introduce RCLASS_CLONED flag for inline cache.

Methods on duplicated class/module refer same constant inline
cache (IC). Constant access lookup should be done for cloned
class/modules but inline cache doesn't check it.
To check it, this patch introduce new RCLASS_CLONED flag which
are set when if class/module is cloned (both orig and dst).
[Bug #15877]

class.c

@@ -308,11 +308,17 @@ class_init_copy_check(VALUE clone, VALUE orig)
 	rb_raise(rb_eTypeError, "can't copy singleton class");
     }
 }
-
+#include "gc.h"
 /* :nodoc: */
 VALUE
 rb_mod_init_copy(VALUE clone, VALUE orig)
 {
+    /* cloned flag is refer at constant inline cache
+     * see vm_get_const_key_cref() in vm_insnhelper.c
+     */
+    FL_SET(clone, RCLASS_CLONED);
+    FL_SET(orig , RCLASS_CLONED);
+
     if (RB_TYPE_P(clone, T_CLASS)) {
 	class_init_copy_check(clone, orig);
     }

internal.h

@@ -1056,6 +1056,7 @@ int rb_singleton_class_internal_p(VALUE sklass);
 #define RCLASS_REFINED_CLASS(c) (RCLASS_EXT(c)->refined_class)
 #define RCLASS_SERIAL(c) (RCLASS_EXT(c)->class_serial)
 
+#define RCLASS_CLONED     FL_USER6
 #define RICLASS_IS_ORIGIN FL_USER5
 
 static inline void

test/ruby/test_class.rb

@@ -329,18 +329,22 @@ class TestClass < Test::Unit::TestCase
     end;
   end
 
-  module M
-    C = 1
-
-    def self.m
-      C
-    end
+  class CloneTest
+    def foo; TEST; end
   end
 
-  def test_constant_access_from_method_in_cloned_module # [ruby-core:47834]
-    m = M.dup
-    assert_equal 1, m::C
-    assert_equal 1, m.m
+  CloneTest1 = CloneTest.clone
+  CloneTest2 = CloneTest.clone
+  class CloneTest1
+    TEST = :C1
+  end
+  class CloneTest2
+    TEST = :C2
+  end
+
+  def test_constant_access_from_method_in_cloned_class
+    assert_equal :C1, CloneTest1.new.foo, '[Bug #15877]'
+    assert_equal :C2, CloneTest2.new.foo, '[Bug #15877]'
   end
 
   def test_invalid_superclass

test/ruby/test_module.rb

@@ -2418,6 +2418,39 @@ class TestModule < Test::Unit::TestCase
     }
   end
 
+  module CloneTestM_simple
+    C = 1
+    def self.m; C; end
+  end
+
+  module CloneTestM0
+    def foo; TEST; end
+  end
+
+  CloneTestM1 = CloneTestM0.clone
+  CloneTestM2 = CloneTestM0.clone
+  module CloneTestM1
+    TEST = :M1
+  end
+  module CloneTestM2
+    TEST = :M2
+  end
+  class CloneTestC1
+    include CloneTestM1
+  end
+  class CloneTestC2
+    include CloneTestM2
+  end
+
+  def test_constant_access_from_method_in_cloned_module
+    m = CloneTestM_simple.dup
+    assert_equal 1, m::C, '[ruby-core:47834]'
+    assert_equal 1, m.m, '[ruby-core:47834]'
+
+    assert_equal :M1, CloneTestC1.new.foo, '[Bug #15877]'
+    assert_equal :M2, CloneTestC2.new.foo, '[Bug #15877]'
+  end
+
   private
 
   def assert_top_method_is_private(method)

vm_insnhelper.c

@@ -785,8 +785,9 @@ vm_get_const_key_cref(const VALUE *ep)
     const rb_cref_t *key_cref = cref;
 
     while (cref) {
-	if (FL_TEST(CREF_CLASS(cref), FL_SINGLETON)) {
-	    return key_cref;
+	if (FL_TEST(CREF_CLASS(cref), FL_SINGLETON) ||
+            FL_TEST(CREF_CLASS(cref), RCLASS_CLONED)) {
+            return key_cref;
 	}
 	cref = CREF_NEXT(cref);
     }
@@ -3722,7 +3723,8 @@ static int
 vm_ic_hit_p(IC ic, const VALUE *reg_ep)
 {
     if (ic->ic_serial == GET_GLOBAL_CONSTANT_STATE()) {
-        return (ic->ic_cref == NULL || ic->ic_cref == vm_get_cref(reg_ep));
+        return (ic->ic_cref == NULL || // no need to check CREF
+                ic->ic_cref == vm_get_cref(reg_ep));
     }
     return FALSE;
 }