUPERSLAB_SIZE>(p) == p;
     }
 
+    bool is_start_of_object(void* p)
+    {
+      return is_multiple_of_sizeclass(
+        sizeclass_to_size(sizeclass),
+        pointer_diff(p, pointer_align_up<SLAB_SIZE>(pointer_offset(p, 1))));
+    }
+
     /**
      * Check bump-free-list-segment for cycles
      *

src/mem/slab.h

@@ -63,7 +63,7 @@ namespace snmalloc
       meta.set_full();
       sl.get_next()->remove();
 
-      SNMALLOC_ASSERT(is_start_of_object(Superslab::get(p), p));
+      SNMALLOC_ASSERT(meta.is_start_of_object(p));
 
       meta.debug_slab_invariant(this);
 
@@ -110,14 +110,6 @@ namespace snmalloc
       bumpptr = newbumpptr;
     }
 
-    bool is_start_of_object(Superslab* super, void* p)
-    {
-      Metaslab& meta = super->get_meta(this);
-      return is_multiple_of_sizeclass(
-        sizeclass_to_size(meta.sizeclass),
-        pointer_diff(p, pointer_offset(this, SLAB_SIZE)));
-    }
-
     // Returns true, if it deallocation can proceed without changing any status
     // bits. Note that this does remove the use from the meta slab, so it
     // doesn't need doing on the slow path.