NIL_REFERENCES: Added mechanism to cut (nil) references during commit

src/kernel/bootstrap/Module.rb

@@ -3,6 +3,15 @@ class Module
   # See also delta/Module.rb
 
   primitive_nobridge '__instvar_get', 'rubyInstvarAt:'
+
+  primitive_nobridge '__maglev_nil_references', '_nilReferences:'
+
+  def maglev_nil_references(switch=true)
+    raise ArgumentError, "A module/class cannot be persistable and marked as nil_references at the same time." if switch and self.maglev_persistable?
+    __maglev_nil_references(switch)
+  end
+
+  primitive 'maglev_nil_references?', '_nilReferences'
 
   def __isBehavior
     true
@@ -465,6 +474,7 @@ def remove_class_variable(name)
   # <tt>Class#maglev_persistable_instances</tt> for controlling whether
   # instances of the class are persistable.
   def maglev_persistable(methodsPersistable = false)
+    raise ArgumentError, "A module/class cannot be persistable and marked as nil_references at the same time." if self.maglev_nil_references?
     methodsPersistable = (methodsPersistable == true)
     self.__set_persistable(methodsPersistable)
   end

src/smalltalk/ruby/Module_ruby.gs

@@ -637,4 +637,20 @@ name
   ].
   ^ name
 %
+method:
+_nilReferences: aBool
+
+self _validatePrivilege ifTrue:[
+  aBool ifTrue:[
+    format := format bitOr: GC_DB_NIL_REFERENCES_MASK.
+  ] ifFalse:[
+    format := format bitAnd: (GC_DB_NIL_REFERENCES_MASK bitInvert) 
+  ].
+  self _refreshClassCache: false .
+].
+%
+method:
+_nilReferences
+  ^ (format bitAnd: GC_DB_NIL_REFERENCES_MASK) ~~ 0
+%